JP2011168695A - Polypropylene resin composition for inorganic physical expansion molding, and foamed article thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polypropylene resin composition for inorganic physical expansion molding capable of obtaining a fine foamed article having fine and uniform bubbles having, for example, an average cell diameter of 1,000 nm or less, and a foamed article thereof. <P>SOLUTION: The polypropylene resin composition for the inorganic physical expansion molding contains a graft copolymer comprising a polymer of an ethylenic unsaturated monomer (b) having a polypropylene resin (a) as a main chain component and a (meth)acrylate or vinyl carboxylate as a side chain component. The polymer of the ethylenic unsaturated monomer (b) constituting the graft copolymer is a crosslinked product in which a number average dispersed particle diameter is 100-1,000 nm and standard deviation relative to the average dispersed particle diameter is 5-20%. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  TECHNICAL FIELD The present invention relates to an inorganic physical foam molding polypropylene resin composition capable of obtaining a fine cell foam having a small cell diameter and uniform cells, and the foam.

  Conventionally, a foam made of a thermoplastic resin has been widely used in the fields of food containers, building materials, and the like due to its excellent heat insulation and shock absorption. As a typical manufacturing method of a thermoplastic resin foam, there are roughly two types, a chemical foaming method and a physical foaming method. The chemical foaming method is a method of foaming by mixing a thermoplastic resin with a low molecular weight chemical foaming agent such as an azo compound and heating it to a temperature equal to or higher than the decomposition temperature of the chemical foaming agent. However, the decomposition residue of the chemical foaming agent causes problems such as discoloration of the resulting foam and food hygiene problems, and the chemical foaming agent itself has a particle size distribution, so the thickness and density of the resulting foam There is a problem of non-uniformity.

  On the other hand, the physical foaming method is a method in which a low-boiling organic physical foaming agent such as butane is supplied to a thermoplastic resin, kneaded, and then foamed by extrusion into a low pressure region. This method has a feature that a wide range of foams from a low magnification to a high magnification can be easily produced by adjusting the amount of foaming agent added to the thermoplastic resin. However, since a foaming agent such as butane has flammability and toxicity, there is a problem that it must be cured until the concentration of the foaming agent remaining in the foamed molded product is lowered.

  In recent years, an inorganic physical foam molding method using an inorganic physical foaming agent such as carbon dioxide or nitrogen has been proposed. Since these inorganic physical foaming agents are harmless and have no concern about environmental burden, they have a feature that a curing period after foam production is unnecessary. Moreover, since the foam diameter of the foam obtained by this method is finer (less than 10 μm) than the foam diameter of conventional foams (about 100 μm or more), it has the characteristics of excellent mechanical characteristics and optical characteristics. This is a foaming agent that is currently attracting attention.

  However, when a polypropylene resin is used as the thermoplastic resin, since it has crystallinity, the viscosity and melt tension at the time of melting are low, and when this resin is foamed, there is a problem that bubbles are easily broken at the time of foaming. For this reason, when polypropylene resin is foamed, it is difficult to obtain a fine (10 μm or less) cell diameter, which is an advantage of an inorganic physical foam molding method, and a low-density foam excellent in appearance and secondary workability. It is difficult to obtain

  As a method for solving this problem, there is a method for improving the melt tension of a polypropylene resin by mixing a polypropylene resin with an organic peroxide having a special structure to cause a crosslinking reaction as a foam molding resin composition. It has been proposed (see, for example, Patent Document 1). By foaming this resin composition, a foam excellent in appearance and secondary processability can be obtained.

  In addition, as a physical foam molding resin composition using carbon dioxide, a thermoplastic resin having low carbon dioxide solubility (for example, polypropylene resin) and a thermoplastic resin incompatible with polypropylene resin and having high carbon dioxide solubility (for example, A method using a polymer alloy comprising (polyethylene glycol) has been proposed (see, for example, Patent Document 2). By foaming this resin composition with carbon dioxide, bubbles are foamed only in a thermoplastic resin having a high solubility of carbon dioxide, so that a foam having a uniform and fine cell diameter can be obtained.

Furthermore, as a polymer alloy material in which a thermoplastic resin having an amorphous property (for example, polymethyl methacrylate resin) is controlled to have a dispersed particle size of 5 μm or less in a thermoplastic resin having crystallinity (for example, a polypropylene resin), A graft copolymer of a thermoplastic resin having crystallinity and an amorphous thermoplastic resin has been proposed (see, for example, Patent Document 3). When this resin composition is foamed in a temperature range where the elastic modulus of the resin composition is 5.0 × 10 ⁸ Pa or less, foaming is performed only from the amorphous thermoplastic resin dispersed in advance. The bubble diameter becomes as fine as 5 μm or less, and a foam excellent in light weight, high strength, heat insulation and optical properties can be obtained.

  On the other hand, a method for obtaining a graft copolymer of a polypropylene resin and a polymer of an ethylenically unsaturated monomer (for example, polymethyl methacrylate) has been proposed (for example, see Patent Document 4). That is, after impregnating an ethylenically unsaturated monomer (for example, methyl methacrylate) and an ethylenically unsaturated monomer having an organic peroxide group in a polypropylene resin, the ethylenically unsaturated monomer This is a method of melt-kneading a raw material obtained by radical polymerization of a mixture under conditions in which decomposition of the organic peroxide in the ethylenically unsaturated monomer having an organic peroxide group does not substantially occur.

JP 2004-339365 A JP 2005-271504 A JP 2008-303236 A Japanese Examined Patent Publication No. 4-76383

  However, in the material described in Patent Document 1, the foam molding condition range for obtaining a foam excellent in appearance and secondary workability is extremely narrow, and thus it is difficult to obtain a foam having a stable quality. It was. In addition, in the materials described in Patent Documents 2 to 4, the dispersion particle size is different when the conditions (the type of molding machine and molding die, plasticizing conditions, thermal history, etc.) at the time of molding the material are changed. It was difficult to obtain a foam having a constantly stable cell diameter.

  Accordingly, an object of the present invention is to provide an inorganic physical foam capable of obtaining a fine cell foam having fine and uniform cells with an average cell diameter of 1000 nm or less, for example, without selecting conditions for foam molding. It is providing the polypropylene resin composition for shaping | molding and its foam.

  In order to achieve the above object, the polypropylene resin composition for inorganic physical foam molding according to the first invention has a main chain component represented by a polypropylene resin (a) and a side chain component represented by the following chemical formula (1) (meta In the polypropylene resin composition containing a graft copolymer composed of a polymer of ethylenically unsaturated monomer (b) which is an acrylate ester or vinyl carboxylate represented by the following chemical formula (2), the graft copolymer The polymer of the ethylenically unsaturated monomer (b) constituting the coalescence is a crosslinked product having a number average particle diameter of 100 to 1000 nm and a standard deviation with respect to the number average particle diameter of 5 to 20%. Features.

（Ｒ^１は水素またはメチル基を示す。Ｒ^２はＣ_ｍＨ_ｍ＋１、ｍ＝１〜４の整数を示す。）

(R ¹ represents hydrogen or a methyl group. R ² represents an integer of C _m H _{m + 1} and m = 1 to 4.)

（Ｒ^３はＣ_ｎＨ_ｎ＋１、ｎ＝１〜４の整数を示す。）
第２の発明の無機系物理発泡成形用ポリプロピレン樹脂組成物は、第１の発明において、前記エチレン性不飽和単量体（ｂ）が、メタクリル酸メチルであることを特徴とする。

^{(R 3} represents an integer of _{C n H n + 1, n} = 1~4.)
The polypropylene resin composition for inorganic physical foam molding of the second invention is characterized in that, in the first invention, the ethylenically unsaturated monomer (b) is methyl methacrylate.

The polypropylene resin composition for inorganic physical foam molding of the third invention is characterized in that, in the first or second invention, the ethylenically unsaturated monomer (b) is vinyl acetate.
The polypropylene resin composition for inorganic physical foam molding according to a fourth aspect of the invention is the invention according to any one of the first to third aspects, wherein the graft copolymer is ethylenically unsaturated in the polypropylene resin (a). A polypropylene resin composition precursor obtained by impregnating and polymerizing a monomer (b), an ethylenically unsaturated monomer (c) having an organic peroxide group, and toluene (d) is used as the organic peroxide. What is obtained by melt kneading at a temperature 65 to 120 ° C. higher than the decomposition start temperature in the temperature rising process of 10 ° C./min using a scanning differential calorimeter of the ethylenically unsaturated monomer (c) having a group It is characterized by being.

  The polypropylene resin composition for inorganic physical foam molding of the fifth invention is the polypropylene resin composition for inorganic physical foam molding of the fourth invention, wherein the ethylenically unsaturated monomer (c) having an organic peroxide group is t-butylperoxymethacryloyloxyethyl. It is carbonate or t-butylperoxyallyl carbonate.

  The foam of the sixth invention is obtained by foaming the propylene resin composition for inorganic physical foam molding according to any one of the first to fifth inventions with an inorganic physical foaming agent. .

According to the present invention, the following effects can be exhibited.
The polypropylene resin composition for inorganic physical foam molding according to the first invention is a specific ethylenic unsaturation wherein the main chain component is a polypropylene resin (a) and the side chain component is represented by the chemical formula (1) or (2). It contains a graft copolymer comprising a polymer of monomer (b). Further, the polymer of the ethylenically unsaturated monomer (b) has a number average particle size of 100 to 1000 nm and a standard deviation of 5 to 20% with respect to the number average particle size is finely and uniformly dispersed cross-linked. Is the body.

  Therefore, in comparison with the polypropylene resin composition for inorganic physical foam molding containing a graft copolymer in which the specific ethylenically unsaturated monomer (b) is not crosslinked, the resin composition is subjected to foam molding. A fine cell foam having a fine and uniform cell diameter can be obtained without depending on conditions.

  In the polypropylene resin composition for inorganic physical foam molding in the second invention, the specific ethylenically unsaturated monomer (b) in the first invention is methyl methacrylate. For this reason, in addition to the effects of the first invention, methyl methacrylate is excellent in affinity with inorganic physical foaming agents such as carbon dioxide gas, and a fine cell foam having a finer and uniform cell diameter is obtained. It is done.

  In the polypropylene resin composition for inorganic physical foam molding in the third invention, the specific ethylenically unsaturated monomer (b) in the first or second invention is vinyl acetate. For this reason, in addition to the effects of the first or second invention, the fine cell foam has a finer and more uniform cell diameter in which vinyl acetate is excellent in affinity with an inorganic physical foaming agent such as carbon dioxide gas. Is obtained.

  In the polypropylene resin composition for inorganic physical foam molding in the fourth invention, the graft copolymer is an ethylene having an ethylenically unsaturated monomer (b) and an organic peroxide group in the polypropylene resin (a). A polypropylene resin composition precursor obtained by impregnating and polymerizing a polymerizable unsaturated monomer (c) and toluene (d), and a scanning type of an ethylenically unsaturated monomer (c) having an organic peroxide group It is formed by melt-kneading at a temperature 65 to 120 ° C. higher than the decomposition start temperature in the temperature rising process of 10 ° C./min using a differential calorimeter.

  Therefore, a method in which the ethylenically unsaturated monomer (c) having an organic peroxide group is not used, or the melt kneading temperature is higher than the decomposition start temperature of the ethylenically unsaturated monomer having an organic peroxide group. Compared with a polypropylene resin composition for inorganic physical foam molding obtained by a method of less than 65 ° C. or more than 120 ° C., fine and uniform air bubbles without depending on the conditions for foam molding of the resin composition A fine cell foam having a diameter is obtained.

  In the polypropylene resin composition for inorganic physical foam molding in the fifth invention, the ethylenically unsaturated monomer (c) having an organic peroxide group in the fourth invention is t-butylperoxymethacryloyloxyethyl carbonate or t. -Butylperoxyallyl carbonate. For this reason, in addition to the effect of 4th invention, while the graft reaction and crosslinking reaction of ethylenically unsaturated monomer (b) advance smoothly, the fine bubble foam which has a fine and uniform bubble diameter Is obtained.

  The foam in the sixth invention is obtained by foaming the polypropylene resin composition obtained by the first to fifth inventions with an inorganic physical foaming agent. Therefore, the foam has fine and uniform air bubbles, and quality such as lightness, mechanical properties, heat resistance, heat insulation, optical properties, etc., compared with the foam obtained by the conventional method. Can exhibit good and stable performance.

DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments embodying the present invention will be described in detail.
In the polypropylene resin composition for inorganic physical foam molding of this embodiment, the main chain component is a polypropylene resin (a), and the side chain component is a (meth) acrylate ester represented by the following chemical formula (1) or the following chemical formula (2). The graft copolymer which consists of a polymer of the ethylenically unsaturated monomer (b) which is vinyl carboxylate shown by these is contained. The polymer of the ethylenically unsaturated monomer (b) constituting the graft copolymer has a number average particle size of 100 to 1000 nm and a standard deviation of 5 to 20% with respect to the number average particle size. It is a crosslinked product dispersed in the resin (a).

（Ｒ^１は水素またはメチル基を示す。Ｒ^２はＣ_ｍＨ_ｍ＋１、ｍ＝１〜４の整数を示す。）

(R ¹ represents hydrogen or a methyl group. R ² represents an integer of C _m H _{m + 1} and m = 1 to 4.)

（Ｒ^３はＣ_ｎＨ_ｎ＋１、ｎ＝１〜４の整数を示す。）
前記グラフト共重合体の主鎖成分であるポリプロピレン樹脂（ａ）は、プロピレン単独重合体、またはプロピレンを主体とし他のエチレンおよび炭素数４以上のα−オレフィンからなる群から選ばれた少なくとも一種のオレフィンとの共重合体で、いずれもプロピレンが共重合体中の７５重量％以上を占めるものをいう。エチレンおよび炭素数４以上のα−オレフィンからなる群から選ばれた少なくとも一種のオレフィンとプロピレンとの共重合体としては、エチレンおよび炭素数４以上のα−オレフィンからなる群から選ばれた少なくとも一種のオレフィンとプロピレンとからなるプロピレン系ランダム共重合体、または、プロピレン単独重合体部分とプロピレン−エチレンランダム共重合体部分とを含有するプロピレン系ブロック共重合体が挙げられる。ポリプロピレン樹脂（ａ）の例としては、例えばアイソタクチックポリプロピレン、結晶性プロピレン−エチレンランダム共重合体、結晶性プロピレン−エチレンブロック共重合体、結晶性プロピレン−ブテン−１ランダム共重合体が挙げられる。

^{(R 3} represents an integer of _{C n H n + 1, n} = 1~4.)
The polypropylene resin (a), which is the main chain component of the graft copolymer, is at least one selected from the group consisting of propylene homopolymers or other ethylene and α-olefins having 4 or more carbon atoms mainly composed of propylene. Copolymers with olefins, all of which propylene accounts for 75% by weight or more of the copolymer. The copolymer of propylene and at least one olefin selected from the group consisting of ethylene and an α-olefin having 4 or more carbon atoms is at least one selected from the group consisting of ethylene and an α-olefin having 4 or more carbon atoms. And a propylene block copolymer containing a propylene homopolymer portion and a propylene-ethylene random copolymer portion. Examples of the polypropylene resin (a) include isotactic polypropylene, crystalline propylene-ethylene random copolymer, crystalline propylene-ethylene block copolymer, and crystalline propylene-butene-1 random copolymer. .

  Among these, isotactic polypropylene, crystalline propylene-ethylene random copolymer, or crystalline propylene-ethylene block copolymer is preferable, and isotactic polypropylene is more preferable. These propylene resins can be used alone or in admixture of two or more.

  Since the polypropylene resin (a) has fluidity that can be molded by a conventional molding machine, specifically, the melt flow rate (MFR) at 230 ° C. and a load of 2.16 kg is 0.2 to 40 g / 10 min. It is preferable that it is 0.5 to 20 g / 10 min. When this melt flow rate is less than 0.2 g / 10 min, the flowability of the polypropylene resin is insufficient and molding becomes difficult. On the other hand, when the melt flow rate exceeds 40 g / 10 min, the mechanical properties of the injection molded article deteriorate.

  The polymer of the specific ethylenically unsaturated monomer (b), which is a side chain component of the graft copolymer, is excellent in affinity with carbon dioxide gas, which is a representative inorganic physical foaming agent. The ethylenically unsaturated monomer (b) used as a raw material for the polymer is a monomer represented by the chemical formula (1) or the chemical formula (2).

  Examples of the ethylenically unsaturated monomer (b) represented by the chemical formula (1) include methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, acrylic acid-n-propyl, and methacrylic acid-n-propyl. , Isopropyl acrylate, isopropyl methacrylate, acrylic acid-n-butyl, methacrylic acid-n-butyl, acrylic acid-sec-butyl, methacrylic acid-sec-butyl, acrylic acid-t-butyl, methacrylic acid-t-butyl Etc. Among these, preferably methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, acrylic acid-n-propyl, methacrylic acid-n-propyl, acrylic acid-n-butyl or methacrylic acid-n-butyl More preferably, it is methyl methacrylate. These ethylenically unsaturated monomers can be used alone or in admixture of two or more.

  Examples of the ethylenically unsaturated monomer (b) represented by the chemical formula (2) include vinyl acetate, vinyl propionate, vinyl butyrate, vinyl valerate, and vinyl pivalate. Among these, vinyl acetate, vinyl propionate or vinyl butyrate is preferable, and vinyl acetate is most preferable. These ethylenically unsaturated monomers can be used alone or in admixture of two or more.

  The polymer of the specific ethylenically unsaturated monomer (b) that is a side chain component of the graft copolymer needs to be a crosslinked product. If it is not a cross-linked product, depending on the conditions when foam-molding the obtained polypropylene resin composition, the dispersed particle size and the uniformity of the dispersed particles of the polymer of a specific ethylenically unsaturated monomer pair (b) The fine bubble foam which changes and has a fine and uniform bubble diameter and is stable over time cannot be obtained.

  Whether the polymer of the specific ethylenically unsaturated monomer (b) is a cross-linked product is determined by placing the polypropylene resin composition in a cylindrical filter paper and extracting with a soluble solvent (for example, xylene) under reflux with Soxhlet extraction. When the mass of the polymer of the ethylenically unsaturated monomer (b) present in the extract was divided by the mass of the polymer of the ethylenically unsaturated monomer (b) charged, 5% It can be confirmed by the following.

  The crosslinked product has a number average particle size of 100 to 1000 nm, and its number average particle size is excellent in lightness, mechanical properties, heat resistance, heat insulation and optical properties, and a stable quality product is obtained. It is necessary that the standard deviation with respect to the diameter is dispersed at 5 to 20%. When the number average particle diameter exceeds 1000 nm, a fine cell foam having an average cell diameter of 1000 nm or less cannot be obtained by foam molding. On the other hand, when the number average particle diameter is less than 100 nm, the dispersed particle diameter of the crosslinked product becomes too fine, and the preparation thereof is difficult. On the other hand, when the standard deviation exceeds 20%, the particle diameter of the dispersed particles of the crosslinked product varies, and a desired fine cell foam cannot be obtained after foam molding. On the other hand, when the standard deviation is less than 5%, it is difficult to produce the crosslinked product.

The number average particle diameter of the dispersed particles of the crosslinked body and the standard deviation measurement method with respect to the number average particle diameter are obtained by preparing ultrathin sections having a thickness of 50 to 100 nm with an ultramicrotome from the obtained polypropylene resin composition (molded body). It is measured from the dispersed particle image of the polymer of the ethylenically unsaturated monomer (b) obtained by observation with a transmission electron microscope (TEM). The number average particle size is determined by counting the number of independent particles that can be confirmed in the field of view within a range of 100 μm ² (10 μm length, 10 μm width) or more, and measuring at least a total of 100 particle sizes with a graduated ruler. It means the number average particle size calculated by averaging. However, when the particle image obtained by TEM observation is not circular, the diameter of the circle when the area occupied by the particle is calculated and then replaced with a circle having the same area is referred to as the particle diameter. The standard deviation with respect to the number average particle size indicating the uniformity of the dispersed particle size of the crosslinked product is calculated by calculating the standard deviation (σ) of each particle size obtained for measuring the number average particle size. It calculated | required by correcting per particle size.

  The mass ratio of the polypropylene resin (a) which is the main chain component of the graft copolymer and the crosslinked product of the ethylenically unsaturated monomer (b) which is the side chain component is preferably 95/5 to 5/95. Range. When the mass of the polypropylene resin (a) of the graft copolymer exceeds 95% by mass, foaming does not occur. On the other hand, when the polypropylene resin (a) is less than 5% by mass, when the polypropylene resin (a) is further mixed with the graft copolymer, uniform dispersibility is not exhibited. It can no longer be obtained.

  Here, it is also possible to add a polypropylene resin (a) to the graft copolymer to the polypropylene resin composition. The addition amount of the polypropylene resin (a) is such that the mass ratio of the polypropylene resin and the polymer of the ethylenically unsaturated monomer (b) in the polypropylene resin composition is 95 regardless of whether or not graft copolymerization is performed. If it is the range of / 5-55 / 45, it will not specifically limit. In this case, a polymer alloy having a sea-island structure in which the polypropylene resin is the sea and the polymer of the ethylenically unsaturated monomer (b) is an island is formed. When the polypropylene resin in the polypropylene resin composition exceeds 95% by mass, foaming of the polypropylene resin composition hardly occurs. On the other hand, if the polypropylene resin in the polypropylene resin composition is less than 45% by mass, the polymer of the ethylenically unsaturated monomer (b) that forms the island of the polymer alloy having the sea-island structure forms the sea. , It becomes difficult for the bubbles to coalesce into a fine bubble foam.

Next, the manufacturing method of the said graft copolymer is demonstrated.
The graft copolymer is a mixture of an ethylenically unsaturated monomer (b), an ethylenically unsaturated monomer having an organic peroxide group (c), and toluene (d) in a polypropylene resin (a). It is obtained by a method of melt-kneading a copolymerized polypropylene resin composition precursor at a temperature 65 to 120 ° C. higher than the decomposition start temperature of the ethylenically unsaturated monomer (c).

  Conventionally known methods are employed as the method for producing the graft copolymer, but the method shown below is the most preferable method. This method consists of the following two steps. That is, an impregnation polymerization step for obtaining a polypropylene resin composition precursor and a grafting step for obtaining a polypropylene resin composition containing a graft copolymer are provided. In the impregnation polymerization step, a polypropylene resin (a) is impregnated with a mixture of an ethylenically unsaturated monomer (b), an ethylenically unsaturated monomer (c) having an organic peroxide group, and toluene (d). And a step of obtaining a polypropylene resin composition precursor by copolymerization with a radical polymerization initiator. The grafting step is a step of obtaining a polypropylene resin composition containing a graft copolymer by melt-kneading a polypropylene resin composition precursor.

  In the impregnation polymerization step, a radical polymerization initiator is added to a mixture of an ethylenically unsaturated monomer (b), an ethylenically unsaturated monomer having an organic peroxide group (c), and toluene (d), If it is the method of heating on the conditions which decomposition | disassembly of the organic peroxide group of the ethylenically unsaturated monomer (c) which has an organic peroxide group does not occur substantially, it will not specifically limit.

  A well-known thing is used as an ethylenically unsaturated monomer (c) which has an organic peroxide group. Specifically, t-butylperoxyacryloyloxyethyl carbonate (decomposition start temperature 135 ° C.), t-amyl peroxyacryloyloxyethyl carbonate (decomposition start temperature 133 ° C.), t-hexyl peroxyacryloyloxyethyl carbonate (decomposition start temperature 130). ° C), t-butylperoxymethacryloyloxyethyl carbonate (decomposition start temperature 136 ° C), t-amyl peroxymethacryloyloxyethyl carbonate (decomposition start temperature 134 ° C), t-hexylperoxymethacryloyloxyethyl carbonate (decomposition start temperature 131 ° C) Conjugated ethylenically unsaturated monomers such as t-butyl peroxyallyl carbonate (decomposition start temperature 130 ° C.), t-amyl peroxyallyl carbonate (decomposition start temperature 1) 8 ° C.), a non-conjugated ethylenically unsaturated monomers such as t- hexyl peroxy allyl carbonate (decomposition temperature 125 ° C.) and the like. Among these, t-butylperoxymethacryloyloxyethyl carbonate (decomposition start temperature 136 ° C.) is used as the conjugated ethylenically unsaturated monomer, and t-butylperoxyallyl carbonate (decomposed) is used as the nonconjugated ethylenically unsaturated monomer. More preferred is a starting temperature of 130 ° C. You may use these individually or in mixture of 2 or more types.

  The amount of the ethylenically unsaturated monomer (c) having an organic peroxide group is such that the ethylenically unsaturated monomer (b) and the ethylenically unsaturated monomer having an organic peroxide group (c Preferably, it is 0.1-5 mass parts with respect to 100 mass parts of mixtures with 0.5, More preferably, it is 0.5-3 mass parts. When the amount used is less than 0.1 part by mass, the polypropylene resin composition precursor has a small amount of active oxygen, and a sufficient graft copolymer cannot be obtained. On the other hand, when the amount used exceeds 5 parts by mass, a large amount of radicals are generated in the grafting step, so the degree of crosslinking of the crosslinked product formed from the polymer of the ethylenically unsaturated monomer (b) increases. The appearance of the molded product formed by molding the polypropylene resin composition is deteriorated, and the molded product is difficult to foam.

  The toluene (d) is not only a solvent for uniformly impregnating the ethylenically unsaturated monomer (b) in the impregnation polymerization step into the polypropylene resin (a), but also the ethylenic property in the impregnation polymerization step. Acts as a molecular weight regulator for polymerizing the unsaturated monomer (b) and a solvent for uniformly reacting a crosslinked product of the polymer of the ethylenically unsaturated monomer (b) in the grafting step It is an important substance.

  0.5-10 mass parts is preferable with respect to 100 mass parts of ethylenically unsaturated monomers (b), and, as for the addition amount of toluene (d), 0.7-2 mass parts is more preferable. When the amount of toluene (d) added is less than 0.5 parts by mass, the polymerization of the ethylenically unsaturated monomer (b) tends to be non-uniform in the impregnation polymerization step, and non-uniform in the subsequent grafting step. Since the reaction occurs, the dispersed particle size of the polymer of the ethylenically unsaturated monomer (b), that is, the crosslinked product becomes non-uniform. On the other hand, when the amount of toluene (d) added exceeds 10 parts by mass, the amount of toluene remaining in the resulting polypropylene resin composition increases, and the appearance during molding deteriorates.

  The radical polymerization initiator is a compound having a decomposition temperature for obtaining a half-life of 10 hours (hereinafter referred to as a 10-hour half-life temperature) of preferably 40 to 90 ° C, more preferably 50 to 75 ° C. This is because, as described above, the polymerization in the impregnation polymerization process must be performed under the condition that the ethylenically unsaturated monomer (c) having an organic peroxide group to be used is not decomposed. Since the 10-hour half-life temperature of the ethylenically unsaturated monomer (c) having an organic peroxide group is 90 to 110 ° C, the polymerization temperature is preferably 90 ° C or lower.

  When the 10-hour half-life temperature of the radical polymerization initiator exceeds 90 ° C., the polymerization temperature increases, and the ethylenically unsaturated monomer (c) having an organic peroxide group may be decomposed during the polymerization. is there. On the other hand, when the 10-hour half-life temperature of the radical polymerization initiator is less than 40 ° C., radicals are generated in the process of impregnating the polypropylene resin (a) with the radical polymerization initiator. As a result, the composition of the resulting polypropylene resin composition precursor tends to be non-uniform, and a non-uniform reaction occurs in the subsequent grafting step. Therefore, the polymer of the ethylenically unsaturated monomer (b), that is, the crosslinked product The dispersed particle size becomes non-uniform. Here, the 10-hour half-life temperature is a temperature at which the decomposition rate of the radical polymerization initiator is 50% when 0.1 mole of the radical polymerization initiator is added to 1 liter of benzene and 10 hours have passed at a certain temperature. Say.

  Examples of such radical polymerization initiators include di-n-propyl peroxydicarbonate (10-hour half-life temperature 40.3 ° C.), diisopropyl peroxydicarbonate (10-hour half-life temperature 40.5 ° C.), di (2 -Ethylhexyl) peroxydicarbonate (10-hour half-life temperature 43.6 ° C), t-hexyl peroxyneodecanate (10-hour half-life temperature 44.7 ° C), t-butylperoxyneodecanate (10-hour half-life temperature) 46.5 ° C.), t-hexyl peroxypivalate (10 hour half-life temperature 53.2 ° C.), t-butyl peroxypivalate (10 hour half-life temperature 55.0 ° C.), di (3,3,5- Trimethylhexanoyl) peroxide (10-hour half-life temperature 59.5 ° C), dilauroyl peroxide (10-hour half-life) 62.0 ° C), t-hexylperoxy-2-ethylhexanoate (10-hour half-life temperature 69.9 ° C), t-butylperoxy-2-ethylhexanoate (10-hour half-life temperature 72.5 ° C) ° C), dibenzoyl peroxide (74 ° C) and the like. You may use these individually or in mixture of 2 or more types.

  The amount of the radical polymerization initiator used is preferably 0.01 to 5 parts by mass, more preferably 0.1 to 3 parts by mass with respect to 100 parts by mass in total of the ethylenically unsaturated monomer mixture. When the amount of the radical polymerization initiator used is less than 0.01 parts by mass, the mixture of the ethylenically unsaturated monomer (b) and the ethylenically unsaturated monomer (c) having an organic peroxide group Polymerization is not performed completely and a good molded product cannot be obtained. On the other hand, when the usage-amount of a radical polymerization initiator exceeds 5 mass parts, the mechanical strength of the polypropylene resin composition molded object obtained will fall by the low molecular weight reduction by radical decomposition of polypropylene resin (a) during superposition | polymerization.

  The weight average molecular weight (Mw) of the copolymer of the mixture of the ethylenically unsaturated monomer (b) and the ethylenically unsaturated monomer (c) having an organic peroxide group is a differential refractive index detector. It is represented by a polystyrene conversion value by gel permeation chromatography (also referred to as gel permeation chromatography, also referred to as GPC). The weight average molecular weight is preferably 50,000 to 3,000,000, more preferably 100,000 to 2,000,000. When this weight average molecular weight is less than 50,000, in order to obtain a crosslinked product of a polymer of ethylenically unsaturated monomer (b), it has an ethylenically unsaturated monomer (b) and an organic peroxide group. The ethylenically unsaturated monomer (c) having an organic peroxide group in the mixture with the ethylenically unsaturated monomer (c) exceeds 10% by mass. Therefore, a lot of radicals are generated in the grafting step, and the mechanical strength of the obtained molded polypropylene resin composition is lowered due to the low molecular weight due to radical decomposition of the polypropylene resin (a). On the other hand, when the weight average molecular weight exceeds 3 million, melt kneading in the subsequent grafting step becomes difficult.

  The method of the impregnation polymerization step is performed by a commonly used aqueous suspension polymerization method. That is, a polypropylene resin (a) and a radical polymerization initiator prepared separately from the ethylenically unsaturated monomer (b), an ethylenically unsaturated monomer (c) having an organic peroxide group, and toluene ( The solution dissolved in the mixture with d) is stirred and dispersed in water in the presence of a suspending agent that can be used for aqueous suspension polymerization. As the suspending agent, for example, water-soluble polymer (partially saponified) polyvinyl alcohol, polyvinyl pyrrolidone, methyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, or the like, or a poorly water-soluble inorganic substance such as calcium phosphate, magnesium oxide or the like is used. .

  At this time, the impregnation of the solution into the polypropylene resin (a) is preferably performed at as high a temperature as possible. However, if the radical polymerization initiator decomposes and starts polymerization during impregnation, the composition of the resulting polypropylene resin composition precursor tends to be non-uniform, and a non-uniform reaction occurs in the subsequent grafting step. The dispersed particle size of the crosslinked polymer of the ethylenically unsaturated monomer (b) becomes non-uniform. Therefore, generally, it is preferable to carry out at a temperature lower by 5 ° C. or more than the 10-hour half-life temperature of the radical polymerization initiator used.

  Further, a mixture of a free ethylenically unsaturated monomer (b), an ethylenically unsaturated monomer (c) having an organic peroxide group, and toluene (d) and a radical polymerization initiator are mixed with a polypropylene resin (a It is preferable that the impregnation is carried out until the amount added is less than 50% by mass, preferably less than 20% by mass. When this amount is 50% by mass or more, the composition of the polypropylene resin composition precursor to be produced tends to be non-uniform, and a non-uniform reaction occurs in the subsequent grafting step. ), The dispersed particle size of the crosslinked polymer becomes non-uniform.

  The total amount of the mixture of the free ethylenically unsaturated monomer (b) and the ethylenically unsaturated monomer having an organic peroxide group (c) and the radical polymerization initiator is an arbitrary amount of the aqueous suspension. And is quickly filtered using a wire mesh of about 300 mesh to separate into a polypropylene resin (a) and a liquid phase, and the mixture of the ethylenically unsaturated monomer in the liquid phase and the radical polymerization initiator. Measure and calculate the amount.

  The polymerization for obtaining the polypropylene resin composition precursor is usually performed at a temperature of 30 to 110 ° C. This is to prevent decomposition of the ethylenically unsaturated monomer (c) having an organic peroxide group during polymerization as much as possible. When this temperature exceeds 110 ° C., when the polymerization time is 5 hours or more, the ethylenically unsaturated monomer (c) having an organic peroxide group is decomposed, and due to radical decomposition of the polypropylene resin (a). By lowering the molecular weight, the mechanical strength of the obtained molded polypropylene resin composition is lowered. In general, the polymerization time is suitably 2 to 20 hours.

In the impregnation polymerization step, a chain transfer agent as a molecular weight regulator or a polyfunctional ethylenically unsaturated monomer can be used in combination so as not to impair workability and physical properties.
In the grafting step, the aforementioned polypropylene resin composition precursor is melt-kneaded at a temperature 65 to 120 ° C. higher than the decomposition start temperature of the ethylenically unsaturated monomer (c) having the organic peroxide group. Done. By this grafting step, a molded product of the polypropylene resin composition is obtained. The organic peroxide group in the ethylenically unsaturated monomer (c) having the organic peroxide group contributes to the graft reaction with the polypropylene resin (a) that becomes the main chain of the graft copolymer by melt kneading. is doing. In addition, when the graft reaction temperature is 65 to 120 ° C. higher than the decomposition start temperature of the ethylenically unsaturated monomer (c) having an organic peroxide group, not only the graft reaction but also the graft copolymer It contributes also to the crosslinking reaction of the polymer of the ethylenically unsaturated monomer (b) which becomes the side chain of

  Here, when the difference between the melt kneading temperature and the decomposition start temperature of the ethylenically unsaturated monomer (c) having an organic peroxide group is less than 65 ° C., the ethylenically unsaturated monomer (b) Since this polymer does not become a cross-linked product, a fine cell foam having a fine and uniform cell diameter cannot be obtained depending on the conditions at the time of foam molding the resulting polypropylene resin composition. On the other hand, when the difference between the melt kneading temperature and the decomposition start temperature of the ethylenically unsaturated monomer (c) having an organic peroxide group exceeds 120 ° C., radicals are instantaneously generated during the melt kneading. It will be deactivated. Therefore, the graft reaction and the cross-linking reaction do not occur, and a fine cell foam having a fine and uniform cell diameter cannot be obtained depending on the conditions at the time of foam molding of the obtained polypropylene resin composition.

  The melt kneading time in the grafting step is preferably 30 to 300 seconds, and most preferably 60 to 120 seconds. When the melt kneading time is less than 30 seconds, uniform kneading is difficult. When the melt kneading time is longer than 300 seconds, the crosslinked polymer of the polypropylene resin (a) or ethylenically unsaturated monomer (b) is decomposed by kneading, and the The saturated monomer (b) polymer cannot be dispersed so that the number average particle diameter of the polymer is 100 to 1000 nm and the standard deviation with respect to the number average particle diameter is 5 to 20%.

  The melt kneading apparatus is not particularly limited as long as it is a known one, but examples thereof include various extruders such as a single screw extruder and a twin screw extruder, and melt kneaders such as a Banbury mixer, a Brabender, a plastograph, a heat roll, and a kneader. It is done. In addition, the polypropylene resin composition may contain an ultraviolet absorber, an antioxidant, a crystal nucleating agent, an antistatic agent, a flame retardant, a filler, a pigment, a colorant, a release agent, a lubricant, an antibacterial agent, and the like as necessary. It can mix | blend in the range which does not impair the characteristic of a polypropylene resin composition.

  Next, the foam is impregnated with an inorganic physical foaming agent pressurized against the molded product of the polypropylene resin composition described above, and after the foaming agent is saturated in the molded product, foaming is performed. There is no particular limitation as long as it can be obtained. There is no restriction | limiting in particular as a foaming method, Both the pressure reduction foaming method which foams by reducing pressure rapidly, and the temperature rising foaming method which heats up and foams can be employ | adopted. However, the foaming temperature is preferably not higher than the temperature (170 ° C.) at which the polypropylene resin (a) flows.

  Examples of the inorganic physical foaming agent include carbon dioxide, nitrogen, helium, argon, nitrous oxide, ethylene, ethane, tetrafluoroethylene, perfluoroethane, tetrafluoromethane, etc. Among these, carbon dioxide or nitrogen is used. Preferably, carbon dioxide is more preferred.

  It is desirable that the expansion ratio when foaming the molded body of the polypropylene resin composition is about 1.1 to 5 times. When the expansion ratio is less than 1.1 times, the obtained foam cannot fully exhibit the function as a foam, and when it exceeds 5 times, the expansion ratio becomes too high and the strength of the foam Is not preferable.

  In order to make the obtained foam into a fine cell foam having fine and uniform cells, the number average cell diameter is preferably 1000 nm or less, and more preferably 50 to 800 nm. When the number average bubble diameter exceeds 1000 nm, the bubbles do not become fine, and the function as a fine bubble foam cannot be expressed. Moreover, it is preferable that the standard deviation with respect to the number average bubble diameter is 5 to 25%. When the standard deviation exceeds 25%, the uniformity of the bubbles cannot be obtained, and the function of the fine bubble foam deteriorates.

  By using the above-mentioned polypropylene resin composition, a fine cell foam having fine and uniform cells can be obtained, and the micro cell foam has physical properties such as lightness, mechanical properties, heat insulating properties and optical properties. Is excellent.

  If necessary, the foam may be subjected to surface treatment such as corona treatment, printing, coating, and vapor deposition as long as the characteristics are not impaired. The foam obtained in this way is a reflective material used in liquid crystal display devices, lighting fixtures, lighting signs, etc., application to the material field requiring low dielectric constant, high strength porous material, heat insulating material, cushioning material, etc. It can be effectively used for various purposes.

Hereinafter, the embodiment will be described more specifically with reference to examples and comparative examples. Various physical property values in each example were measured by the following methods.
(1) Melt flow rate (MFR) of polypropylene resin
The melt flow rate (g / 10 min) at a cylinder temperature of 230 ° C. and a load of 2.16 kg was measured using a melt flow measuring device (melt flow indexer, manufactured by Toyo Seiki Seisakusho, TYPEC-5059D) based on JISK7210. .
(2) Weight average molecular weight (Mw) of polymer of ethylenically unsaturated monomer (b) in polypropylene resin precursor
A polymer obtained by immersing a polypropylene resin precursor in tetrahydrofuran (hereinafter referred to as “THF”) and drying under reduced pressure for 8 hours to obtain a polymer obtained by subjecting the polymer to a gel permeation chromatography apparatus equipped with a differential refractive index detector [GPC, (Manufactured by Shimadzu Corporation)], and the eluate was determined in terms of standard polystyrene with THF as the eluate and a column temperature of 40 ° C.
(3) Dispersibility of cross-linked copolymer of ethylenically unsaturated monomer (b) in polypropylene resin composition and molded body Copolymerization of ethylenically unsaturated monomer (b) in polypropylene resin composition Measurement of the number average particle diameter of the polymer crosslinked product and the standard deviation with respect to the number average particle diameter: From the molded product of the obtained polypropylene resin composition, an ultramicrotome [Ultracut UCT, manufactured by Leica Co., Ltd.] was used, and the thickness was 50 to 100 nm. Ultrathin sections were prepared. The obtained ultrathin slice was observed and photographed for the dispersion state of the ethylenically unsaturated monomer copolymer using a transmission electron microscope (TEM) [JEM-1600EX, manufactured by JEOL Ltd.].

Using a plurality of the obtained TEM photographs, the number of independent particles that can be confirmed in the visual field was counted in a range of 100 μm ² (10 μm in length, 10 μm in width) or more. Further, in the TEM photograph, a plurality of arbitrary photographs were selected so that the total number of particles was 100 or more, the particle diameter was measured with a ruler with a scale, and the number average particle diameter was calculated. Furthermore, the standard deviation (σ) of each particle size was calculated and corrected per number average particle size to obtain the standard deviation with respect to the number average particle size.
(4) Confirmation of crosslinked polymer of ethylenically unsaturated monomer (b) in polypropylene resin composition Uncrosslinked polymer of ethylenically unsaturated monomer (b) in polypropylene resin composition Quantitative determination: 0.5 g of polypropylene resin composition was accurately weighed, and cylindrical filter paper [manufactured by Advantech Co., Ltd., No. 86R] and extracted with xylene using a Soxhlet extractor for 24 hours. The obtained extract was added to 10 times the amount of THF solvent to precipitate the polypropylene resin (a), and the filtered solution was dried under reduced pressure by an evaporator. In the polypropylene resin composition, the mass is measured and divided by the total mass of the ethylenically unsaturated monomer (b) used and the ethylenically unsaturated monomer (c) having an organic peroxide group. The uncrosslinked product (%) of the polymer of ethylenically unsaturated monomer (b) was calculated. In addition, the thing whose this number is 5% or less is judged as a crosslinked body, and the thing over 5% is judged as an uncrosslinked body.
(5) Confirmation of graft copolymer of polypropylene resin (a) and cross-linked polymer of ethylenically unsaturated monomer (b) 0.5 g of polypropylene resin composition was accurately weighed and cylindrical filter paper [ Manufactured by Advantech Co., Ltd. 86R] and extracted with xylene using a Soxhlet extractor for 24 hours. After drying the polymer present in the cylindrical filter paper, the polypropylene resin was quantified by pyrolysis gas chromatography, and the content of the polypropylene resin (a) in the graft copolymer was calculated.
(6) Dispersion state of foamed bubbles of polypropylene resin composition foam Number average cell diameter in polypropylene resin composition foam and measurement of standard deviation with respect to the number average cell diameter: The obtained polypropylene resin composition foam is liquid It was immersed in nitrogen and freeze fractured. The obtained fracture surface was vapor-deposited in gold, and the dispersion state of the foamed bubble diameter was observed and photographed using a scanning electron microscope (SEM) [S-3000N, manufactured by Hitachi High-Tech Co., Ltd.]. Using a plurality of the obtained SEM photographs, the number of independent bubble particles that can be confirmed in the visual field was counted in a range of 400 μm ² (vertical 20 μm, horizontal 20 μm) or more. In addition, in the SEM photograph, a plurality of arbitrary photographs were selected so that the total number of bubble particles was 100 or more, the particle diameter was measured with a ruler with a scale, and the number average bubble diameter was calculated. Furthermore, the standard deviation of each bubble diameter was calculated, and the standard deviation with respect to the number average bubble diameter was determined by correcting it per number average bubble diameter.
(7) Foaming ratio of polypropylene resin composition foam Specific gravity (d ₂ ) of the obtained polypropylene resin composition foam (0.5 g) using a solid specific gravity meter [SD-200L, Alpha Mirage Co., Ltd.]. ) Was measured. The specific gravity (d ₁ ) of the polypropylene resin composition before foaming was also measured by the same method, and the foaming ratio was calculated by the following formula.

Foaming ratio (times) = d ₁ / d ₂
The raw materials used in the examples and comparative examples are as follows.
Polypropylene resin (a): manufactured by Nippon Polypro Co., Ltd., trade name “Novatech PP FY4”, propylene homopolymer (isotactic polypropylene), melt flow rate (MFR) = 5.0 g / 10 min
Ethylenically unsaturated monomer (b): Methyl methacrylate (MMA) manufactured by Mitsubishi Gas Chemical Co., Ltd., Butyl Acrylate (BA) manufactured by Nippon Shokubai Co., Ltd. VAc), vinyl pivalate (VPv) manufactured by Nihon Vinegar Poval Co.
Ethylenically unsaturated monomer having an organic peroxide group (c): t-butylperoxy-2-methacryloyloxyethyl carbonate manufactured by NOF Corporation, trade name “Peromer MEC (MEC)”, NOF Corporation ) T-Butylperoxyallyl monocarbonate, trade name "Peromer AC (AC)"
Toluene (d): Special grade reagent manufactured by Wako Pure Chemical Industries, Ltd. Radical polymerization initiator: Dilauroyl peroxide (LPO) manufactured by NOF Corporation, trade name “PAROIL L”
(Example 1-1)
700 parts by mass of polypropylene resin was placed in a separable flask made of stainless steel having an internal volume of 5000 ml, and 2500 ml of pure water and 2.5 parts by mass of polyvinyl alcohol as a suspending agent were added. Separately, as an ethylenically unsaturated monomer having an organic peroxide group in 300 parts by mass of methyl methacrylate (MMA), 6 parts by mass of t-butylperoxy-2-methacryloyloxyethyl carbonate (MEC), 6 parts by mass of toluene and a radical As a polymerization initiator, 1.5 parts by mass of dilauroyl peroxide (LPO) was dissolved, and this solution was put into the separable flask and stirred. Then, this was kept at 40 ° C. and stirred for about 6 hours to impregnate polypropylene resin with MMA, MEC and LPO. The temperature was then raised to 60 ° C. and maintained at that temperature for 5 hours to complete the polymerization, washed with water and dried to obtain a grafted precursor. The graft precursor MMA and MEC copolymer was extracted with chloroform and dried, and the weight average molecular weight (Mw) was measured.

  Next, this polypropylene resin composition precursor was extruded at 230 ° C. with a single screw extruder (manufactured by Toyo Seiki Seisakusho Co., Ltd.) and grafted to obtain a polypropylene resin composition containing a graft copolymer. The dispersion form of the MMA polymer (PMMA) in this polypropylene resin composition was measured by TEM and shown in Table 1. Further, the graft efficiency of PMMA and the average swelling particle diameter in toluene were measured from the insoluble matter obtained by Soxhlet extraction of this graft copolymer with o-dichlorobenzene at 160 ° C. for 1 hour.

The obtained graft copolymer was cut into a size of 100 mm in length and 100 mm in width, placed in a metal spacer having a length of 100 mm, a width of 100 mm, and a thickness of 0.25 mm, and using a hot press set at 200 ° C., 10 MPa Was held at 25 ° C. for 1 minute and a molded body was obtained. The dispersion form of PMMA in this molded body was measured by TEM and shown in Table 1.
(Example 1-2)
Example 1-1 is the same as Example 1-1 except that polypropylene resin is changed to 950 parts by mass, MMA is changed to 50 parts by mass, MEC is changed to 1 part by mass, toluene is 1 part by mass, and LPO is changed to 0.25 parts by mass. A polypropylene resin composition and a molded body were obtained in the same manner as described above. These were evaluated in the same manner as in Example 1-1, and the results are shown in Table 1.
(Example 1-3)
Example 1-1 is the same as Example 1-1 except that polypropylene is changed to 550 parts by mass, MMA is changed to 450 parts by mass, MEC is changed to 9 parts by mass, toluene is 9 parts by mass, and LPO is changed to 2.25 parts by mass. A polypropylene resin composition and a molded body were obtained in the same manner. These were evaluated in the same manner as in Example 1-1, and the results are shown in Table 1.
(Example 1-4)
In Example 1-1, a polypropylene resin composition and a molded body were obtained in the same manner as in Example 1-1 except that MMA was changed to butyl acrylate (BA). These were evaluated in the same manner as in Example 1-1, and the results are shown in Table 1.
(Example 1-5)
In Example 1-1, a polypropylene resin composition, a molded product and a foam were obtained in the same manner as in Example 1-1 except that MMA was changed to vinyl acetate (VAc) and MEC was changed to AC. These were evaluated in the same manner as in Example 1-1, and the results are shown in Table 1.
(Example 1-6)
In Example 1-1, a polypropylene resin composition, a molded body and a foam were obtained in the same manner as in Example 1-1 except that MMA was changed to vinyl pivalate (VPv) and MEC was changed to AC. These were evaluated in the same manner as in Example 1-1, and the results are shown in Table 1.
(Examples 2-1 to 2-6)
The molded product of the polypropylene resin composition obtained in Examples 1-1 to 1-6 was put into an autoclave whose temperature was adjusted to 40 ° C., pressurized to 10 MPa with carbon dioxide (carbon dioxide), and carbon dioxide was applied to the molded product. Was impregnated for 6 hours. After that, fully open the leak valve of the autoclave, release the pressure in the autoclave at a depressurization rate of 0.5 MPa / sec, and immediately immerse the removed molded body in an oil bath set at 80 ° C. for 1 minute. A foam was obtained by immersion in water at 25 ° C. The foam foam dispersion and foaming ratio of the obtained foam were measured and shown in Table 1.

（実施例１−７）
実施例１−１において、ＭＥＣ６質量部をＭＥＣ０．３質量部に変更した以外は実施例１−１と同様の方法でポリプロピレン樹脂組成物および成形体を得た。これらを実施例１−１と同様の方法で評価し、その結果を表２に示した。
（実施例１−８）
実施例１−１において、ＭＥＣ６質量部をＭＥＣ１５質量部に変更した以外は実施例１−１と同様の方法でポリプロピレン樹脂組成物および成形体を得た。これらを実施例１−１と同様の方法で評価し、その結果を表２に示した。
（実施例１−９）
実施例１−１において、トルエン６質量部をトルエン１．５質量部に変更した以外は実施例１−１と同様の方法でポリプロピレン樹脂組成物および成形体を得た。これらを実施例１−１と同様の方法で評価し、その結果を表２に示した。
（比較例１−１）
実施例１−１において、ＭＥＣ６質量部をＭＥＣ０質量部に、トルエン６質量部をトルエン０質量部に変更した以外は実施例１−１と同様の方法でポリプロピレン樹脂組成物および成形体を得た。これらを実施例１−１と同様の方法で評価し、その結果を表２に示した。
（比較例１−２）
実施例１−１において、トルエン６質量部をトルエン０質量部に、グラフト化反応温度を２００℃に変更した以外は実施例１−１と同様の方法でポリプロピレン樹脂組成物および成形体を得た。これらを実施例１−１と同様の方法で評価し、その結果を表２に示した。
（比較例１−３）
実施例１−１において、トルエン６質量部をトルエン０質量部に、グラフト化反応温度を２６０℃に変更した以外は実施例１−１と同様の方法でポリプロピレン樹脂組成物および成形体を得た。これらを実施例１−１と同様の方法で評価し、その結果を表２に示した。
（実施例２−７〜２−９および比較例２−１〜２−３）
実施例１−７〜１−９および比較例１−１〜１−３で得られたポリプロピレン樹脂組成物の成形体を４０℃に温度調節されたオートクレーブに投入し、炭酸ガス（二酸化炭素）で１０ＭＰａに加圧し、成形体に二酸化炭素を６時間含浸させた。その後、オートクレーブのリークバルブを全開放し、減圧速度０.５ＭＰａ／ｓｅｃでオートクレーブ内の圧力を開放し、取り出した成形体を瞬時にあらかじめ８０℃に設定されたオイルバス中で１分間浸漬し、その後２５℃の水に浸漬して発泡体を得た。得られた発泡体の発泡気泡の分散形態および発泡倍率を測定し、表２に示した。

(Example 1-7)
In Example 1-1, a polypropylene resin composition and a molded body were obtained in the same manner as in Example 1-1, except that 6 parts by mass of MEC was changed to 0.3 parts by mass of MEC. These were evaluated in the same manner as in Example 1-1, and the results are shown in Table 2.
(Example 1-8)
In Example 1-1, a polypropylene resin composition and a molded body were obtained in the same manner as in Example 1-1 except that 6 parts by mass of MEC was changed to 15 parts by mass of MEC. These were evaluated in the same manner as in Example 1-1, and the results are shown in Table 2.
(Example 1-9)
In Example 1-1, a polypropylene resin composition and a molded body were obtained in the same manner as in Example 1-1 except that 6 parts by mass of toluene was changed to 1.5 parts by mass of toluene. These were evaluated in the same manner as in Example 1-1, and the results are shown in Table 2.
(Comparative Example 1-1)
In Example 1-1, a polypropylene resin composition and a molded body were obtained in the same manner as in Example 1-1 except that 6 parts by mass of MEC was changed to 0 parts by mass of MEC and 6 parts by mass of toluene were changed to 0 parts by mass of toluene. . These were evaluated in the same manner as in Example 1-1, and the results are shown in Table 2.
(Comparative Example 1-2)
In Example 1-1, a polypropylene resin composition and a molded body were obtained in the same manner as in Example 1-1 except that 6 parts by mass of toluene was changed to 0 parts by mass of toluene and the grafting reaction temperature was changed to 200 ° C. . These were evaluated in the same manner as in Example 1-1, and the results are shown in Table 2.
(Comparative Example 1-3)
In Example 1-1, a polypropylene resin composition and a molded body were obtained in the same manner as in Example 1-1 except that 6 parts by mass of toluene was changed to 0 parts by mass of toluene and the grafting reaction temperature was changed to 260 ° C. . These were evaluated in the same manner as in Example 1-1, and the results are shown in Table 2.
(Examples 2-7 to 2-9 and Comparative Examples 2-1 to 2-3)
The molded product of the polypropylene resin composition obtained in Examples 1-7 to 1-9 and Comparative Examples 1-1 to 1-3 was put into an autoclave whose temperature was adjusted to 40 ° C., and carbon dioxide gas (carbon dioxide) was used. The pressure was increased to 10 MPa, and the compact was impregnated with carbon dioxide for 6 hours. Thereafter, the autoclave leak valve is fully opened, the pressure in the autoclave is released at a depressurization rate of 0.5 MPa / sec, and the removed molded body is immediately immersed in an oil bath set at 80 ° C. for 1 minute. Thereafter, it was immersed in water at 25 ° C. to obtain a foam. The foam foam dispersion and foaming ratio of the obtained foam were measured and shown in Table 2.

表２に示したように、比較例１−１では有機過酸化物基を有するエチレン性不飽和単量体（ｃ）およびトルエン（ｄ）を含有しないポリプロピレン樹脂組成物を用いたため、ポリプロピレン樹脂（ａ）とエチレン性不飽和単量体（ｂ）の重合体とからなるグラフト共重合体が存在しなかった。従って、グラフト化工程後に得られたポリプロピレン樹脂組成物中に架橋体が存在せず、その成形体におけるエチレン性不飽和単量体（ｂ）の重合体の分散粒径が極めて大きくかつ不均一になるため、成形時の熱履歴によって分散粒径が異なる。さらに、比較例２−１では、比較例１−１のポリプロピレン樹脂組成物の成形体から得られる発泡体は、数平均気泡径が非常に大きくかつ不均一となる。

As shown in Table 2, in Comparative Example 1-1, a polypropylene resin composition containing no ethylenically unsaturated monomer (c) having an organic peroxide group and toluene (d) was used. There was no graft copolymer consisting of a) and a polymer of ethylenically unsaturated monomer (b). Therefore, there is no cross-linked product in the polypropylene resin composition obtained after the grafting step, and the dispersed particle size of the ethylenically unsaturated monomer (b) polymer in the molded product is extremely large and non-uniform. Therefore, the dispersed particle diameter varies depending on the thermal history during molding. Furthermore, in Comparative Example 2-1, the foam obtained from the molded product of the polypropylene resin composition of Comparative Example 1-1 has a very large number average cell diameter and is non-uniform.

  On the other hand, as shown in Table 1 and Table 2, in Examples 1-1 to 1-9, the ethylenically unsaturated monomer (c) having an organic peroxide group was changed to an ethylenically unsaturated monomer. (B) 0.1-5 parts by mass with respect to 100 parts by mass, 0.5-10 parts by mass of toluene (d) with respect to 100 parts by mass of the ethylenically unsaturated monomer (b), and grafting During the conversion step, the mixture was melt-kneaded at a temperature 65 ° C. to 120 ° C. higher than the decomposition start temperature of the ethylenically unsaturated monomer (c) having an organic peroxide group. For this reason, Comparative Example 1-2 melt-kneaded at a temperature lower than 65 ° C. or higher than 120 ° C. from the decomposition start temperature of the ethylenically unsaturated monomer (c) having an organic peroxide group during the grafting step and Compared with the polypropylene resin composition of 1-3, the polymer of the ethylenically unsaturated monomer (b) is cross-linked, and the polypropylene resin (a) is grafted, whereby ethylene due to heat history at the time of molding. The dispersed particle diameter of the polymer crosslinked product of the unsaturated unsaturated monomer (b) is small and uniform. From this, the foam which foamed the molded body of the polypropylene resin composition of Examples 2-1 to 2-9 foamed the molded body of the polypropylene resin composition of Comparative Examples 2-2 and 2-3. It became clear that a uniform fine foam having a small number average cell diameter as compared with the foam can be obtained. Therefore, a foam of a molded product obtained from the polypropylene resin composition can be a useful material for obtaining a fine foam molded product having excellent mechanical properties and reflection characteristics.

Claims (6)

An ethylenically unsaturated monomer in which the main chain component is a polypropylene resin (a) and the side chain component is a (meth) acrylic acid ester represented by the following chemical formula (1) or a vinyl carboxylate represented by the following chemical formula (2) ( In a polypropylene resin composition containing a graft copolymer comprising the polymer of b),
The polymer of the ethylenically unsaturated monomer (b) constituting the graft copolymer is a crosslinked product having a number average particle diameter of 100 to 1000 nm and a standard deviation with respect to the number average particle diameter of 5 to 20%. A polypropylene resin composition for inorganic physical foam molding, characterized in that

(R ¹ represents hydrogen or a methyl group. R ² represents an integer of C _m H _{m + 1} and m = 1 to 4.)

^{(R 3} represents an integer of _{C n H n + 1, n} = 1~4.) 2. The polypropylene resin composition for inorganic physical foam molding according to claim 1, wherein the ethylenically unsaturated monomer (b) is methyl methacrylate. 3. The polypropylene resin composition for inorganic physical foam molding according to claim 1, wherein the ethylenically unsaturated monomer (b) is vinyl acetate. The graft copolymer is impregnated with an ethylenically unsaturated monomer (b), an ethylenically unsaturated monomer (c) having an organic peroxide group, and toluene (d) in a polypropylene resin (a). The polypropylene resin composition precursor obtained by polymerization is subjected to a temperature rising process of 10 ° C./min using a scanning differential calorimeter of the ethylenically unsaturated monomer (c) having the organic peroxide group. The polypropylene resin composition for inorganic physical foam molding according to any one of claims 1 to 3, wherein the polypropylene resin composition is melt kneaded at a temperature 65 to 120 ° C higher than the decomposition start temperature. . The inorganic system according to claim 4, wherein the ethylenically unsaturated monomer (c) having an organic peroxide group is t-butylperoxymethacryloyloxyethyl carbonate or t-butylperoxyallyl carbonate. Polypropylene resin composition for physical foam molding. 6. A foam obtained by foaming the propylene resin composition for inorganic physical foam molding according to any one of claims 1 to 5 with an inorganic physical foaming agent.