JP6514633B2 - Golf ball - Google Patents

Description

  The present invention relates to golf balls.

Generally, as performance of a golf ball (hereinafter, also simply referred to as "ball"), it is desirable to be easy to fly farther in driver shots, and it is desirable to be easier to stop in approach shots. In order to make it easier to fly farther in the driver shot, it is sufficient to reduce the spin of the ball in the driver shot, and in order to make it easier to stop in the approach shot, to increase the spin of the ball in the approach shot Good things are known.
Conventionally, to reduce spin on driver shots, it is effective to increase the moment of inertia of the ball, and to increase spin on approach shots, it is effective to reduce the moment of inertia of the ball It has been thought that it is the target (for example, patent document 1).

JP, 2014-110940, A

  However, by appropriately adjusting the structure of the ball, the inventor of the present invention can reduce the spin on the driver shot as well as the increase in the spin on the approach shot, even when the moment of inertia of the ball is low. I found that.

  An object of the present invention is to provide a golf ball which can reduce spin on driver shots while reducing the moment of inertia.

The golf ball of the present invention is a golf ball provided with a cover, wherein the moment of inertia of the golf ball is I _b (g · cm ² ), and the initial load of 10 kgf is applied to the golf ball. When the deflection hardness is μ (mm) and the Shore D hardness of the cover is D, which is the amount of deformation (mm) of the golf ball in the direction of load until loading of 130 kgf.
The spin change amount prediction index ΔS ′ expressed by the following equation is characterized by being 2.0 or more.
According to the golf ball of the present invention, it is possible to reduce the spin at the driver shot while reducing the moment of inertia.

  In the golf ball of the present invention, the cover is preferably made of urethane. This can further reduce spin on driver shots.

  In the golf ball of the present invention, it is preferable that the spin change amount prediction index ΔS ′ be 2.5 or more. Thereby, it is possible to further reduce the spin on the driver shot while reducing the moment of inertia.

  In the golf ball of the present invention, it is preferable that the spin change amount prediction index ΔS ′ be 3.0 or more. Thereby, it is possible to further reduce the spin on the driver shot while reducing the moment of inertia.

In the golf ball of the present invention, the cover is covered by a top coat;
It is preferable that the elastic work recovery rate of the top coat is 30 to 98%. This can further reduce spin on driver shots.

In the golf ball of the present invention, the outer surface of the cover is provided with a plurality of dimples, and the area of the golf ball in contact with a plane when a load of 700 kgf is applied to the golf ball is PS7. Assuming that the area of a circle of a cross section along the diameter of the golf ball, assuming that there are no dimples on the surface,
(PS7 / VS / μ) · 100 ≧ 6.70 (mm ⁻¹ )
It is preferable to satisfy the following equation. This can further reduce spin on driver shots.

  According to the present invention, it is possible to provide a golf ball capable of reducing the spin on driver shots while reducing the moment of inertia.

FIG. 1 is a cross-sectional view showing an example of an internal structure of a golf ball according to an embodiment of the present invention. It is a figure for demonstrating the spin concerning a golf ball in a driver shot. FIG. 2A is a schematic view showing the driver shot, and FIG. 2B is a graph showing the force acting between the golf ball and the golf club in the driver shot. It is a figure for demonstrating the effect of the golf ball of this invention. It is a figure for demonstrating the effect of the golf ball of this invention. It is a figure for demonstrating the effect of the golf ball of this invention. It is a figure for demonstrating the effect of the golf ball of this invention. It is a figure for demonstrating an example of the dimple applicable to the golf ball of this invention. FIG. 7 (a) is a side view showing an example of a golf ball, and FIG. 7 (b) is a cross-sectional view of an essential part of the golf ball shown in FIG. 7 (a). It is a figure for demonstrating the other example of the dimple applicable to the golf ball of this invention. FIG. 8 (a) is a side view showing another example of the golf ball, and FIG. 8 (b) is a sectional view of an essential part of the golf ball shown in FIG. 8 (a). 9 (a) and 9 (b) are diagrams for explaining the situation when loads of 6864 N and 1961 N are applied to the same golf ball, respectively.

  Embodiments of the present invention will be illustrated and described below with reference to the drawings.

[Configuration of Golf Ball of the Present Invention]
A golf ball according to an embodiment of the present invention, for example, comprises a core and an intermediate layer outside the core, and a cover having an outermost layer.
FIG. 1 is a cross-sectional view showing an example of an internal structure of a golf ball according to an embodiment of the present invention. The golf ball 1 in the example of FIG. 1 is a so-called five-piece golf ball, and is provided on the inner core portion 11, the middle core portion 12 provided on the outer side of the inner core portion 11, and the outer side of the middle core portion 12. An outer core portion 13, an intermediate layer 14 provided on the outer side of the outer core portion 13, and a cover 15 provided on the outer surface of the intermediate layer 14 and having a plurality of dimples 30 formed on the outer surface . The cover 15 is covered by a top coat 16.
However, the golf ball of the present invention may have any internal configuration other than that shown in FIG. For example, the core of the golf ball of the present invention does not have to have a three-layer structure of the inner core portion 11, the middle core portion 12 and the outer core portion 13 as in the example of FIG. It may be of a layer or more structure. Further, the intermediate layer of the golf ball of the present invention may be composed of a plurality of layers.

In the golf ball of the present invention, when the moment of inertia of the ball is I _b (g · cm ² ), the deflection hardness of the ball is μ (mm), and the Shore D hardness of the cover is D,
The spin change amount prediction index ΔS ′ expressed by the following equation is 2.0 or more (ΔS ′ ≧ 2.0).
Here, the moment of inertia (I _b ) of the golf ball is obtained by measurement using a moment of inertia measuring machine (for example, M01-005 manufactured by INERTIA DYNAMICS INC). This measuring machine calculates the moment of inertia of the golf ball from the difference between the period of vibration when the golf ball is placed on the jig of the measuring device and the period of vibration when the golf ball is not placed.
The deflection hardness (μ) of a golf ball is the amount of deformation of the ball in the direction of load from the state where an initial load of 10 kgf (about 98 N) is loaded to the ball to the time when a final load of 130 kgf (about 1275 N) is loaded. (Mm). The higher the deflection hardness value of the golf ball, the softer the golf ball.
The Shore D hardness (D) of the cover is obtained by preparing a sheet-like test piece of 2 mm in thickness from the material constituting the cover and measuring the hardness of the test piece with a durometer “type D” of the ASTM-D2240 standard. Point to the value to be The higher the Shore D hardness value of the cover, the harder the cover.

As can be seen from the equation (1), it is necessary to make the moment of inertia I _b of the golf ball smaller than 82 g · cm ² in order to make the value of the spin change prediction index ΔS ′ positive (larger than zero). is there. The value 82 of the equation (1) is set based on the fact that the moment of inertia of the existing general golf ball is about 81 to 82 g · cm ² . That is, the golf ball of the present invention has a lower moment of inertia than a general golf ball.
In the following, a golf ball in which the moment of inertia of the ball is 82 g · cm ² is referred to as a “reference ball”.
The golf ball of the present invention is suitably adjusted such that the inertia moment I _{b of} the ball, the deflection hardness of the ball, and the Shore D hardness of the cover are such that ΔS′2.02.0. .

  The golf ball according to one embodiment of the present invention satisfies the weight (45.93 g or less) and the outer diameter (42.67 mm or more) defined by USGA and R & A.

  As will be understood from the description of Examples and Comparative Examples described later, according to the golf ball of the present invention, the spin on the driver shot is reduced as well as the spin on the approach shot is reduced while the moment of inertia is reduced. Can be reduced.

[The process of obtaining the formula of the spin change prediction index ΔS ']
As described above, according to the structure of the ball, the inventor of the present invention can reduce the spin on the driver shot as well as the increase in the spin on the approach shot, even if the moment of inertia of the ball is low. It has been found that it is possible to evaluate the actual spin change prediction index by the spin change prediction index ΔS ′ defined by the equation (1).

  Here, how the inventor of the present invention obtains the spin amount prediction indicator ΔS ′ will be described with reference to FIG. FIG. 2A is a schematic view showing a driver shot, and FIG. 2B is a graph showing the force acting between the golf ball 1 and the head 2 of the golf club in the driver shot. In the graph of FIG. 2B, the horizontal axis is time, and the vertical axis is the force acting on the golf ball 1 from the face surface 21 of the head 2 of the golf club. The “contact time” in FIG. 2B refers to the time during which the ball 1 is in contact with the face surface 21. Of the waveforms shown in FIG. 2 (b), the solid waveform is the waveform of the force actually acting on the ball 1, and a waveform having a sine wave-like waveform which is connected smoothly by a part broken line will be described later. It is drawn to obtain the recoil period T.

As shown in FIG. 2, in driver shots, a force (shearing force) acting on the ball 1 from the face surface 21 is initially generated in a direction (positive direction) to cause the ball 1 to backspin, Later, it occurs in a direction (a negative direction) that causes the ball 1 to have a top spin opposite to the backspin. Here, while the face surface 21 and the ball 1 are in contact with each other, the total amount (force) of the force in the direction to cause backspin acting on the ball 1 and the force in the direction to cause topspin If the total amount (impulse) of F is F _back and F _top (including the positive and negative signs), the smaller the absolute value of the sum (F _back + F _top ), It is preferable because the amount of applied spin is low.

In the graph of FIG. 2 (b), the period of the waveform (also referred to as "recoil period") T which is smoothly connected by a part of a broken line is
It is expressed by the equation of Here, K _x is the lateral stiffness of the ball, K _t is the rotational stiffness of the ball, m is the mass of the ball, and I is the moment of inertia of the ball.

As the inventor of the present invention, as a result of repeating various experiments and analysis,
(I) The smaller the recoil period T, the smaller the sum of impulses of the force acting on the ball 1 from the face surface 21 (F _back + F _top ), so the amount of spin decreases.
(Ii) The higher the deflection hardness (μ) of the ball 1 (the softer the ball), the longer the contact time between the face surface 2 and the ball 1 and the total amount of force generated in the direction to generate topspin As the F _top increases, the spin rate decreases,
(Iii) The smaller the Shore D hardness (D) of the cover of the ball 1 (the softer the cover), the higher the friction between the face surface 2 and the ball 1 and the faster the shear force acting on the ball is generated about,
And the knowledge about the relationship of (i)-(iii) was acquired. In (ii) and (iii), it has the meaning which makes the effect of (i) increase or decrease. Then, based on these findings, an index S for predicting the effect of the spin amount on driver shots and approach shots from the structure of a golf ball,
It was defined as The spin prediction index S has the same deflection hardness μ and Shore D hardness D, and means that the larger the value, the lower the spin amount on the driver shot when the ball structure having the inertia moment I as a variable is compared. Do.

In equation (3), the moment of inertia of the ball is
The change amount ΔS of the spin prediction index S when lowered as
It becomes.

In equation (4),
If you
It becomes. Here, I _a is the moment of inertia of the reference ball, and I _b is the moment of inertia of the ball to be evaluated.

In equation (5), since K _t and S are values related to the reference ball, they can be treated as constant coefficients. For convenience, by operating the constant coefficient in equation (5) as follows, the spin change amount prediction index ΔS ′ is
Define as
Substituting the inertia moment I _a = 82 of the reference ball in the equation (6) gives the above equation (1).

[Examples, Comparative Examples]
As described above, in the golf ball of the present invention, the three elements of the ball's moment of inertia (I _b ), the ball's deflection hardness (μ), and the cover's Shore D hardness (D) satisfy ΔS ′ ≧ 2.0. It is properly adjusted to become This makes it possible to reduce the spin on the driver shot as well as to increase the spin on the approach shot while reducing the moment of inertia as compared to the reference ball.

The golf balls of Examples 1 to 13 and Comparative Examples 1 to 14 of the present invention were prepared and evaluated. The results will be described with reference to Tables 1 to 5 and FIGS. The details of Examples 1 to 13 are shown in Table 1, and the details of Comparative Examples 1 to 14 are shown in Table 2.
In Tables 1 and 2, the lower case alphabets a to u described in the "blending" column of the inner core portion 11, the middle core portion 12 and the outer core portion 13 respectively have the blending ratio of the blending ratio a of Table 3. It is pointing to ~ u. In Table 1 and Table 2, the upper case alphabets A to H described in the "blending" column of the middle core portion 12, the outer core portion 13, the mid layer 14, and the cover 15 are each a table of the blending. It is pointed out that it is the composition AH of 4. The compounding numbers in Tables 3 to 4 are expressed in parts by mass.
In Tables 1 and 2, “μ: Deflection hardness (mm)” is the load from when the initial load of 10 kgf (about 98 N) is applied to each ball to when the final load of 130 kgf (about 1275 N) is applied. The amount of deformation (mm) of the ball in the direction.
In Tables 1 and 2, “I _b : moment of inertia (g · cm ² )” is a value obtained by measuring each ball using a moment of inertia measurement machine (M01-005 manufactured by INERTIA DYNAMICS INC) It is.
In Tables 1 and 2, “Shore D hardness” of the intermediate layer 14 and “D: Shore D hardness” of the cover 15 make a sheet-like test piece with a thickness of 2 mm from each material, ASTM-D2240 It is a value obtained by measuring the hardness of the test piece with a standard durometer "type D".
In Tables 1 and 2, “ΔS ′: spin change prediction index” is a value obtained by calculation according to the above equation (1) using the values of μ, D, and I _b of each ball.
In Tables 1 and 2, “driver spin (rpm)” and “approach spin (rpm)” are experimental results of spin amounts when driver shots and approach shots are performed using the respective balls.
In the driver shot experiment, a driver (W # 1) was attached to a golf hitting robot (manufactured by Miyamae Co., Ltd.), and the spin rate when hit at a head speed (HS) of 45 m / s was measured. The club used Bridgestone Sports "TourStage X-Drive 705 TYPE 415 (2011 model)" (loft 9.5 degrees).
In the experiment of the approach shot, a sand wedge (SW) was attached to a golf hitting robot (manufactured by Miyamae Co., Ltd.), and the spin amount when hit at a head speed (HS) of 20 m / s was measured. The club used Bridgestone "TourStage X-WEDGE" (loft 56 degrees).
"Dimple" in Table 1-2, "PS7: Pressed area", "PS2: Pressed area", "VS: Virtual area", "(PS7 / VS / μ) · 100 (mm ^-1 )", " (PS2 / VS / μ) · 100 (mm ⁻¹ ) “top coat” will be described later.

The details of the materials in Table 4 are as follows.
T-8290: trademark Pandex manufactured by DIC Bayer Polymer, MDI-PTMG type thermoplastic polyurethane T-8283: trademark Pandex manufactured by DIC Bayer Polymer, MDI-PTMG type thermoplastic polyurethane T-8260: DIC Trademark Pandex manufactured by Bayer Polymer, MDI-PTMG type thermoplastic polyurethane, high-millan 1706: Mitsui Dupont Polychemicals Co., Ltd. Ionomer high-millan 1557: Mitsui DuPont Polychemicals Co., Ltd. ionomer, high-millan 1605: Mitsui Dupont Polychemical Ionomer · HPF 1000: Dupont HPF
・ HPF2000: Dupont HPF
・ AD1035: Dupont HPF
· AD1172: Dupont HPF
Hytrel 4001: Thermoplastic polyetherester elastomer manufactured by Toray DuPont Co., Ltd. Polyethylene wax: "Sun wax 161P" (manufactured by Sanyo Chemical Industries, Ltd.)
-Isocyanate compound: 4,4'-diphenylmethane diisocyanate * C1 and C2 have the same physical property value and differ only in specific gravity.

  FIG. 3 is a view showing driver spin (rpm) and approach spin (rpm) of the balls of Examples 1 to 5 and Comparative Examples 1 to 7 in which the Shore D hardness (D) of the cover 15 is 47. FIG. 4 is a view showing the driver spin (rpm) and the approach spin (rpm) of the balls of Examples 6 to 7 and Comparative Examples 8 to 14 in which the Shore D hardness (D) of the cover 15 is 61. In FIG. 3 and FIG. 4, the horizontal axis is driver spin (rpm) and the vertical axis is approach spin (rpm). As described above, it is desirable for the driver shot to have a small spin amount and for the approach shot to have a large spin amount. Therefore, in FIGS. 3 and 4, it can be said that the ball performance is more favorable from the lower right to the upper left.

  As seen in FIG. 3 and FIG. 4, when viewing the balls of the comparative example and the example where the Shore D hardness (D) of the cover 15 is the same, the ball of the example satisfying ΔS ′ ≧ 2.0 Compared with the ball of the comparative example, the increase in the spin amount on the approach shot and the reduction in the spin amount on the driver shot can be suitably achieved.

  5 (a) to 5 (f) are diagrams showing the driver spin (rpm) of the balls of the comparative example and the example in which the Shore D hardness (D) and the deflection hardness (μ) of the cover 15 are the same, respectively. is there. 6 (a) to 6 (f) are diagrams showing approach spins (rpm) of the balls of the comparative example and the example in which the Shore D hardness (D) and the deflection hardness (μ) of the cover 15 are the same, respectively. is there.

  As seen in FIGS. 5 and 6, when viewing the balls of the comparative example and the example where the Shore D hardness (D) and the deflection hardness (μ) of the cover 15 are the same, ΔS ′ ≧ 2.0 In the ball of the example to be satisfied, reduction of the spin amount on the driver shot and increase of the spin amount on the approach shot can be achieved as compared with the ball of the comparative example.

From the viewpoint of reducing the amount of spin on driver shots while reducing the moment of inertia of the ball, it is preferable that the ball 1 of the present embodiment has a spin change prediction index ΔS ′ of 2.5 or more, 3 It is more preferable that it is .0 or more.
From the same point of view, the ball 1 of the present embodiment is preferable as I _b ≦ 80 g · cm ² , 2.0 mm ≦ μ ≦ 4.5, and D ≦ 65. Further, it is more preferable that the ball 1 of the present embodiment satisfies 72 g · cm ² ≦ I _b ≦ 79 g · cm ² , 2.5 mm ≦ μ ≦ 3.0 mm, and D ≦ 55.

  The cover 14 of the ball 1 of the present embodiment is preferably made of urethane. As a result, in driver shots, the frictional force between the ball 1 and the face surface 21 of the golf club can be increased, and the amount of spin can be further reduced.

〔dimple〕
Next, the dimples 30 of the ball 1 of the present embodiment will be described in more detail. In the ball 1 of the present embodiment, the dimple 30 can have any shape. FIGS. 7 and 8 are diagrams showing different examples of the dimples 30 applicable to the ball 1 of the present embodiment.

  In the example shown in FIG. 7, each dimple 30 has a convexly curved shape in the inward direction of the golf ball.

  In the example shown in FIG. 8, the bottom surface of each dimple 30 has a shape projecting convexly in the outward direction of the golf ball only at the central portion of the dimple 30. In this case, a pressurized area described later can be provided without impairing the aerodynamic performance of the dimple 30. As shown in FIG. 8 (b), the portion of the dimple 30 which protrudes to the outside of the ball 1 at the center portion of the dimple 30 can also be made flat in the central region. In this case, as shown in FIG. 8B, the outer edge portion of this flat area has a contact area with the face surface 21 at the time of ball striking by making the corner portion chamfered (R attached). This can be effectively increased, which in turn makes it possible to reduce the amount of spin in driver shots.

Here, the ball 1 of the present embodiment is
(PS7 / VS / μ) 100 ≧ 5.70 (mm ^-1 ) (7)
It is preferable to satisfy the equation of
In Formula (7), “PS7” is an area (referred to as “pressure area”) (mm ² ) of the golf ball in contact with a plane when a load of 700 kgf (about 6864 N) is applied to the golf ball. In Equation (7), “VS” is the area of a circle of a cross section along the diameter of the golf ball (referred to as “virtual plane area”) (mm ² ), assuming that there is no dimple 30 on the surface of the golf ball. It is. In Formula (7), "(mu)" is the deflection hardness (mm) of the ball | bowl 1 mentioned above.
Note that “PS7 / VS / μ” in the formula (7) is synonymous with “PS7 / (VS · μ)”. That is, μ in equation (7) is a variable of the denominator.
The contact area between the ball 1 and the face surface 21 of the golf club can be obtained by adopting a configuration in which the pressing area PS7 of the golf ball at the load at the driver shot of a general golfer satisfies the above equation (7). Along with the increase, the frictional force between the ball 1 and the face surface 21 is improved, and as a result, the amount of backspin on the driver shot can be reduced to improve the flight distance.
From the same viewpoint, the ball 1 of the present embodiment is:
(PS7 / VS / μ) · 100 ・ 6.70 (mm ⁻¹ ) (8)
It is more preferable to satisfy the following equation.

Moreover, the ball 1 of the present embodiment is
(PS2 / VS / μ) · 100 ・ 1.70 (mm ⁻¹ ) (9)
It is preferable to satisfy the equation of
In Formula (9), “PS2” is an area (referred to as “pressure area”) (mm ² ) of a golf ball in contact with a plane when a load of 200 kgf (about 1961 N) is applied to the golf ball. The VS and μ are the same as in the equations (7) and (8).
Note that “PS2 / VS / μ” in the formula (9) is synonymous with “PS2 / (VS · μ)”. That is, μ in equation (9) is a variable of the denominator.
The contact area between the ball 1 and the face surface 21 of the golf club can be obtained by adopting a configuration in which the pressing area PS2 of the golf ball at the load in a general golfer's approach shot satisfies the above equation (9). With the increase, the frictional force between the ball 1 and the face surface 21 is improved, and the amount of backspin on the approach shot is increased, so that the ball 1 can be stopped more quickly near the drop point.
Further, by satisfying the above equation (9), the sum (F _back + F _top ) of the impulse of the force acting on the ball 1 from the face surface 21 becomes smaller in the driver shot. The amount of spin can be further reduced because the contact time with is longer, and the total amount (impact) F _{top of the} force generated in the direction causing the top spin is increased.
From the same viewpoint, the ball 1 of the present embodiment is:
(PS2 / VS / μ) · 100 ≧ 1.90 (mm ⁻¹ ) (10)
It is more preferable to satisfy the following equation.

In Tables 1 and 2, the balls of Examples 1 to 10 and Comparative Examples 1 to 14 use the shape of dimples 30 shown in FIG. 7 and the balls of Examples 11 to 13 have the shape of dimples 30 shown in FIG. It was used.
In the balls of Examples 1 to 10 and Comparative Examples 1 to 14, among the six types of dimples 30 having different diameters, the dimple 30 having a diameter of 4.4 mm, which is representative, is as shown in FIG. The depth L of the deepest point was 0.150 mm.
In the balls of Examples 11 to 13, of the six types of dimples 30 having different diameters, the dimple 30 having a diameter of 4.4 mm, which is representative, has a depth at the center point C, as shown in FIG. H is 0.097 mm, depth D of the deepest point is 0.131 mm, distance along the virtual extension surface (two-dot chain line in FIG. 8B) of the outer peripheral surface of the ball 1 from the outer peripheral edge E to the center point C When L1 is 100, the distance L2 along the virtual extension of the outer peripheral surface of the ball 1 from the outer peripheral edge E to the position of the deepest point adjacent is 39, the curvature radius R is 0.5 mm, and the edge angle A2 is 10 It was .5 °.

In Tables 1 and 2, the pressing area PS7, PS2 of each ball was measured by the following method. First, a pressure-sensitive paper (a pressure measurement film manufactured by Fuji Film, for prescale medium pressure) was laid on a flat surface, and golf balls of Examples and Comparative Examples were placed. Then, using an Instron Corporation Model 4204, apply loads of 700 kgf (about 6864 N) and 200 kgf (about 1961 N) to these golf balls, and sum of the areas of the portions where the pressure sensitive paper colored by contact with the golf balls. Was measured using a prescale pressure image analysis system FPD-9270 (manufactured by Fujifilm Corporation). The pressing areas PS7 and PS2 in Tables 1 and 2 are the results of measurement at any one position of the golf ball.
FIG. 9 (a) shows an example of a pressure-sensitive paper that actually developed color when a load of 700 kgf (about 6864 N) is applied to a golf ball, and FIG. 9 (b) shows the same golf ball as FIG. 9 (a). An example of the pressure sensitive paper which actually developed color when a load of 200 kgf (about 1961 N) is applied is shown. In the figure, a round part indicates the dimple 30, and a filled part indicates a colored part.

[Top coat]
Below, top coat 16 which covers cover 15 of ball 1 of this embodiment is explained still in detail. In the ball 1 of the present embodiment, as a method of applying a paint on the outer surface of the cover 15 to form the top coat 16 (coated film layer), any method such as air gun coating or electrostatic coating is used. be able to.
The thickness of the top coat 16 is not particularly limited, but is usually 8 to 22 μm, preferably 10 to 20 μm.

  The top coat 16 preferably has an “elastic work recovery rate” to be described later of 30 to 98%, and more preferably 70 to 90%. When the elastic work recovery rate of the top coat 16 is within the above range, the self-healing recovery function is enhanced while the coating formed on the golf ball surface maintains a certain hardness and elasticity, and the ball has excellent durability and It can contribute to scratch resistance. In addition, when the elastic work recovery rate of the top coat 16 deviates from the above range, a sufficient approach spin may not be obtained.

  The elastic work recovery rate of Top Coat 16 is an ultra-microhardness test method that controls indentation load in micro-Newton (μN) order and tracks indentation depth at indentation with nanometer (nm) accuracy, It is one parameter of the nanoindentation method to evaluate the physical properties of the coating film. In the conventional method, only the size of the deformation mark (plastic deformation mark) corresponding to the maximum load could be measured, but in the nanoindentation method, the relation between the indentation load and the indentation depth by measuring it automatically and continuously. You can get Therefore, it is considered that there is no individual difference as in the conventional visual measurement of deformation marks with an optical microscope, and the physical properties of the coating can be evaluated reliably and accurately. For this reason, the coating on the surface of the golf ball is greatly affected by the impact of the driver and various clubs, and the effect of the coating on various physical properties of the golf ball is not small. It is a very effective evaluation method to measure by the small hardness test method and perform with higher accuracy than before.

  In the balls of each of the Examples and Comparative Examples shown in Tables 1 and 2, a paint is applied to the outer surface of the cover 15 (the outermost layer) on which a large number of dimples 30 are formed by an air spray gun, It formed. In Tables 1 and 2, the alphabets I and J described in the column of "formulation" of the top coat 16 indicate that the preparations are the preparations I and J in Table 5 below, respectively.

  Here, synthesis examples of acrylic polyols (1) and (2) in Table 5 will be described. In the following description, “parts” means “parts by mass”.

Synthesis Example 1 of Acrylic Polyol
In a reactor equipped with a stirrer, a thermometer, a cooling pipe, a nitrogen gas inlet pipe, and a dropping device, 1000 parts of butyl acetate was charged, and the temperature was raised to 100 ° C. while stirring. From there, 220 parts of polyester-containing acrylic monomer (made by Daicel Chemical Industries, Ltd., Plaxel FM-3), 610 parts of methyl methacrylate, 170 parts of 2-hydroxyethyl methacrylate, and 30 parts of 2,2'-azobisisobutyro nitrile The resulting mixture was added dropwise over 4 hours. After completion of the dropwise addition, the reaction was carried out at the same temperature for 6 hours. After completion of the reaction, 180 parts of butyl acetate and 150 parts of polycaprolactone diol (manufactured by Daicel Chemical Industries, Ltd., Praxel L 205AL) are charged and mixed to obtain a solid content of 50%, viscosity of 100 mPa · s (25 ° C), weight average molecular weight of 10, A transparent acrylic polyol resin solution (polyol (1) in Table 5) having a 000, hydroxyl value of 113 mg KOH / g (solid content) was obtained.

Synthesis Example 2 of Acrylic Polyol
In a reactor equipped with a stirrer, a thermometer, a cooling pipe, a nitrogen gas inlet pipe, and a dropping device, 1000 parts of butyl acetate was charged, and the temperature was raised to 100 ° C. while stirring. From there, 620 parts of polyester-containing acrylic monomer (made by Daicel Chemical Industries, Ltd., Plaxel FM-3), 317 parts of methyl methacrylate, 63 parts of 2-hydroxyethyl methacrylate, 12 parts of 2,2'-azobisisobutyro nitrile The resulting mixture was added dropwise over 4 hours. After completion of the dropwise addition, the reaction was carried out at the same temperature for 6 hours. After completion of the reaction, 532 parts of butyl acetate and 520 parts of polycaprolactone diol (manufactured by Daicel Chemical Industries, Ltd., Praxel L 205AL) were charged and mixed to give a solid content of 50%, viscosity 600 mPa · s (25 ° C), weight average molecular weight 70, A transparent acrylic polyol resin solution (polyol (2) in Table 5) having a 000, hydroxyl value of 142 mg KOH / g (solid content) was obtained.

In Tables 1 and 2, the elastic work recovery rate of the top coat 16 of the ball 1 of each example and comparative example was measured as follows. First, a paint sheet having a thickness of 100 μm was prepared from the paint used for the top coat 16. And the elastic work recovery rate was measured on condition of the following using the measuring apparatus of ultra micro hardness meter "ENT-2100" of Elionix company.
-Indenter: Verkovich indenter (material: diamond, angle α: 65.03 °)
・ Load F: 0.2mN
- loading time: 10 seconds - holding time: 1 second, unloading time: based 1 sec Note that the amount of pushing work by returning deformation of the coating film W _elast and (Nm) and mechanical push workload W _total (Nm) to The elastic work recovery rate is calculated by the following equation.
Elastic work recovery rate = (W _elast / W _total ) · 100 (%) ... (11)

  1: Golf ball 2: Head of golf club 11: inner core part 12: middle core part 13: outer core part 14: middle layer 15: cover 16: top coat 21: face surface 30 :dimple

Claims (6)

A golf ball with a cover,
The moment of inertia of the golf ball is I _b (g · cm ² ),
The deflection hardness, which is the amount of deformation (mm) of the golf ball in the load direction from the state where the initial load of 10 kgf is applied to the golf ball to the time when the final load of 130 kgf is applied, is μ (mm)
When the Shore D hardness of the cover is D,
A golf ball, wherein a spin change amount prediction index ΔS ′ represented by the following equation is 2.0 or more.   The golf ball according to claim 1, wherein the cover is made of urethane.   The golf ball according to claim 1, wherein the spin change amount prediction index ΔS ′ is 2.5 or more.   The golf ball according to any one of claims 1 to 3, wherein the spin change amount prediction index ΔS 'is 3.0 or more. The cover is covered by a top coat,
The golf ball according to any one of claims 1 to 4, wherein an elastic work recovery rate of the top coat is 30 to 98%. The outer surface of the cover comprises a plurality of dimples,
When a load of 700 kgf is applied to the golf ball, the area of the golf ball in contact with a plane is PS7.
Assuming that the area of a circle of a cross section along the diameter of the golf ball, assuming that there is no dimple on the surface of the golf ball, VS:
(PS7 / VS / μ) · 100 ≧ 6.70 (mm ⁻¹ )
The golf ball according to any one of claims 1 to 5, which satisfies the following formula.