JPS583814B2 - Polyolefin foam - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing polyolefin foam, and more specifically, the present invention relates to a method for producing polyolefin foam. In the method of obtaining a crosslinked foam by performing a crosslinking reaction and a foaming reaction in an air atmosphere at a high temperature sufficient to decompose the agent, or by irradiating ionizing radiation to a substrate mainly composed of a pyrolytic foaming agent and a polyolefin resin. In this method, a foaming reaction is carried out in an air atmosphere at a temperature high enough to decompose the foaming agent to introduce a crosslinked structure to obtain a crosslinked foam. The present invention relates to a method for producing polyolefin foam, which is characterized by adding a modifier.

The purpose of this is to prevent thermal deterioration of the surface of the foam during the foaming process of polyolefin foam in a high-temperature air atmosphere, and to obtain a foam that has a soft surface, feels good to the touch, and has high strength.

Conventionally, when producing cross-linked polyolefin foam, the viscoelasticity of the polyolefin resin is adjusted in advance to a range suitable for foaming through a cross-linking reaction, and then the blowing agent is decomposed in a high-temperature atmosphere, and the generated gas is incorporated into the cross-linked polyolefin resin. The foam was obtained by trapping.

The blowing agent is most commonly azodicarbonamide,
This substance decomposes at temperatures above 200°C and generates gas.

Therefore, when producing a crosslinked polyolefin foam, the polyolefin is exposed to a high temperature atmosphere of 200° C. or higher, so thermal deterioration naturally becomes a problem.

Thermal deterioration is particularly large in the presence of oxygen, so foaming has been carried out in high-temperature atmospheres with little oxygen, such as in inorganic salt baths, nitrogen or carbon dioxide gas, or glycerin baths. It was expensive, and the process was complicated because substances in the bath that had adhered to the product had to be washed away.

On the other hand, the method of heating and foaming in air has the drawback that if the foaming agent is sufficiently decomposed, the bubbles on the surface are destroyed, giving the surface a rough feel and significantly deteriorating the appearance.

The present invention was developed in view of the above-mentioned drawbacks, and aims to prevent thermal deterioration of the surface of a crosslinked polyolefin foam by using heated air as a heat medium, and to obtain a product that is extremely soft and has a good texture.

The present invention can be carried out by applying a modifier made of quinone dioxime or its ester to the surface of a crosslinked foamable polyolefin resin molding, and then foaming and expanding the molded product using heated air as a heat medium.

That is, in the case of a crosslinked foam using a chemical crosslinking agent, the crosslinking agent and blowing agent of the polyolefin resin are mixed with the polyolefin resin at a temperature at which the crosslinking agent and the blowing agent do not decompose to form a molded product, and then the surface of the molded product is After applying a modifier made of quinone dioxime or its ester, it is heated to a temperature at which the crosslinking agent and the blowing agent decompose to form a crosslinked foam.

In addition, when introducing a crosslinked structure using ionizing radiation,
A blowing agent is mixed with a polyolefin resin at a temperature below the decomposition temperature of the blowing agent to form a molded product, and the molded product is then irradiated with ionizing radiation to form a crosslinked product.

Next, a modifier made of quinone dioxime or its ester is applied to the surface of this crosslinked foamed molded product, and then heated, foamed, and expanded to obtain a crosslinked foamed product.

The mechanism of action of modifiers consisting of quinone dioxime and its esters on crosslinked polyolefin foams is not clear, but in the coexistence of radical-generating crosslinking agents (mainly organic peroxides), they play the role of crosslinking aids and promote crosslinking. It is thought that it exhibits an anti-aging effect when the agent is completely decomposed or in the absence of a crosslinking agent.

According to one theory, quinone dioxime and its ester act as a crosslinking agent in a polymer having a double bond (for example, unvulcanized rubber), and after acting as a crosslinking agent, it is oxidized and exerts an antiaging effect.

Therefore, if a modifying material made of quinone dioxime or its ester is applied to the surface of the cross-linked polyolefin foam material before heating with high-temperature air, both the cross-linking aid effect and anti-aging effect can be achieved. .

For example, when a crosslinked polyolefin foam material is foamed by adding an anti-aging agent to the surface, the foam film on the surface is thin and flexible, and the gel fraction is 40% compared to 55% inside.

Those to which a crosslinking aid (triallyl cyanurate) has been added have a smooth surface, gloss, and toughness, and the gel fraction is 53% compared to the internal 55%.

On the other hand, the product to which quinone dioxime was applied had a state intermediate between the above two examples, that is, the foam film on the surface was thin, the texture was good, and it was tough and had a gel fraction of 47%.

From this result as well, it is presumed that quinone dioxime has both an effect as a crosslinking agent and an anti-aging effect.

Examples of quinone dioximes useful in the present invention include quinone dioxime (also known as benzoquinone dioxime) and its esters such as penzoate, maleate, acetate, toluate, propionate, butyrate, and lactate, and may be monoesters or diesters, respectively.

The polyolefin resins used in the present invention include, for example, high density polyethylene, low density polyethylene, polypropylene, ethylene-vinyl acetate copolymer, ethylene-vinyl chloride copolymer, ethylene-acrylic acid ester copolymer, EPDM, .2-polyptadiene, polybutene, etc., and these may be used alone or in combination.

In addition, these resins include ABS resin, chlorinated polyethylene,
Chlorosulfonated polyethylene, 1,4-polyptadiene, SBR, NBR, etc. may be mixed.

The radical-generating crosslinking agent of the present invention has the function of thermally decomposing to generate radicals and form crosslinks in polyolefin resins, such as di-t-butyl peroxide, t-butylcumyl peroxide, and Milperoxide, αα′-bis-(t-butylperoxy)P-diisopropylbenzene, 2,5-dimethyl-2.5-di(t-butylperoxy)hexane, t
-butylperoxyisoglopylbenzene, etc.

Ionizing radiation according to the present invention includes α rays, β rays, γ rays, neutron beams, proton beams, X-rays, and the like.

Generally, beta rays are used, and the appropriate dose of beta rays from an accelerator is 1 to 10 Mrad.

The thermally decomposable blowing agent that can be used in the present invention is a substance that decomposes to generate gas at a temperature higher than the melting temperature of the polyolefin and higher than the decomposition temperature of the radical-generating crosslinking agent with a half-life of 1 minute. Bisisobutyronitrile, azodicarpolyamide, diazoaminobenzene, N-N' dinitrosobentamethylenetetramine, benzenesulfonylhydrazide, toluenesulfonylhydrazide, etc., or a mixture of two or more thereof may be used.

A convenient method for applying the crosslinked foaming composition to the surface is to dissolve or disperse the modifier made of quinone dioxime or its ester in an organic solvent, and then apply, dip, or spray the modifier.

It may be used with thickeners to adjust the viscosity.

Example 1 0.8 parts of dicumyl peroxide as a crosslinking agent and 15 parts of azodicarbonamide as a blowing agent were added to 100 parts by weight of polyethylene having a density of 0.920 g/cm2 and an M I of 3.2, and the mixture was heated at 120°C. Knead with a roll of 12
Press molding was carried out at 0° C. and a pressure of 200 kg/cm 2 to create a foamed fabric with a thickness of 2 mm.

P-quinone dioxime 4% in methylene chloride, ethylene-vinyl acetate copolymer (vinyl acetate ratio 3) as a thickener.
The foamed fabric was immersed in a solution containing 3%, MI25) and 2%, dried, and then heated in hot air at 230° C. for about 6 minutes to obtain a polyethylene crosslinked foam.

The bubbles on the surface of the foam were not broken, and the film was thin, flexible, and had a good texture.

The amount of P-quinone dioxime applied on the foam material was 2 g/m
It was 2.

Example 2 After blending 20 parts of azodicarbonamide as a blowing agent with 100 parts of MI23 low density polyethylene, the mixture was heated to 120°C.
The mixture was kneaded with a roll to form a sheet with a thickness of 1 mm.

Next, this sheet was exposed to 5 M using an accelerated electron beam irradiation device.
rad irradiation, and further added 8% of quinonedioxime dibenzoate (P.P'-dibenzoylquinonedioxime) and 2% of the same ethylene-vinyl acetate copolymer as in Example 1 as a thickener. A trichlorethylene solution containing the above was coated with a doctor knife, and then heated with hot air at 230°C.

The resulting foam had a surface that was very soft and had a pleasant texture without bursting of the surface cells, whereas the foam that was not coated with quinone dioxime dibenzoate had no bursting of the surface cells. There are also places where
The surface was rough.

Claims (1)

[Claims] 1 A substrate mainly composed of a pyrolytic blowing agent, a radical-generating crosslinking agent, and a polyolefin resin is subjected to a crosslinking reaction and a foaming reaction in an air atmosphere at a high temperature sufficient for the crosslinking agent to generate radicals and for the blowing agent to decompose. or after introducing a crosslinked structure by irradiating a substrate mainly composed of a pyrolytic blowing agent and a polyolefin resin with ionizing radiation, the blowing agent is A method for producing a polyolefin foam, the method comprising performing a foaming reaction in a high-temperature air atmosphere to obtain a crosslinked foam, which comprises applying a modifier consisting of quinone dioxime or an ester thereof to the surface of a substrate before foaming.