JP3425866B2 - Method for producing solid sphere and golf ball produced by the method - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a solid sphere and a golf ball produced by the method, and particularly to a solid core such as a golf ball or a tennis ball core, a billiard ball or a soft baseball. The present invention relates to a method for producing solid spheres and a golf ball produced by the method, which solves the problems of sink marks and wrinkles, which tend to be a problem in injection molding when the spheres are made of a thermoplastic resin or a thermoplastic elastomer.

[0002]

2. Description of the Related Art Solid spheres such as golf ball and tennis ball cores, soft baseballs and billiard balls are currently generally manufactured by press molding, but when a thermoplastic resin composition is used as a constituent material, It is recommended to use an injection molding method suitable for mass production.

However, in the case of manufacturing a solid sphere by injection molding, there is a problem that the resin filled in the cavity shrinks during cooling and a dent, that is, a sink mark is likely to occur on the surface of the molded product. The sink mark in a solid sphere molded product such as a ball is more likely to cause a sink mark problem than other molded products such as daily necessities and industrial parts. That is, in a sphere such as a ball, the entire sphere is subject to appearance, and the sink marks are directly connected to the defective shape of the sphere. Further, when the surface of the sphere is coated, the adhesion of the coating film will be reduced at the sink portion. Therefore, in injection molding, it is required to be small enough not to cause sink marks or to cause no problem.

In order to prevent the occurrence of sink marks or to reduce the extent of sink marks, it is conceivable to increase the injection pressure of the resin with which the cavity is filled or to accelerate the cooling and solidification. But,
The reduction of sink marks by increasing the speed of cooling and solidification or increasing the injection pressure of the resin causes another new problem that bubbles and the like are likely to occur inside the molded product. Particularly, in the case of a resin composition having a small melt index, that is, a fluidity being inferior, it is not easy to increase the injection pressure of the resin, but it only promotes the generation of bubbles. Further, in a resin composition in which dynamically crosslinked rubber powder is dispersed as proposed in Japanese Patent Application Laid-Open No. 8-113679, the decrease in viscosity by increasing the temperature is related to the deterioration of rubber particles. Is difficult. Here, the rubber powder-dispersed resin composition is a material which has attracted attention as a recyclable ball or ball core having elasticity and resilience from the viewpoint of recent environmental measures, and is dynamically crosslinked. Since the rubber powder is finely dispersed in the thermoplastic resin and behaves like an inorganic filler, it can be injection-molded, but its melt index is generally lower than that of other resin compositions.

The above problem becomes more serious as the outer diameter of the solid sphere is larger because the difference in the thermal history between the inside of the sphere and the portion in contact with the mold is likely to increase. Further, in the case of a solid sphere having a large outer diameter, if it is taken out from the mold with insufficient cooling inside, it may be deformed by an external force applied during storage.

The present invention has been made in view of such circumstances, and an object thereof is a method for producing a solid sphere by injection molding of a thermoplastic resin, particularly a resin having poor fluidity. The present invention provides a method for producing a solid sphere by injection molding using a golf ball and a golf ball produced by the method.

[0007]

A method for producing solid spheres according to the present invention is a method for producing a solid sphere having a total volume V by injection molding a thermoplastic resin or an elastomer composition.
The composition is characterized in that the composition is injected N times and the volume V _{n of the} molding portion formed by the Nth injection molding satisfies the following relational expression. 0.4 ≦ V _n /(V/N)≦1.6

The melt index of the thermoplastic resin or elastomer composition is preferably 7 or less,
Particularly preferred are those in which the diene rubber fine particles formed by dynamic crosslinking are dispersed in a thermoplastic resin or a thermoplastic elastomer. The sphere has a diameter of 30 mm to 80 m.
It is preferably m.

The golf ball of the present invention is a one-piece golf ball manufactured by the manufacturing method of the present invention or a multi-piece golf ball having a core and a cover manufactured by the manufacturing method of the present invention.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention reduces the temperature difference between the outermost layer and the inner layer by dividing the injection of resin into the cavity into a plurality of times and reducing the injection amount per injection. Then, the generation of sink marks is suppressed as much as possible, the time required for cooling the resin molding injected at one time is shortened, and the generation of bubbles inside the molded body is suppressed.

First, the thermoplastic resin or elastomer composition to which the production method of the present invention can be applied is not particularly limited in kind as long as it is a resin composition or elastomer composition which can be injection-molded, and a polyolefin such as polyethylene or polypropylene. Resin, polystyrene resin, polyester resin, polyamide resin, acrylic resin, polyether resin, polyacetal resin, fluorine resin, polycarbonate resin, polyurethane resin, ABS resin,
Various thermoplastic resins such as ionomer resins; thermoplastic elastomers composed of soft segments and hard segments; rubber particle-containing resin compositions in which vulcanized rubber fine particles are dispersed in the thermoplastic resin or elastomer; and these 2
Mixtures of more than one species are mentioned.

Here, examples of the thermoplastic elastomer include a polyolefin-based elastomer, a polystyrene-based elastomer, a polyamide-based elastomer, a polyurethane-based elastomer, and a polyester-based elastomer. Examples of the polystyrene-based elastomer include triblock copolymers and star block copolymers in which the hard phase is polystyrene and the soft phase is polybutadiene, polyisoprene, or hydrogenated products thereof. Examples of the polyolefin-based elastomer include those having polyolefin as a hard phase and ethylene-propylene rubber or ethylene-propylene-diene rubber as a soft phase, and mere mechanical blends thereof, micro-dispersed dynamic vulcanizates and the like can be mentioned. Examples of polyamide-based elastomers, polyurethane-based elastomers, and polyester-based elastomers include multi-block copolymers in which the hard phase is polyamide, polyurethane, or polyester, and the soft phase is aliphatic polyether.

Examples of the rubber particle-containing composition include those obtained by dynamically cross-linking the composition containing the diene rubber in the above-mentioned thermoplastic resin or thermoplastic elastomer, and the dynamically cross-linked diene-based composition. Although the rubber particles are finely dispersed, the dynamically crosslinked diene rubber particles behave like an inorganic filler in the thermoplastic resin and thus can be injection molded.

The manufacturing method of the present invention can be applied to any resin or elastomer as long as it is a material which can be injection-molded as described above, and particularly has a melt index of 7
The following is more effective in the so-called resin composition or elastomer composition having poor fluidity. A more effective material has a melt index of 5.0 or less, and more preferably 2.
It is 5 or less. In particular, as in the case of a rubber particle-containing thermoplastic resin composition or a rubber particle-containing elastomer composition, the melt index is low, and yet the viscosity of the thermoplastic resin or thermoplastic elastomer serving as a matrix in relation to the deterioration of rubber is sufficiently lowered. It is effective for a composition in which the injection temperature cannot be raised until the above-mentioned conditions occur. still,
If the melt index is too small, even when the present invention is applied, defects such as wrinkles are likely to occur due to poor fluidity, so the lower limit of the melt index is 0. It is preferably 01 or more, and more preferably 0.05 or more.

Here, the melt index (MI) is a measure showing the fluidity of a thermoplastic material when it is melted, and it is 230 ° C. under a load of 2.16 kg using an extrusion type plastometer specified in JIS K7210. Extrude the thermoplastic material from the orifice and set the extruded amount to 1
It is a value expressed in terms of grams per minute,
Generally, the larger the MI value, the better the fluidity and processability during melting.

In the production method of the present invention, when the thermoplastic resin or elastomer composition as described above is injection-molded to produce a solid sphere having a total volume V, the composition is injected N times. . N corresponding to the number of injections may be an integer of 2 or more, and its upper limit is not limited. As N becomes larger, a sphere having a higher sphericity of the molded product can be manufactured, but since the unit time required for molding one molded product becomes longer, N is preferably about 2 to 4. .

The volume V _{n of the} molding portion formed by the Nth injection molding satisfies the following relational expression. 0.4 ≦ V _n /(V/N)≦1.6

V_n / (V / N) is injected in N times
And the average injection amount per injection (corresponding to V / N) and actual
In this case, indicate the degree of separation from the material injected N times
There is. That is, the material injected each time is the material injected
The average amount of food is preferable. A large amount is injected at one time
Prevents the occurrence of sink marks by dividing into N times
It is difficult to achieve the effect sufficiently, and it is injected once
If the amount becomes too small, the flow of composition in injection molding
This is because defects are likely to occur. Therefore, the Nth
V corresponding to the injection amount_n The value of / (V / N) is shown in the above formula.
, 0.4 or more and 1.6 or less,
The value is extremely close to 1. Incidentally, V _n / (V / N)
The closer to 1, the prevention of the occurrence of the sink mark and the composition
It is expected that compatibility will be achieved in preventing the occurrence of flow defects.
It

The types of materials (thermoplastic resin composition or thermoplastic elastomer composition) injected into the mold may be the same for the first, second, third, ...
It may be changed each time it is ejected. If you inject different materials,
A sphere having a multi-layered structure of a number corresponding to N is formed, and if the same material is injected N times, a sphere similar to the sphere formed by one injection is formed.

Here, the injection molding machine used for applying the manufacturing method of the present invention may be an injection molding machine which is generally used at present, but the mold is made according to the size of the molding part. It is necessary to replace it each time it is ejected. For example, in the mold used for the first injection, as shown in FIG. 1A, the mold ₁ in which the cavity 1a having a capacity corresponding to V ₁ is formed is used, and the mold used for the second injection is ,
As shown in FIG. 1B, a mold 2 having a cavity 2a having a volume corresponding to the total volume of V ₁ and V ₂ , and a molded product 4 molded in the first time can be supported at the center of the cavity 2a. As described above, a plurality of support pins 3 protruding from all sides into the cavity 2a is used. This support pin 3
When the cavity 2a is filled with the material, it is quickly put into the mold 2 (the pin recess 6). In this way, a molded article (sphere) is manufactured in which the surface of the sphere formed in the first time is almost uniformly covered with the material filled in the second time. In FIG. 1, reference numeral 5 denotes a screw, and in the case of a rubber particle-containing composition, the diene rubber is dynamically crosslinked during plasticization of the thermoplastic resin or thermoplastic elastomer serving as a matrix by screw rotation. You can also

The sphere formed as described above is preferably a sphere having a diameter of 30 mm or more. Diameter 30m
This is because in the case of a sphere having a diameter of less than m, the difference in heat history between the central portion and the surface layer portion is small, and generally, the problem of sink is unlikely to occur, and a remarkable effect is obtained with a sphere having a diameter of 30 mm or more. On the other hand, the diameter of the molded sphere is preferably 80 mm or less,
More preferably, it is 50 mm or less. It is necessary to increase the value of N as the diameter of the sphere increases.
Becomes larger, the productivity decreases, but in the case of a sphere with a large diameter, sink marks are less noticeable due to the relationship with the curvature,
Also, the adverse effect on the coating film adhesion is reduced.

The production method of the present invention uses a solid sphere made of a thermoplastic resin or a thermoplastic elastomer, specifically, a golf ball, a billiard ball, a tennis ball, a soft baseball, or a core of these balls. It can be manufactured. Of these, it is particularly suitable for producing a one-piece golf ball which is a one-piece golf ball for recycling and which is formed of a thermoplastic resin composition in which dynamically crosslinked rubber particle powder is dispersed. It is also possible to manufacture a multi-piece golf ball for recycling by changing the type of resin for each injection.

In manufacturing the ball, the surface is painted or surface-treated depending on the type of the ball, and when only the core is manufactured, it is appropriately covered with a cover material or the like.

[0024]

Examples [Measurement / Evaluation Method] Melt Index According to JIS K7210, 230 ° C., load 2.16.
It is a value measured in kg.

In a sink-molded sphere, as shown in FIG. 2, the diameter of the true sphere is D _0, and the diameter obtained from the most recessed part of the sink through the center of the sphere is D _h. As D _h /
When the value of D ₀ × 100 is 98% or more, “◯”, 95 to
The case of 98% was designated as “Δ”, and the case of less than 95% was designated as “x”.

Coating Film Adhesion A urethane coating is applied to the surface of the finally obtained sphere to produce a golf ball, and the obtained golf ball is hit with an initial velocity of 45 m / sec on a metal plate 100 times or It was struck until the coating film cracked. Each sample was subjected to a hitting test with 20 balls, and when all 20 balls were not cracked, "○" was given. When cracking occurred before 100 hits, the coating film was cracked. Indicates the number of hits.

[Relationship Between Kind of Injection Material, Sink and Adhesion of Coating Film] Either A, B or C was used as an injection material, and a sphere having a diameter of 42 mm was injection molded by changing the number of injections.

Here, the material A is an ionomer (Surlyn AD8511 and Surlyn AD851 manufactured by DuPont).
40 parts by weight of butadiene rubber 40
By weight, Takki roll 25 manufactured by Taoka Chemical Co., Ltd. as a crosslinking agent
A composition containing 4 parts by weight of 0-3 (brominated alkylphenol-formaldehyde resin) and having a melt index of 0.05 after the diene rubber was dynamically crosslinked. The material B is Septon 2007 (styrene-based thermoplastic elastomer) manufactured by Kuraray Co., Ltd., and has a melt index of 2.4. Material C is Novatec PP MA4 (polypropylene resin) manufactured by Nippon Polychem, and has a melt index of 5.0.

A screw type injection molding machine is used as the injection molding machine, a mold having a cavity having a capacity corresponding to one injection amount is used, and the second and subsequent times are as shown in FIG. 1 (b). A mold in which various support pins protruded into the cavity was used.

As shown in Table 1, golf ball Nos. 1 to 11,
The molded product was taken out for each injection degree and the degree of sink mark was examined. The coating film adhesion of the finally obtained ball was evaluated according to the above evaluation method. The results are shown in Table 1.

In the evaluation of sink marks, V ₁ , V ₂ , V ₃
Are evaluated by measuring D ₀ and D _h of the sphere produced by the first injection molding, the sphere produced by the second injection molding, and the sphere produced by the third injection molding, respectively.

[0032]

[Table 1]

As can be seen from Table 1, the number of injections (N) 1
In the case of No. 6, the sink marks were large (Nos. 6, 8 and 10), and the lower the melt index of the injection material, the greater the sink marks and the poor coating film adhesion.

If the number of injections is divided into two or more, 1
The sink marks were smaller than those shot in a single shot or did not occur at all. However, when the balance between the first time and the second time is not uniform, the value of V _n / (V / N) is less than 0.4,
When it was more than 1.6, the sink marks were large and the coating film adhesion was poor (No. 1, 5).

[Relationship Between Ball Size, Sink, and Coating Adhesion] Using the above injection molding material A, balls having different diameters were injected once (N) once or twice, and the ball No. ． 12-16 were produced. For each ball,
The sink mark was evaluated for each injection molding, and the coating film adhesion of the finally prepared ball was evaluated. Incidentally, No. Nos. 12 and 13 were coated with an ionomer (thickness: 2.3 mm), and urethane coating was applied to the surface of this ionomer cover layer to examine the coating adhesion. The results are shown in Table 2. Incidentally, No3, 6
The results are also shown.

[0036]

[Table 2]

From Table 2, regardless of the size of the ball, when the number of injections is one, sink marks are generated, and in the evaluation of coating film adhesion, cracks are generated from the sink portion as a starting point, resulting in coating film adhesion. The property was insufficient (No. 14, 6). On the other hand, by setting the number of injections to 2, it was possible to prevent the occurrence of sink marks and improve the adhesion of the coating film.

[0038]

According to the method for producing a solid sphere of the present invention,
Even if the material has poor fluidity, it is possible to manufacture solid spheres with almost no sink marks. Therefore, even if the material has poor fluidity, it is possible to mass-produce solid spheres having excellent sphericity by injection molding with high productivity.

The golf ball of the present invention has a sphericity, an appearance,
It has the same level of coating film adhesion required as a ball as a ball produced by press molding, and it is easy to mass-produce and has excellent recyclability.

[Brief description of drawings]

FIG. 1 is a schematic view showing an embodiment of a mold used in the manufacturing method of the present invention.

FIG. 2 is a diagram for explaining a sink mark evaluation method.

[Explanation of symbols]

1, 2 mold 1a, 2a cavity 3 support pins

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁷ Identification code FI // B29L 31:54 B29L 31:54 (56) References JP-A-9-140831 (JP, A) JP-A-9-143227 (JP, A) JP-A-9-11238 (JP, A) JP-A-61-286112 (JP, A) Actual Kaihei 6-63313 (JP, U) (58) Fields investigated (Int. Cl. ⁷⁾ , DB name) B29C 45/00-45/84 A63B 37/00 A63B 37/04 A63B 37/12

Claims (6)

(57) [Claims] 1. A method for producing a solid sphere having a total volume V by injection-molding a thermoplastic resin or an elastomer composition, wherein the composition is divided into N times (N is an integer of 2 or more). Volume V of the molding part that is injected and formed by the Nth injection molding
_A method for producing a solid sphere, wherein _n satisfies the following relational expression. 0.4 ≦ V _n /(V/N)≦1.6 2. The method for producing a solid sphere according to claim 1, wherein the thermoplastic resin or the elastomer composition has a melt index of 7 or less. 3. The thermoplastic resin or elastomer composition according to claim 1, wherein diene rubber fine particles formed by dynamic crosslinking are dispersed in the thermoplastic resin or thermoplastic elastomer. Manufacturing method of solid sphere. 4. The method for producing a solid sphere according to claim 1, wherein the sphere has a diameter of 30 mm to 80 mm. 5. The solid sphere is a one-piece golf ball.
The manufacturing method according to any one of claims 1 to 4. 6. The solid sphere is a multi-piece golf ball.
The method according to any one of claims 1 to 4, wherein