GOLF BALL

Abstract

In a golf ball having a core and a cover of at least one layer, an outermost layer of the cover is formed to a specific thickness using a resin composition containing a light-harvesting fluorescent dye and a light-reflecting pigment. The golf ball is elegant and highly stylish, and moreover has an excellent visibility.

Description

BACKGROUND OF THE INVENTION

The present invention relates to a golf ball that is highly stylish and has excellent visibility.

Lately, not all golf balls are white; golf balls in a variety of colors are being manufactured in response to the diverse preferences of golfers. For example, many colored golf balls that are elegant and highly stylish have appeared on the market.

In addition, more and more golfers like using colored golf balls not only because they are stylish, but also on account of the visibility of the ball. However, golf balls in colors other than white, yellow and orange have a diminished visibility early in the morning, at dusk and in bad weather, and sometimes become difficult to discern from far away. Hence, although there exist today golf balls in a variety of colors, depending on the time of day and weather in which the game is played, such balls are sometimes difficult to use. Therefore, in order to both expand the range of choice in golf balls and also provide balls which can be easily discerned and enjoyably used by greater numbers of golfers, it is important to further increase the visibility of the golf ball, and in particular to increase the visibility of golf balls in colors other than white, yellow and orange.

Examples of prior-art literature relating to this invention include JP-A 2007-144097, JP-A 2009-045347, JP No. 3570992, JP No. 4422882, JP-A 2008-161375, JP No. 4326018, JP-A 2009-045234, JP-A 2009-045347, JP-A 2010-268857, JP-A 2001-087423 and JP-A 2011-251003.

SUMMARY OF THE INVENTION

It is therefore an object of the invention to provide a golf ball which has an excellent visibility even at dusk and in bad weather, and which moreover is highly stylish.

As a result of extensive investigations, the inventors have discovered that, in a golf ball having a core and a cover of one or more layer, by including both a specific light-harvesting fluorescent dye and a light-reflecting pigment in the material used to form the outermost layer of the cover, it becomes possible to suitably reflect not only light in the visible light region but also light in the ultraviolet light region, i.e., it becomes possible to suitably reflect sunlight, enabling a good coloration to be achieved. By forming the cover of the above material, not only is the coloration good, giving a highly stylish ball, the visibility of golf balls in colors other than white, yellow and orange which have hitherto had a poor visibility at dusk and in bad weather can be increased. Moreover, in white, yellow or orange-colored golf balls which already have a good visibility, an even better visibility can be obtained.

Accordingly, the invention provides the following golf ball.

• [1] A golf ball comprising a core and a cover of one or more layer, wherein the cover has an outermost layer which is formed of a resin composition containing, per 100 parts by weight of resin components:

0.001 to 0.1 part by weight of a light-harvesting fluorescent dye; and

0.05 to 0.7 part by weight of a light-reflecting pigment having a particle size of from 1 to 250 μm, and which has a thickness of from 0.5 to 1.6 mm.

• [2] The golf ball of [1], wherein the compounding ratio between the light-harvesting fluorescent dye and the light-reflecting pigment, expressed as a weight ratio, is from 1:1 to 1:50.
• [3] The golf ball of [1], wherein the content of the light-reflecting pigment and the thickness of the outermost layer satisfy the following condition:

light-reflecting pigment content×outermost layer thickness=from 0.05 to 0.35.

• [4] The golf ball of [1], wherein the light-reflecting pigment is glass flakes having a thickness of from 0.5 to 2 μm and a particle size of from 1 to 250 μm.
• [5] The golf ball of [4], wherein the glass flakes are of one or more type selected from the group consisting of soda lime glass, borosilicate glass, aluminosilicate glass, lead crystal glass, E-glass, A-glass, C-glass, ECR-glass, Duran glass, window glass and laboratory glass.
• [6] The golf ball of [4], wherein the glass flakes are colored with one or more colorant selected from the group consisting of elemental copper, chromium, manganese, iron and cobalt and/or cations or complex anions of combinations thereof, TiO₂, and precious metal elements.
• [7] The golf ball of [1], wherein the light-gathering fluorescent dye is red and the golf ball has an L* value of not more than 55, an a* value of at least 65 and a b* value of not more than 30.
• [8] The golf ball of [1], wherein a layer adjoining an inner side of the cover outermost layer is white in color.

BRIEF DESCRIPTION OF THE DIAGRAMS

FIG. 1 is a schematic cross-sectional diagram showing an example of the construction of a golf ball according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

The invention is described more fully below.

The golf ball of the invention has a solid core (sometimes referred to below simply as the “core”) and a cover of at least one layer. FIG. 1 shows an exemplary construction of the golf ball of the invention. The golf ball G shown in FIG. 1 has two cover layers 2 and 3 formed over the core 1. Here, the cover 2 formed on the inner side is sometimes referred to as the “intermediate layer 2” (which signifies a layer formed between the core 1 and the cover 3), and the cover 3 formed on the outer side is sometimes referred to as the “outermost layer 3.” The core 1 is not limited to a single layer, and may form two or more layers. Numerous dimples D are typically formed on the surface of the cover 3 (outermost layer 3) in order to increase the aerodynamic properties. Each of the above layers is described in detail below.

In the invention, the solid core may be formed of a known rubber composition. Although not subject to any particular limitation, preferred examples include rubber compositions formulated as shown below.

A rubber material may be used as the primary material in the above core-forming material. For example, the core may be formed of a rubber composition containing, in addition to the base rubber: a co-crosslinking agent, an organic peroxide, an inert filler, sulfur, an antioxidant, an organosulfur compound and the like.

Polybutadiene is preferably used as the base rubber of the rubber composition. It is desirable for this polybutadiene to have a cis-1,4 bond content on the polymer chain of at least 60 wt %, preferably at least 80 wt %, more preferably at least 90 wt %, and most preferably at least 95 wt %. Too low a cis-1,4 bond content among the bonds on the molecule may result in a lower rebound. Moreover, the polybutadiene has a 1,2-vinyl bond content on the polymer chain of preferably not more than 2 wt %, more preferably not more than 1.7 wt %, and even more preferably not more than 1.5 wt %. Too high a 1,2-vinyl bond content may lower the rebound.

To obtain a molded and vulcanized rubber composition having a good resilience, the polybutadiene used in the invention is preferably one synthesized with a rare-earth catalyst or a Group VIII metal compound catalyst. Polybutadiene synthesized with a rare-earth catalyst is especially preferred.

Such rare-earth catalysts are not subject to any particular limitation. Exemplary rare-earth catalysts include those made up of a combination of a lanthanide series rare-earth compound with an organoaluminum compound, an alumoxane, a halogen-bearing compound and an optional Lewis base.

Examples of suitable lanthanide series rare-earth compounds include halides, carboxylates, alcoholates, thioalcoholates and amides of atomic number 57 to 71 metals.

In the practice of the invention, the use of a neodymium catalyst in which a neodymium compound serves as the lanthanide series rare-earth compound is particularly advantageous because it enables a polybutadiene rubber having a high cis-1,4 bond content and a low 1,2-vinyl bond content to be obtained at an excellent polymerization activity. Suitable examples of such rare-earth catalysts include those mentioned in JP-A 11-35633, JP-A 11-164912 and JP-A 2002-293996.

To increase the resilience, it is preferable for the polybutadiene synthesized using the lanthanide series rare-earth compound catalyst to account for at least 10 wt %, preferably at least 20 wt %, and more preferably at least 40 wt %, of the rubber components.

Rubber components other than the above-described polybutadiene may be included in the rubber composition, insofar as the objects of the invention are attainable. Illustrative examples of rubber components other than the above-described polybutadiene include other polybutadienes, and other diene rubbers, such as styrene-butadiene rubber, natural rubber, isoprene rubber and ethylene-propylene-diene rubber.

Examples of co-crosslinking agents include unsaturated carboxylic acids and the metal salts of unsaturated carboxylic acids.

Specific examples of unsaturated carboxylic acids include acrylic acid, methacrylic acid, maleic acid and fumaric acid. Acrylic acid and methacrylic acid are especially preferred.

The metal salts of unsaturated carboxylic acids, while not subject to any particular limitation, are exemplified by the above-mentioned unsaturated carboxylic acids neutralized with desired metal ions. Specific examples include the zinc and magnesium salts of methacrylic acid and acrylic acid. The use of zinc acrylate is especially preferred.

The unsaturated carboxylic acid and/or metal salt thereof is included in an amount, per 100 parts by weight of the base rubber, of preferably at least 5 parts by weight, more preferably at least 10 parts by weight, and even more preferably at least 15 parts by weight. The amount included is preferably not more than 60 parts by weight, more preferably not more than 50 parts by weight, even more preferably not more than 40 parts by weight, and most preferably not more than 30 parts by weight. Too much may make the core too hard, giving the ball an unpleasant feel at impact, whereas too little may lower the rebound.

The organic peroxide may be a commercially available product, suitable examples of which include Percumyl D (available from NOF Corporation), Perhexa 3M (NOF Corporation), Perhexa C40 (NOF Corporation) and Luperco 231XL (Atochem Co.). The use of one of these alone is preferred.

The amount of organic peroxide included per 100 parts by weight of the base rubber is preferably at least 0.1 part by weight, more preferably at least 0.3 part by weight, even more preferably at least 0.5 part by weight, and most preferably at least 0.7 part by weight. The upper limit in the amount included is preferably not more than 5 parts by weight, more preferably not more than 4 parts by weight, even more preferably not more than 3 parts by weight, and most preferably not more than 2 parts by weight. Too much or too little organic peroxide may make it impossible to achieve a ball having a good feel, durability and rebound.

Examples of suitable inert fillers include zinc oxide, barium sulfate and calcium carbonate. These may be used singly or as a combination of two or more thereof.

The amount of inert filler included per 100 parts by weight of the base rubber is preferably at least 1 part by weight, and more preferably at least 5 parts by weight. The upper limit in the amount included is preferably not more than 100 parts by weight, more preferably not more than 80 parts by weight, and even more preferably not more than 60 parts by weight. Too much or too little inert filler may make it impossible to achieve a proper weight and a good rebound.

In addition, an antioxidant may be included if necessary. Illustrative examples of suitable commercial antioxidants include Nocrac NS-6, Nocrac NS-30 and Nocrac 200 (all available from Ouchi Shinko Chemical Industry Co., Ltd.), and Yoshinox 425 (available from Yoshitomi Pharmaceutical Industries, Ltd.). These may be used singly or as a combination of two or more thereof.

The amount of antioxidant included can be set to more than 0, and may be set to preferably at least 0.05 part by weight, and more preferably at least 0.1 part by weight, per 100 parts by weight of the base rubber. The maximum amount included, although not subject to any particular limitation, may be set to an amount per 100 parts by weight of the base rubber which is preferably not more than 3 parts by weight, more preferably not more than 2 parts by weight, even more preferably not more than 1 part by weight, and most preferably not more than 0.5 part by weight. Too much or too little antioxidant may make it impossible to achieve a suitable core hardness gradient, a good rebound and durability, and a spin rate-lowering effect on full shots.

In the practice of the invention, an organosulfur compound may be optionally included with the base rubber in order to enhance the core rebound. In cases where an organosulfur compound is included, the content thereof per 100 parts by weight of the base rubber, may be set to preferably at least 0.05 part by weight, more preferably at least 0.1 part by weight, and even more preferably at least 0.2 part by weight. The upper limit in the organosulfur compound content is preferably not more than 5 parts by weight, more preferably not more than 4 parts by weight, and even more preferably not more than 2 parts by weight. Including too little organosulfur compound may make it impossible to obtain a sufficient core rebound-increasing effect. On the other hand, if too much is included, the core hardness may become too low, worsening the feel of the ball on impact, and the durability of the ball to cracking when repeatedly struck may worsen.

The rubber composition containing the various above ingredients is prepared by mixture using a typical mixing apparatus, such as a Banbury mixer or a roll mill. When the core is molded using this rubber composition, molding may be carried out by compression molding or injection molding using a specific mold for molding cores. The resulting molded body is then heated and cured under temperature conditions sufficient for the organic peroxide and the co-crosslinking agent included in the rubber composition to act, thereby giving a core having a specific hardness profile. The vulcanization conditions in this case, while not subject to any particular limitation, are generally set to a vulcanization temperature of about 130 to 170° C., and especially 150 to 160° C., and a vulcanization time of 10 to 40 minutes, and especially 12 to 20 minutes.

The core diameter, although not subject to any particular limitation, may be set to from 30 to 40 mm. In this case, the lower limit is preferably at least 32 mm, more preferably at least 34 mm, and even more preferably at least 35 mm. The upper limit may be set to preferably not more than 39 mm, and more preferably not more than 38 mm.

The deflection of the core when compressed under a final load of 1,275 N (130 kgf) from an initial load of 98 N (10 kgf), although not subject to any particular limitation, may be set within the range of 2.0 to 6.0 mm. The lower limit is preferably at least 2.5 mm, more preferably at least 3.0 mm, and even more preferably at least 3.5 mm. The upper limit is preferably not more than 5.5 mm, and more preferably not more than 5.0 mm. If the core is harder than the above range (smaller deflection), when the ball is struck at a high head speed, a sufficient distance-reducing effect may not be obtained. On the other hand, if the core is softer than the above range (larger deflection), the feel at impact may become too soft and the ball may have a poor durability to cracking when repeatedly struck.

The color of the core 1 is not particularly limited, although in the case of a two-piece solid golf ball in which a one-layer cover is formed over the core 1, it is preferable to make the core white.

In this invention, by using the above material to form the solid core 1, the rebound can be increased, thus making it possible to provide a golf ball capable of achieving a stable trajectory.

The color of the core 1 is not particularly limited, although in the case of a two-piece solid golf ball in which a one-layer cover is formed over the core 1, it is preferable to make the core white.

The above core is not limited to a single-layer construction, and may instead have a multilayer construction of two or more layers. By giving the core a multilayer construction, the spin rate on shots with a driver can be reduced, enabling a further increase in distance to be achieved. Moreover, the spin properties and feel of the ball when struck can be further enhanced. In such cases, the core has at least an inner core layer (inner sphere) and an outer core layer.

Next, the materials of the cover (intermediate layer 2 and outermost layer 3) which is formed over the core are described in detail.

The intermediate layer 2 (cover 2) may be formed primarily of a resin material which is any of various thermoplastic resins or thermoplastic elastomers, such as a known ionomer resin or polyurethane. This intermediate layer 2 may be formed as two or more layers using similar or dissimilar materials, depending on the ball specifications and other considerations. The method of molding the intermediate layer 2 is not subject to any particular limitation; a known method such as injection molding may be suitably selected for this purpose. The thickness of the intermediate layer 2 is not particularly limited, provided it is suitable for the ball specifications and the like. When the cover encasing the core 1 is a single layer, an intermediate layer is not formed; in such cases, the cover has only an outermost layer which is formed over the core using the above-described outermost layer-forming resin composition.

The thickness of the intermediate layer is not particularly limited, and may be set to preferably at least 0.5 mm, more preferably at least 0.8 mm, and even more preferably at least 1.0 mm. There is no particular upper limit, although the thickness may be set to preferably not more than 3.0 mm, more preferably not more than 2.5 mm, and even more preferably not more than 2.0 mm. If the intermediate layer thickness is too small, the durability to cracking on repeated impact may worsen. On the other hand, if the thickness is too large, the feel at impact may worsen.

The color of the intermediate layer 2 is not particularly limited, although it is preferable to make the layer adjoining the inner side of the subsequently described outermost layer 3 white in color.

The above cover 3 (outermost layer 3) is formed of a resin composition obtained by blending a specific light-harvesting fluorescent dye and a specific light-reflecting pigment with the base resin. The various ingredients of the material used to form this cover 3 (outermost layer 3) are described in detail below.

The base resin is the primary ingredient in the outermost layer. Various known thermoplastic resins may be used without particular limitation. Specifically, preferred use may be made of olefinic thermoplastic resins and thermoplastic polyurethanes. Of these, the use of nonionic resins such as olefin-unsaturated carboxylic acid copolymers and olefin-unsaturated carboxylic acid-carboxylic acid ester copolymers, or of ionic resins or thermoplastic polyurethanes, is especially preferred. These may be used singly or as combinations of two or more thereof.

The above ionic resins and nonionic resins are not particularly limited; use may be made of known commercial products. Illustrative examples of ionic resins that may be used include Himilan 1601, Himilan 1605, Himilan 1557, Himilan 1855, Himilan AM7318 and Himilan AM7327 (all available from DuPont-Mitsui Polychemicals Co., Ltd.), and Iotek 8030 and Iotek 7010 (ExxonMobil Chemical). An illustrative example of a nonionic resin is Nucrel NO35C (DuPont-Mitsui Polychemicals Co., Ltd.).

The thermoplastic polyurethane is also not particularly limited; use can be made of know commercial products. Illustrative examples include Pandex T8295 and Pandex T8260 (DIC Bayer Polymer).

In this invention, including the light-harvesting fluorescent dye in the outermost layer-forming material makes it possible also to suitably reflect light in the ultraviolet region. Such a light-harvesting fluorescent dye is not particularly limited in the choice of colors; a color may be suitably selected from among, for example, yellow, orange, red, blue, green, pink and violet. In particular, colors such as red, blue and violet are generally hard to discern from a distance. However, in this invention, by using a light-harvesting fluorescent dye, a visibility-improving effect is achieved. Commercial products such as the Lumogen F series from BASF AG may be used as such light-harvesting fluorescent dyes.

The light-harvesting fluorescent dye is included in an amount of from 0.001 to 0.1 part by weight per 100 parts by weight of the base resin. In this case, the lower limit in the amount of light-harvesting fluorescent dye included may be set to preferably at least 0.005 part by weight, and more preferably at least 0.007 part by weight. The upper limit in the amount of light-harvesting fluorescent dye may be set to preferably not more than 0.07 part by weight, and more preferably not more than 0.05 part by weight. If the amount of light-harvesting fluorescent dye included is too low, a suitable shade of color cannot be achieved and light of a specific wavelength cannot be reflected, as a result of which the visibility at dusk and in bad weather worsens. On the other hand, if too much light-harvesting fluorescent dye is included, the color of the cover becomes too deep, giving the ball as a whole a dark coloring, as a result of which light of a specific wavelength cannot be suitably reflected.

The light-reflecting pigment is included in order to enhance the elegance and sense of quality of the golf ball, and also, by irregularly reflecting light that strikes the cover, to enhance the visibility of the ball. In this invention, examples of light-reflecting pigments that may be compounded include metal powder pigments, glass flakes, mica and pearlescent pigments. From the standpoint of maintaining the cover transparency and also imparting a sense of elegance, the use of glass flakes is especially preferred.

Preferred use may be made of glass flakes which are of one or more type selected from among soda lime glass, borosilicate glass, aluminosilicate glass, lead crystal glass, E-glass, A-glass, C-glass, ECR-glass, Duran glass, window glass and laboratory glass. More specifically, suitable use may be made of glass flakes of the following composition:

50 to 70 wt % SiO₂

• • 1 to 20 wt % Al₂O₃
  • 2 to 20 wt % CaO
  • 0 to 6 wt % MgO
  • 0 to 10 wt % B₂O₃
  • 0 to 30 wt % other ingredients.
    Illustrative examples of other ingredients that may be optionally used include Na₂O, K₂O, ZnO, TiO₂ and BaO.

Preferred use may be made of glass flakes which are colored with one or more colorant selected from the group consisting of elemental copper, chromium, manganese, iron and cobalt and/or cations or complex anions of combinations thereof, TiO₂, and elemental precious metals. By combining the glass flakes colored with such a colorant and the light-harvesting fluorescent dye, it is possible both to impart a perceived color that differs from when a light-harvesting fluorescent dye is used alone, and also to express a perceived color having depth. The amount of colorant included in the glass flakes, although not particularly limited, is set to preferably from 0.2 to 50 wt %, and more preferably from 0.3 to 40 wt %, of the glass flakes as a whole.

Any of the following may be used as the pearlescent pigment: metal oxide-coated mica, basic lead carbonate, bismuth oxychloride, and natural pearl essence. Of these, the selection of a metal oxide-coated mica is preferred because such pigments are nontoxic and have the best chemical stability. In such a metal oxide-coated mica, titanium dioxide or iron oxide is typically used as the metal oxide which coats the mica; by varying the coverage (thickness of the coating layer), various perceived colors and interference effects can be achieved.

It is critical for the light-reflecting pigment to have a particle size of from 1 to 250 μm. In this case, the lower limit in the particle size may be set to preferably at least 5 μm, and more preferably at least 10 μm. The upper limit in the particle size may be set to preferably not more than 220 μm, and more preferably not more than 200 μm. At a light-reflecting pigment particle size outside of the above range, suitable reflection cannot be obtained. Moreover, particularly in cases where the particle size is too large, the durability of the cover is diminished.

The thickness of the light-reflecting pigment, although not particularly limited, is set to preferably from 0.5 to 2 μm. The lower limit in the thickness may be set to more preferably at least 0.8 μm, and the upper limit in the thickness may be set to more preferably not more than 1.5 μm. If the thickness of the light-reflecting pigment falls outside the above range, it may not be possible to obtain a suitable reflection; at a thickness which is too large in particular, the durability of the cover may be diminished.

The above particle size and thickness refer to values obtained by examining the light-reflecting pigment with an optical microscope or an electron microscope, or to values measured with a particle size analyzer using a laser, such as by laser diffractometry.

The aspect ratio of the light-reflecting pigment, although not particularly limited, is preferably from 10 to 1,300, and more preferably from 30 to 700. The refractive index of the light-reflecting pigment, although not particularly limited, is preferably from 1.1 to 2.1, and more preferably from 1.2 to 2.0.

A commercial product may be used as the light-reflecting pigment. Illustrative examples of such products include the Iriodin series, Xirallic series, Colorstream series and Miraval series available from Merck.

The light-reflecting pigment is included in an amount of from 0.05 to 0.7 part by weight per 100 parts by weight of the base resin. Here, the lower limit in the amount of light-reflecting pigment included may be set to preferably at least 0.07 part by weight, and more preferably at least 0.1 part by weight. The upper limit in the amount of light-reflecting pigment may be set to preferably not more than 0.6 part by weight, and more preferably not more than 0.5 part by weight. If the amount of light-reflecting pigment is too low, light cannot be suitably reflected, as a result of which it may not be possible to obtain sufficient visibility. On the other hand, if too much light-reflecting pigment is included, the flowability of the material decreases, inviting molding defects, or the durability of the ball decreases. Moreover, the particles of light-reflecting pigment end up orienting to the direction of resin flow, and are thus unable to suitably reflect light, as a result of which the desired coloration is not obtained. In such cases, the resulting golf ball lacks elegance and stylishness.

The compounding ratio between the light-harvesting fluorescent dye and the light-reflecting pigment, expressed as a weight ratio, although not particularly limited, is preferably from 1:1 to 1:50. Here, the compound ratio, expressed as a weight ratio, is more preferably from 1:2 to 1:40, and even more preferably from 1:3 to 1:30. At a compounding ratio between the light-harvesting fluorescent dye and the light-reflecting pigment outside of the above range, suitable coloration and reflection cannot be obtained, resulting in a poor visibility, weatherability and elegance.

Although not particularly limited, the content of the light-reflecting pigment and the thickness of the outermost layer preferably satisfy the following condition:

light-reflecting pigment content×outermost layer thickness=from 0.05 to 0.35.

The lower limit in the above value may be set to more preferably at least 0.1, and the upper limit may be set to more preferably not more than 0.33.

If the content of the light-reflecting pigment and the thickness of the outermost layer do not satisfy the above condition, short molding may arise, and a suitable reflection may be impossible to obtain. Also, if the above condition is not satisfied, this may be a factor in reducing the visibility of the golf ball over a given distance or more.

Titanium oxide may be optionally included in the outermost layer-forming material. By adjusting the amount of titanium oxide included, the extent to which the underlying layer shows through can be modified, in addition to which the degree of coloration can be changed. In this invention, a known titanium oxide may be used. For example, preferred use may be made of products commercially available under the trade name TIPAQUE (Ishihara Sangyo Kaisha). This titanium oxide may also be used as a white pigment, enabling depth to be imparted to the perceived color of the ball. The amount of such titanium oxide included per 100 parts by weight of the base resin may be set to from 0.01 to 0.1 part by weight. If too little titanium oxide is included, the hiding power may be inadequate, allowing the underlying color to affect ball coloration. On the other hand, including too much may increase the sense of opacity, resulting in a loss of elegance.

In addition, a lubricant may be optionally included in the outermost layer-forming material. In this invention, the lubricant is an ingredient which functions as, for example, a processing aid, a slip enhancer or a dispersant. Exemplary lubricants include liquid paraffin, organic acids such as fatty acids, fatty acid metal salts and fatty amides, as well as acrylic polymers and silicones. The amount of such lubricant included per 100 parts by weight of the base resins may be set to from 0.01 to 3.0 parts by weight. If the amount of lubricant is too small, the material may not have good flow properties, which may make molding impossible to carry out. On the other hand, if too much is included, the lubricant may bleed out, possibly marring the appearance of the ball surface or resulting in poor adhesion with the outermost layer 3 and the inner layer (the intermediate layer 2 or the core 1).

In addition to the above ingredients, it is possible to include also various types of additives. Additives for various resin applications may be used, such as antioxidants, ultraviolet absorbers, flow enhancers and thickeners. The amount in which these additives are included may be suitably selected within a range that does not adversely affect the moldability and other properties of the outermost layer-forming material, and is not particularly limited. Typically, the amount of such additives per 100 parts by weight of the base resin may be set to from 0.05 to 5 parts by weight, and preferably from 0.1 to 4 parts by weight.

It is critical for the thickness of the outermost layer 3 to be set to from 0.5 to 1.6 mm. In this case, the lower limit in the thickness of the outermost layer 3 may be set to preferably at least 0.5 mm, and more preferably at least 0.7 mm. The upper limit in the thickness of the outermost layer 3 may be set to preferably not more than 1.6 mm, and more preferably not more than 1.4 mm. If the outer cover layer 3 is too thin, the underlying material may show through, detracting from the ball coloration. On the other hand, if the outer layer cover 3 is too thick, uniform injection molding may be difficult to carry out, resulting in a loss in the sense of ball quality.

Preparation of the above-described material may be carried out using a known mixing apparatus, such as a single-screw extruder or a twin-screw extruder. In this invention, the use of a twin-screw extruder is preferred. Alternatively, these extruders may be used in a tandem arrangement, such as single-screw extruder/twin-screw extruder or twin-screw extruder/twin-screw extruder. These extruders need not be of a special design; the use of existing extruders will suffice. The method of molding the cover using the above material is not subject to any particular limitation. For example, use may be made of an injection molding process or a compression molding process. In cases where an injection molding process is used, the process may one in which a prefabricated core is placed at a predetermined position in an injection mold, following which the above material is introduced into the mold. Alternatively, in cases where a compression molding process is used, the process may be one in which a pair of half-cups is produced of the above material, the cups are placed over a core, and heat and pressure are applied within a mold. When molding is carried out under applied heat and pressure, the molding conditions employed may be a temperature of from 120 to 170° C. and a molding time of from 1 to 5 minutes.

Although not particularly shown here in a diagram, a clear paint is typically applied to the surface of the cover 3 (outermost layer 3) so as to, for example, protect the ball surface. In such a case, the thickness of the coat of paint, although not subject to any particular limitation, is preferably at least 5 μm, and more preferably at least 10 μm, but preferably not more than 30 μm, and more preferably not more than 20 μm. If the paint coat is too thin, the durability of the coat may be inadequate. On the other hand, if the paint coat is too thick, this may lower the rebound of the ball and may lead to peeling of the paint.

The color tone of the golf ball may be suitably selected and is not particularly limited, although an outstanding effect is achieved when a red color in particular is selected. More specifically, an outstanding effect is achieved within the following ranges in the L*a*b* color space according to JIS Z 8729: an L* value of not more than 55, an a* value of at least 65, and a b* value of not more than 30.

Because the above outermost layer-forming material has a high transmittance, the color of the layer (the core 1 or the intermediate layer 2) adjoining the inner side of the outermost layer 3 may exert an influence on the color tone of the ball. For this reason, although not particularly limited, in order to minimize such an influence, it is preferable to have the layer (core 1 or intermediate layer 2) adjoining the inner side of the outermost layer 3 be white in color.

In the above golf ball, the shapes, number and arrangement of the dimples formed on the surface may be suitably set according to the ball specifications, and are not subject to any particular limitations. For example, the dimple shapes may be suitably selected from among not only circular shapes, but also non-circular polygonal shapes, dewdrop shapes and oval shapes. The diameter of the above dimples, although not particularly limited, is preferably set in the range of 0.5 to 6 mm. In addition, the dimple depth, although not particularly limited, is preferably set in the range of 0.05 to 0.4 mm.

No particular limitation is imposed on the surface coverage by the dimples on the surface of the ball. However, from the standpoint of the aerodynamic properties, the surface coverage is preferably set to at least 70%, more preferably at least 75%, and even more preferably at least 80%.

The ball has a deflection when compressed under a final load of 1,275 N (130 kgf) from an initial load state of 98 N (10 kgf) which, although not particularly limited, may be set to preferably at least 2.5 mm. The upper limit in the deflection may be set to preferably not more than 7 mm.

The golf ball of the invention can be made to conform to the Rules of Golf for competitive play. Specifically, the ball can be formed to a diameter which is not less than 42.67 mm and to a weight which is not more than 45.93 g.

As explained above, the present invention is able to provide a golf ball which is elegant and highly stylish, and which also has an excellent visibility.

EXAMPLES

Working Examples of the invention and Comparative Examples are given below by way of illustration, and not by way of limitation.

Examples 1 to 3, Comparative Example 1

Formation of Core

A solid core was produced by preparing the rubber composition shown in Table 1, then molding and vulcanizing the composition under vulcanization conditions of 155° C. and 15 minutes.

	TABLE 1
	Core
	Formulation	BR730	100
	(parts by weight)	Organic peroxide	1.2
		Zinc oxide	27.19
		Antioxidant	0.1
		Zinc acrylate	28.20
		Organosulfur compound	0.10

Details on the ingredients shown in Table 1 are given below.

• BR730: A polybutadiene rubber synthesized with a neodymium catalyst, available from JSR Corporation
• Organic peroxide: Available under the trade name “Perhexa 3M” from NOF Corporation
• Zinc oxide: Zinc oxide available from Sakai Chemical Co., Ltd.
• Antioxidant: Available under the trade name “Nocrac NS-6” from Ouchi Shinko Chemical Industry Co., Ltd.
• Zinc acrylate: Available from Nihon Jyoryu Kogyo Co., Ltd.
• Organosulfur compound: Zinc salt of pentachlorothiophenol

Formation of Intermediate Layer

Next, an intermediate layer was formed by injection-molding, over the resulting core, an intermediate layer material formulated as shown in Table 2.

	TABLE 2
	Intermediate layer
	Formulation	Nucrel AN4319	100
	(pbw)	Magnesium stearate	70
		Calcium hydroxide	1.9
		Titanium oxide	4.2
	Degree of neutralization (mol %)	100.4

Details on the material shown in Table 2 are given below.

• Nucrel AN4319: An ethylene-methacrylic acid-acrylic acid ester terpolymer available from DuPont-Mitsui Polychemicals Co., Ltd. (acid content, 8.0 wt %; ester content, 17.0 wt %)

Formation of Cover

A cover was formed by injection-molding, over the intermediate layer formed as described above, a cover material formulated as shown in Table 3, thereby fabricating a golf ball having an intermediate layer and a cover over a core. The golf ball of the invention is not particularly limited as to color, although red was selected here as one of the colors most difficult to see at dusk. Simultaneous with formation of the above cover, numerous dimples in the same pattern were formed on the outer surface of the golf balls produced in the Examples of the invention and in the Comparative Example.

	TABLE 3
		Comparative
	Example	Example
	1	2	3	1
Core	Diameter (mm)	37.3	37.3	37.3	37.3
Intermediate	Thickness (mm)	1.45	1.45	1.45	1.45
layer
Cover	Thickness (mm)	1.25	1.25	1.25	1.25
	Formulation	Himilan AM7318	50	50	50	50
	(pbw)	Himilan AM7327	50	50	50	50
		Magnesium stearate	0.09	0.09	0.09	0.09
		Liquid paraffin	0.05	0.05	0.05	0.05
		Titanium oxide	0.01	0.01	0.01	0.01
		SINLOIHI COLOR		1
		FX-303 Red
		Lumogen F Red 305	0.04	0.02	0.04
		Sumiplast Red B-2				0.1
		Miraval	0.2	0.2
		Iriodin			0.2
Ball	Diameter (mm)	42.7	42.7	42.7	42.7
	Surface hardness (Shore D)
	Color tone	L value	45.5	47.8	44.2	43.6
		a value	69.0	78.4	68.7	63.7
		b value	16.1	21.3	17.6	19.0
		YI	172.4	197.7	186.0	183.0
	Compounding ratio of light-harvesting	1:5	1:10	1:5	—
	fluorescent dye to light-reflecting pigment
	Light-reflecting pigment content ×	0.3	0.25	0.3	—
	cover thickness
	Visibility	good	good	fair	NG
	Weatherability	good	good	good	good
	Elegance	Exc	Exc	good	NG

Details on the ingredients shown in Table 3 are given below.

• Himilan AM7318: An ethylene-methacrylic acid copolymeric ionomer neutralized with sodium; available from DuPont-Mitsui Polychemicals Co., Ltd.
• Himilan AM7327: An ethylene-methacrylic acid-butyl acrylate terpolymeric ionomer neutralized with zinc; available from DuPont-Mitsui Polychemicals Co., Ltd.
• SINLOIHI COLOR FX-303 Red: A granular fluorescent red pigment available from Sinloihi Co., Ltd.; mean particle size, 3±1 μm
• Lumogen F Red 305: A light-harvesting fluorescent red dye available from BASF
• Sumiplast Red B-2: A red dye available from Sumika Chemtex Co., Ltd.
• Miraval: A light-reflecting pigment composed of titanium oxide-coated borosilicate glass flakes, available from Merck; thickness, about 1 μm; particle size, 20 to 200 μm
• Iriodin: A light-reflecting pigment composed of metal oxide-coated natural mica flakes, available from Merck; thickness, 0.5 to 10 μm; particle size, 10 to 60 μm

The following properties of the respective golf balls obtained above in Examples 1 to 3 and Comparative Example 1 were rated as described below. The results are shown in Table 3.

Color:

The color tone of the ball after topcoating was measured using a color difference meter (model SC-P, manufactured by Suga Test Instruments Co., Ltd.) and with a C light source having a 2° field, in accordance with JIS Z 8722-1994, Condition c (Measurement of Reflection (diffused illumination, 8° viewing angle (d/8: excluding specularly reflected component)), and was converted to a numerical value based on JIS Z 8729-1994 (L*a*b* color system). A measurement area diameter of 30 mm was used.

Visibility:

A golf ball placed on turf was viewed at a distance of 30 yards by ten amateur golfers, and sensory evaluated based on the following criteria.

• • Good: Eight or more of the ten golfers thought the ball was easy to see on turf.
  • Fair: From four to seven of the ten golfers thought the ball was easy to see on turf.
  • NG: From zero to three of the ten golfers thought the ball was easy to see on turf.

Weatherability:

Each type of ball (n=3) was exposed to sunlight together with an index ball. ΔE was measured at fixed time intervals with a Lab color difference meter. When the ΔE of the index ball became 15 or more, exposure to sunlight was stopped and the ΔE for each ball at that time was measured. The weatherability was rated according to the following ΔE criteria.

• • Excellent: less than 5
  • Good: 5 or more, but less than 13
  • Fair: 13 or more

Elegance:

Sensory evaluations based on the following criteria were carried out by ten skilled amateur golfers.

• • Excellent: Eight or more of the ten golfers thought the ball had an elegant feel.
  • Good: From four to seven of the ten golfers thought the ball had an elegant feel.
  • NG: From zero to three of the ten golfers thought the ball had an elegant feel.

Claims

1. A golf ball comprising a core and a cover of one or more layer, wherein the cover has an outermost layer which is formed of a resin composition containing, per 100 parts by weight of resin components:

0.001 to 0.1 part by weight of a light-harvesting fluorescent dye; and

0.05 to 0.7 part by weight of a light-reflecting pigment having a particle size of from 1 to 250 μm, and which has a thickness of from 0.5 to 1.6 mm.

2. The golf ball of claim 1, wherein the compounding ratio between the light-harvesting fluorescent dye and the light-reflecting pigment, expressed as a weight ratio, is from 1:1 to 1:50.

3. The golf ball of claim 1, wherein the content of the light-reflecting pigment and the thickness of the outermost layer satisfy the following condition:

light-reflecting pigment content×outermost layer thickness=from 0.05 to 0.35.

4. The golf ball of claim 1, wherein the light-reflecting pigment is glass flakes having a thickness of from 0.5 to 2 μm and a particle size of from 1 to 250 μm.

5. The golf ball of claim 4, wherein the glass flakes are of one or more type selected from the group consisting of soda lime glass, borosilicate glass, aluminosilicate glass, lead crystal glass, E-glass, A-glass, C-glass, ECR-glass, Duran glass, window glass and laboratory glass.

6. The golf ball of claim 4, wherein the glass flakes are colored with one or more colorant selected from the group consisting of elemental copper, chromium, manganese, iron and cobalt and/or cations or complex anions of combinations thereof, TiO2, and elemental precious metals.

7. The golf ball of claim 1, wherein the light-gathering fluorescent dye is red and the golf ball has an L* value of not more than 55, an a* value of at least 65 and a b* value of not more than 30.

8. The golf ball of claim 1, wherein a layer adjoining an inner side of the cover outermost layer is white in color.