GOLF BALL AND METHOD OF IMPROVING GOLF BALL PERFORMANCE

Abstract

Golf balls having an outermost layer, which outermost layer has been subjected to impregnation treatment with an isocyanate and/or isothiocyanate-containing olefin compound but has not been topcoated, exhibit at least one improved golf ball attribute, such as scuff resistance or spin performance, compared with similar golf balls that have not been impregnation treated.

Description

BACKGROUND OF THE INVENTION

The present invention relates to a golf ball having an outermost layer that is treated by impregnation with an isocyanate group (here and below, “isocyanate group” encompasses also “isothiocyanate group”)-containing olefin compound, and is not topcoated with a two-part curing urethane clear coating.

Commonly available commercial golf balls are topcoated as the final step in production. However, for some time now, there has been a concern over the environmental impact associated with topcoating, such as from the release of organic solvents and the treatment of coating material residues.

If, for the sake of argument, there did exist a method for not carrying out topcoating as the final step in golf ball production, one would have expected it to have become a groundbreaking manufacturing method.

However, to date, aside from a very small number of patents (e.g., JP-A 8-71175), almost no investigations have actually been carried out on uncoated golf balls—golf balls which are finished without topcoating. This is thus an unexplored area.

Patent Document 1: JP-A 8-71175

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a golf ball in which, by using an organic reactive compound to carry out impregnation treatment on a polymer material in the outermost layer of the golf ball, performance attributes such as scuff resistance and spin are maintained or improved without carrying out topcoating. Another object of the present invention is to provide a golf ball which is able to reduce the environment impact associated with coating material treatment.

The inventors have, in studying organic reactive compounds for treating the surface-most portion of a golf ball, taken the novel approach of investigating various reactive compounds with the object of manufacturing golf balls in a way that dispenses with topcoating but does not compromise the performance of the completed golf ball. As a result, they have discovered that isocyanate group-containing olefin compounds are ideal materials for achieving this object.

Moreover, the inventors have learned from further investigations that golf balls which include as a component thereof (here and below, the cover material or intermediate material in a two-piece solid golf ball composed of a core and a cover encasing the core, or in a multi-piece solid golf ball composed of a core of one or more layer, one or more intermediate layer encasing the core, and a cover of one or more layer encasing the intermediate layer) an outermost layer that has been impregnation treated with the above-mentioned isocyanate group-containing olefin compound and has not been topcoated have excellent properties, especially an improved scuff resistance.

Accordingly, the present invention provides the following golf ball and method of improving golf ball performance.

• [I] A golf ball having an outermost layer, which layer is impregnation treated with an isocyanate and/or isothiocyanate-containing olefin compound and is not topcoated.
• [II] A method of modifying a golf ball having an outermost layer, which method includes the step of impregnating the outermost layer with an isocyanate and/or isothiocyanate-containing olefin compound and not topcoating the outermost layer.

DETAILED DESCRIPTION OF THE INVENTION

The invention is described more fully below.

The present invention provides a golf ball having an outermost layer, which layer is impregnation treated with an isocyanate and/or isothiocyanate-containing olefin compound. In the following description, for the sake of convenience, the isocyanate and/or isothiocyanate-containing olefin compound is referred to simply as the “isocyanate-containing olefin compound.”

Also, as used herein, “impregnation treatment” additionally includes, following impregnation with the organic reactive compound, heat treatment and/or ultraviolet light (UV) irradiation treatment and a period of elapsed time.

The inventors have conducted studies to determine whether a golf ball obtained by impregnation treating the molded outermost layer of a golf ball with an isocyanate group-containing olefin compound, but not topcoating the outermost layer, is capable of withstanding normal use.

The term “impregnation treatment,” as used here and below, refers to treatment that includes impregnation with an organic reactive compound, followed by heat treatment and/or ultraviolet (UV) irradiation treatment and a period of elapsed time.

However, the large number of organic reactive compounds, such as crosslinking agents, which could be used for impregnation-treating the thermoset and/or thermoplastic polymer material in the outermost layer of the golf ball made it impossible to comprehensively examine all such compounds in the studies conducted for this invention.

Therefore, selection of the organic reactive compound was carried out first from a number of initial “decision branches” that include, for example:

• (1) compounds which, because impregnation treatment is to carried out, are liquid, if not necessarily at room temperature, for the sake of convenience at near room temperature;
• (2) compounds which have two or more reactive groups per molecule (i.e., compounds which have a crosslinking action);
• (3) compounds which can be reacted under the influence of heat and/or ultraviolet light; and
• (4) compounds which are, in themselves, homopolymerizing.

In addition, the physical properties of golf balls obtained by carrying out impregnation treatment on the outermost layer of the golf ball but not topcoating the outermost layer, including changes in those properties over time, were evaluated.

As a result, the inventors discovered that isocyanate-containing olefin compounds are preferred as organic reactive compounds which have the effect of maintaining or improving the performance (e.g., feel on impact, scuff resistance, spin, distance) of golf balls obtained by impregnation treatment of the outermost layer of the golf ball with a thermoset and/or thermoplastic polymer material, even when the golf ball is not topcoated, and ultimately arrived at the present invention.

The isocyanate-containing olefin compounds of the invention have been found from investigations to have the following characteristics:

• (1) the isocyanate group exhibits addition reactivity with amide groups (—NHCO—), urethane groups (—NHCOO—), primary and secondary amino groups (—NH₂— and —NH—R, where R is alkyl, aralkyl, allyl, aryl, etc.), hydroxyl groups (—OH) and carboxyl groups (—COOH);
• (2) the olefin group (unsaturated bond) such as the acrylic group (CH₂═CHCO—), methacrylic group (CH₂═C(CH₃)CO—), allyl group (CH₂═CHCH—) and vinyl group (CH₂═CH—) exhibits photocrosslinkability by exposure to ultraviolet light and/or thermal crosslinkability by heat treatment;
• (3) the compound exhibits homopolymerizability or copolymerizability;
• (4) the compound has a good compatibility with urethane materials (including both thermoset and thermoplastic materials), polyester and/or polyether materials and amide materials, and shows a tendency to be easily impregnated therein;
• (5) the compound has a poor compatibility with polyethylene materials (including polyethylene, metallocene polyethylene, ethylene-based acid copolymers and ethylene-based ionomers), styrene elastomer materials and diene materials (e.g., BR, NBR, CR), and shows a tendency to be difficult to impregnate therein; and
• (6) the compound is liquid at ordinary temperatures (20° C.±15° C.).

Specific examples of the isocyanate-containing olefin compound used in the present invention include, but are not limited to, 2-iso(thio)cyanatoethyl methacrylate, 2-iso(thio)cyanatoethyl acrylate, 3-iso(thio)cyanatopropyl acrylate, 1-methyl-2-iso(thio)cyanatoethyl methacrylate, 1,1-dimethyl-2-iso(thio)cyanatoethyl acrylate, allyliso(thio)cyanate, allylthiocyanate, methylvinyliso(thio)cyanate, vinyliso(thio)cyanate, vinylthiocyanate, bis-(2-iso(thio)cyanatoethyl)fumarate, 2-iso(thio)cyanato-2-methylpropylene glycol diacrylate and 2-(2-iso(thio)cyanatoethoxy)ethyl(meth)acrylate. In addition, illustrative examples of isocyanate group-capped derivatives formed with isocyanate groups under the application of heat include 2-[O-(1-methylpropylidenamino)-carboxyamino]ethyl(meth)acrylate, 2-(pyrazoyl-1-carbonylamino)ethyl(meth)acrylate and tris(2-acryloyloxyethyl)isocyanurate.

Of the group of above-mentioned isocyanate-containing olefin compounds, from the standpoint of commercial production, 2-isocyanatoethyl methacrylate, 2-isocyanatoethyl acrylate, 3-isocyanatopropyl acrylate and 2-isocyanato-2-methylpropylene glycol diacrylate are preferred. Taking polymerizability in account, 2-isocyanatoethyl acrylate and 2-isocyanato-2-methylpropylene glycol diacrylate are more preferred.

The above isocyanate-containing olefin compound has a melting point of preferably 80° C. or below, more preferably 60° C. or below, and even more preferably 35° C. or below. Isocyanate-containing olefin compounds which are liquid at temperatures near 0 to 35° C. are suitable for impregnation treatment.

The following conditions (1) to (5) apply to the impregnation treatment of golf balls with the isocyanate-containing olefin compound of the present invention.

• (1) The impregnation temperature is preferably as high as possible within a range up to the melting point of the polymer material making up the outermost layer of the golf ball to be impregnated. However, care must be taken with the homopolymerization of the isocyanate-containing olefin compound. It is desirable for the impregnation temperature to be within a range of from about 0° C. to about 100° C., preferably from about 5° C. to about 80° C., and more preferably from about 10° C. to about 50° C.
• (2) The impregnation time, which depends on both the type of polymer material making up the outermost layer in the golf ball to be impregnated and the impregnation temperature, is preferably within a range of from about 15 seconds to about 100 hours, more preferably from about 1 minute to about 80 hours, and even more preferably from about 30 minutes to about 50 hours.
• (3) Following impregnation, it is essential to either wipe off, or blow off with an air knife, surplus isocyanate-containing olefin compound adhering to the surface layer of the golf ball. If the isocyanate-containing olefin compound is left adhering to the surface layer of the golf ball, the isocyanate-containing olefin compound may homopolymerize, forming irregularities (a thin, uneven layer) on the surface of the golf ball, which may adversely affect the properties of the golf ball.
• (4) Carrying out UV irradiation treatment (photocrosslinking) and/or heat treatment (thermal crosslinking) following impregnation improves the performance of the golf ball. In such a case, the UV irradiation time when using a high-pressure mercury vapor lamp is in a range of from about 5 seconds to about 50 hours, preferably from about 20 seconds to about 25 hours, and more preferably from about 30 seconds to about 10 hours. The irradiation temperature is in a range of from about 0° C. to about 100° C., preferably from about 5° C. to about 80° C., and more preferably from about 10° C. to about 50° C. A higher temperature tends to be better, so long as the temperature is at or below the melting point of the polymer material making up the outermost layer of the golf ball to be impregnated. The heat treatment (thermal crosslinking) temperature is in a range of from about 25° C. to about 100° C., preferably from about 35° C. to about 80° C., and more preferably from about 40° C. to about 60° C. A higher temperature tends to be better, so long as the temperature is at or below the melting point or softening point of the polymer material making up the outermost layer of the golf ball to be impregnated.
• (5) Alternatively, the advantageous effects of the invention can be achieved by allowing the golf ball to stand following impregnation without subjecting the ball to the UV irradiation treatment or heat treatment carried out following impregnation. In such a case, a long period of elapsed time of at least about 200 hours is required. For example, it may be necessary to allow the golf ball to stand in this way for 30 days (720 hours).

The impregnated layer obtained by impregnation treating the outermost layer of the golf ball with the isocyanate-containing olefin compound of the invention has a thickness, as calculated from the difference in the weight of the golf ball before and after impregnation treatment and the difference in the outside diameter of the golf ball before and after impregnation treatment, in a range of preferably from about 5 μm to about 900 μm. The content of the isocyanate-containing olefin compound impregnated into the outermost layer is preferably from about 0.01 g to about 7.00 g, and more preferably from about 0.05 g to about 5.00 g.

The difference in hardness, before and after treatment, of the outermost layer obtained by impregnation treating the golf ball with the isocyanate-containing olefin compound in the present invention is dependent on the polymer material making up the outermost layer of the golf ball to be impregnation treated, although an increase within a range of from about 1 to about 10 Shore D hardness units is preferred.

No particular limitation is imposed on the polymer material in the outermost layer of the golf ball on which impregnation treatment with the isocyanate-containing olefin compound of the invention is to be carried out, provided it is a thermoplastic polymer and/or thermoset polymer commonly used in golf balls. For example, illustrative examples of thermoplastic polymers include polyolefin elastomers (including ethylene ionomers, polyolefins and metallocene polyolefins), polystyrene elastomers, diene polymers, polyacrylate polymers, polyamide elastomers, polyurethane elastomers, polyester elastomers and polyacetals. Illustrative examples of thermoset polymers include thermoset urethanes and silicone polymers.

In the impregnation treatment of the golf ball with the isocyanate-containing olefin compound of the invention, to promote photocrosslinking by UV irradiation treatment or thermal crosslinking by heat treatment of the impregnated isocyanate-containing olefin compound, optional additives may also be suitably included with the isocyanate-containing olefin compound according to the intended application. For example, a photopolymerization initiator (1-hydroxycyclohexyl phenyl ketone, 2-hydroxy-2-methyl-1-phenyl propan-1-one, 2,2-dimethoxy-1,2-diphenylethan-1-one) or a thermal polymerization initiator (diusobutyryl peroxide, diisopropyl peroxydicarbonate, dibenzoyl peroxide) may be added. When these additives are included, the amount of such addition, per 100 parts by weight of the isocyanate-containing olefin compound, is preferably at least 0.1 part by weight, and more preferably at least 0.5 part by weight, but preferably not more than 10 parts by weight, and more preferably not more than 7 parts by weight.

The golf ball used in the present invention is a one-piece solid golf ball, a two-piece solid golf ball composed of a core and a cover encasing the core, or a multi-piece solid golf ball composed of a core of at least one layer, one or more intermediate layer encasing the core, and a cover of at least one layer encasing the intermediate layer. Impregnation treatment of a molded golf ball layer may be carried out in any manufacturing step. In cases where the outermost layer of a commercial golf ball is to be impregnation treated, it is preferable to carry out impregnation treatment of the golf ball after the surface has been trimmed.

The weight of the golf ball following impregnation treatment with the isocyanate-containing olefin compound of the invention is preferably in a range of from about 44.80 g to about 45.70 g.

The outside diameter of the golf ball following impregnation treatment with the isocyanate-containing olefin compound of the invention is preferably in a range of from about 42.65 mm to about 42.80 mm.

EXAMPLES

The following Examples of the invention are provided by way of illustration and not by way of limitation.

Example 1

The following impregnation treatment was carried out using Golf Ball A (which refers to the same symbol A in the table; the same applies below) with a spherically trimmed ionomer cover layer which has not been topcoated (two-part urethane clear coating) in Table 1 and using 2-isocyanatoethyl acrylate as the isocyanate-containing olefin compound.

Five Golf Balls A were placed in a 500 ml beaker containing about 250 ml of 2-isocyanatoethyl acrylate, following which the beaker was placed in an aluminum pouch with fastener and sealed, and the golf balls were held stationary at 23° C. for 10 hours and thereby impregnated. The impregnated Golf Balls A were then removed from the beaker and the surfaces of the Golf Balls A were wiped, following which UV irradiation was carried out for one hour at 40° C. with a high-pressure mercury vapor lamp (H40 paint fadeometer, same model as old FM-1, manufactured by Suga Test Instruments Co., Ltd.). The impregnated golf balls A were held stationary for one day at 23° C., following which the surface hardness of the cover layer was measured. The balls were then finished as conventional golf ball products without carrying out topcoating. The physical properties of these golf balls were measured one week later, yielding the results shown in Table 1. All the impregnation operations prior to UV irradiation were carried out within a draft chamber.

Compared with-the golf balls of Comparative Example 1 which were not impregnation treated but were topcoated, the golf balls of Example 1 which were impregnation treated with 2-isocyanatoethyl acrylate but were not topcoated showed an increase in the ionomer cover layer surface hardness (Shore D) of from 65 to 67, and showed increases in the initial velocity and total distance when the golf balls were hit with a number one wood at a head speed of 46 m/sec. Moreover, the back spin exhibited a desirable decreasing tendency. The golf balls also had an increased scuff resistance.

Examples 2 and 3

Aside from changing the Golf Ball A impregnation time within 2-isocyantoethyl acrylate in Example 1 from 10 hours to 15 hours and 25 hours, respectively, the same procedure was carried out as in Example 1, thereby obtaining impregnation-treated, un-topcoated Golf Balls A according to Examples 2 and 3 of the invention. The properties of these golf balls were measured. Those results are shown in Table 1. As in Example 1, compared with Comparative Example 1, in which the golf balls were not impregnation treated but were topcoated, the surface hardness (Shore D) of the ionomer cover layer rose additionally from 65 to 69 and 70, respectively, the initial velocity and total distance both increased, and the back spin exhibited a desirable decreasing tendency. The golf balls also had an increased scuff resistance.

Example 4

Aside from using Golf Balls B having a urethane/ionomer cover layer instead of the Golf Balls A having an ionomer cover layer used in Example 1, the same procedure was carried out as in Example 1 to give impregnation-treated, un-topcoated Golf Balls B of Example 4. The properties of these golf balls were measured. Those results are shown in Table 1. Compared with Comparative Example 2, in which the golf balls were not impregnation treated but were topcoated, the surface hardness (Shore D) of the urethane/ionomer cover layer increased from 52 to 55, and improvements occurred in the initial velocity, total distance and scuff resistance.

Examples 5 and 6

Aside from using Golf Balls C having a thermoplastic urethane cover layer instead of the Golf Balls A having an ionomer cover layer used in Example 1, and aside from changing the Golf Ball C impregnation time in 2-isocyanatoethyl acrylate to 5 hours and 25 hours, respectively, the same procedure was carried out as in Example 1, thereby giving impregnation-treated, un-topcoated Golf Balls C in Examples 5 and 6. The properties of these golf balls were measured. Those results are shown in Table 1. Compared with Comparative Example 3, in which the golf balls were not impregnation treated but were topcoated, the surface hardness (Shore D) of the thermoplastic urethane cover layer rose from 57 to 60 and 64, respectively. In addition, the initial velocity, total distance and scuff resistance all increased.

Example 7

Aside from using Golf balls D having a thermoset urethane cover layer instead of the Golf Balls C having a thermoplastic urethane cover layer used in Example 6, and aside from using 2-isocyanatoethyl methacrylate containing 3.5 wt % of the photocatalyst Irgacure 184 (available under this trade name from Ciba-Geigy) instead of 2-isocyanatoethyl acrylate, changing the impregnation time to 10 hours and changing the UV irradiation time from 1 hour to 0.5 hour, the same procedure was carried out as in Example 6, thereby giving impregnation-treated, un-topcoated Golf Balls D in Example 7. The properties of these golf balls were measured. Those results are shown in Table 1. Compared with Comparative Example 4, in which the golf balls were not impregnation treated but were topcoated, the surface hardness (Shore D) of the thermoset urethane cover layer rose from 54 to 58. In addition, the initial velocity, total distance and scuff resistance all increased.

Example 8

Aside from using Golf Balls E having a polyoxymethylene ionomer cover layer instead of the Golf Balls D having a thermoset urethane cover layer used in Example 7, the same procedure was carried out as in Example 7, thereby giving impregnation-treated, un-topcoated Golf Balls E in Example 8. The properties of these golf balls were measured. Those results are shown in Table 1. Compared with Comparative Example 5, in which the golf balls were not impregnation treated but were topcoated, the surface hardness (Shore D) of the polyoxymethylene ionomer cover layer rose from 64 to 67. In addition, the initial velocity, total distance and scuff resistance all increased.

Example 9

Aside from using one-piece Golf Balls F having a polybutadiene layer instead of the Golf Balls D having a thermoset urethane cover layer used in Example 7, the same procedure was carried out as in Example 7, thereby giving impregnation-treated, un-topcoated one-piece Golf Balls F of Example 9. The properties of these golf balls were measured. Those results are shown in Table 1. Compared with Comparative Example 6, in which the golf balls were not impregnation treated but were topcoated, the surface hardness (Shore D) of the polybutadiene layer rose from 51 to 54. In addition, the initial velocity, total distance and scuff resistance all increased.

Comparative Example 1

For the purpose of comparison with Examples 1 to 3 of the invention, Golf Balls A having the ionomer cover layer used in Examples 1 to 3 were not subjected to impregnation treatment with 2-isocyanoethyl acrylate, although the operations following UV irradiation in Example 1 were carried out, thereby giving Golf Balls A having an ionomer cover layer according to Comparative Example 1, in which topcoating was carried out in the final step. The properties of these golf balls were measured. Those results are shown in Table 2.

Compared with Examples 1 to 3, in which the golf balls were impregnated treated but were not topcoated, the surface hardness was low and the ball properties were inferior.

Also, on comparing the properties of the Golf Balls A having a UV-irradiated ionomer cover layer obtained in Comparative Example 1 and the Golf Balls A having an original ionomer cover layer that was not UV irradiated, no substantial difference between the two was observed, indicating that UV irradiation did not have an influence on the ball properties.

Comparative Examples 2 to 6

Comparative Examples 2 to 6 correspond respectively to, and serve as controls for, Examples 4 to 9. In these respective comparative examples, golf balls were obtained by repeating the same procedure as in Comparative Example 1; that is, impregnation treatment using 2-isocyanatoethyl acrylate or 2-isocyanatoethyl methacrylate was not carried out on the golf balls having a polymer material cover layer used in the respective examples of the invention, but topcoating was carried out as the final step. The properties of these golf balls were measured. Those results are shown in Table 2. The UV irradiation time was one hour in Comparative Examples 2 and 3, and was 0.5 hour in Comparative Examples 4 to 6.

The golf balls in the respective comparative examples had lower surface hardnesses and inferior ball properties than the impregnation treated, un-topcoated golf balls obtained in the corresponding examples of the invention.

In addition, on comparing the properties of the UV-irradiated golf balls from Comparative Examples 2 to 6 with the properties of the respective original, non-UV irradiated, golf balls, no differences therebetween were observed.

	TABLE 1
	Example
	1	2	3	4	5	6	7	8	9
F) BR-One-piece GB									F
E) POM ionomer-covered GB								E
D) Thermoset PU-covered GB							D
C) Thermoplastic PU-covered GB					C	C
B) Thermoplastic PU/ionomer-covered GB				B
A) Ionomer-covered GB	A	A	A
Isocyanate compound	2-Isocyanatoethylacrylate	2-Isocyanatoethyl-
		methacrylate*
Impregnation time (h)	10	15	25	10	5	25	10	10	10
Cover surface hardness of impregnated	67	69	70	55	60	64	58	67	54
layer (Shore D)
Ball diameter (mm)	42.68	42.72	42.74	42.74	42.67	42.73	42.71	42.73	42.70
Ball weight (g)	45.28	45.36	45.45	45.57	45.14	45.31	45.48	45.58	45.63
Deflection (mm)	3.22	3.22	3.21	3.08	2.62	2.64	2.90	2.78	2.82
Scuff resistance	3	2	1	2	2	1	1	2	1
Initial velocity (m/sec)	63.7	64.0	64.1	64.2	63.7	65.1	64.9	65.0	64.2
Back spin (rpm)	3280	3215	3150	3100	3230	2840	2620	2760	3490
Carry (m)	204	204	205	203	203	203	208	212	207
Total distance (m)	222	224	225	222	221	223	227	222	220
*2-Isocyanatoethyl methacrylate includes 3.5 wt % of 1-hydroxycyclohexyl phenyl ketone (Irgacure 184)

	TABLE 2
	Comparative Example
Items	1	2	3	4	5	6
F) BR-One-piece GB						F
E) POM ionomer-covered GB					E
D) Thermoset PU-covered GB				D
C) Thermoplastic PU-covered GB			C
B) Thermoplastic PU/ionomer-covered GB		B
A) Ionomer-covered GB	A
Cover surface hardness of impregnated layer (Shore D)	65	52	57	54	64	51
Ball diameter (mm)	42.66	42.75	42.64	42.67	42.70	42.67
Ball weight (g)	45.32	45.56	45.16	45.33	45.51	45.58
Deflection (mm)	3.23	3.08	2.57	2.89	2.73	2.81
Scuff resistance	3	3	3	2	3	2
Initial velocity (m/sec)	63.5	64.0	63.6	64.7	64.8	64.0
Back spin (rpm)	3300	3210	3270	2730	2880	3650
Carry (m)	203	202	203	207	211	206
Total distance (m)	221	219	220	225	220	218
*2-Isocyanatoethyl methacrylate includes 3.5 wt % of 1-hydroxycyclohexyl phenyl ketone (Irgacure 184)

Details on the materials and methods of measurement in above Tables 1 and 2 are given below.

The core mentioned above (crosslinked BR body) was produced from the following composition.

	1,4-cis-Polybutadiene rubber	100	parts by weight
	Zinc acrylate	21	parts by weight
	Zinc oxide	5	parts by weight
	Barium sulfate	26	parts by weight
	Dicumyl peroxide	0.8	part by weight

A) Ionomer-Covered GB (3-Piece Golf Ball)

Ionomer cover blend composition: S8940/(S9945+S9910)/titanium oxide/blue pigment=50/50/3/0.02 parts by weight S8940, S9945, S9910 (ionomers produced by DuPont) Titanium oxide (Tipaque 740, produced by Ishihara Sangyo Kaisha, Ltd.)

Blue pigment (Pigment Blue 29, produced by Toyo Ink Mfg. Co., Ltd.)

B) Thermoplastic PU/Ionomer-Covered GB (2-Piece Golf Ball)

Thermoplastic urethane/ionomer cover blend composition: Thermoplastic urethane/Mg-ionomer/titanium oxide/blue pigment=20/80/3/0.02 parts by weight

Thermoplastic urethane (aliphatic urethane, produced by DIC Bayer Polymer Ltd.)

Mg-Ionomer (Bridgestone Sports BSP experimental product)

Titanium oxide (Tipaque PF740, produced by Ishihara Sangyo Kaisha, Ltd.)

Blue pigment (Pigment Blue 29, produced by Toyo Ink Mfg. Co., Ltd.)

C) Thermoplastic PU-Covered GB (2-Piece Golf Ball)

Thermoplastic urethane cover blend composition: Aliphatic urethane/titanium oxide/blue pigment=100/3/0.02 parts by weight

Aliphatic urethane (DIC Bayer Polymer Ltd.)

Titanium oxide (Tipaque PF740, produced by Ishihara Sangyo Kaisha, Ltd.)

Blue pigment (Pigment Blue 29, produced by Toyo Ink Mfg. Co., Ltd.)

D) Thermosetting PU-Covered GB (2-Piece Golf Ball)

Thermoset urethane cover blend composition: PTMG (polytetramethylene ether glycol)—MDI (diphenylmethane diisocyanate) urethane prepolymer (NCO, 7.5 wt %)/4,4′-methylenebis-(2,6-diethyl)aniline/N,N′-dimethylamino-diphenylmethane/trimethylolpropane/titanium oxide/blue pigment=100/50/50/3/3/0.02 parts by weight

PTMG-MDI urethane prepolymer (an aromatic urethane system produced by DIC Bayer Polymer Ltd.)

4,4′-Methylenebis-(2,6-diethyl)aniline (Junsei Chemical Co.)

N,N′-Dimethylamino-diphenylmethane (Junsei Chemical Co.)

Trimethylolpropane (Mitsubishi Gas Chemical Co., Ltd.)

Titanium oxide (Tipaque PF740, produced by Ishihara Sangyo Kaisha, Ltd.)

Blue pigment (Pigment Blue 29, produced by Toyo Ink Mfg. Co., Ltd.)

E) POM/Ionomer-Covered GB (2-Piece Golf Ball)

Polyoxymethylene/ionomer blend composition:

Polyoxymethylene/Na-ionomer/Zn-ionomer/titanium oxide/blue pigment=5/50/45/3/0.02 parts by weight

Polyoxymethylene (AMILAS S761, produced by Toray Industries, Inc.)

Na-Ionomer (S8940, produced by DuPont)

Zn-Ionomer (S9910, produced by DuPont)

Titanium oxide (Tipaque PF740, produced by Ishihara Sangyo Kaisha, Ltd.)

Blue pigment (Pigment Blue 29, produced by Toyo Ink Mfg. Co., Ltd.)

F) BR One-Piece GB

Polybutadiene blend composition: Polybutadiene/zinc acrylate/zinc oxide/barium sulfate/peroxide=100/20/5/15/0.8 parts by weight

Polybutadiene (BR01, produced by JSR Corporation)

Zinc acrylate (Nippon Shokubai Co., Ltd.)

Zinc oxide (Sakai Chemical Industry Co., Ltd.; average particle size, 0.5 μm)

Barium sulfate (Sakai Chemical Industry Co., Ltd.; average particle size, 0.1 μm)

Peroxide (NOF Corporation; dicumyl peroxide)

Deflection

The golf ball was placed on a steel plate, and the deflection (mm) by the ball when compressed under a final load of 1,275 N (130 kgf) from an initial load of 98 N (10 kgf) was measured. This test was carried out at 23±1° C.

Scuff Resistance

The golf balls were held at a temperature of 23±1° C. and hit at a head speed of 33 m/s using a pitching wedge mounted on a swing robot machine, after which damage from the impact was visually rated according to the following scale.

Best:            1 point
Better:          2 points
Good (ordinary): 3 points
Poor:            4 points
Poorer:          5 points
Poorest:         6 points

Initial Velocity, Back Spin, Carry and Total Distance

A golf ball was hit at a head speed of 46 m/sec with a number one wood using a swing machine, and the initial velocity, carry, total distance and back spin of the ball following impact were measured.

Claims

1. A golf ball comprising an outermost layer, wherein the outermost layer is impregnation treated with an isocyanate and/or isothiocyanate-containing olefin compound and is not topcoated.

2. The golf ball of claim 1, wherein the outermost layer is formed of a thermoplastic and/or thermoset polymer.

3. The golf ball of claim 1, wherein the isocyanate and/or isothiocyanate-containing olefin compound in the impregnation-treated outermost layer is subjected to thermal polymerization, photopolymerization and/or addition reaction with functional groups.

4. The golf ball of claim 3, wherein the olefin moiety of the isocyanate and/or isothiocyanate-containing olefin compound is at least one olefin group selected from the group consisting of acrylic, methacrylic, allyl and vinyl groups, and exhibits photopolymerizability on exposure to ultraviolet light and/or thermal polymerizability.

5. The golf ball of claim 3, wherein the isocyanate moiety of the isocyanate-containing olefin compound has an isocyanate group and/or an isocyanate group-capped derivative, and exhibits addition reactivity with at least one functional group selected from the group consisting of amide, urethane, primary amino, secondary amino, hydroxyl and carboxyl groups.

6. The golf ball of claim 3, wherein the isothiocyanate moiety of the isothiocyanate-containing olefin compound has an isothiocyanate group and/or an isothiocyanate group-capped derivative, and exhibits addition reactivity with at least one functional group selected from the group consisting of amide, urethane, primary amino, secondary amino, hydroxyl and carboxyl groups.

7. The golf ball of claim 3, wherein the isocyanate and/or isothiocyanate-containing olefin compound has a melting point of not above 80° C.

8. The golf ball of claim 1, wherein the impregnation layer formed by impregnation of the outermost layer with the isocyanate and/or isothiocyanate-containing olefin compound has a thickness in a range of from about 5 μm to about 900 μm.

9. The golf ball of claim 1, wherein the impregnated layer formed by impregnating the outermost layer with the isocyanate and/or isothiocyanate-containing olefin compound has a surface hardness which is from about 1 to about 10 Shore D hardness units higher than the surface hardness of the outermost layer prior to impregnation treatment.

10. The golf ball of claim 1 which is selected from the group consisting of one-piece golf balls, two-piece solid golf balls composed of a core and a cover encasing the core, and multi-piece solid golf balls composed of a core of at least one layer, one or more intermediate layer encasing the core, and a cover of at least one layer encasing the intermediate layer.

11. A method of modifying a golf ball having an outermost layer, the method comprising the step of impregnating the outermost layer with an isocyanate and/or isothiocyanate-containing olefin compound but not topcoating the outermost layer.

12. The golf ball modifying method of claim 11, wherein the step of impregnating the outermost layer with an isocyanate and/or isothiocyanate-containing olefin compound is carried out at an impregnation temperature which does not exceed the melting point and/or softening point of the polymer material in the outermost layer, and an impregnation time in a range of from about 15 seconds to about 100 hours.

13. The golf ball modifying method of claim 12 which additionally comprises, following the step of impregnating the outermost layer with an isocyanate and/or isothiocyanate-containing olefin compound, the step of photopolymerizing by exposure to ultraviolet light and/or the step of thermal polymerizing by heat treatment.

14. The golf ball modifying method of claim 13, wherein the step of photopolymerizing by exposure to ultraviolet light is carried out at an ultraviolet irradiation temperature in a range of from about 0° C. to about 100° C. and for an ultraviolet irradiation time in a range of from about 5 seconds to about 50 hours.

15. The golf ball modifying method of claim 14, wherein the step of thermal polymerizing by heat treatment is carried out after the step of photopolymerizing by exposure to ultraviolet light, at a heat treatment temperature in a range of from about 25° C. to about 100° C., and for a heat treatment time in a range of from about 5 seconds to about 50 hours.

16. The golf ball modifying method of claim 12 wherein, following the step of impregnating the outermost layer with an isocyanate and/or isothiocyanate-containing olefin compound, the golf ball is left to stand for at least 200 hours without carrying out a photopolymerization step by exposure to ultraviolet light or a thermal polymerization step by heat treatment.