JPH10158423A - Polyolefin resin foam - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a foam which exhibits a high elongation in a high temp. range and can be molded into a complicated shape by compounding a polypropylene resin, a polyethylene resin, and an ionomer resin in a specified ratio. SOLUTION: Here, 'high-temp. range' means 110-120 deg.C. This foam contains 40-90wt.% polypropylene resin (A), 5-50wt.% polyethylene resin (B), and 5-40wt.% ionomer resin (C). Pref. ingredient A has an MI of 0.5-15g/10min, though not limited specifically, and isotactic polypropylene produced by using a stereoregular catalyst is esp. pref. Ingredient B pref. has an MI of 2-40g/10min and a density of 0.90-0.96g/cc. Ingredient C pref. has an MI of 1-10g/10min and a density of 0.90-0.97g/cc. An example of a blowing agent used is azodicarbonamide.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a polyolefin resin foam, and more particularly, to a polyolefin resin foam having improved elongation and moldability in a high temperature region.

[0002]

2. Description of the Related Art Polypropylene resins have the highest melting point among polyolefin resins and have a melting point of 110 to 120.degree.
The polypropylene resin is excellent in elongation, so that a crosslinking aid such as divinylbenzene or diethylene glycol dimethacrylate is added to the polypropylene resin, followed by heating and foaming to form a crosslinked foam (Japanese Patent Publication No. 46-38716,
JP-A-1-12940, JP-A-57-21223
No. 6, JP-A-59-191107, Japanese Patent Publication No. Sho 6
0-28852, Japanese Patent Publication No. 1-272641), and various fields such as interior materials for vehicles.

[0003] However, the cross-linked foam of the conventional polypropylene resin has excellent elongation at 110 to 120 ° C, but its elongation extremely decreases in a high temperature range of 140 to 160 ° C. In order to improve productivity due to demand for cost reduction, molded products obtained by rapid heating of foam during molding and accompanying molding under high temperature molding due to molding distortion caused by insufficient elongation in high temperature region However, there was a problem that the shape retention was poor. Also, with the recent diversification of consumer preferences, molded products having complicated shapes are desired, and foams capable of being formed into deeper shapes are required.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide a polyolefin-based resin foam which solves the above-mentioned problems and has excellent elongation in a high-temperature region and can be formed into a complicated shape.

[0005]

The polyolefin resin foam of the present invention contains 40 to 90% by weight of a polypropylene resin, 5 to 50% by weight of a polyethylene resin and 5 to 40% by weight of an ionomer resin. And

The above-mentioned polypropylene resin is not particularly limited as long as it has been conventionally used for the production of foams, and is a homopolymer of propylene or a copolymer containing propylene as a main component. Any of polypropylene may be used, but isotactic polypropylene produced using a stereoregular catalyst is preferred. The propylene-based copolymer is a copolymer with ethylene or another α-olefin having a propylene content of 90% or more. Examples of the α-olefin include 1-butene, 2-butene, isopropylene, 4-methyl-1-pentene, 1-octene, isooctene, 1-hexene, and 3,3-dimethyl-
1-hexene and the like.

[0007] If the melt index (hereinafter referred to as "MI") of the polypropylene is high, it is too soft to be molded into a desired shape, and if it is low, the moldability of the obtained polyolefin resin foam is reduced. So, 0.
5-15 g / 10 min is preferred. In the present invention, the MI of polypropylene means a value measured based on ASTM D1238.

When the content of the polypropylene in the polyolefin resin foam is large, the moldability is deteriorated due to insufficient elongation in a high-temperature region, and when the content is small, a foam having a high expansion ratio is obtained. Therefore, it is limited to 40 to 90% by weight, and preferably 50 to 80% by weight.

Next, the polyethylene resin is not particularly limited as long as it has been conventionally used for producing a foam. For example, low-density polyethylene, medium-density polyethylene, linear low-density polyethylene, Homopolymers of ethylene such as low-density polyethylene and high-density polyethylene; copolymers with an α-olefin containing 50% by weight or more of ethylene; and those having a melting point of 95 to 135 ° C. are preferable, and MI is preferably 2 to 40 g / 10 min, and density is preferably 0.90 to 0.96 g / cc. In the present invention, the MI of the polyethylene resin is defined as a temperature of 190 based on JIS K7210.
It is the one measured under the conditions of ° C and a load of 2.16 kgf.

The α-olefin copolymerizable with ethylene includes, for example, propylene, 1-butene,
2-butene, isopropylene, 4-methyl-1-pentene, 1-octene, isooctene, 1-hexene, 3,
3-dimethyl-1-hexene and the like.

When the content of the polyethylene resin in the polyolefin resin foam is large, the surface strength of the obtained polyolefin resin foam is reduced, and when the content is small, the content of the obtained polyolefin resin foam is reduced. Since moldability is reduced, it is limited to 5 to 50% by weight,
% By weight is preferred.

Finally, the ionomer resin is a copolymer of ethylene and an unsaturated compound containing a carboxylic acid such as (meth) acrylic acid, for example, sodium,
A metal cation such as potassium, calcium, magnesium, barium, or the like, forms an electrostatic bond between the carboxyl anion in the molecule and the metal cation, whereby the molecules are cross-linked via the metal cation.

The ionomer resin is prepared by first preparing a copolymer of ethylene and an unsaturated compound containing a carboxylic acid such as (meth) acrylic acid, and then converting the carboxyl group in the molecule to sodium, potassium, calcium, or the like. It is obtained by neutralizing with a hydroxide such as magnesium or barium or an alcoholate.

If the content of the ionomer resin in the polyolefin resin foam is large, the surface strength of the obtained polyolefin resin foam is reduced, and if the content is small, the molding of the obtained polyolefin resin foam is reduced. Therefore, the content is limited to 5 to 40% by weight.

The ionomer resin has an MI of 1
10 to 10 g / 10 min is preferable, and 2 to 7 g / 10 min is more preferable. In addition, in this invention, MI of an ionomer resin means what was measured based on JISK7210. The ionomer resin has a density of 0.90
0.97 g / cc, preferably 0.92 to 0.95 g
/ Cc is more preferred.

Next, a method for producing the polyolefin resin foam of the present invention will be described. Polyolefin resin foam, the above-mentioned polypropylene resin, polyethylene resin, ionomer resin and foaming agent, peroxides added as needed, crosslinking aids, antioxidants, antioxidants, ultraviolet absorbers, It is obtained by heating and foaming a foamable polyolefin-based resin composition comprising additives such as an antistatic agent and a pigment.

The foaming agent is not particularly limited as long as it has been conventionally used for producing a foaming agent. For example, azodicarbonamide, oxybenzenesulfonylhydrazide, azobisisobutyronitrile, azodicarboxylic acid Barium, dinilotosopentamethylenetetramine, hydrazodicarbonamide and the like, the amount of which is appropriately adjusted according to the desired expansion ratio, but a large amount breaks bubbles, and a small amount does not cause foaming. The amount is preferably 1 to 50 parts by weight based on 100 parts by weight of the total of the resin, the polyethylene resin and the ionomer resin.

The crosslinking assistant is not particularly limited as long as it has been conventionally used in the production of a foaming agent. For example, polyfunctional monomers such as divinylbenzene, trimethylolpropane triacrylate, ethylene glycol dimethacrylate, etc. And a polymer having an unsaturated double bond such as poly-1,4-butadiene, etc., and the amount thereof is appropriately adjusted. However, if the amount is small, the crosslinking density becomes insufficient and the extension viscosity necessary for foaming is obtained. If the amount is too high, the crosslinking density becomes too high and foaming may not occur. Therefore, the amount is preferably 0.1 to 10 parts by weight based on 100 parts by weight of the total amount of the polypropylene resin, polyethylene resin and ionomer resin.

The peroxide is not particularly limited as long as it has been conventionally used in the production of a foaming agent. Examples thereof include isobutyl peroxide, dicumyl peroxide, and 2,5-dimethyl-2,5. -Di (t-butylperoxy) hexane-3,1,3-bis (t-butylperoxyisopropyl) benzene, t-butylcumyl peroxide, di-t-butylperoxide, t-butylperoxybenzoate, Cyclohexane peroxide, 1,1-bis (t-butylperoxy) cyclohexane, 1,1-bis (t-butylperoxy) 3,
3,5-trimethylcyclohexane, 2,2-bis (t
-Butylperoxy) octane, n-butyl-4,4-
Bis (t-butylperoxy) bellate, benzoyl peroxide, cumyl peroxy neodecaneate, etc. are mentioned.

As a method of heating and foaming the expandable polyolefin-based resin composition, a general-purpose method is used, and the expandable polyolefin-based resin composition is molded using a general-purpose melt kneader such as an extruder. If necessary, after performing a crosslinking treatment described below, the foaming agent is heated to a foaming temperature or higher, and foaming is performed. At the same time, a so-called "extrusion foaming method" is used in which the resin is heated to a temperature equal to or higher than the foaming temperature of the foaming agent, and the resin component is crosslinked as necessary, and foamed simultaneously with extrusion. The foaming temperature refers to a temperature at which the foaming agent is decomposed or vaporized to generate gas.

The heating method used in the post-foaming method is not particularly limited. For example, a hot air heater, a salt bath,
Any material such as a metal bath that can be heated to a temperature higher than the foaming temperature of the foaming agent may be used.

Finally, the foamable polyolefin resin composition is appropriately subjected to a crosslinking treatment in order to obtain an elongational viscosity suitable for foaming. A general-purpose treatment method is used as the crosslinking treatment method. For example, a treatment method by ionizing radiation irradiation, chemical crosslinking with a peroxide, or the like can be used.

First, a method of crosslinking treatment by irradiation with ionizing radiation will be described. The ionizing radiation irradiation method refers to a method in which a foamable polyolefin-based resin composition sheet is formed in advance, and the sheet is irradiated with ionizing radiation, and is a method used when the above-described post-foaming method is employed.

The ionizing radiation is, for example, an electron beam, X
Rays, α-rays, β-rays, γ-rays, and the like. The irradiation amount is preferably 1 to 50 Mrad since a small amount does not cause crosslinking, and a large amount may cause excessive crosslinking. When such a treatment method is used, the above-mentioned crosslinking aid may be added as necessary.

Next, a method of chemically crosslinking with a peroxide will be described. The chemical crosslinking method is to add the above peroxide to the foamable polyolefin resin composition,
A method of decomposing the peroxide and cross-linking the resin component before or simultaneously with foaming, and is used in any of post-foaming and extrusion foaming methods.

[0026]

【Example】

(Examples 1 to 7, Comparative Examples 1 to 4) Ethylene-propylene random copolymer (ethylene content:
3.2 wt%, MI: 2.0 g / 10 min), and as the polypropylene resin (2), an ethylene-propylene random copolymer (ethylene content: 4.8 wt%, MI:
8.0 g / 10 min), and linear low-density polyethylene (density: 0.920 g /
cc, MI: 20 g / 10 min), and as the polyethylene resin (2), low-density polyethylene (density: 0.900
g / cc, MI: 2.0 g / 10 min), ionomer resin (1) (trade name: Himilan 1652, manufactured by Mitsui Dupont Polychemicals, MI: 5 g / 10 min, density: 0.9)
4g / cc), ionomer resin (2) (trade name: Himilan 1555, M, manufactured by DuPont Mitsui Polychemicals, Inc.)
I: 10.0 g / 10 min, density: 0.95 g / cc)
Ionomer resin (3) (trade name: Himilan 1707, manufactured by Mitsui Dupont Polychemicals, MI: 0.9 g / 1)
0 minutes, density: 0.95 g / cc), 10 parts by weight of azodicarbonamide as a foaming agent, 2 parts by weight of trimethylolpropane triacrylate as a crosslinking aid, and 2,6-di-t-butyl-p as an antioxidant -0.5 parts by weight of cresol was supplied to a 150 mmφ vent type single screw extruder, and extruded at a resin temperature of 100 ° C to obtain a foamable polyolefin-based resin composition sheet having a thickness of 1.0 mm.

The resulting foamable polyolefin-based resin composition sheet was irradiated with 4.0 Mrad of ionizing radiation to crosslink, then placed in a hot-air oven heated to 250 ° C., heated and foamed to a thickness of 2.0 mm. Was obtained.

The elongation and vacuum moldability of the obtained polyolefin resin foam were measured by the following methods, and the results are shown in Table 1 or Table 2.

(Elongation) The obtained polyolefin resin foam was heated to 140 ° C. or 160 ° C.
67.

(Vacuum Formability) The obtained polyolefin-based resin foam is heated using a far-infrared heater so that the foam surface becomes 150 ° C., and vacuum-formed using a bottomed cylindrical female mold. The maximum depth (D) at which the foam was molded without breaking was measured, and the ratio (D / L) between the maximum depth (D) and the inner diameter (L) of the female mold was determined by vacuum. Moldability. The larger the value, the better the vacuum formability.

[0031]

[Table 1]

[0032]

[Table 2]

[0033]

Since the polyolefin resin foam of the present invention contains a predetermined amount of each of the polypropylene resin, the polyethylene resin and the ionomer resin, the polyolefin resin foam has excellent properties at around 110 to 120 ° C. which the polypropylene resin has. Elongation, excellent moldability possessed by polyethylene resin, and excellent melt elongation and melt strength based on ionic cross-linking structure possessed by ionomer resin compensate for each weak point and have excellent elongation in high temperature region. In addition, it has excellent moldability that can be formed into a complicated shape.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI C08L 23:02

Claims (1)

[Claims] 1. A polyolefin resin foam comprising 40 to 90% by weight of a polypropylene resin, 5 to 50% by weight of a polyethylene resin and 5 to 40% by weight of an ionomer resin.