High flexural modulus ionomer for improved golf ball durability

Abstract

In one aspect, a golf ball comprises a core including rubber, and at least one intermediate layer disposed over the core. The intermediate layer comprises least one ionomer which includes neutralized ethylene acid copolymer derived from ethylene monomer, and from 7.5 to 15.0 mole% of carboxylic acid comonomer based on the total mole% of the monomers present in the at least one ionomer, where the at least one ionomer has a melt index (I2) of 0.5 to 10.0 dg / min as measured according to ASTM D 1238 (2.16 kg, 190 °C), where 10 to 50 mole% of total acid units of the at least one ionomer are neutralized by zinc and sodium cations.

Description

HIGH FLEXURAL MODULUS IONOMER FOR IMPROVED GOLF BALL DURABILITYCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. Provisional Application Serial No. 63 / 574,634 filed April 4, 2024, the contents of which are incorporated in their entirety herein.BACKGROUND

[0002] Golf balls are designed to provide the best balance of distance and feel without compromising durability. From a materials perspective, the golf ball industry is interested in a variety of resins that provide different combinations of coefficient of restitution (COR), compression, flexural modulus, hardness, scuff resistance and crack durability for a variety of performance targets and markets. Simple 2-piece balls consist of a core and cover. The core is typically polybutadiene rubber (PBR) and the cover is often an ionomer. Performance balls are typically 3-5 piece ball constructions with a PBR core, ionomer mantles (i.e., intermediate layers), and a polyurethane cover.

[0003] There is a continual need for golfballs having higher flexural modulus and improved impact durability of golf ball mantles and covers.SUMMARY

[0004] Embodiments of the present disclosure meet this need for golf balls with higher flexural modulus and improved impact durability by utilizing ionomers or ionomer blends neutralized by Na and Zn, and comprising greater than 7.5 mole% carboxylic acid comonomer, and higher molecular weight (i.e., melt index (L) of 0.5 to 10.0 dg / min).

[0005] In one aspect, a golf ball comprises a core including rubber, and at least one intermediate layer disposed over the core. The intermediate layer includes at least one ionomer comprising a neutralized ethylene acid copolymer derived from ethylene monomer, and from 7.5 to 15 mole% of carboxylic acid comonomer based on the total mole% of the monomers present in the at least one ionomer, where the at least one ionomer has a melt index (I2) of 0.5 to 10.0 dg / min as measured according to ASTM D 1238 (2.16 kg, 190 °C), where 10 to 50 mole% of total acid units of the at least one ionomer are neutralized by zinc and sodium cations.BRIEF DESCRIPTION OF THE DRAWINGS

[0006] To easily identify the discussion of any particular element or act, the most significant digit or digits in a reference number refer to the figure number in which that element is first introduced.

[0007] FIG. 1 is a cross-sectional view of a golf ball in accordance with one embodiment of the present disclosure.

[0008] FIG. 2 is another cross-sectional view of a golf ball in accordance with one embodiment of the present disclosure.DETAIEED DESCRIPTION

[0009] Specific embodiments of the present application will now be described. The disclosure may be embodied in different forms and should not be construed as limited to the embodiments set forth in this disclosure. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the subject matter to those skilled in the art.

[0010] Definitions

[0011] "Polymer" refers to a polymeric compound prepared by polymerizing monomers, whether of the same or a different type. The term polymer thus embraces the term homopolymer (employed to refer to polymers prepared from only one type of monomer, with the understanding that trace amounts of impurities can be incorporated into the polymer structure), and the term copolymer or interpolymer. Trace amounts of impurities (for example, catalyst residues) may be incorporated into and / or within the polymer. A polymer may be a single polymer or a polymer blend.

[0012] As used herein, the term “copolymer” means a polymer formed by the polymerization reaction of at least two structurally different monomers. The term “copolymer” is inclusive of terpolymers. For example, ethylene copolymers, such as ethylene-propylene copolymers, include at least two structurally different monomers (e.g., ethylene-propylene copolymer includes copolymerized units of at least ethylene monomer and propylene monomer) and can optionally include additional monomers or functional materials or modifiers, such as acid, acrylate, or anhydride functional groups. Put another way, the copolymers described herein comprise at least two structurally different monomers,and although the copolymers may consist of only two structurally different monomers, they do not necessarily consist of only two structurally different monomers and may include additional monomers or functional materials or modifiers.

[0013] The term “ionomer” as used herein refers to a polymer that comprises ionic groups that are carboxylate salts, for example, ammonium carboxylates, alkali metal carboxylates, alkaline earth carboxylates, transition metal carboxylates and / or combinations of such carboxylates. Such polymers are generally produced by partially or fully neutralizing the carboxylic acid groups of precursor or parent polymers that are acid copolymers, as defined herein, for example by reaction with a base.

[0014] The term “acid copolymer” as used herein refers to a polymer comprising copolymerized units of an a-olefin, an carboxylic acid, and optionally other suitable comonomer(s).

[0015] Referring to FIG. 1, a golf ball 100 comprises a core 102 including rubber, and at least one intermediate layer 104 disposed over the core 102. The intermediate layer 104 includes at least one ionomer. The ionomer includes neutralized ethylene acid copolymer derived from ethylene monomer, and from 7.5 to 15.0 wt.% of carboxylic acid comonomer based on the total mole% of the monomers present in the at least one ionomer. The ionomer has a melt index (h) of 0.5 to 10.0 dg / min as measured according to ASTM D 1238 (2.16 kg, 190 °C). Moreover, 10 to 50 mole% of total acid units of the at least one ionomer are neutralized by zinc and sodium cations.

[0016] The ionomer includes from greater than 50 to 92.5 mole% ethylene, or in other embodiments from a minimum of 50 mole%, 55 mole%, 60 mole%, 65 mole%, 70 mole%, 75 mole%, 80 mole%, 85 mole%, or 90 mole% ethylene to a maximum of 55 mole%, 60 mole%, 65 mole%, 70 mole%, 75 mole%, 80 mole%, 85 mole%, 90 mole%, or 92.5 mole% ethylene. As detailed below, the balance of the ionomer may include the metal cations defined below.

[0017] In other embodiments, the ionomer includes from 7.5 to 15 mole% carboxylic acid, or in other embodiments from a minimum of 7.5 mole%, 8.0 mole%, 8.5 mole%, 9.0 mole%, 9.5 mole%, 10.0 mole%, 10.5 mole%, 11.0 mole%, 11.5 mole%, 12.0 wt.%, 12.5 mole%, 13.0 mole%, 13.5 mole%, or 14.0 mole%, to a maximum of 8.0 mole%, 8.5 mole%, 9.0 mole%, 9.5 mole%, 10.0 mole%, 10.5 mole%, 11.0 mole%, 11.5 mole%, 12.0 mole %, 12.5mole%, 13.0 mole%, 13.5 mole%, 14.0 mole%, or 15.0 mole% carboxylic acid comonomer. Without being limited by theory, including greater than 7.5 mole% carboxylic acid in the ionomer achieves greater flexural modulus for the ionomer at the same molecular weight. In one or more embodiments, the ionomer may have a flexural modulus of at least 70 ksi (1000 pounds per square inch) as measured in accordance with ASTM D790, or from 70 to 150 Kpsi.

[0018] In further embodiments, the ionomer may include from 20 to 40 wt.% carboxylic acid, or in other embodiments from a minimum of 20 wt.%, 21 wt.%, 21.5 wt.%, 22 wt.%, 23 wt.%, 24 wt.%, 25 wt.%, 26 wt.%, 27 wt.%, 28 wt.%, 29 wt.%, 30 wt.%, 31 wt.%, 32 wt.%, 33 wt.%, 34 wt.%, 35 wt.%, 36 wt.%, 37 wt.%, 38 wt.%, or 39 wt.% to a maximum of 21 wt.%, 21.5 wt.%, 22 wt.%, 23 wt.%, 24 wt.%, 25 wt.%, 26 wt.%, 27 wt.%, 28 wt.%, 29 wt.%, 31 wt.%, 32 wt.%, 33 wt.%, 34 wt.%, 35 wt.%, 36 wt.%, 37 wt.%, 38 wt.%, 39 wt.%, or 40 wt.% carboxylic acid comonomer. The carboxylic acid monomers can include monocarboxylic acids, such as acrylic acid, methacrylic acid, or combinations thereof.

[0019] Further without being limited by theory, increasing durability and stiffness in the golf ball correlates to increased molecular weight in the ionomer. In one or more embodiments, the ionomer or ionomer blend may have a melt index I2 of 0.5 to 10 dg / min, or in further embodiments, may have a melt index (I2) ranging from a minimum of 0.5, 1.0, 1.5, 2,0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, or 9.0 dg / min to a maximum of 1.0, 1.5, 2,0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0, or 10.0 dg / min. In yet another embodiment, the ionomer may have a melt index of 1.0 to 2.0 dg / min.

[0020] In one or more embodiments of the present disclosure, the ethylene acid copolymer prior to neutralization has a melt index (I2) of 10.0 to 60.0 dg / min, In further embodiments, the ethylene acid copolymer or blends thereof prior to neutralization (also called base resin(s)) may have a melt index (I2) ranging from a minimum of 10, 15, 20, 25, 30, 35, 40, 45, 50, or 55 dg / min to a maximum of 15, 20, 25, 30, 35, 40, 45, 50, 55, or 60 dg / min. In yet another embodiment, the ethylene acid copolymer prior to neutralization may have a melt index of 25 to 35 dg / min.

[0021] In addition to the disclosed ethylene acid copolymers described herein, it is contemplated the ionomers may also be a terpolymer. In one embodiment, the terpolymer may comprise additional comonomers, such as alkyl acrylates and / or alkyl methacrylates.

[0022] The ionomers may be neutralized with sodium cations, which are present in the amount of 0.1 to 3 mole% or in other embodiments from a minimum of 0.1, 0.25, 0.5, 0.75, 1.0, 1.5, 2.0, or 2.5 mole% to a maximum of 0.25, 0.5, 0.75, 1.0, 1.5, 2.0, 2.5, or 3.0 mole% sodium cations. Additionally, the ionomers may be neutralized with zinc cations, which are present in the amount of 0 to 3 mole%, or in other embodiments from a minimum of 0.1, 0.25, 0.5, 0.75, 1.0, 1.5, 2.0, or 2.5 mole% to a maximum of 0.25, 0.5, 0.75, 1.0, 1.5, 2.0, 2.5, or 3.0 mole% zinc cations.

[0023] In addition to the zinc and sodium cations, it is contemplated to use other monovalent metal cations (e.g., lithium), divalent metal cations (e.g., magnesium), trivalent metal cations (e.g., aluminum), or combinations thereof.

[0024] As stated above, 10 to 50 mole% of total acid units of the at least one ionomer are neutralized by zinc and sodium cations. In further embodiments, the neutralization may range from a minimum of 10, 15, 20, 25, 30, 35, 40, or 45 mole% of neutralized total acid units to a maximum of 15, 20, 25, 30, 35, 40, 45, or 50 mole% of neutralized total acid units.

[0025] Some embodiments may be directed single ionomer neutralized by Zn and Na cations. In other embodiments, the ionomer includes a blend of a first ionomer and a second ionomer. The first ionomer includes from 7.5 to 15 mole% of carboxylic acid comonomer based on the total mole% of the monomers present in the first ionomer and has 10 to 50 mole% of total acid units of the first ionomer neutralized by sodium cations. The second ionomer includes from 7.5 to 15 mole% of carboxylic acid comonomer based on the total mole% of the monomers present in the second ionomer, and 10 to 50 mole% of total acid units of the second ionomer are neutralized by zinc cations.

[0026] Various amounts are contemplated for the first and second ionomer within the blend. For example, the blend may include a first ionomer in an amount ranging from a minimum of 20, 30, 40, 50, 60, or 70 wt.% to a maximum of 30, 40, 50, 60, 70, or 80 wt.%. Conversely, the blend may include a second ionomer in an amount ranging from a minimum of 20, 30, 40, 50, 60, or 70 wt.% to a maximum of 30, 40, 50, 60, 70, or 80 wt.%. In another embodiment, the blend may include 40 to 60 wt.% of the first ionomer and 40 to 60 wt.% of the second ionomer.

[0027] Similar to above, 10 to 50 mole% of total acid units of the first ionomer are neutralized by sodium cations. In further embodiments, the neutralization of the first ionomermay range from a minimum of 10, 15, 20, 25, 30, 35, 40, or 45 mole% of neutralized acid units to a maximum of 15, 20, 25, 30, 35, 40, 45, or 50 mole% of neutralized acid units. Furthermore, 10 to 50 mole% of total acid units of the second ionomer are neutralized by zinc cations. In further embodiments, the neutralization of the second ionomer may range from a minimum of 10, 15, 20, 25, 30, 35, 40, or 45 mole% of neutralized acid units to a maximum of 15, 20, 25, 30, 35, 40, 45, or 50 mole% of neutralized acid units. In one or more embodiments, the first ionomer may be neutralized to a greater degree, a lesser degree, or the same degree relative to the second ionomer.

[0028] The ethylene acid copolymers can be prepared by standard free-radical copolymerization methods, using high pressure, operating in a continuous manner. Monomers are fed into the reaction mixture in a proportion which relates to the monomer’s activity, and the amount desired to be incorporated. In this way, uniform, near-random distribution of monomer units along the chain is achieved. Unreacted monomers may be recycled. The ethylene acid copolymers may be polymerized according to processes disclosed in U.S. Pat. Nos. 3,404,134; 5,028,674; 6,500,888; and 6,518,365.

[0029] The acid copolymer resins may be neutralized by any conventional procedure, such as those disclosed in U.S. Pat. Nos. 3,404,134 and 6,518,365, and by other procedures that will be apparent to those of ordinary skill in the art. Some of these methods are described in detail in U.S. Pat. No. 8,334,033, issued to Hausmann et al.

[0030] Golf Ball Construction

[0031] Referring again to FIG. 1, the core 102 includes polybutadiene rubber. In the two layer structure of FIG. 1, the intermediate layer 104 may be considered the outer layer or cover. In a three-layer embodiment as depicted in FIG. 2, the golf ball 200 may also include an outer layer 106 disposed over the intermediate layer 104 having the ionomer. In one embodiment, the outer layer 106 includes polyurethane. Additionally, it is contemplated that the golf ball may have 4 layer constructions, 5 layer constructions, or even more layers.

[0032] The golf ball 100 or 200 may have a COR of 0.7 to 0.9 at 125 ft / s. The golf ball 100 or 200 may have an ADC Compression of 50 to 100 mils. Moreover, the golf ball 100 or 200 may have a Shore D Hardness of 50 to 75.

[0033] Additives

[0034] The compositions may additionally comprise small amounts of optional materials including additives for use in polymeric materials. Examples of suitable additives include, without limitation, plasticizers, stabilizers including viscosity stabilizers and hydrolytic stabilizers, primary and secondary antioxidants such as for example IRGANOX® 1010, ultraviolet ray absorbers and stabilizers, anti-static agents, dyes, pigments or other coloring agents, fire-retardants, lubricants, processing aids, slip additives, release agents, and / or mixtures thereof. Additional optional additives may include acid copolymer waxes, such as for example Honeywell wax AC540; TiCh, which is used as a whitening agent; optical brighteners; surfactants; and other components known in the art of golf ball manufacture to be useful but may not be critical to golf ball performance and / or acceptance. Many such additives are described in the Kirk Othmer Encyclopedia of Chemical Technology, 5thedition, John Wiley & Sons (Hoboken, 2005).

[0035] Examples of fillers include metals such as titanium, tungsten, aluminum, bismuth, nickel, molybdenum, iron, steel, lead, copper, brass, boron, boron carbide whiskers, bronze, cobalt, beryllium, zinc, tin, metal oxides including zinc oxide, iron oxide, aluminum oxide, tin oxide, titanium oxide, magnesium oxide, zinc oxide and zirconium oxide, as well as other well-known corresponding salts and oxides thereof. Other commonly used fillers include barium sulfate, lead silicate, tungsten carbide, limestone (ground calcium / magnesium carbonate), zinc sulfate, calcium carbonate, zinc carbonate, barium carbonate, clay, tungsten, and mixtures of any of these.

[0036] These additives may be present in the compositions in quantities that may be from 0.01 to 15%, from 0.01 to 10%, or from 0.01 to 5% of the total composition.

[0037] The optional incorporation of such conventional ingredients into the compositions may be carried out by any known process, for example, by dry blending, by extruding a mixture of the various constituents, by the conventional masterbatch technique, or the like.

[0038] The golf ball is produced via processes familiar to the person skilled in the art e.g., injection molding, overmolding the mantle and / or cover over the core, etc.TEST METHODS

[0039] Density

[0040] Density is measured in accordance with ASTM D792, and expressed in grams / cm3(g / cm3).

[0041] Melt Index (I2)

[0042] Melt Index (I2) is measured in accordance with ASTM D 1238-10 at 190 Celsius and 2.16 kg, Method B, and is expressed in grams eluted / 10 minutes (g / 10 min). For ionomer blends, the melt index (I2) is an arithmetic average based on the weight percentages of the blend components.

[0043] Coefficient of Restitution (COR)

[0044] Coefficient of Restitution (COR) was measured by firing a solid sphere of the resin having a similar density to a golf ball from an air cannon at several velocities over a range of roughly 60 to 180 feet / second. The spheres struck a steel plate positioned three feet away from the point where initial velocity is determined, and rebounded through a speedmonitoring device located at the same point as the initial velocity measurement. The COR of each measurement was determined as the ratio of rebound velocity to initial velocity. The individually determined COR measurements were plotted as a function of initial velocity, and COR at 125 ft / s (i.e. COR125) and COR at 150 ft / s (i.e. COR150) was determined by linear regression.

[0045] Shore D Hardness

[0046] Shore D hardness was measured in accordance with ASTM D-2240 on a standard test specimen.

[0047] ADC Compression (mils)

[0048] ADC Compression, which is the resistance to compression, is the measured distance of deflection of solid spheres upon the application of a compressive load of 200 pounds in accordance with industry specific test measures.

[0049] Flexural Modulus

[0050] Flexural Modulus was measured according to ASTM D790, Method 1, Procedure A, employing a 3 -point test fixture with a 2-inch span length and a crosshead speed of 0.50 inches / minute. The method provides a measurement of the Tangent Modulus of Elasticity (3- Point Flexural Modulus).

[0051] Durability

[0052] Durability measures the loss in COR after repeated shots from an air cannon at a desired velocity at a steel plate positioned 3 ft away. Failure is determined when the COR is only 95% of its initial value. The data reported the number of hits to failure.EXAMPLES

[0053] The following examples are presented to further illustrate the present invention in detail but are not to be construed as limiting the scope of the claims. Unless otherwise indicated, all parts and percentages are by weight.

[0054] Preparation of Ionomers

[0055] Referring to Table 1, single cation ionomers were produced by partially neutralizing a copolymer of ethylene and methacrylic acid with metal cations. Processes for producing ionomers have been previously disclosed in the patent literature, for example in US 8,334,033, US 3,404,134, and US 6,518,365. Mixed Na / Zn ionomers for these examples were produced by dry blending a sodium and a zinc ionomer prior to injection molding solid spheres or overmolding around polybutadiene rubber (PBR) cores to form 2-piece balls.

[0056] Table 1 : Resins

[0057] Preparation of Solid Spheres

[0058] Referring to Table 2 below, 1.55 inch diameter solid spheres were prepared by injection molding on a Nissei FNX 180 injection mold machine at a nozzle temperature of 200 °C. Molding conditions for solid spheres are also provided in U.S. 2016 / 0236039, which is incorporated by reference herein in its entirety.

[0059] Table 2: Golf Ball Properties of Solid 1.55 inch Diameter Spheres

[0060] The solid spheres of Table 2 show the benefits of mixed Na / Zn cations (CE6, CE7, CE8 and EXI) vs. single cation Na (CE1 and CE2) or Zn (CE3, CE4, and CE5) for flexural modulus of the ionomers without significantly altering other key performance properties like coefficient of restitution (COR), ADC Compression, or Hardness. For CE6 and CE7, the flexural modulus was actually higher than either individual ionomer used in the blend. ForCE8 and EXI, the flexural modulus of the mixed ion resin was between that of the Na and Zn ionomer or equivalent to the higher modulus Na ionomer.

[0061] For all cases, the flexural modulus of mixed Na / Zn ionomers remains surprisingly high even with 50 wt.% of the composition comprised of the lower flexural modulus Zn ionomer. Mixed ionomer EXI surprisingly shows higher flexural modulus and higher COR than comparative examples CE6-CE8, even with lower neutralization.

[0062] Preparation of 2-Piece Balls

[0063] Referring to Table 4, thermoplastic ionomer resin compositions were injection molded around 1.540 inch polybutadiene rubber (PBR) thermoset cores. Details of molding a golf ball mantle or cover material around a core are described in US 2005 / 0037866, US 2021 / 0197030, and US 7,375,151. The molded balls of this invention were molded with a retractable pin vertical injection mold machine to a diameter of 1.68 inches. Properties of the 1.540 inch diameter polybutadiene rubber (PBR) cores are provided in Table 3.

[0064] Table 3: Properties of 1.54 in Polybutadiene (PBR) Cores

[0065] Table 4: Two-Piece 1.68 in. Diameter Ball. Ionomer Molded over 1.54 in DiameterCore

[0066] For two-piece 1.68 inch diameter balls molded around 1.540 inch diameter PBR cores, the data of Table 4 shows that for standard Na and Zn ionomers CE1, CE2, and CE4, lower flexural modulus tends to help impact durability. However, high flexural modulus is needed because a high flexural modulus mantle on a soft core produces more spin differential,a desired property for golf ball construction. Spin differential means the difference in spin of the golf ball when stricken by a driver club versus an iron club, wherein lesser spin is desired for a driver and greater spin is desired for an iron. The challenge is to produce a material with a combination of high flexural modulus and high impact durability. Mixed Na / Zn ionomers can do this, as exemplified with CE7, which shows synergistic high flexural modulus and improved impact durability compared to CE1 or CE2. If an even higher stiffness material, such as CE5, is used as the Zn ionomer instead of CE4, then an even higher flexural modulus could be obtained with mixed Na / Zn systems containing CE1 or CE2 while retaining or improving impact durability.

[0067] While particular embodiments of the present disclosure have been illustrated and described, it would be obvious to those skilled in the art that various other changes and modifications can be made without departing from the spirit and scope of the disclosure. It is therefore intended to cover in the appended claims all such changes and modifications that are within the scope of this disclosure.

Claims

CLAIMS1. A golf ball comprising a core comprising rubber, and at least one intermediate layer comprising at least one ionomer disposed over the core wherein: the at least one ionomer comprising neutralized ethylene acid copolymer derived from ethylene monomer, and from 7.5 to 15.0 mole% of carboxylic acid comonomer based on the total mole% of the monomers present in the at least one ionomer; wherein the at least one ionomer has a melt index (I2) of 0.5 to 10.0 dg / min as measured according to ASTM D 1238 (2.16 kg; 190 °C); wherein 10 to 50 mole% of total acid units of the at least one ionomer are neutralized by zinc and sodium cations.

2. The golf ball of claim 1, wherein the ionomer has a melt index (I2) of 1 to 5.0 dg / min.

3. The golf ball of claim 1 or 2, wherein the at least one ionomer comprises 20 to 40 wt.% of carboxylic acid comonomer.

4. The golf ball of any one of claims 1 to 3, wherein the at least one ionomer comprises from 8.0 to 10.0 mole% of carboxylic acid comonomer.

5. The golf ball of any one of claims 1 to 4, wherein the at least one ionomer comprises a blend of a first ionomer and a second ionomer, wherein: the first ionomer comprises from 7.5 to 15.0 mole% of carboxylic acid comonomer based on the total wt.% of the monomers present in the first ionomer, wherein 10 to 50 mole% of total acid units of the first ionomer are neutralized by sodium cations; and the second ionomer comprises from 7.5 to 15.0 mole% of carboxylic acid comonomer based on the total wt.% of the monomers present in the second ionomer, wherein 10 to 50 mole% of total acid units of the second ionomer are neutralized by zinc cations.

6. The golf ball of claim 5, wherein the blend comprises 40 to 60 wt.% of the first ionomer and 40 to 60 wt.% of the second ionomer.

7. The golf ball of any one of claims 1 to 6, wherein the carboxylic acid monomer comprises one or more of acrylic acid, methacrylic acid, or combinations thereof.

8. The golf ball of any one of claims 1 to 7, wherein the core comprises polybutadiene rubber.

9. The golf ball of any one of claims 1 to 8, further comprising an outer layer disposed over the intermediate layer.

10. The golf ball of any one of claims 1 to 9, wherein the outer layer comprises polyurethane.

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