film

Abstract

The objective is to provide a thin thermally conductive film that can easily bond a heat-generating element and a heat-sinking element. [Solution] The present invention relates to a film formed from a resin composition comprising a (meth)acrylic resin and alumina particles, wherein the alumina particles are present in an amount of 50% by volume or more of 100% by volume of the solid content of the resin composition and have one or more peaks in the particle size distribution. When X is the percentage of alumina particles A having a particle size distribution containing the peak with the largest particle size among 100% by mass of alumina particles, Y is the D50 of alumina particles A (μm), and Z is the thickness of the film (μm), The film has a Y dimension of 2.0 μm or more, a Z dimension of less than 100 μm, and satisfies the following formula (1). Z / (Y×X / 100)≧2.5 ···(1)

Description

[Technical Field]

[0001] The present invention relates to a film, and more particularly to a film formed from a resin composition comprising a (meth)acrylic resin and alumina particles. [Background technology]

[0002] The heat generated by energizing electronic components is dissipated through a heat sink. To improve heat dissipation efficiency, a technique is known in which the space between the electronic component and the heat sink is filled with a heat dissipation material. Such heat dissipation materials include thermally conductive resin compositions containing resin and inorganic powder, and alumina powder is known to be usable as the inorganic powder.

[0003] For example, Patent Document 1 discloses a heat dissipation member using a resin composition comprising spherical alumina powder having a specific particle size and number of isolated OH groups, and a silicone resin. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2011-98841 [Overview of the project] [Problems that the invention aims to solve]

[0005] Patent Document 1 discloses a resin composition that has excellent thermal conductivity. TIM (thermal interlayer bonding material) is used sandwiched between a heating element and a heat sink or other heat dissipation element, but depending on the application, the adhesive surface may peel off due to shear stress generated during use, resulting in a decrease in thermal conductivity. In addition, if the TIM is a thick film, there is a problem of reduced thermal conductivity in the thickness direction, so it is desirable to make it as thin as possible.

[0006] Therefore, the present invention aims to provide a thin thermally conductive film that can easily bond a heat-generating element and a heat-sinking element. [Means for solving the problem]

[0007] The present invention, which has achieved the above objectives, is as follows. [1] A film formed from a resin composition comprising a (meth)acrylic resin and alumina particles, The alumina particles are present in an amount of 50% or more by volume of 100% by volume of the solid content of the resin composition, and have one or more peaks in the particle size distribution. When X is the percentage of alumina particles A having a particle size distribution containing the peak with the largest particle size among 100% by mass of alumina particles, Y is the D50 of alumina particles A (μm), and Z is the thickness of the film (μm), A film characterized in that Y is 2.0 μm or more, Z is less than 100 μm, and satisfies the following formula (1). Z / (Y×X / 100)≧2.5 ···(1) [2] The film according to [1], wherein the alumina particles A are spherical. [3] The film according to [1] or [2], wherein the roundness of the alumina particles A is 0.80 or greater. [4] The specific surface area of ​​the alumina particle A is 0.8 m² 2 A film described in any of [1] to [3] that is less than or equal to / g. [5] The film according to any one of [1] to [4], wherein the alumina particles have two or more peaks in the particle size distribution. [6] The film according to [5], wherein the D50 of alumina particles B having a particle size distribution including the second largest peak is 0.1 μm or larger. [7] The film according to claim [5] or [6], wherein the proportion of alumina particles A in 100% by mass of alumina particles is 40 to 80% by mass. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a thin, highly adhesive, and thermally conductive film. [Modes for carrying out the invention]

[0009] The film of the present invention is a film formed from a resin composition containing a (meth)acrylic resin and alumina particles, wherein the alumina particles are present in an amount of 50% by volume or more of 100% by volume of the solid content of the resin composition, and have one or more peaks in the particle size distribution, and when the proportion of alumina particles A having a particle size distribution containing the peak with the largest particle size among 100% by mass of alumina particles is X by mass, the D50 of alumina particles A is Y (μm), and the thickness of the film is Z (μm), Y is 2.0 μm or more, Z is less than 100 μm, and satisfies the following formula (1). Z / (Y×X / 100)≧2.5 ···(1)

[0010] <Resin composition> The resin composition in this invention comprises a (meth)acrylic resin and alumina particles. Suitable resins and alumina particles for constituting the resin composition are described below.

[0011] <(meth)acrylic resin> (Meth)acrylic resins have excellent adhesive properties, as well as excellent release properties, weather resistance, and heat resistance. The (meth)acrylic resin contained in the resin composition is preferably a polymer (hereinafter also referred to as "(meth)acrylic ester polymer") whose main component is a structural unit derived from an alkyl (meth)acrylate ester represented by the following formula (I) (hereinafter also referred to as "structural unit (I)"). For example, it contains 50 parts by mass or more per 100 parts by mass of structural units of the (meth)acrylic resin. The amount of structural units represented by formula (I) per 100 parts by mass of structural units of the (meth)acrylic resin is preferably 60 to 99 parts by mass, more preferably 70 to 98 parts by mass, even more preferably 80 to 97 parts by mass, and even more preferably 85 to 95 parts by mass. In the present specification, "(meth)acrylic resin" means either acrylic resin or methacrylic resin, and "(meth)" in "(meth)acrylate" and the like has the same meaning.

[0012] [Chemical formula] [In the formula, R 10 represents a hydrogen atom or a methyl group, and R 20 represents an alkyl group having 1 to 20 carbon atoms. The alkyl group may have any of linear, branched, or cyclic structures, and a hydrogen atom of the alkyl group may be replaced with an alkoxy group having 1 to 10 carbon atoms.]

[0013] R 20 is preferably an alkyl group having 1 to 10 carbon atoms, more preferably an alkyl group having 1 to 6 carbon atoms, and still more preferably a linear alkyl group having 1 to 6 carbon atoms.

[0014] Examples of the (meth)acrylate represented by the formula (I) include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, i-propyl (meth)acrylate, n-butyl (meth)acrylate, i-butyl (meth)acrylate, n-pentyl (meth)acrylate, n-hexyl (meth)acrylate, i-hexyl (meth)acrylate, n-heptyl (meth)acrylate, n-octyl (meth)acrylate, i-octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n- and i-nonyl (meth)acrylate, n-decyl (meth)acrylate, i-decyl (meth)acrylate, n-dodecyl (meth)acrylate, cyclohexyl (meth)acrylate, isobornyl (meth)acrylate, stearyl (meth)acrylate, t-butyl (meth)acrylate, and the like. Specific examples of the alkoxy group-containing alkyl acrylate include 2-methoxyethyl (meth)acrylate, ethoxymethyl (meth)acrylate, and the like. The structural unit (I) may be one type or two or more types. Among them, it is preferably included n-butyl (meth)acrylate, and preferably included n-butyl (meth)acrylate and methyl (meth)acrylate.

[0015] In 100% by mass of the structural unit (I), R 20 is preferably 80 to 100% by mass, more preferably 85 to 97% by mass of the structural unit (particularly n-butyl (meth)acrylate) in which is a linear alkyl group having 1 to 6 carbon atoms.

[0016] The (meth)acrylate polymer may contain a structural unit derived from another monomer other than the structural unit (I). The structural unit derived from another monomer may be one type or two or more types. Examples of other monomers that the (meth)acrylate polymer may contain include monomers having a polar functional group, monomers having an aromatic group, and acrylamide-based monomers.

[0017] Examples of monomers having polar functional groups include monomers having polar functional groups. Examples of polar functional groups include hydroxyl groups, carboxyl groups, substituted amino groups or unsubstituted amino groups substituted with alkyl groups having 1 to 6 carbon atoms, and heterocyclic groups such as epoxy groups.

[0018] The content of structural units derived from monomers having polar functional groups in the (meth)acrylic acid ester polymer is preferably 10 parts by mass or less, more preferably 0.5 parts by mass or more and 10 parts by mass or less, even more preferably 0.5 parts by mass or more and 5 parts by mass or less, and particularly preferably 1 part by mass or more and 5 parts by mass or less, per 100 parts by mass of the total structural units of the (meth)acrylic acid ester polymer.

[0019] Monomers containing aromatic groups include (meth)acrylic acid esters having one (meth)acryloyl group and one or more aromatic rings (e.g., a benzene ring, a naphthalene ring, etc.) within the molecule, specifically those having a phenyl group, a phenoxyethyl group, or a benzyl group. By including these structural units, the whitening phenomenon of polarizing plates that occurs in high temperature and high humidity environments can be suppressed.

[0020] The content of structural units derived from monomers having aromatic groups in the (meth)acrylic acid ester polymer is preferably 20 parts by mass or less, more preferably 15 parts by mass or less, per 100 parts by mass of the total structural units of the (meth)acrylic acid ester polymer.

[0021] Furthermore, structural units derived from monomers other than structural unit (I) may include structural units derived from styrene monomers, structural units derived from vinyl monomers, structural units derived from monomers having multiple (meth)acryloyl groups in the molecule, and so on.

[0022] The weight-average molecular weight (hereinafter also simply referred to as "Mw") of the (meth)acrylic resin is preferably between 500,000 and 2,500,000. A weight-average molecular weight of 500,000 or more improves the durability of the film in high-temperature, high-humidity environments. A weight-average molecular weight of 2,500,000 or less improves the operability when applying a coating liquid containing the resin composition. The Mw of the (meth)acrylic resin is more preferably between 700,000 and 2,300,000, and even more preferably between 1,000,000 and 2,000,000.

[0023] Furthermore, the molecular weight distribution (Mw / Mn) of the (meth)acrylic resin, expressed as the ratio of the weight-average molecular weight (Mw) to the number-average molecular weight (hereinafter also simply referred to as "Mn"), is usually 2 to 10, preferably 3 to 8, and more preferably 4 to 7.

[0024] In this specification, "weight-average molecular weight" and "number-average molecular weight" are polystyrene-equivalent values ​​measured by gel permeation chromatography (GPC).

[0025] When the (meth)acrylic resin is dissolved in ethyl acetate to form a 20% by mass solution, its viscosity at 25°C is preferably 20 Pa·s or less, and more preferably 0.1 to 15 Pa·s. When the viscosity of the (meth)acrylic resin at 25°C is within the above range, the reworkability of the film formed from the resin is good. The viscosity can be measured using a Brookfield viscometer.

[0026] The glass transition temperature (Tg) of (meth)acrylic resins is, for example, -60 to 20°C, preferably -50 to 15°C, more preferably -45 to 10°C, and even more preferably -40 to 0°C. The glass transition temperature can be measured by differential scanning calorimeter (DSC).

[0027] The (meth)acrylic resin may contain two or more (meth)acrylic acid ester polymers. Examples of such (meth)acrylic acid ester polymers include those in which structural unit (I) derived from the (meth)acrylic acid ester is the main component (for example, containing 50 parts by mass or more per 100 parts by mass of structural unit (I) of the (meth)acrylic resin), and which have a relatively low molecular weight, such as having a weight-average molecular weight in the range of 50,000 to 300,000. The amount of such relatively low molecular weight (meth)acrylic acid ester polymer is preferably 0 to 10% by mass, more preferably 0 to 5% by mass, and even more preferably 0 to 3% by mass, in 100% by mass of the (meth)acrylic resin.

[0028] (Meth)acrylic resins can usually be produced by known polymerization methods such as solution polymerization, bulk polymerization, suspension polymerization, and emulsion polymerization. In the production of (meth)acrylic resins, polymerization is usually carried out in the presence of a polymerization initiator. The amount of polymerization initiator used is usually 0.001 to 5 parts by mass per 100 parts by mass of the total amount of all monomers constituting the (meth)acrylic resin. (Meth)acrylic resins can also be produced by polymerization using active energy rays such as ultraviolet light.

[0029] The resin composition may optionally contain a solvent, a crosslinking agent, and at least one additive such as a silane compound.

[0030] <Solvent> The solvent is not particularly limited as long as it can dissolve the (meth)acrylic resin, but it is preferably a volatile organic solvent. Examples of such organic solvents include ester solvents and ketone solvents. The boiling point of the organic solvent is preferably 100°C or lower.

[0031] <Crosslinking agent> Examples of crosslinking agents include conventional crosslinking agents (e.g., isocyanate compounds, epoxy compounds, aziridine compounds, metal chelate compounds, peroxides, etc.), and isocyanate compounds are particularly preferred from the viewpoint of the pot life of the resin composition, the crosslinking rate, and the durability of the film.

[0032] Isocyanate compounds are compounds having at least two isocyanate groups (-NCO) in their molecule. Specifically, examples include tolylene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, xylylene diisocyanate, hydrogenated xylylene diisocyanate, diphenylmethane diisocyanate, hydrogenated diphenylmethane diisocyanate, naphthalene diisocyanate, and triphenylmethane triisocyanate. Adduct compounds obtained by reacting these isocyanate compounds with polyols such as glycerol and trimethylolpropane, as well as dimers and trimers of these isocyanate compounds, are also examples. Two or more isocyanate compounds may be combined.

[0033] The proportion of the crosslinking agent is, for example, 0.01 to 10 parts by mass, preferably 0.05 to 5 parts by mass, and more preferably 0.1 to 1 part by mass, per 100 parts by mass of (meth)acrylic resin.

[0034] <Silane compounds> Examples of silane compounds include vinyltrimethoxysilane, vinyltriethoxysilane, vinyltris(2-methoxyethoxy)silane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 3-glycidoxypropylethoxydimethylsilane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 3-chloropropylmethyldimethoxysilane, 3-chloropropyltrimethoxysilane, 3-methacryloyloxypropyltrimethoxysilane, and 3-mercaptopropyltrimethoxysilane. Furthermore, the silane compound may contain oligomers derived from the above-mentioned silane compound.

[0035] The silane compound content in the resin composition is typically 0.01 to 10 parts by mass, preferably 0.05 to 5 parts by mass, per 100 parts by mass of (meth)acrylic resin. When the silane compound content is 0.01 parts by mass or more, the adhesion between the film and the adherend tends to improve, and when the content is 10 parts by mass or less, the bleed-out of the silane compound from the film tends to be suppressed.

[0036] The total amount of (meth)acrylic resin and additives in 100% by volume of the solid content of the resin composition is preferably 10 to 50% by volume, more preferably 15 to 45% by volume, and even more preferably 20 to 40% by volume. Note that the solid content volume and solid content mass of the resin composition refer to the volume and mass obtained by subtracting the solvent from the resin composition, respectively.

[0037] The resin composition may contain, individually or in combination of two or more other additives, such as UV absorbers, crosslinking catalysts, tackifiers, and plasticizers. Furthermore, it is also useful to incorporate UV-curable compounds into the resin composition, form a film, and then cure it by irradiating it with UV light to obtain a harder film.

[0038] <Alumina particles> In this specification, "alumina particles" refers to both alumina particles before mixing with the resin and alumina particles after mixing with the resin (for example, alumina particles mixed in a resin composition). Alumina particles are present in the resin composition in an amount of 50% by volume or more of 100% by volume of solid content, preferably 50-90% by volume, more preferably 55-85% by volume, and even more preferably 60-80% by volume. Furthermore, the alumina particle content is preferably 100 to 500 parts by volume, more preferably 120 to 400 parts by volume, and even more preferably 150 to 350 parts by volume, per 100 parts by volume of (meth)acrylic resin.

[0039] Alumina particles mixed in a resin composition have one or more peaks in their particle size distribution. For alumina particle A having a particle size distribution containing the peak with the largest particle size, let X (mass%) be the proportion of alumina particle A in 100% by mass of alumina particles, and Y (μm) be the particle size D50 in the particle size distribution of alumina particle A. X, Y (where Y ≥ 2.0) and the film thickness Z μm (where Z < 100) satisfy the following equation (1). Z / (Y×X / 100)≧2.5 (1) "Particle size D50" refers to the diameter equivalent to 50% of the cumulative volume, and in this specification, "particle size D50" may also be simply referred to as "D50". Furthermore, if there is only one peak in the particle size distribution of alumina particles, alumina particle A having a particle size distribution containing the largest peak means the alumina particle having a particle size distribution containing this single peak. If the film satisfies the above (1), it can achieve good adhesion and preferably also exhibit good thermal conductivity. Thermal conductivity in this invention is evaluated by dividing the thermal conductivity of the film by the film thickness.

[0040] The value of the left side of formula (1) above (Z / (Y×X / 100)) is preferably 3.0 or more, more preferably 4.0 or more, even more preferably 5.0 or more, preferably 30 or less, more preferably 25 or less, even more preferably 20 or less, even more preferably 15 or less, and particularly preferably 12 or less. If it is within the above range, the adhesiveness of the film can be improved, and preferably the thermal conductivity can also be improved.

[0041] The particle size D50 Y (μm) of the alumina particles A is 2.0 μm or more, preferably 3.0 μm or more, more preferably 4.0 μm or more, even more preferably 5.0 μm or more, preferably 45 μm or less, more preferably 20 μm or less, even more preferably 16 μm or less, even more preferably 12 μm or less, and particularly preferably 10 μm or less. If the particle size D50 of the alumina particles A is within the above range, the adhesiveness of the film can be improved, and preferably the thermal conductivity can also be improved.

[0042] The particle size D50 of alumina particles can be determined, for example, by measuring the volume-based particle size distribution of alumina particles using the Microtrac MT3300EXII laser particle size distribution analyzer manufactured by Microtrac-Bell Co., Ltd. via laser diffraction. Alternatively, the particle size distribution can be measured based on the principle of dynamic image analysis compliant with ISO 13322-2, and the particle size (D50) at 50% of the cumulative particle size distribution from the finest particles can be calculated using the cumulative particle size distribution obtained from the measurement results. Specifically, as a measuring device, for example, a CAMSIZER (manufactured by VERDER Scientific) can be used, in which the sample is sequentially introduced into the device, and particles passing in front of the camera are measured while aggregated particles are dispersed by dry air.

[0043] The particle size D50 of the alumina particles can be determined by measuring the particle size distribution of the alumina particles if the alumina particles before mixing into the resin composition are available. If a resin composition containing alumina particles or a film formed from the resin composition is available, the alumina particles can be separated by removing the (meth)acrylic resin, etc., contained in the composition or film, for example by dissolving it with an organic solvent or by thermal decomposition by heating it to a temperature of 500°C or higher, and then measuring the particle size distribution of the obtained alumina particles.

[0044] When alumina particles have two or more peaks in their particle size distribution (for example, when mixing multiple alumina particles with different particle size distributions), the particle size D50 of the alumina particles having a particle size distribution containing each peak can be determined by measuring the particle size distribution of the alumina particles using the laser diffraction method described above. When mixing multiple types of alumina particles with different D50 values, and the D50 values ​​of each alumina particle differ significantly, or the particle size distribution of each alumina particle is sharp, resulting in the tails of the particle size distributions of each alumina particle hardly overlapping, the particle size distribution curve of the mixed alumina particles will appear as multiple peaks spaced apart in the particle size axis direction, with points between the particle size distributions containing each peak where the distribution value is approximately zero. In such cases, each particle size distribution containing each peak can be identified as originating from a single type of alumina particle. On the other hand, when mixing multiple types of alumina particles whose D50 values ​​are close to each other, or whose particle size distributions are broad, and whose respective particle size distributions overlap, the resulting particle size distribution curve of the mixed alumina particles becomes a continuous curve overall, and valleys where the distribution value is minimum are formed between adjacent peaks. In such cases, D50 can be determined by the following procedure. First, for each peak, the region between the valley on the fine-grain side and the valley on the coarse-grain side of the peak is considered to be the particle size distribution region of the alumina particle corresponding to that peak. Note that when determining the valleys on the fine-grain and coarse-grain sides of each peak, the valleys also include the base originating from the particle size distribution of one type of alumina particle (i.e., the part that does not overlap with the particle size distribution of other alumina particles). Next, a tangent line is drawn horizontally (parallel to the x-axis) from the valley closest to the peak within the region, and the D50 of the alumina particle is defined as the particle diameter at which 50% of the cumulative total is reached from the fine particle side of the intersection point between the particle size distribution curve and the tangent line in the region. However, if the intersection point does not exist on the fine particle side, the D50 of the alumina particle is defined as the particle diameter at which 50% of the cumulative total is reached from the valley on the fine particle side.

[0045] The alumina particles (for example, alumina particle A and alumina particle B described later) are preferably spherical (specifically, polyhedral spheres). "Polyhedral sphere" means a shape that is polyhedral and has an average sphericity of 0.70 or higher. When the alumina particles are polyhedral spheres, the viscosity increase when the alumina particles are mixed with the resin can be suppressed, and the particles are in surface contact with each other in the resin composition, making it easier to improve the thermal conductivity. The roundness of the alumina particles A is preferably 0.80 or higher, more preferably 0.80 to 0.99, even more preferably 0.85 to 0.98, and even more preferably 0.90 to 0.95. When the roundness of the alumina particles A is within the above range, it is easier to increase the packing rate of the alumina particles into the (meth)acrylic resin, and sedimentation in the resin composition is less likely to occur, improving dispersibility. In addition, the alumina particles and the (meth)acrylic resin flow more uniformly when heated and pressurized, and voids are less likely to occur after curing. When the average roundness of the alumina particles is high, the kneadability with the (meth)acrylic resin is also good, which has the effect of increasing the fluidity of the liquid resin composition after kneading, making it easier to mold into a film.

[0046] The roundness (average roundness) of alumina particles A can be measured simultaneously with the particle size distribution using a measurement device based on the principle of dynamic image analysis in accordance with ISO 13322-2 (e.g., CAMSIZER X2 (manufactured by VERDER Scientific)). The roundness (SPHT) is analyzed in accordance with ISO 9276-6, and SPHT = 4πA / P 2 It can be determined from the above formula. In the above formula, A is the measured area of ​​the projected particle image, and P is the measured outer circumference of the particle projection image. The average roundness of alumina particles A in a film can be measured by removing the (meth)acrylic resin contained in the film-like resin composition by, for example, dissolving it with an organic solvent or by thermal decomposition by heating it to a temperature of 500°C or higher, separating only the alumina particles A, and using those alumina particles A. Another method for determining the average roundness of alumina particles A is to use image analysis. Cross-sectional observation of the film-like resin composition can be performed using an SEM, and all alumina particles A contained in a predetermined observation area (e.g., 200 μm × 200 μm) can be image-analyzed, and the average roundness can be calculated based on the measurement results of their roundness.

[0047] In addition, when multiple types of alumina particles with different particle size distributions are included as the alumina particles, the particle size distribution of the alumina particles is measured, and the D50 of the alumina particles A and the alumina particles other than the alumina particles A is confirmed from the peak position by the method described above. An appropriate mesh sieve is prepared according to the value of each D50, and the alumina particles A can be separated by sieving.

[0048] The BET specific surface area (hereinafter also simply referred to as "specific surface area") of the alumina particles A measured by the nitrogen adsorption method is preferably 0.8 m 2 / g or less, more preferably 0.1 to 0.8 m 2 / g, still more preferably 0.15 to 0.6 m 2 / g, even more preferably 0.2 to 0.5 m 2 / g, and even more preferably 0.2 to 0.5 m / g.

[0049] The alumina particles may have two or more peaks in the particle size distribution, and it is more preferable to have two peaks. When the alumina particles contain alumina particles other than the alumina particles A, the D50 of the particle size of the alumina particles B having a particle size distribution including the second largest peak is preferably 0.1 μm or more. The D50 of the alumina particles B is preferably 0.1 μm or more and less than 2 μm, more preferably 0.15 to 1.5 μm, still more preferably 0.20 to 1.0 μm, and even more preferably 0.25 to 0.8 μm.

[0050] In addition, the D50 of the particle size of the entire alumina particles is preferably 0.1 to 40 μm, more preferably 1 to 30 μm, and still more preferably 2 to 20 μm.

[0051] The shape of the alumina particles B is not particularly limited, but from the viewpoint of particle packing, it is preferable that the shape is close to spherical (polyhedral sphere), and more preferable that it is spherical (polyhedral sphere). The roundness of the alumina particles B is preferably 0.80 or higher, more preferably 0.80 to 0.99, even more preferably 0.85 to 0.98, and still more preferably 0.90 to 0.95. When the resin composition contains multiple alumina particles, the roundness of all alumina particles is preferably 0.80 or higher, more preferably 0.80 to 0.99, even more preferably 0.85 to 0.98, and still more preferably 0.90 to 0.95. This makes it possible to achieve excellent adhesion and high thermal conductivity in thin films of less than 100 μm.

[0052] The specific surface area of ​​alumina particle B is 1.0 to 10 m². 2 / g is preferred, and 1.3 to 8.0 m 2 / g is more preferable, 2.0 to 7.0 m 2 / g is even more preferable.

[0053] When alumina particles B are included, the ratio of the specific surface area of ​​alumina particles B to the specific surface area of ​​alumina particles A is preferably 3 to 100, more preferably 5 to 80, and even more preferably 8 to 50.

[0054] The content X (mass%) of alumina particles A is preferably 20% by mass or more, more preferably 30% by mass or more, even more preferably 40% by mass or more, even more preferably 45% by mass or more, and particularly preferably 50% by mass or more, out of 100% by mass of the total alumina particles. It may also be 100% by mass or less, preferably 90% by mass or less, more preferably 80% by mass or less, even more preferably 75% by mass or less, even more preferably 72% by mass or less, and particularly preferably 70% by mass or less. If the content of alumina particles A is within the above range, the adhesiveness of the film can be improved, and preferably the thermal conductivity can also be improved. The alumina particle A content X (mass %) may be calculated from the mass of the alumina particles to be mixed, or, as mentioned above, after separating alumina particle A by sieving, the total mass of the alumina particles and the mass of alumina particle A may be determined and then calculated.

[0055] The content of alumina particles B is preferably 0 to 80% by mass, more preferably 10 to 70% by mass, even more preferably 20 to 60% by mass, and still more preferably 25 to 50% by mass, based on 100% by mass of the total alumina particles. If the content of alumina particles B is within the above range, the adhesiveness of the formed film can be improved, and preferably the thermal conductivity can also be improved.

[0056] The D50 of alumina particle A is preferably 8 to 50 times, and more preferably 10 to 45 times, the D50 of alumina particle B. When the resin composition contains multiple alumina particles, the particle size of all alumina particles is preferably 0.1 to 40 μm, more preferably 0.1 to 30 μm, and even more preferably 0.1 to 20 μm. This makes it possible to achieve excellent adhesion and high thermal conductivity in thin films of less than 100 μm.

[0057] Furthermore, the resin composition may contain particles other than alumina particles, but the amount of alumina particles in 100% by mass of the particles in the resin composition is preferably more than 50% by mass, more preferably 70% by mass or more, even more preferably 80% by mass or more, and particularly preferably 90% by mass or more.

[0058] <Method for preparing alumina particles> If the resin composition contains multiple types of alumina particles, the alumina particles to be used (for example, alumina particle A and alumina particle B) may be mixed to prepare the alumina particles to be included in the resin composition. The mixing method is not particularly limited, and known mixing methods such as mortar mixing or rotation-and-revolution mixing under vacuum or atmospheric pressure can be used. When mixing two or more types of alumina particles, a predetermined amount of each may be weighed and all placed in a mixing container and mixed at the same time, or they may be added sequentially and mixed.

[0059] <Methods for producing each alumina particle> The method for producing the alumina particles that make up the alumina particles (alumina particle A and any alumina particle B, etc.) is not particularly limited, and any method is acceptable as long as the required physical properties for each alumina particle are achieved. For example, raw alumina produced by melt growth methods such as the Bayer process, ammonium alum process, ammonium aluminum carbonate hydroxide process (AACH process), solvent extraction method, organoaluminum hydrolysis method (aluminum alkoxide process), CZ process, Bernoulli process, Chiroporous process, Bridgman process, EFG method, etc., can be flame-melted, and the powder can be collected using a cyclone or bag filter as needed, and then classified to obtain alumina raw material powder with the desired particle size distribution. Furthermore, commercially available alumina particles may be used as one or more types of alumina particles, such as alumina particle A and alumina particle B.

[0060] <Method for preparing resin compositions> The resin composition may be prepared by mixing alumina particles, a (meth)acrylic resin, a solvent used as needed, and the aforementioned additives. The mixing order is not limited, however, it is preferable to prepare a solution by dissolving the (meth)acrylic resin in an organic solvent, further mixing in additives as needed to form a mixed resin solution, and then mixing this mixed resin solution with the alumina particles to prepare the resin composition. The resin composition preferably has a solid content concentration of 35 to 70% by mass, and more preferably 40 to 60% by mass.

[0061] (Film and method for manufacturing the same) The film can be formed, for example, by applying the resin composition to the surface of a substrate, removing the solvent by drying to obtain a resin composition layer, and then performing a pressing process. In other words, the mass of the film corresponds to the value obtained by subtracting the mass of the solvent from the mass of the resin composition (the mass of the solid content of the resin composition). Even components that are liquid at 25°C are included in the film's mass if they are contained within the film.

[0062] When drying the resin composition to obtain a resin composition layer, for example, drying at a temperature of 10 to 30°C for 1 to 30 minutes is sufficient. The pressing process can be performed using, for example, a pressure of 0.1 to 5 MPa, a temperature of 70 to 130°C, and a pressing time of 1 to 10 minutes. The pressure may be increased in stages and the pressing process may be repeated multiple times.

[0063] The film thickness Z (μm) is usually less than 100 μm, preferably 70 μm or less, more preferably 50 μm or less, even more preferably 40 μm or less, preferably 2 μm or more, more preferably 5 μm or more, and even more preferably 10 μm or more.

[0064] The thermal conductivity of the film, as evaluated by the method of the embodiments described later, is, for example, 1.5 (W / m·K) or higher, preferably 1.8 (W / m·K) or higher, and more preferably 2.0 (W / m·K) or higher. There is no particular upper limit, but it may be 10 (W / m·K) or lower, or 5.0 (W / m·K) or lower. Furthermore, the thermal conductivity of the film, as evaluated by the method of the examples described later, is preferably 0.05 (W / m·K / μm) or higher, more preferably 0.060 (W / m·K / μm) or higher, and even more preferably 0.070 (W / m·K / μm) or higher. The upper limit is not particularly limited, but may be 0.60 (W / m·K / μm) or 0.30 (W / m·K / μm). [Examples]

[0065] The present invention will be described in more detail below with reference to examples. The present invention is not limited by the following examples, and it is certainly possible to implement it with appropriate modifications within the scope that is consistent with the spirit described below, and all such modifications are included within the technical scope of the present invention.

[0066] The physical properties of the alumina particles used in the examples and comparative examples were measured by the following method.

[0067] (1) Measurement of particle size D50 of alumina particles The particle size D50 of each alumina particle (the particle size at which the cumulative 50% of the volume-based particle size distribution from the finest particle side is reached) was measured by laser diffraction using the "Microtrac MT3300EXII" laser particle size distribution analyzer manufactured by Microtrac-Bell Co., Ltd.

[0068] (2) Measurement of the roundness of alumina particles The average roundness of each alumina particle was measured using a CAMSIZER X2 (manufactured by VERDER Scientific) based on the principle of dynamic image analysis in accordance with ISO 13322-2.

[0069] (3) Measurement of the BET specific surface area of ​​alumina particles As the specific surface area measuring device, a "FlowSorb III 2310" manufactured by Shimadzu Corporation was used, and the nitrogen adsorption BET specific surface area, determined by the nitrogen adsorption single-point method according to the method specified in JIS-Z8830 (2013), was used as the specific surface area of ​​each alumina particle. The measurement conditions were as follows. Carrier gas: Nitrogen / helium mixture Packing sample amount: 0.1g Sample pretreatment conditions: Treatment at 200°C for 20 minutes. Nitrogen adsorption temperature: Liquid nitrogen temperature (-196°C or below) Nitrogen desorption temperature: Room temperature (approximately 20°C)

[0070] Preparation Example 1: Preparation of Acrylic Resin Solution A reaction vessel equipped with a condenser, nitrogen inlet tube, thermometer, and stirrer was charged with a mixed solution of 81.8 parts by mass of ethyl acetate, 90.0 parts by mass of butyl acrylate, 5.0 parts by mass of methyl acrylate, and 5.0 parts by mass of acrylic acid. The internal temperature was raised to 55°C while replacing the air in the apparatus with nitrogen gas to eliminate oxygen. Subsequently, the entirety of a solution prepared by dissolving 0.15 parts by mass of azobisisobutyronitrile (polymerization initiator) in 10 parts by mass of ethyl acetate was added. After adding the polymerization initiator, the temperature was maintained at this level for 1 hour. Then, while maintaining the internal temperature at 54-56°C, ethyl acetate was continuously added to the reaction vessel at an addition rate of 173 parts by mass / hr. When the concentration of the acrylic resin reached 35% by mass, the addition of ethyl acetate was stopped, and the temperature was maintained at this level for another 6 hours from the start of ethyl acetate addition. Finally, ethyl acetate was added to adjust the concentration of the acrylic resin to 20% by mass, and the acrylic resin solution was prepared. The obtained acrylic resin had a weight-average molecular weight (Mw) of 1.6 million and a molecular weight distribution (Mw / Mn) of 4.5. Mw and Mn were measured in standard polystyrene equivalents using two TSKgel GMHHR-H(S) columns from Tosoh Corporation connected in series in a GPC instrument, with tetrahydrofuran as the eluent, under the conditions of a sample concentration of 2 mg / mL, sample introduction volume of 100 μL, temperature of 40°C, and flow rate of 1 mL / min.

[0071] Furthermore, the viscosity of the acrylic resin solution and the glass transition temperature of the acrylic resin were measured under the following conditions, and the results showed that the viscosity was 7500 mPa·s and the glass transition temperature (Tg) was -25°C. (Viscosity of acrylic resin solution) Concentration: 20% by mass Equipment: Modular Compact Rheometer (Anton Paar MCR302e) Geometry: Φ25mm parallel plate Gap: 0.5mm Shear rate: 1 (1 / s) Measurement temperature: 25℃

[0072] (Glass transition temperature of acrylic resins) Equipment: Differential scanning calorimeter (TA Instruments, DSC Q2000)

[0073] Example 1 To 100 parts by mass of the solid content of the acrylic resin solution obtained in Preparation Example 1, 0.15 parts by mass of a crosslinking agent (manufactured by Tosoh Corporation: trade name "Coronate L" (ethyl acetate solution of trimethylolpropane adduct of tolylene diisocyanate (solid content concentration 75% by mass)) and 0.2 parts by mass of a silane coupling agent (manufactured by Shin-Etsu Chemical Co., Ltd.: trade name "KBM-403") were added on an active ingredient basis, and ethyl acetate was further added to bring the solid content concentration to 13% by mass to obtain a mixed resin solution. Next, alumina particle A is DAW-05 (manufactured by Denka Co., Ltd.), and alumina particle B is AA-04 (manufactured by Sumitomo Chemical Co., Ltd., with a roundness of 0.80 or higher and a BET specific surface area of ​​4.6 m²). 2 Mixing the particles ( / g) in a mass ratio of 7:3, then kneading with a rotation-orbit mixer (manufactured by Sinky Co., Ltd.) to obtain mixed alumina particles 1. Mixing the mixed resin solution with the mixed alumina particles 1 so that the volume ratio of the solids in the mixed resin solution to the mixed alumina particles 1 was 35:65, and 2-butanone was added as a solvent so that the solids in the mixed resin solution and the mixed alumina particles accounted for 48.0% by mass of the total, thereby obtaining a resin composition.

[0074] The obtained resin composition was applied using an applicator to the release-treated surface of a separator film made of polyethylene terephthalate film with a release treatment ("PLR-382190" obtained from Lintec Corporation) so that the thickness after pressing (film thickness) described later was 45 μm, and dried at 23°C for 10 minutes to obtain a resin composition layer before molding. Next, the surface of the obtained resin composition layer before molding that was opposite to the surface where the separator film was present was bonded to the release-treated surface of a separator film made of polyethylene terephthalate film with a release treatment ("P-251130" obtained from Lintec Corporation), and vacuum press molding was performed using a press molding machine at a pressure of 0.1 MPa at 100°C for 1 minute, followed by vacuum press molding at a pressure of 3 MPa at 100°C for 3 minutes to obtain a film (a film formed from the resin composition) with separator films bonded to both sides.

[0075] Examples 2-9, Comparative Examples 1-3 A film was obtained in the same manner as in Example 1, except that the film thickness of the resin composition, the mixing ratio of alumina particles A and alumina particles B, and the type of alumina particles A were as shown in Table 1. The alumina particles A used were DAW-01, DAW-10, DAW-20, and DAW-45, all manufactured by Denka Co., Ltd.

[0076] Comparative Example 4 A film was obtained in the same manner as in Example 1, except that a silicone resin (DOWSIL CY52-276A&B, manufactured by Dow-Toray Ltd.) was used instead of the acrylic resin in the acrylic resin solution in Example 1, and the drying conditions after applying the resin composition using an applicator were changed to 120°C for 30 minutes.

[0077] The films obtained in the above examples and comparative examples were evaluated by the following method.

[0078] (1) Measurement of adhesiveness A plasma treatment was performed using Tough Plasma FPE20 TYPE20 (manufactured by Fuji Machine Manufacturing Co., Ltd.) on the peeled surface of the film and the mat surface of aluminum foil (manufactured by Toyo Aluminum Co., Ltd., Lab Foil), and the two surfaces were bonded together with a roller to create a test specimen (tensile section). The peel strength of the film was evaluated as follows. The test specimen was adjusted to a size of 25 mm × 150 mm. Next, the separator film (PLR-382190) was peeled off this test specimen, and the peeled surface and the glass substrate (Corning Eagle XG) were subjected to plasma treatment. Both the treated surfaces of the test specimen and the glass substrate were then attached using a bonding device (Fuji Plastic Machinery Co., Ltd. "Lamipacker"). After standing for 24 hours in an atmosphere of 23°C and 50% RH relative humidity, the test specimen was peeled off the glass substrate at a speed of 300 mm / min in a 90° direction. The condition of the glass substrate surface was observed, and the tackiness was evaluated according to the following criteria A to D. A: Film residue can be seen across the entire surface of the glass substrate. B: Remnants of the film are visible on most of the surface of the glass substrate. C: Some film residue can be seen on a portion of the glass substrate surface. D: No film residue is visible on the glass substrate surface.

[0079] (2) Measurement of thermal conductivity 10 mm square test pieces were cut from the films obtained in the examples and comparative examples, and the thermal conductivity in the thickness direction of the film in these test pieces was measured by thermal wave thermal analysis using an ai-Phase Mobile (ai-Phase Mobile M3 type1, manufactured by ai-Phase Corporation). The measurements were performed under atmospheric conditions at 25°C. The obtained thermal conductivity value (W / m·K) was divided by the thickness Z (μm) to calculate the thermal conductivity (W / m·K / μm), and it was evaluated according to the following criteria. A:0.07(W / m·K / μm) or more B: 0.06 (W / m K / μm) or more, less than 0.07 (W / m K / μm) C: 0.05 (W / m K / μm) or more, less than 0.06 (W / m K / μm) D: Less than 0.05 (W / m·K / μm)

[0080] (3) Measuring the thickness of the film The film thickness obtained in the examples and comparative examples was measured using a Nikon Corporation digital length measuring instrument "DIGIMICRO" (counter "MFC-200", measuring stand "MS-12C"). The total thickness of the film with separator films laminated on both sides and the thickness of the separator films on both sides were measured separately, and the total thickness was calculated by subtracting the thickness of the separator films on both sides from the total thickness.

[0081] Table 1 shows the evaluation results of the films obtained in the examples and comparative examples.

[0082] [Table 1] [Industrial applicability]

[0083] Because the film of the present invention is thermally conductive and adhesive, it can be suitably used as an interlayer thermal bonding material (TIM) for applications such as between electronic components and heat sinks.

Claims

1. A film formed from a resin composition containing (meth)acrylic resin and alumina particles, The alumina particles are present in an amount of 50% or more by volume of 100% by volume of the solid content of the resin composition, and have one or more peaks in the particle size distribution. When X is the percentage of alumina particles A having a particle size distribution containing the peak with the largest particle size among 100% by mass of alumina particles, Y is the D50 of alumina particles A (μm), and Z is the thickness of the film (μm), A film characterized in that Y is 2.0 μm or more, Z is less than 100 μm, and satisfies the following formula (1). Z / (Y×X / 100)≧2.5...(1)

2. The film according to claim 1, wherein the alumina particles A are spherical.

3. The film according to claim 1, wherein the roundness of the alumina particles A is 0.80 or greater.

4. The specific surface area of ​​the alumina particle A is 0.8 m². ２ The film according to claim 1, wherein the amount is less than or equal to / g.

5. The film according to claim 1, wherein the alumina particles have two or more peaks in their particle size distribution.

6. The film according to claim 5, wherein the D50 of alumina particles B having a particle size distribution including the second largest peak in particle size is 0.1 μm or larger.

7. The film according to claim 5, wherein the proportion of alumina particles A is 40 to 80% by mass out of 100% by mass of alumina particles.

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