JP2006002133A - Thermally expansible microcapsule and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide thermally expansible microcapsules having a high maximum foaming temperature, excellent in heat resistance without breaking and shrinking in a high temperature region or during forming processing, and a method for producing the thermally expansible microcapsules. <P>SOLUTION: The thermally expansible microcapsules include a volatile expanding agent as a core agent in a shell comprising a copolymer having segments originating from a nitrile-based monomer and segments originating from a 3-8C radical-polymerizable unsaturated carboxylic acid monomer having radical-polymerizable unsaturated bonds, and 0.1-10 wt.% metal cation. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

The present invention relates to a thermally expandable microcapsule having a high maximum foaming temperature, excellent heat resistance, and not ruptured or shrunk even in a high temperature region or during molding, and a method for producing the thermally expandable microcapsule.

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. In addition, since the elastic modulus suddenly decreases when the glass transition temperature of the shell is exceeded, thermal expansion will occur when molding such as kneading molding, calender molding, extrusion molding, injection molding, etc., where a strong shear force is applied. The microcapsules were ruptured and contracted.
Accordingly, there has been a demand for a thermally expandable microcapsule that has a high maximum foaming temperature, can maintain an expanded state for a long time, has excellent heat resistance, and can withstand high shear.

Japanese Examined Patent Publication No. 42-26524 Japanese Patent Publication No. 5-15499 Japanese Patent No. 2894990 European Patent Application No. 1149628

In view of the present situation, the present invention provides a thermally expandable microcapsule having a high maximum foaming temperature, excellent heat resistance, and not ruptured or shrunk even in a high temperature region or during molding, and a method for producing the thermally expandable microcapsule. The purpose is to provide.

The thermally expandable microcapsule of the present invention has a segment derived from a nitrile monomer, a radical polymerizable unsaturated carboxylic acid having a carboxyl group, and a carbon chain having a radical polymerizable unsaturated bond having 3 to 8 carbon atoms. A volatile swelling agent is included as a core agent in a copolymer having a segment derived from an acid monomer and a shell containing 0.1 to 10% by weight of a metal cation.
The present invention is described in detail below.

The thermally expandable microcapsule of the present invention has a segment derived from a nitrile monomer, a radical polymerizable unsaturated carboxylic acid having a carboxyl group, and a carbon chain having a radical polymerizable unsaturated bond having 3 to 8 carbon atoms. It has a shell containing a copolymer having a segment derived from an acid monomer.
Since a polymer obtained by polymerizing the nitrile monomer is extremely excellent in gas barrier properties, a shell made of a copolymer having a segment derived from a nitrile monomer is also excellent in gas barrier properties. Therefore, the thermally expandable microcapsule of the present invention having such a shell can prevent the volatile expansion agent volatilized at the time of expansion from permeating through the shell and preventing sag at a high temperature.
Examples of the nitrile monomer include acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, α-ethoxyacrylonitrile, fumaronitrile, and any mixture thereof. Of these, acrylonitrile or methacrylonitrile is preferably used. Also preferred is a mixture of acrylonitrile and methacrylonitrile.

When the nitrile monomer is a mixture of acrylonitrile and methacrylonitrile, the preferred lower limit of the ratio of acrylonitrile to methacrylonitrile (acrylonitrile / methacrylonitrile) is 0.5, and the preferred upper limit is 2.0. When it is less than 0.5, the polymerization yield may be deteriorated, and when it exceeds 2.0, the maximum expansion ratio may be lowered. A more preferred lower limit is 0.65, and a more preferred upper limit is 1.0.

The upper limit with preferable content of the segment originating in the said nitrile-type monomer in the said copolymer is 70 weight%. If it exceeds 70% by weight, the degree of crosslinking becomes higher than necessary due to the interaction with the metal cation, and the heat resistance is improved, but the expansion ratio may be drastically lowered.

The copolymer is a radical polymerizable unsaturated carboxylic acid monomer having a carboxyl group and a carbon chain having a radical polymerizable unsaturated bond and having 3 to 8 carbon atoms (hereinafter simply referred to as radical polymerizable unsaturated carboxylic acid). A segment derived from (also referred to as a monomer).
In the radical polymerizable unsaturated carboxylic acid monomer, the lower limit of the carbon number of the carbon chain having a radical polymerizable unsaturated bond is 3, and the upper limit is 8. When it exceeds 8, a molecule | numerator will become bulky and gas barrier property will fall.

The radical polymerizable unsaturated carboxylic acid monomer has one or more free carboxyl groups per molecule for ionic crosslinking with a metal cation described later. For example, acrylic acid, methacrylic acid, ethacrylic acid, crotonic acid, silica Unsaturated monocarboxylic acids such as cinnamate; unsaturated dicarboxylic acids such as maleic acid, itaconic acid, fumaric acid, citraconic acid and chloromaleic acid and their anhydrides or monomethyl maleate, monoethyl maleate, monobutyl maleate, fumaric acid Examples thereof include monoesters of unsaturated dicarboxylic acids such as monomethyl, monoethyl fumarate, monomethyl itaconate, monoethyl itaconate, monobutyl itaconate, and derivatives thereof. These may be used alone or in combination of two or more. Among these, acrylic acid, methacrylic acid, maleic acid, maleic anhydride, and itaconic acid are preferable. Among them, methacrylic acid has a high glass transition temperature and a low bulk. This is more preferable because the gas barrier property is not impaired.

The preferable lower limit of the content of the segment derived from the radical polymerizable unsaturated carboxylic acid monomer in the copolymer is 10% by weight, and the preferable upper limit is 50% by weight. If it is less than 10% by weight, the maximum foaming temperature may be 180 ° C. or less, and if it exceeds 50% by weight, the maximum foaming temperature is increased, but the expansion ratio is unfavorable.

The copolymer may have a segment other than the segment derived from the nitrile monomer and the segment derived from the radical polymerizable unsaturated carboxylic acid monomer, if necessary. Examples of such segments include, but are not limited to, acrylic esters such as methyl acrylate, ethyl acrylate, butyl acrylate, and dicyclopentenyl acrylate; methyl methacrylate, ethyl methacrylate, butyl methacrylate, iso Examples include methacrylic acid esters such as bornyl methacrylate; segments derived from vinyl monomers such as vinyl acetate and styrene. These monomers can be appropriately selected and used depending on the properties required for the thermally expandable microcapsules, and among them, methyl methacrylate, ethyl methacrylate, methyl acrylate and the like are preferably used.
However, the content of such a segment is preferably less than 10% by weight. If it is 10% by weight or more, the gas barrier property of the shell may be lowered.

The minimum with a preferable weight average molecular weight of the said copolymer is 100,000, and a 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 thermally expandable microcapsule of the present invention contains a metal cation in the shell.
When the shell contains a metal cation, the metal cation reacts with the carboxyl group of the copolymer constituting the shell, and the copolymer is considered to be ionically crosslinked. It is possible to obtain a thermally expandable microcapsule that does not rupture 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, the ionic crosslinking mentioned above means that a bridge | crosslinking is formed between the free carboxyl groups which exist as a side chain of the said copolymer. The number of arranged carboxyl groups per metal cation varies depending on the metal species.

The metal cation is not particularly limited as long as it is a metal cation that reacts with the carboxyl group of the copolymer to ionically crosslink the copolymer. For example, Li, Na, K, Z
Examples include ions such as n, Mg, Ca, Ba, Sr, Mn, Al, Ti, Ru, Fe, Ni, Cu, Cs, Sn, Cr, and Pb. These may be used alone or in combination of two or more. Among these, ions of Ca, Zn, and Al are preferable, and Zn ions are particularly preferable.
In addition, although it does not specifically limit as a combination when using the said metal cation 2 or more types, It is preferable to use combining the ion of an alkali metal, and metal cations other than the said alkali metal. By having the alkali metal ion, a functional group such as a carboxyl group is activated, and the reaction between the metal cation other than the alkali metal and the carboxyl group of the copolymer can be promoted.
Examples of the alkali metal include Na, K, and Li.

The lower limit of the content of the metal cation in the shell is 0.1% by weight, and the upper limit is 10% by weight. If the amount is less than 0.1% by weight, the copolymer cannot be sufficiently ionically crosslinked, and the effect of improving the heat resistance cannot be obtained. Even if the amount exceeds 10% by weight, a further effect can be obtained. Absent. A preferred lower limit is 0.5% by weight.
In addition, content of the said metal cation can be measured using an atomic absorption spectrophotometer (AA-680, Shimadzu Corp. make), for example.

Further, in order to appropriately ion-crosslink the carboxyl group and metal cation of the copolymer, the amount of metal cation per free carboxyl group of the copolymer is adjusted according to the desired degree of crosslinking. Although it is necessary, the preferable lower limit of the amount of the metal cation is 0.01 times mol and the preferable upper limit is 0.5 times mol with respect to the amount of carboxylic acid of the copolymer. If it is less than 0.01 times mol, the degree of cross-linking does not increase and it is difficult to obtain an effect on heat resistance. Even if it is blended in excess of 0.5 times mol, no further effect can be obtained. A more preferred lower limit is 0.05 times mol.

In the thermally expandable microcapsule of the present invention, a preferable lower limit of the degree of crosslinking of the shell is 75% by weight. If it is less than 75% by weight, the maximum foaming temperature may be lowered.
The degree of cross-linking includes both covalent cross-linking by a cross-linking agent and cross-linking that is ionically cross-linked by the free carboxyl group of the copolymer and the metal cation.
In the thermally expandable microcapsule of the present invention, part or all of the free carboxyl group of the copolymer is ionized to form a carboxyl anion, and an ionic bond is formed using the metal cation as a counter cation. The degree of crosslinking can be easily adjusted by the content of the metal cation.
Moreover, the said ion bridge | crosslinking can be confirmed by the absorption by the asymmetrical expansion / contraction motion of COO- around 1500-1600 cm < ^-1 >, for example, when an infrared absorption spectrum measurement is performed.

In the thermally expandable microcapsule of the present invention, the preferable lower limit of the degree of neutralization of the shell is 5%. If it is less than 5%, the maximum foaming temperature may be lowered.
In addition, the said neutralization degree represents the ratio of the carboxyl group which the said metal cation couple | bonded among the free carboxyl groups which the said copolymer has.

The shell may contain a crosslinking agent. By containing the said crosslinking agent, the intensity | strength of a shell can be strengthened and it becomes difficult to foam a cell wall at the time of thermal expansion.
The crosslinking agent is not particularly limited, and generally, a monomer having two or more radical polymerizable double bonds is preferably used. Specific examples include, for example, 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, di (meth) acrylate of polyethylene glycol having a molecular weight of 200 to 600, glycerin di (meth) acrylate, tri Methylolpropane di (meth) acrylate, trimethylolpropane tri (meth) acrylate, ethylene oxide modified trimethylolpropane tri (meth) acrylate, pentaerythritol tri (meth) acrylate Triallyl formal tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, dipentaerythritol hexa (meth) acrylate, dimethylol - tricyclodecane (meth) acrylate. Among these, since the thermally expanded microcapsules are difficult to contract even in a high temperature region exceeding 200 ° C., and easily maintain the expanded state, bifunctional crosslinking agents such as di (meth) acrylate of polyethylene glycol are preferred. A trifunctional cross-linking agent such as tri (meth) acrylate of trimethylolpropane is more preferable.

The minimum with preferable content of the said crosslinking agent in the said shell is 0.1 weight%, and a preferable upper limit is 3 weight%. A more preferred lower limit is 0.1% by weight, and a more preferred upper limit is 1% by weight.

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 low molecular weight carbonization such as ethane, ethylene, propane, propene, n-butane, isobutane, butene, isobutene, n-pentane, isopentane, neopentane, n-hexane, heptane, and petroleum ether. Hydrogen; chlorofluorocarbons such as CCl ₃ F, CCl ₂ F ₂ , CClF ₃ , CClF ₂ —CClF ₂ ; tetraalkylsilanes such as tetramethylsilane, trimethylethylsilane, trimethylisopropylsilane, trimethyl-n-propylsilane, etc. It is done. These may be used alone or in combination of two or more.

In the heat-expandable microcapsule of the present invention, it is preferable to use a hydrocarbon having a boiling point of 60 ° C. or higher among the above-described volatile expansion agents. By using such a hydrocarbon, the thermally expandable microcapsule is not easily broken even under high temperature and high shear conditions during molding, and a thermally expandable microcapsule having excellent heat resistance can be obtained.

Examples of the hydrocarbon having a boiling point of 60 ° C. or higher include n-hexane and heptane. In addition, each hydrocarbon having a boiling point of 60 ° C. or higher may be used alone or in combination with a hydrocarbon having a boiling point of less than 60 ° C.
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 is 200 ° C. If it is less than 200 ° C., the microcapsules that have expanded during high temperature or long-time heating may rupture or shrink, and the foaming ratio may decrease.
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.

The method for producing the thermally expandable microcapsule of the present invention is not particularly limited. For example, a step of preparing an aqueous medium, a nitrile monomer, a carbon chain carbon having a carboxyl group and a radically polymerizable unsaturated bond. A step of dispersing an oily mixture containing a radically polymerizable unsaturated carboxylic acid monomer having a number of 3 to 8 and a volatile swelling agent in an aqueous medium, adding a compound that generates a metal cation, and adding the carboxyl group and the metal It can be produced by performing a step of reacting with a cation and a step of polymerizing the monomer by heating the dispersion. Such a method for producing a thermally expandable microcapsule is also one aspect of the present invention.

In the method for producing the thermally expandable microcapsule of the present invention, the step of preparing the aqueous medium is 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, calcium carbonate, barium carbonate, and carbonate. Examples thereof include magnesium.

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 microcapsule, and the like, but the preferred lower limit is 0.1 part by weight, preferably 100 parts by weight of the monomer. 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 of the present invention, a radically polymerizable unsaturated carboxylic acid having a nitrile monomer, a carboxyl group, and a carbon chain having a radically polymerizable unsaturated bond and having 3 to 8 carbon atoms. A step of dispersing an oily mixture containing an acid monomer and a volatile swelling agent in an aqueous medium is performed. In this step, the monomer and the volatile swelling agent may be separately added to the aqueous dispersion medium to prepare an oily mixture in the aqueous dispersion medium. 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.

The polymerization initiator is not particularly limited, and for example, dialkyl peroxide, diacyl peroxide, peroxyester, peroxydicarbonate, azo compound and the like that are soluble in the monomer are preferably used. Specific examples include, for example, dialkyl peroxides such as methyl ethyl peroxide, di-t-butyl peroxide, dicumyl peroxide; isobutyl peroxide, benzoyl peroxide, 2,4-dichlorobenzoyl peroxide, 3, 5 , 5-trimethylhexanoyl peroxide and other diacyl peroxides; 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 Noyl peroxy) peroxye such as diisopropylbenzene Ter; bis (4-t-butylcyclohexyl) peroxydicarbonate, di-n-propyl-oxydicarbonate, diisopropyl peroxydicarbonate, di (2-ethylethylperoxy) dicarbonate, dimethoxybutyl peroxydicarbonate Peroxydicarbonates such as di (3-methyl-3-methoxybutylperoxy) dicarbonate; 2,2′-azobisisobutyronitrile, 2,2′-azobis (4-methoxy-2,4- Examples include azo compounds such as dimethylvaleronitrile, 2,2′-azobis (2,4-dimethylvaleronitrile), 1,1′-azobis (1-cyclohexanecarbonitrile), and the like.

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.

Next, in the method for producing a thermally expandable microcapsule of the present invention, a step of adding a compound that generates the metal cation (hereinafter also referred to as a metal cation supplier) and reacting the carboxyl group with the metal cation is performed. By carrying out this step, the metal cation reacts with the carboxyl group and ion-crosslinks, so that heat resistance is improved and a thermally expandable microcapsule that does not rupture or shrink for a long time in a high temperature region is produced. Is possible. In addition, since the elastic modulus of the shell is improved, even when molding such as kneading molding, calender molding, extrusion molding, injection molding or the like in which a strong shear force is applied, rupture of the thermally expandable microcapsule, There is no contraction.

The metal cation supplier may be added to the dispersion before the monomer is polymerized, or may be added after the monomer is polymerized. Further, the metal cation supplier may be added directly or in the form of a solution such as an aqueous solution.

The metal cation supplier is not particularly limited. For example, the metal cation oxide, hydroxide, phosphate, carbonate, nitrate, sulfate, chloride, nitrite, sulfite, and octylic acid described above. And salts of organic acids such as stearic acid. Of these, hydroxides, chlorides and carboxylates are preferred. Specifically, Zn (OH) ₂ , ZnO, Mg (OH) _{2 and the} like are preferable, and Zn (OH) ₂ is more preferable because there is little decrease in the elastic modulus in the high temperature region.

When the metal cation supplier is added, it is preferable to add an alkali metal hydroxide in advance and then add a metal cation supplier other than the alkali metal hydroxide. By adding the alkali metal hydroxide in advance, a functional group such as a carboxyl group is activated, and the reaction with the metal cation can be promoted.
In addition, Zn (OH) ₂ has low water solubility, and it may not be possible to obtain a desired ionic crosslink by addition. However, by using such a method, for example, after adding NaOH, ZnCl in the aqueous solution is high. By adding ₂ , the same effect as the case of adding Zn (OH) ₂ can be obtained.

The alkali metal hydroxide is not particularly limited, but is preferably a hydroxide of Na, K, or Li, and more preferably a strongly basic Na or K hydroxide.

In the method for producing a thermally expandable microcapsule of the present invention, a thermally expandable microcapsule can be produced by performing a step of polymerizing a monomer by heating the dispersion obtained through the above 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.

The heat-expandable microcapsule of the present invention has a high maximum foaming temperature and does not rupture or shrink even in a high temperature region or during molding, and has extremely excellent heat resistance.

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

(Examples 1-4, Comparative Examples 1-4)
8 L of water, 10 parts by weight of colloidal silica (manufactured by Asahi Denka Co., Ltd.) and 0.3 part by weight of polyvinylpyrrolidone (manufactured by BASF) were charged as a dispersion stabilizer in a polymerization reaction vessel to prepare an aqueous dispersion medium. Next, an oily mixed liquid composed of a monomer, a cross-linking agent, a volatile swelling agent and a polymerization initiator shown in Table 1 was added to the water-soluble dispersion medium, and a metal cation supplier having a compounding quantity shown in Table 1 was added. Was added to prepare a dispersion. The obtained dispersion was stirred and mixed with a homogenizer, charged in a pressure polymerization vessel (20 L) purged with nitrogen, pressurized (0.2 MPa), 6
The reaction product was prepared by reacting at 0 ° C. for 20 hours. The obtained reaction product was repeatedly filtered and washed with water, and then dried to obtain thermally expandable microcapsules.

(Evaluation)
For the thermally expandable microcapsules obtained in Examples 1 to 4 and Comparative Examples 1 to 4, performance (volume average particle diameter, degree of crosslinking, metal cation concentration, foaming start temperature, maximum foaming temperature, maximum displacement) was evaluated. did. The results are shown in Table 1.

(1) Volume average particle diameter The volume average particle diameter was measured using a particle size distribution diameter measuring device (LA-910, manufactured by HORIBA).

(2) Foam start temperature, maximum foam temperature, maximum displacement thermomechanical analyzer (TMA) (TMA2940, manufactured by TA instruments), foam start temperature (Ts), maximum displacement (Dmax) and maximum foam temperature (Tmax) ) Was measured. Specifically, 25 μg of a sample is put into an aluminum container having a diameter of 7 mm and a depth of 1 mm, and heated from 80 ° C. to 220 ° 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, the maximum value of the displacement as the maximum displacement, and the temperature at the maximum displacement as the maximum foaming temperature.

(3) Crosslinking degree After adding 29 g of N, N-dimethylformamide and 1 g of thermally expandable microcapsules to a glass container and shaking for 24 hours to obtain a swelling liquid, the gel content obtained by removing the supernatant by centrifugation is vacuumed. Using a dryer, it was evaporated to dryness at 130 ° C. The weight was measured and the crosslinking degree was obtained by the following formula.

(4) Metal analysis 10 g of the thermally expandable microcapsule obtained was added to 20 ml of 1N hydrochloric acid, and the mixture was stirred for 2 hours, followed by filtration with filter paper. The filtrate was diluted to enter the detection range and analyzed with an atomic absorption spectrophotometer (AA-680, manufactured by Shimadzu Corporation). The amount of metal component contained in the thermally expandable microcapsule (concentration of metal cation in the particle) was calculated from the analysis result.

ADVANTAGE OF THE INVENTION According to this invention, the maximum foaming temperature is high, it is excellent in heat resistance, and the manufacturing method of a thermally expansible microcapsule and a thermally expansible microcapsule which do not rupture and shrink | contract at the time of a high temperature area | region and a shaping | molding process can be provided.

Claims (4)

A segment derived from a nitrile monomer and a segment derived from a radically polymerizable unsaturated carboxylic acid monomer having a carboxyl group and a carbon chain having a radically polymerizable unsaturated bond and having 3 to 8 carbon atoms. A thermally expandable microcapsule characterized in that a volatile expansion agent is included as a core agent in a polymer and a shell containing 0.1 to 10% by weight of a metal cation. The thermally expandable microcapsule according to claim 1, wherein the volatile expansion agent is a hydrocarbon having a boiling point of 60 ° C or higher. The thermally expandable microcapsule according to claim 1 or 2, wherein the maximum foaming temperature is 200 ° C or higher. A method for producing a thermally expandable microcapsule according to claim 1, 2 or 3, wherein a step of preparing an aqueous medium, a nitrile monomer, a carbon chain having a carboxyl group and having a radically polymerizable unsaturated bond. A step of dispersing an oily mixed solution containing a radically polymerizable unsaturated carboxylic acid monomer having 3 to 8 carbon atoms and a volatile swelling agent in an aqueous medium, adding a compound that generates a metal cation, and A method for producing a thermally expandable microcapsule comprising a step of reacting a metal cation and a step of polymerizing a monomer by heating a dispersion.