JP2777705B2 - Method for producing foamed rubber molded article - 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 foamed rubber molded article used for a bottom contact portion or an installation portion of a shoe sole, furniture furniture, an art object, a precision machine, a precision measuring machine, or the like.

[0002]

2. Description of the Related Art Most commonly, a foamed rubber molded article is heated and pressurized after filling a so-called foamable unvulcanized rubber mixture containing a foaming agent and a foaming aid into a press mold cavity. Was manufactured by

According to such a manufacturing method, vulcanization of rubber and generation of gas due to decomposition of a foaming agent occur simultaneously in a mold cavity, and at the time of completion of vulcanization, the vulcanized rubber is in a state of containing gas. When the hermetically closed state of the cavity was released, the cavity was greatly expanded at that moment or after a lapse of time.

[0004] Due to such expansion, when a three-dimensional design such as a shoe sole has a three-dimensional design on the grounding surface, the three-dimensional design itself also expands, loses sharpness, and the size of the sole changes. In addition, the size, which once seems to be constant, has a possibility that the gas contained in the vulcanized rubber may escape with the passage of time and conversely shrink.

In an attempt to improve such disadvantages, Japanese Patent Laid-Open Publication No.
In a press mold cavity as shown in JP-A-125153, an amount of the foamable unvulcanized rubber admixture is set so that the volume in the cavity and the volume when foamed and vulcanized in an open state match, A method of heating and pressurizing and foaming and vulcanizing has been disclosed.

[0006]

Problems to be Solved by the Invention
According to the method for producing a foamed rubber molded article as shown in JP-A No. 53,
Although the above-mentioned disadvantages that existed before that were considerably improved, it is still necessary to sharpen a three-dimensional design such as a shoe sole, and in any case, to accurately determine the size. In fact, for some products, satisfactory results have not been obtained. An object of the present invention is to provide a method capable of obtaining a foamed rubber molded article having no such a defect by using a press mold.

[0007]

According to the present invention, a foamable unvulcanized rubber admixture having a volume smaller than that of the cavity is placed in a lower cavity of a press mold and combined with an upper mold of a press mold. A method for producing a foamed rubber molded article by foaming and vulcanizing by heating and pressurizing, wherein the press mold combined as described above is placed in a vacuum atmosphere, heated and pressurized, and foamed and vulcanized. The method is characterized by the method for producing a foamed rubber molded article described above.

In carrying out the present invention, the vacuum atmosphere is 50 mmHg or less, preferably 30 mmHg or less. In the latter case, in particular, almost no air remains in the cavity, so-called voids and the like do not occur, and A foamed rubber molded article having a three-dimensional sharp design can be obtained.

The above-mentioned vacuum state is caused by the fact that the volume of the foamable unvulcanized rubber admixture increases in the process of foaming due to heating in the lower cavity of the press mold and the volume increases. It does not have to be from the beginning, and may be from a state where the decomposition of the foaming agent has progressed to some extent. Although it differs slightly depending on the vulcanization temperature, in the case of 145 ° C., it is sufficient that the vacuum atmosphere is reached when 1 to 1.5 minutes have passed after the start of heating and pressurization. The heating and pressurizing conditions are usually a temperature of 130 to 150 ° C., a press pressure of 15 to 25 kg / cm ² , a foaming time of 1.5 to 2.5 minutes, and a vulcanization time of 4 to 7 minutes.

[0010] Polyamide fiber, glass fiber and the like can be mixed in the foamable unvulcanized rubber admixture. Usually, fibers having a thickness of 1.6 to 20 deniers, preferably 1.5 to 3 deniers and a length of 3 to 10 mm are used. The expansion of the foam after vulcanization molding is suppressed and accurate dimensional accuracy is obtained. be able to.

[0011]

According to the present invention, the foamable unvulcanized rubber admixture is contained in an amount less than the volume of the lower cavity of the mold. In the process until filling is completed, there is a void in the cavity, so that part is in a vacuum state, and therefore, the residual between the three-dimensional design surface formed in the cavity and the foamable unvulcanized admixture Air disappears, voids are not generated, and the foamed rubber molded article obtained through the subsequent vulcanization step has a sharp three-dimensional design.

[0012]

[Example] Foaming unvulcanized rubber blended compound 1 2 Natural rubber 100 parts by weight 100 parts by weight Sulfur yellow 2 2 Zinc white 1 1 Stearic acid 1 1 Vulcanization accelerator M 1 1 1 Vulcanization accelerator TS 0.4 0.4 老 Antioxidant W 1 〃 1 〃 Wax 1 〃 1 〃 Softener sub 8 〃 8 ポ リ ア ミ ド Polyamide fiber ^{* 1} 15 ２０ 20 〃 Glass fiber ^{* 2} 10 〃-azo type Blowing agent 4 {4} * 1: 15 denier and 2 to 10 mm in length were used. * 2: A thing with a diameter of 10 microns and a length of 3 mm was used.

A foamable unvulcanized rubber mixture as described above was obtained. Each of the admixtures is placed in a mold lower mold cavity (a cavity for manufacturing shoe soles for children's shoes, having a vertical length of 198 mm, an internal volume of 51 cc, and a width of 2 mm on the side and bottom thereof. (A wave design with a depth of 1.5 mm is formed.)

The press mold lower mold and the press mold upper mold are combined, and a silicone sponge vacuum cabin having a pipe leading to a vacuum pump (floor area: 510 mm × 510)
mm, height 72mm) and press the hot plate (temperature 1)
45 ° C.) and set for 2 minutes and 45 seconds under the conditions of a press pressure of 20 kg / cm ² and a vacuum of 5 mmHg in the cabin. By this operation, foaming of the rubber mixture was substantially completed, and subsequently the same conditions were continued for 6 minutes to complete vulcanization to obtain a foam molded article.

Observation after standing at room temperature (15-18 ° C.) for 24 hours revealed that the vertical length was 198.2 mm, the weight was 32 g,
It was possible to produce a shoe sole for a child having a good mold flow condition and a design surface free from voids and chips.

Claims (2)

(57) [Claims] 1. A foamable unvulcanized rubber admixture having a volume smaller than that of the cavity in a press mold lower mold cavity is combined with an upper mold of the press mold, and heated and pressed to foam and mold. In a method for producing a foamed rubber molded article by vulcanizing, the press mold combined as described above is placed in a vacuum atmosphere, heated and pressed, and foamed and vulcanized. Production method. 2. The method according to claim 1, wherein the vacuum atmosphere is 50 mmHg or less.