JPH0710933B2 - Method for producing crosslinked olefin resin foam - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a polyolefin resin crosslinked foam.

[Prior Art] Olefin resin foams are widely used in various fields as heat insulating materials and cushioning materials because they have the characteristics of having closed cells, flexibility, heat insulating properties and high mechanical strength. There is.

As a method for producing such an olefin resin foam, for example, a method utilizing a condensation reaction of vinylalkoxysilane is known. The method for foaming an olefin resin using this vinylalkoxysilane is a foamable resin composition obtained by mixing a chemically decomposable foaming agent with an olefin resin obtained by graft-reacting or copolymerizing vinylalkoxysilane in advance, for example, by an extrusion molding method. A blank sheet is prepared. Then, this foamable resin composition elemental sheet is immersed for a long time in a hot water tank or a steam tank at a temperature lower than the melting point of the resin and lower than the decomposition temperature of the foaming agent to obtain condensation reaction crosslinks necessary for foaming, and then foaming. At the same time as or after foaming by heating to a temperature equal to or higher than the decomposition temperature of the agent, further crosslinking is performed.

[Problems to be Solved by the Invention] In the method for foaming an olefin resin using vinylalkoxysilane described above, since cross-linking proceeds further simultaneously with or after foaming, a highly cross-linked foam having high thermal dimensional stability is obtained. On the other hand, it has the advantage that it can be obtained, but has the following drawbacks.

That is, as a pre-step of the foaming step, a hot water tank or a steam tank requires a long-time treatment in order to obtain the cross-linking necessary for foaming, which causes a problem of extremely low productivity. There is also a problem that the degree of cross-linking in the cross-linking process in the hot water tank or the steam tank is not constant, which tends to cause variations in quality such as bubble diameter and appearance. further,
The problem that this quality variation easily occurs is that when a condensation reaction catalyst such as dibutyltin dilaurate is used to stop the reaction in the hot water tank or the steam tank, partial crosslinking occurs in a molding machine such as an extruder. It is more likely to occur, which makes it more prominent.

The present invention has been made to address such a problem of the conventional art, and improves the productivity, stabilizes the quality, and has the same high dimensional stability as that of the conventional method. It is intended to provide a method of manufacturing.

[Means for Solving the Problem] That is, the present invention is to decompose a chemical decomposition type foaming agent by mixing a mixed raw material containing at least an olefin resin graft-polymerized or copolymerized with vinylalkoxysilane and a chemical decomposition type foaming agent. A step of molding into a desired shape at a temperature lower than a temperature, a step of irradiating the molded article with radiation or an electron beam to radically react and crosslink the olefin resin, and the radically crosslinked molded article to the chemically decomposing type. And a step of heating the foaming agent at a temperature equal to or higher than the decomposition temperature for foaming and causing condensation reaction crosslinking by the vinylalkoxysilane.

As the olefin resin used in the present invention, low density polyethylene (including linear), high density polyethylene, polypropylene, ethylene-propylene copolymer,
Examples thereof include copolymers of ethylene and vinyl acetate, acrylic acid, methacrylic acid and the like, and these are used alone or as a mixture of two or more kinds.

In addition, examples of the vinylalkoxysilane in the present invention include vinyltrimethoxysilane and vinyltriethoxysilane. Then, those obtained by graft-reacting or copolymerizing these vinylalkoxysilanes with an olefin resin in advance are used as starting materials. The graft reaction amount or copolymerization amount of these vinylalkoxysilanes is preferably 0.2 to 2.5% by weight as a monomer ratio,
The range is more preferably 0.7 to 1.5% by weight.

Examples of the chemically decomposable foaming agent include azodicarbonamide, oxybenzenesulfonyl hydrazide, and the like. An appropriate amount of these is added to the above resin material and mixed, and a foamable resin composition element is formed by extrusion molding using this mixed raw material. Make a sheet. If necessary, a lubricant, a flame retardant, an antistatic agent, a coloring agent, etc. can be added to this mixed raw material.

Next, the foamable resin composition elemental sheet is irradiated with radiation or an electron beam to radically crosslink the olefinic resin in the foamable resin composition elemental sheet and crosslink to obtain the resin viscosity necessary for foaming. To get

After that, the foaming is performed by heating to a temperature equal to or higher than the decomposition temperature of the chemical decomposition type foaming agent. During this foaming step, condensation reaction crosslinking with vinylalkoxysilane proceeds simultaneously with or after foaming. The condensation reaction crosslinking with the vinylalkoxysilane is sufficiently achieved by the heating required for foaming and the trace amount of water in the resin or the atmosphere during the heat treatment, for example, air.

[Operation] By irradiating the olefin resin graft-reacted or copolymerized with vinylalkoxylane with radiation or electron beam in advance, the olefin resin undergoes radical reaction cross-linking to obtain the cross-linking necessary for foaming. To be
Crosslinking by radiation or electron beams has high production efficiency and a constant degree of crosslinking. Therefore, in the subsequent foaming step, it is easy to obtain bubbles having a uniform bubble diameter and the appearance quality is stable. Then, by performing the foaming treatment at a temperature equal to or higher than the decomposition temperature of the chemical decomposition type foaming agent,
The condensation reaction crosslinking of vinylalkoxysilane progresses during or after foaming due to the heat during foaming treatment and a small amount of water in the resin or processing atmosphere, and the residual strain of the foam bubbles is alleviated and highly crosslinked, resulting in thermal dimensional stability. A foam having excellent properties is obtained.

[Examples] Next, examples of the present invention will be described.

Example M1 (melt index) 4.5 g / 10 minutes, density 0.924, melting point peak 112 ℃ to 100 parts by weight of low-density polyethylene, 1.2 parts by weight of vinyltrimethoxysilane, 0.2 parts by weight of dicumyl peroxide was added sufficiently. 65mm diameter after mixing
Extruded with a twin screw extruder at a resin temperature of 200 ° C,
A polyethylene (hereinafter abbreviated as GPE) was prepared by graft reaction with vinylmethoxysilane.

Next, 15 parts by weight of azodicarbonamide as a chemically decomposing foaming agent was added to 100 parts by weight of the above GPE and mixed to give a diameter of 65.
Extrusion was carried out under a condition of a resin temperature of 150 ° C. or less by a twin-screw extruder of mm to prepare a foamable resin composition material sheet having a thickness of 1.5 mm.

Next, this foamable resin composition element sheet was irradiated with an electron beam of 3.4 Mrad by an electron beam irradiator to radically crosslink polyethylene.

Then, the radical reaction cross-linkable foamable resin composition elemental sheet is placed in a heating furnace set at about 250 ° C., and foaming treatment is performed to form a foam having a thickness of 4 mm (foaming ratio: about 31 times). Obtained.

The degree of cross-linking of the foam thus obtained was evaluated by the gel fraction evaluation method (measurement method: the test piece was immersed in xylene at 130 ° C. for 24 hours, the insoluble matter was dried and then weighed, and the ratio to the initial weight was measured. Was evaluated). First, the expandable resin composition raw sheet after irradiation with an electron beam was 35%, and after foaming was 72%. Further, the foam had fine and uniform cells, and the appearance was also excellent in surface smoothness.

Further, as a comparison with the present invention, instead of irradiating with an electron beam to crosslink, except for dipping in a hot water bath at 95 ° C for 65 minutes to crosslink, a thickness of 4 mm (foaming ratio:
About 30 times) foam was prepared.

The degree of cross-linking of this foam was measured in the same manner as in the above-mentioned example, and it was 38% in the raw sheet after the hot water bath treatment and 67% after the foaming.

The foams produced in these examples and comparative examples are respectively
It was cut into 150 mm x 150 mm and left in a heating furnace at 120 ° C for 24 hours to measure the dimensional change rate. The results are shown in the table below.

As is clear from the results in this table, the foam according to this example has almost the same thermal dimensional stability as the foam according to the conventional method subjected to the hot water bath treatment, and the bubble diameter is rather fine in terms of quality. The surface smoothness was also excellent.

[Effects of the Invention] As is clear from the above examples, according to the method for producing an olefin resin crosslinked foam of the present invention, since the crosslinking necessary for foaming is obtained by irradiation with an electron beam or radiation, Compared with the conventional treatment using a hot water tank or the like, the production efficiency is significantly improved, and the constant degree of crosslinking also improves the quality of bubbles and appearance. Further, since the crosslinking proceeds during or after foaming as in the conventional method, a foam having excellent thermal dimensional stability can be obtained.

Claims (1)

[Claims] 1. A mixed raw material containing at least an olefin resin graft-polymerized or copolymerized with vinylalkoxysilane and a chemical decomposition type blowing agent is formed into a desired shape at a temperature lower than the decomposition temperature of the chemical decomposition type blowing agent. A step of molding, a step of irradiating the molded article with radiation or an electron beam to radically crosslink the olefin resin, and heating the molded article subjected to radical reaction crosslinking to a temperature not lower than the decomposition temperature of the chemical decomposition type foaming agent. And a step of causing the condensation reaction crosslinking with the vinylalkoxysilane to occur, and a method for producing an olefin-based resin crosslinked foam.