(Meta)acrylic resin foam and method for producing the same

Abstract

To provide a resin foam which is easy to produce so that it acquires a good foam state while having nano-size cells, and a production method thereof, and to provide a heat insulation material having good heat insulation performance.SOLUTION: Provided is a (meth)acrylic resin foam configured of a resin composition comprising a (meth)acrylic resin containing a constitutional unit(s) derived from a (meth)acrylic monomer(s) and nanoparticles and having nano-size cells, where the nanoparticles are provided with organic functional groups on the surface, and an absolute value of the difference between an SP value(s) of the organic functional groups and an SP value of the constitutional unit of the (meth)acrylic resin is 0.3 to 4.0.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a (meth)acrylic resin foam, a heat insulating material, and a method for producing a (meth)acrylic resin foam.

Background Art

[0002] Conventionally, resin foams have been widely used in various scenarios where various properties such as light weight, cushioning properties, and heat insulating properties are required. When producing a resin foam, additives such as a "nucleating agent" and a "cell regulator" are conventionally used to adjust the degree of foaming and the size of the cells. A nucleating agent is usually fine particles composed of a substance with poor affinity for the resin, and provides an environment in which a foaming agent gas is likely to precipitate at the interface with the resin to become nuclei of cells, so it is effective for adjusting the foamability when producing a resin foam.

[0003] By the way, the size of the cells of a general resin foam is usually at least several μm even when small, but attempts have been made to make it into a nano-order size (see Patent Documents 1 and 2 below). A resin foam having nano-sized cells is expected to exhibit much higher heat insulating properties than a general resin foam because the cell size is at the same level as or lower than the mean free path of air. In addition, a resin foam having nano-sized cells can exhibit characteristics different from those of conventional resin foams other than heat insulating properties. For this reason, application methods of a resin foam having nano-sized cells have been studied. Here, Patent Document 1 below describes a method for producing a resin foam having nano-sized cells, and describes using a nano particle as the nucleating agent.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] As described above, in order to exhibit the function of serving as nuclei of bubbles, those having an excessively good affinity with the resin to be foamed are unlikely to become nucleating agents. On the other hand, nucleating agents having a low affinity with the resin tend to aggregate when mixed with the resin. Therefore, it is difficult to manufacture a resin foam having nano-sized bubbles so as to achieve a good foaming state. Therefore, when attempting to apply a resin foam having nano-sized bubbles to a heat insulating material, it is difficult to obtain good heat insulating performance. Thus, an object of the present invention is to solve the above problems, and to provide a resin foam that is easy to manufacture so as to achieve a good foaming state while having nano-sized bubbles, and a method for manufacturing the same, and ultimately to provide a heat insulating material having good heat insulating performance.

Means for Solving the Problems

[0006] The inventors of the present invention have conducted intensive studies to solve the above problems, and have found that in a (meth)acrylic resin foam, the above problems can be solved by using nanoparticles having an organic functional group that exhibits a specific relationship with the resin in terms of the SP value, and thus have completed the present invention.

[0007] To solve the above problems, the present invention provides a (meth)acrylic resin foam composed of a resin composition containing a (meth)acrylic resin containing a structural unit derived from a (meth)acrylic monomer and nanoparticles, and having nano-sized bubbles, wherein the nanoparticles have an organic functional group on the surface, and an absolute value of a difference between the SP value of the organic functional group and the SP value of the structural unit of the (meth)acrylic resin is 0.3 or more and 4.0 or less.

[0008] To solve the above problems, the present invention provides a heat insulating material composed of a resin foam, wherein the resin foam is the above (meth)acrylic resin foam.

[0009] In order to solve the above problems, the present invention provides a method for producing a (meth)acrylic resin foam, comprising: a first step of preparing a resin composition for foaming by polymerizing a monomer composition containing nanoparticles having an organic functional group on the surface and a (meth)acrylic monomer; a second step of preparing a foaming resin composition by adding a foaming agent to the resin composition for foaming; and a third step of foaming the foaming resin composition, to produce a (meth)acrylic resin foam having nano-sized bubbles.

Advantages of the Invention

[0010] In the present invention, since the affinity between the (meth)acrylic resin and the nanoparticles is moderately high, aggregation of the nucleating agents is suppressed, the nanoparticles are easily dispersed homogeneously, and a good effect as a nucleating agent can be expected. Further, in the present invention, by including nanoparticles showing a specific affinity with such a (meth)acrylic resin, a (meth)acrylic resin foam having fine bubbles can be easily obtained without impairing the effect as an original nucleating agent.

Brief Description of the Drawings

[0011]

Figure 1

Figure 2

Figure 3A

Figure 3B

Figure 3C

Figure 4

Mode for Carrying Out the Invention

[0012] Hereinafter, embodiments of the present invention will be described. First, the (meth)acrylic resin foam will be described.

[0013] The (meth)acrylic resin foam of the present embodiment is composed of a resin composition containing a (meth)acrylic resin containing a structural unit derived from a (meth)acrylic monomer and nanoparticles. And the (meth)acrylic resin foam of the present embodiment is a foam having nano-sized bubbles. In the following, the maximum dimension in the cross-sectional shape of the bubble is referred to as the "length" of the bubble, etc., and the maximum dimension of the bubble in the direction orthogonal to the direction of this "length" may be referred to as the "width" of the bubble, etc. Further, in the following, the value obtained by adding the "length" and the "width" and dividing by 2 may be referred to as the "diameter" of the bubble. And, in this specification, "nano-sized bubbles" means that the "diameter" of the bubbles is on the nano order, and "(meth)acrylic resin foam having nano-sized bubbles" means "(meth)acrylic resin foam has bubbles with a diameter of less than 1 μm".

[0014] The (meth)acrylic resin contained in the resin composition constituting the (meth)acrylic resin foam of the present embodiment may be, for example, a resin having only a structural unit derived from one type of (meth)acrylic monomer or a resin having structural units derived from a plurality of types of (meth)acrylic monomers. The (meth)acrylic resin may contain a structural unit derived from a vinyl monomer copolymerizable with the (meth)acrylic monomer.

[0015] Here, the term "(meth)acrylic" in this specification is used with the intention of comprehensively expressing "acrylic" and "methacrylic". That is, the term (meth)acrylic monomer includes acrylic monomers and methacrylic monomers.

[0016] The (meth)acrylic resin in this embodiment can be a resin obtained by polymerizing the above-mentioned (meth)acrylic monomers with each other or a (meth)acrylic monomer and a monomer other than the (meth)acrylic monomer in the presence of a polymerization initiator.

[0017] Examples of the (meth)acrylic monomer that becomes a constituent unit of the (meth)acrylic resin include maleic acid, maleic anhydride, fumaric acid, itaconic acid, itaconic anhydride, crotonic acid, (meth)acrylic acid, (meth)acrylic acid ester, (meth)acrylamide, maleic acid amide, maleic acid imide, and the like.

[0018] Examples of the (meth)acrylic monomer may include those obtained by esterifying the hydroxyl groups at both ends of ethylene glycol such as ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, and triethylene glycol di(meth)acrylate with acrylic acid or methacrylic acid, and those obtained by esterifying the hydroxyl groups of divalent alcohols such as neopentyl glycol di(meth)acrylate, hexanediol di(meth)acrylate, and butanediol di(meth)acrylate with acrylic acid or methacrylic acid.

[0019] The (meth)acrylic monomer in this embodiment is preferably (meth)acrylic acid or a (meth)acrylate. Examples of the (meth)acrylate include alkyl (meth)acrylates such as methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, pentyl (meth)acrylate, amyl (meth)acrylate, isoamyl (meth)acrylate, hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, heptyl (meth)acrylate, octyl (meth)acrylate, decyl (meth)acrylate, dodecyl (meth)acrylate, pentadecyl (meth)acrylate, hexadecyl (meth)acrylate, heptadecyl (meth)acrylate, octadecyl (meth)acrylate; cycloalkyl (meth)acrylates such as cyclopropyl (meth)acrylate, cyclobutyl (meth)acrylate, cyclopentyl (meth)acrylate, cyclohexyl (meth)acrylate; crosslinked cyclic (meth)acrylates such as isobornyl methacrylate; aryl (meth)acrylates such as phenyl (meth)acrylate, tolyl (meth)acrylate, xylyl (meth)acrylate, naphthyl (meth)acrylate, binaphthyl (meth)acrylate, anthryl (meth)acrylate; aralkyl (meth)acrylates such as benzyl (meth)acrylate; and phenoxyalkyl (meth)acrylates such as phenoxyethyl (meth)acrylate.

[0020] The (meth)acrylic monomer in this embodiment is particularly preferably an alkyl (meth)acrylate having an alkyl group with 6 or fewer carbon atoms.

[0021] Examples of the structural units other than the (meth)acrylic monomer include aromatic vinyl monomers such as styrene, α-alkylstyrene, vinyltoluene, chlorostyrene; alkene monomers such as ethylene, propylene, butene; and alkadiene monomers such as butadiene, pentadiene.

[0022] (Meta)acrylic resins preferably have a proportion of (meta)acrylic monomers in their constituent units of 80% by mass or more. The proportion is more preferably 85% by mass or more, even more preferably 90% by mass or more, and particularly preferably 95% by mass or more. That is, the content of constituent units other than (meta)acrylic monomers in the (meta)acrylic resin is preferably 20% by mass or less, more preferably 15% by mass or less, even more preferably 10% by mass or less, and particularly preferably 5% by mass or less. The (meta)acrylic resin more preferably has a proportion of alkyl (meta)acrylate in its constituent units of 85% by mass or more. The proportion is even more preferably 90% by mass or more, and particularly preferably 95% by mass or more.

[0023] Examples of the polymerization initiator for forming the (meta)acrylic resin with these monomers include azo compounds such as azobisisobutyronitrile and azobisdimethylvaleronitrile.

[0024] The polymerization initiator may also be an organic peroxide such as benzoyl peroxide, lauroyl peroxide, t-butyl peroxybenzoate, isopropyl-t-butyl peroxycarbonate, butyl perbenzoate, t-butyl peroxy-2-ethylhexanoate, t-butyl perpivalate, t-butyl peroxyisopropyl carbonate, di-t-butyl peroxyhexahydroterephthalate, 1,1-di(t-butylperoxy)3,3,5-trimethylcyclohexane, 1,1-bis(t-amylperoxy)-3,3,5-trimethylcyclohexane, 1,1-di(t-butylperoxy)cyclohexane, or t-butyl peroxy-2-ethylhexyl monocarbonate. The polymerization initiator may be used alone or in combination of two or more.

[0025] When forming the (meta)acrylic resin with the monomers, a chain transfer agent or a polymerization inhibitor may be used for purposes such as controlling the molecular weight of the produced (meta)acrylic resin.

[0026] The chain transfer agent includes, for example, alkyl mercaptans such as dodecyl mercaptan and lauryl mercaptan; thioglycolic acid esters; mercaptoethanol, α-methylstyrene dimer, and the like. Examples of the polymerization inhibitor include hydroquinones such as hydroquinone, hydroquinone monomethyl ether, para-t-butyl hydroquinone, and para-benzoquinone; phenols such as 2,6-di-t-butyl-4-methylphenol and 6-t-butyl-2,4-dimethylphenol; catechols; amines, and the like.

[0027] Although it is possible to contain a resin other than the (meth)acrylic resin in the resin composition constituting the (meth)acrylic resin foam of the present embodiment, the proportion of the (meth)acrylic resin in all the resins contained in the resin composition is preferably 80% by mass or more. The proportion is more preferably 85% by mass or more, further preferably 90% by mass or more, particularly preferably 95% by mass or more. It is particularly preferable that the resin contained in the (meth)acrylic resin foam is substantially only the (meth)acrylic resin. That is, the proportion of the resin other than the (meth)acrylic resin in all the resins contained in the resin composition is preferably 20% by mass or less, more preferably 15% by mass or less, further preferably 10% by mass or less, particularly preferably 5% by mass or less, and particularly preferably substantially 0% by mass.

[0028] The nanoparticles contained in the resin composition together with the (meth)acrylic resin are provided with an organic functional group on the surface as described above. Examples of the organic functional group include those represented by the following general formula (1) or (2). -R 1 -X ···(1) -Y-R 1 -X ···(2)

[0029] "R" in formulas (1) and (2) 1Specific examples of "」 include, for example, those having a structure in which two hydrogens are removed from any one of linear saturated hydrocarbons, branched saturated hydrocarbons, cyclic saturated hydrocarbons, linear unsaturated hydrocarbons, branched unsaturated hydrocarbons, and cyclic unsaturated hydrocarbons.

[0030] Specific examples of "X" in formulas (1) and (2) include, for example, hydrogen (-H), halogen (-F, -Cl, -Br, ···), hydroxy group (-OH), carboxy group (-COOH), acid anhydride group (-CH-(-CH2-CO-O-)-C=O, -(CO)-O-(CO)-CH3, ···), amino group (-NH2), amide group (-CONH2), sulfonic acid group (-SO3H), nitro group (-NO2), vinyl group (-CH=CH2), acrylic group (-OOCCH=CH2), methacrylic group (-OOCC(CH3)=CH2), isocyanate group (-N=C=O), nitrile group (-CN), mercapto group (-SH), ureido group (-NHCONH2), epoxy group (-CH-(-O-)-CH2), etc.

[0031] Specific examples of "Y" in formula (2) include, for example, heteroatoms such as oxygen, sulfur, and nitrogen (-O-, -S-, -NH-, ···); ketone (-CO-); ester (-COO-); amide (-CONH-), etc.

[0032] As for the organic functional group, the number of carbon atoms is preferably 5 or more, more preferably 6 or more, still more preferably 7 or more, and particularly preferably 8 or more. The number of carbon atoms is preferably 16 or less, more preferably 15 or less, still more preferably 14 or less, and particularly preferably 12 or less. When the number of carbon atoms is at least the above lower limit value, the nanoparticles are easily and homogeneously dispersed in the resin, and the cells of the (meth)acrylic resin foam can be made finer. When the number of carbon atoms is at most the above upper limit value, a good effect as a nucleating agent can be obtained, and the cells of the (meth)acrylic resin foam can be made finer.

[0033] Examples of the organic functional group include a propyl group, a hexyl group, a decyl group, a dodecyl group, an acetoxypropyl group, a cyclohexyl group, a phenyl group, etc., with a hexyl group, a decyl group, a dodecyl group, etc. being particularly preferred.

[0034] The nanoparticles may be composed of organic particles or inorganic particles that form the nanoparticle body other than the organic functional group. The nanoparticles are preferably those in which the surface of inorganic particles is modified with a compound having the organic functional group. Examples of the inorganic particles include metal particles such as iron, cobalt, nickel, tin, zinc, lead, copper, aluminum, tungsten, silver, gold, and platinum group (ruthenium, rhodium, palladium, osmium, iridium); carbon particles such as carbon black, carbon nanofiber, and fullerene; inorganic oxide particles such as silica, alumina, titania, zirconia, zinc oxide, and boron oxide; inorganic hydroxide particles such as aluminum hydroxide and magnesium hydroxide; inorganic nitride particles such as silicon nitride, aluminum nitride, and boron nitride; inorganic carbide particles such as silicon carbide; inorganic carbonate particles such as calcium carbonate; barium titanate particles; barium sulfate particles; clay mineral particles (silicate compound particles), etc.

[0035] Among the above particles, organic particles, carbon black, etc. have hydroxyl groups or carboxyl groups on the surface. Therefore, for example, an organic functional group can be provided on the surface by bonding an organic compound having a hydroxyl group or an alkoxy group at the end to the surface by a condensation reaction. Among the above particles, inorganic hydroxide particles and inorganic oxide particles have many hydroxyl groups on the surface, which is advantageous for providing an organic functional group on the surface. That is, metal oxide particles such as silica particles are suitable as the nanoparticle body.

[0036] Regarding inorganic carbide particles, inorganic nitride particles, etc., although the amount is less compared to inorganic oxide particles, etc., hydroxyl groups are present on the surface. Also, if necessary, the surface hydroxyl groups of the above particles may be increased by performing corona treatment, plasma treatment, etc.

[0037] The nanoparticles of the present embodiment are preferably silica particles surface-modified with a compound having the organic functional group. The silica particles may be dry-process silica (fumed silica) or wet-process silica (sol-gel method silica). The nanosilica may be solid or hollow.

[0038] The organic functional group can be introduced, for example, by a silane coupling agent. For example, if untreated silica particles are surface-treated with a silane coupling agent represented by the following general formula (3), an organic functional group as shown in the above formula (1) can be provided on the surface of the silica particles. (R 2 O) n (R 3 ) 3-n Si-R 1 -X ···(3) (In the formula (3), "R 2 " and "R 3 " represent alkyl groups such as methyl group, ethyl group, and propyl group, and "n" represents an integer from 1 to 3.)

[0039] The absolute value of the difference in the SP value between the organic functional group in the nanoparticles and the structural unit constituting the (meth)acrylic resin is preferably 0.3 or more, more preferably 0.5 or more, still more preferably 0.9 or more, and particularly preferably 1.5 or more. The absolute value of the difference in the SP value between the organic functional group in the nanoparticles and the structural unit constituting the (meth)acrylic resin is preferably 4.0 or less, more preferably 3.8 or less, still more preferably 3.3 or less, and particularly preferably 2.7 or less. When the absolute value of the difference in the SP value from the structural unit constituting the (meth)acrylic resin is equal to or greater than the above lower limit value, a good effect as a nucleating agent can be obtained, and the bubbles in the (meth)acrylic resin foam can be made finer. When the absolute value of the difference in the SP value from the structural unit constituting the (meth)acrylic resin is equal to or less than the above upper limit value, the nanoparticles are likely to be uniformly dispersed in the resin, and the bubbles in the (meth)acrylic resin foam can be made finer.

[0040] Since the nanoparticles as described above are excellent in dispersibility in the resin, it is difficult to impair their performance as the original nucleating agent.

[0041] The SP value (solubility parameter value) of the organic functional group and the structural unit is calculated by the method described in the calculation method of Fedors, "Robert F. Fedors, Polymer Engineering and Science, 14, 147-154 (1974)". That is, the SP value (δ) is a value obtained based on the following formula (I). SP value (δ) = (ΣΔE / ΣV) 1 / 2 ···(I) 〔Unit: (cal / cm 3 ) 1 / 2 〕 ΔE: Evaporation energy (cal / mol) V: Molar molecular volume (cm 3 / mol)

[0042] An example of the evaporation energy and molar molecular volume for each functional group is shown in Table 1 in the examples.

[0043] The absolute value of the difference in SP values is calculated by the following formula (II). Absolute value of the difference in SP values = |SP value (δ1) - SP value (δ2)| ···(II) SP value (δ1): SP value of the structural unit constituting the (meth)acrylic resin SP value (δ2): SP value of the organic functional group in the nanoparticles

[0044] In this embodiment, it is preferable that the surface coverage rate of the organic functional group covering the surface of the nanoparticles is 10% or more. The surface coverage rate is more preferably 15% or more, still more preferably 20% or more, and particularly preferably 25% or more. The surface coverage rate is preferably 90% or less, more preferably 80% or less, still more preferably 40% or less, and particularly preferably 35% or less. When the surface coverage rate is equal to or higher than the above lower limit value, the nanoparticles are likely to be homogeneously dispersed in the resin, and the cells of the (meth)acrylic resin foam can be made finer. When the surface coverage rate is equal to or lower than the above upper limit value, a good effect as a nucleating agent can be obtained, and the cells of the (meth)acrylic resin foam can be made finer.

[0045] Regarding the surface coverage rate, when the main body of the nanoparticles excluding the organic functional group (also referred to as the particle main body) is a metal oxide particle having a surface functional group such as a hydroxyl group, and the organic functional group can be chemically fixed by a condensation reaction with the surface functional group or the like, it can be obtained by the following formula (III). Surface coverage rate = N1 / N ALL ···(III) (Note that "N ALL " is the number of all surface functional groups capable of chemically bonding the organic functional group, and "N1" is the number of surface functional groups to which the organic functional group is bonded.)

[0046] Regarding the surface coverage rate, for example, when the particle main body is untreated silica particles that have not been surface-treated, it can be obtained by the following formula (IV). Surface coverage rate = SiOH1 / SiOH ALL ···(IV) (Note that "SiOH ALL " is the number of all silanol groups before chemically bonding the organic functional group, and "SiOH1" is the number of silanol groups to which the organic functional group is bonded.)

[0047] FIG. 1 shows the case where the nanoparticles are silica particles having an organic functional group on the surface 29This is an example of a Si nuclear magnetic resonance (NMR) spectrum. Peaks are observed that are derived from the Q2 structure (silicon atoms bonded to two hydroxyl groups) around -90 to -95 ppm, the Q3 structure (silicon atoms bonded to one hydroxyl group) around -100 to -105 ppm, and the Q4 structure (silicon atoms not bonded to hydroxyl groups) around -105 to -120 ppm. Also, peaks are observed that are derived from the T2 structure (silicon atoms bonded to two organic functional groups) around -50 to -60 ppm and the T3 structure (silicon atoms bonded to one organic functional group) around -60 to -70 ppm. Note that the Q1 and T1 structures at the ends of the silica are observed, but the peaks are very small and can be ignored here. From the area ratios of these peaks, the number of silanol groups bonded with organic functional groups (SiOH1) and the number of all silanol groups before chemically bonding the organic functional groups (SiOH ALL ) can be calculated using the following formulas (V to XII).

[0048] The number of silanol groups bonded with organic functional groups (SiOH1) can be calculated as follows. Density of silanol groups bonded with organic functional groups (mol%) = (T2 + T3) / (Q2 + Q3 + Q4) × 100 ··· (V) T2: Peak area derived from the T2 structure of silica T3: Peak area derived from the T3 structure of silica Q2: Peak area derived from the Q2 structure of silica Q3: Peak area derived from the Q3 structure of silica Q4: Peak area derived from the Q4 structure of silica Concentration of silanol groups bonded with organic functional groups (mol / g) = ((Density of silanol groups bonded with organic functional groups (mol%)) / 100) / 60.1 ··· (VI) Number of silanol groups bonded with organic functional groups (SiOH1) (pieces / nm 2 ) = (Concentration of silanol groups bonded with organic functional groups (mol / g)) × (Avogadro's constant 6.022 × 10 23 / mol) / (Specific surface area of nanoparticles (nm 2 / g) × 10 18 ) ··· (VII)

[0049] The number of all silanol groups (SiOH) before chemically bonding organic functional groups ALL can be calculated as follows. The density of all silanol groups (mol%) before chemically bonding organic functional groups = (T2 + T3 + 2 × Q2 + Q3) / (Q2 + Q3 + Q4) × 100 ··· (VIII) T2: Peak area derived from the T2 structure of silica T3: Peak area derived from the T3 structure of silica Q2: Peak area derived from the Q2 structure of silica Q3: Peak area derived from the Q3 structure of silica Q4: Peak area derived from the Q4 structure of silica The concentration of all silanol groups (mol / g) before chemically bonding organic functional groups = ((the density of all silanol groups (mol%) before chemically bonding organic functional groups) / 100) / 60.1 ··· (IX) The number of all silanol groups (SiOH) before chemically bonding organic functional groups ALL (pieces / nm 2 ) = (the concentration of all silanol groups (mol / g) before chemically bonding organic functional groups) × (Avogadro's constant 6.022 × 10 23 / mol) / (the specific surface area of the nanoparticles (nm 2 / g) × 10 18 ) ··· (X) Surface coverage rate (%) = (the number of silanol groups (pieces / nm) bonded with organic functional groups 2 ) / (the number of all silanol groups (pieces / nm) that can chemically bond organic functional groups 2 )) × 100 ··· (XI)

[0050] In addition, a calibration curve based on the peak of the spectrum obtained by near-infrared spectroscopy is created using nanoparticles with a known surface coverage rate from the solid NMR measurement, and the surface coverage rate of nanoparticles with an unknown surface coverage rate can be calculated from the calibration curve.

[0051] As a method for creating the calibration formula, first, prepare three or more samples by mixing nanoparticles with a known surface coverage rate from the solid NMR measurement and nanoparticles before surface treatment at different ratios. Next, perform near-infrared spectroscopic measurements on these samples respectively. In the near-infrared region of each obtained spectrum, peaks attributed to the overtones of symmetric and antisymmetric stretching of C-H of organic functional groups are observed at 6000~5500 cm -1 <000033> is observed. Finally, create a calibration formula based on the peaks observed in each spectrum. In creating the calibration formula, the peak area or peak height in this region may be plotted against the surface coverage rate of the surface-coated particles to create the calibration formula, or the calibration formula may be created by multivariate regression analysis such as the PLS regression method.

[0052] The same applies when organic functional groups are present on the surface of nanoparticles mainly depending on physical interactions, such as when the particle body is a metal nanoparticle. The surface coverage rate can be obtained as shown in the following formula (XII). Surface coverage rate = A1 / A ALL ···(XII) (Here, "A ALL " is the surface area of the particle body, and "A1" is the area occupied by the organic functional group within the surface area of the particle body.)

[0053] The specific surface area of the particle body may be geometrically calculated from the particle size by an electron microscope or the like and the addition amount of the constituent raw material of the particle body. When such a calculation is difficult, instead of such a method, the specific surface area of the particle body may be obtained from the adsorption amount of nitrogen or hydrogen. The surface area occupied by the organic functional group can be obtained from the minimum coating area (for example, Sumiko Sagami, "Coupling Treatment of Titanium Oxide with Vinyltriethoxysilane", "Surface Technology", (The Surface Technology Association, 1999), page 86) and the loading amount.

[0054] The content of the nanoparticles in the resin composition is preferably 0.01% by volume or more, more preferably 0.3% by volume or more, still more preferably 0.5% by volume or more, and particularly preferably 1% by volume or more. The content is preferably 30% by volume or less, more preferably 25% by volume or less, still more preferably 22% by volume or less, and particularly preferably 20% by volume or less. When the content of the nanoparticles is not less than the above lower limit value, a good effect as a nucleating agent can be obtained, and the bubbles of the (meth)acrylic resin foam can be made finer. When the content of the nanoparticles is not more than the above upper limit value, the porosity of the bubbles of the (meth)acrylic resin foam can be made larger.

[0055] Regarding the nanoparticles and the (meth)acrylic resin, the stress value in the peeling calculation by classical molecular dynamics is preferably 100 MPa or more. The stress value is more preferably 150 MPa or more, still more preferably 200 MPa or more, and particularly preferably 300 MPa or more. The stress value is preferably 1500 MPa or less, more preferably 1000 MPa or less, still more preferably 900 MPa or less, and particularly preferably 700 MPa or less. When the stress value is not less than the above lower limit value, the nanoparticles are likely to be homogeneously dispersed in the resin, and the bubbles of the (meth)acrylic resin foam can be made finer. When the stress value is not more than the above upper limit value, a good effect as a nucleating agent can be obtained, and the bubbles of the (meth)acrylic resin foam can be made finer.

[0056] The peeling calculation can be performed using force field parameters. The force field parameters are obtained by calculating, based on first-principles calculations, a first potential curve (adsorption energy curve) that is a function of the adsorption energy between the nanoparticle and the (meth)acrylic resin and the distance from the surface of the nanoparticle to the (meth)acrylic resin, and then calculating a second potential curve that is a function of the intermolecular interaction between the surface of the nanoparticle and the (meth)acrylic resin and the distance from the surface of the nanoparticle to the (meth)acrylic resin, and using a curve obtained by fitting the second potential curve to the first potential curve (adsorption energy curve) based on the first-principles calculations.

[0057] That is, for the nanoparticle and the (meth)acrylic resin in the (meth)acrylic resin foam, a first potential curve (adsorption energy curve) that is a function of the adsorption energy between the nanoparticle and the (meth)acrylic resin and the distance from the surface of the nanoparticle to the (meth)acrylic resin is calculated based on first-principles calculations, a second potential curve that is a function of the intermolecular interaction between the surface of the nanoparticle and the (meth)acrylic resin and the distance from the surface of the nanoparticle to the (meth)acrylic resin is calculated based on the force field parameters, and when the force field parameters are fitted so that the second potential curve is matched to the first potential curve (adsorption energy curve) based on the first-principles calculations, it is preferable that the stress value in the peeling calculation by classical molecular dynamics using the fitted force field parameters is 300 MPa or more and 700 MPa or less.

[0058] FIG. 2 is a flowchart showing an example of a procedure for calculating the stress value in the peeling calculation according to the present invention.

[0059] A method for calculating the stress value in the peeling calculation will be described. As a procedure, first, a surface structure model in which a (meth)acrylic resin adheres to the surface of the nanoparticle is created (first step S1). Next, the first potential curve (adsorption energy curve) of the interface between the (meth)acrylic resin and the nanoparticle by first-principles calculation (DFT calculation) is analyzed (second step S2). Then, the force field parameters are optimized so as to reproduce the first potential curve (adsorption energy curve), and a second potential curve is obtained (third step S3). Thermal equilibration of the interface model between the (meth)acrylic resin and the nanoparticle by molecular dynamics calculation using the optimized force field parameters is performed (fourth step S4). Then, peeling analysis of the interface between the (meth)acrylic resin and the nanoparticle by molecular dynamics calculation using the force field parameters is performed (fifth step S5). Finally, the stress value in the peeling calculation is calculated (sixth step S6).

[0060] Next, the details of each step in the procedure for calculating the stress value in the peeling calculation will be described.

[0061] In the first step S1, a surface structure model in which a (meth)acrylic resin RZ adheres to the surface of the nanoparticle PC is created, and the structure optimization of the interface between the (meth)acrylic resin RZ and the nanoparticle PC is performed. As the molecular model of the (meth)acrylic resin RZ, for example, a dimer (a molecule in which two methyl (meth)acrylates are bonded) can be used. As the model of the nanoparticle PC, in order to avoid the influence of the periodic boundary, a structure having a sufficiently large surface area (number of atoms) is prepared. Further, as the model of the nanoparticle PC, a structure obtained by cutting out a stable surface of the particle body SB is prepared, and a surface structure model in which the surface is coated with a predetermined organic functional group FG is created. When the type, coating rate of the organic functional group FG and the particle body SB are changed, they are reflected in the surface structure model. The created surface structure model is first subjected to structure optimization with some atoms as one component by classical molecular dynamics calculation, and then the surface relaxation structure is calculated by first-principles calculation (DFT calculation), and the point charges of each final atom are set.

[0062] In the first step S1, as the simulation software used for classical molecular dynamics calculations, for example, the molecular dynamics simulation engine COGNAC in the material physical property analysis software J-OCTA (manufactured by JSOL Corporation) can be used. As the simulation software used for first-principles calculations (DFT calculations), for example, the first-principles electronic state calculation software SIESTA in the material physical property analysis software J-OCTA (manufactured by JSOL Corporation) can be used.

[0063] In the second step S2, the first potential curve (adsorption energy curve) of the interface between the (meth)acrylic resin RZ and the nanoparticle PC is analyzed by first-principles calculations (DFT calculations). Specifically, the (meth)acrylic resin RZ is placed at a certain distance from the surface structure model created in the first step S1, and then the (meth)acrylic resin RZ is randomly rotated while being pulled away from the surface of the nanoparticle PC. By sampling the interface model (adsorption structure) where at least three or more (meth)acrylic resins RZ are adsorbed on the surface of the nanoparticle PC, the first potential curve (adsorption energy curve) is obtained.

[0064] As the simulation software used for the calculations in the second step S2, for example, the first-principles electronic state calculation software SIESTA in the material physical property analysis software J-OCTA (manufactured by JSOL Corporation) can be used.

[0065] In the third step S3, the force field parameters (Lennard-Jones parameters) are optimized so as to reproduce the first potential curve (adsorption energy curve) obtained in the second step S2, and the second potential curve is obtained. Here, the intermolecular interaction (van der Waals interaction) between the (meth)acrylic resin and the surface of the nanoparticles can be expressed by the following Lennard-Jones potential (U(R)) as a function of the shortest distance (Z = R) in the Z direction from the nanoparticle PC to the geometric mean of the (meth)acrylic resin RZ, with the nanoparticle PC at the origin (Z = 0) in the surface relaxation structure created in the first step S1. U(R)=4Σ ij ε ij {(σ ij / r ij ) 12 -(σ ij / r ij ) 6}···(XIII) In formula (XIII), ε ij ,σ ij are the force field parameters (Lennard-Jones parameters) for each atom (i) constituting the (meth)acrylic resin RZ and each atom (j) constituting the nanoparticle PC, and r ij is the distance between each atom (i) constituting the (meth)acrylic resin RZ and each atom (j) constituting the nanoparticle PC. In order to reproduce the first potential curve (adsorption energy curve) obtained in the second step S2, each force field parameter (ε ij ,σ ij ) is fitted (optimized) using the simulated annealing method and the Nelder-Mead method to obtain the second potential curve.

[0066] Figures 3A to 3C are diagrams schematically showing an example of the calculation procedure of the stress value in the peeling calculation for the fourth step S4 to the sixth step S6.

[0067] In the fourth step S4, thermal equilibration of the interface model between the (meth)acrylic resin and the nanoparticles is performed by molecular dynamics calculations using the force field parameters obtained in the third step S3. First, in the same manner as in the first step S1, a surface structure model in which the (meth)acrylic resin RZ adheres to the surface of the nanoparticle PC is created. At least three or more models of the surface structure model are created by randomly changing the position and orientation of the (meth)acrylic resin RZ. At this time, for example, a decamer (methyl (meth)acrylate) can be used as the molecular model of the (meth)acrylic resin. Next, as an annealing procedure for thermal equilibration, for example, structural relaxation at 300K for 0.1ns, then at 350K for 0.7ns, and finally at 300K for 0.2ns is performed to obtain an interface model (adsorption structure) in which the (meth)acrylic resin RZ is adsorbed on the surface of the nanoparticle PC.

[0068] In the fifth step S5, peeling analysis of the interface between the (meth)acrylic resin RZ and the nanoparticle PC is performed by molecular dynamics calculations using the force field parameters obtained in the third step S3. Specifically, a restraint condition for translating the central carbon atom of the (meth)acrylic resin at a constant velocity (10 m / s) is set for each adsorption structure created in the fourth step S4, and peeling analysis (peeling calculation) is performed to peel off 20 Å in the Z direction from each adsorption structure. The peeling analysis (peeling calculation) is performed for each of the three or more interface models (adsorption structures) obtained in the fourth step S4.

[0069] In the sixth step S6, the stress value in the peeling calculation performed in the fifth step S5 is calculated. Specifically, during the peeling calculation, the vertical force acting on each atom (j) constituting the nanoparticle PC is calculated, and the stress value (P) is obtained by the following equation from the sum of these. P=(Σ j F j / S)···(XIV) F j : The vertical force acting on each atom (j) constituting the nanoparticle PC S: Cross-sectional area of the XY plane of the nanoparticle PC The stress value is calculated every 1 ps, the change over time is determined, and these are integrated to obtain the stress value in the peeling calculation. For all the stress values in the peeling analysis (peeling calculation) of the three or more interface models (adsorption models) obtained in the fifth step S5, the arithmetic mean of all the stress values is taken as the stress value in the peeling calculation in the present invention.

[0070] As the simulation software used in the calculations in the third step S3 to the sixth step S6, for example, the parallelized molecular dynamics engine VSOP in the material property analysis software J-OCTA (manufactured by JSOL Corporation) can be used.

[0071] The fact that the nanoparticles are of nano size can be confirmed, for example, by observing a thin film sample made of a (meth)acrylic resin foam with a transmission electron microscope (TEM). Specifically, a photograph of the thin film sample is taken using a TEM, the area (projection area) of the nanoparticles in the photograph is determined, and it can be confirmed that the nanoparticles are of nano size when the diameter of a circle having the same area as the area is less than 1 μm. The nanoparticles preferably have an average particle diameter (average value obtained when the diameters as described above are determined for a plurality (for example, 20 or more) of randomly selected nanoparticles) of 100 nm or less, more preferably 80 nm or less, and even more preferably 50 nm or less. The average particle diameter of the nanoparticles is preferably 1 nm or more, more preferably 5 nm or more. The average particle diameter is preferably 1 nm or more and 100 nm or less. When the average particle diameter is equal to or greater than the above lower limit value, aggregation of the nucleating agents is suppressed, and the bubbles in the (meth)acrylic resin foam can be made finer. When the average particle diameter is equal to or less than the above upper limit value, a good effect as a nucleating agent can be obtained, and the bubbles in the (meth)acrylic resin foam can be made finer.

[0072] The resin composition constituting the (meth)acrylic resin foam of the present embodiment may contain a plasticizer capable of exerting a plasticizing effect on the (meth)acrylic resin. Examples of the plasticizer include adipic acid esters, trimellitic acid esters, polyesters, phosphate esters, citric acid esters, epoxidized vegetable oils, sebacic acid esters, azelaic acid esters, maleic acid esters, benzoic acid esters, sulfonic acid esters, etc. Examples of the sulfonic acid ester include alkyl sulfonic acid esters. In the alkyl sulfonic acid ester, the number of carbon atoms in the alkyl group can be, for example, 12 to 20.

[0073] In addition to these, the resin composition constituting the (meth)acrylic resin foam of the present embodiment may contain various additives such as lubricants, plasticizers, antioxidants, antistatic agents, light stabilizers, ultraviolet absorbers, flame retardants, pigments, dyes, silane coupling agents, leveling agents, defoaming agents, fluorescent agents, etc.

[0074] As the foaming agent used when producing the (meth)acrylic resin foam, a chemical foaming agent that generates gas by reaction may be used. However, since the chemical foaming agent may also act as a nucleating agent, in the present embodiment, a physical foaming agent is preferred. Examples of the physical foaming agent include inorganic gases and volatile organic solvents. Examples of the inorganic gas include carbon dioxide, nitrogen, argon, helium, water, etc.

[0075] Examples of the volatile organic solvent include chain or cyclic hydrocarbons such as butane, pentane, hexane, octane, nonane, decane, undecane, cyclopentane, cyclohexane; ketones such as cyclopentanone, cyclohexanone, methyl ethyl ketone; esters such as ethyl acetate, butyl acetate; ethers such as tetrahydrofuran; aromatics such as benzene, toluene, xylene, ethylbenzene; nitrogen-containing compounds such as acetonitrile, N,N-dimethylformamide; halogen-containing compounds such as methylene chloride, chloroform, chlorofluorocarbons, etc.

[0076] Among these physical foaming agents, the foaming agent in the present embodiment preferably uses an inorganic gas. The foaming agent preferably contains one or more of carbon dioxide, nitrogen, argon, helium, and water.

[0077] Next, a method for producing a (meth)acrylic resin foam will be described. In the present embodiment, when producing an acrylic resin foam having nano-sized bubbles, it is preferable to perform the following steps (A) to (C). (A) A first step of polymerizing a monomer composition containing nanoparticles having an organic functional group on the surface and a (meth)acrylic monomer to prepare a resin composition for foaming. (B) A second step of preparing a foamable resin composition by adding a foaming agent to the resin composition for foaming. (C) A third step of foaming the foamable resin composition.

[0078] Specifically, the first step (A) can be carried out as follows. First, a silane coupling agent is added to a silica sol in which nano-sized silica particles are dispersed, and a nanoparticle dispersion sol containing nanoparticles surface-modified with an organic functional group is obtained by ultrasonic treatment. Next, the (meth)acrylic monomer is added and replaced with the solvent in the nanoparticle dispersion sol to obtain a monomer dispersion liquid. Next, a polymerization initiator is contained in the monomer dispersion liquid to prepare a monomer composition. Thereafter, the monomer composition is heated to advance the polymerization of the (meth)acrylic monomer, and the resin composition for foaming is obtained.

[0079] By obtaining the nanoparticle dispersion sol, the specific surface area (S: m 2performing measurement of / g), and adding a silane coupling agent in a predetermined amount by mass to 100 parts by mass of the silica particles to the silica sol may be carried out. The specific surface area of the silica particles can be measured by the BET method by nitrogen adsorption (JIS Z8830:2013 (ISO9277:2010) Method for measuring the specific surface area of powders (solids) by gas adsorption).

[0080] The silane coupling agent may be reacted with the silica particles by the integral blend method, and may be mixed with the silica particles together with the (meth)acrylic monomer or added to the (meth)acrylic monomer and then mixed with the silica particles. In terms of efficiently providing organic functional groups on the surface of the silica particles, it is preferably mixed with the silica particles before the (meth)acrylic monomer, and preferably added to the silica sol as described above.

[0081] The "minimum coverage area" can be calculated based on the molecular model of Stuart-briegleb. When the molecular weight of the silane coupling agent is M (g / mol), the minimum coverage area S min (m 2 / g)) is obtained as follows from formula (XV). S min (m 2 / g) = 78.26 × 1000 / M ··· (XV) (Note that "S min " is the minimum coverage area, and "M" is the molecular weight of the silane coupling agent.)

[0082] In this embodiment, the charged coverage rate of the organic functional group (the ratio of the silane coupling agent occupying the surface area of the silica) is obtained from the following formula (XVI) when the addition amount of the silane coupling agent is "X (g)" and the addition amount of the silica is "Y (g)". Charged coverage rate (%) = (X × S min / Y × S) × 100 ···· (XVI) The charging coating rate is preferably 10% or more. For example, since the surface area of 100 g of silica particles is " 2 100 × S (m min )", adding a silane coupling agent so that " 2 X × S (m 2 )" is 10 × S (m )" or more will result in a charging coating rate of 10% or more. X ≧ 10×S×M / 78260 ···(a1)

[0083] As described above, the charging coating rate is more preferably 12% or more, even more preferably 15% or more, and particularly preferably 20% or more. Therefore, for the addition amount (X (parts by mass)) of the silane coupling agent with respect to 100 parts by mass of silica particles, it is more preferable to satisfy the following formula (a2), even more preferable to satisfy the formula (a3), and particularly preferable to satisfy the formula (a4). X ≧ 12×S×M / 78260 ···(a2) X ≧ 15×S×M / 78260 ···(a3) X ≧ 20×S×M / 78260 ···(a4)

[0084] As described above, the charging coating rate is preferably 90% or less, more preferably 80% or less, even more preferably 50% or less, and particularly preferably 40% or less. Therefore, for the addition amount (X (parts by mass)) of the silane coupling agent with respect to 100 parts by mass of silica particles, it is preferable to satisfy the following formula (b1), more preferable to satisfy the formula (b2), even more preferable to satisfy the formula (b3), and particularly preferable to satisfy the formula (b4). X ≦ 90×S×M / 78260 ···(b1) X ≦ 80×S×M / 78260 ···(b2) X ≦ 50×S×M / 78260 ···(b3) X ≦ 40×S×M / 78260 ···(b4)

[0085] In the first step (A), since the nanoparticles exhibit excellent dispersibility with respect to the (meth)acrylic monomer, the formation of agglomerates in the monomer dispersion is suppressed. As a result, the formation of agglomerates of the nanoparticles is also suppressed in the monomer composition containing a polymerization initiator in the monomer dispersion and in the foaming resin composition obtained by heating and polymerizing the monomer composition. Thus, in the present embodiment, since it is easy to improve the dispersion state of the nanoparticles in the foaming resin composition containing the (meth)acrylic resin, the foaming resin composition can be produced by a simple method.

[0086] The second step (B) carried out after the first step (A) can be specifically carried out as follows.

[0087] In order to obtain a foamable resin composition by incorporating a foaming agent into the foaming resin composition, for example, the foaming resin composition is placed in a pressure vessel, the air in the pressure vessel is replaced with the foaming agent gas, and the foaming agent gas is pressured into the pressure vessel until the inside of the pressure vessel is in a pressurized state, and a method can be adopted in which the pressurized state is maintained for a certain period of time or more.

[0088] By holding the foaming resin composition in a pressurized state in this way, the foaming agent is impregnated into the resin composition, and a foamable resin composition in which the foaming agent is dissolved can be obtained. At this time, in order to enhance the impregnation property of the foaming agent, the foaming resin composition may be in a heated state. The heating of the foaming resin composition may be before or after the pressurization of the foaming agent. The inside of the pressure vessel may be, for example, at a gauge pressure of 5 MPa or more and 100 MPa or less, and preferably at a gauge pressure of 10 MPa or more and 50 MPa or less.

[0089] The foaming resin composition in the third step (C) can be carried out by releasing the blowing agent in the pressure vessel in a state where the blowing agent is sufficiently impregnated and decompressing the pressure vessel to atmospheric pressure. This step is preferably carried out in a state where the foaming resin composition is heated so as to be in a moderately softened state. In the first step (A), if the foaming resin composition is placed in a mold in which the molding space and the external space are in communication and the foaming resin composition is housed in the pressure vessel, in the third step, a (meth)acrylic resin foam having a desired shape imparted by the mold can be produced.

[0090] In this embodiment, a (meth)acrylic resin foam having nano-sized bubbles can be produced by such a simple method. The (meth)acrylic resin foam preferably has a porosity representing the volume ratio of the contained bubbles of 10% or more. The porosity is more preferably 15% or more, further preferably 20% or more, particularly preferably 25% or more. The porosity is particularly preferably 30% or more. When the porosity is at least the above lower limit value, the heat insulation performance of the (meth)acrylic resin foam can be further enhanced. The upper limit of the porosity is not particularly limited, but is usually 95% or less. The porosity may be 85% or less or 80% or less for ease of producing the (meth)acrylic resin foam. Considering comprehensively the light weight, heat insulation, and productivity, the porosity is preferably 30% or more and 80% or less.

[0091] (Meta)acrylic resin foam preferably has an average cell diameter of 10 nm or more and 1000 nm or less. The average cell diameter is more preferably 900 nm or less, still more preferably 800 nm or less, and particularly preferably 700 nm or less. The average cell diameter may be 50 nm or more or 100 nm or more. When the average cell diameter is equal to or greater than the above lower limit value, the heat insulation performance of the (meta)acrylic resin foam can be further enhanced. In addition, the (meta)acrylic resin foam produced in the present embodiment preferably has a ratio (area ratio) of cells with a length of 5 μm or more in the cross section of 20% or less. The ratio of such coarse cells is more preferably 15% or less, still more preferably 10% or less, and particularly preferably 5% or less. The average cell diameter and the ratio (area ratio) of cells of the (meta)acrylic resin foam can be determined by the method described in the examples.

[0092] The (meta)acrylic resin foam in which the formation of such coarse cells is suppressed exhibits excellent heat insulation properties when used as a heat insulating material. A heat insulating material composed of a resin foam, wherein the resin foam is the (meta)acrylic resin foam of the present embodiment, can be suitable for applications where high heat insulation properties are required.

[0093] In addition, the (meta)acrylic resin foam of the present embodiment can be used for various applications other than heat insulating materials. That is, the present invention is not limited to the above examples, and technical matters not exemplified above can be appropriately adopted.

Examples

[0094] Hereinafter, examples will be shown to specifically describe the method for producing the (meta)acrylic resin foam. However, the method for producing the acrylic resin foam of the present invention is not limited to the method exemplified below.

[0095] (Example 1) <Preparation of Foaming Resin Composition> (1) Preparation of Monomer Dispersion In a 100 mL eggplant flask, 2.5 g of a methanol silica sol (40% by mass as pure silica), 0.080 g of hexyltrimethoxysilane as a compound for introducing an organic functional group, and 0.005 g of dodecyl phosphoric acid as a reaction accelerator were added, and ultrasonic treatment was carried out for 40 minutes to obtain a nanoparticle dispersion sol in which silica particles having a hexyl group on the surface were dispersed in methanol. Next, a predetermined amount of methyl methacrylate was added as a monomer, and after stirring, methanol in the system was distilled off by an evaporator. The amount of methanol distilled off was estimated from the masses before and after distillation, and 1.0 g or more was distilled off. At this time, since methyl methacrylate was also distilled off simultaneously with methanol, methyl methacrylate was added so that the silica particles became 5.0% by volume to obtain a monomer dispersion liquid. At this time, methyl methacrylate that had been previously distilled under reduced pressure under the conditions of 100 mbar and 50 °C was used.

[0096] At this time, the charging coverage rate was geometrically calculated from the specific surface area of the silica particles and the minimum coverage area of hexyltrimethoxysilane. That is, with respect to the silica particle surface area of 61.0 m 2 30.5 m 2 By adding an amount of hexyltrimethoxysilane that would result in a coating such that the charging coverage rate became 50%, nanoparticles were obtained.

[0097] The surface coverage rate of the nanoparticles (organically modified silica) was 29 determined by Si nuclear NMR measurement. Also, the surface coverage rate was calculated by Equation (IV). That is, 29 From the ratio of the peak area of Si derived from silanol groups obtained by Si nuclear NMR measurement and the Si peak area derived from the silane coupling agent, and the specific surface area of silica, the number of silanol groups (SiOH1) to which organic functional groups were bonded and all the silanol groups (SiOH ALL ) that could chemically bond organic functional groups were calculated, and the surface coverage rate of the nanoparticles was determined from those ratios.

[0098] The apparatus and conditions used for the measurement were as follows. · Equipment: Bruker Biospin Avance NEO spectrometer · Probe: 3.2mm HX-MAS probe · Resonance frequency: 79.46 MHz · Measurement: DPMAS method · Signal detection: CPMG method (During this process, 1 SPINAL64 decoupling was irradiated on the H nucleus for measurement.) · MAS frequency: 20 kHz · Relaxation time: 1250 seconds · Number of integrations: 48 times · 29 Si RF magnetic field: 56 kHz · 1 H RF magnetic field: 100 kHz · Number of CPMG echoes acquired: 8

[0099] The number of silanol groups bonded with organic functional groups (SiOH1) in Example 1 was 2.8 (per nm 2 ), the number of all silanol groups before chemically bonding the organic functional groups (SiOH ALL ) was 7.9 (per nm 2 ), and the surface coverage rate was 35%.

[0100] The SP values of the organic functional groups and the resin structural units were calculated by the method described above. Here, the hexyl group as an organic functional group has an evaporation energy of 7025 cal / mol, a molar molecular volume of 114 cm 3 / mol, and an SP value (δ) of 7.85 cal / cm 3 ) 1 / 2 . The structural unit of polymethyl methacrylate has an evaporation energy of 8080 cal / mol, a molar molecular volume of 81.9 cm 3 / mol, and an SP value (δ) of 9.93 cal / cm 3 ) 1 / 2 . And the absolute value of the difference in SP values between the organic functional group and the constituent resin was calculated by the method described above. As a result, the absolute value of the difference in SP values in Example 1 was 2.1. (2) Preparation of the monomer composition To 10 g of the monomer dispersion, 57.86 mg of benzoyl peroxide and 38.58 mg of azobis(dimethylvaleronitrile) were added as polymerization initiators, and the mixture was stirred at room temperature for 30 minutes to prepare a monomer composition. (3) Preparation of the resin composition for foaming A metal plate with a hole having a depth of 1.0 mm and a diameter of 100 mm was prepared. The monomer composition was poured into the hole of the metal plate, and a commercially available polyimide film (thickness: 50 μm) as a release film was overlaid thereon. Another metal plate was overlaid as an upper lid, and it was heated in an oven at 55 °C for 7 hours and then heated at 105 °C for 2 hours to polymerize and solidify to prepare a resin composition for foaming and a circular tablet made of the resin composition for foaming. The obtained circular tablet was left standing overnight under the conditions of 110 °C and -0.1 MPa.

[0101] <Preparation of (meth)acrylic resin foam> The (meth)acrylic resin foam was prepared by the following procedure. (1) A resin disk having a diameter of 8.0 mm and a thickness of 1.0 mm was cut out as a sample for preparing a (meth)acrylic resin foam from the circular tablet. (2) The resin disk was placed in a pressure vessel having a cylindrical internal space and sealed. (3) The pressure vessel was placed in a small high-temperature chamber set at a temperature of 100 °C, and the inside of the pressure vessel was depressurized at -0.1 MPa for 5 minutes. (4) Carbon dioxide was supplied until the pressure inside the pressure vessel reached 40 MPa. (5) It was left standing for 24 hours to impregnate the resin disk with carbon dioxide and prepare a disk composed of a foaming resin composition. (6) The small high-temperature chamber was kept at the set temperature, the valve of the pressure vessel was opened, and the disk was foamed by rapid depressurization to prepare a (meth)acrylic resin foam. (7) After opening the valve of the pressure vessel, the pressure vessel was immediately placed in a water tank to rapidly cool the (meth)acrylic resin foam and taken out from the pressure vessel.

[0102] <Characteristic Evaluation of (Meth)Acrylic Resin Foam> (Density of Foaming Resin Composition and (Meth)Acrylic Resin Foam) The density ρ0 (g / cm 3 ) of the foaming resin composition before foaming and the density ρ1 (g / cm 3 ) of the (meth)acrylic resin foam were determined by the Archimedes method. Specifically, using an electronic balance (manufactured by Shimadzu Corporation, model: AP224X) equipped with a simple specific gravity measurement kit (manufactured by Shimadzu Corporation, model: SMK-601), the masses of the foaming resin composition and the (meth)acrylic resin foam in air and water were measured respectively, and from both, the density ρ0 (g / cm 3 ) of the foaming resin composition before foaming and the density ρ1 (g / cm 3 ) of the (meth)acrylic resin foam were automatically calculated.

[0103] (Porosity of (Meth)Acrylic Resin Foam) The porosity p (%) of the (meth)acrylic resin foam was calculated from the following formula (XVII) using the density ρ0 (g / cm 3 ) of the foaming resin composition before foaming and the density ρ1 (g / cm 3 ) of the (meth)acrylic resin foam. p (%) = (1 - (ρ1 / ρ0)) × 100 ···(XVII)

[0104] (Expansion Ratio of (Meth)Acrylic Resin Foam) The expansion ratio χ of the (meth)acrylic resin foam was calculated from the following formula (XVIII) using the density ρ0 (g / cm 3 ) of the foaming resin composition before foaming and the density ρ1 (g / cm 3 ) of the (meth)acrylic resin foam. χ = ρ0 / ρ1···(XVIII)

[0105] (Average Bubble Diameter (A)) The average bubble diameter (A) φ of the (meth)acrylic resin foam A was measured by the following method. First, after cooling the disk-shaped (meth)acrylic resin foam produced as described above with liquid nitrogen, it was cut along the center to divide the (meth)acrylic resin foam into two, and two semi-disk-shaped (meth)acrylic resin foams were produced. Using a scanning electron microscope (SEM) (manufactured by Hitachi, Ltd., trade name: S-4800), the cut surface was magnified 10,000 to 15,000 times and photographed to obtain a magnified photograph. Next, bubbles visible to the naked eye in the magnified photograph were filled with black using image processing software (GIMP) (version: 2.10.24), and the remaining area was filled with white to obtain a binarized magnified photograph. By processing this binarized magnified photograph with image processing software (image J (version: 1.51)), the cross-sectional area of the bubbles was obtained, and the average bubble diameter was calculated with the diameter of a circle having the same area as the bubble diameter.

[0106] The average bubble diameter was evaluated as follows. [Evaluation Criteria] ·A: The average bubble diameter is 300 nm or less ·B: The average bubble diameter is greater than 300 nm and 600 nm or less ·C: The average bubble diameter is greater than 600 nm

[0107] (Examples 2 and 3) In the step of preparing the monomer dispersion liquid, instead of using 0.080 g of hexyltrimethoxysilane, 0.040 g (Example 2) and 0.027 g (Example 3) were used respectively, and a (meth)acrylic resin foam was produced in the same manner as in Example 1. At this time, the charging coating rate was calculated by the same method as in Example 1. That is, with respect to the silica particle surface area of 61.0 m 2 15.3 m 2 Coating (Example 2), 10.4 m 2 By adding an amount of hexyltrimethoxysilane for coating (Example 3) to obtain a charging coating rate of 25% (Example 2) and a charging coating rate of 17% (Example 3), nanoparticles were obtained. The values and methods used to calculate the absolute value of the difference in SP values were the same as in Example 1.

[0108] The surface coverage rates of the nanoparticles in Examples 2 and 3 were determined by a calibration equation created by PLS regression from the near-infrared spectroscopic spectra of samples prepared by mixing the nanoparticles (organically modified silica) in Example 1 and the nanoparticles without organic functional groups on the surface (unmodified silica).

[0109] The calibration equation was created as follows. First, samples were prepared by mixing the nanoparticles (organically modified silica) in Example 1 with known surface coverage rates and the nanoparticles without organic functional groups on the surface (unmodified silica) at mass ratios of 100:0, 75:25, 50:50, 25:75, and 0:100 (samples with surface coverage rates of 35.0%, 26.3%, 17.5%, 8.8%, and 0%, respectively). For the above samples, diffuse reflection spectra were measured three times each using an ultraviolet-visible near-infrared spectrometer (V-770, manufactured by JASCO Corporation). The measurement wavelength range was 1550 - 1950 nm, and the wavelength interval was 1 nm. The spectral data in the region from 1600 nm to 1835 nm attributed to organic functional groups among the obtained spectra were used as explanatory variables, and a calibration equation was created by PLS regression using the surface coverage rate values of the nanoparticles in each sample as the target variables. At this time, the number of components in the PLS regression was up to the third component. The PLS regression was executed using the program PLS Regression in the machine learning library scikit-learn. The coefficient of determination of the obtained calibration equation was 1.0, and the root mean square error of the second power was 0.39. From this, it was confirmed that the surface coverage rate of the nanoparticles could be calculated with high accuracy from the created calibration equation.

[0110] Next, for the nanoparticles used in Examples 2 and 3, diffuse reflection spectra were measured three times each using the same measurement method with an ultraviolet-visible near-infrared spectrometer (V-770, manufactured by JASCO Corporation). Using the obtained spectra as explanatory variables, the surface coverage rate of the nanoparticles was calculated using the calibration equation obtained by the created PLS regression. As a result, the surface coverage rates of the nanoparticles in Examples 2 and 3 were 30% and 26%, respectively.

[0111] (Examples 4 - 6) In the step of preparing the monomer dispersion liquid, instead of hexyltrimethoxysilane, acetoxypropyltrimethoxysilane was used, and the amounts of acetoxypropyltrimethoxysilane used were 0.086 g (Example 4), 0.043 g (Example 5), and 0.029 g (Example 6), respectively. A (meth)acrylic resin foam was produced in the same manner as in Example 1 except for this. At this time, the charging coating rate was calculated in the same manner as in Example 1. That is, with respect to the silica particle surface area of 61.0 m 2 respectively 30.5 m 2 coating (Example 4), 15.3 m 2 coating (Example 5), 10.4 m 2 coating (Example 6), by adding acetoxypropyltrimethoxysilane, nanoparticles were obtained such that the charging coating rate was 50% (Example 4), the charging coating rate was 25% (Example 5), and the charging coating rate was 17% (Example 6). The evaporation energy of the acetoxypropyl group is 8965 cal / mol, the molar molecular volume is 99.8 cm 3 / mol, and the SP value (δ) is 9.48 cal / cm 3 ). 1 / 2 The absolute value of the difference between the SP value of the structural unit constituting the (meth)acrylic resin and the SP value of the organic functional group in the nanoparticles is 0.5. The method for calculating the SP value and the method for calculating the absolute value of the SP value difference are the same as in Example 1.

[0112] The surface coating rate of the nanoparticles in Example 4 was calculated in the same manner as in Example 1. The number of silanol groups (SiOH1) to which the organic functional group was bonded in Example 4 was 3.5 (pieces / nm 2 ), the number of all silanol groups (SiOH ALL ) before chemically bonding the organic functional group was 8.2 (pieces / nm 2 ), and the surface coating rate of the nanoparticles was 43%.

[0113] The surface coating rates of the nanoparticles in Examples 5 and 6 were calculated from the calibration curve by PLS regression in the same manner as in Examples 2 and 3 except that the nanoparticles in Example 4 were used. As a result, the surface coating rates of the nanoparticles in Examples 5 and 6 were 30% and 22%, respectively.

[0114] (Examples 7 and 8) In the step of preparing the monomer dispersion liquid, dodecyltrimethoxysilane was used instead of hexyltrimethoxysilane, and the amounts of dodecyltrimethoxysilane used were 0.112 g (Example 7) and 0.056 g (Example 8), respectively. Otherwise, a (meth)acrylic resin foam was produced in the same manner as in Example 1. At this time, the charged coating rate was calculated in the same manner as in Example 1. That is, with respect to the silica particle surface area of 61.0 m 2 30.5 m 2 coating (Example 7) and 15.3 m 2 coating (Example 8) of dodecyltrimethoxysilane were added to obtain nanoparticles with a charged coating rate of 50% (Example 7) and a charged coating rate of 25% (Example 8). The evaporation energy of the dodecyl group is 14105 cal / mol, the molar molecular volume is 210.6 cm 3 / mol, and the SP value (δ) is 8.18 cal / cm 3 ). 1 / 2 The absolute value of the difference between the SP value of the structural unit constituting the (meth)acrylic resin and the SP value of the organic functional group in the nanoparticles is 1.8. The method for calculating the SP value and the method for calculating the absolute value of the SP value difference are the same as in Example 1.

[0115] The surface coating rate of the nanoparticles in Example 7 was calculated in the same manner as in Example 1. The number of silanol groups (SiOH1) to which the organic functional group was bonded in Example 7 was 2.7 (per nm 2 ), the number of all silanol groups (SiOH ALL ) before chemically bonding the organic functional group was 8.3 (per nm 2 ), and the surface coating rate of the nanoparticles was 33%.

[0116] The surface coating rate of the nanoparticles in Example 8 was calculated from the calibration curve by PLS regression in the same manner as in Examples 2 and 3, except that the nanoparticles in Example 7 were used. As a result, the surface coating rate of the nanoparticles in Example 8 was 29%.

[0117] (Comparative Example 1) In the step of preparing the monomer dispersion liquid, a (meth)acrylic resin foam containing nanoparticles without organic functional groups on the surface was prepared in the same manner as in Example 1, except that hexyltrimethoxysilane or the like was not used.

[0118] (Comparative Examples 2 and 3) In the step of preparing the monomer dispersion liquid, methyltrimethoxysilane was used instead of hexyltrimethoxysilane, and the amounts of methyltrimethoxysilane used were 0.053 g (Comparative Example 2) and 0.026 g (Comparative Example 3), respectively. A (meth)acrylic resin foam was prepared in the same manner as in Example 1. At this time, the charging coating rate was calculated by the same method as in Example 1. That is, with respect to the silica particle surface area of 61.0 m 2 30.5 m 2 coating (Comparative Example 2) and 15.3 m 2 coating (Comparative Example 3) of methyltrimethoxysilane were added to obtain nanoparticles with a charging coating rate of 50% (Comparative Example 2) and a charging coating rate of 25% (Comparative Example 3). The evaporation energy of the methyl group is 1125 cal / mol, the molar molecular volume is 33.5 cm 3 / mol, and the SP value (δ) is 5.80 cal / cm 3 ) 1 / 2 and the absolute value of the difference between the SP value of the structural unit constituting the (meth)acrylic resin and the SP value of the organic functional group in the nanoparticles is 4.1. The calculation method of the SP value and the calculation method of the absolute value of the SP value difference are the same as in Example 1.

[0119] The surface coating rate of the nanoparticles in Comparative Example 2 was calculated by the same method as in Example 1. The number of silanol groups (SiOH1) to which the organic functional group was bonded in Comparative Example 2 was 2.8 (pieces / nm 2 ), the number of all silanol groups (SiOH ALL ) before chemically bonding the organic functional group was 9.3 (pieces / nm 2 ), and the surface coating rate of the nanoparticles was 30%.

[0120] The surface coverage rate of the nanoparticles in Comparative Example 3 was calculated from the calibration curve by PLS regression in the same manner as in Examples 2 and 3, except that the nanoparticles of Comparative Example 2 were used. As a result, the surface coverage rate of the nanoparticles in Comparative Example 3 was 15%.

[0121] (Comparative Example 4) A (meth)acrylic resin foam was produced in the same manner as in Example 1, except that no nanoparticles were contained, and the monomer composition was prepared using only methyl methacrylate, benzoyl peroxide, and azobis(dimethylvaleronitrile), and a (meth)acrylic resin foam containing no nanoparticles was produced.

[0122] The production conditions and properties of the (meth)acrylic resin foams obtained in each Example and Comparative Example are shown in Table 2 and Table 3 below, respectively. In addition, an enlarged photograph of the obtained (meth)acrylic resin foam is shown in Fig. 4.

[0123]

Table 1

[0124]

Table 2

[0125]

Table 3

[0126] From the above, it can be seen that according to the present invention, a resin foam that is easy to manufacture so as to have a good foamed state while having nano-sized bubbles can be obtained.

Claims

The (meth)acrylic resin foam is composed of a resin composition containing a (meth)acrylic resin containing a structural unit derived from one or more (meth)acrylic monomers and nanoparticles, and has nano-sized bubbles, wherein the nanoparticles have an organic functional group on the surface, 95% by mass or more of the structural units of the (meth)acrylic resin are structural units derived from the (meth)acrylic monomer, the SP value of the structural unit derived from the (meth)acrylic monomer is, a (meth)acrylic resin foam in which the absolute value of the difference from the SP value of the organic functional group is 0.3 or more and 4.0 or less. The (meth)acrylic resin foam according to claim 1, wherein the surface coverage rate of the organic functional group covering the surface of the nanoparticles is 10% or more and 90% or less. The (meth)acrylic resin foam according to claim 1 or 2, wherein the organic functional group has 5 or more and 16 or less carbon atoms. Based on first-principles calculations, a first potential curve that is a function of the adsorption energy between the nanoparticles and the (meth)acrylic resin and the distance from the surface of the nanoparticles to the (meth)acrylic resin is estimated, Based on force field parameters, a second potential curve that is a function of the intermolecular interaction between the surface of the nanoparticles and the (meth)acrylic resin and the distance from the surface of the nanoparticles to the (meth)acrylic resin is estimated, When the force field parameters are fitted so that the second potential curve is matched to the first potential curve based on the first-principles calculation, the nanoparticles and the (meth)acrylic resin, The (meth)acrylic resin foam according to any one of claims 1 to 3, wherein the stress value in the peeling calculation by classical molecular dynamics using the fitted force field parameters is 100 MPa or more and 1500 MPa or less. The (meth)acrylic resin foam according to any one of claims 1 to 4, wherein the nanoparticles are silica particles surface-modified with a compound having the organic functional group. The (meth)acrylic resin foam according to any one of claims 1 to 5, wherein the proportion of the nanoparticles in the resin composition is 0.01% by volume or more and 30% by volume or less. The (meth)acrylic resin foam according to any one of claims 1 to 6, wherein the average particle diameter of the nanoparticles is 1 nm or more and 100 nm or less. ​ ​ ​ ​ ​ ​ ​ The (meth)acrylic resin foam according to any one of claims 1 to 7, wherein the average bubble diameter is 10 nm or more and 1000 nm or less.

9. The (meth)acrylic resin foam according to any one of claims 1 to 8, wherein the porosity is 10% or more and 95% or less.

10. A heat insulating material composed of a resin foam, wherein the resin foam is the (meth)acrylic resin foam according to any one of claims 1 to 9.

11. A method for producing a (meth)acrylic resin foam for producing the (meth)acrylic resin foam according to any one of claims 1 to 9, a first step of polymerizing a monomer composition containing nanoparticles having an organic functional group on the surface and a (meth)acrylic monomer to prepare a resin composition for foaming; a second step of preparing a foamable resin composition by adding a foaming agent to the resin composition for foaming; a third step of foaming the foamable resin composition, and a method for producing a (meth)acrylic resin foam having nano-sized bubbles.

12. The method for producing a (meth)acrylic resin foam according to claim 11, wherein the foaming agent contains one or more of carbon dioxide, nitrogen, argon, helium, and water.

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