JPH09157431A - Foam comprising modified polypropylene-based resin and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the subject foam useful as a cushioning material, etc., low in density, high in closed cell ratio, thick and high in rigidity, by foaming a specific modified polypropylene resin. SOLUTION: (A) A polypropylene-based resin is mixed in a melting state with (B) a compound containing a reactive unsaturated double bond and (C) a radical polymerization initiator and further blended with (D) a blowing agent at a high temperature under high pressure and extruded to give the objective foam having 5-30% gel fraction of a resin part. (i) An aromatic monovinyl monomer (e.g. styrene) and (ii) a compound containing two or more unsaturated double bonds in the same molecule (e.g. divinylbenzene) are used as the component B and the component D is preferably a physical type blowing agent (e.g. butadiene gas).

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a foam and a method for producing the foam. More specifically, the present invention relates to a foam made of a polypropylene resin, having a high closed cell ratio, a low density, and a beautiful appearance, and a method for producing the foam.

[0002]

2. Description of the Related Art A foam made of a thermoplastic resin is generally used for a heat insulating material, a cushioning material, a core material, a food container, etc. because it is lightweight and has a good heat insulating property and a good shock absorbing property against external stress. ing. Of these, foams made of polypropylene-based resin have good chemical resistance, impact resistance and heat resistance, and are therefore particularly suitable for use as cushioning materials.

[0003] However, polypropylene resins are
Since it is a crystalline resin, the viscosity and tension at the time of melting are low, and when the resin is foamed, the strength of the cell wall is not sufficiently maintained at the time of foaming. 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 polypropylene-based resin, for example, Japanese Patent Publication No. 40420/1985 discloses a method of crosslinking a polymer molecule by adding a crosslinking aid to the polypropylene-based resin. However, this method has a problem in continuous productivity because it requires a crosslinking step and a foaming step, and it is difficult to obtain a thick foam having a high closed cell ratio, a low density, and the like.

Further, Japanese Patent Publication No. 48-4859 discloses that
Polyethylene, peroxide type radical polymerization initiator,
Knead the styrene monomer and blowing agent in the extruder,
A method for producing a foam by extruding while reacting is disclosed, but a polypropylene resin is not disclosed at all.

[0006] Japanese Patent Publication No. 45-41098 discloses a mixture of a polyolefin resin, a compound having two or more unsaturated double bonds in the molecule, and a radically polymerizable vinyl compound. Disclosed is a method for producing the foam.

However, this publication does not describe the gel fraction of the polyolefin resin.
Further, this publication only discloses a method using a thermal decomposition type foaming agent, and does not disclose a method for producing a foam by using a so-called physical type foaming agent such as a volatile type foaming agent. In addition, according to this method, a compound having two or more unsaturated double bonds in the molecule and / or a radically polymerizable vinyl compound is grafted to the polyolefin molecule by heating and is crosslinked by heating. Since the decomposable foaming agent is decomposed to foam, it is difficult to control the reaction because strict temperature control is required, productivity is poor, and it is not economically preferable.

Further, Japanese Patent Laid-Open No. 53-138470 discloses a technique relating to a method for producing a polypropylene resin foam containing a thermal xylene insoluble matter obtained from a mixture of a polypropylene resin and 1,2-polybutadiene. Has been done.

However, this publication merely discloses a technique based on the knowledge obtained by mixing 1,2-polybutadiene as another thermoplastic resin with a polypropylene-based resin, and also has a purpose. There is no disclosure of the amount of hot xylene insolubles required to produce such foams.

In Japanese Patent Publication No. 34573/1989, a polyolefin-based polymer and an inter-impregnated polymer having a gel concentration of 5 to 50% obtained by impregnating a styrene-based monomer into a polyolefin-based polymer are disclosed. A method of making an extruded foam from a mixture is disclosed.

However, according to this method, it takes a long time to impregnate the polyolefin polymer with the styrene monomer, which causes a problem in productivity. Further, the resin which is the inter-impregnation polymer is used as a so-called modifier for improving the foamability of the polyolefin-based resin, and the resin which is the inter-impregnation polymer in the polyolefin-based resin is uniformly dispersed. There is also a problem that mixing and dispersion are difficult and the physical properties of the foam produced by this method are not uniform, and it is difficult to obtain the foam intended by the present invention by this method.

[0012] Further, Japanese Patent Publication No. 5-506875 discloses a method of forming a foamed sheet using polypropylene having a long-chain branched structure as a material, but these use a special resin. Therefore, the raw materials are expensive, and the versatility is poor.

As described above, at present, there has not been found a method for improving the foamability of a polypropylene resin and producing a low density foam having a high closed cell rate using this resin.

[0014]

SUMMARY OF THE INVENTION An object of the present invention is to provide a foam having a high closed cell ratio, a low density, and a beautiful appearance, which is made of a polypropylene resin having an improved foaming property.

Further, an object of the present invention is to have a high closed cell ratio made of a polypropylene resin having an improved foamability,
It is to provide a foam having a low density, a beautiful appearance, high rigidity, and a thick wall.

[0016]

Means for Solving the Problems As a result of intensive studies to solve the above-mentioned problems, the present inventors melted a polypropylene resin, a compound having a reactive unsaturated double bond and a radical polymerization initiator. By kneading and obtaining a resin having a gel fraction within the range of 5 to 30% and foaming the resin by an appropriate method, a foam having a high closed cell ratio, a low density and a beautiful appearance, particularly meat The inventors have found that a thick foam can be obtained, and completed the present invention. The gel fraction of the resin portion of the foam thus produced is in the range of 5 to 30%.

That is, according to the present invention, a polypropylene resin, a compound having a reactive unsaturated double bond and a radical polymerization initiator are melt-kneaded, and a foaming agent is melt-kneaded under high temperature and high pressure and then extruded. The present invention relates to a method for producing a foam having a gel fraction of the resin portion within the range of 5 to 30%.

In the present invention, a polypropylene resin, an aromatic monovinyl monomer, a compound having two or more unsaturated double bonds in the same molecule, and a radical polymerization initiator are melt-kneaded, and a blowing agent is further added. The gel fraction of the resin part obtained by extruding after melt-kneading under high temperature and high pressure is 5
To a method of making a foam within the range of -30%.

The present invention also relates to a method for producing the foam, wherein the foaming agent is a physical type foaming agent.

The present invention also relates to a foam obtained by each of the above production methods.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION Foaming of a resin having a gel fraction within a specific range obtained by melt-kneading a polypropylene resin, a compound having a reactive unsaturated double bond and a radical polymerization initiator in the present invention Although the reason why the property is extremely suitable is not clear, such a resin can be obtained by crosslinking a polymer molecule of a polypropylene resin with a specific compound and introducing a specific graft chain. However, the object of the present invention can be achieved only by modifying a polymer molecule of a polypropylene resin by using a cross-linking aid and / or modifying a polymer chain of a polypropylene resin by introducing a graft chain. It is not possible to obtain a polypropylene resin that can be used.

By foaming such a resin obtained in the production method of the present invention by an appropriate method, it has a high closed cell rate, a low density, an excellent appearance, a high rigidity and a thick foam. You can get your body.

As the polypropylene resin before melt kneading which can be used in the present invention (hereinafter sometimes referred to as polypropylene resin before modification), a homopolymer of propylene, a block of propylene and another monomer is used. A crystalline polymer such as a copolymer or a random copolymer of propylene and another monomer may be mentioned, and the polypropylene homopolymer is preferable from the viewpoint of high rigidity and low cost, and rigidity and resistance A block copolymer of the above-mentioned propylene and another monomer is preferable from the viewpoint of high impact resistance. When the polypropylene resin before modification is a block copolymer of propylene and other monomers or a random copolymer of propylene and other monomers, the high crystallinity characteristic of polypropylene resins From the viewpoint of maintaining high rigidity and good chemical resistance, the propylene monomer component contained is preferably 75% by weight or more, and more preferably 90% by weight or more of the whole.

In the polypropylene resin before modification, other monomers copolymerizable with propylene include:
One or more monomers selected from the group consisting of ethylene, α-olefin, cyclic olefin, diene monomer and vinyl monomer. Also,
This monomer is preferably an ethylene, α-olefin or diene-based monomer because it is easily copolymerized with propylene and is inexpensive.

Examples of the above-mentioned α-olefin copolymerizable with propylene include butene-1, isobutene, pentene-1,3-methyl-butene-1, hexene-1,3-.
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 polymer of the polypropylene resin before modification is preferably in the range of 50,000 to 2,000,000 because it is easily available, and is inexpensive. More preferably, it is in the range of 100,000 to 1,000,000.

The compound having a reactive unsaturated double bond that can be used in the present invention includes an aromatic monovinyl monomer or a compound having two or more unsaturated double bonds in the same molecule.

Examples of the aromatic monovinyl monomer include styrene; o-methylstyrene, m-methylstyrene, p-methylstyrene, α-methylstyrene, β-
Methylstyrene such as methylstyrene, dimethylstyrene and trimethylstyrene; α-chlorostyrene, β-chlorostyrene, o-chlorostyrene, m-chlorostyrene, p-chlorostyrene, dichlorostyrene, trichlorostyrene and other chlorostyrene; 4- Chloromethylstyrene such as chloro-α-methylstyrene; o-bromostyrene, m-bromostyrene, p-bromostyrene,
Bromostyrene such as dibromostyrene and tribromostyrene; fluorostyrene such as o-fluorostyrene, m-fluorostyrene, p-fluorostyrene, difluorostyrene and trifluorostyrene; o-nitrostyrene, m-nitrostyrene, p-nitro styrene,
Examples thereof include nitrostyrenes such as dinitrostyrene and trinitrostyrene; and one or more kinds of vinylphenol such as o-hydroxystyrene, m-hydroxystyrene, p-hydroxystyrene, dihydroxystyrene and trihydroxystyrene.

Of these, methylstyrene such as styrene, α-methylstyrene, p-methylstyrene and the like is preferable from the viewpoint of particularly increasing the closed cell ratio and the expansion ratio of the desired foam.

Examples of the compound having two or more unsaturated double bonds in the same molecule include divinylbenzene such as o-divinylbenzene, m-divinylbenzene and p-divinylbenzene; p-quinonedioxime, p , P-
Quinonedioxime compounds such as dibenzoylquinonedioxime; lauryl methacrylate, ethylene glycol acrylate, triethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate, polyethylene glycol dimethacrylate, trimethylolpropene trimethacrylate, methylolmeth Methacrylate compounds such as acrylates; Allyl compounds such as diaryl fumarate, diaryl phthalate, tetraaryloxyethane, triaryl cyanurate; maleimide, phenylmaleimide,
Maleimide compounds such as N, N'-m-phenylene bismaleimide; maleic anhydride, itaconic acid, 1,2-
One or more of polybutadiene can be used.

The amount of the compound having a reactive unsaturated double bond added is 100% by weight of the polypropylene resin 100 before modification.
0.01 to 50 parts by weight, more preferably 0.
It is preferably from 01 to 40 parts by weight, particularly preferably from 0.01 to 20 parts by weight. When the addition amount of the compound having the reactive unsaturated double bond exceeds the above range, the gel fraction of the resin portion of the target foam tends to exceed 30%, while less than the above range. In this case, the gel fraction of the resin portion of the desired foam tends to be less than 5%.

As the compound having a reactive unsaturated double bond, the aromatic monovinyl monomer and a compound having two or more unsaturated double bonds in the same molecule are used in combination. It is preferable in that the desired foam has a high closed cell rate, a beautiful appearance, high rigidity, and a thick foam can be easily obtained.

When the aromatic monovinyl monomer is used, another vinyl monomer copolymerizable with the aromatic monovinyl monomer may be used in combination.

Other vinyl monomers copolymerizable with the aromatic monovinyl monomer include, for example, vinyl chloride,
Vinylidene chloride, acrylonitrile, methacrylonitrile, acrylamide, methacrylamide, vinyl acetate,
Acrylic acid, methacrylic acid, maleic acid, maleic anhydride, fumaric acid, fumaric acid anhydride, acrylic acid metal salts, methacrylic acid metal salts; methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, acrylic Acrylic acid esters such as stearyl acid and glycyl acrylate; and methacrylic acid esters such as methyl methacrylate, ethyl methacrylate, butyl methacrylate, 2-ethylhexyl methacrylate, stearyl methacrylate, and glycyl methacrylate.

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

Examples of the radical polymerization initiator include peroxides and azo compounds. In the present invention, compounds such as radical polymerization initiators having a 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-
Organic peroxides such as peroxyesters such as butyl peroxyisophthalate are exemplified. Of these,
Particularly, those having high hydrogen abstracting ability are preferable. For example, 1,1-bis (t-butylperoxy) -3,3,5-
Such as trimethylcyclohexane, 1,1-bis (t-butylperoxy) cyclohexane, n-butyl-4,4-bis (t-butylperoxy) valerate, and 2,2-bis (t-butylperoxy) butane; Peroxyketal; 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; t-butylperoxy octate, t- Butyl peroxyisobutyrate, t-butyl peroxylaurate, t-butyl peroxy-3,
5,5-trimethylhexanoate, t-butylperoxyisopropyl carbonate, 2,5-dimethyl-
One or more kinds of peroxyesters such as 2,5-di (benzoylperoxy) hexane, t-butylperoxyacetate, t-butylperoxybenzoate, and di-t-butylperoxyisophthalate. To be

The amount of the radical polymerization initiator added is 0.1 to 100 parts by weight of the polypropylene resin before modification in order to control the gel fraction to 5 to 30%.
20 parts by weight, more preferably 0.1 to 10 parts by weight, especially 0.1.
It is preferably in the range of 1 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.

If necessary, a resin or rubber other than polystyrene resin may be added to the polypropylene resin before modification within a range not impairing the effects of the present invention.
Examples of the resin or rubber other than the polystyrene-based resin include polyethylene; polyα-olefins such as polybutene-1, polyisobutene, polypentene-1, and polymethylpentene-1; ethylene / propylene having a propylene content of less than 75% by weight. Ethylene or α-olefin / α-olefin copolymers such as copolymers, ethylene / butene-1 copolymers, propylene / butene-1 copolymers having a propylene content of less than 75% by weight; propylene content of 75 Less than wt% ethylene / propylene / 5
Ethylene or α-olefin / α-olefin / diene-based monomer copolymers such as ethylidene-2-norbornene copolymer; ethylene / vinyl chloride copolymer, ethylene / vinylidene chloride copolymer, ethylene / acrylonitrile copolymer Polymer, ethylene / methacrylonitrile copolymer, ethylene / vinyl acetate copolymer, ethylene / acrylamide copolymer, ethylene / methacrylamide copolymer, ethylene / acrylic 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 /
Ethylene or α-olefin / vinyl monomer copolymers such as acrylic acid metal salt copolymers and ethylene / methacrylic acid metal salt copolymers; polydiene-based copolymers such as polybutadiene and polyisoprene; polyvinyl chloride, poly Vinyl polymers such as vinylidene chloride, polyacrylonitrile, polyvinyl acetate, poly (ethyl acrylate), poly (butyl acrylate), poly (methyl methacrylate); vinyl polymers such as vinyl chloride / acrylonitrile copolymers and vinyl chloride / vinyl acetate copolymers. Examples thereof include copolymers.

The amount of these other resins or rubbers added to the polypropylene resin before modification varies depending on the type of these other resins or the type of rubber, and is within the range not impairing the effects of the present invention as described above. Although it is sufficient, it is usually preferably about 25% by weight or less.

Further, if necessary, the polypropylene resin before modification may include an antioxidant, a metal deactivator, a phosphorus processing stabilizer, an ultraviolet absorber, an ultraviolet stabilizer, an optical brightener and a metal. Stabilizers such as soap and antacid adsorbents, or additives such as crosslinking agents, chain transfer agents, nucleating agents, lubricants, plasticizers, fillers, reinforcing materials, pigments, dyes, flame retardants, antistatic agents, etc. You may add in the range which does not impair the effect of.

These unmodified 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. Not something.

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 polypropylene resin before modification, It may be added when melt-kneading the polypropylene resin before modification,
Further, it may be added by an appropriate method after melt-kneading.

In the present invention, it is necessary to set the gel fraction of the resin portion of the desired foam within the range of 5 to 30%. That is, it is necessary to melt-knead a polypropylene resin, a compound having a reactive unsaturated double bond and a radical polymerization initiator to obtain a resin having a gel fraction within the range of 5 to 30%.

When the gel fraction is less than 5%, it becomes difficult to produce a rigid and thick foam, while when the gel fraction is more than 30%, the degree of crosslinking is high. If it becomes too high, the moldability of the resin will deteriorate, and it will be difficult to manufacture a foam having good chemical resistance and impact resistance. The reason why the desired foam can be obtained when the gel fraction is within the above range is not clear as described above, but the polypropylene-based resin and the reactive unsaturated double bond are not clear. And a compound having a compound having a reactive unsaturated double bond in the polymer molecule of the polypropylene resin, by reacting by the action of a radical polymerization initiator to appropriately crosslink between polymer molecules of the polypropylene resin By introducing a grafted molecular chain and increasing the degree of entanglement of polymer molecules to an appropriate degree, it has the effect of suppressing the viscosity of the resin from becoming too low during melting. It is presumed that even when it is molded into a body, it prevents the cell wall from breaking and further imparts rigidity to the produced foam.

That is, when the gel fraction is less than 5%, the rupture of the cell wall at the time of foaming cannot be sufficiently prevented, making it difficult to increase the wall thickness, and the rigidity of the foam is insufficient. On the other hand, when the gel fraction exceeds 30%, the fluidity of the resin is lowered, making extrusion molding by a usual extruder difficult, and further, the resin viscosity and the tension are too high, and the formation of bubbles and It hinders growth and makes thickening difficult.

In the present invention, the desired foam is
(1) A polypropylene resin, a compound having a reactive unsaturated double bond and a radical polymerization initiator are melt-kneaded,
Once a modified polypropylene resin having a specific gel fraction is obtained, then in a separate step, a foamed product in which the resin portion has a specific gel fraction is produced by a method of extruding and foaming this modified polypropylene resin. Alternatively, (2) the polypropylene resin, the compound having a reactive unsaturated double bond and the radical polymerization initiator are melt-kneaded, and further, the foaming agent is continuously melt-kneaded and extruded. A foam may be produced in which the resin portion has a specific gel fraction by the production method.

In the case of the above-mentioned production method (1), a polypropylene resin before modification, a compound having a reactive unsaturated double bond, a radical polymerization initiator and other additive materials which are optionally added are mixed. The method and the melt-kneading method are not particularly limited, and for example, a polypropylene resin, a compound having a reactive unsaturated double bond, a radical polymerization initiator, and other additive materials added as necessary are mixed. It may be melt-kneaded later, or after melt-kneading the polypropylene-based resin, a compound having a reactive unsaturated double bond, a radical polymerization initiator and other additive materials added as necessary, at the same time, Or separately, all at once or mixed and mixed,
You may melt-knead.

The heating temperature at the time of melt-kneading varies depending on the type of resin, but it is usually preferably 130 to 400 ° C. from the viewpoint that the polypropylene resin is sufficiently melted and is not easily thermally decomposed. . The melt-kneading time (time after mixing the radical polymerization initiator and the aromatic vinyl monomer) is usually 1 to 60 minutes.

As an apparatus which can be used for the above-mentioned melt-kneading,
Kneaders such as rolls, co-kneaders, Banbury mixers, brabenders, single-screw extruders, twin-screw extruders; horizontal agitators such as twin-screw surface renewers and twin-screw multi-disc devices; vertical agitators such as double helical ribbon agitators An apparatus that can heat a polymer material to an appropriate temperature and knead while applying an appropriate shear stress can be used. Of these, a single-screw extruder or a twin-screw extruder is particularly preferable from the viewpoint of productivity. Also,
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 in the production method (1) can be produced. By extruding and foaming such a modified polypropylene resin, the foamed product of the present invention can be obtained.

As an example of the extrusion foaming method in the above-mentioned production method (1), there is a method in which a foaming agent is pressed into a molten modified polypropylene resin and then extruded by a melt extruder to obtain a foam. To be

In the case of this method, examples of the foaming agent include physical type foaming agents. Among them, preferable physical type foaming agents include, for example, methane, ethane, ethylene, propane, propylene, n-butane, i-butane, Butylene,
Aliphatic hydrocarbons such as n-pentane, i-pentane, neopentane, n-hexane and n-heptane; alicyclic hydrocarbons such as cyclobutane, cyclopentane and cyclohexane; chlorodifluoromethane, dichloromethane,
Dichlorofluoromethane, dichlorodifluoromethane,
Trichlorofluoromethane, chloroethane, dichlorodifluoroethane, 1,1-dichloro-2,2,2-trifluoroethane, 2-chloro-1,1,1,2-tetrafluoroethane, 2-chloro-1,1,1 -Trifluoroethane, 1,1-dichloro-1-fluoroethane, 1
-Chloro-1,1-difluoroethane, difluoroethane, 1,1,2-trifluoroethane, 1,1,1-trifluoroethane, 1,1,1,1-tetrafluoroethane, 1,1,1,2 -Halogenated hydrocarbons such as tetrafluoroethane, octafluoropropane, 1,1,1-trifluoropropane, 2,2-difluoropropane, perfluorocyclobutane, methyl chloride, ethyl chloride; carbon dioxide, nitrogen, oxygen , An inorganic gas such as air; one or more kinds such as water.

Carbon dioxide, nitrogen, oxygen, air,
You may use water etc. as a foaming auxiliary agent.

Although the amount of the foaming agent to be pressed in (added amount) varies depending on the kind of the foaming agent and the target expansion ratio, it is 1 to 30 parts by weight, and further 1 to 20 parts by weight with respect to 100 parts by weight of the modified polypropylene resin. It is preferably within the range of parts by weight. When the amount of the foaming agent added is less than the above range, the foaming ability is insufficient, and there is a tendency that a foam having a desired expansion ratio cannot be obtained. On the other hand, when the amount exceeds the above range, the foaming agent in the extruder is used. There is a tendency that the uniform dispersion and dissolution of does not proceed sufficiently and a homogeneous foam cannot be obtained.

Further, in the case of this method, the modified polypropylene resin is melted in the extruder, and the physical type foaming agent is pressed into the extruder, and the modified polypropylene resin in a molten state is maintained while being kept at high temperature and high pressure. A kneaded product of the modified polypropylene resin and the physical foaming agent, which is kneaded with the resin and sufficiently kneaded, can be molded into a foam by discharging from a die. The melt-kneading temperature and the melt-kneading time in this method may be appropriately selected depending on the type of the foaming agent used and the melt-kneading conditions, and also vary depending on the type of the resin, but the melt-kneading temperature is 130 to 300 ° C. Is usually 1 to 120 minutes.

In the case of the above production method (2), as an apparatus used for melt-kneading the polypropylene resin, the compound having a reactive unsaturated double bond and the radical polymerization initiator, and the melt-kneading of the foaming agent, A single screw extruder or a twin screw extruder can be used.

Also in this production method, the polypropylene resin before modification, the compound having a reactive unsaturated double bond, the radical polymerization initiator and other additive materials which are added as necessary are mixed and melted. The kneading method is not particularly limited.

The heating temperature during the melt-kneading of the polypropylene resin, the compound having a reactive unsaturated double bond, and the radical polymerization initiator (the melt-kneading until the foaming agent is melt-kneaded) depends on the kind of resin. But usually 130
It is preferably from 400 to 400 ° C. because the polypropylene resin is sufficiently melted and is not easily thermally decomposed. The time of melt-kneading at this time (time after mixing the radical polymerization initiator and the aromatic vinyl monomer) is usually 1 to 60 minutes.

The heating temperature and the melt-kneading time after the melt-kneading of the foaming agent may be appropriately selected depending on the foaming agent and the melt-kneading conditions used, and the melt-kneading temperature may vary depending on the kind of the resin. Is 130-300
C. and melt-kneading time are usually 1 to 120 minutes.

In this manufacturing method, as the foaming agent, it is preferable to use the same amount as that of the manufacturing method of the above (1), and the same foaming aid may be used.

In each of the above-mentioned production methods of the present invention, a polypropylene resin, a compound having a reactive unsaturated double bond and a radical polymerization initiator are melt-kneaded to give a resin having a gel fraction of 5 to 30%. Since it is prepared and foamed by an appropriate method, the strength of the cell wall at the time of foaming is high, and therefore, it is possible to suppress the rupture of the cell wall, so even if a physical foaming agent is used, the closed cell rate is high, It is possible to obtain a thick foam having a low density and a beautiful appearance.

In the production method of the present invention, if necessary, talc; calcium silicate; silica; higher aliphatic metal salts such as sodium stearate, calcium stearate, magnesium stearate, potassium stearate; polyvalent carvone. A mixture of an acid and sodium carbonate or sodium bicarbonate may be added as a foam control agent, and a lead salt such as dibasic lead stearate; an organotin such as octyltin maleate; an epoxy such as epoxidized soybean oil. Organic phosphoric acid esters such as tricresyl phosphite; antioxidants such as hindered phenols may be added as stabilizers. These foam regulators or stabilizers may be used alone, respectively.
More than one kind may be mixed and used. In addition, the modified polypropylene resin is added to the foam regulator, the stabilizer, and / or
Alternatively, a blended oil or the like may be used to uniformly disperse other additives.

The density of the thus-obtained foam of the present invention is preferably from 0.01 to 0. 0, from the viewpoints of lightness, heat insulation, cushioning against external stress, and compressive strength.
It is preferably 5 g / cm ³ , and 0.015 to 0.
More preferably, it is 2 g / cm ³ . In addition, the closed cell ratio of the foam of the present invention is preferably 50% or more, and preferably 70%, from the viewpoint that it has suitable heat resistance, good external force buffering property, and suitable compressive strength. It is more preferable that the above is satisfied.

Further, in the method for producing a foam of the present invention, the shape that can be produced is a plate shape such as a sheet shape or a board shape,
There are various shapes such as a hollow shape such as a tube shape and a bag shape, a columnar shape such as a columnar shape, an elliptic shape, a prismatic shape, and a columnar shape such as a strand shape, and the plate-shaped foam has a wide range of uses.
As the plate-like foam, for example, a sheet-like foam capable of secondary molding that can be used for vacuum molding or the like is preferably used because of its high closed cell rate or small drawdown during secondary molding. In addition, as a relatively thick board-like foam (a plate-like foam having a thickness of about 5 to 100 mm) that is used as a cushioning material or a core material, it has a high closed cell rate or a low density. It is preferably used because of its advantages.

[0068]

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

In the present invention, the gel fraction of the resin (or the resin portion of the foam), the density of the foam, the closed cell ratio of the foam and the thickness of the foam (plate-like foam) are measured by the following methods. .

<Gel Fraction of Resin (or Resin Part of Foam)> 0.5 g of resin (or resin part of foam) was weighed and put in a 200 mesh bag and heated to 125 ° C. 50 ml Soak in xylene and stir for 1 hour. Take out the bag containing the resin and put another 125 ° C
After immersing in 50 ml of xylene heated to, and stirring for 4 hours, the bag is taken out, the residual resin is dried, and the residual resin is weighed. The percentage of the measured value of this residual resin to the measured value of the resin (or the resin portion of the foam) before being dipped in xylene is the gel fraction.

<Foam Density> It is calculated from the weight and the volume obtained by the submersion method.

<Closed Cell Ratio of Foam> Using a multi-pic meter manufactured by Yuasa Ionics Co., Ltd., ASTM D-28
Measure according to 56.

<Thickness of Foam (Plate Foam)> The thickness is measured using a caliper.

Example 1 100 parts by weight of a propylene homopolymer (manufactured by Sumitomo Chemical Co., Ltd., Nobrene D501) as a polypropylene resin, and styrene as an aromatic vinyl monomer (manufactured by Wako Pure Chemical Industries, Ltd., special grade) ) 3 parts by weight, 3 parts by weight of divinylbenzene (manufactured by Wako Pure Chemical Industries, Ltd., special grade) as a compound having two or more unsaturated double bonds in the same molecule, and α, α'as a radical polymerization initiator. -Bis (t-butylperoxy-m-isopropyl) benzene (produced by NOF Corporation,
Perbutyl P) (0.6 parts by weight) is melt-kneaded using a twin-screw extruder (LABOTEX) manufactured by Japan Steel Works, Ltd., and melt-extruded to form a rod-shaped modified polypropylene resin having a diameter of 4 mm. A molded product was obtained. This rod-shaped modified polypropylene-based resin molded product was shredded into a length of 3 mm to obtain modified polypropylene-based resin pellets.

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 temperature of the cylinder of this twin-screw extruder was set to 200 ° C., the temperature of the feed section was set to 160 ° C., and the screw was heated to 100 rpm for each shaft.

The gel fraction of the obtained modified polypropylene resin was measured and found to be 10%.

Using the modified polypropylene resin pellets, a plate-like foam was produced by the following method.

Modified polypropylene resin pellets 10
0 parts by weight, blended oil (Koshigaya Chemical Co., Ltd., Super Ease) 0.05 parts by weight, and sodium bicarbonate-citric acid (Nagawa Kasei Co., Ltd., Cerbon SG / IC) as a foam nucleating agent. 1 part by weight was mixed for 15 minutes using a ribbon blender.

This mixture was fed to a tandem type extruder (first-stage extruder cylinder diameter 40 mmφ, second-stage extruder cylinder diameter 50 mmφ), and inside the first-stage extruder 2
After being melted at 30 ° C., 8 parts by weight of butane gas (isobutane gas; normal butane / isobutane mixing ratio 15/85 by weight) as a foaming agent was kneaded with 100 parts by weight of the modified polypropylene resin. Then, this was cooled in the second stage extruder to a resin temperature of 150 ° C. and extruded from a rectangular die having a slit width of 60 mm and a slit thickness of 0.6 mm to obtain a plate-shaped foam.

When the density, closed cell ratio and thickness of the obtained plate-like foam were measured, the density was 0.028 g / c.
m ³ , the closed cell rate is 82%, and the thickness is 36 m.
m.

Example 2 100 parts by weight of a propylene homopolymer (manufactured by Sumitomo Chemical Co., Ltd., Nobrene D501) as a polypropylene resin and styrene (manufactured by Wako Pure Chemical Industries, Ltd.) as an aromatic vinyl monomer. ) 5 parts by weight, 2 parts by weight of divinylbenzene (Wako Pure Chemical Industries, Ltd., special grade) as a compound having two or more unsaturated double bonds in the same molecule, and α, α'as a radical polymerization initiator. -Bis (t-butylperoxy-m-isopropyl) benzene (produced by NOF Corporation,
Perbutyl P) 0.8 part by weight, blended oil (Koshigaya Chemical Co., Ltd., Super Ease) 0.05 part by weight, and sodium bicarbonate-citric acid (Nagawa Kasei Co., Ltd. Cerbon) as a foam nucleating agent. SG / IC) 0.1 part by weight was mixed for 15 minutes using a ribbon blender.

This mixture was fed to a tandem type extruder (first-stage extruder cylinder diameter 40 mmφ, second-stage extruder cylinder diameter 50 mmφ), and was fed into the first-stage extruder 2
After melting at 30 ° C., 8 parts by weight of butane gas (iso-rich butane gas; normal butane / isobutane mixing ratio 15/85 by weight) was injected as a blowing agent to 100 parts by weight of polypropylene resin before modification. Knead
This is cooled in the second stage extruder so that the resin temperature is 150 ° C., and the slit width is 60 mm and the slit thickness is 0.6 mm.
It was extruded from the rectangular die to produce a plate-shaped foam.

The gel fraction, density, closed cell content and thickness of the resin portion of the obtained plate-like foam were measured. The gel fraction of the resin portion was 12% and the density was 0.030 g / cm 3.
³ , the closed cell rate is 80%, the thickness is 34 mm
Met.

Example 3 The type and amount of polypropylene resin, aromatic vinyl monomer, compound having two or more unsaturated double bonds in the same molecule and radical polymerization initiator supplied to the ribbon blender are shown in Table 1. Modified polypropylene resin pellets were obtained in the same manner as in Example 1, except that the pellets were replaced as shown in.

Using the modified polypropylene resin pellets thus obtained, a plate-like foam was obtained in the same manner as in Example 1.

The gel fraction of the resin portion of this plate-shaped foam,
The density, closed cell rate and thickness were evaluated in the same manner as in Example 1. The results are shown in Tables 1 and 2.

Comparative Example 1 A propylene homopolymer (Sumitomo Chemical Co., Ltd., Nobrene D501) was not modified, and this propylene homopolymer was used in place of the modified polypropylene resin pellets. A plate-shaped foam was manufactured according to the method for manufacturing a foam.

The gel fraction of the propylene homopolymer used was measured. Table 1 shows the results.

The density, closed cell rate and thickness of this plate-shaped foam were evaluated in the same manner as in Example 1. Table 2 shows the results.

Comparative Example 2 The type and amount of the polypropylene resin, the aromatic vinyl monomer, the compound having two or more unsaturated double bonds in the same molecule and the radical polymerization initiator supplied to the twin-screw extruder were selected. Modified polypropylene resin pellets were obtained in the same manner as in Example 1 except that the pellets were replaced as shown in Table 1.

The gel fraction of this modified polypropylene resin pellet was measured. Table 1 shows the results.

Using the obtained modified polypropylene resin pellets, an extrusion foaming was tried in the same manner as in Example 1, but the extrusion molding was impossible.

[0093]

[Table 1]

[0094]

[Table 2]

[0095]

The polypropylene resin, the compound having a reactive unsaturated double bond, and the radical polymerization initiator are melt-kneaded to form a modified polypropylene resin, which has a low density and a closed cell ratio. A foam with high wall thickness, high rigidity and high rigidity is obtained.

Claims (4)

[Claims] 1. A polypropylene resin, a compound having a reactive unsaturated double bond and a radical polymerization initiator are melt-kneaded, and a foaming agent is further melt-kneaded under high temperature and high pressure,
The gel fraction of the resin part obtained by extrusion is 5 to 3
A method of making foams in the range of 0%. 2. A polypropylene resin, an aromatic monovinyl monomer, a compound having two or more unsaturated double bonds in the same molecule, and a radical polymerization initiator are melt-kneaded, and a blowing agent is further added under high temperature and high pressure. A method for producing a foam obtained by extruding after melt-kneading, in which the gel fraction of the resin portion is in the range of 5 to 30%. 3. The method according to claim 1, wherein the foaming agent is a physical type foaming agent. 4. A foam obtained by the method according to any one of claims 1 to 3.