Thermally expandable microcapsules, foamable resin composition, and foam

Abstract

The present invention provides: thermally expandable microcapsules which have a high foam expansion ratio and make it possible to produce a molded body that is lightweight and has an excellent appearance; and a foamable resin composition and a foam which use the thermally expandable microcapsules. The present invention provides thermally expandable microcapsules in which a volatile expanding agent is encapsulated as a core agent in a shell that comprises a polymer, wherein: the shell contains silicon dioxide and a polymer which is obtained by polymerizing a monomer composition that contains a carbonyl-group-containing monomer; and volatile matter content is 0.55-2 wt% after rest for one hour at a temperature of 70°C.

Description

Thermally expandable microcapsules, foamable resin composition, and foam

[0001] The present invention relates to a thermally expandable microcapsule, and a foamable resin composition and a foam using the thermally expandable microcapsule.

[0002] To date, in order to reduce the weight and improve the functionality of resin materials, materials have been foamed using foaming agents, and thermally expandable microcapsules and chemical foaming agents have generally been used as such foaming agents.

[0003] A widely known thermally expandable microcapsule is one in which a liquid volatile blowing agent that becomes gaseous at a temperature below the softening point of the shell polymer is encapsulated in a thermoplastic shell polymer. For example, Patent Document 1 discloses a method for producing thermally expandable microcapsules encapsulating a volatile blowing agent by adding, with stirring, an oil-based mixture in which a volatile blowing agent such as a low-boiling-point aliphatic hydrocarbon is mixed with a monomer, together with an oil-soluble polymerization catalyst, to an aqueous dispersion medium containing a dispersant, and then performing suspension polymerization.

[0004] Special Publication No. 42-26524

[0005] However, when the thermally expandable microcapsules obtained by this method are used as a foaming agent, the resulting molded article has defects such as dents, resulting in poor appearance. Furthermore, when measures to prevent the above-mentioned poor appearance are taken, this leads to a decrease in foaming performance, resulting in problems such as insufficient density of the resulting molded article.

[0006] The present invention aims to provide a thermally expandable microcapsule that can be used to produce a molded article that has a high expansion ratio, is lightweight, and has an excellent appearance, and to provide a foamable resin composition and a foam that use the thermally expandable microcapsule.

[0007] Disclosure (1) is a thermally expandable microcapsule having a polymer shell encapsulating a volatile expanding agent as a core agent, the shell comprising a polymer obtained by polymerizing a monomer composition containing a carbonyl group-containing monomer, and silicon dioxide, the thermally expandable microcapsule having a volatile content of 0.55% by weight or more and 2% by weight or less when left to stand at 70°C for 1 hour. Disclosure (2) is a thermally expandable microcapsule according to Disclosure (1) having a volatile content of 20% by weight or more and 30% by weight or less when left to stand at 210°C for 20 minutes. Disclosure (3) is a thermally expandable microcapsule according to Disclosure (1) or (2), in which the ratio of the volatile content when left to stand at 70°C for 1 hour to the volatile content when left to stand at 210°C for 20 minutes is 8% or less. The present disclosure (4) is a thermally expandable microcapsule according to any one of the present disclosures (1) to (3), which exhibits a weight increase rate of 60% by weight or less when left standing for 12 hours at a temperature of 50°C and a humidity of 80% or more. The present disclosure (5) is a thermally expandable microcapsule according to any one of the present disclosures (1) to (4), which exhibits an average particle size of 10 μm or more and 45 μm or less. The present disclosure (6) is a thermally expandable microcapsule according to any one of the present disclosures (1) to (5), which exhibits a maximum foaming temperature (Tmax) of 180°C or more and 225°C or less. The present disclosure (7) is a foamable resin composition containing the thermally expandable microcapsule according to any one of the present disclosures (1) to (6) and a thermoplastic resin. The present disclosure (8) is a foam obtained using the foamable resin composition according to the present disclosure (7). The present invention will be described in detail below.

[0008] As a result of extensive research, the present inventors have found that the volatile content of thermally expandable microcapsules is closely related to the performance of the resulting molded article. Therefore, the present inventors have discovered that, by controlling the volatile content within a predetermined range for thermally expandable microcapsules containing silicon dioxide and a polymer obtained by polymerizing a monomer composition containing a carbonyl group-containing monomer in the shell, it is possible to obtain thermally expandable microcapsules that can be used to produce molded articles that have a high expansion ratio, are lightweight, and have excellent appearance, and have completed the present invention.

[0009] The thermally expandable microcapsules of the present invention have a volatile content of 0.55% by weight or more and 2% by weight or less when left standing at 70°C for 1 hour. A volatile content of 0.55% by weight or more can achieve both improved appearance and foamability of the molded article. A volatile content of 2% by weight or less can particularly improve the appearance of the molded article. Furthermore, such thermally expandable microcapsules are less likely to aggregate during foaming, contributing to improved foaming performance. Furthermore, such thermally expandable microcapsules have excellent fluidity when formed into a multi-particle aggregate, allowing for stable injection from a hopper or the like during molding, for example. The preferred lower limit of the volatile content when left standing at 70°C for 1 hour is 0.57% by weight, more preferably 0.6% by weight, and the preferred upper limit is 1.8% by weight, even more preferably 1.5% by weight. In this specification, the volatile content when left standing at 70°C for 1 hour can be measured from the weight change after heating in an oven at 70°C and humidity of less than 20% for 1 hour. In the measurement of the volatile content, when the humidity is less than 20%, the difference in weight change due to differences in humidity is negligible.

[0010] In the present invention, by adjusting the components of the thermally expandable microcapsules or by adjusting the reaction process, washing process, and drying process when producing the thermally expandable microcapsules, it is possible to control the volatile content when left standing at a temperature of 70°C for 1 hour, the volatile content when left standing at a temperature of 210°C for 20 minutes as described below, the volatile content ratio, weight gain rate, and average circularity.

[0011] The thermally expandable microcapsules of the present invention preferably have a volatile content of 20% by weight or more and 30% by weight or less when left standing at 210°C for 20 minutes. A volatile content of 20% by weight or more ensures sufficient expandability. Furthermore, a volatile content of 30% by weight or less ensures a high-quality appearance when formed into a foamed molded article. A more preferred lower limit of the volatile content when left standing at 210°C for 20 minutes is 23% by weight, an even more preferred lower limit is 25% by weight, a more preferred upper limit is 28% by weight, and an even more preferred upper limit is 27% by weight. In this specification, the volatile content when left standing at 210°C for 20 minutes can be measured from the weight change after heating in an oven at 210°C and humidity less than 20% for 20 minutes.

[0012] The thermally expandable microcapsules of the present invention preferably have a ratio of volatile content when left standing at 70°C for 1 hour to volatile content when left standing at 210°C for 20 minutes ([volatile content when left standing at 70°C for 1 hour / volatile content when left standing at 210°C for 20 minutes] x 100) of 8% or less. By keeping this ratio at 8% or less, aggregation after expansion is suppressed, and an expanded molded product with a good appearance (smooth) and a high expansion ratio can be obtained. A more preferred upper limit is 7.5%, an even more preferred upper limit is 5%, and an even more preferred upper limit is 3%. There are no particular restrictions on the preferred lower limit, but it is 0%.

[0013] The thermally expandable microcapsules of the present invention preferably have a weight gain of 60% by weight or less when left to stand for 12 hours at a temperature of 50°C and a humidity of 80% or more. Having a weight gain of 60% by weight or less can improve the appearance of a foamed molded article. The upper limit of the weight gain is more preferably 50% by weight, even more preferably 35% by weight, and preferably 10% by weight, even more preferably 20% by weight. In this specification, the weight gain can be measured from the weight change when the microcapsules are left to stand for 12 hours at a temperature of 50°C and a humidity of 80% or more using a thermo-hygrostat. When the humidity is 80% or more, the difference in weight change due to differences in humidity is negligible.

[0014] The thermally expandable microcapsules of the present invention have a maximum foaming temperature (Tmax) of preferably 180°C (lower limit) and 225°C (upper limit). By setting the temperature within the above range, heat resistance is improved, and when a composition containing the thermally expandable microcapsules is molded at high temperatures, the thermally expandable microcapsules can be prevented from bursting or shrinking. Furthermore, aggregation of the thermally expandable microcapsules during molding can be suppressed, resulting in a good appearance. A more preferred lower limit is 185°C, an even more preferred lower limit is 190°C, and a more preferred upper limit is 222°C, and an even more preferred upper limit is 220°C. In this specification, the maximum foaming temperature refers to the temperature at which the diameter of the thermally expandable microcapsule reaches its maximum (maximum displacement) when the diameter is measured while heating the thermally expandable microcapsule from room temperature. The temperature at which the displacement begins to increase is referred to as the foaming initiation temperature.

[0015] The upper limit of the foaming initiation temperature (Ts) is preferably 170° C. By setting the temperature to 170° C. or less, foaming becomes easy and a desired foaming ratio can be achieved. The upper limit is more preferably 165° C., the lower limit is preferably 145° C., and the upper limit is even more preferably 165° C.

[0016] Furthermore, the maximum displacement (Dmax) of the thermally expandable microcapsules of the present invention measured by thermomechanical analysis preferably has a lower limit of 350 μm and an upper limit of 1600 μm, more preferably a lower limit of 500 μm and an upper limit of 1500 μm. By setting the Dmax within the above range, the expansion ratio is improved and the desired expansion performance is obtained. Note that the maximum displacement refers to the value at which the diameter of a predetermined amount of thermally expandable microcapsules as a whole is maximum when the diameter is measured while heating a predetermined amount of thermally expandable microcapsules from room temperature.

[0017] The preferred lower limit of the average particle size (volume average particle size) of the thermally expandable microcapsules of the present invention is 10 μm, and the preferred upper limit is 45 μm. By setting the size within the above range, the resulting molded product will have an appropriate amount of bubbles, a sufficient expansion ratio, and excellent appearance. A more preferred lower limit is 15 μm, an even more preferred lower limit is 20 μm, a more preferred upper limit is 35 μm, an even more preferred upper limit is 32 μm, and a particularly preferred upper limit is 30 μm. The CV value of the volume average particle size of the thermally expandable microcapsules of the present invention is preferably 35% or less, typically 10% or more, and preferably 15% or more. The above average particle size (volume average particle size) and CV value can be measured using a particle size distribution diameter measuring instrument or the like.

[0018] The preferred lower limit of the average circularity of the thermally expandable microcapsules of the present invention is 0.910, and the preferred upper limit is 0.980. By keeping the value within this range, the appearance during molding can be made smooth and free of dents. A more preferred lower limit is 0.920, and a more preferred upper limit is 0.970. The average circularity is calculated by measuring the circularity using an image obtained during wet measurement using, for example, a Mastersizer 3000 (manufactured by Malvern Panalytical). The circularity represents the value obtained by dividing the area calculated from the image of the thermally expandable microcapsule by the area of ​​the circumscribed circle of the image of the thermally expandable microcapsule (image area of ​​the thermally expandable microcapsule / area of ​​the circumscribed circle of the image of the thermally expandable microcapsule). Alternatively, the average circularity may be calculated by measuring the circularity using an image obtained during dry measurement using a CALPAS (Japan Laser Co., Ltd.).

[0019] The shell constituting the thermally expandable microcapsule of the present invention contains a polymer obtained by polymerizing a monomer composition containing a carbonyl group-containing monomer, and silicon dioxide.

[0020] The shell contains silicon dioxide. The silicon dioxide may be attached to the surface of the shell or may be mixed within the shell. The silicon dioxide also includes silicon dioxide hydrates. Examples of the silicon dioxide include those contained in silica fine particles and colloidal silica. The colloidal silica is a colloid of silicon dioxide or silicon dioxide hydrate. The colloidal silica containing silicon dioxide preferably has an average particle size of 10 to 300 nm.

[0021] In the thermally expandable microcapsules of the present invention, the preferred lower limit of the silicon dioxide content is 1 wt%, and the preferred upper limit is 5 wt%. By setting the silicon dioxide content to 1 wt% or more, the average particle size of the thermally expandable microcapsules can be maintained stable, and by setting the silicon dioxide content to 5 wt% or less, thermally expandable microcapsules with excellent foaming performance can be obtained. The more preferred lower limit of the silicon dioxide content is 1.5 wt%, and the more preferred upper limit is 3 wt%, and the even more preferred lower limit is 1.7 wt%, and the even more preferred upper limit is 2.8 wt%.

[0022] The shell contains a polymer obtained by polymerizing a monomer composition containing a carbonyl group-containing monomer, and silicon dioxide.

[0023] Examples of the carbonyl group-containing monomer include the above-mentioned radically polymerizable unsaturated carboxylic acid monomers having 3 to 8 carbon atoms, radically polymerizable unsaturated carboxylic acid ester monomers having 3 to 8 carbon atoms, and polyfunctional carboxylic acid ester monomers.

[0024] The radically polymerizable unsaturated carboxylic acid monomer having 3 to 8 carbon atoms can be, for example, one having one free carboxyl group per molecule for ionic crosslinking. Specific examples include unsaturated carboxylic acids and their anhydrides, which can be used alone or in combination of two or more. Examples of the unsaturated carboxylic acid 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, citraconic acid, and chloromaleic acid. Of these, acrylic acid, methacrylic acid, maleic acid, maleic anhydride, and itaconic acid are particularly preferred.

[0025] The preferred lower limit of the content of the radically polymerizable unsaturated carboxylic acid monomer having 3 to 8 carbon atoms in the monomer composition is 5% by weight, and the preferred upper limit is 50% by weight. By making it 5% by weight or more, the maximum foaming temperature can be increased, and by making it 50% by weight or less, the foaming ratio can be improved. The preferred lower limit is 10% by weight, and the preferred upper limit is 30% by weight.

[0026] The radically polymerizable unsaturated carboxylic acid ester monomer having 3 to 8 carbon atoms is preferably, for example, a (meth)acrylic acid ester, and in particular, alkyl methacrylates such as methyl methacrylate, ethyl methacrylate, and n-butyl methacrylate are preferred. Also preferred are alicyclic, aromatic, and heterocyclic methacrylic acid esters such as cyclohexyl methacrylate, benzyl methacrylate, and isobornyl methacrylate.

[0027] The preferred lower limit of the content of the radically polymerizable unsaturated carboxylic acid ester monomer having 3 to 8 carbon atoms in the monomer composition is 0.01 wt %, and the preferred upper limit is 35 wt %. By setting the content of the radically polymerizable unsaturated carboxylic acid ester monomer having 3 to 8 carbon atoms to 0.01 wt % or more, the dispersibility of the composition using the thermally expandable microcapsules can be improved, and by setting the content to 35 wt % or less, the gas barrier properties of the cell walls can be improved, thereby improving thermal expandability. The more preferred lower limit of the content of the radically polymerizable unsaturated carboxylic acid ester monomer having 3 to 8 carbon atoms is 0.05 wt %, and the more preferred upper limit is 30 wt %.

[0028] The polyfunctional carboxylic acid ester monomer refers to a carboxylic acid ester monomer having two or more radically polymerizable double bonds, and is different from the radically polymerizable unsaturated carboxylic acid ester monomer having 3 to 8 carbon atoms. The polyfunctional carboxylic acid ester monomer functions as a crosslinking agent. By including the polyfunctional carboxylic acid ester monomer, the strength of the shell can be increased, making the cell walls less likely to break during thermal expansion.

[0029] Specific examples of the polyfunctional carboxylic acid ester monomer include di(meth)acrylates and tri- or higher functional (meth)acrylates. Examples of the di(meth)acrylates include ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, and 1,4-butanediol di(meth)acrylate. Other examples include 1,6-hexanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, glycerin di(meth)acrylate, trimethylolpropane di(meth)acrylate, and dimethylol-tricyclodecane di(meth)acrylate. Furthermore, di(meth)acrylates of polyethylene glycol having a weight average molecular weight of 200 to 600 may also be used. Examples of the trifunctional (meth)acrylate include trimethylolpropane tri(meth)acrylate, ethylene oxide-modified trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, triallyl formal tri(meth)acrylate, etc. Examples of the tetrafunctional or higher (meth)acrylate include pentaerythritol tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, etc. Among these, trifunctional (meth)acrylates such as trimethylolpropane tri(meth)acrylate and bifunctional (meth)acrylates such as polyethylene glycol provide relatively uniform crosslinking to the acrylonitrile-based shell.

[0030] The preferred lower limit of the content of the polyfunctional carboxylic acid ester monomer in the monomer composition is 0.1 wt %, and the preferred upper limit is 1.0 wt %. By setting the content of the polyfunctional carboxylic acid ester monomer to 0.1 wt % or more, the effect as a crosslinking agent can be fully exhibited, and by setting the content of the polyfunctional carboxylic acid ester monomer to 1.0 wt % or less, the expansion ratio of the thermally expandable microcapsules can be improved. The more preferred lower limit of the content of the polyfunctional carboxylic acid ester monomer is 0.15 wt %, and the more preferred upper limit is 0.9 wt %.

[0031] The monomer composition preferably contains a nitrile monomer such as acrylonitrile or methacrylonitrile in addition to the carbonyl group-containing monomer. The addition of the nitrile monomer can improve the gas barrier properties of the shell. In addition to the carbonyl group-containing monomer and the nitrile monomer, the monomer composition may contain vinylidene chloride, divinylbenzene, vinyl acetate, a styrene monomer, or the like.

[0032] The preferred lower limit of the content of the nitrile monomer in the monomer composition is 40% by weight, and the preferred upper limit is 90% by weight. By making it 40% by weight or more, the gas barrier properties of the shell can be improved and the expansion ratio can be increased. By making it 90% by weight or less, heat resistance can be improved and yellowing can be prevented. The more preferred lower limit is 50% by weight, and the more preferred upper limit is 80% by weight.

[0033] In particular, from the viewpoints of heat resistance, expansion ratio, light weight, hardness, and abrasion resistance, the monomer composition preferably contains 40 to 90% by weight of a nitrile monomer and 10 to 60% by weight of a carbonyl group-containing monomer.

[0034] The monomer composition contains a polymerization initiator to polymerize the monomers. Suitable examples of the polymerization initiator include dialkyl peroxides, diacyl peroxides, peroxyesters, peroxydicarbonates, and azo compounds. Specific examples include dialkyl peroxides such as methyl ethyl peroxide, di-t-butyl peroxide, and dicumyl peroxide; and diacyl peroxides such as isobutyl peroxide, benzoyl peroxide, 2,4-dichlorobenzoyl peroxide, and 3,5,5-trimethylhexanoyl peroxide. Other examples include t-butyl peroxypivalate, t-hexyl peroxypivalate, t-butyl peroxyneodecanoate, t-hexyl peroxyneodecanoate, 1-cyclohexyl-1-methylethyl peroxyneodecanoate, and 1,1,3,3-tetramethylbutyl peroxyneodecanoate. Other examples include peroxyesters such as cumyl peroxy neodecanoate and (α,α-bis-neodecanoylperoxy)diisopropylbenzene; bis(4-t-butylcyclohexyl)peroxydicarbonate, di-n-propyl-oxydicarbonate, and diisopropyl peroxydicarbonate. Further examples include peroxydicarbonates such as di(2-ethylethylperoxy)dicarbonate, dimethoxybutyl peroxydicarbonate, and di(3-methyl-3-methoxybutylperoxy)dicarbonate. Additionally, other examples include azo compounds such as 2,2'-azobisisobutyronitrile, 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile), 2,2'-azobis(2,4-dimethylvaleronitrile), and 1,1'-azobis(1-cyclohexanecarbonitrile).

[0035] The weight-average molecular weight of the polymer constituting the shell preferably has a lower limit of 100,000 and an upper limit of 2,000,000. When the weight-average molecular weight is 100,000 or more, a decrease in the strength of the shell can be suppressed, and when the weight-average molecular weight is 2,000,000 or less, an excessive increase in the strength of the shell can be suppressed, and a decrease in the expansion ratio can be suppressed.

[0036] The shell may further contain, as necessary, a stabilizer, an ultraviolet absorber, an antioxidant, an antistatic agent, a flame retardant, a silane coupling agent, a coloring agent, and the like.

[0037] The thermally expandable microcapsules of the present invention have a volatile expanding agent encapsulated in the shell as a core agent. The volatile expanding agent is a substance that becomes gaseous at a temperature below the softening point of the polymer that constitutes the shell, and is preferably a low-boiling organic solvent. Examples of the volatile expanding agent include low-molecular-weight hydrocarbons such as ethane, ethylene, propane, propene, n-butane, isobutane, butene, isobutene, n-pentane, isopentane, neopentane, n-hexane, heptane, petroleum ether, isooctane, octane, decane, isododecane, dodecane, and hexanedecane. Also, CCl ３ F, CCl ２ F ２ , CClF ３ , CClF ２ -CClF ２ and chlorofluorocarbons such as tetramethylsilane, trimethylethylsilane, trimethylisopropylsilane, trimethyl-n-propylsilane, and tetraalkylsilanes such as tetramethylsilane, trimethylethylsilane, trimethylisopropylsilane, and trimethyl-n-propylsilane. Among these, isobutane, n-butane, n-pentane, isopentane, n-hexane, isooctane, isododecane, and mixtures thereof are preferred. These volatile expanding agents may be used alone or in combination of two or more. Furthermore, as the volatile expanding agent, a thermally decomposable compound that is thermally decomposed into a gaseous form by heating may be used.

[0038] In the thermally expandable microcapsules of the present invention, among the above-mentioned volatile expanding agents, it is preferable to use low-boiling-point hydrocarbons having 5 or less carbon atoms. By using such hydrocarbons, it is possible to obtain thermally expandable microcapsules with a high expansion ratio and rapid expansion start. Furthermore, as the volatile expanding agent, a thermally decomposable compound that is thermally decomposed into a gaseous form when heated may be used.

[0039] The method for producing the thermally expandable microcapsules of the present invention is not particularly limited, but they can be produced, for example, by carrying out the steps of preparing an aqueous medium, dispersing an oily mixture containing a monomer composition and a volatile expanding agent in the aqueous medium, and polymerizing the monomer. The monomer composition can be, for example, one containing 40 to 90 wt % of the above-mentioned nitrile monomer and 10 to 60 wt % of the carbonyl group-containing monomer.

[0040] When producing the thermally expandable microcapsules of the present invention, the first step is to prepare an aqueous medium. Specifically, for example, a polymerization reaction vessel is charged with water, a dispersion stabilizer containing silicon dioxide, and optionally a co-stabilizer to prepare an aqueous dispersion medium containing silicon dioxide. Furthermore, alkali metal nitrite, stannous chloride, stannic chloride, potassium dichromate, etc. may also be added as necessary.

[0041] Examples of the silicon dioxide-containing dispersion stabilizer include colloidal silica. As the colloidal silica, alkaline colloidal silica having a colloidal solution (aqueous dispersion) with a pH of more than 7 may be used, or acidic colloidal silica having a pH of less than 7 may be used. Of these, alkaline colloidal silica is more preferred. Furthermore, the colloidal silica preferably contains 10 to 50% by weight of silicon dioxide as a solid content and is monodispersed.

[0042] Examples of dispersion stabilizers other than silicon dioxide include calcium phosphate, magnesium hydroxide, aluminum hydroxide, ferric hydroxide, barium sulfate, calcium sulfate, sodium sulfate, calcium oxalate, calcium carbonate, barium carbonate, and magnesium carbonate.

[0043] The amount of the dispersion stabilizer containing silicon dioxide to be added is determined appropriately depending on the particle size of the thermally expandable microcapsules, but the preferred lower limit is 2.5 parts by weight and the preferred upper limit is 7 parts by weight relative to 100 parts by weight of the oily mixture (oil phase).The more preferred lower limit is 3 parts by weight and the even more preferred upper limit is 5 parts by weight.The amount of the oil phase refers to the total amount of the monomer and the volatile expanding agent.

[0044] Examples of the auxiliary stabilizer include a condensation product of diethanolamine and an aliphatic dicarboxylic acid, a condensation product of urea and formaldehyde, etc. Further examples include polyvinylpyrrolidone, polyethylene oxide, polyethyleneimine, tetramethylammonium hydroxide, gelatin, methylcellulose, polyvinyl alcohol, dioctyl sulfosuccinate, sorbitan ester, various emulsifiers, etc.

[0045] The combination of the dispersion stabilizer and the auxiliary stabilizer is not particularly limited, and examples thereof include a combination of colloidal silica and a condensation product, and a combination of colloidal silica and a water-soluble nitrogen-containing compound.Among these, a combination of colloidal silica and a condensation product is preferred.Furthermore, as the condensation product, a condensation product of diethanolamine and an aliphatic dicarboxylic acid is preferred, and a condensation product of diethanolamine and adipic acid or a condensation product of diethanolamine and itaconic acid is particularly preferred.

[0046] Examples of the water-soluble nitrogen-containing compound include polyvinylpyrrolidone, polyethyleneimine, polyoxyethylene alkylamine, polydialkylaminoalkyl(meth)acrylates such as polydimethylaminoethyl methacrylate and polydimethylaminoethyl acrylate, polydialkylaminoalkyl(meth)acrylamides such as polydimethylaminopropyl acrylamide and polydimethylaminopropyl methacrylamide, polyacrylamides, polycationic acrylamides, polyamine sulfones, and polyallylamines. Among these, polyvinylpyrrolidone is preferably used.

[0047] The amount of the above condensation product or water-soluble nitrogen-containing compound is determined appropriately depending on the particle size of the thermally expandable microcapsules, but the preferred lower limit is 0.05 parts by weight and the preferred upper limit is 0.2 parts by weight per 100 parts by weight of the oily mixture.

[0048] In addition to the dispersion stabilizer and co-stabilizer, inorganic salts such as sodium chloride and sodium sulfate may be added. By adding an inorganic salt, it is possible to obtain thermally expandable microcapsules with a more uniform particle shape. The amount of the inorganic salt added is usually preferably 0 to 100 parts by weight per 100 parts by weight of the monomer.

[0049] The aqueous dispersion medium containing the dispersion stabilizer is prepared by blending the dispersion stabilizer and / or co-stabilizer with deionized water, and the pH of the aqueous phase is determined appropriately depending on the type of dispersion stabilizer and / or co-stabilizer used. For example, when silicon dioxide is used as the dispersion stabilizer, polymerization is carried out in an acidic medium, and 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 magnesium hydroxide or calcium phosphate is used, polymerization is carried out in an alkaline medium.

[0050] Next, in the method for producing thermally expandable microcapsules, a step of dispersing an oily mixture containing a monomer composition and a volatile expanding agent in an aqueous medium is carried out. Specifically, for example, a step of dispersing an oily mixture containing a monomer composition containing 40 to 90 wt% of the above-mentioned nitrile-based monomer and 10 to 60 wt% of a carbonyl group-containing monomer, and a volatile expanding agent, in an aqueous medium is carried out. In this step, the monomer composition and the volatile expanding agent may be added separately to an aqueous dispersion medium to prepare the oily mixture in the aqueous dispersion medium. However, typically, the two are premixed to form an oily mixture, which is then added to the aqueous dispersion medium. In this case, the oily mixture and the aqueous dispersion medium may be prepared in separate containers, and the oily mixture may be dispersed in the aqueous dispersion medium by mixing with stirring in the separate container (primary dispersion), which may then be added to the polymerization reaction vessel. A polymerization initiator is used to polymerize the monomer. The polymerization initiator may be added to the oily mixture in advance, or it may be added after the aqueous dispersion medium and the oily mixture are mixed and stirred in the polymerization reaction vessel.

[0051] Examples of the step of dispersing the oily mixture containing the monomer composition and the volatile swelling agent in an aqueous medium include a method of stirring using a stirring blade such as a retreating blade, a batch-type high-speed rotation high-shear disperser (e.g., JP-A-7-96167), a continuous-type high-speed rotation high-shear disperser (e.g., JP-A-2000-191817), etc. Also included are methods of passing the mixture through an in-tube dispersing device such as a line mixer or a static in-tube mixer (static mixer).

[0052] In the present invention, a static in-tube mixer is preferably used in the process of dispersing the oily mixture containing the monomer composition and the volatile expanding agent in an aqueous medium. The use of the static in-tube mixer allows for in-tube mixing rather than in a tank, and for static mixing without the use of impellers, thereby enabling the thermally expandable microcapsules of the present invention to be produced conveniently. Furthermore, it is preferable to prepare primary dispersions of the oily mixture and the aqueous dispersion medium in separate containers in advance, and then introduce them into the static in-tube mixer under pressure. The static in-tube mixer (static mixer) comprises a cylindrical body with both ends open, and is fitted with multiple plate-like elements each having a large number of holes formed therein. The plate-like elements are stacked such that the centers of the holes in at least some of the adjacent plate-like elements do not align, but at least some of the openings face each other. By performing this process, the thermally expandable microcapsules of the present invention can be produced conveniently. The pressurization is preferably carried out at 1 to 6 MPa. The number of holes in the elements is preferably determined by the flow rate. Furthermore, the pressure can be set by adjusting the hole diameter and flow rate. The hole diameter is preferably 1 to 3 mm. The flow rate is preferably 100 to 500 L / min. Specifically, a combination of a hole diameter of 2 mm and a flow rate of 200 L / min is preferred.

[0053] The thermally expandable microcapsules of the present invention can be produced by subjecting the dispersion obtained through the above-mentioned steps to a step of polymerizing the monomer by heating, and a step of washing. The thermally expandable microcapsules produced by this method have a high maximum foaming temperature, excellent heat resistance, and do not burst or shrink even when molded at high temperatures.

[0054] The method for producing thermally expandable microcapsules of the present invention includes a washing step. Examples of such washing steps include immersion washing, running water washing, and shower washing. Furthermore, methods that combine these with ultrasonic waves or vibrations can also be applied. Furthermore, the washing step can be performed in conjunction with a dehydration step to improve production efficiency. Specifically, the following methods can be used: After the slurry supplied by the compression dehydrator is turned into a wet cake, a predetermined amount of washing water (preferably ion-exchanged water) is supplied into the dehydrator and the mixture is squeezed again. The washing water is then supplied again and squeezed. This process is repeated several times. The amount and ratio of the slurry and washing water supplied to the dehydrator, as well as the number of washes, are important factors in removing inorganic salts such as sodium chloride and sodium sulfate. This process enables the removal of inorganic salts and prevents corrosion of equipment used in semiconductor applications and automotive component applications (molding applications). The amount of washing water in the washing step is preferably 2.5 to 5 times the volume of the polymerized slurry.

[0055] In the method for producing thermally expandable microcapsules of the present invention, a drying step is then carried out, which serves the purpose of volatilizing the liquid component and also adjusts the silicon dioxide content of the shell.

[0056] The drying step can be performed using methods such as natural drying, hot air drying (fluidized bed drying), and vacuum drying. The drying temperature is preferably 30° C. or higher, more preferably 32° C. or higher, and even more preferably 35° C. or higher, and is preferably 70° C. or lower, more preferably 68° C. or lower, and even more preferably 65° C. or lower. The drying time (total drying time) in the drying step is preferably 12 hours or longer, more preferably 13 hours or longer, and more preferably 14 hours or longer, and is preferably 20 hours or shorter, and more preferably 18 hours or shorter.

[0057] The drying step may be performed at a constant temperature, or by changing the drying temperature stepwise. When changing the drying temperature stepwise, the drying step may be performed multiple times. The number of drying steps is preferably 2 to 4, and more preferably 3 times (first drying step to third drying step). In this case, the average drying temperature in the first drying step is preferably 40°C or less, the average drying temperature in the second drying step is greater than 40°C but less than 50°C, and the average drying temperature in the third drying step is preferably greater than 50°C.

[0058] As the drying method, vacuum drying is particularly preferred. In this case, a method using a heated vacuum vibration dryer or the like can be mentioned. The vacuum value range in the vacuum drying is preferably -0.065 to -0.100 MPa, more preferably -0.070 to -0.095 MPa, and even more preferably -0.075 to -0.090 MPa. The vacuum value can be measured using a vacuum manometer or vacuum gauge.

[0059] A foamable resin composition obtained by adding a matrix resin such as a thermoplastic resin to the thermally expandable microcapsules of the present invention, or a masterbatch pellet can be obtained by mixing the thermally expandable microcapsules with a base resin such as a thermoplastic resin. Furthermore, a foamable resin composition obtained by adding a matrix resin such as a thermoplastic resin to the masterbatch pellets is added, and the mixture is molded using a molding method such as injection molding, and then the thermally expandable microcapsules are foamed by heating during molding, thereby producing a foam.

[0060] The foamable resin composition of the present invention preferably contains 0.1 to 10 parts by weight of thermally expandable microcapsules per 100 parts by weight of the matrix resin.

[0061] The foamable resin composition may also contain a chemical foaming agent. The chemical foaming agent is not particularly limited as long as it is powdery at room temperature, and any conventionally commonly used chemical foaming agent can be used. Chemical foaming agents are classified into organic and inorganic foaming agents, each of which is further classified into thermal decomposition and reactive types. Commonly used organic thermal decomposition foaming agents include azodicarbonamide (ADCA), N,N'-dinitropentamethylenetetramine (DPT), and 4,4'-oxybisbenzenesulfonylhydrazide (OBSH). Examples of inorganic thermal decomposition foaming agents include bicarbonates, carbonates, and combinations of bicarbonates and organic acid salts. It is preferable to use a thermal decomposition chemical foaming agent as the chemical foaming agent. The performance of a thermal decomposition chemical foaming agent is determined by its decomposition temperature, gas generation rate, and particle size.

[0062] The decomposition temperature of the chemical foaming agent is preferably 180 to 200°C. The decomposition temperature can be adjusted as needed by combining a urea-based or zinc-based foaming assistant with the chemical foaming agent. The gas generation rate of the chemical foaming agent is preferably 220 to 240 ml / g. The gas generation rate is the volume of gas generated when the chemical foaming agent decomposes. This gas becomes the gas inside the bubbles, and therefore affects the expansion ratio. Furthermore, the bubble diameter can be reduced by using the chemical foaming agent in combination with citrate or zinc oxide.

[0063] The chemical foaming agent is usually a powder, and the smaller the particle size, the greater the number of particles per unit weight. The greater the number of particles, the greater the number of bubbles generated. The preferred lower limit of the average particle size (median diameter) of the chemical foaming agent is 4 μm, and the preferred upper limit is 20 μm. By keeping the particle size within the above range, the resulting molded article will have an appropriate amount of bubbles, a sufficient expansion ratio, and an excellent appearance. The more preferred lower limit is 5 μm, and the more preferred upper limit is 10 μm.

[0064] The molding method for the foamed molded article is not particularly limited, and examples thereof include kneading molding, calendar molding, extrusion molding, injection molding, etc. In the case of injection molding, the process is not particularly limited, and examples thereof include the short-short method in which a resin material is partially placed in a mold and foamed, and the core-back method in which the mold is fully filled with the resin material and then opened to the desired foaming point.

[0065] According to the present invention, it is possible to produce thermally expandable microcapsules that can produce molded articles that have a high expansion ratio, are lightweight, and have excellent appearance, and to produce foamable resin compositions and foamed articles using the thermally expandable microcapsules. Furthermore, the thermally expandable microcapsules of the present invention can be suitably used in automotive parts, paints, adhesives, and inks.

[0066] The following examples will further illustrate the present invention, but the present invention is not limited to these examples.

[0067] Example 1 (Preparation of Thermally Expandable Microcapsules) 330 parts by weight of colloidal silica (average particle size 20 nm) with a solids content of 20% by weight, 12 parts by weight of polyvinylpyrrolidone, 1096 parts by weight of sodium chloride, and 0.85 parts by weight of sodium nitrite were added to 3300 parts by weight of ion-exchanged water and mixed to prepare an aqueous dispersion medium. Alkaline colloidal silica was used as the colloidal silica (aqueous dispersion). 390 parts by weight (28% by weight) of acrylonitrile, 585 parts by weight (42% by weight) of methacrylonitrile, 420 parts by weight (29.9% by weight) of methacrylic acid, and 1.4 parts by weight (0.1% by weight) of methyl methacrylate were mixed to prepare a homogeneous monomer composition solution (the percentage in parentheses is the weight percentage of the total monomer composition). To this, 11.1 parts by weight of 2,2'-azobis(isobutyronitrile), 8.3 parts by weight of 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile), and 440 parts by weight of n-pentane were added and mixed in Tank 1. Next, an aqueous dispersion medium was charged into Tank 2, and the oily mixture from Tank 1 was added to Tank 2 and mixed to obtain a primary dispersion. At this time, the pH of the primary dispersion was 3.5 to 4.0. The obtained primary dispersion was passed through a static in-tube mixer (Static Mixer, manufactured by Fujikin Co., Ltd., Dispersion-kun) at a flow rate of 200 L / min and a pressure of 1.5 MPa. The passed liquid was charged into an autoclave. The element-type static disperser used had a pestle-shaped plate-shaped element with a thickness of 5 mm, an effective diameter of 15 mm, and a hole diameter of 2 mm, and had 78 holes so that adjacent plate-shaped elements of different types could at least partially face each other. The number of units consisting of a combination of the first element and the second element was set to 10 sets so that the fluid passed through the holes of each plate-like element. The atmosphere was then replaced with nitrogen, and the reaction was carried out for 15 hours at a reaction temperature of 60 ° C. The reaction pressure was 0.5 MPa, and the stirring was carried out at 200 rpm. 8000 L of the obtained polymerized slurry was then divided and fed to a compression dehydration device (Ishigaki Co., Ltd., filter press), and after dehydration, a predetermined amount of washing water was fed to the dehydrator, and a washing process was carried out to obtain pre-drying thermally expandable microcapsules. In the washing process, 1000 L of washing water was used for 300 L of the polymerized slurry.

[0068] The obtained pre-dried thermally expandable microcapsules were vacuum-dried (total drying time: 12.5 hours, vacuum value: -0.085 MPa) using a heated vacuum vibration dryer (Chuo Kakoki Co., Ltd., VU type) to obtain thermally expandable microcapsules. Specifically, the vacuum drying was performed at set temperatures of 45, 50, and 55°C for 5.5 hours (first drying step) (with a temperature increase of 10°C / hr). Subsequently, the microcapsules were dried at set temperatures of 60 and 65°C for 1.5 hours (second drying step) (with a temperature increase of 10°C / hr). After the temperature increase was 5°C / hr, the microcapsules were dried at a set temperature of 70°C, an initial drying temperature of 43°C, and a final drying temperature of 60°C for 5.5 hours (third drying step). The set temperature refers to the jacket temperature of the dryer, and the drying time refers to the actual drying time. The drying temperatures and times at each set temperature are shown in Tables 2 and 3.

[0069] (Production of Foam Precursor) The formulation shown in Table 1 was mixed using a Henschel mixer (dried up at 120°C) to obtain a foamable resin composition. 300 g of the obtained foamable resin composition was heated and kneaded for 3 minutes using an 8-inch lab roll machine. The roll temperature was set to a temperature 30°C to 50°C below the foaming initiation temperature. Next, the kneaded roll sheet was used as the material and molded into a 1-2 mm thick, 150 mm long x 150 mm wide pressed sheet (foam precursor) using a press set at the same temperature as the roll. The pressing conditions were 3 minutes of preheating, 3 minutes of pressurization, and 3 minutes of cooling, with a surface pressure of 5-8 MPa during preheating and 20 MPa during pressurization and cooling.

[0070] (Examples 2 to 6, Comparative Examples 1 to 6) The obtained pre-drying thermally expandable microcapsules were subjected to the drying and washing processes under the drying conditions (first to third drying processes, total drying time, vacuum value) and washing conditions (amount of washing water per 300 L of polymerized slurry) shown in Tables 2 and 3, respectively, in the same manner as in Example 1, to obtain thermally expandable microcapsules and foam precursors.

[0071] Comparative Example 7 (Preparation of Thermally Expandable Microcapsules) 330 parts by weight of colloidal silica (average particle size 20 nm) with a solids content of 20% by weight, 12 parts by weight of polyvinylpyrrolidone, 1,096 parts by weight of sodium chloride, and 0.85 parts by weight of sodium nitrite were added to 3,300 parts by weight of ion-exchanged water and mixed to prepare an aqueous dispersion medium. Note that alkaline colloidal silica was used as the colloidal silica (aqueous dispersion). 978 parts by weight (70% by weight) of acrylonitrile and 418 parts by weight (30% by weight) of methacrylonitrile were mixed to prepare a homogeneous monomer composition (the percentage in parentheses is the weight percentage of the total monomer composition). To this, 11.1 parts by weight of 2,2'-azobis(isobutyronitrile), 8.3 parts by weight of 2,2'-azobis(2,4-dimethylvaleronitrile), and 440 parts by weight of n-pentane were added and mixed in Tank 1. Next, the aqueous dispersion medium was charged into Tank 2, and the oily mixture from Tank 1 was added to Tank 2 and mixed to obtain a primary dispersion. At this time, the pH of the primary dispersion was 3.5 to 4.0. The resulting primary dispersion was passed through a static in-tube mixer (Static Mixer, manufactured by Fujikin Co., Ltd., Dispersion-kun) at a flow rate of 200 L / min and a pressure of 1.5 MPa. The passed liquid was then placed in an autoclave. The element-type static disperser used had a pestle-shaped plate-shaped element with a thickness of 5 mm, an effective diameter of 15 mm, and a hole diameter of 2 mm. It had 78 holes, allowing at least a portion of adjacent plate-shaped elements of different types to face each other. The number of units consisting of a combination of a first element and a second element was set to 10, so that the fluid passed through the holes of each plate-shaped element. The atmosphere was then purged with nitrogen, and the reaction was carried out at a reaction temperature of 60°C for 15 hours. The reaction pressure was 0.5 MPa, and the stirring speed was 200 rpm. Thereafter, 8000 L of the obtained polymerization slurry was divided and fed to a compression dehydration device (Ishigaki Co., Ltd., filter press), and after dehydration, a predetermined amount of washing water was fed to the dehydrator to perform a washing process, thereby obtaining pre-drying thermally expandable microcapsules. Note that in the washing process, washing was performed using 1000 L of washing water for 300 L of the polymerization slurry.

[0072] The obtained pre-drying thermally expandable microcapsules were subjected to the drying and washing processes under the drying conditions (first to third drying processes, total drying time, vacuum value) and washing conditions (amount of washing water per 300 L of polymerized slurry) shown in Tables 2 and 3, respectively, in the same manner as in Example 1, to obtain thermally expandable microcapsules and foam precursors.

[0073]

[0074] (1) Evaluation of thermally expandable microcapsules (1-1) Foaming initiation temperature, maximum foaming temperature, and maximum displacement The foaming initiation temperature (Ts), maximum displacement (Dmax), and maximum foaming temperature (Tmax) were measured using a thermomechanical analyzer (TMA) (TMA2940, manufactured by TA Instruments). Specifically, 25 μg of sample was placed in an aluminum container with a diameter of 7 mm and a depth of 1 mm, and heated from 80°C to 220°C at a heating rate of 5°C / min with a force of 0.1 N applied from above. The displacement in the vertical direction of the measuring probe was measured, and the temperature at which the displacement began to increase was defined as the foaming initiation temperature, the maximum value of the displacement as the maximum displacement, and the temperature at the maximum displacement as the maximum foaming temperature.

[0075] (1-2) Average particle size (volume average particle size) and average circularity The volume average particle size was measured using a particle size distribution diameter measuring instrument (LA-950, manufactured by HORIBA). The average circularity was measured by the above-mentioned method using an image obtained during wet measurement using a Mastersizer 3000 (manufactured by Malvern Panalytical).

[0076] (1-3) Volatile content (1 hour at 70°C, 20 minutes at 210°C) Approximately 10 g of thermally expandable microcapsules was weighed into an aluminum cup and heated at 70°C for 1 hour. After being allowed to cool to 40°C or below in a desiccator, the microcapsules were weighed. The volatile content was calculated using the following formula. The volatile content after heating at 210°C for 20 minutes was also measured in the same manner. The ratio of the volatile content after standing at 70°C for 1 hour to the volatile content after standing at 210°C for 20 minutes was also calculated ([volatile content after standing at 70°C for 1 hour / volatile content after standing at 210°C for 20 minutes] x 100). V = [(B - C) / (B - A)] x 100 V: Volatile content (wt%) A: Weight of aluminum cup (g) B: Mass of aluminum cup containing sample (g) C: Weight of aluminum cup containing sample after heating and cooling (g)

[0077] (1-4) Weight gain rate The volatile content before and after leaving the sample standing at a temperature of 50°C and a humidity of 80% or higher for 12 hours was measured in the same manner as in (1-3) "70°C, 1 hour," and the weight gain rate was calculated using the following formula: D = (E - F) / E x 100 D: Weight gain rate E: Volatile content after leaving the sample standing at a temperature of 50°C and a humidity of 80% or higher for 12 hours F: Volatile content before leaving the sample standing at a temperature of 50°C and a humidity of 80% or higher for 12 hours

[0078] (1-5) SiO ２ A small amount (approximately 0.01 g) of the thermally expandable microcapsules was collected and analyzed by an EDS energy dispersive X-ray analyzer (JSM-6510, manufactured by JEOL Ltd.) to determine the SiO ２ The content (silicon dioxide content in the thermally expandable microcapsules) was measured.

[0079] (1-6) Degree of aggregation of thermally expandable microcapsules during expansion 0.05 g of thermally expandable microcapsules were weighed and placed in an aluminum cup, and the degree of aggregation of the expanded thermally expandable microcapsules after standing at 200°C for 1.5 minutes was confirmed using a microscope. Note that the case where no aggregation was observed was rated "absent," the case where slight aggregation was observed was rated "present," and the case where most of the thermally expandable microcapsules were aggregated was rated "strong aggregation."

[0080] (1-7) Hopper fluidity Using a container for measuring bulk specific gravity as described in JIS K7370, the obtained thermally expandable microcapsules were poured into the top of the hopper, and then allowed to fall under their own weight, and the number of seconds until the hopper was empty (when all the thermally expandable microcapsules had fallen) was measured.

[0081] (2) Evaluation of Foam (Molded Product) (2-1) Appearance (Number of Dimples) The obtained press sheet (foam precursor) was placed on a Teflon (registered trademark) sheet and heated in a gear oven at 200°C for 10 minutes to foam the thermally expandable microcapsules. After 10 minutes, the foam sample was removed from the gear oven and allowed to cool for 30 minutes or more. The appearance of the foam sample after cooling was observed, and the number of dents was counted from the surface irregularities. Note that, for the foam precursor obtained in Comparative Example 7, the density was 1 g / cm ３ Since the value exceeded 100%, no external observation was performed.

[0082] (2-2) Density Measurement The density of the resulting foam (density after foaming) was measured according to JIS K-7112 Method A (underwater displacement method).

[0083]

[0084]

[0085] According to the present invention, it is possible to provide a thermally expandable microcapsule that can be used to produce a molded article that has a high expansion ratio, is lightweight, and has an excellent appearance, as well as a foamable resin composition and a foam that use the thermally expandable microcapsule.

Claims

1. A thermally expandable microcapsule having a polymer shell and a volatile expanding agent encapsulated therein as a core agent, the shell comprises a polymer obtained by polymerizing a monomer composition containing a carbonyl group-containing monomer, and silicon dioxide; A thermally expandable microcapsule having a volatile content of 0.55% by weight or more and 2% by weight or less when left to stand at 70°C for 1 hour.

2. 2. The thermally expandable microcapsule according to claim 1, which has a volatile content of 20% by weight or more and 30% by weight or less when allowed to stand at a temperature of 210° C. for 20 minutes.

3. 2. The thermally expandable microcapsule according to claim 1, wherein the ratio of volatile matter when left standing at a temperature of 70°C for 1 hour to the volatile matter when left standing at a temperature of 210°C for 20 minutes is 8% or less.

4. 4. The thermally expandable microcapsule according to claim 1, which has a weight increase rate of 60% by weight or less when left to stand for 12 hours at a temperature of 50° C. and a humidity of 80% or more.

5. The thermally expandable microcapsule according to any one of claims 1 to 3, having an average particle size of 10 µm or more and 45 µm or less.

6. The thermally expandable microcapsule according to any one of claims 1 to 3, having a maximum foaming temperature (Tmax) of 180°C or more and 225°C or less.

7. A foamable resin composition comprising the thermally expandable microcapsules according to any one of claims 1 to 3 and a thermoplastic resin.

8. A foam obtainable by using the foamable resin composition according to claim 7.