JP6370219B2 - Thermally expandable microcapsules and foamed molded articles - Google Patents

Description

The present invention uses a thermally expandable microcapsule capable of producing a foamed molded article having excellent heat resistance, high expansion ratio, hardly yellowing and having an excellent appearance, and the thermally expandable microcapsule. The present invention relates to a foamed molded product.

Thermally expandable microcapsules are used in a wide range of applications as a design-imparting agent and a lightening agent, and are also used in paints for the purpose of weight reduction such as foamed ink and wallpaper.
As such a heat-expandable microcapsule, one in which a volatile expansion agent that becomes gaseous at a temperature below the softening point of the shell polymer is included in a thermoplastic shell polymer is widely known. In Patent Document 1, an oily mixed liquid obtained by mixing a volatile expansion agent such as a low-boiling point aliphatic hydrocarbon with a monomer is added to an aqueous dispersion medium containing a dispersant together with an oil-soluble polymerization catalyst while stirring. A method for producing thermally expandable microcapsules encapsulating a volatile swelling agent by performing suspension polymerization is disclosed.

However, although the thermally expandable microcapsule obtained by this method can be thermally expanded at a relatively low temperature of about 80 to 130 ° C., the expanded microcapsule is ruptured or contracted when heated at a high temperature or for a long time. In other words, since the expansion ratio is reduced, there is a drawback that it is not possible to obtain thermally expandable microcapsules having excellent heat resistance.

On the other hand, in Patent Document 2, a polymer obtained from a polymerization component 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 is shelled. And a method for producing a thermally expandable microcapsule encapsulating a volatile expansion agent is disclosed.
Patent Document 3 uses a polymer obtained from a polymerization component 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 uses a volatile swelling agent. In the thermally expandable microcapsules encapsulating, a thermally expandable microcapsule in which the non-nitrile monomer is a methacrylic acid ester or an acrylic acid ester is disclosed.

The heat-expandable microcapsules obtained by these methods have excellent heat resistance compared to conventional microcapsules and do not foam at 140 ° C. or lower, but actually continue heating at 130 to 140 ° C. for about 1 minute. Some of the microcapsules are thermally expanded, and it has been difficult to obtain thermally expandable microcapsules having excellent heat resistance with a maximum foaming temperature of 180 ° C. or higher.

Furthermore, Patent Document 4 discloses an ethylenically unsaturated monomer having 85% by weight or more of a nitrile group for the purpose of obtaining a thermally expandable microcapsule having a maximum foaming temperature of 180 ° C. or higher, preferably 190 ° C. or higher. There is disclosed a thermally expandable microcapsule comprising a foaming agent having a shell polymer comprising a homopolymer or a copolymer and 50% by weight or more of isooctane.
In such a heat-expandable microcapsule, although the maximum foaming temperature is a very high value, the subsequent expanded state cannot be maintained, and it has been difficult to use for a long time in a high temperature region.

Furthermore, in Patent Documents 5 to 9, by defining the monomer constituting the shell of the thermally expandable microcapsule, it has good foaming performance in a wide range of foaming temperature, particularly in a high temperature region (160 ° C. or higher), A thermally expandable microcapsule with improved heat resistance is disclosed. However, this heat-expandable microcapsule has a high maximum foaming temperature, but when used for molding processes such as kneading molding, calendar molding, extrusion molding, injection molding, etc., in which strong shearing force is applied, particularly injection molding, In the melt-kneading process, due to heat resistance and strength problems of the heat-expandable microcapsules, a phenomenon called “sag” occurs or is crushed, and the resulting molded body is yellowed. was there. Further, in the step of foaming the thermally expandable microcapsules, the expansion ratio is low and the expansion ratio varies, so that the thermally expandable microcapsules do not sufficiently foam, and the resulting molded product has an appearance and light weight. It was inferior in terms of functionality such as sex.
In addition, white spots caused by aggregation of the thermally expandable microcapsules occurred on the surface of the foamed molded product, and the appearance of the foamed molded product was significantly impaired.
Therefore, there has been a need for a thermally expandable microcapsule that has excellent heat resistance and expansion ratio and is capable of producing a foamed molded article that is hardly yellowed and has an excellent appearance.

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

The present invention uses a thermally expandable microcapsule capable of producing a foamed molded article having excellent heat resistance, high expansion ratio, hardly yellowing and having an excellent appearance, and the thermally expandable microcapsule. An object of the present invention is to provide a foamed molded product. Note that “difficult to yellow” means that “yellowing due to the addition of thermally expandable microcapsules hardly occurs”.

The present invention relates to a thermally expandable microcapsule in which a volatile expansion agent is included as a core agent in a polymer shell, and the shell is a polymerization composed of at least one selected from acrylonitrile and methacrylonitrile. Monomer (I) 44 to 63 wt%, a radical polymerizable unsaturated carboxylic acid monomer (II) 15 to 30 wt% having a carboxyl group and 3 to 8 carbon atoms, (meth) acrylic acid ester, The polymerizable monomer containing 25.2 to 40% by weight of a polymerizable monomer (IV) selected from vinylidene chloride, vinyl acetate, and a styrene monomer, with respect to the content of the polymerizable monomer (IV) (I) It consists of a polymer which polymerizes the monomer composition whose content ratio is 2.02 or less, and foaming start temperature is 130. 175 ° C., the maximum foaming temperature is thermally expandable microcapsule is a one hundred and seventy-five to one hundred and eighty-eight ° C..
The present invention is described in detail below.

As a result of intensive studies, the inventors of the present invention contain a polymerizable monomer (I), a radical polymerizable unsaturated carboxylic acid monomer (II), a crosslinking monomer (III) and a polymerizable monomer (IV), and When the ratio is within a predetermined range, a thermally expandable microcapsule capable of producing a foamed molded article having a high foaming ratio and an excellent appearance, capable of realizing stable foaming performance in a high temperature range. Has been found, and the present invention has been completed.

The shell constituting the thermally expandable microcapsule of the present invention has 44 to 63% by weight of polymerizable monomer (I) consisting of at least one selected from acrylonitrile and methacrylonitrile, a carboxyl group, and a carbon number. 3 to 8 radically polymerizable unsaturated carboxylic acid monomer (II) 15 to 30% by weight, crosslinkable monomer (III) 0.1 to 3.0% by weight having two or more double bonds in the molecule, From a polymer obtained by polymerizing a monomer composition containing 21 to 40% by weight of a polymerizable monomer (IV) selected from (meth) acrylic acid ester, vinylidene chloride, vinyl acetate and a styrene monomer. Become.

The polymerizable monomer (I) is composed of at least one selected from acrylonitrile and methacrylonitrile.
By adding the polymerizable monomer (I), the gas barrier property of the shell can be improved.

The minimum of content of the polymerizable monomer (I) in the said monomer composition is 44 weight%, and an upper limit is 63 weight%. If it is less than 44% by weight, the gas barrier property of the shell is lowered, so that the expansion ratio may be lowered. If it exceeds 63% by weight, the heat resistance may not be increased, and yellowing may easily occur. A preferred lower limit is 50% by weight and a preferred upper limit is 60% by weight.

As the radically polymerizable unsaturated carboxylic acid monomer (II) having a carboxyl group and having 3 to 8 carbon atoms, for example, one having at least one free carboxyl group per molecule for ionic crosslinking may be used. Specifically, for example, unsaturated monocarboxylic acids such as acrylic acid, methacrylic acid, ethacrylic acid, crotonic acid and cinnamic acid, unsaturated acids such as maleic acid, itaconic acid, fumaric acid, citraconic acid and chloromaleic acid Dicarboxylic acids and their anhydrides or monoesters and derivatives of unsaturated dicarboxylic acids such as monomethyl maleate, monoethyl maleate, monobutyl maleate, monomethyl fumarate, monoethyl fumarate, monomethyl itaconate, monoethyl itaconate, monobutyl itaconate These may be used alone or in combination of two or more It may be used in combination. Of these, acrylic acid, methacrylic acid, maleic acid, maleic anhydride, and itaconic acid are particularly preferable.

The lower limit of the content of the segment having the carboxyl group and derived from the radically polymerizable unsaturated carboxylic acid monomer (II) having 3 to 8 carbon atoms in the monomer composition is 15% by weight, and the upper limit is 30% by weight. It is. If it is less than 15% by weight, the maximum foaming temperature may be less than 175 ° C. If it exceeds 30% by weight, the maximum foaming temperature is improved but the foaming ratio is lowered. A preferred lower limit is 17% by weight and a preferred upper limit is 28% by weight.

The monomer composition contains a crosslinkable monomer (III) having two or more double bonds in the molecule. The crosslinkable monomer (III) has a role as a crosslinking agent. By containing the crosslinkable monomer (III), the strength of the shell can be enhanced, and the cell wall is less likely to be broken during thermal expansion.

Examples of the crosslinkable monomer (III) include monomers having two or more radically polymerizable double bonds. Specific examples include divinylbenzene, ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, Triethylene glycol di (meth) acrylate, propylene glycol di (meth) acrylate, 1,4-butanediol di (meth) acrylate, 1,6-hexanediol di (meth) acrylate, 1,9-nonanediol di (meth) ) Acrylate, polyethylene glycol di (meth) acrylate having a weight average molecular weight of 200 to 600, glycerin di (meth) acrylate, trimethylolpropane di (meth) acrylate, trimethylolpropane tri (meth) acrylate, ethyl Oxide-modified trimethylolpropane tri (meth) acrylate, pentaerythritol tri (meth) acrylate, triallyl formal tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, dipentaerythritol hexa (meth) acrylate, dimethylol-tricyclode Examples include candi (meth) acrylate. Among these, trifunctional ones such as trimethylolpropane tri (meth) acrylate and bifunctional (meth) acrylates such as polyethylene glycol are relatively uniformly crosslinked in the shell mainly composed of acrylonitrile. Since the microcapsules that have been applied and thermally expanded even in a high temperature region exceeding 200 ° C. are difficult to contract and easily maintain the expanded state, a so-called “sag” phenomenon can be suppressed and is preferably used.

The lower limit of the content of the crosslinkable monomer (III) in the monomer composition is 0.1% by weight, and the upper limit is 3.0% by weight. If the content of the crosslinkable monomer (III) is less than 0.1% by weight, the effect as a crosslinking agent may not be exhibited, and the crosslinkable monomer (III) is added in an amount exceeding 3.0% by weight. In such a case, the expansion ratio of the thermally expandable microcapsule is lowered. The minimum with preferable content of the said crosslinkable monomer (III) is 0.15 weight%, and a preferable upper limit is 2.0 weight%.

The monomer composition contains a polymerizable monomer (IV) composed of at least one selected from (meth) acrylic acid esters, vinylidene chloride, vinyl acetate, and styrene monomers. By containing the polymerizable monomer (IV), the miscibility of the thermally expandable microcapsule and a matrix resin such as a thermoplastic resin is improved, and the foamed molded article using the thermally expandable microcapsule has an excellent appearance. Have.
Of these, (meth) acrylic acid esters are preferable, and in particular, alkyl methacrylates such as methyl methacrylate, ethyl methacrylate, and n-butyl methacrylate, or cyclohexyl methacrylate, benzyl methacrylate, isobornyl methacrylate, and the like. Aliphatic, aromatic, and heterocyclic ring-containing methacrylates are preferred.

The upper limit of the content of the polymerizable monomer (IV) in the monomer composition is 21% by weight, and the lower limit is 40% by weight. When the content of the polymerizable monomer (IV) is less than 21% by weight, the appearance of the foamed molded article using the heat-expandable microcapsule is deteriorated, and when it exceeds 40% by weight, the gas barrier property of the cell wall is deteriorated. However, thermal expansibility tends to deteriorate. The minimum with preferable content of the said polymerizable monomer (IV) is 22 weight%, and a preferable upper limit is 35 weight%. The minimum with more preferable content of the said polymerizable monomer (IV) is 23 weight%, and a more preferable upper limit is 30 weight%.

By adjusting the content of the polymerizable monomer (I) relative to the content of the polymerizable monomer (IV) in the monomer composition, a foamed molded article with little yellowing can be obtained.
The upper limit with the preferable ratio of the polymerizable monomer (I) with respect to the said polymerizable monomer (IV) is 3.0. When the ratio of the polymerizable monomer (I) to the polymerizable monomer (IV) exceeds 3.0, the foamed molded article using the thermally expandable microcapsule may be yellowed.
A more preferable upper limit of the ratio of the polymerizable monomer (I) to the polymerizable monomer (IV) is 2.7. Moreover, the minimum with the preferable ratio of the polymerizable monomer (I) with respect to the said polymerizable monomer (IV) is 1.0.

The monomer composition preferably contains a metal cation salt.
By containing the metal cation salt, ionic cross-linking occurs between the radical polymerizable unsaturated carboxylic acid monomer (II) and the carboxyl group, so that the cross-linking efficiency can be increased and the heat resistance can be increased. Become. As a result, it is possible to obtain a thermally expandable microcapsule that does not burst or shrink for a long time in a high temperature region. In addition, since the elastic modulus of the shell is difficult to decrease even in a high temperature region, even when molding processing such as kneading molding, calender molding, extrusion molding, injection molding, etc. to which a strong shear force is applied, the thermal expansion micro Capsule rupture and shrinkage do not occur.
In addition, when ion crosslinking occurs instead of covalent bonding, the particle shape of the thermally expandable microcapsule becomes close to a true sphere, and distortion is less likely to occur. This is because ionic bond cross-linking is weaker than covalent bond cross-linking, so that when the volume of the thermally expandable microcapsule shrinks during conversion from the monomer during polymerization to the polymer, shrinkage occurs uniformly. This is thought to be the cause.

The metal cation of the metal cation salt is not particularly limited as long as it is a metal cation that reacts with the radical polymerizable unsaturated carboxylic acid monomer (II) to be ionically crosslinked, and examples thereof include Na, K, Li, Zn, Examples include ions such as Mg, Ca, Ba, Sr, Mn, Al, Ti, Ru, Fe, Ni, Cu, Cs, Sn, Cr, and Pb. Among these, ions of Ca, Zn, and Al, which are divalent to trivalent metal cations, are preferable, and Zn ions are particularly preferable. These metal cation salts may be used independently and may use 2 or more types together.

In addition, although it does not specifically limit as a combination when using the said metal cation salt 2 or more types, It is using combining the ion of alkali metal or alkaline-earth metal, and metal cations other than the said alkali metal or alkaline-earth metal. preferable. By having the alkali metal or alkaline earth metal ion, a functional group such as a carboxyl group is activated, and a reaction between a metal cation other than the alkali metal and the carboxyl group can be promoted. Examples of the alkali metal or alkaline earth metal include Na, K, Li, Ca, Ba, and Sr. Among them, it is preferable to use strong basic Na, K, and the like.

The preferable lower limit of the content of the metal cation salt is 0.1% by weight, and the preferable upper limit is 10% by weight with respect to the total amount of monomers. If it is less than 0.1% by weight, the effect of heat resistance may not be obtained. If it exceeds 10% by weight, the expansion ratio may be remarkably deteriorated. A more preferred lower limit is 0.5% by weight, and a more preferred upper limit is 5% by weight.

In the monomer composition, a polymerization initiator is contained in order to polymerize the monomer.
As the polymerization initiator, for example, dialkyl peroxide, diacyl peroxide, peroxyester, peroxydicarbonate, azo compound and the like are preferably used. Specific examples include, for example, dialkyl peroxides such as methyl ethyl peroxide, di-t-butyl peroxide, and dicumyl peroxide; isobutyl peroxide, benzoyl peroxide, 2,4-dichlorobenzoyl peroxide, 3, 5 Diacyl peroxide such as 1,5-trimethylhexanoyl peroxide; t-butyl peroxypivalate, t-hexyl peroxypivalate, t-butyl peroxyneodecanoate, t-hexylperoxyneodecanoate, 1-cyclohexyl-1-methylethylperoxyneodecanoate, 1,1,3,3-tetramethylbutylperoxyneodecanoate, cumylperoxyneodecanoate, (α, α-bis-neodecane Noo Peroxy) Perio such as diisopropylbenzene Xyester; bis (4-t-butylcyclohexyl) peroxydicarbonate, di-n-propyl-oxydicarbonate, diisopropylperoxydicarbonate, di (2-ethylethylperoxy) dicarbonate, dimethoxybutylperoxydi Peroxydicarbonates such as carbonate and di (3-methyl-3-methoxybutylperoxy) dicarbonate; 2,2′-azobisisobutyronitrile, 2,2′-azobis (4-methoxy-2,4 -Azo compounds such as dimethylvaleronitrile, 2,2'-azobis (2,4-dimethylvaleronitrile), 1,1'-azobis (1-cyclohexanecarbonitrile), and the like.

The preferable lower limit of the weight average molecular weight of the polymer constituting the shell is 100,000, and the preferable upper limit is 2 million. If it is less than 100,000, the strength of the shell may be reduced, and if it exceeds 2 million, the strength of the shell becomes too high, and the expansion ratio may be reduced.

The shell may further contain a stabilizer, an ultraviolet absorber, an antioxidant, an antistatic agent, a flame retardant, a silane coupling agent, a colorant, and the like as necessary.

In the thermally expandable microcapsule of the present invention, a volatile expansion agent is included as a core agent in the shell.
The volatile swelling agent is a substance that becomes gaseous at a temperature below the softening point of the polymer constituting the shell, and a low-boiling organic solvent is suitable.
Examples of the volatile swelling agent include ethane, ethylene, propane, propene, n-butane, isobutane, butene, isobutene, n-pentane, isopentane, neopentane, n-hexane, heptane, petroleum ether, isooctane, octane, decane, isododecane, dodecane, low molecular weight hydrocarbons such as hexane _{decane; CCl 3 F, CCl 2 F} 2, CClF 3, chlorofluorocarbons such as CClF ₂ -CClF 2; tetramethylsilane, trimethylethyl silane, trimethyl isopropyl silane, trimethyl And tetraalkylsilanes such as -n-propylsilane. Of these, isobutane, n-butane, n-pentane, isopentane, n-hexane, isooctane, isododecane, and mixtures thereof are preferable. These volatile swelling agents may be used alone or in combination of two or more.
Further, as the volatile expansion agent, a thermally decomposable compound that is thermally decomposed by heating to become gaseous may be used.

In the thermally expandable microcapsule of the present invention, it is preferable to use a low-boiling hydrocarbon having 5 or less carbon atoms among the above-described volatile expansion agents. By using such a hydrocarbon, it is possible to obtain a thermally expandable microcapsule having a high expansion ratio and promptly starting foaming.
Moreover, it is good also as using the thermal decomposition type compound which thermally decomposes by heating and becomes a gaseous state as a volatile expansion | swelling agent.

In the thermally expandable microcapsule of the present invention, a preferable lower limit of the maximum foaming temperature (Tmax) is 175 ° C. When the temperature is lower than 175 ° C., the heat resistance is lowered, and thus the thermally expandable microcapsules are ruptured and contracted in a high temperature region or during molding. Moreover, it foams by shear at the time of masterbatch pellet manufacture, and an unfoamed masterbatch pellet cannot be manufactured stably. A more preferred lower limit is 180 ° C and a preferred upper limit is 240 ° C.
In the present specification, the maximum foaming temperature is when the diameter of the thermally expandable microcapsule becomes maximum when the diameter is measured while heating the thermally expandable microcapsule from room temperature (maximum displacement). It means temperature.

Moreover, the preferable upper limit of foaming start temperature (Ts) is 175 degreeC. When the temperature exceeds 175 ° C., particularly in the case of injection molding, in the core back foam molding in which the mold is fully filled with a resin material and then the mold is expanded to the desired position, the resin temperature is cooled during the core back foaming process, and the expansion ratio May not go up. A preferred lower limit is 130 ° C and a more preferred upper limit is 160 ° C.

The preferable lower limit of the volume average particle diameter of the thermally expandable microcapsule of the present invention is 5 μm, and the preferable upper limit is 100 μm. If the thickness is less than 5 μm, the resulting molded body has too small bubbles, which may result in insufficient weight reduction of the molded body. If the thickness exceeds 100 μm, the resulting molded body has excessively large bubbles, resulting in strength and the like. May cause problems. A more preferred lower limit is 10 μm, and a more preferred upper limit is 45 μm.

The method for producing the thermally expandable microcapsule of the present invention is not particularly limited. For example, the step of preparing an aqueous medium, the polymerizable monomer (I) 44 to at least one selected from acrylonitrile and methacrylonitrile 63% by weight, 15 to 30% by weight of a radically polymerizable unsaturated carboxylic acid monomer (II) having a carboxyl group and having 3 to 8 carbon atoms, and a crosslinkable monomer having two or more double bonds in the molecule (III) 0.1 to 3.0% by weight and 21 to 40% by weight of polymerizable monomer (IV) consisting of at least one selected from (meth) acrylic acid ester, vinylidene chloride, vinyl acetate and styrene monomer A step of dispersing an oily mixture containing a monomer composition containing a volatile swelling agent in an aqueous medium, and the monomer It can be prepared by carrying out the step of engaging.

When producing the heat-expandable microcapsules of the present invention, a step of preparing an aqueous medium is first performed. In a specific example, for example, an aqueous dispersion medium containing a dispersion stabilizer is prepared by adding water, a dispersion stabilizer and, if necessary, an auxiliary stabilizer to a polymerization reaction vessel. Moreover, you may add alkali metal nitrite, stannous chloride, stannic chloride, potassium dichromate, etc. as needed.

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 and the like. Can be mentioned.

The addition amount of the dispersion stabilizer is not particularly limited and is appropriately determined depending on the type of dispersion stabilizer, the particle size of the microcapsules, and the like. The upper limit is 20 parts by weight.

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

Further, the combination of the dispersion stabilizer and the auxiliary stabilizer is not particularly limited. For example, a combination of colloidal silica and a condensation product, a combination of colloidal silica and a water-soluble nitrogen-containing compound, magnesium hydroxide or calcium phosphate, A combination with an emulsifier may be mentioned. In these, the combination of colloidal silica and a condensation product is preferable.
Further, the condensation product is preferably a condensation product of diethanolamine and an aliphatic dicarboxylic acid, particularly a condensation product of diethanolamine and adipic acid or a condensation product of diethanolamine and itaconic acid.

Examples of the water-soluble nitrogen-containing compound include polyvinyl pyrrolidone, polyethyleneimine, polyoxyethylene alkylamine, polydialkylaminoalkyl (meth) acrylate represented by polydimethylaminoethyl methacrylate and polydimethylaminoethyl acrylate, and polydimethylamino. Examples thereof include polydialkylaminoalkyl (meth) acrylamides represented by propylacrylamide and polydimethylaminopropylmethacrylamide, polyacrylamide, polycationic acrylamide, polyamine sulfone, and polyallylamine. Of these, polyvinylpyrrolidone is preferably used.

The amount of colloidal silica added is appropriately determined depending on the particle size of the thermally expandable microcapsule, but the preferred lower limit is 1 part by weight and the preferred upper limit is 20 parts by weight with respect to 100 parts by weight of the vinyl monomer. A more preferred lower limit is 2 parts by weight, and a more preferred upper limit is 10 parts by weight. Further, the amount of the condensation product or the water-soluble nitrogen-containing compound is also appropriately determined depending on the particle size of the thermally expandable microcapsule, but a preferable lower limit is 0.05 parts by weight and a preferable upper limit with respect to 100 parts by weight of the monomer. Is 2 parts by weight.

In addition to the dispersion stabilizer and auxiliary stabilizer, inorganic salts such as sodium chloride and sodium sulfate may be added. By adding an inorganic salt, a thermally expandable microcapsule having a more uniform particle shape can be obtained. Usually, the amount of the inorganic salt added is preferably 0 to 100 parts by weight with respect to 100 parts by weight of the monomer.

The aqueous dispersion medium containing the above dispersion stabilizer is prepared by blending a dispersion stabilizer or auxiliary stabilizer with deionized water, and the pH of the aqueous phase at this time depends on the type of dispersion stabilizer or auxiliary stabilizer used. As appropriate. For example, when silica such as colloidal silica is used as a dispersion stabilizer, polymerization is performed in an acidic medium. 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 using magnesium hydroxide or calcium phosphate, it is polymerized in an alkaline medium.

Next, in the method for producing a thermally expandable microcapsule, 44 to 63% by weight of polymerizable monomer (I) consisting of at least one selected from acrylonitrile and methacrylonitrile, a carboxyl group, and a carbon number of 3 -8 radical polymerizable unsaturated carboxylic acid monomer (II) 15 to 30% by weight, crosslinkable monomer (III) 0.1 to 3.0% by weight having two or more double bonds in the molecule, A monomer composition containing 21 to 40% by weight of a polymerizable monomer (IV) selected from at least one selected from (meth) acrylic acid ester, vinylidene chloride, vinyl acetate, and a styrene monomer, and a volatile swelling agent A step of dispersing the oily mixture to be dispersed in an aqueous medium. In this step, the monomer composition and the volatile swelling agent may be separately added to the aqueous dispersion medium to prepare an oily mixture in the aqueous dispersion medium. And then added to the aqueous dispersion medium. At this time, the oil-based mixed liquid and the aqueous dispersion medium are prepared in separate containers in advance, and the oil-based mixed liquid is dispersed in the aqueous dispersion medium by mixing with stirring in another container, and then the polymerization reaction container. It may be added.
In order to polymerize the monomer, a polymerization initiator is used. However, the polymerization initiator may be added in advance to the oily mixed solution, and the aqueous dispersion medium and the oily mixed solution are added to the polymerization reaction vessel. It may be added after stirring and mixing.

As a method of emulsifying and dispersing the oily mixed liquid in an aqueous dispersion medium with a predetermined particle size, a method of stirring with a homomixer (for example, manufactured by Tokushu Kika Kogyo Co., Ltd.) or the like, a line mixer or an element type static disperser For example, a method of passing through a static dispersion device such as the above.
The above-mentioned static dispersion device may be supplied with the aqueous dispersion medium and the polymerizable mixture separately, or may be supplied with a dispersion that has been mixed and stirred in advance.

The thermally expandable microcapsule of the present invention can be produced by performing a step of polymerizing a monomer by, for example, heating the dispersion obtained through the above-described steps. The thermally expandable microcapsules produced by such a method have a high maximum foaming temperature, excellent heat resistance, and do not rupture or shrink even in a high temperature region or during molding. Moreover, since heat resistance is high, it does not foam by shear at the time of masterbatch pellet manufacture, and an unfoamed masterbatch pellet can be manufactured stably.

A resin composition or a master batch pellet obtained by adding a matrix resin such as a thermoplastic resin to the thermally expandable microcapsule of the present invention is molded using a molding method such as injection molding, and the above thermal expansion is performed by heating during molding. Foamed molded articles can be produced by foaming the conductive microcapsules. Such a foam-molded article is also one aspect of the present invention.
The foamed molded article of the present invention obtained by such a method has high appearance quality, has closed cells uniformly formed, has excellent lightness, heat insulation, impact resistance, rigidity, etc. It can be suitably used for applications such as building materials for automobiles, automobile members, and shoe soles.

The thermoplastic resin is not particularly limited as long as the object of the present invention is not impaired. For example, general thermoplastic resins such as polyvinyl chloride, polystyrene, polypropylene, polypropylene oxide, and polyethylene; polybutylene terephthalate, nylon, Engineering plastics such as polycarbonate and polyethylene terephthalate are listed. Further, thermoplastic elastomers such as ethylene, vinyl chloride, olefin, urethane, and ester may be used, or these resins may be used in combination.

The amount of thermally expandable microcapsules added to 100 parts by weight of the thermoplastic resin is 0.5 to 20 parts by weight, preferably 1 to 10 parts by weight. Moreover, it can also use together with chemical foaming agents, such as sodium hydrogencarbonate (bicarbonate) and ADCA (azo type). Use thermal expansion microcapsules together when foaming by injecting physical gas (water vapor, nitrogen, carbon dioxide, etc.) or supercritical fluid (carbon dioxide, nitrogen, etc.) into molten thermoplastic resin. You can also.

The method for producing the master batch pellet is not particularly limited. For example, a matrix resin such as a thermoplastic resin and raw materials such as various additives are kneaded in advance using a same-direction twin-screw extruder or the like. Next, after heating to a predetermined temperature and adding a foaming agent such as the thermal expansion microcapsule of the present invention, the kneaded product obtained by further kneading is cut into a desired size with a pelletizer to form a pellet. And a method of preparing master batch pellets. At this time, when thermally expandable microcapsules with low heat resistance were used, there was a problem that foaming occurred due to shearing by kneading. If fine foaming occurs at this point, it is difficult to obtain a desired foaming ratio in subsequent foam molding, and the variation also increases.
Alternatively, a master batch pellet in the form of a pellet may be manufactured by kneading a matrix resin such as a thermoplastic resin or a raw material such as a thermally expandable microcapsule with a batch kneader and then granulating with a granulator. .
The kneader is not particularly limited as long as it can knead without destroying the thermally expandable microcapsules, and examples thereof include a pressure kneader and a Banbury mixer.

The molding method of the foamed molded product of the present invention is not particularly limited, and examples thereof include kneading molding, calendar molding, extrusion molding, injection molding, and the like. In the case of injection molding, the construction method is not particularly limited, and a short shot method in which a resin material is partially filled in a mold and foamed, or a core back method in which a mold is fully filled with a resin material and then the mold is opened to a desired position Etc.

According to the present invention, since excellent heat resistance is obtained, it is possible to obtain a thermally expandable microcapsule that can be suitably used for kneading molding, calender molding, extrusion molding, injection molding, etc. to which a strong shear force is applied. it can. Moreover, the foaming molding which has high foaming ratio and has a desired foaming characteristic is obtained. Furthermore, the obtained foamed molded article can be excellent in appearance and hardly yellowed.

Examples of the present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples.

Example 1
(Production of thermally expandable microcapsules)
After adding 130 parts by weight of colloidal silica having a solid content of 20% by weight, 6 parts by weight of polyvinylpyrrolidone and 640 parts by weight of sodium chloride to 2,000 parts by weight of ion-exchanged water, the pH was adjusted to 3.5 to prepare an aqueous dispersion medium. .
238 parts by weight of acrylonitrile, 113 parts by weight of methacrylonitrile, 113 parts by weight of methacrylic acid, 287 parts by weight of methyl methacrylate, and 3 parts by weight of trimethylolpropane trimethacrylate were mixed to obtain a monomer composition of a uniform solution. To this, 10 g of 2,2′-azobis (isobutyronitrile) and 238 parts by weight of normal pentane were added and mixed in an autoclave.
Thereafter, the aqueous dispersion medium was charged into an autoclave, stirred for 10 minutes at 1,000 rpm, purged with nitrogen, and reacted at a reaction temperature of 60 ° C. for 15 hours. The reaction pressure was 0.5 MPa, and stirring was performed at 200 rpm. The obtained polymerization slurry was pre-dehydrated with a dehydrator (centre) and then dried to obtain thermally expandable microcapsules.

(Production of foamed molded product)
To 100 parts by weight of polyvinyl chloride resin, 70 parts by weight of dioctyl phthalate as a plasticizer, 3 parts by weight of carbon black as a black pigment, and 3 parts by weight of thermally expandable microcapsules obtained in Example 1 were mixed. Subsequently, using an injection molding machine having a clamping force of about 350 tons and a screw diameter of 60 mm, injection molding was performed at an injection pressure of about 1860 kg / cm ² and a cylinder temperature of 190 ° C., and a disk-shaped foam having a diameter of 250 mm × thickness of 3 mm. A molded body was obtained.

(Examples 2-3, Reference Examples 4-7, Example 9, Reference Example 10, Comparative Examples 1-5)
Thermally expandable microcapsules and acrylonitrile, methacrylonitrile, methacrylic acid, methyl methacrylate, trimethylolpropane trimethacrylate were mixed in the composition shown in Tables 1 and 2 to obtain a monomer composition, as in Example 1. A foamed molded product was obtained.

( Reference Example 8)
Acrylonitrile, methacrylonitrile, methacrylic acid, methyl methacrylate and trimethylolpropane trimethacrylate were mixed in the composition shown in Table 1 to obtain a monomer composition, and 3.8 parts by weight of zinc hydroxide, which is a metal cation salt, was further added. A thermally expandable microcapsule and a foamed molded product were obtained in the same manner as in Example 1 except that.

(Evaluation method)
The performance of the obtained thermally expandable microcapsule and foamed molded article was evaluated by the following method. The results are shown in Tables 1 and 2.

(1) Evaluation of thermally expandable microcapsules (1-1) Volume average particle size The particle size distribution size measuring device (LA-950, manufactured by HORIBA) was used to measure the volume average particle size.

(1-2) Foaming start temperature, maximum foaming temperature Using a thermomechanical analyzer (TMA) (TMA2940, manufactured by TA instruments), the foaming start temperature (Ts) and the maximum foaming temperature (Tmax) were measured. Specifically, 25 μg of a sample is placed in an aluminum container having a diameter of 7 mm and a depth of 1 mm, and heated from 80 ° C. to 250 ° C. at a temperature rising rate of 5 ° C./min with a force of 0.1 N applied from above. Then, the displacement in the vertical direction of the measurement terminal was measured, and the temperature at which the displacement began to rise was defined as the foaming start temperature. Further, the expansion ratio was measured, and the temperature at which the expansion ratio was the maximum was defined as the maximum expansion temperature.

(2) Evaluation of foamed molded article (2-1) Measurement of density The density of the obtained molded article was measured by a method based on JIS K-7112 A method (underwater substitution method).

(2-2) Appearance (molded product surface)
The number of white spots on the surface of the molded product was visually counted.

(2-3) Yellowness (YI)
The yellowness of the surface of the molded product was measured using a color difference meter (NR-3000, manufactured by Nippon Denshoku Industries Co., Ltd.) to obtain a YI value.

According to the present invention, a thermally expandable microcapsule capable of producing a foamed molded article having excellent heat resistance, a high expansion ratio, hardly yellowing, and having an excellent appearance, and the thermally expandable microcapsule It is possible to provide a foamed molded article using the above.

Claims (4)

A thermally expandable microcapsule in which a volatile expansion agent is encapsulated as a core agent in a polymer shell,
The shell is a polymerizable monomer (I) 44 to 63% by weight consisting of at least one selected from acrylonitrile and methacrylonitrile, a radical polymerizable unsaturated carboxylic acid having a carboxyl group and 3 to 8 carbon atoms. 15 to 30% by weight of acid monomer (II), and 2 to 40% by weight of polymerizable monomer (IV) consisting of at least one selected from (meth) acrylic acid ester, vinylidene chloride, vinyl acetate and styrene monomer And a ratio of the content of the polymerizable monomer (I) to the content of the polymerizable monomer (IV) is 2.02 or less. Is a thermally expandable microcapsule characterized by having a maximum foaming temperature of 175 to 188 ° C. The thermal expansion property according to claim 1, wherein the monomer composition contains a metal cation salt, and the content of the metal cation salt is 0.1 to 10% by weight based on the total amount of the monomers. Micro capsule. Volatile swelling agent, isobutane, n- butane, n- pentane, isopentane, hexane n-, or claim 1, characterized in that at least one member selected from the group consisting of isooctane and isododecane 2 wherein Thermally expandable microcapsules. Foamed molded characterized by the claims 1, 2 or be obtained by using the thermally expandable microcapsule of the 3 described.