JP2013053275A - Method for manufacturing thermally expandable micro-capsule - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a thermally expandable microcapsule capable of manufacturing with good productivity the thermally expandable microcapsule with a large particle diameter while aggregation is suppressed.SOLUTION: The method for manufacturing the thermally expandable microcapsule includes: a first adding process for preparing an aqueous dispersing medium by adding a colloidal silica into water; an emulsifying process for preparing an emulsifying liquid by suspending an oily substance including a polymerizable monomer including a carboxy group-containing monomer, a volatile liquid, and a polymerization initiator into the aqueous dispersion medium; a second adding process for adding a colloidal silica into the emulsifying liquid; and a polymerizing process for polymerizing the polymerizable monomer.

Description

The present invention relates to a method for producing a heat-expandable microcapsule capable of producing a heat-expandable microcapsule having a large particle size with high productivity while suppressing aggregation.

Conventionally, as a member for medical use or automobiles, railways, railroads, railways, bridges, buildings, etc., a base resin such as rubber or thermoplastic elastomer is formed into a plate shape, etc., cushioning properties, vibration damping properties, etc. A molded body having excellent performance is used. In addition, in order to further improve performance such as cushioning properties and vibration damping properties, it has been studied to foam-mold the base resin.

As a method of foam-molding the base resin, for example, a method of foam-molding by adding a chemical foaming agent such as azodicarbonamide, which decomposes when heated to generate a gas, solubility of gas such as carbon dioxide gas For example, a method in which gas is generated by increasing the solubility in the base resin and then lowering the solubility of the gas. According to these methods, for example, it is possible to obtain a foamed molded article having relatively large bubbles having a diameter exceeding 500 μm. However, such a foamed molded article has insufficient fatigue resistance against repeated compression, and has low strength, and the surface of the molded article may swell, tear or peel off during use.

On the other hand, as a method of foam-molding a base resin, a method of foam-molding by adding a thermally expandable microcapsule containing a volatile liquid as a core agent to a shell containing a polymer is also proposed. As such a thermally expandable microcapsule, for example, in Patent Document 1, a monomer as a main component is acrylonitrile, and a monomer containing a carboxyl group or a monomer having a group that reacts with a carboxyl group is polymerized as an essential component. A thermally expandable microcapsule having a polymer obtained as a shell and enclosing a liquid having a boiling point equal to or lower than the softening temperature of the polymer is described.

When the thermally expandable microcapsule is used, the bubbles in the foamed molded product are formed by the shell of the thermally expandable microcapsule. As a result, the thermal expansion microcapsule shell works like a reinforcing material and improves fatigue resistance and strength against repeated compression compared to using chemical foaming agents that decompose and generate gas when heated. Is done. However, when the thermally expandable microcapsule is used, it is difficult to increase the bubbles in the foamed molded article, and the performance such as cushioning and vibration damping properties or weight reduction becomes insufficient. There is a need for thermally expandable microcapsules that can form large bubbles after foaming.

WO99 / 43758 pamphlet

Generally, a thermally expandable microcapsule is produced by polymerizing a polymerizable monomer in a state where an oily substance containing a polymerizable monomer, a volatile liquid, and a polymerization initiator is suspended in an aqueous dispersion medium. . At this time, a dispersion stabilizer is added to the aqueous dispersion medium in order to suspend the oily substance, and colloidal silica is frequently used as such a dispersion stabilizer. In recent years, carboxyl group-containing monomers such as acrylic acid and methacrylic acid are often added to the polymerizable monomer in order to enhance the heat resistance and durability of the thermally expandable microcapsules. The present inventor examined reducing the amount of colloidal silica added to produce a thermally expandable microcapsule having a large particle size, but when the amount of colloidal silica added is reduced when a carboxyl group-containing monomer is used, Since the highly water-soluble carboxyl group-containing monomer is easily eluted in the aqueous dispersion medium, the thermally expandable microcapsule is likely to aggregate due to the eluted monomer, and the thermally expandable microcapsule is stably produced. That was difficult.

An object of this invention is to provide the manufacturing method of the thermally expansible microcapsule which can manufacture the thermally expansible microcapsule with a large particle diameter with sufficient productivity, suppressing aggregation.

The present invention includes a first addition step of preparing an aqueous dispersion medium by adding colloidal silica to water, a polymerizable monomer containing a carboxyl group-containing monomer in the aqueous dispersion medium, a volatile liquid, and a polymerization initiator. A thermally expandable microcapsule comprising: an emulsification step of preparing an emulsion by suspending an oily substance containing sucrose; a second addition step of adding colloidal silica to the emulsion; and a polymerization step of polymerizing the polymerizable monomer. It is a manufacturing method.
The present invention is described in detail below.

In the method for producing a thermally expandable microcapsule, a polymerizable monomer is polymerized in a state in which an oily substance containing a polymerizable monomer, a volatile liquid, and a polymerization initiator is suspended in an aqueous dispersion medium. It was noted that colloidal silica has two actions, that is, an action of suspending an oily substance in an aqueous dispersion medium and an action of stabilizing droplets after suspension. The present inventor can suspend an oily substance with a target droplet diameter by adding colloidal silica to an aqueous dispersion medium in advance, and then add colloidal silica to the obtained emulsion. As a result, even when a carboxyl group-containing monomer is used, it is found that a thermally expandable microcapsule can be produced with good productivity while stabilizing the droplet after suspension and suppressing aggregation. It came to.

In the method for producing a thermally expandable microcapsule of the present invention, first, a first addition step of preparing an aqueous dispersion medium by adding colloidal silica to water is performed.
By adding colloidal silica to the aqueous dispersion medium in advance, it is possible to suspend the oily substance with a target droplet size and produce a thermally expandable microcapsule having a large particle size.

The colloidal silica added in the first addition step has a preferable lower limit of the average particle diameter of 1 nm and a preferable upper limit of 100 nm. If the average particle size is less than 1 nm, the secondary aggregate of colloidal silica becomes too small, so that the droplet size of the oily substance becomes small, and the particle size of the thermally expandable microcapsule may become small, exceeding 100 nm. Then, since the secondary aggregate of colloidal silica becomes too large, the droplet after suspension becomes unstable, and the thermally expandable microcapsule tends to aggregate and cannot be obtained stably.

In the first addition step, the addition is preferably performed so that the amount of colloidal silica added is 7 to 23 parts by weight with respect to 100 parts by weight of the polymerizable monomer. If the amount of colloidal silica added is less than 7 parts by weight, the effect as a dispersion stabilizer may be insufficient and a thermally expandable microcapsule may not be obtained. The droplet size may be reduced, and the particle size of the thermally expandable microcapsule may be reduced. As for the addition amount of colloidal silica, a more preferable lower limit is 10 parts by weight, and a more preferable upper limit is 20 parts by weight.
Here, the amount of colloidal silica added in the first addition step means the amount of colloidal silica added in the first addition step.

The aqueous dispersion medium may further contain an auxiliary stabilizer.
The auxiliary stabilizer is not particularly limited, and examples thereof include a condensation product of diethanolamine and an aliphatic dicarboxylic acid, a condensation product of urea and formaldehyde, a water-soluble nitrogen-containing compound, polyethylene oxide, tetramethylammonium hydroxide, gelatin, Examples include methyl cellulose, polyvinyl alcohol, dioctyl sulfosuccinate, sorbitan ester, and various emulsifiers. Among these, a condensation product of diethanolamine and an aliphatic dicarboxylic acid and a water-soluble nitrogen-containing compound are preferable.

The condensation product of diethanolamine and aliphatic dicarboxylic acid is preferably a condensation product of diethanolamine and adipic acid or a condensation product of diethanolamine and itaconic acid.
The water-soluble nitrogen-containing compound is not particularly limited, and examples thereof include polydialkylaminoalkyl (meth) acrylates such as polyvinylpyrrolidone, polyethyleneimine, polyoxyethylene alkylamine, polydimethylaminoethyl methacrylate and polydimethylaminoethyl acrylate, polydimethyl Examples thereof include polydialkylaminoalkyl (meth) acrylamides such as aminopropylacrylamide and polydimethylaminopropylmethacrylamide, polyacrylamide, polycationic acrylamide, polyamine sulfone and polyallylamine. Of these, polyvinylpyrrolidone is preferred.

The amount of the auxiliary stabilizer to be added is not particularly limited and can be appropriately determined depending on the particle size of the target thermally expandable microcapsule, but the preferable lower limit with respect to 100 parts by weight of the polymerizable monomer is preferably 0.05 parts by weight. The upper limit is 2 parts by weight.

The aqueous dispersion medium may further contain an inorganic salt such as sodium chloride or sodium sulfate. By containing such an inorganic salt in the aqueous dispersion medium, thermally expandable microcapsules having a more uniform particle shape can be obtained. The amount of the inorganic salt added is not particularly limited, but a preferable upper limit with respect to 100 parts by weight of the polymerizable monomer is 100 parts by weight.
The aqueous dispersion medium may contain an alkali metal nitrite, stannous chloride, stannic chloride, potassium dichromate, etc., if necessary.

Examples of a method for preparing an aqueous dispersion medium by adding colloidal silica to water include a method of adding water, colloidal silica, and an auxiliary stabilizer, if necessary, to a polymerization reaction vessel.
The pH of the aqueous dispersion medium can be appropriately determined. For example, the pH of the aqueous dispersion medium is adjusted to 3 to 4 by adding an acid such as hydrochloric acid as necessary. The polymerization can be carried out with

In the method for producing a thermally expandable microcapsule of the present invention, a polymerizable monomer containing a carboxyl group-containing monomer, a volatile liquid, and an oily substance containing a polymerization initiator are then suspended in the aqueous dispersion medium. Then, an emulsification step for preparing an emulsion is performed.
The emulsification means that an oily substance is suspended in an aqueous dispersion medium, and the diameter of a droplet made of the oily substance is measured using a particle size distribution meter (for example, “LA-950” manufactured by Horiba, Ltd.). This means a state where the droplet diameter is about 10 to 100 μm, and the liquid in such a state is called an emulsion.

By containing a carboxyl group-containing monomer in the polymerizable monomer, the heat resistance and durability of the thermally expandable microcapsule can be improved. In general, a carboxyl group-containing monomer is highly water-soluble and easily eluted in an aqueous dispersion medium. However, according to the method for producing a heat-expandable microcapsule of the present invention, by adding colloidal silica to an emulsion in a step described later. Even when a carboxyl group-containing monomer is used, the thermally expandable microcapsules can be produced with good productivity while stabilizing the droplets after suspension and suppressing aggregation.

Examples of the monomer having a carboxyl group include unsaturated monocarboxylic acids such as acrylic acid, methacrylic acid, ethacrylic acid, crotonic acid, and cinnamic acid, and unsaturated dicarboxylic acids such as maleic acid, itaconic acid, fumaric acid, and citraconic acid. An acid etc. are mentioned. These salts and anhydrides may be used. Of these, acrylic acid and methacrylic acid are preferred.

The preferable lower limit of the content of the carboxyl group-containing monomer in the polymerizable monomer is 1% by weight, and the preferable upper limit is 50% by weight. When the content of the carboxyl group-containing monomer is less than 1% by weight, the heat-expandable microcapsule may have insufficient heat resistance or durability, and when it exceeds 50% by weight, the heat-expandable microcapsule Agglomeration tends to occur and cannot be stably obtained, or the gas barrier property of the shell may be hindered and the expansion ratio may be lowered. The minimum with more preferable content of the said carboxyl group-containing monomer is 5 weight%, and a more preferable upper limit is 40 weight%.

The polymerizable monomer preferably contains a nitrile monomer. By containing a nitrile monomer in the polymerizable monomer, high heat resistance and gas barrier properties can be imparted to the thermally expandable microcapsules.
The nitrile monomer is not particularly limited, and examples thereof include acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, α-ethoxyacrylonitrile, fumaronitrile, or a mixture thereof. Of these, acrylonitrile and methacrylonitrile are particularly preferred. These may be used independently and 2 or more types may be used together.

The preferable lower limit of the content of the nitrile monomer in the polymerizable monomer is 50% by weight, and the preferable upper limit is 99% by weight. When the content of the nitrile monomer is less than 50% by weight, the gas barrier property of the shell of the heat-expandable microcapsule may be lowered, and thus the expansion ratio may be lowered. The content of the group-containing monomer may decrease, and the heat resistance or durability of the thermally expandable microcapsule may be insufficient. The more preferable lower limit of the nitrile monomer is 60% by weight, and the more preferable upper limit is 95% by weight.

The polymerizable monomer may contain a monomer other than the nitrile monomer and the carboxyl group-containing monomer (hereinafter also simply referred to as another monomer).
The other monomers are not particularly limited and can be appropriately selected according to the characteristics required for the thermally expandable microcapsule. Examples thereof include divinylbenzene, ethylene glycol di (meth) acrylate, and 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, trimethylolpropane di (meth) acrylate, trimethylolpropane tri (meth) acrylate, ethylene oxide Iido-modified trimethylolpropane tri (meth) acrylate, pentaerythritol tri (meth) acrylate, triallyl formal tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, dipentaerythritol hexa (meth) acrylate, dimethylol-tricyclode Examples include candi (meth) acrylate. Examples of the other monomer include acrylic acid 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 chloride, vinylidene chloride, vinyl acetate, and styrene. These may be used independently and 2 or more types may be used together.

Although content of the said other monomer in the said polymerizable monomer is not specifically limited, A preferable upper limit is 40 weight%. When the content of the other monomer exceeds 40% by weight, the content of the nitrile monomer is lowered, the heat resistance or gas barrier property of the thermally expandable microcapsule is lowered, and rupture and shrinkage are likely to occur at a high temperature. , Foaming ratio may decrease.

Examples of the volatile liquid include low molecular weight hydrocarbons such as ethane, ethylene, propane, propene, n-butane, isobutane, butene, isobutene, n-pentane, isopentane, neopentane, n-hexane, heptane, and petroleum ether. 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. . Of these, isobutane, n-butane, n-pentane, isopentane, n-hexane, petroleum ether, and mixtures thereof are preferred. These may be used independently and 2 or more types may be used together.

Among the volatile liquids, it is preferable to use a low-boiling hydrocarbon having 10 or less carbon atoms. By using such hydrocarbons, it is possible to obtain thermally expandable microcapsules having a high expansion ratio and promptly starting foaming.
Further, as the volatile liquid, a thermally decomposable compound that is thermally decomposed by heating and becomes gaseous may be used.

The content of the volatile liquid is preferably 10 parts by weight with respect to 100 parts by weight of the polymerizable monomer, and 50 parts by weight with respect to the preferred upper limit. When the content of the volatile liquid is less than 10 parts by weight, the shell of the thermally expandable microcapsule becomes too thick and may not be foamed at a high temperature. When the content of the volatile liquid exceeds 50 parts by weight, The strength of the shell may decrease, and the expansion ratio may decrease.

The polymerization initiator is not particularly limited, and examples thereof include dialkyl peroxide, diacyl peroxide, peroxyester, peroxydicarbonate, and azo compound.
The dialkyl peroxide is not particularly limited, and examples thereof include methyl ethyl peroxide, di-t-butyl peroxide, dicumyl peroxide, isobutyl peroxide and the like.

The diacyl peroxide is not particularly limited, and examples thereof include benzoyl peroxide, 2,4-dichlorobenzoyl peroxide, 3,5,5-trimethylhexanoyl peroxide, and the like.

The peroxy ester is not particularly limited, and examples thereof include t-butyl peroxypivalate, t-hexyl peroxypivalate, t-butyl peroxyneodecanoate, t-hexyl peroxyneodecanoate, 1- Cyclohexyl-1-methylethylperoxyneodecanoate, 1,1,3,3-tetramethylbutylperoxyneodecanoate, cumylperoxyneodecanoate, (α, α-bis-neodecanoylper And oxy) diisopropylbenzene.

The peroxydicarbonate is not particularly limited. For example, bis (4-t-butylcyclohexyl) peroxydicarbonate, di-n-propyl-peroxydicarbonate, diisopropyl peroxydicarbonate, di (2-ethylethyl) Peroxy) dicarbonate, dimethoxybutyl peroxydicarbonate, di (3-methyl-3-methoxybutylperoxy) dicarbonate, and the like.

The azo compound is not particularly limited. For example, 2,2′-azobisisobutyronitrile, 2,2′-azobis (4-methoxy-2,4-dimethylvaleronitrile), 2,2′-azobis ( 2,4-dimethylvaleronitrile), 1,1′-azobis (1-cyclohexanecarbonitrile) and the like.

The content of the polymerization initiator is preferably 0.1 parts by weight and preferably 5 parts by weight with respect to 100 parts by weight of the polymerizable monomer. When the content of the polymerization initiator is less than 0.1 parts by weight, the polymerization reaction of the polymerizable monomer does not proceed sufficiently and a thermally expandable microcapsule may not be obtained. If the polymerization reaction of the polymerizable monomer starts abruptly, agglomeration is likely to occur, or the polymerization may run away, resulting in a safety problem.

The oily substance may further contain a metal cation salt. By containing a metal cation salt in the oily substance, an ionic bridge between the carboxyl group of the carboxyl group-containing monomer and the metal cation can be formed. As a result, the heat-expandable microcapsules increase the cross-linking efficiency of the shell, improve the heat resistance, do not easily burst or shrink even at high temperatures, and improve the expansion ratio. In addition, by forming ionic crosslinks, the heat-expandable microcapsules are less likely to lower the elastic modulus of the shell even at high temperatures. Such heat-expandable microcapsules are ruptured and shrunk even when they are blended into a base resin and then molded by a molding method such as kneading molding, calender molding, extrusion molding, injection molding, etc. in which a strong shear force is applied. It is difficult to occur and the expansion ratio is improved.

The metal cation forming the metal cation salt is not particularly limited as long as it is a metal cation capable of forming an ionic bridge with the carboxyl group of the carboxyl group-containing monomer, for example, 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.
The metal cation salt is preferably a hydroxide of the metal cation. These may be used independently and 2 or more types may be used together.

When two or more of the above metal cation salts are used in combination, for example, a salt composed of an alkali metal or alkaline earth metal ion and a salt composed of a metal cation other than the alkali metal or alkaline earth metal may be used in combination. preferable. The alkali metal or alkaline earth metal ions can activate the carboxyl group, and can promote the formation of ion bridges between the carboxyl group and a metal cation other than the alkali metal or alkaline earth metal.
The alkali metal or alkaline earth metal is not particularly limited, and examples thereof include Na, K, Li, Ca, Ba, and Sr. Of these, strong basic Na and K are preferred.

Although content of the said metal cation salt is not specifically limited, The preferable minimum with respect to 100 weight part of polymerizable monomers is 0.1 weight part, and a preferable upper limit is 10 weight part. When the content of the metal cation salt is less than 0.1 parts by weight, the effect of improving the heat resistance of the thermally expandable microcapsule may not be sufficiently obtained. The expansion ratio of the microcapsule may be reduced.

The oily substance may further contain a thermosetting resin. By adding a thermosetting resin to the oily substance, the heat-expandable microcapsules have heat resistance by reacting and curing the carboxyl group of the carboxyl group-containing monomer and the thermosetting resin when the thermally expandable microcapsules are heated and foamed. Property and durability can be further improved.
As said thermosetting resin, an epoxy resin, a phenol resin, a melamine resin, a urea resin, a polyimide resin, a bismaleimide resin etc. are mentioned, for example. Of these, epoxy resins and phenol resins are preferred.

The epoxy resin is not particularly limited, and examples thereof include bisphenol A type epoxy resin, bisphenol F type epoxy resin, phenol novolac type epoxy resin, cresol novolac type epoxy resin, dicyclopentadiene type epoxy resin, glycidylamine type epoxy resin and the like. Can be mentioned.
Examples of the phenol resin include novolac type phenol resins, resol type phenol resins, benzylic ether type phenol resins, and the like. Of these, novolac type phenol resins are preferred.

The thermosetting resin preferably does not have a radical polymerizable double bond. When it does not have a radical polymerizable double bond, the thermosetting resin does not directly bond to the main chain of the polymer obtained by polymerizing the polymerizable monomer. In such a case, the flexibility of the shell can be kept high before the thermal expansion of the thermally expandable microcapsule, and the carboxyl group of the carboxyl group-containing monomer and the thermosetting resin are not the first time when the thermally expandable microcapsule is heated and foamed. And can be cured.

Moreover, it is preferable that the said thermosetting resin has 2 or more of functional groups which react with a carboxyl group in 1 molecule. By having two or more functional groups that react with the carboxyl group in one molecule, the thermosetting resin can have stronger curability, and thus the heat resistance and durability of the thermally expandable microcapsules. Can be greatly improved.
Examples of the functional group that reacts with the carboxyl group include an epoxy group, a phenol group, a methylol group, and an amino group. Among these, an epoxy group is preferable. The functional groups that react with two or more carboxyl groups in one molecule may be the same or two or more functional groups.

Examples of thermosetting resins that do not have a radical polymerizable double bond and have two or more functional groups that react with carboxyl groups in one molecule include epoxy resins, phenol resins, urea resins, and melamine resins. Sorbitol polyglycidyl ether (manufactured by Nagase ChemteX, Denacol EX-622), polyglycerol polyglycidyl ether (Denacol EX-622), diglycerol polyglycidyl ether (Denacol EX-421), glycerol polyglycidyl ether (Denacol EX- 313), pentaerythritol polyglycidyl ether (Denacol EX-411), resorcinol diglycidyl ether (Denacol EX-201), 1,6-hexanediol diglycidyl ether (Denacol EX-212), Ethi Emissions, such as polyethylene glycol diglycidyl ether (Denacol EX-810) and the like.

As for the content of the thermosetting resin, a preferable lower limit with respect to the whole oily substance excluding the thermosetting resin is 0.01% by weight, and a preferable upper limit is 30% by weight. When the content of the thermosetting resin is less than 0.01% by weight, thermosetting characteristics may not appear at the time of heating and foaming, and when it exceeds 30% by weight, the gas barrier property of the shell of the heat-expandable microcapsule may be reduced. And foaming may be inhibited. The minimum with more preferable content of the said thermosetting resin is 0.1 weight%, and a more preferable upper limit is 15 weight%.
The ratio of the thermosetting resin to the carboxyl group-containing monomer is preferably 1 or more (carboxyl group-containing monomer / thermosetting resin ≧ 1). By setting it as the said range, sclerosis | hardenability can be ensured, reducing the unreacted part of a thermosetting resin.

The oily substance 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.

The method of preparing the emulsion by suspending the oily substance in the aqueous dispersion medium is not particularly limited. For example, a method of stirring with a homomixer or a homodisper (for example, manufactured by Tokushu Kika Kogyo Co., Ltd.), a static mixer ( Examples thereof include a method using a static dispersion device such as Noritake Engineering Co., Ltd., a line mixer, an element type static dispersion device, a membrane emulsification method, an ultrasonic dispersion method, a microchannel method, and the like.
The aqueous dispersion medium and the oily substance may be separately supplied to the static dispersion apparatus, and the obtained emulsion is supplied by stirring and mixing the aqueous dispersion medium and the oily substance in advance. May be.

The polymerizable substance, the volatile liquid, and the polymerization initiator may be separately added to the aqueous dispersion medium to prepare an oily substance in the aqueous dispersion medium. The polymerizable monomer, the volatile liquid, and the polymerization initiator are mixed to form an oily substance, and then added to the aqueous dispersion medium. In this case, the aqueous dispersion medium and the oily substance are prepared in separate containers in advance, and mixed with stirring in another container to suspend the oily substance in the aqueous dispersion medium. May be.
The polymerization initiator may be added in advance to the oily substance, or may be added after the aqueous dispersion medium and the oily substance are stirred and mixed in a polymerization reaction vessel.

In the method for producing a thermally expandable microcapsule of the present invention, a second addition step of adding colloidal silica to the emulsion is then performed.
By adding colloidal silica to the emulsified liquid, even when a carboxyl group-containing monomer is used, the suspended droplets are stabilized, and heat-expandable microcapsules are produced with high productivity while suppressing aggregation. be able to. In the second addition step, colloidal silica is added to the “emulsion”. That is, when an oily substance is suspended in an aqueous dispersion medium and the diameter of the droplet made of the oily substance is measured using a particle size distribution meter (for example, “LA-950” manufactured by Horiba, Ltd.), the droplet diameter Is in a state of about 10 to 100 μm, and then colloidal silica is added.

The average particle size and the like of the colloidal silica added in the second addition step may be the same as or different from those of the colloidal silica added in the first addition step.

In the second addition step, the addition is preferably performed so that the amount of colloidal silica added is 3 to 16 parts by weight with respect to 100 parts by weight of the polymerizable monomer. If the amount of colloidal silica added is less than 3 parts by weight, the thermally expandable microcapsule tends to aggregate and may not be stably obtained. If it exceeds 16 parts by weight, the excess colloidal silica is polymerized. Since it inhibits, a thermally expansible microcapsule with a favorable characteristic may not be obtained. A more preferred lower limit of the amount of colloidal silica added is 7 parts by weight, and a more preferred upper limit is 13 parts by weight.
Here, the amount of colloidal silica added in the second addition step means the amount of colloidal silica added in the second addition step.

Moreover, in a 2nd addition process, it is preferable to add so that the total addition amount of colloidal silica may be 16-33 weight part with respect to 100 weight part of polymerizable monomers. When the total amount of colloidal silica added is less than 16 parts by weight, the thermally expandable microcapsules tend to aggregate and may not be stably obtained. When the amount exceeds 33 parts by weight, the excess colloidal silica is polymerized. Therefore, a thermally expandable microcapsule having good characteristics may not be obtained. A more preferable lower limit of the total amount of colloidal silica added is 20 parts by weight, and a more preferable upper limit is 30 parts by weight.
In addition, the total addition amount of colloidal silica means the total addition amount of colloidal silica including the colloidal silica added in the 1st addition process.

Moreover, it is preferable that the ratio of the addition amount of colloidal silica in a 1st addition process and the addition amount of colloidal silica in a 2nd addition process is 1: 2.5-2.5: 1, and is 1: 2-2. : 1 is more preferable.

In the method for producing the thermally expandable microcapsule of the present invention, a polymerization step for polymerizing the polymerizable monomer is then performed.
The method for polymerizing the polymerizable monomer is not particularly limited, and examples thereof include a method for polymerizing the polymerizable monomer by heating. As a result, a thermally expandable microcapsule containing a volatile liquid as a core agent in a shell containing a polymer obtained by polymerizing a polymerizable monomer is obtained. The obtained thermally expandable microcapsules may be subsequently subjected to a dehydration step, a drying step, and the like.

In the method for producing a thermally expandable microcapsule of the present invention, the polymerization step may be performed after the second addition step, or the second addition step and the polymerization step may be performed as one step. . That is, for example, colloidal silica may be added to the emulsion during polymerization of the polymerizable monomer.

According to the method for producing a heat-expandable microcapsule of the present invention, a heat-expandable microcapsule having a large particle size can be produced with high productivity while suppressing aggregation.
The volume average particle diameter of the thermally expandable microcapsule obtained by the method for producing the thermally expandable microcapsule of the present invention is not particularly limited, but a preferable lower limit is 35 μm and a preferable upper limit is 80 μm. When the volume average particle diameter is less than 35 μm, when the thermally expandable microcapsules are blended and molded into the base resin, the foamed foam has too small bubbles, and performance such as cushioning and damping properties or light weight When the thickness exceeds 80 μm, the foamed molded product may have too large air bubbles, and the fatigue resistance to repeated compression or the strength may be insufficient. A more preferable lower limit of the volume average particle diameter is 40 μm, and a more preferable upper limit is 60 μm.
The volume average particle diameter can be measured using a particle size distribution meter (for example, “LA-950” manufactured by Horiba, Ltd.).

The maximum foaming temperature (Tmax) of the thermally expandable microcapsule obtained by the method for producing the thermally expandable microcapsule of the present invention is not particularly limited, but a preferable lower limit is 200 ° C. When the maximum foaming temperature is less than 200 ° C., the heat-expandable microcapsules have low heat resistance, are liable to burst and shrink at high temperatures, and the foaming ratio may be reduced. In addition, for example, when producing a master batch pellet using thermally expandable microcapsules, foaming may occur due to shearing force during pellet production, and unfoamed master batch pellets may not be produced stably. A more preferable lower limit of the maximum foaming temperature is 210 ° C.
The maximum foaming temperature means the temperature at which the thermally expandable microcapsule reaches the maximum displacement when the diameter is measured while heating the thermally expandable microcapsule from room temperature.

As for the foaming start temperature (Ts) of the thermally expandable microcapsule obtained by the method for producing the thermally expandable microcapsule of the present invention, a preferable lower limit is 130 ° C., and a preferable upper limit is 200 ° C. If the foaming start temperature exceeds 200 ° C., the foaming ratio may not be increased, particularly in the case of injection molding, even if an attempt is made to mix the thermally expandable microcapsules with the base resin. A more preferable upper limit of the foaming start temperature is 180 ° C.

The use of the heat-expandable microcapsule obtained by the method for producing the heat-expandable microcapsule of the present invention is not particularly limited. For example, the heat-expandable microcapsules obtained by the method for producing the heat-expandable microcapsules of the present invention are blended into a base resin and molded using a molding method such as injection molding or extrusion molding, thereby providing heat insulation and heat insulation. A foamed molded product having properties such as sound insulation, sound absorption, vibration proofing, and weight reduction can be produced.

ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the thermally expansible microcapsule which can manufacture a thermally expansible microcapsule with a large particle diameter with sufficient productivity, suppressing aggregation can be provided.

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

Example 1
In a polymerization reaction vessel, 250 parts by weight of water, 16 parts by weight of colloidal silica (manufactured by Asahi Denka), 0.1 part by weight of sodium nitrite, 85 parts by weight of sodium chloride, and polyvinylpyrrolidone (manufactured by BASF) 0. 2 parts by weight were added to prepare an aqueous dispersion medium. Next, 100 parts by weight of the polymerizable monomer having the mixing ratio shown in Table 1, and 1 part by weight of JER-828US (Mitsubishi Chemical Corporation) and 0.5 part by weight of JER-630 (Mitsubishi Chemical Corporation) as thermosetting resins. 1 part by weight of azobisisobutyronitrile (AIBN) and 1 part by weight of 2,2′-azobis (2,4-dimethylvaleronitrile) (ADVN) as a polymerization initiator, and 30 parts by weight of normal pentane as a volatile liquid An oily substance consisting of 5 parts by weight and isooctane was added to an aqueous dispersion medium, stirred and mixed using a homogenizer (PT-MR3100 manufactured by KINEMATICA), and suspended to prepare an emulsion.
To the obtained emulsion, 10 parts by weight of colloidal silica (Asahi Denka Co., Ltd.) was added. Then, the emulsified liquid is stirred and mixed with a homogenizer (PT-MR3100 manufactured by KINEMATICA), charged into a pressure polymerizer purged with nitrogen, and reacted at 60 ° C. for 2 hours while being pressurized (0.5 MPa). The product was obtained. The obtained reaction product was repeatedly filtered and washed with water, and then dried to obtain thermally expandable microcapsules.

(Example 2)
An aqueous dispersion medium was prepared in the same manner as in Example 1 except that the addition amount of colloidal silica (manufactured by Asahi Denka Co., Ltd.) was changed from 16 parts by weight to 10 parts by weight. Thereafter, in the same manner as in Example 1, thermally expandable microcapsules were obtained.

(Example 3)
An aqueous dispersion medium was prepared in the same manner as in Example 1 except that the addition amount of colloidal silica (manufactured by Asahi Denka Co., Ltd.) was changed from 16 parts by weight to 20 parts by weight. Thereafter, in the same manner as in Example 1, thermally expandable microcapsules were obtained.

Example 4
Thermally expandable microcapsules were obtained in the same manner as in Example 1 except that the amount of colloidal silica (Asahi Denka Co., Ltd.) added to the emulsion was changed from 10 parts by weight to 7 parts by weight.

(Example 5)
Thermally expandable microcapsules were obtained in the same manner as in Example 1 except that the amount of colloidal silica (Asahi Denka Co., Ltd.) added to the emulsion was changed from 10 parts by weight to 13 parts by weight.

(Example 6)
A thermally expandable microcapsule was obtained in the same manner as in Example 1 except that the blending ratio of the polymerizable monomer was changed as shown in Table 1.

(Comparative Example 1)
An aqueous dispersion medium was prepared in the same manner as in Example 1 except that no colloidal silica was added. Thereafter, an attempt was made to obtain thermally expandable microcapsules in the same manner as in Example 1, but an emulsion could not be obtained.

(Comparative Example 2)
Thermally expandable microcapsules were obtained in the same manner as in Example 1 except that colloidal silica was not added to the emulsion.

(Comparative Example 3)
Example 1 except that the amount of colloidal silica (manufactured by Asahi Denka Co., Ltd.) added to the aqueous dispersion medium was changed from 16 parts by weight to 26 parts by weight, and then the colloidal silica was not added to the emulsion. In the same manner, thermally expandable microcapsules were obtained.

<Evaluation>
The following evaluation was performed about the thermally expansible microcapsule obtained by the Example and the comparative example. The results are shown in Table 1.

(1) Measurement of average particle diameter The volume average particle diameter of thermally expandable microcapsules was measured using a particle size distribution analyzer ("LA-950" manufactured by Horiba, Ltd.).

(2) Measurement of average particle diameter after thermal expansion About 0.1 g of thermally expandable microcapsules is collected in an aluminum cup, placed in an oven adjusted to 180 ° C. for 15 minutes, taken out, allowed to cool, and then a particle size distribution meter. (Horiba Seisakusho "LA-950") was used to measure the volume average particle size of the thermally expandable microcapsules.

(3) Aggregation evaluation (productivity)
The slurry after polymerization was scraped off with a metal mesh of 5 mm mesh, and the weight of the aggregate remaining on the mesh was measured. A case where the weight of the aggregate was 2% by weight or less of the total slurry amount was judged as ◎, a case where it exceeded 2% by weight and less than 5% by weight, and a case where it was 5% by weight or more were judged as ×. .

ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the thermally expansible microcapsule which can manufacture a thermally expansible microcapsule with a large particle diameter with sufficient productivity, suppressing aggregation can be provided.

Claims (3)

A first addition step of preparing an aqueous dispersion medium by adding colloidal silica to water;
An emulsification step of preparing an emulsion by suspending a polymerizable monomer containing a carboxyl group-containing monomer, a volatile liquid, and an oily substance containing a polymerization initiator in the aqueous dispersion medium;
A second addition step of adding colloidal silica to the emulsion;
A method for producing a thermally expandable microcapsule comprising a polymerization step of polymerizing the polymerizable monomer. 2. The production of thermally expandable microcapsules according to claim 1, wherein in the first addition step, the colloidal silica is added so that the amount of colloidal silica is 7 to 23 parts by weight with respect to 100 parts by weight of the polymerizable monomer. Method. The thermally expandable microcapsule according to claim 1 or 2, wherein in the second addition step, the colloidal silica is added in an amount of 3 to 16 parts by weight with respect to 100 parts by weight of the polymerizable monomer. Manufacturing method.