JPS63251438A - Production of flame-retarding foam - Google Patents

Abstract

PURPOSE:To obtain a low-density flame-retarding foam suitable as a construction material or the like, by irradiating a sheet containing a vinyl acetate/ ethylene copolymer, an inorganic substance, a halogenated flame retardant, a blowing agent and a chemical crosslinking agent with an ionizing radiation and expanding the sheet by heating. CONSTITUTION:100pts.wt. resin (A) based on a vinyl acetate/ethylene copolymer of a vinyl acetate content of 50-90wt.% is mixed with 30-300pts.wt. inorganic substance (B) (e.g., aluminum hydroxide), 5-50pts.wt. halogenated flame retardant (C) (e.g., decabromodiphenyl oxide), a blowing agent (D) (e.g., azodicarbonamide) and a chemical crosslinking agent (E) (e.g., dicumyl peroxide). The mixture is molded into a sheet and at least one surface of the obtained expandable sheet is irradiated with an ionizing radiation (e.g., electron beams). The treated sheet is expanded by heating to obtain a flame-retarding foam of a high expansion ratio.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a method for manufacturing flame retardant foam.

The flame-retardant foam produced by the method of the present invention can be used as a building material,
In particular, it is used in fields such as long insulating folded plate roofs and wall materials.

[Conventional method] As a method for producing flame-retardant foam, a method is known in which a vinyl acetate-ethylene copolymer is mixed with a hydrated metal oxide, a halogenated flame retardant, and a foaming agent, and the mixture is heated and foamed. (
(Japanese Patent Application Laid-open No. 116727/1983).

In addition, in the method for producing a foam, the resin is crosslinked as necessary, and as a means for crosslinking,
It is also well known that there are methods using chemical crosslinking agents or irradiation with ionizing radiation.

Furthermore, on one or both sides of the foamable sheet made of vinyl acetate-ethylene copolymer, inorganic powder, and inorganic powder,
A method is also known in which polyolefin films containing no inorganic substances are laminated and heated and foamed (Japanese Patent Laid-Open No. 56-849).
4γ Publication).

[Problems to be Solved by the Invention] However, in the method disclosed in JP-A-56-116727, due to the escape of foaming gas during foaming,
It is not always possible to obtain a foam with a sufficiently low density, that is, a foam with a high expansion ratio. Although the method disclosed in the publication requires crosslinking, either a method using a chemical crosslinking agent or a method of irradiating ionizing radiation may be adopted as the means for crosslinking. It is said that
This publication does not state that both crosslinking methods may be used in combination, nor does it disclose any advantages of using both crosslinking methods in combination. Furthermore, from the viewpoint of improving the cross-linking method, there is no suggestion whatsoever of the idea of obtaining a foam with a high expansion ratio.

In addition, the method disclosed in JP-A-56-84947 prevents mutual adhesion of foamable sheets by laminating polyolefin films that do not contain inorganic substances.
Furthermore, the purpose of this publication is to improve the thermal lamination processability of the resulting foam, and there is no disclosure of scales for increasing the expansion ratio by laminating films.

The present invention provides a method for producing a flame-retardant vinyl acetate-ethylene copolymer foam having a high expansion ratio.

[Means for Solving Problem 1] The method for producing a flame-retardant foam of the present invention comprises adding 100 parts by weight of a resin whose main component is a vinyl acetate-ethylene copolymer having a vinyl acetate content of 50 to 90% by weight. On the other hand, inorganic matter is 30-3
00 parts by weight, 5 to 50 parts by weight of a halogen flame retardant, a foaming agent and a chemical crosslinking agent are mixed and formed into a sheet, one or both sides of this foamable sheet is irradiated with ionizing radiation, and then heated and foamed. It is characterized by

The resin used in the present invention is vinyl acetate-containing tj
The main component is 50 to 90% by weight of vinyl acetate-ethylene copolymer.

The density of the copolymer is preferably 1.0 to 1.2C110Tl, and the molecular weight is preferably 0.1 to 350, more preferably 10 to 150, in terms of melt index at 190'C.

If the vinyl acetate content of the copolymer is too low, it will not be possible to obtain a high expansion ratio when highly loaded with inorganic substances, and problems such as drip phenomenon during combustion, flashover at high temperatures, and increase in combustion heat will occur. Flammability decreases. On the other hand, if it is too large, it will not be possible to obtain a product with a high expansion ratio, and handling in the manufacturing process will become difficult.

Of course, the copolymer may be used alone as the resin, but other resins or elastomers may be mixed therein to the extent that the effects of the present invention are not impaired. Other resins include, for example, ethylene-α- such as polyethylene and ethylene-propylene copolymer.
Examples include olefin copolymers, crystalline vinyl acetate-ethylene copolymers containing vinyl acetate with an ff of 140% or less, and ethylene-vinyl acetate-vinyl chloride copolymers. In addition, elastomers include 1,2-polybutadiene,
Examples include ethylene-propylene rubber and butyl rubber.

When mixing the above resin or elastomer, the content of the main component, a vinyl acetate-ethylene copolymer with a vinyl acetate content of 50 to 90% by weight, may vary depending on the type of other resin or elastomer to be mixed. varies, but usually at least 50% by weight, preferably 60-90% by weight
It is.

The inorganic substances used in the present invention include hydrated metal oxides,
Examples include metal oxides, carbonates, silicates, and 5A acid salts, with hydrated metal oxides being particularly preferred. Examples of hydrated metal oxides include aluminum hydroxide, magnesium hydroxide, calcium hydroxide, basic magnesium carbonate, talc, and kaolin clay.

Furthermore, a coupling agent may be used to improve the affinity between the resin and the inorganic substance. Examples of the coupling agent include a silane coupling agent and a titanate coupling agent.

The amount of inorganic substances to be mixed is based on 100 parts by weight of resin.
The amount is 30 to 300 parts by weight, preferably 70 to 200 parts by weight. If the mixing amount is too small, combustion properties cannot be imparted, and if the mixing amount is too large, high foaming may occur. Examples include phenyl oxide, ethylene bistetraphthalimide, hexabromobenzene and the like.

The mixing amount of the halogen flame retardant is 5 to 50 parts by weight, preferably 15 to 3 parts by weight, per 100 parts by weight of the resin.
It is 5 parts by weight. If the mixing amount is too small, flame retardancy cannot be imparted, and if the mixing amount is too large, the smoke generation Afi will increase and the smoke emission regulations will not be passed.

Further, a flame retardant aid may be used in combination with the halogen flame retardant. Examples of flame retardant aids include antimony trioxide and zinc borate.

The blowing agent used in the present invention is a thermally decomposable blowing agent, and examples thereof include azodicarbonamide, hydrazodicarbonamide, azodicarboxylic acid barium salt, di-1-rosopentamethylenetetramine, and the like.

Note that the mixing amount of the blowing agent is not particularly limited;
Although it may be selected as appropriate depending on the purpose, use, etc. of the foam, it is preferably 20 to 40 parts by weight based on 100 parts by weight of the resin.

Chemical crosslinking agents used in the present invention include common chemical crosslinking agents such as dicumyl peroxide, ditertiary butyl peroxide, and 1,3-bis(tertiary butylperoxyisopropyl)benzene, as well as silane crosslinking agents. can be used.

The amount of the chemical crosslinking agent mixed is preferably 0.01 to 15 parts by weight, and preferably 1 to 5 parts by weight, based on 100 parts by weight of the resin.

Further, in order to increase the crosslinking efficiency, it is more preferable to use a crosslinking aid such as divinylbenzene, sialylbenzene, i~lyrinolpropane triacrylate, etc. in combination.

In addition to the above-mentioned components, various additives such as antioxidants, colorants, carbon black, lubricants, and inorganic surface treatment agents may be added as necessary to the extent that they do not impair the effects of the present invention. It may be mixed with resin.

The method of the present invention involves mixing the above-described components, that is, a resin whose main component is vinyl acetate-ethylene copolymer, with an inorganic substance, a halogenated flame retardant, a blowing agent, and a chemical crosslinking agent, and molding the mixture into a sheet. After irradiating one or both sides of a foamable sheet with ionizing radiation, the sheet is heated and foamed.

Known methods can be used for mixing and molding.

The ionizing radiation to be irradiated is alpha rays, beta rays, gamma rays, X rays, accelerated proton beams, electron beams, neutron beams, etc. The intensity and irradiation time of the ionizing 1i31 radiation are It varies depending on the thickness of the foam and the purpose of the foam, and can be selected appropriately, but usually ionizing radiation of 0.5 to 2 ONrad is used.
Preferably, ionizing radiation of 1.0 to 5°0) 1 rad is irradiated. If the ionizing radiation is too weak, it will not be possible to suppress the escape of foaming gas during foaming, and if it is too strong, coarse bubbles will be generated and the density will not decrease.

The ionizing radiation may be irradiated on only one side of the foamable sheet, but it is preferable to irradiate both sides.

By irradiating the ionizing radiation in this manner, the resin near the surface of the foamed example sheet can be crosslinked, and the melt tension of the resin near the surface can be increased.

= 9- As a result, the heating for foaming performed after irradiation with ionizing radiation can be strengthened, and the escape of foaming gas can be suppressed, so that a foam with a high expansion ratio can be obtained.

After irradiating with ionizing radiation, it is heated and foamed. Heating methods include foaming by heating with hot air and an infrared heater on a wire mesh belt conveyor, a method of suspending the sheet from the top and heating with hot air and an infrared heater, and a method of heating and foaming with hot air and an infrared heater. Examples include a method of floating the foam on top of a liquid molten fluid and heating it from above with an infrared heater or hot air to foam it. In addition to this, various well-known foaming methods may be used.

In this heating step, crosslinking by a chemical crosslinking agent and foaming by gas generated by decomposition of the blowing agent are performed. If cross-linking is not done in advance by irradiation with ionizing radiation, cross-linking and foaming will proceed competitively, and especially at the beginning of this heating process, sufficient cross-linking will not occur and the blowing agent will decompose. The generated scum escapes and does not contribute to foaming. In the method of the present invention, since crosslinking is performed by irradiation with ionizing radiation prior to this heating, escape of foaming gas is suppressed and a foam with a high expansion ratio can be obtained.

If the crosslinking using a chemical crosslinking agent is only electron beam crosslinking, in the case of an inorganic highly filled sheet, crosslinking at the center of the sheet will be insufficient due to poor electron beam transmission, making it impossible to obtain a low-density foam.

Use of a chemical crosslinking agent has the effect of uniform crosslinking, improved gas retention, and a low density foam. In addition, by using it in conjunction with crosslinking by ionizing radiation irradiation, crosslinking near the sheet surface is promoted and the melt tension of the resin is increased, which has the advantage of further improving gas retention and promoting lower density of the foam. is obtained.

In the method of the present invention, it is more preferable to bond a non-foamable thermoplastic resin sheet to one or both sides of the foamable sheet.

As the thermoplastic resin used for the sheet to be laminated, low density polyethylene, high density polyethylene, polypropylene, vinyl acetate-ethylene copolymer, etc. can be used. Moreover, the thickness of the sheet to be laminated is preferably 10 to 500 μm.

The bonding method is a method in which one or both of the foamed sheets 1 to 1 and the non-foamed sheets are heated and pressed together with a hot roll at 50 to 120'C, and bonding with an adhesive is not performed.

When bonding non-foaming thermoplastic resin sheets, ionizing radiation is irradiated after bonding. This is because the melt tension of the thermoplastic resin sheet is increased to prevent the sheet from melting and peeling off during foaming.

By laminating non-foaming thermoplastic resin sheets,
It is possible to further reduce the escape of foaming gas during heating and foaming, and a low-density foam can be obtained.

[Example] Example 1 Vinyl acetate content 61% by weight, density 1.05 (1/rem,
Vinyl acetate-ethylene copolymer with a melt index of 50 to 150 (Dainippon Ink & Chemicals Co., Ltd., Evasurene 450P) 10,000 weight aluminum hydroxide powder (Showa Denko Co., Ltd., Hisilite H-42M, particle size: 1 m)
100 parts by weight, decabromodiphenyl (Vinihole AC#1 manufactured by Hydraulic Chemical Co., Ltd.) 3 as a halogen flame retardant
A composition obtained by mixing 0 parts by weight of dicumyl peroxide and 5 parts by weight of dicumyl peroxide (manufactured by Mitsui Petrochemical Industries, Ltd.) was heated at 110'C.
After kneading with a mixing roll at a temperature of 3. It was molded into Ommmm-t.

An electron beam 2. It was OMrad irradiated and then placed on a melt bath heated to 220'C for 3 minutes to foam.

The density of the resulting foam was 0.076910+f.

Example 2 The same procedure as in Example 1 was carried out except that both sides of the foamable sheet were irradiated with an electron beam of 1.5 Mrad.

The density of the 1q ladar foam was 0.054 g/can.

Comparative Example 1 The same procedure as in Example 1 was conducted except that electron beam irradiation was not performed.

The density of the obtained foam was 0.0859/cmf.

Comparative Example 2 The same procedure as in Example 1 was carried out except that the chemical crosslinking agent dicumyl peroxide was not blended.

Due to the high inorganic loading, the transmission of electron beams was inhibited and crosslinking did not occur to the center, resulting in numerous extremely large bubbles and a good foam was not obtained.

Example 3 After thermocompression-bonding low-density polyethylene sheets 1 to 50 μm thick on both sides of a foam sheet, electron beams 2 to 2 were applied to both sides of the laminate. The same procedure as in Example 1 was conducted except that QMrad irradiation was performed.

The density of the obtained foam was 0.048a/-.

[Effects of the Invention] Since the method of the present invention uses crosslinking by ionizing actinic radiation and crosslinking by a chemical crosslinking agent, it is possible to produce a foam with a low density, that is, a foam with a high expansion ratio. be able to.

Claims (2)

[Claims] (1) 30 to 300 parts by weight of an inorganic substance, 5 to 50 parts by weight of a halogen flame retardant, to 100 parts by weight of a resin whose main component is a vinyl acetate-ethylene copolymer with a vinyl acetate content of 50 to 90% by weight; A method for producing a flame-retardant foam, which comprises mixing a foaming agent and a chemical crosslinking agent, molding the mixture into a sheet, irradiating one or both sides of the foaming sheet with ionizing radiation, and then heating and foaming. . (2) A claim characterized in that after a non-foamable thermoplastic resin sheet is laminated on one or both sides of a foamable sheet, one or both sides of this laminate is irradiated with ionizing radiation. 2. A method for producing a flame-retardant foam according to item 1.