This invention relates to an anisotropic golf club shaft and more particularly to a method of improving the strength of the anisotropic golf club shaft and enhancing productivity thereof.
Needless to say, it is advantageous to hit a golf ball straight to get a good score and fly it a long distance. However, many golfers puzzle over the fact that golf balls hit are likely to be curved, i.e., they fly a so-called hook ball or a slice ball.
The golf ball is curved because the orientation of the orbit of a club head and the orientation (orientation of line normal to face of club head) of the face of the club head are not coincident with each other at an impact time. That is, when the face (orientation of line normal to face of the club head) of the club head is directed to the right with respect to the orbit of the club head, the golf ball is curved to the right (slice in the case of right-handed player), whereas when the face of the club head is directed to the left with respect to the orbit of the club head, the golf ball is curved to the left (slice in the case of right-handed player).
Thus, to fly the golf ball straight to an aimed direction, it is necessary to correct the orientation of the face of the club head at an impact time. But it is not easy to correct a swinging form. Thus, many players puzzle over how to correct their swinging forms.
In Japanese Laid-Open Patent Publication No. 3-227616, the present applicant describes that in a hollow or solid shaft having an anisotropic material such as fiber reinforced resin or the like formed at at least one part of the shaft, a fibrous angle of the anisotropic material is differentiated (varied) partly in a circumferential direction of the shaft and at at least one part of the shaft in the thickness direction thereof to differentiate the principal elastic axis of the shaft from the principal geometric axis. In this manner, the principal elastic axis can set at an arbitrary position.
In the hollow shaft in which the principal elastic axis is differentiated from the principal geometric axis to set it at an arbitrary position, when a load is so applied downward to the shaft that the load does not pass through a point located on the principal elastic axis, the hollow shaft is flexed and twisted, as shown in FIGS. 15 and 16. That is, as shown in FIG. 15, supposing that one end of a hollow shaft 10 is denoted by a fixed end 10c and that the other end thereof is denoted by a free end 10d, a principal elastic axis E is not coincident with a principal geometric axis G, and the free end 10d is positioned upward from a point Q located on the principal elastic axis E. When a load W not passing through the point Q located on the principal elastic axis E is applied to the free end 10d of the shaft 10, the shaft 10 is flexed and twisted, as shown in FIG. 16.
Further, the present applicant proposed a golf club to which a hollow shaft having the above-described anisotropic property is applied, as disclosed in Japanese Laid-Open. Patent Publication No. 10-328338. According to the disclosure made therein, the shaft is twisted by the flexure thereof when the golf club is swung so that when a hooker or a slicer uses the golf club, the orientation (orientation of line normal to face of club head) of the face of the club head is self-corrected. In the golf club, the club head is installed on the end of the anisotropic shaft which is flexed and twisted such that a line normal to the face of the club head is oriented to the direction in which a golf ball is to be flied, i.e., the face of the club head is oriented to a specific direction owing to twisting of the shaft at a desired angle caused by flexure thereof which occurs when the golf club is swung.
In the above Japanese Laid-Open Patent Publication No. 10-328338, an anisotropic shaft is manufactured by winding on a mandrel (a molding core rod) a semi-circumference prepreg in a region of 0xc2x0xe2x89xa6xcex8 less than 180xc2x0 (first semi-circumference region) and in a region of 180xc2x0xe2x89xa6xcex8360xc2x0 (second semi-circumference region) in the circumferential direction of the shaft, respectively such that reinforcing fibers of both prepregs incline in opposite directions with respect to the axial direction of the shaft. A plurality of layers each consisting of two semi-circumference prepregs inclining in opposite directions is wound on the mandrel to produce the anisotropic shaft. According to this method, an uncontinuous portion of the reinforcing fibers is formed in the boundary between the first semi-circumference region and the second semi-circumference region. Thus, the strength of the shaft is low at the uncontinuous portion. Further, two semi-circumference prepregs are used to form one layer. Thus, it takes long to manufacture the golf club shaft and further, there may be a variation in the characteristics of products. To solve the problems, the present applicant proposed a golf club shaft and a method of manufacturing the golf club shaft, as disclosed in Japanese Laid-Open Patent Publication No. 11-76480.
In the golf club shaft and the method of manufacturing the golf club shaft, a hoop layer whose reinforcing fibers are substantially perpendicular to the axial direction of the shaft is layered on the boundary (uncontinuous portion of reinforcing fiber) between the first semi-circumference region consisting of one semi-circumference prepreg whose reinforcing fibers incline in one direction and the second semi-circumference region consisting of the other semi-circumference prepreg whose reinforcing fibers incline in the opposite direction. This is to prevent deterioration of the strength of the boundary therebetween. The two semi-circumference prepregs whose reinforcing fibers incline in opposite directions are bonded to the hoop layer to prepare a composite prepreg sheet in advance. The composite prepreg sheet is wound on the peripheral surface of the mandrel to manufacture the golf club shaft, thereby a period of time of manufacturing can be short and a degree of variation in the characteristics of products can be reduced.
However, in the proposal disclosed in Japanese Laid-Open Patent Publication No. 11-76480, it is possible to allow the strength and productivity of the shaft to be higher than those of the shaft not provided with the hoop layer. But the shaft has a seam (boundary between two semi-circumference prepregs) present in each layer, namely, in one turn of each layer consisting of the first and second semi-circumference prepregs. Thus, the strength of the shaft is still low.
It is ideal that the edges of the two prepregs are butted each other at the seam without forming a gap therebetween and overlapping them on each other. But it is difficult to butt them each other in such an ideal state in factories because they are operated for a mass production. Thus, there is necessarily a variation in the finish of the seam. In other words, in order to accomplish such an ideal butting of the prepregs, it is necessary for skilled operators to work without sparing any effort and time, which lowers the productivity of the shaft greatly. The above-described gap between the two prepregs and the overlapping thereof are defects of the shaft in its construction. Thus, in much consideration of the durability of the shaft, namely, such a defect cannot be ignored.
In the case of the conventional shaft (principal elastic axis and principal geometric axis are coincident with each other), in order to allow the shaft to have a uniform property in its circumferential direction, a prepreg is wound by at least one turn, without changing the material thereof. In the case of the anisotropic shaft, the semi-circumference prepreg is used. Thus, when the same amount of prepreg is used to manufacture the anisotropic shaft and the conventional shaft, the total number of prepregs to be used in the former is more than that of prepregs to be used in the latter. Further, in the case of the anisotropic shaft, it is necessary to butt two prepregs each other for each circumference (turn), and the width of the semi-circumfeence prepreg is small, which makes it troublesome to handle it. Thus, the productivity of the anisotropic shaft is low.
The present invention has been made in view of the above-described situation. It is an object of the present invention to improve strength and productivity of an anisotropic golf club shaft which can be flexed and twisted by differentiating its principal elastic axis and principal geometric axis from each other, then can be used preferably by the hooker or slicer.
In order to achieve the object, there is provided a golf club shaft having a plurality of fiber reinforced resinous layers which are layered one upon another in a winding state,
wherein one or more layers of said layers are inclined fiber reinforced resinous layers in which reinforcing fibers are oriented at angles not 0 and 90xc2x0 with respect to an axis of said golf club shaft and, at least one layer of said inclined fiber reinforced resinous layers is wound by an unintegral turns more than one turn so as to apply an anisotropic property to the shaft.
When a fiber reinforced resinous layer (prepreg) whose reinforcing fibers incline with respect to the axis of the shaft is wound, let it be supposed that the number of turns thereof is xe2x80x9cX+Yxe2x80x9d (X is an integer more than 1 (one turn), Y is a value more than 0 and less than 1). In this case, a part of the entire fiber reinforced resinous layer (prepreg) wound by X turns, namely, by an integral number of times in a semi-circumference region (0xc2x0xe2x89xa6180xc2x0) and a part of the entire fiber reinforced resinous layer wound by the integral number of times in a circumference region (180xc2x0xe2x89xa6xcex8360xc2x0) are symmetrical with respect to the axis of the shaft, and the reinforcing fibers incline in the same direction with respect to the axis of the shaft. But the fiber reinforced resinous layer (prepreg) wound at Y turns forms a part in which the orientation of the reinforcing fiber thereof is different from that of the reinforcing fibers of the other parts not only in the circumferential direction of the shaft but also in the thickness direction thereof.
Accordingly, in the golf club shaft of the present invention having the above-described construction, the angle of the reinforcing fiber is partly different from that of the reinforcing fiber of the other parts in the circumferential direction of the shaft and further, at at least one part in the thickness direction thereof. Thus, the shaft is flexed and twisted.
In the golf club shaft of the present invention, as the part of the fiber reinforced resinous layer wound by X turns and the part of the fiber reinforced resinous layer wound by Y turns are composed by one prepreg sheet. Thus, the shaft of the present invention is formed without an uncontinuous portion between the part wound by X and the part wound by Y. Therefore, the shaft has a higher degree of strength than the conventional anisotropic shaft which is composed of the semi-circumference prepregs. Further, because the prepreg of the present invention has one circumference or more, i.e., it is wound by one turn or more, the number of the prepregs of the shaft of the present invention is smaller than that of the prepregs of the conventional anisotropic shaft formed of the semi-circumference prepregs. Furthermore, in the present invention, it is unnecessary to perform prepreg-butting operation. Thus, the shaft of the present invention can be manufactured in a higher productivity than the conventional shaft.
Preferably, the unintegral turns of the fiber reinforced resinous layers wound by more than 1 (one turn) is N+0.5 (N is an integer of one or more ). The way of winding the prepreg efficiently allows a part in which the prepreg is wound by 0.5 turns to be anisotropic.
According to the present invention, there is provided a golf club shaft having a first inclined fiber reinforced resinous layer in which reinforcing fibers are oriented at an angle of xcex1xc2x0(0xc2x0 less than xcex1 less than 90xc2x0) with respect to an axis of the golf club shaft and a second inclined fiber reinforced resinous layer in which reinforcing fibers are oriented at an angle of xe2x88x92xcex1xc2x0 with respect thereto and which is adjacently layered in a winding state at one portion or more of the golf club shaft, wherein a winding start position of the first inclined fiber reinforced resinous layer and a winding start position of the second inclined fiber reinforced resinous layer are spaced at 180xc2x0 in a circumferential direction of the golf club shaft and the first inclined fiber reinforced resinous layer and the second inclined fiber reinforced resinous layer are wound by N+0.5 turns (N is an integer of one or more) respectively.
In the above construction in which the reinforcing fibers are adjacently layered one on the other and incline in opposite directions, the semi-circumference region of one of the first and second inclined fiber reinforced resinous layers at the winding termination side thereof and the semi-circumference region of the other of the first and second inclined fiber reinforced resinous layers at the winding termination side thereof are positioned in a first circumference region (0xc2x0xe2x89xa6xcex8 less than 180xc2x0) of the shaft and a second circumference region (180xc2x0xe2x89xa6xcex8 less than 360xc2x0) thereof, respectively. Similarly, the semi-circumference region of one of the first and second inclined fiber reinforced resinous layer at the winding start side thereof and the semi-circumference region of the other of the first and second inclined fiber reinforced resinous layers at the winding termination side thereof are positioned in the first circumference region (0xc2x0xe2x89xa60 xcex8 less than 180xc2x0) of the shaft and the second circumference region (180xc2x0xe2x89xa6xcex8 less than 360xc2x0) thereof, respectively. Consequently, it can be the that the construction is substantially same as the construction in which the semi-circumference prepregs whose reinforcing fibers incline in the opposite directions are wound on the first circumference region (0xc2x0xe2x89xa6xcex8 less than 180xc2x0) of the conventional anisotropic shaft and the second circumference region (180xc2x0xe2x89xa6xcex8 less than 360xc2x0) thereof, respectively. Thus, the shaft having the construction is flexed and twisted.
In the golf club shaft of the present invention, because the semi-circumference prepreg is not used, there is no seam formed between the semi-circumference prepregs. Thus, the shaft of the present invention has a higher degree of strength than the conventional anisotropic shaft which is composed of the semi-circumference prepregs. Further, because the prepreg of the present invention has one circumference or more, i.e., it is wound by one turn or more, the number of the prepregs of the shaft of the present invention is smaller than that of the prepregs of the conventional anisotropic shaft formed of the semi-circumference prepregs. Furthermore, in the present invention, it is unnecessary to perform prepreg-butting operation. Thus, the shaft of the present invention can be manufactured in a higher productivity than the conventional shaft.
In manufacturing the golf club shaft of the present invention, prepregs composing the first inclined fiber reinforced resinous layer and the second inclined fiber reinforced resinous layer are bonded to each other, by dislocating at 180xc2x0, from each other, ends of the respective two prepregs at a winding start side thereof before prepregs are wound on the mandrel, such that when the two prepregs are wound on the mandrel, winding start positions of the two prepregs are dislocated at 180xc2x0 in a circumferential direction of the mandrel. Then, the two prepregs bonded to each other are wound on the mandrel. According to the method, it is possible to decrease a number of winding prepregs separately on the mandrel and thus improve the productivity of the shaft.
In the present invention, as reinforcing fibers of the fiber reinforced resin, it is possible to use a glass fiber, a carbon fiber, various organic fibers, an alumina fiber, a silicon carbide fiber, metal fiber and/or fibers consisting of a mixture of these fibers, a woven cloth or a mat. As resin, it is possible to use polyamide, epoxy, polyester, and the like.
It is possible to form the golf club shaft of only the fiber reinforced resinous layer. Further, it is possible to use an unanisotropic layer such as a fiber reinforced rubber layer and a rubber layer having an orientation in combination with the fiber reinforced resinous layer. In addition, it is possible to use a resin layer or rubber layer not containing fiber at a part of the golf club shaft.
The anisotropic part which allows the shaft to flex and twist may be provided partly thereon in its axial direction. That is, the anisotropic part may be provided on the shaft entirely or partly in its axial direction.