JPH09123248A - Manufacture of foam made of polypropylene resin - Google Patents

Abstract

PROBLEM TO BE SOLVED: To manufacture a polypropylene resin foam having high foaming magnification, high closed cell rate and beautiful appearance through simple steps. SOLUTION: This method for manufacturing a foam made of a polypropylene resin comprises the steps of (a) supplying a mixture of a polypropylene resin, an aromatic vinyl monomer and a radical polymerization initiator to a first stage biaxial screw type extruder of a tandem type, (b) melting and kneading the mixture by the first stage biaxial screw type extruder, (c1) press injecting a foaming agent to the melted and kneaded material in the extruder, continuously feeding the material press injected with the agent to a second stage uniaxial screw tape extruder, (d) cooling the melted and kneaded material to the temperature suitable for foaming in the second stage extruder, and (e) passing the kneaded material through a die and extruding it in a low-pressure atmosphere.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a foam made of polypropylene resin having a high closed cell ratio, a high expansion ratio and a beautiful appearance.

[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 in a molten state are low, and when the resin is foamed, the strength of the cell wall is not sufficiently maintained during foaming. Further, since this resin has a low gas barrier property, when the resin is foamed, the gas generated from the foaming agent is easily dissipated to the outside from the bubbles.
Therefore, it has been difficult to obtain a foam having excellent appearance, a high closed cell ratio and a low density by foaming the polypropylene resin.

As a method of improving the foaming property of a polypropylene resin, for example, a method of adding a crosslinking aid to a polypropylene resin to crosslink polymer molecules (Japanese Patent Publication No. Sho 45)
No. 40420) and a method of crosslinking polymer molecules by irradiating a polypropylene resin with an electron beam (see JP-B-44-26953), and the like, but these methods also improve foamability. It is not sufficient, and also has a drawback that it requires a special device and a complicated process.

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 reacting and extruding is disclosed, but polypropylene is not disclosed at all. Further, this method uses a single-screw extruder, so that the resin is not propelled stably in the extruder, the polymerization reaction and the kneading state become heterogeneous, and a continuous and homogeneous foam is formed. Was difficult.

As described above, by improving the foamability of the polypropylene resin and using this resin, a foam having a high expansion ratio, a high closed cell ratio and a beautiful appearance can be produced by a relatively simplified process. The current situation is that no method has been found.

[0007]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a foam having a high expansion ratio, a high closed cell ratio and a beautiful appearance by a simple method.

[0008]

Means for Solving the Problems As a result of intensive studies to solve the above-mentioned problems, the present inventors have found that a polypropylene-based resin, an aromatic vinyl monomer and a radical polymerization initiation can be carried out by using a specific extruder. By kneading the agent at a temperature at which the polypropylene resin can be melted and the radical polymerization initiator can be substantially decomposed, a foaming agent is press-fitted and extruded under a low pressure atmosphere. The inventors have completed the present invention by finding that a foam having a high closed cell rate and a beautiful appearance can be obtained.

That is, the present invention uses a tandem extruder in which the first stage is a twin-screw type extruder and the second stage is a single-screw type extruder, and (a) the tandem type extruder is used. A mixture of a polypropylene resin, an aromatic vinyl monomer and a radical polymerization initiator is supplied to the first-stage twin-screw type extruder of the machine, and (b) the mixture is fed into the first-stage twin-screw extruder. The polypropylene resin is melted by a screw type extruder and kneaded at a temperature at which the radical polymerization initiator can be substantially decomposed to obtain a melt kneaded body. A foaming agent is press-fitted in the twin-screw type extruder at the second stage, and the melt-kneaded body in which the foaming agent is press-fitted is continuously fed to the second-stage single-screw type extruder, (d) the melting The kneaded body is a single-screw type extruder for the second stage. Temperature cooling suitable for foaming at the inner,
(E) The present invention relates to a method for producing a foamed product made of a polypropylene resin, which is obtained by passing the melt-kneaded product through a die and extruding it under a low pressure atmosphere.

Further, the present invention uses a tandem extruder in which the first stage is a twin screw type extruder and the second stage is a single screw type extruder, and (a) the tandem type extruder is used. A mixture of a polypropylene resin, an aromatic vinyl monomer and a radical polymerization initiator is supplied to the first-stage twin-screw type extruder of the machine, and (b) the mixture is fed into the first-stage twin-screw extruder. The polypropylene-based resin can be melted by a screw type extruder and kneaded at a temperature at which the radical polymerization initiator can be substantially decomposed to form a melt-kneaded body, and (c2) the melt-kneaded body is used as a second It is continuously fed to the single-screw type extruder of the second stage, and the foaming agent is press-fitted in the single-screw type extruder of the second stage, and (d) the melt-kneaded body is the second-stage single screw type. Cool to a temperature suitable for foaming in a die extruder, (e The melt-kneaded material was passed through a die, a process for the preparation of foam made of a polypropylene resin extruded into a low-pressure atmosphere.

It is preferable that the two screws of the twin-screw type extruder be of the same rotation type and of the complete meshing type.

The mixture is a polypropylene resin 10
It is preferably composed of 0 part by weight, 0.1 to 100 parts by weight of an aromatic vinyl monomer, and 0.01 to 10 parts by weight of a radical polymerization initiator.

The aromatic vinyl monomer is preferably styrene or methylstyrene.

Further, according to the present invention, even when a foam such as a plate-like foam having a thickness of 10 mm or more is used, the polypropylene resin has a high expansion ratio, a high closed cell ratio and a beautiful appearance. The present invention relates to a method for producing a foam made of.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION By using the tandem type extruder, a polypropylene resin, an aromatic vinyl monomer and a radical polymerization initiator are homogeneously melt-kneaded by a first twin-screw extruder. As a result, the aromatic vinyl monomer can be homogeneously graft-copolymerized with the polymer molecules of the polypropylene resin, and the propulsion speed of the melt-kneaded product in the extruder is stabilized, so that the melt The kneaded body is sent to the second-stage single-screw type extruder. Further, as described above, even in the second-stage single-screw type extruder, the propulsion speed of the melt-kneaded body becomes stable, and a continuous and homogeneous foam can be obtained.

Further, in the production method of the present invention, there are two types of methods of press-fitting the foaming agent into the melt-kneaded body (described later). Whichever method is selected, a desired foamed body can be obtained. it can.

In (a), a mixture of polypropylene resin, aromatic vinyl monomer and radical polymerization initiator is fed to the first twin-screw extruder of the tandem extruder. At this time, there is no particular limitation on the method for supplying the polypropylene resin, the aromatic vinyl monomer, and the radical polymerization initiator to the first-stage twin-screw extruder. The monomer and the radical polymerization initiator may be supplied to the first-stage twin-screw extruder, or the polypropylene resin particles impregnated with the aromatic vinyl monomer in advance and the radical polymerization initiator may be mixed. The mixture may be supplied to the first-stage twin-screw extruder, or the polypropylene resin may be supplied to the first-stage twin-screw extruder and then the first-stage twin-screw extruder. The aromatic vinyl monomer and the radical polymerization initiator may be fed simultaneously or separately, all at once or in a divided manner, from the middle part of the screw type extruder.

Next, in the above (b), under the temperature at which the polypropylene resin can be melted in the first-stage twin-screw type extruder and the radical polymerization initiator can be substantially decomposed. Then, the polypropylene resin, the aromatic vinyl monomer, and the radical polymerization initiator are melt-kneaded to graft-copolymerize the aromatic vinyl monomer with the polymer molecules of the polypropylene resin.

The temperature at which the radical polymerization initiator can be substantially decomposed means that the radical polymerization initiator thermally decomposes to release radicals, and the radicals effectively act to cause the aromatic vinyl monomer to become the polypropylene. It means the temperature required to start the graft copolymerization on the polymer molecule of the base resin. The melting temperature at the time of melt kneading is preferably 160 to 400 ° C. from the viewpoint that the resin melts, the radical polymerization initiator decomposes, and the resin does not thermally decompose.
It is more preferably 80 to 300 ° C.

Further, the time required for the melt-kneading is that a sufficient graft copolymerization reaction occurs between the polypropylene resin and the aromatic vinyl monomer, so that the polypropylene resin, the aromatic vinyl monomer and the radical are used. It is preferably 20 seconds to 60 minutes, more preferably 30 seconds to 50 minutes after the polymerization initiator is mixed.

As the first-stage extruder used in the present invention, a twin-screw extruder is used for sufficiently homogeneously kneading the polypropylene resin, the aromatic vinyl monomer and the radical polymerization initiator. It is essential to use, and the two screws of the twin-screw type extruder are the same direction rotating type and the complete meshing type, so that the polypropylene resin, the aromatic vinyl monomer, and the radical polymerization start It is preferable in that the agent and the agent are kneaded more sufficiently and homogeneously.

The above-mentioned co-rotating type means that two screws rotate in the same direction, and the completely meshing type means that the distance between the centers of the two screws in the extruder is two. It has a structure smaller than the sum of radii.

Subsequently, the foaming agent is pressed into the melt-kneaded product obtained in (b) above. There are two types of methods for press-fitting the foaming agent into the melt-kneaded body, as described above. One of them is a method (c1) of press-fitting the foaming agent in the first-stage twin-screw type extruder, and the other is a method of pressing the foaming agent in the second-stage single-screw type extruder. It is a method (c2) of press-fitting.

In the case of (c1), the foaming agent is applied to the melt-kneaded body under a high pressure from any part of the cylinder of the first-stage twin-screw type extruder, for example, the part near the intermediate part or the outlet part. After being press-fitted in, the melt-kneaded body in which the foaming agent is press-fitted is continuously sent to the second-stage single-screw type extruder.

In the case of (c2), the melt-kneaded body obtained by being melt-kneaded by the first-stage twin-screw extruder is the second-stage single-screw extruder. To the melt-kneaded body from any part of the cylinder of the second-stage single-screw extruder, for example, a part such as a feed part or an intermediate part, preferably a feed part. The blowing agent is pressed in at high pressure.

The method (c1) and the method (c)
In addition to the method 2), a method in which a foaming agent is press-fitted between the outlet of the first-stage twin-screw extruder and the feed section of the second-stage single-screw extruder is also possible. Well, even in that case, a desired foam can be obtained.

As described above, the melt-kneaded body is continuously fed from the first-stage twin-screw type extruder to the second-stage single-screw-type extruder to obtain a homogeneous melt-kneaded body. It has the advantage of propelling in the extruder at a stable speed.

Subsequently, in (d), the melt-kneaded body in which the foaming agent is press-fitted is cooled to a temperature suitable for foaming. This temperature is a temperature at which the melt-kneaded body in which the foaming agent is press-fitted can maintain viscoelasticity that can withstand the growth of bubbles when foaming, and such a temperature is relative to the melting point of the melt-kneaded body. It is usually within the range of -25 ° C to + 10 ° C.

Further, in the above (e), the above-mentioned foaming agent is press-fitted, and the melt-kneaded body cooled to a temperature suitable for foaming is passed through a die and extruded under a low pressure atmosphere of about normal pressure. To obtain a foam made of polypropylene resin.

In this way, a foam made of polypropylene resin having a high expansion ratio, a high closed cell rate, an excellent appearance and suitable mechanical properties can be obtained.

The polypropylene resin usable in the present invention is a crystal such as a homopolymer of propylene, a block copolymer of propylene and another monomer, or a random copolymer of propylene and another monomer. Polymers are preferred, the polypropylene homopolymer is preferable from the viewpoint of high rigidity and low cost, and the block of the propylene and other monomers from the viewpoint of high rigidity and high impact resistance. Copolymers are preferred. When the polypropylene resin is a block copolymer of propylene and other monomers or a random copolymer of propylene and other monomers, the polypropylene resin has high crystallinity, high rigidity and From the viewpoint of maintaining good chemical resistance, the content of the propylene monomer component is preferably 75% by weight or more, and more preferably 90% by weight or more of the whole.

In the polypropylene resin, other monomers copolymerizable with propylene are 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 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 polypropylene resin is 50,000 to 20 because it is easily available.
It is preferably in the range of 100,000, and more preferably in the range of 100,000 to 1,000,000 from the viewpoint of being inexpensive.

Further, other resins, rubbers or additives may be added to the polypropylene resin as long as the effects of the present invention are not impaired.

The shape and size of these polypropylene resins are not limited, and they may be in the form of particles or pellets.

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 or methylstyrene is preferred because the closed cell ratio and expansion ratio of the foam of the present invention can be particularly increased.

The addition amount of the aromatic vinyl monomer is 0. 0 with respect to 100 parts by weight of the polypropylene resin.
It is preferably from 1 to 100 parts by weight, particularly preferably from 0.1 to 50 parts by weight.

If the amount of the aromatic vinyl monomer added is less than the above range, the effect of improving the foamability of the polypropylene resin tends to be insufficient, while if it is more than the above range, The polypropylene resin tends to impair the excellent chemical properties, physical properties, mechanical properties, and the like, and also requires a large amount of radical polymerization initiator, which tends to be disadvantageous in terms of cost.

The aromatic vinyl monomer may be used in combination with the aromatic vinyl monomer and another vinyl monomer copolymerizable with the aromatic vinyl monomer.

Other vinyl monomers copolymerizable with the aromatic vinyl monomer include, for example, vinyl chloride, vinylidene chloride, acrylonitrile, methacrylonitrile, acrylamide, methacrylamide, vinyl acetate,
Acrylic acid, methacrylic acid, maleic acid, maleic anhydride, metal salts of acrylic acid, metal salts of methacrylic acid, methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, stearyl acrylate,
Acrylic acid esters such as 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 vinyl monomer and another vinyl monomer copolymerizable with the aromatic vinyl monomer are used in combination, the aromatic vinyl monomer is added to 100 parts by weight of the aromatic vinyl monomer. Other vinyl monomers copolymerizable with the group vinyl monomer are preferably used in an amount of less than 100 parts by weight, more preferably less than 75 parts by weight.

The radical polymerization initiator is generally a peroxide or an azo compound. In order for the graft reaction to occur between the polypropylene-based polymer and the vinyl monomer or between the polypropylene-based polymer and the polypropylene-based polymer, the presence of a compound such as a radical polymerization initiator having a so-called hydrogen abstraction ability is required. is there.

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 10 to prevent the polypropylene resin from being excessively lowered in melt viscosity and is economical.
It is preferably 0.01 to 10 parts by weight, more preferably 0.1 to 5 parts by weight, based on 0 parts by weight.

The foaming agent is preferably a volatile foaming agent, for example, aliphatic hydrocarbons such as propane, butane, pentane, hexane and heptane; alicyclic hydrocarbons such as cyclobutane, cyclopentane and cyclohexane. Chlorodifluoromethane, difluoromethane,
Trifluoromethane, trichlorofluoromethane, dichlorodifluoromethane, chloromethane, dichloromethane, chloroethane, dichlorotrifluoroethane, dichlorofluoroethane, chlorodifluoroethane, dichloropentafluoroethane, tetrafluoroethane, difluoroethane, pentafluoroethane, trifluoroethane, trichloro Examples thereof include halogenated hydrocarbons such as trifluoroethane, dichlorotetrafluoroethane, chloropentafluoroethane, and perfluorocyclobutane; inorganic gases such as carbon dioxide, nitrogen, and air; and one or more species such as water.

The amount of the foaming agent added (the amount of press-fitting) varies depending on the type of the foaming agent and the target expansion ratio.
It is preferably in the range of 0.5 to 100 parts by weight with respect to 00 parts by weight.

Further, within the range that does not impair the effects of the present invention,
Inorganic fine powder such as talc, calcium silicate, silica,
Higher fatty acid metal salts such as sodium stearate, calcium stearate, magnesium stearate, potassium stearate, and foam control agent such as sodium bicarbonate-citric acid,
Additives such as stabilizers such as dibasic lead stearate, octyltin maleate, epoxidized soybean oil, and hindered phenolic antioxidants can be appropriately blended, and addition of these foam regulators and stabilizers can be added. These substances may be used alone or in combination of two or more.

Further, in order to improve the dispersibility of the additives, for example, blended oil may be used.

The density of the foam is 0.01 to 0.5 g.
/ Cm ³ , especially 0.015 to 0.2 g / cm ³ is light weight, heat insulating property, buffering force from external stress,
It is preferable in that the characteristics such as compressive strength are preferable.

The expansion ratio of the foam is preferably 3 to 90 times from the same viewpoint as the density.
It is more preferably 4.5 to 60 times.

In addition, the closed cell ratio of the foam is preferably 50% or more, and more preferably 70% or more from the viewpoint that it has suitable heat resistance, good buffering property against external stress, and suitable compressive strength. Is preferred.

According to the manufacturing method of the present invention, such density,
A foam having an expansion ratio and a closed cell ratio can be easily obtained.

The foam obtained according to the present invention may have any shape such as a sheet, a plate, a rod or a pipe, but the effect of the present invention can be exhibited, but a foam having a high closed cell rate can be obtained. In this respect, it is possible to exert a particularly excellent effect which has never been obtained, particularly in the production of a plate-like foam having a thickness of 10 mm or more.

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

Example 1 100 parts by weight of propylene homopolymer (Sumitomo Chemical Co., Ltd., Nobrene D501, melt flow index at 230 ° C .: 0.4 g / 10 min) and α, α'-bis (t- Butyl peroxy-m-isopropyl) benzene (manufactured by NOF Corporation, Perbutyl P, 1-minute half-life temperature 175 ° C.) 3.5 parts by weight and blended oil (manufactured by Koshigaya Chemical Co., Ltd., Super Ease) 05 parts by weight and baking soda
Citric acid (manufactured by Eiwa Chemical Co., Ltd., Cerbon SG / K) 0.
1 part by weight was mixed with a ribbon blender and 20 parts by weight of styrene monomer (manufactured by Wako Pure Chemical Industries, Ltd., special grade) was added to the mixture, and the first stage extruder had a cylinder bore of 32 mmφ and a maximum screw. Effective length (L / D) 25.5
Co-rotating twin-screw extruder (Japan Steel Works, LA
BOTEX), the second stage extruder is a tandem type extruder consisting of a single screw extruder having a cylinder diameter of 50 mmφ, and is fed to the first stage twin screw type extruder, and the heating temperature is 230 ° C. Screw rotation speed is 80 rp
m, melt-kneaded to graft-copolymerize the styrene monomer to the polypropylene polymer molecule, and from the blowing agent pressure inlet provided in the middle of the cylinder of the twin-screw type extruder, isorich butane is used as the blowing agent. (Normal butane / isobutane ratio 15/85) was press-fitted in a ratio of 8 parts by weight to 100 parts by weight of the melt-kneaded body,
Further, the mixture was melt-kneaded and continuously sent to the second-stage single-screw extruder.

Then, in the second-stage single-screw extruder, the melt-kneaded body was cooled to a temperature of 150 ° C. and propelled at a screw rotation speed of 8 rpm to obtain the second-stage single-screw extruder. It was foamed by passing through a cylindrical die (orifice diameter 3 mm) attached to the tip and extruding.

The density, the expansion ratio and the closed cell ratio of the obtained rod-shaped foam were measured by the following methods, and the appearance was visually evaluated by the following evaluation criteria.

Density of foam: Calculated from the weight and the volume obtained by the submersion method.

Expansion ratio: Given the approximate density of the modified polypropylene resin as 0.91 (g / cm ³ ), the following formula: Expansion ratio (times) = 0.91 (cm ³ ) / density of foam ( cm ³ ).

Independent bubble ratio: Using a multi-pycnometer (product name, manufactured by Yuasa Ionics Co., Ltd.), ASTM D
-Measurement according to 856.

Evaluation Criteria for Appearance: ◯: No unfoamed part, unevenness, fluff, wrinkle, or rustle is observed. X: Unfoamed parts, irregularities, fluff, wrinkles, and stains are seen.

As a result, the density was 0.029 g / cm ³ , the expansion ratio was 31 times, the closed cell ratio was 83%, and the appearance was evaluated as ◯.

Example 2 A foamed product was obtained in the same manner as in Example 1 except that the supply amount of α, α'-bis (di-t-butylperoxy-m-isopropyl) benzene was changed to 1 part by weight. This foam was evaluated in the same manner as in Example 1. As a result, the density of the obtained foam was 0.035 g / cm ³ , and the expansion ratio was 26.
Double, the closed cell ratio is 74%, and the appearance is evaluated as ○.
Met.

Example 3 A foam was obtained in the same manner as in Example 1 except that the supply amount of styrene monomer was changed to 10 parts by weight, and this foam was evaluated in the same manner as in Example 1. As a result, the density of the obtained foam was 0.033 g / cm ³ , and the expansion ratio was 28.
Double, the closed cell ratio is 75%, and the appearance is evaluated as ○.
Met.

Comparative Example 1 A foam was obtained in the same manner as in Example 1 except that α, α'-bis (di-t-butylperoxy-m-isopropyl) benzene and styrene monomer were not supplied. Was evaluated in the same manner as in Example 1. As a result, the density of the obtained foam was 0.23 g / cm ³ , the expansion ratio was 4, the closed cell ratio was 16%, and the appearance was evaluated as x.

Comparative Example 2 A foam was obtained in the same manner as in Example 1 except that styrene monomer was not supplied, and this foam was evaluated in the same manner as in Example 1. As a result, the density of the obtained foam is 0.09.
It was g / cm ³ , the expansion ratio was 10 times, the closed cell ratio was 22%, and the appearance was evaluated as x.

Comparative Example 3 A foam was obtained in the same manner as in Example 1 except that α, α'-bis (di-t-butylperoxy-m-isopropyl) benzene was not supplied. Evaluation was made in the same manner as 1. As a result, the density of the obtained foam is 0.1.
It was 1 g / cm ³ , the expansion ratio was 8 times, the closed cell ratio was 21%, and the appearance was evaluated as x.

Example 4 100 parts by weight of a propylene homopolymer (manufactured by Sumitomo Chemical Co., Ltd., Nobrene D501, melt flow index at 230 ° C .: 0.4 g / 10 minutes) and α, α'-bis (t- Butyl peroxy-m-isopropyl) benzene (manufactured by NOF Corporation, Perbutyl P, 1-minute half-life temperature 175 ° C.) 3.5 parts by weight and blended oil (manufactured by Koshigaya Chemical Co., Ltd., Super Ease) 05 parts by weight and baking soda
Citric acid (manufactured by Eiwa Chemical Co., Ltd., Cerbon SG / K) 0.
The same tandem extruder as that used in Example 1 was prepared by mixing 1 part by weight with a ribbon blender and adding 20 parts by weight of styrene monomer (manufactured by Wako Pure Chemical Industries, Ltd., special grade) to the mixture. To the first-stage twin-screw type extruder and heated to 230 ° C. to adjust the screw rotation speed to 10
At 0 rpm, melt kneading was carried out to graft-copolymerize styrene monomer to polypropylene polymer molecules, and isorich butane was used as a foaming agent from a foaming agent pressure inlet provided in the middle of the cylinder of the twin-screw type extruder. (Normal butane / isobutane ratio is 15/8
5) was press-fitted at a ratio of 8 parts by weight to 100 parts by weight of the melt-kneaded body, further melt-kneaded, and continuously fed to the second stage single-screw extruder.

Next, in the second-stage single-screw extruder, the melt-kneaded body was cooled to a temperature of 150 ° C. and propelled at a screw rotation speed of 10 rpm to obtain the second-stage single-screw extruder. Slit width 60m attached to the tip
m, a rectangular die having a slit thickness of 0.6 mm was extruded, extruded, and passed through a molding die directly connected to the rectangular die to obtain a plate-shaped foam. As a result, the obtained plate-shaped foam had a thickness of 20 mm and a density of 0.035 g.
/ Cm ³ , the expansion ratio was 26 times, the closed cell ratio was 79%, and the appearance was evaluated as ◯.

The density, the expansion ratio, the closed cell ratio and the appearance were evaluated in the same manner as in Example 1, and the thickness was measured using a caliper.

Example 5 A plate-like foam was prepared in the same manner as in Example 4 except that the amount of α, α'-bis (di-t-butylperoxy-m-isopropyl) benzene supplied was changed to 1 part by weight. The body was removed, and this plate-shaped foam was evaluated in the same manner as in Example 4. As a result, the thickness of the obtained plate-shaped foam was 17 mm, the density was 0.045 g / cm ³ , the expansion ratio was 20 times, the closed cell ratio was 70%, and the appearance was evaluated. Was ○.

Example 6 In the same manner as in Example 4 except that the amount of styrene monomer supplied was changed to 10 parts by weight, a plate-shaped foam was obtained, and this plate-shaped foam was used as an example. Evaluation was made in the same manner as in 4. As a result, the thickness of the plate-shaped foam obtained was 19 m.
m, the density was 0.043 g / cm ³ , the expansion ratio was 21 times, the closed cell ratio was 71%, and the appearance was evaluated as ◯.

Comparative Example 4 A plate-like foam was obtained in the same manner as in Example 4 except that α, α'-bis (di-t-butylperoxy-m-isopropyl) benzene and styrene monomer were not supplied. This plate-shaped foam was evaluated in the same manner as in Example 4. As a result, the obtained plate-shaped foam had a thickness of 4 mm, a density of 0.28 g / cm ³ , a foaming ratio of 3, and a closed cell ratio of 16%. Was x.

Comparative Example 5 A plate-shaped foam was obtained in the same manner as in Example 4 except that styrene monomer was not supplied, and this plate-shaped foam was used in Example 4.
The evaluation was performed in the same manner as described above. As a result, the thickness of the obtained plate-shaped foam was 5 mm, the density was 0.19 g / cm ³ , the expansion ratio was 5 times, the closed cell ratio was 20%, and the appearance was evaluated. Was x.

Comparative Example 6 A plate-like foam was obtained in the same manner as in Example 4 except that α, α'-bis (di-t-butylperoxy-m-isopropyl) benzene was not added. The foam was evaluated in the same manner as in Example 4. As a result, the obtained plate-shaped foam had a thickness of 4 mm and a density of 0.20 g / cm ^3.
The expansion ratio was 5 times, the closed cell ratio was 20%, and the appearance was evaluated as x.

[0078]

According to the present invention, a polypropylene resin foam having a high closed cell ratio, a high expansion ratio and a beautiful appearance can be manufactured by a simple process.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical display location B29L 7:00

Claims (6)

[Claims] 1. A tandem extruder in which the first stage is a twin-screw type extruder and the second stage is a single-screw type extruder, and (a) the first tandem type extruder is used.
A mixture of a polypropylene resin, an aromatic vinyl monomer and a radical polymerization initiator is supplied to the twin-screw type extruder at the first stage, and (b) the mixture is fed to the first-stage twin-screw type extruder. Then, the polypropylene resin is melted and kneaded at a temperature at which the radical polymerization initiator can be substantially decomposed to obtain a melt kneaded body, and (c1) the melt kneaded body has a second stage A foaming agent is press-fitted in an axial screw type extruder, and the melt-kneaded body in which the foaming agent is press-fitted is
Continuously feed to the single-screw type extruder of the stage,
(D) The melt-kneaded product is cooled to a temperature suitable for foaming in the second-stage single-screw type extruder, and (e) the polypropylene is extruded in a low-pressure atmosphere by passing the melt-kneaded product through a die. A method of manufacturing foam made of resin. 2. A tandem extruder in which the first stage is a twin-screw type extruder and the second stage is a single-screw type extruder, and (a) the first tandem type extruder is used.
A mixture of a polypropylene resin, an aromatic vinyl monomer and a radical polymerization initiator is supplied to the twin-screw type extruder at the first stage, and (b) the mixture is fed to the first-stage twin-screw type extruder. Then, the polypropylene resin can be melted and kneaded at a temperature at which the radical polymerization initiator can be substantially decomposed to obtain a melt kneaded body, and (c2) the melt kneaded body is used as a second stage single Continuously to the axial-screw type extruder, press-fitting the foaming agent in the second-stage single-screw type extruder, and (d) the melt-kneaded body in the second-stage single-screw type extruder. Cool to a temperature suitable for foaming,
(E) A method for producing a foam made of a polypropylene resin, which is obtained by passing the melt-kneaded product through a die and extruding it in a low-pressure atmosphere. 3. The manufacturing method according to claim 1, wherein the two screws of the twin-screw type extruder are co-rotating type and completely meshing type. 4. The polypropylene resin 1 is used as the mixture.
4. The production method according to claim 1, 2 or 3, comprising 00 parts by weight, 0.1 to 100 parts by weight of an aromatic vinyl monomer, and 0.01 to 10 parts by weight of a radical polymerization initiator. 5. The method according to claim 1, 2, 3 or 4, wherein the aromatic vinyl monomer is styrene or methylstyrene. 6. The foam made of the polypropylene resin is a plate-like foam having a thickness of 10 mm or more.
The manufacturing method of 2, 3, 4 or 5.