Baseball or softball bat, bat base member and elastic sleeve

A ball-hitting portion is integrally coated with an elastic body, and thus a bat with durability that can carry the ball far can be obtained. The baseball or softball bat includes a tip portion, a ball-hitting portion, a tapered portion and a grip portion. A depression in the ball-hitting portion is integrally coated with the elastic body having a high rebound property value as a physical property. Thus, when hitting the ball, the elastic body will be compressed and deform, and energy loss due to the ball deformation will be suppressed. Moreover, the ball is carried additionally with a restoring force of the elastic body. Consequently, the bat has rebound property superior to a conventional one, and can carry the ball farther.

This application claims priority from Japanese Patent Application No. 2001-135294, filed 2 May 2001 and Japanese Patent Application No. 2002-101547 filed 3 Apr. 2002.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to improvements in rebound property of a baseball or softball bat.

2. Description of the Background Art

Baseball or softball bats (hereinafter, referred to as a “bat”) made of various materials are commercially available. Some are made of wood or metal such as titanium, titanium alloy, aluminum alloy or the like. Others are made of fiber-reinforced plastic in which a matrix resin is impregnated and cured in carbon fiber, glass fiber or the like.

When a bat is structured with only one of those materials, however, it is difficult to change a property value of the bat to a large extent. Therefore, a bat made from a combination of various materials has been developed.

In order to achieve a significant change in a value of rebound property of the bat, a variety of bats coated with an elastic body have been developed. For example, Japanese Patent Laying-Open No. 62-106784 discloses a cushion bat with a shape identical to a conventional one, of which core portion extending to entire length thereof is coated with an elastic body. Japanese Utility Model Laying-Open No. 63-156667 discloses a bat packed with a rubber sponge, having two rubber sponges bonded to a wooden core. In addition, Japanese Patent Laying-Open No. 2000-153013 discloses a baseball bat, in which a circumferential surface of a core member made of light metal pipe is coated with an elastic body except for a grip portion. Further, Japanese Patent Laying-Open No. 7-275413 discloses a ball-game bat, in which a core member made of carbon fiber is coated with a hard urethane layer, and a protection layer composed of glass fiber having a synthetic resin impregnated is provided thereon.

In the bats disclosed in Japanese Patent Laying-Open No. 62-106784, Japanese Utility Model Laying-Open No. 63-156667 and Japanese Patent Laying-Open No. 2000-153013, an object of coating with an elastic body is to obtain a bat capable of lowering the impact and vibration in ball-hitting, and suppressing a hit distance of the ball for safe use. Accordingly, the elastic body is used, having a physical property that will suppress the hit distance. These bats are suited, for example, for a use in a narrow space, hitting table tennis ball, or toss batting. Moreover, an object of Japanese Patent Laying-Open No. 7-275413 is to reduce manufacturing cost as well as to improve manufacturing process and a method of adjusting weight and “crack” in hitting the ball. Therefore, appearance and rebound property are not changed at all, compared with a conventional bat.

On the other hand, a baseball or softball bat is required to have durability and a property to carry the ball far. The conventional bat as described above is not satisfactory for such requirements.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a bat having good durability and capable of carrying a ball farther, a bat base member forming such a bat as well as an elastic sleeve.

Inventor has made various attempts and finally implemented a bat structure capable of carrying the ball far. The inventor has found that a high rebound property value of the bat is effective for increasing hit distance of the ball, and that, for improving the rebound property value, it is effective to reduce deformation of the ball in hitting.

In order to reduce deformation of the ball when it is hit, it is possible, for example, to coat the surface of the bat with an elastic body. For a bat used in a baseball or softball game, however, not only durability and rebound property but also mass and balance are important. If the bat is entirely coated with the elastic body, the mass of the bat will be larger, and it becomes difficult to achieve a design with these properties being well-balanced.

According to the above-described findings of the inventors, a baseball or softball bat according to one aspect of the present invention includes a tip portion, a ball-hitting portion, a tapered portion and a grip portion. The ball-hitting portion has a depression integrally coated with an elastic body that has a physical property to attain a high rebound property value.

Thus, when hitting the ball, the elastic body will be compressed and deform, and energy loss due to the ball deformation can be suppressed. Further, the ball will be carried farther with a restoring force of the elastic body. Consequently, the bat can be obtained, that has a rebound property superior to a conventional one and capable of carrying the ball farther. In other words, presence of the elastic body can reduce the extent of deformation of the ball when it is hit, and the restoring force of the elastic body is additionally made use of. Thus, the bat can carry the ball farther. In particular, even when hitting a soft ball such as a rubber baseball or a rubber softball, rebound property of the bat can be improved.

In addition, since only a portion of the bat, that is, the depression of the ball-hitting portion, is coated with the elastic body, an increase of the mass of the bat can be suppressed, than when it is entirely coated.

In games, a batter releases the bat when he starts running after hitting the ball. If the bat is coated with the elastic body up to the tip portion, the tip portion may soon be damaged by friction with the ground. Meanwhile, the bat according to the present invention can avoid such damage because the elastic body coats only the ball-hitting portion. (When the batter releases the bat after hitting, possibility of breaking the elastic body due to contact with the ground can be lowered.)

The bat according to the present invention can have the tip portion, the ball-hitting portion with the depression, the tapered portion and the grip portion formed with a hard material similar to the conventional bat. Therefore, the bat can have rigidity comparable to the conventional one, and thus the bat is durable.

In addition, in the bat according to the present invention, as vibration in ball-hitting is absorbed by the elastic body, batter's hands will not be benumbed. Moreover, a time period during which the ball is in contact with the ball-hitting portion is extended because the elastic body deforms when hitting. Therefore, a feel that the ball is being on the bat can be obtained, and hitting feel will be improved.

In the baseball or softball bat according to one aspect as described above, in order to avoid fractures at a corner in the bottom portion of the depression due to stress concentration and at a corner in the upper portion thereof due to the impact of the ball, desirably, the depression is formed in the following manner. Namely, it is formed with a ball-hitting center portion having an outer diameter smaller than that of the ball-hitting portion. An outer diameter thereof from an end of a tip portion side of the ball-hitting center portion to the boundary of the tip portion and an outer diameter from an end of a tapered portion side of the ball-hitting center portion to the boundary of the tapered portion are gradually increased.

In addition, in the baseball or softball bat according to one aspect as described above, the depression of the ball-hitting portion may include a center portion bottom wall, distance of which from the central axis of the bat is smaller than that from the central axis to an outermost circumferential portion of the ball-hitting portion; a stepped portion bottom wall, distance of which from the central axis of the bat is larger than that from the central axis to the center portion bottom wall and is smaller than that from the central axis to the outermost circumferential portion of the ball-hitting portion, and positioned at both ends of the center portion bottom wall in a direction along the central axis, and extending in a direction substantially the same as the central axis; and a sidewall connecting the center portion bottom wall with the stepped portion bottom wall. The sidewall may be inclined relative to the central axis.

When the stepped portion bottom wall is formed in an end portion of the depression, it appears that a convex portion is formed on the sidewall thereof. Accordingly, contact area of the wall surface of the depression with the elastic body can be made larger. Thus, when hitting the ball at the above-described end portion of the elastic body, separation will be unlikely, and a bat with good durability can be obtained.

In the baseball or softball bat according to one aspect as described above, the ball-hitting portion may include an outermost circumferential portion positioned in a region outside the depression and having a largest outer diameter; a small outer diameter portion provided as a wall surface of the depression and having an outer diameter smaller than that of the outermost circumferential portion; and a medium outer diameter portion provided as a wall surface of the depression, extending in a direction substantially the same with the central axis of the baseball or softball bat, positioned at an end portion of the depression and having an outer diameter larger than that of the small outer diameter portion and smaller than that of the outermost circumferential portion.

In the baseball or softball bat according to one aspect as described above, preferably, the elastic body is of a synthetic resin foam having JIS C hardness of 20 to 80, specific gravity of 0.25 to 0.70 and tensile stress (tensile strength) of 1.0 MPa to 4.0 MPa in 300% elongation. More preferably, the elastic body has JIS C hardness of 20 to 50, specific gravity of 0.25 to 0.50 and tensile stress of 1.0 MPa to 1.8 MPa in 300% elongation. In this case, using what is called a “soft” synthetic resin foam as described above will effectively improve a rebound property value of the bat.

In addition, in the baseball or softball bat according one aspect as described above, the synthetic resin foam preferably uses a polyurethane foam, in view of manufacturing cost and formability. In other words, if what is called the “soft” polyurethane foam is used as the elastic body, the hit distance of the ball can effectively be improved, and an increase of the manufacturing cost of the bat can be suppressed.

In general, polyurethane can be categorized into three types: soft, semi-hard and hard. A soft polyurethane foam used as the elastic body in the present invention includes what is classified as soft and semi-hard, not including hard. Here, hard polyurethane is generally elongated a few percent to several tens of percent. Hard polyurethane with such elongation capability is not suitable for the polyurethane foam as the elastic body in the present invention.

The baseball or softball bat according to one aspect as described above may be provided with a protection film formed on an outermost layer of the elastic body.

In such a case, as the protection film can suppress abrasion of the elastic body, durability of the bat can be improved. In particular when a soft synthetic resin foam as described above is used as the elastic body, durability of the bat can effectively be improved by forming the protection film.

In the baseball or softball bat according to one aspect as described above, the protection film may include at least one of a synthetic resin sheet and a synthetic resin tube.

In the baseball or softball bat according to one aspect as described above, preferably, the protection film has a thickness of not smaller than 0.1 mm and not larger than 1.0 mm, and includes a thermoplastic polyurethane.

In this case, workability in forming the protection film and adhesiveness of the elastic body with the same can be effectively improved.

In order to enhance durability of the bat, desirably, a synthetic resin sheet or tube having sufficient abrasion-resistance coats, and is formed on, the outermost layer of the above synthetic resin foam. In addition, considering workability and adhesiveness, desirably, the synthetic resin sheet or tube is a thermoplastic polyurethane sheet or tube having a thickness of 0.1 mm to 1.0 mm.

In this case, durability of the bat can be improved without impairing the property of the elastic body encapsulated inside the depression.

Moreover, the above thermoplastic polyurethane sheet or tube is desirably transparent or translucent. The above sheet is printed on one surface, and is fused and adhered in a tube-like shape to the surface of the elastic body with the printed surface facing inward. Thus, the print can be clearly viewed through the sheet, to enhance the appearance of the bat. Even after a prolonged use of the bat, the print will not separate.

In the baseball or softball bat according to one aspect as described above, preferably, the depression is formed on the entire circumference of the ball-hitting portion.

In such a case, no matter which portion of the entire circumference of the ball-hitting portion a batter may hit the ball, hit distance of the same can be improved.

A bat base member according to another aspect of the present invention constitutes a baseball or softball bat including a tip portion, a ball-hitting portion, a tapered portion and a grip portion. In a region to be the ball-hitting portion, a depression is formed.

Using such a bat base member, the bat according to the present invention can be readily manufactured by integrally coating the depression with the elastic body.

In the bat base member according to another aspect as described above, the region to be the ball-hitting portion may include an outermost circumferential portion positioned in a region outside the depression and having a largest outer diameter; a small outer diameter portion provided as a wall surface of the depression and having an outer diameter smaller than that of the outermost circumferential portion; and a medium outer diameter portion provided as a wall surface of the depression, extending in a direction substantially the same with the central axis of the bat, positioned at an end portion of the depression and having an outer diameter larger than that of the small outer diameter portion and smaller than that of the outermost circumferential portion.

In this case, a region with a small thickness can be formed in an end portion of the elastic body coating the depression. Therefore, a bat can be readily formed, in which the elastic body is unlikely to separate from the bat base member.

An elastic sleeve according to another aspect of the present invention constitutes a baseball or softball bat including a tip portion, a ball-hitting portion, a tapered portion and a grip portion, and is fit into a depression formed in the ball-hitting portion. The elastic sleeve includes a smallest inner diameter portion positioned in a center portion therein and having a smallest inner diameter; and an enlarged inner diameter portion positioned at an end portion thereof, having an inner diameter larger than that of the smallest inner diameter portion and extending in a direction substantially the same with the elastic sleeve.

Using such an elastic sleeve, a bat according to the present invention can readily be manufactured by integrally coating the depression of the ball-hitting portion with the elastic sleeve.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following, embodiments of the present invention will be described in detail with reference to the figures. It is noted that the same reference characters refer to the same or corresponding components in the figures.

Referring toFIGS. 1 and 2, a first embodiment of a bat according to the present invention will be described.

A bat according to the present invention has a depression of a ball-hitting portion integrally coated with an elastic body that has a largest rebound property confirmed in various experiments. As shown inFIGS. 1 and 2, a baseball or softball bat1includes a tip portion10, a ball-hitting portion11, a tapered portion12and a grip portion13. A bat base member7constituting bat1is provided with a depression2in a portion to be ball-hitting portion11. Desirably, the depression is formed with a ball-hitting center portion11ahaving an outer diameter smaller than that of ball-hitting portion11, and an outer diameter thereof from an end11bof a tip portion side of ball-hitting center portion11ato the boundary of tip portion10and an outer diameter from an end11cof a tapered portion side of ball-hitting center portion11ato the boundary of tapered portion12are gradually increased. Depression2formed on the entire circumference of ball-hitting portion11is integrally coated with an elastic body3. Here, depression2may be formed partially in a circumferential direction of ball-hitting portion11. At an end portion of grip portion13, a grip end4is fit in and secured to a bat base member7.

In such a bat1according to the present invention, when hitting the ball, elastic body3will be compressed and deform, and energy loss due to the ball deformation can be suppressed. Further, the ball will be carried additionally with a restoring force of elastic body3. Consequently, bat1can be obtained, having a rebound property superior to a conventional one and capable of carrying the ball farther. In particular, even when hitting a soft ball such as a rubber baseball or a rubber softball, rebound property of bat1can be improved.

In addition, since only a portion of bat1, that is, depression2of ball-hitting portion11, is coated with elastic body3, an increase of the mass of bat1can be suppressed, compared with when bat1is entirely coated.

In games, a batter releases bat1when he starts running after hitting the ball. If bat1is coated with the elastic body as far as tip portion10, the elastic body and the like may soon be damaged by friction of tip portion10with the ground. Bat1according to the present invention can avoid such damage because elastic body3coats only ball-hitting portion11.

Bat1according to the present invention can have tip portion10, ball-hitting portion11with depression2, tapered portion12and grip portion13formed with a hard material similar to the conventional one, as described below. Therefore, bat1can have rigidity comparable to the conventional one, and thus bat1is durable.

In addition, in bat1according to the present invention, as vibration in ball-hitting is absorbed by elastic body3, batter's hands will not be benumbed. Moreover, a time period during which the ball is in contact with ball-hitting portion11is extended because elastic body3deforms when hitting. Therefore, a feel that the ball is being on bat1can be obtained, and hitting feel will be improved.

Moreover, depression2is formed on the entire circumference of ball-hitting portion11. Therefore, with no matter which portion of the entire circumference of ball-hitting portion11a batter may hit the ball, hit distance of the same can be improved.

As shown inFIG. 3, a corner2ain a bottom portion and a corner2bin an upper portion of depression2may be rounded, and a sidewall2cof depression2may be formed perpendicularly to a central axis6(seeFIG. 1) in a direction of bat length.

The whole bat, having depression2formed in ball-hitting portion11(bat base member7), may be formed with any of the conventional materials, such as wood, metal or fiber-reinforced plastic. Tip portion10and grip end4can be formed integrally with bat base member7as a whole bat, or may be formed separately for attachment.

Desirably, elastic body3integrally coats depression2of ball-hitting portion11, using injection molding or cast molding of a synthetic resin. Alternatively, elastic body3as an elastic sleeve may be formed separately so as to fit with a shape of depression2of ball-hitting portion11for adhering.

The elastic body3may be of a material having a low ratio of energy loss when restituting after elastic deformation, and a material such as ionomer, butadiene-based rubber and the like as well as an air bag can be used. Considering mass, ratio of energy loss, manufacturing cost and formability, a polyurethane foam having JIS C hardness of 20 to 80, specific gravity of 0.25 to 0.70 and tensile stress of 1.0 MPa to 4.0 MPa in 300% elongation is preferred. The range of those figures was determined for a reason as described below. When hardness is set to 20 or lower, it becomes difficult to form a bat. When it is set to 80 or higher, rebound property will not be improved, compared with a conventional bat. Similarly, when specific gravity is set to 0.25 or lower, it becomes difficult to form a bat, and when it is set to 0.70 or higher, rebound property will not be improved, compared with the conventional bat. In addition, when tensile stress in 300% elongation is set to 1.0 MPa or lower, it becomes difficult to form a bat, and when it is set to 4.0 MPa or higher, rebound property will not be improved, compared with the conventional bat.

If priority is given to rebound property, for elastic body3, a polyurethane foam having JIS C hardness of 20 to 50, specific gravity of 0.25 to 0.50 and tensile stress of 1.0 MPa to 1.8 MPa in 300% elongation is preferred.

Referring toFIG. 4, a second variation of the bat will be described.FIG. 4corresponds to FIG.1.

As shown inFIG. 4, bat1basically has a similar structure to bat1shown inFIGS. 1 and 2. On the surface of elastic body3, however, a sheet5as a protection film is formed.

Thus, as sheet5provides protection of elastic body3, durability of bat1can be improved. In particular, when a synthetic resin foam is used for elastic body3, durability of the bat can effectively be improved by arranging such a sheet5.

For sheet5formed and used for integral coating of an outermost layer of elastic body3composed of the synthetic resin foam and the like, desirably, a synthetic resin sheet or tube having a good abrasion-resistance is used. Considering workability and adhesiveness, desirably, the synthetic resin sheet or tube is a thermoplastic polyurethane sheet or tube having a thickness of not smaller than 0.1 mm and not larger than 1.0 mm.

Here, if the thickness of the synthetic resin sheet or tube is less than 0.1 mm, strength of the sheet or tube itself is not sufficient, and does not enhance durability. On the other hand, if the thickness exceeds 1.0 mm, sheet5itself becomes hard, and may impair property of elastic body3encapsulated inside. Desirably, the thermoplastic polyurethane sheet or tube having a JIS A hardness of 80 to 100 and tensile strength of 450 to 500 kg/cm2is used. If JIS A hardness is less than 80, strength of the sheet or tube itself is not sufficient, and does not enhance durability. On the other hand, if JIS A hardness exceeds 100, sheet5itself becomes hard, and may impair the property of elastic body3encapsulated inside. The same will also apply to tensile strength.

Moreover, the synthetic resin sheet used for sheet5is desirably transparent or translucent. Sheet5is printed on one surface, and is fused and adhered in a tube-like shape, with the printed surface facing inward. Then the tube is formed integrally with elastic body3. Thus, the print can be clearly viewed through the sheet, to enhance the appearance of the bat. Even after a prolonged use of bat1, the print will not separate.

Referring toFIGS. 5to7, a second embodiment of a bat according to the present invention will be described.

As shown inFIGS. 5to7, bat1basically has the same structure as the one shown inFIG. 4except for the shape of depression2. In other words, depression2may include a center portion bottom wall8as a small outer diameter portion of ball hitting center portion11a, distance of which from central axis6of baseball or softball bat1is smaller than distance R1(seeFIG. 7) from central axis6to an outermost circumferential portion of ball-hitting portion11; an end portion region15as a stepped portion bottom wall (see FIG.5), distance of which from central axis6is larger than distance R2(seeFIG. 7) from central axis6to center portion bottom wall8of ball-hitting center portion11aand is smaller than distance R1from central axis6to outermost circumferential portion9of ball-hitting portion11, and positioned at both ends of ball-hitting center portion11ain a direction along central axis6and extending in a direction substantially the same as central axis6; and a sidewall26connecting ball-hitting center portion11awith end portion region15as a medium outer diameter portion. Sidewall26is inclined relative to central axis6.

In this case, in an enlarged inner diameter portion17(see FIG.5), which is an end portion of elastic body3(seeFIG. 5) as an elastic sleeve positioned on end portion region15, elastic body3has a thickness relatively smaller than in a smallest inner diameter portion16(see FIG.5), which is a center portion of elastic body3. (Elastic body3includes smallest inner diameter portion16as well as enlarged inner diameter portion17positioned at an end portion of elastic body3, having an inner diameter larger than that of smallest inner diameter portion16and extending in a direction substantially the same as elastic body3(a direction in which central axis6extends)).

In addition, when end portion region15is formed in an end portion of depression2, it appears that a convex portion (a stepped portion14, seeFIG. 7) is formed on the side surface thereof. Accordingly, contact area of the side surface of depression2with elastic body3can be made larger. Thus, when hitting the ball at the end portion of elastic body3, separation of elastic body3will be unlikely, and bat1with good durability can be obtained.

Depression2of bat1may specifically be shaped in a following manner. For example, as shown inFIG. 7, assume that distance R1from central axis6of bat1to the outermost circumference of ball-hitting portion11(seeFIG. 5) is set to 34.5 mm and distance R2from central axis6to ball-hitting center portion11ais set to 20 mm. In this example, distance T, which is a depth from the outermost circumferential surface of ball-hitting portion11(seeFIG. 5) to the surface of end portion region15, can be set to not smaller than 1.0 mm and not larger than 10.0 mm. Preferably, distance T is set to not smaller than 1.5 mm and not larger than 7.0 mm. More preferably, distance T is set to not smaller than 2.0 mm and not larger than 4.0 mm. If distance T is less than 1.0 mm, the thickness of elastic body3(seeFIG. 5) arranged on end portion region15will be too small. This may cause elastic body3to separate or to break easily. On the other hand, if distance T is over 10.0 mm, the body strength of bat base member7, which is a body of bat1(see FIG.5), may not be sufficient (sufficient strength cannot be achieved).

Width L of end portion region15may be set to not smaller than 3.0 mm and not larger than 30.0 mm. In addition, preferably, width L is set to not smaller than 5.0 mm and not larger than 25.0 mm. More preferably, width L is set to not smaller than 10.0 mm and not larger than 20.0 mm. If width L is less than 3.0 mm, contact area of elastic body3(seeFIG. 5) with end portion region15will be too small, resulting in easy separation of elastic body3from end portion region15. If width L is over 30.0 mm, the size of a portion where elastic body3of a sufficient thickness is arranged will be smaller in ball-hitting portion11(see FIG.5). That is, the portion capable of maximizing the hit distance of the ball will be made smaller.

The inclination angle of the surface of end portion region15relative to central axis6of bat1(seeFIG. 5) can be set to not smaller than −18° and not larger than +18°. Here, inclination angle of −18° means that when a tip portion10(seeFIG. 5) side of bat1in end portion region15is inclined toward central axis6side, a phantom straight line along the surface of end portion region15in FIG.7and central axis6cross with an angle of 18°. Similarly, inclination angle of +18° means that when a grip portion13(seeFIG. 5) side of bat1in end portion region15is inclined toward central axis6side, a phantom straight line along the surface of end portion region15in FIG.7and central axis6cross with an angle of 18°. In addition, preferably, the inclination angle is set to not smaller than −12° and not larger than +12°. More preferably, the inclination angle is set to not smaller than −6° and not larger than +6°.

If the inclination angle of end portion region15is less than −18° or over +18°, elastic body3tends to separate from bat base member7(see FIG.5).

Further, as shown inFIG. 7, sidewall26connecting end portion region15with center portion bottom wall8of ball-hitting center portion11a(a center portion of depression2) may be inclined relative to central axis6, or may extend substantially perpendicularly to central axis6.

Referring toFIG. 8, a variation of the second embodiment of the bat according to the present invention will be described.FIG. 8corresponds to FIG.5.

As shown inFIG. 8, though bat1basically has the same structure as the one shown inFIGS. 5to7, a sheet5(seeFIG. 5) is not formed on the surface of elastic body3of ball-hitting portion11. That is, the surface of elastic body3is exposed. In this case as well, the same effect as with the bat shown inFIGS. 5to7can be obtained.

In the following, results from two experiments conducted to verify the effect of a polyurethane foam used for a material of elastic body3(seeFIG. 1) will be discussed.

First, using an experiment apparatus as shown inFIG. 9, a rebound experiment of a ball-hitting portion model was conducted.

As shown inFIG. 9, the experiment apparatus included a pitching machine20, a high-speed video camera21and an image analyzer (not shown). Two types of ball-hitting portion models22as a hit target of a ball23were provided. One was of an iron plate only, and the other was prepared by bonding an elastic body to an iron plate. In the experiment, ball23was fed from pitching machine20to impact fixed ball-hitting portion model22. High-speed video camera21filmed the impact from right beside. Then, restitution coefficient was calculated from the speed of ball23before and after the impact.

The elastic body used for the ball-hitting portion model was a polyurethane foam sheet having JIS C hardness of 40 to 80 and specific gravity of 0.35 to 0.66, and was prepared by bonding two square sheets with a side of 10 cm long and a thickness of 10 mm.

The present experiment was conducted using a rubber baseball, the reason for which is as follows. When hitting a rubber baseball or softball, elastic deformation of the ball is too larger and rebound property of the bat cannot fully be taken advantage of. Accordingly, significant difference in rebound property cannot be observed, not matter which bat may be used. Therefore, in order to verify the effect of a structure of the ball-hitting portion capable of improving rebound property of the bat even for such a soft ball, a rubber baseball was used. Thus, though degrees may vary, similar effect can be obtained in both leather baseball and leather softball.

Next, an equation of calculating restitution coefficient e and description of the reference characters are provided in Equation 1. The method of measuring data is also shown below.
e=V·BALL (OUT)/V·BALL (IN)  [Equation 1]e: restitution coefficientV·BALL (OUT): velocity of gravity center of the ball after impact (m/s)V·BALL (IN): velocity of gravity center of the ball before impact (m/s)

The velocity of gravity center of the ball in the above equation was obtained by analyzing with an image analyzer, an image filmed by the high-speed video camera.

Next, a result of a rebound experiment, in which a rubber baseball impacts each ball-hitting portion model with a speed of 30 m/s, is shown in Table 1 below.

As can be seen from the experiment result in Table 1, restitution coefficient is higher in a model having an elastic body bonded than in a model of an iron plate with a flat surface. In addition, as the hardness, specific gravity and elasticity modulus of the elastic body become smaller, the restitution coefficient will be larger.

Next, using an experiment apparatus as shown inFIG. 10, a rebound experiment of the bat was conducted.

As shown inFIG. 10, the experiment apparatus included a pitching machine20, a high-speed video camera21, an image analyzer (not shown) and a bat stand24.

In the experiment, ball23was fed from pitching machine20to impact a bat25mounted on bat stand24. High-speed video camera21filmed the impact from directly above. Then, restitution coefficient was calculated from the speed of ball23before and after the impact and the speed of bat25. Note that restitution coefficient e was calculated with Equation 2.
e=−{V BL(OUT)−(V BT(PAL)+a·V BT(ROT))}/V BL(IN)  [Equation 2]e: restitution coefficientV BL (OUT): velocity of gravity center of the ball after impact (m/s)V BT (PAL): translation speed of gravity center of the bat after impact (m/s)a: distance from gravity center of the bat to a ball-hitting position (more positive on the side of grip portion)V BT (ROT): rotational angular velocity around gravity center of the bat after impact (rad/s)V BL (IN): velocity of gravity center of the ball before impact (m/s)

Using the experiment apparatus shown inFIG. 10, restitution coefficient was found for the bat according to the present invention shown inFIGS. 1 and 2. For the rebound experiment, a conventional rubber-baseball bat made of metal and a rubber-baseball bat made of fiber-reinforced plastic, of the present invention shown inFIGS. 1 and 2, were used, of which specifications are shown in Table 2. Here, the elastic body of the bat of the present invention is of a polyurethane foam, having JIS C hardness of 43, specific gravity of 0.35 and elasticity modulus (tensile stress in 300% elongation) of 1.23 MPa. The elastic body integrally coats the depression of the ball-hitting portion to a thickness of 20 mm.

TABLE 2TotalCenter ofMoment ofLengthMassGravityInertiaBat(mm)(g)(mm)(kg · cm2)Present8407215261754InventionConventional8377245181774ExampleCenter of gravity is given as the length from a grip end.Moment of inertia is a value measured at 11 cm away from the grip end.

An experiment result, in which a rubber baseball impacts the ball-hitting portion of the bat at 130 km/h, is shown in Table 3.

As can be seen from the result in Table 3, the bat of the present invention has a restitution coefficient approximately 10% higher. Therefore, the bat of the present invention can carry the ball farther than the conventional one.

In addition, using the experiment apparatus shown inFIG. 10, restitution coefficient was found for the bat according to the present invention shown inFIGS. 5 and 6. For the rebound experiment, a conventional rubber-baseball bat made of metal and a rubber-baseball bat made of fiber-reinforced plastic, of the present invention shown inFIGS. 5 and 6, were used, of which specifications are shown in Table 4.

Here, distance T, which is a depth of end portion region15in depression2(seeFIG. 5) of the bat according to the present invention used in the experiment, was set to 4.0 mm, width L of end portion region15was set to 15.0 mm, and inclination angle of the surface of end portion region15relative to central axis6(seeFIG. 7) of bat1(seeFIG. 5) was set to 0° (the surface of end portion region15is generally parallel to central axis6).

The elastic body of the bat according to the present invention is of a polyurethane foam, having JIS C hardness of 43, specific gravity of 0.35 and elasticity modulus (tensile stress is 300% elongation) of 1.23 MPa. The elastic body integrally coats the center portion of the depression of the ball-hitting portion to a thickness of 20 mm. In addition, on the outermost layer of the polyurethane foam as elastic body3(see FIG.5), a thermoplastic polyurethane tube is integrally formed. Here, the thermoplastic polyurethane tube is provided as a sheet5(seeFIG. 5) with a thickness of 0.3 mm, obtained by fusing and adhering a sheet having JIS A hardness of 91 and tensile strength of 474 kg/cm2.

An experiment result, in which a rubber baseball impacts the ball-hitting portion of the bat at 130 km/h similarly to the example shown inFIGS. 1 and 2, is shown in Table 5.

As can be seen from the result in Table 5, the bat of the present invention has a restitution coefficient approximately 7% higher. Therefore, the bat of the present invention can carry the ball farther than the conventional one.

Thus, the bat according to the present invention shown inFIGS. 1 and 2orFIGS. 5 and 6has a restitution coefficient higher than the conventional one, probably because of the following reasons. In the conventional bat, when hitting the ball, a ball-hitting surface will flexure and the ball considerably deforms. Then, the ball is carried while the ball-hitting surface and the ball restitute. On the other hand, in a bat according to the present invention, the thermoplastic polyurethane tube with a thickness of 0.3 mm and the elastic body (or elastic body3, seeFIG. 1) are initially compressed, and the impact energy in ball-hitting is converted to compression energy. As the ball is compressed and deforms thereafter, the extent of deformation of the ball in hitting will be smaller. As a result, energy loss due to ball deformation is lowered, and restoring force of the elastic body is added. Thus, rebound property is improved.

In addition, it goes without saying that the thermoplastic polyurethane tube integrally formed on the outermost layer of the elastic body functions without impairing the property of the elastic body encapsulated inside, and has good durability.

In the following, examples of a rubber-baseball bat according to the present invention will be described with reference to the drawings.

In order to verify the effect of the bat according to the present invention shown inFIGS. 1 and 2, an actual hitting test was conducted.

A rubber-baseball bat1used in the test as an example of the bat according to the present invention shown inFIGS. 1 and 2, was hollow and made of fiber-reinforced plastic. In the bat, a tip portion10, a ball-hitting portion11having a depression2, a tapered portion12and an outer shell of a grip portion13(a bat base member7) were formed with internal pressure molding. A grip end4separately formed with a synthetic resin was inserted and adhered to the end of grip portion13. After sandblasting depression2of ball-hitting portion11, the bat was cast molded, using a mold designed to integrally coat depression2with elastic body3. Here, for elastic body3, a polyurethane foam having JIS C hardness of 43, specific gravity of 0.35 and elasticity modulus (tensile stress in 300% elongation) of 1.23 MPa was used.

Outer diameter of ball-hitting portion11was 70 mm, and outer diameter of ball-hitting center portion11aextending from a position 40 mm away to a position 260 mm away from a bat tip end was 30 mm. An outer diameter from an end11bof a tip portion side of ball-hitting center portion11ato the boundary of tip portion10and an outer diameter from an end11cof a tapered portion side of ball-hitting center portion11ato the boundary of tapered portion12were gradually increased.

An actual hitting test was conducted, using rubber-baseball bat1according to the present invention as described above and a conventional rubber-baseball bat made of metal. A result is shown in Table 6.

The result of the above actual hitting test is the average of five amateur baseball club members. As were predicted through the results of the rebound experiment, the bat according to the present invention could carry the ball farther than the conventional one.

In order to verify the effect of the bat according to the present invention shown inFIGS. 5 and 6, an actual hitting test, similar to that in Example 1, was conducted.

A rubber-baseball bat1shown inFIGS. 5 and 6basically has the same structure with the bat in Example 1. Bat1was hollow and made of fiber-reinforced plastic. In the bat, a tip portion10, a ball-hitting portion11having a depression2, a tapered portion12and an outer shell of a grip portion13were formed with internal pressure molding. A grip end4separately formed with a synthetic resin was inserted and adhered to the end of grip portion13. In depression2formed in ball-hitting portion11, an end portion region15was formed in the end portion thereof, as shown in FIG.5. After sandblasting depression2of ball-hitting portion11, the bat was cast molded, using a mold designed to integrally coat depression2with elastic body3and a tube as a sheet5obtained by fusing and adhering a thermoplastic polyurethane sheet of a thickness of 0.3 mm on the outermost layer. Here, for elastic body3, a polyurethane foam having JIS C hardness of 43, specific gravity of 0.35 and elasticity modulus (tensile stress in 300% elongation) of 1.23 MPa was used, as in the bat in Example 1. In addition, for sheet5formed on the surface of elastic body3, a tube obtained by fusing and adhering a thermoplastic polyurethane sheet of a thickness of 0.3 mm was used. The tube has JIS A hardness of 91 and tensile strength of 474 kg/cm2.

An outer diameter of ball-hitting portion11was 70 mm, and an outer diameter of ball-hitting center portion11aextending from a position 40 mm away to a position 260 mm away from a bat tip end was 30 mm. As shown inFIG. 7, sidewall26connecting end portion regions15positioned at both ends of depression2with the bottom wall in the center portion of depression2was inclined relative to central axis6of bat1(see FIG.5). (As shown inFIG. 5, the outer diameter from an end11bof a tip portion side of ball-hitting center portion11ato the boundary of end portion region15positioned on tip portion10side and the outer diameter from an end11cof a tapered portion side of ball-hitting center portion11ato the boundary of end portion region15positioned on tapered portion12side were gradually increased.)

An actual hitting test was conducted, using rubber-baseball bat1in the above example and a conventional rubber-baseball bat made of metal. A result is shown in Table 7.

The result of the above actual hitting test is the average of five amateur baseball club members. As were predicted through the results of the rebound experiment, the bat according to the present invention could carry the ball farther than the conventional one.

Thus, in the present invention, the elastic body will be compressed and deform in hitting the ball, and energy loss due to the ball deformation will be suppressed. Further, the ball will be carried additionally with a restoring force of the elastic body. Consequently, the bat can be obtained, having rebound property superior to a conventional one and capable of carrying the ball farther.

In particular, even when hitting the soft ball such as a rubber baseball or a rubber softball, rebound property of the bat can be improved.

Moreover, the outermost layer of the elastic body is coated with a thermoplastic polyurethane sheet or tube of a thickness of 0.1 mm to 1.0 mm having a good abrasion-resistance. Thus, durability of the bat can be improved without impairing the property of the elastic body encapsulated inside. In addition, stepped portions (end portion regions) are provided in both the vicinities of a tip portion and a tapered portion. Thus, the elastic body and the thermoplastic polyurethane sheet will not separate even in the end portion, exhibiting good durability.

The above thermoplastic polyurethane sheet is desirably transparent or translucent. The sheet is printed on one surface, and is fused and adhered in a tube-like shape, with the printed surface facing inward. Thus, the print can be clearly viewed through the sheet, to enhance the appearance. Even after a prolonged use of bat, the print will not separate.

In games, a batter releases the bat when he starts running after hitting the ball. If the bat is coated with the elastic body up to the tip portion, the tip portion may soon be damaged by friction with the ground. Meanwhile, the bat according to the present invention can avoid such damage because the elastic body coats only the ball-hitting portion.

The bat according to the present invention can have the tip portion, the ball-hitting portion with the depression, the tapered portion and the grip portion formed with a hard material similar to the conventional one. Therefore, the bat can have rigidity comparable to the conventional one, and thus the bat is durable.

In addition, in a bat according to the present invention, as vibration in ball-hitting is absorbed by the elastic body, batter's hands will not be benumbed. Moreover, a time period during which the ball is in contact with the ball-hitting portion is extended because the elastic body deforms when hitting. Therefore, a feel that the ball is being on the bat can be obtained, and hitting feel will be improved.