Thermally expandable microcapsules

Abstract

The purpose of this invention is to provide a thermally expandable microcapsule that combines excellent heat resistance and expansion ratio, and is also suitable for use in injection molding and other applications where strong shear forces are applied. The thermally expandable microcapsule has a shell made of thermoplastic resin and microparticles composed of a foaming agent and thermoplastic resin encapsulated within the shell. The particle size of the thermally expandable microcapsule is 10 μm or more and 50 μm or less, and the cross-sectional area of ​​the microparticles relative to the total cross-sectional area of ​​the shell and the microparticles is 5% or more and 60% or less for a cross-section obtained by slicing the thermally expandable microcapsule.

Description

Technical Field

[0001] This utility model relates to a thermally expandable microcapsule. Background Technology

[0002] Thermally expandable microcapsules are used in a wide range of applications as design enhancers and lightweight agents, and can also be used in coatings aimed at lightweighting, such as foaming inks and wallpapers.

[0003] As such thermally expandable microcapsules, there are known thermally expandable microcapsules in which a volatile expanding agent that becomes gaseous at a temperature below the softening point of the shell polymer is encapsulated in a thermoplastic shell (outer shell) polymer. For example, Patent Document 1 discloses a thermally expandable microsphere comprising an outer shell made of thermoplastic resin and a non-fluorinated foaming agent encapsulated in the outer shell and having a boiling point below the softening point of the thermoplastic resin, with an average particle size of 1 to 100 μm and an encapsulation rate of 5 to 30% by weight of the non-fluorinated foaming agent.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: International Publication No. WO2007 / 046273 Utility Model Content

[0007] The problem to be solved by the utility model

[0008] However, when using conventional thermally expandable microcapsules in injection molding where strong shear forces are applied, a problem arises during the melt-mixing process within the barrel: insufficient heat resistance and strength cause the microcapsules to rupture, resulting in a poorly foamed molded product. While methods have been implemented to highly cross-link the polymer forming the shell of the thermally expandable microcapsules, these microcapsules suffer from a low foaming ratio.

[0009] The purpose of this invention is to provide a thermally expandable microcapsule that can balance excellent heat resistance and foaming ratio, and is also suitable for use in injection molding and other processes where strong shear forces are applied.

[0010] Solution for solving the problem

[0011] The first aspect of this utility model is a thermally expandable microcapsule, which has a shell made of thermoplastic resin and microparticles made of a foaming agent and thermoplastic resin encapsulated within the shell. The microcapsule has a particle size of 10 μm or more and 50 μm or less, and the cross-sectional area of ​​the microparticles relative to the total cross-sectional area of ​​the shell and the cross-sectional area of ​​the microparticles is 5% or more and 60% or less for a cross-section obtained by cutting the microcapsule.

[0012] In the second aspect of this utility model, based on the thermally expandable microcapsule described in the first aspect, the ratio of the cross-sectional area of ​​the microparticle to the total cross-sectional area of ​​the outer shell and the cross-sectional area of ​​the microparticle is 10% or more and 50% or less.

[0013] In the third aspect of this utility model, based on the thermally expandable microcapsules described in the first or second aspect, the ratio of the cross-sectional area of ​​the microparticles to the total cross-sectional area of ​​the outer shell and the cross-sectional area of ​​the microparticles is 20% or more and 30% or less.

[0014] In the fourth aspect of this utility model, based on the thermally expandable microcapsules described in any of the first to third aspects, the cross-sectional area of ​​the outer shell is 100 μm. 2 Above and 900μm 2 the following.

[0015] In the fifth aspect of this utility model, based on the thermally expandable microcapsules described in any of the first to fourth aspects, the cross-sectional area of ​​the outer shell is 200 μm. 2 Above and 800μm 2 the following.

[0016] In the sixth aspect of this utility model, based on the thermally expandable microcapsules described in any one of aspects 1 to 5, the cross-sectional area of ​​the outer shell is 300 μm. 2 Above and 600μm 2 the following.

[0017] According to the seventh aspect of this utility model, based on the thermally expandable microcapsule described in any one of the first to sixth aspects, an inorganic layer with a thickness of 0.01 μm or more and 3 μm or less is provided on the outer side of the outer shell.

[0018] According to the eighth aspect of this utility model, based on the thermally expandable microcapsule described in any one of the first to seventh aspects, an inorganic layer with a thickness of 0.05 μm or more and 2 μm or less is provided on the outer side of the outer shell.

[0019] According to the ninth aspect of this utility model, based on the thermally expandable microcapsule described in any one of the first to eighth aspects, an inorganic layer with a thickness of 0.1 μm or more and 1 μm or less is provided on the outer side of the outer shell.

[0020] According to the tenth aspect of this utility model, based on the thermally expandable microcapsules described in any one of the first to ninth aspects, the particle size of the microparticles is 2 μm or more and 10 μm or less.

[0021] According to the 11th aspect of this utility model, based on the thermally expandable microcapsules described in any one of the 1st to 10th aspects, the microcapsules contain 2 or more but less than 10 of the aforementioned microparticles.

[0022] The above-mentioned thermally expandable microcapsules are described in detail below.

[0023] The applicant conducted in-depth research and found that by keeping the particle size within a specified range and encapsulating thermoplastic resin microcapsules containing thermoplastic resin microparticles within the microcapsules, and keeping the ratio of the cross-sectional area of ​​the microparticles to the total cross-sectional area of ​​the outer shell and the cross-sectional area of ​​the microparticles within a specified range, it is possible to produce a thermoplastic microcapsule that can achieve both excellent heat resistance and foaming ratio, and is also suitable for use in injection molding and other processes where strong shear forces are applied.

[0024] exist Figure 1 The diagram shows a cross-sectional view of the aforementioned thermally expandable microcapsule. The aforementioned thermally expandable microcapsule has an outer shell 1 and a plurality of microparticles 2 enclosed within the outer shell 1.

[0025] In the aforementioned thermally expandable microcapsules, the cross-sectional area of ​​the microparticle 2 relative to the total cross-sectional area of ​​the outer shell 1 and the cross-sectional area of ​​the microparticle 2 is 5% or more and 60% or less.

[0026] The aforementioned thermally expandable microcapsules have an outer shell made of thermoplastic resin and microparticles composed of a foaming agent and thermoplastic resin encapsulated within the outer shell. For a cross-section obtained by slicing the thermally expandable microcapsules, the ratio of the cross-sectional area of ​​the microparticles to the total cross-sectional area of ​​the outer shell and the microparticles is 5% or more and 60% or less. By setting it to 5% or more, the thermally expandable microcapsules exhibit good foaming properties in injection molding and other processes where strong shear forces are applied. By setting it to 60% or less, the thermally expandable microcapsules achieve an excellent foaming ratio.

[0027] The ratio of the cross-sectional area of ​​the aforementioned particles to the total cross-sectional area of ​​the shell and the cross-sectional area of ​​the particles is preferably 10% or more, more preferably 20% or more, and preferably 50% or less, more preferably 30% or less.

[0028] The ratio of the cross-sectional area of ​​the aforementioned particles to the total cross-sectional area of ​​the shell and the particles refers to the value obtained by measuring the cross-sectional area of ​​the shell and the particles based on the image analysis of the microscopic photograph obtained by cutting through the center of the thermally expandable microcapsule, and then calculating the ratio of the cross-sectional area of ​​the particles to the total cross-sectional area of ​​the shell and the particles based on this measurement.

[0029] It should be noted that the above values ​​are the average of those calculated from multiple thermally expandable microcapsules.

[0030] In the aforementioned thermally expandable microcapsules, the "cross-sectional area of ​​the outer shell," "cross-sectional area of ​​the microparticles," and "ratio of the cross-sectional area of ​​the microparticles to the total cross-sectional area of ​​the outer shell and the cross-sectional area of ​​the microparticles" can be adjusted not only by the composition of the outer shell, foaming agent, microparticles, and inorganic layer, but also by the type and amount of polymerization initiator added during the manufacture of the aforementioned thermally expandable microcapsules and the polymerization temperature in the polymerization process.

[0031] The cross-sectional area of ​​the aforementioned outer shell is preferably 100 μm. 2 Above and 900μm 2 The following is an example of setting the micrometer to 100μm. 2 In summary, the thermally expandable microcapsules can withstand strong shear forces. (Setting the diameter to 900 μm...) 2 The following thermally expandable microcapsules can achieve excellent foaming ratio.

[0032] The cross-sectional area of ​​the aforementioned outer shell is more preferably 200 μm. 2 The above is further preferred to be 300μm. 2 The above, and more preferably 800μm 2 Hereinafter, 600μm is further preferred. 2 the following.

[0033] The thickness of the aforementioned outer shell is preferably 2 μm or more and 10 μm or less. By setting it to 2 μm or more, the thermally expandable microcapsules can withstand strong shear forces. By setting it to 10 μm or less, the thermally expandable microcapsules can achieve excellent foaming ratios.

[0034] The thickness of the aforementioned outer shell is more preferably 3 μm or more, even more preferably 4 μm or more, and more preferably 8 μm or less, even more preferably 7 μm or less.

[0035] Regarding the thickness of the aforementioned shell, it can be determined by analyzing the cross-section obtained from cutting the thermally expandable microcapsule using image analysis from a microscope photograph.

[0036] It should be noted that the above values ​​are the average of those calculated from multiple thermally expandable microcapsules.

[0037] Preferably, the outer side of the aforementioned outer shell has an inorganic layer with a thickness of 0.01 μm or more and 3 μm or less.

[0038] By having the aforementioned inorganic layer, it is possible to suppress the fusion of thermally expanding microcapsules with each other during molding.

[0039] Furthermore, it is more preferable to have an inorganic layer with a thickness of 0.05 μm or more and 2 μm or less on the outer side of the aforementioned outer shell, and even more preferably, it is preferable to have an inorganic layer with a thickness of 0.1 μm or more and 1 μm or less on the outer side of the aforementioned outer shell.

[0040] Regarding the thickness of the aforementioned inorganic layer, it can be determined by analyzing the cross-section obtained from cutting the thermally expandable microcapsules, based on the image analysis of the microscope photograph.

[0041] It should be noted that the above values ​​are the average of those calculated from multiple thermally expandable microcapsules.

[0042] The particle size of the aforementioned thermally expandable microcapsules is greater than 10 μm and less than 50 μm.

[0043] Because the particle size is 10 μm or more, an excellent foaming ratio can be obtained; and because the particle size is 50 μm or less, the surface of the resulting foamed molded article is smooth. The particle size is preferably 15 μm or more and 45 μm or less, more preferably 20 μm or more and 40 μm or less.

[0044] It should be noted that the particle size of the aforementioned thermally expandable microcapsules refers to the value obtained by measuring the particle size based on the image analysis of a microscopic photograph of a cross-section obtained by cutting through the center of the thermally expandable microcapsule.

[0045] It should be noted that the above values ​​are the average of those calculated from multiple thermally expandable microcapsules.

[0046] For the aforementioned thermally expandable microcapsules, the ratio of the thickness of the outer shell to half of the particle size [thickness of outer shell / (particle size / 2)] is preferably 0.2 or more and 0.5 or less. By setting it within the above range, the thermally expandable microcapsules can achieve excellent foaming ratio.

[0047] The thickness of the outer shell is more preferably 0.3 or more, and more preferably 0.4 or less, relative to half the particle size.

[0048] For the aforementioned thermally expandable microcapsules, the ratio of the thickness of the inorganic layer to the particle size (thickness of the inorganic layer / particle size) is preferably 0.01 or more and 0.1 or less. Setting it to 0.01 or more ensures good thermal weldability. Setting it to 0.1 or less ensures good foaming properties.

[0049] The ratio of the thickness of the inorganic layer to the particle size is more preferably 0.05 or more, and more preferably 0.09 or less.

[0050] The cross-sectional area of ​​the aforementioned particles is preferably 15 μm. 2 Above and 650μm2 The following is an example of setting the micrometer to 15μm. 2 The above ensures good durability. Setting it to 650μm... 2 The following steps ensure good foaming properties.

[0051] The cross-sectional area of ​​the aforementioned particles is more preferably 50 μm. 2 The above is further preferred to be 100μm. 2 The above, and more preferably 400μm 2 Hereinafter, 300μm is further preferred. 2 the following.

[0052] The particle size of the above-mentioned microparticles is preferably 2 μm or more and 10 μm or less.

[0053] Since the particle size is 2 μm or more, good durability is achieved; since the particle size is 10 μm or less, good foaming properties are achieved. More preferably, the particle size is 3 μm or more and 8 μm or less, and even more preferably, 4 μm or more and 6 μm or less.

[0054] Regarding the particle size of the aforementioned microparticles, it can be determined by analyzing the cross-section obtained from cutting the thermally expandable microcapsules, based on the image analysis of the microscope photograph.

[0055] It should be noted that the above values ​​are the average of those calculated from multiple thermally expandable microcapsules.

[0056] In the aforementioned thermally expandable microcapsules, the thickness of the outer shell, the thickness of the inorganic layer, the particle size of the thermally expandable microcapsule, the thickness of the outer shell / (particle size / 2), the thickness of the inorganic layer / particle size, and the particle size of the microparticles can be adjusted not only by the composition of the outer shell, foaming agent, microparticles, and inorganic layer, but also by the type and amount of polymerization initiator added during the manufacture of the aforementioned thermally expandable microcapsules and the polymerization temperature in the polymerization process.

[0057] The aforementioned thermally expandable microcapsules have a shell made of thermoplastic resin.

[0058] As the aforementioned thermoplastic resin, polymers of (meth)acrylonitrile and copolymers containing (meth)acrylonitrile are suitable, for example. In the case of copolymers, other monomers (comonomers) can be monomers such as halogenated vinylidene, vinylidene halide, styrene monomers, (meth)acrylate monomers, vinyl acetate, butadiene, vinylpyridine, chloroprene, etc.

[0059] The thermoplastic resin described above is preferably a polymer formed by polymerizing a monomer composition containing a nitrile monomer (I) and a carboxyl monomer (II).

[0060] It should be noted that the so-called monomer composition refers to a composition containing raw material monomers, and the content of the monomer composition is synonymous with the content of structural units in thermoplastic resins.

[0061] That is, the above-mentioned thermoplastic resin preferably has structural units derived from nitrile monomers (I) and structural units derived from carboxyl-containing monomers (II).

[0062] The aforementioned nitrile monomers (I) are not particularly limited, and examples include acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, α-ethoxyacrylonitrile, fumaric acid, or mixtures thereof. It is preferred that they contain acrylonitrile, and particularly preferred that they contain both acrylonitrile and methacrylonitrile. They can be used alone or in combination of two or more.

[0063] The content of the structural units derived from the nitrile monomer (I) in the aforementioned thermoplastic resin is preferably 45% by weight or more, and more preferably 95% by weight or less. Setting it to 45% by weight or more improves the gas barrier properties of the shell, thereby increasing the foaming ratio. Setting it to 95% by weight or less improves heat resistance. More preferably, the content is 50% by weight or more, and more preferably 90% by weight or less.

[0064] In the structural units derived from the nitrile monomer (I), the weight ratio (acrylonitrile / methacrylonitrile) of the structural units derived from acrylonitrile to the structural units derived from methacrylonitrile is preferably 1.05 or more. By setting it to 1.05 or more, the heat resistance and gas barrier properties of the obtained thermally expandable microcapsules can be improved. The weight ratio is more preferably 1.1 or more.

[0065] As the aforementioned carboxyl-containing monomer (II), for example, a free radical polymerizable unsaturated carboxylic acid monomer having a carboxyl group and having 3 to 8 carbon atoms can be used.

[0066] Specifically, examples include unsaturated monocarboxylic acids, monoesters of unsaturated dicarboxylic acids, and their derivatives, which can be used individually or in combination.

[0067] Examples of unsaturated carboxylic acids include: acrylic acid, methacrylic acid, ethylacrylic acid, crotonic acid, cinnamic acid, and other unsaturated monocarboxylic acids; maleic acid, itaconic acid, fumaric acid, citraconic acid, chloromaleic acid, and other unsaturated dicarboxylic acids.

[0068] Examples of monoesters of the aforementioned unsaturated dicarboxylic acids include monomethyl maleate, monoethyl maleate, monobutyl maleate, monomethyl fumarate, monoethyl fumarate, monomethyl itaconic acid, monoethyl itaconic acid, and monobutyl itaconic acid.

[0069] Among them, acrylic acid, methacrylic acid, maleic acid, maleic anhydride, and itaconic acid are preferred, with methacrylic acid being more preferred.

[0070] The content of the structural units having the aforementioned carboxyl groups in the thermoplastic resin is preferably 5% by weight or more, and more preferably 25% by weight or less. Setting it to 5% by weight or more improves the heat resistance of the obtained thermally expandable microcapsules. Furthermore, setting it to 25% by weight or less improves the powder flowability of the obtained thermally expandable microcapsules. More preferably, the content is 10% by weight or more, and more preferably 20% by weight or less.

[0071] In the above-mentioned thermoplastic resin, the weight ratio of the structural unit from methacrylonitrile to the structural unit having a carboxyl group (methacrylonitrile / carboxyl-containing monomer (II)) is preferably 0.8 or more.

[0072] The aforementioned thermoplastic resin may contain structural units derived from polymeric monomers having two or more double bonds within the molecule, but preferably does not. Because the polymer does not contain these structural units, it exhibits a high foaming ratio even during molding in high-temperature regions.

[0073] As polymerizable monomers, monomers having two or more free radical polymerizable double bonds can be cited as examples. Specific examples include: divinylbenzene, di(meth)acrylate, (meth)acrylate with more than three functions, etc.

[0074] Examples of the aforementioned 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, glycerol di(meth)acrylate, trimethylolpropane di(meth)acrylate, and dihydroxymethyl-tricyclodecane di(meth)acrylate. Furthermore, di(meth)acrylates of polyethylene glycol with a weight-average molecular weight of 200 to 600 can also be used.

[0075] Examples of trifunctional (meth)acrylates include: trimethylolpropane tri(meth)acrylate, ethylene oxide-modified trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, and triallyl formaldehyde tri(meth)acrylate. Examples of quadrifunctional or higher (meth)acrylates include pentaerythritol tetra(meth)acrylate and dipentaerythritol hexa(meth)acrylate.

[0076] The aforementioned thermoplastic resin may also include structural units derived from nitrile monomers (I) and structural units derived from other monomers other than structural units having carboxyl groups.

[0077] Other examples of the monomers mentioned above include vinyl monomers such as (meth)acrylates, vinyl chloride, vinylidene chloride, vinyl acetate, and styrene. They can be used alone or in combination of two or more.

[0078] In addition, (meth)acrylates are preferred, and particularly preferred are alkyl methacrylates such as methyl methacrylate, ethyl methacrylate, and n-butyl methacrylate, alkyl acrylates such as methyl acrylate, ethyl acrylate, and n-butyl acrylate, or methacrylates containing alicyclic, aromatic, or heterocyclic rings such as cyclohexyl methacrylate, benzyl methacrylate, and isobornyl methacrylate.

[0079] The content of the structural units derived from other monomers in the aforementioned thermoplastic resin is preferably 0% by weight or more, more preferably 1% by weight or more, and preferably 15% by weight or less, more preferably 13% by weight or less. By setting it within the above range, the dispersibility of the composition using thermally expandable microcapsules can be improved, and the gas barrier properties of the capsule wall can be improved, thereby improving thermal expansion properties.

[0080] To polymerize the above monomers, a polymerization initiator is added to the above monomer composition.

[0081] As polymerization initiators, dialkyl peroxides, diacyl peroxides, peroxide esters, peroxydicarbonates, azo compounds, etc., are suitable for use.

[0082] Specific examples include: dialkyl peroxides such as methyl ethyl peroxide, di-tert-butyl peroxide, and diisopropylbenzene peroxide; diacyl peroxides such as isobutyl peroxide, benzoyl peroxide, 2,4-dichlorobenzoyl peroxide, and bis(3,5,5-trimethylhexanoyl) peroxide.

[0083] Other examples include: tert-butyl peroxypentanoate, tert-hexyl peroxypentanoate, tert-butyl peroxyneodecanate, tert-hexyl peroxyneodecanate, 1-cyclohexyl-1-methylethyl peroxyneodecanate, and 1,1,3,3-tetramethylbutyl peroxyneodecanate.

[0084] Other examples include: cumene peroxynedecanoate, diisopropylbenzene (α,α-bis-neodecanoyl peroxy)diisopropylbenzene, bis(4-tert-butylcyclohexyl)dicarbonate peroxide, di-n-propyl dicarbonate peroxide, diisopropyl dicarbonate peroxide, etc.

[0085] In addition, examples include: di(2-ethylethyl peroxide) dicarbonate, dimethoxybutyl peroxide dicarbonate, di(3-methyl-3-methoxybutyl peroxide) dicarbonate, and other peroxide dicarbonates.

[0086] Especially preferred are azo compounds such as 2,2'-azobisisobutyronitrile, 2,2'-azobis(4-methoxy-2,4-dimethylpentanitrile, 2,2'-azobis(2,4-dimethylpentanitrile), and 1,1'-azobis(1-cyclohexanenitrile).

[0087] The addition amount of the polymerization initiator relative to the total amount (100 parts by weight) of the monomers is preferably 0.7 parts by weight or more, and more preferably 3.5 parts by weight or less. By setting it to the above range, in addition to the "cross-sectional area of ​​the shell", "cross-sectional area of ​​the particles", and "ratio of the cross-sectional area of ​​the particles to the total cross-sectional area of ​​the shell and the cross-sectional area of ​​the particles", the shapes of the thermally expandable microcapsules can be adjusted to a specified range. The addition amount is more preferably 0.8 parts by weight or more, and more preferably 3.0 parts by weight or less.

[0088] The aforementioned outer shell may also contain a metal cation salt. By containing a metal cation salt in the outer shell, when the copolymer constituting the outer shell contains carboxyl groups, the metal cations from the metal cation salt react with the carboxyl groups, causing ionic cross-linking of the copolymer. This improves heat resistance, enabling the production of thermally expandable microcapsules that do not rupture or shrink over long periods in high-temperature regions. Furthermore, since the elastic modulus of the outer shell does not easily decrease even in high-temperature regions, the thermally expandable microcapsules will not rupture or shrink even under molding processes such as injection molding where strong shear forces are applied.

[0089] It should be noted that the aforementioned ionic crosslinking means crosslinking with the free carboxyl groups present as side chains of the copolymer. It should also be noted that the number of carboxyl groups in each monovalent metal cation varies depending on the type of metal.

[0090] The metal cations mentioned above are not particularly limited as long as they react with the carboxyl groups of the copolymer to cause ionic crosslinking of the copolymer. Examples include ions of Li, Na, K, Zn, Mg, Ca, Ba, Sr, Mn, Al, Ti, Ru, Fe, Ni, Cu, Cs, Sn, Cr, Pb, etc. They can be used alone or in combination of two or more. Among them, Ca, Zn, and Al ions are preferred, and Zn ions are particularly preferred.

[0091] It should be noted that there is no particular limitation on the combination of two or more of the above-mentioned metal cations, but it is preferable to use alkali metal ions and metal cations other than the alkali metals mentioned above. By having ions containing the alkali metals mentioned above, functional groups such as carboxyl groups are activated, which can promote the reaction between metal cations other than the alkali metals mentioned above and the carboxyl groups present in the copolymer.

[0092] Examples of alkali metals mentioned above include Na, K, and Li.

[0093] The content of the aforementioned metal cation salt in the outer shell is preferably 0.5% by weight or more, and more preferably 10% by weight or less. By setting it within the above range, heat resistance can be improved. The content is more preferably 0.8% by weight or more, and more preferably 8% by weight or less.

[0094] The inorganic layer formed on the outer side of the aforementioned shell is not particularly limited as long as it is composed of inorganic compounds, but is preferably selected from at least one of the group consisting of Si-based compounds and Mg-based compounds.

[0095] By having the aforementioned inorganic layer, it is possible to suppress the fusion of thermally expanding microcapsules with each other during molding.

[0096] The preferred Si-based and Mg-based compounds are oxides, hydroxides, carbonates, or bicarbonates containing silicon and magnesium.

[0097] These Si-based and Mg-based compounds can be used alone or in combination of two or more.

[0098] In addition to colloidal silica and silica sol, other examples of Si-based compounds include No. 3 water glass, sodium orthosilicate, and sodium metasilicate. Colloidal silica is preferred.

[0099] Examples of the aforementioned Mg-based compounds include magnesium oxide, magnesium hydroxide, magnesium hydroxide, hydrotalcite, dihydrotalcite, magnesium carbonate, basic magnesium carbonate, calcium magnesium carbonate, magnesium phosphate, magnesium hydrogen phosphate, magnesium pyrophosphate, and magnesium borate. Among these, magnesium hydroxide is preferred.

[0100] In addition to the aforementioned inorganic compounds, calcium phosphate, aluminum hydroxide, ferric hydroxide, barium sulfate, calcium sulfate, sodium sulfate, calcium oxalate, calcium carbonate, and barium carbonate can also be added, for example. Furthermore, inorganic salts such as sodium chloride and sodium sulfate, alkali metal salts of nitrite, stannous chloride, stannous chloride, and potassium dichromate can also be added as needed.

[0101] The aforementioned outer shell may further contain stabilizers, ultraviolet absorbers, antioxidants, antistatic agents, flame retardants, silane coupling agents, pigments, etc., as needed.

[0102] The aforementioned thermally expandable microcapsules contain a foaming agent within the aforementioned outer shell as a core agent.

[0103] The aforementioned foaming agent is a gaseous substance that becomes gaseous at a temperature below the softening point of the polymer constituting the outer shell, and is suitable as a low-boiling-point organic solvent.

[0104] Examples of volatile expanding agents include: ethane, ethylene, propane, propylene, n-butane, isobutane, butene, isobutene, n-pentane, isopentane, neopentane, n-hexane, heptane, petroleum ether, isooctane, octane, decane, isododecane, dodecane, hexadecane, and other low molecular weight hydrocarbons.

[0105] In addition, examples include: chlorofluorocarbons such as CCl3F, CCl2F2, CClF3, and CClF2-CClF2; and tetraalkylsilanes such as tetramethylsilane, trimethylethylsilane, trimethylisopropylsilane, and trimethyln-propylsilane. Among these, isobutane, n-butane, n-pentane, isopentane, n-hexane, isooctane, isododecane, and mixtures thereof are preferred. These volatile expanding agents can be used alone or in combination of two or more.

[0106] In addition, thermally decomposable compounds that decompose upon heating and become gaseous can be used as volatile expanding agents.

[0107] In the aforementioned thermally expandable microcapsules, the maximum expansion temperature can be increased by using high-boiling-point hydrocarbons with 8 or more carbon atoms, and the foaming ratio can be increased by using low-boiling-point hydrocarbons with 5 or fewer carbon atoms, thereby enabling foaming to begin rapidly.

[0108] In addition, thermally decomposable compounds that decompose upon heating and become gaseous can be used as foaming agents.

[0109] The preferred lower limit of the maximum foaming temperature (Tmax) of the aforementioned thermally expandable microcapsules is 150°C, and the preferred upper limit is 230°C. By setting the maximum foaming temperature to 150°C or higher, the heat resistance is increased, thus preventing the thermally expandable microcapsules from rupturing or shrinking during high-temperature regions and molding processes. Furthermore, foaming caused by shearing during masterbatch manufacturing can be prevented, thereby ensuring stable production of unfoamed masterbatch. A more preferred lower limit of the maximum foaming temperature is 170°C, and a more preferred upper limit is 220°C.

[0110] It should be noted that, 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) while the microcapsule is heated from room temperature and its diameter is measured.

[0111] The preferred lower limit of the foaming start temperature (Ts) of the above-mentioned thermally expandable microcapsules is 100°C, the preferred upper limit is 200°C, the more preferred lower limit is 110°C, and the more preferred upper limit is 190°C.

[0112] In addition, the preferred lower limit of the maximum displacement (Dmax) of the above-mentioned thermally expandable microcapsules, as determined by thermomechanical analysis, is 500 μm, and the preferred upper limit is 2000 μm.

[0113] It should be noted that the above maximum displacement refers to the value when the diameter of the specified amount of thermally expandable microcapsules reaches its maximum while the specified amount of thermally expandable microcapsules are heated from room temperature and their diameter is measured.

[0114] The preferred lower limit for the true specific gravity of the aforementioned thermally expandable microcapsules is 0.95 g / cm³. 3 If the true specific gravity is 0.95 g / cm³ 3 The above methods can produce molded products with high foaming properties.

[0115] The preferred lower limit for the above-mentioned true specific gravity is 1.0 g / cm³. 3 The preferred upper limit is 1.10 g / cm³. 3 .

[0116] The aforementioned true specific gravity refers to the specific gravity of the raw material only, excluding the pores, and can be measured, for example, by inserting a specified amount of thermally expandable microcapsules into a dry automatic density meter.

[0117] There are no particular limitations on the method for manufacturing the above-mentioned thermally expandable microcapsules. For example, it can be manufactured by performing the following steps: a step of preparing an aqueous dispersion medium; a step of dispersing an oily mixture containing a monomer composition, a volatile expanding agent, a metal cation salt, etc., in the aqueous dispersion medium; and a step of polymerizing the above-mentioned monomer composition.

[0118] As the above-mentioned monomer composition, monomer compositions containing the above-mentioned nitrile monomer (I), carboxyl monomer (II), and other monomers can be used.

[0119] In manufacturing the aforementioned thermally expandable microcapsules, the first step is to prepare an aqueous dispersion medium. Specifically, for example, an aqueous dispersion medium containing silica is prepared by adding a dispersion stabilizer containing water and silica, along with any necessary auxiliary stabilizers, to a polymerization reactor. Additionally, alkali metal salts of nitrite, stannous chloride, stannous chloride, potassium dichromate, etc., may be added as needed.

[0120] Colloidal silica can be cited as an example of the aforementioned silica-containing dispersant and stabilizer.

[0121] As the aforementioned colloidal silica, alkaline colloidal silica with a pH greater than 7 in the colloidal solution (aqueous dispersion) can be used, or acidic colloidal silica with a pH less than 7 can be used. Among these, alkaline colloidal silica is more preferred.

[0122] Furthermore, the colloidal silica mentioned above preferably contains 10 to 50% by weight of silica as a solid component and is monodisperse.

[0123] Other dispersion stabilizers besides silica include, for example, calcium phosphate, magnesium hydroxide, aluminum hydroxide, iron hydroxide, barium sulfate, calcium sulfate, sodium sulfate, calcium oxalate, calcium carbonate, barium carbonate, and magnesium carbonate.

[0124] The amount of the silica-containing dispersant stabilizer added is appropriately determined based on the particle size of the thermally expandable microcapsules. 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). A further preferred lower limit is 3 parts by weight, and a further preferred upper limit is 5 parts by weight. It should be noted that the amount of the oil phase mentioned above refers to the combined amount of the monomer and the volatile expander.

[0125] Examples of auxiliary stabilizers mentioned above include the condensation products of diethanolamine and aliphatic dicarboxylic acids, and the condensation products of urea and formaldehyde. Other examples include polyvinylpyrrolidone, polyethylene oxide, polyethyleneimine, tetramethylammonium hydroxide, gelatin, methylcellulose, polyvinyl alcohol, dioctyl sulfosuccinate, sorbitol ester, and various emulsifiers.

[0126] In addition to auxiliary stabilizers, condensation products and water-soluble nitrogen compounds can also be added.

[0127] As the condensation product mentioned above, the condensation product of diethanolamine and aliphatic dicarboxylic acid is preferred, and the condensation product of diethanolamine and adipic acid and the condensation product of diethanolamine and itaconic acid are particularly preferred.

[0128] Examples of water-soluble nitrogen compounds include polyvinylpyrrolidone, polyethyleneimine, polyoxyethylene alkylamine, and poly(meth)acrylate dialkylaminoalkyl esters, such as poly(dimethylaminoethyl methacrylate) and poly(dimethylaminoethyl methacrylate). Other examples include poly(dialkylaminoalkyl(meth)acrylamide), such as poly(dimethylaminopropylacrylamide) and poly(dimethylaminopropylmethacrylamide), polyacrylamide, polycationic acrylamide, polyamine sulfone, and polyallylamine. Polyvinylpyrrolidone is particularly suitable for use among these.

[0129] Next, in the method for manufacturing thermally expandable microcapsules, a step is performed to disperse an oily mixture containing a monomer composition and a volatile expander in an aqueous dispersion medium.

[0130] Specifically, a step is performed to disperse an oily mixture containing a monomer composition and a volatile expanding agent in an aqueous dispersion medium. In this step, the monomer composition and the volatile expanding agent can be added separately to the aqueous dispersion medium to prepare the oily mixture, but typically the two are mixed beforehand to form an oily mixture before being added to the aqueous dispersion medium. Alternatively, the oily mixture and the aqueous dispersion medium can be prepared in separate containers beforehand, and then mixed while stirring in another container to disperse the oily mixture in the aqueous dispersion medium before adding it to the polymerization reaction vessel. In this step, an inorganic compound is present at the interface between the oil droplets formed by the oily mixture and the aqueous dispersion medium, resulting in the formation of an inorganic layer on the surface constituting the outer shell of the obtained thermally expandable microcapsules.

[0131] It should be noted that a polymerization initiator is used to polymerize the above monomers. However, the polymerization initiator can be added to the oily mixture in advance or after the aqueous dispersion medium and the oily mixture are stirred and mixed in the polymerization reaction vessel.

[0132] As a method for emulsifying and dispersing the above-mentioned oily mixture in an aqueous dispersion medium with a specified particle size, examples include: stirring using a homogenizer (e.g., manufactured by Tokusoki Chemical Co., Ltd.); and passing it through a static dispersion device such as a pipeline mixer or a unit-type static disperser.

[0133] It should be noted that either an aqueous dispersion medium and a polymerizable mixture can be supplied to the aforementioned static dispersion device, or a pre-mixed and stirred dispersion can be supplied.

[0134] The aforementioned thermally expandable microcapsules can be manufactured by the following steps: a step of polymerizing monomers by heating the dispersion obtained through the above steps; a step of cleaning; and a step of drying.

[0135] The polymerization temperature in the process of polymerizing the above-mentioned monomers is preferably 45°C or higher, and more preferably 68°C or lower. By setting it to the above range, in addition to the "cross-sectional area of ​​the shell", "cross-sectional area of ​​the particles", and "the ratio of the cross-sectional area of ​​the particles to the total cross-sectional area of ​​the shell and the cross-sectional area of ​​the particles", the shapes of the above-mentioned thermally expandable microcapsules can be adjusted to a specified range. The above-mentioned polymerization temperature is more preferably 48°C or higher, and more preferably 66°C or lower.

[0136] Masterbatch particles can be obtained by mixing the aforementioned thermally expandable microcapsules with a resin (base resin). Furthermore, a foaming resin composition can be obtained by adding a matrix resin such as a thermoplastic resin to the aforementioned thermally expandable microcapsules. Ink containing the aforementioned thermally expandable microcapsules and resin can be used as a foaming ink. The composition containing the aforementioned thermally expandable microcapsules and resin is preferably used in applications such as adhesives, rubber sheets, foam sheets, flooring materials, bedrock consolidation materials, coatings, coating materials, reinforcing fibers, composite materials, electronic components, and molding materials. The molding materials are preferably used in molding processes such as injection molding, extrusion molding, blow molding, rotational molding, vacuum forming, blow molding, calendering, slush molding, dip molding, foaming molding, and molding based on thermal dissolution lamination, inkjet printing, photoforming, and laser sintering.

[0137] The resin used in the aforementioned base resin is not particularly limited, and thermoplastic resins and curing resins commonly used in foam molding can be used. Specifically, examples of the aforementioned thermoplastic resins include: low-density polyethylene (LDPE), polyolefins such as polypropylene (PP), polyvinyl acetate, ethylene-vinyl acetate copolymer (EVA), vinyl chloride, polystyrene, thermoplastic elastomers, ethylene-methyl methacrylate copolymer (EMMA), etc.

[0138] Among these, LDPE, EVA, EMMA, and thermoplastic elastomers are preferred due to their low melting point and ease of processing. They can be used individually or in combination of two or more.

[0139] In addition, examples of the aforementioned curable resins include epoxy resins, (meth)acrylic resins, urethane resins, phenolic resins, cyanate resins, isocyanate resins, maleimide resins, benzoxazine resins, silicone resins, fluororesins, polyimide resins, and phenoxy resins. Among these, epoxy resins are preferably included. These curable resins can be used alone or in combination of two or more.

[0140] The content of the aforementioned thermally expandable microcapsules in the masterbatch particles is not particularly limited, but the preferred lower limit is 10 parts by weight relative to 100 parts by weight of the aforementioned thermoplastic resin, and the preferred upper limit is 90 parts by weight.

[0141] There are no particular limitations on the method for manufacturing the aforementioned masterbatch granules. Examples include: pre-mixing raw materials such as base resin and various additives using a co-rotating twin-screw extruder; then, heating to a predetermined temperature and adding a foaming agent such as thermally expandable microcapsules, further mixing, and then using a granulator to cut the resulting mixture into desired sizes and granules to produce masterbatch. Alternatively, the raw materials such as base resin and thermally expandable microcapsules can be mixed using a batch mixing mill, and then granulated using a granulator to produce granular masterbatch.

[0142] As for the aforementioned mixing machine, there are no particular limitations as long as it can mix in a way that does not damage the thermally expandable microcapsules. Examples include: pressure kneaders, Banbury mixers, etc.

[0143] Furthermore, foamed molded articles can be obtained using the aforementioned thermally expandable microcapsules and foaming masterbatch. In particular, the aforementioned thermally expandable microcapsules are also suitable for applications requiring post-processing at high temperatures, thus enabling the production of foam sheets with high appearance quality, such as textured surfaces.

[0144] Specifically, a foamed molded body can be obtained by mixing and molding the above-mentioned thermally expandable microcapsules or a foaming masterbatch containing the above-mentioned thermally expandable microcapsules and a matrix resin.

[0145] In addition, it can improve gas barrier properties during heating and expansion, thereby improving durability, and can also increase foaming ratio and heat resistance.

[0146] There are no particular limitations on the forming method for the aforementioned foamed molded articles. Examples include compounding, calendering, extrusion, and injection molding. In the case of injection molding, there are no particular limitations on the process method. Examples include short-shot molding, in which resin material is partially added to the mold and foamed, and core-removal molding, in which the mold is completely filled with resin material and then opened to the desired degree of foaming.

[0147] Utility Model Effect

[0148] This invention provides a thermally expandable microcapsule that combines excellent heat resistance and foaming ratio, and is also suitable for use in injection molding and other processes where strong shear forces are applied. Attached Figure Description

[0149] Figure 1 This is a schematic diagram showing a cross-section of the aforementioned thermally expandable microcapsules. Detailed Implementation

[0150] The following examples are provided for further explanation, but are not limited to these examples.

[0151] (Examples 1-9, Comparative Examples 1-9)

[0152] (Preparation of thermally expandable microcapsules)

[0153] An aqueous dispersion medium was prepared by adding 8 L of water and the amount of dispersant (colloidal silica or magnesium hydroxide) shown in Table 1 to a polymerization reactor. Next, an oily mixture consisting of the shell material (monomer), foaming agent, and polymerization initiator shown in Table 1 was added to the aqueous dispersion medium and suspended to prepare a dispersion. The resulting dispersion was stirred and mixed using a homogenizer and then added to a pressurized polymerizer that had undergone nitrogen purging. The polymer was reacted for 20 hours under pressure (0.2 MPa) at the polymerization temperature shown in Table 1 to obtain the reaction product. The reaction product was repeatedly filtered and washed with water, and then dried to obtain thermally expandable microcapsules.

[0154] (Preparation of masterbatch pellets)

[0155] 100 parts by weight of a propylene-based elastomer and 10 parts by weight of a fatty acid ester as a lubricant were compounded using a Banbury mixer. At approximately 100°C, 100 parts by weight of the obtained thermally expandable microcapsules were added to the 100 parts by weight of the propylene-based elastomer. The mixture was further compounded for 30 seconds and then extruded, simultaneously granulated to obtain masterbatch granules. The propylene-based elastomer used had a melt index of 3.7 g / 10 min, a melting point of 75°C, a propylene content of 91% by weight, and an ethylene content of 9% by weight.

[0156] (Fabrication of foamed molded parts [injection molded parts])

[0157] The masterbatch granules were mixed with 100 parts by weight of PA66 resin (Zytel 103HSL NC010 (Celanese)) to obtain mixed granules containing 6% by weight of masterbatch granules. The resulting mixed granules were fed into the hopper of a spiral injection molding machine equipped with an accumulator for melt mixing. The core was removed to a depth of 2 mm using a core-removal method, followed by injection molding to obtain a plate-shaped molded body. It should be noted that the molding conditions were set as follows: barrel temperature 260℃, injection speed 100 mm / s, cooling time 20 s, back pressure 5 MPa, holding pressure 0 MPa, and mold temperature 80℃.

[0158] (evaluate)

[0159] The thermally expandable microcapsules and foamed articles obtained in the Examples and Comparative Examples were evaluated for the following properties. The results are shown in Table 1.

[0160] (1) Preliminary particle size determination

[0161] The volume average particle size of the obtained thermally expandable microcapsules was determined using a particle size distribution measuring instrument (LA-910, manufactured by HORIBA).

[0162] (2) The ratio of the cross-sectional area of ​​the particle to the cross-sectional area of ​​the shell and the total cross-sectional area of ​​the particle.

[0163] The obtained thermally expandable microcapsules were solidified using an embedding medium (Epok 812) under an optical microscope. After solidification, the cross-section was cut using an ultramicrotome, and the resulting cross-section was sputtered with platinum. The cross-section of the thermally expandable microcapsules obtained by central cutting was observed and photographed using a scanning electron microscope (2000-3000x).

[0164] The obtained microscopic images were processed using image analysis (“Avizo 3D Pro 2022.2”, manufactured by Thermo Fisher Scientific) to determine the cross-sectional area of ​​the shell and the cross-sectional area of ​​the particles. Based on the obtained cross-sectional areas of the shell and the particles, the ratio of the particle's cross-sectional area to the sum of the shell's and particle's cross-sectional areas was calculated. The ratio of the particle's cross-sectional area to the sum of the shell's and particle's cross-sectional areas was measured for any 100 thermally expandable microcapsules, and the average value was calculated.

[0165] It should be noted that, for thermally expandable microcapsules that are the objects of measurement for “cross-sectional area of ​​the shell” and “cross-sectional area of ​​the particles”, thermally expandable microcapsules with a particle size of ±2 μm obtained in “(1) Particle size pre-determination” are selected.

[0166] (3) Particle size, outer shell, and thickness of inorganic layer

[0167] Based on the microscope images obtained in (2) above, image analysis (“Avizo 3D Pro 2022.2”, Thermo Fisher Scientific) was used to determine the particle size, shell thickness, and thickness of the inorganic layer formed on the outer side of the shell of the thermally expandable microcapsules. The “particle size”, “shell thickness”, and “inorganic layer thickness” of any 100 thermally expandable microcapsules were measured, and the average values ​​were calculated.

[0168] (4) Average number of particles, particle size

[0169] Based on the microscope images obtained in (2) above, image analysis (“Avizo 3D Pro 2022.2”, manufactured by Thermo Fisher Scientific) was used to count the number of particles encapsulated in the thermally expandable microcapsules. Additionally, the particle size was measured. For any 100 thermally expandable microcapsules, the “number of particles” and “particle size” were measured, and the average values ​​were calculated.

[0170] (5) Determination of foaming start temperature and maximum foaming temperature

[0171] The foaming initiation temperature (Ts) and maximum foaming temperature (Tmax) were determined using a thermomechanical analysis apparatus (TMA2940, manufactured by TA Instruments). Specifically, a 25 μg sample was placed in an aluminum container with a diameter of 7 mm and a depth of 1 mm. Under a force of 0.1 N applied from above, the sample was heated from 80 °C to 220 °C at a heating rate of 5 °C / min. The vertical displacement of the measuring terminals was measured. The temperature at which the displacement began to rise was defined as the foaming initiation temperature, the maximum value of the displacement was defined as the maximum displacement, and the temperature at which the maximum displacement was reached was defined as the maximum foaming temperature.

[0172] (6) Heat fusion weldability

[0173] (a) 10 g of thermally expandable microcapsules were added to a beaker and heated at Tmax °C for 10 minutes to foam them. The volume average particle size of the foamed thermally expandable microcapsules was measured using a particle size distribution analyzer (LA-910, HORIBA) [a].

[0174] (b) Add 10 g of thermally expandable microcapsules and a stirrer to a beaker, and heat at Tmax °C for 10 minutes while stirring to foam them. The volume average particle size of the foamed thermally expandable microcapsules was measured using a particle size distribution analyzer (LA-910, HORIBA) [b].

[0175] (c) Calculate “volume average particle size [b] / volume average particle size [a]” based on the obtained volume average particle size [a] and [b], and evaluate it according to the following criteria. It should be noted that when the evaluation is ×, during molding, the thermally expandable microcapsules are thermally fused together and locally exist in the foamed molded body, resulting in a deterioration in the appearance of the obtained foamed molded body.

[0176] ◎: Volume average particle size [b] / volume average particle size [a] is less than 1 and greater than 0.8.

[0177] 〇: Volume average particle size [b] / volume average particle size [a] is less than 0.8 and greater than 0.6.

[0178] ×: Volume average particle size [b] / Volume average particle size [a] is less than 0.6

[0179] (7) Foaming ratio of injection molded parts

[0180] The specific gravity of the obtained foamed molded body [injection molded body] was measured using a hydrometer MD-200S (manufactured by MIRAGE). Additionally, the expansion ratio was determined by measuring the specific gravity of the unexpanded thermoplastic resin used in the foamed molded body and dividing the specific gravity of the unexpanded thermoplastic resin by the specific gravity of the foamed molded body.

[0181] Table 1

[0182]

[0183] Industrial applicability

[0184] This invention provides a thermally expandable microcapsule that combines excellent heat resistance and foaming ratio, and is also suitable for use in injection molding and other processes where strong shear forces are applied.

Claims

1. A thermally expandable microcapsule comprising a shell made of thermoplastic resin and microparticles composed of a foaming agent and thermoplastic resin encapsulated within the shell, characterized in that, The thermally expandable microcapsules have a particle size of 10 μm or more and 50 μm or less. With respect to the cross-section obtained by cutting the thermally expandable microcapsule, the ratio of the cross-sectional area of ​​the microparticle to the total cross-sectional area of ​​the outer shell and the cross-sectional area of ​​the microparticle is more than 5% and less than 60%.

2. The thermally expandable microcapsule according to claim 1, characterized in that, The ratio of the cross-sectional area of ​​the particle to the total cross-sectional area of ​​the shell and the cross-sectional area of ​​the particle is more than 10% and less than 50%.

3. The thermally expandable microcapsule according to claim 1, characterized in that, The ratio of the cross-sectional area of ​​the particle to the total cross-sectional area of ​​the shell and the cross-sectional area of ​​the particle is more than 20% and less than 30%.

4. The thermally expandable microcapsule according to claim 1, characterized in that, The cross-sectional area of the housing is 100 μm 2 Above and 900 μm 2 Below.

5. The thermally expandable microcapsule according to claim 1, characterized in that, The cross-sectional area of the housing is 200 μm 2 Above and 800 μm 2 Below.

6. The thermally expandable microcapsule according to claim 1, characterized in that, The cross-sectional area of the housing is 300 μm 2 Above and 600 μm 2 Below.

7. The thermally expandable microcapsule according to claim 1, characterized in that, The outer side of the outer shell has an inorganic layer with a thickness of more than 0.01 μm and less than 3 μm.

8. The thermally expandable microcapsule according to claim 1, characterized in that, The outer side of the outer shell has an inorganic layer with a thickness of more than 0.05 μm and less than 2 μm.

9. The thermally expandable microcapsule according to claim 1, characterized in that, The outer side of the outer shell has an inorganic layer with a thickness of more than 0.1 μm and less than 1 μm.

10. The thermally expandable microcapsule according to claim 1, characterized in that, The particle size is greater than 2 μm and less than 10 μm.

11. The thermally expandable microcapsule according to claim 1, characterized in that, It contains two or more but less than ten of the aforementioned particles.

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