JPH09309966A - Foam made from modified polypropylene resin composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a foam having a low apparent density, a high closed cell content, and a wide cross section. SOLUTION: This foam is produced by melt mixing a modified polypropylene resin compsn. with a blowing agent and subjecting the resultant mixture to extrusion foaming. The resin compsn. is prepd. by melt mixing a polypropylene resin, an arom. vinyl monomer, and a free-radical polymn. initiator at a temp. capable of melting the resin and decomposing the initiator and has a melt viscosity of 1×10<3> Pa.sec or higher at 180 deg.C under a shear rate of 122sec<-1> .

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a foam made of a modified polypropylene resin composition. More specifically, the present invention relates to a foam made of a modified polypropylene resin composition having a low apparent density and a high closed cell rate.

[0002]

2. Description of the Related Art Foams made of thermoplastic resin are generally used for heat insulating materials, shock absorbing materials, core materials, food containers, etc. because they are lightweight and have good heat insulating properties and good shock absorbing properties against external stress. . Of these, foams made of polypropylene-based resin have good chemical resistance, impact resistance and heat resistance, and are therefore particularly suitable for use as cushioning materials.

[0003] However, polypropylene resins are
Since it is a crystalline resin, its melting viscosity rapidly decreases when it is heated to a temperature above its melting point. Therefore, when this resin is foamed, the temperature range suitable for foaming is very narrow. In addition, since the melt viscosity becomes low as described above, it is difficult to maintain the resin pressure at the die part at a sufficiently high value, especially when extrusion molding is performed using a die having a wide opening area. It is difficult to obtain a good foam.

Further, polypropylene resins have a low tensile strength in a molten state, and the foam film cannot easily withstand the growth of bubbles during foaming and is easily broken, which makes it difficult to produce a good foam. It was a factor.

As a method for solving such a problem,
A method is conceivable in which a polypropylene resin having a high degree of polymerization is used to maintain a high melt viscosity above the melting point. However, polypropylene resins having a high degree of polymerization cannot be stably extruded because of poor fluidity in the molten state. Further, even if this resin is used, it is difficult to suppress the bubble breaking phenomenon, and therefore a good foam cannot be obtained.

Further, Japanese Patent Publication No. 5-506875 discloses a method in which a polypropylene resin having a long-chain branched structure is used as a material, and this is extruded and foamed to form a foam. Since the resin has a low shear viscosity when melted, it is difficult to maintain a die pressure suitable for extrusion, especially when foaming using a die with a large opening area, and therefore the apparent density is low, It was difficult to obtain a foam having a high closed cell ratio and a wide cross-sectional area.

[0007]

DISCLOSURE OF THE INVENTION The object of the present invention is to foam a modified polypropylene resin composition by using a foaming agent so that the closed cell ratio is high, the apparent density is low, and the appearance is beautiful. The object is to provide a foam having a large body and also a large cross section.

[0008]

Means for Solving the Problems As a result of intensive studies to solve the above problems, the present inventors have found that a modified polypropylene resin composition having a specific melt viscosity obtained by a specific method and a foaming agent. The present invention has been completed by finding that a foam having a high closed cell ratio, a low apparent density, a beautiful appearance, and a foam having a wide cross-sectional area can be obtained by melt-kneading and then extruding Came to do.

That is, in the present invention, a polypropylene resin (hereinafter, the polypropylene resin before melt kneading is referred to as "raw material polypropylene resin"), an aromatic vinyl monomer and a radical polymerization initiator are used as raw materials. Measured under the condition that the polypropylene resin is melted and kneaded at a temperature at which the radical polymerization initiator can be decomposed and melted and kneaded at a temperature of 180 ° C. and a shear rate of 122 sec ^−1. The present invention relates to a foamed product of a modified polypropylene resin composition in which a modified polypropylene resin composition having a melt viscosity of 1 × 10 ³ Pa · sec or more and a foaming agent are melt-kneaded and then extruded to foam.

The apparent density of the foam is preferably 45 kg / m ³ or less.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The foam of the present invention is obtained by obtaining a specific modified polypropylene resin composition having a specific melt viscosity, and foaming the modified polypropylene resin composition using a foaming agent. available.

The modified polypropylene resin composition having the specific melt viscosity is obtained by melt-kneading the raw material polypropylene resin, the aromatic vinyl monomer and the radical polymerization initiator under specific temperature conditions. To be

It is not clear why the specific modified polypropylene resin composition obtained by such a method has good foamability, but it is generated from the radical polymerization initiator during the melt kneading. One of the causes is that the radicals cause the hydrogen abstraction reaction of the polymer molecules of the raw material polypropylene resin, followed by the main chain cleavage reaction of the polymer molecules and the aromatic vinyl monomer graft reaction. Can be guessed. At the same time, a slight cross-linking reaction between polymer molecules of the raw material polypropylene resin is considered to occur, and it can be presumed that this is also one of the causes.

By such a reaction, a modified polypropylene resin composition having a desired melt viscosity can be obtained under specific conditions. Since the modified polypropylene resin composition has a suitable melt viscosity, a die suitable for extrusion foam molding can be easily prepared even when the resin composition is extrusion foam-molded using a die having a large opening area. Can be held at pressure.

The modified polypropylene resin composition has a high melt viscosity and good fluidity when melted. It can be presumed that the reason why the melt viscosity becomes high is that the degree of entanglement of the polymer molecules in the raw polypropylene resin is increased due to the slight crosslinking reaction between the polymer molecules. It can be presumed that the reason why the fluidity becomes good is due to the presence of a low-molecular weight component generated by the cleavage reaction of the main chain of the polymer molecule during melt-kneading.

[0016] Such a modified polypropylene resin composition has a higher strength of a foam film at the time of foaming as compared with a conventional polypropylene resin, and is less likely to break even when foamed at a high expansion ratio. Therefore, the modified polypropylene resin composition and the foaming agent are melt-kneaded and then extruded to obtain a foam having a low apparent density and a high closed cell rate.

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 include propylene homopolymers, which are preferred because they have high rigidity and are inexpensive, and block copolymers of propylene and other monomers are preferred because of high rigidity and high impact resistance. Polymers 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, other monomer copolymerizable with propylene is selected from the group consisting of ethylene, α-olefin, cyclic olefin, diene monomer and vinyl monomer. Chosen 1
Species or two or more 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.

When the melt flow index of the raw material polypropylene resin was measured at 230 ° C.,
It is preferably within the range of 01 to 8 g / 10 minutes,
More preferably, it is within the range of 0.05 to 4 g / 10 minutes. The melt flow index is 0.01 g /
When a raw material polypropylene resin lower than 10 minutes is used, the resulting modified polypropylene resin composition tends to have insufficient fluidity, while when a raw material polypropylene resin higher than 8 g / 10 minutes is used, The melt viscosity of the modified polypropylene resin composition obtained tends not to be sufficiently high.

Further, as the raw material polypropylene resin,
It is also possible to use a mixture of two or more kinds of resins having different melt flow indexes in the form of pellets or powder, or a mixture obtained by melt-kneading.

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

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

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

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

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

The amount of the aromatic vinyl monomer used is 3 to 5 relative to 100 parts by weight of the raw polypropylene resin.
0 parts by weight, particularly 3 to 30 parts by weight, sufficiently improves the melt viscosity characteristics of the raw material polypropylene resin, and has suitable heat resistance, chemical resistance, mechanical properties and the like of the raw material polypropylene resin. Is preferred in that it does not impair

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

As such a radical polymerization initiator,
Generally, peroxides, azo compounds and the like can be mentioned, and specifically, ketone peroxides such as methyl ethyl ketone peroxide and methyl acetoacetate peroxide; 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-
Peroxyketals such as bis (t-butylperoxy) butane; permethane hydroperoxide, 1,
1,3,3-tetramethylbutyl hydroperoxide, diisopropylbenzene hydroperoxide,
Hydroperoxides such as cumene hydroperoxide; dicumyl peroxide, 2,5-dimethyl-
2,5-di (t-butylperoxy) hexane, α, α
'-Bis (t-butylperoxy-m-isopropyl)
Benzene, t-butyl cumyl peroxide, di-t-
Dialkyl peroxides such as butyl peroxide and 2,5-dimethyl-2,5-di (t-butylperoxy) hexyne-3; diacyl peroxides such as benzoyl peroxide; di (3-methyl-3-methoxybutyl) ) Peroxydicarbonates such as peroxydicarbonate and di-2-methoxybutylperoxydicarbonate; t-butylperoxyoctate, t-butylperoxyisobutyrate, t-butylperoxylaurate, t- Butylperoxy-3,5,5-trimethylhexanoate, t-butylperoxyisopropyl carbonate, 2,5-dimethyl-2,5-di (benzoylperoxy) hexane, t-butylperoxyacetate, t- Butyl peroxybenzoate, di-
One or more organic peroxides such as peroxyesters such as t-butyl peroxyisophthalate may be used. Of these, those having a particularly high hydrogen abstraction ability are preferable, and examples of such a radical polymerization initiator include 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 amount of the radical polymerization initiator used may be appropriately adjusted according to the amount of the aromatic vinyl monomer used, but the melt viscosity of the obtained modified polypropylene resin composition is sufficiently improved, and From the standpoint of economy, it is usually 0.
It is preferably in the range of 01 to 4 parts by weight, and 0.1
More preferably, it is within the range of 2 parts by weight.

When the amount of the radical polymerization initiator used is less than the above range, the modification effect tends not to be sufficiently obtained, while when it is more than the above range, foaming having a suitable shape and appearance is obtained. There is a tendency to get stuck.

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

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

In the present invention, the temperature at which the raw material polypropylene resin can be melted means that the crystal part of the resin is melted,
It is a temperature range showing fluidity, and specifically, a temperature range above the melting point of the resin measured by DSC. Further, in the present invention, the temperature at which the radical polymerization initiator can be decomposed means the temperature at which substantially most of the radical polymerization initiator is decomposed within the reaction time described below. Usually, when the one-minute half-life temperature of the radical polymerization initiator is T,
In the temperature range of T-20 ° C to T + 50 ° C, the radical polymerization initiator can be decomposed well. In the present invention, the temperature at which the raw material polypropylene resin can be dissolved and the radical polymerization initiator can be decomposed is usually 13
It is in the range of 0 to 400 ° C. Therefore, the melt-kneading temperature for obtaining the modified polypropylene resin composition is preferably in the range of 130 to 400 ° C.,
More preferably, it is in the range of 160 to 400 ° C. Under such conditions, the raw material polypropylene resin can be sufficiently melted and is not easily decomposed by heat. Further, the time for the reaction is preferably 30 seconds to 60 minutes, and more preferably 1 to 30 minutes.

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

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

1 of the modified polypropylene resin composition
In order to keep the pressure in the die of the resin composition at the time of foaming at a sufficiently high value, the melt viscosity measured under the conditions of a shear rate of 122 sec ⁻¹ at 80 ° C. is 1 × 10 ³ Pa.
・ It must be more than sec. Further, from the viewpoint that a foam having a lower apparent density can be obtained,
It is preferably in the range of 1 × 10 ³ to 1 × 10 ⁴ Pa · sec.

The melt viscosity measured under the above conditions is 1 × 1.
A foam having a low apparent density and a high closed cell ratio can also be obtained by melt-kneading a modified polypropylene resin composition having a pressure of less than 0 ³ Pa · sec and a foaming agent and then extruding the mixture. When a foam is manufactured using such a resin composition, the operating conditions are strict and the foaming is stable because the range of setting conditions such as die temperature and discharge rate suitable for foaming the resin composition is narrow. Is insufficient in that it is difficult to carry out.

By foaming the modified polypropylene resin composition of the present invention thus obtained, the desired foam is obtained.

As an example of the method for foaming the modified polypropylene resin composition, (1) the modified polypropylene resin composition and the foaming agent are melt-kneaded in a melt extruder and then extruded by a melt extruder. Examples thereof include a method of obtaining a foam, and (2) a method of obtaining a foam by extruding with a melt extruder after adding or press-fitting a foaming agent to a modified polypropylene resin composition in a molten state. The method is not limited to.

As the melt extruder that can be used in each of the above-mentioned methods, a single-screw, twin-screw or multi-screw extruder, and a tandem type extruder in which two or more of these extruders are connected in series can be used. Any thing can be used. An onrator may be used to uniformly knead the modified polypropylene resin composition and the foaming agent, and an accumulator may be used to adjust the extrusion rate.

In the case of the above method (1), examples of the foaming agent include a pyrolytic foaming agent, and among them, a preferable pyrolytic foaming agent is, for example, N, N'-dinitrosopentamethylenetetramine, N, N'-dimethyl-
Nitroso-based foaming agents such as N, N'-dinitrosoterephthalamide; azo-based foaming agents such as azodicarbonamide and barium azodicarboxylate; sulfo such as p, p'-oxybisbenzenesulfonyl hydrazide and p-toluenesulfonyl semicarbazide Hydrazide type foaming agents; one or more kinds of trihydrazinotriazine and the like.

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

Further, in order to control the bubble diameter of the foamed body to an appropriate size, sodium bicarbonate may be added, if necessary.
A foam nucleating agent such as citric acid or talc may be used in combination. The 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.

Further, in the case of the above method (1), for example, the modified polypropylene resin composition and the thermal decomposition type foaming agent are both supplied to a melt extruder and foamed while being melt-kneaded at an appropriate temperature. A gas can be generated by thermally decomposing the agent, 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 and the kneading conditions to be used, and vary depending on the type of the resin. Is usually

In the case of the above method (2), the modified polypropylene resin composition and the decomposition type foaming agent are rolled,
A kneader such as a co-kneader, a Banbury mixer or a Brabender; a biaxial surface renewing machine, a horizontal agitator such as a biaxial multi-circular slope device; a vertical agitator such as a double helical ribbon agitator and the like, and then a melt extruder. A method of extruding and foaming may be used.

In the case of the above-mentioned method (2), examples of the foaming agent include volatile foaming agents. Among them, preferable volatile foaming agents include aliphatic compounds such as propane, butane, pentane, hexane and heptane. Hydrocarbons; cycloaliphatic hydrocarbons such as cyclobutane, cyclopentane, cyclohexane; chlorodifluoromethane, difluoromethane, trifluoromethane, trichlorofluoromethane, dichloromethane, dichlorofluoromethane, dichlorodifluoromethane, trichlorofluoromethane, chloromethane, Chloroethane, dichlorotrifluoroethane, dichlorofluoroethane, chlorodifluoroethane, dichloropentafluoroethane, tetrafluoroethane, difluoroethane, pentafluoroethane, trifluoroethane, diqua Halohydrocarbons such as rotetrafluoroethane, trichlorotrifluoroethane, tetrachlorodifluoroethane, chloropentafluoroethane, perfluorocyclobutane; inorganic gases such as carbon dioxide, nitrogen, air; one or two kinds such as water The above is mentioned.

The amount of the above-mentioned foaming agent used (kneading amount) 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 foam nucleating agent used, if necessary, is usually preferably 0.01 to 1 part by weight based on 100 parts by weight of the modified polypropylene resin composition.

In the case of the above method (2), for example, the modified polypropylene resin composition is melted in an extruder, and the volatile foaming agent is pressed into the extruder and melted while maintaining a high pressure. A kneaded product of the modified polypropylene resin composition in the state 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., although it depends on the type of resin.
The melt-kneading time is usually 1 to 120 minutes.

The shape of the die used to obtain the foam of the present invention may be appropriately selected depending on the shape of the desired foam. That is, for example, a die with a circular opening is used to obtain a rod-shaped foam, and a die with a rectangular opening is used to obtain a plate-shaped foam.

The foam of the present invention can be usually molded into an apparent density of about 15 to 180 kg / m ³ by appropriately selecting the manufacturing conditions, but it is suitable for applications such as cushioning packaging materials and building materials. , apparent density 45 kg / m ³ or less, preferably is suitably used with a low apparent density 15~45kg / m ^3.

Further, as described above, a foam having a closed cell ratio of 60% or more is preferable, and a foam having a closed cell ratio of 70% or more is more preferable for use in applications such as cushioning packaging materials and building materials. According to the present invention, a foam having such a closed cell ratio can be easily obtained.

[0055]

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 Propylene homopolymer (Mitsui Petrochemical Co., Ltd., Hypol B200P, melt flow index at 230 ° C., load 2.16 kg, 0.5 g / 10 min) 100
Parts by weight, 10 parts by weight of styrene monomer, and α, α'-bis (t-butylperoxy-m) as a radical polymerization initiator.
-Isopropyl) benzene (Nippon Oil & Fats Co., Ltd., Perbutyl P, 1 minute half-life temperature 175 ° C) 1 part by weight and stabilizer IRGANOX B225 (product name, Nippon Ciba-Geigy Co., Ltd.) 0.2 parts by weight 0.1 parts by weight of calcium stearate is melt-kneaded using a twin-screw extruder (LABOTEX) manufactured by Japan Steel Works, Ltd., and melt-extruded to give a rod-shaped modified polypropylene resin composition having a diameter of 4 mm. A molded product was obtained. The molded product of the rod-shaped modified polypropylene resin composition was chopped to a thickness of 3 mm to obtain pellets of the modified polypropylene resin composition.

The twin-screw extruder was of the same-direction twin-screw type, and had a cylinder hole diameter of 32 mmφ and a maximum screw effective length (L / D) of 25.5. Set the temperature of the cylinder of this twin-screw extruder to 200 ° C,
The feed temperature was set to 180 ° C. and heated, and the rotation speed of the screw was set to 100 rpm for each shaft.

The melt viscosity of the modified polypropylene resin composition (melt viscosity measured at 180 ° C. under a shear rate of 122 sec ⁻¹ ) was measured by the following method. Table 1 shows the results.

Method of measuring melt viscosity: According to a Capillograph manufactured by Toyo Seiki Co., Ltd., using a die having an orifice of 1 mmφ × 10 mm, the shear rate was 180 ° C.
It is measured under the condition of 122 sec ^-1 .

100 parts by weight of the pellets of the modified polypropylene resin composition, 0.05 parts by weight of blended oil (Koshigaya Chemical Co., Ltd., Super Ease), and sodium bicarbonate-citric acid (Eiwa) as a foam nucleating agent. 0.1 part by weight of Cerbon SC / K manufactured by Kasei Co., Ltd. was mixed for 15 minutes using a ribbon blender. A tandem type extruder (the first stage extruder has a cylinder diameter of 40 mm
φ, the second stage extruder cylinder diameter is 50 mmφ, and melted at 230 ° C. in the first stage extruder, and then the isorich butane gas (normal butane / isobutane mixing ratio by weight ratio is 15 as a foaming agent). / 85) to 100 parts by weight of the modified polypropylene resin composition and kneaded by kneading, and this is cooled in the second stage extruder so that the temperature of the resin composition is 150 ° C., and 6 mmφ × 25 mm
It was extruded from a die having an orifice of 2 to obtain a round rod-shaped foam.

The apparent density, diameter and closed cell ratio of the obtained round rod-shaped foam were measured by the following methods. The results are shown in Table 2.

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

Straight diameter: Measured with a caliper.

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

Example 2 Pellets of a modified polypropylene resin composition were obtained in the same manner as in Example 1 except that the amount of radical polymerization initiator used was as shown in Table 1.

The melt viscosity of this modified polypropylene resin composition (melt viscosity measured under the condition of a shear rate of 122 sec ⁻¹ at 180 ° C.) was measured by the same method as in Example 1. Table 1 shows the results.

Next, a round rod-shaped foam was produced in the same manner as in Example 1 except that this modified polypropylene was used.

The apparent density, diameter and closed cell ratio of this round rod-shaped foam were evaluated in the same manner as in Example 1. The results are shown in Table 2.

Comparative Example 1 Pellets of a modified polypropylene resin composition were obtained in the same manner as in Example 1 except that the amounts of styrene monomer and radical polymerization initiator used were as shown in Table 1.

The melt viscosity of this modified polypropylene resin composition (melt viscosity measured under the condition of a shear rate of 122 sec ⁻¹ at 180 ° C.) was measured by the same method as in Example 1. Table 1 shows the results.

Next, a round rod-shaped foam was produced in the same manner as in Example 1 except that this modified polypropylene was used.

The apparent density, diameter and closed cell ratio of this round rod-shaped foam were evaluated in the same manner as in Example 1. The results are shown in Table 2.

Comparative Example 2 Propylene homopolymer (Mitsui Petrochemical Co., Ltd., Hypol B200P) was not modified, but the propylene homopolymer was used instead of using the pellets of the modified polypropylene resin composition. Then, a round rod-shaped foam was produced according to the method for manufacturing the round rod-shaped foam of Example 1. The melt viscosity of the propylene homopolymer used was measured by the same method as in Example 1. Table 1 shows the results.

The apparent density, diameter and closed cell ratio of this round rod-shaped foam were evaluated in the same manner as in Example 1. The results are shown in Table 2.

Comparative Example 3 A polypropylene resin having a long-chain branched structure (PF-8, manufactured by Himont Co., Ltd.) was used in place of the propylene homopolymer (manufactured by Mitsui Petrochemical Co., Ltd., Hypol B200P).
A round rod-shaped foam was produced in the same manner as in Comparative Example 2 except that 14) was used. The melt viscosity of the polypropylene resin used was measured in the same manner as in Example 1. Table 1 shows the results.

The apparent density, diameter and closed cell ratio of this round rod-shaped foam were evaluated in the same manner as in Example 1. The results are shown in Table 2.

[0077]

[Table 1]

[0078]

[Table 2]

From the above results, the melt viscosity measured at 180 ° C. and the shear rate of 122 sec ⁻¹ was 1 × 1.
By foaming the modified polypropylene resin composition having a pressure of 0 ³ Pa · sec or more with a foaming agent, a foam having a low apparent density, a high closed cell rate and a wide cross-sectional area can be obtained. I understand. In addition, even if a polypropylene resin having a long-chain branched structure or a commercially available polypropylene resin having a high melt viscosity is foamed with a foaming agent, the apparent density is low, the closed cell ratio is high, and the foam has a wide cross-sectional area. I know I can't.

[0080]

According to the present invention, it is possible to provide a foam having a low apparent density, a high closed cell ratio and a wide cross-sectional area.

Claims (2)

[Claims] 1. A polypropylene resin, an aromatic vinyl monomer, and a radical polymerization initiator at a temperature at which the polypropylene resin can be melted and at a temperature at which the radical polymerization initiator can decompose. 18 obtained by melt-kneading
A modified polypropylene resin composition having a melt viscosity of 1 × 10 ³ Pa · sec or more measured at 0 ° C. and a shear rate of 122 sec ⁻¹ is melt-kneaded with a foaming agent and then extruded to foam. A foam made of a modified polypropylene resin composition. 2. The foam according to claim 1, which has an apparent density of 45 kg / m ³ or less.