JPH09278918A - Foam comprising modified polypropylene-based resin composition and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce the subject low-density foam, comprising a specific modified polypropylene-based resin composition, having a high closed-cell ration and a beautiful appearance, excellent in heat resistance and useful as a cushioning material, etc. SOLUTION: This foam comprising a modified polypropylene-based resin composition is obtained by melt kneading (A) the modified polypropylene-based resin composition prepared by melt kneading (i) a polypropylene-based resin with (ii) a polyethylene-based resin, (iii) an aromatic vinyl monomer (preferably any one or more of styrene, methylstyrene and vinylbenzene) and (iv) a radical polymerization initiator [preferably any one or more of a peroxy ketal, a dialkyl peroxide, a diacyl peroxide and a peroxy ester) with (B) a foaming agent (e.g. butane gas) and then extruding and expanding the kneaded mixture. For example, the amount of the component (iii) is preferably 1-30 pts.wt. based on 100 pts.wt. component A and that of the component (iv) is preferably within the range of 0.1-1 pt.wt. based on 100 pts.wt. component A. The amount of the component (iii) is 1-30 pts.wt. based on 100 pts.-wt. total amount of the components (i) and (ii) and that of the component B is preferably within the range of 0.5-100 pts.wt. based on 100 pts.wt. component A.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a foam made of a modified polypropylene resin composition and a method for producing the foam. More specifically, a polypropylene-based resin, a polyethylene-based resin, a modified polypropylene-based resin composition obtained by melt-kneading an aromatic vinyl monomer and a radical polymerization initiator, which has excellent heat resistance and a high closed cell rate. The present invention relates to a foam having a low density and a beautiful appearance, and a method for producing the foam.

[0002]

2. Description of the Related Art A foam made of a thermoplastic resin is generally used for a heat insulating material, a cushioning material, a core material, a food container, etc. because it is lightweight and has a good heat insulating property and a good shock absorbing property against external stress. ing. Of these, foams made of polypropylene-based resin have good chemical resistance, impact resistance and heat resistance, and are therefore particularly suitable for use as cushioning materials.

[0003] However, polypropylene resins are
Since it is a crystalline resin, the viscosity and tension at the time of melting are low, and when the resin is foamed, the strength of the cell wall is not sufficiently maintained at the time of foaming. Further, since this resin has a low gas barrier property, when the resin is foamed, the gas generated from the foaming agent is easily dissipated to the outside from the bubbles. Therefore, by foaming the polypropylene resin,
It was difficult to obtain a foam having an excellent appearance and a high closed cell ratio and a low density.

As a method for improving the foamability of a polypropylene resin, for example, a method of adding a crosslinking aid to the polypropylene resin to crosslink its molecules (see, for example, JP-B-45-40420) and polypropylene resins. A method of blending polyethylene and foaming it (see, for example, Japanese Patent Publication No. 44-2574), a method of blending polystyrene with polypropylene resin and foaming it (for example, Japanese Patent Publication No. 43-1337).
5), a method of blending a polypropylene resin with polystyrene and polyphenylene ether, and foaming this (see JP-A-6-25655).
And so on.

However, even if these methods are used,
The effect of improving foamability is not sufficient.

[0006] Further, when it is intended to improve the foaming property of the polypropylene resin by blending a resin having a low heat distortion temperature, the high heat resistance, which is one of the characteristics of the polypropylene resin, may be impaired. is there.

In Japanese Patent Publication No. 48-4859,
Polyethylene, peroxide type radical polymerization initiator,
Knead the styrene monomer and blowing agent in the extruder,
A method for producing a foam by reacting and extruding is disclosed, but polypropylene is not disclosed at all.

As described above, the polypropylene resin is sufficiently improved in foamability, and the resin has a high expansion ratio,
At present, no method has been found for producing a foam having a high closed cell rate and a low density.

[0009]

SUMMARY OF THE INVENTION An object of the present invention is to provide a modified polypropylene resin composition having improved foamability, which is excellent in heat resistance, has a high expansion ratio, and has a high closed cell ratio.
It is to provide a foam having a low density and a beautiful appearance.

[0010]

DISCLOSURE OF THE INVENTION The present invention is a foam comprising a modified polypropylene resin composition obtained by melt-kneading a polypropylene resin, a polyethylene resin, an aromatic vinyl monomer and a radical polymerization initiator. Regarding

The aromatic vinyl monomer is preferably composed of one or more selected from the group consisting of styrene, methylstyrene and divinylbenzene.

It is preferable that the radical polymerization initiator comprises one or more selected from the group consisting of peroxyketal, dialkyl peroxide, diacyl peroxide and peroxy ester.

The present invention also relates to a method for producing a foam, in which the modified polypropylene resin composition and a foaming agent are melt-kneaded and then extruded to foam.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION As a result of intensive studies to solve the above problems, the present inventors have found that a polypropylene resin,
A modified resin obtained by kneading a polyethylene resin, an aromatic vinyl monomer and a radical polymerization initiator at a temperature at which the polypropylene resin melts and at a temperature at which the radical polymerization initiator can decompose. The foamability of the high-quality polypropylene resin composition is remarkably improved with respect to the foamability of the polypropylene resin before being melt-kneaded (hereinafter also referred to as “raw polypropylene resin”), and also has excellent heat resistance. By foaming the modified polypropylene resin composition, it was found that a foam having excellent heat resistance, a high closed cell ratio, a low density and a beautiful appearance can be obtained, and the present invention was completed. It was

In the present invention, although the reason why the foamability of the modified polypropylene resin composition is remarkably improved is not clear, the raw material polypropylene resin, polyethylene resin, aromatic vinyl monomer and radical polymerization initiator If any of them is lacking, the object of the present invention cannot be achieved.

The modified polypropylene resin composition thus obtained has a high cell wall strength during foaming.
The cell walls are not easily destroyed when foaming.

By foaming such a modified polypropylene resin composition, the closed cell ratio is high, the density is low, the appearance is excellent, the heat resistance is good, and the mechanical properties are good. A foam having can be obtained.

Examples of the raw material polypropylene resin that can be used in the present invention include propylene homopolymers, block copolymers of propylene and other monomers, and random copolymers of propylene and other monomers. Examples of the crystalline polymer, the polypropylene homopolymer is preferable from the viewpoint of high rigidity and low cost, and from the viewpoint of high rigidity and high impact resistance, the propylene and other monomers Block copolymers are preferred. When the raw polypropylene resin is a block copolymer of propylene and other monomers or a random copolymer of propylene and other monomers, the high crystallinity and high rigidity characteristic of polypropylene resins From the viewpoint of maintaining good chemical resistance, the content of the propylene monomer component is preferably at least 75% by weight, more preferably at least 90% by weight.

In the raw material polypropylene resin,
As other monomers copolymerizable with propylene, one or more selected from the group consisting of ethylene, α-olefin, cyclic olefin, diene monomer and vinyl monomer Monomers. Further, as the monomer, ethylene, α-olefin or diene-based monomer is preferable because it is easily copolymerized with propylene and is inexpensive.

Examples of the α-olefin copolymerizable with propylene include butene-1, isobutene, pentene-1, 3-methyl-butene-1, hexene-1, 3-hexene.
Methyl-pentene-1, 4-methyl-pentene-1,
Α-olefins having 4 to 12 carbon atoms, such as 3,4-dimethyl-butene-1, heptene-1, 3-methyl-hexene-1, octene-1, and decene-1. Examples of the cyclic olefin copolymerizable with propylene include cyclopentene, norbornene, 1,4.
5,8-Dimethano-1,2,3,4,4a, 8,8a-
6-octahydronaphthalene and the like. Also,
Examples of the diene-based monomer copolymerizable with propylene include 5-methylene-2-norbornene, 5-ethylidene-2-norbornene, 1,4-hexadiene, methyl-1,4-hexadiene, 7- Methyl-1,6-octadiene and the like can be mentioned. Further, examples of the vinyl monomer copolymerizable with the above-mentioned propylene include vinyl chloride,
Examples thereof include vinylidene chloride, acrylonitrile, vinyl acetate, acrylic acid, methacrylic acid, maleic acid, ethyl acrylate, butyl acrylate, methyl methacrylate, maleic anhydride and the like.

Of these monomers, ethylene or butene-1 is more preferable because it is inexpensive.

The molecular weight (weight average molecular weight) of the raw material polypropylene resin is preferably in the range of 50,000 to 2,000,000 from the viewpoint of easy availability, and is 100,000 to 1,000,000 from the viewpoint of being inexpensive. More preferably, it is within the range.

Examples of the polyethylene resin usable in the present invention include low density polyethylene, high density polyethylene, straight chain low density polyethylene, and those modified by graft copolymerization. Among them, particularly preferable ones Is low density polyethylene.

From the viewpoint of improving the foamability and heat resistance, and not impairing the originally suitable characteristics of the polypropylene resin, the amount of the polyethylene resin added is 100 parts by weight of the raw polypropylene resin. The amount is preferably 0.1 to 50 parts by weight, more preferably 1 to 30 parts by weight.

The raw material polypropylene resin and polyethylene resin may be in the form of particles or pellets, and the size and shape thereof are not particularly limited.

Examples of the aromatic vinyl monomer usable in the present invention include styrene; o-methylstyrene, m
-Methylstyrene such as methylstyrene, p-methylstyrene, α-methylstyrene, β-methylstyrene, dimethylstyrene and trimethylstyrene; α-chlorostyrene, β-chlorostyrene, o-chlorostyrene, m-
Chlorostyrene such as chlorostyrene, p-chlorostyrene, dichlorostyrene and trichlorostyrene; bromostyrene such as o-bromostyrene, m-bromostyrene, p-bromostyrene, dibromostyrene and tribromostyrene; o-fluorostyrene, m -Fluorostyrene such as fluorostyrene, p-fluorostyrene, difluorostyrene and trifluorostyrene; nitrostyrene such as o-nitrostyrene, m-nitrostyrene, p-nitrostyrene, dinitrostyrene and trinitrostyrene; o-hydroxystyrene , Vinylphenol such as m-hydroxystyrene, p-hydroxystyrene, dihydroxystyrene and trihydroxystyrene; o-divinylbenzene, m-divinylbenzene, p
-Divinylbenzene such as divinylbenzene; one or more kinds of isopropenylstyrene such as o-diisopropenylbenzene, m-diisopropenylbenzene and p-diisopropenylbenzene. Of these, methylstyrene such as styrene, α-methylstyrene, and p-methylstyrene, divinylbenzene, or a mixture of divinylbenzene isomers are preferable because they are inexpensive.

The amount of the aromatic vinyl monomer added is 0.1 to 50 parts by weight, particularly 1 to 30 parts by weight, based on 100 parts by weight of the total amount of the raw material polypropylene resin and polyethylene resin. It is preferable that the modified polypropylene resin composition has a remarkable effect of improving foamability.

When the amount of the aromatic vinyl monomer added is less than the above range, the effect of improving the foamability tends to be small, while when it is more than the above range, a large amount of radical polymerization initiator is added. Since it is necessary, it tends to be disadvantageous in terms of cost.

The aromatic vinyl monomer may be used in combination with the aromatic vinyl monomer and another vinyl monomer copolymerizable with the aromatic vinyl monomer.

Other vinyl monomers copolymerizable with the aromatic vinyl monomer include, for example, vinyl chloride, vinylidene chloride, acrylonitrile, methacrylonitrile,
Acrylamide, methacrylamide, vinyl acetate, acrylic acid, methacrylic acid, maleic acid, maleic anhydride,
Acrylic acid esters such as metal acrylates, metal methacrylates, methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, stearyl acrylate, glycyl acrylate; methyl methacrylate, ethyl methacrylate, Butyl methacrylate,
Examples thereof include methacrylic acid esters such as 2-ethylhexyl methacrylate, stearyl methacrylate, and glycyl methacrylate.

When the aromatic vinyl monomer and another vinyl monomer copolymerizable with the aromatic vinyl monomer are used in combination, the aromatic vinyl monomer is added to 100 parts by weight of the aromatic vinyl monomer. It is preferable that another vinyl monomer copolymerizable with the aromatic vinyl monomer is used in an amount of less than 100 parts by weight.
It is more preferable to use together less than 75 parts by weight. If the amount of the other vinyl monomer copolymerizable with the aromatic vinyl monomer exceeds the above range, it tends to be impossible to obtain a foam having a suitable shape and appearance.

The radical polymerization initiator generally includes a peroxide or an azo compound. In the present invention, a compound such as a radical polymerization initiator having a hydrogen abstraction ability with respect to the polymer molecule of the polypropylene resin. The existence of is necessary.

Examples of the radical polymerization initiator include peroxides and azo compounds. Specific examples thereof include ketone peroxides such as methyl ethyl ketone peroxide and methyl acetoacetate peroxide;
1-bis (t-butylperoxy) -3,3,5-trimethylcyclohexane, 1,1-bis (t-butylperoxy) cyclohexane, n-butyl-4,4-bis (t-butylperoxy) Peroxy ketals such as valerate, 2,2-bis (t-butylperoxy) butane; permethane hydroperoxide, 1,1,
3,3-tetramethylbutyl hydroperoxide,
Hydroperoxides such as diisopropylbenzene hydroperoxide and cumene hydroperoxide; dicumyl peroxide, 2,5-dimethyl-2,
5-di (t-butylperoxy) hexane, α, α′-
Bis (t-butylperoxy-m-isopropyl) benzene, t-butylcumyl peroxide, di-t-butylperoxide, 2,5-dimethyl-2,5-di (t
-Butylperoxy) hexyne-3 and other dialkyl peroxides; benzoyl peroxide and other diacyl peroxides; di (3-methyl-3-methoxybutyl) peroxydicarbonate, di-2-methoxybutylperoxydicarbonate, etc. Peroxydicarbonate; t-butylperoxyoctate, t-butylperoxyisobutyrate, t-butylperoxylaurate, t-butylperoxy-3,5,5-trimethylhexanoate, t- Butyl peroxyisopropyl carbonate, 2,5-dimethyl-2,5-di (benzoylperoxy) hexane, t-butyl peroxyacetate, t-butyl peroxybenzoate, di-t-
Organic peroxides such as peroxyesters such as butyl peroxyisophthalate are exemplified. Of these,
Particularly, those having high hydrogen abstracting ability are preferable. For example, 1,1-bis (t-butylperoxy) -3,3,5-
Such as trimethylcyclohexane, 1,1-bis (t-butylperoxy) cyclohexane, n-butyl-4,4-bis (t-butylperoxy) valerate, and 2,2-bis (t-butylperoxy) butane; Peroxyketal; dicumyl peroxide, 2,5-dimethyl-
2,5-di (t-butylperoxy) hexane, α, α
'-Bis (t-butylperoxy-m-isopropyl)
Benzene, t-butyl cumyl peroxide, di-t-
Dialkyl peroxides such as butyl peroxide and 2,5-dimethyl-2,5-di (t-butylperoxy) hexyne-3; diacyl peroxides such as benzoyl peroxide; t-butylperoxy octate, t- Butyl peroxyisobutyrate, t-butyl peroxylaurate, t-butyl peroxy-3,
5,5-trimethylhexanoate, t-butylperoxyisopropyl carbonate, 2,5-dimethyl-
One or more kinds of peroxyesters such as 2,5-di (benzoylperoxy) hexane, t-butylperoxyacetate, t-butylperoxybenzoate, and di-t-butylperoxyisophthalate. To be

The amount of the radical polymerization initiator added is based on 100 parts by weight of the raw material polypropylene resin because the melt viscosity of the modified polypropylene resin composition does not excessively decrease and it is economical. It is preferably in the range of 0.01 to 5 parts by weight, and more preferably in the range of 0.1 to 1 part by weight.

When the amount of the radical polymerization initiator added is less than the above range, the modifying effect tends not to be sufficiently obtained, while when it is more than the above range, it has a suitable shape and appearance. Foams tend not to be obtained.

If necessary, a resin or rubber other than a polyethylene resin may be added to the raw material polypropylene resin within a range that does not impair the effects of the present invention. Examples of the resin or rubber other than the polyethylene resin include poly-α-olefins such as polybutene-1, polyisobutene, polypentene-1, and polymethylpentene-1; ethylene / propylene copolymer having a propylene content of less than 75% by weight. Or ethylene- [alpha] -olefin / [alpha] such as ethylene, ethylene / butene-1 copolymer and propylene / butene-1 copolymer having a propylene content of less than 75% by weight.
-Olefin copolymer; propylene content of 75% by weight
Less than ethylene / propylene / 5-ethylidene-2-norbornene copolymer or other ethylene or α-olefin / α-olefin / diene monomer copolymer; ethylene / vinyl chloride copolymer, ethylene / vinylidene chloride copolymer Polymer, ethylene / acrylonitrile copolymer, ethylene / methacrylonitrile copolymer, ethylene / vinyl acetate copolymer, ethylene / acrylamide copolymer, ethylene / methacrylamide copolymer, ethylene / acrylic acid copolymer, Ethylene / methacrylic acid copolymer, ethylene / maleic acid copolymer, ethylene / ethyl acrylate copolymer, ethylene / butyl acrylate copolymer, ethylene / methyl methacrylate copolymer, ethylene / maleic anhydride copolymer Coalescence, ethylene / acrylic acid metal salt copolymer, ethylene / meta Ethylene or α-olefin / vinyl monomer copolymers such as acrylic acid metal salt copolymers, ethylene / styrene copolymers, ethylene / methylstyrene copolymers, ethylene / divinylbenzene copolymers; polyisobutene, polybutadiene, Polydiene-based copolymers such as polyisoprene; vinyl monomers such as styrene / butadiene random copolymers / diene-based monomer random copolymers; vinyl monomers such as styrene / butadiene / styrene block copolymers / Diene monomer / vinyl monomer block copolymer; Hydrogenation (styrene / butadiene random copolymer), etc. (Vinyl monomer / diene monomer random copolymer); Hydrogenation ( Hydrogenation of styrene / butadiene / styrene block copolymer (vinyl monomer / diene monomer / vinyl) Polymer block copolymer); vinyl monomer / diene monomer / vinyl monomer graft copolymer such as acrylonitrile / butadiene / styrene copolymer, methyl methacrylate / butadiene / styrene copolymer; poly Vinyl polymers such as vinyl chloride, polyvinylidene chloride, polyacrylonitrile, polyvinyl acetate, polyethyl acrylate, butyl polyacrylate and polymethyl methacrylate; vinyl chloride / acrylonitrile copolymers, vinyl chloride / vinyl acetate copolymers , Vinyl-based copolymers such as acrylonitrile / styrene copolymer, methyl methacrylate / styrene copolymer, and the like.

The addition amount of these other resins or rubbers to the raw material polypropylene resin varies depending on the type of the resin or the type of the rubber and may be within the range not impairing the effects of the present invention as described above, but is usually 25. It is preferably about 10% by weight or less.

Further, if necessary, the raw material polypropylene resin may be an antioxidant, a metal deactivator, a phosphorus processing stabilizer, an ultraviolet absorber, an ultraviolet stabilizer, a fluorescent brightener, a metallic soap, an antacid. Additives such as stabilizers or crosslinking agents such as adsorbents, chain transfer agents, nucleating agents, lubricants, plasticizers, fillers, reinforcing materials, pigments, dyes, flame retardants, antistatic agents, etc. do not impair the effects of the present invention. You may add in the range.

These raw material polypropylene resins (which may contain various additive materials) may be in the form of particles or pellets, and their size and shape are not particularly limited. is not.

When the above-mentioned additive material (other resin, rubber, stabilizer and / or additive) is used, even if this additive material is previously added to the raw material polypropylene resin, this raw material is used. It may be added at the time of melting the polypropylene resin, or may be added by an appropriate method after melt-kneading.

Further, the mixing method and melt-kneading method of the raw material polypropylene resin, polyethylene resin, aromatic vinyl monomer, radical polymerization initiator and other additive materials added as necessary are particularly limited. Alternatively, for example, raw material polypropylene-based resin, polyethylene-based resin, aromatic vinyl monomer, radical polymerization initiator and may be melt-kneaded after mixing with other additives added as necessary, After melt-kneading the raw material polypropylene-based resin and polyethylene-based resin, the aromatic vinyl monomer, radical polymerization initiator and other additional materials added as necessary,
They may be mixed simultaneously or separately, collectively or separately, and then melt-kneaded.

The heating temperature at the time of melt-kneading is 130 to 4
The temperature of 00 ° C. is preferred in that the raw material polypropylene resin is sufficiently melted and hardly thermally decomposed. The time of melt-kneading (the time after mixing the polyethylene resin, the aromatic vinyl monomer and the radical polymerization initiator) is generally 1 to 60 minutes.

The melt kneading apparatus includes a roll,
Kneader, Banbury mixer, Brabender, kneading machine such as single-screw extruder or twin-screw extruder, horizontal agitator such as twin-screw surface renewing machine or twin-screw multi-disc device or vertical agitator such as double-helical ribbon stirrer An example is an apparatus capable of heating a molecular material to an appropriate temperature and kneading while applying an appropriate shear stress. Of these, an extruder is particularly preferable in terms of productivity. The melt-kneading may be repeated a plurality of times in order to mix the respective materials sufficiently uniformly.

The modified polypropylene resin composition of the present invention can be produced as described above.

By foaming such a modified polypropylene resin composition, the foam of the present invention is obtained.

As an example of the method for producing the foam of the present invention, (1)
A method in which a modified polypropylene resin composition and a foaming agent are melt-kneaded in a melt extruder and then extruded by a melt extruder to obtain a foam. (2) A method in which a molten modified polypropylene resin composition is obtained. After adding or press-fitting a foaming agent, a method of extruding with a melt extruder to obtain a foam may be used.

In the case of the above method (1), examples of the foaming agent include thermal decomposition type foaming agents. Among them, preferable thermal decomposition type foaming agents include, for example, N, N'-dinitrosopentamethylenetetramine, N, N'-dimethyl-N, N '
-Nitroso-based foaming agents such as dinitrosoterephthalamide; azo-based foaming agents such as azodicarbonamide and barium azodicarboxylic acid; sulfohydrazide-based foaming agents such as p, p'-oxybisbenzenesulfonyl hydrazide and p-toluenesulfonyl semicarbazide 1 type (s) or 2 or more types, such as trihydrazino triazine.

The addition amount (kneading amount) of the above-mentioned foaming agent may be selected according to the kind of the foaming agent and the target expansion ratio, but with respect to 100 parts by weight of the modified polypropylene resin composition,
It is preferably in the range of 0.5 to 100 parts by weight.

In order to control the bubble diameter of the foamed body to an appropriate size, sodium bicarbonate may be added, if necessary.
A foam nucleating agent such as citric acid or talc may be used in combination. The amount of the foaming nucleating agent used, if necessary, is usually preferably 0.01 to 1 part by weight with respect to 100 parts by weight of the modified polypropylene resin composition.

Further, in order to prevent shrinkage of the foam, a known shrinkage inhibitor may be used in combination, if necessary. Examples of shrinkage inhibitors include partial esters of fatty acids and polyols, fatty acid amides, and the like. The addition amount of the shrinkage-preventing agent, which is used as necessary, is usually the modified polypropylene resin composition 1
It is preferably 0.1 to 5 parts by weight with respect to 00 parts by weight.

In the case of the above method (1), the modified polypropylene resin composition and the pyrolytic foaming agent are both supplied to a melt extruder, and the foaming agent is melted and kneaded at an appropriate temperature. A gas can be generated by thermal decomposition, and the molten modified polypropylene resin composition containing the gas is discharged from a die to form a foam. The melt-kneading temperature and the melt-kneading time in this method may be appropriately selected depending on the foaming agent used and the kneading conditions. The melt-kneading temperature is 130 to 400 ° C. and the melt-kneading time is 1 to 6 although it depends on the type of resin.
It is usually 0 minutes.

Also in this method, in order to prevent the shrinkage of the foam, a known shrinkage inhibitor may be used in combination, if necessary. Examples of shrinkage inhibitors include partial esters of fatty acids and polyols, fatty acid amides, and the like. The addition amount of the shrinkage inhibitor used as necessary is usually 0.1 to 5 parts by weight based on 100 parts by weight of the modified polypropylene resin composition.

In the case of the above method (2), examples of the foaming agent include volatile foaming agents. Among them, preferred volatile foaming agents include propane, butane, pentane, and the like.
Aliphatic hydrocarbons such as hexane and heptane; alicyclic hydrocarbons such as cyclobutane, cyclopentane, and cyclohexane; chlorodifluoromethane, difluoromethane, trifluoromethane, trichlorofluoromethane,
Dichloromethane, dichlorofluoromethane, dichlorodifluoromethane, trichlorofluoromethane, chloromethane, chloroethane, dichlorotrifluoroethane, dichlorofluoroethane, chlorodifluoroethane, dichloropentafluoroethane, tetrafluoroethane, difluoroethane, pentafluoroethane, trifluoroethane, Halogenated hydrocarbons such as dichlorotetrafluoroethane, trichlorotrifluoroethane, tetrachlorodifluoroethane, chloropentafluoroethane, perfluorocyclobutane; inorganic gases such as carbon dioxide, nitrogen, air; one or two such as water The above is mentioned.

The addition amount (kneading amount) of the foaming agent varies depending on the kind of the foaming agent and the target expansion ratio, but is 0.5 to 100 parts by weight of the modified polypropylene resin composition.
It is preferably in the range of 100 parts by weight.

Also in this method, in order to control the bubble diameter of the foam to an appropriate size, if necessary,
A foam nucleating agent such as sodium bicarbonate-citric acid or talc may be used in combination. The amount of the foam nucleating agent used as necessary is usually the modified polypropylene resin composition 10
It is preferably 0.01 to 1 part by weight with respect to 0 part by weight.

Also in this method, in order to prevent shrinkage of the foam, a known shrinkage inhibitor may be used in combination, if necessary. Examples of the anti-shrinkage agent include partial esters of fatty acids and polyols, and fatty acid amides. The addition amount of the shrinkage inhibitor used as necessary is usually 0.1 to 5 parts by weight based on 100 parts by weight of the modified polypropylene resin composition.

Further, in the case of the method (2), the modified polypropylene resin composition is melted in the extruder, and the volatile foaming agent is press-fitted into the extruder and is kept in a molten state while being kept at a high pressure. A kneaded product of the modified polypropylene resin composition and a sufficiently kneaded kneaded product of the modified polypropylene resin composition and the volatile foaming agent can be discharged from a die to form a foam. The melt-kneading temperature and the melt-kneading time in this method may be appropriately selected according to the foaming agent used and the kneading conditions, and the melt-kneading temperature is 130 to 300 ° C. and the melt-kneading time is 1 to 120 minutes, although it depends on the type of resin. It is usually

The foam according to the present invention has a density of 0.01 to 0.5 g / cm 3 from the viewpoint that it is suitable for its lightness, heat insulation, buffering against external stress and compressive strength.
³ is preferable, and 0.015 to 0.3 g / cm ³
Is more preferable.

The foam of the present invention preferably has a closed cell ratio of 50% or more from the viewpoint that it has suitable heat resistance, good cushioning against external force, and suitable compressive strength. It is preferably 70% or more, and more preferably 70% or more.

In addition, in the method for producing a foam according to the present invention, the shape that can be produced is a plate shape such as a sheet shape or a board shape, a hollow shape such as a tube shape or a bag shape, a columnar shape, an elliptic shape or a prismatic shape. Various shapes such as a columnar shape such as a strand shape can be cited, and a plate-like shape has a wide range of uses. As the plate-shaped foam, for example, a sheet-shaped foam capable of secondary molding that can be used for vacuum molding or the like is preferable because of its high closed cell rate or small drawdown during secondary molding. It is used as a relatively thick board-like foam used as a cushioning material or a core material, and is preferably used because of its high closed cell ratio or low density.

Next, the present invention will be described in detail based on examples, but the present invention is not limited to such examples.

Example 1 95 parts by weight of propylene homopolymer (Sumitomo Chemical Co., Ltd., Noblene D501, melt flow index 0.4 g / 10 minutes at 230 ° C.) and polyethylene (Sumitomo Chemical Co., Ltd., Sumikasen F101, 5 parts by weight of melt flow index at 190 ° C. 0.3 g / 10 minutes) and styrene monomer (manufactured by Wako Pure Chemical Industries, Ltd., special grade) 10
Parts by weight and α, α′-bis (t
-Butylperoxy-m-isopropyl) benzene (Nippon Oil & Fats Co., Ltd., Perbutyl P, 1 minute half-life temperature 17
(5 ° C.) 1.0 part by weight is melt-kneaded using a twin-screw extruder (LABOTEX) manufactured by Japan Steel Works, Ltd., and melt-extruded to obtain a rod-shaped modified polypropylene resin having a diameter of 4 mm. A molded product of the composition was obtained. The molded product of the rod-shaped modified polypropylene resin composition was chopped to a thickness of 3 mm to obtain pellets of the modified polypropylene resin composition.

The twin-screw extruder was of the same-direction twin-screw type, and had a cylinder hole diameter of 32 mmφ and a maximum screw effective length (L / D) of 25.5. The twin-screw extruder was heated at a set temperature of the cylinder section of 200 ° C. and at a set temperature of the feed section of 160 ° C., and the rotation speed of the screw was set to 100 rpm for each axis.

The melt shear viscosity of the obtained modified polypropylene resin composition was measured with a Capillograph manufactured by Toyo Seiki Co., Ltd. under the conditions of 180 ° C. and 122 sec ⁻¹ . The melt shear viscosity was 187,000 Pa · s. there were.

Using the pellets of the modified polypropylene resin composition, a round rod-shaped foam was produced by the following method.

100 parts by weight of modified polypropylene resin pellets, blended oil (Koshigaya Chemical Co., Ltd.)
Manufactured by Super Ease Co., Ltd.) 0.05 part by weight, stearic acid monoglyceride 0.5 part by weight as an anti-shrinking agent, and sodium bicarbonate-citric acid (Cerbon SG / IC manufactured by Eiwa Chemical Co., Ltd.) as a foam nucleating agent Parts by weight were mixed for 15 minutes using a ribbon blender. A tandem type extruder (the first stage extruder has a cylinder diameter of 40 mm
φ, second stage extruder cylinder diameter is 50 mmφ, melted at 230 ° C. in the first stage extruder, and then as a foaming agent, butane gas (isorich butane gas; normal butane / isobutane mixing ratio is weight ratio). 15/8
8) by weight with respect to 100 parts by weight of the modified polypropylene resin composition was kneaded and kneaded, and this was cooled in the second stage extruder so that the temperature of the resin composition was 150 ° C. It was extruded from a 6 mmφ × 25 mm circular die to form a round rod-shaped foam.

The density, the expansion ratio and the closed cell ratio of the obtained rod-shaped foam were measured by the following methods, and the appearance was visually evaluated by the following evaluation criteria.

Density of foam: Calculated from the weight and the volume obtained by the submersion method.

Closed cell ratio: Using a multi-pycnometer (product name, Yuasa Ionics Co., Ltd.), ASTM D
-Measurement according to 856.

Evaluation Criteria for Appearance: Good: No unfoamed part, fluff, or wrinkle is observed. X: An unfoamed part, fluff, and wrinkles are seen.

As a result, the density was 29 kg / m ³ ,
The closed cell rate was 81%, and the external appearance was evaluated as good.

Examples 2 to 4 The types and amounts of polypropylene resin, polyethylene resin, aromatic vinyl monomer, and radical polymerization initiator supplied to the twin-screw extruder were changed as shown in Table 1. In the same manner as in Example 1, pellets of the modified polypropylene resin composition were obtained.

The melt shear viscosity of the obtained modified polypropylene resin composition was measured by the same method as in Example 1. The results are shown in Table 2.

Using the pellets of the modified polypropylene resin composition, a round rod-shaped foam was obtained in the same manner as in Example 1.

The density, closed cell rate and appearance of this round rod-shaped foam were evaluated in the same manner as in Example 1. Table 3 shows the results.

Comparative Example 1 Propylene homopolymer (Sumitomo Chemical Co., Ltd., Nobrene D501) was not modified, but instead of using pellets of the modified polypropylene resin composition, the propylene homopolymer (this propylene Using the melt shear viscosity of the homopolymer shown in Table 2, a round rod-shaped foam was produced according to the method for producing a round rod-shaped foam of Example 1.

The density, closed cell rate and appearance of this round rod-shaped foam were evaluated in the same manner as in Example 1. Table 3 shows the results.

Comparative Example 2 Pellets of the modified polypropylene resin composition were obtained in the same manner as in Example 1 except that the polyethylene resin was not added. The melt shear viscosity of this modified polypropylene resin composition was measured by the same method as in Example 1. The results are shown in Table 2.

A round rod-shaped foam was produced in the same manner as in Example 1, using this modified polypropylene resin composition. The density, closed cell ratio and appearance of this round rod-shaped foam were evaluated in the same manner as in Example 1. Table 3 shows the results.
Shown in

Comparative Example 3 A modified polypropylene resin was prepared in the same manner as in Example 1 except that the radical polymerization initiator α, α'-bis (di-t-butylperoxy-m-isopropyl) benzene was not added. A pellet of the composition was obtained. The melt shear viscosity of this modified polypropylene resin composition was measured by the same method as in Example 1. The results are shown in Table 2.

A round rod-shaped foam was produced in the same manner as in Example 1, using this modified polypropylene resin composition. The density, closed cell ratio and appearance of this round rod-shaped foam were evaluated in the same manner as in Example 1. Table 3 shows the results.
Shown in

Comparative Example 4 Melt kneading was carried out in the same manner as in Example 1 except that the styrene monomer which was an aromatic vinyl monomer was not added.
The resin composition had a low viscosity and could not be formed into a strand.

[0083]

[Table 1]

[0084]

[Table 2]

[0085]

[Table 3]

[0086]

[Table 4]

The modified polypropylene resin compositions of the examples have high melt viscosities, and the foams produced from the resin compositions have low density, high closed cell ratio, and excellent appearance, while comparisons are made. It can be seen that the foam in the example has a high density and a low closed cell rate. Further, a resin composition obtained by melt-kneading a raw material polypropylene resin with a polyethylene resin and an aromatic vinyl monomer, and a resin composition obtained by melt-kneading a raw polypropylene resin with a polyethylene resin and a radical polymerization initiator. It can be seen that the product has a low viscosity and cannot be pelletized. In addition, a foam produced by using a resin composition obtained by adding only an aromatic vinyl monomer and a radical polymerization initiator to a raw polypropylene resin without adding a polyethylene resin and melt-kneading the foamed resin ( It is understood that although the resin composition having a low density, a high closed cell ratio and a good appearance, which can be molded into a resin composition having a good foamability, is improved, its effect is low.

[0088]

EFFECTS OF THE INVENTION A polypropylene resin, a polyethylene resin, an aromatic vinyl monomer, and a radical polymerization initiator, which are raw materials, are melt-kneaded to obtain a modified polypropylene resin composition, which has a low density by foaming. A foam with a high closed cell ratio, a beautiful appearance and excellent heat resistance can be obtained.

Claims (4)

[Claims] 1. A foam comprising a modified polypropylene resin composition obtained by melt-kneading a polypropylene resin, a polyethylene resin, an aromatic vinyl monomer and a radical polymerization initiator. 2. The foam according to claim 1, wherein the aromatic vinyl monomer is one or more selected from the group consisting of styrene, methylstyrene and divinylbenzene. 3. The foam according to claim 1, wherein the radical polymerization initiator is one or more selected from the group consisting of peroxyketal, dialkyl peroxide, diacyl peroxide and peroxy ester. . 4. The method for producing a foam according to claim 1, wherein the modified polypropylene resin composition and the foaming agent are melt-kneaded and then extruded to foam.