JPS6151541B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention particularly relates to a method for producing a foamed resin sheet containing a large amount of inorganic material.

In general, plastic foams are used in a wide range of applications such as building materials, packaging materials, and flotation materials because they are lightweight and have excellent properties such as heat insulation, sound absorption, and shock absorption.

Among them, polyolefin foam sheets are widely used for a wide range of purposes because of their superior chemical, mechanical, and electrical properties compared to other plastics. However, the major drawback of this polyolefin is that it is easily flammable, and in order to prevent disasters caused by fires, in recent years, materials using these polyolefins have been required to be made strictly flame retardant from a safety standpoint. requested.

As a method for making polyolefin flame retardant, it is generally known to mix a halogen flame retardant or a relatively large amount of powdered inorganic material with the polyolefin.

The former method of mixing halogen-based flame retardants has the advantage of relatively easily producing flame-retardant products, but when this flame-retardant material burns in a fire, it releases harmful gases such as hydrogen halides. Fires occur that pose a great danger to people, and even if direct damage from the heat of the fire is avoided, serious drawbacks such as corrosion of expensive equipment due to the corrosive hydrogen halides generated cannot be avoided. It was hot.

The latter method of making polyolefin flame retardant by mixing inorganic substances does not have such a dangerous effect, but on the other hand, as a result of the inorganic substance being blended in a relatively large amount with polyolefin, there is a decrease in foamability when trying to obtain a foamed sheet. More specifically, it is unavoidable that it is difficult to obtain a foamed sheet with a low density. As a result of various studies regarding this problem, the present inventors found that if an ethylene/vinyl acetate copolymer with a vinyl acetate content of 50 to 90%, which is a special polyolefin resin, is selected and used, a large amount of inorganic substances can be produced. It has been found that a good foam with an extremely low density can be obtained even when . As a result of studying its industrial manufacturing method, it was found that sheets of the composition in which inorganic powder was mixed into the resin were extremely adhesive to each other; It has been found that it has the disadvantage of significantly lowering the temperature.

Therefore, the inventors of the present invention completed the present invention as a result of intensive studies to solve the above-mentioned problems regarding a method for producing a flame-retardant polyolefin foam sheet that does not generate harmful gases.

That is, this invention provides a resin whose main component is a vinyl acetate ethylene copolymer with a vinyl acetate content of 50 to 90%.
50 to 500 parts by weight of inorganic powder per 100 parts by weight,
1 to 50 parts by weight of a foaming agent are mixed and formed into a sheet, a polyolefin containing no or only a small amount of inorganic material is laminated on one or both sides of this foamable sheet, and the laminated product is heated to foam. This is a method for producing an inorganic highly filled resin foam sheet.

In this invention, the surface of the special polyolefin layer containing a blowing agent and a large amount of inorganic material is laminated and covered with a polyolefin layer that does not contain inorganic material or contains only a small amount of inorganic material. In this way, the thermal bonding processability of the resulting foam is significantly improved.

In this invention, the resin constituting the foamable sheet is a vinyl acetate/ethylene copolymer with a vinyl acetate content of 50 to 90% by weight, and an ethylene acetate copolymer with a vinyl acetate content of less than 50% with respect to this copolymer. It is a resin made by mixing one or more of vinyl copolymers, polyethylene, polypropylene, ethylene propylene copolymers, ethylene/vinyl acetate/vinyl chloride copolymers, etc. at a ratio of less than 50%.

Next, as inorganic substances in this invention, hydrated metal oxides such as aluminum hydroxide, basic calcium carbonate, and magnesium hydroxide; metal oxides such as alumina and titania; carbonates such as calcium carbonate; talc, clay, etc. Silicates; Sulfates such as gypsum; Residues such as blast furnace slag, etc., but those used especially for flame retardation are aluminum hydroxide,
Magnesium hydroxide, basic magnesium carbonate,
These include hydroxides such as hard clay, among which aluminum hydroxide is most preferred as it imparts excellent flame retardancy. These minerals have an average particle size of 10
It is preferable that it is in the form of a powder with a size of less than μ, and the amount to be added to the resin used varies depending on the application, etc.
Usually 80 to 400 per 100 parts by weight, particularly preferably 100
It is added in a range of ~250 parts by weight.

In this invention, a coupling agent may be used together with the inorganic substance, which is preferable because it improves the expansion ratio per unit weight of the blowing agent. The coupling agent used may be either titanium-based or silane-based, but titanium-based coupling agents are particularly preferred because they significantly improve the expansion ratio. The amount of this coupling agent is 0.1 to 100 parts by weight of inorganic material.
10 parts by weight is preferred.

The blowing agent used in this invention is one that usually generates decomposition gas when heated, such as P,P'-oxybisbenzenesulfonyl hydrazide, azodicarbonamide, dinitrosopentamethylenetetramine bicarbonate, etc. These include sodium and magnesium carbonate.

A foaming agent, an inorganic substance, etc. are added and kneaded to the above-mentioned special polymer, and this is formed into a sheet shape by a desired method to obtain a foamable sheet, which contains no or only a small amount of inorganic substance on one or both sides. Polyolefin films are laminated together.
In particular, in order to obtain a foam with a high expansion ratio by adding 5 parts by weight or more of a blowing agent, it is necessary to create a cross-linked foam, and for this purpose, ionizing radiation such as electron beams and gamma rays must be applied at 0.5 to 20 Mrad. It is necessary to irradiate within a range or use 0.1 to 10 parts by weight of a chemical crosslinking agent, such as an organic peroxide, such as dicumyl peroxide. When using a chemical crosslinking agent, it is added during kneading so that it is included in the foamable sheet. In addition, in the case of electron beam irradiation, it is common to irradiate the entire polyolefin film after laminating it.

Various polyolefins such as polyethylene, polypropylene, ethylene/vinyl acetate, etc. can be used as the polyolefin for lamination, but polyethylene is particularly preferred. This polyolefin for lamination preferably does not contain any inorganic substances. This is because the less inorganic substances are included, the thinner the film will be.
However, it does not matter if it contains a small amount of inorganic matter.
Specifically, the content of inorganic substances in 100 parts by weight of the polymer is 20 parts by weight or less, preferably 5 parts by weight or less.

The film thickness of this polyolefin for lamination is 10 to 300.
[mu], particularly preferably 20 to 100[mu], and specifically, if it is 50[mu] or less, there is less risk of impairing the flame retardancy of the sheet as a whole, and it is preferable.

Next, the foaming method in this invention is carried out by heating the foaming agent to a temperature higher than the decomposition temperature in a foaming furnace. Specifically, the sheet is placed on an endless belt made of stainless wire gauze installed in the foaming furnace, and This is done by blowing hot air or infrared heating. The sheet thickness after foaming is generally 2 to 20 mm. For the foam sheet of this invention,
In order to improve its properties, various additives such as antioxidants, ultraviolet absorbers, various pigments, lubricants such as stearate, and crosslinking aids such as polyfunctional monomers are appropriately added.

The present invention will be specifically explained below with reference to Examples.

Example 1 and Comparative Example 1 Vinyl acetate ethylene copolymer with a vinyl acetate content of 61% by weight, a density of 1.0521 cm ³ , and a melt index of 30 to 50 (Dainippon Ink Co., Ltd. product, Evasuren)
450-P) 100 parts by weight, aluminum hydroxide powder (Higilite H-42M, Showa Denko, particle size 1)
μ) 150 parts by weight, azodicarbonamide as a blowing agent (Vinihole AC#1L, Eiwa Kasei Co., Ltd.)
A composition containing 23 parts by weight, 4.5 parts by weight of dicumyl peroxide (product of Mitsui Petrochemical Industries, Ltd.), and 0.7 parts by weight of trimethylolpropane triacrylate (NK Ester A-TMPT, Shin Nakamura Chemical Industries, Ltd.) was mixed in a Banbury mixer. After kneading at a temperature of 120°C, the mixture was formed into a mm-thick sheet by hot pressing (Sheet A). Further, a low density polyethylene film having a thickness of about 50 μm was laminated and adhered to both sides of this sheet A by heating and pressing without using an adhesive (sheet B).

When the sheets (A) were stacked in a roll, the sheets stuck to each other, but the sheets (B) did not stick to each other at all.

Next, the sheets (A) and (B) were placed in a hot air constant temperature bath heated to 195° C. for 15 minutes and taken out. The density of the obtained foam is 0.067 g/cm ³ and 0.065, respectively.
g/cm ³ , and there was almost no difference. However, the surface of the foam sheet (B) to which the polyethylene film was bonded was white, but the sheet (A) was colored pale yellow.

Furthermore, in order to check the thermal bonding property with an iron plate, the iron plate was heated with a gas burner and the foamed sheets (A) and (B) were pressure-bonded. In the case of sheet (A), the adhesive strength was insufficient and it could be easily peeled off, but with sheet (B), the adhesive surface could not be peeled off and the foam broke. By laminating polyethylene films in this manner, the thermal lamination properties of the foam are significantly improved.

Claims (1)

[Claims] 1. 50 to 500 parts by weight of inorganic powder, 1 to 100 parts by weight of blowing agent to 100 parts by weight of resin whose main component is vinyl acetate ethylene copolymer with vinyl acetate content of 50 to 90%.
50 parts by weight are mixed and formed into a sheet, a polyolefin film containing no or only a small amount of inorganic material is laminated on one or both sides of this foamable sheet, and the laminated product is heated to foam. A method for producing a highly inorganic-filled resin foam sheet.