JPH09111033A - Preliminarily foamed granule and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain preliminarily foamed granules capable of being preliminarily foamed at a low temperature and capable of being molded in a mold at low temperature. SOLUTION: This method for producing a preliminarily foamed granules comprises preparing an aqueous suspension containing 100 pts.wt. of polypropylene resin granules, 0.1-100 pts.wt. of a vinylic monomer and 0.1-10 pts.wt. of a radical polymerization initiator, heating the aqueous suspension at a temperature substantially not decomposing the radical polymerization initiator and substantially not polymerizing the vinylic monomer to impregnate the polypropylene granules with the vinylic monomer and the radical polymerization initiator in the aqueous dispersion, and further heating the aqueous dispersion at a higher temperature than a temperature substantially capable of completing the melting of crystals in the polypropylene resin granules to graft- copolymerize the vinylic monomer to the polypropylene resin granules and preliminarily foam the modified polypropylene resin granules.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to pre-expanded particles obtained by pre-expanding polypropylene resin particles graft-copolymerized with an aromatic vinyl monomer, a method for producing the pre-expanded particles, and expansion of the pre-expanded particles. Regarding a molded body.

[0002]

2. Description of the Related Art A foamed molded product of polypropylene resin is useful as a packaging material, a heat insulating material, a cushioning material or a core material and is widely used. Such a polypropylene resin foam-molded article can be produced by various production methods. As an example of these, pre-expanded beads are once produced, and the pre-expanded beads are put into a desired mold and steam-expanded article is produced. The molding method (in-mold molding method) can be mentioned.

Various methods have been carried out as a method for producing pre-expanded particles. For example, a method in which a polypropylene resin particle contains a foaming agent and is heated to foam (see, for example, JP-A-58-65734). ), A method in which a polypropylene-based resin particle contains a foaming agent, is heated and melted, and is then extruded in a strand shape to foam (for example, see JP-A-58-76230).

Conventionally, as a resin material for the pre-expanded particles made of these polypropylene resins, a propylene homopolymer, a block copolymer of an α-olefin having 2 or 4 to 12 carbon atoms and propylene, or a carbon number. Random copolymers of α-olefin of 2 or 4 to 12 and propylene have been used. Usually, the block copolymer and the random copolymer have 2 carbon atoms.
Alternatively, the α-olefin component of 4 to 12 is contained within the range of about 25% by weight or less based on the whole.

However, especially the homopolymer of propylene and the block copolymer of α-olefin having 2 or 4 to 12 carbon atoms and propylene have DS of the resin itself.
Peak temperature of the DSC chart measured by C (hereinafter, "D
(Sometimes called "peak temperature of SC chart") is about 1
The peak temperature of the DSC chart of the pre-expanded particles obtained from them is as high as 60 ° C. or higher, and the peak temperature of the DSC chart of the portion annealed by the heat treatment in the pre-expansion step is higher than that. Will have.

Although the random copolymer has a lower peak temperature (about 130 to 160 ° C.) on the DSC chart than the homopolymer of propylene and the block copolymer, the polyethylene resin is still used. Peak temperature of DSC chart (about 100-130 ℃
It is higher than the (degree). Further, the pre-expanded particles obtained from these resins also have the same or higher peak temperatures on the DSC chart.

When the peak temperature of the DSC chart of the pre-expanded particles is high, the heating temperature at the time of re-expansion when the foamed molded product is naturally increased. In such a case, for example, in the in-mold molding method, the steam temperature must be increased, and therefore the steam pressure must be increased, high energy is required, and the mold clamping force of the molding machine must be increased. There is a problem that it must be done.

As described above, there is a demand for pre-expanded particles capable of lowering the peak temperature of the DSC chart of the polypropylene resin and its pre-expanded particles and lowering the heating temperature during in-mold molding.

Further, Japanese Patent Publication No. 58-53003 discloses that crystalline propylene polymer particles, a vinyl or vinylidene monomer, and a decomposition temperature for obtaining a half-life of 10 hours are 8
An aqueous suspension containing a radical polymerization initiator having a temperature of 5 to 130 ° C. is substantially free from decomposition of the radical polymerization initiator, and the vinyl or vinylidene monomer starts polymerization substantially independently. The crystalline propylene polymer particles are impregnated with the vinyl or vinylidene monomer by heating under a non-heated condition so that the amount of the free vinyl or vinylidene monomer is 2 or less.
Modification to obtain a vinyl or vinylidene monomer by increasing the temperature of the aqueous suspension below the melting point of the propylene polymer to complete the polymerization of the vinyl or vinylidene monomer. It describes a resin which is obtained by mixing a crystalline polypropylene polymer with another crystalline polypropylene polymer and which has preferable moldability and mechanical properties. However, since this resin contains a large amount of polymer molecules to which a vinyl or vinylidene monomer is not grafted, the peak temperature of the DSC chart cannot be lowered sufficiently.

[0010]

It is an object of the present invention to prevent deterioration of mechanical properties such as rigidity and impact resistance of polypropylene resins, heat resistance or chemical resistance from a range that causes no problems in practical use. A modified polypropylene resin particle is obtained by graft-copolymerizing a vinyl monomer with the resin resin particle, and the peak temperature of the DSC chart is lower than the peak temperature of the DSC chart of the polypropylene resin particle before graft copolymerization. The purpose is to obtain pre-expanded particles having a low peak temperature on the DSC chart by using polypropylene resin particles.

Another object of the present invention is to lower the molding temperature of the foamed molded product by using the pre-expanded particles.

[0012]

The present invention provides 100 parts by weight of polypropylene resin particles, 0.1 to 100 parts by weight of a vinyl monomer based on 100 parts by weight of the polypropylene resin particles, and the polypropylene. An aqueous suspension containing 0.1 to 10 parts by weight of a radical polymerization initiator with respect to 100 parts by weight of the resin particles is prepared, and the radical polymerization initiator is not substantially decomposed to produce a vinyl monomer. Are heated to a temperature at which they do not substantially polymerize to impregnate polypropylene resin particles with a vinyl monomer and a radical polymerization initiator in the aqueous suspension, and further to add the aqueous suspension to the polypropylene resin. The crystals in the particles are heated to a temperature at which they can substantially complete melting, and the vinyl monomer is graft-copolymerized with the polypropylene resin particles to obtain modified polypropylene resin particles. Polypropylene resin particles (hereinafter,
Sometimes referred to as "modified polypropylene resin particles."
And a method for producing pre-expanded particles for pre-expanding.

In the above manufacturing method, the amount of the radical polymerization initiator is preferably 0.5 to 5 parts by weight based on 100 parts by weight of the polypropylene resin particles.

In the above production method, the amount of the vinyl monomer is 1 with respect to 100 parts by weight of the polypropylene resin particles.
It is preferably from 50 to 50 parts by weight.

The present invention also provides 100 parts by weight of polypropylene resin particles and 100 parts of the polypropylene resin particles.
Aqueous suspension containing 0.1 to 100 parts by weight of vinyl monomer, and 0.1 to 10 parts by weight of radical polymerization initiator, based on 100 parts by weight of the polypropylene resin particles. A liquid was prepared and heated to a temperature at which the radical polymerization initiator was not substantially decomposed and the vinyl monomer was not substantially polymerized, so that the vinyl monomer was added to the polypropylene resin particles in the aqueous suspension. Body and a radical polymerization initiator are impregnated, and the aqueous suspension is further heated to a temperature not lower than a temperature at which the crystals in the polypropylene resin particles can substantially complete melting, and the polypropylene resin particles are vinyl When a monomer is graft-copolymerized, one or more vinyl graft chains composed of a vinyl monomer are grafted onto the polypropylene polymer molecule in an average number of 1 or more, and the weight average molecular weight of the vinyl graft chain is 200 or more. That give a modified polypropylene resin particles, relates to pre-expanded particles that may by prefoaming the reforming polypropylene resin particles.

In the pre-expanded particles, the amount of the radical polymerization initiator is 0.5 to 5 parts by weight based on 100 parts by weight of the polypropylene resin particles.

In the pre-expanded particles, the amount of the vinyl monomer is from 1 to 50 parts by weight, based on 100 parts by weight of the polypropylene resin particles.

In the pre-expanded particles, the peak temperature of the DSC chart of the modified polypropylene resin particles is DSC of the polypropylene resin particles before graft copolymerization.
1 ° C or higher, preferably 5 ° C, higher than the peak temperature in the chart
More preferably, it is lower.

The present invention also relates to a foamed molded product obtained by in-molding the pre-foamed particles.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION The modified polypropylene resin particles according to the present invention are graft copolymer resin particles obtained by graft-reacting a vinyl monomer onto a polypropylene resin molded into particles.

The modified polypropylene resin particles are prepared by dissolving the radicals in an aqueous suspension containing a specific amount of polypropylene resin particles, a specific amount of a vinyl monomer and a specific amount of a radical polymerization initiator. The polymerization initiator is not substantially decomposed, by heating to a temperature at which the vinyl monomer is not substantially polymerized, substantially the entire polypropylene resin particles, the vinyl monomer and the radical polymerization initiator And further heating the aqueous suspension to a temperature not lower than the temperature at which the crystals of the polypropylene resin particles can substantially complete the melting, thereby adding vinyl monomers to the polymer molecules of the polypropylene resin particles. Obtained by radical copolymerization.

The peak temperature on the DSC chart of the modified polypropylene resin particles thus obtained is lower than the peak temperature on the DSC chart of the polypropylene resin particles before graft copolymerization. Therefore, such modified polypropylene resin particles can be pre-expanded at a lower temperature. Further, when the pre-expanded particles are molded in-mold to produce a foam molded article, the in-mold molding can be performed at a lower temperature.

The mechanism by which the peak temperature of the DSC chart of the modified polypropylene resin particles is lower than the peak temperature of the DSC chart of the polypropylene resin particles before graft copolymerization is not clear, but the polypropylene resin before graft copolymerization is not clear. It is speculated that the peak temperature of the DSC chart becomes low because the crystal structure in the particles is disturbed by the graft copolymerization.

Further, as a result of the experiments by the present inventors, in order to suitably lower the peak temperature of the DSC chart by graft copolymerization as described above, grafting is carried out per one molecule of the graft copolymer. It has been found that it is necessary to make the average number of vinyl graft chains one or more.

In the method for producing modified polypropylene resin particles according to the present invention, the degree of decrease in the peak temperature of the DSC chart of the polypropylene resin particles depends on the polypropylene resin particles before the graft copolymerization, the radical polymerization initiator and vinyl. It depends on various factors such as the type and amount of the monomer, the method for preparing the aqueous suspension, the heating temperature of the aqueous suspension, the type of equipment used and the operating conditions.

The pre-expanded particles composed of the modified polypropylene resin particles are obtained by graft-copolymerizing a vinyl monomer onto the polypropylene resin particles to obtain modified polypropylene resin particles, and pre-expanding the modified polypropylene resin particles. However, the preferred characteristics of polypropylene-based resin are not lower than the practical range such as rigidity, chemical resistance, impact resistance and heat resistance.

Examples of the polypropylene resin particles before the graft copolymerization include homopolymers of propylene, block copolymers of propylene and other monomers, and random copolymers of propylene and other monomers. The above-mentioned homopolymer is preferable from the viewpoint of high rigidity and low cost, and the above-mentioned propylene and others from the viewpoint that the peak temperature of the DSC chart is lower than other polymers. Particles of a random copolymer with the above monomer are preferable, and particles of a block copolymer of the above-mentioned propylene and another monomer are preferable from the viewpoints of high rigidity and high impact resistance. If the polypropylene resin particles before graft copolymerization are particles made of block copolymers or random copolymers of propylene and other monomers, high crystallinity and high rigidity characteristic of polypropylene resins And from the viewpoint of maintaining good chemical resistance, the propylene component contained is 75% by weight of the whole.
It is preferably at least above, and more preferably at least 90% by weight.

In the polypropylene resin particles before the graft copolymerization, the other monomer copolymerizable with the propylene is α-olefin, cyclic olefin, diene monomer and vinyl monomer. One or more monomers selected from the group of monomers may be mentioned. Of these monomers, α-olefin and diene-based monomers are preferable because they are easily copolymerized with propylene and are inexpensive.

Examples of the α-olefin copolymerizable with the above-mentioned propylene include ethylene, butene-1, isobutene, pentene-1,3-methyl-butene-1, hexene-1,3-methyl-pentene-1. , 4-methyl-pentene-1,3,4-dimethyl-butene-1, heptene-
Examples include α-olefins having 2 or 4 to 12 carbon atoms such as 1,3-methyl-hexene-1, octene-1, and decene-1. In addition, examples of the cyclic olefin copolymerizable with propylene include cyclopentene, norbornene, 1,4,5,8-dimethano-1,2,3,4, and
4a, 8,8a-6-octahydronaphthalene and the like. Examples of the diene monomer copolymerizable with the propylene include 5-methylene-2-norbornene, 5-ethylidene-2-norbornene, 1,4-hexadiene, methyl-1,4-hexadiene, 7-methyl-1,6-octadiene and the like. Examples of the vinyl monomer copolymerizable with the propylene include vinyl chloride, vinylidene chloride, acrylonitrile,
Vinyl acetate, acrylic acid, methacrylic acid, maleic acid,
Examples thereof include ethyl acrylate, butyl acrylate, methyl methacrylate, maleic anhydride, styrene, methylstyrene and divinylbenzene.

Of these monomers, ethylene and butene-1 are more preferable because they are inexpensive.

Molecular weight (weight average molecular weight) of polymer molecules of the polypropylene resin particles before the graft copolymerization
Is preferably in the range of 50,000 to 2,000,000 from the viewpoint of industrial availability, and more preferably in the range of 100,000 to 1,000,000 from the viewpoint of being inexpensive.

If necessary, other resin or rubber may be added to the polypropylene resin particles before the graft copolymerization within a range not impairing the effects of the present invention. Examples of the other resins or rubbers include poly-α-olefins such as polyethylene, polybutene-1, polyisobutene, polypentene-1, and polymethylpentene-1; ethylene / propylene copolymers having a propylene content of less than 75% by weight, Ethylene / butene-1 copolymer, propylene containing less than 75% by weight of propylene /
Α-olefin / α-olefin copolymers such as butene-1 copolymers; α-olefin / α-such as ethylene / propylene / 5-ethylidene-2-norbornene copolymers with a propylene content of less than 75% by weight Olefin / diene-based monomer copolymer; ethylene / vinyl chloride copolymer, ethylene / vinylidene chloride copolymer, ethylene / acrylonitrile copolymer, 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 / metal acrylate copolymer, ethylene / metal methacrylate copolymer, ethylene / styrene copolymer Coalescing,
Α-Olefin / vinyl monomer copolymers such as ethylene / methylstyrene copolymers and ethylene / divinylbenzene copolymers; polydiene copolymers such as polyisobutene, polybutadiene, polyisoprene; styrene / butadiene random copolymers. Vinyl monomer / diene monomer random copolymer such as styrene / butadiene / styrene block copolymer vinyl monomer / diene monomer / vinyl monomer block copolymer; hydrogenation Hydrogenation of (styrene / butadiene random copolymer) and the like (vinyl monomer / diene monomer random copolymer); hydrogenation (styrene / butadiene / styrene block copolymer)
Hydrogenation of vinyl (vinyl monomer / diene monomer / vinyl monomer block copolymer); vinyl monomer such as acrylonitrile / butadiene / styrene copolymer, methyl methacrylate / butadiene / styrene copolymer Polymer / diene monomer / vinyl monomer graft copolymer; such as polyvinyl chloride, polyvinylidene chloride, polyacrylonitrile, polyvinyl acetate, polyethyl acrylate, butyl polyacrylate, polymethyl methacrylate, polystyrene, etc. Vinyl polymer; vinyl chloride / acrylonitrile copolymer,
Vinyl chloride / vinyl acetate copolymer, acrylonitrile /
Examples thereof include styrene copolymers and vinyl copolymers such as methyl methacrylate / styrene copolymers.

The amount of the other resin or rubber added to the polypropylene resin particles before graft copolymerization is
It depends on the type of the resin or rubber, and it may be within the range that does not impair the effects of the present invention as described above, and is preferably about 25% by weight or less.

Further, if necessary, the polypropylene resin particles before the graft copolymerization may include an antioxidant, a metal deactivator, a phosphorous processing stabilizer, an ultraviolet absorber, an ultraviolet stabilizer and a fluorescent brightening agent. , Metal soap, stabilizers or crosslinkers such as antacid adsorbents, chain transfer agents, nucleating agents, lubricants, plasticizers, fillers, reinforcing materials, pigments, dyes, flame retardants, antistatic agents and other additives. It may be contained within a range that does not impair the effects of the invention.

The polypropylene resin particles before the graft copolymerization may be in the form of particles, but the pre-expanded particles produced by using the polypropylene resin particles can be easily molded in the mold, that is, spherical or spherical. The polypropylene resin particles before graft copolymerization preferably have a spherical shape, a shape close to a spherical shape, a cylindrical shape, or the like in order to have a shape close to or a columnar shape.

The size of the polypropylene resin particles before graft copolymerization is, for example, when the polypropylene resin particles before graft copolymerization are spherical, the polypropylene resin particles before graft copolymerization are graft copolymerized. It is preferable to adjust the size so that the diameter of the pre-expanded particles obtained by pre-expanding after polymerization is about 0.3 to 10 mm. Further, when the shape of the particles is not spherical, it is preferable to adjust the size to the same level as that of the spherical shape.

As the polypropylene resin particles before graft copolymerization in the above-mentioned shape, for example, commercially available polypropylene particles may be used as they are. However, for example, the polypropylene resin is formed into a strand shape by an extruder and then pelletized. You may use the polypropylene resin particle shape | molded by the method etc. to a desired shape.

The vinyl monomer usable in the present invention includes
For example, styrene; o-methylstyrene, m-methylstyrene, p-methylstyrene, α-methylstyrene, β
-Methylstyrene such as methylstyrene, dimethylstyrene and trimethylstyrene; α-chlorostyrene, β-
Chlorostyrene such as chlorostyrene, o-chlorostyrene, m-chlorostyrene, p-chlorostyrene, dichlorostyrene, trichlorostyrene; o-bromostyrene, m-bromostyrene, p-bromostyrene, dibromostyrene, tribromostyrene, etc. Bromostyrene; o-fluorostyrene, m-fluorostyrene, p
-Fluorostyrene such as fluorostyrene, difluorostyrene, trifluorostyrene; nitrostyrene such as o-nitrostyrene, m-nitrostyrene, p-nitrostyrene, dinitrostyrene, trinitrostyrene; o-hydroxystyrene, p-hydroxystyrene , M-hydroxystyrene, dihydroxystyrene,
Vinylphenol such as trihydroxystyrene; o-
Divinylbenzene such as divinylbenzene, m-divinylbenzene and p-divinylbenzene; aromatic vinyl unit amount such as o-diisopropenylbenzene, m-diisopropenylbenzene, p-diisopropenylbenzene and other diisopropenylbenzene One or more types of body may be mentioned. Of these, methylstyrene such as styrene, α-methylstyrene, and p-methylstyrene, divinylbenzene, or a mixture of divinylbenzene isomers are preferable because they are inexpensive.

Other vinyl monomers which can be used in the present invention include, for example, vinyl chloride, vinylidene chloride, acrylonitrile, methacrylonitrile, acrylamide, methacrylamide, vinyl acetate, acrylic acid, methacrylic acid, maleic acid, anhydrous. Maleic acid, acrylic acid metal salts, methacrylic acid metal salts, methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, stearyl acrylate, acrylate esters such as glycidyl acrylate; methyl methacrylate,
One or more of methacrylates such as ethyl methacrylate, butyl methacrylate, 2-ethylhexyl methacrylate, stearyl methacrylate and glycidyl methacrylate may be used.

The vinyl monomer and the other vinyl monomer may be used in combination.

Of these vinyl monomers, the aromatic vinyl monomers or methacrylic acid esters or acrylic acid esters are preferable from the viewpoints of versatility and economy, and above all, styrene, methyl methacrylate or butyl acrylate is preferable. Is particularly preferable.

The amount of the vinyl monomer is 100 parts by weight of the polypropylene resin particles before graft copolymerization.
It is preferably 0.1 to 100 parts by weight, and 1 to 50
More preferably, it is parts by weight. If the amount of the vinyl monomer is less than the above range, the average number of vinyl graft chains grafted on the graft copolymer molecule tends to be less than 1, and in that case, the peak temperature of the DSC chart. Does not decrease favorably, while on the other hand, if it is more than the above range, it is necessary to use a large amount of radical polymerization initiator in order to achieve the desired number of vinyl graft chains, which is disadvantageous in terms of cost. Tend.

The radical polymerization initiator that can be used in the present invention is generally a peroxide or an azo compound.

In order for the graft copolymerization reaction to occur suitably between the polymer of the polypropylene resin particles and the vinyl monomer, the presence of a radical polymerization initiator having a high hydrogen abstraction ability is necessary. Examples of such radical polymerization initiators include ketone peroxides such as methyl ethyl ketone peroxide and methyl acetoacetate peroxide; 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; permentan hydroperoxide, 1,1,3,3- Hydroperoxides such as tetramethylbutyl hydroperoxide, diisopropylbenzene hydroperoxide, cumene hydroperoxide; dicumyl peroxide,
2,5-Dimethyl-2,5-di (t-butylperoxy) hexane, α, α′-bis (t-butylperoxy-m-isopropyl) benzene, t-butylcumyl peroxide, di-t- Butyl peroxide, 2,5-
Dialkyl peroxides such as dimethyl-2,5-di (t-butylperoxy) hexyne-3; diacyl peroxides such as benzoyl peroxide; di (3-
Methyl-3-methoxybutyl) peroxydicarbonate, peroxydicarbonate such as 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 ,
Examples thereof include organic peroxides such as peroxyesters such as t-butylperoxyacetate, t-butylperoxybenzoate, and di-t-butylperoxyisophthalate. Of these, those having a particularly high hydrogen abstraction ability are preferable, and examples thereof include 1,1-bis (t-butylperoxy) -3,3,5-trimethylcyclohexane,
Peroxyketals such as 1,1-bis (t-butylperoxy) cyclohexane, n-butyl-4,4-bis (t-butylperoxy) valerate and 2,2-bis (t-butylperoxy) butane Dicumyl peroxide, 2,5-dimethyl-2,5-di (t-butylperoxy) hexane, α, α′-bis (t-butylperoxy-m-isopropyl) benzene, t-butylcumylper Oxide, di-t-butyl peroxide,
Dialkyl peroxides such as 2,5-dimethyl-2,5-di (t-butylperoxy) hexyne-3 and diacyl peroxides such as benzoyl peroxide; t-butylperoxyoctate, t-butylperoxyiso Butyrate, t-butylperoxylaurate, t-butylperoxy-3,5,5-trimethylhexanoate, t-butylperoxyisopropyl carbonate, 2,5-dimethyl-2,5-di (benzoylper) (Oxy) hexane, t-butylperoxyacetate, t-butylperoxybenzoate, peroxyesters such as di-t-butylperoxyisophthalate, and the like, or one or more of them.

The amount of the radical polymerization initiator is such that the peak temperature of the DSC chart of the modified polypropylene resin particles is the DSC of the polypropylene resin particles before graft copolymerization.
From the viewpoint of being sufficiently lower than the peak temperature of the chart and being advantageous in terms of cost, 0.1 to 100 parts by weight of the polypropylene resin particles before the graft copolymerization is used.
The amount is preferably 10 parts by weight, more preferably 0.5 to 5 parts by weight.

The modified polypropylene-based resin particles produced by the above-mentioned production method, when produced by using a larger amount of radical polymerization initiator than conventional ones, have a graft copolymerization weight of the modified polypropylene-based resin particles. The average number of vinyl graft chains grafted on one united molecule can be particularly higher than the number of graft chains of conventionally known modified polypropylene resin particles.

As an example of a suitable combination of the polypropylene resin particles before the graft copolymerization, the vinyl monomer and the radical polymerization initiator, the polypropylene resin particles before the graft copolymerization are polypropylene homopolymer, propylene / 1 of ethylene random copolymer, propylene / butene random copolymer, propylene / ethylene block copolymer or propylene / butene block copolymer
Particles of one kind or two or more kinds, wherein the vinyl monomer is styrene, α-methylstyrene, p-methylstyrene,
Particles comprising one or more resins of divinylbenzene, methyl methacrylate or butyl acrylate, wherein the radical polymerization initiator is α, α′-bis (t-butylperoxy-m-isopropyl) benzene, 2 , 5-dimethyl-2,5-di (t-butylperoxy) hexyne-3, or di-t-butylperoxide, which is a single type or a combination of two or more types, and is a polypropylene system before graft copolymerization. When the resin particles contain rubber or other resin, the rubber component or other resin component is ethylene / propylene copolymer, ethylene / propylene / diene copolymer, polybutadiene, polyisoprene, styrene / butadiene random copolymer. Polymer, styrene / butadiene / styrene block copolymer, polyethylene, ethylene / acetic acid 1 of vinyl copolymer, ethylene / (meth) acrylic acid metal salt copolymer or polystyrene
One kind or a combination of two or more kinds can be mentioned. The modified polypropylene-based resin particles obtained by the above-mentioned combination have a particularly low peak temperature in the DSC chart, and the pre-expanded temperature of the pre-expanded particles can be lowered, and the pre-expanded particles can also be reduced. It can lower the in-mold forming temperature of the particles.

As a particularly preferable combination of the polypropylene resin particles before the graft copolymerization and the vinyl monomer, the polypropylene resin particles before the graft copolymerization are polypropylene homopolymer, propylene /
Particles composed of an ethylene random copolymer or a propylene / ethylene block copolymer, in which the vinyl monomer is styrene, may be mentioned. In this case, the radical polymerization initiator may be mentioned in the examples of the preferable combination. Any of the above is preferably used.

Next, a method for producing the modified polypropylene resin particles in the present invention will be described.

First, an aqueous suspension is prepared by adding polypropylene resin particles before graft copolymerization, a vinyl monomer, and a radical polymerization initiator together with an emulsifier and / or a dispersant, if necessary, to an aqueous solvent and stirring. To prepare.
As the emulsifier, dispersant and aqueous solvent, for example, known ones can be used in appropriate amounts.

The method of adding the polypropylene resin particles, the vinyl monomer, the radical polymerization initiator, and optionally the emulsifier and / or the dispersant to the aqueous solvent is not limited.

Subsequently, the polypropylene resin particles are impregnated with the vinyl monomer and the radical polymerization initiator in the aqueous suspension by heating the aqueous suspension.

The upper limit of the heating temperature of the aqueous suspension at the time of impregnation is set so that the graft copolymerization starts before the vinyl monomer and the radical polymerization initiator are sufficiently impregnated into the polypropylene resin particles. In order to suppress it, the radical polymerization initiator to be used does not substantially decompose and the vinyl monomer does not substantially polymerize, but the 10-hour half-life temperature of the radical polymerization initiator to be used It is preferable that the temperature is 10 ° C. lower than that.

Further, when the impregnation temperature is low, the impregnation takes a long time. Therefore, the lower limit of the impregnation temperature is preferably 50 ° C. lower than the 10-hour half-life temperature of the radical polymerization initiator used in order to reduce workability and the time required for impregnation.

Further, the heating time of the aqueous suspension at this time (time kept at the above temperature) may be appropriately selected depending on the heating temperature and the shape and size of the polypropylene resin particles before graft copolymerization. However, it is preferably within 5 hours from the economical point of view.

This heating is carried out under pressure if necessary. Moreover, it is preferable that the stirring is performed in a stirring state.

The preparation of the aqueous suspension and the impregnation are carried out at the same time, that is, for example, polypropylene resin particles, vinyl monomer and radical polymerization initiator are added to the aqueous solvent, and if necessary, further. By adding an emulsifier and / or a dispersant and stirring the polypropylene resin particles at a temperature at which the vinyl monomer and the radical polymerization initiator can be impregnated, an aqueous suspension is obtained and a polypropylene resin is obtained. The particles may be impregnated with a vinyl monomer and a radical polymerization initiator.

Then, an aqueous suspension containing polypropylene resin particles impregnated with a vinyl monomer and a radical polymerization initiator is further added, and the crystals in the polypropylene resin particles substantially complete melting. The graft copolymerization reaction is initiated by heating to a temperature not lower than the allowable temperature.

Here, the temperature at which the crystals in the polypropylene resin particles can substantially complete the melting means the peak temperature of the DSC chart in the DSC measurement of the polypropylene resin particles.

FIG. 1 shows polypropylene resin particles before graft copolymerization (Noblene, D5, manufactured by Sumitomo Chemical Co., Ltd.).
01) shows a DSC chart.

The DSC chart shown in FIG. 1 is a differential scanning calorimeter (DSC) device (manufactured by Perkin Elmer, DSC).
-7) was used to make the sample weight 10 mg, the temperature was raised to 200 ° C at 50 ° C / min in a nitrogen atmosphere, this temperature was kept for 5 minutes, and the temperature was lowered to 50 ° C at 10 ° C / min. Was held for 5 minutes and then the temperature was raised at 10 ° C./minute.

In FIG. 1, point A indicates the peak temperature of the DSC chart in the DSC measurement of the polypropylene resin particles.

The graft copolymerization reaction by heating to a temperature above the temperature at which the crystals in the polypropylene resin particles can substantially complete the melting is usually carried out under pressure using a device such as a pressure-resistant closed container. . At this time, the heating temperature may be a temperature equal to or higher than the temperature at which the crystals in the polypropylene-based resin particles to be used can substantially complete the melting, as described above, and the pressure-resistant temperature of the container such as the pressure-resistant closed container to be used is equal to or lower than that. If In addition, this heating temperature is preferably equal to or higher than the 10-hour half-life temperature of the radical polymerization initiator. When the polymerization is carried out at a temperature lower than the above temperature range, the radical polymerization initiator is not sufficiently thermally decomposed and the graft copolymerization of the remaining vinyl monomer tends not to be completed sufficiently.

The polymerization time (time kept at the above temperature) is preferably about 30 minutes to 5 hours. If the polymerization time is shorter than the above range, the radical polymerization initiator remains and the polymerization tends to be insufficiently completed, while if it is longer than the above range, it tends to be economically disadvantageous.

The aqueous suspension containing the modified polypropylene resin particles is filtered, washed with water, and dried to obtain
Modified polypropylene resin particles can be obtained.

The peak temperature of the DSC chart of the modified polypropylene resin particles produced as described above is lower than the peak temperature of the DSC chart of the polypropylene resin particles before graft copolymerization. Further, the modified polypropylene resin particles can be pre-expanded at a relatively low temperature, and the pre-expanded particles obtained by the pre-expansion can be molded in a mold at a low temperature.

The modified polypropylene resin particles which can be produced by the above-mentioned production method have a graft chain (vinyl graft chain) composed of a vinyl monomer per one graft copolymer molecule of the modified polypropylene resin particles. One or more, preferably 2 to 100, are grafted on average.

If the average number of the vinyl graft chains is less than 1 per graft copolymer molecule, the peak temperature of the DSC chart will not be sufficiently lowered, and in order to exceed 100, a large amount of radicals is generally required. Requires an initiator,
Sometimes it is not economically feasible. The average number of vinyl graft chains is 2 per graft copolymer molecule.
When it is at least this number, the peak temperature of the DSC chart of the modified polypropylene resin particles can be further suitably reduced.

The number of vinyl graft chains is represented by the following formula: (Number of vinyl graft chains) = (weight average molecular weight of modified polypropylene resin particles) × (vinyl grafted to 1 part by weight of modified polypropylene resin particles) It can be represented by (part by weight of graft chain) / (weight average molecular weight of vinyl graft chain).

The weight average molecular weight of the vinyl graft chain is preferably in the range of 200 to 30,000, more preferably in the range of 300 to 25,000 from the viewpoint of lowering the peak temperature of the DSC chart. preferable.

DS of the modified polypropylene resin particles
The peak temperature of the C chart is preferably 1 ° C. or more lower than the peak temperature of the DSC chart of the polypropylene resin particles before graft copolymerization, more preferably 5 ° C. or more. D of the modified polypropylene resin particles
The peak temperature of the SC chart is lower than the peak temperature of the DSC chart of the polypropylene resin particles before graft copolymerization by 1 ° C. or more, so that the foaming temperature during depressurizing foaming and the molding temperature during in-mold molding of prefoamed particles are high. It becomes low, energy is advantageous, and the fusion property of pre-expanded particles is improved,
It is preferable from the viewpoint of improving the appearance of the foamed molded product, etc.
If the temperature is lower than the above, the foaming temperature during depressurizing foaming and the molding temperature during in-mold molding of the pre-foamed particles become lower, which is further advantageous in terms of energy, and the fusion property of the pre-foamed particles is further improved. It is preferable because the appearance of the molded product is further improved.

The modified polypropylene resin particles according to the present invention have a peak temperature of the DSC chart lower than that of the polypropylene resin particles before graft copolymerization, and the mechanical properties, heat resistance and Since the chemical resistance is not lower than the practically usable range, it is suitable as a material for pre-expanded particles.

For the pre-expanded particles, for example, the modified polypropylene resin particles are first made to contain a foaming agent, and then this is decompressed, that is, the modified polypropylene resin particles impregnated with the foaming agent are added. It can be produced by keeping it under pressure and then foaming it by releasing it under a low pressure atmosphere.

The depressurizing foaming method is not particularly limited, but for example, a method of impregnating modified polypropylene resin particles with a foaming agent in a gas state to pre-foam (impregnating in the gas phase and preliminarily Foaming method), modified polypropylene resin particles impregnated with a foaming agent in a liquid state to pre-foam (method of impregnating in liquid phase and pre-foaming), modified polypropylene resin particles dispersed in water Conventionally known methods such as a method of impregnating with a foaming agent and pre-foaming (a method of impregnating with a water dispersion system and pre-foaming) can be mentioned. Of these, the method of impregnation with the water dispersion system and pre-foaming is particularly preferable from the viewpoint of productivity.

Preferred blowing agents include, for example, propane, butane, isobutane, pentane, hexane, heptane and other aliphatic hydrocarbons; cyclobutane, cyclopentane, cyclohexane and other alicyclic hydrocarbons; chlorodifluoromethane, dichloromethane, Halogenated hydrocarbons such as dichlorofluoromethane, dichlorodifluoromethane, trichlorofluoromethane, chloroethane, dichlorotrifluoroethane, dichlorotetrafluoroethane, trichlorotrifluoroethane, tetrachlorodifluoroethane, perfluorocyclobutane; carbon dioxide, nitrogen, One or more inorganic gases such as air may be used.

The addition amount (kneading amount) of the foaming agent varies depending on the type of the foaming agent and the target expansion ratio, but is within the range of 1 to 100 parts by weight with respect to 100 parts by weight of the modified polypropylene resin particles. Is normal, and it is preferable that it is in the range of 1 to 50 parts by weight from the viewpoint of cost.

The expansion ratio of the pre-expanded particles is 2
It is usually in the range of 100 to 100 times, but in order to make the shock absorbing performance of external force, which is one of the characteristics of the foamed molded article, suitable, it is foamed in the range of 10 to 80 times. More preferable.

Since the pre-expanded particles of the present invention are produced by using the modified polypropylene resin particles which can be produced by the production method of the present invention as described above, the DSC of the pre-expanded particles is
The peak temperature of the chart is low, so that fusion of pre-expanded particles can occur at a lower temperature than that of conventional polypropylene resin particles. Therefore, the pre-expanded particles of the present invention can be formed into a foam-molded article under a low foam-molding temperature.

The molding method of the foam molded article is not particularly limited, but for example, a method of filling pre-foamed particles in a mold and then introducing steam into the mold to mold the foam molded article. , A method of filling pre-expanded particles in a mold and then compressing under heating to form an expanded molded article,
A method of filling pre-expanded particles in a mold in a heated and pressurized state to form a foamed molded product, after giving a secondary foaming ability to the pre-expanded particles, and then filling in a mold under heating to form a foamed molded product There is a conventionally known method such as a method of doing.

The characteristics of the pre-expanded particles and the resin portion of the foamed molded article produced in this manner are almost the same as the characteristics of the modified polypropylene resin particles used for the production thereof.

That is, the resin portion of the pre-expanded particles and the foamed molded article of the present invention is a graft copolymer of a polypropylene resin and a vinyl monomer, and the graft copolymer in one graft copolymer molecule is used. The average number of vinyl graft chains is 1 or more, preferably 2 to 100. The weight average molecular weight of the vinyl graft chain is 200 to
It is preferably 30,000, and preferably 300 to 25,000.
Is more preferable. The vinyl monomer is preferably styrene, methylstyrene, divinylbenzene, methyl methacrylate or butyl acrylate. Further, it is preferable that the peak temperature of the DSC chart of this resin portion is lower than the peak temperature of the DSC chart of the polypropylene resin particles before graft copolymerization by 1 ° C. or more, preferably 5 ° C. or more.

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

[0083]

【Example】

Examples 1 to 5 and Comparative Example 1 Pressure-resistant techno, pressure-resistant closed reaction tank (10 L autoclave) TAS10J3 type reactor in polypropylene resin particles before graft copolymerization shown in Table 1, aqueous solvent, vinyl monomer, A radical polymerization initiator, a dispersant and an emulsifier were added in the amounts shown in Table 1, and the mixture was stirred at room temperature at a stirring speed of 250 rpm to obtain an aqueous suspension.

[0084]

[Table 1]

[0085]

[Table 2]

Next, this aqueous suspension was heated to 100 ° C. in the pressure-resistant closed reaction vessel and stirred at 250 rpm for 60 minutes under a pressure condition of ¹ Kgf / cm ² to give a graft copolymer. The polypropylene resin particles before polymerization were impregnated with a vinyl monomer and a radical polymerization initiator.
Further, an aqueous suspension containing polypropylene resin particles impregnated with a vinyl monomer and a radical polymerization initiator is heated to 170 ° C. in the pressure-resistant closed reaction tank, and then heated to 10 ° C.
250 rp for 60 minutes under a pressure of Kgf / cm ^2.
complete the graft copolymerization by stirring at m.
Modified polypropylene resin particles were obtained.

Under the above-mentioned conditions of impregnation, the graft copolymerization does not substantially proceed, but it may sometimes proceed to some extent.

The modified polypropylene resin particles obtained were washed with water and dried to remove unreacted residual vinyl monomers, radical polymerization initiators and dispersants, and emulsifiers.

The peak temperature of the DSC chart of the polypropylene resin particles before the graft copolymerization was measured by a differential scanning calorimetry (DSC) device (manufactured by Perkin Elmer, DSC-
Using 7), the sample weight was 10 mg, the temperature was raised to 200 ° C. at 50 ° C./min in a nitrogen atmosphere, this temperature was kept for 5 minutes, and the temperature was lowered to 50 ° C. at 10 ° C./min. 5
It was 160 ° C. when measured by raising the temperature at 10 ° C./min after holding for 1 minute. In the present invention, DS
The peak temperature of the C chart is the main peak of the endothermic peaks detected when measured under this condition. Table 2 shows the results.

DS of the modified polypropylene resin particles
The peak temperature of the C chart was measured by the same method as the peak temperature of the DSC chart of the polypropylene resin particles before graft copolymerization described above. Table 2 shows the results.

DS of the modified polypropylene resin particles measured by the same method with the above-mentioned differential operation calorimeter.
The C chart is shown in FIG. 2 (Example 1 only). In FIG. 2, the horizontal axis represents temperature and the vertical axis represents the amount of heat.

Next, the number of vinyl graft chains grafted on the polymer of the modified polypropylene resin particles is calculated by the following formula: (Number of vinyl graft chains) = (weight average of polymers of modified polypropylene resin particles) Molecular weight) × (number of parts by weight of vinyl graft chain grafted to 1 part by weight of modified polypropylene resin particle) / (weight average molecular weight of vinyl graft chain).

The weight average molecular weight of the polymer of the modified polypropylene resin particles is determined by high temperature gel permeation chromatography (GPC) (refractive index (RI) detector) (Japan Waters) of the xylene insoluble matter of the modified polypropylene resin particles. It was determined by measuring with a 150 CV GPC system manufactured by Co., Ltd. and converting it into polystyrene. Further, the number of parts by weight of the vinyl graft chain grafted to 1 part by weight of the modified polypropylene resin particles is determined by an infrared spectrophotometer (IR) (Shimadzu Corporation) of the xylene insoluble matter of the modified polypropylene resin particles. FTIR made
8100 system) and the height of the peak near 1370 cm ⁻¹ derived from polypropylene and the height of the peak derived from vinyl monomer (for example, in the case of styrene, the peak around 700 cm ⁻¹ derived from the benzene ring). height)
It was calculated from the ratio. The weight-average molecular weight of the vinyl graft chain is determined by measuring the xylene-soluble content of the modified polypropylene resin particles at room temperature GPC (UV spectrophotometer (UV) detector).
(510 GPC system manufactured by Nippon Waters Co., Ltd.) and measured by polystyrene conversion. Table 2
Shows the weight average molecular weight of the polymer of the modified polypropylene resin particles, the number of parts by weight of vinyl graft chains grafted to 1 part by weight of the modified polypropylene resin particles, the weight average molecular weight of vinyl graft chains and the number of vinyl graft chains.

[0094]

[Table 3]

Obtained modified polypropylene resin particles 1
00 parts by weight, 2 parts by weight of tribasic calcium phosphate as a dispersant, 0.05 parts by weight of sodium dodecylbenzenesulfonate as an emulsifier, 300 parts by weight of water and 9 parts by weight of butane are put into a pressure tight techno closed container (10 L autoclave). Then, these were heated to the temperature shown in Table 3 for about 1 hour with stirring, and the stirring was continued at this temperature for about 15 minutes. After that, 3 parts by weight of butane as a foaming agent was added to the closed container, and the inside of the closed container was 20 kgf / c.
The content in the closed container is agitated for about 15 minutes at m ² , and the modified polypropylene resin particles are pre-expanded by releasing the contents into the atmosphere at room temperature and normal pressure. I got it. The expansion ratio of the pre-expanded particles was determined by the following formula: expansion ratio (times) = (volume of foam (cm ³ ) / weight of foam (g)) × 0.9 (g / cm ³ ). (Here, 0.9 g / cm ³ is an approximate density of the modified polypropylene resin particles). Table 3 shows the results.

[0096]

[Table 4]

Transfer the pre-expanded particles to another closed container,
At 80 ° C, the air inside this closed container is 7 kgf /
It was pressurized to cm ² and kept for 1 hour.

Subsequently, about 1 pre-expanded particles after pressure treatment
30 to 140 g is filled in a molding die having a cavity of 25 cm × 25 cm × 5 cm, and 130 to 163 ° C.
Molding was carried out under 12 levels of temperature conditions at every 3 ° C. to obtain foamed molded products under the respective conditions. The fusion rate of pre-expanded particles in these foamed molded articles, the foamed molded article is broken by human power, and the ratio of the number of fused particles to the number of all particles in this fracture surface is visually counted, Based on the relationship between the molding temperature condition and the fusion rate, the in-mold molding temperature at which the fusion rate (the ratio of the number of fused particles to the total number of particles shown in the cross section) exceeds 60% ( The temperature condition) was determined. As to whether the particles are fused or not, whether or not the breakage occurs inside the particles of the pre-expanded particle unit is visually evaluated whether it occurs at the particle interface, and this breakage occurs inside the particles. It was judged that what was present was fused. Table 4 shows the results. The expansion ratio of the foamed molded product was measured by the same method as the method for measuring the expansion ratio of the pre-expanded particles. Table 4 shows the results.

[0099]

[Table 5]

Comparative Example 1 The same polypropylene resin particles as in Example 1 (polypropylene resin particles before graft copolymerization, weight average molecular weight 850000) were used as they were without graft copolymerization, and the same amount of foam as in Example 1 was used. Agent, dispersant and emulsifier and the same amount of water as in Example 1, and heating temperature to 1
Pre-expanded particles were obtained in the same manner as in Example 1 except that the temperature was 60 ° C.

When the expansion ratio of the pre-expanded particles was measured by the same method as in Example 1, the expansion ratio was 24 times.

Using the pre-expanded particles at 163 ° C., a foamed molded article was produced in the same manner as in Example 1, and the fusion rate of the pre-expanded particles was measured by the same method as in Example 1. The fusion rate was Was about 10%.

[0103]

The modified polypropylene resin particles of the present invention have a peak temperature on the DSC chart lower than the peak temperature on the DSC chart of the polypropyne resin particles before graft copolymerization. The pre-expanded particles of the present invention are produced by pre-expanding the modified polypropylene resin particles, and therefore, when a foamed molded article is molded using this, the foamed molded article is molded at a lower temperature. You can get Further, the modified polypropylene resin particles may be pre-expanded to obtain pre-expanded particles under low temperature conditions.

Further, the modified polypropylene resin particles and pre-expanded particles which can be produced by the production method of the present invention have sufficient rigidity, chemical resistance, impact resistance and heat resistance, which are characteristics of polypropylene resin, for practical use. Is.

[Brief description of the drawings]

FIG. 1 is a DSC chart for explaining a temperature at which crystals in polypropylene-based resin particles before graft copolymerization can substantially complete melting.

2 is a DS of the modified polypropyne-based resin particles of Example 1. FIG.
It is a C chart.

Claims (9)

[Claims] 1. 100 parts by weight of polypropylene resin particles, 0.1 to 100 parts by weight of vinyl monomer, and 100 parts by weight of polypropylene resin particles, per 100 parts by weight of polypropylene resin particles. 0.1-1
By preparing an aqueous suspension containing 0 part by weight of a radical polymerization initiator, and heating to a temperature at which the radical polymerization initiator is not substantially decomposed and the vinyl monomer is not substantially polymerized, A temperature at which the polypropylene resin particles are impregnated with a vinyl monomer and a radical polymerization initiator in an aqueous suspension, and the crystals in the polypropylene resin particles can complete melting of the aqueous suspension. A method for producing pre-expanded particles, which comprises heating to the above temperature, graft-copolymerizing a vinyl monomer onto the polypropylene resin particles to obtain modified polypropylene resin particles, and pre-expanding the modified polypropylene resin particles. 2. The method for producing pre-expanded particles according to claim 1, wherein the amount of the radical polymerization initiator is 0.5 to 5 parts by weight with respect to 100 parts by weight of the polypropylene resin particles. 3. The method for producing pre-expanded particles according to claim 1, wherein the amount of the vinyl monomer is 1 to 50 parts by weight based on 100 parts by weight of the polypropylene resin particles. 4. 100 parts by weight of polypropylene-based resin particles, 0.1 to 100 parts by weight of vinyl monomer based on 100 parts by weight of the polypropylene-based resin particles, and 100 parts by weight of the polypropylene-based resin particles. 0.1-1
By preparing an aqueous suspension containing 0 part by weight of a radical polymerization initiator, and heating to a temperature at which the radical polymerization initiator is not substantially decomposed and the vinyl monomer is not substantially polymerized, A temperature at which the polypropylene resin particles are impregnated with a vinyl monomer and a radical polymerization initiator in an aqueous suspension, and the crystals in the polypropylene resin particles can complete melting of the aqueous suspension. By heating to the above temperature to graft-copolymerize the vinyl monomer to the polypropylene resin particles, the polypropylene-based polymer molecule is grafted with one or more vinyl graft chains of the vinyl monomer on average, Pre-expanded particles obtained by obtaining modified polypropylene resin particles having a chain weight average molecular weight of 200 or more and pre-expanding the modified polypropylene resin particles. 5. The pre-expanded particles according to claim 4, wherein the amount of the radical polymerization initiator is 0.5 to 5 parts by weight with respect to 100 parts by weight of the polypropylene resin particles. 6. The pre-expanded particles according to claim 4, wherein the amount of the vinyl monomer is 1 to 50 parts by weight based on 100 parts by weight of the polypropylene resin particles. 7. The D of the modified polypropylene resin particles
The pre-expanded particles according to claim 4, 5 or 6, wherein the peak temperature of the DSC chart measured by SC is lower by 1 ° C or more than the peak temperature of the DSC chart of the polypropylene resin particles before graft copolymerization measured by DSC. 8. The D of the modified polypropylene resin particles
The pre-expanded particles according to claim 4, 5 or 6, wherein the peak temperature of the DSC chart measured by SC is 5 ° C or more lower than the peak temperature of the DSC chart of the polypropylene resin particles before graft copolymerization measured by DSC. 9. A foam-molded article obtained by in-mold molding of the pre-expanded particles according to any one of claims 4 to 8.