JP3186800B2 - Foamable polyolefin 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 foamable polyolefin resin composition, and more particularly, to a composition having excellent heat resistance.
Expandable polyolefin-based resin composition suitable for producing a crosslinked polyolefin-based resin foam capable of performing secondary processing of a complicated shape, and a crosslinked polyolefin-based resin foam obtained by crosslinking and foaming the composition About.

[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.

[0005] On the other hand, the method of developing crosslinking by irradiating ionizing radiation with a resin makes it easy to keep irradiation conditions constant. However, conventionally, only highly reactive polyfunctional monomers were used as cross-linking aids, so if the gel fraction was increased to obtain the required viscosity during foaming, the resulting foam would be more than necessary during molding. It becomes hard and elongation becomes insufficient. In such a state, it is particularly difficult to process the molded product into a complicated and deep shaped product, and the foam may be damaged. When the amount of the polyfunctional monomer is reduced as a means for improving the moldability, uniform foaming cannot be performed, and a foam having a uniform appearance cannot be obtained.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a crosslinked polyolefin-based resin foam having uniform heat resistance, toughness, moldability, and uniform appearance by uniformly and efficiently developing uniform crosslinks into a resin composition by irradiation with ionizing radiation. It is an object of the present invention to provide a foamable polyolefin-based 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 foamable polyolefin resin 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 or more vinyl groups are contained on an aromatic ring as a crosslinking aid. Alternatively, it has been found that the above object can be achieved by using a polyfunctional monomer to which a substituted vinyl group is directly bonded and a specific monofunctional monomer, and the present invention has been completed based on the knowledge.

[0009]

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
Relative to 100 parts by weight of a mixture of an amount%, (c) the polyfunctional monomer 0.5 to 10 parts by weight of an aromatic 2 or more vinyl groups or substituted vinyl group in the ring is directly bonded, (d) Monofunctional monomer represented by the following general formula [1] 0.5 to 0.5
5 parts by weight,

[0010]

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(Wherein R ¹ is a hydrogen atom or a methyl group,
R ² is a linear, branched or cyclic alkyl group having 1 to 20 carbon atoms, a phenyl group or a substituted phenyl group. And (e) 1 to 50 parts by weight of a pyrolytic foaming agent.

According to the present invention, there are further provided (a) a polypropylene having a melt index of 0.5 to 12;
40 to 100% by weight of a pyrene-based resin and (b)
Polyethylene resin having a weight of 2 to 50, 0 to 60 layers
Relative to 100 parts by weight of a mixture of an amount%, (c) 2 or more vinyl groups or substituted vinyl aromatic ring
0.5 to 10 weight of a polyfunctional monomer having a group directly bonded
And (d) a monofunctional monomer represented by the following general formula [2]:
5 parts by weight,

[0013]

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(Wherein R ³ is a phenyl group or a substituted phenyl group.) (E) It contains 1 to 50 parts by weight of a pyrolytic foaming agent .
Characteristic foamable polyolefin resin composition is provided
Can be Further, according to the present invention, there is provided a crosslinked polyolefin resin foam obtained by crosslinking and foaming these foamable polyolefin resin compositions.

Hereinafter, the present invention will be described in detail.

The polypropylene resin used in the present invention comprises:
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 comprises:
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. As the copolymer, for example, propylene-α containing 85% by weight or more of a propylene part
Olefin copolymers and propylene-ethylene copolymers can be mentioned. Examples of the α-olefin include 1-hexene, 4-methyl-1-pentene, 1-octene, and 1-hexene.
Butene, 1-pentene and the like are exemplified.

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 an ethylene portion of 80% by weight or more. Examples of the α-olefin include 1-hexene and 4-methyl- as in the case of the copolymer containing propylene as a main component.
Examples thereof include 1-benthene, 1-octene, 1-butene, and 1-pentene.

In the present invention, the polypropylene resin is blended at a ratio of 40 to 100 parts by weight and the polyethylene resin at a ratio 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 parts by weight of the polypropylene resin and 15 to 55 parts by weight of the polyethylene resin.

In the present invention, two kinds of monomers, that is, a polyfunctional monomer in which two or more vinyl groups or substituted vinyl groups are directly bonded to an aromatic ring and a monofunctional monomer are used as a crosslinking assistant.

Specific examples of the polyfunctional monomer include divinylbenzene, divinylnaphthalene, divinylcarbazole, divinylpyridine, and their nuclear-substituted compounds and closely related homologs. These polyfunctional monomers are blended at a ratio of 0.5 to 10 parts by weight based on 100 parts by weight of the total of the polypropylene resin and the polyethylene resin. If this proportion is less than 0.5 part by weight, crosslinkage is insufficient and a homogeneous foam cannot be obtained. Conversely, if it exceeds 10 parts by weight, the crosslinking density becomes too high, and there is a problem in the moldability of the foam. Occurs. A preferred compounding ratio is 0.8 to 5 parts by weight based on 100 parts by weight of the total of the resin components.

These polyfunctional monomers may be used alone, or may be used in combination of two or more kinds, or as a mixture with another polyfunctional crosslinking aid.
In the case of this mixed use, 30% or more of the total amount of the crosslinking aid is the polyfunctional monomer of the present invention, and the total amount of the crosslinking aid is 0.5 to 0.5% based on 100 parts by weight of the total of the resin component. 1
It is preferably within the range of 0 parts by weight. Other common polyfunctional crosslinking assistants include trimethylolpropane tri (meth) acrylate, 1,6-hexanediol di (meth) acrylate 2,2-bis [4- (acryloxydiethoxy) phenyl] propane And the like, which are active against ionizing radiation.

One of the monofunctional monomers that can be used as a crosslinking aid in the present invention is (meth) acrylate represented by the following general formula [1].

[0025]

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(Wherein R ¹ is a hydrogen atom or a methyl group,
R ² is a linear, branched or cyclic alkyl group having 1 to 20 carbon atoms, a phenyl group or a substituted phenyl group. ) Specific examples of the (meth) acrylate which is a monofunctional monomer include methyl (meth) acrylate and n-
Butyl (meth) acrylate, t-butyl (meth) acrylate, n-hexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, n-octyl (meth) acrylate, isononyl (meth) acrylate,
Lauryl (meth) acrylate, dodecyl (meth) acrylate, cyclohexyl (meth) acrylate, stearyl (meth) acrylate, phenyl (meth) acrylate and the like can be mentioned.

Another one of the monofunctional monomers that can be used in the present invention is a styrene represented by the following general formula [2].

[0028]

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(Wherein R ³ is a phenyl group or a substituted phenyl group.) Specific examples of the monofunctional styrenes include styrene, o-, p-methylstyrene,
o-, p-ethylstyrene and the like.

These monofunctional monomers are blended at a ratio of 0.5 to 5 parts by weight with respect to 100 parts by weight of the total of the polypropylene resin and the polyethylene resin. When the monofunctional monomer is blended at this ratio and crosslinked, the monofunctional monomer functions as a plasticizer fixed in the molecule, and shows sufficient elongation at the time of molding even when the gel fraction is high. If the proportion is less than 0.5 part by weight, the effect of adding the monofunctional monomer will not be obtained, and if it exceeds 5 parts by weight, the crosslinking density will be too high, and the foam will have difficulty in moldability. A preferred compounding ratio is 0.8 to 3.5 parts by weight based on 100 parts by weight of the total of the resin components.

The pyrolytic foaming agent used in the present invention is one that generates a decomposed 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 1 part by weight based on a total of 100 parts by weight 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 may contain, depending on its purpose,
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 foamable polyolefin 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. A crosslinked foam can be obtained by irradiating the obtained foamable resin composition sheet with ionizing radiation to crosslink and then heating the sheet above the decomposition temperature of the foaming agent to 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 Mrad.
It is.

The crosslinked foam thus obtained is a foam having a good appearance, and is excellent in heat resistance, toughness, and moldability. It can be processed into a molded body. Specific applications of the crosslinked foam of the present invention include interior materials for vehicles.

[0036]

The reason for such a result is not clear, but is presumed as follows. Among the crosslinking assistants used in the present invention, a polyfunctional monomer in which two or more vinyl groups or substituted vinyl groups are directly bonded to an aromatic ring,
When irradiated with ionizing radiation due to its high reactivity, it rapidly develops crosslinking in the resin. At that time, in the present invention, since a monofunctional monomer such as (meth) acrylate or styrene is blended and crosslinked, even if the gel fraction is high, sufficient elongation is exhibited due to the plasticizer. Therefore, it is considered that a foam having excellent moldability and toughness could be obtained.

[0037]

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, 20 parts by weight of polyethylene (MI: 7), 2.5 parts by weight of divinylbenzene as a crosslinking aid with respect to 100 parts by weight of the total of polypropylene and polyethylene, 1.0 part by weight of lauryl methacrylate, 13 parts by weight of azodicarbonamide as a foaming agent, 2,6-di-t-butyl-p-cresol dilauryl thiodipropionate, an antioxidant, and an appropriate amount of a metal toxicant, methylbenzotriazole, were added to a 6-inch sheet. Roll, 1
The mixture was mixed at 70 ° C. at a speed of 20 rotations / minute for 5 minutes and formed into a plate. The prepared plate was formed into a 1 mm sheet at 180 ° C. under a pressure of 100 kg / cm 2, and irradiated with 6 Mrad of electron beam to crosslink. After that, put into the open of 250 ℃ for 5 minutes,
A crosslinked foam was obtained.

The obtained crosslinked foam was subjected to vacuum molding, and the appearance and vacuum moldability were evaluated. The external appearance was visually observed, and the H / D value was measured for vacuum formability. The greater the H / D value, the better the moldability.

Examples 2 to 6 and Comparative Examples 1 to 3
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 (Example) and Table 2.
(Comparative Example)

[0042]

[Table 1]

[0043]

[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 taken. 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) TMPT = trimethylolpropane trimethacrylate Note 6) If closed cells could not be formed, they could not be foamed and thus could not be evaluated for moldability. Note 7) Frame 1 = divinylbenzene frame 2 = divinylnaphthalene frame 3 = lauryl methacrylate frame 4 = cyclohexyl methacrylate.

As is clear from Tables 1 and 2, the crosslinked foams of Examples 1 to 6 according to the present invention are more excellent in vacuum moldability at high temperature (160 ° C.) than those of Comparative Examples 1 to 4. Therefore, it is a foam having excellent moldability and a uniform appearance.

Example 7 2.6 parts by weight of divinylbenzene was used as a cross-linking aid with respect to 100 parts by weight of the total of polypropylene and polyethylene, and 1.5 parts by weight of ethylvinylbenzene were used.
A crosslinked foam was obtained in the same manner as in Example 1 except for using parts by weight.

The obtained crosslinked foam was subjected to vacuum molding, and the appearance and vacuum moldability were evaluated.

[Examples 8 to 12] A foamable resin composition sheet was prepared according to the formulation shown in Table 3 in the same manner as in Example 7, irradiated with an electron beam, and then heated and foamed to form a crosslinked foam. I got

Table 3 shows the above results.

[0050]

[Table 3]

Note 8) Frame 5 = ethylvinylbenzene Frame 6 = p-methylstyrene.

As is clear from Table 3, the crosslinked foams of Examples 7 to 12 according to the present invention are superior in vacuum moldability at high temperature (160 ° C.) to those of Comparative Examples 1 to 4 described above. Therefore, it is a foam having excellent moldability and homogeneity in appearance.

[0053]

According to the present invention, a polyfunctional monomer in which two or more vinyl groups or substituted vinyl groups are directly bonded to an aromatic ring and a specific monofunctional monomer are used as a crosslinking aid. Provide a foamable polyolefin-based resin composition that develops uniform cross-linking into a resin composition and has excellent heat resistance, toughness, and moldability, and is suitable for producing a crosslinked polyolefin-based resin foam having a uniform appearance. be able to.

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

Claims (3)

(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) two or more vinyl groups or substituted vinyl on the aromatic ring
0.5 to 10 weight of a polyfunctional monomer having a group directly bonded
And (d) a monofunctional monomer represented by the following general formula [1]:
5 parts by weight, and(Where R¹Is a hydrogen atom or a methyl group, R^TwoIs the carbon number
1-20 linear, branched or cyclic alkyl
Group, a phenyl group or a substituted phenyl group. And (e) containing 1 to 50 parts by weight of a pyrolytic foaming agent.
A foamable polyolefin resin composition characterized by the following: (2 ) Melt index is 0.5 to 12
40 to 100% by weight of a polypropylene resin,
(b) polyethylene having a melt index of 2 to 50
Based on 100 parts by weight of a mixture with 0 to 60% by weight of the base resin
And (c) two or more vinyl groups or substituted vinyls on the aromatic ring.
0.5 to 10 weight of a polyfunctional monomer having a group directly bonded
And (d) a monofunctional monomer represented by the following general formula [2]:
5 parts by weight, and (In the formula, R ³ is a phenyl group or a substituted phenyl group.) (E) It is necessary to contain 1 to 50 parts by weight of a pyrolytic foaming agent .
A foamable polyolefin resin composition characterized by the following: 3. A crosslinked polyolefin-based resin foam obtained by crosslinking and foaming the foamable polyolefin-based resin composition according to claim 1 or 2.