JP7583537B2 - Thermally expandable microcapsules, molding resin composition, and foamed molded product - Google Patents

Description

The present invention relates to thermally expandable microcapsules, a molding resin composition using the thermally expandable microcapsules, and a foamed molded article made using the molding resin composition.

In the past, in order to reduce the weight and improve the functionality of resin materials, materials have been foamed using foaming agents, and thermally expandable microcapsules and chemical foaming agents have generally been used as such foaming agents.
Thermally expandable microcapsules are used in a wide range of applications, such as design-imparting agents and weight-reducing agents, and are also used in foaming inks, wallpapers, and other lightweight paints.
As such a thermally expandable microcapsule, one in which a volatile expanding agent that becomes gaseous at a temperature below the softening point of the shell polymer is encapsulated in a thermoplastic shell polymer is widely known. For example, Patent Document 1 discloses a method for producing a thermally expandable microcapsule encapsulating a volatile expanding agent by adding an oily mixture in which a volatile expanding agent such as a low-boiling aliphatic hydrocarbon is mixed with a monomer to an aqueous dispersion medium containing a dispersant together with an oil-soluble polymerization catalyst while stirring, and carrying out suspension polymerization.

However, although the thermally expandable microcapsules obtained by this method can be thermally expanded at relatively low temperatures of around 80 to 130°C, when heated at high temperatures or for long periods of time, the expanded microcapsules burst or shrink, reducing the expansion ratio, and this has the drawback that it is not possible to obtain thermally expandable microcapsules with excellent heat resistance.

On the other hand, Patent Document 2 discloses a method for producing a thermally expandable microcapsule containing a volatile expanding agent, using as a shell a polymer obtained from polymerization components containing 80 to 97% by weight of a nitrile monomer, 20 to 3% by weight of a non-nitrile monomer, and 0.1 to 1% by weight of a trifunctional crosslinking agent.
Patent Document 3 describes a thermally expandable microcapsule that uses a polymer obtained from polymerization components containing 80% by weight or more of a nitrile monomer, 20% by weight or less of a non-nitrile monomer, and 0.1 to 1% by weight of a crosslinking agent, and encapsulates a volatile expanding agent. In such a thermally expandable microcapsule, a methacrylic acid ester or an acrylic acid ester is used as the non-nitrile monomer.

The thermally expandable microcapsules obtained by these methods are said to have superior heat resistance compared to conventional microcapsules, and do not foam at temperatures below 140°C. However, in reality, some microcapsules will expand when heated at 130-140°C for about one minute, and it has been difficult to obtain thermally expandable microcapsules with excellent heat resistance and a maximum foaming temperature of 180°C or higher.

Furthermore, Patent Document 4 discloses a thermally expandable microcapsule comprising a shell polymer made of a homopolymer or copolymer of an ethylenically unsaturated monomer having 85% by weight or more of a nitrile group and a foaming agent containing 50% by weight or more of isooctane. The aim of such a thermally expandable microcapsule is to make the maximum foaming temperature 180° C. or higher.
In reality, however, although the maximum foaming temperature is very high, it is weak against shear during molding and is unable to maintain the expanded state thereafter, making it difficult to use for long periods of time in high temperature ranges.
In addition, Patent Documents 5 to 9 disclose thermally expandable microcapsules that have good foaming performance over a wide range of foaming temperatures, particularly in the high temperature range (160°C or higher), and have improved heat resistance, by specifying the monomers that constitute the shell of the thermally expandable microcapsule.

Special Publication No. 42-26524 Special Publication No. 5-15499 Patent No. 2894990 European Patent Application No. 1149628 International Publication No. 2003/099955 JP 2009-113037 A JP 2009-299071 A JP 2013-32542 A JP 2013-28818 A

Conventional thermally expandable microcapsules have a high maximum foaming temperature, but have a problem with durability in molding processes that apply strong shear forces, such as kneading molding, calendar molding, extrusion molding, injection molding, etc. In particular, when used in injection molding, problems with the heat resistance and strength of the thermally expandable microcapsules in the melt-kneading process cause a phenomenon known as "sagging" or collapse, resulting in yellowing of the molded product.
Furthermore, in the process of expanding the thermally expandable microcapsules, the expansion ratio is low and varies, so that the thermally expandable microcapsules do not expand sufficiently, and the resulting molded body is inferior in terms of appearance and functionality such as light weight.
Furthermore, white spots due to aggregation of the thermally expandable microcapsules appear on the surface of the foamed molded article, significantly impairing the appearance of the foamed molded article.
For this reason, there is a need for thermally expandable microcapsules that have excellent heat resistance and expansion ratio, and that are capable of producing foamed molded articles that are resistant to yellowing and have excellent appearance.

On the other hand, attempts have been made to improve the expansion ratio while preventing defects in the appearance of molded articles by using thermally expandable microcapsules in combination with a chemical foaming agent.
However, when they are used in combination in this way, the generated gas cannot be contained within the system, and problems occur such as the bubbles becoming open, and voids and gas escape occurring, resulting in a problem of reduced strength of the obtained foamed molded article.

The present invention aims to provide a thermally expandable microcapsule that can be used to produce molded articles that are durable against strong shear during molding, have high heat resistance and expansion ratio, are resistant to yellowing and have an excellent appearance, and are lightweight, hard, and highly abrasion-resistant.
Another object of the present invention is to provide a thermally expandable microcapsule which overcomes the problems of the generation of voids and gas escape and the decrease in strength that occur when a chemical foaming agent is used in combination.
Furthermore, the present invention aims to provide a thermally expandable microcapsule which has excellent fluidity when made into a multi-particle aggregate and can be steadily injected from a hopper or the like during molding.
Another object of the present invention is to provide a molding resin composition and a foam molded article using the thermally expandable microcapsules.

The present invention relates to a thermally expandable microcapsule having a maximum foaming temperature of 185°C or higher, in which a volatile expanding agent is encapsulated in the shell as a core agent, and the shell contains a copolymer having 35 to 45% by weight of nitrile polymer units and 55 to 65% by weight of polymer units of a carbonyl compound in which the α carbon is a quaternary carbon.
The present invention will be described in detail below.

The shell that constitutes the thermally expandable microcapsule of the present invention contains a copolymer (hereinafter also referred to as the shell-constituting copolymer) having a nitrile polymer unit and a polymer unit of a carbonyl compound in which the α carbon is a quaternary carbon.
The presence of the nitrile polymer unit can improve the gas barrier property of the shell. The nitrile polymer unit means a repeating unit of a nitrile compound.
Furthermore, by having polymer units of a carbonyl compound in which the α carbon is a quaternary carbon, it is possible to increase the heat resistance and extensional viscosity while maintaining the gas barrier properties of the shell, thereby improving the expansion ratio.

The above-mentioned shell-forming copolymer has a nitrile polymer unit content of 35 to 45% by weight. By keeping the content within this range, durability against shearing during molding, in which strong shearing forces are applied, can be maintained.
The preferred lower limit of the content of the nitrile polymer unit in the shell constituent copolymer is 36% by weight, and the preferred upper limit is 42% by weight.

The above nitrile compounds include aliphatic unsaturated nitriles such as acrylonitrile and methacrylonitrile. Among these, acrylonitrile and methacrylonitrile are preferred.

The above shell constituent copolymer has 55 to 65% by weight of polymer units of a carbonyl compound in which the α carbon is a quaternary carbon. By keeping it within the above range, it is possible to increase the heat resistance and extensional viscosity and improve the expansion ratio while maintaining the gas barrier properties of the shell. In addition, compatibility with chemical foaming agents is also improved. The preferred lower limit of the content of polymer units of a carbonyl compound in which the α carbon is a quaternary carbon in the above shell constituent copolymer is 58% by weight, and the preferred upper limit is 63% by weight.

Examples of carbonyl compounds in which the α carbon becomes a quaternary carbon include the above-mentioned radically polymerizable unsaturated carboxylic acids having 3 to 8 carbon atoms, radically polymerizable unsaturated carboxylic acid esters having 3 to 8 carbon atoms, and polyfunctional carboxylic acid esters. Note that "the α carbon becomes a quaternary carbon" means that the α carbon becomes a quaternary carbon after polymerization.

As the radically polymerizable unsaturated carboxylic acid having 3 to 8 carbon atoms, for example, one having one or more carboxyl groups per molecule can be used.
The radical polymerizable unsaturated carboxylic acid having 3 to 8 carbon atoms also includes its anhydride. These may be used alone or in combination of two or more kinds.
Examples of the radically polymerizable unsaturated carboxylic acids having 3 to 8 carbon atoms include unsaturated monocarboxylic acids such as methacrylic acid and ethacrylic acid, and unsaturated dicarboxylic acids such as citraconic acid and chloromaleic acid.
Among these, methacrylic acid is particularly preferred.

When the carbonyl compound in which the α carbon is a quaternary carbon contains a radically polymerizable unsaturated carboxylic acid having 3 to 8 carbon atoms, the preferred lower limit of the polymer unit content of the radically polymerizable unsaturated carboxylic acid having 3 to 8 carbon atoms in the shell-constituting copolymer is 5% by weight, and the preferred upper limit is 50% by weight. By making it 5% by weight or more, the maximum foaming temperature can be increased, and by making it 50% by weight or less, the foaming ratio can be improved. The preferred lower limit is 10% by weight, and the preferred upper limit is 30% by weight.

As the radically polymerizable unsaturated carboxylic acid ester having 3 to 8 carbon atoms, for example, methacrylic acid esters are preferred. In particular, methacrylic acid alkyl esters such as methyl methacrylate, ethyl methacrylate, and n-butyl methacrylate, or methacrylic acid esters containing an alicyclic ring, an aromatic ring, or a heterocyclic ring, such as cyclohexyl methacrylate, benzyl methacrylate, and isobornyl methacrylate, are preferred.

The polyfunctional carboxylic acid ester refers to a carboxylic acid ester having two or more radically polymerizable double bonds, and is different from the radically polymerizable unsaturated carboxylic acid ester having 3 to 8 carbon atoms.
The polyfunctional carboxylate ester acts as a crosslinking agent. By including the polyfunctional carboxylate ester, the strength of the shell can be increased, and the cell walls are less likely to break during thermal expansion.

When the carbonyl compound in which the α carbon is a quaternary carbon contains a radically polymerizable unsaturated carboxylic acid ester having 3 to 8 carbon atoms, the preferred lower limit of the polymer unit content of the radically polymerizable unsaturated carboxylic acid ester having 3 to 8 carbon atoms in the shell-constituting copolymer is 10% by weight, and the preferred upper limit is 25% by weight. By making the polymer unit content of the radically polymerizable unsaturated carboxylic acid ester having 3 to 8 carbon atoms 10% by weight or more, the dispersibility of the composition using the thermally expandable microcapsules can be improved, and by making it 25% by weight or less, the gas barrier properties of the cell wall can be improved, and the thermal expansion can be improved. The more preferred lower limit of the polymer unit content of the radically polymerizable unsaturated carboxylic acid ester having 3 to 8 carbon atoms is 15% by weight, and the more preferred upper limit is 22% by weight.

Specific examples of the polyfunctional carboxylate include dimethacrylate and tri- or higher functional methacrylate.
Examples of the dimethacrylate include ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, triethylene glycol dimethacrylate, propylene glycol dimethacrylate, 1,4-butanediol dimethacrylate, etc. Other examples include 1,6-hexanediol dimethacrylate, 1,9-nonanediol dimethacrylate, glycerin dimethacrylate, trimethylolpropane dimethacrylate, dimethylol-tricyclodecane dimethacrylate, etc. Furthermore, dimethacrylate of polyethylene glycol having a weight average molecular weight of 200 to 600 may be used.
Examples of the trifunctional methacrylate include trimethylolpropane trimethacrylate, ethylene oxide modified trimethylolpropane trimethacrylate, pentaerythritol trimethacrylate, triallyl formal trimethacrylate, etc. Examples of the tetrafunctional or higher methacrylate include pentaerythritol tetramethacrylate, dipentaerythritol hexamethacrylate, etc.
Among these, trifunctional methacrylates such as trimethylolpropane trimethacrylate and bifunctional methacrylates such as polyethylene glycol provide relatively uniform crosslinking to the shell mainly composed of acrylonitrile.

When the carbonyl compound in which the α carbon is a quaternary carbon contains a polyfunctional carboxylate, the preferred lower limit of the polymer unit content of the polyfunctional carboxylate in the shell-constituting copolymer is 0.1% by weight, and the preferred upper limit is 1.0% by weight. By making the polymer unit content of the polyfunctional carboxylate ester 0.1% by weight or more, the effect as a crosslinking agent can be fully exerted, and by making the polymer unit content of the polyfunctional carboxylate ester 1.0% by weight or less, the expansion ratio of the thermally expandable microcapsule can be improved. The more preferred lower limit of the polymer unit content of the polyfunctional carboxylate ester is 0.15% by weight, and the more preferred upper limit is 0.9% by weight.

In the above shell-constituting copolymer, the content ratio ([I]/[II]) of the content [I] of the nitrile polymer unit to the content [II] of the polymer unit of the carbonyl compound in which the α carbon is a quaternary carbon is preferably 0.50 to 0.72. By keeping it within the above range, the cells derived from the chemical foaming agent can be made uniform, and a relatively high hardness can be maintained even if the specific gravity is reduced by foaming (even if the weight is reduced). The preferred lower limit of the above content ratio is 0.55, and the preferred upper limit is 0.70.

The above-mentioned shell-forming copolymer may contain other polymer units in addition to the above-mentioned nitrile polymer units and polymer units of a carbonyl compound in which the α carbon is a quaternary carbon.
Examples of the other polymer units include polymer units of vinylidene chloride, divinylbenzene, vinyl acetate, styrene-based monomers, and the like.
The other polymer units may also have a polymer unit of a carbonyl compound in which the α carbon is not a quaternary carbon, among the radically polymerizable unsaturated carboxylic acid having 3 to 8 carbon atoms, the radically polymerizable unsaturated carboxylic acid ester having 3 to 8 carbon atoms, and the polyfunctional carboxylic acid ester.
Examples of such carbonyl compounds in which the α-carbon is not a quaternary carbon include unsaturated monocarboxylic acids such as acrylic acid, crotonic acid, and cinnamic acid, and unsaturated dicarboxylic acids such as maleic acid, itaconic acid, and fumaric acid.

The weight average molecular weight of the shell constituent copolymer preferably has a lower limit of 200,000. By making the weight average molecular weight 200,000 or more, it is possible to improve the strength of the shell. In the present invention, the weight average molecular weight can be measured, for example, in gel permeation chromatography using DMF as an eluent and two-stranded Shodex LF-804 as a column, with a monodisperse polystyrene standard. In addition, when the shell constituent copolymer is crosslinked, the weight average molecular weight can be obtained by measuring the soluble portion using DMF.
In addition, the above shell constituent copolymer preferably has a concentration of polymers having a weight average molecular weight of less than 1000 of 1% by weight or less, more preferably 0.8% by weight or less. By setting the concentration of the above polymers having a weight average molecular weight of less than 1000 to 1% by weight or less, it is possible to prevent a decrease in shell strength due to low molecular weight substances. The concentration of the polymers having a weight average molecular weight of less than 1000 is, for example, 0.1% by weight or more. The polymers having a weight average molecular weight of less than 1000 have, for example, a weight average molecular weight of 500 or more. In addition, the concentration of the polymers having a weight average molecular weight of less than 500 is preferably 0.5% by weight or less.
The concentration of the polymer having a weight average molecular weight of less than 1000 in the above shell-constituting copolymer can be calculated based on the relative value of the DMF-soluble component based on polystyrene.

The shell constituting the thermally expandable microcapsule preferably has a gelation degree of 70% or more.
When the gelation degree is 70% or more, the resin can maintain resistance to shear during molding. The gelation degree is more preferably 72 to 90%.
The gelation degree can be measured by a DMF swelling method (a method conforming to ASTM D2765 except that N,N-dimethylformamide is used as the solvent).

The shell may further contain stabilizers, UV absorbers, antioxidants, antistatic agents, flame retardants, silane coupling agents, colorants, etc., as necessary.

The thermally expandable microcapsules of the present invention have a volatile expansion agent encapsulated in the shell as a core agent. The volatile expansion agent is a substance that becomes gaseous at a temperature below the softening point of the polymer that constitutes the shell, and a low-boiling point organic solvent is preferable.

Examples of the core agent include ethane, ethylene, propane, propene, n-butane, isobutane, butene, isobutene, n-pentane, isopentane, neopentane, n-hexane, heptane, petroleum ether, chlorofluorocarbons, and tetraalkylsilanes. Examples of the chlorofluorocarbons include CCl ₃ F, CCl ₂ F ₂ , CClF ₃ , and CClF ₂ -CClF _2. Examples of the tetraalkylsilanes include tetramethylsilane, trimethylethylsilane, trimethylisopropylsilane, and trimethyl-n-propylsilane. Among these, isobutane, n-butane, n-pentane, isopentane, n-hexane, and mixtures thereof are preferred. Two or more of these volatile expanding agents may be used in combination.
Examples of hydrocarbons having 8 or more carbon atoms include isooctane, octane, decane, isododecane, dodecane, and hexanedecane.
These volatile expanding agents may be used alone or in combination of two or more kinds.
Furthermore, as the volatile expanding agent, a pyrolytic compound that is pyrolyzed by heating to become gaseous may be used.

In addition, in the above-mentioned thermally expandable microcapsules, the content of the core agent is preferably 15 to 30% by weight. By keeping it within this range, it is possible to improve the foaming ratio while providing excellent durability against shear during molding. A more preferred lower limit of the content of the core agent is 18% by weight, and a more preferred upper limit is 24% by weight.

The thermally expandable microcapsule of the present invention has a lower limit of the maximum foaming temperature (Tmax) of 185°C. By setting the temperature at 185°C or higher, the heat resistance can be increased, and the thermally expandable microcapsule can be prevented from bursting or shrinking in high temperature regions or during molding. In addition, the masterbatch pellets are not foamed by shear during production, and unfoamed masterbatch pellets can be stably produced. The preferred lower limit is 185°C, the more preferred lower limit is 190°C, the even more preferred lower limit is 195°C, the preferred upper limit is 240°C, the more preferred upper limit is 230°C, and the even more preferred upper limit is 225°C.
In this specification, the maximum foaming temperature means the temperature at which the diameter of a thermally expandable microcapsule becomes maximum (maximum displacement) when the diameter of the thermally expandable microcapsule is measured while being heated from room temperature.
The thermally expandable microcapsules of the present invention preferably have a lower limit of 300 μm and an upper limit of 1000 μm for the maximum displacement (Dmax). Within the above ranges, an appropriate expansion ratio is obtained, and desired expansion performance is obtained.

The preferred upper limit of the foaming start temperature (Ts) is 170°C. By setting it to 170°C or lower, in the case of injection molding, particularly in core-back foaming molding in which the mold is fully filled with resin material and then opened to the desired foaming point, it is possible to prevent the resin temperature from cooling during the core-back foaming process, preventing the foaming ratio from increasing. The preferred lower limit is 120°C, and the more preferred upper limit is 150°C.

The preferred lower limit of the volume average particle diameter of the thermally expandable microcapsule of the present invention is 5 μm, and the preferred upper limit is 100 μm. If it is less than 5 μm, the bubbles in the obtained molded body are too small, so that the weight reduction of the molded body may be insufficient, and if it exceeds 100 μm, the bubbles in the obtained molded body are too large, so that there may be problems in terms of strength, etc. More preferably, the lower limit is 10 μm, and the more preferred upper limit is 45 μm.
The preferred lower limit of the CV value of the volume average particle diameter of the thermally expandable microcapsules of the present invention is 20%, and the preferred upper limit is 40%.
The volume average particle size and CV value can be measured using a particle size distribution diameter measuring instrument (LA-950, manufactured by HORIBA Co., Ltd.) or the like.

The method for producing the thermally expandable microcapsules of the present invention is not particularly limited. For example, they can be produced by carrying out the steps of preparing an aqueous medium, dispersing a monomer composition containing a nitrile compound, a carbonyl compound whose alpha carbon is a quaternary carbon, and other monomers, and an oily mixture containing a volatile expanding agent, in the aqueous medium, and polymerizing the monomers.

When producing the thermally expandable microcapsules of the present invention, the first step is to prepare an aqueous medium. As a specific example, an aqueous dispersion medium containing a dispersion stabilizer is prepared by adding water, a dispersion stabilizer, and, if necessary, a co-stabilizer to a polymerization reaction vessel. In addition, alkali metal nitrite, stannous chloride, stannic chloride, potassium dichromate, etc. may be added if necessary.

Examples of the dispersion stabilizer include silica, calcium phosphate, magnesium hydroxide, aluminum hydroxide, ferric hydroxide, barium sulfate, calcium sulfate, sodium sulfate, calcium oxalate, calcium carbonate, barium carbonate, magnesium carbonate, etc.

The amount of the dispersion stabilizer added is not particularly limited and is determined appropriately depending on the type of dispersion stabilizer, the particle size of the microcapsules, etc., but the preferred lower limit is 0.1 parts by weight and the preferred upper limit is 20 parts by weight per 100 parts by weight of monomer.

Examples of the auxiliary stabilizer include a condensation product of diethanolamine and an aliphatic dicarboxylic acid, and a condensation product of urea and formaldehyde. Other examples include polyvinylpyrrolidone, polyethylene oxide, polyethyleneimine, tetramethylammonium hydroxide, gelatin, methylcellulose, polyvinyl alcohol, dioctyl sulfosuccinate, sorbitan ester, various emulsifiers, etc.

The combination of the dispersion stabilizer and the auxiliary stabilizer is not particularly limited, and examples thereof include a combination of colloidal silica and a condensation product, a combination of colloidal silica and a water-soluble nitrogen-containing compound, a combination of magnesium hydroxide or calcium phosphate and an emulsifier, etc. Among these, the combination of colloidal silica and a condensation product is preferred.
Furthermore, as the above-mentioned condensation product, a condensation product of diethanolamine and an aliphatic dicarboxylic acid is preferable, and a condensation product of diethanolamine and adipic acid or a condensation product of diethanolamine and itaconic acid is particularly preferable.

Examples of the water-soluble nitrogen-containing compound include polyvinylpyrrolidone, polyethyleneimine, polyoxyethylene alkylamine, polydialkylaminoalkyl (meth)acrylates such as polydimethylaminoethyl methacrylate and polydimethylaminoethyl acrylate, and the like. Other examples include polydialkylaminoalkyl (meth)acrylamides such as polydimethylaminopropyl acrylamide and polydimethylaminopropyl methacrylamide, polyacrylamides, polycationic acrylamides, polyamine sulfones, polyallylamines, and the like. Among these, polyvinylpyrrolidone is preferably used.

The amount of colloidal silica added is appropriately determined depending on the particle size of the thermally expandable microcapsules, with a preferred lower limit of 1 part by weight and a preferred upper limit of 10 parts by weight per 100 parts by weight of the oil phase. A more preferred lower limit is 2 parts by weight and a more preferred upper limit is 5 parts by weight. The amount of the condensation product or water-soluble nitrogen-containing compound is also appropriately determined depending on the particle size of the thermally expandable microcapsules, with a preferred lower limit of 0.05 parts by weight and a preferred upper limit of 1 part by weight per 100 parts by weight of the oil phase.

In addition to the above dispersion stabilizer and auxiliary stabilizer, inorganic salts such as sodium chloride and sodium sulfate may be added. By adding an inorganic salt, it is possible to obtain thermally expandable microcapsules with a more uniform particle shape. The amount of the inorganic salt added is usually preferably 0 to 100 parts by weight per 100 parts by weight of the monomer.

The aqueous dispersion medium containing the above-mentioned dispersion stabilizer is prepared by mixing the dispersion stabilizer and/or co-stabilizer with deionized water, and the pH of the aqueous phase is determined appropriately depending on the type of dispersion stabilizer and/or co-stabilizer used. For example, when silica such as colloidal silica is used as the dispersion stabilizer, polymerization is carried out in an acidic medium, and to make the aqueous medium acidic, an acid such as hydrochloric acid is added as necessary to adjust the pH of the system to 3 to 4. On the other hand, when magnesium hydroxide or calcium phosphate is used, polymerization is carried out in an alkaline medium.

Next, in the method for producing a thermally expandable microcapsule, a step is carried out in which an oily mixture containing a nitrile compound, a carbonyl compound whose α-carbon is a quaternary carbon, a monomer composition containing other monomers, and a volatile expanding agent is dispersed in an aqueous medium. In this step, the monomer composition and the volatile expanding agent may be added separately to an aqueous dispersion medium to prepare an oily mixture in the aqueous dispersion medium, but usually, the two are mixed in advance to prepare an oily mixture, and then added to the aqueous dispersion medium. At this time, the oily mixture and the aqueous dispersion medium may be prepared in separate containers, and the oily mixture may be dispersed in the aqueous dispersion medium by mixing them while stirring in another container, and then added to the polymerization reaction vessel.
In addition, a polymerization initiator is used to polymerize the above monomers. The polymerization initiator may be added to the above oily mixed liquid in advance, or may be added after the aqueous dispersion medium and the oily mixed liquid are stirred and mixed in a polymerization reaction vessel.

The monomer composition contains a polymerization initiator in order to polymerize the monomers.
As the polymerization initiator, for example, dialkyl peroxides, diacyl peroxides, peroxy esters, peroxydicarbonates, azo compounds, etc. are preferably used. Specific examples include dialkyl peroxides such as methyl ethyl peroxide, di-t-butyl peroxide, dicumyl peroxide, etc.; diacyl peroxides such as isobutyl peroxide, benzoyl peroxide, 2,4-dichlorobenzoyl peroxide, 3,5,5-trimethylhexanoyl peroxide, etc.; t-butyl peroxypivalate, t-hexyl peroxypivalate, t-butyl peroxyneodecanoate, t-hexyl peroxyneodecanoate, 1-cyclohexyl-1-methylethyl peroxyneodecanoate, 1,1,3,3-tetramethylbutyl peroxyneodecanoate, cumyl peroxyneodecanoate, (α,α-bis-neodecanoyl peroxide), peroxy esters such as bis(4-t-butylcyclohexyl)peroxydicarbonate, di-n-propyl-oxydicarbonate, diisopropyl peroxydicarbonate, di(2-ethylethylperoxy)dicarbonate, dimethoxybutyl peroxydicarbonate, and di(3-methyl-3-methoxybutylperoxy)dicarbonate; and azo compounds such as 2,2'-azobisisobutyronitrile, 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile, 2,2'-azobis(2,4-dimethylvaleronitrile), and 1,1'-azobis(1-cyclohexanecarbonitrile).
In the present invention, in order to preferentially polymerize acrylonitrile, it is preferable to use t-butyl peroxypivalate or 2,2'-azobisisobutyronitrile as a polymerization initiator, which makes it possible to increase the ratio of polyacrylonitrile, which has high plasticizer resistance, compared to polymethacrylonitrile.

Examples of a method for emulsifying and dispersing the above-mentioned oily mixture in an aqueous dispersion medium to a predetermined particle size include a method of stirring the mixture using a homomixer (e.g., manufactured by Tokushu Kika Kogyo Co., Ltd.) or a method of passing the mixture through a static dispersion device such as a line mixer or an element-type static disperser.
The aqueous dispersion medium and the polymerizable mixture may be supplied separately to the static dispersing device, or a dispersion liquid which has been previously mixed and stirred may be supplied.

The thermally expandable microcapsules of the present invention can be produced by, for example, carrying out a step of polymerizing the monomer by heating the dispersion liquid obtained through the above-mentioned steps. The thermally expandable microcapsules produced by such a method have a high maximum foaming temperature, excellent heat resistance, and do not burst or shrink even in high temperature regions or during molding. In addition, since they have high heat resistance, they do not foam due to shear during the production of master batch pellets, and unfoamed master batch pellets can be stably produced.
The content of the nitrile polymer unit and the polymer unit of the carbonyl compound whose α carbon is a quaternary carbon, as defined in the present invention, and the maximum foaming temperature can be controlled within a predetermined range by adjusting the polymerization temperature and polymerization pressure in the step of polymerizing the above-mentioned monomers.
The polymerization temperature is preferably 50 to 90° C. The polymerization temperature may be kept constant during the polymerization, or may be increased stepwise in several steps.
The polymerization pressure is preferably 0.5 to 1.0 MPa by pressurizing with nitrogen. Before the polymerization pressure is adjusted to the above pressure, it is preferable to carry out nitrogen substitution or vacuum operation.

The present invention also provides a molding resin composition containing a matrix resin, the thermally expandable microcapsules of the present invention, and a chemical foaming agent.
Such a molding resin composition is durable against strong shear during molding, has a high expansion ratio, and is resistant to yellowing, making it possible to produce a foamed molded article having an excellent appearance.
Furthermore, such a molding resin composition can overcome the problems of the generation of voids and gas escape and the decrease in strength that occur when a chemical foaming agent is used in combination.

Examples of the matrix resin include polyolefin resins, polystyrene resins, ABS resins, AS resins, vinyl chloride resins, polyamide resins, polyethylene terephthalate resins, polylactic acid resins, etc. Among these, vinyl chloride resins are preferred.
As the vinyl chloride resin, in addition to vinyl chloride homopolymers, copolymers of vinyl chloride monomers and monomers having unsaturated bonds copolymerizable with vinyl chloride monomers, graft copolymers in which vinyl chloride monomers are graft-copolymerized onto polymers, etc. These polymers may be used alone or in combination of two or more.

Examples of the monomer having an unsaturated bond copolymerizable with the vinyl chloride monomer include α-olefins, vinyl esters, vinyl ethers, (meth)acrylic acid esters, aromatic vinyls, halogenated vinyl vinyls, and N-substituted maleimides. One or more of these may be used.
Examples of the α-olefins include ethylene, propylene, butylene, etc., examples of the vinyl esters include vinyl acetate, vinyl propionate, etc., and examples of the vinyl ethers include butyl vinyl ether, cetyl vinyl ether, etc.
Examples of the (meth)acrylic acid esters include methyl (meth)acrylate, ethyl (meth)acrylate, butyl acrylate, and phenyl methacrylate, and examples of the aromatic vinyls include styrene and α-methylstyrene.
Furthermore, examples of the vinyl halides include vinylidene chloride and vinylidene fluoride, and examples of the N-substituted maleimides include N-phenylmaleimide and N-cyclohexylmaleimide, with ethylene and vinyl acetate being preferred.

The polymer to be graft-copolymerized with vinyl chloride is not particularly limited as long as it is a polymer to be graft-copolymerized with vinyl chloride. Examples of such polymers include ethylene-vinyl acetate copolymer, ethylene-vinyl acetate-carbon monoxide copolymer, ethylene-ethyl acrylate copolymer, ethylene-butyl acrylate-carbon monoxide copolymer, ethylene-methyl methacrylate copolymer, ethylene-propylene copolymer, etc. Other examples include acrylonitrile-butadiene copolymer, polyurethane, chlorinated polyethylene, chlorinated polypropylene, etc., which may be used alone or in combination of two or more.
Moreover, the vinyl chloride may be graft-copolymerized with an acrylic resin emulsion rubber.
The polymerization method for the PVC is not particularly limited, and any of the conventionally known methods such as water suspension polymerization, bulk polymerization, solution polymerization, and emulsion polymerization can be used.

The degree of polymerization of the vinyl chloride resin is preferably 600 to 1200. By keeping it within the above range, a product that satisfies both fluidity and product strength can be obtained. A more preferable lower limit of the degree of polymerization of the vinyl chloride resin is 800, and a more preferable upper limit is 1000.

In the molding resin composition of the present invention, the content of the matrix resin is preferably 40 parts by mass or less and 60 parts by mass or less per 100 parts by mass of the molding resin composition. By adding the matrix resin in this range, it is possible to maintain a good appearance of the molded product while maintaining the physical properties.
The lower limit of the content of the matrix resin is preferably 45 parts by mass, and the upper limit thereof is preferably 55 parts by mass.

The molding resin composition of the present invention preferably contains 0.1 to 1.5 parts by weight of thermally expandable microcapsules and 0.5 to 3.0 parts by weight of a chemical foaming agent per 100 parts by weight of matrix resin.

The chemical foaming agent is not particularly limited as long as it is in a powder form at room temperature, and any of those conventionally used chemical foaming agents can be used.
The above chemical foaming agents are classified into organic foaming agents and inorganic foaming agents, each of which is further classified into thermal decomposition type and reactive type.
As organic thermal decomposition type foaming agents, ADCA (azodicarbonamide), DPT (N,N'-dinitropentamethylenetetramine), OBSH (4,4'-oxybisbenzenesulfonylhydrazide), etc. are often used.
Inorganic thermal decomposition type foaming agents include hydrogen carbonate, carbonate, and a combination of hydrogen carbonate and organic acid salt. As the above-mentioned chemical foaming agent, it is preferable to use a thermal decomposition type chemical foaming agent. The performance of the thermal decomposition type chemical foaming agent is determined by the decomposition temperature, the amount of gas generated, and the particle size.

The decomposition temperature of the above chemical foaming agent is preferably 180 to 200°C.
The decomposition temperature can be adjusted by using, in combination with a urea-based or zinc-based foaming assistant, if necessary.
The gas generation amount of the chemical foaming agent is preferably 220 to 240 ml/g. The gas generation amount is the volume of gas generated when the chemical foaming agent decomposes. This gas becomes the gas in the bubbles, and therefore affects the expansion ratio.
Furthermore, by using the above chemical foaming agent in combination with citrate or zinc oxide, it is possible to reduce the bubble diameter.

The chemical foaming agent is usually in the form of a powder, and the smaller the particle size, the greater the number of particles per unit weight. The greater the number of particles, the greater the tendency for the number of bubbles to be generated.
The preferred lower limit of the average particle size (median size) of the chemical foaming agent is 4 μm, and the preferred upper limit is 20 μm. By setting it within the above range, the bubbles in the obtained molded body are appropriate, a sufficient expansion ratio is obtained, and the appearance can be excellent. The more preferred lower limit is 5 μm, and the more preferred upper limit is 10 μm.

In the molding resin composition of the present invention, the ratio of the average particle size of the thermally expandable microcapsules to the average particle size of the chemical foaming agent (average particle size of the thermally expandable microcapsules/average particle size of the chemical foaming agent) is preferably 1.0 to 7.5. By keeping it within the above range, the thermally expandable microcapsules tend to act as a nucleating agent when the bubbles derived from the chemical foaming agent grow.

In the molding resin composition of the present invention, the ratio of the chemical foaming agent content to the polymer unit content of the carbonyl compound in which the α-carbon of the copolymer constituting the thermally expandable microcapsule is a quaternary carbon (chemical foaming agent content/polymer unit content of the carbonyl compound in which the α-carbon is a quaternary carbon) is preferably 1.0 to 4.5. By keeping it within the above range, when the bubbles derived from the chemical foaming agent grow, the thermally expandable microcapsules tend to act as a nucleating agent, which makes it easier to suppress the generation of large voids and to generate uniform cells. The upper limit of the above ratio is more preferably 4.0, even more preferably 3.5, and the lower limit is more preferably 1.5, even more preferably 2.0, and even more preferably 2.5.

The molding resin composition of the present invention preferably contains a plasticizer.
Examples of the plasticizer include polypropylene glycol, phthalates such as dioctyl phthalate, dibutyl phthalate, and butyl benzyl phthalate, and aliphatic carboxylates such as dioctyl adipate, isodecyl succinate, dibutyl sebacate, and butyl oleate. Other examples include glycol esters such as pentaerythritol ester, phosphates such as trioctyl phosphate and tricresyl phosphate, epoxy plasticizers such as epoxidized soybean oil and epoxy benzyl stearate, and chlorinated paraffin. These plasticizers may be used alone or in combination of two or more.

The content of the plasticizer in the molding resin composition of the present invention is not particularly limited, but the lower limit is 60 parts by weight and the preferred upper limit is 80 parts by weight relative to 100 parts by weight of the vinyl chloride resin. When the content of the plasticizer is within this range, the plasticizer can exhibit shapeability and does not bleed out from the foamed molded product. The preferred lower limit of the content of the plasticizer is 65 parts by weight and the preferred upper limit is 75 parts by weight.

The molding resin composition of the present invention may be mixed with additives such as lubricants, processing aids, heat resistance improvers, UV absorbers, heat stabilizers, light stabilizers, fillers, thermoplastic elastomers, and pigments, as necessary.

The molding resin composition of the present invention may also be used as masterbatch pellets.
The method for producing the master batch pellets is not particularly limited, and examples thereof include a method in which raw materials such as a matrix resin such as a vinyl chloride resin and various additives are pre-kneaded using a same-rotation twin-screw extruder, etc., and then heated to a predetermined temperature, and the molding resin composition of the present invention is cut into a desired size using a pelletizer to form pellets into the master batch pellets.
Furthermore, the molding resin composition of the present invention may be granulated in a granulator to produce master batch pellets in the form of pellets.
The kneading machine is not particularly limited as long as it can knead the thermally expandable microcapsules without destroying them, and examples thereof include a pressure kneader and a Banbury mixer.

The molding resin composition of the present invention is molded by a known molding method, and the heat-expandable microcapsules are expanded by heating during molding to produce a foamed molded article. Such a foamed molded article also constitutes the present invention.
The foamed molded product of the present invention obtained by such a method has a high appearance quality, has uniformly formed closed cells, and is excellent in light weight, heat insulation, impact resistance, rigidity, etc., and can be suitably used for applications such as building materials for housing, automotive parts, and shoe soles.

The molding method for the foamed molded article of the present invention is not particularly limited, and examples include kneading molding, calendar molding, extrusion molding, and injection molding. In the case of injection molding, the process is not particularly limited, and examples include the short-short method in which a portion of the resin material is placed in a mold and foamed, and the core-back method in which the mold is fully filled with the resin material and then opened to the desired point of foaming.

When producing the foamed molded article of the present invention, it is preferable to add a molding resin composition obtained by adding a chemical foaming agent and a matrix resin such as a thermoplastic resin to the thermally expandable microcapsules of the present invention, and mold the product using a molding method such as injection molding. The molding resin composition may also be produced by adding a matrix resin such as a thermoplastic resin to a master batch pellet obtained by mixing the thermally expandable microcapsules of the present invention, the chemical foaming agent, and a base resin such as a thermoplastic resin.

The thermally expandable microcapsules, molding resin compositions, and foamed molded articles of the present invention, for example in the above forms, can be advantageously used in automobile interior materials such as door trims and instrument panels, automobile exterior materials such as bumpers, building materials such as wood powder plastics, shoe soles, artificial cork, etc.

According to the present invention, it is possible to obtain a thermally expandable microcapsule capable of producing a molded article that exhibits durability against strong shear during molding, has high heat resistance and expansion ratio, is resistant to yellowing, has an excellent appearance, is lightweight, has high hardness, and is excellent in abrasion resistance. Also, it is possible to obtain a thermally expandable microcapsule that overcomes the problems of the generation of voids and gas escape and the decrease in strength that occur when a chemical foaming agent is used in combination. Furthermore, it is possible to obtain a thermally expandable microcapsule that has excellent fluidity when made into an aggregate of multiple particles, and can be stably charged from a hopper or the like during molding.
In addition, by using the thermally expandable microcapsules, it is possible to obtain a molding resin composition and a foam molded article having the above-mentioned excellent properties.

The following examples further illustrate aspects of the present invention, but the present invention is not limited to these examples.

Example 1
(Preparation of Thermally Expandable Microcapsules)
187 g of colloidal silica having a solid content of 20% by weight, 2.3 g of polyvinylpyrrolidone, and 630 g of sodium chloride were added to 2,000 g of ion-exchanged water, mixed, and the pH was adjusted to 3.5 to prepare an aqueous dispersion medium.
405g (43.33 parts by weight) of acrylonitrile, 88.4g (9.46 parts by weight) of methacrylonitrile, 232.7g (24.90 parts by weight) of methacrylic acid, 204.8g (21.912 parts by weight) of methyl methacrylate, and 3.7g (0.398 parts by weight) of trimethylolpropane trimethacrylate were mixed to obtain a monomer composition of a homogeneous solution. 7.5g of 2,2'-azobis(isobutyronitrile), 7.5g of 2,2'-azobis(2,4-dimethylvaleronitrile), and 224.3g (24 parts by weight) of normal pentane were added to the monomer composition and charged into an autoclave and mixed.
The aqueous dispersion medium was then charged into an autoclave and stirred at 1,000 rpm for 10 minutes, then purged with nitrogen, and reacted at a reaction temperature of 60° C. for 10 hours, and then at 80° C. for 2 hours. The reaction pressure was 0.5 MPa, and the stirring speed was 200 rpm. The obtained polymerized slurry was pre-dehydrated in a dehydrator (central) and then dried to obtain thermally expandable microcapsules.

(Examples 2 to 7, Comparative Examples 1 to 6)
Thermally expandable microcapsules were obtained in the same manner as in Example 1, except that acrylonitrile, methacrylonitrile, methacrylic acid, methyl methacrylate, trimethylolpropane trimethacrylate, isopentane, normal pentane, isooctane, and colloidal silica were mixed in the composition shown in Table 1 to form a monomer composition. Polymerization was also performed under the conditions shown in Table 1.

(Example 8)
(Preparation of molding resin composition and foamed molded product)
100 parts by weight of vinyl chloride resin was mixed with 2.0 parts by weight of tin stabilizer (ONZ142AF, manufactured by Sankyo Kigosei Co., Ltd.) as a thermal stabilizer. After heating to 100°C, 72 parts by weight of dioctyl phthalate was added as a plasticizer and mixed while maintaining the temperature at 100°C. After that, it was cooled to 70°C, and 0.94 parts by weight of the thermally expandable microcapsules obtained in Example 1, 1.32 parts by weight of a chemical foaming agent (ADCA, average particle size 6 μm), and 2.0 parts by weight of a foaming assistant (zinc compound) were added to obtain a molding resin composition.
The obtained molding resin composition was wound around two rolls at a temperature of 95 to 105° C. and a rotation speed of 10 rpm, and then kneaded for 3 minutes and 6 minutes to obtain roll products.
The rolled product was then placed in a mold 150 mm square and 2 mm thick, preheated at 100° C. for 3 minutes under a pressure of 2 MPa, pressed for 1 minute, and then cooled for 2 minutes to obtain a pressed product.
The pressed product (150 mm square) was divided into 16 equal parts, which were then placed in a hot air oven set at 180° C. and heated for 4 and 6 minutes to obtain foamed molded articles.

(Examples 9 to 14, Comparative Examples 7 to 13)
A molding resin composition and a foamed molded article were obtained in the same manner as in Example 8, except that the thermally expandable microcapsules and the chemical foaming agent were changed to the compositions shown in Table 2 and mixed.

(Evaluation Method)
The performance of the obtained thermally expandable microcapsules and foamed molded articles was evaluated by the following methods. The results are shown in Tables 1 and 2.

(1) Evaluation of Thermally Expandable Microcapsules (1-1) Shell Composition Analysis The composition ratio of the shell components of the obtained thermally expandable microcapsules was measured using solid-state NMR under the following conditions.
<DD/MAS measurement conditions>
Equipment: ECZ-400R (JEOL)
Temperature: Room temperature Observation nucleus: 13C
Observation frequency: 100.5253MHz
Probe: 8 mm CPMAS probe Reference material: Adamantane (internal standard: 28.46 ppm)
Pulse width: 6.5 μsec
Acquisition time: 50.93 msec
Pulse repetition time: 60 sec
Magic angle rotation speed: 7kHz
Accumulation count: 1024 times Measurement mode: Single pulse (DD/MAS) method Sample amount: 350 mg
<CP/MAS measurement conditions>
Equipment: ECZ-400R (JEOL)
Temperature: Room temperature Observation nucleus: 13C
Observation frequency: 100.5253MHz
Probe: 4 mm CPMAS probe Reference material: Adamantane (internal standard: 28.46 ppm)
Pulse width: 6.5 μsec
Acquisition time: 50.93 msec
Pulse repetition time: 5 sec
Magic angle rotation speed: 12kHz
Number of measurements: 2048 Measurement mode: Cross polarization (CP/MAS) method, Dipolar Dephasing method Contact time: 3 msec
delay time: 1.667msec
Sample amount: 120 mg

(1-2) Volume average particle diameter: The volume average particle diameter and CV value were measured using a particle size distribution diameter measuring instrument (LA-950, manufactured by HORIBA).

(1-3) Foaming start temperature, maximum foaming temperature, and maximum displacement Using a thermomechanical analyzer (TMA) (TMA2940, manufactured by TA instruments), the foaming start temperature (Ts), maximum foaming temperature (Tmax), and maximum displacement (Dmax) were measured. Specifically, 25 μg of the sample was placed in an aluminum container with a diameter of 7 mm and a depth of 1 mm, and heated from 80° C. to 250° C. at a heating rate of 5° C./min with a force of 0.1 N applied from above. The displacement in the vertical direction of the measuring terminal was measured, and the temperature at which the displacement began to increase was taken as the foaming start temperature. In addition, the foaming ratio was measured, and the temperature at which the foaming ratio was maximized was taken as the maximum foaming temperature.

(1-4) Core agent content 0.05 g of the thermally expandable microcapsules were weighed [weight A]. Then, the microcapsules were placed in an oven set at 210°C for 20 minutes, heated, left at room temperature for 10 minutes, and weighed on a balance [weight B]. The core agent content was calculated from the obtained [weight A] and [weight B] using the following formula.
Core agent content (wt%)=(1-(B/A))×100

(1-5) Degree of gelation The degree of gelation was measured in accordance with the method of ASTM D2765, except that N,N-dimethylformamide was used as the solvent.

(1-6) Hopper fluidity: Using a container for measuring bulk specific gravity as described in JIS K7370, the obtained thermally expandable microcapsules were poured into the top of the hopper, and then the microcapsules were allowed to fall under their own weight, and the number of seconds until the hopper became empty (when all the thermally expandable microcapsules had fallen) was measured.

(1-7) Concentration of polymers with a weight average molecular weight of less than 1000: 5 ml of a solvent (dimethylformamide with 0.05 M lithium bromide added) was added to about 10 mg of a sample, and the mixture was gently stirred at room temperature. After visually checking for unwanted substances, the mixture was filtered using a 0.45 μm filter. The molecular weight distribution of the obtained measurement solution was measured under the following measurement conditions, and the concentration of polymers with a weight average molecular weight of less than 1000 was measured.
The concentration of the polymer having a weight average molecular weight of less than 1000 in the above shell-constituting copolymer was calculated based on the relative value of the DMF-soluble component based on polystyrene.
(Measurement conditions)
Apparatus: Gel permeation chromatography (GPC) (JASCO)
Detector: Differential refractive index detector RI (JASCO RI-4030)
Column: Shodex LF-804, 2 columns connected Flow rate: 0.8 mL/min
Column temperature: 40°C
・Injection amount: 0.200ml
・Standard sample: Tosoh monodisperse polystyrene

(2) Evaluation of foamed molded products (2-1) Measurement of density The density of the obtained molded products was measured according to JIS K-7112 Method A (underwater displacement method).

(2-2) Yellowness (b*)
The yellowness of the surface of the molded article was measured using a color computer (CM-3600d, manufactured by Konica Minolta Japan) to obtain a YI value.

(2-3) A Hardness The A hardness of the obtained foamed molded product was measured by a method in accordance with JIS K 6253.

(2-4) Amount of Wear The abraded volume per 1000 revolutions was measured under a load of 26.5 N according to the Acron abrasion test method (JIS K 6264).

According to the present invention, it is possible to provide a thermally expandable microcapsule capable of producing a molded article that exhibits durability against strong shear during molding, has high heat resistance and expansion ratio, is resistant to yellowing, has an excellent appearance, is lightweight, has high hardness, and is excellent in abrasion resistance. It is also possible to provide a thermally expandable microcapsule that overcomes the problems of the generation of voids and gas escape and the decrease in strength that occur when a chemical foaming agent is used in combination. Furthermore, it is possible to provide a thermally expandable microcapsule that has excellent fluidity when made into an aggregate of multiple particles, and can be stably charged from a hopper or the like during molding.
In addition, by using the thermally expandable microcapsules, it is possible to provide a molding resin composition and a foam molded article having the above-mentioned excellent properties.

Claims (9)

A thermally expandable microcapsule having a maximum foaming temperature of 190 ° C. or higher, the shell of which contains a volatile expanding agent as a core agent.
The shell contains a copolymer having 35 to 45% by weight of nitrile polymer units and 55 to 65% by weight of polymer units of a carbonyl compound in which the α carbon is a quaternary carbon,
A thermally expandable microcapsule, characterized in that the carbonyl compound in which the α carbon is a quaternary carbon is a radically polymerizable unsaturated carboxylic acid having 3 to 8 carbon atoms, a radically polymerizable unsaturated carboxylic acid ester having 3 to 8 carbon atoms, or a polyfunctional carboxylic acid ester. The thermally expandable microcapsule according to claim 1, characterized in that it contains 15 to 30% by weight of a core agent. The thermally expandable microcapsule according to claim 1 or 2, characterized in that the degree of gelation is 70% or more. The thermally expandable microcapsule according to claim 1, 2 or 3, characterized in that the copolymer constituting the shell has a concentration of polymers with a weight-average molecular weight of less than 1000 of 1% by weight or less. A molding resin composition containing a matrix resin, the thermally expandable microcapsules of claim 1, 2, 3 or 4, and a chemical foaming agent. The molding resin composition according to claim 5, characterized in that the matrix resin is a vinyl chloride resin. The molding resin composition according to claim 5 or 6, characterized in that it contains 0.1 to 1.5 parts by weight of thermally expandable microcapsules and 0.5 to 3.0 parts by weight of a chemical foaming agent per 100 parts by weight of matrix resin. The molding resin composition according to claim 5, 6 or 7, characterized in that the ratio of the content of the chemical foaming agent in the molding resin composition to the polymer unit content of the carbonyl compound in which the α-carbon of the copolymer constituting the thermally expandable microcapsule is a quaternary carbon (content of the chemical foaming agent/polymer unit content of the carbonyl compound in which the α-carbon is a quaternary carbon) is 1.0 to 4.5. A foamed molded article produced using the molding resin composition according to claim 5, 6, 7 or 8.