JPH09278917A - Foam comprising modified polypropylene-based resin composition and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce the subject low-density foam, having a high closed-cell ratio and a beautiful appearance, excellent in heat resistance and useful as a cushioning material, etc., by expanding a specific modified polypropylene-based resin composition. SOLUTION: The 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 1,3-butadiene monomer and (iii) a radical polymerization initiator [e.g. α,α'-bis(t-butylperoxy-m-isopropyl)benzene] with (B) a foaming agent (e.g. butane gas) and then extruding and expanding the kneaded mixture. For example, the amount of the component (ii) is preferably 1-20 pts.wt. based on 100 pts.wt. component A and that of the component (iii) is preferably within the range of 0.5-5 pts.wt. component (ii) based on 100 pts.wt. component A. The amount of the component B is preferably within the range of 0.5-100 pts.wt. based on 100 pts.wt. component A. The melt kneading temperature is usually 230-140 deg.C and the melt kneading time is usually about 1-60min.

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 same. More specifically, the present invention relates to a foam made of a modified polypropylene resin composition obtained by melt-kneading a polypropylene resin, a 1,3-butadiene monomer and a radical polymerization initiator, and a method for producing the same.

[0002]

2. Description of the Related Art In general, a foam made of a thermoplastic resin is lightweight and has a good heat insulating property and a good shock absorbing property against external stress, so that it is widely used as a heat insulating material, a shock absorbing material, a core material, a food container, etc. It's being used. Among them, a foam made of a polypropylene resin has good chemical resistance, impact resistance and heat resistance, and is therefore particularly preferably used as a cushioning material.

[0003] However, polypropylene resins are
Since it is a crystalline resin, its viscosity and tensile strength at the time of melting are low, and when this 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 is difficult to obtain a foam having a high closed cell ratio and a low density, which has an excellent appearance by foaming a polypropylene resin.

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. Examples include a method of blending polyethylene and foaming the same (see, for example, Japanese Patent Publication No. 44-2574).

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

Further, JP-A-4-3642 discloses a method in which a propylene-non-conjugated diene copolymer is obtained by melt-kneading a propylene polymer and a non-conjugated diene, and foamed. However, there is no mention of a method using 1,3-butadiene.

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.

[0008]

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.

[0009]

Means for Solving the Problems As a result of intensive studies to solve the above problems, the present inventors have found that a polypropylene resin, a 1,3-butadiene monomer and a radical polymerization initiator are added to the polypropylene. The foaming property of the modified polypropylene resin composition obtained by kneading at a temperature at which the resin is melted and at a temperature at which the radical polymerization initiator is decomposed, the polypropylene resin before being melt-kneaded. (It may be referred to as "raw material polypropylene resin" hereinafter), which has significantly improved foamability, and has excellent heat resistance. By foaming this modified polypropylene resin composition, it has excellent heat resistance. The inventors have completed the present invention by finding that a foam having a high closed cell rate and a low density and a beautiful appearance can be obtained.

That is, the present invention provides a foamed product obtained by foaming a modified polypropylene resin composition obtained by melt-kneading a raw material polypropylene resin, 1,3-butadiene monomer and a radical polymerization initiator. Regarding manufacturing method.

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

The present invention also relates to a foam made of the modified polypropylene resin composition produced by each of the above production methods.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The modified polypropylene resin composition of the present invention comprises a raw polypropylene resin and 1,3
-Being obtained by melt-kneading a butadiene monomer and a radical polymerization initiator and having a high viscosity at the time of melting, especially an extensional viscosity at the time of melting, a foam obtained by foaming this modified polypropylene resin composition is It is characterized by a high expansion ratio, a high closed cell ratio and a low density.

In the present invention, the reason why the foamability of the modified polypropylene resin composition is remarkably improved is not clear, but among the raw material polypropylene resin, 1,3-butadiene monomer and radical polymerization initiator. However, the object of the present invention cannot be achieved regardless of which one is missing.

The modified polypropylene resin composition thus obtained has a high cell wall strength at the time of 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 from 100,000 to 1,000,000 from the viewpoint of low cost. More preferably, it is within the range.

If necessary, other resins or rubbers may be added to the raw material polypropylene resin within the range that does not impair the effects of the present invention. Examples of the other resin or rubber include polyethylene; poly-α-olefins such as polybutene-1, polyisobutene, polypentene-1 and polymethylpentene-1;
Less than 5% by weight of ethylene or α-olefin / α-olefin copolymer such as ethylene / propylene copolymer, ethylene / butene-1 copolymer and propylene content of less than 75% by weight of propylene / butene-1 copolymer. Polymer; ethylene or α-olefin / α-olefin / diene monomer copolymer such as ethylene / propylene / 5-ethylidene-2-norbornene copolymer having a propylene content of less than 75% by weight; ethylene / chloride Vinyl copolymer,
Ethylene / vinylidene chloride copolymer, ethylene / acrylonitrile copolymer, ethylene / methacrylonitrile copolymer, ethylene / vinyl acetate copolymer, ethylene / acrylamide copolymer, ethylene / methacrylamide copolymer, ethylene / acryl 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, ethylene / acrylic acid metal salt copolymer, ethylene / methacrylic acid Ethylene or α-olefin / such as metal salt copolymer, ethylene / styrene copolymer, ethylene / methylstyrene copolymer, ethylene / divinylbenzene copolymer
Vinyl monomer copolymer; polydiene copolymer such as polyisobutene, polybutadiene, polyisoprene; vinyl monomer / diene monomer random copolymer such as styrene / butadiene random copolymer; styrene / butadiene / Vinyl monomer such as styrene block copolymer /
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 monomer block copolymer); acrylonitrile / butadiene / styrene copolymer, methyl methacrylate / butadiene / Vinyl monomer such as styrene copolymer / diene monomer / vinyl monomer graft copolymer;
Vinyl polymers such as polyvinyl chloride, polyvinylidene chloride, polyacrylonitrile, polyvinyl acetate, polyethyl acrylate, polybutyl acrylate, polymethyl methacrylate; vinyl chloride / acrylonitrile copolymer, vinyl chloride / vinyl acetate copolymer Examples thereof include coalesce, acrylonitrile / styrene copolymer, and vinyl copolymer such as methyl methacrylate / styrene copolymer.

The amount of these other resins or rubbers added to the raw material polypropylene resin varies depending on the type of the resin or the type of 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 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 raw 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.

When the above-mentioned additive material (other resin, rubber, stabilizer and / or additive) is used,
This additive material may be added in advance to the raw material polypropylene resin or may be added when the raw material polypropylene resin is melted, and a modified polypropylene resin composition is produced. Then, it may be added to the modified polypropylene resin composition by an appropriate method.

The modified polypropylene resin composition in the present invention comprises a polypropylene resin, a 1,3-butadiene monomer, another vinyl monomer copolymerizable with the 1,3-butadiene monomer, and a radical. It may be produced by melt-kneading with a polymerization initiator.

Other vinyl monomers copolymerizable with the 1,3-butadiene monomer include, for example, vinyl chloride, vinylidene chloride, styrene, acrylonitrile, methacrylonitrile, acrylamide, methacrylamide, vinyl acetate and acryl. Acid, methacrylic acid, maleic acid, maleic anhydride, acrylic acid metal salt, methacrylic acid metal salt, methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, stearyl acrylate, glycyl acrylate, etc. Acrylic ester; Methyl methacrylate, Ethyl methacrylate,
Examples thereof include methacrylic acid esters such as butyl methacrylate, 2-ethylhexyl methacrylate, stearyl methacrylate, and glycyl methacrylate.

When the 1,3-butadiene monomer and another vinyl monomer copolymerizable with the 1,3-butadiene monomer are used in combination, the 1,3-butadiene monomer is used. Other vinyl monomers copolymerizable with 1,3-butadiene monomer are preferably used together in an amount of less than 100 parts by weight, more preferably less than 75 parts by weight, based on 100 parts by weight. preferable. If the amount of the other vinyl monomer copolymerizable with the 1,3-butadiene monomer exceeds the above range, it tends to be impossible to obtain a foam having a suitable shape and appearance.

The amount of the 1,3-butadiene monomer added is 0.1 to 50 parts by weight, particularly 1 to 20 parts by weight, based on 100 parts by weight of the raw material polypropylene resin. It is preferable in that the foamability of the base resin is sufficiently improved and the preferable properties such as heat resistance, chemical resistance and mechanical properties of the raw material polypropylene resin particles are not impaired.

Examples of the radical polymerization initiator generally include peroxides and azo compounds. In the present invention, compounds such as radical polymerization initiators having hydrogen abstraction ability with respect to polymer molecules of polypropylene resin are used. The existence of is necessary.

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 added in an amount of 100 parts by weight based on 100 parts by weight of the raw polypropylene resin because the melt viscosity of the modified polypropylene resin composition is not excessively lowered and it is economical. It is preferably in the range of 0.1 to 10 parts by weight, and more preferably in the range of 0.5 to 5 parts 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.

Such raw material polypropylene resin,
The mixing method and melt-kneading method of the 1,3-butadiene monomer, the radical polymerization initiator and other additive materials added as necessary are not particularly limited,
For example, a raw material polypropylene-based resin may be prepared by mixing a raw material polypropylene-based resin impregnated with a 1,3-butadiene monomer, a radical polymerization initiator, and other additive materials that are added as necessary and then melt-kneading. After melt-kneading, 1,3-butadiene monomer, a radical polymerization initiator and other additive materials to be added if necessary, are mixed simultaneously or separately, collectively or dividedly, You may melt-knead.

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. Also, the time of melt-kneading (radical polymerization initiator and 1,3-
The time after mixing the butadiene monomers is generally 3
It is 0 second to 60 minutes.

Examples of the melt kneading device include a kneader, a Banbury mixer, a Brabender, a single screw extruder,
A kneading machine such as a twin-screw extruder, a twin-screw surface renewing machine, a horizontal stirrer such as a double-screw multi-disk device, or a vertical stirrer such as a double helical ribbon stirrer can be used to heat a polymer material to an appropriate temperature. An apparatus that can be kneaded while applying shear stress is used. Of these, a single-screw or twin-screw extruder is particularly preferable from the viewpoint of productivity. The melt-kneading may be repeated a plurality of times in order to mix the respective materials sufficiently uniformly.

As described above, the modified polypropylene resin composition of the present invention can be manufactured.

The foam of the present invention is obtained by foaming such a modified polypropylene resin composition.

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-mentioned 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 depending on 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.

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

In the case of the above method (1), the modified polypropylene resin composition and the thermal decomposition type 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.

In the case of the above method (2), examples of the foaming agent include volatile type foaming agents. Among them, preferable volatile type foaming agents include, for example, propane, butane, pentane,
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 above-mentioned 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, a foam nucleating agent such as sodium bicarbonate-citric acid or talc may be used together, if necessary, in order to control the bubble diameter of the foam to an appropriate size. 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 the case of the above 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 of the present invention has a density of 0.01 to 0.5 g / cm 3 from the viewpoint that it is suitable for its light weight, heat insulating property, buffering force against external stress and compressive strength.
³ is preferable and 0.015 to 0.2 g / cm ³
Is more preferable.

The foam of the present invention preferably has a closed cell content 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 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 shape shape or a prismatic shape. Various shapes such as a columnar shape such as a strand shape and a particle shape can be given.

[0052]

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 10 parts by weight of 1,3-butadiene monomer. And α'as a radical polymerization initiator
1 part by weight of bis (t-butylperoxy-m-isopropyl) benzene (manufactured by NOF CORPORATION, Perbutyl P, 1-minute half-life temperature 175 ° C.), manufactured by Japan Steel Works, Ltd.,
By melt-kneading using a twin-screw extruder (LABOTEX) and melt-extruding, a rod-shaped modified polypropylene resin composition molded product having a diameter of 4 mm was obtained. The molded product of the rod-shaped modified polypropylene resin composition is 3 m
Then, pellets of the modified polypropylene-based resin composition were obtained by chopping to a thickness of m.

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.

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, and sodium bicarbonate-citric acid (Ewakasei Co., Ltd.) as a foam nucleating agent.
(Manufactured by Cerbon SG / IC) 0.1 part by weight 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 and the second-stage extruder cylinder diameter was 50 mmφ),
After being melted at 230 ° C. in a multi-stage extruder, butane gas (isorich butane gas; normal butane / isobutane mixing ratio 15/85 by weight) as a foaming agent was added to 100 parts by weight of the modified polypropylene resin composition. 8 parts by weight and kneaded, and this is cooled in the second stage extruder to a resin temperature of 150 ° C., and the orifice is 6 mmφ.
It was extruded from a × 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.

Foam 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
-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 0.040 g / cm ³ , the closed cell ratio was 86%, and the appearance was evaluated as ◯.

Examples 2 to 6 Polypropylene resin to be fed to a twin-screw extruder, 1,3-
Pellets of the modified polypropylene resin composition were obtained in the same manner as in Example 1 except that the types and amounts of the butadiene monomer and radical polymerization initiator were changed as shown in Table 1.

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

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

Comparative Example 1 Propylene homopolymer (Nobrene D501, manufactured by Sumitomo Chemical Co., Ltd.) was not modified, but instead of using pellets of the modified polypropylene resin composition, this propylene homopolymer was used. A round rod-shaped foam was produced according to the method for manufacturing the round rod-shaped foam of Example 1.

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

Comparative Example 2 When melt kneading was carried out in the same manner as in Example 1 except that the 1,3-butadiene monomer was not added, the melting temperature of the resin was extremely lowered, and strands could not be formed. .

[0068]

[Table 1]

[0069]

[Table 2]

[0070]

[Table 3]

[0071]

The modified polypropylene resin composition obtained by melt-kneading the raw material polypropylene resin, the 1,3-butadiene monomer and the radical polymerization initiator has a low density and is independent. A foam with a high bubble ratio, a beautiful appearance, and excellent heat resistance can be obtained.

Claims (3)

[Claims] 1. A method for producing a foam obtained by foaming a modified polypropylene resin composition obtained by melt-kneading a polypropylene resin, a 1,3-butadiene monomer and a radical polymerization initiator. 2. The method according to claim 1, wherein the modified polypropylene resin composition and the foaming agent are melt-kneaded and then extruded to foam. 3. A foam comprising a modified polypropylene resin composition produced by the production method according to claim 1.