JP5543717B2 - Thermally expandable microcapsule and method for producing thermally expandable microcapsule - Google Patents

Description

The present invention relates to a thermally expandable microcapsule capable of realizing a high expansion ratio while having excellent heat resistance. The present invention also relates to 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 heat-expandable microcapsules obtained by this method can be thermally expanded by gasification of a volatile expansion agent at a relatively low temperature of about 80 to 130 ° C., they expand when heated at a high temperature or for a long time. There has been a problem that the expansion ratio is reduced by the escape of gas from the microcapsules. In addition, due to problems with heat resistance and strength of the thermally expandable microcapsules, a phenomenon called “sag” has occurred and sometimes collapsed at high temperatures.

On the other hand, Patent Document 2 discloses a thermally foamable microsphere in which a propellant containing 50 wt% or more of isooctane is encapsulated in a polymer shell obtained from an ethylenically unsaturated monomer containing 85 wt% or more of a nitrile-containing monomer. Has been.
Such heat-foamable microspheres, although using the nitrile-containing monomer, have solved the problem of outgassing to some extent, but have low heat resistance and still have sag.

Patent Document 3 discloses a single monomer having a glass transition temperature of 80 ° C. or higher, which contains a polymerizable monomer having two or more polymerizable double bonds and acrylic amide and / or isobornyl methacrylate. A heat-expandable microcapsule having a copolymer composed of 10 to 80% by weight of a monomer capable of forming a coal as a shell and containing a volatile expansion agent is disclosed.
Such a heat-expandable microcapsule has improved heat resistance by increasing the glass transition temperature of the shell portion, but the problem of outgassing has not been solved.

Japanese Examined Patent Publication No. 42-26524 Japanese Patent No. 3659497 Japanese Patent No. 3659979

An object of the present invention is to provide a thermally expandable microcapsule capable of realizing a high expansion ratio while having excellent heat resistance. Another object of the present invention is to provide a method for producing 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 shell made of a thermoplastic resin, the shell contains a clay mineral, and the content of the clay mineral is 0. .01～2.0 a thermally expandable microcapsule Ru wt% der.
The present invention is described in detail below.

The thermally expandable microcapsule of the present invention has a shell made of a thermoplastic resin.
The thermoplastic resin is not particularly limited, but is preferably a resin obtained by polymerizing a monomer mixture containing the nitrile monomer (I).

Examples of the nitrile monomer (I) include acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, α-ethoxyacrylonitrile, fumaronitrile, and mixtures thereof. Of these, acrylonitrile and methacrylonitrile are particularly preferred.
By adding the nitrile monomer (I), the gas barrier property of the shell can be improved.

The minimum with preferable content of the nitrile-type monomer (I) in the said monomer mixture is 30 weight%, and a preferable upper limit is 90 weight%. When the content of the nitrile monomer (I) in the monomer mixture is less than 30% by weight, the gas barrier property of the shell is lowered, and the expansion ratio may be lowered. If the content of the nitrile monomer (I) in the monomer mixture exceeds 90% by weight, the heat resistance may not increase. The minimum with more preferable content of the nitrile-type monomer (I) in the said monomer mixture is 40 weight%, and a more preferable upper limit is 80 weight%.

The monomer mixture preferably further contains a radically polymerizable unsaturated carboxylic acid monomer (II) having a carboxyl group and having 3 to 8 carbon atoms.
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 preferable 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 10% by weight, and the preferable upper limit is 50% by weight. When the content of the radical polymerizable unsaturated carboxylic acid monomer (II) is less than 10% by weight, the maximum foaming temperature may be 180 ° C. or less, and the radical polymerizable unsaturated carboxylic acid monomer (II) When the content exceeds 50% by weight, the maximum foaming temperature is improved, but the foaming ratio is lowered. The more preferable lower limit of the content of the radical polymerizable unsaturated carboxylic acid monomer (II) is 10% by weight, and the more preferable upper limit is 40% by weight.

The monomer mixture preferably contains a polymerizable monomer (III) having two or more double bonds in the molecule. The polymerizable monomer (III) has a role as a crosslinking agent. By containing the said polymerizable monomer (III), the intensity | strength of a shell can be strengthened and it becomes difficult to break a cell wall at the time of thermal expansion.

Examples of the polymerizable 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, Ethylene 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, trimethylolpropane di (meth) acrylate, trimethylolpropane tri (meth) acrylate, ethylene oxide modification Trimethylolpropane tri (meth) acrylate, pentaerythritol tri (meth) acrylate, triallyl formal tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, dipentaerythritol hexa (meth) acrylate, dimethylol-tricyclodecandi ( And (meth) acrylate. Among these, a bifunctional compound such as polyethylene glycol is a phenomenon called so-called “sag” because microcapsules that are thermally expanded are difficult to contract even in a high-temperature region exceeding 200 ° C. and are easily maintained in an expanded state. Is preferably used.

The minimum with preferable content of the said polymerizable monomer (III) in the said monomer mixture is 0.1 weight%, and a preferable upper limit is 3 weight%. When the content of the polymerizable monomer (III) is less than 0.1% by weight, the effect as a crosslinking agent may not be exhibited, and when the polymerizable monomer (III) is added in an amount exceeding 3% by weight. The particle shape of the thermally expandable microcapsule becomes distorted, resulting in a decrease in bulk specific gravity. A more preferable lower limit of the content of the polymerizable monomer (III) is 0.1% by weight, and a more preferable upper limit is 1% by weight.

The monomer mixture may further contain a metal cation salt (IV).
By containing the metal cation salt (IV), ionic crosslinking occurs with the carboxyl group of the radical polymerizable unsaturated carboxylic acid monomer (II), so that the crosslinking efficiency is increased and the heat resistance is increased. Is possible. 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 (IV) 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. For example, Na, K, Li , Zn, Mg, Ca, Ba, Sr, Mn, Al, Ti, Ru, Fe, Ni, Cu, Cs, Sn, Cr, Pb, and the like. 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 (IV) may be used alone or in combination of two or more.

The minimum with preferable content of the said metal cation salt (IV) in the said monomer mixture is 0.1 weight%, and a preferable upper limit is 10 weight%. When the content of the metal cation salt (IV) is less than 0.1% by weight, the effect of heat resistance may not be obtained. When the content of the metal cation salt (IV) exceeds 10% by weight The foaming ratio may be remarkably deteriorated. The minimum with more preferable content of the said metal cation salt (IV) is 0.5 weight%, and a more preferable upper limit is 5 weight%.

In addition to the nitrile monomer (I) and the radical polymerizable unsaturated carboxylic acid monomer (II), other monomers other than these may be added to the monomer mixture. 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. Examples include methacrylic acid esters, vinyl monomers such as vinyl chloride, vinylidene chloride, vinyl acetate, and styrene. These other 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 content of other monomers in all monomers constituting the shell is preferably less than 10% by weight. When the content of the other monomer exceeds 10% by weight, the gas barrier property of the cell wall is lowered and the thermal expansion property is easily deteriorated, 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 , 5-trimethylhexanoyl peroxide, diacyl 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 Noyl peroxy) peroxye such as diisopropylbenzene Steal, bis (4-t-butylcyclohexyl) peroxydicarbonate, di-n-propyl-oxydicarbonate, diisopropylperoxydicarbonate, di (2-ethylethylperoxy) dicarbonate, dimethoxybutylperoxydicarbonate Peroxydicarbonates such as di (3-methyl-3-methoxybutylperoxy) dicarbonate, 2,2′-azobisisobutyronitrile, 2,2′-azobis (4-methoxy-2,4- And 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 thermoplastic resin constituting the shell is 100,000, and the preferable upper limit is 2 million. When the weight average molecular weight is less than 100,000, the strength of the shell may be reduced. When the weight average molecular weight exceeds 2 million, the strength of the shell becomes too high, and the expansion ratio may be reduced.

The shell contains a clay mineral.
By containing the clay mineral, even when heated at a high temperature or for a long time, gas does not escape from the expanded microcapsules, and a high expansion ratio can be realized. Further, the heat resistance of the thermally expandable microcapsule can be improved, and it is possible to prevent the “sag” from occurring in the thermally expandable microcapsule and causing it to be crushed at a high temperature.

It does not specifically limit as said clay mineral, For example, the layered silicate etc. which have an exchangeable metal cation between layers are mentioned.

Examples of the layered silicate include smectite such as montmorillonite, bentonite, saponite, hectorite, beidellite, stevensite, nontronite, vermiculite, halloysite, and swellable mica (swelling mica). Montmorillonite, bentonite and / or swellable mica are preferably used. These layered silicates may be natural products or synthetic products. Moreover, these layered silicates may be used independently and 2 or more types may be used together. In addition, the layered silicate used by this invention means the silicate mineral which has an exchangeable metal cation between layers.

As the layered silicate, it is preferable to use smectite or swelling mica having a large shape anisotropy defined by the following formula (1). By using a layered silicate having a large shape anisotropy, the formed shell has a higher strength.
Shape anisotropy = Area of crystal surface (A) / Area of crystal side surface (B) (1)
In the formula, the crystal surface (A) means the layer surface, and the crystal side surface (B) means the layer side surface.

The exchangeable metal cation existing between the crystal layers of the layered silicate is a metal ion such as sodium ion or calcium ion existing on the crystal surface of the layered silicate, and these metal ions are other cations. Since it has a cation exchange property with an active substance, various substances having a cationic property can be inserted (intercalated) or supplemented between crystal layers of the layered silicate.

The cation exchange capacity of the layered silicate is not particularly limited, and is preferably 50 to 200 milliequivalent / 100 g. If the cation exchange capacity of the layered silicate is less than 50 milliequivalents / 100 g, the amount of the cationic substance inserted or captured between the crystal layers of the layered silicate is reduced by the cation exchange. On the contrary, if the cation exchange capacity of the layered silicate exceeds 200 milliequivalents / 100 g, the bonding force between the crystal layers of the layered silicate becomes too strong, and the crystal flakes May become difficult to peel.

In the thermally expandable microcapsule of the present invention, it is preferable to disperse the layered silicate as uniformly as possible in the shell made of the thermoplastic resin. In order to realize such uniform dispersion, it is preferable that the crystal layer of the layered silicate be previously non-polarized by cation exchange with a cationic surfactant. By making the crystal layer of the layered silicate nonpolar in advance, the layered silicate can be more finely dispersed in the shell made of the thermoplastic resin.

The cationic surfactant is not particularly limited, and examples thereof include quaternary ammonium salts and quaternary phosphonium salts. Among them, the number of carbon atoms can be sufficiently depolarized between crystal layers of the layered silicate. A quaternary ammonium salt (an alkyl ammonium salt having 6 or more carbon atoms) having one or more alkyl chains of 6 or more is preferably used. These cationic surfactants may be used alone or in combination of two or more.

The quaternary ammonium salt is not particularly limited. For example, lauryl trimethyl ammonium salt, stearyl trimethyl ammonium salt, trioctyl methyl ammonium salt, distearyl dimethyl ammonium salt, di-cured tallow dimethyl ammonium salt, distearyl dibenzyl ammonium salt N-polyoxyethylene-N-lauryl-N, N-dimethylammonium salt, stearylbenzyldimethylammonium salt, dioctadecyldimethylammonium salt, oleylbis (2-hydroxyethyl) methylammonium salt, and the like. These quaternary ammonium salts may be used alone or in combination of two or more.

The quaternary phosphonium salt is not particularly limited, and examples thereof include dodecyltriphenylphosphonium salt, methyltriphenylphosphonium salt, lauryltrimethylphosphonium salt, stearyltrimethylphosphonium salt, trioctylmethylphosphonium salt, distearyldimethylphosphonium salt, Examples include stearyl dibenzylphosphonium salt. These quaternary phosphonium salts may be used alone or in combination of two or more.

The layered silicate can improve dispersibility in a shell made of a thermoplastic resin by performing the chemical treatment as described above.
The chemical treatment of the layered silicate is not limited to the cation exchange method using the cationic surfactant (hereinafter also referred to as “chemical modification (1) method”). For example, the chemical treatment (2 ) Method to chemical modification (6) The various chemical treatment methods can also be used. These chemical modification methods may be used alone or in combination of two or more. In addition, the layered silicate whose dispersibility in the shell is improved by various chemical treatment methods shown below including the chemical modification (1) method is also referred to as “organized layered silicate”.

In the chemical modification (2) method, the hydroxyl group present on the crystal surface of the organically modified layered silicate chemically treated by the chemical modification (1) method is chemically bonded even if it does not have a functional group or chemical bond capable of chemically bonding with this. In this method, chemical treatment is performed with a compound having one or more functional groups having high affinity at the molecular end.

In the chemical modification (3) method, the hydroxyl group present on the crystal surface of the organically modified layered silicate that has been chemically modified by the chemical modification (1) method is chemically bonded even if there is no functional group or chemical bond capable of chemically bonding with this. In this method, chemical treatment is performed with a compound having one or more functional groups and reactive functional groups having high affinity at the molecular ends.

The chemical modification (4) method is a method in which the crystallized surface of the organically modified layered silicate chemically treated by the chemical modification (1) method is chemically treated with a compound having an anionic surface activity.
The chemical modification (5) method is a chemical treatment (4) method in which chemical treatment is performed with a compound having an anionic surface activity and having one or more reactive functional groups in addition to the anion site in the molecular chain.
The chemical modification (6) method includes, for example, a maleic anhydride-modified polyolefin resin in addition to the organically modified layered silicate chemically treated by any one of the chemical modification (1) method to the chemical modification (5) method. This is a method using a composition to which a resin having a functional group capable of reacting with an organically modified layered silicate is added.

In the chemical modification (2) method, the functional group capable of chemically bonding to a hydroxyl group or the functional group having a large chemical affinity without chemical bonding is not particularly limited, and examples thereof include an alkoxyl group and a glycidyl group (epoxy group). , Carboxyl groups (including dibasic acid anhydrides), hydroxyl groups, isocyanate groups, aldehyde groups, and other functional groups, and other functional groups having high chemical affinity with hydroxyl groups. These functional groups may be used independently and 2 or more types may be used together.

In addition, the functional group capable of chemically bonding to the hydroxyl group or the compound having a chemical group having a large chemical affinity without chemical bonding is not particularly limited, and examples thereof include silane compounds and titanate compounds having the functional groups exemplified above. , Glycidyl compounds, carboxylic acids, alcohols, etc., among which silane compounds are preferably used. These compounds may be used independently and 2 or more types may be used together.

The silane compound is not particularly limited, and examples thereof include vinyltrimethoxysilane, vinyltriethoxysilane, vinyltris (β-methoxyethoxy) silane, γ-aminopropyltrimethoxysilane, γ-aminopropylmethyldimethoxysilane, γ -Aminopropyldimethylmethoxysilane, γ-aminopropyltriethoxysilane, γ-aminopropylmethyldiethoxysilane, γ-aminopropyldimethylethoxysilane, methyltriethoxysilane, dimethyldimethoxysilane, trimethylmethoxysilane, hexyltrimethoxysilane, Hexyltriethoxysilane, N-β- (aminoethyl) γ-aminopropyltrimethoxysilane, N-β- (aminoethyl) γ-aminopropyltriethoxysilane, N-β- (aminoethyl) γ Aminopropylmethyldimethoxysilane, octadecyltrimethoxysilane, octadecyltriethoxysilane, γ-methacryloxypropylmethyldimethoxysilane, γ-methacryloxypropylmethyldiethoxysilane, γ-methacryloxypropyltrimethoxysilane, γ-methacryloxypropyltri An ethoxysilane etc. are mentioned. These silane compounds may be used independently and 2 or more types may be used together.

In the chemical modification (4) method and the chemical modification (5) method, as a compound having an anionic surface activity or a compound having an anionic surface activity and having one or more reactive functional groups in addition to the anion site in the molecular chain The layer silicate is not particularly limited as long as it can be chemically treated by ionic interaction, for example, sodium laurate, sodium stearate, sodium oleate, higher alcohol sulfate, secondary higher alcohol sulfate, Examples thereof include unsaturated alcohol sulfate salts. These compounds may be used independently and 2 or more types may be used together.
Further, as the chemical modification (6) method, for example, a method using a composition in which a resin having a functional group capable of reacting with an organically modified layered silicate such as a maleic anhydride-modified polyolefin resin is added as a dispersant is exemplified. It is done. This enhances the compatibility between the organic layered silicate by mixing a resin having a part having a high chemical affinity with the organic layered silicate and a part having a high chemical affinity with the resin composed of a curable component as a dispersant. This is a method for reducing the energy required for dispersion of the layered silicate.

The resin having a functional group capable of reacting with the organically modified layered silicate used as the dispersant is not particularly limited, and examples thereof include maleic anhydride-modified polyolefin oligomers and maleic anhydride-modified polyolefin polymers. Among these, AB type diblock oligomers and AB type diblock polymers having different properties at both ends are preferably used. That is, AB having different properties at both ends of a portion having a high chemical affinity with the organically modified layered silicate (A site) and a portion having a high chemical affinity with the resin composed of the curable component (B site). Since the mold resins easily exhibit their chemical affinity efficiently, they exhibit an excellent dispersion effect.

The method for obtaining a highly dispersed state using the AB type resin is not particularly limited. For example, the AB type resin that functions as a curable component, an organic layered silicate, and a dispersant is used in an extruder. For example, melt-kneading can be performed collectively.

The layered silicate is preferably partly or wholly dispersed in 10 layers or less in the shell of the thermally expandable microcapsule obtained.
The fact that part or all of the layered silicate is dispersed in 10 layers or less means that part or all of the layered molecules of the layered silicate, which is originally a tens of layers, is peeled off and widely dispersed. This also means that the interaction between the lamellar silicate crystal flake layers is weakened, and the same effect as described above can be obtained. The number of layered silicate layers is preferably 5 or less, more preferably 3 or less. More preferably, it is dispersed in a single layer shape (flaky shape).

In addition, the fact that part or all of the layered silicate is dispersed in 10 layers or less specifically means that 10% or more of the aggregate of layered silicate is dispersed in 10 layers or less. More preferably, 20% or more of the layered silicate aggregate is dispersed in 10 layers or less.
In addition, the dispersion state of the layered silicate is observed with a transmission electron microscope at a magnification of 50,000 to 100,000 times, and the number of layered silicate aggregates (X) that can be observed in a certain area, The number (Y) of laminated assemblies dispersed in 10 layers or less can be counted and calculated by the following formula (2).
Ratio of layered silicate dispersed in 10 layers or less (%) = (Y / X) × 100 (2)

The layered silicate preferably has an average interlaminar distance of (001) plane measured by wide angle X-ray diffraction method of 3 nm or more.
In addition, the average interlayer distance of the layered silicate referred to in the present specification means the average interlayer distance when the layered silicate fine flaky crystal is used as a layer, and is obtained by X-ray diffraction peak and transmission electron microscope photography. That is, it can be calculated by a wide-angle X-ray diffraction method.
The average interlayer distance is preferably 6 nm or more. When the average interlayer distance between the layered silicate crystal flake layers is 6 nm or more, the layered silicate crystal flake layers are separated into layers, and the interaction between the layered silicate crystal flake layers becomes so weak that it can be almost ignored. There is an advantage that the dispersion state in the shell of the crystal flakes constituting the layered silicate proceeds in the direction of destabilization stabilization.

The clay mineral containing the layered silicate preferably has a dispersion diameter in the shell of 0.001 to 5 μm. If the dispersion diameter is less than 0.001 μm, the effect of preventing outgassing and heat resistance may be insufficient, and if the dispersion diameter exceeds 5 μm, the expansion ratio may decrease. .

Although it does not specifically limit as a shape of the said clay mineral, It is preferable that average length is 0.01-3 micrometers, thickness is 0.001-1 micrometer, and aspect-ratio is 20-500, More preferably, average length is 0.05 to 2 μm, thickness is 0.01 to 0.5 μm, and aspect ratio is 50 to 200.

The minimum with preferable content of the said clay mineral is 0.01 weight%, and a preferable upper limit is 10 weight%. If the content of the clay mineral is less than 0.01% by weight, the effect of preventing outgassing and heat resistance may be insufficient. If it exceeds 10% by weight, shell formation becomes difficult. Sometimes. A more preferable lower limit of the content of the clay mineral is 0.1% by weight, and a more preferable upper limit is 2.0% 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, the preferable lower limit of the maximum displacement (Dmax) measured by thermomechanical analysis is 300 μm. If the maximum displacement is less than 300 μm, the foaming ratio is lowered, and the desired foaming performance cannot be obtained. A more preferable lower limit of the maximum displacement is 400 μm.
Note that the maximum amount of displacement is the amount of displacement in the height direction of the entire predetermined amount of the thermally expandable microcapsule when the displacement in the height direction is measured while heating the predetermined amount of the thermally expandable microcapsule from room temperature. This is the maximum value.

In the thermally expandable microcapsule of the present invention, a preferable lower limit of the maximum foaming temperature (Tmax) is 150 ° C. When the maximum foaming temperature is less than 150 ° C., the heat resistance is lowered, and thus the thermally expandable microcapsule may be ruptured or shrunk in a high temperature region or during molding. A more preferable lower limit of the maximum foaming temperature is 180 ° C.

In the thermally expandable microcapsule of the present invention, the preferable upper limit of the foaming start temperature (Ts) is 180 ° C. When the foaming start temperature exceeds 180 ° C., particularly in the case of injection molding, the foaming ratio may not increase. The minimum with said preferable foaming start temperature is 130 degreeC, and a more preferable upper limit is 160 degreeC.
In the present specification, the maximum foaming temperature is the temperature at which the thermally expandable microcapsule reaches the maximum displacement when the displacement in the height direction is measured while heating the thermally expandable microcapsule from room temperature. Means.

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. Examples include hydrogen, chlorofluorocarbons such as CCl ₃ F, CCl ₂ F ₂ , CClF ₃ , and CClF ₂ -CClF ₂ , tetraalkylsilanes such as tetramethylsilane, trimethylethylsilane, trimethylisopropylsilane, and trimethyl-n-propylsilane. It is done. Of these, isobutane, n-butane, n-pentane, isopentane, n-hexane, petroleum ether, and mixtures thereof are preferred. These volatile swelling agents may be used alone or in combination of two or more.

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 preferred lower limit of the content of the volatile swelling agent used as the core agent is 10% by weight, and the preferred upper limit is 40% by weight.
The thickness of the shell varies depending on the content of the core agent, but if the core agent content is reduced and the shell becomes too thick, the foaming performance is reduced, and if the core agent content is increased, the shell strength is reduced. To do. When the content of the core agent is 10 to 40% by weight, it becomes possible to achieve both the prevention of the sag of the thermally expandable microcapsule and the improvement of the foaming performance.

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 volume-average particle size of the thermally expandable microcapsule is less than 5 μm, the resulting molded body has too small bubbles, which may result in insufficient weight reduction of the molded body. When the volume average particle diameter exceeds 100 μm, the resulting molded article has excessively large bubbles, which may cause problems in terms of strength and the like. The minimum with a more preferable volume average particle diameter of the said thermally expansible microcapsule is 10 micrometers, and a more preferable upper limit is 70 micrometers.

The method for producing the thermally expandable microcapsule of the present invention is not particularly limited. For example, an aqueous medium is prepared, and an oily mixture containing a polymerizable monomer, a volatile swelling agent and a clay mineral is added to the aqueous medium. It can manufacture by performing the process to disperse | distribute and the process to superpose | polymerize the said polymerizable 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 kind of the dispersion stabilizer, the particle size of the thermally expandable microcapsule, and the like. Parts, and the preferred 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, an oily mixed liquid containing a polymerizable monomer, a volatile swelling agent and a clay mineral is dispersed in an aqueous medium. In this step, the polymerizable monomer, the volatile swelling agent, and the clay mineral may be separately added to the aqueous dispersion medium to prepare an oily mixture in the aqueous dispersion medium. After mixing the monomer and the volatile swelling agent, a clay mineral is added to form an oily mixture, 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. The polymerizable monomer includes the nitrile monomer (I), a radically polymerizable unsaturated carboxylic acid monomer (II) having a carboxyl group and having 3 to 8 carbon atoms, and 2 double bonds in the molecule. One or more polymerizable monomers (III) or the like can be used.
In addition, a polymerization initiator is used to polymerize the polymerizable monomer. The polymerization initiator may be added to the oily mixed solution in advance, and the aqueous dispersion medium and the oily mixed solution are subjected to a polymerization reaction. You may add, after stirring and mixing in a container.

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 expansion ratio, excellent heat resistance, and do not rupture or shrink even in a high temperature region or during molding.

The foamed molded product obtained using the thermally expandable microcapsule of the present invention has high appearance quality, uniform closed cells, and is excellent in lightness, heat insulation, impact resistance, rigidity, etc. Thus, it can be suitably used for applications such as residential building materials, automobile members, and shoe soles.

According to the present invention, it is possible to provide a thermally expandable microcapsule capable of realizing a high expansion ratio while having excellent heat resistance. Moreover, this invention can provide the manufacturing method of this thermally expansible microcapsule.

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 1-2, Comparative Examples 1-3)
(Production of thermally expandable microcapsules)
In a polymerization reaction vessel, 8 L of water, 10 parts by weight of colloidal silica (manufactured by Asahi Denka) and 0.3 part by weight of polyvinylpyrrolidone (manufactured by BASF) as a dispersion stabilizer and 0.7 part by weight of 1N hydrochloric acid are charged. An aqueous dispersion medium was prepared. Next, a clay mineral of the type shown in Table 1 is added to an oily mixed liquid composed of a monomer, a cross-linking agent, a volatile swelling agent and a polymerization initiator shown in Table 1, and then added to an aqueous dispersion medium. By doing so, a dispersion was prepared. 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 addition, as the clay mineral, Lucent STN (layered silicate, manufactured by Corp Chemical Co.) and Somasif MTE (layered silicate, manufactured by Corp Chemical Co.) were used.

(Evaluation)
The following evaluation was performed about the thermally expansible microcapsule obtained in Examples 1-2 and Comparative Examples 1-3. The results are shown in Table 2.

(1) Confirmation of clay mineral (1-1) Content rate About 0.5 g of the obtained thermally expandable microcapsules were weighed and burned at 600 ° C. for 5 hours to obtain ash. Thereafter, the obtained ash was subjected to fluorescent X-ray measurement, and the ratio (Z%) of Mg element in the ash was measured. From the measured weight (Xg) of the thermally expandable microcapsule and the weight of ash (Yg), the content of clay mineral was calculated according to the following (3).
Clay mineral content (% by weight) = (Y / X) × Z (3)

(1-2) Presence site About the shell cross section of the obtained thermally expansible microcapsule, the mapping image of Mg component was output using SEM-EDS (made by HORIBA), and the presence or absence of Mg component was confirmed.
Furthermore, it was visually confirmed whether the Mg component was present in an aggregated state or in a uniformly dispersed state in the shell.

(1-3) Particle diameter Using the mapping image of the Mg component obtained in (1-2) above, the particle diameter of the clay mineral was measured using a caliper. The particle diameter was the average of the long diameter and the short diameter, and the average value of 50 particle diameters was calculated.

(1-4) Type With reference to the result of the fluorescence analysis performed in (1-1) above, the type of clay mineral is confirmed from the composition ratio of Na, K, Ca, Li, Si, Fe, Al, Mg, etc. did.

(2) Performance Evaluation of Thermally Expandable Microcapsule (2-1) Foaming Ratio About 0.1 g of the obtained thermally expandable microcapsule was weighed and placed in a 10 mL graduated cylinder. Then, it put into the oven heated at 150 degreeC for 5 minutes, and measured the volume of the thermally expansible microcapsule expanded in the measuring cylinder. The case where it was 8 mL or more was marked as 場合, the case where it was 5 mL or more and less than 8 mL, ◯, the case where it was 2 mL or more and less than 5 mL, or the case where it was less than 2 mL.

(2-2) Slip The sample measured in (2-1) above is further placed in an oven heated to 200 ° C. for 10 minutes, and the volume (H) of particles in the graduated cylinder is measured. (2-1) The ratio (H / L) to the volume (L) measured in (1) was calculated. ◎ when H / L is 0.8 or more, ◯ when H / L is 0.6 or more and less than 0.8, Δ when H / L is 0.4 or more and less than 0.6, The case where H / L was less than 0.4 was set as x.

As shown in Table 2, it can be seen that the thermally expandable microcapsules obtained in Examples 1 and 2 have high heat resistance without causing sag. Moreover, since the thermally expansible microcapsule obtained in Examples 1-2 has high foaming ratio, it turns out that it has favorable foaming performance.
On the other hand, it can be seen that the thermally expandable microcapsules obtained in Comparative Examples 1 to 3 have a low expansion ratio and sag.

According to the present invention, it is possible to provide a thermally expandable microcapsule capable of realizing a high expansion ratio while having excellent heat resistance. Moreover, according to this invention, the manufacturing method of this thermally expansible microcapsule can be provided.

Claims (5)

A thermally expandable microcapsule in which a volatile expansion agent is encapsulated as a core agent in a shell made of a thermoplastic resin, the shell containing a clay mineral, and the content of the clay mineral is 0.01 to 2 thermally expandable microcapsule characterized by 2.0 wt% der Rukoto. Clay minerals, thermally expandable microcapsule according to claim 1 Symbol mounting characterized in that it is a layered silicate. Clay minerals, smectite, claim 1 or thermally expandable microcapsule of 2, wherein the bentonite or swellable mica. Clay minerals, thermally expandable microcapsule according to claim 1, 2 or 3, wherein in that it is non-polarized. Claim 1, 2, 3 or 4 heat-expandable microcapsule according dispersed diameter in the clay mineral shell characterized in that it is a 0.001 to 5.