GB2284175A

GB2284175A - Mould having good releasability

Info

Publication number: GB2284175A
Application number: GB9423871A
Authority: GB
Inventors: Hidenori Hiraoka; Mikio Yamada
Original assignee: Sumitomo Rubber Industries Ltd
Current assignee: Sumitomo Rubber Industries Ltd
Priority date: 1993-11-26
Filing date: 1994-11-25
Publication date: 1995-05-31
Also published as: AU7902194A; JPH07148742A; GB9423871D0

Abstract

Disclosed is a mold having excellent releasability when molding a golf ball, especially a core of a golf ball or an ionomer covered golf ball body. The mold comprises a mold body and a tungsten carbide layer in the range of from 2 to 20 mu m on the inner surface of the mold body.

Description

MOLD HAVING GOOD RELEASABILITY The present invention relates to a mold having good releasability, especially showing excellent releasability when molding a golf ball.

Hitherto, there have been production problems when molding rubber articles or plastic aritlcles, especially poor releasability following molding golf ball bodies or cores of golf halls. These problems are more serious when golf balls having jonomer coves or cores of golf balbusing asa CD crosslinking agent a metal salt of an a,ss-unsaturated carboxylic acid are produced by molding.

In order to improve the problems of releasability, an aqueous fluorine-containing releasing agent or a fluorine-containing resin has been applied to a mold. The aqueous fluorine-containing releasing agent, however, stains the mold badly and it takes time to clean the stains. It also takes time to apply the agent to the mold. The fluorine-containing coating has improved the annoying cleaning and applying processes, but peeling of the coating generally begins from contact surface between an upper mold and a lower mold, which makes it difficult to use the mold after about 20 times.

A baking type silicone releasing agent which has higher releasability is also used for a mold which is used for ionomer resin covered golf balls(e.g.a so called two-piece golf ball or an ionomer covered thread wound golf ball), since the onomer resin has good affinity to mold metal. Even this silicone releasing agent coating, however, is slightly taken away by the ionomer resin when molding. releasing ability manages to continue at most for about 20 molding processes, but does not continue more times, similar to the fluorine-containing resin.

The present invention provides a mold having excellent releasability when molding a golf ball, especially a core of a golf ball or an ionomer covered golf ball body. The mold of the present invention comprises a mold body and a tungsten carbide layer in the range of fran 2 to 20 m an the inner surface of said mold body, The tungsten carbide is generally expressed by a chemical formula as W2C which is formed on the mold, for example by reacting tungsten fluoride with benzene in a hydrogen gas atmosphere in which the mold is contained.

The reaction formula is considered to be as follow.

The reaction of forming the tungsten carbide may preferably be carried out at a temperature of 350 to 550 C for 0.5 to 2 hours.

E tungsten al on the ffE mold has a thickness in the in af of 2 tD 20 m, preferably 8 to 15 Rm. Thickness of less than 2 gm is poor in uniformity of the coating surface, and more than 20 m may easily result in peeling of * tungsten carbide coating.

The mold to be coated with tungsten carbide can be anyone which is used for molding rubber articles or plastic articles. The mold is preferably formed from stainless steel, aluminum, copper or the like which is generally used for molding a core of a golf ball or an ionomer resin covered golf ball.

The mold which is coated with tungsten carbide, used in the present invention, has excellent releasability, which is suitable for molding, especially golf balls.

EXAMPLES The present invention is illustrated by the following Examples which, however, are not to be construed as limiting the present invention to their details.

Example Molding of a one piece golf ball The following ingredients were mixed and molded in a mold for one piece golf balls at a temperature of 175 OC for 20 minutes to form a one piece golf ball.

Ingredients NO by weiaht Butadiene rubber 100 Zinc oxide 23 Methacrylic acid 21 Antioxidant 0.5 Dicumyl peroxide 1.5 Molding of a core of a two piece golf ball The following ingredients were mixed and molded in a mold for core of two piece golf balls at a temperature of 150 "C for 25 minutes to form a two piece golf ball.

Ingredients NO by weight Butadiene rubber 100 Zinc oxide 20 Zinc acrylate 30 Antioxidant 0.5 Dicumyl peroxide 1.5 Molding of an ionomer cover An ionomer resin composition was prepared by mixing from the following ingredients and covered on the core obtained in Example 2 by injection molding at a temperature of 200 to 250 "C to form a two piece golf ball.

Ingredients % by weight lonomer resin r 100 Titanium dioxide 1 *1 Available from Mitsui Polychemical Co., Ltd. as Himilane 1706.

In the above three Examples, the following four mold 1 to 4 were used for molding, and their releasability is evaluated, and the results are shown in Table 1.

Mold 1: This mold was prepared by forming tungsten carbide coating on a mold and is an embodiment of the present invention. The coating had a thickness of 12 jim.

Mold 2 : A fluorine containing releasing agent which is available from DAIKIN INDUSTRIES, LTD. company as DAIFREE ME 413 was diluted 5 to 20 times, and sprayed on a mold which had been heated.

Mold 3 : A fluorine resin which is available from Nippon Fusso Kogyo K.K. company as 006XL (mainly containing tetrafluoro ethylenehexafluoropropylene copolymer) was applied on a mold and baked.

Mold 4 : A silicone releasing agent which is available from FREKOTE INC company as FREKOTE 33 was spray-coated 2 to 5 times on a mold which had been heated to 50 to 80 "C, and then baked at 200 "C.

Evaluation of releasability is as follow.

Excellent: Releasability is perfect and a molded article was easily taken out by hand.

Good: Releasability is good and a molded article was taken out by hand with twisting.

Fairly good: Releasability is not good and a molded article was taken out by knocking with a mallet.

Poor: Releasability is poor and it was impossible to take out a molded article even by knocking with a mallet.

Table 1

Example Comparative Examples Mold 1 Mold 2 Mold 3 No coating Mold 4 Third cycle One piece Excellent Excellent Excellent Poor Excellent Two piece Excellent Excellent Excellent Poor Excellent lonomer Excellent Poor Excellent Poor Excellent 20th cycle One piece Excellent Poor Good 1 Poor Two piece Excellent Good Fairly goodi --- Poor lonomer Excellent --- Fairly good*1 Fairly good One week One piece Excellent *2 Poor --- -- Two piece Excellent *2 Poor --- -- Ionomer Excellent Poor --- --- --- Poor *1 The coating on the contact surface between an upper mold and a lower mold is peeled off.

t2 The mold has been stained.

Claims

CLAIMS:

1. A mold having good releasability comprising a mold body and a tungsten carbide layer in the range of from 2 to 20 Hm on the inner surface of the mold body.

2. A mold as claimed in claim 1, being suitable for molding a gold ball.

3. A mold as claimed in claim 1 or claim 2 wherein the mold is made of stainless steel, aluminum or copper.

4. A mold as claimed in any one of claims 1 to 3 wherein the tungsten carbide layer is formed by reacting tungsten fluoride with benzene in a hydrogen gas atmosphere.

5. A mold as claimed in claim 4 wherein the reaction is conducted at a temperature of 350 to 5500C for 0.5 to 2 hours.

6. A mold as claimed in claim 1 substantially as hereinbefore described.

7. A mold substantially as hereinbefore described with reference to the example.