JP3186801B2 - Crosslinked polyolefin foamed resin composition - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cross-linked polyolefin foamed resin composition, and more particularly, it has excellent heat resistance, is capable of secondary processing of a complicated shape, and is suitable for a molding method and application. A cross-linked polyolefin-based foamed resin composition suitable for continuously producing a cross-linked polyolefin-based resin foam whose flexibility can be freely controlled,
And a crosslinked polyolefin-based resin foam sheet obtained by crosslinking and foaming the composition.

[0002]

2. Description of the Related Art Foams made of polyolefin resins are widely used as heat-resistant materials and miscellaneous goods because of their excellent flexibility and heat resistance. It is widely used as a heat insulating material for doors, instrument panels and the like. For this reason, a crosslinked polyolefin foam is molded from a sheet by vacuum molding or compression molding to produce a product. However, conventional polyolefin foams, especially polyethylene foams, cannot be used due to low heat resistance because they are formed at a high temperature of 120 to 200 ° C. in vacuum molding or compression molding, and polyolefin resins using polypropylene as a component Foams are used.

Conventionally, crosslinking in a method for producing a polyolefin-based resin foam includes 1) a method of heating and crosslinking a resin composition to which an organic peroxide is added, and 2) irradiating the resin composition with ionizing radiation. There is a method of cross-linking, and both are performed industrially. However, these cross-linking methods are effective for cross-linking polyethylene, but are not suitable for the above-mentioned polypropylene-based polyolefin-based resin. This is because, in any of the above crosslinking methods, the cutting of the molecular chain proceeds simultaneously with the crosslinking, and the resin deteriorates. From this fact, in the crosslinking of a resin containing polypropylene as a main component, a method of adding a polyfunctional monomer, for example, divinylbenzene, diethylene glycol dimethacrylate, or trimethylolpropane triacrylate, and irradiating with ionizing radiation is performed. Yes (Special Publication 46-38
No. 716, JP-A-57-212236, JP-B-60-
No. 11935, JP-A-61-69844). According to JP-B-46-38716, compounds having two or more vinyl-type double bonds in the molecule or aromatic compounds having one vinyl group and (meth) acryloyloxy group are known as crosslinking aids. Are proposed as combinations of organic compounds having two or more of the following. And an aromatic hydrocarbon compound having two or more vinyl groups in the former,
It is described that the latter crosslinking aid is preferably used when crosslinking with an organic peroxide.

[0004]

However, when crosslinking is carried out using an organic peroxide, it is necessary to put an organic peroxide which is a decomposable substance into the extruder. In this case, control of the reaction is extremely difficult and may be dangerous.

Further, when crosslinking is carried out using these conventional polyfunctional monomers, the compatibility of the polyfunctional monomers with the respective resin components in the resin composition is different, so that the polyfunctional monomers have the best compatibility. When the resin component is localized in the resin component portion and irradiated with ionizing radiation, offset crosslinking occurs.

Recently, high heat resistance has been required for foams. As a countermeasure, there is a method of improving the resin composition itself. On the other hand, a method of adjusting the degree of crosslinking is also often used. In the latter method, the gel fraction of the foam itself is often increased in order to improve the heat resistance, but the foam obtained by increasing the gel fraction by increasing the amount of the conventional polyfunctional monomer is used. Is harder than necessary at the time of molding and becomes insufficient in elongation. In such a state, it is difficult to process into a particularly complicated and deep-shaped molded body while having high heat resistance, and the foam may be damaged. When the amount of the polyfunctional monomer is reduced and the gel fraction is reduced as a means for improving the molding processability, it is possible to process a molded article having a complicated and deep shape, but the heat resistance becomes insufficient.

An object of the present invention is to provide a crosslinked polyolefin resin foam having uniform heat resistance, toughness, moldability, and uniform appearance by uniformly and efficiently developing a uniform crosslink in a resin composition by irradiation with ionizing radiation. It is an object of the present invention to provide a crosslinked polyolefin-based foamed resin composition suitable for producing a resin.

Another object of the present invention is to provide a crosslinked polyolefin resin foam obtained by crosslinking and foaming the above crosslinked polyolefin resin foam composition.

The present inventors have conducted intensive studies and have found that a mixture of polypropylene and polyethylene having a specific melt index is used as a resin component, and that two vinyl groups are present on an aromatic ring as a crosslinking aid. Divinylbenzene, which is a bifunctional monomer directly bonded, ethylvinylbenzene, which is a monofunctional monomer having one vinyl group and one alkyl group directly bonded to an aromatic ring, and an aromatic saturated hydrocarbon It has been found that the above object can be achieved by using a mixture of compounds in an appropriate ratio, and the present invention has been completed based on the knowledge.

[0010]

Thus, according to the present invention, (a) 40 to 100% by weight of a polypropylene resin having a melt index of 0.5 to 12, and (b) a melt index of 2 to 50 are used. 0 to 60-fold a polyethylene-based resin
100 parts by weight of the mixture of the amount% (c) divinylbenzene 35-90 wt%, ethylvinylbenzene 3-58 wt%, aromatic saturated hydrocarbon compound
0.5 % to 10% of a three-component crosslinking aid of 7% by weight or less .
A foamable polyolefin-based resin composition comprising 0 parts by weight and (d) 1 to 50 parts by weight of a pyrolytic foaming agent.

Further, according to the present invention, there is provided a crosslinked polyolefin resin foam obtained by crosslinking and foaming the above crosslinked polyolefin resin foam composition.

Hereinafter, the present invention will be described in detail.

The polypropylene resin used in the present invention is:
Melt index (hereinafter abbreviated as MI: ASTM
D1238) is 0.5 to 12, preferably 1 to 10, more preferably 1 to 5.
belongs to. When the MI of the polypropylene is less than 0.5, a problem arises in appearance when a resin foam obtained from the resin composition is formed into a sheet, and when it exceeds 12, the heat resistance of the foam becomes insufficient.

The polypropylene resin used in the present invention is:
As long as the above-mentioned MI value is satisfied, any of a propylene homopolymer, a copolymer containing propylene as a main component, and a mixture thereof may be used. Examples of the copolymer include a random or block copolymer of propylene and ethylene or α-olefin. Examples of the α-olefin include 1-hexene, 4-methyl-1-pentene, 1-octene, 1-butene, 1-pentene and the like.

The polyethylene resin used in the present invention is M
I is 2 to 50, preferably 3 to 30, more preferably 4 to 25. M of polyethylene
When I is less than 2, a problem arises in appearance when a resin foam obtained from the resin composition is formed into a sheet, and when I exceeds 50, a problem arises in heat resistance of the foam.

The polyethylene resin used in the present invention may satisfy the above-mentioned MI, and may be any of an ethylene homopolymer, a copolymer containing ethylene as a main component, and a mixture thereof. Examples of the copolymer include an ethylene-α-olefin copolymer and an ethylene-propylene copolymer containing 80% or more of an ethylene part. As the α-olefin, 1-hexene and 4-methyl-1 are used as in the case of the copolymer containing propylene as a main component.
-Pentene, 1-octene, 1-butene, 1-pentene and the like.

In the present invention, the polypropylene resin is blended in an amount of 40 to 100 parts by weight and the polyethylene resin in an amount of 0 to 60 parts by weight. By setting the content within the above range, it is possible to obtain a crosslinked foam having good physical properties at high temperatures, moldability, and appearance. A more preferred mixing ratio is 45 to 80% by weight of the polypropylene resin and 15 to 55% by weight of the polyethylene resin.

In the present invention, divinylbenzene which is a bifunctional monomer, ethylvinylbenzene which is a monofunctional monomer, and an aromatic saturated hydrocarbon compound are used as a crosslinking assistant. Preferred examples of the aromatic saturated hydrocarbon compound include diethylbenzene.

These crosslinking aids include divinylbenzene 3
5 to 90% by weight, 3 to 58% by weight of ethylvinylbenzene, and 7 parts by weight or less of the aromatic saturated hydrocarbon compound are mixed and mixed, and the total amount of the polypropylene resin and the polyethylene resin is 100 parts by weight. Add 0.5 to 10.0 parts by weight.

With respect to the monomer mixing ratio in the crosslinking assistant, if the amount of divinylbenzene is less than 35% by weight and the amount of ethylvinylbenzene exceeds 58% by weight, the foam having low gel fraction and heat resistance and containing abnormal foaming is obtained. Will be. On the other hand, if the content of divinylbenzene exceeds 90% by weight and the content of ethylvinylbenzene is less than 3% by weight, the gel fraction becomes too high, the crosslinking becomes uneven and the flexibility is lost. The preferred mixing ratio of these is 45 to 8 divinylbenzene.
The proportion is 5% by weight, 35 to 49% by weight of ethylvinylbenzene, and 6% by weight or less of the aromatic saturated hydrocarbon compound.

When the amount of the crosslinking aid in the resin composition is less than 0.5 part by weight, crosslinking becomes insufficient and a uniform foam cannot be obtained. Conversely, if the amount exceeds 10 parts by weight, the crosslink density becomes too high, and there is a problem in moldability. The preferred compounding ratio is based on 100 parts by weight of the total of the resin components.
0.8 to 5 parts by weight.

Among these crosslinking aids, ethylvinylbenzene acts as a plasticizer fixed in the molecule, and can provide sufficient elongation during molding even when the gel fraction is high.

The pyrolysis type foaming agent used in the present invention is one which generates a decomposition gas by heating.
Examples include azodicarbonamide, benzenesulfonyl hydrazide, dinitrosopentamethylenetetramine, toluenesulfonyl hydrazide, 4,4-oxybis (benzenesulfonyl hydrazide) and the like. These may be used alone or as a mixture of two or more.

The pyrolytic foaming agent is used in an amount of 100 parts by weight of the total of the polypropylene resin and the polyethylene resin.
It can be used in an appropriate amount within the range of ５０50 parts by weight depending on the desired expansion ratio. A preferable mixing ratio is 4 to 25 parts by weight based on 100 parts by weight of the total of the resin components.

The composition of the present invention contains
An antioxidant, a stabilizer, a pigment and the like can be blended.
Antioxidants and stabilizers may be any as long as they prevent oxidative degradation of the polymer. For example, commercially available phenolic antioxidants, phosphorus antioxidants, amine antioxidants, sulfur antioxidants, etc. And these can be used alone or in combination.

The crosslinked polyolefin-based foamed resin composition of the present invention is prepared by subjecting each component to a pyrolytic foaming agent using a general-purpose kneading device such as a single-screw extruder, a twin-screw extruder, a Banbury mixer, a kneader mixer, or a roll. The mixture is melt-kneaded at a temperature lower than the decomposition temperature, and is usually formed into a sheet. Irradiating the resulting foamable resin composition sheet with ionizing radiation to crosslink,
Thereafter, the sheet is heated to a temperature equal to or higher than the decomposition temperature of the foaming agent and foamed to obtain a crosslinked foam. Examples of the ionizing radiation include α-rays, β-rays, γ-rays, and electron beams, and the irradiation dose is usually 1 to 20 Mra.
d.

The crosslinked foam thus obtained is a foam having a good appearance, and is excellent in heat resistance, toughness and moldability, does not break at the time of molding at a high temperature, and has a complex and deep shape. It can be processed into a molded body.

[0028]

The reason for such a result is not clear, but is presumed as follows. Among the crosslinking aids used in the present invention, divinylbenzene, which is a bifunctional monomer , has high reactivity and rapidly develops crosslinking in a resin when irradiated with ionizing radiation. At this time, in the present invention, since ethyl vinyl benzene, which is a monofunctional monomer , is blended and crosslinked, even if the gel fraction is high, sufficient elongation is exhibited due to its plasticization. for that reason,
It is considered that a foam having excellent moldability and toughness was obtained. The aromatic saturated hydrocarbon compound is obtained
Improve the flexibility of the foam.

[0029]

EXAMPLES The present invention will be described below in detail with reference to examples, but the present invention is not limited to these examples.

Example 1 Polypropylene (MI: 1.
5) 80 parts by weight and polyethylene (MI: 7.0) 20
Parts by weight, based on 100 parts by weight of the total of these resin components,
3.0 parts by weight of a mixture containing 55% by weight of divinylbenzene, 40% by weight of ethylvinylbenzene, and 5% by weight of diethylbenzene as a crosslinking aid, 13 parts by weight of azodicarbonamide as a pyrolytic foaming agent, and an antioxidant 2 , 6-di-t-butyl-p-cresol dilaurylthiodipropionate and a metal toxic inhibitor methylbenzotriazole in an appropriate amount were added to a 17-inch roll with
The mixture was mixed at 0 ° C. at a speed of 20 revolutions / minute for 5 minutes and formed into a plate. The prepared plate was formed into a 1.2 mm sheet at 180 ° C. under a pressure of 110 kg / cm 2, and irradiated with 5.0 Mrad of electron beam to crosslink. Then, it was thrown into an open at 250 ° C. for 5 minutes to obtain a crosslinked foam.

The obtained crosslinked foam was subjected to vacuum molding, and the appearance and vacuum moldability were evaluated. The appearance was evaluated as to whether the appearance was uniform or non-uniform by ○ or ×.
/ D value was measured. The greater the H / D value, the better the moldability.

The heat resistance was evaluated by pressing at 140 ° C. under a constant pressure to evaluate whether the cells in the sheet were broken or not.

Examples 2 to 6 and Comparative Examples 1 to 5
According to the formulation shown in Table 2, a foamable resin composition sheet was prepared in the same manner as in Example 1, irradiated with an electron beam, and then heated and foamed to obtain a crosslinked foam.

The above results are shown in Table 1 (Examples 1 to 6) and Table 2.
(Comparative Examples 1 to 5) are shown together.

[0035]

[Table 1]

[0036]

[Table 2]

Note 1) Regarding Tm (melting point), a polymer sample was heated at a rate of 5 ° C./min using a DSC manufactured by Seiko Electronics Co., Ltd., and the endothermic maximum peak temperature was determined. Note 2) MI was determined by ASTM D1238. Note 3) All azodicarbonamides were used as blowing agents. Note 4) H / D is defined by the following measurement method. The foam is heated by a far-infrared heater so that the surface temperature of the foam becomes 150 to 160 ° C., and vacuum-formed using a cylindrical female mold. Display as a ratio. Note 5) Measurement was not possible because the desired foam was not obtained. Note 6) Trimethylolpropane trimethacrylate (alone) was used as a crosslinking aid.

As is clear from Tables 1 and 2, the crosslinked foams of Examples 1 to 6 according to the present invention are superior in vacuum moldability at high temperatures to those of Comparative Examples 1 to 5, and therefore It is a foam with excellent workability, excellent heat resistance and uniform appearance.

[0039]

According to the present invention, the appearance is improved by using divinylbenzene, which is a bifunctional monomer, ethylvinylbenzene, which is a monofunctional monomer, and an aromatic saturated hydrocarbon compound as cross-linking aids. Moreover, it is possible to provide a crosslinked polyolefin-based foamed resin composition which is tough and suitable for producing a crosslinked polyolefin-based resin foam having excellent moldability at high temperatures.

The crosslinked polyolefin resin foam obtained by crosslinking and foaming the above resin composition has improved heat dimensional stability and heat resistance.

Claims (2)

(57) [Claims] (1) Melt index is 0.5 to 12
Polypropylene resin 40 to 100Weight percent,
(b) polyethylene having a melt index of 2 to 50
System resin 0-60100 parts by weight of the mixture with
hand, (c) 35-90% by weight of divinylbenzene, ethylvinyl
Benzene 3 to 58% by weight, aromatic saturated hydrocarbon compound
Less than 7% by weight of three components0.5 to 10.
0 parts by weight,(d) Containing 1 to 50 parts by weight of a pyrolytic foaming agent
A foamable polyolefin resin composition characterized by the following: 2. A crosslinked polyolefin resin foam obtained by crosslinking and foaming the foamable polyolefin resin composition according to claim 1.