JPH08193142A - Method for producing polyolefin resin foam - Google Patents

Abstract

(57) [Summary] [Purpose] The production of a polyolefin resin foam that gives excellent flame retardancy without using a halogen-containing compound and that does not adversely affect the foaming characteristics and the mechanical strength of the molded product. Provide a way. [Composition] Melt-kneading a resin composition comprising a polyolefin resin consisting of 100 to 15% by weight of a polyethylene resin and 0 to 85% by weight of a polypropylene resin, neutralized thermally expandable graphite and a thermally decomposable organic foaming agent. Then, after being formed into a sheet and cross-linked, it is heated and foamed.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for producing a polyolefin resin foam.

[0002]

2. Description of the Related Art Since resin foams have excellent heat insulation properties, they are used as building materials, transportation equipment such as automobiles, packaging materials, household daily necessities,
It has been used in a wide range of other applications, but among them, polyolefin resin foams are particularly excellent in chemical stability,
It has excellent properties such as heat insulation, electrical insulation, and light weight. Recently, with the expansion of applications of polyolefin resin foams, flame retardancy has been required, and flame retardancy is imparted by various methods.

As a method for making the above polyolefin resin flame-retardant, for example, a method of adding a halogen-containing compound is generally performed, and the addition of the halogen-containing compound surely imparts a high degree of flame retardancy. Although the molding processability and the mechanical strength of the molded product are relatively small, a large amount of smoke may be generated during processing or combustion, and there is a risk of corroding peripheral equipment. Therefore, a method of imparting flame retardancy without using a halogen-containing compound has been strongly demanded.

As a method of imparting flame retardancy without using a halogen-containing compound, for example, hydrated metal oxides such as aluminum hydroxide, magnesium hydroxide and basic magnesium carbonate which do not generate smoke during combustion are added. The method is disclosed in JP-A-49-5171 and JP-A-3-269029. However, in order to impart sufficient flame retardancy to a flammable polyolefin resin by using the above hydrated metal hydroxide, it is necessary to add a large amount of hydrated metal oxide, and therefore, it is obtained. The mechanical strength of the molded body was sometimes significantly reduced. Further, in the case of a foam, the added hydrated metal oxide adversely affects the foaming characteristics, making it difficult to obtain a foam having a fine closed cell structure.

Further, as a method of imparting flame retardancy to a polyolefin resin foam, a method of adding thermally expandable graphite is disclosed in Japanese Patent Laid-Open No. 4-363341. It requires a step of attaching a dispersion liquid in which a flame retardant is dispersed in order to attach graphite to the surface of the expandable particles, and a step of further drying it.
Further, although this method is applicable to bead foaming, there is no description that it is applicable to sheet foaming.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned drawbacks and provides excellent flame retardancy without using a halogen-containing compound, and also has foaming characteristics and mechanical strength of a molded article. It is an object of the present invention to provide a method for producing a polyolefin resin foam that does not adversely affect the above.

[0007]

The method for producing a polyolefin resin foam of the present invention comprises melt-kneading a resin composition comprising a polyolefin resin, neutralized thermally expandable graphite and a pyrolytic organic foaming agent. Then, after being formed into a sheet shape and cross-linked, it is heated and foamed.

The polyolefin resin used in the present invention is a polyethylene resin, or a polyethylene resin and a polypropylene resin.

The polyethylene resin may be either an ethylene homopolymer (polyethylene), a copolymer containing ethylene as a main component, or a mixture thereof. As the copolymer containing ethylene as a main component, Examples include ethylene-α-olefin copolymers.
Examples of the α-olefin include propylene and 1
-Hexene, 4-methyl-1-pentene, 1-octene, 1-butene, 1-pentene and the like.

Examples of the copolymer containing ethylene as a main component and containing a monomer other than the above α-olefin include, for example,
Examples thereof include ethylene-vinyl acetate copolymers and ethylene-ethyl acrylate copolymers.

The above-mentioned copolymer containing ethylene as a main component is preferably one containing an ethylene component in an amount of 80% by weight or more.

If the melt index (the value measured according to ASTM D1238, hereinafter referred to as "MI") of the above-mentioned polyethylene resin becomes small, the appearance of the sheet-shaped molded product obtained when it is made into a sheet becomes poor, Since the mechanical strength decreases as it increases, 0.1-40 is preferable.

The polypropylene-based resin may be either a propylene homopolymer (polypropylene), a copolymer containing propylene as a main component, or a mixture thereof. As a copolymer containing propylene as a main component, For example, a propylene-α-olefin copolymer can be mentioned. Further, as the above-mentioned copolymer containing propylene as a main component, one containing 85% by weight or more of a propylene component is preferable.

Examples of the α-olefin include ethylene, 1-hexene, 4-methyl-1-pentene, 1
-Octene, 1-butene, 1-pentene and the like.

When the MI of the polypropylene resin is small, the appearance of the sheet-shaped molded product obtained when formed into a sheet is poor, and when it is large, the heat resistance is deteriorated.
0.2-20 is preferable.

The proportion of the polypropylene resin in the above polyolefin resin is 0 to 85% by weight because the flexibility of the obtained foam is lost if the proportion is too large.

As the neutralized thermally expandable graphite used in the present invention, powders of conventionally known substances, for example, natural flaky graphite, pyrolytic graphite, quiche graphite, etc., are added to concentrated sulfuric acid and concentrated nitric acid. , A graphite intercalation compound produced by treatment with a strong oxidizer such as perchloric acid, perchlorate, permanganate, dichromate, hydrogen peroxide, etc., while maintaining the carbon layered structure. It is obtained by neutralizing the crystalline compound of.

The above-mentioned neutralization treatment is carried out by further neutralizing the acid-treated thermally expandable graphite with ammonia, an aliphatic lower amine, an alkali metal compound, an alkaline earth metal compound or the like. Examples of the aliphatic lower amine include monomethylamine, dimethylamine, trimethylamine, ethylamine, propylamine, butylamine, and the like, and examples of the alkali metal compound and alkaline earth metal compound include potassium, sodium, calcium, barium, Examples thereof include hydroxides such as magnesium, oxides, carbonates, sulfates, organic acid salts and the like.

When the particle size of the above-mentioned neutralized thermally expandable graphite becomes finer, the expansion degree of the thermally expandable graphite becomes smaller,
As a result, the flame retardancy of the resulting polyolefin resin foam is reduced, and when it is large, the dispersibility is poor when kneading with the polyolefin resin, and the physical properties of the obtained foam are degraded, so 20 to 200 mesh is preferable.

In the method for producing a resin foam of the present invention, since the neutralized heat-expandable graphite is used, stable molding is possible without corrosion of the inner surface of the molding machine or the mold.

In the resin composition used in the present invention,
If the blending amount of the above-mentioned neutralized heat-expandable graphite is small, sufficient flame retardancy cannot be obtained, and if it is large, the mechanical strength is significantly lowered. Therefore, it is 5 with respect to 100 parts by weight of the polyolefin resin. ~ 100 parts by weight.

The above-mentioned resin composition contains, in addition to the above-mentioned neutralized heat-expandable graphite, a hydrated metal oxide, red phosphorus as a flame retardant aid within a range not impairing the foamability of the resin composition. Phosphorus compounds such as As the hydrated metal oxide, aluminum hydroxide, magnesium hydroxide,
Examples thereof include basic magnesium carbonate. Further, as the above-mentioned red phosphorus, from the viewpoint of moisture resistance and safety (preventing spontaneous ignition during kneading), it is preferable that the surface of the red phosphorus particles is coated with a resin. Examples of phosphorus compounds other than red phosphorus include ammonium polyphosphate and the like.

In the above resin composition, the amount of the flame retardant auxiliary compounded varies depending on the amount of the neutralized heat-expandable graphite. When the amount is large, a high degree of flame retardancy is obtained but the foaming property is impaired. Therefore, 100 parts by weight or less is preferable with respect to 100 parts by weight of the polyolefin resin.

Commercially available products of the above-mentioned neutralized expansive graphite include "CA-60S" manufactured by Nippon Kasei Co., Ltd., and commercially available products of the above aluminum hydroxide include "B703S" manufactured by Nippon Light Metal Co., Ltd. To be Examples of commercially available red phosphorus include "Nova Red 120" manufactured by Rin Kagaku Kogyo Co., Ltd.

The thermal decomposition type organic foaming agent used in the present invention is not particularly limited as long as it generates a decomposition gas upon heating, and examples thereof include azodicarbonamide, dinitrosopentamethylenetetramine, toluenesulfonylhydrazide, 4,4-oxybis (benzenesulfonyl hydrazide) and the like may be mentioned, and these may be used alone or in combination of two or more kinds.

In the above resin composition, if the blending amount of the above pyrolyzable organic foaming agent is small, a predetermined foaming ratio cannot be obtained, and if the blending amount is large, huge bubbles are partially formed.
Since a foam having a uniform cell structure cannot be obtained, it is 1 to 40 parts by weight with respect to 100 parts by weight of the polyolefin resin.

A cross-linking aid may be added to the above resin composition, if necessary. The cross-linking aid is not particularly limited as long as it is a functional monomer and causes a cross-linking reaction with an electron beam, radiation or a peroxide, but at least one vinyl group or allyl group is contained in one molecule. It is preferable to use an aromatic or aliphatic compound containing the above; a compound containing at least one (meth) acryloyloxy group in one molecule.

Examples of such crosslinking aids include divinylbenzene, diallylbenzene, divinylnaphthalene, trimethylolpropane methacrylate, ethylvinylbenzene, 1,9-nonanediol dimethacrylate, 1-nonanemonomethacrylate, 1,6. -Hexanediol dimethacrylate, 2,2- [4- (acryloxydiethoxy) phenyl] propane, 1,2,4-benzenetricarboxylic acid triallyl ester, 1,2-benzenecarboxylic acid diallyl ester, 1,3- Examples thereof include benzenedicarboxylic acid diallyl ester, 1,4-benzenedicarboxylic acid diallyl ester, trimellitic acid triallyl ester, and related homologs thereof. These may be used alone or in combination of two or more kinds. Good.

In the above resin composition, when the amount of the above-mentioned crosslinking aid is small, crosslinking is insufficient and a homogeneous foam cannot be obtained, and the foam strength at high temperature is insufficient. Becomes higher, which causes problems in moldability.
0.05 to 100 parts by weight of polyolefin resin
10 to 10 parts by weight.

In the above resin composition, when the proportion of polyethylene-based resin exceeds 80% by weight, the self-crosslinking property of the polyethylene-based resin allows a crosslinking means such as electron beam irradiation to be applied without a crosslinking aid. A sufficient crosslinked product can be obtained.

If necessary, an antioxidant, a stabilizer, a pigment, a metal damage inhibitor, a lubricant, etc. may be added to the above resin composition. The mixing amount of the antioxidant is preferably 0.1 to 5 parts by weight with respect to 100 parts by weight of the polyolefin resin. Further, as the stabilizer, phenol-based, sulfur-based and amine-based stabilizers are preferable.

In the above resin composition, for example, each component of polyolefin resin, thermally expansive graphite and thermally decomposable organic foaming agent is kneaded in a single screw extruder, a twin screw extruder, a Banbury mixer, a kneader mixer or a roll. It is melt-kneaded by using an apparatus and molded into a sheet.

A polyolefin resin foam is obtained by irradiating the sheet-shaped molded product obtained above with ionizing radiation to crosslink it and heat-foam it in a hot air oven or the like.

The above-mentioned ionizing radiation irradiation and foaming operation are
It may be carried out continuously or batchwise. Examples of the ionizing radiation include electron beams, γ rays, X rays,
A neutron beam or the like can be used, but an electron beam is preferable in terms of workability and effect. The irradiation dose of ionizing radiation is 1 to
A range of 10 Mrad is preferred.

[0035]

Next, embodiments of the present invention will be described. (Examples 1 to 6 and Comparative Examples 1 to 6) Predetermined amounts of the polyolefin-based resin, neutralized thermally expandable graphite, aluminum hydroxide, red phosphorus, crosslinking aid and heat shown in Tables 1 and 2 Decomposition type organic foaming agent, Labo Plastomill (manufactured by Toyo Seiki)
Was melt-kneaded at a molding temperature shown in Tables 1 and 2 for 5 minutes to obtain a resin composition, and the resin composition was press-molded at a molding temperature shown in Tables 1 and 2 to obtain a sheet having a thickness of 1 mm. A shaped body was obtained. Then, the sheet-shaped molded product was irradiated with a dose corresponding to an absorbed dose of 3 Mrad using an electron beam accelerator to crosslink, and then the sheet-shaped molded product was heated and foamed in an oven whose temperature was adjusted to 230 ° C. A foamed sheet was obtained.

With respect to the above-mentioned heat-expandable graphite, 1 g each of neutralized heat-expandable graphite (treated product) and non-neutralized heat-expandable graphite (untreated product) was added to 1000 cm ³ of pure water. Then, after stirring for a certain period of time at the water temperature shown in the table, p
When measured with an H meter, the untreated product had a pH of 3.
33, the neutralized product had a pH of 9.50.

The following performance tests were carried out using the foamed sheets obtained in the above Examples and Comparative Examples, and the results are shown in Tables 1 and 2. (A) Flame Retardancy Test Based on JIS D1201, the flammability classification of the foamed sheet was evaluated. (B) Appearance The foamed sheets were visually observed, and those having a good appearance were evaluated as ◯ and those having a poor appearance were evaluated as x.

[0038]

[Table 1]

[0039]

[Table 2]

In Tables 1 and 2, the following components were used. -PP: polypropylene (MI = 1.5) -LLDPE: linear low-density polyethylene (density = 0.
92, MI = 7) LDPE: low density polyethylene (density = 0.92, M
I = 3.4) -EVA: ethylene-vinyl acetate copolymer (vinyl acetate content 19% by weight, density = 0.92, MI = 2.5) -thermally expandable graphite: Nippon Kasei Co., Ltd. "CA-" 60S "-Aluminum hydroxide:" B703S "manufactured by Nippon Light Metal Co., Ltd.-Red phosphorus:" Novarred 120 "manufactured by Neighbor Chemical Co., Ltd.-Crosslinking aid (1): divinylbenzene-Crosslinking aid (2): trimethylolpropane tri Methacrylate-Crosslinking aid (3): Triallyl stearyl trimellitic-Blowing agent: Azodicarbonamide

[0041]

The structure of the method for producing a polyolefin resin foam of the present invention is as described above, and it is excellent without using the halogen-containing compound without adversely affecting the foaming characteristics and the mechanical strength of the molded article. It is possible to provide a foam having excellent flame retardancy. In addition, since the expandable graphite that has been neutralized is used, it is possible to stably produce a molded product having an excellent appearance without moldability and corrosion of the mold due to acid. Therefore, the polyolefin-based resin foam obtained in the present invention does not generate a halogen-based gas during combustion or processing, and can be used in a wide range of applications where flame retardancy is required, including automobile parts.

Claims (1)

[Claims] 1. 100 parts by weight of a polyolefin resin comprising 100 to 15% by weight of a polyethylene resin and 0 to 85% by weight of a polypropylene resin, 5 to 100 parts by weight of neutralized heat-expandable graphite, and a thermal decomposition type. Organic foaming agent 1 to 4
A method for producing a polyolefin resin foam, which comprises melt-kneading 0 part by weight of a resin composition, molding it into a sheet-like shape, crosslinking it, and then foaming it by heating.