Abstract:
A club head composed of a club head body and a single- or multi-layered coating film covering the club head body, wherein the coating film includes a coating layer having good scratch or scuff resistance and high resilience. The club head keeps a good appearance even after repeated shots because of its good scratch or scuff resistance and its ability to repair scuffs by itself with the lapse of time even though it is temporarily damaged.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]     This non-provisional application claims priority under 35 U.S.C. §119(a) on Patent Application No. 2004-179028 filed in Japan on Jun. 17, 2004, the entire contents of which are hereby incorporated by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     The present invention relates to a club head excelling in surface durability.  
         [0003]     Club heads for golf, park golf, grand golf, and gate ball usually have a coating film for their surface protection and good appearance. Such coating film is required to have not only good appearance but also good resistance to impact and wear resulting from repeated shots by the club or stick.  
         [0004]     A club head coating material to meet this requirement is disclosed in JP-A 2003-126306. It is composed of 100 pbw of acrylic resin (solids) and 1.0 to 10.0 pbw of polyethylene wax. It forms a coating film which exhibits good wear resistance and peel resistance owing to the outstanding impact resistance of the acrylic resin.  
         [0005]     This conventional coating material, however, is not entirely satisfactory. Even though it forms an impact- and wear-resistant coating film on the club head, the coating film is subject to scuff which propagates to deteriorate the head&#39;s appearance. So, there has been a demand for club heads which keep their good appearance even after repeated shots.  
       SUMMARY OF THE INVENTION  
       [0006]     The present invention was completed in view of the foregoing. It is an object of the present invention to provide a club head which keeps a good appearance even after repeated shots because of its good scratch or scuff resistance and its ability to repair scuffs by itself with the lapse of time even though it is temporarily damaged.  
         [0007]     As the result of their extensive studies, the present inventors found that the above-mentioned object is achieved by a club head composed of a club head body and a coating film covering the club head body, wherein the coating film includes a layer having good scratch or scuff resistance and high resilience. This finding led to the present invention.  
         [0008]     The first aspect of the present invention is directed to a club head composed of a club head body and a single- or multi-layered coating film covering the club head body, wherein the coating film includes a coating layer having good scratch or scuff resistance and high resilience.  
         [0009]     The second aspect of the present invention is directed to the club head as defined above in which the coating layer having good scratch or scuff resistance and high resilience is one which is formed from any of a coating compound containing polydimethylsiloxane copolymer, polycaprolactone, and polysiloxane, a coating compound containing polydimethylsiloxane copolymer whose skeleton has polycaprolactone and polysiloxane introduced thereinto, a coating compound containing polydimethylsiloxane copolymer whose skeleton has polycaprolactone introduced thereinto and polysiloxane, and a coating compound containing polydimethylsiloxane copolymer whose skeleton has polysiloxane introduced thereinto and polycaprolactone.  
         [0010]     The third aspect of the present invention is directed to the club head as defined in the first aspect which the coating layer having good scratch or scuff resistance and high resilience is formed after a deposited layer has been formed by ion plating on the surface of the club head body.  
         [0011]     The fourth aspect of the present invention is directed to the club head as defined in the first aspect which is intended for golf, park golf, grand golf, and gate ball.  
         [0012]     The club head according to the present invention keeps its good appearance even after repeated shots. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0013]     The invention will be described below in more detail with reference to its preferred embodiments.  
         [0014]     The club head according to the present invention is composed of a club head body and a single- or multi-layered coating film covering the club head body. It is characterized in that the coating film includes a coating layer having good scratch or scuff resistance and high resilience.  
         [0015]     The term “a coating layer having good scratch or scuff resistance and high resilience” as used in the present invention implies a coating layer which repairs its scuffs by itself with the lapse of time even when it is damaged slightly by scuffs or dents (hereinafter, such function described as self-healing ability). This function is ascribed to the good resilience of the coating film.  
         [0016]     The coating film varies in resilience and the self-healing function relies on resilience. Resilience depends on the molecular structure of the block copolymer consisting of soft segments and hard segments. Hard segments form crystalline domains and soft segments form amorphous domains. Crystalline domains function as crosslinking sites (which prevent amorphous domains from plastic deformation). Thus, the coating film as a whole exhibits resilience, and the degree of resilience varies depending on the kind and composition of monomer units constituting the block copolymer and also on the arrangement of monomer units in the polymer chains.  
         [0017]     There are no restrictions on the coating compound which forms the above-mentioned coating film having scratch or scuff resistance and high resilience. It may be selected from clear resins based on acrylate, urethane, polycarbonate, polystyrene, polyester, silicone, and fluoroplastics, in the form of homopolymer, copolymer, or blend. Its typical examples are listed below. 
    (1) One containing polydimethylsiloxane copolymer, polycaprolactone, and polysiloxane.     (2) One containing polydimethylsiloxane copolymer whose skeleton has polycaprolactone and polysiloxane introduced thereinto.     (3) One containing polydimethylsiloxane copolymer whose skeleton has polycaprolactone introduced thereinto and polysiloxane.     (4) One containing polydimethylsiloxane copolymer whose skeleton has polysiloxane introduced thereinto and polycaprolactone.    
 
         [0022]     Each of the coating compounds (1) to (4) listed above contains polydimethylsiloxane copolymer (A), polycaprolactone (B), and polysiloxane (C). Each of polycaprolactone (B) and polysiloxane (C) may be present in the skeleton of dimethylpolysiloxane copolymer (A) or may be present separately in the coating compound.  
         [0023]     The polydimethylsiloxane copolymer (A) mentioned above should preferably be a copolymer composed of polydimethylsiloxane segments and polymer chains formed from vinyl monomers. It may also be a block copolymer or a graft copolymer.  
         [0024]     Examples of the vinyl monomer mentioned above include methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, octyl acrylate, cyclohexyl acrylate, tetrahydrofurfuryl acrylate, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, 2-ethylhexyl methacrylate, stearyl methacrylate, lauryl methacrylate, methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, n-butyl vinyl ether, isobutyl vinyl ether, styrene, α-methylstyrene, acrylonitrile, methacrylonitrile, vinyl acetate, vinyl chloride, vinylidene chloride, vinyl fluoride, vinylidene fluoride, glycidyl acrylate, glycidyl methacrylate, acryl glycidyl ether, acrylic acid, methacrylic acid, itaconic acid, crotonic acid, maleic acid, maleic anhydride, citraconic acid, acrylamide, methacrylamide, N-methylol acrylamide, N,N-dimethylacrylamide, N,N-dimethylaminoethyl methacrylate, N,N-diethylaminoethyl methacrylate, and diacetoneacrylamide. Additional examples include vinyl monomers having OH group, such as 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl acrylate, 2-hydroxypropyl methacrylate, and allyl alcohol. Another example is a reaction product of Cadura E with any of acrylic acid, methacrylic acid, itaconic acid, crotonic acid, and maleic acid.  
         [0025]     Examples of the polycaprolactone (B) mentioned above include difunctional polycaprolactone, trifunctional polycaprolactone, and tetrafunctional polycaprolactone.  
         [0026]     Examples of the polysiloxane (C) mentioned above include polymers of partial hydrolyzate of silane compound having hydrolyzable silyl groups or addition products obtained by adding the radical-polymerizable silane compound mentioned above to organosilica sol (which is a stable dispersion of silicon dioxide fine powder in an organic solvent). The silane compound is exemplified by tetramethoxysilane, tetraethoxysilane, methyltrimethoxysilane, methyltriethoxysilane, dimethyldimethoxysilane, dimethyldiethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropyltriethoxysilane, γ-glycidoxypropylmethyldimethoxysilane, γ-glycidoxypropylmethyldiethoxysilane, γ-methacryloxypropyltrimethoxysilane, γ-methacryloxytriethoxysilane, γ-methacryloxypropylmethyldimethoxysilane, γ-methacryloxypropylmethyldiethoxysilane, γ-acryloxypropylmethyltrimethoxysilane, and γ-acryloxypropylmethyldimethoxysilane.  
         [0027]     Incidentally, introduction of the polycaprolactone (B) and/or the polysiloxane (C) into the skeleton of the polydimethylsiloxane copolymer (A) may be accomplished by copolymerization for the polydimethylsiloxane copolymer in the presence of the polycaprolactone (B) and/or the polysiloxane (C).  
         [0028]     The content of polydimethylsiloxane should preferably be 0.5 to 35 wt % in the polydimethylsiloxane copolymer (A) including one which has polycaprolactone (B) and/or polysiloxane (C) connected to the molecule thereof. The polydimethylsiloxane moiety protects the surface of the coating film from scuffs by its lubricating action to reduce the coefficient of friction.  
         [0029]     The content of polycaprolactone (B) should preferably be 2 to 60 wt % in the solids of the coating material. Polycaprolactone (B) imparts high resilience to the coating film, thereby allowing the coating film to absorb external force applied thereto.  
         [0030]     The content of polysiloxane (C) should preferably be 0.5 to 25 wt % in the solids of the coating material. Polysiloxane (C) imparts stain resistance, weather resistance, and heat resistance to the coating film and increases the surface hardness of the coating film.  
         [0031]     The coating compound composed of the components (1) to (4) mentioned above may be cured by using a crosslinking agent which is capable of urethane-crosslinking and/or melamine-crosslinking the polydimethylsiloxane copolymer (A) including one which has polycaprolactone (B) and/or polysiloxane (C) connected to the skeleton thereof. Examples of the urethane-crosslinking agent include polyisocyanate and blocked-polyisocyanate, such as methylene-bis-4-cyclohexyl-isocyanate, trimethylolpropane adduct of tolylene diisocyanate, trimethylolpropane adduct of hexamethylene diisocyanate, trimethylolpropane adduct of isophoronediisocyanate, isocyanurate of tolylene diisocyanate, isocyanurate of hexamethylene diisocyanate, isocyanurate of isophorone diisocyanurate, and biuret of hexamethylene diisocyanate. Examples of the melamine cross-linking agent include alkoxymethylol melamine.  
         [0032]     Any commercial product may be used as the coating compound that gives rise to a coating film having scratch or scuff resistance and high resilience. It is available from Natoko Paint Co., Ltd. under a trade name of “Self-healing clear”, which is a special coating compound based on acrylic resin.  
         [0033]     The coating compound used to form the coating film on the club head body may optionally be incorporated with any known paint additives listed below.  
         [0034]     Leveling agent, such as Disparon L-1980-50 (from Kusumoto Chemicals, Ltd.) 
        UV light absorber, such as Tinuvin-P (from Ciba Specialty Chemicals K.K.) and ASL-23 (Shonan Kagaku)     Fluorescent brightening agent, such as Ubitex OB (from Ciba Specialty Chemicals K.K.), Hostalux KSN (from Hoechst Japan), and Hakkol PY-1800 (from Hakkol Chemical Co., Ltd.)     Slip agent, such as Disparon 1711 (from Kusumoto Chemicals, Ltd.) and Granol 450 (from Kyoeisha Chemical Co., Ltd.)     Light stabilizer, such as Adekastab LA-77 (from Asahi Denka Co., Ltd.) and Tinuvin 622LD (from Ciba Specialty Chemicals K.K.)     Curing catalyst, such as dibutyltin dilaurate, lead naphthenate, lead octylate, aluminum chelates, and tertiary amines.     Antifoaming agent, such as Disparon OX-710 (from Kusumoto Chemicals, Ltd.)     Thickening agent, such as Disparon AS-415 (from Kusumoto Chemicals, Ltd.)     Coloring pigment, such as titanium dioxide.     Plasticizer, such as dioctyl phthalate and dioctyl adipate.        
 
         [0044]     It may also be incorporated with other resins such as polyester polyol and polyether polyol.  
         [0045]     The coating compound may be used as an enamel coating compound after incorporation with pigments or as a clear coating compound without pigments.  
         [0046]     The club head body (before coating) according to the present invention may be constructed from any material which will not impair the features of the present invention. Examples of such materials include titanium alloy, soft iron, stainless steel (and other steels), pure titanium, aluminum alloy, copper alloy, nickel alloy, tungsten alloy, amorphous alloy, carbon fiber-reinforced plastics (CFRP), and wood. They may be used alone or in combination with one another. The club head body is not specifically restricted in its structure. It is possible to form the entire club head with the above-mentioned material or it is possible to form a plate from the above-mentioned material and attach it to a separately formed club head.  
         [0047]     Prior to coating, the club head body should preferably undergo surface treatment for better coating adhesion. Surface treatment includes dry process, polishing, primer application, and pin-hole filling (which are explained below).  
         [0048]     Dry surface treatment denotes any of ion plating, corona treatment, plasma treatment, UV light irradiation, and electron beam irradiation, which activates the surface of the club head.  
         [0049]     Polishing treatment denotes any process of polishing the club head body with a wire brush or by sand-blasting.  
         [0050]     Primer application is intended to form a primer layer which exhibits good adhesion to both the club head body and the coating layer thereon and which also facilitates detection of pinholes in the surface of the club head body. The primer layer may be formed from a liquid thermosetting polyester resin, which is cured after application.  
         [0051]     Pin-hole filling is accomplished by applying a two-pack putty to pin-holes in the surface of the club head body.  
         [0052]     The club head body according to the present invention should preferably be one which has a vapor deposition layer (formed by ion plating) and a self-healing coating layer formed thereon. Ion plating is a process for forming a vapor deposition layer from a metal or a metal carbide, nitride, or boride.  
         [0053]     Examples of the metal carbide, nitride, and boride include Ti compounds (such as TiC, TiCN, and TiB), Ta compounds (such as TaN, TaC, and TaB), Cr compounds (such as CrN, CrC, and CrB), Zr compounds (such as ZrN, ZrC, and ZrB), Nb compounds (such as NbN, NbC, and NbB), Hf compounds (such as HfN, HfC, and HfB), W compounds (such as WN, WC, and WB), Si compounds (such as SiN and SiC), Mo compounds (such as MoB), V compounds (such as VN, VC, and VB), and B compounds (such as BN, BC, MnB, and CoB). They may be used alone or in combination with one another.  
         [0054]     The vapor deposition layer formed by ion plating should have a thickness no larger than 0.01 μm, preferably no larger than 0.05 μm, and no smaller than 50 μm, preferably no smaller than 10 μm.  
         [0055]     According to the present invention, the coating film covering the club head body is composed of one layer or more than one layer, and it includes one self-healing layer. The coating layer having the self-healing function may be formed directly on the surface of the club head body or indirectly with an enamel coating layer or the like interposed between it and the surface of the club head body. The coating layer having the self-healing function exhibits good adhesion to the club head body if the club head body is coated with a deposited layer formed by ion plating. Generally, if a coating layer is formed after a deposited layer is formed on a club head body by ion plating, the coating layer tends to be peeled off easily. However, contrary to the conventional production, according to the present invention, the combination of the coating layer having the self-healing function and the deposited layer formed by ion plating exhibits good adhesion to the club shaft body.  
         [0056]     The coating layer having the self-healing function may be formed by any method, such as brush coating, spray coating, and electrostatic coating, which is usually employed to coat the surface of club heads.  
         [0057]     The coating layer having the self-healing function may have a thickness no smaller than 1 μm, preferably no smaller than 10 μm, and no larger than 50 μm, preferably no larger than 30 μm.  
         [0058]     The self-healing layer should have a thickness which accounts for no less than 5%, preferably no less than 10%, and more preferably no less than 20%, of the total thickness of single layer or multiple layers covering the club head body. The coating layer will be poor in scratch or scuff resistance if this requirement is not met.  
         [0059]     Incidentally, the total thickness of the single layer or multiple layers covering the club head body is usually no smaller than 5 μm, preferably no smaller than 10 μm, and no larger than 100 μm, preferably no larger than 70 μm.  
         [0060]     The club head according to the present invention is suitable for golf, park golf, grand golf, and gate ball. Its shape and weight should conform to their respective game rules.  
         [0061]     The club head according to the present invention is coated with a coating layer which includes a layer having good scratch or scuff resistance and high resilience. Therefore, the coating layer applied to the outermost surface of the club head relieves external force (owing to its lubricating function) and restores its original shape (owing to its high resilience). Thus, the coating film is hardly subject to scuff and damage.  
       EXAMPLES  
       [0062]     The invention will be described in more detail with reference to the following Examples, which are not intended to restrict the scope thereof.  
         [0000]     Preparation of Coating Compound (1)  
         [0063]     Tetraethoxysilane (320 pbw) was mixed with ethanol (106 pbw), deionized water (21 pbw), and 1% hydrochloric acid (1 pbw). The resulting solution was allowed to stand at 85° C. for two hours and then gradually heated, during which ethanol was recovered. The solution was kept at 180° C. for 30 minutes and then cooled. Thus there was obtained viscous polysiloxane (1).  
         [0064]     VPS-0501 (20 pbw) was mixed with toluene (50 pbw), methyl isobutyl ketone (50 pbw), methyl methacrylate (30 pbw), butyl methacrylate (26 pbw), 2-hydroxyethyl methacrylate (23 pbw), methacrylic acid (1 pbw), and 1-thioglycerin (0.5 pbw). VPS-0501 is a polymerization initiator containing polydimethylsiloxane units, available from Wako Pure Chemical Industries, Ltd. The resulting mixture was allowed to react at 80° C. for eight hours. Thus there was obtained polydimethylsiloxane block copolymer (1), which contains 50% solids and has a Gardner-Holtz viscosity of X.  
         [0065]     Coating compound (1) was prepared by mixing together 75 pbw of the block copolymer (1), 10 pbw of the polysiloxane (1) mentioned above, 15 pbw of “Placcel 308”, and 36 pbw of “Tekenate D-170N”. “Placcel 308” is polycaprolactone having a molecular weight of 850 and an OH value of 195 KOH mg/g, available from Daicel Chemical Industries, Ltd. “Takenate D-170N” (36 pbw) is HMDI isocyanurate as a crosslinking agent containing 100% solids and 20.7% NCO, available from Takeda Pharmaceutical Company Limited.  
         [0000]     Preparation of Coating Compound (2)  
         [0066]     Coating compound (2) was prepared from 100 pbw of acryl polyol resin (from Taihou Toryo), 75 pbw of an adduct of hexamethylene diisocyanate (as a non-yellowing polyisocyanate), 0.005 pbw of dibutyltin dilaurate (as a curing catalyst), and 250 pbw of 2:3:5 (by weight) mixed solvent of butyl acetate, MIBK, and propylene glycol monomethyl ether acetate (PMA).  
       Examples 1 and 2 and Comparative Examples 1 and 2  
       [0067]     The surface of a titanium plate (measuring 100 by 100 mm) was coated by spraying with each of the coating compounds (1) and (2) prepared as mentioned above. The coating layer was 20 μm thick. The coated samples were tested for characteristic properties. The results are shown in Table 1.  
                                                                                                                                         TABLE 1                                       Comparative                Example   Example                1   2   1   2                        Coating compound   (1)   (1)   (2)   (2)       Ion plating   yes   no   yes   no            Properties   Brush   Immediately after test   Δ   Δ   Δ   X       of club   test   10 seconds after test   ◯   ◯   Δ   X            head   Wear resistance test   ◯   ◯   Δ   X           Weather resistance   ◯   ◯   ◯   ◯           Adhesion test   ◯   ◯   Δ   Δ           Driver shot test   ◯   ◯   Δ   X                  
 
 Ion Plating 
 
         [0068]     The samples marked with “yes” have a 5 μm thick Cr layer formed by ion plating which was performed before the coating compound was applied to the surface of the titanium plate (100 by 100 mm).  
         [0000]     Brush Test  
         [0069]     The sample club head was rubbed three times with a brass wire brush and then examined for scuffs immediately after rubbing and 10 seconds after rubbing. The results were rated in terms of decrease in gloss according to the following criterion. 
        ◯: no decrease in gloss     Δ: slight decrease in gloss     X: considerable decrease in gloss 
 
 Wear Resistance Test 
       
 
         [0073]     The samples were tested by using a Taber abrasion tester No. 101 (from Yasuda Seiki Seisakusho) according to JIS K-5600-5-9. The loss of weight after test was measured, and the results were rated according to the following criterion. 
        ◯: almost no change in weight     Δ: slight change in weight     X: considerable change in weight 
 
 Weather Resistance 
       
 
         [0077]     The samples were exposed for 200 hours in a sunshine weather-o-meter and then visually examined for the appearance of the coating film. The results were rated according to the following criterion. 
        ◯: No change in color 
 
 Adhesion 
       
 
         [0079]     Adhesion was evaluated by cross-hatch test according to JIS K-5400. The results were rated according to the following criterion. 
        ◯: no peeling     Δ: some peeling 
 
 Driver Shot Test 
       
 
         [0082]     The titanium plate coated with the coating compound mentioned above was fixed to the hitting surface of a driver head. The club head was swung 100 times in such a way that the head hits the mat in a golf practice range. The titanium plate was visually examined. The results were rated according to the following criterion. 
        ◯: no decrease in gloss     Δ: slight decrease in gloss     X: considerable decrease in gloss        
 
         [0086]     Japanese Patent Application No. 2004-179028 is incorporated herein by reference.  
         [0087]     Although some preferred embodiments have been described, many modifications and variations may be made thereto in light of the above teachings. It is therefore to be understood that the invention may be practiced otherwise than as specifically described without departing from the scope of the appended claims.