Patent Publication Number: US-2003224871-A1

Title: Golf ball intermediate layer

Description:
BACKGROUND OF THE INVENTION  
       [0001] This invention relates generally to golf ball intermediate layers and, more particularly, to golf ball intermediate layers made from a composition that optimizes ball performance.  
       [0002] Golf balls generally include a core and at least one cover layer surrounding the core. Balls can be classified as two-piece, wound, or multi-layer balls. Two-piece balls include a spherical inner core and an outer cover layer. Wound balls include a core, a rubber thread wound under tension around the core to a desired diameter, and a cover layer, typically of balata material. Multi-layer balls include a core, a cover layer, and one or more intermediate layers. Generally, two-piece balls have good durability and ball distance when hit, but poor “feel”—the overall sensation transmitted to the golfer while hitting the ball—and low spin rate, which results in poor ball control. Wound balls having balata covers generally have high spin rate, leading to good control, and good feel, but they have short distance and poor durability in comparison to two-piece balls. A good way to optimize the requirements of good speed, spin, feel, and durability is through a multi-layer construction.  
       [0003] Multi-layer balls generally have performance characteristics between those of two-piece and wound balls; that is, multi-layer balls exhibit distance and durability inferior to two-piece balls but superior to wound balata balls, and they exhibit feel and spin rate inferior to wound balata balls but superior to two-piece balls. In particular, use of an intermediate layer to improve spin rate often can lead to substantial loss of ball speed, and therefore distance. Therefore, efforts have focused on designing intermediate layers for golf balls on producing layers that provide high spin rate without loss of ball distance or durability. These efforts have not met with complete success.  
       [0004] Material characteristics of the compositions used in any intermediate layer in multi-layer balls are among the important factors that determine the performance of the resulting golf balls. In particular, the composition of intermediate layers is important in determining the ball&#39;s speed and spin rate. Various materials having different physical properties are used to make intermediate layers to create a ball having the most desirable performance possible. Most intermediate layers incorporate soft or hard ionomeric resins. Such ionomeric resins generally are ionic copolymers of an olefin and a metal salt of a unsaturated carboxylic acid, or ionomeric terpolymers having a co-monomer within its structure. These resins vary in resiliency, flexural modulus, and hardness. Examples of these resins include those marketed under the name SURLYN manufactured by E. I. DuPont de Nemours &amp; Company of Wilmington, Del., and IOTEK manufactured by Exxon Mobil Corporation of Irving, Tex. Many intermediate layers also incorporate elastomeric resins along with the ionomeric layers. Elastomeric resins used in golf ball covers include a variety of thermoplastic or thermoset elastomers available. Examples of these elastomers include those marketed under the name PEBAX manufactured by Atofina Chemicals of Philadelphia, Pa. Other materials commonly used in intermediate layers include polyester elastomer, such as HYTREL, manufactured by E. I. DuPont de Nemours &amp; Company, and thermoplastic urethane, such as ESTANE, manufactured by BF Goodrich of Cleveland, Ohio.  
       [0005] Each of the materials discussed above has particular characteristics that can lead to good golf ball properties when used in an intermediate layer. However, none of these materials optimizes all of the important properties of a ball intermediate layer, and improvement of one of these properties by use of a particular material often can lead to worsening of another. Therefore, to improve golf ball properties, some of the materials discussed above are blended to produce improved intermediate layers. As discussed above, ideally an intermediate layer should provide good spin rate, without sacrificing the ball&#39;s speed. Therefore, an ionomer often is combined in an intermediate layer with an elastomer. In fact, most non-wound intermediate layers incorporate ionomer resins. The resulting blend will provide acceptable ball spin and speed. A number of patents disclose preferred intermediate layers incorporating elastomers and ionomer resins.  
       [0006] A particular material that has been disclosed for use in golf ball compositions is a triblock copolymer having a first polymer block comprising an aromatic vinyl compound, a second polymer block comprising a conjugated diene compound, and a hydroxyl group located at a block copolymer, or the hydrogenation product of this triblock copolymer. The hydroxyl group can be at the terminal block copolymer or elsewhere in the block copolymer structure. The aromatic vinyl compound preferably is selected from the group consisting of styrene, methylstyrene, 4-propylstyrene, 1,3-dimethylstyrene, vinylnaphthalene, and vinlyanthracene. The conjugated diene compound preferably is selected from the group consisting of 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene, and 1,3-hexadiene. The triblock copolymer preferably has a number average molecular weight between about 30,000 and about 1,000,000. An example of this material in which the triblock copolymer having a hydroxyl group is located at the terminal block copolymer is sold under the trade name HG-252 by Kuraray Company of Kurashiki, Japan.  
       [0007] The material is described in detail in U.S. Pat. No. 5,693,711 to Akiba et al. (“the Akiba &#39;711 patent”), herein incorporated by reference. The Akiba &#39;711 patent discloses and claims compositions incorporating the specified triblock polymer and ionomer, as well as golf ball cover compositions incorporating both of these, with the weight ratio of ionomer to block polymer ranging from 98:2 to 50:50. The disclosed cover composition provides flexibility and toughness to the ball cover. The Akiba &#39;711 patent does not, however, discuss use of the material in intermediate layers, or compositions incorporating the triblock copolymer without also incorporating ionomer.  
       [0008] A patent that illustrates the prior understanding of use of the specified triblock copolymer in intermediate layers for golf balls is U.S. Pat. No. 5,948,862 to Sano et al., which discloses use in intermediate layers of thermoplastic elastomer having terminal OH groups, such as the specified triblock copolymer, only in combination with ionomer or specified block copolymers. Also, U.S. Pat. No. 6,334,820 B 1 to Sasaki discloses and claims golf ball intermediate layers incorporating the specified triblock copolymer and a hard ionomer having specified hardness and flexural modulus. The hard ionomer is described as providing the resulting ball with increased resilience. This is consistent with the previous understanding of use of the triblock copolymer as requiring blending with a hard polymer, such as the hard ionomers specified in the Sasaki patent, to avoid poor resilience in the resulting balls.  
       [0009] It has been demonstrated that the specified triblock copolymer, like most elastomers, can be used to make satisfactory golf ball intermediate layer when blended with hard, non-elastomeric materials, such as high acid copolymeric ionomers. However, even with blending of materials to improve properties, use of the materials discussed above is not completely satisfactory. In general, it is difficult to make an intermediate layer that provides good performance without blending into the layer non-elastomeric materials, such as copolymeric ionomers having high acid-content copolymers. Also, the need to blend these materials itself provides for possible manufacturing difficulties and the need for increased monitoring and quality control during the manufacturing process.  
       [0010] In view of the above discussion, it is apparent that golf ball intermediate layers are needed that allow the optimization of many ball performance properties without the worsening of other properties. The ball intermediate layers also should provide little or no processing and preparation difficulties. The present invention fulfills this need and other needs, and provides further related advantages.  
       SUMMARY OF THE INVENTION  
       [0011] The present invention is embodied in a golf ball intermediate layer consisting essentially of one or more specified triblock polymers, hydrogenation products of these triblock copolymers, or specified block copolymers, or mixtures of these. Each of the triblock copolymers and their hydrogenation products incorporate: a first polymer block comprising an aromatic vinyl compound; a second polymer block comprising a conjugated diene compound; and a hydroxyl group located at a block copolymer. Each block copolymer is a hydrogenated diene block copolymer having a polystyrene-reduced number-average molecular weight of from 50,000 to 600,000. Each hydrogenated diene block copolymer is a hydrogenation product of: (a) an A-B block copolymer, in which A is an alkenyl aromatic compound polymer block, and B is either a conjugated diene homopolymer block, in which the vinyl content of the conjugated diene portion is more than 60%, or an alkenyl aromatic compound-conjugated diene random copolymer block in which the vinyl content of the conjugated diene portion is from 15% to 60%, or; (b) an A-B-C block copolymer, in which A and B are as defined above, and C is an alkenyl aromatic compound-conjugated diene copolymer tapered block in which the proportion of the alkenyl aromatic compound increases gradually, or; (c) an A-B-A block copolymer in which A and B are as defined above. In each block copolymer, the weight proportion of the alkenyl aromatic compound to conjugated diene is from 5/95 to 60/40, and the content of the bound alkenyl aromatic compound in at least one block A is at least 3% by weight, and the total of the bound alkenyl aromatic compound contents in the two block A&#39;s or the block A and the block C is from 5% to 25% by weight based on the total monomers. Also, in the hydrogenated diene block copolymer, which as described above is a hydrogenation product, at least 80% of the double bond unsaturations of the conjugated diene portion is saturated by the hydrogenation.  
       [0012] In each triblock copolymer, the aromatic vinyl compound preferably is selected from the group consisting of styrene, methylstyrene, 4-propylstyrene, 1,3-dimethylstyrene, vinylnaphthalene, and vinlyanthracene, and the conjugated diene compound preferably is selected from the group consisting of 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene, and 1,3-hexadiene. Each triblock copolymer preferably has a number average molecular weight between about 30,000 and about 1,000,000. Preferably, the ratio by weight of triblock copolymer to hydrogenated diene block copolymer ranges between 99:1 and 1:99.  
       [0013] The intermediate layer can further comprise fillers, stabilizers, colorants, processing aids, antioxidants, or mixtures of these. The fillers used can be heavy fillers having specific gravity greater than about 2. The present invention also is embodied in a golf ball incorporating a core, a cover, and the above-specified intermediate layer situated between the core and the cover. In these golf balls, the core can include an inner core and one or more outer cores encasing the inner core. The core also can include liquid. The golf ball can incorporate one or more layers situated between the core and the cover, or a layer of rubber thread situated between the core and the cover. The ball covers can include copolymeric ionomer, terpolymeric ionomer, or mixtures thereof. The ball covers also can include elastomeric material.  
       [0014] Preferably, the intermediate layer of the present invention has a thickness between about 0.005 in. and about 0.1 in, more preferably between about 0.01 in. and about 0.05 in., and most preferably between about 0.02 in. and about 0.05 in. The intermediate layer can be prepared using injection molding, compression molding, or by depositing a powder material over a golf ball portion.  
       [0015] The present invention also resides in an intermediate layer consisting essentially of the above-specified triblock copolymer, in which the aromatic vinyl comprises styrene or a-methylstyrene and the conjugated diene compound comprises isoprene or 1,3-butadiene, preferably having a thickness of about 0.1 inches. The present invention also resides in an intermediate layer consisting essentially of the above-specified block copolymers.  
       [0016] Other features and advantages of the present invention should become apparent from the following detailed description of the preferred embodiments.  
       DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0017] The present invention resides in an intermediate layer for a golf ball that consists essentially of one or more specified triblock polymers, hydrogenation products of these triblock copolymers, or specified block copolymers, or mixtures of these. Therefore, the intermediate layer is substantially free of non-elastomeric (particularly ionomeric) polymers. The intermediate layer provides for excellent golf ball properties without introducing processing difficulties. As described above, each triblock copolymer incorporates: a first polymer block comprising an aromatic vinyl compound; a second polymer block comprising a conjugated diene compound; and a hydroxyl group located at a block copolymer, or a hydrogenation product of the triblock copolymer, or mixtures of these. The aromatic vinyl compound preferably is selected from the group consisting of styrene, methylstyrene, 4-propylstyrene, 1,3-dimethylstyrene, vinylnaphthalene, and vinlyanthracene, and the conjugated diene compound preferably is selected from the group consisting of 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene, and 1,3-hexadiene. Each triblock copolymer preferably has a number average molecular weight between about 30,000 and about 1,000,000.  
       [0018] In view of the prior understanding and disclosures discussing use of the specified triblock copolymer in ball compositions, it has been surprisingly found that this triblock copolymer can be used successfully as essentially the entire composition of an intermediate layer. As discussed above, prior understanding of ball manufacture has been that the specified triblock copolymer are preferred for use in golf ball layers only when blended with harder polymers, typically high acid-content copolymeric ionomers. This blending has been considered necessary, because the softness of the specified triblock polymer has made it apparently unsuitable for its exclusive use in intermediate layers. Generally, soft elastomeric materials in ball compositions have contributed to improved feel and spin rate of the resulting balls, at the expense of ball speed. Addition of ionomers, particularly copolymeric ionomers, to these compositions has been believed necessary to produce balls having acceptable speed when hit.  
       [0019] In view of the above, it has been surprisingly observed that use of a composition consisting essentially of the specified triblock copolymer in an intermediate layer unexpectedly provides for superior ball properties. These superior properties exist despite the common perception that ball layers incorporating only a soft elastomer, such as the specified triblock copolymer, would produce balls having unacceptable properties, such as a low coefficient of restitution and resulting low ball speed. This perception is reflected in the patents previously discussed incorporating soft elastomers blended with harder components. In contrast to these patents, the intermediate layers of the present invention are free of harder bulk polymer materials, such as high acid-content ionomers.  
       [0020] It also has been found that, in addition to the above-specified triblock copolymer, an additional type of specified block copolymer can be used in ball intermediate layers, either alone, or in combination with the specified triblock copolymer, to produce intermediate layers having improved properties. This specified block copolymer is described in U.S. Pat. Nos. 5,191,024 and 5,306,779, both to Shibata et al. (the “Shibata &#39;024” and “Shibata &#39;779” patents, respectively), herein incorporated by reference.  
       [0021] Each specified block copolymer in the intermediate layer of the present invention is a hydrogenated diene block copolymer having a polystyrene-reduced number-average molecular weight of 50,000 to 600,000. Each specified block copolymer is a hydrogenation product of either: (i) an A-B block copolymer, in which A is an alkenyl aromatic compound polymer block, and B is either (1) a conjugated diene homopolymer block, in which the vinyl content of the conjugated diene portion is more than 60%, (described in the &#39;024 patent), or (2) an alkenyl aromatic compound-conjugated diene random copolymer block having 15% to 60% of vinyl content of the conjugated diene portion (described in the &#39;779 patent); or (ii) an A-B-C block copolymer in which A and B are as defined above, and C is an alkenyl aromatic compound-conjugated diene copolymer tapered block, in which the proportion of the alkenyl aromatic compound increases gradually; or (iii) an A-B-A block copolymer in which A and B are as defined above. In the specified block copolymer, the weight proportion of the alkenyl aromatic compound to the conjugated diene is from 5/95 to 60/40. Also, in the specified block copolymer, the content of the bound alkenyl aromatic compound in at least one block A is at least 3% by weight, and the total of the bound alkenyl aromatic compound contents in the two block A&#39;s or the block A and the block C is 3% to 50% by weight based on the total monomers. In the specified block copolymer, which as stated above is a hydrogenation product, at least 80% of the double-bond unsaturations of the conjugated diene portion is saturated by the hydrogenation.  
       [0022] An intermediate layer within the scope of the present invention consists essentially of one or more of the above-specified triblock copolymer or its hydrogenation products, one or more of the above-specified block copolymer, or a mixture of these compounds. Preferred mixtures have weight ratios of the specified triblock copolymer to the specified block copolymer ranging between 99:1 and 1:99.  
       [0023] Suitability of the specified block copolymer alone in an intermediate layer is surprising, because it, like the specified triblock copolymer, is an elastomeric material considered too soft to be suitable for use in an intermediate layer without incorporation of a harder material, such as a copolymeric ionomer. Likewise, layers consisting essentially of only the specified triblock copolymer and/or the specified block copolymer are surprisingly found to provide good ball properties when used in an intermediate layer.  
       [0024] In addition to the specified triblock copolymer and/or specified block copolymer, intermediate layers of the present invention also can consist of small amounts of materials commonly added to ball compositions, such as colorants, stabilizers, antioxidants, processing aids, fillers, or mold release agents. Compositions within the scope of the present invention also can incorporate inorganic fillers, such as titanium dioxide, calcium carbonate, zinc sulfide or zinc oxide. Additional fillers can be chosen to impart additional density to blends of golf balls and ball compositions within the scope of the present invention, such as zinc oxide, barium sulfate, tungsten or any other metallic powder having density greater than that of base polymeric resin, preferably having a specific gravity greater than about 2. Any organic or inorganic fibers, either continuous or non-continuous, also can be included the compositions. Intermediate layers of the present invention can be used in a variety of ball designs, including balls having solid, liquid, or multi-layer cores, with our without wound layers. Any of these ball configurations can incorporate an intermediate layer consisting essentially of the specified triblock copolymer and/or block copolymer.  
       [0025] Preferred thicknesses for the intermediate layers of the present invention are between about 0.005 in. and about 0.1 in., more preferably between about 0.01 in. and about 0.05 in., and most preferably between about 0.02 in. and about 0.05 in. Intermediate layers of the present invention can be prepared using a variety of methods, including: 1) injection molding of the entire layer, 2) injection molding to form half cups, which are compression molded to form the entire layer; compression molding from a sheet of the material or 3) coating a ball portion with a powder consisting of the material.  
       [0026] Balls incorporating intermediate layers of the present invention can have a wide variety of suitable covers. The specified triblock copolymer may be used as part of the cover composition, as well as a variety of ionomeric, non-ionomeric resins, or combinations of these, known for use in ball covers. Nonlimiting examples of suitable ionomeric cover materials include copolymeric ionomers and terpolymeric ionomers, or mixtures of these. Copolymeric ionomers are obtained by neutralizing at least a portion of carboxylic groups in a copolymer of an a-olefin and an α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms, with a metal ion. Examples of suitable a-olefins include ethylene, propylene, 1-butene, and 1-hexene. Examples of suitable unsaturated carboxylic acids include acrylic, methacrylic, ethacrylic, alphachloroacrylic, crotonic, maleic, fumaric, and itaconic acid. Copolymeric ionomers include ionomers having varied acid contents and degrees of acid neutralization, neutralized by monovalent or bivalent cations, such as lithium, sodium, potassium, magnesium, calcium, barium, lead, tin, zinc, aluminum, or a combination of these cations.  
       [0027] Terpolymeric ionomers suitable as cover materials are obtained by neutralizing at least portion of carboxylic groups in a terpolymer of an α-olefin, and an α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms and an α,β-unsaturated carboxylate having 2 to 22 carbon atoms with metal ion. Examples of suitable α-olefins include ethylene, propylene, 1-butene, and 1-hexene. Examples of suitable unsaturated carboxylic acids include acrylic, methacrylic, ethacrylic, alphachloroacrylic, crotonic, maleic, fumaric, and itaconic acid. Terpolymeric ionomers include ionomers having varied acid contents and degrees of acid neutralization, neutralized by monovalent or bivalent cations, such as lithium, sodium, potassium, magnesium, calcium, barium, lead, tin, zinc, aluminum, or a combination of these cations.  
       [0028] Nonlimiting examples of suitable non-ionomeric polymers for use as cover materials with balls incorporating intermediate layers within the scope of the present invention include thermoplastic elastomer, thermoset elastomer, thermoplastic rubber, thermoplastic vulcanizate, polycarbonate, polyolefin, polyamide, copolymeric polyamide, polyesters, polyurethane, polyarylate, polyacrylate, polyphenyl ether, modified-polyphenyl ether, high-impact polystyrene, diallyl phthalate polymer, metallocene catalyzed polymers, acrylonitrile-styrene-butadiene (ABS), styrene-acrylonitrile (SAN) (including olefin-modified SAN and acrilonitrile styrene acrylonitrile), styrene-maleic anhydryde (S/MA) polymer, styrenic copolymer, styrenic terpolymer, cellulose polymer, liquid crystal polymer (LCP), ehtylene-propylene-diene-monomer (EPDM), ethylene vinyl acetate (EVA), and polysiloxane. Suitable polyamides include resins obtained by: 1) polycondensation of a dicarboxylic acid, such as oxalic acid, adipic acid, sebacic acid, terephthalic acid, isophthalic acid or 1,4 cyclohexylidicarboxylic acid, with a diamine, such as ethylenediamine, tetramethylenediamine, pentamethylenediamine, hexamethylenediamine or decamethylenediamine, 1,4-cyclohexyldiamine or m-xylylenediamine, 2) a ring-opening polymerization of cyclic lactam, such as ε-caprolactam or ω-laurolactam; polycondensation of an aminocarboxylic acid, such as 6-aminocaproic acid, 9-aminononaoic acid, 11-aminoudecanoic acid or 12-aminododecanoic acid, or 3) copolymerization of a cyclic lactam with a dicarboxylic acid and a diamine. Specific examples of suitable polyamides include Nylon 6; Nylon 4,6; Nylon 6,6; Nylon 6,9; Nylon 6,10; Nylon 6,12; Nylon 11; Nylon 12; copolymerized Nylon; Nylon 6/6, 6; Nylon 6/6, T; Nylon 6, 6/6, 10; and Nylon MXD6  
       [0029] Examples of suitable non-ionomeric polymers for use in cover materials with golf balls incorporating intermediate layers within the scope of the present invention include those sold under the trademarks LEXAN, VALOX, NORYL, and NORYL GTX, marketed by GE Plastics of Pittsfield, Mass., CRISTAMID and RILSAN marketed by ATOFINA Chemicals of Philadelphia, Pa., GRILAMID marketed by EMS-CHEMIE of Sumter, S.C., ZYTEL marketed by E. I. DuPont de Nemours &amp; Co. of Wilmington, Del., TENITE marketed by Eastman Chemical Company of Kingsport, Tenn., EXXPOL marketed by Exxon Mobil of Houston, Tex., and ESTANE marketed by B F Goodrich of Cleveland, Ohio.  
       [0030] Balls incorporating intermediate layers within the scope of the present invention also incorporate core compositions known for use in golf balls. An example of a suitable core formulation comprises a thermoplastic elastomer, such as crosslinked diene elastomer of the polybutadiene cis-1,4 type containing a reaction product with zinc oxide and zinc diacrylate, along with a crosslinking agent, such as dicumyl peroxide or sulfur-containing compounds. 
     
    
    
     EXAMPLE  
     [0031] Multi-layer golf balls were prepared to test the performance of intermediate layers within the scope of the present invention. The balls were labeled as Types 1 to 4, with two dozen in each type. Type 1 to 3 balls incorporated cores having diameters of 1.48 inches and intermediate layers having thicknesses of 0.1 inches, while Type 4 balls incorporated cores having diameters of 1.58 inches. All of the ball cores had compressions of 75. Type 1 balls incorporated intermediate layers within the scope of the present invention, consisting entirely of the triblock copolymer, marketed as HG-252, described above. Type 2 and 3 balls incorporated intermediate layers within the scope of the prior art. These intermediate layers comprised blends of SURLYN 9120, SURLYN 8140, and PEBAX 3533. Type 4 balls did not incorporate intermediate layers and were provided as comparison to represent typical two-piece balls.  
     [0032] Cover layers having thickness of 0.05 inches were placed on all of the balls. Type 1, 2, and 4 balls had covers comprising ionomer blends having a Shore D hardness of 62. Type 3 balls had covers comprising ionomer blends having a Shore D hardness of 57. The percentage compositions of the intermediate layers and hardnesses of the cover materials are provided in Table below.  
               TABLE 1                          Ball Constructions                                         Ball Type   1   2   3   4                                                     Intermediate Layer               None           HG-252 %   100   0   0           Surlyn 9120 %   0   15   15           Surlyn 8140 %   0   15   15           Pebax 3533 %   0   70   70           Cover Material Hardness   62   62   57   62           Shore D                      
 
     [0033] Testing  
     [0034] In addition to the balls discussed above, several golf balls currently available on the market were tested for the same parameters. These balls included the HP Tour manufactured by Acushnet Corporation of Fairhaven, Mass., the Revolution manufactured by MaxFli Golf of Greenville, S.C., and the Tour Accuracy, manufactured by Nike Corporation of Beaverton, Oreg.  
     [0035] All of the balls were tested for spin rate and speed when hit with an 8-iron, and speed when hit with a driver. The balls also were tested for ball compression and surface hardness on the Shore D scale (as distinguished from the cover material hardness shown in Table 1). As discussed above, high spin rate when hit by a short iron is desirable, because it allows for improved control of the ball when hit. High ball speed is desirable, because it leads to greater flying distance of the ball. Low PGA compression provides for improved ball feel. In addition to these properties, the balls also were tested for shear-cut resistance by hitting them with a pitching wedge at controlled speed. Three of each type of ball were used for this testing. Each ball was assigned a numerical score from 1 (no visible damage) to 5 (substantial material displaced), and these scores were averaged for each ball type to produce the shear-cut resistance numbers below.  
     [0036] Results  
     [0037] Results of the tests are show in Table 2 below.  
               TABLE 2                          Ball Performance                                                 8 Iron   8 Iron       Driver   Shear           Hardness   Spin   Speed   PGA   Speed   Re-       Ball Type   (Shore D)   (rpm)   (mph)   Comp.   (mph)   sistance               1   60   8,376   109.5   74   159.6   1.0       2   62   7,799   109.6   81   159.5   1.8       3   58   7,907   109.1   79   159.5   2.7       4   62   7,473   110.3   80   160.6   1.8       HP Tour   58   7,653   109.3   71   158.6   2.0       Revolution   54   8,206   109.3   78   159.6   2.6       Tour   49   8,110   110.5   77   158.1   4.2       Accuracy                  
 
     [0038] Discussion  
     [0039] 1 Comparison of Type 1 and 2 Balls  
     [0040] As discussed above, Type 1 balls incorporated intermediate layers within the scope of the present invention. Type 2 balls represents prior art balls identical to Ball Type 1, except for incorporation of conventional intermediate layers comprising copolymeric ionomer and polyetheramide elastomer.  
     [0041] It is commonly believed that golf ball speed for a multi-layer ball increases with increasing high acid copolymeric ionomer content in the ball intermediate layer composition. Therefore, it was expected that Type 1 balls, incorporating no ionomeric material in their intermediate layers would show lower ball speed than Type 2 balls, incorporating 30% copolymeric ionomer in their mantles. However, as the data indicate, Type 1 balls actually showed comparable driver and 8 Iron speed to Type 2 balls. Despite the higher speeds, Type 1 balls also demonstrated substantially higher 8 Iron spin rates. These data indicate that Type 1 balls will travel approximately the same distance as Type 2 balls when hit with the same force, and also demonstrate superior controllability when hit with an 8 Iron.  
     [0042] In addition to good ball speed and spin performance, Type 1 balls had lower PGA compressions than Type 2 balls, indicating better “feel” when hit. Also, Type 1 balls showed substantially superior shear-cut resistance. In general, exclusive use of the triblock copolymer in the intermediate layers provided for superior overall properties in golf balls. These results would not be expected based on the previous understanding of soft elastomers such as the triblock copolymer and the known performance characteristics of intermediate layers.  
     [0043] 2. Comparison of Type 1 and 3 Balls  
     [0044] Type 3 balls represent prior art balls similar to Type 2 balls, except for a greater percentage of terpolymeric Ionomer in the ball covers. Increasing terpolymeric ionomer content in a cover for a multi-layer ball is a known method for attempting to lower cover hardness, improve ball feel, and increase spin rate, at the cost of other aspects of ball performance, such as ball speed or shear-cut resistance. In this case, ball speeds for Type 1 and Type 3 balls are essentially identical. However, demonstrated spin rates are much lower for Type 3 balls than for Type 1 balls. Also, though Type 3 balls demonstrated lower PGA compressions than Type 2 balls, they demonstrated PGA compressions higher than Type 1 balls. Further, shear-cut resistance for Type 3 balls was markedly worse than for Type 1, and even Type 2, balls. These data indicate that use of the intermediate layers of the present invention is far superior in improving golf ball properties than modification of ball cover compositions, as is more commonly attempted.  
     [0045] 3. Comparison of Type 1 and 4 Balls  
     [0046] Type 4 balls have a two-piece structure; i.e., having no intermediate layer. The cores were slightly larger than those in Type 1 balls; essentially, the portion of the Type 1 balls that comprised the core and intermediate layer were the core of the Type 4 balls.  
     [0047] As discussed above, two-piece balls are known to provide superior ball speed and durability than comparable multi-layer balls, at the cost of reduced spin and inferior “feel.” This reduction in spin and feel generally increases with use of softer mantles. Therefore, it would be expected that Type 4 balls would show substantially higher ball speed than Type 1 balls incorporating soft HG-252 intermediate layers. As expected, Type 1 balls incorporating intermediate layers within the scope of the present invention demonstrated superior 8 Iron spin rates to the two-piece Type 4 balls. However, Type 4 balls demonstrated only slightly higher ball speeds than Type 1 balls, and they exhibited worse shear-cut resistance than the Type 1 balls. Type 1 balls also exhibited much lower PGA compressions than Type 4 balls, indicating that the Type 1 balls have far superior “feel.” The data indicate that use of intermediate layers of the present invention can overcome the traditional disadvantages of multi-layer balls incorporating prior art intermediate layers.  
     [0048] 4. Comparison of Type 1 and Marketed Balls  
     [0049] The marketed balls represent a wide range of prior art balls, each having two-piece, multi-layer, or wound constructions. Type 1 balls demonstrated higher spin rate, comparable ball speeds, and far superior durability than the marketed balls. PGA compression for the Type 1 balls was lower than for all but the HP Tour balls, which had the lowest spin rates. In general, Type 1 balls demonstrate a superior combination of performance characteristics than the marketed balls. Specifically, Ball Type 1 demonstrated superior ball speed, spin rate, and shear-cut resistance than the HP Tour, a two-piece ball. Ball Type 1 demonstrated superior ball spin rate and shear-cut resistance than the Revolution, a ball having a wound core and a thermoset polyurethane cover. Finally, Ball Type 1 showed superior spin rate, ball speed, and, remarkably, shear-cut resistance than the Tour Accuracy, a ball having a thermoplastic polyurethane cover.  
     [0050] Generally, it is difficult to produce golf balls having high spin rate when hit by a short iron, long distance when hit, low PGA compression, soft hit-feel, and good durability. Type 1 balls incorporating intermediate layers within the scope of the present invention exhibited all of these. As discussed above, these performance results contradict the prior understanding of the effect of exclusive use of soft elastomers such as the specified triblock copolymer, and they demonstrate the utility of the intermediate layers of the present invention in maximizing desirable ball properties.  
     [0051] Although the invention has been disclosed in detail with reference only to the preferred embodiments, those skilled in the art will appreciate that additional golf ball intermediate layers can be made without departing from the scope of the invention.