JP3139789B2 - Polyolefin foamable resin composition and crosslinked polyolefin resin foam - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polyolefin foamable resin composition, and more particularly, to a composition having excellent heat resistance.
The present invention relates to a polyolefin-based foamable 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. .

[0002]

2. Description of the Related Art Polyolefin resin foams are widely used as heat insulating materials and miscellaneous goods because of their excellent flexibility and heat insulating properties. More recently, in the field of interior materials for vehicles such as automobiles, It is widely used as a heat insulating material for ceilings, doors, instrument panels, and the like. For this reason, a crosslinked polyolefin foam is formed from a sheet material by vacuum forming or compression molding to produce a product. However, since vacuum molding and compression molding are performed at a high temperature of 120 to 200 ° C., conventional polyolefin foams, especially polyethylene foams, have low heat resistance and cannot be used, and polyolefin resin foams using polypropylene as a component cannot be used. The body is used.

[0003] Conventionally, crosslinking in a method for producing a polyolefin-based foam is carried out by heating a resin composition to which an organic peroxide is added, or by irradiating the resin composition with ionizing radiation. And both are performed industrially. However, these cross-linking methods are effective for cross-linking polyethylene, but are not suitable for the above-mentioned polyolefin resin containing polypropylene as a main component. The reason for this is that in any of the above-mentioned cross-linking methods, the cutting of the molecular chain proceeds simultaneously with the cross-linking of the polypropylene, thereby deteriorating the resin. 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. (Japanese Patent Publication 46-38716)
No., JP-A-57-212236, JP-B-60-119
No. 35, JP-A-61-69844).

Among them, according to JP-B-46-38716, (1) a compound having two or more vinyl-type double bonds in a molecule, and (2) an aromatic compound having one vinyl group are used as a crosslinking assistant. Two types of combinations of a compound and an organic compound having two or more (meth) acryloyloxy groups have been proposed. The aromatic hydrocarbon compounds belonging to the former and the latter compounds are described as being favorably used for crosslinking with organic peroxides. However, in order to develop crosslinking in the resin by the organic peroxide, it is necessary to put the organic peroxide which is a decomposable substance into the extruder. In this case, control of the reaction is extremely difficult, and the working environment often involves danger.

[0005] On the other hand, in the method of developing crosslinking by irradiating the resin with ionizing radiation, the irradiation conditions can be kept constant and the crosslinking reaction can be easily controlled. However, regardless of which method is used, if the gel fraction is increased to obtain the necessary viscosity at the time of foaming, cross-linking proceeds unevenly, and the cross-linking point between the cross-linking points increases. The molecular weight is reduced, and as a result, the resulting foam is partially unnecessarily hard and has insufficient elongation during molding. In such a state, it is difficult to process this into a molded body having a complicated shape and a deep concave portion, and the foam may be damaged. Further, when the amount of the polyfunctional monomer is reduced as a means for improving the molding processability, not only uniform foaming cannot be performed, but also the strength of the foamed cell may be reduced.

[0006]

DISCLOSURE OF THE INVENTION The present invention efficiently and continuously develops crosslinking in a resin composition with ionizing radiation and a small amount of a crosslinking assistant, and has excellent heat resistance, toughness, moldability, and appearance. To provide a polyolefin foamable resin composition suitable for producing a homogeneous homogenous crosslinked polyolefin resin foam, and a crosslinked polyolefin resin foam obtained by crosslinking and foaming the polyolefin foamable resin composition. The purpose is to provide.

The inventors of the present invention have conducted intensive studies, and as a result, as a resin component, a polypropylene having a specific melt index.
Pyrene, or using a mixture of polypropylene and polyethylene having a specific melt index, and,
It has been found that the above object can be achieved by using a specific polyfunctional monomer as a crosslinking aid, and the present invention has been completed based on this finding.

[0008]

Thus, the polyolefin foamable resin composition of the first invention has a melt index of 0.5 to 12 and a polypropylene resin of 40 to 100 weights.
% Of a resin component having a melt index of 2 to 50 and 60 to 0 % by weight of a polyethylene resin.
0.5 to 99.5% by weight of 1,2,4-benzenetricarboxylic acid triallyl ester and 99.5 to 0.5% by weight of 1,9-nonanediol dimethacrylate based on parts by weight
And 0.3 to 8 parts by weight of a cross-linking aid consisting of a mixture of the above, and 1 to 30 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 polyolefin foamable resin composition.

Hereinafter, the present invention will be described in detail for each component of the composition.

Polypropylene The polypropylene used in the present invention is not particularly limited.
Either a polypropylene homopolymer, a copolymer containing propylene as a main component, or a mixture thereof may be used. As the copolymer, for example, 85% by weight of a polypropylene part
A polypropylene-α-olefin copolymer containing the above can be mentioned. As the α-olefin, ethylene, 1
-Hexene, 4-methyl-1-pentene, 1-octene, 1-butene, 1-pentene and the like.

The polypropylene used in the present invention has a melt index (abbreviated as MI; measured by ASTM D1238) of 0.5 to 12, preferably 1 to 10, and more preferably 1 to 5. MI of polypropylene
Is less than 0.5, there is a problem in appearance when forming into a sheet, and when the MI exceeds 12, heat resistance becomes insufficient.

Polyethylene The polyethylene used in the present invention may be either a polyethylene homopolymer, a copolymer containing ethylene as a main component, or a mixture thereof. As the copolymer, for example,
A polyethylene-α-olefin copolymer containing at least 80% of a polyethylene portion can be mentioned. As the α-olefin, propylene, 1-hexene, 4-methyl-1-
Examples thereof include pentene, 1-octene, 1-butene, and 1-pentene.

The polyethylene used in the present invention has an MI of 2 to 50, preferably 3 to 30, and more preferably 4 to 30.
25. If the MI of the polyethylene is less than 2, a problem arises in appearance when forming a sheet, and if the MI exceeds 50, a problem arises in heat resistance.

[0015] The resin component is polypropylene 40-100.
% Of polyethylene and 60 to 0 % by weight of polyethylene. By being within the range of these compounding ratios, it is possible to obtain a crosslinked foam having good physical properties at high temperatures, moldability, and appearance. A particularly desirable ratio of polypropylene in the resin component is in the range of 50 to 90 % by weight .

Crosslinking Aids The crosslinking aid used in the composition of the first invention is 0.5 to 99.5% by weight of 1,2,4-benzenetricarboxylic acid triallyl ester which is a polyfunctional monomer. , and 99.5 to 0.5% by weight 9-nonanediol dimethacrylate
Is a mixture of

By mixing these two kinds of polyfunctional monomers, ie, 1,2,4-benzenetricarboxylic acid triallyl ester and 1,9-nonanediol dimethacrylate, uniform crosslinking can be realized, and heat resistance and toughness are obtained. A crosslinked polyolefin-based resin foam having both properties, elongation and flexibility, is obtained. When the content of 1,2,4-benzenetricarboxylic acid triallyl ester is 50% by weight or more, uniform crosslinking can be realized with a small amount, and heat resistance and moldability are more excellent. On the other hand, if the content is less than 50% by weight, a foam in which moldability and flexibility are more important than heat resistance can be molded.

In the composition of the first invention, the crosslinking aid is added in an amount of 0.3 to 8 parts by weight based on 100 parts by weight of the total amount of the resin components polypropylene and polyethylene. If this ratio is less than 0.3 parts by weight, a crosslinked product is insufficient and a homogeneous foam cannot be obtained, and the product lacks extensibility. On the other hand, if the proportion of the crosslinking aid exceeds 8 parts by weight, the crosslinking density becomes too high, and there is a problem in moldability.
A particularly preferred mixing ratio of the crosslinking aid is in the range of 0.5 to 6 parts by weight.

In the composition of the first invention , the above-mentioned crosslinking aid may be used as it is, or may be used by mixing it with another polyfunctional crosslinking aid. In such a case, the crosslinking aid of the present invention comprises 40 % of the total amount of the crosslinking aid.
% Or more, and the total amount of the crosslinking assistant must be in the range of 0.3 to 8 parts by weight. Examples of other common crosslinking aids include trimethylolpropane tri (meth)
Acrylate, divinylbenzene, 1,6-hexanediol di (meth) acrylate, 2,2-bis [4-
(Acryloxydiethoxy) phenyl] propane and the like which are active against ionizing radiation.

Thermal decomposition type foaming agent The thermal decomposition type foaming agent used in the present invention generates a decomposed gas by heating. Specifically, azodicarbonamide, benzenesulfonylhydrazide, dinitrosopentamethylenetetramine, Examples thereof include toluenesulfonyl hydrazide and 4,4-oxybis (benzenesulfonyl hydrazide). These may be used alone,
Two or more kinds may be used as a mixture.

The thermal decomposition type foaming agent has a total amount of resin components of 10%.
And to 0 parts by weight from 1 to 30 parts by weight, preferably from 2 to 2
Within the range of 5 parts by weight, it can be used in an appropriate amount depending on the desired expansion ratio.

Other Ingredients The composition of the present invention may contain an antioxidant,
Stabilizers, pigments, metal harm inhibitors and the like can be added. The antioxidant is used in an amount of 0.1 to 5.0 based on 100 parts by weight of the total of the polypropylene resin and the polyethylene resin.
Can be used within the range of parts by weight. A preferable mixing ratio is 0.5 to 3.5 parts by weight based on 100 parts by weight of the total of the resin components. As the stabilizer, any of known phenol-based, phosphorus-based, sulfur-based, and amine-based stabilizers can be used.

Molding The polyolefin foamable resin composition of the present invention is prepared by subjecting each component to thermal decomposition foaming using a general-purpose kneading apparatus 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 of the agent, 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. As the ionizing radiation, α-ray, β-ray, γ-ray, electron beam and the like can be used, and the irradiation dose is usually 1 to 20 Mrad.

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

[0025]

The reason for such a result is not clear, but is presumed as follows.

[0026] Among the mixed crosslinking aid in the composition of the first invention, 1,2,4-benzenetricarboxylic acid triallyl ester, compared to multi-functional monomers which have been conventionally used, high reactivity, polyolefin Due to the good compatibility with the system resin, even if the addition amount is small, crosslinking is rapidly developed in the resin when irradiated with ionizing radiation. At that time, since the amount of the crosslinking aid added is small, the influence of the crosslinking aid in the crosslinking state is small, and the reactivity is high, so that the required irradiation dose can be reduced, so that the original resin has excellent properties. Flexibility is not lost even in the crosslinked state.

Also, 1,9-nonanediol dimethacrylate is excellent in compatibility with polypropylene resin and polyethylene resin because its chemical structure is similar to polyolefin. Moreover, since 1,9-nonanediol dimethacrylate itself has a flexible structure, by mixing it, a uniform and highly flexible crosslink is formed in a mixed matrix of a polypropylene resin and a polyethylene resin. The structure can be expanded. Therefore, by forming a foam using such a cross-linking aid, good elongation and good elongation can be obtained even if the cross-linking is performed so as to have a gel fraction necessary and sufficient to obtain a foam having uniform closed cells. A molded article having excellent moldability and toughness at the same time can be obtained.

[0028]

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 60 parts by weight of polypropylene (MI: 1.5), 40 parts by weight of polyethylene (MI: 7), and 0.8% of 1,2,4-benzenetricarboxylic acid triallyl ester as a crosslinking aid Parts by weight, 1.2 parts by weight of 1,9-nonanediol dimethacrylate, 15 parts by weight of azodicarbonamide as a foaming agent, and an appropriate amount of an antioxidant and a metal damage inhibitor were added. The obtained compound was mixed on a 6-inch roll at 170 ° C. at a speed of 20 rotations / minute for 5 minutes to form a plate. The obtained plate was heated at 180 ° C., 1
3. Formed into a 1 mm sheet under a pressure of 00 kg / cm ² ,
Crosslinking was performed by electron beam irradiation at 0 Mrad. Then, this is 25
It was put into an oven at 0 ° C. for 5 minutes to obtain a crosslinked foam.

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

Examples 2 to 6 and Comparative Examples 1 to 5 Formulations were prepared according to the formulations shown in Table 1 and
In the same manner as in Example 1, a foamable resin composition sheet was prepared, and after irradiating the sheet with an electron beam, the sheet was heated and foamed to obtain a crosslinked foam. These results are collectively shown in Table 1.

[0032]

[Table 1]

Note 1) For 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 (melt index) is
Determined according to ASTM D1238.

Note 3) Azodicarbonamide was used as a foaming agent.

Note 4) H / D is defined as follows. 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) Those having no closed cells could not be foamed, and thus could not be evaluated for moldability.

As can be seen from Table 1, the crosslinked foams of the examples have a significantly higher temperature (160
° C), and is a foam which is excellent in molding processability and uniform in appearance.

[0039]

According to the present invention, as a crosslinking aid, 1,
A mixture of 2,4-benzenetricarboxylic acid triallyl ester and 1,9-nonanediol dimethacrylate was used.
By using it, the appearance is good, it is tough, it does not cause breakage problems such as tearing at high temperature molding, the moldability is improved without impairing the appearance, it has excellent flexibility, and the heating dimension A crosslinked polyolefin-based resin foam having improved stability and improved heat resistance can be provided.

Claims (2)

(57) [Claims] 1. 100 parts by weight of a resin component comprising a mixture of 40 to 100% by weight of a polypropylene resin having a melt index of 0.5 to 12 and 60 to 0 % by weight of a polyethylene resin having a melt index of 2 to 50, 1,
Crosslinking aid 0.3 to 8 consisting of a mixture of 0.5 to 99.5% by weight of 2,4-benzenetricarboxylic acid triallyl ester and 99.5 to 0.5% by weight of 1,9-nonanediol dimethacrylate Parts by weight, and a pyrolytic foaming agent 1 to 3
A polyolefin-based foamable resin composition containing 0 parts by weight. 2. The polyolefin foam according to claim 1.
Crosslinking characterized by crosslinking and foaming the resin composition
Polyolefin resin foam.