JPH09302127A - Production of foam comprising modified polypropylene-based resin - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the subject foam low in apparent density, high in closed cell ratio, beautiful in appearance, useful as a heat insulating material, etc., by expanding a specific modified polypropylene-based resin composition. SOLUTION: (A) A modified polypropylene-based resin composition obtained by melting and blending (i) a polypropylene-based resin with (ii) an aromatic vinyl monomer and (iii) a radical polymerization initiator at a temperature to melt the component (i) is melted and blended blended with (B) a blowing agent consisting essentially of isobutane, extruded and expanded. Preferably the monomer of the component (ii) is any of styrene, methylstyrene and divinylbenzene and the component (iii) is any of a peroxy ketal, a dialkyl peroxide and a peroxy ester.

Description

Detailed Description of the Invention

[0001]

The present invention relates to a method for producing a foam comprising a modified polypropylene resin composition. More specifically, the present invention relates to a method for producing a foamed product made of a modified polypropylene resin composition having a high closed cell ratio, a low apparent density and a beautiful appearance.

[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 in a molten state are low, and when the resin is foamed, the strength of the cell wall is not sufficiently maintained during 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, it has been difficult to obtain a foam having excellent appearance, a high closed cell ratio and a low density by foaming the polypropylene resin.

As a method for improving the foamability of a polypropylene resin, for example, a method of crosslinking a polymer molecule by adding a crosslinking aid to the polypropylene resin (see, for example, Japanese Patent Publication No. 45-40420), or a polypropylene resin made of polyethylene. And the method of foaming the same (see, for example, Japanese Patent Publication No. 44-2574), the method of blending polystyrene with polypropylene resin and foaming the same (see, for example, Japanese Patent Publication No. 43-13375). . However, even by these methods, it is difficult to obtain a foam having a high closed cell rate and a low density.

Further, Japanese Patent Publication No. 48-4859 discloses that
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.

Chlorofluorohydrocarbons (CFC 114, CFC 12, CFC 142b) have been used as a foaming agent for foaming polypropylene or polyethylene into a foam. However, chlorofluorohydrocarbons in general, and saturated chlorofluorohydrocarbons in particular, are stable compounds, and when released into the air, they reach the stratosphere without being decomposed in the troposphere surrounding the earth's surface, and destroy the ozone layer. It is said that its use should be avoided.

Japanese Patent Publication No. 7-119314 discloses a method of foaming a thermoplastic resin with a foaming agent containing Freon 134a, but this method has a drawback that the foaming agent is expensive.

In Japanese Patent Publication No. 6-49793,
A method for producing a foamed body in which a mixture of polyethylene and a fatty acid amide is foamed using a blowing agent mainly containing isobutane is disclosed, but a polypropylene resin is not disclosed at all.

As described above, there has been found a method of improving the foamability of a polypropylene resin and using the resin and an inexpensive and environment-friendly foaming agent to produce a foam having a high closed cell rate and a low apparent density. It was the current situation that it was not issued.

[0010]

The object of the present invention is to provide a modified polypropylene resin composition having an improved foaming property and an inexpensive and environmentally friendly foaming agent, which has a high closed cell ratio and an apparent density. It is to provide a foam having a low appearance and a beautiful appearance.

[0011]

Means for Solving the Problems As a result of intensive studies to solve the above problems, the present inventors have found that a modified polypropylene resin composition obtained by a specific method and a specific foaming agent are used in an extruder. The inventors have found that a foam having a high closed cell ratio, a low apparent density, and a beautiful appearance can be obtained at low cost by melt-kneading and then extruding, and thus the present invention has been completed.

That is, according to the present invention, a polypropylene resin (hereinafter, the polypropylene resin before melt-kneading is referred to as "raw material polypropylene resin"), an aromatic vinyl monomer and a radical polymerization initiator are used as raw materials. A modified polypropylene resin composition is obtained by melt-kneading at a temperature at which the polypropylene resin can be melted, and the modified polypropylene resin composition and a foaming agent containing isobutane as a main component are melt-kneaded in an extruder. Then, the present invention relates to a method for producing a foam made of a modified polypropylene resin composition which is extruded and foamed.

The present invention also relates to the above process, wherein the aromatic vinyl monomer is at least one monomer selected from the group consisting of styrene, methylstyrene and divinylbenzene.

The present invention also relates to the above process, wherein the radical polymerization initiator is at least one selected from the group consisting of peroxyketals, dialkyl peroxides, diacyl peroxides and peroxyesters.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION The features of the method for producing a foam of the present invention are:
By obtaining a specific modified polypropylene resin composition having improved foamability and foaming the specific modified polypropylene resin composition with a foaming agent containing isobutane as a main component, a desired closed cell ratio is obtained. And has an apparent density,
This is to obtain a foam with a beautiful appearance.

The modified polypropylene resin composition comprises
It can be obtained by melt-kneading a raw material polypropylene resin, an aromatic vinyl monomer, and a radical polymerization initiator.

Although the reason why the modified polypropylene resin composition has improved foamability is not clear,
If any one of the raw material polypropylene resin, the aromatic vinyl monomer and the radical polymerization initiator is lacking, a modified polypropylene resin composition having desired properties cannot 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.

If necessary, other resin or rubber may be added to the raw material polypropylene resin within a range that does not impair the effects of the present invention.

Further, if necessary, the above-mentioned raw material polypropylene resin may be an antioxidant, a metal deactivator, a phosphorus processing stabilizer, an ultraviolet absorber, an ultraviolet stabilizer, an optical brightener,
Stabilizers or crosslinkers such as metal soaps, antacid adsorbents, chain transfer agents, nucleating agents, lubricants, plasticizers, fillers, reinforcing materials, pigments,
Additives such as dyes, flame retardants, and antistatic agents may be added as long as the effects of the present invention are not impaired.

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

The kneading material (other resin, rubber,
When a stabilizer and / or an additive) is used, even if this kneading material is added to the raw material polypropylene resin in advance, it is added when the raw material polypropylene resin is melted. May be. Further, the modified polypropylene resin composition may be added to the modified polypropylene resin composition by an appropriate method after producing the modified polypropylene resin composition.

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, styrene, methylstyrene or divinylbenzene are preferable because they are inexpensive.

The amount of the aromatic vinyl monomer used is 100 parts by weight of the raw polypropylene resin.
0.1 to 50 parts by weight, particularly 0.1 to 30 parts by weight, sufficiently improves the foamability of the raw material polypropylene-based resin, and has suitable heat resistance and chemical resistance of the raw material polypropylene-based resin. It is preferable in that characteristics such as mechanical characteristics are not impaired.

The above radical polymerization initiator generally includes a peroxide or an azo compound. In the present invention, a radical polymerization initiator or the like having a hydrogen abstraction ability with respect to the polymer molecules of the raw material polypropylene resin is used. The presence of compound is required.

Examples of the radical polymerization initiator include peroxides and azo compounds, and specifically, 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-
One or more organic peroxides such as peroxyesters such as butylperoxyisophthalate may be used. Among these, those having a particularly high hydrogen abstraction ability are preferable, and as such a radical polymerization initiator,
For example, 1,1-bis (t-butylperoxy) -3,
3,5-trimethylcyclohexane, 1,1-bis (t
-Butylperoxy) cyclohexane, n-butyl-
4,4-bis (t-butylperoxy) valerate,
Peroxyketals such as 2,2-bis (t-butylperoxy) butane; 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, Dialkyl peroxides such as 2,5-dimethyl-2,5-di (t-butylperoxy) hexyne-3; diacyl peroxides such as benzoyl peroxide; t-butylperoxyoctate, t-butylperoxyiso Butyrate, t-butylperoxylaurate, t-butylperoxy-3,5,5-trimethylhexanoate, t-
Butyl peroxyisopropyl carbonate, 2,5-
One or two of peroxyesters such as dimethyl-2,5-di (benzoylperoxy) hexane, t-butylperoxyacetate, t-butylperoxybenzoate, and di-t-butylperoxyisophthalate, or 2
There are more than one seed.

The radical polymerization initiator is used in an amount of 100 parts by weight 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 1.5 parts by weight.

When the amount of the radical polymerization initiator used 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.

The modified polypropylene resin composition of the present invention comprises a raw material polypropylene resin, an aromatic vinyl monomer, a radical polymerization initiator and, if necessary, other copolymerizable copolymers with the aromatic vinyl monomer. It may be produced by melt-kneading with a vinyl monomer.

The mixing method and melt-kneading method of such raw material polypropylene resin, aromatic vinyl monomer, radical polymerization initiator, and other kneading materials added as necessary are not particularly limited. For example,
Raw material polypropylene-based resin, aromatic vinyl monomer, radical polymerization initiator and may be melt-kneaded after mixing other kneading materials added as necessary, or after melt-kneading the raw material polypropylene-based resin, An aromatic vinyl monomer, a radical polymerization initiator, and other kneading materials added as necessary may be mixed together, melted and kneaded, either simultaneously or separately.

In the present invention, the temperature at which the raw material polypropylene resin can be melted means the temperature range in which the crystalline part of the resin melts and exhibits fluidity. Specifically, it is measured by DSC of this resin. The temperature range above the melting point.
Further, in the present invention, the temperature at which the raw material polypropylene resin, the aromatic vinyl monomer and the radical polymerization initiator are melt-kneaded is the temperature at which the radical polymerization initiator can decompose,
That is, the temperature range in which substantially most of the radical polymerization initiator decomposes within the reaction time described below is preferable. Usually, when the one-minute half-life temperature of the radical polymerization initiator is T,
In the temperature range of T-20 ° C to T + 50 ° C, the radical polymerization initiator can be decomposed well. In the present invention, the temperature at which the raw material polypropylene resin can be dissolved and the radical polymerization initiator can be decomposed is usually 13
It is in the range of 0 to 400 ° C. Therefore, the melt-kneading temperature for obtaining the modified polypropylene resin composition is preferably in the range of 130 to 400 ° C.
Under such conditions, the raw material polypropylene resin can be sufficiently melted and is not easily decomposed by heat. Further, the time for the reaction is preferably 1 to 60 minutes.

The melt kneading device is a roll,
Kneader, Banbury mixer, Brabender, Single-screw extruder, Twin-screw extruder, etc.
Examples of such devices include a horizontal stirrer such as a multi-shaft disk device or a vertical stirrer such as a double helical ribbon stirrer, which can heat a polymer material to an appropriate temperature and knead it while applying an appropriate shear stress. Of these, especially uniaxial or 2
The axial extruder is preferable from the viewpoint of productivity. Further, the melt kneading may be repeated a plurality of times for uniform mixing.

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

By foaming the modified polypropylene resin composition thus obtained with a foaming agent containing isobutane as a main component, a desired foamed product can be obtained. As a specific method of foaming, for example, first, a modified polypropylene resin composition is melted in an extruder, and then the foaming agent is pressed into the molten modified polypropylene resin composition, Is kneaded while being kept at a high pressure, and then discharged from a die for extrusion foaming.

Examples of the foaming agent containing isobutane as a main component include isobutane alone or a mixed gas containing 80% by weight or more of isobutane. Among the commercially available products, for example, isobutane / normabutane weight ratio is used. Examples include isorich butane gas having a ratio of 85/15. However, normal butane alone or an isobutane / normal butane weight ratio of 25
When industrial butane, normal pentane, or isopentane having a ratio of / 75 is used as a foaming agent, the expansion of the foam increases during extrusion foaming, and a foam having a low apparent density cannot be obtained.

In addition to the foaming agent containing isobutane as a main component, a small amount of other volatile type foaming agent or decomposing type foaming agent can be mixed with the foaming agent.

Examples of the volatile blowing agent include aliphatic hydrocarbons such as propane, normal butane, pentane, hexane and heptane; alicyclic hydrocarbons such as cyclobutane, cyclopentane and cyclohexane; chlorodifluoromethane and difluoro. Methane, trifluoromethane, trichlorofluoromethane, dichloromethane, dichlorofluoromethane, dichlorodifluoromethane, trichlorofluoromethane, chloromethane, chloroethane,
Dichlorotrifluoroethane, dichlorofluoroethane, chlorodifluoroethane, dichloropentafluoroethane, tetrafluoroethane, difluoroethane, pentafluoroethane, trifluoroethane, dichlorotetrafluoroethane, trichlorotrifluoroethane,
Halogenated hydrocarbons such as tetrachlorodifluoroethane, chloropentafluoroethane and perfluorocyclobutane; inorganic gases such as carbon dioxide, nitrogen and air;
One or more of water and the like can be used.

As a preferable pyrolyzable foaming agent which can be mixed, for example, a nitroso-based foaming agent such as N, N'-dinitrosopentamethylenetetramine and N, N'-dimethyl-N, N'-dinitrosoterephthalamide; One or more azo type foaming agents such as azodicarbonamide and barium azodicarboxylate; and sulfohydrazide type foaming agents such as p, p′-oxybisbenzenesulfonyl hydrazide and p-toluenesulfonyl semicarbazide.

The amount of the above-mentioned foaming agent used (kneading amount) varies depending on the type of the foaming agent and the target expansion ratio, but is usually 100 parts by weight of the modified polypropylene resin composition.
It is preferably in the range of 0.5 to 40 parts by weight.

If necessary, a foam nucleating agent such as sodium bicarbonate-citric acid or talc may be used in combination to control the cell diameter of the foam. The amount of the foam nucleating agent used as necessary is usually 0.1 to 1.0 part by weight based on 100 parts by weight of the modified polypropylene resin composition.

Further, in order to prevent the 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 amount of the shrinkage inhibitor used as necessary is 0.1 to 100 parts by weight of the resin.
It is preferably 5 parts by weight.

The melt-kneading temperature and the melt-kneading time in the melt-kneading of the modified polypropylene resin composition and the foaming agent may be appropriately selected depending on the foaming agent used and the kneading conditions, and may vary depending on the kind of the resin. , Melt-kneading temperature is 130 to 400 ° C., melt-kneading time is 1 to 1
It is usually 20 minutes.

The apparent density of the foam according to the present invention is 10 to 500 kg / m from the viewpoint that it has suitable characteristics such as light weight, heat insulation, buffering against external stress, and compressive strength.
It is preferably in the range of ³ to 15 to 300 kg /
More preferably, it is in the range of m ³ . In addition, from the viewpoint that properties such as heat insulating property, cushioning property, and compressive strength are suitable, the closed cell ratio thereof is preferably 50% or more, and more preferably 70% or more.

Further, 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 cylindrical shape, an elliptic cylinder shape or a prismatic shape. There are various shapes such as columnar shape such as strand shape.

[0049]

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

Example 1 100 parts by weight of propylene homopolymer (Sumitomo Chemical Co., Ltd., Nobrene D501, melt flow index 0.4 g / 10 minutes at 230 ° C.) and styrene monomer 1
0 part by weight and 1 part by weight of α, α′-bis (t-butylperoxy-m-isopropyl) benzene (Nippon Yushi Co., Ltd., Perbutyl P, 1-minute half-life temperature 175 ° C.) as a radical polymerization initiator Was melt-kneaded using a twin-screw extruder (LABOTEX) manufactured by Japan Steel Works, Ltd., and melt-extruded to obtain a molded product of a rod-shaped modified polypropylene resin composition having a diameter of 4 mm. 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. Set the temperature of the cylinder of this twin-screw extruder to 200 ° C,
The feed temperature was set to 160 ° C. and heated, and the rotation speed of the screw was set to 100 rpm for each shaft.

100 parts by weight of the pellets of the modified polypropylene resin composition, 0.05 part by weight of blended oil (Koshigaya Chemical Co., Ltd., Super Ease), and baking soda-citric acid (Eiwa Chemical Co., Ltd., Cerbon SC / K) 0.1 part by weight was mixed for 15 minutes using a ribbon blender. This mixture was supplied to a tandem extruder (first-stage extruder cylinder diameter 40 mmφ, second-stage extruder cylinder diameter 50 mmφ), melted at 230 ° C. in the first-stage extruder, and then used as a foaming agent. 9 parts by weight of isobutane gas (isobutane 100%) was pressed into 100 parts by weight of the modified polypropylene resin composition and kneaded, and the temperature of the resin composition was adjusted to 15 in the second stage extruder.
It was cooled to 0 ° C. and extruded from a die having an orifice of 6 mmφ × 25 mm to obtain a round rod-shaped foam.

The apparent density 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. Table 1 shows the results.

Apparent density: Calculated from the weight and the volume obtained by the submersion method.

Closed cell ratio: Using a multi-pycnometer (product name, manufactured by Yuasa Ionics Co., Ltd.), ASTM D
Measure according to -2856.

Evaluation Criteria for Appearance: ◯: No unfoamed part, fluff, or wrinkle is observed. B: No unfoamed part is seen, but fluff and wrinkles are seen. X: Unfoamed parts, fluff, and wrinkles are seen.

Example 2 Isobutane gas (isobutane 100%) was used as a foaming agent.
In the same manner as in Example 1 except that an isorich butane gas having a mixing ratio of isobutane / normal butane of 85/15 by weight was used (the amount of foaming agent injected was also the same as in Example 1). A rod-shaped foam was produced.

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

Example 3 Isobutane gas (isobutane 100%) was used as a foaming agent.
In the same manner as in Example 1 except that a mixed gas having an isobutane / isopentane mixing ratio of 85/15 by weight was used (the amount of the foaming agent to be injected was also the same as in Example 1). Was produced.

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

Comparative Example 1 A propylene homopolymer (Noblen D501, manufactured by Sumitomo Chemical Co., Ltd.) was used without modification, instead of using pellets of the modified polypropylene resin composition. A round rod-shaped foam was produced according to the method for manufacturing the round rod-shaped foam of Example 1.

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

Comparative Example 2 A round rod-shaped foam was prepared in the same manner as in Comparative Example 1 (the same amount as that of Comparative Example 1 was used except that the blowing agent was changed as shown in Table 1).

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

Comparative Examples 3 to 4 Round rod-shaped foams were produced in the same manner as in Example 1 except that the blowing agent was changed as shown in Table 1 (the amount of foaming agent pressed in was also the same as in Example 1).

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

[0067]

[Table 1]

From the above results, it is understood that the foams of Examples 1, 2 and 3 have a low apparent density, a high closed cell ratio and an excellent appearance. However, as in Comparative Examples 1 and 2, when the propylene homopolymer is used instead of the modified polypropylene resin composition of the present invention and this is foamed, the apparent density, the closed cell ratio and the appearance are all suitable. It turns out that only non-foam can be obtained.
Further, when a foaming agent not containing isobutane as a main component is used as in Comparative Examples 2, 3 and 4, the obtained foam has an apparent density and a closed cell ratio which are more preferable than those in Examples 1, 2 and 3. It turns out that it doesn't become.

[0069]

The modified polypropylene resin composition obtained by melt-kneading the raw material polypropylene resin, the aromatic vinyl monomer and the radical polymerization initiator based on the production method of the present invention contains isobutane as a main component. By foaming using a foaming agent, a foam having a low apparent density, a high closed cell ratio and a beautiful appearance can be obtained.

Claims (3)

[Claims] 1. A modified polypropylene resin composition is obtained by melt-kneading a polypropylene resin, an aromatic vinyl monomer and a radical polymerization initiator at a temperature at which the polypropylene resin can be melted. A method for producing a foam comprising a modified polypropylene resin composition, which comprises melt-kneading the modified polypropylene resin composition and a foaming agent containing isobutane as a main component in an extruder, and then extruding and foaming. 2. The method according to claim 1, wherein the aromatic vinyl monomer is at least one monomer selected from the group consisting of styrene, methylstyrene and divinylbenzene. 3. The method according to claim 1, wherein the radical polymerization initiator is at least one selected from the group consisting of peroxyketal, dialkyl peroxide, diacyl peroxide and peroxy ester.