JPH0563190B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to solid golf balls. [Prior Art] Conventionally, the composition of the inner core of a solid golf ball such as a two-piece golf ball has been disclosed in, for example, Japanese Patent Publication No. 19615-1980, Japanese Patent Publication No. 9347-1987, Japanese Patent Application Laid-open No. 92225-1982, Japanese Patent Publication No. 53-83834
Publication No. 1987-21933, Japanese Patent Application Laid-Open No. 1983-21933
A large number of patent applications have been filed, as seen in Publication No. 21932, which states that a solid golf ball with good flight characteristics can be obtained by using a metal salt of acrylic acid or a metal salt of methacrylic acid as a co-crosslinking agent. is reported. [Problems to be solved by the invention] However, the above solid golf ball has the following problems:
It has good flight characteristics, but some users dislike it because it gives a hard feel. For example, most solid golf balls currently on the market have a ball compression between 95 and 105, which is higher than the ball compression of thread-wound golf balls, which is 80 to 100. This causes a hard feel. Although it is rare to find solid golf balls with ball compression comparable to thread-wound golf balls, they are softer and have a lower coefficient of repulsion and poor flight characteristics. There is a desire for a solid golf ball that has good flight characteristics. [Means for Solving the Problems] In view of the above-mentioned circumstances, the present inventors have conducted various studies and found that when forming the inner core, zinc acrylate is used as a co-crosslinking agent to form a co-crosslinking agent of 25 to 45 parts by weight per 100 parts by weight of rubber. 5 to 25% by weight of palmitic acid, stearic acid, or myristic acid based on zinc acrylate as a co-crosslinking aid, and 20% or more of zinc oxide based on zinc acrylate as a co-crosslinking aid. 100
60 parts by weight or less, 2,5-di-tert
- When compounding a reaction rate retardant consisting of butylhydroquinone in an amount of 1 to 3% by weight based on zinc acrylate, the ball compression is indicated by PGA.
It was discovered that a solid golf ball with good flight characteristics could be obtained with a golf ball of 80 to 95, and the present invention was completed. In other words, it is believed that the above zinc acrylate causes a polymerization and grafting reaction with a peroxide-based initiator such as dicumyl peroxide, and functions as a co-crosslinking agent, as well as a reactive filler, to achieve the desired hardness. The blending amount is determined so as to obtain the desired weight, but in order to obtain higher impact resilience, it is desirable to reduce the blending amount as much as possible. Based on such circumstances, the present invention, as shown in Experimental Examples 1 to 3 below,
We discovered the factors that increase ball compression, and while reducing the amount of zinc acrylate blended, set the ball compression to 80 to 95, lower than conventional solid golf balls, and experimental example 4.
As shown in ~5, a reaction rate retardant consisting of 2,5-di-tert-butylhydroquinone is added to suppress the runaway reaction of zinc acrylate and reduce the width of the hardness distribution of the inner core, resulting in ball compression. The objective is to provide a solid golf ball that has low friction, good feel, and good flight characteristics. In the present invention, zinc acrylate is blended in an amount of 25 to 45 parts by weight per 100 parts by weight of rubber, but this is because if the amount of zinc acrylate is less than 25 parts by weight, ball compression and coefficient of restitution will be low. This is because if it exceeds , the ball compression will become too high. Furthermore, higher fatty acids such as palmitic acid, stearic acid, and myristic acid are blended in an amount of 5 to 25% by weight, preferably 10 to 20% by weight, based on zinc acrylate; If it is less than 5% by weight, it will be difficult to achieve the desired ball compression and the durability will be low, and if it exceeds 25% by weight, the volume fraction of rubber such as polybutadiene will be small and the impact resilience will be inhibited. be. Zinc oxide is blended in an amount of 20% by weight or more based on zinc acrylate, because if the amount of zinc oxide is less than 20% by weight based on zinc acrylate, it becomes difficult to achieve the desired ball compression.
In addition to acting as a co-crosslinking aid, zinc oxide also functions as a weight adjuster for the inner core, so the upper limit of its amount is not particularly limited, and may vary depending on other ingredients, the size of the golf ball, etc. Although it can be varied in various ways, it is 60 parts by weight per 100 parts by weight of rubber. The reaction rate retarder consists of 2,5-di-tert-butylhydroquinone, and the reaction rate retarder is 1 to 3% by weight based on zinc acrylate as described above.
It is blended. This is because if the reaction rate retardant is less than 1% by weight, it will have little effect in suppressing the crosslinking reaction in the center of the inner core, and it will be difficult to obtain an inner core with a narrow hardness distribution. This is because if the amount exceeds % by weight, the crosslinking reaction becomes too slow, resulting in poor production efficiency. In the present invention, ball compression is
The reason for specifying 80 to 95 on the PGA display is that to obtain a golf ball with good feeling, it is necessary to keep the ball compression to 95 or less, and if the ball compression is less than 80, the rebound is large and the flight characteristics are poor. This is because it is difficult to obtain a good golf ball. In order to obtain the inner core of the solid golf ball of the present invention, a rubber serving as a base material, an initiator, and the like are required in addition to the above-mentioned components. As the rubber, for example, butadiene rubber such as high-cis-1,4-polybutadiene, a blend of butadiene rubber, natural rubber, or styrene-butadiene rubber can be used.
Those containing at least % by weight are preferred. As the initiator, peroxides such as dicumyl peroxide and 1,1-bis(tert-butylperoxy)3,3,5-trimethylcyclohexane are preferably used. The amount of these initiators used is usually 0.5 to 5.0 per 100 parts by weight of rubber.
Parts by weight. In addition, the rubber composition for the inner core may optionally contain additives such as anti-aging agents, fillers such as barium sulfate, calcium carbonate, silica, etc. in addition to the above-mentioned components. The cover that covers the inner core is preferably made of, for example, an ionomer as the main material, to which other polymers such as nylon or additives such as titanium dioxide, dyes, pigments, and anti-aging agents are added. Ru. Furthermore, the present invention is applicable not only to two-piece solid golf balls as described above, but also to three-piece solid golf balls having a multilayer structure of three or more layers, such as a three-piece solid golf ball in which an intermediate layer is formed on the inner core and a cover is coated on the intermediate layer. This also applies to Tsudo golf balls. [Example] Next, the present invention will be explained in further detail with reference to experimental examples and examples. In addition, all the blending parts in the experimental examples and examples are based on parts by weight. Experimental Example 1 Using zinc acrylate as a co-crosslinking agent, the relationship between the amount of zinc acrylate blended and the ball compression (ball hardness) indicated by PGA was investigated, and the results are shown in FIG. In addition, the amount of zinc acrylate on the horizontal axis in Figure 1 is based on rubber (cis-
The number of parts is based on 100 parts by weight (1,4-polybutadiene). The rubber composition obtained by kneading with a roll based on the formulations A and B shown in Table 1, a rubber composition with a diameter of about 30 mm,
A plug with a length of approximately 50 mm was prepared and crosslinked by heat compression molding at 165°C for 30 minutes (hereinafter referred to as vulcanization) to obtain a solid inner core with a diameter of 38.1 mm. The cis-1,4-polybutadiene used was manufactured by Nippon Synthetic Rubber.
Co., Ltd.'s BR01, and the same applies to subsequent formulations.

[Table] Next, the solid inner core was covered with a cover by injection molding to obtain a two-piece solid golf ball with a diameter of 42.8 mm. The cover used was Sorin 1707 (trade name, an ionomer manufactured by DuPont). The composition that forms the inner core of a two-piece solid golf ball depends on the hardness, weight, rebound, and
The material is determined with consideration to crack resistance, but the first consideration is weight and hardness. The hardness referred to herein is the hardness of the ball after being covered with a cover, and will be expressed in terms of ball compression using PGA hereinafter. As shown in Figure 1, in order to achieve a ball compression of 80 to 95 on the PGA scale with formulation A,
Formulation B requires 35 to 45 parts by weight of zinc acrylate, but the filler is changed from barium sulfate to zinc oxide.
In this case, when zinc acrylate is 30 to 40 parts by weight, the ball compression is 80 to 95, which is less zinc acrylate than in the case of formulation A. The results show that increasing the amount of zinc acrylate (with the amount of initiator held constant) increases the ball compression. It was found that the ball compression was even higher when zinc acrylate and zinc oxide were combined. That is, graft crosslinking to polybutadiene,
The more zinc acrylate that has a three-dimensional structure, the higher the crosslinking density, and the addition of zinc oxide forms pseudo-ionic bonds with the grafted zinc acrylate, making the network structure denser. It is estimated that the hardness, or ball compression, increases. Note that this phenomenon was unique to zinc acrylate and was not observed in any other zinc acrylate. Experimental Example 2 The effects of adding various fillers containing zinc oxide were investigated, and the results are shown in FIG. The formulation used was formulation C shown in Table 2, and the ball compression was measured on a two-piece solid golf ball obtained by preparing a solid inner core in the same manner as in Experimental Example 1 and then applying a cover coating. I did it.

[Table] As shown in Figure 2, substances that lower ball compression when added (for example, Ca(OH))
₂ , MgO), those with little ball compression change (e.g. SiO ₂ , BaSO ₄ , Fe ₂ O ₃ ,
There are substances such as CaCO ₃ , ZrO ₂ , Fe powder, Zn powder, MgCO ₃ ), and substances that have the effect of slightly increasing ball compression (ZnO ₂ ), but zinc oxide (ZnO) is by far the most effective in improving ball compression. It has the effect of increasing Experimental Example 3 Next, the effect of adding palmitic acid was investigated, and the results are shown in FIG. The formulations were formulations D and E shown in Table 3, and compression measurements were made on two-piece solid golf balls obtained by preparing a solid inner core in the same manner as in Experimental Example 1 and then covering it. Ta.

[Table] As shown in FIG. 3, in formulation D, which does not contain zinc oxide, the more palmitic acid is added, the more the vulcanization is inhibited and the ball compression is lowered. However, zinc oxide is similar to zinc acrylate.
If 20% by weight or more is added, curve E in Figure 3
As shown, the ball compression increases as the amount of palmitic acid added increases. As described above, only when zinc acrylate, zinc oxide, and palmitic acid are blended, the crosslinked structure becomes stronger and an excellent highly elastic body can be obtained.
This is because in a system that does not contain zinc oxide, palmitic acid has almost no ionic bond interaction with zinc acrylate, making the atmosphere in the rubber acidic and suppressing the generation of peroxide radicals. As the amount of palmitic acid added increases, the ball compression decreases, but the presence of zinc oxide causes an ionic bonding action, which strengthens the crosslinked structure and increases the ball compression. It is thought that it becomes a highly elastic body. In addition, in order to investigate whether zinc salts of higher fatty acids have the effect of increasing ball compression even in the absence of zinc oxide, we used Formulation F containing zinc stearate. The relationship between the amount of addition and ball compression was investigated, and it is shown in Figure 3 for convenience. However, when zinc stearate is used alone and zinc oxide is not included, there is no ionic bonding effect. ,
Ball compression decreased as the amount of zinc stearate increased, due to its role as a plasticizer. Experimental Example 4 Using the formulations G to L shown in Table 4, Experimental Example 1 was conducted.
A solid inner core was prepared in the same manner as described above, and then covered with a cover to obtain a two-piece solid golf ball. The ball compression and restitution coefficient of these two-piece solid golf balls were measured and the results are shown in Table 4.

[Table] As shown in formulations G to J in Table 4, the restitution coefficient is approximately proportional to the ball compression, and the lower the ball compression, the lower the restitution coefficient. Therefore, if you place importance on feel and make the ball softer, that is, lower the ball compression, the rebound will be lowered. However, Nokrac NS-7 (trade name, Ouchi Shinko Chemical Industry Co., Ltd., 2,5
-Di-tert-butylhydroquinone) in formulations K and L, the ball compression is compounded in formulation I.
It showed a high repulsion coefficient even though it was lower. Based on the above findings, the present invention provides 2,5-di-
Tert-butylhydroquinone is used as a reaction rate retardant, and the reason why a golf ball with a high coefficient of restitution despite a low ball compression can be obtained when 2,5-di-tert-butylhydroquinone is used is , 2,5-di-tert-butylhydroquinone acts as a reaction rate retardant,
This is thought to be based on slowing down the vulcanization rate and suppressing runaway reactions such as polymerization and grafting reactions of zinc acrylate. Experimental Example 5 In order to examine the vulcanization characteristics of individual materials using the formulations shown in Table 5, a test was first conducted using a cuelastrometer, and the results are shown in FIG. The test is
It was carried out at 160°C and Arc±1°.

[Table] As shown in Figure 4, blend P vulcanizes more slowly and has a lower degree of vulcanization than blends M and N. Usually, such a formulation has a low degree of vulcanization, so ball compression is difficult to produce, and it is often not suitable for golf balls. However, in reality, as shown below, a golf ball with a high coefficient of restitution can be obtained even though the ball compression is low. That is, using the above formulations M, N, and P, a solid inner core was obtained by vulcanization at 160°C for 30 minutes in the same manner as in Experimental Example 1, and then a cover was applied. Measure the repulsion coefficient and send the results to the sixth
Shown in the table. In addition, the hardness distribution of the inner core of the golf ball was investigated, and the results are shown in Table 6. In addition,
The hardness of the inner core is measured using a JIS-C type hardness meter.

[Table] As shown in Table 6 above, in the case of formulation P, the restitution coefficient is higher than in the cases of formulations M and N, although the ball compression is lower. This means that the hardness distribution of their inner core is
With N, the surface part is hard and the center part is soft, and there is a considerable difference in the degree of vulcanization, whereas with formulation P, the hardness is low overall, the hardness distribution is narrow, and the hardness is uniformly vulcanized. This is thought to be due to the fact that In other words, in the case of the inner core of a golf ball, there is a distance from the surface to the center, so under normal conditions the vulcanization rates between the surface and the center are quite different.
The surface side is close to the press and the reaction is controlled by the press temperature, but in the center of the inner core, the press temperature is reached once due to the amount of heat given from the outside.
The polymerization and grafting reaction of zinc acrylate progresses, and once the reaction begins, the reaction rapidly progresses due to self-heating. Therefore, the reaction rate is faster at the center than at the surface, and when the surface is brought to the desired degree of vulcanization, the center becomes over-vulcanized, resulting in a hardness distribution of outer hardness and inner softness. By adding tert-butylhydroquinone (in Table 5, it is indicated by the product name Nokrac NS-7), the runaway reaction of zinc acrylate in the center is suppressed, and the hardness distribution from the surface to the center is improved. A uniform vulcanizate with a small width can be obtained. Examples 1 to 3 and Comparative Examples 1 to 2 Rubber compositions for the inner core having the formulations shown in Table 7 were heated at 160°C.
A solid inner core was prepared by vulcanization for 30 minutes, and the solid inner core was then covered with a cover by injection molding to obtain a two-piece solid golf ball having a diameter of 42.8 mm. The resulting two-piece solid golf ball was measured for ball weight, ball compression, and restitution coefficient. The results are shown in Table 7. The cover formulation was 100 parts by weight of Surlyn 1707 (mentioned above) and 2 parts by weight of titanium dioxide.

【table】

[Table] As shown in Table 7, the balls of Examples 1 to 3 of the present invention had a high coefficient of restitution, good feel, and excellent flight characteristics despite having low ball compression. It is shown that. On the other hand, the ball of Comparative Example 1, which is the mainstream of conventional two-piece solid golf balls, has a high coefficient of restitution and good flight characteristics, but has high ball compression and a hard feel when hit. The feeling is bad. Further, the ball of Comparative Example 2 had low ball compression and good feeling, but had a low repulsion coefficient and poor flight characteristics. [Effects of the Invention] As explained above, according to the present invention, the feel of a solid golf ball was improved, and a solid golf ball with good feel and good flight characteristics was obtained.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the relationship between the blending amount of zinc acrylate and ball compression, and FIG. 2 is a diagram showing the influence of the addition of various fillers on ball compression. FIG. 3 is a diagram showing the relationship between the amount of palmitic acid added and ball compression, and FIG. 4 is a diagram showing the relationship between the amount of palmitic acid added and the ball compression, and FIG.
FIG. 3 is a diagram showing the vulcanization characteristics of N and P.

Claims (1)

[Claims] 1. 25 to 45 parts by weight of zinc acrylate as a co-crosslinking agent to 100 parts by weight of rubber, and palmitic acid, stearic acid or myristic acid as a co-crosslinking agent to zinc acrylate. 5 to 25% by weight, a reaction consisting of 2,5-di-tert-butylhydroquinone, containing 20% by weight or more of zinc oxide based on zinc acrylate as a co-crosslinking aid, and 60 parts by weight or less based on 100 parts by weight of rubber. A solid golf ball having an inner core containing 1 to 3% by weight of a speed retardant based on zinc acrylate, and having a ball compression of 80 to 95 on the PGA scale. 2. The solid golf ball according to claim 1, wherein the rubber contains 90% by weight or more of high-cis polybutadiene.