JPS582812B2 - Polyolefin foam - Google Patents

Description

Detailed Description of the Invention The present invention aims to prevent thermal deterioration of the surface of the foam and obtain a foam with a smooth surface and high strength in the foaming process of polyolefin foam in a high-temperature atmosphere. Regarding the manufacturing method, please refer to the following for details: Cross-linking a base material mainly composed of a pyrolytic blowing agent, a radical-generating cross-linking agent, and a polyolefin resin in an atmosphere at a high enough temperature that the cross-linking agent generates radicals and the blowing agent decomposes. In the method of obtaining a crosslinked foam by carrying out reaction and foaming reaction, it is possible to obtain a foam with a smooth surface and high surface strength by applying a crosslinking agent and/or a crosslinking aid to the surface of the substrate before foaming. This is a manufacturing method for polyolefin foam.

Conventional method for obtaining polyolefin foam by foaming a base material mainly composed of a pyrolytic foaming agent, a radical-generating crosslinking agent, and a polyolefin resin in a high-temperature air atmosphere (
So-called chemically crosslinked polyolefine foam) has inferior surface smoothness compared to a method of crosslinking by electron beam irradiation instead of using a crosslinking agent (so-called electron beam crosslinked polyolefine foam).

The reason is that with radical-generating cross-linking agents, all the radicals generated by thermal decomposition do not act on the cross-linking reaction of polyolefin (this is a competitive reaction with the scission reaction (deterioration) of the polyolefin main chain, and in the presence of air, the latter This increases the ratio of crosslinking, resulting in poor crosslinking efficiency.

For example, in an electron beam crosslinked polyolefin foam, the degree of crosslinking (gel fraction) on the surface is 90% or more of that in the interior, but in a chemically crosslinked polyolefin foam, it is about 70%.

Therefore, in the process of foaming chemically crosslinked polyolefin foam in high-temperature air, due to insufficient surface crosslinking, the bubbles cannot withstand the pressure of the gas generated by the blowing agent and tend to burst on the surface, resulting in a lack of surface smoothness. It's hot.

Furthermore, due to the splitting reaction of the polyolefin main chain, the surface strength was low and it tended to tear easily.

If the amount of crosslinking agent mixed is increased in an attempt to improve this drawback, the overall foaming ratio will decrease, the cushioning properties and heat insulation properties of the foam will deteriorate, and problems will also occur in the extrusion molding of the foam material. .

For this reason, there are methods of blocking air during the foaming process, such as foaming in nitrogen gas, a glycerin bath, or an inorganic salt bath, but these methods are expensive and require cleaning of the substances in the bath that have adhered to the product. It is complicated and complex.

The present invention was made in view of the above problems, and its purpose is to smooth the surface of a foam, improve its texture, and increase its surface strength.

In other words, when producing chemically crosslinked polyolefin foam, applying a crosslinking agent and/or a crosslinking aid to the surface of the raw fabric before foaming prevents thermal deterioration of the foam surface during the subsequent foaming process, resulting in a smooth surface and high strength. This invention relates to a method for producing polyolefin foam, which is characterized by obtaining a large foam.

As a technique related to the present invention, for example, Japanese Patent Application Laid-Open No. 48-885
There is a method described in Publication No. 5, in which a crosslinking agent is applied to the polyethylene surface and the temperature is below 110°C (70 to 90°C).
The method is characterized in that the crosslinking agent is permeated and diffused into the crosslinking agent by heating it to a temperature of 0° C.) and then crosslinked, and the purpose and process thereof are different from those of the present invention.

That is, the present invention aims to improve surface smoothness and surface strength, and there is no need for the crosslinking agent to diffuse into the interior, so a heating process at 70 to 90°C for permeation and diffusion is not necessary. The aim is to obtain a crosslinked foam at a temperature higher than the decomposition temperature of the direct blowing agent (approximately 200°C).

Moreover, as a substance applied to the surface, a crosslinking aid alone without using a crosslinking agent exhibits similar or better effects.

In chemically crosslinked polyolefin foam, a crosslinking reaction is caused by a crosslinking agent, but when a crosslinking aid is used in combination with the crosslinking agent, the effect is greatly enhanced.

This is to reduce the ratio of the main chain cleavage reaction of radicals generated from the crosslinking agent and to increase the efficiency of the crosslinking reaction.

For this reason, foams that are foamed in a high-temperature atmosphere after applying a crosslinking aid to the surface of the foam material have less surface deterioration than those that are coated with a crosslinking agent.

However, even when a crosslinking agent is applied, the surface deterioration is much less than when no crosslinking agent is applied, and a smooth and strong product can be obtained.

When comparing with the naked eye a foam made by foaming raw foam in high-temperature air, and a foam made by applying a crosslinking agent and/or crosslinking aid to the surface of the foaming raw material and foaming it in high-temperature air, the former shows that the former is foamed. The foam inside the body reaches the surface of the skin and ruptures, which melts into a crater shape, or the surface deteriorates due to heat.In the latter case, the foam bubbles reach the surface but do not burst. The surface is smooth and feels good on the skin.

The crosslinking agent and/or crosslinking aid used in the present invention can be applied by dipping, coating, or spraying if it is liquid, or by heating and melting, dipping, or coating if it is solid. You may.

Alternatively, it may be diluted with an organic solvent, or may be used together with a thickener to adjust the viscosity.

Examples of the polyolefin used in the present invention include high-density polyethylene, low-density polyethylene, polypropylene, ethylene-vinyl acetate copolymer, ethylene-vinyl chloride copolymer, ethylene-acrylic ester copolymer, EP
These include DM, 1.2-polybutadiene, and polybutene, and these can be used alone or in combination.

Examples of crosslinking aids that can be used in the present invention include acrylates such as triacrylic formal and trimethylolpropane triacrylate, methacrylates such as triethylene glycol dimethacrylate and tetraethylene glycol dimethacrylate, diallylphthalate, and These are allyl-based polyfunctional monomers such as allyl inocyanurate and triallyl cyanurate, and these monomers may be used alone or in combination.

Examples of crosslinking agents that can be used in the present invention include di-t-butyl peroxide, t-butylcumyl peroxide, dicumyl peroxide, 2,5-dimethyl 2,5-
Di(t-butylperoxy)hexane, 2,5-dimethyl 2,5=di(1-butylperoxy)hexane = 3,
1,3-bis(1-butylperoxyinoglobil)benzene, t-butylhydroperoxide, di-t-amylperoxide, diisopyrbenzene hydroperoxide, etc., or a mixture of two or more thereof. There may be.

The thermally decomposable blowing agent 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. Azobisisobutyronitrile, azodicarbonamide, diazoaminobenzene, N-N'-
Dinitrosopentamethylenetetramine, toluenesulfonyl hydrazide, etc., or a mixture of two or more thereof may be used.

Example I 15 parts of azodicarbonamide as a blowing agent was added to 100 parts of low density polyethylene with an MI (melt index) of 1.0.
After adding 0.8 parts of dicumyl peroxide as a crosslinking agent, the mixture was kneaded with rolls at 120°C without decomposing the crosslinking agent and blowing agent, and heated and pressed at the same temperature to form a sheet with a thickness of 4 mm. Molded.

Coat this with a doctor knife with a solution of 6% 1,3-bis(1-butylperoxyisoglobil)benzene dissolved in trichlorethylene, and after drying,
Cut out a small piece of 0mm x width 50mm from the sheet, 23
When the mixture was left in a dryer at 0°C for 6 minutes to foam, a foam with an extremely smooth and glossy surface was obtained.

The bubbles on the surface of the foam were not broken at all.

Example 2 After blending 15 parts of azodicarbonamide as a blowing agent and 0.8 parts of dicumyl peroxide as a crosslinking agent into 100 parts of low density polyethylene of MI20, a crosslinking agent,
3mm thick using an extruder without decomposing the foaming agent.
It was extruded as a foamed fabric with a width of 400 mm.

While spraying a solution of dicumyl peroxide dissolved in methylene chloride at 10% on both sides of this foamed material, the material was foamed in a heating furnace at a maximum temperature of 245°C, resulting in a thickness of 9.
A foam with a very smooth* and glossy surface of 1.0 mm was obtained.

No signs of foam rupture were observed on the surface of the foam.

Example 3 A solution of 6% triallyl cyanurate, a crosslinking agent, dissolved in methylene chloride was sprayed on both sides of the foam fabric prepared in the same manner as in Example 1, and then heated in the same manner as in Example 1 to thicken the material. A foam with a very smooth and glossy surface of 9 mm in length was obtained.

There were no signs of foam rupture on the surface of the foam.

Comparative Example In the same manner as in Example 2, except that a solution of dicumyl peroxide in methylene chloride was not sprayed onto the foam material and the foam material was passed through a heating furnace without surface treatment, the foam was foamed to a thickness of 8 m.
A foam of m was obtained.

There were spots on the surface where the bubbles had burst, and craters similar to those on the moon were also visible.

Example 2 Example 30 The results of measuring the surface gel fraction, apparent specific gravity of the entire foam, tensile strength, elongation, and tear strength (all according to JISK-76767) of the foam of Example 30 and the foam of Comparative Example are shown below. .

As can be seen here, it should be noted that the tear strength is improved.

Claims (1)

[Claims] 1 A base material mainly composed of a pyrolytic blowing agent, a radical-generating cross-linking agent, and a polyolefin resin is subjected to a cross-linking reaction and a foaming reaction in an atmosphere at a high temperature sufficient for the cross-linking agent to generate radicals and for the blowing agent to decompose. A method for producing a polyolefin in-foam, which comprises applying a crosslinking agent and/or a crosslinking aid to the surface of a substrate before foaming.