JPH03287637A - Preparation of flame-retardant resin foam - Google Patents

Abstract

PURPOSE:To improve flame retardance and moldability by irradiating a compsn. comprising an ultralow-density PE, a hydrated metal oxide, a halogenated flame retardant, an auxiliary flame retardant, and a blowing agent with an ionizing radiation to crosslink the compsn. and heating it to foam. CONSTITUTION:100 pts.wt. mixture comprising 10-100wt.% ultralow-density PE having a density of 0.880-0.910g/cm<3> and an MI of 0.2-20 and 90-0wt.% other thermoplastic resin (e.g. a low-density PE having a density of 0.910-0.930g/cm<3> and an MI of 0.2-20) is compounded with 30-300 pts.wt. hydrated metal oxide having a mean particle diameter 0.01-20mum [e.g. Al(OH)3], 5-40 pts.wt. halogenated flame retardant (e.g. decabromodiphenyl ether), 2-20 pts.wt. auxiliary flame retardant (e.g. Sb2O3), and 10-50 pts.wt. blowing agern (e.g. azodicarbonamide) to give a compsn., which is molded, irradiated with an ionizing radiation at a dose of 11-10Mrad to crosslink, and heated at 200-280 deg.C to foam.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention relates to a method for producing a flame-retardant resin foam filled with a large amount of inorganic material.

[Prior Art] It is known to add inorganic substances or flame retardants to produce flame retardant resins. However, when producing a resin foam, a large amount of inorganic substances impedes foamability, making it difficult to obtain a foam with a closed cell structure, and a sufficient flame retardant effect cannot be obtained using a flame retardant alone.

In order to solve this problem, it was proposed to produce closed-cell flame-retardant resin foam using ethylene-vinyl acetate copolymer as the main component of the resin (Japanese Patent Laid-Open No. 56-11
(See Publication No. 6727).

[Problem to be solved by the invention]

However, this known method has the following drawbacks.

(1) When the vinyl acetate content exceeds 20%, the adhesiveness increases, making it difficult to take off the resulting foamable sheets and foams. In addition, free acetic acid is likely to be generated due to thermal decomposition at high temperatures, the resin deteriorates during melt-kneading, and the physical properties of the resulting foam deteriorate. Furthermore, this type of resin has a low melting point, and the resulting foam can be thermally processed (laminated, bottom shaped, etc.)
During this process, the bubbles collapse or change dimensions (stretch), resulting in poor workability.

(2) On the other hand, a vinyl acetate-ethylene copolymer with a vinyl acetate content of less than 20% does not have good compatibility with inorganic substances, so if the amount of inorganic substances loaded is large, the two components will adhere to each other in the mixture. Due to insufficient properties, the physical properties deteriorate and the foamability is also adversely affected, making it difficult to obtain a foam having a fine closed cell structure.

It is therefore an object of the present invention to propose a method which makes it possible to produce resin foams with good flame retardancy, without exhibiting the above-mentioned drawbacks of the conventional methods, even at high inorganic loadings.

[Means for Solving the Problems] As a result of various studies, the present inventors have found that the above problems can be solved by using a specific resin as the raw material resin.

The present invention comprises 100 parts by weight of ultra-low density polyethylene or a mixture thereof with other thermoplastic resins, 3 parts by weight of hydrated metal oxide,
0 to 300 parts by weight, 5 to 40 parts by weight of halogen flame retardant,
A composition consisting of 2 to 20 parts by weight of a flame retardant aid and a blowing agent,
This is a method for producing a flame-retardant resin foam, which is characterized by crosslinking by irradiation with ionizing radiation and then foaming by heating.

According to the invention, very low density polyethylene (VLDPE or ULDPE) is used as the raw resin alone or in a mixture with other thermoplastic resins. The ratio of ultra-low density polyethylene to the total resin content is generally 10 to 1.
00% by weight, preferably 50 to 100% by weight. Ultra-low density polyethylene is generally 0.880-0.910g
/cnj density and a melt index (MI) of 0.2-20, preferably 0.885-0.905 g/aa
and a Ml of 0.8 to 15.

Other thermoplastic resins that may be used in combination with ultra-low density polyethylene include, for example, low-density polyethylene (density 0
．． 910~0.930g/c+fl, MlO,2~
20, preferably density 0.910-0.930g/al
l, former 1.0-10) (LDPE), linear low-density polyethylene (density 0.910-0
．． 930 g/cd, Ml 0.2-20, preferably density 0.915-0.925 g/cTII, Ml 1.
0~10) (LLDPE), high density polyethylene (
Density 0.940-0.965g/cnt.

Ml 0.2-20, preferably density 0.945-0.
960g/c crawl, gate 1.0~10) (HDPE),
Ethylene-ethylene acrylate copolymer, ethylene-
Propylene copolymer, ethylene-vinyl acetate-vinyl chloride copolymer, ethylene-vinyl acetate copolymer (vinyl acetate content is 5% by weight or more and less than 20% by weight), and ethylene-vinyl acetate-carbon oxide terpolymer At least one ethylene polymer selected from the group consisting of:

Examples of hydrated metal oxides include aluminum hydroxide,
Magnesium hydroxide, calcium hydroxide, basic magnesium carbonate, heart clay, talc, mica, kaolin clay, asbestos, hydrated calcium silicate, and attapulgite are used alone or as a mixture of two or more. These hydrated metal oxides are usually used in the form of fine powder, and the average particle size is 0.01 to 20% based on the expansion ratio.
μm Preferably 0.05 to 10 μm. The hydrated metal oxide is added in an amount of 30 to 300 parts by weight, preferably 50 to 180 parts by weight, per 100 parts by weight of the resin.

Halogenated flame retardants include halogenated aromatic,
Aliphatic, araliphatic and cycloaliphatic compounds such as decabromodiphenyl ether, hexabromohenzene, tris(2,3-dibromopropyl)isocyanurate, 2
, 2-bis(4-hydroxy-3,5-dibromophenyl)propane or mixtures of these compounds, particularly preferably decaflorodiphenyl ether. The amount of the halogen flame retardant added is 5 to 40 parts by weight, preferably 10 to 30 parts by weight, per 100 parts by weight of the resin.

As the flame retardant aid, for example, antimony trioxide, zinc borate, red phosphorus, etc., especially antimony trioxide, are used in an amount of 2 to 20 parts by weight, preferably 5 to 15 parts by weight, based on 100 parts by weight of the resin content.

As the blowing agent, common thermally decomposable chemical blowing agents such as azudicarbonamide, sodium bicarbonate, dinitropentamethylenetetramine, P,P oxybishenzenesulfonnihtrazine, etc. are used. The amount of foaming agent added varies depending on the density of the resulting foam, but the resin content is 10
About 0.1 to 0.0 parts by weight in an amount of 10 to 50 parts by weight.
A foam with a density of 0.2 g/cJ is obtained.

The resin composition used in the method of the present invention usually contains various additives, such as antioxidants, organic and inorganic colorants (e.g. carbon black), lubricants, antistatic agents, surface treatment agents, etc., as necessary. It can be contained in an amount of

A resin composition consisting of the above-mentioned components is mixed in a conventional manner using a Banbury mixer, a kneader, a two-roll mill, etc. to form pellets, and the pellets are extruded using an extruder.
Preferably, it is formed into a foamable sheet. After mixing the resin composition, extrusion formation may be performed without pelletizing.

The shape of the foamable molded article may be arbitrary depending on the intended use of the product.

The foamable molded product thus obtained is crosslinked by irradiation with ionizing radiation, such as electron beams, α-rays, β-rays, T-rays, X-rays, and neutron beams, and then heated and foamed. The irradiation dose is generally 1-10 Mrad. Heating for foaming is carried out using conventional equipment, such as air temperature baths, hot air ovens, molten salt baths, etc. The heating temperature is generally 200-280'C.

(Example) Examples 1 to 8 Density 0.905g/c+fl and MI Log/min
100 parts by weight of ultra-low density polyethylene VLDPE (Fselen VL 700 manufactured by Shiku Kagaku), fine aluminum hydroxide powder (Showa light metal type Hisilite former 42M)
A composition containing 50 to 200 parts by weight, 25 parts by weight of azodicarbonamide, 20 parts by weight of decabromodiphenyl ether, 5 parts by weight of antimony trioxide, and 1 part by weight of a phenolic antioxidant is temperature-controlled to 100 to 125 °C. The mixture was kneaded using a mixing roll, and pressed at 120° C. into a 1.5-thick sheet. This sheet was irradiated using an electron beam accelerator so that the absorbed dose was 5 Mrad.

Next, this sheet was placed in a hot air dryer whose temperature was controlled to 230°C and foamed.

The amount of aluminum hydroxide used, the properties of the obtained foam sheet, and the results of the flame retardant test are summarized in Table 1.

Flame retardancy test: A foam test piece was made by heating and laminating a foam sheet of the same size to a 22cm x 22cm x O, 3mm galvanized iron plate, and this test piece was rated according to JIS A-
The test was conducted according to the surface flame retardant test of No. 13211975.

In addition, tdθ is the time-temperature area (integral) that is an index of the calorific value during combustion, tdθ = 0 indicates that there is no difference from pearlite (standard product), and CA is the smoke generation index that is an index of the amount of smoke produced. In the coefficient, CA<30 indicates a passing value as a noncombustible material.

Example 9 Compositions as described in Examples 1-8, with the exception that VLDPE
Instead, a 50:50% mixture of the same VLDPE and ethylene-vinyl acetate copolymer VEA (vinyl acetate VA content 20%, Evaflex 460 manufactured by Mitsui Polychemicals) was used.
A foam sheet was produced in the same manner as in Examples 1 to 8 using a mixture containing 100 parts by weight and 150 parts by weight of aluminum hydroxide. Its properties and flame retardant test results are shown in Table 1.

Examples 10 and 11 The procedure was the same as in Example 9, except that VLDPE and low-density polyethylene LDPE (Sumikisen L40 manufactured by Shiku Kagaku) were used.
2) or 75F with linear low density polyethylene L-LDPE (Ultra Zex 2080-C manufactured by Shiku Kagaku)
A composition containing a 25% mixture was used. Table 1 shows the properties of the obtained foam sheet and the results of the flame retardancy test.

As a comparative example, Table 1 also shows the results when EVA (VA20χ) described in Example 9 was used instead of VLDPE.

(Margins below this page) As shown in Table 1, the foams of Examples of the present invention all had excellent flame retardancy. Comparative examples also showed good flame retardancy, but the foaming composition showed stickiness, making workability poor, and moldability was also poor.

[Effects of the Invention] When ultra-low density polyethylene is used according to the present invention, compared to the case where known ethylene-vinyl acetate copolymer is used,
Since there is no generation of free acetic acid, there is no deterioration of the resin during molding.
Even when large amounts of hydrated metal oxides and other additives are added, there is little decrease in strength. In addition, it has low adhesiveness, so it has excellent moldability.
The foamable molded product is also easy to handle. Furthermore, since the foam sheet obtained according to the present invention has a high melting point, when it is heated and laminated with a colored iron plate, a galvanized iron plate, etc., there is little collapse of the bubbles in the foam, and there is little elongation of the sheet, resulting in good workability.

Although the foam obtained by the method of the present invention is a foam of flammable thermoplastic resin, it is made by combining very low density polyethylene (VLDPE) with a hydrated metal oxide, a halogen flame retardant, and a flame retardant aid. It exhibits high flame retardancy and low smoke generation.

Claims (1)

[Claims] 100 parts by weight of ultra-low density polyethylene or a mixture thereof with other thermoplastic resins, 30 to 300 parts by weight of hydrated metal oxide
Parts by weight, 5 to 40 parts by weight of halogen flame retardant, 2 parts by weight of flame retardant aid
A method for producing a flame-retardant resin foam, comprising crosslinking a composition comprising ~20 parts by weight and a foaming agent by irradiating with ionizing radiation, and then foaming by heating.