JPH10316789A - Extruded polypropylene resin foam - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an extruded foam which has a beautiful surface and does not exhibit postshrinkage while having a relatively low apparent specific gravity by melt mixing a polypropylene resin with a satd. higher fatty acid and a blowing agent and extruding the melt mixture from a die into a low-pressure zone. SOLUTION: A mixture comprising 100 pts.wt. polypropylene resin and 0.2-3 pts.wt. satd. higher fatty acid is melt mixed with 5-100 pts.wt. blowing agent to give a foamable compsn., which is extruded through a die into a low-pressure zone to give an extruded polypropylene resin foam having an apparent density of 10-100 kg/m<3> . Pref., the polypropylene resin is a modified one which is obtd. by melt mixing 100 pts.wt. propylene homo- or copolymer (A) with 3-15 pts.wt. at least one free-radical-polymerizable monomer (B) selected from among arom. vinyl monomers and conjugated unsatd. monomers and a free-radical initiator (C) at a temp. at which ingredient A is melted and ingredient C is decomposed (170-300 deg.C).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to an extruded polypropylene resin foam containing a saturated higher fatty acid. More specifically, the present invention relates to a polypropylene-based resin extruded foam containing a saturated higher fatty acid and having a beautiful surface with suppressed post-shrinkage.

[0002]

2. Description of the Related Art Foams made of polypropylene-based resin are suitably used as various cushioning materials, packaging materials, heat insulating materials and building materials because of their excellent rigidity, chemical resistance, impact resistance and heat resistance.

[0003] However, polypropylene-based resins generally allow low molecular gas to permeate easily, and a foaming agent used for foaming is easily scattered to the outside from bubbles. Therefore, when trying to obtain a polypropylene resin extruded foam having a relatively low density such as a density of 100 kg / m ³ or less, undesired phenomena such as post-shrinkage of the foam due to dissipation of the foaming agent and wrinkling of the surface. Until now, it has been difficult to obtain a foam having a beautiful surface with small post-shrinkage.

Therefore, for example, Japanese Patent Publication No. 58-30896
In Japanese Patent Application Laid-Open Publication No. H11-157, a method of adding a higher fatty acid ester of a polyhydric alcohol and foaming the polyolefin resin is disclosed as a method for preventing shrinkage of the polyolefin resin. However,
Even if this method is used, the effect of preventing post-shrinkage of the polypropylene resin is not sufficient.

Further, Japanese Patent Publication No. 7-119314 proposes using 1,1,1,2-tetrafluoroethane as one component of a foaming agent.

However, since 1,1,1,2-tetrafluoroethane has low solubility in a polypropylene-based resin, there is a problem that a cell wall is broken at the time of foaming and bubbles are likely to become coarse. Was.

As described above, a method for producing an extruded foam of a polypropylene-based resin having a relatively low density and no post-shrinkage and having a beautiful surface without impairing the excellent properties of the polypropylene-based resin has been found. It has not been done yet.

[0008]

SUMMARY OF THE INVENTION In view of the foregoing, an object of the present invention is to provide an extruded polypropylene resin foam having a relatively low apparent density and no post-shrinkage, and having a beautiful surface. It is in.

[0009]

According to the present invention, a saturated higher fatty acid of 0.2 to 100 parts by weight of a polypropylene resin is used.
A mixture obtained by mixing 3 parts by weight and a foaming agent are melt-kneaded to form a foamable composition, and then the foamable composition is extruded from a die to a low pressure region to obtain an apparent density of 10 to 100 kg /.
It relates to a polypropylene resin extruded foam of m ³ .

In this case, the polypropylene resin is at least one kind of radical polymerizable monomer selected from the group consisting of (A) a polypropylene resin, (B) an aromatic vinyl monomer and a conjugated unsaturated monomer. Monomer and (C)
The radical polymerization initiator has a temperature at which the polypropylene resin (A) can be melted, and the radical polymerization initiator (C)
Is preferably a modified polypropylene resin obtained by melt-kneading at a temperature at which it can be decomposed.

It is preferable that the foaming agent is at least one selected from the group consisting of propane, normal butane and isobutane.

Further, the saturated higher fatty acid is preferably stearic acid.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The inventors of the present invention have conducted intensive studies to solve the above-mentioned problems. As a result, a foaming composition was prepared by melt-kneading a mixture of a polypropylene resin and a saturated higher fatty acid and a foaming agent. The polypropylene resin extruded foam obtained by extruding the foamable composition into a low pressure region, having a small post-shrinkage even if it has a relatively low apparent density, and having a beautiful surface. The present invention has been completed.

That is, according to the present invention, a foaming composition is obtained by melt-kneading a mixture obtained by mixing 0.2 to 3 parts by weight of a saturated higher fatty acid with 100 parts by weight of a polypropylene resin and a foaming agent. It is a polypropylene resin extruded foam having an apparent density of 10 to 100 kg / m ³ obtained by extruding the foamable composition from a die to a low pressure region.

The polypropylene resin usable in the present invention includes a propylene homopolymer, a block copolymer of propylene containing 75% by weight or more of propylene and another monomer, a graft copolymer, and a random copolymer. It may be any of the coalescing, a polypropylene resin (A) to be described later, a modified polypropylene resin obtained by modifying the polypropylene resin (A), and a polymerization operation at the time of production in two stages. It also includes a polypropylene-based resin obtained by performing the above steps in multiple stages. As the polypropylene-based resin, it is preferable to use a modified polypropylene-based resin because conditions under which good extrusion foaming is possible are wide.

As a method for obtaining the modified polypropylene resin, the polypropylene resin (A), the radical polymerizable monomer (B) and the radical polymerization initiator (C) are melted by melting the polypropylene resin (A). Melting at a temperature at which the radical polymerization initiator (C) can be decomposed, and a polypropylene resin (A), a radical polymerizable monomer (B) and a radical polymerization initiator (C) in an aqueous medium. ) And a radical polymerization initiator (C)
A method in which the reaction is carried out at a temperature at which the resin can be decomposed, a method in which the polypropylene-based resin (A) is irradiated with low-level radiation under the condition that the oxygen concentration in the atmosphere is kept low, and a degree in which the main chain cleavage of the resin does not occur preferentially. Melt-kneading the polypropylene resin (A) and the radical polymerization initiator (C) under the above temperature conditions.

Among these methods, a polypropylene resin (A), a radical polymerizable monomer (B) and a radical polymerization initiator are preferred because a modified polypropylene resin having stable physical properties can be easily obtained. Agent (C)
A temperature at which the polypropylene resin (A) can be melted,
A method of melt-kneading at a temperature at which the radical polymerization initiator (C) can be decomposed is particularly preferable.

In the present invention, the polypropylene resin (A) that can be used to obtain the modified polypropylene resin may be a propylene homopolymer, a block copolymer of propylene with another monomer, or propylene and another monomer. A crystalline polymer such as a random copolymer with a monomer may be mentioned, and the rigidity is high, and the polypropylene homopolymer is preferable in that it is inexpensive, and both rigidity and impact resistance are high. Is preferably a block copolymer of the propylene and another monomer. When the polypropylene resin (A) is a block copolymer of propylene and another monomer or a random copolymer of propylene and another monomer, the high crystallinity characteristic of the polypropylene resin, From the viewpoint of maintaining high rigidity and good chemical resistance, the propylene monomer component contained is
5% by weight or more, preferably 90% by weight
More preferably, it is the above.

Other monomers copolymerizable with propylene to obtain the polypropylene resin (A) include:
One or more monomers selected from the group consisting of ethylene, α-olefin, cyclic olefin, diene monomer and vinyl monomer.

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 monomer copolymerizable with the propylene include 5-methylene-2-norbornene, 5-ethylidene-2-norbornene, 1,4-hexadiene, methyl-1,4-hexadiene, and 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, ethyl acrylate, butyl acrylate, methyl methacrylate, And maleic anhydride.

Of these monomers, ethylene, α-olefin or diene monomers are preferred, and ethylene or butene-1 is more preferred because it is easily copolymerized with propylene and is inexpensive.

In the present invention, as the polypropylene resin (A), from the viewpoint of buffer characteristics, a propylene homopolymer and a propylene content of 96 to 99.9% by weight and an ethylene content of 0.1 to 4% by weight are used. Certain ethylene-propylene random copolymers are particularly preferably used.

The melt flow index (230 ° C.) of the polypropylene resin (A) is not particularly limited. However, it is necessary to consider that the obtained modified polypropylene resin has a viscosity suitable for extrusion foaming. Then
0.01 to 8 g / 10 minutes, especially 0.01 to 4
It is preferably about g / 10 minutes.

Further, if necessary, a kneading material such as another resin or rubber may be added to the polypropylene resin (A) as long as the effects of the present invention are not impaired.

Specific examples of other resins or rubbers which can be used by mixing with the polypropylene resin (A) include, for example, polyethylene, polybutene-1, polyisobutene, polypentene-1, polymethylpentene-1 and the like. α-olefins; polydiene-based polymers such as polybutadiene and polyisoprene; polystyrene;
Vinyl polymers such as polyvinyl chloride, polyvinylidene chloride, polyacrylonitrile, polyvinyl acetate, polyethyl acrylate, polybutyl acrylate, and polymethyl methacrylate; rubbers such as ethylene-propylene rubber and ethylene-propylene-diene rubber Is raised.

The polypropylene resin (A) may further contain, if necessary, an antioxidant, a metal deactivator, a phosphorus-based processing stabilizer, an ultraviolet absorber, an ultraviolet stabilizer, a fluorescent brightener, a metal soap, The present invention relates to a kneading material such as an additive such as a stabilizer such as an acid adsorbent or a crosslinking agent, a chain transfer agent, a nucleating agent, a lubricant, a plasticizer, a filler, a reinforcing material, a pigment, a dye, a flame retardant, and an antistatic agent. May be added within a range that does not impair the effect of the above.

The polypropylene resin (A) (which may contain various kneading materials) may be in the form of particles or pellets, and the size and shape are particularly limited. is not.

The components such as the kneading material which can be mixed with the polypropylene resin (A) to maintain the crystallinity, rigidity, chemical resistance and heat resistance characteristic of the polypropylene resin. Therefore, it is preferably 30% by weight or less, more preferably 15% by weight or less of the total amount with the polypropylene resin (A).

Further, the above-mentioned kneading material (other resin, rubber,
(A stabilizer and / or an additive), even if the kneading material is added to the polypropylene resin (A) in advance, the kneading material may be added to the polypropylene resin (A).
May be added at the time of melting. Further, the modified polypropylene resin may be added to the modified polypropylene resin by an appropriate method after the modified polypropylene resin is produced.

The radically polymerizable monomer (B) used in the present invention is selected from the group consisting of an aromatic vinyl compound and a conjugated diene compound, since it does not cause an excessive decrease in melt viscosity during the modification. At least one selected is preferred.

Examples of the aromatic vinyl monomer include styrene; methyl styrene such as o-methyl styrene, m-methyl styrene, p-methyl styrene, α-methyl styrene, β-methyl styrene, dimethyl styrene, trimethyl styrene, etc. Chlorostyrenes such as α-chlorostyrene, β-chlorostyrene, o-chlorostyrene, m-chlorostyrene, p-chlorostyrene, dichlorostyrene and trichlorostyrene; o-bromostyrene, m-bromostyrene, p-bromostyrene , Bromostyrene such as dibromostyrene and tribromostyrene; o-fluorostyrene, m-fluorostyrene, p
-Fluorostyrene such as fluorostyrene, difluorostyrene and trifluorostyrene; nitrostyrene such as o-nitrostyrene, m-nitrostyrene, p-nitrostyrene, dinitrostyrene and trinitrostyrene; o-hydroxystyrene, m-hydroxystyrene , P-hydroxystyrene, dihydroxystyrene,
Vinylphenol such as trihydroxystyrene; o-
Divinylbenzene such as divinylbenzene, m-divinylbenzene and p-divinylbenzene; and isopropenylstyrene such as o-diisopropenylbenzene, m-diisopropenylbenzene and p-diisopropenylbenzene. Or a mixture of two or more. Among them, styrene, α-methylstyrene, methylstyrene such as p-methylstyrene, divinylbenzene, and a mixture of vinylbenzene isomers are preferable because they are inexpensive.

Examples of the conjugated diene compound include isoprene, 1,3-butadiene, chloroprene, 2-phenyl-1,3-butadiene and the like, and these may be used alone or in combination of two or more. be able to. Of these, isoprene and 1,
3-Butadiene is preferred because it is inexpensive.

The amount of the radical polymerizable monomer (B) used is
In order to obtain a sufficient modifying effect, the amount is preferably at least 3 parts by weight, especially at least 5 parts by weight, based on 100 parts by weight of the polypropylene resin (A). In order not to impair properties such as heat resistance, chemical resistance and mechanical properties, it is preferably 15 parts by weight or less, especially 12 parts by weight or less based on 100 parts by weight of the polypropylene resin (A). .

When the aromatic vinyl compound and the conjugated diene compound are used in combination, the ratio (weight ratio) between the amounts of the two is used.
Can be arbitrarily selected.

The radical polymerization initiator generally includes an organic peroxide, an azo compound, an inorganic peroxide and the like. Among the radical polymerization initiator (C) used in the present invention, among these, an organic peroxide is preferable. Oxides are preferred.

Examples of the organic peroxide include ketone peroxides such as methyl ethyl ketone peroxide and methyl acetoacetate peroxide;
-Bis (t-butylperoxy) -3,3,5-trimethylcyclohexane, 1,1-bis (t-butylperoxy) cyclohexane, n-butyl-4,4-bis (t
-Butylperoxy) valerate, 2,2-bis (t-
Peroxyketals such as butylperoxy) butane;
Permethane hydroperoxide, 1,1,3,3-
Hydroperoxides such as tetramethylbutyl hydroperoxide, 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) hexyne-3; diacyl peroxides such as benzoyl peroxide; di (3-methyl-3-methoxybutyl) peroxydicarbonate and di-2-methoxybutylperoxydicarbonate. 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-butylperoxyacetate, t-butylperoxybenzoate, di-t-
Examples thereof include peroxyesters such as butyl peroxyisophthalate, and these can be used alone or as a mixture of two or more. Among these, those having a particularly high hydrogen abstracting ability are preferable. Examples of such radical polymerization initiators include 1,1-bis (t-butylperoxy) -3,3,5-trimethylcyclohexane and 1,1 Peroxy ketals such as -bis (t-butylperoxy) cyclohexane, n-butyl-4,4-bis (t-butylperoxy) valerate and 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, -T-butyl peroxide,
Dialkyl peroxides such as 2,5-dimethyl-2,5-di (t-butylperoxy) hexine-3; diacyl peroxides such as benzoyl peroxide; t-butylperoxyoctate, t-butylperoxyiso Butyrate, t-butylperoxylaurate, t-butylperoxy-3,5,5-trimethylhexanoate, t-butylperoxyisopropyl carbonate, 2,5-dimethyl-2,5-di (benzoylper It is preferable to use peroxyesters such as (oxy) hexane, t-butylperoxyacetate, t-butylperoxybenzoate, and di-t-butylperoxyisophthalate alone or as a mixture of two or more.

The amount of the radical polymerization initiator (C) used is preferably at least 0.05 part by weight, especially 0.1 part by weight, per 100 parts by weight of the polypropylene resin (A) in order to obtain a sufficient modifying effect. Parts or more. In order to prevent the melt viscosity of the obtained modified polypropylene resin from excessively lowering and the economical efficiency from decreasing, 5 parts by weight based on 100 parts by weight of the polypropylene resin (A). It is preferably at most 2 parts by weight, especially at most 2 parts by weight.

The method of mixing and melt-kneading the polypropylene resin (A), the radical polymerizable monomer (B) and the radical polymerization initiator (C) are not particularly limited. For example, the polypropylene resin (A) , A radical polymerizable monomer (B), a radical polymerization initiator (C), and other additives (kneading agents) added as necessary, and then melt-kneading the mixture. After melt-kneading the resin (A), the radical polymerizable monomer (B), the radical polymerization initiator (C), and other optional materials to be added as needed are added to the resin simultaneously or separately. Or divided and mixed, and then melt-kneaded.

In the present invention, in order to obtain a modified polypropylene-based resin, the polypropylene-based resin (A) is melted and the radical polymerization initiator (C) is decomposed under a temperature condition sufficient to decompose. It is important to cause the reaction by melt-kneading.

In the present invention, the temperature at which the polypropylene resin (A) can be melted is a temperature range in which the crystal part of the resin melts and shows fluidity. It refers to the temperature range above the melting point measured by scanning calorimetry (DSC).

In the present invention, the temperature at which the radical polymerization initiator (C) can decompose is the temperature at which most of the radical polymerization initiator decomposes, for example, 80% or more of the radical polymerization initiator within the reaction time described later. Refers to the range.

Usually, the temperature at which the polypropylene resin (A) can be dissolved and the temperature at which the radical polymerization initiator (C) can be decomposed are in the range of 170 to 300 ° C. Therefore, the melt-kneading temperature for obtaining the modified polypropylene resin is preferably in the range of 170 to 300 ° C, particularly preferably in the range of 180 to 250 ° C. Under such conditions, the polypropylene resin (A) is sufficiently melted and hardly thermally decomposed. The time for the reaction is about 0.5 to 60 minutes, preferably 1 to 1 minute.
Preferably, the time is about 0 minutes.

The melt kneading apparatus includes a roll,
Kneaders such as co-kneaders, Banbury mixers, Brabenders, single-screw extruders, twin-screw extruders, twin-screw surface renewers,
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 screw extruder is preferable in terms of productivity and uniform denaturation. Further, the melt kneading may be repeated a plurality of times for uniform mixing.

Thus, the modified polypropylene resin of the present invention can be produced.

Next, in the present invention, a polypropylene resin or a modified polypropylene resin is mixed with a saturated higher fatty acid.

Saturated higher fatty acids preferably used in the present invention include monovalent saturated fatty acids having 6 to 24 carbon atoms in one molecule.

Specific examples of the saturated higher fatty acid suitably used in the present invention include caprylic acid, capric acid, lauric acid, myristic acid, valmitic acid, stearic acid,
Behenic acid. These can be used alone or in combination of two or more. Among them, stearic acid is preferably used because it is inexpensive.

The above-mentioned specific example may be a mixture containing two or more kinds of saturated higher fatty acids as its components. In the present invention, such a mixture is named most of the saturated higher fatty acids contained therein. Expressed by the name of the one with the highest content.

In some cases, the saturated higher fatty acid is a mixture containing, as an auxiliary component, unsaturated fatty acids other than the saturated higher fatty acids, fatty acid esters, and polyhydric alcohols such as glycerin. Such a mixture also
If the sum of the contents of the auxiliary components other than the saturated fatty acid does not exceed 50% by weight of the total, it is suitably used in the present invention.

The amount of the saturated higher fatty acid to be used is 0.2 to 100 parts by weight of the polypropylene resin or the modified polypropylene resin in order to obtain a sufficient post-shrinkage preventing effect and a surface condition improving effect. Parts by weight,
It is preferably at least 0.3 part by weight, and in order to prevent undesirable phenomena in the production of the foam such as a decrease in the closed cell ratio, it is further at most 3 parts by weight, especially at least 2 parts by weight from the viewpoint of economy. Part or less.

The method for obtaining the mixture of the polypropylene resin and the saturated higher fatty acid is not particularly limited. For example, a method of simply dry-blending the polypropylene resin and the saturated higher fatty acid, a method of preparing the polypropylene resin and the saturated higher fatty acid in advance. May be obtained by melt-kneading the mixture to obtain pellets of the mixture, or a method of melting the polypropylene resin and then adding a saturated higher fatty acid to the molten polypropylene resin by an appropriate method and mixing.

The polypropylene resin (A), the radical polymerizable monomer (B) and the radical polymerization initiator (C) are mixed at a temperature at which the polypropylene resin (A) can be melted and the radical polymerization initiator (C In the case of using a modified polypropylene resin obtained by melting and kneading at a temperature at which) can be decomposed, the polypropylene resin (A), the radical polymerizable monomer (B) and the radical polymerization initiator (C) are melted. When kneading, a method of adding and mixing by an appropriate method may be used.

The extruded foam of the present invention is obtained by melt-kneading the mixture of the polypropylene resin and the saturated higher fatty acid and a foaming agent to obtain a foamable composition, and then extruding the foamable composition from a die to a low pressure region. Obtained by the method.

Examples of the foaming agent used in the present invention include a pyrolytic foaming agent and a volatile foaming agent.

Preferred pyrolytic foaming agents include, for example, N, N'-dinitrosopentamethylenetetramine,
Nitroso foaming agents such as N, N'-dimethyl-N, N'-dinitrosoterephthalamide; azo foaming agents such as azodicarbonamide and barium azodicarboxylate;
p, p'-oxybisbenzenesulfonyl hydrazide,
sulfohydrazide-based blowing agents such as p-toluenesulfonyl semicarbazide; 1 such as trihydrazinotriazine
Species or two or more species.

Specific examples of the volatile foaming agent suitably used in the present invention include aliphatic hydrocarbons such as propane, butane, isobutane, pentane, isopentane, neopentane, hexane and heptane; cyclobutane,
Alicyclic hydrocarbons such as 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 and perfluorocyclobutane; inorganic gases such as carbon dioxide, nitrogen and air; one or two kinds of water and the like The above is mentioned.

Among these foaming agents, volatile foaming agents are preferable because they have a wide range of density of foams that can be produced and are economical, and furthermore, they are economical.
It is more preferable to use at least one selected from the group consisting of propane, butane, and isobutane since the addition of a saturated higher fatty acid has a large post-shrinkage preventing effect.

The use amount (kneading amount) of the foaming agent may be appropriately adjusted according to the type of the foaming agent and the target density of the extruded foam, and is preferably 100 parts by weight of the polypropylene resin or the modified polypropylene resin. On the other hand, it is preferably in the range of 5 to 100 parts by weight.

There is no particular limitation on the method of adding the foaming agent to obtain the foamable composition. When a pyrolytic foaming agent is used as the foaming agent, for example, a raw material other than the foaming agent and the foaming agent are used in advance. A method of obtaining a foamable composition by dry-blending and then melt-kneading to obtain a foamable composition, or a method of adding a foaming agent to a material other than the molten foaming agent by an appropriate method and melt-kneading to obtain a foamable composition is preferable. When a volatile foaming agent is used as the foaming agent, a method in which the foaming composition is obtained by adding or press-fitting the foaming agent to a raw material other than the molten foaming agent is preferable.

Further, a foaming nucleating agent such as talc and sodium bicarbonate-citric acid used for controlling the bubble diameter of the foam, and pigments, stabilizers, fillers, flame retardants, antistatic agents and the like may be used as required. You may use it in the range which does not impair the effect of this invention.

In the present invention, a foam is obtained by extruding the foamable composition from a die to a low pressure region. Here, the low pressure region refers to a pressure region outside the extruder with respect to a die pressure in the extruder.

Examples of the apparatus used to obtain the foam include, for example, a single-screw, twin-screw or multi-screw extruder, or a tandem extruder in which one or two kinds selected from them are connected in series. Can be used. Further, the foaming composition is uniformly kneaded, the onlator used for the purpose of cooling, the speed of extruding the foaming composition from the die is adjusted, and the accumulator used for the purpose of cooling is also suitably used as a part of the apparatus for extrusion foaming. Used.

The extruded foam of the present invention thus obtained is
Since its apparent density is 10 to 100 kg / m ³ , it has excellent properties such as light weight, heat insulation, buffering of external stress, and compressive strength, but has a good balance of the properties. The apparent density is preferably at least 15 kg / m ^3, more preferably at least 18 kg / m ³ , and is preferably at most 40 kg / m ³ , preferably at most 36 kg / m ³ .

Further, the closed cell ratio of the extruded foam of the present invention is preferably 60% or more from the viewpoint that a foam having excellent buffering property against external stress and compressive strength can be obtained.
More preferably, it is at least 70%.

As described above, the foam of the present invention has excellent properties such as light weight, heat insulation, buffering of external stress, compressive strength and the like, and has a beautiful appearance. It is useful in other applications.

[0066]

Next, the present invention will be described in detail with reference to examples, but the present invention is not limited to these examples.

Production Example 1 Ethylene propylene random copolymer (3 wt% ethylene content, melt flow index at 230 ° C.
4 g / 10 min) 100 parts by weight, 10 parts by weight of styrene monomer, and α, α′-bis (t-butylperoxy-m-isopropyl) benzene (1 minute half-life temperature 175 ° C.) 0 as a radical polymerization initiator And 0.5 parts by weight were melt-kneaded using a twin screw extruder (LABOTEX) manufactured by Nippon Steel Works, Ltd., and melt-extruded to obtain 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
A pellet of the modified polypropylene-based resin composition (hereinafter, referred to as “resin 1”) was obtained by chopping to a thickness of mm.

Examples 1 to 3 Resin 1 or propylene homopolymer (PF-814, manufactured by Himont, 230 ° C.) as a polypropylene resin
Flow index: 4 g / 10 min, hereinafter referred to as “resin 2”) 100 parts by weight of pellets, stearic acid (Lunack S, manufactured by Kao Corporation) in the amount shown in Table 1
-98) and a blended oil (Koshigaya Chemical Industry Co., Ltd.)
(Super Ease) 0.05 parts by weight and 0.1 parts by weight of sodium bicarbonate-citric acid (Serubon SG / K, manufactured by Eiwa Chemical Co., Ltd.) as a foam nucleating agent were mixed for 15 minutes using a ribbon blender. . This mixture is supplied to a tandem-type extruder (the first-stage extruder cylinder diameter is 40 mmφ, the second-stage extruder cylinder diameter is 50 mmφ), and is melted at 230 ° C. in the first-stage extruder. 8 parts by weight of butane gas (iso-rich butane gas; the mixture ratio of normal butane / isobutane is 15/85 by weight) is press-mixed with 100 parts by weight of the resin 1 or 2 and kneaded. After cooling so that the resin temperature becomes 145 ° C, a circular die (4mmφ × 25mm)
The mixture was discharged under atmospheric pressure to obtain a round rod-shaped extruded foam.

With respect to the obtained extruded round rod-shaped foam, the cross-sectional area of the foam was measured by the following method immediately after foaming, 5 minutes and 24 hours later, and the shrinkage rate after 5 minutes and 24 hours was calculated.
Further, the closed cell ratio, apparent density, and surface state of the foam after 24 hours were also evaluated by the following methods. Table 2 shows the results.

[Evaluation method] Shrinkage rate after 5 minutes and after 24 hours At 10 points of the foam, the foam was cut perpendicular to the extrusion direction to expose the cross section, and the outer periphery was copied on paper. , And the weight of the portion was measured. The cross-sectional area of the foam was calculated from the ratio of the average of the weight of the paper at 10 places to the weight of the paper of known area. The shrinkage rate after 5 minutes and 24 hours is
Calculated according to the following formula from the foam cross-sectional area of the foam after minutes and 24 hours.

[0071]

(Equation 1)

Closed cell rate The foam after 24 hours was measured by an air pycnometer according to the method described in ASTM D-2856.

Apparent density The foam was measured after 24 hours according to the method described in JIS-K6767.

Surface Condition A visual judgment was made according to the following criteria.

：: No wrinkles on the foam surface due to post-shrinkage are observed. ×: Wrinkles and swelling are observed on the foam surface due to post-shrinkage. Comparative Examples 1 and 2 Saturated higher fatty acids were added at the mixing ratio shown in Table 1. Except for nothing, a round rod-shaped foam was obtained in the same manner as in Example 1, and after 5 minutes, 2
After 4 hours, the shrinkage, closed cell ratio, apparent density, and surface condition were evaluated in the same manner as described above. Table 2 shows the results.

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[Table 1]

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[Table 2]

From the results shown in Table 2, the extruded foam obtained by adding the saturated higher fatty acid has a very small shrinkage after 24 hours of foaming, which is smaller than that after 5 minutes. It can be seen that post-shrinkage is suppressed. On the other hand, when no addition is made, it can be seen that the shrinkage rate after 24 hours is larger than the value after 5 minutes and post-shrinkage has occurred.

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The extruded polypropylene resin foam of the present invention has excellent heat resistance and rigidity inherently possessed by the polypropylene resin, and has a beautiful surface with reduced post-shrinkage.

Therefore, the extruded polypropylene resin foam of the present invention can be suitably used for various cushioning materials, packaging materials, heat insulating materials, building materials and the like.

Claims (4)

[Claims] 1. A foaming composition obtained by melt-kneading a mixture obtained by mixing 0.2 to 3 parts by weight of a saturated higher fatty acid with 100 parts by weight of a polypropylene resin and a foaming agent. An extruded polypropylene resin foam having an apparent density of 10 to 100 kg / m ³ obtained by extruding the composition from a die to a low pressure region. 2. The radical polymerizable monomer selected from the group consisting of (A) a polypropylene resin, (B) an aromatic vinyl monomer and a conjugated unsaturated monomer, wherein the polypropylene resin is And (C) a modified polypropylene resin obtained by melt-kneading the radical polymerization initiator at a temperature at which the polypropylene resin (A) can be melted and at which the radical polymerization initiator (C) can be decomposed. An extruded polypropylene resin foam according to claim 1. 3. The extruded polypropylene resin foam according to claim 1, wherein the foaming agent is at least one selected from the group consisting of propane, normal butane and isobutane. 4. The extruded polypropylene resin foam according to claim 1, wherein the saturated higher fatty acid is stearic acid.