JPH07179641A - Production of polyolefin resin foam - Google Patents

Abstract

PURPOSE:To produce a resin foam reduced in lowering of mechanical strengths and excelling in foaming characteristics and flame retardancy. CONSTITUTION:This resin foam is produced by melt-kneading a resin composition which comprises 100 pts.wt. polyolefin resin composition comprising 100-15wt.% polyethylene resin and 0-85wt.% polypropylene resin, 5-100 pts.wt. heat-expandable graphite and 1-40 pts.wt. heat-decomposable organic blowing agent, molding the melt into a sheet under crosslinking conditions and expanding the crosslinked sheet by heating.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention shows remarkable flame retardancy,
The present invention relates to a method for producing a polyolefin-based resin foam, which does not generate toxic halogen-based gas during combustion, and has less deterioration in molding processability and mechanical strength of molded articles.

[0002]

2. Description of the Related Art Resin foam has excellent heat insulation properties,
It is used in a wide range of applications such as transportation equipment such as automobiles, packaging materials, household daily necessities, etc. Among them, polyolefin resin foams have excellent chemical stability, heat insulation, electrical insulation, lightweight, etc. It has excellent characteristics.
Since the performance of the flame-retardant material has been required with the expansion of the uses of the polyolefin-based resin foam, the flame-retardant treatment is applied to the polyolefin-based resin which is originally flammable by various methods.

As a method of making a polyolefin resin flame-retardant, a method of adding a halogen-containing compound is generally used. This certainly imparts a high degree of flame retardancy,
The deterioration of molding processability and the mechanical strength of molded products are relatively small, but a large amount of smoke is generated during processing and combustion, and there are problems of corrosiveness to equipment and toxicity to humans. Particularly in recent years, halogen-free flame retardancy has been strongly demanded in terms of safety.

Under such circumstances, research on flame retardancy of resins by addition of hydrated metal oxides which do not generate toxic gas during combustion of aluminum hydroxide, magnesium hydroxide, basic magnesium carbonate, etc. is actively conducted. (Japanese Patent Application Laid-Open No. 49-5171 and Japanese Patent Application Laid-Open No. 3-26902)
No. 9, etc.). However, in order to impart sufficient flame retardancy to a polyolefin resin that is easily flammable only by adding these hydrated metal oxides, it is necessary to add a large amount of hydrated metal oxides. And the foamability is also adversely affected, making it difficult to obtain a foam having a fine closed cell structure.

Further, in Japanese Patent Laid-Open No. 4-363341, there is an example of a foam using heat-expandable graphite as a flame retardant. In this case, it is difficult to adhere the heat-expandable graphite to the surface of the expandable particles. It requires a step of attaching a dispersion liquid in which the combustion agent is dispersed to the expandable particles and a step of further drying it, and this foaming method is bead foaming and cannot be used for sheet foaming. there were.

[0006]

In view of the above, it is an object of the present invention to provide a method for producing a resin foam which has a small decrease in mechanical strength, is excellent in foaming characteristics, and is excellent in flame retardancy. To do.

[0007]

The gist of the present invention is, in the production of a polyolefin resin foam, a polyolefin resin composition comprising 100 to 15% by weight of a polyethylene resin and 0 to 85% by weight of a polypropylene resin. A resin composition comprising 100 parts by weight, 5 to 100 parts by weight of heat-expandable graphite and 1 to 40 parts by weight of a thermal decomposition type organic foaming agent is melt-kneaded, molded into a sheet and crosslinked, and then heat-foamed. is there.

The polyolefin resin composition used in the present invention comprises a polyethylene resin and a polypropylene resin. The polyethylene resin may be a polyethylene homopolymer, a copolymer containing ethylene as a main component, or a mixture thereof. As the above copolymer,
For example, ethylene-α-containing 80% by weight or more of ethylene
Examples thereof include olefin copolymers. Examples of the α-olefin include propylene, 1-hexene, 4-methyl-1-pentene, 1-octene, 1-butene, 1-pentene and the like.

Examples of copolymers with monomers other than α-olefins include ethylene-vinyl acetate copolymers and ethylene-ethyl acrylate copolymers. The MI of the polyethylene resin is preferably 0.1 to 40. When the MI is less than 0.1, there is a problem in appearance when formed into a sheet, and when the MI exceeds 40, there is a problem in material strength.

The polypropylene resin is not particularly limited, and may be a polypropylene homopolymer, a copolymer containing propylene as a main component, or a mixture thereof. Examples of the copolymer include a propylene-α-olefin copolymer containing 85% by weight or more of propylene. Examples of the α-olefin include ethylene, 1-hexene, 4-methyl-1-pentene, 1-octene, 1-butene, 1-pentene and the like.

The polypropylene resin is a melt index (hereinafter abbreviated as MI. ASTM D1238).
Was measured according to. Is preferably 0.2 to 20. If the MI of the polypropylene resin is less than 0.2, it becomes difficult to form a sheet, and if the MI exceeds 20, the heat resistance deteriorates.

The proportion of the polypropylene resin contained in the polyolefin resin composition is 0 to 85% by weight.
Is. When it exceeds 85% by weight, the flexibility as a foam is lost, so the content is limited to the above range.

The heat-expandable graphite used in the present invention is a known substance, and powders of natural scaly graphite, pyrolytic graphite, quiche graphite, etc. are concentrated sulfuric acid and concentrated nitric acid, perchloric acid, perchlorate, This is a crystalline compound in which a carbon layered structure is maintained while being treated with a strong oxidizing agent such as permanganate, dichromate, or hydrogen peroxide to generate a graphite intercalation compound.

The thermally expandable graphite obtained by the acid treatment as described above is preferably further neutralized with ammonia, an aliphatic lower amine, an alkali metal compound, an alkaline earth metal compound or the like. Examples of the aliphatic lower amines include monomethylamine, dimethylamine, trimethylamine, ethylamine, propylamine, butylamine and the like. Examples of the alkali metal compound and the alkaline earth metal compound include, for example, hydroxides, oxides of potassium, sodium, calcium, magnesium and the like,
Carbonates, sulfates, organic acid salts and the like can be mentioned.

The particle size of the above-mentioned thermally expandable graphite is 20 to 200.
A mesh is preferable. When it is finer than 200 mesh, the degree of expansion of graphite is low and the flame retardancy is lowered,
If it is larger than the mesh, the degree of expansion becomes large, the dispersibility is poor when kneading with the resin, and deterioration of the physical properties cannot be avoided.

The thermally expandable graphite is used in an amount of 5 to 100 parts by weight based on 100 parts by weight of the polyolefin resin composition. If it exceeds 100 parts by weight, the mechanical properties are largely deteriorated and it cannot withstand use. If it is less than 5 parts by weight, sufficient flame retardancy cannot be obtained, so that the content is limited to the above range.

In addition to the above-mentioned thermally expansive graphite, a flame retardant aid such as hydrated metal oxide or red phosphorus may be blended within a range that does not hinder foaming of the resin. Examples of the hydrated metal oxide include aluminum hydroxide, magnesium hydroxide, basic magnesium carbonate and the like. As the red phosphorus, commercially available red phosphorus may be used, but from the viewpoint of moisture resistance and safety (spontaneous ignition during kneading), it is preferable to use red phosphorus particles whose surface is coated with a resin. The amount of the flame retardant aid added varies depending on the amount of the thermally expandable graphite to be blended, but is preferably 100 parts by weight or less with respect to 100 parts by weight of the polyolefin resin composition.
If it exceeds 100 parts by weight, high flame retardancy is obtained, but the foaming property is impaired.

The thermal decomposition type organic foaming agent used in the present invention is not particularly limited as long as it generates a decomposition gas by heating. Examples of the thermal decomposition type organic foaming agent include azodicarbonamide, dinitrosopentamethylenetetramine, toluenesulfonyl hydrazide, 4,4-
Oxybis (benzenesulfonyl hydrazide) etc. are mentioned. These may be used alone or in combination of two or more. The blending ratio of the thermal decomposition type organic foaming agent is 1 to 40 parts by weight with respect to 100 parts by weight of the resin component. When the amount is less than 1 part by weight, a predetermined expansion ratio cannot be obtained, and when the amount is more than 40 parts by weight, a uniform foam cannot be obtained, such as partial formation of huge bubbles.

When the proportion of the polyethylene resin in the polyolefin resin composition is 80% by weight or less,
It is preferable to use a crosslinking aid when crosslinking. 80
When the content exceeds 10% by weight, due to the self-crosslinking property of the polyethylene resin, a sufficient crosslinked product can be obtained by applying a crosslinking means such as electron beam irradiation without a crosslinking aid.

As the above-mentioned cross-linking aid, any one may be used as long as it is a functional monomer and causes a cross-linking reaction with an electron beam, radiation or a peroxide, and two or more kinds are mixed and used. You can also do it. At least 1 vinyl group or allyl group per molecule is used as the above-mentioned crosslinking aid.
It is preferable to use an aromatic or aliphatic compound containing one or more compounds, a compound containing at least one acryloyloxy group or methacryloyloxy group in one molecule, and the like.

Examples of the crosslinking aid include divinylbenzene, diallylbenzene, divinylnaphthalene, trimethylolpropane trimethacrylate, ethylvinylbenzene, 1,9-nonanediol dimethacrylate, 1-nonanemonomethacrylate, 1,6- Hexanediol dimethacrylate, 2,2-bis [4- (acryloxydiethoxy) phenyl] propane, 1,2,4
-Benzenetricarboxylic acid triallyl ester, 1,2
-Benzenedicarboxylic acid diallyl ester, 1,3-benzenedicarboxylic acid diallyl ester, 1,4-benzenedicarboxylic acid diallyl ester, trimellitic acid triallyl ester, and related analogs thereof.

The above crosslinking aid is preferably blended in a proportion of 0.05 to 10 parts by weight with respect to 100 parts by weight of the above polyolefin resin composition. If it is less than 0.05 parts by weight, the cross-linking is insufficient and a homogeneous foam cannot be obtained.
If the material strength becomes insufficient at high temperature and the amount exceeds 10 parts by weight, the crosslink density becomes too high, which causes a problem in moldability.

An antioxidant, a stabilizer, a pigment, a metal damage inhibitor or the like may be added to the above polyolefin resin composition depending on its purpose. The above antioxidant is preferably used in the range of 0.1 to 5 parts by weight with respect to 100 parts by weight of the resin component. As the stabilizer, any known stabilizer such as phenol-based, phosphorus-based, sulfur-based or amine-based stabilizer can be used.

In the present invention, each component of the above-mentioned polyolefin resin, heat-expandable graphite and heat-decomposable organic foaming agent is a device such as a single screw extruder, a twin screw extruder, a Banbury mixer, a kneader mixer or a roll. Melted and kneaded to form a sheet. The sheet-shaped molded product obtained as described above is crosslinked by irradiating with ionizing radiation and heat-foamed in a hot air oven or the like to obtain a polyolefin resin foam.

The irradiation of ionizing radiation and the foaming operation may be carried out continuously or batchwise. Examples of the ionizing radiation include electron beams, γ rays, X rays, neutron rays and the like. An electron beam is preferable from the viewpoints of ease of handling and effects. The irradiation dose is preferably in the range of 1 to 10 Mrad.

[0026]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited thereto.

Examples 1 to 6 The various components shown in Table 1 were mixed with a Labo Plastomill using
Each resin composition was obtained by melt-kneading at 60 rpm for 5 minutes at the molding temperature shown in Table 1. The obtained resin composition was pressed at a molding temperature similar to that at the time of kneading to form a sheet having a thickness of 1.0 mm. Next, this sheet was irradiated with a dose corresponding to an absorbed dose of 3.0 Mrad using an electron beam accelerator to crosslink. Next, this sheet was heat-foamed in an oven whose temperature was adjusted to 230 ° C. to obtain a foamed sheet.

In Table 1, PP is polypropylene with MI = 1.5, LLDPE is density = 0.92, MI = 7.0 linear low density polyethylene, LDPE is density = 0.92,
Low density polyethylene with MI = 3.4, EVA represents an ethylene-vinyl acetate copolymer with vinyl acetate content 19%, density = 0.92, MI = 2.5. Thermally expandable graphite is CA-
60S (manufactured by Nippon Kasei) was used. As the red phosphorus, Novarred 120 (manufactured by Rin Kagaku Kogyo Co., Ltd.) was used. Further, divinylbenzene was used as the crosslinking aid 1, trimethylolpropane trimethacrylate was used as the crosslinking aid 2, and triallyl triallyl ester was used as the crosslinking aid 3.
Azodicarbonamide was used as a foaming agent.

The following tests were conducted on each of the obtained sheets, and the evaluation results are shown in Table 1. Combustion test The combustibility category was evaluated according to JIS D1201. Appearance Visual defects were checked visually such as foaming unevenness.
In the table, ◯ means good appearance and x means poor appearance.

[0030]

[Table 1]

Comparative Examples 1 to 6 Polyolefin resin foams were obtained in the same manner as in Examples 1 to 6 except that the components and blending amounts of the polyolefin resin composition were changed as shown in Table 2. The same tests as in Examples 1 to 6 were performed on each of the obtained foams, and the evaluation is shown in Table 2.

[0032]

[Table 2]

[0033]

Industrial Applicability According to the method of the present invention, a polyolefin resin foam having a self-extinguishing property can be produced without containing a halogen compound. The polyolefin-based resin foam produced by the method of the present invention can be suitably used for applications of foams requiring flame retardancy, particularly as automobile parts.

Claims (1)

[Claims] 1. Polyethylene resin 100 to 15% by weight
100 parts by weight of a polyolefin resin composition comprising 0 to 85% by weight of a polypropylene resin, and a thermally expandable graphite 5
Of 100 to 100 parts by weight and 1 to 40 parts by weight of a thermal decomposition type organic foaming agent are melt-kneaded, molded into a sheet shape, crosslinked, and then heat-foamed. Production method.