JP2009221429A - Thermally expandable microcapsule and foamed molded body - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thermally expandable microcapsule suitably usable in knead-molding, calender-molding, extrusion-molding, injection-molding, etc., each requiring strong shearing force, as it has an excellent heat resistance, broad foaming temperature profile and high rate of expansion, and to provide a foamed molded body using the thermally expansible microcapsule. <P>SOLUTION: This thermally expandable microcapsule has a thermally expandable microcapsule as a core in which a volatile expanding material is included in a shell comprising a polymer, which has 160°C or lower foaming initiation temperature, 200°C or higher maximum foaming temperature, where the shell is obtained by polymerizing a monomer mixture comprising 40-94 wt.% of at least one polymerizable monomer selected from methacrylonitrile and vinylidene chloride, 5-50 wt.% of a radically polymerizable unsaturated 3-8C carboxylic acid monomer, and 1-30 wt.% of an amide-based polymerizable monomer where the number of carbons of a hydrocarbon bonding to the amide nitrogen atom is 4 or more. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

The present invention has excellent heat resistance, has a wide foaming temperature range, and has a high foaming ratio, so that it can be suitably used for kneading molding, calendar molding, extrusion molding, injection molding, etc. to which a strong shearing force is applied. The present invention relates to a thermally expandable microcapsule and a foam-molded product using 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 impossible 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, Patent Document 5 defines a monomer that constitutes the shell of the heat-expandable microcapsule, thereby having good foaming performance in a wide range of foaming temperature, particularly in a high temperature range (160 ° C. or higher), and heat resistance. A heat-expandable microcapsule with improved s 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, a so-called “sag” phenomenon may occur or may be crushed due to heat resistance and strength problems of the thermally expandable microcapsules.

Patent Document 6 discloses a thermally expandable microcapsule using as a shell a polymer obtained by polymerizing a monomer containing a carboxyl group and a monomer having a group that reacts with the carboxyl group. In such a heat-expandable microcapsule, the three-dimensional cross-linking density increases, so that even when the shell after foaming is very thin, it exhibits a strong resistance to shrinkage, and the heat resistance is drastically improved.
However, even when such a method is used, there are still problems in heat resistance and strength, and there is a limit to the expansion ratio after molding such as injection molding.
Therefore, even when used for kneading molding, calender molding, extrusion molding, injection molding, etc., which has excellent heat resistance and expansion ratio and a strong shear force is applied, it is difficult to cause sag etc. There was a need for thermally expandable microcapsules that could be made.
Japanese Examined Patent Publication No. 42-26524 Japanese Patent Publication No. 5-15499 Japanese Patent No. 2894990 European Patent Application No. 1149628 International Publication WO2003 / 099955 International Publication No. WO 1999/43758

The present invention has excellent heat resistance, has a wide foaming temperature range, and has a high foaming ratio, so that it can be suitably used for kneading molding, calendar molding, extrusion molding, injection molding, etc. to which a strong shearing force is applied. It is an object of the present invention to provide a thermally expandable microcapsule and a foam-molded product using the thermally expandable microcapsule.

The present invention is a thermally expandable microcapsule in which a volatile expansion agent is encapsulated as a core agent in a polymer shell, the foaming start temperature is 160 ° C. or lower, the maximum foaming temperature is 200 ° C. or higher, and The shell is a radical polymerization having 3 to 8 carbon atoms having a carboxyl group and 40 to 94% by weight of a polymerizable monomer (I) consisting of at least one selected from acrylonitrile, methacrylonitrile and vinylidene chloride. Polymerizable unsaturated carboxylic acid monomer (II) 5 to 50% by weight and polymerizable monomer (III) 1 having an amide bond and the total number of carbon atoms of hydrocarbons bonded to the nitrogen atom of the amide bond being 4 or more It is a thermally expandable microcapsule made of a polymer obtained by polymerizing a monomer mixture containing -30% by weight.
The present invention is described in detail below.

As a result of intensive studies, the present inventors have found that the foaming temperature range is widened by setting the foaming start temperature of the thermally expandable microcapsule to 160 ° C. or less and the maximum foaming temperature to 200 ° C. or more. It was found that a high expansion ratio can be obtained.
As a result of further intensive studies, the present inventors have found that the polymerizable monomer (I), the radical polymerizable unsaturated carboxylic acid monomer (II) and the hydrocarbon having an amide bond and bonded to the nitrogen atom of the amide bond are as follows. When a thermally expandable microcapsule having a shell obtained by polymerizing a monomer mixture containing a predetermined amount of polymerizable monomers (III) having a total number of carbon atoms of 4 or more is used for molding processing such as injection molding. The present inventors have found that heat-expandable microcapsules can be prevented from sagging and that heat-expandable microcapsules having a wide foaming temperature range and a high expansion ratio can be obtained, thereby completing the present invention.

The shell constituting the thermally expandable microcapsule of the present invention has 40 to 94% by weight of a polymerizable monomer (I) consisting of at least one selected from acrylonitrile, methacrylonitrile and vinylidene chloride, and has a carboxyl group, The total number of carbon atoms of hydrocarbons having 5 to 50% by weight of a radically polymerizable unsaturated carboxylic acid monomer (II) having 3 to 8 carbon atoms and an amide bond and bonded to the nitrogen atom of the amide bond is 4 or more. It consists of a polymer obtained by polymerizing a monomer mixture containing 1 to 30% by weight of the polymerizable monomer (III).

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

The lower limit of the content of the polymerizable monomer (I) in the monomer mixture is 40% by weight, and the upper limit is 94% by weight. When it is less than 40% by weight, the gas barrier property of the shell is lowered, so that the expansion ratio may be lowered. If it exceeds 94% by weight, the heat resistance may not increase. A preferred lower limit is 50% by weight and a preferred upper limit is 80% by weight.

Examples of the radically polymerizable unsaturated carboxylic acid monomer (II) having a carboxyl group and having 3 to 8 carbon atoms include unsaturated monocarboxylic acids such as acrylic acid, methacrylic acid, ethacrylic acid, crotonic acid, and cinnamic acid. Unsaturated dicarboxylic acids such as carboxylic acid, maleic acid, itaconic acid, fumaric acid, citraconic acid, chloromaleic acid and their anhydrides or monomethyl maleate, monoethyl maleate, monobutyl maleate, monomethyl fumarate, monoethyl fumarate, itacone Examples thereof include monoesters of unsaturated dicarboxylic acids such as monomethyl acid, monoethyl itaconate, monobutyl itaconate and derivatives thereof, and these may be used alone or in combination of two or more. Of these, acrylic acid, methacrylic acid, maleic acid, maleic anhydride, and itaconic acid are particularly preferable.

The lower limit of the content of the radical polymerizable unsaturated carboxylic acid monomer (II) having a carboxyl group and having 3 to 8 carbon atoms in the monomer mixture is 5% by weight, and the upper limit is 50% by weight. If it is less than 5% by weight, the maximum foaming temperature may be 200 ° C. or less. If it exceeds 50% by weight, the maximum foaming temperature is improved, but the foaming ratio is lowered. A preferred lower limit is 10% by weight and a preferred upper limit is 40% by weight.

The monomer mixture has an amide bond, and the total number of carbon atoms of hydrocarbons bonded to nitrogen atoms of the amide bond is 4 or more (hereinafter also referred to simply as polymerizable monomer (III)). ).
Since the polymerizable monomer (III) has an amide bond and is a bulky monomer, it greatly contributes to improving the heat resistance of the thermally expandable microcapsule. As described above, the reason why the heat resistance is improved is not clear, but it is considered that the mobility of the molecular chain is suppressed by the bulk of the amide bond and the carbon hydrogen bonded to the nitrogen atom.
Conventionally, a monomer having an amide bond is considered not to contribute to improvement of heat resistance. For example, in International Publication WO1999 / 43758, in consideration of reactivity with a carboxyl group, a basic group such as an amino group is considered. It is described that a monomer combined with a strong functional group is used. This is because, in Examples of International Publication WO1999 / 43758, N, N-dimethylaminopropylacrylamide and N, N-dimethylaminoethyl acrylate are used. In contrast to this, N, N-dimethylacrylamide is used in the comparative example.
In contrast, the present inventors have found that when the total number of carbon atoms of hydrocarbons bonded to the nitrogen atom of the amide bond is 4 or more, a thermally expandable microcapsule having excellent heat resistance can be obtained. The present invention has been completed.

Examples of the polymerizable monomer (III) having the amide bond and having 4 or more carbon atoms of the hydrocarbon bonded to the nitrogen atom of the amide bond include N-butylacrylamide, N-sec-butylacrylamide, N -Tert-butylacrylamide, N, N-diisopropylacrylamide, N, N-dibutylacrylamide, N-dodecylacrylamide and the like.

The minimum of the total carbon number of the hydrocarbon couple | bonded with the nitrogen atom of the amide bond which the said polymerizable monomer (III) has is four. If it is less than 4, the bulk of the carbon hydrogen bonded to the nitrogen atom of the amide bond is insufficient and the heat resistance is lowered. A preferred lower limit is 4 and a preferred upper limit is 8.
For example, even a bulky alkyl group having 4 or more carbon atoms, such as a tert-butyl group, does not contribute to the improvement of heat resistance when bonded to a part of the ester bond, and is bonded to the nitrogen atom of the amide bond. In some cases, the effect of improving heat resistance can be exhibited.

The lower limit of the content of the polymerizable monomer (III) in the monomer mixture is 1% by weight, and the upper limit is 30% by weight. If it is less than 1% by weight, the maximum foaming temperature may be 200 ° C. or less. If it exceeds 30% by weight, the maximum foaming temperature is improved, but the foaming ratio is lowered. A preferred lower limit is 3% by weight and a preferred upper limit is 10% by weight.

The monomer mixture may contain a metal cation salt.
By containing the metal cation salt, ionic cross-linking occurs with the carboxyl group of the radical polymerizable unsaturated carboxylic acid monomer (II), so that cross-linking efficiency can be increased and 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.

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 minimum of content of the said metal cation salt in the said monomer mixture is 0.1 weight%, and an upper limit is 10 weight%. If it is less than 0.1% by weight, the effect of heat resistance is not obtained, and if it exceeds 10% by weight, the expansion ratio is significantly deteriorated. A preferred lower limit is 0.5% by weight and a preferred upper limit is 5% by weight.

The monomer mixture preferably further contains a polymerizable monomer having two or more double bonds in the molecule. The polymerizable monomer has a role as a crosslinking agent.
By containing the said polymerizable monomer, the intensity | strength of a shell can be strengthened and it becomes difficult to break a cell wall at the time of thermal expansion.
The polymerizable monomer is not particularly limited as long as it is different from the radically polymerizable unsaturated carboxylic acid monomer (II) and polymerizable monomer (III) having the carboxyl group and having 3 to 8 carbon atoms. In general, monomers having two or more radically polymerizable double bonds are 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.

In the monomer mixture, the total number of carbon atoms of the polymerizable monomer (I), the radical polymerizable unsaturated carboxylic acid monomer (II), the hydrocarbon having an amide bond and bonded to the nitrogen atom of the amide bond is In addition to four or more polymerizable monomers (III), other monomers other than these may be added. Examples of the other monomer include acrylic esters such as methyl acrylate, ethyl acrylate, butyl acrylate, and dicyclopentenyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, and isobornyl methacrylate. And vinyl monomers such as methacrylic acid esters, vinyl acetate, and styrene. These monomers can be appropriately selected and used depending on the properties required for the thermally expandable microcapsules, and among these, methyl methacrylate, ethyl methacrylate, methyl acrylate and the like are preferably used. The amount of these monomers in all monomers constituting the cell wall by polymerization is preferably less than 10% by weight. If it exceeds 10% by weight, the gas barrier property of the cell wall is lowered and the thermal expansibility tends to deteriorate, which is not preferable.

The monomer mixture contains a polymerization initiator 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, 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 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. Of these, isobutane, n-butane, n-pentane, isopentane, and mixtures thereof are preferred. These volatile swelling agents may be used alone or in combination of two or more. In order to widen the foaming temperature range, it is necessary to lower the foaming start temperature while maintaining the heat resistance, but the improvement in heat resistance is achieved by the above-described shell configuration, and in order to reduce the foaming start temperature, the vapor pressure is reduced. High hydrocarbons are particularly preferred. For example, isobutane, n-butane, n-pentane, and isopentane.

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, the lower limit of the maximum foaming temperature (Tmax) is 200 ° C. When the temperature is lower than 200 ° C., the heat resistance is lowered, so that the thermally expandable microcapsule is ruptured and contracted in a high temperature region or during molding. Moreover, foaming is performed by shearing at the time of producing the master batch pellets, and unfoamed master batch pellets cannot be stably produced. A preferred lower limit is 210 ° C and a preferred upper limit is 240 ° C.
The upper limit of the foaming start temperature (Ts) is 160 ° C. When the temperature exceeds 160 ° C, especially in the case of injection molding, in core back foam molding, where the mold is fully filled with a resin material and then the mold is expanded, the resin temperature is cooled during the core back foaming process, and the expansion ratio Does not go up. A preferred lower limit is 130 ° C and a preferred upper limit is 150 ° 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.

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 40 μm.

The method for producing the thermally expandable microcapsule of the present invention is not particularly limited. For example, a polymerizable monomer comprising at least one selected from the step of preparing an aqueous medium, acrylonitrile, methacrylonitrile, and vinylidene chloride (I ) 40 to 94% by weight, 5 to 50% by weight of a radically polymerizable unsaturated carboxylic acid monomer (II) having a carboxyl group and 3 to 8 carbon atoms, an amide bond, and nitrogen of the amide bond A step of dispersing an oily mixture containing 1 to 30% by weight of a polymerizable monomer (III) having a total number of carbon atoms of hydrocarbons bonded to atoms of 4 or more and a volatile swelling agent in an aqueous medium; and It can be produced by performing a step of polymerizing the monomer.

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, 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 microcapsules, and the like, but a preferred lower limit is preferably 0.1 parts by weight with respect to 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, 40 to 94% by weight of a polymerizable monomer (I) consisting of at least one selected from acrylonitrile, methacrylonitrile and vinylidene chloride, a carboxyl group, and carbon The radical polymerizable unsaturated carboxylic acid monomer (II) having a number of 3 to 8 is 5 to 50% by weight and the total number of carbon atoms of the hydrocarbon having an amide bond and bonded to the nitrogen atom of the amide bond is 4 or more. A step of dispersing an oily mixed liquid containing 1 to 30% by weight of a certain polymerizable monomer (III) 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.

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.

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).

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.
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-short method in which a part of a resin material is put into 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, it has excellent heat resistance, has a wide foaming temperature range, and has a high foaming ratio, so that it can be suitably used for kneading molding, calendar molding, extrusion molding, injection molding, etc. to which a strong shearing force is applied. A heat-expandable microcapsule and a foam-molded product using the heat-expandable microcapsule can be provided.

Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to these examples.

(Examples 1-12, Comparative Examples 1-10)
(Production of thermally expandable microcapsules)
8 L of water, 5 parts by weight of colloidal silica (manufactured by Asahi Denka Co., Ltd.) and 0.3 part by weight of polyvinylpyrrolidone (manufactured by BASF Corp.) were charged as a dispersion stabilizer in a polymerization reaction vessel to prepare an aqueous dispersion medium. Subsequently, the dispersion liquid was prepared by adding the oil-based liquid mixture which consists of a monomer of the compounding quantity shown in Table 1 to an aqueous dispersion medium. The resulting dispersion is stirred and mixed with a homogenizer, charged into a nitrogen-substituted pressure polymerization vessel (20 L), pressurized (0.2 MPa), and reacted at 60 ° C. for 20 hours to prepare a reaction product. did. The obtained reaction product was repeatedly filtered and washed with water, and then dried to obtain thermally expandable microcapsules.
In Table 1, the polymerizable monomer (I) is the monomer (I), the radical polymerizable unsaturated carboxylic acid monomer (II) is the monomer (II), has an amide bond, and is bonded to the nitrogen atom of the amide bond. The polymerizable monomer (III) in which the total number of carbon atoms of the hydrocarbon is 4 or more was defined as the monomer (III). As the monomer (III), N-tert-butylacrylamide (total number of carbon atoms of hydrocarbons bonded to nitrogen atoms (hereinafter the same): 4) and N, N-dibutylacrylamide (8) were used. Other monomers include N, N-dimethylacrylamide, tert-butyl group, which is a polymerizable monomer having an amide bond and the total number of carbon atoms of hydrocarbons bonded to the nitrogen atom of the amide bond is 2. Tert-butyl acrylate and methyl methacrylate having an ester bond but having an ester bond.

(Preparation of master batch pellet)
100 parts by weight of low-density polyethylene in powder form and pellets and 10 parts by weight of stearic acid as a lubricant are kneaded with a Banbury mixer. When the temperature reaches about 100 ° C., 100 parts by weight of the thermally expandable microcapsules obtained are mixed. The mixture was added, kneaded for 30 seconds, extruded, and pelletized at the same time to obtain master batch pellets.

(Production of molded body)
Master batch pellets of the addition amount shown in Table 2 and 100 parts by weight of polypropylene resin are mixed, and the resulting mixed pellets are supplied to a hopper of a screw type injection molding machine equipped with an accumulator, melt kneaded, and injected. Molding was performed to obtain a plate-like molded body. The molding conditions were as follows: cylinder temperature: 200 ° C., injection speed: 60 mm / sec, mold opening delay time: 0 seconds, mold temperature: 40 ° C. In Example 13, a chemical foaming agent (Polyslen EE275 (Eiwa Chemical Co., Ltd.)) was added at an addition amount shown in Table 2 in addition to the master batch pellet containing the thermally expandable microcapsules.

(Comparative Example 11)
A molded product was prepared in the same manner as in Example 1 except that 4 parts by weight of a chemical foaming agent (Polyslen EE275 (Eiwa Chemical Co., Ltd.)) was used without adding a master batch pellet containing thermally expandable microcapsules. did.

(Evaluation)
The following performance was evaluated about the thermally expansible microcapsule obtained in Examples 1-12 and Comparative Examples 1-10, and the molded object obtained in Examples 1-13 and Comparative Examples 1-11. The results are shown in Tables 1 and 2.

(1) Evaluation of thermally expandable microcapsules (1-1) Volume average particle size The volume average particle size was measured using a particle size distribution size meter (LA-910, manufactured by HORIBA).

(1-2) Foaming start temperature, maximum foaming temperature, maximum displacement amount Thermomechanical analyzer (TMA) (TMA2940, manufactured by TA instruments), foaming start temperature (Ts), maximum displacement amount (Dmax), and maximum foaming The 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.

(2) Evaluation of molded body (2-1) Foaming ratio A value obtained by dividing the plate thickness of the molded body after foaming by the plate thickness of the molded body before foaming was calculated as the foaming ratio. And the average value and standard deviation of the expansion ratio of 10 molded articles were obtained.

(2-2) Appearance (molded product surface, cross section)
The presence or absence of silver streaks on the surface of the molded product and the state of bubbles in the cross section were visually observed.

(2-3) Measurement of density The density of the obtained molded body was measured by a method based on JIS K-7112 A method (submersion method in water).

As shown in Table 2, in Examples 1 to 13, molded articles having a high average foaming ratio were obtained. The appearance quality on the surface of the molded product was also good. On the other hand, Comparative Example 5 had a lower foaming ratio than Example 1, and other Comparative Examples 1 to 4 and 6 to 9 also showed a lower average foaming ratio than the Examples.
Comparative Example 10 uses Tert-butyl acrylate in place of N-tert-butylacrylamide in Example 1, but Tmax is 200 ° C. or lower, compared to Tmax 240 ° C. in Example 1. The heat resistance was poor and the expansion ratio was low.
Thus, it was shown that the effect of adding a predetermined amount of the polymerizable monomer (III) to the monomer mixed solution is great. In Comparative Example 11, a chemical foaming agent was used alone, but the average foaming ratio was high, but the variation was large and the appearance was poor.

According to the present invention, it has excellent heat resistance, has a wide foaming temperature range, and has a high foaming ratio, so that it can be suitably used for kneading molding, calendar molding, extrusion molding, injection molding, etc. to which a strong shearing force is applied. A heat-expandable microcapsule and a foam-molded product using the heat-expandable microcapsule can be provided.

Claims (2)

A thermally expandable microcapsule in which a volatile expansion agent is encapsulated as a core agent in a polymer shell,
The foaming start temperature is 160 ° C. or lower, the maximum foaming temperature is 200 ° C. or higher, and
The shell has 40 to 94% by weight of a polymerizable monomer (I) selected from acrylonitrile, methacrylonitrile and vinylidene chloride, and has a carboxyl group and has 3 to 8 carbon atoms. 5 to 50% by weight of unsaturated carboxylic acid monomer (II), polymerizable monomer (III) 1 having an amide bond, and the total number of carbon atoms of hydrocarbons bonded to the nitrogen atom of the amide bond is 4 or more A thermally expandable microcapsule comprising a polymer obtained by polymerizing a monomer mixture containing 30% by weight. A foam-molded article comprising the thermally expandable microcapsule according to claim 1.