Method and Apparatus for Manufacturing a Nozzle Plate for Ink-Jet Printers

The invention relates to a method of manufacturing a nozzle plate for an ink-jet printer and more particularly to a method including a single operation in which a plate is first pressed locally into a circular aperture in a pressing die by a pressing and punching tool whose dimensions correspond to the internal dimensions of a nozzle to be formed, and the plate is subsequently punched during further pressing to form the nozzle, using an elastic block as a cushion forming the press mold.

The invention also relates to an apparatus for performing the method.

The method itself as well as the apparatus are known from German Offenlegungsschrift 30 42 483, to which U.S. Pat. No. 4,425,777 corresponds. It has been found that in nozzle plates thus manufactured the quality of the nozzle edges at the exit end depends to a comparatively high degree on the surface structure of the nozzle plate material. For example, during the punching of the plates the nozzle edges thus formed are torned off irregularly, which is inter alia due to excessive expansion of the material of the nozzle plate, thus giving rise to asymmetrical or rough nozzle edges.

The object of the invention is to manufacture nozzle plates for ink-jet printers, having edges which are smoother than those of known nozzles.

According the invention this object is achieved by positioning a metal foil tightly against that side of the plate which is remote from the tool, and pressing and punching the foil through the circular aperture together with the plate. The metal foil is made of a material which is harder than that of the nozzle plate and does not have a preferred mechanical orientation that is, an isotropic material.

After the punching operation, the remainder of the metal foil thus acts as a kind of additional die which provides a symmetrical shape of the nozzle edge and at the same time provides an increased material density, resulting in smoother nozzle edges.

Preferably, an apparatus for performing the method comprises a pressing and punching tool and a cushion which receives the tool and which carries a pressing die with a circular aperture for the formation of a nozzle, the metal foil overlying the pressing die so that it covers the circular aperture and can be fixed tightly between the pressing die and the plate in which a nozzle is to be formed.

Thus, for the formation of the ink-jet nozzles the nozzle plate to be formed can be arranged directly on the metal foil. Before the pressing and punching a hold-down device which is connected to the pressing and punching tool presses both the plate and the metal foil underneath it against the pressing die and the cushion, respectively, so that the metal foil is tightened firmly between the pressing die and the plate.

Preferably, the isotropic metal foil consists either of an amorphous material, for example amorphous iron, or of a micro crystalline material of very small grain size, for example electroformed chromium. The thickness of the metal foil preferably amounts to from approximately 20 to 25 .mu.m.

Such metal foils of amorphous or micro crystalline material which does not have a preferred mechanical orientation, for example rolling direction or the like, is most suitable for the precise separation of the part formed (blank) from the remainder of the material, and hence for the manufacture of high-precision nozzles with accurately defined and smooth edges.

The invention will be described in more detail, by way of example, with reference to the drawings.

FIG. 1 is a sectional elevation of an apparatus for performing the method in accordance with the invention,

FIG. 2 is a similar view of the apparatus of FIG. 1 during the pressing operation, and

FIG. 3 shows the apparatus of FIG. 1 after the punching operation.

A press plate 1 which carries a pressing and punching tool 2 is arranged so as to be slidable in a hold-down device 4. When a pressure P is exerted on the press plate 1, the hold-down device 4 is moved in the direction indicated by the arrow P until the lower side of the hold-down device 4 bears on the plate 5 in which the nozzle is to be formed. When the pressure is increased, the tool 2 passes through an opening 3 in the hold-down device 4.

On that side of the plate 5 which is remote from the tool 2 a metal foil 6 is positioned against the plate 5. The metal foil 6 overlies a pressing die 7 which has a circular aperture 8 for the formation of the desired nozzles. The pressing die 7 itself bears on a hard elastic block or cushion 9 which is arranged in a recess in an anvil 10 which is preferably made of steel or cast iron. The cushion 9 is made of lead or another suitable material having similar mechanical properties.

The cushion 9 may be constructed, for example, so that a part thereof projects through the circular aperture 8 and is in direct contact with the lower surface of the metal foil 6. The cushion 9 may further be arranged in the anvil 10 in such a way that after termination of each punching operation, it can be displaced together with the metal foil 6 and the pressing die 7, for example, perpendicularly to the plane of drawing of FIG. 1, so that subsequently an unused portion of the metal foil 6 and the cushion 9 will be situated opposite the tool 2. This requires a displacement over a distance equal to the distance between two adjacent circular apertures 8 in the pressing die 7.

If the cushion 9 does not project into a circular aperture 8, only the metal foil 6 and the cushion 9 need be displaced after each punching operation.

The shape of the tool 2 corresponds to the desired shape of the nozzle. The tool has a smoothly polished surface of homogeneous hardness. The homogeneous hardness can be obtained, for example, by means of a salt bath. In the present embodiment the leading part of the tool 2 has a diameter of 50 .mu.m which increases to 300 .mu.m at the opposite side.

The plate 5 consists of pure nickel which has been subjected to soft annealing in order to reduce its hardness. The nickel plate 5 has been polished on the side facing the metal foil 6. It has a thickness of approximately 300 .mu.m.

The metal foil 6 has a thickness of from 20 to 25 .mu.m and is made of a material which is much harder than the material of the plate 5. For example, the metal foil 6 may consist of amorphous iron having a vickers hardness of from 800 to 1000 VH.sub.02. However, the metal foil 6 may alternatively consist of a micro-crystalline material, for example electroformed chromium. Materials of this type are isotropic; that is they do not have a preferred mechanical orientation, for example a rolling direction or the like, so that the blank can be separated with a very sharp and smooth edge and smooth nozzles edges can be formed. It will be apparent that, for example, silicon and borium may be added to the amorphous iron foil 6 to increase its hardness, so that even more accurate nozzle edges can be formed.

The pressing die 7 which is arranged underneath the metal foil 6 is made of steel and has a thickness of the order of magnitude of that of the plate 5.

FIG. 1 shows the situation prior to the pressing and punching operation and FIG. 2 illustrates the pressing operation. The leading part of the tool 2 has penetrated into the plate 5 and has pressed part of the plate 5 and the metal foil 6 into the die aperture 8 and into the cushion 9. When the pressure P on the tool 2 is sustained, the actual punching operation commences, the part of the plate 5 and the metal foil 6 being further stretched in front of the tool 2. The blanks 5a, 6a formed from the plate 5 and the metal foil 6 are pressed into the cushion 9 by the force exerted on the tool 2. After the punching operation and after the return of the tool 2 and the hold-down device 4, the cushion 9, together with the blanks 5a, 6a, is so positioned in the anvil 10 that subsequently the tool 2 faces unused parts of the metal foil 6 and the cushion 9. Ink-jet nozzles manufactured by this pressing punching operation are very accurate and have acute, smooth edges, which provide symmetrical wetting.

When a plurality of nozzles are to be formed in the plate 5, the relevant pressing and punching tool may be laterally displaced after each pressing and punching operation. However, it is alternatively possible to arrange a plurality of simultaneously operated tools adjacent each other. In that case a displacement of the tools is not necessary, because the relevant nozzle orifices are then formed simultaneously instead of successively.