GOLF BALL MANUFACTURING METHOD

A golf ball manufacturing method includes an inner layer molding step of molding an inner layer that includes an outer surface with a recess, an inner film formation step, after the inner layer molding step, of coating the outer surface of the inner layer with inner film paint to form an inner film, an inner film removal step, after the inner film formation step, of removing the inner film except for a portion thereof covering a surface of the recess to obtain an inner ball that includes the inner layer and the inner film, and a cover layer molding step, after the inner film removal step, of molding a cover layer that includes an outer surface with dimples on an outer circumferential side of the inner ball to obtain a golf ball. The inner layer and inner film are different colors, and the cover layer is transparent or semi-transparent.

TECHNICAL FIELD

The present disclosure relates to a golf ball manufacturing method.

This application is based on and claims priority to Japanese patent application No. 2020-101129, filed on Jun. 10, 2020, the entire content of which is incorporated herein by reference.

BACKGROUND

A known golf ball has a coating formed by printing or painting on the outer circumferential side of a cover layer. For example, see patent literature (PTL) 1.

CITATION LIST

Patent Literature

SUMMARY

The above-described golf ball has the problem, however, of the coating easily peeling due to impact, such as when the ball is hit.

It would be helpful to provide a golf ball manufacturing method that can achieve a golf ball capable of reducing peeling of the coating.

A golf ball manufacturing method of the present disclosure includes:

an inner layer molding step of molding an inner layer that includes an outer surface with a recess;

an inner film formation step, after the inner layer molding step, of coating the outer surface of the inner layer with inner film paint to form an inner film;

an inner film removal step, after the inner film formation step, of removing the inner film except for a portion of the inner film covering a surface of the recess to obtain an inner ball that includes the inner layer and the inner film; and

a cover layer molding step, after the inner film removal step, of molding a cover layer that includes an outer surface with dimples on an outer circumferential side of the inner ball to obtain a golf ball, wherein

the inner layer and the inner film are different colors from each other, and

the cover layer is transparent or semi-transparent.

In the golf ball manufacturing method of the present disclosure, the inner layer is preferably molded in the inner layer molding step using a mold for inner layer molding.

In the golf ball manufacturing method of the present disclosure, a depth of the recess is preferably 5 mm or less.

The golf ball manufacturing method of the present disclosure preferably further includes a drying step, after the inner film formation step and before the inner film removal step, of drying the inner film.

In the golf ball manufacturing method of the present disclosure, the cover layer is preferably molded in the cover layer molding step by injection molding using a mold for cover layer molding, and

the golf ball manufacturing method preferably further includes a positioning step for cover layer molding, after the inner film removal step and before the cover layer molding step, of positioning the inner ball in a cavity of the mold for cover layer molding so that the inner film does not face a gate for the injection molding in a radial direction.

The golf ball manufacturing method of the present disclosure preferably further includes

a positioning step for printing, after the cover layer molding step, of positioning the golf ball relative to a printing member so that the inner film does not face a printing portion of the printing member in a radial direction; and

a printing step, after the positioning step for printing, of printing on an outer surface of the golf ball using the printing member.

The golf ball manufacturing method of the present disclosure preferably further includes

a coating layer formation step, after the cover layer molding step, of coating an outer circumferential side of the cover layer with coating layer paint to form a coating layer so that the golf ball includes the coating layer on the outer circumferential side of the cover layer, wherein

the coating layer includes matte particles.

The present disclosure can provide a method of manufacturing a golf ball to achieve a golf ball capable of reducing peeling of the coating.

DETAILED DESCRIPTION

A golf ball manufacturing method of the present disclosure can be used to manufacture any type of golf ball, such as a two-piece golf ball, a three-piece golf ball, a four-piece golf ball, a five-piece golf ball, a six-piece golf ball, or a wound golf ball.

Embodiments of a golf ball manufacturing method according to the present disclosure are described below with reference to the drawings.

Constituent elements that are common across drawings are labeled with the same reference signs.

A golf ball manufacturing method according to an embodiment of the present disclosure is described below with reference toFIGS. 1 to 12. The golf ball manufacturing method according to the present embodiment includes an inner layer molding step, an inner film formation step, a drying step, an inner film removal step, a cover layer molding step, a surface treatment step, a printing step, and a coating layer formation step. Each step is described below.

In the inner layer molding step, an inner layer12that includes an outer surface having one or a plurality of recesses121is molded (FIGS. 1 to 3).

An inner ball14(FIG. 3) that includes at least the inner layer12is obtained by the inner layer molding step. The inner ball14obtained by the inner layer molding step includes the inner layer12as the outermost circumferential layer. In the present disclosure, the “inner ball” indicates a ball in a state before formation of the cover layer, described below.

In the inner layer molding step, the inner layer12is preferably molded using a mold2for inner layer molding, as in the example inFIGS. 1 and 2. In this case, the inner layer12is preferably molded by injection molding or compression molding (molding) using the mold2for inner layer molding.

The mold2for inner layer molding includes a cavity surface23for inner layer molding configured to mold the outer surface of the inner layer12, as illustrated inFIGS. 1 and 2. The cavity surface23for inner layer molding defines a cavity20for inner layer molding. The cavity surface23for inner layer molding includes one or a plurality of projecting surfaces231that project towards the inner circumferential side. The projecting surface231is configured to mold the recess121(FIG. 3) of the inner layer12.

When a plurality of recesses121is formed in the inner layer12, for example, use of the mold2for inner layer molding to mold the inner layer12enables the positions of the recesses121relative to each other to be determined as expected easily in one process. The positions, relative to each other, of a plurality of inner films13that cover a surface121aof each recesses121in the inner ball14(FIG. 5) obtained after the inner film removal step, described below, can thereby easily be set as expected.

In the inner layer molding step, the inner layer12may be molded on the outer circumferential side of a core ball10, as in the example inFIGS. 1 to 3. In this case, the inner ball14obtained by the inner layer molding step includes the core ball10and the inner layer12positioned on the outer circumferential side of the core ball10. The core ball10includes one or a plurality of layers. For example, the core ball10includes one or a plurality of rubber layers. In the example inFIGS. 1 to 3, the core ball10is formed by one rubber layer. The rubber forming the one or plurality of rubber layers that the core ball10can include is preferably butadiene rubber, for example. When the core ball10includes a plurality of rubber layers, the rubber forming each rubber layer preferably has a different composition. When the core ball10includes a plurality of rubber layers, the rubber forming each rubber layer preferably has a different hardness. The core ball10can include one or a plurality of resin layers on the outer circumferential side of the one or plurality of rubber layers.

For example, when the core ball10includes only one or a plurality of rubber layers as in the example inFIGS. 1 to 3, the inner layer12may be formed from rubber or from resin. In the example inFIGS. 1 to 3, the inner layer12is, for example, formed from resin.

When the core ball10includes one or a plurality of resin layers in addition to the one or plurality of rubber layers on the outer circumferential side of the one or plurality of rubber layers, the inner layer12is formed from resin.

The rubber that can form the inner layer12is preferably butadiene rubber, for example.

The inner layer12may be molded in the inner layer molding step without use of the core ball10. In this case, the inner ball14obtained by the inner layer molding step includes only the inner layer12. The inner layer12is preferably formed from rubber but may be formed from resin in this case.

In the example inFIGS. 1 to 3, the inner layer12(FIG. 3) is molded by injection molding using the mold2for inner layer molding. In other words, in the example inFIGS. 1 to 3, the mold2for inner layer molding is a mold for injection molding.

An example configuration of the mold2for inner layer molding for the case of the mold2for inner layer molding being a mold for injection molding, as in the example inFIGS. 1 to 3, is described below.

As illustrated inFIGS. 1 and 2, the mold2for inner layer molding includes a first mold portion21for inner layer molding and a second mold portion22for inner layer molding. The first mold portion21for inner layer molding and the second mold portion22for inner layer molding are configured to face each other. In the example inFIG. 1, the first mold portion21for inner layer molding and the second mold portion22for inner layer molding are configured to face each other in the vertical direction, and the first mold portion21for inner layer molding is configured to be positioned on the upper side of the second mold portion22for inner layer molding in the vertical direction. The first mold portion21for inner layer molding and the second mold portion22for inner layer molding may, however, be configured to face each other in any direction other than the vertical direction. The first mold portion21for inner layer molding may be configured to be positioned on any side, other than the upper side in the vertical direction, of the second mold portion22for inner layer molding.

In the present disclosure, the direction in which the first mold portion21for inner layer molding and the second mold portion22for inner layer molding are arranged facing each other in the mold2for inner layer molding (in the example in the drawings, the vertical direction) is referred to as the “axial direction of the mold for inner layer molding IAD”. The direction perpendicular to the axial direction of the mold for inner layer molding IAD (in the example in the drawings, the horizontal direction) is referred to as the “perpendicular-to-axis direction of the mold for inner layer molding IPD”.

The first mold portion21for inner layer molding and the second mold portion22for inner layer molding each include the cavity surface23for inner layer molding, which is recessed in a substantially hemispherical shape. When a divided face21F, within the outer surface of the first mold portion21for inner layer molding, facing the second mold portion22for inner layer molding and a divided face22F, within the outer surface of the second mold portion22for inner layer molding, facing the first mold portion21for inner layer molding are joined (i.e., when the mold2for inner layer molding is closed), the cavity surface23for inner layer molding in the first mold portion21for inner layer molding and the cavity surface23for inner layer molding in the second mold portion22for inner layer molding continuously form a substantially spherical cavity surface23for inner layer molding, which defines the cavity20for inner layer molding (FIG. 1).

The mold2for inner layer molding includes a plurality of gates25G configured for injection of a molten material (such as molten resin) into the cavity20for inner layer molding. Each gate25G opens to the cavity surface23for inner layer molding, i.e., communicates with the cavity20for inner layer molding. The gates25G may be arranged at intervals in the circumferential direction, as in the example inFIGS. 1 and 2. Each gate25G may open to the divided face21F of the first mold portion21for inner layer molding and the divided face22F of the second mold portion22for inner layer molding, as in the example inFIG. 1. In greater detail, the mold2for inner layer molding may include a main runner241(FIG. 2) through which molten material passes, a ringed runner242continuing downstream from the main runner241and extending in a ring along the circumferential direction, a plurality of nozzle-shaped runners243extending towards the inner circumferential side from the ringed runner242, and the plurality of gates25G communicating between the nozzle-shaped runners243and the cavity20for inner layer molding, as in the example inFIGS. 1 and 2. In this case, the ringed runner242, each nozzle-shaped runner243, and each gate25G may open to the divided face21F of the first mold portion21for inner layer molding and the divided face22F of the second mold portion22for inner layer molding, as in the example inFIGS. 1 and 2.

In the molded article obtained immediately after injection molding, the inner ball14(FIG. 3) is formed continuously with excess portions molded by the ringed runner242, the nozzle-shaped runners243, and the gates25G. The inner ball14is obtained from this molded article by removing the excess portions. At this time, inner layer gate traces125G′ (FIG. 3) from the injection molding might remain on the outer surface of the inner layer12of the inner ball14at positions corresponding to the gates25G. For the sake of convenience, the inner layer gate traces125G′ are omitted from the drawings afterFIG. 3.

The first mold portion21for inner layer molding and the second mold portion22for inner layer molding of the mold2for inner layer molding preferably each include a degassing hole27and a degassing pin (pin)28P, inserted in the degassing hole27, as in the example inFIG. 1. The amount of air bubbles remaining in the inner layer12molded by the inner layer molding step can thus be reduced. The degassing hole27communicates with the cavity20for inner layer molding. In this way, gas produced at the time of injection molding inside the cavity20for inner layer molding is ejected outside the cavity20for inner layer molding through the degassing hole27.

In this case, inner layer degassing pin traces (inner layer pin traces)128P′ (FIG. 3) might remain on the outer surface of the inner layer12of the inner ball14obtained by the inner layer molding step at positions corresponding to the degassing pins (pins)28P. For the sake of convenience, the inner layer degassing pin traces (inner layer pin traces)128P′ are omitted from the drawings afterFIG. 3.

When the inner layer12is molded on the outer circumferential side of the core ball10in the inner layer molding step, the first mold portion21for inner layer molding and the second mold portion22for inner layer molding of the mold2for inner layer molding each preferably include a plurality of support pins (pins)26P, as in the example inFIG. 1. This configuration can suppress eccentricity of the core ball10inside the cavity20for inner layer molding, thereby suppressing eccentricity of the core ball10in the inner ball14(FIG. 3) obtained by the inner layer molding step. Each support pin26P extends in the axial direction of the mold for inner layer molding IAD and is configured to move back and forth in the axial direction of the mold for inner layer molding IAD. When the core ball10is housed inside the cavity20for inner layer molding and the mold2for inner layer molding is closed, each support pin26P supports the core ball10so that the core ball10is positioned in the center of the cavity20for inner layer molding (FIG. 1). During injection molding (for example, while molten material is being injected inside the cavity20for inner layer molding), each support pin26P recedes gradually to the outside of the cavity20for inner layer molding.

In this case, inner layer support pin traces (inner layer pin traces)126P′ (FIG. 3) might remain on the outer surface of the inner layer12of the inner ball14obtained by the inner layer molding step at positions corresponding to the support pins (pins)26P. For the sake of convenience, the inner layer support pin traces (inner layer pin traces)126P′ are omitted from the drawings afterFIG. 3.

After the inner layer molding step, the outer surface of the inner layer12is coated with inner film paint in the inner film formation step, thereby forming an inner film13(FIG. 4).

The inner ball14obtained by the inner film formation step includes at least the inner layer12and the inner film13that covers the outer circumferential side of the inner layer12.

In the inner film formation step, it suffices to form the inner film13by coating at least the entire bottom surface121abof the recess121on the outer surface of the inner layer12with the inner film paint so as to cover at least the entire bottom surface121abof the recess121. In the inner film formation step, the inner film13is preferably formed by coating at least the entire surface121a(the bottom surface121aband side surfaces121as) of the recess121on the outer surface of the inner layer12with the inner film paint so as to cover at least the entire surface121aof the recess121. The inner film13is more preferably formed in the inner film formation step by coating the entire outer surface of the inner layer12with the inner film paint so as to cover the entire outer surface of the inner layer12, as this approach facilitates the operation to coat with the inner film paint.

The method for coating with the inner film paint is preferably spray painting or dipping, for example.

The inner layer12and the inner film13(and therefore the inner film paint) are different colors from each other. Here, “different colors from each other” refers to how the hue, saturation, and/or brightness differ from each other. The inner layer12and the inner film13preferably have different hues from each other. The inner layer12and the inner film13preferably have different color tones from each other.

The inner layer12and the inner film13(and therefore the inner film paint) are each preferably opaque.

The inner film13(and therefore the inner film paint) is preferably colored. Here, “colored” refers to having a hue other than white and to not being colorless and transparent.

After the inner film formation step and before the inner film removal step, described below, the inner film13is dried in the drying step (FIG. 4).

Performance of the drying step facilitates the below-described inner film removal step and can reduce smearing of the inner film13, which covers the surface121aof the recess121, while the below-described inner film removal step is performed.

However, the drying step may be omitted.

After the inner film formation step, the inner film13formed by the inner film formation step is removed, except for the portion of the inner film13covering the surface121aof the recess121, in the inner film removal step (FIGS. 5 and 6). Only the inner film13other than the portion of the inner film13covering the surface121aof the recess121in the inner film13formed by the inner film formation step is preferably removed in the inner film removal step. In the case of performing the above-described drying step, the inner film removal step is performed after the drying step.

The inner ball14obtained by the inner film removal step includes at least the inner layer12and the inner film13that covers only the surface121aof the recess121on the outer surface of the inner layer12. It suffices for the inner film13to cover at least the entire bottom surface121abof the recess121, but the inner film13preferably covers the entire surface121a(bottom surface121aband side surfaces121as) of the recess121, as in the example inFIG. 5.

Examples of the method for removing only the inner film13other than the portion of the inner film13covering the surface121aof the recess121in the inner film13formed by the inner film formation step include using a barrel grinding machine to grind the inner ball14(FIG. 4), obtained by the inner film formation step, gradually from the outer circumferential side to the position of the outer surface of the inner layer12.

After the inner film removal step, a cover layer15including the outer surface that has multiple dimples151is molded on the outer circumferential side of the inner ball14(FIGS. 7 to 9).

A golf ball1including the inner ball14and the cover layer15positioned on the outer circumferential side of the inner ball14is obtained by the cover layer molding step. The golf ball1obtained by the cover layer molding step includes the cover layer15as the outermost circumferential layer. The cover layer15covers the outer surface of the inner ball14. The dimples151are formed on the cover layer15but not on the inner ball14(and therefore not on the inner layer12). In other words, the cover layer15has a maximum thickness equal to or greater than (preferably exceeding) the depth of the dimples151. The maximum thickness of the cover layer15corresponds to the thickness of the cover layer15when measured at a portion other than the dimples151(land portion) on the outer surface of the cover layer15.

The cover layer15is, for example, formed from urethane or ionomer.

The cover layer15is transparent or semi-transparent. As illustrated inFIG. 9, the exterior of the inner ball14can thereby be seen through the cover layer15when the golf ball1is viewed.

In the present disclosure, “transparent” refers to a visible light transmittance of 60% or higher, “semi-transparent” refers to a visible light transmittance of 30% or higher and less than 60%, and “opaque” refers to a visible light transmittance of less than 30%. The “visible light transmittance” is the average of the measured values of light transmittance as measured every 1 nm in the 380 to 780 nm wavelength region. The “visible light transmittance” can be calculated by using a sample of the same thickness and material as the cover layer, or a sample of the cover layer directly peeled off from a finished product golf ball, and measuring the light transmittance every 1 nm in the 380 to 780 nm wavelength region using, for example, any appropriate ultraviolet-visible spectrophotometer.

The cover layer15is preferably transparent. This enables clearer viewing of the exterior of the inner ball14through the cover layer15when the golf ball1is viewed. For the same reason, the visible light transmittance of the cover layer15is more preferably 70% or more, and even more preferably 80% or more.

The cover layer15is preferably colorless but may be colored.

In the cover layer molding step, the cover layer15is preferably molded using a mold3for cover layer molding, as in the example inFIG. 7. In this case, the cover layer15is preferably molded by injection molding or compression molding (molding) using the mold3for cover layer molding.

The mold3for cover layer molding includes a cavity surface33for cover layer molding configured to mold the outer surface of the cover layer15, as illustrated inFIG. 7. The cavity surface33for cover layer molding defines a cavity30for cover layer molding. The cavity surface33for cover layer molding includes multiple protruding surfaces331for dimple molding that project towards the inner circumferential side. The protruding surfaces331for dimple molding are configured to mold the dimples151of the cover layer15.

In the example inFIG. 7, the cover layer15is molded by injection molding using the mold3for cover layer molding. In other words, in the example inFIG. 7, the mold3for cover layer molding is a mold for injection molding.

An example configuration of the mold3for cover layer molding for the case of the mold3for cover layer molding being a mold for injection molding, as in the example inFIG. 7, is described below.

The mold3for cover layer molding has a similar configuration to that of the mold2for inner layer molding illustrated inFIG. 1. As illustrated inFIG. 7, the mold3for cover layer molding includes a first mold portion31for cover layer molding and a second mold portion32for cover layer molding. The first mold portion31for cover layer molding and the second mold portion32for cover layer molding are configured to face each other. In the example inFIG. 7, the first mold portion31for cover layer molding and the second mold portion32for cover layer molding are configured to face each other in the vertical direction, and the first mold portion31for cover layer molding is configured to be positioned on the upper side of the second mold portion32for cover layer molding in the vertical direction. The first mold portion31for cover layer molding and the second mold portion32for cover layer molding may, however, be configured to face each other in any direction other than the vertical direction. The first mold portion31for cover layer molding may be configured to be positioned on any side, other than the upper side in the vertical direction, of the second mold portion32for cover layer molding.

In the present disclosure, the direction in which the first mold portion31for cover layer molding and the second mold portion32for cover layer molding are arranged facing each other in the mold3for cover layer molding (in the example in the drawings, the vertical direction) is referred to as the “axial direction of the mold for cover layer molding CAD”. The direction perpendicular to the axial direction of the mold for cover layer molding CAD (in the example in the drawings, the horizontal direction) is referred to as the “perpendicular-to-axis direction of the mold for cover layer molding CPD”.

The first mold portion31for cover layer molding and the second mold portion32for cover layer molding each include the cavity surface33for cover layer molding, which is recessed in a substantially hemispherical shape. When a divided face31F, within the outer surface of the first mold portion31for cover layer molding, facing the second mold portion32for cover layer molding and a divided face32F, within the outer surface of the second mold portion32for cover layer molding, facing the first mold portion31for cover layer molding are joined (i.e., when the mold3for cover layer molding is closed), the cavity surface33for cover layer molding in the first mold portion31for cover layer molding and the cavity surface33for cover layer molding in the second mold portion32for cover layer molding continuously form a substantially spherical cavity surface33for cover layer molding, which defines the cavity30for cover layer molding (FIG. 7).

The mold3for cover layer molding includes a plurality of gates35G configured for injection of a molten material (such as fused urethane or molten ionomer) into the cavity30for cover layer molding. Each gate35G opens to the cavity surface33for cover layer molding, i.e., communicates with the cavity30for cover layer molding. The gates35G may be arranged at intervals in the circumferential direction, as in the example inFIG. 7. Each gate35G may open to the divided face31F of the first mold portion31for cover layer molding and the divided face32F of the second mold portion32for cover layer molding, as in the example inFIG. 7. In greater detail, the mold3for cover layer molding may include a main runner (not illustrated) through which molten material passes, a ringed runner342continuing downstream from the main runner and extending in a ring along the circumferential direction, a plurality of nozzle-shaped runners343extending towards the inner circumferential side from the ringed runner342, and the plurality of gates35G communicating between the nozzle-shaped runners343and the cavity30for cover layer molding, as in the example inFIG. 7. In this case, the ringed runner342, each nozzle-shaped runner343, and each gate35G may open to the divided face31F of the first mold portion31for cover layer molding and the divided face32F of the second mold portion32for cover layer molding, as in the example inFIG. 7.

In the molded article obtained immediately after injection molding, the golf ball1(FIG. 8) is formed continuously with excess portions molded by the ringed runner342, the nozzle-shaped runners343, and the gates35G. The golf ball1is obtained from this molded article by removing the excess portions. At this time, cover layer gate traces155G′ (FIG. 8) from the injection molding might remain on the outer surface of the cover layer15of the golf ball1at positions corresponding to the gates35G. For the sake of convenience, the cover layer gate traces155G′ are omitted from the drawings afterFIG. 8.

The first mold portion31for cover layer molding and the second mold portion32for cover layer molding of the mold3for cover layer molding preferably each include a degassing hole37and a degassing pin (pin)38P, inserted in the degassing hole37, as in the example inFIG. 7. The amount of air bubbles remaining in the cover layer15molded by the cover layer molding step can thus be reduced. The degassing hole37communicates with the cavity30for cover layer molding. In this way, gas produced at the time of injection molding inside the cavity30for cover layer molding is ejected outside the cavity30for cover layer molding through the degassing hole37.

In this case, cover layer degassing pin traces (cover layer pin traces)158P′ (FIG. 8) might remain on the outer surface of the cover layer15of the golf ball1obtained by the cover layer molding step at positions corresponding to the degassing pins (pins)38P. For the sake of convenience, the cover layer degassing pin traces (cover layer pin traces)158P′ are omitted from the drawings afterFIG. 8.

The first mold portion31for cover layer molding and the second mold portion32for cover layer molding of the mold3for cover layer molding preferably each include a plurality of support pins (pins)36P, as in the example inFIG. 7. This configuration can suppress eccentricity of the inner ball14inside the cavity30for cover layer molding, thereby suppressing eccentricity of the inner ball14in the golf ball1(FIG. 8) obtained by the cover layer molding step. Each support pin36P extends in the axial direction of the mold for cover layer molding CAD and is configured to move back and forth in the axial direction of the mold for cover layer molding CAD. When the inner ball14is housed inside the cavity30for cover layer molding and the mold3for cover layer molding is closed, each support pin36P supports the inner ball14so that the inner ball14is positioned in the center of the cavity30for cover layer molding (FIG. 7). During injection molding (for example, while molten material is being injected inside the cavity30for cover layer molding), each support pin36P recedes gradually to the outside of the cavity30for cover layer molding.

In this case, cover layer support pin traces (cover layer pin traces)156P′ (FIG. 8) might remain on the outer surface of the cover layer15of the golf ball1obtained by the cover layer molding step at positions corresponding to the support pins (pins)36P. For the sake of convenience, the cover layer support pin traces (cover layer pin traces)156P′ are omitted from the drawings afterFIG. 8.

After the cover layer molding step, surface treatment is performed on the cover layer15in the surface treatment step.

The surface treatment on the cover layer15is preferably plasma treatment, for example. A stamp16(FIG. 10) formed by the below-described printing step and a coating layer17(FIG. 11) formed by the below-described coating layer formation step thereby adhere more firmly to the outer circumferential side of the cover layer15.

However, the surface treatment step may be omitted.

After the cover layer molding step, a mark, logo, or the like is printed on the outer surface of the golf ball1in the printing step.

The printing step can, for example, be a pad printing step. In the pad printing step, a printing member4formed by the printing pad of a pad printing machine (not illustrated) is used for pad printing on the outer surface of the golf ball1(FIG. 10).

In the case of performing the aforementioned surface treatment step, the printing step is performed after the surface treatment step. The printing step is performed once or multiple times. The stamp16is formed on the outer circumferential side of the cover layer15by the printing.

The golf ball1obtained by the printing step includes at least the inner ball14, the cover layer15positioned on the outer circumferential side of the inner ball14, and one or a plurality of stamps16positioned on the outer circumferential side of the cover layer15.

The printing member4used in the pad printing step is provided in the pad printing machine (not illustrated). Ink K is applied to a printing portion of the printing member4(the tip of the printing member4, at the lower end inFIG. 10). The printing portion of the printing member4is pressed against the outer surface of the golf ball1, thereby transferring the ink K applied to the printing portion of the printing member4onto the outer surface of the golf ball1to form the stamp16.

As illustrated inFIG. 12, the stamp16may represent one or more characters (numbers, letters, or the like), symbols, and/or patterns, for example. The stamp16may thereby represent a mark, logo, and/or design, for example.

The stamp16(and therefore the ink K) is preferably opaque, as this facilitates visibility of the stamp16. The stamp16(and therefore the ink K) and the inner layer12are preferably different colors, as this facilitates visibility of the stamp16. The stamp16(and therefore the ink K) and the inner film13may be different colors from each other or the same color as each other. Here, “the same color as each other” refers to how the hue, saturation, and brightness are all the same.

The printing step may be a thermal transfer printing step or the like instead of a pad printing step.

The printing step need not be performed.

After the cover layer molding step, the outer circumferential side of the cover layer15is coated with coating layer paint in the coating layer formation step, thereby forming the coating layer17(FIGS. 11, 12). In the case of performing the aforementioned surface treatment step, the coating layer formation step is performed after the surface treatment step. In the case of performing the aforementioned printing step, the coating layer formation step is preferably performed after the printing step but may be performed before the printing step.

The golf ball1obtained by the coating layer formation step includes at least the inner ball14, the cover layer15positioned on the outer circumferential side of the inner ball14, and the coating layer17positioned on the outer circumferential side of the cover layer15.

In the coating layer formation step, the entire outer surface of the cover layer15is preferably coated with the coating layer paint, thereby forming the coating layer17to cover the entire outer surface of the cover layer15.

The coating layer17is formed to a thickness that does not completely fill the dimples151, as illustrated inFIG. 11. In other words, the thickness of the coating layer17is less than the depth of the dimples151. The thickness of the coating layer17is preferably 10 μm to 15 μm.

The coating layer17is preferably transparent or semi-transparent. As illustrated inFIG. 12, the exterior of the inner ball14can thereby be seen through the coating layer17(and the cover layer15) when the golf ball1is viewed. The coating layer17is preferably colorless but may be colored.

The method for coating with the coating layer paint is preferably spray painting or dipping, for example.

The coating layer formation step need not be performed.

The effects of the present embodiment are now described.

As described above, the golf ball manufacturing method according to the present disclosure includes an inner layer molding step of molding an inner layer12including an outer surface with a recess121, an inner film formation step, after the inner layer molding step, of coating the outer surface of the inner layer12with inner film paint to form an inner film13, an inner film removal step, after the inner film formation step, of removing the inner film13except for a portion thereof covering a surface121aof the recess121to obtain an inner ball14that includes the inner layer12and the inner film13, and a cover layer molding step, after the inner film removal step, of molding a cover layer15including an outer surface with dimples151on an outer circumferential side of the inner ball14to obtain a golf ball1. The golf ball1obtained in this way includes the inner ball14and the cover layer15that covers the outer surface of the inner ball14and includes an outer surface with the dimples151. The inner ball14includes the inner layer12, which includes an outer surface with the recess121, and the inner film13that covers only the surface121aof the recess121on the outer surface of the inner layer12. The inner layer12and the inner film13are different colors from each other, and the cover layer15is transparent or semi-transparent.

By the inner layer12and the inner film13being different colors from each other, the golf ball1can have a design represented by the contrast between the inner layer12and inner film13, thereby improving the designability of the golf ball1. By the cover layer15being transparent or semi-transparent, the design can be seen through the cover layer15when the golf ball1is viewed.

Since the inner film13is covered by the cover layer15, which has a maximum thickness equal to or greater than the depth of the dimples151, peeling of the inner film13(film) due to impact, such as when the golf ball1is hit, can more effectively be suppressed than if the inner film13were formed on the outer circumferential side of the cover layer15. The formation position of the inner film13could be restricted by the presence of the dimples151if the inner film13were formed on the outer circumferential side of the cover layer15. In the present embodiment, however, the inner film13can be formed at any position regardless of the position of the dimples151. The degree of freedom for design is thereby increased.

The expected design can easily be achieved when the inner film13that covers only the surface121aof the recess121on the outer surface of the inner layer12is obtained through the inner layer molding step, the inner film formation step, and the inner film removal step.

Details, preferred configurations, modifications, and the like of the golf ball manufacturing method of the present disclosure are now described.

In each example described in the present disclosure, a projection height L1(FIG. 1) of the projecting surface231of the cavity surface23for inner layer molding in the mold2for inner layer molding is preferably 5 mm or less and more preferably is 3 mm. This configuration can suppress unevenness in the flow of material inside the cavity20for inner layer molding due to the presence of the projecting surface231in the inner layer molding step. Eccentricity of the core ball10inside the cavity20for inner layer molding, for example, can therefore be suppressed.

The “projection height L1” (FIG. 1) of the projecting surface231is defined as the distance from the base of the projecting surface231to the projection tip of the projecting surface231as measured along a perpendicular to the base of the projecting surface231. The “base” of the projecting surface231refers to an imaginary surface yielded by extending the cavity surface23for inner layer molding smoothly towards the projecting surface231, as illustrated by the dashed line inFIG. 1.

For the same reason, in each example described in the present disclosure, a depth L1′ (FIG. 3) of the recess121in the inner layer12is preferably 5 mm or less and more preferably is 3 mm or less.

The “depth L1” (FIG. 3) of the recess121is defined as the distance from the open end face of the recess121to the bottom surface121abof the recess121as measured along a perpendicular to the open end face of the recess121. The “open end face” of the recess121refers to an imaginary surface yielded by extending the outer surface of the inner layer12smoothly towards the recess121, as illustrated by the dashed line inFIG. 3.

In each example described in the present disclosure, the projection height L1(FIG. 1) of the projecting surface231of the cavity surface23for inner layer molding in the mold2for inner layer molding used in the inner layer molding step (FIGS. 1 to 3) is preferably 0.5 mm or more. When the inner film13covering the outer circumferential side of the inner layer12is ground using a grinder, for example, during the inner film removal step (FIGS. 5 and 6), this range can help to prevent the inner film13covering the surface121aof the recess121from also being ground.

For the same reason, in each example described in the present disclosure, the depth L1′ (FIG. 3) of the recess121in the inner layer12is preferably 0.5 mm or more.

In each example described in the present disclosure, the inner film13(and therefore the inner film paint) preferably includes polyurethane, in particular a two-component curable polyurethane that uses a polyol and a polyisocyanate. This configuration can suppress peeling of the inner film13when the cover layer15and the inner film13rub together due to impact, such as when the golf ball1is hit.

In the example illustrated inFIG. 5, the thickness L2(FIG. 5) of the inner film13covering the surface121aof the recess121in the inner layer12is smaller than the depth L1′ (FIG. 5) of the recess121in the inner layer12.

In each example described in the present disclosure, however, the thickness L2(FIG. 13) of the inner film13covering the surface121aof the recess121in the inner layer12may be the same as the depth L1′ (FIG. 13) of the recess121in the inner layer12.

The thickness L2of the inner film13covering the surface121aof the recess121in the inner layer12is preferably 10 μm to 15 μm.

In each example described in the present disclosure, a pretreatment step of pretreating the inner layer12is preferably performed after the inner layer molding step (FIGS. 1 to 3) and before the inner film formation step (FIG. 4).

The pretreatment of the inner layer12is preferably plasma treatment and/or primer treatment, for example. The inner film13formed in the inner film formation step thereby adheres more firmly to the outer circumferential side of the inner layer12. Consequently, peeling of the inner film13when the cover layer15and the inner film13rub together due to impact, such as when the golf ball1is hit, can be suppressed.

However, the pretreatment step may be omitted.

In each example described in the present disclosure, when the mold2for inner layer molding used in the inner layer molding step (FIGS. 1 to 3) is a mold for injection molding, the projecting surface231of the cavity surface23for inner layer molding in the mold2for inner layer molding preferably does not overlap the gate25G in the radial direction, as illustrated inFIG. 1. This configuration can more reliably achieve the expected shape of the recess121(FIG. 3) molded by the projecting surface231.

In the present disclosure, “overlap in the radial direction” refers to overlapping when viewing a projection in the radial direction.

For the same reason, in each example described in the present disclosure, the recess121of the inner layer12in the inner ball14preferably does not overlap the inner layer gate traces125G′ of the injection molding in the radial direction, as illustrated inFIG. 3.

In each example described in the present disclosure, the projecting surface231of the cavity surface23for inner layer molding in the mold2for inner layer molding used in the inner layer molding step preferably does not overlap the pins26P,28P (support pins26P and/or degassing pins28P) in the radial direction, as illustrated inFIG. 1. This configuration can more reliably achieve the expected shape of the recess121(FIG. 3) molded by the projecting surface231.

For the same reason, in each example described in the present disclosure, the recess121of the inner layer12in the inner ball14preferably does not overlap the inner layer pin traces126P′,128P′ (inner layer support pin traces126P′ and/or inner layer degassing pin traces128P′) in the radial direction, as illustrated inFIG. 3.

In each example described in the present disclosure, a positioning step for cover layer molding (FIG. 7) of positioning the inner ball14in the cavity30for cover layer molding of the mold3for cover layer molding is preferably performed after the inner film removal step (FIGS. 5 and 6) and before the cover layer molding step (FIGS. 7 to 9).

The positioning step for cover layer molding may be performed automatically by an inner ball positioning apparatus (not illustrated) or may be performed manually. In the case of the positioning step for cover layer molding being performed by the inner ball positioning apparatus, the inner ball positioning apparatus preferably detects the position of the inner film13of the inner ball14relative to the cavity30for cover layer molding by image processing, and based on the detection result, positions the inner ball14within the cavity30for cover layer molding.

In the case of molding the cover layer15by injection molding using the mold3for cover layer molding in the cover layer molding step (FIGS. 7 to 9), the inner ball14is preferably positioned within the cavity30for cover layer molding in the positioning step for cover layer molding in such a way that the inner film13covering the surface121aof the recess121does not face the gate35G in the radial direction (i.e., does not overlap the gate35G in the radial direction), as in the example inFIG. 7. In this way, when the injection molding is performed in the cover layer molding step (FIGS. 7 to 9), high-temperature and high-pressure molten material injected from the gate35G into the cavity30for cover layer molding can be prevented from directly contacting the inner film13and causing the inner film13to melt away.

For the same reason, in each example described in the present disclosure, the inner film13covering the surface121aof the recess121in the golf ball1preferably does not overlap the cover layer gate traces155G′ from the injection molding in the radial direction, as illustrated inFIG. 8.

In each example described in the present disclosure, the inner ball14may be positioned within the cavity30for cover layer molding of the mold3for cover layer molding in the positioning step for cover layer molding in such a way that the inner film13covering the surface121aof the recess121does not face the pins36P,38P (support pin36P and/or degassing pin38P) in the radial direction (i.e., does not overlap the pins36P,38P in the radial direction), as in the example inFIG. 7. This configuration can suppress a decrease in visibility of the inner film13covering the surface121aof the recess121due to the cover layer pin traces156P′,158P′ when the golf ball1(FIG. 8) is viewed from the exterior. Alternatively, the inner ball14may be positioned within the cavity30for cover layer molding of the mold3for cover layer molding in the positioning step for cover layer molding in such a way that the inner film13covering the surface121aof the recess121faces the pins36P,38P (support pin36P and/or degassing pin38P) in the radial direction (i.e., overlaps the pins36P,38P in the radial direction).

Similarly, in each example described in the present disclosure, the inner film13covering the surface121aof the recess121need not overlap the cover layer pin traces156P′,158P′ (cover layer support pin trace156P′ and/or cover layer degassing pin trace158P′) in the radial direction in the golf ball1, as illustrated inFIG. 8. Alternatively, the inner film13covering the surface121aof the recess121may overlap the cover layer pin traces156P′,158P′ (cover layer support pin trace156P′ and/or cover layer degassing pin trace158P′) in the radial direction in the golf ball1.

In each example described in the present disclosure, a positioning step for printing (FIG. 10) of positioning the golf ball1relative to the printing member4so that the inner film13covering the surface121aof the recess121does not face the printing portion of the printing member4in the radial direction is preferably performed after the cover layer molding step (FIGS. 7 to 9) and before the printing step (FIG. 10). This configuration can suppress a decrease in visibility of the inner film13covering the surface121aof the recess121due to the stamp16when the golf ball1(FIG. 10) obtained by the printing step (FIG. 10) is viewed from the exterior. In the case of the printing step being a pad printing step, the golf ball1is positioned relative to the printing member4in the positioning step for printing in such a way that the inner film13covering the surface121aof the recess121does not face the printing portion of the printing member4, formed by the printing pad of the pad printing machine, in the radial direction. On the other hand, in the case of the printing step being a thermal transfer printing step, the golf ball1is positioned relative to the printing member in the positioning step for printing in such a way that the inner film13covering the surface121aof the recess121does not face the printing portion of the printing member, formed by a thermal transfer film, in the radial direction.

The positioning step for printing may be performed automatically by a golf ball positioning apparatus (not illustrated) or may be performed manually. In the case of the positioning step for printing being performed by the golf ball positioning apparatus, the golf ball positioning apparatus preferably detects the position of the inner film13of the golf ball1relative to the printing portion of the printing member by image processing, and based on the detection result, positions the golf ball1relative to the printing member.

For the same reason, in each example described in the present disclosure, the inner film13in the golf ball1preferably does not overlap the stamp16in the radial direction, as illustrated inFIG. 10.

In each example described in the present disclosure, the coating layer17(FIGS. 11 to 12; hence, the coating layer paint as well) preferably includes matte particles. This enables the coating layer17to be a matte layer without gloss or luster. The golf ball1can thereby have an uneven outer surface due to the dimples151, as illustrated inFIG. 12, while at the same time rendering the dimples151barely visible, so that the dimples151appear not to exist when the golf ball1is viewed from the exterior. This can improve the visibility of the inner film13and therefore the designability. When the coating layer17(hence, the coating layer paint as well) includes matte particles, the coating layer paint is less likely to smear during the coating layer formation step (FIGS. 11 and 12). The coating layer paint (hence, the coating layer17as well) thereby more accurately follows the shape of the dimples151, and the expected flight performance of the golf ball1can be achieved.

The coating layer17that includes matte particles (hence, the coating layer paint as well) is not restricted, but urethane paint is preferably used. Since the golf ball needs to withstand severe usage conditions, a two-component curable urethane paint is preferable, with a non-yellowing urethane paint being particularly preferable.

In the case of a two-component curable urethane paint, any of various polyols such as saturated polyester polyol, acrylic polyol, or polycarbonate polyol is preferably used as the main agent, and as an isocyanate, a non-yellowing polyisocyanate is preferably used, examples of which include an adduct such as hexamethylene diisocyanate, isophorone diisocyanate, or hydrogenated xylylene diisocyanate; biuret; isocyanurate; and mixtures thereof.

Examples of the matte particles include silica-based, melamine-based, and acrylic-based particles. Specifically, examples include silica, polymethyl methacrylate, butyl polymethacrylate, polystyrene, and butyl polyacrylate. The particles may be organic or inorganic, but silica is particularly preferable.

From the perspective of quenching and coatability, the specific surface area of the matte particles is preferably 200 m2/g to 400 m2/g as the BET specific surface area, more preferably 250 m2/g to 350 m2/g.

From the perspective of spin performance and quenching, the average primary particle size of the matte particles is preferably 1.0 μm to 3.0 μm, more preferably 2.0 μm to 2.8 μm. If this value exceeds 3.0 μm, the ball surface becomes rough, which may adversely affect the spin and reduce performance. If this value is too small, on the other hand, the quenching effect may decrease.

The content of the matte particles is preferably 5 to 10 parts by mass per 100 parts by mass of the main agent (the total content of a resin component and a solvent) in the paint compound of the coating layer17. If the content is too large, the viscosity of the paint composition increases, and the workability of the paint tends to worsen. If the content is too small, the quenching effect may decrease.

The average roughness Ra of the surface of the coating layer17is preferably 0.5 to 1.0 to make the spin amount of the ball during approach compatible with quenching. The average roughness Ra of the surface of the coating layer17refers to the arithmetic average roughness of JIS B0601 (1994).

The reflectance of the coating layer17measured by a gloss meter is preferably 5.0 or less at an angle of incidence of 20°, 20.0 or less at an angle of incidence of 60°, and 40.0 or less at an angle of incidence of 85°. When the reflectance is adjusted to satisfy the aforementioned numerical ranges, the coating layer17can be provided with a good matte effect. The conditions for measuring the reflectance with the aforementioned gloss meter are measurement of an ABS resin plate, coated to a thickness of 20 μm, using the “micro-TRI-gloss” produced by BYK.

INDUSTRIAL APPLICABILITY

A golf ball manufacturing method of the present disclosure can be used to manufacture any type of golf ball, such as a two-piece golf ball, a three-piece golf ball, a four-piece golf ball, a five-piece golf ball, a six-piece golf ball, or a wound golf ball.