JPH0710934B2 - Method for producing flame-retardant resin crosslinked foam - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a flame-retardant olefin resin crosslinked foam, and more specifically, a flame-retardant resin having a beautiful surface, uniform cells, and high thermal dimensional stability. The present invention relates to a method for producing a crosslinked foam.

2. Description of the Related Art Flame-retardant olefin resin crosslinked foams highly filled with inorganic substances are known (Japanese Patent Publication No. 62-17217, etc.).

By the way, conventionally, as a method for producing such a crosslinked foam, chemical crosslinking with an organic peroxide, an azide compound, a silane compound, or the like, or crosslinking by irradiation with ionizing radiation such as electron beam or radiation is known. There is.

That is, a foamable resin composition containing a crosslinking agent such as an organic peroxide and a thermal decomposition type foaming agent, molded into a sheet at a temperature below the temperature at which the foaming agent decomposes, and after pre-crosslinking by heating as desired, A method of chemically cross-linking while foaming by heating above the decomposition temperature of the foaming agent, or a foamable resin composition containing a thermally decomposable foaming agent is molded into a sheet at a temperature below the temperature at which the foaming agent decomposes, and ionized. This is a method in which after irradiating with irradiating radiation to crosslink, the composition is heated above the decomposition temperature of the foaming agent to foam.

However, in the chemical cross-linking method using an organic peroxide or the like, in the surface layer portion of the foamable sheet, oxygen and radicals react during foaming, so the cross-linking reaction particularly in the skin layer portion becomes insufficient, and the surface is not smooth. It becomes a coarse foam. Cross-linking using a silane compound requires long-term treatment in warm water or steam to cause a cross-linking reaction, which causes problems in productivity and cost.

Further, in the method of crosslinking by electron beam or radiation irradiation, a certain degree of crosslinking is imparted before foaming, but when a large amount of hydrated metal oxide, flame retardant, or flame retardant aid is filled, foaming stability decreases. Therefore, high cross-linking cannot be performed, and the thermal dimensional stability of the resulting foam is poor.

The object of the present invention is to use a flame-retardant resin composition obtained by filling an olefin resin with a hydrated metal oxide, a flame retardant, or a flame retardant aid, to give a beautiful surface and uniform bubbles. Then, it is to provide a method for producing a crosslinked foam having excellent thermal dimensional stability.

The inventors of the present invention have conducted extensive studies to overcome the above-mentioned problems of the prior art, and as a result, a resin composition containing an olefin resin, a hydrated metal oxide, a flame retardant, a flame retardant aid and a thermal decomposition type foaming agent. In the case of producing a flame-retardant crosslinked foam from a product, vinylalkoxysilane is mixed with the composition and molded into a desired shape (usually a sheet) at a temperature lower than the decomposition temperature of the foaming agent. The olefinic resin is radically crosslinked by ionizing radiation, and the vinylalkoxysilane is graft-reacted with the olefinic resin. Then, the reacted molded product is heated and foamed at a temperature not lower than the decomposition temperature of the foaming agent. A flame-retardant cross-linked foam that has a beautiful surface and uniform cells, and has high cross-linking and excellent thermal dimensional stability. It was found that the obtained.

The present invention has been completed based on these findings.

Means for Solving the Problems Thus, according to the present invention, a mixed raw material containing at least an olefinic resin, a hydrated metal oxide, a flame retardant, a flame retardant aid, a thermal decomposition type foaming agent and a vinylalkoxysilane. A step of molding into a desired shape at a temperature lower than the decomposition temperature of the heat-decomposable foaming agent, and irradiating the molded product with an electron beam or radiation to radically crosslink the olefin resin, And a step of graft-reacting the olefinic resin with the radical-reactive cross-linking, and heating the radical-crosslinked molded article to a temperature equal to or higher than the decomposition temperature of the heat-decomposable foaming agent for foaming, and causing condensation reaction cross-linking by the vinyl alkoxysilane. A method for producing a flame-retardant resin crosslinked foam comprising the steps of:

Hereinafter, the configuration of the present invention will be described in detail.

(Each component) Examples of the olefin resin used in the present invention include polyethylene (low to high density, ultra low density), ethylene-vinyl acetate copolymer (EVA), ethylene-ethyl acrylate copolymer, ethylene- Acrylic acid copolymer, ethylene-
Methyl methacrylate copolymer, ethylene-α-olefin copolymer (including linear low-density polyethylene), polypropylene, propylene-butene copolymer, propylene-ethylene copolymer, and the like, and mixtures thereof. be able to.

As the hydrated metal oxide, for example, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, barium hydroxide, tin oxide hydrate, basic magnesium carbonate, hydrotalcite, heart crew, talc, mica, etc.
And mixtures thereof.

The hydrated metal oxide is added in an amount of 40 to 500 parts by weight, preferably 50 to 300 parts by weight, based on 100 parts by weight of the olefin resin. If it is less than 40 parts by weight, the effect due to blending the inorganic powder is small, and conversely, if the blending ratio is too large, it becomes difficult to obtain a foam having a high expansion ratio, for example, when forming a foam. .

Examples of the flame retardant include halogen-based flame retardants such as decabromodiphenyl ether, pentabromochlorocyclohexane, hexabromocyclododecane, 2,3,5,6-pentabromoethylbenzene, and 1,2-bis (2,4,5 -Tribromophenoxy) ethane, chlorinated paraffin, hexachloropentacyclodecane, hexabromobenzene, tetrabromobisphenol A / derivative, and the like.

These flame retardants can be used alone or in combination of two or more, and are usually added in an amount of 3 to 30 parts by weight, preferably 5 to 20 parts by weight, based on 100 parts by weight of the olefin resin. To do.

By combining the flame retardant and the flame retardant auxiliary, the flame retarding effect can be enhanced. As the flame retardant aid, for example,
Examples thereof include antimony trioxide, sodium antimonate, tin oxide, red phosphorus and the like.

When these flame retardant aids are used, the amount is usually 1 to 20 parts by weight, preferably 2 to 15 parts by weight, based on 100 parts by weight of the synthetic resin.

Examples of the thermal decomposition type foaming agent include compounds that generate gas by decomposing with heat such as azodicarbonamide, 4,4′-oxybis (benzenesulfonylhydrazide), azobisisobutyronitrile, and barium azodicarboxylate. Can be illustrated.

The thermal decomposition type foaming agent is usually added in an amount of 2 to 30 parts by weight, preferably 5 to 25 parts by weight, based on 100 parts by weight of the olefin resin.

Examples of vinylalkoxysilanes include vinyltrimethoxysilane and vinyltriethoxysilane.

The blending amount of these vinylalkoxysilanes is 0.2 to 2.5 parts by weight, preferably 0.7 to 1.5 parts by weight, based on 100 parts by weight of the olefin resin.

Further, a reaction inhibitor such as mercaptan may be added to suppress the polymerization between vinylalkoxysilanes.

In addition, a lubricant, a colorant, an antistatic agent, etc. can be added.

(Method for Producing Crosslinked Foam) In the present invention, crosslinking by irradiation with ionizing radiation and chemical crosslinking by vinylalkoxylane are carried out in combination.

Specifically, a resin composition containing an olefin resin, a hydrated metal oxide, a flame retardant, a flame retardant aid, a vinylalkoxysilane and a thermal decomposition type foaming agent is molded into a desired shape, usually a sheet. In the process of irradiating with an electron beam or radiation to crosslink, grafting vinylalkoxysilane onto an olefin resin, and further heating to a temperature above the decomposition temperature of the foaming agent to foam, condensation reaction crosslinking with vinylalkoxysilane is performed simultaneously with foaming. Give rise to.

In order to mold the foamable resin composition into a sheet or the like, it is usually carried out by an extruder at a temperature lower than the decomposition temperature of the foaming agent.

After giving the resin the viscoelasticity necessary for foaming by irradiation with ionizing radiation (electron beam or radiation), the resin is heated to a temperature above the decomposition temperature of the foaming agent to cause foaming, and crosslinking by the condensation reaction of the grafted vinylalkoxysilane. Do.

EXAMPLES The present invention will be described more specifically with reference to Examples and Comparative Examples below.

In addition, the method of the physical property test is as follows.

<Crosslinking degree; measuring method of gel fraction> The test piece was immersed in xylene at 130 ° C for 24 hours, the non-dissolved portion was dried and then weighed, and evaluated as a ratio to the initial weight. However, the content of a component such as aluminum hydroxide that does not dissolve in xylene was calculated and calculated by subtracting it from the initial weight and the dry weight.

<Flame Retardancy Test Method> A 22 × 22 cm foam test piece was attached to a zinc iron plate having the same size and a thickness of 0.3 mm, and measured according to JIS A-1321-1975 surface combustion test method.

tdθ: Time, temperature, area serving as an index of calorific value during combustion CA: Smoke generation coefficient serving as an index of smoke generation Here, tdθ = 0 and CA <30 are indices as noncombustible materials.

<Appearance> ◯: Surface smoothness X: Surface is not smooth but rough <Thermal dimensional stability> The heat shrinkage rate (%) at 120 ° C of the 150 × 150 mm test piece was measured vertically and horizontally.

Example 1 150 parts by weight of aluminum hydroxide, 20 parts by weight of decabromodiphenyl ether as a flame retardant, and 10 parts by weight of antimony trioxide were used per 100 parts by weight of a vinyl acetate-ethylene copolymer (vinyl acetate content: 20% by weight). 65 parts in diameter after adding parts by weight, 1.2 parts by weight of vinyltrimethoxysilane and 25 parts by weight of azodicarbonamide as a thermal decomposition type foaming agent and thoroughly mixing
Was extruded at a resin temperature of 130 ° C. to prepare a foamable resin composition elemental sheet having a thickness of 1.5 mm.

Next, the foamable resin composition sheet was irradiated with an electron beam of 3.4 Mrad by an electron beam irradiator for radical reaction cross-linking, and vinyl trimethoxysilane was graft-reacted.

Thereafter, the radically reactive crosslinkable foamable resin composition sheet was placed in a heating furnace set at about 250 ° C. and subjected to foaming treatment to obtain a foam having a thickness of 5 mm (foaming ratio: 20 times).

When the degree of crosslinking of the foam thus obtained was measured by the gel fraction evaluation method, the foamable resin composition elemental sheet after irradiation with an electron beam was 30%, and after foaming it was 65%. .

Further, the foam had high flame retardancy with uniform cells and excellent surface smoothness in appearance, but had good heat resistance.

[Examples 2 to 5] Foams were obtained in the same manner as in Example 1 except that the use ratios of aluminum hydroxide and azodicarbonamide were changed as shown in Table 1.

[Example 6] A foam was obtained in the same manner as in Example 1 except that the olefin resin was changed to a vinyl acetate-ethylene copolymer (vinyl acetate content: 15% by weight).

Example 7 A foam was obtained in the same manner as in Example 1 except that the vinyl acetate-ethylene copolymer (vinyl acetate content 25% by weight) was used instead of the olefin resin.

Example 8 80 parts by weight of vinyl acetate-ethylene copolymer (vinyl acetate content 25% by weight) as olefin resin and low density polyethylene (density 0.922 g / cm ³ , melt index 4.0 g / mi)
n., melting point peak 111 ° C.) A foam was obtained in the same manner as in Example 1 except that 20 parts by weight of the mixture was used.

[Example 9] Ultra low density polyethylene (VLDPE;
A foam was obtained in the same manner as in Example 1 except that 100 parts by weight of a density of 0.905 g / cm ³ and a melt index of 10 g / min.) Was used and the irradiation dose was 6.2 Mrad.

[Comparative Example 1] The irradiation dose was 4.5 M without adding vinyltrimethoxysilane.
The thickness is 5 mm in the same manner as in Example 1 except that rad is used.
A foam having an expansion ratio of about 20 times was obtained. The gel fraction of this foam was 40%.

[Comparative Example 2] (Chemical crosslinking method) 150 parts by weight of aluminum hydroxide and 20 parts by weight of decabromodiphenyl ether as a flame retardant per 100 parts by weight of vinyl acetate-ethylene copolymer (vinyl acetate content 20% by weight). , 10 parts by weight of antimony trioxide, 1.2 parts by weight of vinyltrimethoxysilane, 25 parts by weight of azodicarbonamide as a pyrolyzable foaming agent, 3.0 parts by weight of dicumyl peroxide, and 100 to 120 ° C in a small laboratory kneader. Knead at a temperature of 130 ℃, and form a sheet with a thickness of 1.5 mm by a hot press at 130 ℃, and heat it under a pressure for 15 minutes at a temperature of 150 ℃ by a heat press to decompose the cross-linking agent. Cross-link,
This small piece was placed in a heating furnace set at 220 ° C. and subjected to foaming treatment to obtain a foam having a thickness of 5 mm (foaming ratio of about 20 times).

The results of Examples and Comparative Examples are collectively shown in Table 1.

EFFECTS OF THE INVENTION According to the present invention, a flame-retardant foam having uniform cells with a beautiful surface can be obtained, and even a highly filled sheet for obtaining high flame retardancy can be stably foamed. Then, during foaming or post-crosslinking progresses, and becomes highly crosslinked, so that a crosslinked foam having excellent thermal dimensional stability can be obtained.

Claims (1)

[Claims] 1. A resin composition containing an olefin resin, a hydrated metal oxide, a flame retardant, a flame retardant aid, a pyrolytic foaming agent and a vinylalkoxysilane, which is below the decomposition temperature of the pyrolytic foaming agent. Molded into a desired shape at a temperature of, the resulting molded product is irradiated with an electron beam or radiation to radically crosslink the olefin resin, and the vinylalkoxysilane is graft-reacted with the olefin resin. A flame-retardant resin cross-linked foam, wherein the radical-reactive cross-linked molded article is heated to a temperature not lower than the decomposition temperature of the thermal decomposition type foaming agent for foaming, and condensation reaction cross-linking is caused by the vinyl alkoxysilane. Body manufacturing method.