Patent Description:
For an iron golf club such as a wedge, it is required that a consistent backspin be applied irrespective of climate including weather, temperature, and/or humidity. In order to reduce a decrease in the amount of backspin with a wet face surface in a situation such as a rainy day, for example, <CIT> (PTL <NUM>) discloses an iron-type golf club head including, between scorelines provided in the face, grooves thinner than the scorelines. PTL <NUM> discloses a head of a golf club, wherein a large number of polygonal face grooves centering on a sweet spot area are provided concentrically on the face surface. PTL <NUM> discloses a gold club head with a striking surface including a toe area and striking area, the toe area including cruciform patterns and the striking area including parallel grooves and at least one pattern made by electro-etching.

In order to further improve spin performance in the wet state, however, it is desirable to discharge a water drop on the face more effectively.

The present invention has been made to solve the above problem and has an object to provide an iron golf club head that has high drainage performance and facilitates application of backspin also in the wet state.

To solve the above problem, according to the present invention, an iron golf club head with a plurality of scorelines in a face surface is provided according to the disclosure of the appended claims.

Thus, when a ball is hit in a wet state, a water drop squeezed between the face and the ball can be discharged efficiently to the scorelines, leading to improved spin performance in the wet state.

The present invention can provide an iron golf club head that facilitates application of backspin also in the wet state.

<FIG> is a front view of an iron golf club head (hereinafter referred to as "head" as appropriate) <NUM> according to the present invention.

Referring to <FIG>, head <NUM> includes a neck portion <NUM>, which is connected with a shaft, and a main body <NUM>, which is a ball hitting portion. Main body <NUM> includes a face <NUM>, which is a ball hitting surface, a sole <NUM>, which is a bottom of head <NUM>, a top edge <NUM>, which is an upper edge portion of head <NUM>, a heel <NUM>, which connects a lower end of neck portion <NUM> and sole <NUM>, a toe <NUM>, which connects sole <NUM> and top edge <NUM> at a position at which toe <NUM> faces heel <NUM>, and a leading edge <NUM>, which defines a boundary between face <NUM> and sole <NUM>. Head <NUM> may be of any type as long as it is an iron-type golf club head, and particularly, is preferably a wedge-type iron golf club head that is required to facilitate application of backspin.

Face <NUM> is provided with a plurality of scorelines <NUM>. Scorelines <NUM> are provided at a vertical interval of about <NUM> in a toe-heel direction. Scoreline <NUM> has a width of, for example, not less than <NUM> and not more than <NUM> and a depth of, for example, not less than <NUM> and not more than <NUM>. Scorelines <NUM> can be formed by forging, casting, engraving, or the like.

A microgroove <NUM> narrower than scoreline <NUM> is provided between scorelines <NUM>. In the present invention, microgrooves <NUM> mainly function as a drainage path for discharging a water drop adhering to face <NUM> to scorelines <NUM> when a ball is hit.

<FIG> shows one microgroove <NUM> in Embodiment <NUM>. Microgroove <NUM> includes at least an inclined groove <NUM> extending in a direction from a lower right to an upper left of face <NUM> as seen from the front, that is, a heel leading edge-toe top edge direction (hereinafter referred to as "HL-TT direction") while inclining to be connected to an upper scoreline <NUM>.

Inclined groove 20a is provided in microgroove <NUM> for the following reason. Inventors of the present invention used a high-speed camera to check a motion of a water drop when a ball was hit with the water drop adhering to face <NUM>. Specifically, "T7" available from MIZUNO Corporation was fixed to a golf robot "mechanical golfer" available from Miyamae Co. and was set such that a carry of <NUM> yards was provided. Subsequently, a sprayer was used to spray water onto the ball twice and the surface of face <NUM> twice to achieve a wet state, and then, the ball was hit with the golf robot. Subsequently, images of the state of the surface of face <NUM> when the ball was hit were taken with a high-speed camera "Fastcam SA-X2" available from Photron Limited. Images were taken every <NUM> up to <NUM> after hitting of the ball.

The inventors checked the taken images to find out that a water drop squeezed between face <NUM> and the ball flowed toward top edge <NUM>. During golf swing, a centrifugal force in the HL-TT direction is generated on the surface of face <NUM>. Accordingly, minute inclined groove 20a extending in the HL-TT direction is provided between scorelines <NUM>, and the upper end of inclined groove 20a is connected to scoreline <NUM>, thereby effectively discharging a water drop on face <NUM> to scoreline <NUM>.

In the present invention, microgrooves, each of which includes at least inclined groove 20a extending in the HL-TT direction while inclining to be connected to an upper scoreline <NUM>, are provided between scorelines <NUM> based on the above finding. In head <NUM> according to Embodiment <NUM>, an approximately Y-shaped microgroove <NUM> with inclined groove 20a as a left inclination of "Y"-shape is disposed between scorelines <NUM> for further enhanced drainage performance. Microgroove <NUM> in Embodiment <NUM> will now be described in detail.

Referring to <FIG>, microgroove <NUM> is composed of inclined groove 20a extending in the HL-TT direction, an upper groove 20b extending in the direction from the lower left to the upper right of face <NUM> as seen from the front, that is, the tow leading edge-heel top edge direction (hereinafter referred to as "TL-HT" direction), and a lower groove 20c extending substantially perpendicular to scoreline <NUM>. Microgroove <NUM> can be provided through publicly known laser machining. Microgroove <NUM> has a groove width of, for example, <NUM> to <NUM> and a depth of, for example, <NUM> to <NUM>.

Inclined groove 20a and upper groove 20b are gently curved in a projecting manner toward top edge <NUM>. This can increase an area which is occupied by microgroove <NUM> machined in face <NUM>, leading to an enhanced drainage effect. It should be noted that inclined groove 20a and upper groove 20b may have a linear shape or a shape curved in a projecting manner toward leading edge <NUM>.

Although an angle formed between inclined groove 20a and upper groove 20b may have any value, from the perspective of increased density at which microgroove <NUM> is machined, the angle is made to such an extent that inclined groove 20a of microgroove <NUM> preferably intersects upper grooves 20b of microgrooves <NUM> third to fifth on the left from the relevant microgroove <NUM>, as will be described below.

<FIG> is a partially enlarged view of face <NUM>, which shows two scorelines <NUM> and microgrooves <NUM> formed therebetween. In Embodiment <NUM>, microgrooves <NUM> of the same shape are successively disposed such that inclined groove 20a of microgroove <NUM> and upper groove 20b of its adjacent microgroove <NUM> intersect each other.

Inclined groove 20a and upper groove 20b each have an upper end connected to an upper line <NUM>, and lower groove 20c is connected to a lower scoreline <NUM>. The lower end of lower groove 20c may not be necessarily connected to lower scoreline <NUM>.

Although microgroove <NUM> may have any Y shape and may be disposed at any interval between scorelines <NUM> as long as it includes groove 20a, microgroove <NUM> preferably has a Y shape in which, when a part between scorelines <NUM> is divided into two equal parts parallel to scorelines <NUM>, an area where microgrooves <NUM> provided in a region on the top edge <NUM> side are machined is larger than an area where microgrooves <NUM> provided in a region on the leading edge <NUM> side are machined. The reason for this is as follows: since a water drop adhering to face <NUM> flows toward top edge <NUM> when a ball is hit, a large number of microgrooves <NUM> can be machined on the top edge <NUM> side between two scorelines <NUM> for enhanced drainage effect, as described above.

From the viewpoint of an enhanced drainage effect, a longer inclined groove 20a is more preferable. In contrast, when securing spin performance in the dry state is desired together with drainage performance in the wet state, lower groove 20c is desirably secured for a certain length. In other words, an excessively short lower groove 20c results in a small area of a smooth region sandwiched between adjacent lower grooves 20c. In the dry state, a spin is applied more easily when face <NUM> and the ball contact in a larger area, and accordingly, the smooth region is preferably present in a large area on face <NUM>.

To attain drainage performance in the wet state and spin performance in the dry state, thus, the lower end of inclined groove 20a is preferably set such that, when a length between scorelines <NUM> is divided into four equal parts, the lower edge is located above lower scoreline <NUM> by at least a quarter of the length. As a result, microgrooves <NUM> can be disposed densely in the region on the top edge <NUM> side with the smooth region left in the region between scorelines <NUM> in a certain range, attaining spin performance in the wet state and spin performance in the dry state.

From the viewpoint of arithmetic mean roughness Ra of the surface of face <NUM> (which conforms to JIS B <NUM>, will be referred to as "surface roughness (Ra)"), the shape and arrangement of microgroove <NUM> described above can be defied as follows.

When a part between scorelines <NUM> between which Y-shaped microgrooves <NUM> are provided is divided into two equal parts, inclined grooves 20a and upper grooves 20c inclined at a constant angle with respect to scoreline <NUM> are mainly machined in the region on the top edge <NUM> side, and lower grooves 20c perpendicular to scoreline <NUM> are mainly machined in the region on the leading edge <NUM> side. Thus, the surface roughness (Ra) in the toe-heel direction (hereinafter referred to as "TH direction") in the region on the top edge <NUM> side is greater than the surface roughness (Ra) in the TH direction in the region on the leading edge <NUM> side.

From the viewpoint of the surface roughness (Ra) in the TH direction, thus, it suffices that microgroove <NUM> has such a Y shape that includes groove 20a connected to upper scoreline <NUM> and satisfies relation "TH-direction surface roughness (Ra) on the leading edge <NUM> side < TH-direction surface roughness (Ra) on the top edge <NUM> side". As long as such a condition (hereinafter referred to as "condition <NUM>") is satisfied, lengths of inclined groove 20a, upper groove 20b, and lower groove 20c, an angle formed between upper groove 20b and lower groove 20c, the length between inclined groove 20a and upper groove 20b which is measured on upper scoreline <NUM>, the interval between adjacent microgrooves 20a, or the like may have any value.

When microgroove <NUM> has an approximately Y shape, in comparison between the surface roughness (Ra) in the TH direction and the surface roughness (Ra) in the top edge <NUM>-leading edge <NUM> direction (hereinafter referred to as "UD direction") between two scorelines <NUM>, the surface roughness (Ra) in the TH direction is greater than the surface roughness (Ra) in the UD direction.

From the viewpoint of the surface roughnesses (Ra) in the TH direction and the UD direction, it suffices that microgroove <NUM> has such a Y shape that includes inclined groove 20a connected to upper scoreline <NUM> and satisfies relation "UD-direction surface roughness (Ra) < TH-direction surface roughness (Ra)". As long as such a condition (hereinafter referred to as "condition <NUM>") is satisfied, lengths of inclined groove 20a, upper groove 20b, and lower groove 20c, an angle formed between upper groove 20b and lower groove 20c, the interval between adjacent microgrooves 20a, or the like may have any value.

Microgrooves <NUM> disposed between two scorelines <NUM> may have different Y shapes. <FIG> is a partially enlarged view of face <NUM> in which two types of microgrooves <NUM> with lower grooves 20c of different lengths are disposed alternately. As shown in <FIG>, also when microgrooves <NUM> with lower grooves 20c of different lengths are disposed, from the viewpoint of drainage performance, microgroove <NUM> preferably has a Y shape in which, when a part between scorelines <NUM> is divided into two equal parts in parallel with scorelines <NUM>, an area where microgrooves <NUM> provided in the region on the top edge <NUM> side are machined is larger than the area in which microgrooves <NUM> provided in the region on the leading edge <NUM> side are machined.

In the case where securing spin performance in the dry state is taken into consideration, when a length between scorelines <NUM> is divided into four equal parts, the lower end of inclined groove 20a with a shorter lower groove 20c is preferably set to be located above lower scoreline <NUM> by at least a quarter of the length. Moreover, from the viewpoint of surface roughness (Ra), it suffices that such a Y shape that satisfies condition <NUM> or condition <NUM> is provided.

Microgroove <NUM> according to the present invention is configured as described above. Iron golf club head <NUM> according to the present invention can be obtained by forming scorelines <NUM> in a head main body molded through forging or casting and then providing microgrooves <NUM> described above between scorelines <NUM>. Head <NUM> may be subjected to plating such as nickel (Ni)-chrome (Cr) plating, or the surface of face <NUM> may be subjected to milling. The iron golf club according to the present invention can be obtained by inserting a shaft (not shown) into neck portion <NUM> of the thus obtained head <NUM> for fixing and then attaching a grip to the shaft.

As described above, in iron golf club head <NUM> according to Embodiment <NUM>, microgrooves <NUM> each including at least inclined groove 20a are disposed between two scorelines <NUM>, where inclined groove 20a extends in the heel leading edge-toe top edge direction and is connected to upper scoreline <NUM>. Thus, a water drop that is squeezed between face <NUM> and the ball and flows toward top edge <NUM> can be discharged effectively to upper scoreline <NUM>. This leads to enhanced spin performance in the wet state.

Since it suffices that microgroove <NUM> according to the present invention includes inclined groove 20a extending in the HL-TT direction to be connected to upper scoreline <NUM>, the shape of microgroove <NUM> is not necessarily limited to the Y shape. For example, inclined groove 20a extending linearly in the HL-TT direction (for convenience of illustration, one inclined groove 20a is indicated by the bold line in <FIG>) itself may serve as microgroove <NUM>, and such inclined grooves 20a may be provided at predetermined intervals, as shown in <FIG>. In this case, drainage performance can be enhanced by connecting inclined grooves 20a with short longitudinal grooves.

Alternatively, as shown in <FIG>, inclined grooves 20a of semi-cylindrical shape which extend in the HL-TT direction (for convenience of illustration, one inclined groove 20a is indicated by the bold line in <FIG>) themselves may serve as microgrooves <NUM>, and such inclined grooves 20a may be provided at predetermined intervals. Inclined grooves 20a are formed by repetitively arranging, in the TH direction, shallow U-shaped grooves curved in a projecting manner toward leading edge <NUM> and then arranging such repetitive arrangements in the UD direction while displacing the repetitive arrangements from each other at predetermined intervals. In this case, drainage performance can be enhanced by connecting microgrooves <NUM> with arc-shaped grooves.

As examples of the present invention, heads <NUM> of Examples <NUM> to <NUM> with microgrooves <NUM> of different shapes were produced, and shafts were attached to heads <NUM>, thereby producing golf clubs according to Examples <NUM> to <NUM>. In all of heads <NUM> according to Examples <NUM> to <NUM>, microgrooves <NUM> were laser-machined with a laser beam machine in face <NUM> of "T7" available from MIZUNO Corporation (loft angle: <NUM>°, bounce angle: <NUM>°, lie angle: <NUM>°, number of scorelines: <NUM>, interval between scorelines: <NUM>). Microgrooves <NUM> of Examples <NUM> to <NUM> will be described in detail as follows.

In Example <NUM>, Y-shaped microgrooves <NUM> of the same shape were provided between scorelines <NUM>, as shown in <FIG>. Inclined grooves 20a and upper grooves <NUM> were shaped to be curved gently and upwardly. Inclined grooves 20a and upper grooves 20b were connected to upper scoreline <NUM>, and lower grooves 20c were connected to lower scoreline <NUM>. In microgroove <NUM>, the length of lower groove 20c was <NUM>, and the length between inclined groove 20a and upper groove 20b, measured on upper scoreline <NUM>, was <NUM>. Inclined groove 20a had a width of <NUM> and a depth of <NUM>. Lower grooves 20c of adjacent microgrooves <NUM> were disposed at an interval of <NUM>.

In Example <NUM>, two types of Y-shaped microgrooves <NUM> with lower grooves 20c of different lengths were provided between scorelines <NUM>, as shown in <FIG>. Inclined groove 20a and upper groove 20b each had a linear shape. In a first microgroove <NUM> with a longer lower groove 20c, the length of lower groove 20c was <NUM>, and the length between inclined groove 20a and upper groove 20b measured on upper scoreline <NUM> was <NUM>. In a second microgroove <NUM> with a shorter lower groove 20c, the length of lower groove 20c was <NUM>, and the length between inclined groove 20a and upper groove 20b measured on upper scoreline <NUM> was <NUM>. First and second microgrooves <NUM> were alternately and repetitively provided at an interval of <NUM>. Also, in both of first and second microgrooves <NUM>, inclined grooves 20a and upper grooves 20b were connected to upper scoreline <NUM>, and lower grooves 20c were connected to lower scoreline <NUM>.

In Example <NUM>, linear inclined grooves 20a extending in the HL-TT direction were provided in the TH direction at an interval of <NUM>, as shown in <FIG>. In Example <NUM>, inclined groove 20a itself was microgroove <NUM>. Inclined groove 20a was extended at an angle of about <NUM>° with respect to the scoreline. Inclined grooves 20a were connected to each other at an interval of <NUM> by short longitudinal grooves perpendicular to scorelines <NUM>.

In Example <NUM>, shallow U-shaped grooves were repetitively arranged to provide continuous semicircular inclined grooves 20a extending in the HL-TT direction at an interval of <NUM> in the TH direction, as shown in <FIG>. In Example <NUM>, inclined groove 20a itself was microgroove <NUM>. The shallow U-shape had a width of <NUM> and a height of <NUM>.

On the other hand, "T7" available from MIZUNO Corporation was prepared as Comparative Example <NUM>. The specific configuration of the head of Comparative Example <NUM> was identical to those of Examples <NUM> to <NUM> except for that no microgrooves <NUM> were provided.

An amount of backspin and a carry were measured in each of the wet state and the dry state using Examples <NUM> to <NUM> and Comparative Example <NUM>. The amount of backspin was measured with a "mechanical golfer" available from Miyamae Co. by measuring the number of rotations of backspin in <NUM>-yard shot with the iron golf clubs according to Examples <NUM> to <NUM> and Comparative Example <NUM>. The number of rotations of backspin of a ball was measured with a ball trajectory measuring device "TRACKMAN" available from TrackMan. A ball "MPS" available from MIZUNO Corporation was used. In the measurement in the wet state, a sprayer was used to spray water onto the ball twice and the surface of face <NUM> twice to reproduce the wet state, and the ball was hit.

Also, for each of Examples <NUM> to <NUM> and Comparative Example <NUM>, the surface roughness (Ra) between scorelines <NUM> was measured in the TH direction and the UD direction. For the TH direction, surface roughness (Ra) was measured for each of a region on the top edge <NUM> side and a region on the leading edge <NUM> side when a part between scorelines <NUM> was divided into two equal parts. For the UD direction, surface roughness (Ra) was measured at the center of a scoreline between the fourth and fifth scorelines.

The measurement of surface roughness (Ra) was evaluated based on JIS B0601-<NUM> with "SURFTEST SJ-<NUM>" available from Mitutoyo Corporation. The measuring conditions were as follows: a measurement length of <NUM>, a reference length of <NUM>, and a cutoff value of <NUM>. Surface roughness (Ra) was measured three times for each measurement condition, and an average thereof was set as a measured value. Table <NUM> shows the results of the robot test and the measured values of the surface roughness (Ra).

The results of Table <NUM> reveal that an amount of backspin in the wet state is higher than that in the dry state in all of Examples <NUM> to <NUM>. The present invention can thus provide an iron golf club that facilitates application of backspin also in the wet state.

Claim 1:
An iron golf club head (<NUM>) with a plurality of scorelines (<NUM>) in a face surface, the iron golf club head (<NUM>) comprising a microgroove (<NUM>) between two adjacent scorelines (<NUM>) of the plurality of scorelines (<NUM>), the microgroove (<NUM>) being narrower than the scorelines (<NUM>), the microgroove (<NUM>) including at least an inclined groove (20a) extending in a heel leading edge-toe top edge direction, which groove (20a) is connected to an upper scoreline (<NUM>) of the two adjacent scorelines (<NUM>),
wherein when a part between the two adjacent scorelines (<NUM>) is divided into two equal parts in a top edge-leading edge direction, a surface roughness (Ra) in a toe-heel direction on a top edge side is greater than a surface roughness (Ra) in the toe-heel direction on a leading edge side.