Golf club head

Abstract

The golf club head has a ball striking face including a sweet spot. The striking face comprises a high-friction portion with high surface roughness, a low-friction portion with low surface roughness, and a middle-friction portion with surface roughness therebetween. When the striking face is divided into four regions by imaginary first and second axes passing through the sweet spot and intersecting with each other, the high-friction portion is located in one of the four regions closest to the heel and closest to the sole portion, and the low-friction portion is located in one of the four regions closest to the toe and closest to the crown portion.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a golf club head.BACKGROUND ART

[0002] The golf club head has a striking face for striking the ball, and the striking face has a sweet spot. The sweet spot is a point at which a straight line drawn from the center of gravity of the head to the striking face perpendicularly thereto intersects with the striking face. It is recognized as being advantageous to strike the ball at the sweet spot in terms of distance and direction.

[0003] On the other hand, if the ball is struck at a position which is off from the sweet spot to the left or right or up or down, then the golf club head will rotate slightly around the center of gravity of the head, and the spin rate of the ball due to the gear effect on the ball will change. (see Patent Document 1 for the gear effect)

[0004] In general, when the ball is struck at a position on the heel side of the sweet spot of the striking face, there is a tendency to increase the sidespin in a direction promoting a slice (hereinafter sometimes simply referred to as the slice spin).

[0005] On the other hand, when the ball is struck a position on the sole side of the sweet spot of the striking face, there is a tendency to increase the backspin.

[0006] Patent Document 1: Japanese Patent No. 4430968SUMMARY OF THE INVENTIONProblems to be Solved by the Invention

[0007] If the above-mentioned sidespin and backspin increase, the flight distance of the ball will decrease and the direction of the ball will become worse.

[0008] Therefore, there is a demand for a golf club head capable of suppressing a decrease in the flight distance of the ball even when the striking position varies from the sweet spot.

[0009] The present disclosure was devised in view of the above-described problems, and

[0010] a primary objective of the present disclosure is to provide a golf club head which can suppress a decrease in the flight distance of the ball even when the ball striking position varies from the sweet spot.Means for Solving the Problems

[0011] According to the present disclosure, a golf club head comprises a crown portion, a sole portion, a toe, a heel, and a striking face for striking a ball including a sweet spot,

[0012] wherein

[0013] the striking face comprises

[0014] a high-friction portion with high surface roughness,

[0015] a low-friction portion with low surface roughness, and

[0016] a middle-friction portion with surface roughness which is lower than that of the high-friction portion and higher than that of the low-friction portion, and

[0017] when the striking face is divided into four regions by an imaginary first axis passing through the sweet spot and an imaginary second axis passing through the sweet spot and intersecting the imaginary first axis,

[0018] the high-friction portion is located in one of the four regions which is closest to the heel and closest to the sole portion, and

[0019] the low-friction portion is located in one of the four regions which is closest to the toe and closest to the crown portion.Effects of the Invention

[0020] In the golf club head according to the present disclosure, as the frictionally-different portions are specifically-arranged as described above, it is possible to suppress decrease in the flight distance of the ball when the striking position deviates from the sweet spot.BRIEF DESCRIPTION OF THE DRAWINGS

[0021] FIG. 1 is a front view of a golf club head as an embodiment of the present disclosure.

[0022] FIG. 2 is a plan view of the golf club head.

[0023] FIG. 3 is a cross-sectional view thereof taken along line III-III in FIG. 2.

[0024] FIG. 4 is an enlarged view of the striking face thereof showing an example of the arrangement of the fine grooves.

[0025] FIG. 5 is a front view of the striking face showing a modified example of the arrangement of the fine grooves.

[0026] FIG. 6 is an enlarged cross-sectional view showing the fine groove taken in a direction perpendicular to the longitudinal direction of the fine groove.

[0027] FIG. 7 is a graph showing a surface roughness distribution of the frictionally-different portions of the striking face.

[0028] FIG. 8 is a front view of the striking face showing another example of the arrangement of the fine grooves.

[0029] FIG. 9 is a front view of the striking face showing still another example of the arrangement of the fine grooves.

[0030] FIG. 10 is a front view of a golf club head whose striking face is further provided with a decorative design.

[0031] FIG. 11 is a front view of a golf club head as an embodiment of the present disclosure.DETAILED DESCRIPTION OF THE INVENTION

[0032] Embodiments of the present disclosure will now be described in detail in conjunction with accompanying drawings.

[0033] The drawings may contain exaggerations and dimensional ratios different from the actual ratios in order to aid the understanding of the present disclosure.

[0034] For the different embodiments, the same reference numerals are given to the same or common elements, and duplicate explanations are omitted.

[0035] The specific configurations illustrated in the embodiments and the drawings are for understanding the present disclosure, and the present disclosure is not limited to such specific configurations.

[0036] As described above, FIG. 1 is a front view of a golf club head 1 (hereinafter, sometimes simply referred to as the head 1) as an embodiment of the present disclosure, FIG. 2 is a plan view thereof, and FIG. 3 is a cross-sectional view thereof taken along line III-III in FIG. 2.

[0037] As shown in FIGS. 1 to 3, the head 1 in the present embodiment is a wood-type head provided with a hollow (i) therein. The wood-type means a driver, a fairway wood, a hybrid, etc.

[0038] The head 1 in the present embodiment is for a driver.

[0039] The head 1 comprises a face portion2, a crown portion 3, a sole portion 4, a hosel portion 5, a toe 6, and a heel 7.

[0040] In FIGS. 1 to 3, the head 1 is shown under its reference state.

[0041] The reference state of a head is such a state that

[0042] the head is placed on a horizontal plane HP at a lie angle α and a loft angle β specified for the head, and

[0043] the axis (CL) of the club shaft (not shown) lies within a reference vertical plane VP.

[0044] Instead of the axis of the club shaft, the center line CL of a shaft insertion hole 5a formed in the hosel portion 5 of the head can be used in the case of the club head alone.

[0045] In this application including the specification and claims, dimensions, positions, directions and the like relating to the club head refer to those under the reference state unless otherwise noted.

[0046] In this specification, the reference state of the head is associated with an xyz coordinate system such that

[0047] the x-axis is parallel to the horizontal plane HP and perpendicular to the reference vertical plane VP;

[0048] the y-axis is parallel to both the horizontal plane HP and the reference vertical plane VP; and

[0049] the z-axis is orthogonal to both the x-axis and the y-axis.

[0050] Based on this, three directions regarding the head are defined as follows:

[0051] a front-rear direction is defined as being parallel to the x-axis;

[0052] a toe-heel direction is defined as being parallel to the y-axis; and

[0053] a crown-sole direction is defined as being parallel to the z-axis.

[0054] In the front-rear direction of the head,

[0055] the front side means the side of the face portion 2, and

[0056] the rear side means the opposite side to the front side.

[0057] The head 1 in the present embodiment is essentially made of a metal material or metal materials.

[0058] The metal materials suitable for the head 1 include stainless steel, maraging steel, titanium, titanium alloy, magnesium alloy, aluminum alloy and the like, but not to be particularly limited thereto.

[0059] Non-metallic materials such as resin and fiber-reinforced resin may be used for a portion of the head 1.

[0060] The face portion 2 has the front surface defining a striking face 10 for striking the ball.

[0061] The striking face 10 includes a sweet spot SS, and a loft angle β of 40 degrees or less is specified therefor, for example.

[0062] The sweet spot SS is a point at which a straight line drawn from the center of gravity of the head (not shown) perpendicularly to the striking face 10 intersects with the striking face 10.

[0063] FIG. 3 is a cross-sectional view of the head 1 taken along a vertical plane which is perpendicular to the reference vertical plane VP and includes the sweet spot SS.

[0064] The loft angle β means the angle of the striking face 10 with respect to the above-mentioned center line CL (reference vertical plane VP), i.e., the real loft angle.

[0065] Specifically, in the vertical cross section passing through the sweet spot SS and being perpendicular to the reference vertical plane VP, the loft angle β is an angle formed between the tangent line passing through the sweet spot SS and the reference vertical plane VP.

[0066] When a ball is struck with the striking face of the head having a loft angle β, then, based on the frictional force between the ball and the striking face, spin is generated on the struck ball.

[0067] When the loft angle β is small, the backspin rate decreases as the surface roughness (friction coefficient) of the striking face increases. But, when the loft angle β is large, the backspin rate increases as the surface roughness (friction coefficient) of the striking face increases.

[0068] This has been confirmed, for example, by “Analysis of mechanism of golf ball spinning during impact” Mechanical Dynamics and Measurement Control Lecture Papers Vol. B, No. 98-9 I, in Japan Society of Mechanical Engineers.

[0069] This phenomenon is thought to be caused by the recoil occurring in the ball.

[0070] The recoil is a type of resilience which causes the torsional elastic deformation occured inside the ball due to contact with the striking face to return to its original state.

[0071] When the recoil is strong, the spin rate decreases (recoil phenomenon).

[0072] That is, in a golf club head with a small loft angle β, when the surface roughness of the striking face becomes greater, the recoil effect becomes relatively increased, and the spin rate of the ball becomes decreased.

[0073] Further, in a golf club head with a small loft angle β, when the surface roughness of the striking face becomes smaller, the recoil effect is suppressed more, and the spin rate of the ball is increased more.

[0074] Thus, the present disclosure is based on the golf club head having the striking face whose loft angle β is not more than 40 degrees, and the present disclosure can be more suitably applied to the golf club head whose loft angle β is 5 to 40 degrees, still more suitably 5 to 32 degrees since the recoil phenomenon is more effectively occured when the loft angle is within such ranges.

[0075] FIG. 4 is an enlarged view of the striking face 10 of the head 1 shown FIG. 1.

[0076] In the present embodiment, as shown in FIG. 4, the striking face 10 comprises

[0077] a high-friction portion 10H with high surface roughness,

[0078] a low-friction portion 10L with low surface roughness, and

[0079] a middle-friction portion 10M with surface roughness which is lower than that of the high-friction portion 10H but higher than that of the low-friction portion 10L.

[0080] In the present embodiment, the high-friction portion 10H has the highest surface roughness in the striking face 10, and the low-friction portion 10L has the lowest surface roughness in the striking face 10.

[0081] When the striking face 10 is divided into four regions by an imaginary first axis V1 which passes through the sweet spot SS and an imaginary second axis V2 which passes through the sweet spot SS and intersects with the imaginary first axis V1,

[0082] the high-friction portion 10H is located in one of the four regions which is closest to the heel 7 and closest to the sole portion 4 among the four regions, and

[0083] the low-friction portion 10L is located in one of the four regions which is closest to the toe 6 and closest to the crown portion 3 among the four regions.

[0084] The imaginary first axis V1 and imaginary second axis V2 are respectively straight lines drawn on the striking face 10, passes the sweet spot SS.

[0085] As described above, when the ball is struck at a position on the striking face closer to the heel than the sweet spot, the slicing spin increases.

[0086] Further, when the ball is struck at a position on the striking face closer to the sole portion than the sweet spot, the backspin rate increases.

[0087] These increases in spin rate reduce the flight distance of the ball, so when the ball is struck on the heel side and the sole portion side of the sweet spot of the striking face, the flight distance is significantly reduced.

[0088] On the other hand, in the head 1 in the present embodiment, the high-friction portion 10H is located closest to the heel 7 and closest to the sole portion 4 among the four regions, so when the ball hits the high-friction portion 10H, the recoil phenomenon suppresses an increase in spin rate of the struck ball, and a decrease in the flight distance of the struck ball can be prevented.

[0089] Also, the variation of flight direction of the struck ball to the right side or left side can be reduced.

[0090] Further, in the head 1 in the present embodiment, the low-friction portion 10L is located closest to the toe 6 and closest to the crown portion 3 among the four regions.

[0091] When the ball is struck by the low-friction portion 10L, the increase in backspin rate due to the gear effect becomes smaller than that when the ball is struck at a position closer to the heel 7 and sole portion 4 than the sweet spot SS.

[0092] If the surface roughness of the low-friction portion 10L is increased, then the variation in flight distance of the struck ball when the striking position varies, will increase. From this perspective, in the head 1 in the present embodiment, the low-friction portion 10L is positioned in the region closest to the toe 6 and closest to the crown portion 3 among the four regions. Thereby, the variation in flight distance is reduced even when the striking position varies.

[0093] As described above, in the present embodiment, by appropriately setting the distribution of surface roughness of the portions of the striking face 10, the head 1 can control the spin of the struck ball by utilizing the recoil phenomenon. Thereby, it is possible to suppress the decrease in flight distance and the variation in flight direction to the right side or left side.

[0094] The imaginary first axis V1 extends in the crown-sole direction, and the imaginary second axis V2 extends in the toe-heel direction.

[0095] Preferably, the imaginary first axis V1 is parallel to the crown-sole direction, and the imaginary second axis V2 is parallel to the toe-heel direction, therefore, the imaginary first axis V1 is orthogonal to the imaginary second axis V2 as in the present embodiment.

[0096] However, the imaginary first axis V1 may be inclined at a nonzero angle θ1 with respect to the crown-sole direction, and the imaginary second axis V2 may be inclined at a nonzero angle θ2 with respect to the toe-heel direction.

[0097] The angles θ1 and θ2 may be not more than 15 degrees, for example.

[0098] Preferably, the intersecting angle between the imaginary first axis V1 and the imaginary second axis V2 is substantially 90 degrees.

[0099] The striking face 10 is divided by the imaginary first axis V1 and the imaginary second axis V2 into four regions: a toe-side upper region A1, a heel-side upper region A2, a toe-side lower region A3, and a heel-side lower region A4.

[0100] In the present embodiment, the high-friction portion 10H is provided in the heel-side lower region A4,

[0101] the low-friction portion 10L is provided in the toe-side upper region A1, and

[0102] the middle-friction portion 10M is provided in each of the heel-side upper region A2 and the toe-side lower region A3.

[0103] In order to obtain the above-described effects, major areas of the respective regions A1 to A4 are formed as the respective friction portions as described above.

[0104] More specifically, not less than 60% of the area of the heel-side lower region A4 is formed as the high-friction portion 10H,

[0105] not less than 60% of the area of the toe-side upper region A1 is formed as the low-friction portion 10L, and

[0106] not less than 60% of the area of the heel-side upper region A2 and not less than 60% of the area of the toe-side lower region A3 are each formed as the middle-friction portion 10M.

[0107] Preferably, substantially the entire area of the heel-side lower region A4 is formed as the high-friction portion 10H, substantially the entire area of the toe-side upper region A1 is formed as the low-friction portion 10L, and substantially the entire area of the heel-side upper region A2 and substantially the entire area of the toe-side lower region A3 are each formed as the middle-friction portion 10M.

[0108] In order to change the surface roughness of the striking face 10,

[0109] fine grooves 20 are formed on the striking face 10 having a smooth surface, and

[0110] their groove widths, groove lengths, groove depths and / or spacings between the grooves are arranged so that the striking face 10 has the high-friction portion 10H, the middle-friction portion 10M and the low-friction portion 10L.

[0111] In the present embodiment, as shown in FIG. 4. the fine grooves 20 are formed in the high-friction portion 10H and the middle-friction portion 10M.

[0112] Although not shown in the drawings, the impact area of the striking face 10 may be provided with grooves so called face lines which comply with the Rules of Golf.

[0113] In this application, the fine groove 20 is a groove having a groove depth smaller than those of grooves (face lines) which are provided in the impact area and comply with the Rules of Golf.

[0114] Specifically, the fine groove 20 is defined as having a groove depth of less than 0.025 mm.

[0115] In the case that the face lines are provided, the surface roughness of the striking face 10 is measured at positions on the striking face 10 not provided with the face lines.

[0116] The fine grooves 20 extend in the toe-heel direction and / or the crown-sole direction.

[0117] In the present embodiment, the region closer to the sole portion 4 than the sweet spot SS (i.e., each of the toe-side lower region A3 and the heel-side lower region A4) is provided with a plurality of fine grooves 20 extending in the toe-heel direction (hereinafter referred to as the first fine grooves 21). The first fine grooves 21 in this example extend continuously from a toe side to a heel side of the regions A3 and A4 merged. The first fine grooves 21 are arranged at intervals in the crown-sole direction.

[0118] In this example, the first fine grooves 21 are arranged at substantially constant intervals in the crown-sole direction.

[0119] In the present embodiment, the region closer to the heel 7 than the sweet spot SS (i.e., each of the heel-side upper region A2 and the heel-side lower region A4) is provided with a plurality of fine grooves 20 extending in the crown-sole direction (hereinafter referred to as the second fine grooves 22).

[0120] The second fine grooves 22 in this example extend continuously from a crown side to a sole side of the regions A2 and A4 merged. The second fine grooves 22 are arranged at intervals in the toe-heel direction.

[0121] In this example, the second fine grooves 22 are arranged at substantially constant intervals in the toe-heel direction.

[0122] In the present embodiment, the heel-side lower region A4 is provided with both the first fine grooves 21 and the second fine grooves 22, and

[0123] in the heel-side lower region A4, the first fine grooves 21 intersect with the second fine grooves 22.

[0124] Further, in the heel-side lower region A4, the density of the fine grooves 20 (total length of the fine grooves 20 contained per unit surface area) is highest as compared with the other regions A1 to A3.

[0125] Thus, the high-friction portion 10H is formed in the heel-side lower region A4.

[0126] In the present embodiment, on the other hand, the toe-side lower region A3 is provided with only the first fine grooves 21, the heel-side upper region A2 is provided with only the second fine grooves 22, and

[0127] the toe-side upper region A1 is not provided with fine grooves 20.

[0128] However, the toe-side upper region A1 may be provided with the fine grooves 20. In this case, the number of the fine grooves 20 has to be less than that of any other region.

[0129] As a result, the middle-friction portion 10M is formed in each of the toe-side lower region A3 and the heel-side upper region A2, and

[0130] the low-friction portion 10L is formed in the toe-side upper region A1.

[0131] When the striking face 10 is viewed from the front of the head in a perpendicular direction to the striking face 10, the fine grooves 20 in the present embodiment extend nonlinearly, although the fine grooves 20 may extend linearly.

[0132] As compared with the linear fine grooves 20, the non-linear fine grooves 20 may have a larger total groove length and thereby can effectively provide high-frictional property to the high-friction portion 10H and the like.

[0133] In the present embodiment, the non-linear fine grooves 20 each extend zigzag in a triangular waveform, but may extend in a wavy manner or gently-curved zigzag manner as shown in FIG. 5. Further, the fine groove 20 may be in the form of a dashed line, namely, a series of separate short lines.

[0134] The fine groove 20 can be formed using a variety of methods, including machining, laser milling, etching and the like.

[0135] In the present embodiment, the fine grooves 20 are formed using a laser milling method.

[0136] In the laser milling method, a computer-controlled laser is irradiated onto the striking face 10 while moving in a predetermined pathway. Thereby, a fine groove 20 is formed along the pathway.

[0137] By controlling the laser output, moving speed, etc., the groove width, groove depth, etc. of the fine groove 20 can be adjusted. For example, the groove width of the fine groove 20 is set in a range from 0.05 to 2.0 mm, preferably 0.05 to 0.4 mm.

[0138] FIG. 6 shows a cross section of the fine groove 20 in the striking face 10 taken perpendicularly to the longitudinal direction of the fine groove 20.

[0139] In the cross section shown in FIG. 6, the fine groove 20 formed by the laser milling has a substantially triangular cross section (or V-shape) such that the groove width continuously decreases as the groove depth increases.

[0140] However, the cross-sectional shape of the fine groove may be an arc shape.

[0141] Incidentally, when a fine groove is formed by machining rather than laser milling, the fine groove may have a pair of substantially parallel groove walls.

[0142] In the laser milling method, the part irradiated with the laser is locally melted and removed to form the fine grooves 20, and

[0143] some of the removed material rises up near the groove edges 20e of the fine groove 20 forming protruding portions 30 as shown in FIG. 6.

[0144] The protruding portion 30 locally protrudes from the flat surface portion 10P of the striking face 10 which is of the striking face 10 before lasering.

[0145] Such protruding portion 30 forms a ridge on the striking face 10, and can more effectively increase the surface roughness there. The protruding height of the protruding portion 30 can be adjusted by adjusting the laser output.

[0146] The preferred protruding height for the protruding portion 30 may be in a range from 1 to 3 micrometers from the flat surface portion 10P.

[0147] In this application, the above-mentioned groove depth of the fine grooves 20 refers to the groove depth (from the flat surface portion 10P) not including the protruding height of the protruding portion 30.

[0148] The fine groove 20 is formed such that, as shown in FIG. 6, the groove center line GCL becomes substantially parallel to the normal direction to the flat surface portion 10P of the striking face 10.

[0149] As another example, the fine groove 20 can be formed such that the groove center line GCL is inclined with respect to the above-mentioned normal direction.

[0150] FIG. 7 shows the preferred ranges of surface roughness for the high-friction portion 10H, the middle-friction portion 10M, and the low-friction portion 10L.

[0151] In FIG. 7, the horizontal axis represents the maximum height roughness Rz (micrometer), and the vertical axis represents the arithmetic mean roughness Ra (micrometer).

[0152] In the present embodiment, the surface roughness of the striking face 10 can be specified by using the maximum height roughness Rz and / or the arithmetic mean roughness Ra.

[0153] The maximum height roughness Rz can be used to evaluate and specify the maximum unevenness of each region of the striking face 10.

[0154] The arithmetic mean roughness Ra can be used to evaluate and specify the average roughness state of each region of the striking face 10.

[0155] The maximum height roughness Rz and arithmetic mean roughness Ra are measured in accordance with Japanese Industrial Standards (JIS) B 0601:2013, Geometrical Product Specifications (GPS)—Surface texture: Profile method—Terms, definitions and surface texture parameters.

[0156] As shown in FIG. 7, it is preferable that the high-friction portion 10H has

[0157] the maximum height roughness Rz in a range from 18 to 30 micrometers, and

[0158] the arithmetic mean roughness Ra in a range from 2.5 to 5.0 micrometers;it is preferable that the low-friction portion 10L has

[0159] the maximum height roughness Rz of not more than 10 micrometers, and

[0160] the arithmetic mean roughness Ra of not more than 1.8 micrometers;it is preferable that the middle-friction portion 10M has

[0161] the maximum height roughness Rz in a range from 8 to 20 micrometers, and

[0162] the arithmetic mean roughness Ra in a range from 1.0 to 3.3 micrometers.

[0163] FIG. 8 shows still another example of the arrangement of the fine grooves 20.

[0164] In this example, the fine grooves 20 include those extending in an arc shape as shown in FIG. 8 (hereinafter referred to as the third fine grooves 23).

[0165] Preferably, the third fine grooves 23 are arranged concentrically around the sweet spot SS of the striking face 10. In this example, each third fine groove 23 extends in a circular arc whose center is located on the sweet spot SS.

[0166] In the example shown in FIG. 8, the heel-side upper region A2, the toe-side lower region A3 and the heel-side lower region A4 are provided with the concentrically arranged third fine grooves 23. But, the toe-side upper region A1 is provided with no fine grooves 20.

[0167] Further, in this example, the spacings between the third fine grooves 23 in the heel-side lower region A4 are

[0168] smaller than the spacings between the third fine grooves 23 in the heel-side upper region A2, and

[0169] smaller than the spacings between the third fine grooves 23 in the toe-side lower region A3.

[0170] Thereby, the density of the fine grooves 20 is highest in the heel-side lower region A4, and the high-friction portion 10H is formed in the heel-side lower region A4.

[0171] The toe-side upper region A1 has a smooth surface without the fine grooves, and is formed as the low-friction portion 10L.

[0172] The heel-side upper region A2 and the toe-side lower region A3 each have the density of the fine grooves 20 lower than that of the heel-side lower region A4, and

[0173] the middle-friction portion 10M is formed in each of the regions A2 and A3.

[0174] In each of the toe-side upper region A1, the heel-side upper region A2, the toe-side lower region A3 and the heel-side lower region A4 of the striking face 10,

[0175] the surface roughness can be made constant or variable within that region by forming or not forming the fine grooves 20, and by adjusting the spacings and / or depths of the fine grooves 20 if they are formed.

[0176] When the ball is struck at a position farther away from the sweet spot SS of the striking face 10, the gear effect tends to be greater.

[0177] The above-described recoil phenomenon tends to become stronger as the surface roughness of the striking face 10 is greater. Therefore, it is preferable that, in the heel-side lower region A4, the surface roughness increases continuously or stepwise as the distance from the sweet spot SS increases toward the heel 7 and / or the sole portion 4.

[0178] In order to obtain the above-described surface roughness in the heel-side lower region A4, the spacings between the fine grooves 20 located in the high-friction portion 10H in the heel-side lower region A4 are preferably made smaller continuously or stepwise as the distance from the sweet spot SS increases, for example as shown in FIG. 9.

[0179] In this example, the spacings (Pz1, Pz2, Pz3 - - - ) between the first fine grooves 21 decrease as the distance from the sweet spot Ss toward the sole portion 4 increases such that Pz1>Pz2>Pz3 - - - , and

[0180] the spacings (Py1, Py2, Py3 - - - ) between the second fine grooves 22 decrease as the distance from the sweet spot SS toward the heel 7 increases such that Py1>Py2>Py3 - - - .

[0181] In addition to or instead of varying the spacings between the fine grooves 20, the depths of the fine grooves 20 located in the high-friction portion 10H may be varied so as to increase continuously or stepwise as the distance from the sweet spot SS increases.

[0182] Therefore, when the ball is struck at a position in the high-friction portion 10H farther away from the sweet spot SS, a greater recoil phenomenon occurs, and as a result, the occurrence of a greater gear effect can be suppressed.

[0183] In the above-described embodiments, the fine grooves 20 extending from the heel-side upper region A2 to the heel-side lower region A4 are each extended while keeping its mode (zigzag shape, wavy shape, arched shape or linear shape) over its substantially entire length from the region A2 to the region A4, and the fine grooves 20 extending from the toe-side lower region A3 to the heel-side lower region A4 are each extended while keeping its mode over its substantially entire length from the region A3 to the region A4. Such fine grooves arrangement is preferable, but not essential as follows.

[0184] FIG. 10 is a front view of a golf club head 1 as another embodiment of the present disclosure. This shows a more concrete example.

[0185] The striking face 10 in the present embodiment is also provided with fine grooves 20, which not only adjust the surface roughness as described above, but also provides a decorative design.

[0186] In the present embodiment, when distinguished by decorative design features of the fine grooves 20 formed in the striking face 10, the striking face 10 can be sectioned into a toe-side section B1, a heel-side section B2, a crown-side section B3, a sole-side section B4, and a center section B5 surrounded by the sections B1-B4.

[0187] In the embodiment shown in FIG. 10, too, by changing the groove depths of the fine grooves 20, the heel-side lower region A4 is formed as the high-friction portion 10H,

[0188] the toe-side upper region A1 is formed as the low-friction portion 10L, and

[0189] each of the heel-side upper region A2 and the toe-side lower region A3 is formed as the middle-friction portion 10M.

[0190] Specifically, in all fine grooves 20, regardless of the design features thereof,

[0191] the groove depths d1 of the fine grooves 20 extending within the heel-side lower region A4 are largest,

[0192] the groove depths d3 of the fine grooves 20 extending within the toe-side upper region A1 are smallest, and

[0193] the groove depths d2 of the fine grooves 20 extending within the heel-side upper region A2 and the toe-side lower region A3 are intermediate between d1 and d2, namely,

[0194] the relationship d1>d2>d3 is satisfied.

[0195] In the striking face 10 in the present embodiment, the sections B1-B5 distinguished by decorative design features of the fine grooves 20 do not correspond to the portions 10H, 10L and 10M defined by the actual surface roughness.

[0196] Thus, the head 1 in the present embodiment can suppress a decrease in the flight distance of the ball even when the striking position varies from the sweet spot, without hindering the decorative design provided by the fine grooves on the striking face 10.

[0197] While detailed description has been made of preferable embodiments of the present disclosure, the present disclosure can be embodied in various forms without being limited to the illustrated embodiments.Comparison Tests

[0198] Two types of golf club heads having the same shape and a loft angle of 10.5 degrees were experimentally manufactured as Example according to the present disclosure and Comparative example.

[0199] As shown in FIG. 11, the striking face 10 of the head 1 as Example was provided with linear fine grooves 20 to adjust the surface roughness.

[0200] But, the Comparative example head was provided with no fine grooves in the striking face.

[0201] The two heads were respectively attached to identical club shafts to form golf clubs.

[0202] Then, each golf club was attached to a swing robot, and a ball hitting test was conducted.

[0203] In the ball hitting test, the backspin and sidespin of the ball were measured as follows.<Ball Hitting Test>

[0204] In the ball hitting test, the ball was hit at a head speed of 42 m / s, and

[0205] the backspin and sidespin of the hit ball were measured when the center of the contact area between the ball and the striking face was at each of the following five hitting positions:

[0206] hitting position 1: the sweet spot

[0207] hitting position 2: 5 mm toward the crown portion and 15 mm toward the toe from the sweet spot, i.e. a position in the toe-side upper region,

[0208] hitting position 3: 10 mm toward the sole portion and 15 mm toward the toe from the sweet spot, i.e. a position in the toe-side lower region,

[0209] hitting position 4: 15 mm towards the heel from the sweet spot.

[0210] hitting position 5: 10 mm towards the sole portion and 15 mm towards the heel from the sweet spot, i.e. a position in the heel-side lower region.

[0211] In the Example and Comparative example, the surface roughness of the striking face at each hitting position is shown in Table 1. Here, the surface roughness was set without regard for the restrictions of the Rules of Golf.

[0212] The measurement was made, first setting the measurement range to 4 mm from the hitting position, and within that range, surface roughness was measured in multiple directions with a reference length of 0.8 mm. Then, the largest value among these measurements was adopted.TABLE 1position in toe-heel direction15 mm toward toesweet spot15 mm toward heelExamplearithmetic mean roughness Ra distributionposition5 mm toward crown1.51.54in crown-solesweet spot1.51.54direction10 mm toward sole4412Examplemaximum height roughness Rz distributionposition5 mm toward crown13.513.526in crown-solesweet spot13.513.526direction10 mm toward sole262675Comparative Examplearithmetic mean roughness Ra distributionposition5 mm toward crown1.51.51.5in crown-solesweet spot1.51.51.5direction10 mm toward sole1.51.51.5Comparative Examplemaximum height roughness Rz distributionposition5 mm toward crown13.513.513.5in crown-solesweet spot13.513.513.5direction10 mm toward sole13.513.513.5

[0213] The ball hitting test results are shown in Table 2.TABLE 2position in toe-heel direction15 mm toward toesweet spot15 mm toward heelExamplebackspin rate (rpm)position5 mm toward crown24932661—in crown-solesweet spot248224432460direction10 mm toward sole276227612632Examplesidespin rate (rpm)position5 mm toward crown−66−45—in crown-solesweet spot−53−2293direction10 mm toward sole111193298Comparative Examplebackspin rate (rpm)position5 mm toward crown25082645—in crown-solesweet spot242324542450direction10 mm toward sole277528362743Comparative Examplesidespin rate (rpm)position5 mm toward crown−139−11—in crown-solesweet spot−1215199direction10 mm toward sole167258433

[0214] From the test results, it was confirmed that, as compared to the Comparative example, the variations of the backspin and sidespin of the ball hit by the Example were kept small even when the striking position varies from the sweet spot.

[0215] Therefore, it is expected that a decrease in the flight distance of the ball and a deterioration in the flight direction of the ball can be prevented.Statement of the Present Disclosure

[0216] The present disclosure is as follows.[Present Disclosure 1]

[0217] A golf club head comprising a crown portion, a sole portion, a toe, a heel, and a striking face for striking a ball including a sweet spot,

[0218] wherein

[0219] the striking face comprises

[0220] a high-friction portion with high surface roughness,

[0221] a low-friction portion with low surface roughness, and

[0222] a middle-friction portion with surface roughness which is lower than that of the high-friction portion and higher than that of the low-friction portion, and

[0223] when the striking face is divided into four regions by an imaginary first axis passing through the sweet spot and an imaginary second axis passing through the sweet spot and intersecting the imaginary first axis,

[0224] the high-friction portion is located in one of the four regions which is closest to the heel and closest to the sole portion, and

[0225] the low-friction portion is located in one of the four regions which is closest to the toe and closest to the crown portion.[Present Disclosure 2]

[0226] The golf club head according to Present Disclosure 1, wherein the imaginary first axis extends in a crown-sole direction of the head, and

[0227] the imaginary second axis extends in a toe-heel direction of the head.[Present Disclosure 3]

[0228] The golf club head according to Present Disclosure 1 or 2, wherein

[0229] the surface roughness of the high-friction portion increases as a distance from the sweet spot increases.[Present Disclosure 4]

[0230] The golf club head according to Present Disclosure 1, 2 or 3, wherein

[0231] each of the high-friction portion and the middle-friction portion is provided with fine grooves whose groove depths are less than 0.025 mm.[Present Disclosure 5]

[0232] The golf club head according to Present Disclosure 4, wherein said fine grooves extend in the toe-heel direction and / or the crown-sole direction.[Present Disclosure 6]

[0233] The golf club head according to Present Disclosure 4, wherein said fine grooves each extend in an arc shape and are arranged concentrically around the sweet spot.[Present Disclosure 7]

[0234] The golf club head according to Present Disclosure 4, 5 or 6, wherein

[0235] in the high-friction portion, spacings between said fine grooves become smaller continuously or stepwise as a distance from the sweet spot increases.[Present Disclosure 8]

[0236] The golf club head according to any one of Present Disclosures 4 to 7, wherein

[0237] in the high-friction portion, the groove depths of said fine grooves increase continuously or stepwise as a distance from the sweet spot increases.[Present Disclosure 9]

[0238] The golf club head according to any one of Present Disclosures 4 to 8, wherein

[0239] with respect to at least one of the fine grooves, along a groove edge of the fine groove, there is formed a convex portion locally protrudes from the striking face in a cross section of the striking face in a direction perpendicular to a longitudinal direction the fine groove.[Present Disclosure 10]

[0240] The golf club head according to any one of Present Disclosures 1 to 9, wherein

[0241] the high-friction portion has

[0242] a maximum height roughness Rz in a range from 18 to 30 micrometers and

[0243] an arithmetic mean roughness Ra in a range from 2.5 to 5.0 micrometers.[Present Disclosure 11]

[0244] The golf club head according to any one of Present Disclosures 1 to 10, wherein

[0245] the low-friction portion has

[0246] a maximum height roughness Rz of not more than 10 micrometers, and

[0247] an arithmetic mean roughness Ra of not more than 1.8 micrometers.[Present Disclosure 12]

[0248] The golf club head according to any one of Present Disclosures 1 to 11, wherein

[0249] the middle-friction portion has

[0250] a maximum height roughness Rz in a range from 8 to 20 micrometers, and

[0251] an arithmetic mean roughness Ra in a range from 1.0 to 3.3 micrometers.DESCRIPTION OF THE REFERENCE SIGNS1 Golf club head

[0253] 6 Toe

[0254] 7 Heel

[0255] 10 Striking surface

[0256] 10H High-friction portion

[0257] 10L Low-friction portion

[0258] 10M Intermediate-friction portion

[0259] 20 Fine groove

[0260] 20e Groove edge

[0261] 21 First fine groove

[0262] 22 Second fine groove

[0263] 23 Third fine groove

[0264] 30 Protruding portion

[0265] A1 Toe-side upper region

[0266] A2 Heel-side upper region

[0267] A3 Heel-side lower region

[0268] A4 Heel-side lower region

[0269] SS Sweet Spot

[0270] V1 Imaginary first axis

[0271] V2 Imaginary second axis

Claims

1. A golf club head comprising a crown portion, a sole portion, a toe, a heel, and a striking face for striking a ball including a sweet spot,whereinthe striking face comprisesa high-friction portion with high surface roughness,a low-friction portion with low surface roughness, anda middle-friction portion with surface roughness which is lower than that of the high-friction portion and higher than that of the low-friction portion, andwhen the striking face is divided into four regions by an imaginary first axis passing through the sweet spot and an imaginary second axis passing through the sweet spot and intersecting the imaginary first axis,the high-friction portion is located in one of the four regions which is closest to the heel and closest to the sole portion, andthe low-friction portion is located in one of the four regions which is closest to the toe and closest to the crown portion.

2. The golf club head according to claim 1, whereinthe imaginary first axis extends in a crown-sole direction of the head, andthe imaginary second axis extends in a toe-heel direction of the head.

3. The golf club head according to claim 1, whereinthe surface roughness of the high-friction portion increases as a distance from the sweet spot increases.

4. The golf club head according to claim 2, whereinthe surface roughness of the high-friction portion increases as a distance from the sweet spot increases.

5. The golf club head according to claim 1, whereineach of the high-friction portion and the middle-friction portion is provided with fine grooves whose groove depths are less than 0.025 mm.

6. The golf club head according to claim 2, whereineach of the high-friction portion and the middle-friction portion is provided with fine grooves whose groove depths are less than 0.025 mm.

7. The golf club head according to claim 3, whereineach of the high-friction portion and the middle-friction portion is provided with fine grooves whose groove depths are less than 0.025 mm.

8. The golf club head according to claim 5, whereinsaid fine grooves extend in the toe-heel direction and / or the crown-sole direction.

9. The golf club head according to claim 4, whereinsaid fine grooves each extend in an arc shape and are arranged concentrically around the sweet spot.

10. The golf club head according to claim 5, whereinin the high-friction portion, spacings between said fine grooves become smaller continuously or stepwise as a distance from the sweet spot increases.

11. The golf club head according to claim 8, whereinin the high-friction portion, spacings between said fine grooves become smaller continuously or stepwise as a distance from the sweet spot increases.

12. The golf club head according to claim 9, whereinin the high-friction portion, spacings between said fine grooves become smaller continuously or stepwise as a distance from the sweet spot increases.

13. The golf club head according to claim 5, whereinin the high-friction portion, the groove depths of said fine grooves increase continuously or stepwise as a distance from the sweet spot increases.

14. The golf club head according to claim 9, whereinin the high-friction portion, the groove depths of said fine grooves increase continuously or stepwise as a distance from the sweet spot increases.

15. The golf club head according to claim 10, whereinin the high-friction portion, the groove depths of said fine grooves increase continuously or stepwise as a distance from the sweet spot increases.

16. The golf club head according to claim 5, whereinwith respect to at least one of the fine grooves, along a groove edge of the fine groove, there is formed a convex portion locally protrudes from the striking face in a cross section of the striking face in a direction perpendicular to a longitudinal direction the fine groove.

17. The golf club head according to claim 1, whereinthe high-friction portion has a maximum height roughness Rz in a range from 18 to 30 micrometers and an arithmetic mean roughness Ra in a range from 2.5 to 5.0 micrometers.

18. The golf club head according to claim 17, whereinthe low-friction portion has a maximum height roughness Rz of not more than 10 micrometers, and an arithmetic mean roughness Ra of not more than 1.8 micrometers.

19. The golf club head according to claim 18 whereinthe middle-friction portion has a maximum height roughness Rz in a range from 8 to 20 micrometers, and an arithmetic mean roughness Ra in a range from 1.0 to 3.3 micrometers.

Images