Surface Metallizing Method

The present invention provides a method of producing a metallized polybutylene terephthalate part, which comprises using a molded part consisting chiefly of a polybutylene terephthalate resin composition containing 2-40% by weight of potassium-titanate fiber relative to the total weight of the composition, and subjecting the molded part to sputtering or vacuum metallizing, thereby forming a metallized coat thereon.

Potassium-titanate fibers used for the purpose of the invention refer to white, needle-shape single-crystal fibers having a chemical composition expressed by K.sub.2 O.nTiO.sub.2 (where n is 1 or more). The average length of the fibers is 5.50.mu., preferably 10-20.mu., and the average diameter thereof is 0.1-0.8.mu., preferably 0.2-0.5.mu.. The amount of potassium-titanate fibers added to the polybutylene terephthalates is such that it constitutes 2-40% by weight, preferably 3-30% by weight, relative to the resulting composition as a whole.

Heretofore, potassium-titanate fibers have been used simply for producing a white color in resins. By this invention, however, it has been proved that polybutylene terephthalates containing potassium-titanate fibers provide various advantages such as good coat adhesion, good surface mirror-effect, and high craze resistance, if the surface is metallized by sputtering or vacuum deposition. Needless to say, potassium-titanate fibers can serve as a good reinforcement for the polybutylene terephthalates, depending upon the amount added.

A known surface treatment may be used in order to strengthen the bond between the potassium-titanate fibers and the resin. for example, silane coupling agents, such as amino-silne and epoxy-silane, and titanate coupling agents may be used for the purpose. Most preferable are silane coupling agents.

In the method of the present invention, potassium-titanate fibers may be used in the form of a mixture with some other filler. For example, any of the following may be used as such filler: calcium carbonate having a mean particle diameter of 4.mu. or below, kaolin or any material of the kaolin group (including kaolinite, sericite, etc.) having a crystal form of hexagonal plate with a mean particle diameter of 0.1-0.3.mu., wollastonite having a block shape of 10.mu. or below in mean particle diameter, and processed mineral fiber having a mean fiber length of 4-6.mu. and an aspect ratio of 40-60 (as composed of 43% SiO.sub.2, 39% CaO, and 8% Al.sub.2 O.sub.3, for example).

Polybutylene terephthalates available for the purpose of the present invention are not limited to polybutylene terephthalate resins alone. They may take the form of a copolymer consisting chiefly of polybutylene terephthalate or may be used in mixture with other thermoplastic resins. For example, they may be mixed with any of the following: polyolefins such as polyethylene and polypropylene, ethylene carboxylate copolymers such as ethylene alkylacrylate copolymer and the like, vinyl compounds such as polystyrene, and styrene-butadiene-acrylonitrille copolymer, polyesters such as polyethyelene terephthalate and polycarbonate, rubber-like materials such as polybutadiene and the like, and derivatives of these materials. Further, it is possible to introduce into the polybutylene terephthalates any multipolymer consisting of polyacrylate, any elastomer such as segment-type copolyester, any stabilizer, surface-active agent, or the like.

The mixture of potassium-titantate fiber with polybutylene terephthalate resin may be extruded according to a conventional method. For the purpose of sputtering or vacuum metallizing, any method can be used which is conventionally employed with respect to resins having good coating performance such as ABS and the like. After the molded part is degreased with a suitable solvent, the molded part is coated of witha base coat of urethane or acrylic urethane or acrylic ester; then the coat is dried. Sputtering or vacuum metallizing is effected thereafter. When a sputtering apparatus is employed,chrome alloy or aluminum is evaporated under an argon gas pressure of 1.times.10.sup.-3 -2.times.10.sup.-4 Torr to produce a thin metallic layer of 300-100 .ANG. on the molded part, thereby imparting metallic luster to the part. when a metallizing apparatus is employed, aluminum is evaporated under a pressure of 1.times.10.sup.-3 -1.times.10.sup.-4 Torr to form a thin metallic layer of 200-500 .ANG. on the part, thereby imparting metallic luster to the part. For general-purpose uses, it is a usual practice to protect the metal layer by applying a top coat to the metal layer. The product thus obtained has a mirror-like surface and its metallized coat is strongly bonded to the substrate, and is free from the possibility of crazing due to temperature changes or the like. Thanks to these excellent properties, the metallized products can be advantageously utilized in various industrial applications.

Potassium-titanate fiber was added to polybutylene terephthalate (Polyplastics K.K.'s product; trade name: Juranex) so that the former amounted to 15 wt % relative to the total weight of the composition. Employing a molding machine, the composition was injection-molded into a flat plate. After degreasing, the plate was coated with base coat EXP1474U/EXP1475C (weight ratio 100/30), manufactured by Fujikura Kasei K.K., and was then subjected to forced drying for 60 min at 140.degree. C.

Subsequently, chrome alloy was sputtered employing a sputtering apparatus and under an argon gas pressure of 1.times.10.sup.-3 Torr to form a layer 400-500 .ANG. in thickness on the plate. The layer was coated with top coat EXP1380, a product of Fujikura Kasei K.K., and then subjected to forced drying for 30 min at 70.degree. C. The metalized part was visually evaluated as to its appearance. The part was found to have a mirror-like surface and good luster. The metallized coat was not subject to crazing. To evaluate the bond of the metallized coat to the base coat, rule lines were drawn crosswise by knife on the coat, 11 lines each way, to form 100 checkers; and the checkers were subjected to Scotch tape test, a forced peel test, using JIS adhesive cellophane tape. The result was that all the checkers remained unpeeled.

A molded part containing 7.5% by weight of potassiumtitanate fiber was prepared. The part was metallized on the surface by sputtering as in Example 1. In this case, too, the part had a mirror-like surface, with good luster, and no crazing was obseerved. The bond strength of the coat was also evaluated using the forced peel test described in Example 1. The result was that all the checkers (100) remained unpeeled.

A molded part containing 4.3% by weight of potassium-titanate fiber was prepared. The part was metallized by sputtering and evaluated in the same manner as in Example 1. In this case, too, good results were obtained in all respects: mirror-like appearance, crazing, and a strongly bonded coat (with all checkers remaining unpeeled).

The potassium-titanate fiber contained in the composition was 30% by weight. After molding, the part was metallized sputtering and evaluated in the same manner as in Example 1. Evaluation results were good in all respects: mirror-like appearance, no crazing, and good bond strength of the coat (with all the checkers remaining unpeeled).

A molded part containing 15% by weight of potassiumtitanate fiber and 5% by weight of polycarbonate was metallized by sputtering as in Example 1. Good results were seen in all respects: nirror-like appearance, no crazing, and good bond strength of the coat (with all the checkers remaining unpeeled).

In examples 1 to 5, vacuum metallization with aluminum was carried out instead of sputtering. Evaluation was made in the same way as in the other examples. Vacuum metallization was effected by employing a vacuum metallizing apparatus so as to produce an aluminum layer 3-400 .ANG. in thickness on the molded part. The product obtained had a mirror-like appearance on the surface and no crazing was observed. The bond of the coat to the substrate was satisfactory (with all the checkers remaining unpeeled).

A flat plate was molded from a polybutylene terephthalate composition that did not contain potassium-titanate fiber. The Plate was metallized by sputtering as in Example 1. The Product had a mirror-like surface and good luster, but crazing was observed.

A part was molded from a composition containing 30% glass fiber. Sputtering was effected as in Example I. No crazing was observed, but the appearance did not have a mirror-like luster.

The composition of Reference Example 2 was reformulated to contain 17% by weight glass fiber instead of 30% by weight glass fiber; The molded part was subjected to sputtering. The product did not have a mirror-like luster.

Glass fiber was added in corresponding amount in place of potassium-titanate fiber. Sputtering was effected as in Example 1. The product was not satisfactory in appearance in this case either; a mirror-like luster was not obtained.

Reference Examples 1 to 4 were repeated but vacuum metallization with aluminum was effected in place of sputtering. the products were evaluated in the same manner. The results were no better than those in Reference Examples 1 to 4.