JPH0363987B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing a foam made of an elastomer with rubber-like elasticity, and particularly to a method for producing a rubber foam that has a closed cell structure but has the same flexibility as an open cell foam. Related. Rubber foams made from natural rubber or various synthetic rubbers have been used for a wide variety of purposes. As a method for manufacturing these rubber foams, in addition to a method in which a diaphragm of foam formed by mechanical stirring of rubber latex is fixed with a curing agent, so-called out-of-mold foaming is widely used. In this method, a decomposable blowing agent such as azodicarbonamide, a crosslinking agent, and other compounding agents are kneaded into the rubber raw material to form a raw material compound, which is then filled into a mold with a filling rate of 100% and firmly pressed using a press. The blowing agent in the raw material compound is decomposed by closing the mold and heating it. When the mold is opened with the internal pressure increased in this manner, the raw material compound rapidly expands due to the foaming action of the decomposed gas generated from the foaming agent, yielding a rubber foam. The rubber foam produced by the above-mentioned out-of-mold foaming has finer cells and a denser structure than that obtained by mechanical foaming. In addition, in normal cases, the cell structure is almost 100% closed cells.
Due to this closed cell structure, rubber foams produced by out-of-mold foaming lack flexibility and have poor adaptability to applications such as packing, sealing materials, printing rolls, and cosmetic puffs. Therefore, when performing out-of-mold foaming, it has been conventional practice to knead oil into the raw material compound to impart flexibility to the resulting closed-cell rubber foam. However, with the conventional oil addition method, only about 100 parts by weight of oil can be mixed into 100 parts by weight of the rubber raw material, and the flexibility is almost equivalent to that of open-cell or resin foam with a high open-cell ratio. It was difficult to obtain sex. In view of the above circumstances, the inventors conducted intensive research to produce a rubber foam with excellent flexibility by out-of-mold foaming, and as a result, they used polynorbornene resin as the rubber elastomer and kneaded it into the raw material compound. When naphthenic oil is used as the oil to be mixed, the amount of
The inventors have discovered that it is possible to add as much as 200 to 500 parts by weight of oil, and that it is possible to impart excellent flexibility to a product comparable to that of open-cell foam, and have thus arrived at the present invention. That is, the present invention prepares a raw material compound by adding and kneading 200 to 500 parts by weight of naphthenic oil, an appropriate amount of a blowing agent, a crosslinking agent, and other compounding agents to 100 parts by weight of a polynorbornene resin. After filling the compound into the mold at a filling rate of 100%, the mold is tightly closed with a press and heated to decompose the foaming agent, and then the mold is opened to expand the raw material compound to form a foam. A method for producing a rubber foam, characterized in that: The polynorbornene resin used as a rubber raw material in the present invention is a polymer obtained by polymerizing a bisdiene oligomer obtained from cyclopentadiene by a Diels-Alder reaction. The polynorbornene resin was developed by CDFCHIMIE in France, and is imported and sold in Japan by Zeon Co., Ltd. under the trade name "Nosolex". The naphthenic oil used in the present invention is composed of cyclic saturated hydrocarbons, and those having 3 to 8 carbon atoms are known, but cyclopentane having 5 carbon atoms and cyclohexane having 6 carbon atoms are the most common. As the blowing agent, crosslinking agent, and other compounding agents in the present invention, the same ones used in conventional out-of-mold foaming can be used. That is, as the blowing agent, for example, azodicarbonamide, dinitrosopentamethylenetetramine, p-toluenesulfonylhydrazine, azobisisobutyronitrile, diazoaminoazobenzene, toluenesulfonyl semicarbazide, etc. may be used. In addition, as a crosslinking agent, for example, dicumyl peroxide,
2,5-dimethyl-2,5-(tertiarybutyl)peroxide, 1,3bis(tertiarybutylperoxy-isopropyl)benzene, m
- Organic peroxides such as octadecyl azide formate, tert-butyl peroxycumene, etc. can be used. Other compounding agents include fillers such as titanium oxide (TiO ₂ ) and calcium carbonate, pigments such as zinc white, and others. When carrying out the present invention, naphthene oil is added to 100 parts by weight of the above polynorbornene resin.
200 to 500 parts by weight of a blowing agent, a crosslinking agent, and other compounding agents may be kneaded using a roll or a Banbury mixer to form a raw material compound, and this may be foamed by conventional out-of-mold foaming. The foaming step at this time may be either one-stage foaming that achieves the desired expansion ratio in one step, or two-stage foaming that achieves the desired expansion ratio through two foaming steps. Single-stage foaming is suitable for obtaining foams with high expansion ratios, according to which the density
Low-density foaming of up to about 0.05g/ ^cm3 is possible, resulting in products with a softer feel. On the other hand, in two-stage foaming, a foaming ratio up to a density of about 0.2 g/cm ³ can only be obtained, but in this case a product with good impact resilience can be obtained. According to the above-described manufacturing method of the present invention, as shown in the examples below, a rubber foam can be manufactured that has significantly superior flexibility compared to conventional rubber foam manufactured by out-of-mold foaming. is possible. An embodiment of the present invention will be described below. Example "Nosolex 150NA" 100 parts by weight (trade name of polynorbornene resin sold by Zeon Corporation) Naphthene oil 300 〃 Calcium carbonate 300 〃 TiO ₂ 20 〃 Zinc white 5 〃 Urea 2 〃 Azodicarbonamide 20 〃 Zinc Milperoxide 2 A raw material composition having the above-mentioned formulation was kneaded with a heated roll to obtain a sheet-like compound. This compound sheet was filled into a press mold at a filling rate of 100%, and two-stage foaming was performed under the following conditions to obtain a rubber foam with a density of 0.2 g/cm ³ . Primary foaming: 147°C x 15 minutes Secondary foaming: 165°C x 10 minutes When the compound sheet was foamed in one step under the following conditions, a rubber foam with a density of 0.05 g/cm ³ was obtained. Conditions: 160°C x 18 minutes Among the products manufactured above, a rubber foam with a density of 0.2 g/cm ³ obtained by two-stage foaming (example product)
and a rubber foam with a density of 0.2 g/cm ³ produced from EDPM by similar out-of-mold foaming.
When the elastic modulus and hardness were measured, the results shown in the following table were obtained. From this result, it is clear that the rubber foam produced by the method of the present invention has significantly superior flexibility compared to conventional products.

[Table] As detailed above, the method for producing a rubber foam according to the present invention has the characteristics of out-of-mold foaming in that a rubber foam with a dense cell structure can be obtained, and it also has the characteristics that cannot be achieved with conventional production methods. It has remarkable effects, such as being able to produce a rubber foam with excellent flexibility that has never been achieved before.

Claims (1)

[Claims] 1 Prepare a raw material compound by adding and kneading 200 to 500 parts by weight of naphthenic oil, appropriate amounts of blowing agents, crosslinking agents, and other compounding agents to 100 parts by weight of polynorbornene resin, and mix the raw material compound to a filling rate of 100. % in a mold, the mold is tightly closed with a press and heated to decompose the foaming agent, and then the mold is opened to expand the raw material compound to form a foam. A method for producing a rubber foam.