GOLF CLUB HEAD AND METHOD OF MANUFACTURING THE SAME

[0001] The present application claims priority to Japanese Patent Application No. 2024-187762 filed on October 24, 2024. The entire contents of this Japanese Patent Application are hereby incorporated by reference.

[0002] The present disclosure relates to golf club heads and methods of manufacturing golf club heads.

[0003] Various materials can be used in the manufacture of a golf club head. A golf club head that includes two or more different materials is also known as a composite golf club head.

[0004] US Patent No. 6,390,932 B1 discloses a golf club head that includes a striking face formed of a distinct material (polymer) having predetermined material properties. The distinct material used in the striking face can influence the flight characteristics of a struck golf ball.

[0005] From the viewpoint of performances of a golf club head such as spin performance, it is preferable that score lines be formed on the striking face. On the other hand, when the striking face is formed of a material distinct from the material(s) of the other part(s) of the golf club head, the score lines may reduce the durability strength of the distinct material. Additionally, when the striking face is formed of a distinct material, it may be difficult to ensure a sufficient adhesion strength of this distinct material.

[0006] One of the objectives of the present disclosure is to provide a golf club head that includes a striking face formed by a urethane layer having enhanced durability strength and adhesion strength.

[0007] In one aspect, a golf club head of the present disclosure includes a face portion that includes a striking face. The face portion includes a face main portion and a urethane layer member that is disposed outside the face main portion and made of a polyurethane. The urethane layer member includes a plurality of score lines that are formed on its outer surface and extend from a toe side to a heel side, and a plurality of inner surface protrusions that are formed on its inner surface and extend from the toe side to the heel side corresponding to the respective score lines. The face main portion includes a plurality of body grooves that are formed on its outer surface and extend from the toe side to the heel side corresponding to the respective inner surface protrusions. The inner surface protrusions are inserted into the respective body grooves.

[0031] Hereinafter, the present disclosure will be described in detail based on preferred embodiments with appropriate references to the accompanying drawings. The same or corresponding elements in the following embodiments are denoted by the same reference symbols. Repeated explanations are omitted as appropriate.

[0032] In the present disclosure, a reference state, a reference perpendicular plane, a toe-heel direction, a face-back direction, an up-down direction, a face center, a vertical cross section, a horizontal cross section, and a front elevation view are defined as follows.

[0033] The reference state is defined as a state where a head is placed at a predetermined lie angle on a ground plane HP. As shown in FIG. 23, in the reference state, a shaft axis line Z lies on (is contained in) a plane VP that is perpendicular to the ground plane HP. The shaft axis line Z is defined as the center line of a shaft. The shaft axis line Z normally coincides with the center line of a hosel hole. The plane VP is referred to as the reference perpendicular plane. The predetermined lie angle is shown in a product catalog, for example.

[0034] It is known that a golf club may include an adjustment mechanism enabling adjustment of its loft angle, lie angle and face angle. This adjustment may be achieved, for example, by changing the rotational position of a sleeve provided at a tip portion of the shaft. In such a club, the sleeve may be detachably fixed to the head using a fixing means such as a screw. For this reason, in this club, the shaft is attachable to and detachable from the head. This club enables adjustment of the angle of the shaft axis line Z relative to the hosel hole. In a club having such an adjustment mechanism, the face angle and the loft angle may be set to neutral and the lie angle may be set to its maximum value when the club is in the reference state. The term “neutral” refers to the center of the adjustment range.

[0035] In the reference state, the face angle is 0°. That is, in a planar view of a head as viewed from above, a line normal to its striking face at the face center is set to be perpendicular to the toe-heel direction. The definitions of the face center and the toe-heel direction are explained below.

[0036] In the present disclosure, the toe-heel direction is defined as the direction of an intersection line NL between the reference perpendicular plane VP and the ground plane HP (see FIG. 23). A toe side in the toe-heel direction is also simply referred to as “toe side”. A heel side in the toe-heel direction is also simply referred to as “heel side”.

[0037] In the present disclosure, the face-back direction is defined as a direction that is perpendicular to the toe-heel direction and is parallel to the ground plane HP. A face side in the face-back direction is also simply referred to as “face side”. A back side in the face-back direction is also simply referred to as “back side”.

[0038] In the present disclosure, the up-down direction is defined as a direction that is perpendicular to the toe-heel direction and is perpendicular to the face-back direction. In other words, the up-down direction in the present disclosure is a direction perpendicular to the ground plane HP. An upper side in the up-down direction is also referred to as “upper side” or “crown side”. A lower side in the up-down direction is also referred to as “lower side” or “sole side”.

[0039] In the present disclosure, the face center is determined in the following manner. First, a point Pr is selected roughly at the center of a striking face in the up-down direction and the toe-heel direction. Next, a plane that passes through the point Pr, extends in the direction of a line normal to the striking face at the point Pr, and is parallel to the toe-heel direction is determined. An intersection line between this plane and the striking face is drawn, and a midpoint Px of this intersection line is determined. Next, a plane that passes through the midpoint Px, extends in the direction of a line normal to the striking face at the midpoint Px, and is parallel to the up-down direction is determined. An intersection line between this plane and the striking face is drawn, and a midpoint Py of this intersection line is determined. Next, a plane that passes through the midpoint Py, extends in the direction of a line normal to the striking face at the midpoint Py, and is parallel to the toe-heel direction is determined. An intersection line between this plane and the striking face is drawn, and a midpoint Px of this intersection line is newly determined. Next, a plane that passes through this newly-determined midpoint Px, extends in the direction of a line normal to the striking face at this midpoint Px, and is parallel to the up-down direction is determined. An intersection line between this plane and the striking face is drawn, and a midpoint Py of this intersection line is newly determined. By repeating the above-described steps, points Px and Py are sequentially determined. In the course of repeating these steps, when the distance between a newly-determined midpoint Py and a midpoint Py determined in the immediately preceding step first becomes less than or equal to 0.5 mm, the newly-determined midpoint Py (the midpoint Py determined last) is defined as the face center.

[0040] In the present disclosure, the vertical cross section is defined as any cross section of a head taken along a flat plane perpendicular to the toe-heel direction. In the present disclosure, the horizontal cross section is defined as any cross section of a head taken along a flat plane perpendicular to the up-down direction. In other words, the horizontal cross section in the present disclosure is defined as any cross section of a head taken along a flat plane parallel to the ground plane HP.

[0041] In the present disclosure, the front elevation view refers to an orthogonal projection of a head obtained by projecting the head in a projecting direction that is a direction of a line normal to the striking face at the face center. Unless otherwise specified, the shapes, areas, dimensions, and similar features of regions, parts, or areas of a face portion are determined based on the front elevation view. A drawing prepared as the front elevation view is also referred to simply as a front view in the present disclosure.

[0042] Note that the plan view of a head refers to a projected figure obtained by projecting the head which is in the reference state onto a plane parallel to the ground plane HP. In the present disclosure, the plan view of a head is also referred to as a planar view.

[0043] FIG. 1 is a plan view of a golf club head 100 according to a first embodiment. FIG. 2 is a side view of the head 100 as viewed from the toe side. FIG. 3A is a front view of the head 100. FIG. 3B shows a cross-sectional contour line of the outer surface of the head 100 in a cross section E1 taken along line E1 in FIG. 3A. FIG. 4 is a front view of a head body 100a. FIG. 5 is a cross-sectional view taken along line A-A in FIG. 3A. FIG. 6 is a partially enlarged view of FIG. 5. FIG. 7 is an enlarged view of a portion surrounded by circle F7 in FIG. 6.

[0044] As shown in FIG. 1 to FIG. 7, the head 100 includes a face portion 102, a crown portion 104, a sole portion 106, and a hosel portion 108.

[0045] The head 100 may be a wood type head. Alternatively, the head 100 may be a hybrid type head. Further alternatively, the head 100 may be an iron type head. Even further alternatively, the head 100 may be a putter type head. In the present embodiment, the head 100 is a wood type head. The head 100 is a driver head. As shown in FIG. 5, the head 100 has a hollow structure. The head 100 includes a hollow interior H.

[0046] As shown in FIG. 5, the face portion 102 includes a striking face 102a and a face inner surface 102b. The striking face 102a is brought into contact with a golf ball at impact between the head 100 and the golf ball. The striking face 102a is the outer surface of the face portion 102. The striking face 102a is also simply referred to as a face. The face inner surface 102b is the inner surface of the face portion 102. The face inner surface 102b faces the hollow interior H.

[0047] The striking face 102a is a curved surface. The striking face 102a is a curved surface that is convex toward the outside of the head 100. As shown in FIG. 1, the striking face 102a includes a bulge BG. The bulge BG is the curvature (roundness) in the toe-heel direction (horizontal direction). As shown in FIG. 2 and FIG. 5, the striking face 102a includes a roll RL. The roll RL is the curvature in the up-down direction (vertical direction).

[0048] The crown portion 104 forms the upper surface of the head 100. The crown portion 104 includes a crown outer surface 104a and a crown inner surface 104b. The crown inner surface 104b faces the hollow interior H.

[0049] The sole portion 106 forms the lower surface of the head 100. The sole portion 106 includes a sole outer surface 106a and a sole inner surface 106b. The sole inner surface 106b faces the hollow interior H.

[0050] The hosel portion 108 is disposed on a heel-side part of the head 100. The hosel portion 108 has a hosel hole 108a. A shaft (not shown in the drawings) can be inserted into the hosel hole 108a. Alternatively, a sleeve (not shown in the drawings) attached to the tip portion of the shaft can be inserted into the hosel hole 108a.

[0051] As shown in FIG. 3A, the striking face 102a includes a face center Fc as defined above. Additionally, the striking face 102a (and a striking face zone 121 discussed later) includes a face center region Rc. The face center region Rc is defined as a region extending in the toe-heel direction from a position at a distance of 20mm from the face center Fc toward the toe side to a position at a distance of 20mm from the face center Fc toward the heel side.

[0052] The striking face 102a has a peripheral edge that can be defined as follows. As shown in FIG. 3A, there are a large number of flat planes each of which contains a line normal to the striking face 102a at the face center Fc, for example, flat planes E1, E2, and E3 in FIG. 3A. FIG. 3B shows a cross-sectional contour line of the head outer surface in a cross section taken along the flat plane E1. In each cross section taken along the flat planes such as the flat plane E1, when a curvature radius r of the cross-sectional contour line of the head outer surface is sequentially observed from the face center Fc toward the outside of the striking face 102a, a point at which the curvature radius r becomes 200mm for the first time is defined as a point Q1. A set of the points Q1 can be defined as the peripheral edge (peripheral edge Q1) of the striking face 102a.

[0053] As shown in FIG. 6, the head 100 includes a urethane layer member U1. The urethane layer member U1 is provided as a constituent member of the face portion 102. The head 100 is constituted by the head body 100a and the urethane layer member U1. FIG. 4 is a front view of the head body 100a. The head body 100a refers to part of the head 100 that excludes the urethane layer member U1. The head body 100a is made of a metal. There is no limitation on the material of the head body 100a. The material of the head body 100a may alternatively be a carbon fiber reinforced resin, for example. The head body 100a may be made of a plurality of materials. The head body 100a may be constituted by a plurality of members.

[0054] As shown in FIG. 6, the face portion 102 includes a face main portion M1 and the urethane layer member U1 disposed outside the face main portion M1. The urethane layer member U1 is located on the outer side of the face main portion M1. Of the face portion 102, a part that is formed by the head body 100a is the face main portion M1. The face main portion M1 is made of a metal (titanium alloy). There is no limitation on the material of the face main portion M1. The material of the face main portion M1 may alternatively be a carbon fiber reinforced resin, for example. The face main portion M1 may be made of a plurality of materials. The face main portion M1 may be constituted by a plurality of members. The urethane layer member U1 is made of a polyurethane.

[0055] As shown in FIG. 7, the face main portion M1 includes an outer surface 120 and an inner surface 122. The face main portion M1 is part of the head body 100a. The inner surface 122 of the face main portion M1 faces the hollow interior H. The inner surface 122 of the face main portion M1 forms the face inner surface 102b. The outer surface 120 of the face main portion M1 is a region on the head body 100a that corresponds to the striking face 102a. This region is also referred to as the striking face zone 121. The outer surface 120 (striking face zone 121) of the face main portion M1 extends parallel to the striking face 102a. The outer surface 120 (striking face zone 121) of the face main portion M1 includes the bulge BG. The outer surface 120 (striking face zone 121) of the face main portion M1 includes the roll RL.

[0056] The urethane layer member U1 is disposed on the outer surface 120 of the face main portion M1. The inner surface 124 of the urethane layer member U1 is in contact with the outer surface 120 of the face main portion M1 (however, an adhesive layer 125 is interposed between the inner surface 124 and the outer surface 120). Another layer (other layers) may be interposed between the outer surface 120 and the urethane layer member U1. Examples of such layer(s) include a primer layer in addition to the adhesive layer 125. The outer surface 126 of the urethane layer member U1 forms the striking face 102a. The face main portion M1 supports the urethane layer member U1 from inside the head 100.

[0057] In the present embodiment, the entirety of the outer surface 120 of the face main portion M1 is covered by the urethane layer member U1. In the present embodiment, the urethane layer member U1 covers the entirety of the outer surface 120 (striking face zone 121) and extends beyond the contour of the outer surface 120 (striking face zone 121). The urethane layer member U1 may cover a part of the outer surface 120 of the face main portion M1. The outer surface 120 of the face main portion M1 may include a portion covered by the urethane layer member U1 and a portion exposed outside the head 100 without being covered by the urethane layer member U1. In the portion exposed to the outside, the face main portion M1 constitutes the striking face 102a. In the portion covered by the urethane layer member U1, the face main portion M1 does not constitute the striking face 102a, and instead, the urethane layer member U1 constitutes the striking face 102a.

[0058] As shown in FIG. 4, the head body 100a includes a step recess 130 that receives the urethane layer member U1. The step recess 130 is filled with the urethane layer member U1 to form the head 100. The step recess 130 includes a stepped portion (sidewall) 130a that extends along its contour line. The position of the stepped portion 130a coincides with the contour line k1 of the urethane layer member U1 (see FIG. 3A). The height of the stepped portion 130a is substantially equal to the thickness of the urethane layer member U1. Accordingly, at the contour line k1 of the urethane layer member U1, the outer surface of the head 100 is substantially flush (smoothly continuous). At the contour line k1 of the urethane layer member U1, no step (no surface step) is substantially formed on the outer surface of the head 100. The height of the surface step at the contour line k1 can be less than or equal to 0.1 mm.

[0059] As shown in FIG. 3, the urethane layer member U1 includes a score line 140 formed on its outer surface 126. That is, the striking face 102a includes the score line 140. The urethane layer member U1 (striking face 102a) includes a plurality of score lines 140. Each score line 140 extends from the toe side to the heel side. The score lines 140 extend parallel to each other.

[0060] The score lines 140 are grooves. In a vertical cross section (FIG. 7), the cross-sectional shape of each score line 140 is U-shaped. The entire cross section of each score line 140 is depicted as a curve that is convex toward the face main portion M1. Additionally, edges Eg on both sides of each score line 140 in the cross section are rounded.

[0061] Each score line 140 has a groove width Wg. The groove width Wg can be measured according to the 30 degree method of measurement on file with the R&A and USGA. Each score line 140 has a groove depth Dg. The groove depth Dg is measured from a straight line Ls that connects the measurement points identified in the 30 degree method of measurement.

[0062] As shown in FIG. 4 and FIG. 7, the face main portion M1 includes a body groove 146. The body groove 146 is located on the outer surface 120 of the face main portion M1. The face main portion M1 includes a plurality of body grooves 146. Each body groove 146 extends from the toe side to the heel side. The body grooves 146 are arranged at positions corresponding to the positions of respective inner surface protrusions 142 (discussed later). The cross-sectional shape of each body groove 146 is U-shaped. Each body groove 146 has a cross-sectional shape that is a circular arc. Each body groove 146 has a shape of a concave curved surface. Alternatively, the cross-sectional shape of each body groove 146 may be rectangular. In this case, the cross-section of each body groove 146 can include a first side surface, a second side surface, a bottom surface connecting these side surfaces, and corner portions defining both ends of the bottom surface.

[0063] As shown in FIG. 7, the urethane layer member U1 includes an inner surface protrusion 142 formed on its inner surface 124. The urethane layer member U1 includes a plurality of the inner surface protrusions 142. Each inner surface protrusion 142 extends from the toe side to the heel side. The inner surface protrusions 142 are arranged at positions corresponding to the positions of the respective score lines 140. The inner surface protrusions 142 and the corresponding score lines 140 are formed simultaneously by curving the urethane layer member U1 (at the positions of the inner surface protrusions 142). The inner surface protrusions 142 extend while being aligned with the corresponding score lines 140.

[0064] As shown in FIG. 7, the inner surface protrusions 142 are inserted into the respective body grooves 146. The inner surface protrusions 142 are fitted into the respective body grooves 146. The urethane layer member U1 bends at the positions of the body grooves 146 as a result of its insertion into the body grooves 146. The urethane layer member U1 extends while following the inner surfaces of the body grooves 146. The inner surface protrusions 142 are fitted into the respective body grooves 146. The shape of the body grooves 146 is transferred to form the inner surface protrusions 142. Although the inner surface protrusions 142 are inserted into the body grooves 146, the inner surface protrusions 142 do not necessarily have to be fitted into the body grooves 146.

[0065] A double-pointed arrow t1 in FIG. 7 indicates the thickness of the urethane layer member U1. The thickness t1 of the urethane layer member U1 can be measured in a vertical cross section such as the one shown in FIG. 7. As shown in FIG. 7, an inscribed circle CL1 that is inscribed in the urethane layer member U1 is defined in the vertical cross section of the urethane layer member U1. Such an inscribed circle CL1 can be described at any position in the urethane layer member U1. The diameter of the inscribed circle CL1 can represent the thickness t1 of the urethane layer member U1. By defining the inscribed circle CL1, the thickness t1 can be measured at any position, including curved portions of the urethane layer member U1. The thickness t1 of the urethane layer member U1 is substantially constant. The term “substantially constant” means that the thickness t1 of the urethane layer member U1 varies in a range from -10% to +10%, more preferably from -7% to +7%, and even more preferably from -5% to +5%.

[0066] As shown in FIG. 4, each body groove 146 includes a first groove-width portion 148 and a second groove-width portion 150 having a groove width smaller than that of the first groove-width portion 148. A double-pointed arrow W1 in FIG. 4 indicates the groove width of the first groove-width portion 148. A double-pointed arrow W2 in FIG. 4 indicates the groove width of the second groove-width portion 150. The groove width W1 of the first groove-width portion 148 is greater than the groove width W2 of the second groove-width portion 150. Although the body grooves 146 are not grooves specified in the Rules of Golf, the groove width W1 and the groove width W2 are measured according to the 30 degree method of measurement on file with the R&A and USGA.

[0067] The second groove-width portion 150 is connected to the first groove-width portion 148. Each second groove-width portion 150 is connected to the toe side and/or the heel side of the first groove-width portion 148. In the embodiment of FIG. 4, the second groove-width portions 150 are connected respectively to both the toe side and the heel side of the first groove-width portion 148 in every body groove 146. The second groove-width portion 150 connected to the toe side of the first groove-width portion 148 extends toward the toe side from the toe side end of the first groove-width portion 148. The second groove-width portion 150 connected to the heel side of the first groove-width portion 148 extends toward the heel side from the heel side end of the first groove-width portion 148.

[0068] In the head body 100a (FIG. 4), at least one of the first groove-width portions 148 extends across the face center region Rc (see FIG. 3A). In the head body 100a, multiple first groove-width portions 148 extend across the face center region Rc.

[0069] The second groove-width portions 150 do not necessarily need to be present. Each body groove 146 may alternatively be constituted only by the first groove-width portion 148.

[0070] As can be understood from comparing FIG. 3A and FIG. 4, the score lines 140 are formed at positions corresponding to the positions of the first groove-width portions 148. The urethane layer member U1 is inserted into the first groove-width portions 148. The inner surface protrusions 142 are fitted into the respective first groove-width portions 148. The inner surface protrusions 142 are fitted into the corresponding first groove-width portions 148 together with the adhesive layer 125. The groove width W1 of each first groove-width portion 148 enables insertion of the urethane layer member U1 having the thickness t1 into the first groove-width portions 148. The groove width W1 of each first groove-width portion 148 can preferably be greater than twice the thickness t1 of the urethane layer member U1.

[0071] The score lines 140 are not formed at positions corresponding to the positions of the second groove-width portions 150. The urethane layer member U1 is not inserted into the second groove-width portions 150. The inner surface protrusions 142 are not formed at positions corresponding to the positions of the second groove-width portions 150. The inner surface protrusions 142 are not fitted into the second groove-width portions 150. The groove width W2 of each second groove-width portion 150 does not enable insertion of the urethane layer member U1 having the thickness t1 into the second groove-width portions 150. The groove width W2 of each second groove-width portion 150 can be smaller than the thickness t1 of the urethane layer member U1.

[0072] Alternatively, the urethane layer member U1 may be inserted into the second groove-width portions 150. In this case, the urethane layer member U1 may not be fully inserted into the second groove-width portions 150. That is, the urethane layer member U1 may be inserted such that it does not follow the inner surfaces of the second groove-width portions 150, which may result in empty spaces between the urethane layer member U1 and the inner surfaces of the second groove-width portions 150. In other words, inner surface protrusions formed when the urethane layer member U1 is inserted into the second groove-width portions 150 may not be fitted into the second groove-width portions 150. In this case, score lines that differ from the score lines 140 may be formed at positions corresponding to the second groove-width portions 150. These different score lines each have a groove width Wg that is smaller than those of the score lines 140 formed at the positions corresponding to the first groove-width portions 148.

[0073] As shown in FIG. 4, each body groove 146 includes a toe side end Et and a heel side end Eh. In the present embodiment, the toe side end Et and the heel side end Eh of each body groove 146 are ends of the second groove-width portions 150. For each body groove 146, the toe side end Et is the end of the second groove-width portion 150 located on the toe side of the first groove-width portion 148. For each body groove 146, the heel side end Eh is the end of the second groove-width portion 150 located on the heel side of the first groove-width portion 148.

[0074] Each body groove 146 extends from the toe side end Et, through the striking face zone 121, to the heel side end Eh, with the both ends Et and Eh located outside the peripheral edge Q2 of the striking face zone 121. The toe side end Et is located outside the peripheral edge Q2 of the striking face zone 121. The heel side end Eh is located outside the peripheral edge Q2 of the striking face zone 121.

[0075] Each body groove 146 is open toward the heel side at the heel side end Eh. In other words, each body groove 146 has an opening that is open toward the heel side at the heel side end Eh. As shown in the enlarged portion of FIG. 4, each body groove 146 (second groove-width portion 150) includes a first side surface s1, a second side surface s2, and a bottom surface b1. At the heel side end Eh, there is no step between the bottom surface b1 and the outer surface 120 adjacent to the bottom surface b1. Since the outer surface 120 of the face main portion M1 includes the bulge BG, the bottom surface b1 is also curved and follows this bulge BG. The depth of each body groove 146 (the height of the first side surface s1 and the second side surface s2) decreases continuously toward the heel side end Eh and becomes zero at the heel side end Eh. The heel side end Eh forms a suction opening K1 by being open toward the heel side. Similarly, each body groove 146 is open toward the toe side at the toe side end Et. The toe side end Et forms a suction opening K1 by being open toward the toe side. The functional aspects of the suction openings K1 will be discussed later.

[0076] FIG. 8 is a front view of a head 200 according to a second embodiment. FIG. 9 is a front view showing a head body 200a of the head 200. The head 200 has the same configuration as the head 100, except for the configurations of the body grooves 146 and the score lines 140.

[0077] As shown in FIG. 9, in the head body 200a, one of the body grooves 146 includes a first groove-width portion 148 that has a gap, and a second groove-width portion 150 that spans the gap. This second groove-width portion 150 is also referred to as an intermediate narrow portion 152. Except for the presence of the intermediate narrow portion 152, the head body 200a has the same configuration as the head body 100a of the first embodiment.

[0078] As shown in FIG. 8, the score line 140 is not formed at the position corresponding to the position of the intermediate narrow portion 152. A gap 141 of one score line 140 is formed at the position corresponding to the position of the intermediate narrow portion 152. The head body 200a includes a single intermediate narrow portion 152. The head 200 includes a single gap 141. Except for the presence of the gap 141, the head 200 has the same configuration as the head 100 of the first embodiment.

[0079] In the head 200, the gap 141 is located in a region corresponding to the face center Fc. The region corresponding to the face center Fc can be defined as a region surrounded by a circle having a radius of 10 mm and centered on the face center Fc. More preferably, the region corresponding to the face center Fc can be defined as a region surrounded by a circle having a radius of 5 mm and centered on the face center Fc. The presence of the gap 141 makes the face center Fc visible to the user.

[0080] FIG. 10 is a front view of a head 300 according to a third embodiment. FIG. 11 is a front view of a head body 300a in the head 300. The head 300 has the same configuration as the head 100 except for the configurations of the body grooves 146 and the score lines 140.

[0081] As shown in FIG. 11, among the body grooves 146 of the head body 300a, multiple body grooves 146 each include a first groove-width portion 148 having one or more gaps, and one or more second groove-width portions 150 (one or more intermediate narrow portions 152) that span the respective one or more gaps. In these body grooves 146 of the present embodiment, each body groove 146 includes multiple (two) intermediate narrow portions 152. Except for the presence of the intermediate narrow portions 152, the head body 300a has the same configuration as the head body 100a of the first embodiment.

[0082] As shown in FIG. 10, the score lines 140 are not formed at the positions corresponding to the positions of the intermediate narrow portions 152. Gaps 141 of the score lines 140 are formed at the positions corresponding to the positions of the respective intermediate narrow portions 152. The head body 300a includes a plurality of intermediate narrow portions 152. The head 300 includes a plurality of gaps 141. Except for the presence of the gaps 141, the head 300 has the same configuration as the head 100 of the first embodiment.

[0083] In the head 300, the gaps 141 are located in a face central zone Ft. The face central zone Ft can be defined as a region surrounded by a circle having a radius of 20mm and centered on the face center Fc. The gaps 141 are arranged annularly around the face center Fc. The gaps 141 make a preferable impact zone visible to the user.

[0084] FIG. 12 is a front view of a head 400 according to a fourth embodiment. FIG. 13 is a front view of a head body 400a in the head 400. The head 400 has the same configuration as the head 100 except for the configurations of the body grooves 146 and the score lines 140.

[0085] As shown in FIG. 13, among the body grooves 146 of the head body 400a, multiple body grooves 146 each include a first groove-width portion 148 having a gap, and a second groove-width portion 150 (intermediate narrow portion 152) that spans the gap. In these body grooves 146 of the present embodiment, each body groove 146 includes a single intermediate narrow portion 152. Except for the presence of the intermediate narrow portions 152, the head body 400a has the same configuration as the head body 100a of the first embodiment.

[0086] As shown in FIG. 12, the score lines 140 are not formed at the positions corresponding to the positions of the intermediate narrow portions 152. Gaps 141 of the score lines 140 are formed at the positions corresponding to the positions of the respective intermediate narrow portions 152. The head body 400a includes a plurality of intermediate narrow portions 152. The head 400 includes a plurality of gaps 141. Except for the presence of the gaps 141, the head 400 has the same configuration as the head 100 of the first embodiment.

[0087] In the head 400, the gaps 141 form a region in which the score lines 140 are not disposed within the face central zone Ft. The gaps 141 constitute the region in which the score lines 140 are absent, the region having a substantially circular shape surrounding the face center Fc. The gaps 141 make a preferable impact zone visible to the user.

[0088] FIG. 14 is a front view of a head 500 according to a fifth embodiment. The head 500 has the same configuration as the head 100 except for the configurations of the body grooves 146 and the score lines 140. Although not shown in the drawings, the body grooves of a head body 500a of the head 500 are arranged at positions corresponding to the positions of the score lines 140.

[0089] As shown in FIG. 14, in the head 500, the score lines 140 extend beyond the contour of the striking face 102a. That is, each score line 140 includes an on-face portion 140a located on the striking face 102a and out-of-face portions 140b that extend continuously from the respective opposite ends of the on-face portion 140a and are located outside the striking face 102a. The urethane layer member U1 extends beyond the contour of the striking face 102a, and the out-of-face portions 140b are formed in a part of the urethane layer member U1 that is located outside the striking face 102a. The urethane layer member U1 is inserted into the body grooves (not shown) to form the on-face portion 140a and the out-of-face portions 140b. In the head body 500a of the head 500, the body grooves (not shown) extend beyond the contour of the region (striking face zone 121) corresponding to the striking face 102a.

[0090] The head 500 includes a lengthened score line 160 that is disposed on the urethane layer member U1 and extends beyond the contour of the urethane layer member U1. In the embodiment of FIG. 14, the uppermost score line 140 is lengthened to form the lengthened score line 160. A part of the lengthened score line 160 forms the score line 140. The lengthened score line 160 includes an out-of-urethane-layer portion 162. The out-of-urethane-layer portion 162 extends continuously from the score line 140 and is located outside the urethane layer member U1. In the present embodiment, the out-of-urethane-layer portion 162 extends continuously from the out-of-face portion 140b. The out-of-urethane-layer portion 162 is disposed on the outer surface of the head body 500a. The out-of-urethane-layer portion 162 is formed by the second groove-width portion 150 disposed on the head body 500a. The second groove-width portion 150 is exposed outside the head 500 without being covered by the urethane layer member U1, thereby forming the out-of-urethane-layer portion 162.

[0091] In the present embodiment, the out-of-urethane-layer portion 162 is located outside the striking face 102a. Alternatively, the out-of-urethane-layer portion 162 may be disposed in the striking face 102a.

[0092] FIG. 15A is a front view of a head 600 according to a sixth embodiment. FIG. 15B is a front view of a head body 600a in the head 600. The head 600 has the same configuration as the head 100 except for the configuration of the body grooves 146.

[0093] As shown in FIG. 15A, the configuration of the score lines 140 in the head 600 is the same as that of the head 100. The head 600 has the same appearance as the head 100.

[0094] As shown in FIG. 15B, the head body 600a includes a plurality of body grooves 146. The body grooves 146 are arranged at positions corresponding to the positions of the respective score lines 140. The urethane layer member U1 is inserted into the body grooves 146, thereby forming the score lines 140.

[0095] The body grooves 146 of the head body 600a do not include the second groove-width portions 150 as shown in the head body 100a (FIG. 4). In the head body 600a, each body groove 146 has a constant groove width. This constant groove width is equal to the groove width W1 of the first groove-width portion 148 in the head body 100a.

[0096] In the head body 600a, each of the body grooves 146 has suction openings K2. The suction openings K2 are located at both ends of each body groove 146. One suction opening K2 is located at the toe side end Et of each body groove 146. The other suction opening K2 is located at the heel side end Eh of each body grooves 146.

[0097] The suction openings K2 of the head body 600a differ from the suction openings K1 (FIG. 4) of the head body 100a. The suction openings K1 of the head body 100a are formed by the both ends Et and Eh of each body groove 146 being open in the respective extending directions of the body groove 146. In contrast, the suction openings K2 of the head body 600a are formed by through holes h1 that penetrate through the face main portion M1. Each of the through holes h1 extends from the bottom surface b1 of the body groove 146 to the inner surface 122 (see FIG. 5) of the face main portion M1. In other words, each through hole h1 extends from the bottom surface b1 of the body groove 146 to the hollow interior H of the head 600. The hollow interior H communicates with the hosel hole 108a, allowing air to pass between the hollow interior H and the outside of the head 600.

[0098] The positions of the suction openings K2 are not limited to the both ends Et and Eh of the body grooves 146. The suction openings K2 may be located at any positions on the body groove 146 between the toe side end Et and the heel side end Eh. A suction opening K2 may be located at a position aligned with the face center Fc, for example.

[0099] FIG. 16A and FIG. 16B are front views of a head 700 according to a seventh embodiment. In FIG. 16A, markings 170 are indicated by hatching. In FIG. 16B, the markings 170 are indicated by solid black. FIG. 16B more closely represents the actual appearance of the head 700. FIG. 17 is an enlarged cross-sectional view of a part of the face portion 102 in the head 700. Except for the presence of the markings 170, the head 700 has the same configuration as the head 100 of the first embodiment.

[0100] In the present embodiment, the urethane layer member U1 has transparency. The urethane layer member U1 is transparent or semi-transparent.

[0101] As shown in FIG. 17, the markings 170 are formed on the outer surface 120 of the face main portion M1. Examples of methods for forming the markings 170 include ink application, painting, vapor deposition, plating, or laser marking. Although each marking 170 is formed as a thin layer, the markings 170 are depicted by thick solid lines in FIG. 17 for enhanced clarity. The markings 170 are formed in the body grooves 146. The markings 170 are formed in the entirety of the respective body grooves 146 (first groove-width portions 148).

[0102] The transparency of the urethane layer member U1 allows the markings 170 to be visible from outside the head 700. The markings 170 are arranged at positions corresponding to the positions of the score lines 140. Each marking 170 has a line shape. Such a marking 170 having a line shape (linear marking 170) is also referred to as a marking line 172. The marking lines 172 are aligned with the score lines 140. Each marking line 172 has a line width denoted by Wm. The line width Wm is measured in the same direction as the measurement of the groove width Wg of the corresponding score line 140. The line width Wm is larger than the groove width Wg of the score lines 140. In the present embodiment, the line width Wm of the markings 170 is equal to the groove width W1 (see FIG. 4) of the first groove-width portions 148. In the front elevation view (FIG. 16B), the score lines 140 are encompassed by the respective marking lines 172. The marking lines 172 (markings 170) are more conspicuous than the score lines 140.

[0103] As can be imagined from FIG. 16B, the presence of the marking lines 172 makes the score lines 140 difficult to see. However, the score lines 140 are present, and the performance (e.g., spin performance) brought about by the score lines 140 remains unchanged. Meanwhile, the marking lines 172 accentuate the lines corresponding to the score lines 140.

[0104] FIG. 18 is a front view of a head 800 according to an eighth embodiment. The head 800 includes a head body 800a and a urethane layer member U1. The urethane layer member U1 of the head 800 also has transparency. Except for the configuration of the markings 170, the head 800 has the same configuration as the head 700 of the seventh embodiment.

[0105] Of the marking lines 172 of the head 800, at least one marking line 172 has a line gap 174. The line gap 174 is formed as a gap in the marking line 172. In the present embodiment, multiple (three) marking lines 172 have line gaps 174. The head 800 includes multiple (six) line gaps 174. Except for the presence of the line gaps 174, the head 800 has the same configuration as the head 700 of the seventh embodiment.

[0106] In the head 800, the line gaps 174 are located in the face central zone Ft. The line gaps 174 are arranged annularly around the face center Fc. The line gaps 174 make a preferable impact zone visible to the user. The line gaps 174 are located in the marking lines 172 having a width greater than that of the score lines 140, which can enhance the visual effect of the line gaps 174.

[0107] In the head 800, the body grooves 146 (first groove-width portions 148) are present at positions corresponding to the positions of the line gaps 174. Accordingly, the score lines 140 are also present at the positions of the line gaps 174.

[0108] FIG. 19 is a front view of a head 900 according to a ninth embodiment. The head 900 includes a head body 900a and a urethane layer member U1. The urethane layer member U1 of the head 900 also has transparency. Except for the configuration of the markings 170, this head 900 has the same configuration as the head 700 of the seventh embodiment.

[0109] In the present embodiment, the head 900 includes a single marking 170. The marking 170 forms a FIGURE(diagram). In the present embodiment, the figure is a circle. The marking 170 is dot-shaped. Except for the presence of the marking 170, the head 900 has the same configuration as the head 100 of the first embodiment.

[0110] In the head 900, the dot-shaped marking 170 is located in a region corresponding to the face center Fc. The region corresponding to the face center Fc can be defined as a region surrounded by a circle having a radius of 10 mm and centered on the face center Fc. More preferably, the region corresponding to the face center Fc can be defined as a region surrounded by a circle having a radius of 5 mm and centered on the face center Fc. The presence of the marking 170 makes the face center Fc visible to the user.

[0111] The head 100 is manufactured by fixing the urethane layer member U1 to the outer surface of the head body 100a (outer surface 120 of the face main portion M1, step recess 130). A urethane layer member U1 that has already been shaped may be fixed to the head body 100a. Alternatively, as described in the manufacturing method below, a sheet-shaped urethane layer member U1 (urethane sheet U2) that has not yet been shaped may be fixed to the head body 100a while being shaped on the head body 100a.

[0112] FIG. 20 to FIG. 22 are conceptual diagrams illustrating an example of a manufacturing method for the head 100. FIG. 20 and FIG. 22 are cross-sectional views taken along a vertical cross section of the head 100. FIG. 21 is a cross-sectional view taken along a horizontal cross section of the head 100. FIG. 20 to FIG. 22 sequentially illustrate the progress of the manufacturing process, progressing in order from FIG. 20 through FIG. 22. Hatchings are omitted from FIG. 20 to FIG. 22. All of the above-described embodiments (heads 100, 200, 300, 400, 500, 600, 700, 800, 900) can be manufactured by this method. For the heads including the marking(s) 170 (heads 700, 800, 900), the marking(s) 170 is/are formed on the outer surface 120 of the face main portion M1 prior to the manufacturing process.

[0113] In this manufacturing method, a urethane sheet U2 that forms the urethane layer member U1 is prepared (first step). The urethane sheet U2 is made of a urethane resin that constitutes the urethane layer member U1. The urethane sheet U2 is shaped on the outer surface 120 of the face main portion M1 to form the urethane layer member U1. The urethane sheet U2 may include the adhesive layer 125 (see FIG. 7).

[0114] A vacuum adhesion device 180 that adheres a sheet to a workpiece under vacuum can be used in the manufacturing method. The vacuum adhesion device 180 includes a vacuum chamber 182 that is configured to be evacuated to a vacuum state, a head holder 184 that is disposed in the vacuum chamber 182 and is configured to hold the head 100, an opening 186 that connects the inside and outside of the vacuum chamber 182, and a sheet holding portion 188 that is configured to hold the urethane sheet U2 in a state where the urethane sheet U2 is stretched over the opening 186. The head holder 184 (or the sheet holding portion 188) is configured to adjust the distance between the head 100 and the urethane sheet U2.

[0115] As shown in FIG. 20, the head 100 is set to the head holder 184. In the next step, the head holder 184 is driven so that the urethane sheet U2 is pressed against the outer surface 120 of the face main portion M1 (see FIG. 21 and FIG. 22). Concurrently, the vacuum chamber 182 is evacuated to a vacuum state. That is, while the urethane sheet U2 is pressed against the outer surface 120 of the face main portion M1, the space between the face main portion M1 and the urethane sheet U2 is evacuated to a vacuum state (second step). In this second step, the urethane sheet U2 may be heated to a predetermined temperature. The second step may be performed while heating the urethane sheet U2. The outer surface 120 of the face main portion M1 includes the bulge BG. Accordingly, in the second step, the urethane sheet U2 first comes into contact with part of the outer surface 120 of the face main portion M1. As the pressing amount of the head 100 against the urethane sheet U2 increases, the contact area between the urethane sheet U2 and the outer surface 120 of the face main portion M1 gradually increases as well. The contact area finally expands to the entirety of the region (step recess 130) where the urethane layer member U1 is positioned (see FIG. 21 and FIG. 22). Next, the urethane sheet U2 is cut according to the contour line k1 of the urethane layer member U1.

[0116] In the second step, air inside the body grooves 146 escapes through the suction openings K1. As described above, the toe side end Et and the heel side end Eh of each body groove 146 can constitute the suction openings K1 (see FIG. 4). During the second step, while air is evacuated from the body grooves 146 through the suction openings K1, the urethane sheet U2 is drawn into the body grooves 146. As a result, the inner surface protrusions 142 are formed on the inner surface 124 of the urethane layer member U1, and the score lines 140, corresponding to the respective inner surface protrusions 142, are formed on the outer surface 126 of the urethane layer member U1.

[0117] The adhesion of the urethane sheet U2 may be completed in the second step. In this case, the adhesive layer 125 (see FIG. 7) may be included in the urethane sheet U2. Alternatively, after shaping the urethane sheet U2 in the second step to obtain a shaped urethane layer member U1, this shaped urethane layer member U1 may be removed from the face main portion M1. For example, this method can be employed when the urethane sheet U2 does not include the adhesive layer 125. In this case, an adhesive may be applied to the shaped urethane layer member U1 or the face main portion M1, and the shaped urethane layer member U1 may be adhered to the face main portion M1.

[0118] The above-described embodiments can exhibit the following advantageous effects.

[0119] The score lines 140 are formed on the outer surface 126 of the urethane layer member U1. This can prevent a golf ball from sliding on the outer surface 126 of the urethane layer member U1 at impact, which can stabilize the backspin rate.

[0120] The inner surface protrusions 142 of the urethane layer member U1 are formed corresponding to the respective score lines 140 on the outer surface 126 of the urethane layer member U1. This structure can prevent the urethane layer member U1 from being locally thinned due to the presence of the score lines 140. Furthermore, despite the presence of the score lines 140, the thickness t1 of the urethane layer member U1 can be substantially constant. Since the urethane layer member U1 is prevented from being locally thinned, the durability strength of the urethane layer member U1 can be improved.

[0121] The inner surface protrusions 142 of the urethane layer member U1 are inserted into the respective body grooves 146 of the face main portion M1. This structure can suppress lateral sliding of the urethane layer member U1 relative to the face main portion M1, which can improve the adhesion strength of the urethane layer member U1. When the inner surface protrusions 142 are fitted into the respective body grooves 146, the adhesion strength can be further enhanced.

[0122] When the urethane layer member U1 has transparency, the marking(s) 170 formed on the outer surface 120 of the face main portion M1 can be visible from outside the urethane layer member U1. Accordingly, the marking(s) 170 visible from outside the striking face 102a can be freely formed, regardless of the positions of the score lines 140. The specifications (position, shape, color, etc.) of the marking(s) 170 can be freely determined. Since the marking(s) 170 is/are protected by the urethane layer member U1, the marking(s) 170 will not be worn off due to impact with golf balls.

[0123] As shown in the head 700 of FIG. 16B, the linear markings 170 (marking lines 172) can be formed at positions corresponding to the positions of the score lines 140 of the urethane layer member U1. This configuration can improve the visibility of the score lines 140.

[0124] As shown in the head 700 of FIG. 16B, the line width Wm of the linear markings 170 (marking lines 172) can be larger than the groove width Wg of the score lines 140. This configuration can further improve the visibility of the score lines 140.

[0125] Each of the linear markings 170 may have a shape of a solid line or a dashed line. Of the linear markings 170 of the head 800 in FIG. 18, multiple linear markings 170 each have a dashed portion. The entirety of each linear marking 170 may have a shape of a dashed line.

[0126] The marking 170 may be a dot-shaped marking or a short linear marking. In the head 900 of FIG. 19, the dot-shaped marking 170 is formed at a position aligned with the face center Fc. This configuration can improve the visibility of the position of the face center Fc. The dot-shaped marking 170 may be dimensioned such that it is contained entirely in a circle having a radius of 3 mm. The short linear marking 170 may be dimensioned such that it is contained entirely in a circle having a radius of 3 mm.

[0127] The above-described manufacturing method utilizes a vacuum forming process that includes a step (vacuum step) in which the urethane sheet U2 is pressed against the outer surface of the face main portion M1 while the space between the face main portion M1 and the urethane sheet U2 is evacuated to a vacuum state. This vacuum forming process can improve the adhesion between the face main portion M1 and the urethane layer member U1.

[0128] The face main portion M1 includes the body grooves 146 formed on its outer surface 120 and extending from the toe side to the heel side, and the suction openings K1 or K2 formed in the body grooves 146. In the above-described vacuum step, while air is evacuated from the body grooves 146 through the suction openings K1 or K2, the urethane sheet U2 is drawn into the body grooves 146. Accordingly, the inner surface protrusions 142 are formed on the inner surface 124 of the urethane layer member U1, and the score lines 140, corresponding to the respective inner surface protrusions 142, are formed on the outer surface 126 of the urethane layer member U1. Since air is evacuated from the body grooves 146 through the suction openings K1 or K2, the urethane layer member U1 (urethane sheet U2) can be drawn into the body grooves 146. Furthermore, the urethane layer member U1 (urethane sheet U2) can be fitted and adhered to the inner surfaces of the body grooves 146. As a result, the inner surface protrusions 142 can be formed on the inner surface 124 of the urethane layer member U1, and the score lines 140 can be formed on the outer surface 126 of the urethane layer member U1.

[0129] The outer surface 120 of the face main portion M1 includes the striking face zone 121, which corresponds to the striking face 102a. In each of the body grooves 146, its toe side end and/or its heel side end is located on or outside the peripheral edge Q2 of the striking face zone 121. Since the striking face zone 121 of the face main portion M1 includes the bulge BG, the body grooves 146 extending to reach the peripheral edge Q2 facilitate the escape of air inside the body grooves 146. The inner surface protrusions 142 can be reliably and highly precisely formed by evacuating air from the body grooves 146. As a result, the adhesion strength of the urethane layer member U1 can be enhanced and the score lines 140 can be precisely formed.

[0130] The suction opening(s) K1 of each body groove 146 is formed by the toe side end Et and/or the heel side end Eh of each body groove 146 being open. Accordingly, the suction openings K1 of the body grooves 146 can be easily formed. Additionally, since the outer surface 120 (striking face zone 121) of the face main portion M1 includes the bulge BG, air can easily escape from the body grooves 146 through the toe side end Et and/or the heel side end Eh.

[0131] In the head body 100a (FIG. 4), the head body 200a (FIG. 9), the head body 300a (FIG. 11), and the head body 400a (FIG. 13), each body groove 146 includes the first groove-width portion 148 and the second groove-width portions 150. The second groove-width portions 150 are connected to the respective opposite ends of the first groove-width portion 148. The groove width W2 of the second groove-width portions 150 is smaller than the groove width W1 of the first groove-width portions 148. The groove width W2 of the second groove-width portions 150 is dimensioned to prevent complete insertion of the urethane layer member U1 into the second groove-width portions 150. Considering that the outer surface 120 of the face main portion M1 includes the bulge BG, the second groove-width portions 150 are less likely to be filled by the urethane layer member U1 in the above-described vacuum step compared to the first groove-width portions 148. During the above-described vacuum step, air can easily escape from the first groove-width portions 148 through the second groove-width portions 150. That is, the second groove-width portions 150 can function as suction openings. Since the second groove-width portions 150 are grooves, the second groove-width portions 150 are open toward the normal direction of the outer surface 120 of the face main portion M1. These openings enable the second groove-width portions 150 to function as suction openings.

[0132] In the head body 100a (FIG. 4), the head body 200a (FIG. 9), the head body 300a (FIG. 11), and the head body 400a (FIG. 13), the urethane layer member U1 is not inserted into the second groove-width portions 150. Accordingly, in these heads, the score lines 140 are not formed at positions corresponding to the positions of the second groove-width portions 150. In these heads, the groove width W2 of the second groove-width portions 150 is smaller than the thickness t1 of the urethane layer member U1. The groove width W2 of the second groove-width portions 150 is appropriately determined, which can prevent the score lines 140 from being formed at positions corresponding to the positions of the second groove-width portions 150. Accordingly, the second groove-width portions 150 can be arranged, regardless of the positions of the score lines 140. For example, the second groove-width portions 150 can extend to reach the peripheral edge Q2 of the outer surface 120 (striking face zone 121) of the face main portion M1. Furthermore, the second groove-width portions 150 can extend beyond the peripheral edge Q2 of the outer surface 120 (striking face zone 121) of the face main portion M1. In the embodiment of FIG. 4, the second groove-width portions 150 extend beyond the peripheral edge Q2 of the outer surface 120 (striking face zone 121) of the face main portion M1. The outer surface 120 of the face main portion M1 includes the bulge BG. Accordingly, during the above-described vacuum step, air can easily escape from the first groove-width portions 148 through the second groove-width portions 150.

[0133] As shown in the head 200 (FIG. 8), the head 300 (FIG. 10), and the head 400 (FIG. 12), the gaps 141 in the score lines 140 can be formed by arranging the second groove-width portions 150. These gaps 141 can serve as visual markers. For example, the gaps 141 can serve as markers for indicating a region around the face center Fc (see FIG. 10 and FIG. 12). As shown in the head body 200a (FIG. 9), the head body 300a (FIG. 11), and the head body 400a (FIG. 13), the body grooves 146 do not have any gaps at positions corresponding to the gaps 141 of the score lines 140. That is, the body grooves 146 are continuous because of the presence of the intermediate narrow portions 152 at positions corresponding to the gaps 141. Accordingly, even when the score lines 140 include the gaps 141, air can be smoothly evacuated from inside the first groove-width portions 148.

[0134] In the head body 100a (FIG. 4), the head body 200a (FIG. 9), the head body 300a (FIG. 11), and the head body 400a (FIG. 13), at least one of the first groove-width portions 148 extends across the face center region Rc. In the head body 100a (FIG. 4) and the head body 200a (FIG. 9), multiple first groove-width portions 148 extend across the face center region Rc. These configurations allow the score lines 140 to extend across the face center region Rc where golf ball impact points are located with high probability. Additionally, these configurations enable an increase in the groove width Wg of the score lines 140 in the face center region Rc where golf ball impact points are located with high probability. As a result, the backspin rate of the hit ball can be stabilized.

[0135] The head body 100a (FIG. 4), the head body 200a (FIG. 9), the head body 300a (FIG. 11), and the head body 400a (FIG. 13) each include a body groove 146 that includes: a first groove-width portion 148 extending across the face center region Rc; and at least one second groove-width portion 150 connected to the toe side end and/or heel side end of the first groove-width portion 148. Accordingly, the score line 140 is formed corresponding only to the first groove-width portion 148 positioned in the face center region Rc, which can make the score line 140 conspicuous. This can facilitate easier alignment of the striking face 102a toward the target point when addressing a golf ball.

[0136] The urethane layer member U1 can exhibit a spin performance that differs from that of a striking face made of metal. The urethane layer member U1 can improve feel at impact with a golf ball. From the viewpoint of enhancing the advantageous effects brought about by the urethane layer member U1, the thickness t1 of the urethane layer member U1 is preferably greater than or equal to 0.3 mm, more preferably greater than or equal to 0.32 mm, and even more preferably greater than or equal to 0.35 mm. An excessively great thickness t1 hinders the precise formation of the score lines 140. From this viewpoint, the thickness t1 of the urethane layer member U1 is preferably less than or equal to 1.0 mm, more preferably less than or equal to 0.9 mm, further more preferably less than or equal to 0.8 mm, further more preferably less than or equal to 0.7 mm, and even more preferably less than or equal to 0.6 mm.

[0137] From the viewpoints of spin performance and drainage performance, the groove width Wg of the score lines 140 is preferably greater than or equal to 0.3 mm, more preferably greater than or equal to 0.32 mm, and even more preferably greater than or equal to 0.35 mm. In order to make the groove width Wg excessively large, it is necessary to make the groove width W1 of the body grooves 146 (first groove-width portions 148) excessively large. From this viewpoint, the groove width Wg of the score lines 140 is preferably less than or equal to 0.9 mm, more preferably less than or equal to 0.85 mm, and even more preferably less than or equal to 0.8 mm.

[0138] From the viewpoints of spin performance and drainage performance, the groove depth Dg of the score lines 140 is preferably greater than or equal to 0.1 mm, more preferably greater than or equal to 0.12 mm, and even more preferably greater than or equal to 0.15 mm. For the score lines 140 formed by bending the urethane layer member U1, an excessively large groove depth Dg tends to cause an excessively large groove width Wg. From this viewpoint, the groove depth Dg of the score lines 140 is preferably less than or equal to 0.35 mm, more preferably less than or equal to 0.32 mm, and even more preferably less than or equal to 0.3 mm.

[0139] Examples of the method for attaching the urethane layer member U1 to the face main portion M1 include the use of an adhesive. This adhesive may be included in the urethane sheet U2 which forms the urethane layer member U1 as described in the above embodiment. Alternatively, the adhesive may be applied on the face main portion M1. Further alternatively, the use of an adhesive is not always necessary. For example, the urethane layer member U1 may be attached to the face main portion M1 solely through adhesion. By evacuating air between the urethane layer member U1 and the face main portion M1, the urethane layer member U1 and the face main portion M1 can be adhered to each other without the use of adhesive.

[0140] As the adhesive for attaching the urethane layer member U1 to the face main portion M1, an adhesive that has an excellent joining strength for joining between the two members can be preferably used. Examples of the adhesive include adhesives with product names “Chemlok 218E”, “Chemlok 210” and “Chemlok IMB1040” (“Chemlok” is a registered trademark) manufactured by Lord Japan, Inc. Other examples of the adhesive include adhesives with product names “METALOC C-12” and “METALOC UA” (“METALOC” is a registered trademark) manufactured by Toyokagaku kenkyusho co., ltd. Still other examples of the adhesive include a two-component epoxy adhesive. Examples of the two-component epoxy adhesive include adhesives with product names “DP420” and “DP460” put on the market by 3M Japan limited.

[0141] The method for forming the urethane layer member U1 is not limited. For example, the urethane layer member U1 may be separately formed from the head body, and then attached to the head body. For example, the urethane layer member U1 may be formed on the face main portion M1 by pressing the urethane sheet U2 against the face main portion M1 of the head body 100a using a mold. In this case, the mold may include protrusions for forming the score lines 140. However, this method tends to cause thinning of the urethane sheet U2 in the body grooves 146 due to pressing by the mold. From this viewpoint, the urethane layer member U1 is preferably produced by the manufacturing method including the vacuum step as described in the above embodiments.

[0142] From the viewpoint of enhancing the adhesion strength of the urethane layer member U1, the outer surface 120 of the face main portion M1 may be roughened. A method for roughening the outer surface 120 of the face main portion M1 is not limited. The outer surface of the face main portion may be roughened by using a mold, or by surface processing. Examples of the method of surface processing include blast processing such as shotblasting and sandblasting, metal etching processing, CNC processing, laser processing, and any combination of these processings. CNC stands for Computerized Numerical Control.

[0143] The urethane layer member U1 is made of a polyurethane. The polyurethane is a polymer having a urethane bond. Examples of the polyurethane include a thermoplastic polyurethane and a thermosetting polyurethane. The thermoplastic polyurethane is a polyurethane that exhibits plasticity by heating. In general, the thermoplastic polyurethane means a polyurethane having a linear chain structure of a high molecular weight to a certain extent. The thermosetting polyurethane is a polyurethane obtained by polymerization through a reaction between a low molecular weight urethane prepolymer and a curing agent (chain extender) when forming the urethane layer member. The thermosetting polyurethane is also referred to as two-component curing type polyurethane. Examples of the thermosetting polyurethane include a polyurethane having a linear chain structure and a polyurethane having a three-dimensional crosslinked structure, which can be obtained by controlling the number of the functional group of the prepolymer or curing agent (chain extender). The polyurethane may be a thermoplastic elastomer.

[0144] The thermoplastic polyurethane is not limited, as long as the thermoplastic polyurethane has a plurality of polyurethane bonds within a molecule and exhibits thermo-plasticity. For example, the thermoplastic polyurethane includes a reaction product having a urethane bond formed in a molecule by reacting a polyisocyanate with a polyol, and further with a polyamine as necessary.

[0145] The polyisocyanate component constituting the thermoplastic polyurethane is not particularly limited, as long as the polyisocyanate component has two or more isocyanate groups. Examples of the polyisocyanate component include an aromatic polyisocyanate such as 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, a mixture of 2,4-toluene diisocyanate and 2,6-toluene diisocyanate (TDI), 4,4’-diphenylmethane diisocyanate (MDI), 1,5-naphthylene diisocyanate (NDI), 3,3’-bitolylene-4,4’-diisocyanate (TODI), xylylene diisocyanate (XDI), tetramethylxylylene diisocyanate (TMXDI), para-phenylene diisocyanate (PPDI); and an alicyclic polyisocyanate or aliphatic polyisocyanate such as 4,4’-dicyclohexylmethane diisocyanate (H₁₂MDI), hydrogenated xylylene diisocyanate (H₆XDI), hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), and norbornene diisocyanate (NBDI). The above polyisocyanate components may be used solely or as a mixture of two or more of them.

[0146] From the viewpoint of enhancing abrasion resistance, the polyisocyanate component of the polyurethane is preferably the aromatic polyisocyanate. When the aromatic polyisocyanate is used, the resultant polyurethane has enhanced mechanical properties, and thus the obtained urethane layer member has excellent abrasion resistance. Further, from the viewpoint of enhancing weather resistance, the polyisocyanate component of the polyurethane is preferably a non-yellowing polyisocyanate (such as TMXDI, XDI, HDI, H₆XDI, IPDI, H₁₂MDI, and NBDI), and more preferably 4,4’-dicyclohexylmethane diisocyanate (H₁₂MDI). Since 4,4’-dicyclohexylmethane diisocyanate (H₁₂MDI) has a rigid structure, the resultant polyurethane has enhanced mechanical properties, and the obtained urethane layer member U1 has excellent abrasion resistance. From the viewpoint of improving the ball sticking feeling, another polyisocyanate component may be selected.

[0147] The polyol component constituting the thermoplastic polyurethane is not particularly limited as long as the polyol component has a plurality of hydroxyl groups. Examples of the polyol component include a low molecular weight polyol and a high molecular weight polyol. Examples of the low molecular weight polyol include a diol such as ethylene glycol, diethylene glycol, triethylene glycol, 1,3-butanediol, 1,4-butanediol, neopentyl glycol, and 1,6-hexanediol; and a trial such as glycerin, trimethylolpropane, and hexanetriol. Examples of the high molecular weight polyol include a polyether polyol such as polyoxyethylene glycol (PEG), polyoxypropylene glycol (PPG), and polyoxytetramethylene glycol (PTMG); a condensed polyester polyol such as polyethylene adipate (PEA), polybutylene adipate (PBA), and polyhexamethylene adipate (PHMA); a lactone polyester polyol such as poly-ε-caprolactone (PCL); a polycarbonate polyol such as polyhexamethylene carbonate; and an acrylic polyol. The above polyol components may be used solely or as a mixture of two or more of them.

[0148] An average molecular weight of the high molecular weight polyol is not particularly limited, and is preferably, for example, greater than or equal to 400, and more preferably greater than or equal to 1000. This is because an excessively small average molecular weight of the high molecular weight polyol makes the resultant polyurethane hard, which can result in deterioration of feeling at impact with a golf ball. An upper limit of the average molecular weight of the high molecular weight polyol is not particularly limited, and it is preferably less than or equal to 10000, and more preferably less than or equal to 8000.

[0149] The polyamine which can constitute the thermoplastic polyurethane as necessary is not particularly limited, as long as it has at least two amino groups. Examples of the polyamine include an aliphatic polyamine such as ethylene diamine, propylene diamine, butylene diamine, and hexamethylene diamine; an alicyclic polyamine such as isophorone diamine, and piperazine; and an aromatic polyamine.

[0150] The aromatic polyamine is not particularly limited, as long as it has at least two amino groups directly or indirectly bonded to an aromatic ring. Herein, the “indirectly bonded to an aromatic ring” means that the amino groups are bonded to an aromatic ring via, for example, a lower alkylene group. The aromatic polyamine may be, for example, a monocyclic aromatic polyamine having at least two amino groups bonded to one aromatic ring, or a polycyclic aromatic polyamine having at least two aminophenyl groups each having at least one amino group bonded to one aromatic ring.

[0151] Examples of the monocyclic aromatic polyamine include: a type wherein amino groups such as phenylenediamine, tolylenediamine, diethyltoluenediamine, and dimethylthiotoluenediamine, are directly bonded to an aromatic ring; and a type wherein amino groups such as xylylenediamine are bonded to an aromatic ring via a lower alkylene group. Further, the polycyclic aromatic polyamine may be either a poly(aminobenzene) having at least two aminophenyl groups directly bonded to each other, or a compound having at least two aminophenyl groups bonded to each other via a lower alkylene group or an alkylene oxide group. Among them, a diaminodiphenylalkane having two aminophenyl groups bonded to each other via a lower alkylene group is preferable, 4,4’-diaminodiphenylmethane and a derivative thereof are particularly preferable.

[0152] The configuration of the thermoplastic polyurethane is not particularly limited. Examples of the configuration include: a configuration where the thermoplastic polyurethane is composed of the polyisocyanate component and the high molecular weight polyol component; a configuration where the thermoplastic polyurethane is composed of the polyisocyanate component, the high molecular weight polyol component and the low molecular weight polyol component; a configuration where the thermoplastic polyurethane is composed of the polyisocyanate component, the high molecular weight polyol component, the low molecular weight polyol component and the polyamine component; and a configuration where the thermoplastic polyurethane is composed of the polyisocyanate component, the high molecular weight polyol component and the polyamine component.

[0153] Examples of the thermoplastic polyurethane include an MDI-based polyurethane in which MDI is used as the polyisocyanate component, and a hydrogenated MDI-based polyurethane in which H₁₂MDI is used as the polyisocyanate component.

[0154] Specific examples of the thermoplastic polyurethane include product names “Elastollan XNY90A”, “Elastollan XNY97A”, “Elastollan XNY585”, “Elastollan 1180A10”, “Elastollan 1185A50”, “Elastollan 1190A10TR”, “Elastollan 1195A50STR” and “Elastollan 1164D50” put on the market by BASF Japan Ltd.

[0155] In the present disclosure, the material of the urethane layer member U1 is not specifically limited as long as the material contains a polyurethane as a basis resin component. When the polyurethane is a thermoplastic polyurethane, the content of the thermoplastic polyurethane contained in the resin component constituting the material of the urethane layer member U1 is preferably greater than or equal to 50% by weight, more preferably greater than or equal to 70% by weight, and even more preferably greater than or equal to 90% by weight. In addition, it is also preferable that the resin component constituting the material of the urethane layer member U1 substantially consists only of a polyurethane (for example, only a thermoplastic polyurethane).

[0156] In addition to the resin component, the material of the urethane layer member U1 of the present disclosure may further contain, for example, a pigment component such as a white pigment (e.g. titanium oxide), a blue pigment and a red pigment, a weight adjusting agent such as calcium carbonate and barium sulfate, a dispersant, an antioxidant, an ultraviolet absorber, a light stabilizer, a fluorescent material or fluorescent brightener, as long as they do not impair the performance of the urethane layer member.

[0157] The Shore D hardness of the striking face 102a is not limited. From the viewpoint of feeling at impact with a golf ball, the Shore D hardness can be set within a predetermined range. The lower limit of the Shore D hardness of the striking face 102a can be greater than or equal to 65, further can be greater than or equal to 70, and still further can be greater than or equal to 75. The upper limit of the Shore D hardness of the striking face 102a can be less than or equal to 99, further can be less than or equal to 95, and still further can be less than or equal to 90.

[0158] The Shore D hardness of the striking face 102a is measured in a finished head. After a head 2 is stored at a temperature of 23°C for two weeks, the hardness of the striking face of the head is measured using ASKER Durometer Type D. The measurement is made by pressing the durometer against the striking face of the head. The number n of times of the measurements is 10. The average value of 10 data is considered as a measured value. The Shore D hardness is measured at a position at which the body grooves 146 or score lines 140 are not present.

[0159] Examples of a preferable material of the head body include metals and fiber reinforced plastics. Examples of the metals include titanium alloys, pure titanium, stainless steel, aluminum alloys, maraging steel, and soft iron. Examples of the fiber reinforced plastics include carbon fiber reinforced plastics. The head body may include a portion made of a metal and a portion made of a fiber reinforced plastic.

[0160] Examples of a preferable material of the face main portion M1 include metals and fiber reinforced plastics. Examples of the metals include titanium alloys, pure titanium, stainless steel, aluminum alloys, maraging steel, and soft iron. Examples of the fiber reinforced plastics include carbon fiber reinforced plastics. The face main portion M1 may include a portion made of a metal and a portion made of a fiber reinforced plastic.

[0161] The following clauses are a part of invention included in the present disclosure.

[0162] A golf club head including a face portion that includes a striking face, wherein

[0163] the face portion includes a face main portion and a urethane layer member that is disposed outside the face main portion and made of a polyurethane,

[0164] the urethane layer member includes a plurality of score lines that are formed on its outer surface and extend from a toe side to a heel side, and a plurality of inner surface protrusions that are formed on its inner surface and extend from the toe side to the heel side corresponding to the respective score lines,

[0165] the face main portion includes a plurality of body grooves that are formed on its outer surface and extend from the toe side to the heel side corresponding to the respective inner surface protrusions, and

[0166] the inner surface protrusions are inserted into the respective body grooves.

[0167] The golf club head according to clause 1, wherein the urethane layer member has a substantially constant thickness.

[0168] The golf club head according to clause 1 or 2, wherein

[0169] the urethane layer member has transparency, and

[0170] a marking is formed in at least one of the body grooves.

[0171] The golf club head according to clause 3, wherein

[0172] the marking has a line shape, and

[0173] the marking has a line width that is larger than a width of the score lines.

[0174] A method of manufacturing a golf club head including a face main portion and a urethane layer member that is disposed outside the face main portion, the urethane layer member having an outer surface that forms a striking face,

[0175] the method comprising:

[0176] a first step of preparing a urethane sheet that forms the urethane layer member; and

[0177] a second step of evacuating a space between the face main portion and the urethane sheet to a vacuum state while pressing the urethane sheet against an outer surface of the face main portion, wherein

[0178] the face main portion includes a plurality of body grooves that are formed on its outer surface and extend from a toe side to a heel side, and suction openings that are formed in the respective body grooves, and

[0179] in the second step, while air is evacuated from the body grooves through the suction openings, the urethane sheet is drawn into the body grooves, whereby inner surface protrusions are formed on an inner surface of the urethane layer member, and score lines, corresponding to the respective inner surface protrusions, are formed on the outer surface of the urethane layer member.

[0180] The method of manufacturing a golf club head according to clause 5, wherein

[0181] the striking face includes a bulge,

[0182] the outer surface of the face main portion includes a striking face zone that corresponds to the striking face, and

[0183] each of the body grooves extends from its toe side end, through the striking face zone, to its heel side end, with the toe side end and/or the heel side end located on or outside a peripheral edge of the striking face zone.

[0184] The method of manufacturing a golf club head according to clause 5 or 6, wherein

[0185] the suction openings of the body grooves are formed by the toe side end and/or the heel side end of each of the body grooves being open.

[0186] 100, 200, 300, 400, 500, 600, 700, 800, 900 ... Golf club head

[0187] 100a, 200a, 300a, 400a, 500a, 600a, 700a, 800a, 900a ... Head body

[0188] 102 ... Face portion

[0189] 102a ... Striking face

[0190] 104 ... Crown portion

[0191] 106 ... Sole portion

[0192] 108 ... Hosel portion

[0193] 120 ... Outer surface of the face main portion

[0194] 121 ... Striking face zone of the head body

[0195] 122 ... Inner surface of the face main portion

[0196] 124 ... Inner surface of the urethane layer member

[0197] 126 ... Outer surface of the urethane layer member

[0198] 130 ... Step recess

[0199] 130a ... Stepped portion

[0200] 140 ... Score line

[0201] 141 ... Gap of the score line

[0202] 142 ... Inner surface protrusion

[0203] 146 ... Body groove

[0204] 148 ... First groove-width portion of the body groove

[0205] 150 ... Second groove width portion of the body groove

[0206] 160 ... Lengthened score line

[0207] 170 ... Marking

[0208] 172 ... Marking line

[0209] 180 ... Vacuum adhesion device

[0210] 182 ... Vacuum chamber

[0211] 184 ... Head holder

[0212] 186 ... Opening

[0213] 188 ... Sheet holding portion

[0214] Fc ... Face center

[0215] U1 ... Urethane layer member

[0216] U2 ... Urethane sheet

[0217] M1 ... Face main portion

[0218] K1, K2 ... Suction opening

[0219] Et ... Toe side end of the body groove

[0220] Eh ... Heel side end of the body groove

[0221] The above descriptions are merely illustrative and various modifications can be made without departing from the principles of the present disclosure.

[0222] The terminology used in the description of the various described embodiments herein is for the purpose of describing particular embodiments only and is not intended to be limiting. The use of the terms “a”, “an”, “the”, and similar referents in the context of throughout this disclosure (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. As used throughout this disclosure, the word “may” is used in a permissive sense (i.e., meaning “having the potential to”), rather than the mandatory sense (i.e., meaning “must”). Similarly, as used throughout this disclosure, the terms “comprising,” “having,” “including,” and “containing” are to be construed as open-ended terms (i.e., meaning “including, but not limited to,”) unless otherwise noted.

[0223] Although the terms first, second, third, etc. may be used herein to describe various elements, components, regions, layers, sections, steps, processings, and/or operations, these elements, components, regions, layers, sections, steps, processings, and/or operations should not be limited by these terms. These terms may be only used to distinguish one element, component, region, layer, section, step, processing, or operation from another element, component, region, layer, section, step, processing, or operation. Terms such as “first,” “second,” and other numerical terms when used herein do not imply a sequence or order unless clearly indicated by the context. Thus, a first element, component, region, layer, section, step, processing, or operation discussed herein could be termed a second element, component, region, layer, section, step, processing, or operation without departing from the teachings of the example embodiments.