Golf club head

Abstract

When at least the central part of the face portion is formed with a two-layer face portion consisting of a surface face member and a back face member, the positioning accuracy and durability of the surface face member are improved. [Solution] At least the central part of the face portion 14 is formed of a two-layer face portion 34 in which a surface face member 30 constituting the face surface 1402 and a back face member 32 constituting the back surface 3001 of the surface face member 30 are superimposed. The thickness of the surface face member 30 is less than the thickness of the back face member 32, the surface face member 30 has a thickness of 0.5 mm to 2.0 mm, and the back face member 32 has a thickness of 2.0 mm to 4.0 mm. The surface face member 30 and the back face member 32 are provided with a plurality of interlocking structures 42 that can be joined in the thickness direction of the back face member 32.

Description

Technical Field

[0001] The present invention relates to a golf club head.

Background Art

[0002] As a golf club head having a hollow structure, there has been proposed a structure in which an outer peripheral edge portion of a face plate made of a fiber reinforced resin material or the like constituting a face portion is joined to an opening of a head body made of a metal material (see Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in the above prior art, there is a problem that the positioning accuracy of the face plate with respect to the opening of the head body varies due to a gap generated between the outer peripheral edge portion of the face plate and the wall portion constituting the opening of the head body. In addition, due to the structure of joining the outer peripheral edge portion of the face plate to the opening of the head body, the thinner the face plate, the more likely it is to be deformed or cracked, and there is also a problem in terms of durability. Such problems of positioning accuracy and durability are considered to occur similarly in a golf club head in which at least a central portion of the face portion is formed of at least a two-layer structure face portion in which a surface face member constituting a face surface and a back face member constituting a back face of the face portion are overlapped. The present invention has been made in view of the above circumstances, and an object thereof is to provide a golf club head that is advantageous in improving the positioning accuracy and durability of a surface face member when at least a central portion of the face portion is formed of at least a two-layer structure face portion including a surface face member and a back face member. [Means for solving the problem]

[0005] To achieve the above objective, one embodiment of the present invention is a hollow golf club head, It comprises a face portion and a hollow head body that supports the face portion, At least the central part of the face portion consists of a surface face member that constitutes the face surface and the surface face component The surface face member is formed by stacking a back face member that constitutes the back surface of the surface face member with at least two layers, the thickness of the surface face member is smaller than the thickness of the back face member, the surface face member has a thickness of 0.5 mm or more and 2.0 mm or less, the back face member has a thickness of 2.0 mm or more and 4.0 mm or less, and the surface face member and the back face member are provided with a plurality of interlocking structures that can be joined in the thickness direction of the back face member. The uneven structure is provided at least two locations on either side of the center point of the face surface, and the uneven structure provided at the two locations is a first uneven structure and a second uneven structure, the first uneven structure has a first convex portion and a first concave portion that have an elongated shape with a length greater than the width extending, and the second uneven structure has a second convex portion and a second concave portion that have an elongated shape with a length greater than the width extending, and in a reference state in which the golf club head is set up with respect to a horizontal plane according to predetermined lie angle and loft angle, the center point of the face surface is passed through The cross section obtained by cutting the head body with a plane that includes the normal and is perpendicular to the horizontal plane is defined as the face center reference cross section, and the cross section obtained by cutting the head body with a plane that includes the normal passing through the center point of the face surface and is perpendicular to the face center reference cross section is defined as the X plane, and when the face surface is viewed from the front, the first angle θ is defined as the angle between the extending direction of the first convex portion and the first concave portion and the X plane, and the second angle φ is defined as the angle between the extending direction of the second convex portion and the second concave portion and the X plane, and the absolute value of the difference between the first angle θ and the second angle φ is 45° or more and 90° or less. It is characterized by the following: [Effects of the Invention]

[0006] According to one embodiment of the present invention, it is advantageous in improving the positioning accuracy of the surface face member relative to the back face member, and because the surface face member and the back face member are stacked on top of each other, deformation and cracking of the surface face member can be suppressed even when the thickness of the surface face member is smaller than the thickness of the back face member, which is advantageous in improving durability. [Brief explanation of the drawing]

[0007] [Figure 1] This is a front view of the golf club head according to the first embodiment, as seen from the front of the face. [Figure 2] This is a cross-sectional view along line AA in Figure 1. [Figure 3] (A) is an enlarged cross-sectional view of the crown area of ​​Figure 2, and (B) is an enlarged cross-sectional view of the sole area of ​​Figure 2. [Figure 4] This is a cross-sectional view along line BB in Figure 1. [Figure 5] This is a cross-sectional view along line CC in Figure 1. [Figure 6]It is a front view of the head body with the surface face member removed. [Figure 7] It is a rear view of the surface face member seen from the side opposite to the face surface. [Figure 8] It is an enlarged perspective view of the D portion in FIG. 6. [Figure 9] It is an enlarged perspective view of the E portion in FIG. 6. [Figure 10] It is an enlarged perspective view of the F portion in FIG. 7. [Figure 11] It is an enlarged perspective view of the G portion in FIG. 7. [Figure 12] It is a sectional view taken along the H-H line in FIG. 8. [Figure 13] It is a sectional view taken along the I-I line in FIG. 8. [Figure 14] It is a sectional view taken along the J-J line in FIG. 9. [Figure 15] It is a sectional view taken along the K-K line in FIG. 9. [Figure 16] It is a sectional view taken along the L-L line in FIG. 10. [Figure 17] It is a sectional view taken along the M-M line in FIG. 10. [Figure 18] It is a sectional view taken along the N-N line in FIG. 11. [Figure 19] It is a sectional view taken along the O-O line in FIG. 11. [Figure 20] It is the first explanatory diagram showing the method of defining the center point Pc of the face surface. [Figure 21] It is the second explanatory diagram showing the method of defining the center point Pc of the face surface. [Figure 22] It is the third explanatory diagram showing the method of defining the center point Pc of the face surface. [Figure 23] It is the fourth explanatory diagram showing the method of defining the center point Pc of the face surface. [Figure 24] It is a sectional view of the golf club head showing the relationship between the center of gravity point G0 of the golf club head and the center of gravity point FG on the face surface. [Figure 25] It is a front view of the golf club head explaining the definition of the contour line I of the face surface. [Figure 26] It is a sectional view of the golf club head explaining the definition of the contour line I of the face surface. [Figure 27] This is a front view of a golf club head explaining the definition of the center point Pc of the clubface. [Figure 28] These are schematic cross-sectional views showing modified versions of the uneven structure of the surface face member and the back face member, with (A) showing the first modified version, (B) showing the second modified version, (C) showing the third modified version, and (D) showing the fourth modified version. [Figure 29] This is a schematic cross-sectional view showing a fifth modified example of the uneven structure of the front face member and the back face member. [Figure 30] This is a schematic cross-sectional view showing a sixth modified example of the uneven structure of the front face member and the back face member. [Figure 31] (A) is an enlarged cross-sectional view showing an example of the cross-sectional shape of the recess in Figure 30, and (B) is an enlarged cross-sectional view showing another example of the cross-sectional shape of the recess in Figure 30. [Figure 32] This is a schematic cross-sectional view showing a seventh modified example of the uneven structure of the front face member and the back face member. [Figure 33] This is a schematic cross-sectional view showing an eighth modified example of the uneven structure of the front face member and the back face member. [Figure 34] This is a front view of the head body of a golf club head according to the second embodiment, with the surface face member removed. [Figure 35] This is a rear view of the golf club head according to the third embodiment, showing the surface face member as viewed from the opposite side of the face surface. [Figure 36] This is a front view of the head body of a golf club head according to the fourth embodiment, with the surface face member removed. [Figure 37] This is a rear view of the golf club head according to the fourth embodiment, showing the surface face member as viewed from the opposite side of the face surface. [Figure 38] This is a plan view of the golf club head according to the fifth embodiment, as seen from the crown side. [Figure 39] This is a side view of the golf club head according to the fifth embodiment, as seen from the toe side. [Figure 40]This is a bottom view of the golf club head according to the fifth embodiment, as seen from the sole side. [Figure 41] This is a side view of the golf club head according to the fifth embodiment, as seen from the heel side. [Figure 42] This figure shows the evaluation results of the experimental example under condition 1 of the first experiment. [Figure 43] This figure shows the evaluation results of the experimental example under condition 2 of the first experiment. [Figure 44] This figure shows the evaluation results of the experimental example under condition 3 of the first experiment. [Figure 45] This figure shows the evaluation results of the experimental example under condition 1 of the second experiment. [Figure 46] This figure shows the evaluation results of the experimental example under condition 2 of the second experiment. [Figure 47] This figure shows the evaluation results of the experimental example under condition 3 of the second experiment. [Figure 48] This is a front view of a golf club head, showing Experimental Example 1 of the first experiment. [Figure 49] (A) is a plan view of the golf club head shown in Experimental Example 2 of Experiment 2, viewed from the crown side, and (B) is a bottom view viewed from the sole side. [Figure 50] (A) is a side view of the golf club head shown from the toe side, representing Experimental Example 3 of Experiment 2, and (B) is a side view shown from the heel side. [Figure 51] This diagram shows a golf club head positioned in a standard configuration, viewed from the front, and illustrates the measurement points for the amount of misalignment on the surface face. [Modes for carrying out the invention]

[0008] (First Embodiment) First, the first embodiment will be described. As shown in Figures 1 and 2, in this embodiment, the golf club head 10A is a hollow-structured wood-type golf club head (driver). The golf club head 10A comprises a face portion 14 and a hollow head body 12 that supports the face portion 14. The head body 12 is made of a metal material, and as the metal material, one or more types such as stainless steel, maraging steel, pure titanium, titanium alloy, or aluminum alloy can be used. Examples of such titanium alloys include 6-4Ti and 8-1-1Ti.

[0009] The head body 12 comprises a crown portion 16 that supports the face portion 14, a sole portion 18, and a side portion 20. The face portion 14, crown portion 16, sole portion 18, and side portion 20 each have a thickness, and a hollow portion 22 is provided inside them. The face portion 14 has vertical height and extends horizontally. The crown portion 16 has a smaller thickness than the face portion 14 and extends from the upper part of the face portion 14 toward the rear. The surface of the face portion 14, which is located opposite the hollow portion 22, is the face surface 1402 that strikes the ball. The crown portion 16 is provided with a hosel 28 that connects to the shaft S, located on the face surface 1402 side and closer to the heel 26. The golf club 100 is formed when the shaft S is connected to the hosel 28. The sole portion 18 extends from the lower part of the face portion 14 toward the rear. The side portion 20 extends between the toe edge and heel edge of the face portion 14, between the crown portion 16 and the sole portion 18, passing through the back of the face. Note that the symbols 1602, 1802, and 2002 represent the crown surface, sole surface, and side surface, respectively.

[0010] Next, we will describe the various parts of the golf club head 10A according to the embodiment, but before that, we will define the "center point Pc of the face surface 1402" which serves as the reference point for each part of the golf club head 10A.

[0011] (Specifications for the center point Pc of face surface 1402) The method for defining the center point Pc of the face surface 1402 is described below. The center point Pc of the face surface 1402 is the geometric center of the face surface 1402, and various conventionally known methods can be used to define the center point Pc, including the first and second definition methods exemplified below.

[0012] [A] First method for defining the center point Pc of the face surface 1402: This is a method for defining the center point Pc when the boundary between the face 1402 and the rest of the golf club head 10A is clear, in other words, when the periphery of the face 1402 is defined by a ridge. In this case, the face 1402 is clearly defined. Figures 20 to 23 are explanatory diagrams showing the method for defining the center point Pc of the face surface 1402.

[0013] (1) First, as shown in Figure 20, the golf club head 10A is placed on the horizontal surface HP so that the lie angle and face angle are set to the specified values. The state of the golf club head 10A at this time is considered the reference state. The set values ​​for the lie angle and face angle are, for example, the values ​​listed in the product catalog.

[0014] (2) Next, find the provisional center point c0 in the direction connecting the crown portion 16 and the sole portion 18. That is, as shown in Figure 20, a perpendicular line f0 is drawn that intersects the approximate center point of a line parallel to the horizontal plane HP connecting the toe 24 and heel 26 (hereinafter referred to as the horizontal line). The provisional center point c0 is defined as the midpoint between point a0, where the perpendicular line f0 intersects with the upper edge of the face surface 1402, and point b0, where the perpendicular line f0 intersects with the lower edge of the face surface 1402.

[0015] (3) Next, draw a horizontal line g0 passing through the provisional center point c0 as shown in Figure 21. (4) Next, as shown in Figure 22, the midpoint between point d0, where the horizontal line g0 intersects with the toe-side edge of the face surface 1402, and point e0, where the horizontal line g0 intersects with the heel-side edge of the face surface 1402, is set as the provisional center point c1.

[0016] (5) Next, as shown in Figure 23, draw a perpendicular line f1 passing through the temporary center point c1, and set the midpoint of point a1 where this perpendicular line f1 intersects with the upper edge of the face surface 1402 and point b1 where the perpendicular line f1 intersects with the lower edge of the face surface 1402 as the temporary center point c2. If the provisional center points c1 and c2 coincide, that point is defined as the center point Pc of the face surface 1402. If the provisional center points c1 and c2 do not coincide, repeat steps (2) through (5). Since the face surface 1402 is a curved surface, when determining the midpoint of the horizontal line g0 and the midpoints of the perpendicular lines f0 and f1, the lengths of the horizontal line g0 and the perpendicular lines f0 and f1 should be the lengths that follow the curved surface of the face surface 1402. The face center line CL is defined as a straight line that passes through the center point Pc and extends in a direction perpendicular to the toe-heel direction.

[0017] [B] A second method for defining the center point Pc of the face surface 1402: Next, we will explain the definition of the center point Pc when the periphery of the face surface 1402 and the other part of the golf club head 10A are connected by a curved surface, and the face surface 1402 cannot be clearly defined.

[0018] As shown in Figure 24, the golf club head 10A is hollow, the symbol G0 indicates the center of gravity of the golf club head 10A, and the symbol Lp is the straight line connecting the center of gravity G0 and the center of gravity FG on the face surface 1402. In other words, the straight line Lp is the perpendicular line of the face surface 1402 passing through the center of gravity G0. In other words, the point obtained by projecting the center of gravity G0 of the golf club head 10A onto the face surface 1402 is the center of gravity FG on the face surface 1402. Here, as shown in Figure 25, we consider a number of planes H1, H2, H3, ..., Hn that include the straight line Lp connecting the centroid G0 and the centroid FG on the face surface 1402.

[0019] As shown in Figure 26, the radius of curvature r0 of the outer surface of the golf club head 10A is measured in the cross-section obtained when the golf club head 10A is fractured along each of the planes H1, H2, H3, ..., Hn. When measuring the radius of curvature r0, the face line, punch marks, etc. on the face surface 1402 are treated as if they are not present. The radius of curvature r0 is measured continuously from the center point Pc of the face surface 1402 outwards (upwards and downwards in Figure 26). Then, in the measurement, the portion where the radius of curvature r0 first falls below a predetermined value is defined as the contour line I representing the periphery of the face surface 1402. The specified value is, for example, 200 mm. The region enclosed by contour lines I, determined based on a number of planes H1, H2, H3, ..., Hn, is defined as a face surface 1402, as shown in Figures 25 and 26.

[0020] Next, as shown in Figure 27, the golf club head 10A is placed on a horizontal surface (horizontal plane HP) such that the lie angle and face angle are at the specified values. The straight line LT extends vertically, passing through the toe-side point PT of the face surface 1402. The straight line LH extends vertically, passing through the heel-side point PH on the face surface 1402. Line LC is parallel to lines LT and LH. The distance between line LC and line LT is equal to the distance between line LC and line LH. The symbol Pu indicates the upper point of the face surface 1402, and the symbol Pd indicates the lower point of the face surface 1402. Both the upper point Pu and the lower point Pd are intersections of the line LC and the contour line I. The center point Pc is defined as the midpoint of the line segment connecting the upper point Pu and the lower point Pd.

[0021] Next, the face portion 14 of this embodiment will be described in detail. Figure 1 is a front view of the golf club head 10A according to this embodiment, and Figure 2 is a cross-sectional view of line AA in Figure 1, that is, a cross-sectional view broken at the face center line CL. In this embodiment, the face portion 14 is formed of at least a two-layer face portion 34 in which a surface face member 30 constituting the face surface 1402 and a back face member 32 constituting the back surface of the surface face member 30 are superimposed. In this embodiment, the face portion 14 is formed by a two-layer face portion 34, and the two-layer face portion 34 is provided over the entire area of ​​the face portion 14.

[0022] (Surface face member 30) The surface face member 30 has a thickness of 0.5 mm or more and 2.0 mm or less, and the thickness of the back face member 32 is 2.0 mm or more and 4.0 mm or less, with the thickness of the surface face member 30 being less than the thickness of the back face member 32. The surface face member 30 is made of a synthetic resin material or a fiber-reinforced resin material. Examples of such synthetic resin materials include thermoplastic resins such as polyphenylene sulfide (PPS), polyether ether ketone (PEEK), PA6, PA66, polyurethane (TPU), thermoplastic elastomer (TPE), and polycarbonate. Examples of thermosetting resins include phenolic resins, epoxy resins, melamine resins, urea resins, polyurethane resins, unsaturated polyester resins, diallyl phthalate resins, silicon resins, and polyimide resins. Fiber-reinforced materials include glass beads, discontinuous glass, carbon, or aramid.

[0023] (Rear face member 32) The back face member 32 is integrally molded with the head body 12, excluding the back face member 32, by casting. Therefore, the back face member 32 is made of the same metal material (e.g., titanium alloy) as the metal material that constitutes the head body 12. Of course, the head body 12 may be constructed by casting, the back face member 32 by rolling a plate, and these may be welded together to form the head body 12. Various conventionally known structures can be adopted. (gap Δt) As shown in Figure 3, the rear face member 32 is provided with a surface face member receiving recess 36 for accommodating the surface face member 30, and the surface face member 30 and the rear face member 32 are overlapped and bonded together within the surface face member receiving recess 36 via an adhesive 38, which will be described later. With the front face member 30 and the back face member 32 stacked on top of each other, a gap Δt of 0.1 mm to 1.0 mm is secured between the outer peripheral surface 3002 of the front face member 30 and the inner peripheral surface 3602 of the recess 36 that accommodates the front face member. The gap Δt is filled with adhesive (synthetic resin material) 40. This adhesive 40 may be the same adhesive 38 used to bond the surface face member 30 and the back face member 32, or it may be an adhesive different from the adhesive 38.

[0024] (Adhesive 38) The following are examples of adhesives 38 used to bond the front face member 30 and the back face member 32. The adhesive 38 can be a thermosetting adhesive 38 that is liquid and hardens when heated, or a thermoplastic hot melt adhesive. The hardness of the cured adhesive 38 at 25°C is between Shore A 40 and 95. The tanδ of the cured adhesive 38 at temperatures between 25°C and 80°C is between 0.05 and 0.4. If the hardness and tanδ of the adhesive 38 after curing are within the above range, it is advantageous in suppressing variations in the high initial velocity area, flight distance, and durability, which will be discussed later. If the hardness and tanδ of the adhesive 38 after curing are outside the above range, the above effect will be reduced. For example, the following can be used as adhesive 38. In the case of thermal curing, • Bond MOS8 (product name), an elastic epoxy resin-based elastic adhesive from Konishi Corporation. • Cemedyne Co., Ltd.'s epoxy-modified silicone elastic adhesive, Cemedyne EP001K (product name) ThreeBond Corporation's two-component, room-temperature curing, high-strength adhesive, threebond 3953 (product name) • Sekisui Bond #55 (product name) from Sekisui Fuller Co., Ltd. • Fixelon (product name) from Aicello Co., Ltd. • Metaseal (product name) from Fujimori Kogyo Co., Ltd. The aforementioned MOS8 (product name), EP001K (product name), and 3953 (product name) are two-component modified silicone / epoxy resins, while Sekisui Bond #55 (product name) is a one-component modified silicone. Additionally, fixelon (product name) and metaseal (product name) are tape-type products.

[0025] In the case of thermosetting, the adhesive 38 may contain a silyl group-terminated polymer and an organometallic catalyst necessary for the silyl groups to form a crosslinked structure through a condensation reaction. Furthermore, the terminal groups of the silyl group-terminated polymer may be represented by the following structural formula 1, and the number of such terminal groups may be an average of 1.5 to 3 per polymer molecule.

[0026] [ka]

[0027] (However, n=2 or 3, n+m=3, and R: includes at least one of CH3-, C2H5-, or C3H7-) Furthermore, the adhesive 38 may also contain an amine catalyst necessary for the epoxy resin and epoxy resin to crosslink through an addition reaction, along with the silyl group-terminated polymer.

[0028] (Uneven structure 42) As shown in Figure 1, the front face member 30 and the back face member 32 are provided with multiple interlocking structures 42 that can be joined in the thickness direction of the back face member 32. Therefore, the front face member 30 and the back face member 32 are positioned by the uneven structure 42 and bonded together with adhesive 38 to form the golf club head 10A. As shown in Figures 4 and 5, the uneven structure 42 is composed of a protrusion 44 provided on one of the surface face member 30 and the back face member 32, and a recess 46 provided on the other that can be connected to the protrusion 44. Figures 4 and 5 show the case where a protrusion 44 is provided on the front face member 30 and a recess 46 is provided on the back face member 32. In this embodiment, with the convex portion 44 and the concave portion 46 joined together and the front face member 30 and the back face member 32 joined with adhesive 38, as shown in Figure 1, the boundary line 48 between the front face member 30 and the back face member 32 is visible, and the area where the convex portion 44 and the concave portion 46 are joined together is not visible from the face surface 1402.

[0029] In this embodiment, as shown in Figures 4 and 6, the rear face member 32 is provided with two recesses 46: a toe-side recess 46T provided on the toe side and a heel-side recess 46H provided on the heel side. As shown in Figures 5 and 7, the surface face member 30 is provided with two protrusions 44: a toe-side protrusion 44T that connects to the toe-side recess 46T and a heel-side protrusion 44H that connects to the heel-side recess 46H. The uneven structure 42 is independently provided at two spaced-apart locations on the face portion 14. Furthermore, in this embodiment, as shown in Figure 1, when the face surface 1402 is viewed from the front, the uneven structure 42 is provided at least two locations on either side of the center point Pc of the face surface 1402. In other words, the two uneven structures 42 are composed of a first uneven structure 42A and a second uneven structure 42B. The first uneven structure 42A consists of a toe-side protrusion 44T as a first convex portion having an elongated shape (approximately rectangular) that extends with a length greater than its width, and a toe-side recess 46T as a first recess having an elongated shape (approximately rectangular) that extends with a length greater than its width. The second uneven structure 42B consists of a heel-side protrusion 44H as a second convex portion having an elongated shape (approximately rectangular) that extends with a length greater than its width, and a heel-side recess 46H as a second recess having an elongated shape (approximately rectangular) that extends with a length greater than its width.

[0030] The arrangement of the uneven structure 42 will be described in detail below. As shown in Figures 6 and 7, in a standard state in which the golf club head 10A is set up with predetermined lie angles and loft angles relative to the horizontal plane HP, the cross-section obtained by cutting the head body 12 with a plane that includes the normal passing through the center point Pc of the face surface 1402 and is perpendicular to the horizontal plane HP is defined as the Y plane, and the cross-section obtained by cutting the head body 12 with a plane that includes the normal passing through the center point Pc of the face surface 1402 and is perpendicular to the Y plane is defined as the X plane. When the face surface 1402 is viewed from the front, the face surface 1402 is divided into four quadrants by the X-plane and the Y-plane, and the uneven structure 42 is composed of a first uneven structure 42A and a second uneven structure 42B, which are provided in at least two diagonally opposite quadrants among the four quadrants.

[0031] Then, in Figures 6 and 7, the X and Y planes are defined as the X and Y axes, respectively, by the lines that intersect them with planes perpendicular to them. The coordinates of the center point Pc of the face surface 1402 are set as the origin (0,0). The direction from the origin toward the heel along the X axis is defined as the positive direction, and the direction from the origin toward the toe along the X axis is defined as the negative direction. The direction from the origin toward the crown portion 16 along the Y axis is defined as the positive direction, and the direction from the origin toward the sole portion 18 along the Y axis is defined as the negative direction. The values ​​of the X and Y coordinates are defined accordingly. Note that in Figure 7, the surface face member 30 is viewed from the opposite side of the face surface 1402, so the positive and negative directions of the X-axis are reversed compared to Figure 6. In Figures 6 and 7, the four quadrants demarcated by the X-axis (X-plane) and the Y-axis (Y-plane) are defined as follows: First quadrant Q1: The range where both the X and Y coordinates are positive. Second quadrant Q2: The range where the X coordinate is negative and the Y coordinate is positive. Third quadrant Q3: The range where both the X and Y coordinates are negative. Quadrant Q4: The range where the X coordinate is positive and the Y coordinate is negative.

[0032] Therefore, in this embodiment, as shown in Figure 7, the toe-side recess 46T and the heel-side recess 46H of the rear face member 32 are provided in the second quadrant Q2 and the fourth quadrant Q4, respectively. In other words, the toe-side recess 46T and the heel-side recess 46H of the rear face member 32 are provided in at least diagonal areas. Furthermore, as shown in Figure 6, the toe-side protrusion 44T and heel-side protrusion 44H of the surface face member 30 are located in the second quadrant Q2 and the fourth quadrant Q4, respectively. In other words, the toe-side protrusion 44T and heel-side protrusion 44H of the surface face member 30 are located in at least diagonal areas. In this way, when the toe-side recess 46T and heel-side recess 46H of the rear face member 32 are provided in diagonal areas, and the toe-side protrusion 44T and heel-side protrusion 44H of the front face member 30 are provided in diagonal areas, in other words, when the uneven structure 42 is provided at least two locations on either side of the center point Pc of the face surface 1402, it is advantageous in suppressing positional misalignment of the front face member 30 with respect to the rear face member 32 in the crown-sole direction and the toe-heel direction.

[0033] Furthermore, as shown in Figure 1, in a reference state in which the golf club head 10A is set up with predetermined lie angles and loft angles relative to the horizontal plane HP, the cross section obtained by cutting the head body 12 in a plane that includes the normal passing through the center point Pc of the face surface 1402 and is perpendicular to the horizontal plane HP is defined as the face center reference cross section P0 (Y plane). The first plane P1 is defined as being parallel to the face center reference cross-section P0 and located 20 mm away from the face center reference cross-section P0 towards the toe. The second plane P2 is defined as being parallel to the face center reference cross-section P0 and located 20 mm away from the face center reference cross-section P0 towards the heel. The region of the face portion 14 sandwiched between the first plane P1 and the second plane P2 is defined as the impact area IA. The impact area IA roughly coincides with the area where the impact points are concentrated. In this case, the toe-side recess 46T and heel-side recess 46H of the rear face member 32, and the toe-side protrusion 44T and heel-side protrusion 44H of the front face member 30 are provided in locations other than the impact area IA. In the aforementioned uneven structure 42, the thickness of the back face member 32 and the front face member 30 changes locally, causing the amount of deflection and rigidity of the two-layer face portion 34 to change locally. In this embodiment, since the uneven structure 42 is located outside the impact area IA where impact points are concentrated, it is advantageous in improving durability, suppressing changes in the amount of deflection and rigidity of the two-layer face section 34, and is also considered advantageous in stably obtaining the distance and high initial velocity area (sweet spot) required for the golf club head 10A. On the other hand, if such an uneven structure 42 is provided within the impact area IA where impact points are concentrated, it would be disadvantageous in terms of improving durability, as it would easily cause changes in the amount of deflection and rigidity of the two-layer face section 34, and it is possible that the effect of stably obtaining the distance and high initial velocity area (sweet spot) required of the golf club head 10A would decrease.

[0034] In this embodiment, as shown in Figures 6 and 8, the toe-side recess 46T of the rear face member 32 has an elongated shape (approximately rectangular) that extends in a direction intersecting the outer circumference (contour) of the face surface 1402 when viewed from the face surface 1402 side. Furthermore, as shown in Figure 7, the toe-side protrusion 44T of the front face member 30, which corresponds to the toe-side recess 46T of the rear face member 32, also has an elongated shape (approximately rectangular) that extends in a direction that intersects with the outer circumference of the face surface 1402, corresponding to the toe-side recess 46T. As the toe-side recess 46T and toe-side protrusion 44T exhibit an elongated shape that extends in a direction intersecting the outer circumference of the face surface 1402, this is particularly advantageous in suppressing positional misalignment of the surface face member 30 relative to the back face member 32 in the crown-sole direction. Here, when viewing the face surface 1402 from the front, if we define the first angle θ as the angle between the extending direction of the toe-side recess 46T (which is the first recess 46) and the toe-side protrusion 44T (which is the first protrusion 44) and the X-plane, then, as shown in Figure 8, the first angle θ is, for example, 10°.

[0035] Furthermore, as shown in Figures 6 and 8, the heel-side recess 46H of the rear face member 32 has an elongated shape (approximately rectangular) that extends along the outer circumference (contour) of the face surface 1402 when viewed from the face surface 1402 side. Furthermore, as shown in Figure 7, the heel-side protrusion 44H of the front face member 30, which corresponds to the heel-side recess 46H of the rear face member 32, also exhibits an elongated shape (approximately rectangular) that extends along the outer circumference of the face surface 1402, corresponding to the heel-side recess 46H. As the heel-side recess 46H and heel-side protrusion 44H have an elongated shape that extends along the outer circumference of the face surface 1402, this is particularly advantageous in suppressing positional misalignment of the surface face member 30 relative to the back face member 32 in the toe-heel direction. Here, when viewing the face surface 1402 from the front, if we define the second angle φ as the angle between the extending direction of the heel-side recess 46H (which is the second recess 46) and the heel-side protrusion 44H (which is the second protrusion 44) and the X-plane, then as shown in Figure 9, the second angle φ is, for example, 70°.

[0036] Here, it is advantageous for enhancing the effect of suppressing misalignment between the back face member 32 and the front face member 30 when the uneven structure 42 is joined, such that the absolute value of the difference (θ-φ) between the first angle θ and the second angle φ is within the range of 45° to 90°. If the absolute value of the difference (θ-φ) falls below or exceeds the range of 45° to 90°, the effect of suppressing the positional misalignment between the back face member 32 and the front face member 30 when the uneven structure 42 is joined together decreases. In this embodiment, the absolute value of the difference (θ-φ) = 10°-70° is 60°, which satisfies the condition that it is within the above range.

[0037] (Toe side uneven structure 42) Furthermore, as shown in Figure 12, which is a cross-sectional view of line HH in Figure 8, the longitudinal ends of the bottom surface 4602 of the toe-side recess 46T of the rear face member 32 and the surface 3210 of the rear face member 32 are either obtuse at an angle or connected by an arc 50 with a radius of curvature of R0.2 mm or more and R1.5 mm or less. Furthermore, as shown in Figure 16, which is a cross-sectional view along line LL in Figure 10, the longitudinal ends of the toe-side protrusion 44T of the surface face member 30 and the back surface 3001 of the surface face member 30 are either obtuse at an angle, or connected by an arc 50 with a radius of curvature of R0.2 mm or more and R1.5 mm or less. Therefore, when the toe-side recess 46T of the rear face member 32 and the toe-side protrusion 44T of the front face member 30 are connected, stress concentration between the longitudinal ends of the toe-side recess 46T and the longitudinal ends of the toe-side protrusion 44T is alleviated, thereby improving the durability of the front face member 30 and the rear face member 32. On the other hand, if the longitudinal ends of the bottom surface 4602 of the toe-side recess 46T and the surface 3210 of the back face member 32 form an acute angle, or if the longitudinal ends of the bottom surface of the toe-side recess 46T and the surface 3210 of the back face member 32 are connected by an arc with a radius of curvature less than R0.2 mm to R1.5 mm, stress concentration occurs between the longitudinal ends of the toe-side recess 46T and the longitudinal ends of the toe-side protrusion 44T, thus reducing the effectiveness of ensuring the durability of the surface face member 30 and the back face member 32. Furthermore, if both ends of the bottom surface 4602 of the toe-side recess 46T and the surface 3210 of the rear face member 32 are connected by an arc with a radius of curvature exceeding the range of R0.2 mm to R1.5 mm, the effect of ensuring positional accuracy when the toe-side recess 46T of the rear face member 32 and the toe-side protrusion 44T of the front face member 30 are joined is reduced.

[0038] Furthermore, as shown in Figure 13, which is a cross-sectional view of line II in Figure 8, the bottom surface 4602 of the toe-side recess 46T of the rear face member 32 is connected to the surface 3210 of the rear face member 32 at an obtuse angle, or by an arc 50 with a radius of curvature of R0.2 mm or more and R1.5 mm or less. Furthermore, as shown in Figure 17, which is a cross-sectional view along the MM line in Figure 10, the ends of the tow-side protrusion 4T of the surface face member 30 in the width direction perpendicular to the longitudinal direction and the back surface 3001 of the surface face member 30 are either obtuse at an angle or connected by an arc 50 with a radius of curvature of R0.2 mm or more and R1.5 mm or less. Therefore, when the toe-side recess 46T of the rear face member 32 and the toe-side protrusion 44T of the front face member 30 are connected, stress concentration between the widthwise ends of the toe-side recess 46T and the widthwise ends of the toe-side protrusion 44T is mitigated, thereby improving the durability of the front face member 30 and the rear face member 32. On the other hand, if the widthwise ends of the bottom surface of the toe-side recess 46T and the surface 3210 of the rear face member 32 form an acute angle, or if the widthwise ends of the bottom surface 4602 of the toe-side recess 46T and the surface 3210 of the rear face member 32 are connected by an arc with a radius of curvature less than R0.2 mm to R1.5 mm, then stress concentration occurs between the widthwise ends of the toe-side recess 46T and the widthwise ends of the toe-side protrusion 44T, which reduces the effectiveness of ensuring the durability of the surface face member 30 and the rear face member 32. Furthermore, if both ends of the bottom surface 4602 of the toe-side recess 46T and the surface 3210 of the rear face member 32 are connected by an arc with a radius of curvature exceeding the range of R0.2 mm to R1.5 mm, the effect of ensuring positional accuracy when the toe-side recess 46T of the rear face member 32 and the toe-side protrusion 44T of the front face member 30 are joined is reduced.

[0039] Furthermore, as shown in Figure 4, in the toe-side uneven structure 42, the dimensions perpendicular to the depth direction of the recess 46 and the dimensions perpendicular to the height of the protrusion 44 are 1 mm or more and 10 mm or less. When the recess 46 and the protrusion 44 are joined by adhesive 38, the dimensions by which the recess 46 and the protrusion 44 interlock in the depth direction of the recess 46 and the height direction of the protrusion 44 are 0.2 mm or more and 2.0 mm or less, excluding the thickness of the adhesive 38. More specifically, the longitudinal length L1 (see Figure 12), which is the dimension perpendicular to the depth direction of the toe-side recess 46T of the rear face member 32, and the width W1 (see Figure 13), which is the dimension perpendicular to both the depth direction and the longitudinal direction of the toe-side recess 46T of the rear face member 32, are between 1 mm and 10 mm. Furthermore, the longitudinal length L1' (see Figure 16), which is the dimension perpendicular to the height direction of the toe-side protrusion 44T of the rear face member 32, and the width W1' (see Figure 17), which is the dimension perpendicular to both the height direction and the longitudinal direction of the toe-side protrusion 44T of the front face member 30, are 1 mm or more and 10 mm or less. As shown in Figure 4, when the toe-side recess 46T of the rear face member 32 and the toe-side protrusion 44T of the front face member 30 are joined by adhesive 38, the interlocking dimension Dt between the toe-side recess 46T and the toe-side protrusion 44T is in the range of 0.2 mm to 2.0 mm, excluding the thickness of the adhesive 38. Therefore, it is advantageous in ensuring the durability of the surface face member 30 by suppressing stress concentration that occurs between the toe-side recess 46T and the toe-side protrusion 44T, while also ensuring positional accuracy when the toe-side recess 46T and the toe-side protrusion 44T are joined. On the other hand, if the length L1 (L1') and width W1 (W1') fall below the above range, the strength of the toe-side protrusion 44T of the surface face member 30 and the toe-side recess 46T of the back face member 32 decreases, resulting in a decrease in the effectiveness of ensuring the durability of the surface face member 30 and the back face member 32. In other words, stress concentrates in the uneven areas, and a notch effect occurs, which reduces the strength of the material. Furthermore, if the length L1 and width W1 exceed the above range, the thickness (increase in rigidity due to shape) of the surface face member 30 and the back face member 32 will increase locally. This raises concerns that the amount of deflection and rigidity of the two-layer face section 34, consisting of the surface face member 30 and the back face member 32, will change locally, potentially affecting distance and the high initial velocity area. Furthermore, if the above dimension Dt exceeds the above range, stress concentration occurs between the toe-side recess 46T and the toe-side protrusion 44T, which reduces the effectiveness of ensuring the durability of the surface face member 30 and the back face member 32. Furthermore, if the dimension Dt in the thickness direction falls below the above range, the effect of ensuring positioning accuracy when the toe-side recess 46T and the toe-side protrusion 44T are joined together decreases.

[0040] (Heel-side uneven structure 42) Furthermore, as shown in Figure 14, which is a cross-sectional view of the JJ line in Figure 9, the longitudinal ends of the bottom surface 4604 of the heel-side recess 46H of the rear face member 32 and the surface 3210 of the rear face member 32 are either obtuse at an angle or connected by an arc 50 with a radius of curvature of R0.2 mm or more and R1.5 mm or less. Furthermore, as shown in Figure 18, which is a cross-sectional view along the NN line in Figure 11, the longitudinal ends of the heel-side protrusion 44H of the surface face member 30 and the back surface 3001 of the surface face member 30 are either obtuse at an angle, or connected by an arc 50 with a radius of curvature of R0.2 mm or more and R1.5 mm or less. Therefore, when the heel-side recess 46H of the rear face member 32 and the heel-side protrusion 44H of the front face member 30 are connected, stress concentration between the longitudinal ends of the heel-side recess 46H and the longitudinal ends of the heel-side protrusion 44H is alleviated, thereby improving the durability of the front face member 30 and the rear face member 32. On the other hand, if the longitudinal ends of the bottom surface 4604 of the heel-side recess 46H and the surface 3210 of the back face member 32 form an acute angle, or if the longitudinal ends of the bottom surface 4604 of the heel-side recess 46H and the surface 3210 of the back face member 32 are connected by an arc with a radius of curvature less than R0.2 mm to R1.5 mm, stress concentration occurs between the longitudinal ends of the heel-side recess 46H and the longitudinal ends of the heel-side protrusion 44H, thus reducing the effectiveness of ensuring the durability of the surface face member 30 and the back face member 32. Furthermore, if both longitudinal ends of the bottom surface 4604 of the heel-side recess 46H and the surface 3210 of the rear face member 32 are connected by an arc with a radius of curvature exceeding the range of R0.2 mm to R1.5 mm, the effect of ensuring positional accuracy when the heel-side recess 46H of the rear face member 32 and the heel-side protrusion 44H of the surface face member 30 are joined is reduced.

[0041] Furthermore, as shown in Figure 15, which is a cross-sectional view of the KK line in Figure 9, the bottom surface 4604 of the heel-side recess 46H of the back face member 32 is connected to the surface 3210 of the back face member 32 at an obtuse angle, or by an arc 50 with a radius of curvature of R0.2 mm or more and R1.5 mm or less. Furthermore, as shown in Figure 19, which is a cross-sectional view of line OO in Figure 11, both ends of the heel-side protrusion 44H of the surface face member 30 in the width direction perpendicular to the longitudinal direction and the back surface 3001 of the surface face member 30 are either obtuse at an angle or connected by an arc 50 with a radius of curvature of R0.2 mm or more and R1.5 mm or less. Therefore, when the heel-side recess 46H of the rear face member 32 and the heel-side protrusion 44H of the front face member 30 are connected, stress concentration between the widthwise ends of the heel-side recess 46H and the widthwise ends of the heel-side protrusion 44H is alleviated, thereby improving the durability of the front face member 30 and the rear face member 32. On the other hand, if the widthwise ends of the bottom surface 4604 of the heel-side recess 46H and the surface 3210 of the rear face member 32 form an acute angle, or if the widthwise ends of the bottom surface 4604 of the heel-side recess 46H and the surface 3210 of the rear face member 32 are connected by an arc with a radius of curvature less than the range of R0.2 mm to R1.5 mm, stress concentration occurs between the widthwise ends of the heel-side recess 46H and the widthwise ends of the heel-side protrusion 44H, thus reducing the effectiveness of ensuring the durability of the surface face member 30 and the rear face member 32. Furthermore, if both ends of the bottom surface 4604 of the heel-side recess 46H and the surface 3210 of the rear face member 32 are connected by an arc with a radius of curvature exceeding the range of R0.2 mm to R1.5 mm, the effect of ensuring positional accuracy when the heel-side recess 46H of the rear face member 32 and the heel-side protrusion 44H of the front face member 30 are joined is reduced.

[0042] Furthermore, as shown in Figure 5, similar to the heel structure 42 on the toe side, in the uneven structure 42 on the heel side, the dimensions perpendicular to the depth direction of the recess 46 and the dimensions perpendicular to the height of the protrusion 44 are 1 mm or more and 10 mm or less. When the recess 46 and the protrusion 44 are joined by adhesive 38, the dimensions by which the recess 46 and the protrusion 44 interlock in the depth direction of the recess 46 and the height direction of the protrusion 44 are 0.2 mm or more and 2.0 mm or less, excluding the thickness of the adhesive 38. More specifically, the longitudinal length L2 (see Figure 14), which is the dimension perpendicular to the depth direction of the heel-side recess 46H of the surface face member 30, and the width W2 (see Figure 15), which is the dimension perpendicular to both the depth direction and the longitudinal direction of the heel-side recess 46H of the surface face member 30, are between 1 mm and 10 mm. Furthermore, the length L2' (see Figure 18), which is the dimension perpendicular to the height direction of the heel-side protrusion 44H of the rear face member 32, and the width W2' (see Figure 19), which is the dimension perpendicular to the depth direction and the longitudinal direction of the heel-side protrusion 44H of the rear face member 32, are between 1 mm and 10 mm. As shown in Figure 5, when the heel-side recess 46H of the rear face member 32 and the heel-side protrusion 44H of the front face member 30 are joined by adhesive 38, the interlocking dimension Dh between the heel-side recess 46H and the heel-side protrusion 44H is in the range of 0.2 mm to 2.0 mm, excluding the thickness of the adhesive 38. Therefore, it is advantageous in ensuring the durability of the surface face member 30 by suppressing stress concentration that occurs between the heel-side recess 46H and the heel-side protrusion 44H, while also ensuring positional accuracy when the heel-side recess 46H and the heel-side protrusion 44H are joined. On the other hand, if the length L2 (L2') and width W2 (W2') fall below the above range, the strength of the heel-side protrusion 44H of the surface face member 30 and the heel-side recess 46H of the rear face member 32 decreases, resulting in a disadvantageous notch effect that reduces the effectiveness of ensuring the durability of the surface face member 30 and the rear face member 32. Furthermore, if the length L2 and width W2 exceed the above range, the thickness (increase in rigidity due to shape) of the surface face member 30 and the back face member 32 will increase locally. This raises concerns that the amount of deflection and rigidity of the two-layer face section 34, consisting of the surface face member 30 and the back face member 32, will change locally, potentially affecting distance and the high initial velocity area. Furthermore, if the above dimension Dh exceeds the above range, stress concentration occurs between the heel-side recess 46H and the heel-side protrusion 44H, which reduces the effectiveness of ensuring the durability of the surface face member 30 and the back face member 32. Furthermore, if the dimension Dh in the thickness direction falls below the above range, the effect of ensuring positional accuracy when the heel-side recess 46H and heel-side protrusion 44H are joined together will decrease.

[0043] According to this embodiment, at least the central part of the face portion 14 is formed of a two-layer face portion 34 in which a surface face member 30 constituting the face surface 1402 and a back face member 32 constituting the back surface 3001 of the surface face member 30 are superimposed. The thickness of the surface face member 30 is smaller than the thickness of the back face member 32, the surface face member 30 has a thickness of 0.5 mm or more and 2.0 mm or less, and the back face member 32 has a thickness of 2.0 mm or more and 4.0 mm or less. The surface face member 30 and the back face member 32 are provided with a plurality of uneven structures 42 that can be joined in the thickness direction of the back face member 32. Therefore, this is advantageous in improving the positioning accuracy of the surface face member 30 relative to the back face member 32, and because the surface face member 30 and the back face member 32 are stacked on top of each other, even if the thickness of the surface face member 30 is smaller than the thickness of the back face member 32, deformation and cracking of the surface face member 30 can be suppressed, which is advantageous in improving durability. Furthermore, in this embodiment, the two-layer face portion 34 is configured to include an adhesive 38 that joins the surface face member 30 and the back face member 32, which is advantageous in that it can suppress deformation and cracking of the surface face member 30 and improve durability. Furthermore, the fact that the adhesive 38 has a hardness and tanδ within the range described above after curing is advantageous in improving durability, enhancing feel, and ensuring initial ball speed. Furthermore, in this embodiment, the uneven structure 42 is composed of a protrusion 44 provided on one of the front face member 30 and the back face member 32, and a recess 46 provided on the other that can be coupled to the protrusion 44. With the protrusion 44 and the recess 46 coupled and the front face member 30 and the back face member 32 joined by adhesive 38, the recess 46 is not open to the surface of the face portion 14 surrounding the face surface 1402. Therefore, the uneven structure 42 is not visible from the outside of the golf club head 10A, which is advantageous in improving the design of the golf club head 10A.

[0044] (Modified version of the first embodiment) Next, a modified example of the first embodiment will be described with reference to Figures 28-33. In the following description, parts and components similar to those in the first embodiment will be denoted by the same reference numerals, and their descriptions will be omitted. The description will focus on the parts that differ. The first embodiment described a case in which the recesses 46 and protrusions 44 constituting the uneven structure 42 are elongated in shape. However, in each of the following modified examples, the shape of the recesses 46 and protrusions 44 constituting the uneven structure 42 is different from that of the first embodiment, and in other respects, it is the same as the first embodiment. Therefore, in the following 1-8 modified examples, only a schematic cross-sectional view showing the uneven structure 42 will be used for explanation.

[0045] (First variation) Since the uneven structure 42 may be provided on either the toe side or the heel side, the explanation will not distinguish between the toe side and the heel side. Furthermore, in each of the following modifications, we will describe the case in which a protrusion 44 is provided on the front face member 30 and a recess 46 that can be coupled to the protrusion 44 is provided on the back face member 32. However, it goes without saying that the recess 46 may be provided on the front face member 30 and the protrusion 44 may be provided on the back face member 32. Figure 28(A) is a schematic cross-sectional view showing the uneven structure 42-1 of the first modified example. A cylindrical protrusion 44 is formed on the back surface 3001 of the front face member 30, and a recess 46 consisting of a circular cross-section hole into which the protrusion 44 can be connected is formed on the surface 3210 of the back face member 32. In the figure, the symbol A indicates a plan view of the protrusion 44 as seen from the back surface 3001 side of the surface face member 30, and the same applies to the following modified examples. In other words, the recess 46 has a bottom surface 4620 and an inner surface 4622 that rises from the outer circumference of the bottom surface 4620, and the protrusion 44 has a top surface 4420 and an outer surface 4422 that connects to the top surface 4420. The cross-section of the recess 46 in the direction perpendicular to the depth direction and the cross-section of the protrusion 44 in the direction perpendicular to the height direction are circular. Even with this first modification, the positioning of the surface face member 30 relative to the rear face member 32 is reliably achieved. It goes without saying that the cross-section of the recess 46 in the direction perpendicular to the depth direction and the cross-section of the protrusion 44 in the direction perpendicular to the height direction may be polygonal.

[0046] (Second variation) Figure 28(B) is a schematic cross-sectional view showing the uneven structure 42-2 of the second modified example. A hemispherical protrusion 44 is formed on the back surface 3001 of the front face member 30, and a hemispherical recess 46 is formed on the surface 3210 of the back face member 32, to which the protrusion 44 can be connected. This second modification also ensures that the front face member 30 is reliably positioned relative to the back face member 32.

[0047] (Third variation) Figure 28(C) is a schematic cross-sectional view showing the uneven structure 42-3 of the third modified example. Multiple cylindrical protrusions 44 are formed on the back surface 3001 of the front face member 30, arranged in a straight line, and multiple recesses 46 are formed on the surface 3210 of the back face member 32, each consisting of a circular cross-section hole into which the protrusions 44 can be connected. Even with this third modification, the positioning of the surface face member 30 relative to the back face member 32 is reliably achieved.

[0048] (Fourth variation) Figure 28(D) is a schematic cross-sectional view showing the uneven structure 42-4 of the fourth modified example. Multiple triangular cross-sectional protrusions 44 are formed on the back surface 3001 of the front face member 30, and multiple triangular cross-sectional recesses 46 are formed on the surface 3210 of the back face member 32, into which each protrusion 44 can be connected. Even with this fourth modification, the positioning of the surface face member 30 relative to the rear face member 32 is reliably achieved.

[0049] (Fifth variation) Figure 29 is a schematic cross-sectional view showing the uneven structure 42-5 of the fifth modified example. A square pyramidal protrusion 44 is formed on the back surface 3001 of the surface face member 30, and a square pyramidal recess 46 is formed on the back surface 3210 of the back face member 32, to which the protrusion 44 can be connected. Even with this fifth modification, the positioning of the surface face member 30 relative to the back face member 32 is reliably achieved.

[0050] (Sixth variation) Figure 30 is a schematic cross-sectional view showing the uneven structure 42-6 of the sixth modified example. On the back surface 3001 of the front face member 30, a protrusion 44 is formed by combining a pair of opposing trapezoidal surfaces 4430 and a pair of opposing triangular surfaces 4432, and on the surface 3210 of the back face member 32, a recess 46 is formed that can be connected to the protrusion 44. Figures 31(A) and (B) show enlarged cross-sectional views of the recess 46. Furthermore, Figure 31(A) shows an example where the corner where the bottom surface of the recess 46 and the side surface connected to the bottom surface intersect is formed by a curved surface 52. In this case, a curved surface corresponding to the shape of the curved surface 52 is formed on the convex portion 44 side. Furthermore, Figure 31(B) shows an example where the corner where the side surface of the recess 46 and the surface 3210 of the back face member 32 intersect is formed with a curved surface 54. In this case, a curved surface corresponding to the shape of the curved surface 54 is formed on the side of the convex portion 44. By providing such curved surfaces on the convex portion 44 and concave portion 46, stress concentration at the corners when the convex portion 44 and concave portion 46 are joined can be reduced, which is advantageous in improving the durability of the surface face member 30 and the back face member 32, including the uneven structure 42. Even with this sixth modification, the positioning of the surface face member 30 relative to the back face member 32 is reliably achieved.

[0051] (Seventh variation) Figure 32 is a schematic cross-sectional view showing the uneven structure 42-7 of the seventh modified example. The recess 46 is composed of a through hole 4630 formed in the rear face member 32. The protrusion 44 is composed of a pin 4440 formed on the surface face member 30 and insertable into the through hole 4630. In this embodiment, the outer surface of the pin 4440 is formed as a tapered surface, with the outer diameter decreasing from the base to the tip, and the through hole 4630 is formed as a tapered surface corresponding to the above-mentioned tapered surface. The through hole 4630 has an entrance opening 4630A into which the pin 4440 is inserted, and a rear opening 4630B where the tip of the inserted pin is located. A thick reinforcing portion 4632 is formed at the location of the rear face member 32 where the rear opening 4630B is located. This seventh modification also ensures that the front face member 30 is reliably positioned relative to the back face member 32. Furthermore, the reinforcement section 4632 improves durability.

[0052] (Variation 8) Figure 33 is a schematic cross-sectional view showing the uneven structure 42-8 of the eighth modified example. The protrusion 44 is composed of a male screw member 56 that is separate from the surface face member 30 and has a head 5602 that can be accommodated in the insertion hole 3010 formed in the surface face member 30, and a male screw portion 5604 that can be inserted into the insertion hole 3010. The recess 46 is formed through the rear face member 32 and consists of a female thread 4640 that can be screwed into the male thread portion 5604. A thick reinforcing portion 4642 is formed at the location where the female thread 4640 is formed on the back face member 32, which is located opposite the front face member 30. This ensures that the front face member 30 is positioned correctly relative to the back face member 32. Even with this eighth modification, the positioning of the surface face member 30 relative to the rear face member 32 is reliably achieved. Furthermore, the reinforcement section 4642 improves durability.

[0053] (Second Embodiment) Next, a second embodiment will be described with reference to Figures 34 and 35. The second embodiment applies the uneven structure 42-1 shown in the first modified example of Figure 28(A) described above to the first embodiment. Therefore, as shown in Figure 34, the surface 3210 of the rear face member 32 is provided with a toe-side recess 46T and a heel-side recess 46H. As shown in Figure 35, the back surface 3001 of the surface face member 30 is provided with a toe-side protrusion 44T that can be coupled to a toe-side recess 46T and a heel-side protrusion 44H that can be coupled to a heel-side recess 46H. The uneven structure 42, consisting of a toe-side recess 46T and a toe-side protrusion 44T, and the uneven structure 42, consisting of a heel-side recess 46H and a heel-side protrusion 44H, are provided in a region excluding the impact area IA, similar to the first embodiment. Furthermore, similar to the first embodiment, the two uneven structures 42 are provided flanking the center point Pc of the face surface 1402. The same effects as those of the first embodiment are achieved in this second embodiment as well.

[0054] (Third embodiment) Next, a third embodiment will be described with reference to Figures 36 and 37. The golf club head 10A of the third embodiment also comprises a face portion 14 and a head body 12 that supports the face portion 14, similar to the first embodiment. In the third embodiment, the two-layer face portion 34 is provided in the central part of the face portion 14, and the rear face member 32 is integrally formed with the head body 12. More specifically, a recess 36 for accommodating the front face member 30 is formed in the central part of the rear face member 32. Furthermore, a toe-side recess 46T and a heel-side recess 46H are formed on the bottom surface 3610 of the surface face member housing recess 36 on the toe side, and a toe-side protrusion 44T that can be coupled to the toe-side recess 46T and a heel-side recess 46H that can be coupled to the heel-side recess 46H are formed on the back surface 3001 of the surface face member 30. Furthermore, the uneven structure 42-1 shown in the first modified example of Figure 28(A) described above is also applied in the third embodiment. The uneven structure 42, consisting of a toe-side recess 46T and a toe-side protrusion 44T, and the uneven structure 42, consisting of a heel-side recess 46H and a heel-side protrusion 44H, are provided in a region excluding the impact area IA, similar to the first embodiment. Furthermore, the uneven structure 42 consisting of a toe-side recess 46T and a toe-side protrusion 44T, and the uneven structure 42 consisting of a heel-side recess 46H and a heel-side protrusion 44H, are provided on either side of the center point Pc of the face surface 1402. Then, with the toe-side recess 46T and the toe-side protrusion 44T joined together, and the heel-side recess 46H and the heel-side protrusion 44H joined together, and the surface face member 30 and the back face member 32 joined together with adhesive 38, the boundary line 48 between the surface face member 30 and the back face member 32 is visible, and the area where the protrusion 44 and the recess 46 are joined together is not visible from the face surface 1402. In this third embodiment, the same effects as in the first embodiment are achieved.

[0055] (Fourth embodiment) Next, a fourth embodiment will be described with reference to Figures 38-41. The golf club head 10A of the fourth embodiment also comprises a face portion 14 and a head body 12 that supports the face portion 14. In the fourth embodiment, the two-layer face portion 34 is provided over the entire face portion 14, and, similar to the first to third embodiments, the uneven structure 42 is composed of a protrusion 44 provided on one of the front face member 30 and the back face member 32, and a recess 46 provided on the other that can be coupled to the protrusion 44. More specifically, in the fourth embodiment, the first protrusion 44A, second protrusion 44B, third protrusion 44C, and fourth protrusion 44D, which constitute the protrusion 44, are provided projecting in the face-back direction in the vicinity of the crown portion 16, toe portion 24, sole portion 18, and heel portion 26 of the outer periphery of the surface face member 30. Furthermore, in the outer periphery of the back face member 32, near the crown portion 16, toe portion 24, sole portion 18, and heel portion 26, a first recess 46A, a second recess 46B, a third recess 46C, and a fourth recess 46C are formed, which can be connected to the first protrusion 44, second protrusion 44, third protrusion 44, and fourth protrusion 44, respectively. Then, the first protrusions 44A, second protrusions 44B, third protrusions 44C, and fourth protrusions 44D are joined to the first recesses 46A, second recesses 46B, third recesses 46C, and fourth recesses 46D, and with the surface face member 30 and the back face member 32 joined by adhesive 38, the boundary line 48 between the surface face member 30 and the back face member 32, including the area where the first protrusions 44, second protrusions 44, third protrusions 44, and fourth protrusions 44 are joined to the first recesses 46, second recesses 46, third recesses 46, and fourth recesses 46, is visible from the face surface 1402.

[0056] The recessed portion 46 and the protruding portion 44 have a length L along the boundary line 48, and the recessed portion 46 has a depth D perpendicular to the boundary line 48 and a thickness T (T is not shown) perpendicular to the boundary line 48 and the depth. The protrusion 44 has a height H that is smaller than the depth D of the recess 46 in a direction perpendicular to the boundary line 48. The recessed portion 46 and the protruding portion 44 have an engagement depth K such that the recessed portion 46 and the protruding portion 44 interlock in a direction perpendicular to the boundary line 48. The length L of the recess 46 and the protrusion 44 is 1 mm or more and 50 mm or less, the depth D is 1 mm or more and 10 mm or less, the interlocking depth K is 0.3 mm or more and 10.0 mm or less including the thickness of the adhesive 38, and the thickness T of the recess 46 is 0.5 mm or more and 2.0 mm or less. If the length L of the recesses 46 and protrusions 44 is within the above range, the depth D is within the range of 1 mm to 10 mm, the engagement depth K is within the range of 0.3 mm to 10.0 mm including the thickness of the adhesive 38, and the thickness T of the recesses 46 is within the range of 0.5 mm to 2.0 mm, it is advantageous for ensuring positional accuracy when each recess 46 and each protrusion 44 are joined. If any of the above values ​​fall below the above range, the strength of the protrusion 44 decreases, and the effect of ensuring the durability of the surface face member 30 decreases. Furthermore, if any of the above values ​​exceed the above ranges, the dimensions of the surface face member 30 and the back face member 32 will increase locally, which may cause localized changes in the amount of deflection and rigidity of the two-layer face section 34 consisting of the surface face member 30 and the back face member 32, potentially affecting distance and the high initial velocity area. In the fourth embodiment, a case was described in which a protrusion 44 is provided on the front face member 30 and a recess 46 is provided on the back face member 32. However, it goes without saying that the opposite may also be true: a recess 46 may be provided on the front face member 30 and a protrusion 44 on the back face member 32. In this fourth embodiment, as in the first embodiment, it is advantageous in improving the positioning accuracy of the surface face member 30 relative to the back face member 32. Furthermore, because the surface face member 30 and the back face member 32 are stacked on top of each other, even if the thickness of the surface face member 30 is smaller than the thickness of the back face member 32, deformation and cracking of the surface face member 30 can be suppressed, which is advantageous in improving durability.

[0057] In the embodiments described above, the case in which at least the central part of the face portion 14 is composed of a two-layer face portion 34 consisting of a front face member 30 and a back face member 32 was explained. However, it is optional, for example, to place another face member made of, for example, a synthetic resin material on top of the surface face member 30 to create a three-layer face structure, and of course, at least the central part of the face portion 14 may be composed of three or more layers.

[0058] Next, experimental examples of the present invention will be described. Figures 42-47 show the experimental results of the golf club head 10 according to the present invention (hereinafter referred to as the golf club head 10 unless otherwise specified). Ten golf club heads were prepared as samples for each experimental example, and the following four evaluation items were measured to determine the index (evaluation score), and the total score of the four indices was also calculated.

[0059] (1) Positioning accuracy The positioning accuracy was calculated using the following procedure. Ten golf club heads 10 are created for each experimental example, and after the adhesive 38 has cured, the average value of the displacement of the surface face member 30 relative to the back face member 32 is measured as the average displacement. The positioning accuracy index was calculated by multiplying the reciprocal of the value An / Ar (An = Ar) obtained by dividing the average positional displacement amount Ar of Experimental Example 1, which corresponds to the comparative example, by 100. A larger index indicates a better evaluation. For example, if An / Ar is 0.9, multiplying its reciprocal (Ar / An) by 100 gives (1 / 0.9)*100=111. If An / Ar is 0.8, multiplying its reciprocal (Ar / An) by 100 gives (1 / 0.8)*100=125.

[0060] Here, we will explain the measurement points for the displacement amount with reference to Figure 51. Figure 51 shows a front view of the golf club head 10 in its reference position, and is an explanatory diagram indicating the measurement points for the positional displacement amount on the surface face member 30. In the figure, in addition to the face-center reference section P0, the first plane P1, and the second plane P2, the third plane P3, the fourth plane P4, and the fifth plane P5 are defined. The third plane P3 is a plane parallel to the horizontal plane HP and passing through the center point Pc of the face surface 14, the fourth plane P4 is a plane parallel to the third plane P3 and spaced 12 mm away from the third plane P3 in the crown direction, and the fifth plane P5 is a plane parallel to the third plane P3 and spaced 12 mm away from the third plane P3 in the sole direction. The measurement points for positioning accuracy are defined by 12 intersections where the contour line R of the surface face member 30 intersects with the face center reference cross section P0 and the first to fifth planes P1-P5. In other words, measurement points C4, C3, and C5 are points located closer to the crown side at the intersection of the contour line R and the face center reference cross section P0, the second plane P2, and the first plane P1. Measurement points S4, S3, and S5 are points located closer to the sole side at the intersections of the contour line R and the face center reference cross section P0, the second plane P2, and the first plane P1. Measurement points H3, H2, and H4 are located near the heel side of the intersection between the contour line R and the third plane P3, the fourth plane P4, and the fifth plane P5. Measurement points T3, T2, and T4 are located near the toe side of the intersection between the contour line R and the third plane P3, the fourth plane P4, and the fifth plane P5. At each of the 12 measurement points defined in this manner, C4, C3, C5, S4, S3, S5, H3, H2, H4, T3, T2, and T4, the amount of positional displacement was measured, and the average of these 12 positional displacement amounts was calculated as the average positional displacement.

[0061] (2)Durability A golf ball was repeatedly struck against the face 1402 of a golf club head 10 fixed to a shaft using an air cannon. The number of hits required before deformation or damage to the face 1424 was measured and indexed. The ball speed was set to 50 m / s. The point of impact was the center point Pc of the face 1402. In this case, the measurement results of the golf club head 10A in Experimental Example 1, which corresponds to the comparative example, are shown as an index with a value of 100. A higher index indicates a better evaluation.

[0062] (3) Initial velocity A golf club equipped with a golf club head 10 was mounted on a swing robot, and actual hitting tests were conducted under the following conditions. The average initial velocity at 9 impact points was evaluated as an index. The index for Experimental Example 1, which corresponds to a comparative example, is set to 100, and a higher index indicates a faster initial velocity and a better evaluation. Head speed: 40 m / s The number of RBIs was calculated as follows, totaling 9 RBIs, with the player hitting the ball 5 times at each RBI location. Three impact points: the center point Pc of the face surface 140214A, a point 7mm away from the center point Pc in the to direction on a straight line passing through the center point Pc and perpendicular to the face center line CL, and a point 7mm away in the toe-heel direction. Three impact points: one point on the face center line CL, 5 mm away from the center point Pc in the direction of the crown 16; and two points on a line passing through this point and perpendicular to the face center line CL, 7 mm away from the first point in the direction of the toe and 7 mm away in the direction of the toe and heel. Three impact points: one point on the face center line CL, 5 mm away from the center point Pc in the direction of the sole 18; and two points on a line passing through this point and perpendicular to the face center line CL, 7 mm away from the first point in the direction of the toe and 7 mm away in the direction of the toe and heel.

[0063] (4) Feel The quality of the feel of the ball is primarily determined by the sound the golfer hears when hitting the ball with the golf club head. The golfer evaluates the feel by comprehensively considering three elements: the reverberation, pitch, and volume of the sound. Generally, a ball that has a moderately short reverberation and a moderately low pitch feels softer and receives a higher rating for feel. Additionally, a ball that is at a moderate pitch (approximately 3000-5000Hz) and a moderate volume (90-100 phons) also receives a higher rating for feel. The method for evaluating the feel of the ball is as follows: Using a specialized swing robot, a golf club is swung at a head speed of 40 m / s with the center point Pc as the point of impact. The sound of the golf ball being hit is measured using a sound level meter, and the vibration waveform data of the impact sound is sampled and recorded at a predetermined sampling period. Next, we calculate the reverberation parameter T. The reverberation parameter T represents the degree of decay of the sound of the ball being hit. In calculating the reverberation parameter T, first, the recorded vibration waveform data is analyzed, with the first sample data (starting point data) on the time axis being used as the reference number. From this number, a block group α is created in which the sound pressure vibration waveform is sequentially divided into a predetermined number of samples, for example, 100 samples. Then, the sum of the squares of the levels of the vibration waveforms is calculated for each block Ak of ​​block group α, and the logarithm of this sum of squares (hereafter referred to as the block value) is calculated for each block. Then, from each block in block group α, the block with the highest sound pressure value is extracted as the starting block. A value that is a predetermined amount (30 dB in this embodiment) lower than the block value of this maximum sound pressure block is set as the ending block value, and for the multiple blocks after the starting block, the ending block where the block value is first less than or equal to the ending block value is extracted. Then, the reverberation parameter T is defined as the time interval between the earliest sample data points on the time axis for each of these starting and ending blocks. Therefore, the reverberation parameter T corresponds to the reverberation time of the ball impact sound, and the shorter the reverberation parameter T, the shorter the reverberation and the softer the feel of the impact tends to be perceived. The feel of the impact, including the pitch and volume of the sound, was evaluated and shown as an index where the reciprocal of the reverberation parameter T of the golf club head 10A in Experimental Example 1, which corresponds to a comparative example, is 1 / T, with 100 being the index. A larger index indicates a better evaluation of the feel of the impact. Furthermore, while the above-mentioned reverberation parameter T, as well as the methods for calculating height and magnitude, can be those described in, for example, Japanese Patent No. 4840106, the method for evaluating the reverberation time of the ball impact is not limited, and it is possible to determine the reverberation time of the ball impact and evaluate the feel of the ball impact using various conventionally known methods. In addition to evaluating the feel of the ball by calculating reverberation parameters and reverberation time, it is also acceptable to have a golfer actually swing a golf club and hit the ball, and then evaluate the feel by listening to the sound of the ball being hit.

[0064] (5) Total score The total score was calculated by summing the four indices mentioned above: positioning accuracy, durability, initial velocity, and feel. The total score for Experimental Example 1 of Experiment 1, which corresponds to the comparative example, is set to 400, indicating that a higher total score indicates a better evaluation.

[0065] Let me explain the experimental conditions. The experiment consisted of two variations, Experiment 1 and Experiment 2, depending on the two types of uneven structures 42, as described below. 1) First experiment: Uneven structure 42 corresponding to the first to third embodiments With the convex portion 44 and the concave portion 46 joined together and the front face member 30 and the back face member 32 joined with adhesive 38, the boundary line 48 between the front face member 30 and the back face member 32 is visible, while the area where the convex portion 44 and the concave portion 46 are joined is not visible from the face surface 1402. 2) Second experiment: Uneven structure 42 corresponding to the fourth embodiment With the convex portion 44 and the concave portion 46 joined together and the front face member 30 and the back face member 32 joined with adhesive 38, the boundary line 48 between the front face member 30 and the back face member 32 is visible, and the area where the convex portion 44 and the concave portion 46 are joined together is visible from the face surface 1402.

[0066] (Experiment 1: Uneven structure 42 corresponding to the first to third embodiments) First, let me explain the first experiment. Experimental Example 1 is a comparative example and has basically the same structure as the first embodiment. It is formed by a two-layer face portion 34 in which a surface face member 30 constituting the face surface 1402 and a back face member 32 constituting the back surface of the surface face member 30 are superimposed. The two-layer structure includes an adhesive 38 that joins the surface face member 30 and the back face member 32. Note that the adhesive 38 used in Experimental Example 1 does not satisfy the requirements of claim 16 (hardness of adhesive 38, tanδ), and is the same as the adhesive used in Experimental Example 18, which will be described later. The front face member 30 and the back face member 32 are provided with two interlocking structures 42 that can be joined in the thickness direction of the back face member 32. Although the thickness of the front face member 30 is less than the thickness of the back face member 32, unlike the present invention, the thickness of the front face member 30 is 0.4 mm, which is below the range of 0.5 mm to 2.0 mm of the present invention, and the thickness of the back face member 32 is 4.1 mm, which is above the range of 2.0 mm to 4.0 mm of the present invention. Therefore, the provisions of claim 1 of the present invention are not met, and the present invention is outside its scope. Furthermore, in Experimental Example 1, as shown in Figure 48, two uneven structures 42 are provided within the impact area IA, flanking the center point Pc of the face surface 1402. The two recessed / protruding structures 42 consist of two recesses 46 provided on the rear face member 32 and two protrusions 44 provided on the front face member 30, and both the recesses 46 and protrusions 44 have a rectangular shape (elongated shape) with a length and a width smaller than the length. The specifications of each part of Experimental Example 1 are as follows: Head body material 12: Titanium alloy Ti-8al-1mo-1v Face backing material: Titanium alloy Ti-6al-4v Material of face surface component: CFRP Loft angle 10.5° Lie angle 59° Head weight: 200g Head volume: 460cc

[0067] The golf club head 10 used in Experimental Example 2-18 corresponds to the present invention, is a hollow-type driver, and shares the following specifications, except for the parameters specified in each experimental example. Head body material 12: Titanium alloy Ti-8al-1mo-1v Material for Layer 36: Titanium alloy Ti-6al-4v Thickness of the 3rd layer 36: 3.0mm (center point Pc of face surface 1402) Loft angle 10.5° Lie angle 59° Head weight: 200g Head volume: 460cc

[0068] Experimental example 2, 5-18 has a structure similar to the first embodiment (Figure 1), where the recess 46 and protrusion 44 are rectangular (elongated). Experimental Example 3 shows that the cross-sectional shape of the recessed portion 46 and convex portion 44 of the uneven structure 42 in the first embodiment is not rectangular (elongated), but rather, as in the first modified example (Figure 28(A)), the cross-sectional shape is circular. Experimental Example 4 is similar to the third embodiment (Figure 34) in that the two-layer face portion 34 is provided in the central part of the face portion 14, but the recess 46 and protrusion 44 are rectangular (elongated) in shape, similar to the first embodiment.

[0069] (Condition 1: Figure 42 / Experimental Examples 2-7) As shown in Figure 42, Experimental Example 1 is a comparative example and is outside the scope of the present invention. Experimental examples 2, 3, 6, and 7 satisfy the requirements of claims 1, 2, 3 (or 4), 5, 6, 7, 8, 13, 14, 15, and 16. Experimental examples 4 and 5 are outside the scope of the present invention, as the thicknesses of the front face member 30 and the back face member 32 are outside the range specified in claim 1. Therefore, compared to Experimental Examples 1, 4, and 5, which are outside the scope of the present invention, Experimental Examples 2, 3, 6, and 7, which are within the scope of the present invention, are superior in positioning accuracy, durability, initial velocity, feel, and overall score.

[0070] (Condition 2: Figure 43 / Experimental Example 8-13) Experimental examples 12 and 13 satisfy the requirements of claims 1, 2, 3, 6, 7, 8, 13, 14, 15, and 16. Experimental Example 8 does not satisfy the provisions of claim 1, experimental example 9 does not satisfy the provisions of claims 6 and 14, and experimental examples 10 and 11 do not satisfy the provisions of claim 5. Therefore, compared to experimental examples 8-11, experimental examples 12 and 13 are superior in positioning accuracy, durability, initial velocity, feel, and overall score. In particular, it is clear that in Experimental Example 8, the positioning accuracy is reduced because only one uneven structure 42 is provided, and in Experimental Example 9, the durability is disadvantageous because the uneven structure 42 is located within the impact area IA. Furthermore, in experimental examples 10 and 11, the length and width of the recess 46 (protrusion 44) are outside the specified range, which is disadvantageous in terms of positioning accuracy and durability.

[0071] (Condition 3: Figure 44 / Experimental Examples 14-18) Experimental examples 16 and 17 satisfy the requirements of claims 1, 2, 3, 6, 7, 8, 13, 14, 15, and 16. Experimental examples 14 and 15 do not satisfy the requirements of claim 5. Furthermore, experimental example 18, like experimental example 1, does not satisfy the requirements of claim 16 (hardness of adhesive 38, tanδ). The adhesive 38 used in Experimental Examples 1 and 18 is Scotch-Weld DP460 (product name), an epoxy adhesive manufactured by 3M Japan Ltd. Furthermore, the adhesive 38 used in Experimental Example 2-17 satisfies the requirements of claim 16 (hardness of adhesive 38, tanδ) and is the aforementioned Bond MOS8 (product name) from Konishi Corporation. Therefore, compared to experimental examples 14, 15, and 18, experimental examples 16 and 17 are superior in positioning accuracy, durability, initial velocity, feel, and overall score. In particular, in Experimental Example 8, the positioning accuracy is reduced because only one uneven structure 42 is provided. Furthermore, in Experimental Examples 14 and 15, the depth dimension of the recess 46 and the amount of engagement between the recess 46 and the protrusion 44 are outside the specified range, making them disadvantageous in terms of positioning accuracy and durability. Furthermore, in experimental example 18, it can be seen that the hardness and tanδ of adhesive 38 are outside the specified range, resulting in a disadvantage in terms of initial velocity.

[0072] (Experiment 2: Uneven structure 42 corresponding to the fourth embodiment) Next, we will describe the second experiment. The second experiment uses a golf club head 10B corresponding to the fourth embodiment. Experimental Example 1 uses the same equipment as Experiment 1, so details are omitted.

[0073] The golf club head 10B used in Experimental Example 2-21 corresponds to the present invention, is a hollow-type driver, and shares the following specifications, except for the parameters specified in each experimental example. Head body material 12: Titanium alloy Ti-8al-1mo-1v Material for Layer 36: Titanium alloy Ti-6al-4v Thickness of the 3rd layer 36: 3.0mm (center point Pc of face surface 1402) Loft angle 10.5° Lie angle 59° Head weight: 200g Head volume: 460cc

[0074] Experimental Example 2-18 has a structure that is basically the same as the fourth embodiment (Figures 38-41), except for the parts described in each experimental example. With the convex portion 44 and the concave portion 46 joined together and the surface face member 30 and the back face member 32 joined with adhesive 38, the boundary line 48 between the surface face member 30 and the back face member 32, including the area where the convex portion 44 and the concave portion 46 are joined, is visible from the face surface 1402.

[0075] (Condition 1: Figure 45 / Experimental Example 2-9) Experimental Example 1, as shown in Figure 45, is a comparative example identical to the first experimental example described above, and is outside the scope of the present invention. In Experimental Example 2, as shown in Figures 49(A) and (B), the uneven structure 42 is provided in two locations, on the crown portion 16 side and the sole portion 18 side. In Experimental Example 3, as shown in Figures 50(A) and (B), the uneven structure 42 is provided in two locations, on the heel side 24 and the toe side 26. Experimental Example 8 is provided with only one uneven structure 42, as shown in any one of Figures 38-41. Experimental Examples 4-7 and Experimental Examples 9-18, described later, have a structure in which two uneven structures 42 are provided, one on the crown portion 16 side and one on the sole side, as shown in Figures 38 and 40, or a structure in which two uneven structures 42 are provided, one on the toe side and one on the heel side, as shown in Figures 39 and 41.

[0076] Experimental examples 2, 3, 6, and 7 satisfy the requirements of claims 1, 6, 11-16. Experimental examples 4 and 5 are outside the scope of the present invention, as the thicknesses of the front face member 30 and the back face member 32 are outside the range specified in claim 1. Experimental Example 8 has only one uneven structure 42, which falls outside the scope of Claim 1 and is therefore outside the scope of the present invention. Experimental example 9 satisfies the requirements of claims 1, 11-16, but does not satisfy the requirements of claim 6 because the two uneven structures 42 are not arranged on either side of the center point Pc of the face surface 1402. Therefore, compared to Experimental Examples 1, 4, 5, and 8, which are outside the scope of the present invention, Experimental Examples 2, 3, 6, 7, and 9, which are within the scope of the present invention, are superior in positioning accuracy, durability, initial velocity, feel, and overall score. In particular, in experimental example 8, the positioning accuracy is reduced because there is only one uneven structure 42. Furthermore, in experimental example 9, since the two uneven structures 42 are not positioned with the center point Pc of the face surface 1402 in between, the balance of stress applied to the uneven structures 42 is uneven, which is disadvantageous in terms of durability.

[0077] (Condition 2: Figure 46 / Experimental Examples 11-13) Experimental examples 10 and 11 satisfy the requirements of claims 1, 6, 11-12, and 14-16, but do not satisfy the requirements of claim 13. Experimental examples 12 and 13 satisfy the requirements of claims 1, 6, and 11-16. Therefore, compared to experimental examples 10 and 11, experimental examples 12 and 13 are superior in positioning accuracy, durability, initial velocity, feel, and overall score. In particular, in experimental examples 10 and 11, the length and width dimensions of the recess 46 are either below or above the specified range, which is disadvantageous in terms of positioning accuracy and durability.

[0078] (Condition 3: Figure 47 / Experimental Examples 14-18) Experimental examples 14 and 15 satisfy the requirements of claims 1, 6, 11-12, and 14-16, but do not satisfy the requirements of claim 13. Experimental examples 16 and 17 satisfy the requirements of claims 1, 6, and 11-16. Experimental example 18 satisfies the requirements of claims 1, 6, and 11-15, but does not satisfy the requirements of claim 16. In other words, experimental example 18, like experimental example 1, does not satisfy the requirements of claim 16 (hardness of adhesive 38, tanδ), while experimental example 2-17 satisfies the requirements of claim 16 (hardness of adhesive 38, tanδ). As with the first experiment, the adhesive 38 used in Experimental Examples 1 and 18 was Scotch-Weld DP460 (trade name), and the adhesive 38 used in Experimental Example 2-17 was Bond MOS8 (trade name). Therefore, compared to experimental examples 14, 15, and 18, experimental examples 16 and 17 are superior in positioning accuracy, durability, initial velocity, feel, and overall score. In particular, in experimental examples 14 and 15, the depth dimension of the recess 46 and the amount of engagement between the recess 46 and the protrusion 44 are below or above the specified range, which is disadvantageous in terms of positioning accuracy and durability. Furthermore, in experimental example 18, it can be seen that the hardness and tanδ of adhesive 38 are outside the specified range, resulting in a disadvantage in terms of initial velocity.

[0079] In this embodiment, the case where the golf club head 10 is a hollow wood-type golf club head (driver) has been described, but the present invention is of course also applicable to hollow utility clubs and fairway woods. [Explanation of symbols]

[0080] 10A, 10B Golf Club Heads 12 Head Body 14 Face section 1402 Face 16 Crown section 1602 Crown surface 18. Sole 1802 Sole 20 Side section 2002 Side view 22 Hollow part 24 Tou 26 heels 28 Hosel 30 Surface Face Member 3001 Back 3002 Outer surface 3010 Through hole 32 Rear Face Component 3210 Surface 34 Two-layer structure face section 14 36 Surface Face Member Receiving Recess 3602 Inner surface 3610 Base 38, 40 Adhesives 42 uneven structure 42A 1st uneven structure 42B 2nd uneven structure 42-1 Uneven structure 42-2 Uneven structure 42-3 Uneven structure 42-4 Uneven structure 42-5 Uneven structure 42-6 Uneven structure 42-7 Uneven structure 42-8 Uneven structure 44 Convex part 44H Heel side protrusion 44T Tow side protrusion 4420 Top surface 4422 External surface 4430 Trapezoidal surface 4432 Triangular surface part 4440 pins 44A First protrusion 44B Second protrusion 44C Third protrusion 44D Fourth protrusion 46 recess 46H Heel side recess 46T Toe side recess 4602 Bottom 4604 Bottom 4620 Bottom 4622 Inner surface 4630 Through hole 4630A Inlet opening 4630B Rear opening 4632 Reinforcement section 4640 Female thread 4642 Reinforcement section 46A First recess 46B Second recess 46C Third recess 46D Fourth recess 48 Boundary Line 50 arc 52 Curved surface 54 Curved surface 56 Male threaded member 5602 Head 5604 Male threaded section 100 Golf Club Heads S shaft PC Face Center Point HP horizontal plane P0 Face Center Reference Section P1 1st plane P2 2nd plane IA Impact Area θ 1st angle φ 2nd angle

Claims

1. A hollow-structured golf club head, It comprises a face portion and a hollow head body that supports the face portion, At least the central portion of the face portion is formed by a two-layer face portion in which a surface face member constituting the face surface and a back face member constituting the back surface of the surface face member are superimposed. The thickness of the surface face member is smaller than the thickness of the back face member. The aforementioned surface face member has a thickness of 0.5 mm or more and 2.0 mm or less, and the aforementioned back face member has a thickness of 2.0 mm or more and 4.0 mm or less. The surface face member and the back face member are provided with a plurality of interlocking structures that can be joined in the thickness direction of the back face member. The aforementioned uneven structure is provided at least two locations on either side of the center point of the face surface, The aforementioned uneven structures provided at the two locations are a first uneven structure and a second uneven structure, The first uneven structure has a first convex portion and a first concave portion, which have an elongated shape and a length greater than the width, The second uneven structure has a second protrusion and a second recess, which are elongated in shape and have a length greater than the width. In a reference state in which the golf club head is positioned relative to a horizontal plane according to predetermined lie angles and loft angles, the cross section obtained by cutting the head body with a plane that includes the normal passing through the center point of the face and is perpendicular to the horizontal plane is defined as the face center reference cross section, and the cross section obtained by cutting the head body with a plane that includes the normal passing through the center point of the face and is perpendicular to the face center reference cross section is defined as the X plane. When the face surface is viewed from the front, the first angle θ is defined as the angle between the extending direction of the first protrusion and the first recess and the X-plane, and the second angle φ is defined as the angle between the extending direction of the second protrusion and the second recess and the X-plane. The absolute value of the difference between the first angle θ and the second angle φ is 45° or more and 90° or less. A golf club head characterized by the following features.

2. The two-layer face portion is configured to include an adhesive that joins the front face member and the back face member. The golf club head as described in feature 1.

3. The aforementioned uneven structure is composed of a protrusion provided on one of the surface face member and the back face member, and a recess provided on the other that can be coupled to the protrusion. The golf club head comprises the face portion and the head body that supports the face portion. The aforementioned two-layer face portion is provided over the entire area of ​​the face portion, The rear face member is integrally formed with the head body, With the convex portion and the concave portion joined together and the surface face member and the back face member bonded together with adhesive, the boundary line between the surface face member and the back face member is visible, and the portion where the convex portion and the concave portion are joined together is not visible from the face surface. The golf club head as described in feature 2.

4. The aforementioned uneven structure is composed of a protrusion provided on one of the surface face member and the back face member, and a recess provided on the other that can be coupled to the protrusion. The golf club head comprises the face portion and the head body that supports the face portion. The aforementioned two-layer face portion is provided in the central part of the face portion, The rear face member is integrally formed with the head body, With the convex portion and the concave portion joined together and the surface face member and the back face member bonded together with adhesive, the boundary line between the surface face member and the back face member is visible, and the portion where the convex portion and the concave portion are joined together is not visible from the face surface. The golf club head as described in feature 2.

5. The dimension perpendicular to the depth direction of the recess and the dimension perpendicular to the height of the protrusion are 1 mm or more and 10 mm or less. In the state in which the recess and the protrusion are joined by the adhesive, the interlocking dimensions of the recess and the protrusion in the depth direction of the recess and the height direction of the protrusion are 0.2 mm or more and 2.0 mm or less, including the thickness of the adhesive. A golf club head according to claim 3 or 4, characterized by the features described herein.

6. In a reference state in which the golf club head is positioned relative to a horizontal plane according to predetermined lie angles and loft angles, the cross section obtained by cutting the head body with a plane that includes a normal passing through the center point of the face and is perpendicular to the horizontal plane is defined as the face center reference cross section. When the area of ​​the face sandwiched between a first plane located parallel to the face center reference cross section and 20 mm away from the face center reference cross section toward the toe, and a second plane located parallel to the face center reference cross section and 20 mm away from the face center reference cross section toward the heel, the impact area of ​​the face is defined as follows: The aforementioned uneven structure is provided in the area of ​​the face portion excluding the impact area. The golf club head as described in feature 1.

7. The rear face member is provided with a surface face member receiving recess for accommodating the surface face member, and the surface face member and the rear face member are stacked within the surface face member receiving recess. With the aforementioned surface face member and the rear face member stacked on top of each other, a gap is secured between the outer peripheral surface of the surface face member and the inner peripheral surface of the recess that accommodates the surface face member. The aforementioned gap is filled with adhesive. The golf club head as described in feature 1.

8. The adhesive has a hardness of Shore A 40 or higher and 95 or lower at 25°C after curing, and a tanδ of 0.05 or higher and 0.4 or lower at 25°C to 80°C after curing. The golf club head as described in feature 2.

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