JP2000044712A - Sponge rubber composition and production of the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a rubber composition which can give an article having a low specific gravity, a low hardness, and a reduced shrinkage by mixing a sponge rubber compound with a specified amount of a thermoplastic synthetic resin having a good affinity for the sponge rubber compound and melting at the decomposition temperature of a blowing agent or below. SOLUTION: There is provided a sponge rubber composition obtained by mixing a sponge rubber compound with 0.1-100 phr of a thermoplastic synthetic resin having a good affinity for the compound and melting at the decomposition temperature of a blowing agent used or below. This composition is packed into a mold in a packing ratio of 100%, foamed, and crosslinked, and the pressure is released to obtain an article. The sponge rubber compound is obtained by mixing a rubber such as EPDM with a crosslinking agent such as an organic peroxide, a white filler such as zinc oxide or silica, and a softener such as a paraffinic oil in a specified ratio. The thermoplastic resin used is, for example, a polystyrene which does not harden the sponge.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a sponge rubber composition having a low specific gravity and a low hardness.

[0002]

2. Description of the Related Art A compound is a mixture obtained by adding various compounds to rubber so that it can be molded and processed as it is. Sponge rubber is obtained by blending a foaming agent with rubber and making the rubber porous by a gas generated by thermal decomposition of the foaming agent prior to the progress of vulcanization. Crosslinking is the chemical bonding between molecules of a linear polymer to form a network. phr is parts per hundred parts of rubber, and is the number of parts of a compounding agent per 100 parts of rubber.

[0003] A rubber compound to which a crosslinking agent and a foaming agent are added is filled in a mold by 100%, crosslinked and foamed under high pressure (often two-stage vulcanization), and then the sponge is released by releasing the pressure. A rubber composition is obtained. When producing a sponge rubber composition having a low specific gravity, a large amount of a foaming agent is generally added. However, in many cases, the balance between cross-linking and foaming is lost, and after the completion of cross-linking / foaming, the resin shrinks greatly. As a result, not only can products with low specific gravity not be obtained,
Due to shrinkage of the product (raw material and sponge sheet after slicing), the thickness dimension largely varies.

[0004]

SUMMARY OF THE INVENTION The present invention provides a rubber compound containing a crosslinking agent and a foaming agent in a mold at 100%.
An object of the present invention is to provide a sponge rubber composition having a low specific gravity, a low hardness and a small product shrinkage obtained by filling, crosslinking and foaming under high pressure, and then releasing the pressure.

[0005]

Means for Solving the Problems The sponge rubber composition according to the present invention comprises a sponge rubber compound containing 0.1 to 100 phr of a thermoplastic synthetic resin having a high affinity for a sponge rubber compound and melting at a decomposition temperature or lower of a foaming agent or lower. It is a sponge rubber composition for low specific gravity, low hardness or decorative puff added. The method for producing a sponge rubber composition according to the present invention comprises the steps of: adding a thermoplastic synthetic resin having good affinity and melting at a temperature not higher than the decomposition temperature of a foaming agent to a rubber compound to which a crosslinking agent and a foaming agent are added; This is a method for producing a sponge rubber composition for low specific gravity, low hardness or decorative puff in which the pressure is released after foaming / crosslinking under high pressure after foaming and crosslinking under high pressure.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, a thermoplastic resin is added to a sponge rubber compound to cause crosslinking and foaming. The thermoplastic resin has a good affinity for the rubber raw material as the base material and does not harden the sponge. Use a thermoplastic synthetic resin having a suitable dissolution temperature according to the decomposition temperature of the blowing agent to be used. The amount of thermoplastic synthetic resin added is such that the physical properties of the original rubber sponge do not change significantly (0.1 to 100 phr)
It is desirable to adjust to about 50 phr. In other words, at less than 0.1 phr, the shrinkage variation is large, and
If it exceeds 0 phr, the physical properties of the original rubber sponge will change significantly.

[0007]

EFFECTS OF THE INVENTION In the sponge rubber composition obtained by the present invention, the thickness deviation due to shrinkage variation is reduced. The shape during cross-linking and foaming is stable, so the inclination during stacking is small, and the size of the raw material is small (volume ratio 17% reduction)
As a result, production and transportation efficiency will increase.

[0008]

[Examples] EPDM polymer is Mitsui EPT 3045 manufactured by Mitsui Chemicals, Inc. White filler is Shiraishi Hua O manufactured by Shiraishi Industry Co., Ltd. and NipsilVN3 manufactured by Nippon Silica Industry Co., Ltd. Paraffin oil is Diana manufactured by Idemitsu Kosan Co. Process PS-430, organic peroxide is Parkmill D-40 manufactured by NOF Corporation, and foaming agent is Cellogen O manufactured by Uniroyal.
T and polyethylene are AC manufactured by Allied Corporation of the United States.
617 was used. Using the same mold, molding was performed under the same foaming conditions. The sponge rubber having a thickness of about 30 mm obtained after releasing the pressure was sliced to a thickness of 8 mm. Next, annealing was performed at 80 ° C. for 8 hours, and the sponge shrinkage before and after the annealing was measured. The tensile strength and elongation were measured according to JIS K 6301, and the sponge hardness was measured using an Asker CSS hardness tester manufactured by Kobunshi Keiki Co., Ltd. [Example 1] Product name Addition number Addition number Conventional product Invention product EPDM polymer Mitsui EPT3045 100phr 100phr White filler White gloss O 80 80 Nipsil VN3 30 30 Zinc oxide 16 16 Paraffin oil Tyana Processes PS-430 40 40 Organic excess Oxide Hardmill D-40 5 5 Blowing agent Cellophane OT 12 12 Polyethylene A-C617-3 Sponge thickness 31.4mm 29.5mm Sponge shrinkage 22% 10% Sponge hardness (Asker CSS) 19 ° 18 ° Tensile strength (JIS K 6301 ) 650kpa 660kpa elongation (JIS K 6301) 540% 510%

Claims (4)

[Claims] 1. A sponge rubber composition having a low specific gravity and a low hardness, wherein 0.1 to 100 phr of a thermoplastic synthetic resin having a good affinity for a sponge rubber compound and melting at a temperature lower than a decomposition temperature of a foaming agent is added to the sponge rubber compound. 2. A sponge rubber composition for a cosmetic puff, wherein 0.1 to 100 phr of a thermoplastic synthetic resin having a good affinity for a sponge rubber compound and melting at a temperature not higher than the decomposition temperature of a foaming agent is added to the sponge rubber compound. 3. To a rubber compound to which a crosslinking agent and a foaming agent are added, a thermoplastic synthetic resin having good affinity and melting at a temperature not higher than the decomposition temperature of the foaming agent is added, and 100% is filled in a mold. A method for producing a low-specific-gravity, low-hardness sponge rubber composition in which pressure is released after foaming / crosslinking. 4. To a rubber compound to which a crosslinking agent and a foaming agent are added, a thermoplastic synthetic resin having good affinity and melting at a temperature not higher than the decomposition temperature of the foaming agent is added, and 100% is filled in a mold. A method for producing a sponge rubber composition for cosmetic puffs in which pressure is released after foaming / crosslinking.