US20120129624A1

US20120129624A1 - Golf club grip

Info

Publication number: US20120129624A1
Application number: US13/240,737
Authority: US
Inventors: Hiromasa Ito; Yoshifumi Nakajima; Tadahiro TAKECHI
Original assignee: Bridgestone Sports Co Ltd
Current assignee: Bridgestone Sports Co Ltd
Priority date: 2010-11-22
Filing date: 2011-09-22
Publication date: 2012-05-24
Also published as: CN102475958A

Abstract

A golf club grip having a double construction includes a cylindrical inside layer part made of a first rubber having a first hardness, and a cylindrical outside layer part made of a second rubber having a second hardness lower than the first hardness, which part covers the cylindrical inside layer part. The cylindrical inside layer part has a length 1 to 4 cm longer than the length of a half of the entire length of the grip. The cylindrical inside layer part is provided with a plurality of longitudinal projecting strips formed on the outer peripheral surface thereof, and the plurality of longitudinal projecting strips extend from the proximal end side of the cylindrical inside layer part to a portion of 70 to 80% of the entire length of the cylindrical inside layer part along the axis line direction of the cylindrical inside layer part, and are formed at fixed intervals in the circumferential direction. The cylindrical outside layer part is provided with a plurality of circumferential grooves, which are formed at fixed intervals in the axis line direction, on the outer peripheral surface of a portion covering a portion of the cylindrical inside layer part in which the longitudinal projecting strips are formed. The cylindrical outside layer part is provided with a plurality of longitudinal grooves formed on the outer peripheral surface on the distal end side of the circumferential grooves.

Description

CROSS-REFERENCE TO RELATED APPLICATION

This Application claims priorities from Japanese Patent Application No. 2010-259676 filed Nov. 22, 2010, Japanese Patent Application No. 2010-276828 filed Dec. 13, 2010, Japanese Patent Application No. 2011-95899 filed Apr. 22, 2011, and Japanese Patent Application No. 2011-95900 filed Apr. 22, 2011, which are incorporated herein by reference in their entirety.

BACKGROUND OF THE INVENTION

The present invention relates to a golf club grip.
Generally, a golf club is formed with a head, a shaft, and a grip. The conventional grip is formed of rubber, the main component of which is, for example, natural rubber. By forming the grip of such a material, the grip feel at the time when a golfer grips a golf club is improved, the anti-slipping effect of the grip is improved, and the resistance to deterioration in the grip is improved.
Japanese Utility Model Application Publication No. 62-9476 discloses a grip that is formed of a material having a two-layer construction consisting of an inside layer part and an outside layer part, in which the inside layer part is softer than the outside layer part throughout the entire length of the grip. Also, Japanese Utility Model Application Publication No. 62-82066 discloses a grip that is formed of a two-layer material in which the inside layer part is harder than the outside layer part throughout the entire length of the grip to improve the grip feel.
Generally, when a golfer grips a golf club grip, the proximal end side of the grip is gripped by one hand as the axis at the swinging time, and the other hand is attached to the one hand on the distal end side of the grip to feel the ball hitting feeling by means of the palm of the other hand. Therefore, if the grip is made soft, the ball hitting feeling is not transmitted very much, and on the other hand, if the grip is made hard, the grip is not broken in to the hand, and moreover strong ball hitting vibrations are transmitted too greatly to the hand serving as the axis of swing, so that an adverse influence is exerted on the wrist and the elbow.
The grip described in Japanese Utility Model Application Publication No. 62-9476 has a drawback in that the hand gripping the distal end side of the grip is less liable to feel the ball hitting feeling. The grip described in Japanese Utility Model Application Publication No. 62-82066 has a problem in that the grip is less liable to be broken in to the hand gripping the proximal end side of the grip, and moreover heavy ball hitting vibrations are transmitted to the elbow and the like.
Also, the way of gripping the golf club (the manner of gripping) is very important for controlling the height, carry, and direction of shot. As the manner of gripping, Vardon grip, interlock grip, and the like can be used. In any manner of gripping, in the case in which the proximal end side of the grip is gripped by one hand as the axis of swing, the golf club is held stably by attaching the thumb of the one hand onto the grip to determine the direction of the golf club.
Japanese Utility Model Registration No. 2533541 discloses a grip in which the ball hitting feeling can be felt satisfactorily by the hand attached to the distal end side of grip, the gripping feeling is good and strong ball hitting vibrations are not transmitted to the wrist, elbow, etc. of the hand gripping the proximal end side of grip, and moreover a hook or slice of a shot can be prevented positively by supporting the belly of the thumb of that hand. This grip is a golf club grip formed of a material having a two-layer construction consisting of an inside layer part and an outside layer part, in which the inside layer part on the proximal end side of the grip is softer than the outside layer part thereon, and the inside layer part on the distal end side of the grip is harder than the outside layer part thereon.
Also, a grip formed of a silicone resin, not formed of rubber, is described in Japanese Patent Application Publication No. 2010-188019. This grip can restrain the shift of the collision angle between the head face and the ball. Conventionally, it has been thought that the shift of ball hitting direction results from the torsion of the shaft. However, even if the torsional rigidity of the shaft is improved, there occurs a phenomenon that the ball hitting direction shifts from the direction intended by the golfer. In the study on the causes for this phenomenon, the present inventor paid attention to the fact that the grip, which is a constituent element of the golf club, is far more elastic than the shaft. That is, the present inventor obtained knowledge that although it is apparent that the impact force produces the torsional deformation of the shaft, the shift of the collision angle between the head face and the ball depends greatly on the elastic deformation of grip caused by the impact force. As a result, the grip described in Japanese Patent Application Publication No. 2010-188019 has been developed.
The grip described in Japanese Patent Application Publication No. 2010-188019 is a golf club grip including a cylindrical inside layer part formed of a first resin and a cylindrical outside layer part that is insert molded using a second resin having a lower hardness than that of the first resin so as to cover the cylindrical inside layer part with the cylindrical inside layer part being used as an insert member. In this grip, engagement protrusions engaging with the cylindrical outside layer part are provided on the outer peripheral surface of the cylindrical inside layer part, and the engagement protrusions are arranged in parallel in the circumferential direction at a first pitch and arranged in parallel in the longitudinal direction at a second pitch.
Also, to improve the feeling of ease of swinging of the golf club, the weight of the grip is also adjusted. The weight of recent golf clubs has become lighter as a whole due to the development of new head materials and the reduced weights of shafts. The lighter golf club increases the head speed, which leads to an increase in carry of a hit ball, but poses a problem that a mistake shot may occur because of inconstant trajectory of swing caused by bringing the golf club onto an erroneous trajectory because of its lightness when the golf club is swung up or when the swung-up golf club is swung down.
To solve this problem, there has conventionally been known a golf club in which a heavy substance, what is called a counterbalancing member, is mounted on the golf club grip. The golf club of this type has been configured as described below. The counterbalancing member is, for example, a thin sheet made of lead, and is wound on a portion near the grip end, in which a grip member is to be mounted on the club shaft, of the club shaft. Thereafter, the ordinarily used grip member is fitted onto the shaft from over the thin sheet made of lead wound on the shaft, and is fixed to the shaft with an adhesive or the like. Alternatively, a separate member including a weight is mounted at the grip end of the grip member (refer to Japanese Patent Application Publication No. 6-142244). In this case, the moment of inertia of the golf club with the grip being a pivot point is unchanged before and after the counterbalancing member is mounted, so that even a golf player having little strength can use a relatively heavy golf club. Therefore, even if the golf player uses the relatively heavy golf club, the player can give the same carry of golf ball as in the case of using the lightweight golf club. Furthermore, since the weight of the entire golf club can be increased, swinging can be performed in a correct and stable trajectory, and therefore a mistake shot can be prevented.
With the method in which the counterbalancing member is mounted on the grip, uncomfortable feeling is given to the golf player, and also the appearance is bad. Accordingly, there has been developed a golf club grip in which an auxiliary member is embedded in the grip itself (refer to Japanese Patent Application Publication No. 11-319172). This grip is formed mainly of an elastic body such as rubber, and is manufactured by molding a semi-cylindrical base material half body constituting a region on the outside of the shaft center axis line and a semi-cylindrical base material half body constituting a region on the inside (back surface side), and then by bonding these two half bodies so as to face to each other. By containing a metallic material in the base material half body constituting a region on the inside to increase the weight of this base material half body, the weight of the base material half body constituting a region on the inside is made 5 to 30 g heavier than the weight of the base material half body constituting a region on the outside. For example, metal powder is contained in the base material half body constituting a region on the inside, or metal fibers or metal sheets are contained in the base material half body constituting a region on the inside. As the metal, a metal material consisting of tungsten, titanium, aluminum, nickel, boron, titanium-nickel alloy, lead, copper, silver, gold, low-carbon steel, and the like can be used, and it is said that tungsten is especially preferable.

SUMMARY OF THE INVENTION

The grip described in Japanese Utility Model Registration No. 2533541 solves problems in Japanese Utility Model Application Publication No. 62-9476 and Japanese Utility Model Application Publication No. 62-82066, and is configured so that because, on the proximal end side of grip gripped by the hand serving as the axis of swing (the left hand for a right-handed person), the inside layer part formed of a soft material is deformed, the grip can be gripped surely, the grip feel is good, and the ball hitting feeling is satisfactorily transmitted from the inside layer part formed of a hard material to the hand on the distal end side (the right hand). However, it has been desired to further improve the grip feel and the ball hitting directivity.
The grip described in Japanese Patent Application Publication No. 2010-188019 is formed of a silicone resin, not formed of rubber, so that the torsional rigidity is improved as compared with the rubber grip. However, when this grip is mounted on the shaft, the solvent for mounting (white gas) takes a long time to vaporize. To examine this phenomenon, the portion in which the grip is in contact with the shaft was observed by cutting the grip one week after the grip had been mounted, and as a result, it was found that the inner peripheral surface of grip was wet (the solvent did not vaporize sufficiently). That is, the force for bonding the grip to the shaft was weak.
Accordingly, an object of the present invention is to provide a golf club grip in which the gripping feeling and the ball hitting directivity are improved, and the force for bonding the grip to the shaft is strong.
Also, a grip having a multi-colored appearance has been on the market. However, the boundary of color is unclear, for example, because colors are mixed in the joint portion of rubber products having different colors, and no grip in which colors are divided clearly is found. Even if colors are divided clearly by using rubbers having different colors, the demands have not been met in terms of clarifying the roles of the right and left hands and enhancing the fashionability.
Accordingly, another object of the present invention is to provide a golf club grip in which the gripping feeling and the ball hitting directivity are improved, the force for bonding the grip to the shaft is strong, and the colors are divided clearly.
Furthermore, according to the invention disclosed in Japanese Patent Application Publication No. 11-319172, a difference in weight is made so that the base material half body located in the region on the inside of the shaft center axis line is heavier than the base material half body located in the region on the opposite side, that is, on the outside of the shaft center axis line (the head side). This difference in weight is 5 to 30 g, preferably 10 to 25 g. By this difference in weight, the weight ratio between the outside and the inside with respect to the shaft center axis line of the whole of golf club is decreased, so that it is said that the stability at the swinging time is improved, and the operability of the club and the reproducibility of swing are improved. If the difference in weight is less than 5 g, the effects of the present invention cannot be achieved sufficiently. If the difference in weight is greater than 30 g, the weight of grip becomes too heavy, and the total balance of golf club is disturbed unfavorably.
In this conventional example, to embed metal fibers (for example, tungsten) in the rubber base material half body constituting the region on the inside, the metal fibers should be set exactly in the mold beforehand when this base material half body is molded by vulcanization, which requires much time and labor. Also, since the torsional rigidities of the base material half bodies on the inside and on the outside are different, the torsional deformation of the grip at the time when a golfer hits a ball is different between the inside half and the outside half, so that there is a fear that the hit ball will not fly in the direction intended by the golfer.
Accordingly, still another object of the present invention is to provide a golf club grip in which counterbalance is achieved, the ease of swing is increased, a shift of collision angle caused by the torsional deformation at the time when the head collides with the ball is prevented, and also the manufacture is easy.
Also, in the above-described conventional example, the gripping feeling (swinging feeling, etc.) for each base material half body is different, so that some golfers have an uncomfortable feeling.
Accordingly, still another object of the present invention is to provide a golf club grip in which counterbalance is achieved, the ease of swinging is increased, a shift of collision angle caused by the torsional deformation at the time when the head collides with the ball is prevented, and the grip feel is good.
A first mode of the present invention is a golf club grip having a double construction in which a rubber cylindrical inside layer part is covered by a rubber cylindrical outside layer part having a hardness lower than that of the cylindrical inside layer part, wherein the cylindrical inside layer part is formed so as to be 1 to 4 cm longer than the length of a half of the entire length of the grip; the cylindrical inside layer part is formed so as to be harder than the cylindrical outside layer part; a plurality of longitudinal projecting strips are formed at fixed intervals in the circumferential direction on the outer peripheral surface of the cylindrical inside layer part so as to extend from the proximal end side of the cylindrical inside layer part to a portion of 70 to 80% of the entire length of the cylindrical inside layer part along the axis line direction of the cylindrical inside layer part; a plurality of circumferential grooves are formed at fixed intervals in the axis line direction on the outer peripheral surface of a portion of the cylindrical outside layer part that covers a portion of the cylindrical inside layer part in which the longitudinal projecting strips are formed; and a plurality of longitudinal grooves are formed on the outer peripheral surface on the distal end side of the circumferential grooves of the cylindrical outside layer part.
According to the first mode of the present invention, by the above-described configuration, the cylindrical outside layer part and the cylindrical inside layer part can be integrated, the torsion of the whole of the grip can be prevented by the combination of the longitudinal projecting strips and the circumferential grooves, and the presence of the circumferential grooves can resist the centrifugal force of the head at the swinging time on the grip proximal end side. Therefore, the gripping feeling on the grip proximal end side (the portion gripped by the left hand for a right-handed person) is harder than the gripping feeling on the grip distal end side (the portion gripped by the right hand), so that the torsion of the portion gripped by the left hand, which serves as the axis at the swinging time, becomes small. Therefore, the ball hitting directivity is improved, and moreover, since the cylindrical outside layer part is soft, an adverse influence of ball hitting vibration is less liable to occur. Also, in the case in which the cylindrical inside layer part is made of rubber, and the grip is fixed to the shaft by using a common solvent for mounting (white gas) and a double-faced adhesive tape, the solvent vaporizes in a short period of time, and the fixing of the grip to the shaft becomes firm in a short period of time of about a half day or even less.
A second mode of the present invention is a golf club grip having a double construction in which a rubber cylindrical inside layer part is covered by a rubber cylindrical outside layer part having a hardness lower than that of the cylindrical inside layer part, in which the cylindrical inside layer part is formed so as to be 1 to 4 cm longer than the length of a half of the entire length of the grip; a plurality of longitudinal projecting strips are formed at fixed intervals in the circumferential direction on the outer peripheral surface of the cylindrical inside layer part so as to extend from the proximal end side of the cylindrical inside layer part to a portion of 70 to 80% of the entire length of the cylindrical inside layer part along the axis line direction of the cylindrical inside layer part; a ring-shaped protrusion is formed in the circumferential direction on the distal end side of the portion in which these longitudinal projecting strips are formed; a plurality of circumferential grooves are formed on the outer peripheral surface of a first cylindrical outside layer part, which covers the portion in which these longitudinal projecting strips are formed and is formed in the portion between the proximal end side and the ring-shaped protrusion, so as to be at fixed intervals in the axis line direction; a second cylindrical outside layer part, which covers the distal end side of the ring-shaped protrusion of the cylindrical inside layer part and ranges from the ring-shaped protrusion to the grip distal end, is formed; a plurality of longitudinal grooves are formed on the outer peripheral surface of the second cylindrical outside layer part; and the first and second cylindrical outside layer parts have different colors.
According to the second mode of the present invention, by the above-described configuration, the cylindrical outside layer part and the cylindrical inside layer part can be integrated, the torsion of the whole of the grip can be prevented by the combination of the longitudinal projecting strips and the circumferential grooves, and the presence of the circumferential grooves can resist the centrifugal force of the head at the swinging time on the grip proximal end side. Therefore, the grip feel on the grip proximal end side (the portion gripped by the left hand for a right-handed person) is harder than the grip feel on the grip distal end side (the portion gripped by the right hand), so that the torsion of the portion gripped by the left hand, which serves as the axis at the swinging time, becomes small. Therefore, the ball hitting directivity is improved, and moreover, since the cylindrical outside layer part is soft, an adverse influence of ball hitting vibration is less liable to occur. Also, in the case in which the cylindrical inside layer part is made of rubber, and the grip is fixed to the shaft by using a common solvent for mounting (white gas) and a double-faced adhesive tape, the solvent vaporizes in a short period of time, and the fixing of the grip to the shaft becomes firm in a short period of time of about a half day or even less. Furthermore, since the first and second cylindrical outside layer parts the colors of which are different with the portion of the ring-shaped protrusion on the cylindrical inside layer part being a boundary are coveringly formed, the colors are divided clearly, so that the fashionability is improved, and the division of roles of the right hand and the left hand is perceived strongly.
A third mode of the present invention is a golf club grip having a double construction in which a rubber cylindrical inside layer part and a rubber cylindrical outside layer part are provided, wherein a tungsten sheet having a thickness of 0.2 to 2.0 mm is interposed between the inside layer part and the outside layer part in the back surface portion of the inside layer part. The tungsten sheet may be interposed not only in the back surface portion but also in the side portion and in the upper portion. As the tungsten sheet, a sheet having a specific gravity of 8 or larger, which is molded by mixing tungsten powder in a thermoplastic resin material, may be used.
According to the third mode of the present invention, since the golf club grip is configured as described above, the tungsten sheet serves as a conventional counterbalancing member, so that even a golf club, the weight of which is reduced, is easy to be swung, and moreover, the appearance is good. The back surface portion of grip in which the tungsten sheet is interposed swells slightly and performs a function of preventing the slippage, and can prevent the collision angle between the ball and the face from being changed by the torsional deformation at the ball hitting time. Also, in the case in which the conventional powder is used, if the powder is mixed with rubber before vulcanization, there is a possibility that the powder will scatter or leftover mixing occurs. In the case in which the tungsten sheet is cut as in the present invention, a prescribed weight can be added, and the variations in weight as the grip decrease. Furthermore, since the thermoplastic resin is used, rubber is vulcanized by adding heat of about 120 to 160° C. Therefore, the resin material becomes fitted with the mold at the molding time, and an effect of being deformed (curved) properly with respect to rubber can be anticipated.
A fourth mode of the present invention is a golf club grip having a double construction in which a cylindrical inside layer part using a rubber compound having a large specific gravity and an outside layer part using a rubber compound having a specific gravity less than that of the inside layer part are provided, wherein the length of the inside layer part is shorter than the length of the outside layer part.
According to the fourth mode of the present invention, by the above-described configuration, for example, the inside layer part can be made a vulcanization molded product of rubber compound in which metal powder or barium sulfate is kneaded, and the specific gravity of this inside layer part can be made 1.3 to 1.6. Therefore, the inside layer part serves as a conventional counterbalancing member, so that even a golf club the weight of which is reduced is easy to be swung. Moreover, the grip feel is good, and the collision angle between the ball and the face can be prevented from being changed by the torsional deformation at the ball hitting time.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded perspective view showing a cylindrical inside layer part and a cylindrical outside layer part of a golf club grip in accordance with one embodiment of the present invention.

FIG. 2 is a plan view of the cylindrical inside layer part shown in FIG. 1.

FIG. 3 is a sectional view showing a state in which the golf club grip shown in FIG. 1 is completed.

FIG. 4 is an exploded perspective view showing a cylindrical inside layer part and a cylindrical outside layer part of a golf club grip in accordance with another embodiment of the present invention.

FIG. 5 is a plan view of the cylindrical inside layer part shown in FIG. 4.

FIG. 6 is a sectional view showing a state in which the golf club grip shown in FIG. 4 is completed.

FIG. 7 is a sectional view for explaining molding of a cylindrical outside layer part of the golf club grip shown in FIG. 4.

FIG. 8 is an exploded perspective view showing a golf club grip in accordance with still another embodiment of the present invention.

FIG. 9 is a sectional view showing a state in which the golf club grip shown in FIG. 8 is completed.

FIG. 10 is an exploded perspective view showing a golf club grip in accordance with still another embodiment of the present invention.

FIG. 11 is a sectional view for explaining vulcanization molding of the golf club grip shown in FIG. 10.

FIG. 12 is a flow chart for explaining one example of a method for manufacturing a tungsten sheet shown in FIG. 8 and FIG. 10.

FIG. 13 is a longitudinal sectional view of a golf club grip in accordance with still another embodiment of the present invention.

FIG. 14 is a transverse sectional view taken along the line A-A of the golf club grip shown in FIG. 13.

FIG. 15 is a sectional view of a golf club grip in accordance with still another embodiment of the present invention.

FIG. 16 is a sectional view for explaining molding of the golf club grip shown in FIG. 15.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of a golf club grip in accordance with the present invention will now be described with reference to the accompanying drawings.
First, an embodiment of the golf club grip shown in FIGS. 1 to 3 is explained. Both of a cylindrical inside layer part 1 and a cylindrical outside layer part 2 of the golf club grip shown in FIG. 1 are members made of rubber. The cylindrical inside layer part 1 is molded first, this molded cylindrical inside layer part 1 is set in a mold as an insert member, and the cylindrical outside layer part 2 is molded so as to cover the cylindrical inside layer part 1. In FIG. 1, for convenience of explanation, these inner and outside layer parts are shown as if being molded separately. After the cylindrical outside layer part 2 has been molded, the cylindrical inside layer part 1 is covered by the cylindrical inside layer part 1.
The rubber used as the molding material for the cylindrical inside layer part 1 and the cylindrical outside layer part 2 contains natural rubber (NR) as the main component. A rubber compound in which, for example, 80 to 100 parts by weight of NR, 0 to 20 parts by weight of SBR (styrene-butadiene rubber) or EPDM, 1 part by weight of antiaging agent, 1 part by weight of stearic acid, 10 to 30 parts by weight of carbon black, 5 to 10 parts by weight of softening agent, 2 parts by weight of processing aid, 5 parts by weight of zinc oxide, 1 to 2 parts by weight of vulcanization accelerator, 0.5 part by weight of vulcanization accelerating additive, and 1 to 2 parts by weight of sulfur are blended is vulcanization molded into a grip shape. In the cylindrical inside layer part 1 and the cylindrical outside layer part 2, the composition of the rubber compound is changed, and the cylindrical inside layer part 1 is molded so as to be hard. Therefore, in the cylindrical inside layer part 1, as the SBR, an SBR containing 50% or more of styrene may be used. For the cylindrical outside layer part 2, a cylindrical part that is formed by molding and vulcanizing a rubber compound containing 45 to 90 parts by weight of diene-based rubber, 5 to 30 parts by weight of ethylene-propylene binary copolymer and/or ethylene-propylene-diene ternary copolymer, and 5 to 25 parts by weight of chlorobutyl rubber can be used suitably. The diene-based rubber is preferably at least one kind selected from the group consisting of natural rubber, isoprene rubber, styrene-butadiene rubber, nitrile-butadiene rubber, and chloroprene rubber. The use of such a rubber compound provides a grip that has a high coefficient of dynamic friction, is less liable to slip, has excellent wear resistance and weather resistance, and therefore has high durability and long service life. Furthermore, the grip formed of the above-described rubber compound has excellent low-temperature characteristics, is not sticky, and gives very good grip feel. Also, a grip end 3 is colored by using silica, talc, or the like as a reinforcing agent in place of carbon black and by adding a pigment. Also, to increase the hardness, a resin containing 5 to 20 parts by weight of SBR containing 50% or more of styrene (high-styrene SBR) may be added.
As shown in FIG. 2, the cylindrical inside layer part 1 is formed with a plurality of longitudinal projecting strips 4, each of which has a length of 8 to 11 cm from the grip end 3 side, a thickness (projection height) of 0.2 to 0.6 mm, and a width of 0.6 to 1.5 mm, on the outer peripheral surface thereof. The interval between the two longitudinal projecting strips 4 on the grip end 3 side may be 3 mm. The grip end 3 is formed of a rubber compound harder than that of the cylindrical inside layer part 1, and is integrated with the cylindrical inside layer part 1. Also, on the distal end side (having a length of one-fourth to one-fifth the entire length of the cylindrical inside layer part 1) of the cylindrical inside layer part 1, projecting strips 5 are formed.
The grip end 3 has a type A hardness as prescribed in JIS K6253 (hereinafter, the term “hardness” means the type A hardness as prescribed in JIS K6253) of 65 to 75, the cylindrical inside layer part 1 has a hardness of 65 to 75, and the cylindrical outside layer part 2 has a hardness of 40 to 50. The above-described values of the hardness are nonrestrictive, and the cylindrical outside layer part 2 may be softer than the cylindrical inside layer part 1 in terms of physical property.
In the portion of the cylindrical outside layer part 2 that covers the portion of the cylindrical inside layer part 1 in which the longitudinal projecting strips 4 are formed, plural circumferential grooves 6 are formed on the outer peripheral surface thereof. The circumferential grooves 6 are so narrow that the width of each of the grooves 6 is about 0.1 to 0.3 mm, and are arranged in parallel at intervals of about 1.5 mm in the axis line direction. Plural slantwise grooves 7 are also formed so as to cross the circumferential grooves 6. These grooves 6 and 7 yield an antislipping effect. The circumferential grooves 6 make it easy for an opposing force to act in the grip portion against the centrifugal force of the head at the time of swing. Also, on the outer peripheral surface on the distal end side of the circumferential grooves 6 of the cylindrical outside layer part 2, plural longitudinal grooves 8 are formed, and also a plurality of slantwise grooves 9 are formed so as to cross the longitudinal grooves 8.
The entire length of the cylindrical inside layer part 1 is made 1 to 4 cm longer than a half of the grip entire length (the entire length including the grip end 3). If the difference between the length of the cylindrical inside layer part 1 and a half of the grip entire length exceeds 4 cm, the total weight of the grip increases. Even if the cylindrical inside layer part 1 is lengthened more than necessary, the improvement in function as a grip is not observed.
Between the circumferential grooves 6 and the longitudinal grooves 8 of the cylindrical outside layer part 2, a gap S₂is provided. This gap S₂corresponds to a gap S₁located at the distal end of the cylindrical inside layer part 1. At the upper and lower ends of the gap S₂, two annular grooves 6A are formed.
As shown in FIG. 3, the grip end 3 is formed with an engagement part 3A and a flange part 3B. The engagement part 3A is engaged with and fixed to the rear end of the cylindrical inside layer part 1. The outside diameter of the flange part 3B is equal to the outside diameter on the proximal end side of the cylindrical outside layer part 2. In the hollow portion surrounded by an inner wall 1A of the cylindrical inside layer part 1 and in the hollow portion surrounded by an inner wall 2A of the cylindrical outside layer part 2, a shaft (not shown) is inserted, whereby the grip is mounted on the shaft. The shaft and the grip are fixed to each other as described below. For example, a double-faced adhesive tape is stuck onto the shaft, a solvent for mounting is applied to this tape and the inner wall surface of the shaft, and the shaft is inserted into the hollow portion of the grip quickly. After about ten hours has elapsed, the grip was cut out, and it was found that both of the inner wall surface of shaft and the tape were in a dry state.
The wall thicknesses of the cylindrical inside layer part 1 and the cylindrical outside layer part 2 are made such that the wall thickness of the cylindrical inside layer part 1 is larger than the wall thickness of the cylindrical outside layer part 2 at least in the portion covering the cylindrical inside layer part 1. The impact force at the time when a golfer hits a ball gives torsional deformation to the grip, and this torsional deformation depends greatly on the deformation of the soft cylindrical outside layer part 2. However, since the cylindrical inside layer part 1 that is hard and thick in wall thickness is covered by the cylindrical outside layer part 2 that is soft and thin in wall thickness, the torsional rigidity of the whole of grip is improved. Also, the longitudinal projecting strips 4 formed on the cylindrical inside layer part 1 contribute to the improvement in the torsional rigidity of grip. If the torsional rigidity is improved, the ball hitting directivity is also improved.
Next, an embodiment of the golf club grip shown in FIGS. 4 to 7 is explained. In this embodiment, the same reference numerals are applied to the elements that are the same as those in the embodiment of the golf club grip shown in FIGS. 1 to 3, and the detailed explanation thereof is omitted. In this embodiment, as shown in FIGS. 4 and 5, between the proximal end of the projecting strips 5 and the distal end of the longitudinal projecting strips 4 of the cylindrical inside layer part 1, a ring-shaped protrusion 10 is formed along the circumferential direction. On both sides of this protrusion 10, a pair of rings 10A and 10B each having a wall thickness larger than the thicknesses (protrusion heights) of the longitudinal projecting strips 4 and the protrusion 10 are formed. The ring-shaped protrusion 10 is formed so as to be thicker than the rings 10A and 10B.
In a portion of a first cylindrical outside layer part 2A that covers the portion of the cylindrical inside layer part 1 in which the longitudinal projecting strips 4 are formed, that is, the portion between the grip end 3 and the ring-shaped protrusion 10, the plurality of circumferential grooves 6 are formed on the outer peripheral surface thereof. Also, on the outer peripheral surface of a second cylindrical outside layer part 2B formed on the distal end side of the ring-shaped protrusion 10 of the cylindrical inside layer part 1, the plurality of longitudinal grooves 8 are formed, and the plurality of slantwise grooves 9 are also formed so as to cross the longitudinal grooves 8. The first and second cylindrical outside layer parts 2A and 2B divided by the ring-shaped protrusion 10 use rubbers having colors different from each other.
The first cylindrical outside layer part 2A and the second cylindrical outside layer part 2B the colors of which are divided clearly in the portion of the ring-shaped protrusion 10 can be molded by changing the hardness of rubber. The second cylindrical outside layer part 2B (the distal end side) is preferably harder than the first cylindrical outside layer part 2A (the proximal end side). It is preferable that the second cylindrical outside layer part 2B have a hardness of 45 to 55 because of its thin wall, and the first cylindrical outside layer part 2A be so soft that the longitudinal projecting strips 4 of the cylindrical inside layer part 1 can be felt (for example, the hardness being 35 to 45). This configuration can be realized, for example, by increasing the blending ratio of carbon black or silica of the inside layer part 1 as compared with the outside layer part 2.
The grip end 3 has a color different from that of a body portion (the portion excluding the grip end 3) of the cylindrical inside layer part 1. Since materials having different colors are vulcanization molded, as shown in FIGS. 4 and 5, the boundary thereof becomes wavy, and the colors are less liable to be divided clearly.
The first cylindrical outside layer part 2A and the second cylindrical outside layer part 2B the colors of which are different are molded as described below. First, the cylindrical inside layer part 1 is molded by injection molding. At this time, to mold a hollow portion in the cylindrical inside layer part 1, as shown in FIG. 7, the material is injected to around a mandrel 11, the mandrel 11 is not removed after molding, and the cylindrical inside layer part 1 with the mandrel 11 is inserted into a space surrounded by an upper mold 12, a lower mold 13, and a back end mold 11A. At this time, a hole 3C located on the central axis of the grip end 3 is fitted on a pin of the back end mold 11A to prevent the mandrel 11 from being off-center. Also, on the grip proximal end side and the grip distal end side of the ring-shaped protrusion 10, rubber sheets 14 and 15 having different colors are wound on the cylindrical inside layer part 1. The upper and lower molds 12 and 13 are fastened to each other to compression mold the rubber sheets 14 and 15, and the resulting rubber sheet 14 becomes the first cylindrical outside layer part 2A, and the rubber sheet 15 becomes the second cylindrical outside layer part 2B.
Furthermore, an embodiment of the golf club grip shown in FIGS. 8 to 12 is explained. In this embodiment, the same reference numerals are applied to the elements that are the same as those in the embodiments of the golf club grip shown in FIGS. 1 to 3 and FIGS. 4 to 7, and the detailed explanation thereof is omitted. In this embodiment, as shown in FIGS. 8 and 9, a tungsten sheet 20 is used in addition to the cylindrical inner and outside layer parts 1 and 2. As shown in FIG. 10, the inside layer part 1 can also be provided with the ring-shaped protrusion 10 and the pair of rings 10A and 10B.
As shown in FIG. 11, the inside layer part 1 with the mandrel 11 is inserted into a space surrounded by the upper mold 12, the lower mold 13, and the back end mold 11A, and the tungsten sheet 20 is placed in a portion located in the back surface portion of the inside layer part 1. The inside layer part 1 with the mandrel 11 and the tungsten sheet 20 are set in the mold as an insert member, and the outside layer part 2 is molded so as to cover the inside layer part 1. In the case in which the outside layer part 2 having the first outside layer part 2A and the second outside layer part 2B is molded, as shown in FIG. 11, on the grip proximal end side and the grip distal end side of the ring-shaped protrusion 10, the rubber sheets 14 and 15 having different colors are wound on the inside layer part 1. The method for molding the grip is not limited to the above-described method. For example, vulcanization (molding) may be accomplished using a mold for compression by holding the tungsten sheet 20 between unvulcanized (not-molded) rubber sheets for the inside layer part and the outside layer part. In this case as well, an integrated grip in which the tungsten sheet 20 is placed between the outside layer part 2 and the inside layer part 1 can be obtained.
The tungsten sheet 20 is (injection) molded by mixing tungsten powder in a pellet-form thermoplastic resin material. The thickness thereof is 0.2 to 2.0 mm, and the specific gravity thereof is in the range of 8 to 13. For example, the tungsten sheet 20 having a thickness of 2 mm, a width of 5 mm, and a length of 100 mm had a specific gravity of 12 and a weight of 12 g. Also, as the tungsten sheet 20 having the same specific gravity and the same weight, a tungsten sheet having a thickness of 1 mm, a width of 10 mm, and a length of 100 mm was able to be obtained. For such a tungsten sheet 20, a tungsten sheet having a specific gravity of 11 or more is preferably used as a counterbalancing member. Also, such a tungsten sheet 20 provides specific gravity performance equal to or greater than that of lead, and requires no control of usage and disposal, unlike lead. Furthermore, such a tungsten sheet 20 has great flexibility. Therefore, it can be bent freely, and can fit a curved or intricately shaped portion, that is, a portion formed with the longitudinal projecting strips 4 of the inside layer part 1 (an irregularly-shaped portion) in this embodiment. Furthermore, this tungsten sheet 20 can be worked by scissors or the like and can easily be caused to fit an intricately shaped portion by being heated because it is thermoplastic. As a thermoplastic resin used, a vinyl resin, phenolic resin, polyethylene resin, olefin elastomer, and styrene elastomer are suitable. Also, if the tungsten sheet 20 is formed with holes 20A or slits 20B, it is fixed more stably to between the inside layer part 1 and the outside layer part 2. The tungsten sheet 20 not having these holes 20A or slits 20B or the tungsten sheet 20 having either one of them can also be used.
FIG. 12 is a flow chart for explaining one example of a method for manufacturing the tungsten sheet 20. As shown in FIG. 12, first, 90 wt % or more of tungsten metal powder is kneaded with thermoplastic elastomer by using an agitation mixer such as a kneader. By doing this, a composite material of tungsten and elastomer is obtained. The specific gravity of this composite material is preferably in the range of 8 to 13. The composite material is extrusion molded or injection molded into a sheet, whereby the tungsten sheet is obtained. The tungsten metal powder may be mixed with and regulated by any additive agent (plasticizer, release agent, lubricant, etc.) before being kneaded with elastomer.
Finally, an embodiment of the golf club grip shown in FIGS. 13 to 16 is explained. In this embodiment, the same reference numerals are applied to the elements that are the same as those in the embodiments of the golf club grip shown in FIGS. 1 to 3 and FIGS. 4 to 7, and the detailed explanation thereof is omitted. In this embodiment, a cylindrical inside layer part 30 is vulcanization molded by kneading barium sulfate and/or metal powder in the rubber compound, for example, in the case in which the inside layer part is molded first, that is, the inside layer part 30 is a rubber compound having a large specific gravity. Next, the outside layer part 2 is molded so as to cover the inside layer part 30. FIG. 14, which is a sectional view taken along the line A-A of FIG. 3, shows a shaft 31 in addition to the grip. Also, as shown in FIG. 15, the inside layer part 30 can be provided with the ring-shaped protrusion 10 and the pair of rings 10A and 10B. The reason why the inside layer part 30 is formed by the rubber compound having a high specific gravity and the outside layer part 2 is formed by the rubber compound having a low specific gravity is that the rubber compound constituting the inside layer part 30 contains barium sulfate and metal powder, and thus, there are possibilities that the rubber compound of the inside layer part 30 will become brittle and the touch will be deteriorated. Both of the inside layer part 30 and the outside layer part 2 can be molded by molding an unvulcanized sheet and by compression molding these sheets simultaneously.
The rubber used as the molding material for the inside layer part 30 contains natural rubber (NR) as the main component. Barium sulfate having a blending ratio of 15 parts by weight can be kneaded in a rubber compound in which, for example, 80 to 100 parts by weight of NR, 0 to 20 parts by weight of EPDM, 1 part by weight of antiaging agent, 1 part by weight of stearic acid, 10 to 30 parts by weight of carbon black, 5 to 10 parts by weight of softening agent, 2 parts by weight of processing aid, 5 parts by weight of zinc oxide, 1 to 2 parts by weight of vulcanization accelerator, 0.5 part by weight of vulcanization accelerating assistant, and 1 to 2 parts by weight of sulfur are blended. Together with or in place of barium sulfate, metal powder may be kneaded. As the metal powder, a powder of tungsten, copper, lead, or the like can be used.
As shown in FIG. 16, the inside layer part 30 is molded by injecting the material to around the mandrel 11. Then, the inside layer part 30 with the mandrel 11 is set in a space in the mold, and the outside layer part 2 is molded so as to cover the inside layer part 30.

EXAMPLES

The inside layer part 30 was formed by the rubber compound described below. In this rubber compound, barium sulfate and/or metal powder were mixed. A blend example in which barium sulfate and/or metal powder were not mixed is shown in Table 1 as a basic blend example. Examples 1 to 7 are shown in Table 2 to Table 8. The weight of grip of example 1 was about 50 g. The unit in the tables is parts by weight. In the evaluation of “rubber kneading workability” in the tables, “excellent” is indicated by “A”, “good” by “B”, and “somewhat difficult” by “C”.

TABLE 1

Basic blend example

	Blended material of rubber compound	Blending ratio

	Natural rubber (NR)	85
	Ethylene-propylene-diene rubber (EPDM)	15
	Antiaging agent	1
	Stearic acid	1
	Carbon black	15
	Silica (SiO₂)	5
	Barium sulfate	0
	Softening agent	10
	Processing aid	2
	Zinc oxide	5
	Vulcanization accelerator	1.5
	Vulcanization accelerating assistant	0.5
	Sulfur	1.8
	Specific gravity	1.1
	Rubber kneading workability	A
	Increase in grip weight	0

TABLE 2

Example 1

	Blended material of rubber compound	Blending ratio

	Natural rubber (NR)	85
	Ethylene-propylene-diene rubber (EPDM)	15
	Antiaging agent	1
	Stearic acid	1
	Carbon black	15
	Silica (SiO₂)	0
	Barium sulfate	25
	Softening agent	10
	Processing aid	2
	Zinc oxide	5
	Vulcanization accelerator	1.5
	Vulcanization accelerating assistant	0.5
	Sulfur	1.8
	Specific gravity	1.6
	Rubber kneading workability	C
	Increase in grip weight	About 10 g increase

TABLE 3

Example 2

	Blended material of rubber compound	Blending ratio

	Natural rubber (NR)	85
	Ethylene-propylene-diene rubber (EPDM)	15
	Antiaging agent	1
	Stearic acid	1
	Carbon black	15
	Silica (SiO₂)	0
	Barium sulfate	20
	Softening agent	10
	Processing aid	2
	Zinc oxide	5
	Vulcanization accelerator	1.5
	Vulcanization accelerating assistant	0.5
	Sulfur	1.8
	Specific gravity	1.5
	Rubber kneading workability	B
	Increase in grip weight	About 8 g increase

TABLE 4

Example 3

	Blended material of rubber compound	Blending ratio

	Natural rubber (NR)	85
	Ethylene-propylene-diene rubber (EPDM)	15
	Antiaging agent	1
	Stearic acid	1
	Carbon black	15
	Silica (SiO₂)	5
	Barium sulfate	15
	Softening agent	10
	Processing aid	2
	Zinc oxide	5
	Vulcanization accelerator	1.5
	Vulcanization accelerating assistant	0.5
	Sulfur	1.8
	Specific gravity	1.4
	Rubber kneading workability	B
	Increase in grip weight	About 7 g increase

TABLE 5

Example 4

	Blended material of rubber compound	Blending ratio

	Natural rubber (NR)	85
	Ethylene-propylene-diene rubber (EPDM)	15
	Antiaging agent	1
	Stearic acid	1
	Carbon black	15
	Silica (SiO₂)	5
	Barium sulfate	10
	Softening agent	10
	Processing aid	2
	Zinc oxide	5
	Vulcanization accelerator	1.5
	Vulcanization accelerating assistant	0.5
	Sulfur	1.8
	Specific gravity	1.3
	Rubber kneading workability	A
	Increase in grip weight	About 5 g increase

TABLE 6

Example 5

	Blended material of rubber compound	Blending ratio

	Natural rubber (NR)	85
	Ethylene-propylene-diene rubber (EPDM)	15
	Antiaging agent	1
	Stearic acid	1
	Carbon black	15
	Silica (SiO₂)	5
	Barium sulfate	5
	Softening agent	10
	Processing aid	2
	Zinc oxide	5
	Vulcanization accelerator	1.5
	Vulcanization accelerating assistant	0.5
	Sulfur	1.8
	Specific gravity	1.2
	Rubber kneading workability	A
	Increase in grip weight	About 2 g increase

TABLE 7

Example 6

	Blended material of rubber compound	Blending ratio

	Natural rubber (NR)	85
	Ethylene-propylene-diene rubber (EPDM)	15
	Antiaging agent	1
	Stearic acid	1
	Carbon black	15
	Silica (SiO₂)	5
	Barium sulfate	5
	Tungsten metal powder	2
	Softening agent	10
	Processing aid	2
	Zinc oxide	5
	Vulcanization accelerator	1.5
	Vulcanization accelerating assistant	0.5
	Sulfur	1.8
	Specific gravity	1.5
	Rubber kneading workability	A
	Increase in grip weight	About 8 g increase

TABLE 8

Example 7

	Blended material of rubber compound	Blending ratio

	Natural rubber (NR)	85
	Ethylene-propylene-diene rubber (EPDM)	15
	Antiaging agent	1
	Stearic acid	1
	Carbon black	15
	Silica (SiO₂)	5
	Barium sulfate	5
	Tungsten metal powder	1
	Softening agent	10
	Processing aid	2
	Zinc oxide	5
	Vulcanization accelerator	1.5
	Vulcanization accelerating assistant	0.5
	Sulfur	1.8
	Specific gravity	1.4
	Rubber kneading workability	A
	Increase in grip weight	About 5 g increase

Barium sulfate is used for improving the performance of rubber, for example, the physical properties of vulcanized rubber and the workability of unvulcanized rubber and for increasing the quantity for cost reduction, and is contained in a white filler. As a black filler, carbon black was used. The barium sulfate used is settling barium sulfate in which the particles are amorphous, very fine, and soft, and the specific gravity is 4.3. The specific gravity of carbon black serving as a filler is 1.8, the specific gravity of silica (SiO₂) is 2.1, the specific gravity of calcium carbonate is 2.6, and the specific gravity of tungsten powder is 19.3. In the examples given in Table 7 and Table 8, the grip weight may be increased by mixing only barium sulfate of filler, which is compatible with rubber. However, a small amount of tungsten powder was mixed to attain the intended weight. The tungsten metal powder used was subjected to coupling treatment to prevent oxidation.
While the invention has been described in connection with a preferred embodiment, it is not intended to limit the scope of the invention to the particular form set forth, but on the contrary, it is intended to cover such alternatives, modifications, and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims.

Claims

1. A golf club grip having a double construction, comprising:

a cylindrical inside layer part made of a first rubber having a first hardness, the cylindrical inside layer part having a length 1 to 4 cm longer than the length of a half of the entire length of the grip; and

a cylindrical outside layer part made of a second rubber having a second hardness lower than the first hardness, which covers the cylindrical inside layer part,

wherein the cylindrical inside layer part comprises a plurality of longitudinal projecting formed on the outer peripheral surface thereof, the plurality of longitudinal projecting strips extending from the proximal end side of the cylindrical inside layer part to a portion of 70 to 80% of the entire length of the cylindrical inside layer part along the axis line direction of the cylindrical inside layer part, and being formed at fixed intervals in the circumferential direction;

the cylindrical outside layer part comprises plural circumferential grooves, which are formed at fixed intervals in the axis line direction, on the outer peripheral surface of a portion covering a portion of the cylindrical inside layer part in which the longitudinal projecting strips are formed; and

the cylindrical outside layer part comprises a plurality of longitudinal grooves formed on the outer peripheral surface on the distal end side of the circumferential grooves.

2. The golf club grip according to claim 1, wherein as for the wall thicknesses of the cylindrical inside layer part and a portion of the cylindrical outside layer part which covers the cylindrical inside layer part, the cylindrical inside layer part is formed so as to be thicker than the cylindrical outside layer part.

3. The golf club grip according to claim 1, wherein the cylindrical inside layer part is provided with a ring-shaped protrusion extending in the circumferential direction on the distal end side of the area in which the longitudinal projecting strips are formed; and

the cylindrical outside layer part covers the portion of the cylindrical inside layer part in which the longitudinal projecting strips are formed, and is provided with a first cylindrical outside layer part ranging from the proximal end side of the cylindrical inside layer part to the ring-shaped protrusion and a second cylindrical outside layer part ranging from the ring-shaped protrusion to the grip distal end, which covers the distal end side of the ring-shaped protrusion of the cylindrical inside layer part, and the first cylindrical outside layer part and the second cylindrical outside layer part have different colors.

4. The golf club grip according to claim 3, wherein as for the wall thicknesses of the cylindrical inside layer part and a portion of the cylindrical outside layer part which covers the cylindrical inside layer part, the cylindrical inside layer part is formed so as to be thicker than the cylindrical outside layer part.

5. The golf club grip according to claim 3, wherein the second cylindrical outside layer part constituting the cylindrical outside layer part has a hardness higher than that of the first cylindrical outside layer part.

6. A golf club grip comprising:

a cylindrical and rubber inside layer part;

a cylindrical and rubber outside layer part which covers the inside layer part; and

a tungsten sheet having a thickness of 0.2 to 2.0 mm, which is located between the inside layer part and the outside layer part.

7. The golf club grip according to claim 6, wherein the tungsten sheet is formed by molding a mixture of a thermoplastic resin material and tungsten powder, and has a specific gravity of 8 or more.

8. The golf club grip according to claim 6, wherein the inside layer part is formed so as to be 1 to 4 cm longer than the length of a half of the entire length of the grip, and the inside layer part is thicker than the outside layer part.

9. The golf club grip according to claim 6, wherein the tungsten sheet has a width of 5 to 10 mm and a length of 80 to 120 mm.

10. A golf club grip having a double construction, comprising:

a cylindrical inside layer part made of a first rubber compound having a first specific gravity; and

a cylindrical outside layer part made of a second rubber compound having a second specific gravity smaller than the first specific gravity, which part covers the inside layer part, wherein

the inside layer part is shorter than the outside layer part.

11. The golf club grip according to claim 10, wherein the inside layer part contains at least one of barium sulfate and metal powder, and the specific gravity thereof is 1.3 to 1.6.

12. The golf club grip according to claim 10, wherein the specific gravity of the outside layer part is 1.0 to 1.15.

13. The golf club grip according to claim 10, wherein the inside layer part has a plurality of longitudinal projecting strips on the outer peripheral surface.