JPH0776284B2 - Method for producing olefin resin foam - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing an olefin resin foam.

[Conventional technology]

Olefin resin foams having closed cells are widely used in various fields as heat insulating materials and cushioning materials because they are flexible and have high heat insulating properties and mechanical strength.

In order to produce this kind of olefin resin foam,
It is common to crosslink using known chemical crosslinking agents or by ionizing radiation (eg electron beam) crosslinking methods. Further, for example, Japanese Patent Laid-Open Nos. 51-66334 and 5
As described in JP-A-5-75432, an olefinic resin is graft-bonded with an alkoxysilane compound in the presence of an organic peroxide, and then the graft-bonded resin is mixed with a blowing agent and other additives. However, a method of crosslinking and foaming is used.

[Problems to be Solved by the Invention]

In the known method, the conventional crosslinking method using a chemical crosslinking agent tends to cause partial crosslinking during thermoforming. In the cross-linking method using ionizing radiation, since the cross-linking structure is determined before foaming, the cross-linking degree is limited both above and below, it is difficult to increase the final cross-linking degree, and the thermal dimensional stability tends to be poor. Further, in the method described in the above publication, since the decomposition temperature of the organic peroxide is generally higher than the decomposition temperature of the foaming agent, a) first, an alkoxysilane compound is graft-bonded to the olefin resin using the organic peroxide. Therefore, it is necessary to perform a complicated step of b) kneading and molding the obtained graft resin with a foaming agent, and c) giving an appropriate degree of crosslinking necessary for foaming, and then heat-foaming, thereby improving productivity. Is extremely low, and a solution to this point has been desired.

Therefore, it is an object of the present invention to provide a method for producing an olefin resin foam excellent in thermal dimensional stability with a simplified process and increased productivity.

[Means for Solving the Problems]

The present inventors have completed the present invention as a result of extensive studies to solve the above problems.

The present invention molds a mixed raw material containing an olefin resin, an alkoxysilane compound having an acryloyl group and / or a methacryloyl group in the molecule and a chemical decomposition type foaming agent at a temperature lower than the decomposition temperature of the chemical decomposition type foaming agent. After irradiating the obtained molded product with ionizing radiation, it is heated to a temperature not lower than the decomposition temperature of the chemical decomposition type foaming agent,
It is a method for producing an olefin resin foam.

The present invention will be described in more detail below.

Examples of the olefin resin used in the present invention include low-density to high-density polyethylene, linear polyethylene, polypropylene, ethylene-propylene copolymer,
Examples thereof include copolymers of ethylene and other monomers such as vinyl acetate, acrylic acid, and methacrylic acid. These are used alone or as a mixture of two or more kinds.

Examples of the alkoxylane compound having an acryloyl group and / or a methacryloyl group used in the present invention include (meth) acryloyloxyalkyl-trimethoxysilane. One or more acryloyl groups and / or methacryloyl groups are preferably contained in the molecule. The amount of the alkoxysilane compound added is generally 0.1 to 15 parts by weight, preferably 1 to 3 parts by weight, based on 100 parts by weight of the olefin resin.

The chemical decomposition type foaming agent used in the present invention,
For example, azodicarbonamide, oxybenzenesulfonyl hydrazide, azobisisobutyronitrile, N, N'-
Examples thereof include dinitrosopentamethylenetetramine. The amount of the foaming agent added is 0.5 to 40 parts by weight, preferably 10 to 30 parts by weight, based on 100 parts by weight of the olefin resin.

In the mixed raw material consisting of an olefin resin, the above-mentioned alkoxysilane compound and a foaming agent, if necessary, common additives such as lubricants, flame retardants, antistatic agents, antioxidants, anti-aging agents, ultraviolet absorbers and inorganic materials are added. In addition, organic fillers, colorants and the like can be added. A reaction inhibitor such as mercaptan may be added to suppress the polymerization between the alkoxysilane compounds.

The mixed raw material is melted and kneaded at a temperature lower than the decomposition temperature of the foaming agent, and then molded. For this purpose, for example, a Banbury mixer, a kneader mixer, etc., as well as a single-screw or multi-screw extruder can be used. The molded product may have any shape, but is preferably extruded into a sheet.

Then, by irradiating the obtained formed product with ionizing radiation, the olefinic resin in the formed product is radically reactively crosslinked to obtain the necessary crosslinking for foaming. Simultaneously with this reaction, radicals are generated from the olefin resin to graft bond the alkoxysilane compound to the olefin resin. Ionizing radiation refers to α rays, β rays, γ rays, and electron rays. Of these, electron beams are particularly preferable.

The crosslinked / grafted molded product thus obtained is heated to a temperature equal to or higher than the decomposition temperature of the chemical decomposition type foaming agent to foam. In this foaming step, the condensation-crosslinking reaction with the alkoxysilane compound proceeds simultaneously with or after foaming.
This reaction is sufficiently carried out by the heat required for dividing the foaming agent and a trace amount of water in the resin mixture or in the atmosphere during the heat treatment, for example, in the air.

[Work]

According to the method of the present invention, by irradiating the molded product with ionizing radiation, a radical cross-linking reaction occurs in the olefin resin, and the cross-linking necessary for foaming is obtained, and at the same time, the molded radical causes the alkoxy silane compound Graft-bonds to the olefin resin. Since the above-mentioned alkoxy lan compound is in a state of being simply mixed at the time of molding, it does not cause partial cross-linking and hinder the moldability. Further, since uniform crosslinking is obtained by ionizing radiation, uniform bubbles can be easily obtained in the subsequent foaming step, and stable quality and improved production efficiency can be achieved. Furthermore, by advancing the condensation-crosslinking reaction of the alkoxysilane compound at the time of foaming or thereafter, the residual strain of bubbles is alleviated and the degree of crosslinking is increased, and a foam having excellent thermal dimensional stability is obtained.

〔Example〕

 The present invention will be described below with reference to examples.

Low density polyethylene (MI: 4.5, density: 0.924g / cm ³ , MP: 1
12 ° C) 1.5 parts by weight of 3-methacryloxypropyltrimethoxysilane was added to 100 parts by weight, 13 parts by weight of azodicarbonamide and 1 part by weight of a phenolic antioxidant were further added, and this mixture was uniaxial extruder (150φ). Was extruded at a resin temperature of 140 ° C to form a sheet (thickness: 1.6 mm).

Next, an electron beam of 2.2M is applied to this sheet by an electron beam irradiation machine.
Irradiation was performed at a dose of rad to cause grafting and crosslinking. The crosslinking index of this sheet was 31%. Further, when this sheet was foamed in a foaming oven (250 ° C.), a foam having a thickness of 4.3 mm and a density of 0.0323 g / cm ³ was obtained. The crosslinking index of this foamed sheet was 67%.

The cross-linking index is 100 times the value obtained by dividing the weight of a foam piece left in xylene at 120 ° C for 24 hours and then vacuum drying the residue at 80 ° C for 8 hours by the weight of the foam before treatment. .

Comparative Example 1 Low density polyethylene (MI = 4.5, density: 0.924 g / cm ³ , M.P1
12 ° C) 100 parts by weight, vinylmethoxysilane 1.5 parts by weight and organic peroxide 0.1 parts by weight (dicumyl peroxide: 1 minute half-life 71 ° C) are extruded at a resin temperature of 180 ° C by a 65φ twin-screw extruder, It was formed into a sheet and then crushed. Azodicarbonamide (13 parts by weight) and a phenolic antioxidant (1 part by weight) were added to the crushed resin, and the mixture was extruded to a thickness of 1.6 mm at a temperature not higher than the decomposition temperature of the foaming agent to form a sheet. This molded product was passed through an oil bath (length: 2 m), the temperature of which was adjusted to 110 ° C., at a speed of 2 m / hr. The crosslinking index of the sheet at this point is 21
%Met.

When this sheet was heated and foamed in a hot air oven at 250 ° C., a foam having a thickness of 3.9 mm and a density of 0.0323 g / cm ³ was obtained. The crosslinking index of this foamed sheet was 59%.

Comparative Example 2 Low density polyethylene (MI = 4.5, density: 0.924 g / cm ³ , M.P1
12 ° C.) 13 parts by weight of azodicarbonamide and 1 part by weight of phenolic antioxidant were added to 100 parts by weight of a single screw extruder (15
0φ) was extruded at a resin temperature of 140 ° C. to form a sheet (thickness: 1.6 mm). This sheet was irradiated with an electron beam at a dose of 2.5 Mrad. The crosslinking index of this sheet was 38%. Further, when this sheet was foamed in a foaming oven at 250 ° C., a foam having a thickness of 4.0 mm and a density of 0.0319 g / cm ³ was obtained.
The cross-linking index of this foam sheet was also 38%.

Comparative Example 3 When the irradiation dose was changed to 4.0 Mrad under the conditions of Comparative Example 2, the crosslinking index of the raw sheet was 58%. Then, when this was foamed in a foaming oven at 250 ° C., a stable foam could not be obtained.

The results of Examples and Comparative Examples 1 and 2 are summarized in the following table.

As is clear from this result, Comparative Example 2 shows that the final crosslinking degree cannot be increased by the crosslinking method using ionizing radiation. Further, as shown in Comparative Example 1, the method using a conventional silane compound requires extremely complicated steps in order to obtain the same result as that of the present invention (Example).

[Effect of the Invention] According to the method of the present invention, since no organic peroxide is used, the process is simplified as compared with the conventional method, and the production efficiency is remarkably improved. In addition, the molding process is stable and the degree of crosslinking is uniformly stabilized, so that uniform cells are obtained and the quality of the foam is greatly improved. Furthermore, the obtained foam is also excellent in thermal dimensional stability.

Claims (1)

[Claims] 1. A mixed raw material containing an olefin resin, an alkoxysilane compound having an acryloyl group and / or a methacryloyl group in the molecule, and a chemical decomposition type foaming agent,
Molding at a temperature below the decomposition temperature of the chemical decomposition type foaming agent,
A method for producing an olefin-based resin foam, which comprises irradiating the obtained molded product with ionizing radiation and then heating it to a temperature not lower than the decomposition temperature of the chemical decomposition type foaming agent.