JPH1087868A - Production of modified polypropylene resin foam - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a production process whereby a PP resin foam having a low density, a high closed cell content, and a beautiful appearance is produced without adversely affecting the environment by using a PP resin modified by a specific method and a specific blowing agent. SOLUTION: A mixture comprising a PP resin, an isoprene monomer. and a free-radical initator is melt mixed, kneaded, and reacted to give a modified PP resin, which is mixed with a blowing agent mainly comprising isobutane in an extruder and then extruded into the outside of the extruder. The blowing agent may be isobutane alone or a mixture contg. at least 80wt.% isobutane. Pref. 0.1-50 pts.wt. isoprene monomer is added to 100 pts.wt. PP resin.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a foam made of a modified polypropylene resin using a foaming agent which has less adverse effect on the environment and having good physical properties and appearance, and a method for producing the foam.

[0002]

2. Description of the Related Art A foam made of a thermoplastic resin is widely used for a heat insulating material, a cushioning material, a core material, a food container and the like because of its light weight and good heat insulating property and cushioning property. Among them, a foam of a polypropylene resin has high chemical resistance, impact resistance, and heat resistance, and is particularly useful as a cushioning material.

[0003] There are various methods for producing a foam made of a polypropylene-based resin. Among them, a resin is melted by an extruder, and then a low-boiling liquid or a gas as a foaming agent is pressed into the foam to be suitable for foaming. The so-called extrusion foaming method in which the resin is cooled to a temperature and then extruded into a low-pressure region to foam is an economically advantageous method.

[0004] However, since the polypropylene resin has a low melt viscosity unlike the polyethylene resin, the production method used for foaming the polyethylene resin (for example, JP-B-48-4859, JP-B-6-49793, etc.) It is generally difficult to produce a good foam even if is applied as it is.

Further, a polypropylene resin is cross-linked (Japanese Patent Publication No. 45-40420) or a polypropylene resin is blended with polyethylene or polystyrene (Japanese Patent Publication No. 44-2574 or Japanese Patent Publication No. 43-13375). However, even with these methods, a foam having a high closed cell ratio and a low density is inferior.

The low-boiling liquid or gas used as a foaming agent may be chlorine atom-containing fluorinated carbon (CFC) or chlorine atom-containing fluorinated fluorinated compound partially containing a hydrogen atom because of its relatively good foamability. Attempts have been made to use chlorofluorocarbon-based gases such as carbon (HCFC). However, use of CFC is prohibited because it has a high ozone depletion potential and adversely affects the environment. HCFC is also not preferred because its ozone depletion potential is not zero. Although the use of hydrogenated fluorocarbon (HFC) having an ozone depletion potential of zero is also being studied, HFCs have a problem of high global warming potential and are not always preferable.

Therefore, at present, no method has been found for producing a foam comprising a polypropylene resin having good foam properties without adversely affecting the environment.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for producing a foam made of a modified polypropylene resin with less environmental problems and at a low cost.

The inventors of the present invention have conducted intensive studies to solve the above-mentioned problems, and as a result, surprisingly, a polypropylene resin modified by a specific method is used, and isobutane as a main component is used as a foaming agent. By using a foaming agent,
The present inventors have found that the above problems can be solved, that is, a foam made of a polypropylene-based resin having a low density and a high closed cell ratio and having a beautiful appearance can be produced at low cost without adversely affecting the environment, and completed the present invention. did.

[0010]

That is, the present invention relates to a modified polypropylene resin obtained by melting and kneading a mixture of a polypropylene resin, an isoprene monomer and a radical polymerization initiator, and reacting the mixture with isobutane. The present invention relates to a method for producing a modified polypropylene resin foam, in which a foaming agent as a component is added, kneaded in an extruder, and then discharged outside the extruder.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, first, a mixture of a polypropylene resin, an isoprene monomer and a radical polymerization initiator is melt-kneaded to cause a reaction to obtain a modified polypropylene resin.

The heating temperature of the mixture is a temperature at which the raw material polypropylene resin melts and does not thermally decompose, and is higher than the decomposition temperature of the radical polymerization initiator. Usually 130-40
The temperature is appropriately set within a range of 0 ° C, preferably 150 to 250 ° C.

Examples of the starting polypropylene resin usable in the present invention include crystalline polymers such as a homopolymer of propylene, a random copolymer of propylene and another monomer or a block copolymer. When the polypropylene resin is a random copolymer or a block copolymer of propylene and other monomers, it retains the high crystallinity, high rigidity and good chemical resistance characteristic of the polypropylene resin. From the viewpoint, the content of the propylene monomer component is preferably 75% by weight or more of the whole, and more preferably 90% by weight or more of the whole.

In the raw material polypropylene resin,
Other monomers copolymerizable with propylene include one or more monomers selected from the group consisting of ethylene, α-olefin, cyclic olefin, diene monomer and vinyl monomer. I can raise my body.

Examples of the above-mentioned α-olefin copolymerizable with propylene include butene-1, isobutene, pentene-1, 3-methylbutene-1, hexene-1, 3-methylpentene-1, and 4-methylpentene. -1, 3, 4-
Α-olefins having 4 to 12 carbon atoms, such as dimethylbutene-1, octene-1, and decene-1. Examples of the cyclic olefin copolymerizable with propylene include cyclopentene and norbornene. Examples of the diene monomer copolymerizable with the 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. Examples of the vinyl monomer copolymerizable with the propylene include vinyl chloride, vinylidene chloride, acrylonitrile,
Vinyl acetate, acrylic acid, methacrylic acid, maleic acid,
Examples include ethyl acrylate, butyl acrylate, methyl methacrylate, and maleic anhydride.

Of these monomers, ethylene, α-olefin or diene monomers are preferred from the viewpoint of inexpensiveness, and ethylene or butene-1 is more preferred.

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 from 100,000 to 1,000,000 from the viewpoint of low cost. More preferably, it is within the range.

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

The amount of the other resin or rubber to be added to the starting polypropylene resin depends on the type of the resin or rubber and may be within a range not to impair the effects of the present invention. It is preferably about 25 parts by weight or less based on 100 parts (parts by weight, hereinafter the same) of the base resin.

Further, an antioxidant, a metal deactivator, a phosphorus-based processing stabilizer, an ultraviolet absorber, an ultraviolet stabilizer, a fluorescent whitening agent,
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 additive materials) may be in the form of particles or pellets, and their size and shape are not particularly limited. Absent.

Further, the above-mentioned additive materials (other resins, rubbers,
In the case where a stabilizer and / or an additive is used, this additive material may be added when the raw polypropylene resin is melted, even if it is previously added to the raw polypropylene resin. It may be added to the modified polypropylene resin composition by an appropriate method after the modified polypropylene resin composition is produced.

In the present invention, a modified polypropylene resin obtained by blending an isoprene monomer and a radical polymerization initiator with the polypropylene resin and melt-kneading the mixture is used.

The amount of the isoprene monomer is 0.1 to 50 parts per 100 parts of the starting polypropylene resin.
Parts, especially 0.1 to 30 parts, is preferred in that the effect of improving the foaming property becomes remarkable in the modified polypropylene resin composition.

The radical polymerization initiator generally includes a peroxide or an azo compound. In the present invention, the presence of the radical polymerization initiator having a hydrogen abstracting ability with respect to the polymer molecule of the polypropylene resin is considered. 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-butyl peroxide, 2,5-dimethyl-2,5-di (t
Dialkyl peroxides such as -butylperoxy) hexine-3; diacyl peroxides such as benzoyl peroxide; di (3-methyl-3-methoxybutyl) peroxydicarbonate and di (2-methoxybutyl) peroxydicarbonate Peroxy dicarbonate such as t-butyl peroxy octate, t-butyl peroxy isobutyrate, t-butyl peroxy laurate, t-butyl peroxy-3,5,5-trimethylhexanoate, t -Butylperoxyisopropyl carbonate, 2,5-dimethyl-2,5-di (benzoylperoxy) hexane, t-butylperoxyacetate, t-butylperoxybenzoate, di-t
Organic peroxides such as peroxyesters such as -butylperoxyisophthalate. Among these, those having a particularly high hydrogen abstracting ability are preferable. For example, 1,1-bis (t-butylperoxy) -3,3,3
5-trimethylcyclohexane, 1,1-bis (t-butylperoxy) cyclohexane, n-butyl-4,4
-Bis (t-butylperoxy) valerate, 2,2-
Peroxy ketals such as 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-butyl peroxide, 2,5-dimethyl-2,5
Dialkyl peroxides such as di- (t-butylperoxy) hexine-3; diacyl peroxides such as benzoyl peroxide; t-butylperoxyoctate, t-butylperoxyisobutyrate, and t-butylperoxylau. Rate, t-butylperoxy-
3,5,5-trimethylhexanoate, t-butylperoxyisopropyl carbonate, 2,5-dimethyl-2,5-di (benzoylperoxy) hexane, t-
One or more of peroxyesters such as butylperoxyacetate, t-butylperoxybenzoate, and di-t-butylperoxyisophthalate are exemplified.

The amount of the radical polymerization initiator to be added is 100 parts by weight of the starting polypropylene resin (A) from the viewpoint that the melt viscosity of the modified polypropylene resin composition does not excessively decrease and is economical. Preferably in the range of 0.01 to 5 parts, more preferably in the range of 0.1 to 1.5 parts. When the addition amount of the radical polymerization initiator is less than the above range, there is a tendency that the modifying effect cannot be sufficiently obtained.On the other hand, when it is more than the above range, a foam having a suitable shape and appearance is obtained. There is a tendency not to be obtained.

The method of mixing and melt-kneading the raw material polypropylene resin, isoprene monomer, radical polymerization initiator and other optional materials added as required are not particularly limited.
After mixing the raw material polypropylene resin, isoprene monomer, radical polymerization initiator and other optional materials added if necessary, the mixture may be melt-kneaded, or the raw material polypropylene resin may be melt-kneaded, and then mixed. The isoprene monomer, the radical polymerization initiator, and other additives added as necessary may be mixed simultaneously or separately, collectively or separately, and then melt-kneaded.

The heating temperature during the melt-kneading is from 130 to 4
It is preferable that the temperature is 00 ° C. in that the raw material polypropylene-based resin is sufficiently melted and hardly thermally decomposed, and particularly preferably 150 to 250 ° C. The time for melt-kneading is generally 1 to 60 minutes.

As the melt kneading apparatus, rolls,
Kneaders such as co-kneaders, Banbury mixers, Brabenders, kneading extruders such as single-screw extruders or twin-screw extruders, horizontal stirrers such as twin-screw surface renewers or twin-screw multi-disc units, or double helical ribbon stirrers For example, there is a device such as a vertical stirrer capable of heating a polymer material to an appropriate temperature and kneading while applying an appropriate shear stress. Of these, extruders are particularly preferred from the viewpoint of productivity. Further, the melt-kneading may be repeated a plurality of times in order to sufficiently uniformly mix the respective materials.

A foaming agent containing isobutane as a main component is dissolved or dispersed in the modified polypropylene-based resin thus obtained and foamed, whereby a desired foam is obtained. As a specific method of foaming, for example, first, a modified polypropylene-based resin is usually placed in an extruder such as a single-screw extruder, a twin-screw extruder, or a tandem-type extruder, usually in an extruder for 13 minutes.
The foaming agent is melted at 0 to 400 ° C., preferably 150 to 250 ° C., and the foaming agent is then pressed into the melted modified polypropylene-based resin, and while maintaining the high pressure, 1 to 1
There is a method in which the mixture is kneaded for 120 minutes and then discharged from a die to extrude and foam.

In the present invention, a foaming agent containing isobutane as a main component, which is inexpensive and has little adverse effect on the environment, is used as the foaming agent.

The foaming agent containing isobutane as a main component includes, for example, isobutane alone or a mixed gas containing 80% by weight or more of isobutane. Among commercially available ones, for example, isobutane / normal butane is used. Iso-rich butane gas having a weight ratio of 85/15 is exemplified. However, normal butane alone or isobutane / normal butane weight ratio of 2
When 5/75 industrial butane, normal pentane, or isopentane is used as a foaming agent, the foam shrinks greatly 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, other volatile foaming agents and decomposable foaming agents are used as the foaming agent in an amount of 100 parts or less per 100 parts of isobutane.
Preferably, 0.1 to 75 parts may be mixed.

Examples of the volatile foaming agent include aliphatic hydrocarbons such as propane or normal butane, pentane, hexane and heptane; alicyclic hydrocarbons such as cyclobutane, cyclopentane and cyclohexane; chlorodifluoromethane, difluoro Methane, trifluoromethane, trichlorofluoromethane, dichlorodifluoromethane, chloromethane, dichloromethane, chloroethane, dichlorotrifluoroethane, dichlorofluoroethane, chlorodifluoroethane, dichloropentafluoroethane, tetrafluoroethane, difluoroethane,
Halogenated hydrocarbons such as pentafluoroethane, trifluoroethane, trichlorotrifluoroethane, dichlorotetrafluoroethane, chloropentafluoroethane, and perfluorocyclobutane; inorganic gases such as carbon dioxide, nitrogen, and air; water; Species or two or more species.

Preferred decomposable foaming agents that can be mixed include nitroso foaming agents such as N, N'-dinitrosopentamethylenetetramine and N, N'-dimethyl-N, N'-dinitrosoterephthalamide; One or two or more azo foaming agents such as dicarbonamide and barium azodicarboxylate; and sulfohydrazide foaming agents such as p, p'-oxybisbenzenesulfonylhydrazide and p-toluenesulfonylsemicarbazide.

As other foaming agents, normal butane, isopentane, chloroethane and the like are particularly preferred from the viewpoint of ease of handling.

The amount of the foaming agent containing isobutane as a main component is not particularly limited, but is usually preferably in the range of 0.5 to 40 parts based on 100 parts of the modified polypropylene resin.

In the present invention, if necessary, it is possible to use various additives known in the production of foams. For example, a foam nucleating agent (eg, sodium bicarbonate-citric acid, talc, etc.), a stabilizer, a flame retardant, and the like for reducing the size of bubbles may be added. The addition amount of the foam nucleating agent is 0.1 to 1.
0 parts is preferred.

Further, a known shrinkage inhibitor may be used, if necessary, to assist in preventing shrinkage of the foam. Examples of the anti-shrinkage agent include partial esters of fatty acids and polyols, and fatty acid amides. The amount of the anti-shrink agent used as required is preferably 0.1 to 5 parts with respect to 100 parts of the resin.

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

The effects of the present invention can be exerted on foams of any shape. For example, a sheet-like, block-like, board-like, rod-like, pipe-like, bead-like, tube-like, or bag-like foam can be used. These can be further secondary molded and processed into a desired shape.

[0043]

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

Example 1 100 parts of propylene homopolymer (Noblen D501 manufactured by Sumitomo Chemical Co., Ltd., melt flow index at 230 ° C., 0.4 g / 10 minutes), 10 parts of isoprene monomer, and a radical polymerization initiator Α, α'-bis (t-butylperoxy-m-isopropyl) benzene (Perbutyl P manufactured by NOF Corporation, 1 minute half-life temperature 175 ° C)
One part is a twin screw extruder (LAVO) manufactured by Japan Steel Works, Ltd.
The mixture was melt-kneaded using TEX) 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, had a cylinder bore diameter of 32 mmφ, and had a maximum effective screw length (L / D) of 25.5. The twin-screw extruder was heated at a set temperature of the cylinder section of 200 ° C. and a set temperature of the feed section at 160 ° C., and the rotation speed of the screw was set at 100 rpm.

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

100 parts of pellets of the modified polypropylene resin composition, 0.05 part of blended oil (Super Ease manufactured by Koshigaya Chemical Industry Co., Ltd.), and sodium bicarbonate-citric acid (manufactured by Eiwa Chemical Co., Ltd.) as a foam nucleating agent Cerbon SG / I
C) 0.1 part was mixed for 15 minutes using a ribbon blender. This mixture was supplied to a tandem extruder (the first-stage extruder cylinder diameter was 40 mmφ, the second-stage extruder cylinder diameter was 50 mmφ), and the mixture was heated at 230 ° C. in the first-stage extruder.
And then melted with isobutane gas (100% isobutane) as a foaming agent.
9 parts were press-fitted into 0 parts and kneaded. This was cooled in a second-stage extruder so that the resin temperature became 150 ° C., and the orifice was extruded from a circular die of 6 mmφ × 25 mm to form a round rod-shaped foam. did.

The apparent density and closed cell rate of the obtained round rod-shaped foam were measured by the following methods, and the appearance was visually evaluated according to the following evaluation criteria.

Apparent density of foam: Calculated from polymerization and volume obtained by submergence method.

Closed cell rate: Multi-pycnometer (product name, manufactured by Yuasa Ionics Co., Ltd .; ASTM D-
It was measured according to 2856.

Evaluation criteria for appearance: ：: No unfoamed portion, fluff and wrinkles are observed.

Δ: No unfoamed portion is observed, but fluff and wrinkles are observed.

×: Unfoamed part, fluff and wrinkles are seen.

As a result, the apparent density was 33 kg / m ³ , the closed cell ratio was 75%, and the appearance was evaluated as ○.

Examples 2-3 Using the pellets of the modified polypropylene resin composition obtained in Example 1 as a blowing agent, a mixture of isobutane (i-Bu) and normal butane (n-Bu) (mixing weight ratio: i −
Bu / n-Bu = 85/15. Example 2) and a mixture of isobutane (i-Bu) and isopentane (mixing weight ratio: i-Bu / isopentane = 85/15; Example 3)
A round rod-shaped foam was obtained in the same manner as in Example 1 except that the above was used.

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 (Nobrene D501, manufactured by Sumitomo Chemical Co., Ltd.) was not modified, and instead of using pellets of a modified polypropylene resin composition, this propylene homopolymer was used. According to the method for producing a round rod-shaped foam of Example 1, a round 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.

Comparative Example 2 A round rod-like foam was produced in the same manner as in Comparative Example 1 except that the foaming agent was changed as shown in Table 1 (the press-in amount of the foaming agent was the same as in Comparative 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 Examples 3 and 4 Round bar-shaped foams were prepared in the same manner as in Example 1 except that the foaming agent was changed as shown in Table 1 (the press-in amount of the foaming agent was 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.

[0063]

[Table 1]

From the above results, Examples 1, 2, and 3
It can be seen that the foam in the above has a low apparent density, a high closed cell ratio and excellent appearance. However, as in Comparative Examples 1 and 2, when the modified polypropylene-based resin composition of the present invention is not used and a propylene homopolymer is used and foamed, the apparent density, closed cell rate and appearance are not suitable. It turns out that you can only recover. Further, when a foaming agent containing no isobutane as a main component was used as in Comparative Examples 2, 3 and 4, the apparent density and closed cell ratio of the obtained foam were changed to those of Examples 1 and 2.
It turns out that it is not suitable as compared with 3 and 3.

[0065]

According to the production method of the present invention, a modified polypropylene resin composition obtained by melting and kneading a raw material polypropylene resin, an isoprene monomer and a radical polymerization initiator is mixed with a blowing agent containing isobutane as a main component. By using and foaming, a foam having a low apparent density, a high closed cell rate and a beautiful appearance can be produced at a low cost with little adverse effect on the environment.

Claims (1)

[Claims] 1. A foaming agent containing isobutane as a main component is added to a modified polypropylene resin obtained by melting and kneading a mixture of a polypropylene resin, an isoprene monomer and a radical polymerization initiator and reacting the mixture. A method of producing a modified polypropylene-based resin foam that is kneaded inside and then discharged outside the extruder.