Thermally expandable microcapsules

Abstract

The present invention provides a heat-expandable microcapsule which does not require a special molding machine even when an engineering plastic or the like is used, has excellent heat resistance in a high temperature region, has high foaming performance even in a high temperature region, and also has excellent moldability. The heat-expandable microcapsule of the present invention has a volatile expanding agent as a core agent enclosed in a shell containing a polymer, and the difference between the Tg% of the foaming starting temperature Ts and the Tg% of Ts+20°C is 3% or less in TG / DTA measurement.

Description

Technical Field

[0001] This invention relates to thermally expandable microcapsules. Background Technology

[0002] In recent years, with the trends of lightweighting and electrification in automotive applications, there has been a growing trend to replace metal parts in automobiles with lightweight foamed molded materials. Therefore, the practical application of foamed molded materials is being actively researched.

[0003] As a method for manufacturing foamed molded articles, for example, a method is implemented to foam a resin material using a foaming agent, which typically uses thermally expandable microcapsules or chemical foaming agents. As such thermally expandable microcapsules, thermally expandable microcapsules containing a volatile expanding agent that becomes gaseous at temperatures below the softening point of the thermoplastic polymer are widely known.

[0004] Patent Document 1 discloses a thermally expandable microsphere consisting of a shell and a foaming agent, wherein the shell comprises a thermoplastic resin, the foaming agent is encapsulated within the shell and vaporized by heating, and the thermoplastic resin comprises a nitrile monomer (A) that must contain methacrylonitrile, a carboxyl-containing monomer (B), and a monomer (C) having a group that reacts with the carboxyl group.

[0005] Patent document 2 discloses a thermally expandable microsphere consisting of a shell and a foaming agent, wherein the shell comprises a thermoplastic resin, and the foaming agent is encapsulated within the shell and vaporized by heating. The thermoplastic resin comprises: an nitrile monomer (A) that must contain acrylonitrile and methacrylonitrile, a carboxyl-containing monomer (B), and a monomer (C) having one polymerizable double bond.

[0006] In addition, as a method for foaming engineering plastics and super engineering plastics (hereinafter referred to as engineering plastics, etc.) with high heat resistance, a method is adopted to dissolve the molten resin of engineering plastics by shearing and mixing it with a high-pressure supercritical fluid and then performing foaming injection molding.

[0007] Existing technical documents

[0008] Patent documents

[0009] Patent Document 1: International Publication No. 2016 / 190178

[0010] Patent Document 2: International Publication No. 2016 / 084612 Summary of the Invention

[0011] The problem that the invention aims to solve

[0012] However, foam injection molding using supercritical fluids requires specialized molding machines, making it difficult to integrate into manufacturing equipment. On the other hand, when using thermally expandable microcapsules from Patent Documents 1 and 2 in the foaming molding of engineering plastics, it is difficult to maintain the encapsulated volatile expander through thermal expansion in high-temperature regions, resulting in problems with foaming performance.

[0013] The purpose of this invention is to provide a thermally expandable microcapsule that does not require a special molding machine even when using engineering plastics, exhibits excellent heat resistance in high-temperature regions, has high foaming performance even in high-temperature regions, and also has excellent formability.

[0014] Methods for solving problems

[0015] This disclosure (1) relates to a thermally expandable microcapsule containing a volatile expanding agent as a core agent within a shell containing a polymer, wherein the difference between the Tg% of the foaming initiation temperature Ts and the Tg% of Ts+20℃ in TG / DTA determination is less than 3%.

[0016] This disclosure (2) relates to the thermally expandable microcapsules of this disclosure (1), wherein the maximum foaming temperature Tmax is above 240°C.

[0017] This disclosure (3) relates to the thermally expandable microcapsules of disclosure (1) or (2), wherein the foaming initiation temperature Ts is above 185°C.

[0018] This disclosure (4) relates to thermally expandable microcapsules in any combination with any of the present disclosures (1) to (3), wherein the polymer contains 45% by weight or more and 65% by weight or less of structural units derived from a nitrile monomer (I) and 35% by weight or more and 55% by weight or less of structural units derived from a carboxyl-containing monomer (II), wherein the nitrile monomer (I) comprises acrylonitrile.

[0019] This disclosure (5) relates to the thermally expandable microcapsules of this disclosure (4), wherein the nitrile monomer (I) comprises methacrylonitrile and acrylonitrile, the weight ratio of the structural unit derived from the acrylonitrile to the structural unit derived from the methacrylonitrile (acrylonitrile / methacrylonitrile) is 1.05 or more, and the weight ratio of the structural unit derived from the methacrylonitrile to the structural unit derived from the carboxyl-containing monomer (II) (methacrylonitrile / carboxyl-containing monomer (II)) is 0.8 or less.

[0020] This disclosure (6) relates to thermally expandable microcapsules in any combination with any of the present disclosures (1) to (5), wherein the degree of gelation, as determined using N,N-dimethylformamide (DMF) solvent, is less than 30% by weight.

[0021] This disclosure (7) relates to thermally expandable microcapsules in any combination of any of the present disclosures (1) to (6), wherein the polymer does not contain structural units derived from polymeric monomers having two or more double bonds in the molecule.

[0022] This disclosure (8) relates to thermally expandable microcapsules in any combination with any of the present disclosures (1) to (7), wherein the content of the metal cation salt in the shell is 0.5% by weight or more and 10% by weight or less.

[0023] The present invention will now be described in detail.

[0024] As an embodiment of the present invention, the thermal expansion microcapsules, in TG / DTA measurements, show a difference of less than 3% between the Tg% of the foaming initiation temperature Ts and the Tg% of Ts+20°C.

[0025] By satisfying the above relationships, it is possible to produce thermally expandable microcapsules that exhibit excellent heat resistance in high-temperature regions, minimal silver streaks during foaming, and excellent formability. Furthermore, by using such thermally expandable microcapsules, molded articles can be obtained even with engineering plastic-based resins without the use of special molding machines.

[0026] The difference (Tg%(Ts+20℃)-Tg%(Ts)) is preferably 3% or less, more preferably 2% or less. The smaller the difference (Tg%(Ts+20℃)-Tg%(Ts)), the better, for example, it is 0% or more. From the viewpoint of foaming properties, it is preferably 0.5% or more, more preferably 1.0% or more.

[0027] In addition, the above-mentioned Tg% (Ts + 20°C) is preferably 0% or more, preferably 5% or less, and more preferably 3% or less.

[0028] The aforementioned Tg% refers to the rate of change of the sample's weight, which can be measured using a thermogravimetric / differential calorimetry (TG / DTA) apparatus. Specifically, it can be calculated as follows: Place 20 μg of the sample into an aluminum container with a diameter of 5 mm and a depth of 2 mm. Heat the sample from 40 °C to 350 °C at a heating rate of 5 °C / min. Measure the weight change of the sample, using the weight at 40 °C as a baseline (0% weight change). Measure the Tg% at the foaming initiation temperature Ts obtained from the TMA measurement results and the Tg% at the foaming initiation temperature Ts + 20 °C, and calculate the difference. It is considered that the difference between the Tg% at Ts and the Tg% at Ts + 20 °C corresponds to the change in state, such as the outflow weight of the gas from the foaming initiation temperature to the high-temperature region.

[0029] The aforementioned difference (Tg%(Ts+20℃)-Tg%(Ts)) can be adjusted by the type and ratio of monomer components in the polymer, the weight-average molecular weight (Mw) of the polymer, polymerization conditions, and the content of metal cation salts in the shell. In particular, the aforementioned difference can be achieved by optimizing the weight ratio of structural units derived from acrylonitrile to structural units derived from methacrylonitrile (acrylonitrile / methacrylonitrile), the weight ratio of structural units derived from methacrylonitrile to structural units derived from carboxyl-containing monomers (II) (hereinafter also referred to as "carboxyl-containing structural units") (methacrylonitrile / carboxyl-containing monomers (II)), and the ratio of other monomers.

[0030] The preferred lower limit for the true density of the thermally expandable microcapsules of the present invention is 1.08 g / cm³. 3 The preferred upper limit is 1.50 g / cm³. 3 By setting the value within the above range, the uniformity of the thermally expandable microcapsules can be improved. A more preferred lower limit is 1.10 g / cm³. 3 A more preferred upper limit is 1.40 g / cm³. 3 .

[0031] It should be noted that true density can be measured using a true density meter (Ultrapyc 5000, Anton Parr, etc.) under conditions of 12 psi pressure, 25°C temperature, and helium gas.

[0032] Regarding the thermally expandable microcapsules, which are one embodiment of the present invention, the maximum foaming temperature (Tmax) is preferably 240°C or higher. By setting it to 240°C or higher, the heat resistance is increased, and when the composition containing the thermally expandable microcapsules is molded in a high-temperature region, the rupture and shrinkage of the thermally expandable microcapsules can be prevented. In addition, the aggregation of the thermally expandable microcapsules during molding can be suppressed, resulting in a good appearance. The Tmax is more preferably 245°C or higher, more preferably 290°C or lower, and more preferably 270°C or lower.

[0033] 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 its diameter is measured from room temperature.

[0034] Furthermore, the foaming initiation temperature (Ts) is preferably 185°C or higher. By setting it to 185°C or higher, thermally expandable microcapsules with excellent heat resistance can be produced. More preferably, Ts is 190°C or higher, more preferably 290°C or lower, and even more preferably 250°C or lower.

[0035] The aforementioned Ts can be adjusted by factors such as the type of nuclear agent.

[0036] Regarding the thermally expandable microcapsules, which are one embodiment of the present invention, the degree of gelation measured using N,N-dimethylformamide (DMF) solvent is preferably 30% by weight or less. By setting it to the above range, a high foaming ratio can be exhibited even in high-temperature regions.

[0037] The degree of gelation mentioned above can be determined according to the method of ASTM D2765.

[0038] As an embodiment of the present invention, the preferred lower limit for the volume average particle size of the thermally expandable microcapsules is 1 μm, and the preferred upper limit is 100 μm. If it is less than 1 μm, the bubbles in the resulting molded article are too small, and therefore the foaming ratio is sometimes insufficient. If it exceeds 100 μm, the bubbles in the resulting molded article become too large, and therefore sometimes become a problem in terms of appearance. A more preferred lower limit is 3 μm, and a more preferred upper limit is 50 μm.

[0039] The volume-average particle size of the aforementioned thermally expandable microcapsules can be determined using a particle size distribution measuring device based on laser diffraction and scattering.

[0040] The shell of the thermally expandable microcapsule, which is one embodiment of the present invention, contains a polymer.

[0041] The polymer described above is preferably a polymer formed by polymerizing a monomer composition containing a nitrile monomer (I) and a carboxyl-containing monomer (II).

[0042] That is, the polymers described above preferably have structural units derived from nitrile monomers (I) and structural units derived from carboxyl-containing monomers (II).

[0043] The aforementioned nitrile monomers (I) are not particularly limited, and examples include acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, α-ethoxyacrylonitrile, fumaric acid, or mixtures thereof. Acrylonitrile is preferred, and acrylonitrile and methacrylonitrile are particularly preferred. They can be used alone or in combination of two or more.

[0044] The content of structural units derived from the aforementioned nitrile monomer (I) in the polymer is preferably 45% by weight or more, and more preferably 65% ​​by weight or less. Setting it to 45% by weight or more improves the foaming ratio. Setting it to 65% by weight or less improves heat resistance. More preferably, the content is 48% by weight or more, and more preferably 60% by weight or less.

[0045] In the structural units derived from the aforementioned 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 difference between the Tg% of the foaming initiation temperature Ts and the Tg% of Ts+20°C in the obtained thermally expandable microcapsules is easily reduced to 3% or less. Therefore, the heat resistance and formability are improved. The aforementioned weight ratio is more preferably 1.10 or more, more preferably 2.00 or less, and more preferably 1.50 or less.

[0046] The content of the structural units derived from acrylonitrile in the polymer is preferably 23% by weight or more, more preferably 26% by weight or more, more preferably 43% by weight or less, and more preferably 37% by weight or less.

[0047] The content of structural units derived from the above-mentioned methacrylonitrile in the polymer is preferably 15% by weight or more, more preferably 20% by weight or more, more preferably 31% by weight or less, and more preferably 28% by weight or less.

[0048] 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.

[0049] Specifically, examples include unsaturated monocarboxylic acids, unsaturated carboxylic acids of unsaturated dicarboxylic acids or their anhydrides, or monoesters of unsaturated dicarboxylic acids, which can be used alone or in combination of two or more.

[0050] 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.

[0051] 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.

[0052] Among them, acrylic acid, methacrylic acid, maleic acid, maleic anhydride, and itaconic acid are preferred, with methacrylic acid being more preferred.

[0053] The content of the carboxyl-containing structural units in the polymer is preferably 35% by weight or more, and more preferably 55% by weight or less. Setting it to 35% by weight or more improves the heat resistance of the obtained thermally expandable microcapsules. Furthermore, setting it to 55% by weight or less improves the powder flowability of the obtained thermally expandable microcapsules. More preferably, the content is 40% by weight or more, and more preferably 53% by weight or less.

[0054] In the above polymer, the weight ratio of the structural unit derived from methacrylonitrile to the structural unit containing a carboxyl group (methacrylonitrile / carboxyl-containing monomer (II)) is preferably 0.8 or less. By setting it to 0.8 or less, the difference between the Tg% of the foaming initiation temperature Ts and the Tg% of Ts+20°C in the obtained thermally expandable microcapsules is easily reduced to 3% or less. Therefore, the heat resistance and formability are improved. The above weight ratio is preferably 0 or more, more preferably 0.35 or more, and more preferably 0.75 or less.

[0055] The polymer described above may contain structural units derived from polymerizable monomers having two or more double bonds within the molecule, but preferably not. By omitting these structural units from the polymer, a high foaming ratio can be exhibited even during molding in high-temperature regions.

[0056] As polymerizable monomers, examples include monomers having two or more free radical polymerizable double bonds, such as divinylbenzene, di(meth)acrylate, and (meth)acrylate with more than three functions.

[0057] 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 dimethyloltricyclodecane di(meth)acrylate. Furthermore, di(meth)acrylates of polyethylene glycol with a weight-average molecular weight of 200 to 600 can also be used.

[0058] 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.

[0059] The polymer may contain structural units derived from the nitrile monomer (I) and structural units derived from other monomers other than structural units having carboxyl groups.

[0060] Other monomers mentioned above, besides (meth)acrylates, include vinyl chloride, vinylidene chloride, vinyl acetate, styrene, and other vinyl monomers. They can be used alone or in combination of two or more. Among these, (meth)acrylates are preferred, and particularly preferred are alkyl methacrylates such as methyl methacrylate, ethyl methacrylate, and n-butyl methacrylate, or methacrylates containing alicyclic, aromatic, or heterocyclic rings such as cyclohexyl methacrylate, benzyl methacrylate, and isobornyl methacrylate.

[0061] The content of structural units derived from the other monomers in the polymer is preferably 0% by weight or more, more preferably 0.1% by weight or more, preferably 1.5% by weight or less, and more preferably 1.3% by weight or less. By setting the content within the above range, the dispersibility of the composition using thermally expandable microcapsules can be improved, and thermal expansion can also be improved.

[0062] The weight-average molecular weight (Mw) of the above-mentioned polymer is preferably 200,000 or more, more preferably 250,000 or more, preferably 500,000 or less, and more preferably 450,000 or less.

[0063] By setting it to the above range, it is easy to make the difference between the Tg% of the foaming initiation temperature Ts and the Tg% of Ts+20℃ less than 3% in the obtained thermally expandable microcapsules.

[0064] Regarding the aforementioned weight-average molecular weight, for example, the weight-average molecular weight can be determined in gel permeation chromatography using DMF as the eluent and two connected Shodex LF-804 columns, by means of a monodisperse polystyrene standard.

[0065] To polymerize the above monomers, a polymerization initiator is added to the above monomer composition.

[0066] As polymerization initiators, dialkyl peroxides, diacyl peroxides, peroxide esters, peroxydicarbonates, azo compounds, etc., are suitable for use.

[0067] Specific examples include: dialkyl peroxides such as methyl ethyl peroxide, di-tert-butyl peroxide, and dicumyl peroxide; and diacyl peroxides such as isobutyl peroxide, benzoyl peroxide, 2,4-dichlorobenzoyl peroxide, and bis(3,5,5-trimethylhexanoyl) peroxide.

[0068] 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.

[0069] Other examples include: cumyl peroxynedecanoate, (α,α-bis-neodecanoyl peroxy)diisopropylbenzene, etc.; bis(4-tert-butylcyclohexyl)dicarbonate peroxide, di-n-propyl-oxydicarbonate, diisopropyl peroxydicarbonate, etc.

[0070] In addition, examples of peroxide dicarbonates include di(2-ethylethyl peroxide) dicarbonate, dimethoxybutyl peroxide dicarbonate, and di(3-methyl-3-methoxybutyl peroxide) dicarbonate.

[0071] In addition, examples include 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).

[0072] The aforementioned shell may contain a metal cation salt. By including a metal cation salt in the shell, when the copolymer constituting the shell contains carboxyl groups, the metal cations derived from the aforementioned 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, even in high-temperature regions, the elastic modulus of the shell does not easily decrease. Therefore, even under molding processes such as compounding, calendering, extrusion, and injection molding with strong shear forces, the thermally expandable microcapsules will not rupture or shrink.

[0073] It should be noted that the aforementioned ionic crosslinking refers to the formation of crosslinks between free carboxyl groups existing as side chains of the copolymer. It should also be noted that the number of carboxyl groups per monovalent metal cation varies depending on the type of metal.

[0074] The metal cations used 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, and Pb. 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 suitable.

[0075] 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 a combination of alkali metal ions and metal cations other than alkali metals. By having the ions of the above-mentioned alkali metals, functional groups such as carboxyl groups are activated, which can promote the reaction between metal cations other than alkali metals and the carboxyl groups of the above-mentioned copolymers.

[0076] Examples of alkali metals mentioned above include Na, K, and Li.

[0077] The content of the aforementioned metal cation salt in the shell is 0% by weight or more, 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 further improved. The aforementioned content is more preferably 0.8% by weight or more, and more preferably 8% by weight or less.

[0078] The shell constituting the thermally expandable microcapsule, as an embodiment of the present invention, preferably further contains at least one inorganic compound selected from Si-based and Mg-based compounds.

[0079] By containing the aforementioned inorganic compounds, it is possible to suppress the fusion of thermally expanding microcapsules in the resin during molding.

[0080] As the aforementioned Si-based and Mg-based compounds, oxides, hydroxides, carbonates, or bicarbonates containing silicon and magnesium are preferred.

[0081] These Si-based and Mg-based compounds can be used alone or in combination of two or more.

[0082] In addition to colloidal silica and silica sol, other examples of Si-based compounds include No. 3 water glass, sodium orthosilicate, and sodium metasilicate. Among these, colloidal silica is preferred.

[0083] 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.

[0084] 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. Furthermore, inorganic salts such as sodium chloride and sodium sulfate, alkali metal salts of nitrite, stannous chloride, stannous chloride, and potassium dichromate can be added as needed.

[0085] The content of the aforementioned inorganic compound relative to the thermally expandable microcapsules is 0.01% by weight, preferably up to 7% by weight. By setting it to 0.01% by weight or more, the fusion of the thermally expandable microcapsules with each other in the resin during molding can be suppressed. By setting it to 7% by weight or less, the resin dispersibility during molding can be further improved. A more preferred lower limit is 0.3% by weight, and a more preferred upper limit is 5% by weight.

[0086] It should be noted that the content of the above-mentioned inorganic compounds can be calculated based on the weight of the monomer composition forming the thermally expandable microcapsules and the volatile expander.

[0087] The shell may further contain stabilizers, ultraviolet absorbers, antioxidants, antistatic agents, flame retardants, silane coupling agents, colorants, etc., as needed.

[0088] As one embodiment of the present invention, the thermally expandable microcapsule contains a volatile expanding agent as a core agent within the aforementioned shell.

[0089] The aforementioned volatile expanding agent is a gaseous substance that becomes gaseous at a temperature below the softening point of the polymer constituting the shell, and is suitable as a low-boiling-point organic solvent.

[0090] 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.

[0091] 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.

[0092] In addition, as a volatile expanding agent, a thermally decomposable compound that becomes gaseous through thermal decomposition by heating can be used.

[0093] In particular, as the aforementioned nucleating agent, it is preferable to contain 50% by weight or more of a nucleating agent having 8 or more carbon atoms, more preferably 70% by weight or more, and even more preferably 90% by weight or more.

[0094] In the thermally expandable microcapsules, which is one embodiment of the present invention, 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, thus enabling rapid foaming.

[0095] In addition, as a volatile expanding agent, a thermally decomposable compound that becomes gaseous through thermal decomposition by heating can be used.

[0096] There are no particular limitations on the method for manufacturing thermally expandable microcapsules, which is one embodiment of the present invention. For example, it can be manufactured by performing 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 monomer composition.

[0097] As the above-mentioned monomer composition, monomer compositions containing the above-mentioned nitrile monomer (I), carboxyl-containing monomer (II), or other monomers can be used.

[0098] In manufacturing thermally expandable microcapsules, as one embodiment of the present invention, a step of preparing an aqueous dispersion medium is first performed. Specifically, for example, an aqueous dispersion medium containing silica is prepared by adding a dispersion stabilizer containing water and silica, and an auxiliary stabilizer as needed, to a polymerization reaction vessel. Additionally, alkali metal salts of nitrite, stannous chloride, stannous chloride, potassium dichromate, etc., may be added as needed.

[0099] Colloidal silica can be cited as an example of the aforementioned dispersing stabilizer containing silica.

[0100] 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.

[0101] Furthermore, the colloidal silica mentioned above preferably contains 10 to 50% by weight of silica as a solid component and is monodisperse.

[0102] 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.

[0103] The amount of the dispersant stabilizer containing the aforementioned silica is appropriately determined based on the particle size of the thermally expandable microcapsules. Relative to 100 parts by weight of the oily mixture (oil phase), the preferred lower limit is 2.5 parts by weight, and the preferred upper limit is 7 parts by weight. 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.

[0104] Examples of auxiliary stabilizers mentioned above include: condensation products of diethanolamine and aliphatic dicarboxylic acids, and 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.

[0105] In addition to auxiliary stabilizers, condensation products and water-soluble nitrogen compounds can also be added.

[0106] 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.

[0107] Examples of the aforementioned water-soluble nitrogen compounds include: polyvinylpyrrolidone, polyethyleneimine, polyoxyethylene alkylamine, and poly(meth)acrylate dialkylaminoalkyl esters, represented by poly(dimethylaminoethyl methacrylate) and poly(dimethylaminoethyl methacrylate). Other examples include: poly(dialkylaminoalkyl(meth)acrylamide), represented by poly(dimethylaminopropylacrylamide) and poly(dimethylaminopropylmethacrylamide), polyacrylamide, polycationic acrylamide, polyamine sulfone, and polyallylamine. Polyvinylpyrrolidone is particularly suitable for use among these.

[0108] 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.

[0109] 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 prepare the 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 containing the oily mixture and the aqueous dispersion medium, resulting in the inorganic compound being present on the surface of the obtained thermally expandable microcapsules.

[0110] It should be noted that, in order to polymerize the above monomers, a polymerization initiator is used. The polymerization initiator can be added to the above oily mixture in advance, or it can be added after the aqueous dispersion medium and the oily mixture are stirred and mixed in the polymerization reaction vessel.

[0111] 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 using a static dispersion device such as a pipeline mixer or a component-type static disperser.

[0112] It should be noted that an aqueous dispersion medium and a polymerizable mixture can be supplied to the above-mentioned static dispersion device, or a pre-mixed and stirred dispersion can be supplied.

[0113] As one embodiment of the present invention, the thermally expandable microcapsules can be manufactured by subjecting the dispersion obtained through the above-described process to a process of polymerization of monomers by heating, a process of cleaning, and a process of drying.

[0114] In the polymerization process described above, the polymerization temperature is preferably 50°C or higher, and more preferably 60°C or lower. Furthermore, the polymerization time is preferably 4 hours or higher, and more preferably 24 hours or lower. Additionally, the polymerization pressure is preferably 0.1 MPa or higher, and more preferably 1 MPa or lower.

[0115] Masterbatch granules can be obtained by mixing the thermally expandable microcapsules of the present invention with a resin (base resin). Alternatively, a foaming resin composition can be obtained by adding a matrix resin such as a thermoplastic resin to the thermally expandable microcapsules of the present invention. Ink containing the above-mentioned thermally expandable microcapsules and resin can also be used as a foaming ink. The composition containing the thermally expandable microcapsules and resin of the present invention is preferably used in adhesives, rubber sheets, foam sheets, flooring materials, bedrock consolidation materials, coatings, coating materials, reinforcing fibers, composite materials, electronic components, molding materials, and the like. The molding materials described above are preferably used in: injection molding, extrusion molding, blow molding, rotational molding, vacuum forming, blow molding, calendering, slush molding, dip molding, foaming molding, molding based on hot melt lamination, inkjet printing, photoforming, laser sintering, and other molding methods.

[0116] The resin used in the above-mentioned base resin is not particularly limited, and thermoplastic resins and curing resins commonly used in foam molding can be used. Specifically, examples of the above-mentioned thermoplastic resins include: polyolefins such as low-density polyethylene (LDPE) and polypropylene (PP), polyvinyl acetate, ethylene-vinyl acetate copolymer (EVA), vinyl chloride, polystyrene, thermoplastic elastomers, ethylene-methyl methacrylate copolymer (EMMA), etc.

[0117] Among these, LDPE, EVA, EMMA, and thermoplastic elastomers are preferred due to their low melting point and ease of processing. These can be used individually or in combination of two or more.

[0118] In addition, examples of 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.

[0119] The content of the above-mentioned thermally expandable microcapsules in the above-mentioned masterbatch pellets is not particularly limited. Relative to 100 parts by weight of the above-mentioned thermoplastic resin, the lower limit is preferably 10 parts by weight, and the upper limit is preferably 90 parts by weight.

[0120] As a method for manufacturing the above-mentioned masterbatch pellets, there is no particular limitation. For example, it can be cited: premixing raw materials such as a base resin and various additives using a co-rotating twin-screw extruder or the like. Next, it is heated to a specified temperature, and after adding a foaming agent such as thermally expandable microcapsules, further kneading is performed, and the kneaded product thus obtained is cut into a desired size using a granulator to form a pellet shape, thereby manufacturing a masterbatch. In addition, it is also possible to knead raw materials such as a base resin and thermally expandable microcapsules using a batch kneader and then granulate using a granulator to manufacture a masterbatch in pellet form.

[0121] As the above-mentioned kneader, there is no particular limitation as long as it can knead without destroying the thermally expandable microcapsules. For example, a pressure kneader, a Banbury mixer, etc. can be cited.

[0122] In addition, the above-mentioned thermally expandable microcapsules and foaming masterbatch can be used to obtain a foamed molded body. In particular, the above-mentioned thermally expandable microcapsules can also be suitably used for applications that require post-processing at high temperatures, and thus a foamed sheet with high appearance quality such as an uneven shape can be obtained.

[0123] Specifically, by kneading and molding the above-mentioned thermally expandable microcapsules or a foaming masterbatch containing the above-mentioned thermally expandable microcapsules with a matrix resin, a foamed molded body can be obtained.

[0124] According to the present invention, during heating and expansion, durability can be improved, and the foaming ratio and heat resistance can also be increased.

[0125] As a method for forming the above-mentioned foamed molded body, there is no particular limitation. For example, kneading molding, calendering molding, extrusion molding, injection molding, etc. can be cited. In the case of injection molding, the processing method is not particularly limited. Examples include a short shot method (Japanese: ショートショート法) in which a part of the resin material is added to the mold and foamed, and a method in which the mold is opened to the core that wants to foam after filling the resin material into the mold.

[0126] Advantages of the Invention

[0127] According to the present invention, a thermally expandable microcapsule can be provided, which does not require a special molding machine even when using engineering plastics, etc., has excellent heat resistance in a high-temperature region, has high foaming performance even in a high-temperature region, and also has excellent formability. Detailed Embodiments

[0128] Hereinafter, examples will be listed to more specifically illustrate the embodiments of the present invention, but the present invention is not limited to these examples.

[0129] (Examples 1-16, Comparative Examples 1-14)

[0130] (Preparation of thermally expandable microcapsules)

[0131] An aqueous dispersion medium was prepared by adding 8 L of water, 5 parts by weight of colloidal silica (as a dispersant), and 0.3 parts by weight of polyvinylpyrrolidone to a polymerization reactor. Next, an oily mixture containing the monomers and metal cation salts in the amounts shown in Tables 1 and 2 was added to the aqueous dispersion medium and suspended to prepare a dispersion. The resulting dispersion was homogenized and mixed, then placed in a nitrogen-replaced pressure polymerizer. The reaction was carried out under pressure as shown in Tables 1 and 2, and at the polymerization temperatures and times shown in Tables 1 and 2, thereby obtaining the reaction product. The obtained reaction product was repeatedly filtered and washed with water, then dried to obtain thermally expandable microcapsules.

[0132] (Preparation of masterbatch granules)

[0133] 100 parts by weight of a propylene elastomer and 10 parts by weight of a fatty acid ester as a lubricant were mixed using a Banbury internal mixer. At approximately 100°C, 100 parts by weight of the resulting thermally expandable microcapsules were added relative to the 100 parts by weight of the propylene elastomer, and the mixture was further mixed for 30 seconds. Extrusion and granulation were then performed simultaneously to obtain masterbatch granules. The propylene 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.

[0134] (Production of foamed molded bodies)

[0135] The masterbatch granules were mixed with 100 parts by weight of PA66 resin (Zytel 103HSL NC010 (Celanese)) to obtain a mixed granule containing 6% by weight of masterbatch granules. The obtained mixed granule was fed into the hopper of a screw-type injection molding machine equipped with a reservoir for melt mixing. Injection molding was performed using a core retraction method with a core retraction amount of 2 mm to obtain a plate-shaped molded body. It should be noted that the molding conditions were set as follows: barrel temperature 260℃, injection speed 100mm / s, cooling time 20s, back pressure 5MPa, holding pressure 0MPa, and mold temperature 80℃.

[0136] (Evaluation Method)

[0137] The obtained thermally expandable microcapsules were evaluated using the following methods. The results are shown in Tables 1 and 2.

[0138] (1) Determination of volume average particle size

[0139] The volume average particle size of the obtained thermally expandable microcapsules was determined using a particle size distribution diameter measuring instrument (LA-910, manufactured by HORIBA).

[0140] (2) Determination of foaming initiation temperature and maximum foaming temperature

[0141] The foaming initiation temperature (Ts) and maximum foaming temperature (Tmax) were determined using a thermomechanical analysis (TMA) 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 250 °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.

[0142] (3) Tg% determination

[0143] The rate of change of weight (Tg%) of thermally expandable microcapsules was determined using a thermogravimetric / differential thermal analysis (TG / DTA) apparatus (TG / DTA6200 (manufactured by Hitachi, Ltd.)). Specifically, a 20 μg sample was placed in an aluminum container with a diameter of 5 mm and a depth of 2 mm, and heated from 40 °C to 350 °C at a heating rate of 5 °C / min. The weight change of the sample was measured, and the difference between the Tg% at the foaming initiation temperature Ts obtained by the TMA measurement and the Tg% at the foaming initiation temperature Ts + 20 °C was calculated.

[0144] (4) Degree of gelation

[0145] Thermally expandable microcapsules were immersed in DMF for 24 hours, and the degree of gelation in DMF was determined. Specifically, the solution was adjusted to 3% by weight of the sample, allowed to stand for 24 hours, and then centrifuged at 3000 rpm for 3 minutes to separate the solvent from the sample. After removing the solvent from the supernatant, the sample was dried using a vacuum dryer. The degree of gelation was calculated based on the dried weight of the gel and the weight of the sample using the following formula.

[0146] Degree of gelation = (dry weight of gel / weight of polymer contained in the sample) × 100

[0147] (5) Weight-average molecular weight (Mw)

[0148] Add 5 ml of solvent (dimethylformamide with 0.05 M lithium bromide) to 10 mg of the obtained thermally expandable microcapsules and stir slowly at room temperature. After visually confirming the presence of unwanted substances, filter the solution using a 0.45 μm filter. For the resulting assay solution, determine the molecular weight distribution and the weight-average molecular weight (Mw) of the polymer constituting the shell under the following assay conditions.

[0149] (Measurement conditions)

[0150] • Apparatus: Gel permeation chromatography (GPC) (manufactured by JASCO)

[0151] • Detector: Differential refractive index detector RI (JASCO RI-4030)

[0152] • Columns: Shodex LF-804 2-pin connector

[0153] • Flow rate: 0.8 mL / min

[0154] Column temperature: 40℃

[0155] Injection volume: 0.200 mL

[0156] • Standard sample: Monodisperse polystyrene manufactured by Tosoh Corporation

[0157] (6) Specific gravity

[0158] The density of the obtained foamed molded body was determined according to the JIS K 7112 A method (water displacement method).

[0159] The specific gravity mentioned above is an indicator of the heat resistance, which is the subject of this invention. In cases of poor heat resistance, the material expands in a high-temperature region and then contracts, thus increasing its specific gravity. Therefore, in the case of obtaining a lightweight foamed molded body, it can be said that the thermally expandable microcapsules have excellent heat resistance.

[0160] (7) Surface properties (formability)

[0161] The L* value of the surface of the obtained foamed molded body was measured using a color computer (CM-3600d, manufactured by Konica Minolta Japan). The color difference was measured with the unfoamed state (black) as the reference, and the evaluation was carried out according to the following criteria.

[0162] Regarding foamed molded bodies, if the color difference is small, there will be fewer silver streaks, and they can be molded under a wide range of molding conditions, so it can be said that they have excellent formability.

[0163] ◎: Color difference is 0 or more and less than 2.

[0164] 〇: Color difference exceeding 2 but less than 6.

[0165] △: Color difference exceeds 6.

[0166] [Table 1]

[0167]

[0168] [Table 2]

[0169]

[0170] Industrial availability

[0171] According to the present invention, a thermally expandable microcapsule can be provided that does not require a special molding machine even when using engineering plastics, has excellent heat resistance in high-temperature regions, high foaming performance even in high-temperature regions, and excellent formability.

Claims

1. A thermally expandable microcapsule, comprising a volatile expanding agent as a core agent encapsulated within a polymer-containing shell. In TG / DTA measurements, the difference between the Tg% at the foaming initiation temperature Ts and the Tg% at Ts+20℃ is less than 3%.

2. The thermally expandable microcapsule according to claim 1, wherein, The maximum foaming temperature Tmax is above 240℃.

3. The thermally expandable microcapsule according to claim 1 or 2, wherein, The foaming initiation temperature Ts is above 185℃.

4. The thermally expandable microcapsule according to claim 1, 2 or 3, wherein, The polymer contains 45% by weight and 65% by weight of structural units derived from a nitrile monomer (I) and 35% by weight and 55% by weight of structural units derived from a carboxyl-containing monomer (II), wherein the nitrile monomer (I) comprises acrylonitrile.

5. The thermally expandable microcapsule according to claim 4, wherein, The nitrile monomer (I) comprises methacrylonitrile and acrylonitrile, wherein the weight ratio of the structural units derived from the acrylonitrile to the structural units derived from the methacrylonitrile, i.e., the acrylonitrile / methacrylonitrile ratio, is 1.05 or more. The weight ratio of the structural unit derived from methacrylonitrile to the structural unit derived from the carboxyl-containing monomer (II), i.e., methacrylonitrile / carboxyl-containing monomer (II), is 0.8 or less.

6. The thermally expandable microcapsule according to claim 1, 2, 3, 4 or 5, wherein, The degree of gelation, measured using N,N-dimethylformamide (DMF) solvent, was less than 30% by weight.

7. The thermally expandable microcapsules according to claim 1, 2, 3, 4, 5 or 6, wherein, The polymer does not contain structural units derived from polymeric monomers having more than two double bonds within the molecule.

8. The thermally expandable microcapsule according to claim 1, 2, 3, 4, 5, 6 or 7, wherein, The content of the metal cation salt in the shell is more than 0.5% by weight and less than 10% by weight.

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