Method for manufacturing thermosetting resin sheets

Abstract

The present invention relates to a method for producing a thermosetting resin sheet containing an inorganic filler and a thermosetting resin, and provides a method for producing a thermosetting resin sheet that, when a slurry-like thermosetting resin composition is applied to a base sheet, can improve the wettability of the thermosetting resin composition to the base sheet ("repellency after application and drying"), can suppress large irregularities on the surface of the coating film ("surface irregularities during application"), and can suppress cracking of the thermosetting resin composition after it has been applied to the base sheet and dried ("handling properties"). [Solution] A slurry-like resin composition is prepared, comprising an inorganic filler containing boron nitride aggregate particles, a thermosetting resin containing epoxy resin, a solvent with a boiling point of 100°C or higher, and a solvent with a boiling point of less than 100°C, wherein the solvent with a boiling point of 100°C or higher accounts for 40% or more of the total amount of solvent, and the solid content concentration is 50% or more by mass and 80% or less by mass. This method for manufacturing a thermosetting resin sheet involves applying the slurry-like resin composition onto a base sheet having a tape peel strength (180-degree peel test in accordance with JIS Z0237:2009 using cellophane adhesive tape conforming to JIS Z1522:2009, measured at 0.1 N / 10 mm or more and 5 N / 10 mm or less) to form a coated sheet, continuously heating the coated sheet for 60 seconds or more in a temperature range of 40°C or more and less than 100°C, then heating it in a temperature range of 100°C or higher to remove the solvent, and finally winding the coated sheet into a roll.

Description

Technical Field

[0001] The present invention relates to a method for producing a thermosetting resin sheet containing an inorganic filler and a thermosetting resin, which can be used as a heat dissipation member, an insulating member, or the like.

Background Art

[0002] In recent years, in the field of electric and electronic devices, heat generation associated with the high density of integrated circuits has become a major problem, and how to dissipate heat has become an urgent issue. For example, when performing stable operation of semiconductor devices used for controlling central processing units of personal computers, motors of electric vehicles, etc., heat sinks, heat dissipation fins, etc. are indispensable for heat dissipation, and a member that can achieve both heat conductivity and insulation is required as a member for coupling the semiconductor device and the heat sink, etc.

[0003] Conventionally, ceramic substrates with high thermal conductivity such as alumina substrates and aluminum nitride substrates have been used as members that can achieve both heat conductivity and insulation. However, ceramic substrates have problems such as being easily cracked by impact, being difficult to thin-filmize, and being difficult to miniaturize. Therefore, heat dissipation sheets using thermosetting resins such as epoxy resins and inorganic fillers have been proposed.

[0004] Regarding heat dissipation sheets using thermosetting resins and inorganic fillers, various resin sheets containing boron nitride as an inorganic filler have been proposed (see Patent Documents 1 to 8). Boron nitride is an insulating ceramic and has attracted particular attention in the field of electric and electronic materials in recent years because it has characteristics such as excellent thermal conductivity, solid lubricity, chemical stability, and heat resistance.

[0005] As an example of a method for manufacturing a heat dissipation sheet using a thermosetting resin and an inorganic filler, a slurry-like thermosetting resin composition containing a thermosetting resin, an inorganic filler, and a solvent is prepared, the slurry-like thermosetting resin composition is applied to a base sheet to form a film in the shape of a sheet, the solvent is removed by drying, and further pressure is applied as necessary to form a sheet to produce a thermosetting resin sheet. Then, the thermosetting resin sheet thus produced is cured to produce a heat dissipation sheet. (See paragraphs

[0138] to

[0150] of Patent Document 8.) [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2015-6980 [Patent Document 2] Japanese Patent Publication No. 2015-189823 [Patent Document 3] Japanese Patent Publication No. 2015-195287 [Patent Document 4] Japanese Patent Publication No. 2016-011358 [Patent Document 5] Japanese Patent Publication No. 2016-135731 [Patent Document 6] Japanese Patent Publication No. 2019-119883 [Patent Document 7] Japanese Patent Publication No. 2021-6507 [Patent Document 8] Japanese Patent Publication No. 2023-147229 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] As described above, when manufacturing thermosetting resin sheets in this manner, the presence of inorganic fillers sometimes resulted in large irregularities on the surface of the coating film when the slurry-like thermosetting resin composition was applied to the base sheet and dried. This caused problems where the surface irregularities could not be smoothed out even after subsequent pressing. Furthermore, when a slurry-like thermosetting resin composition was applied to a substrate sheet, the poor wettability to the substrate sheet sometimes caused the edges of the coating to curl inward, resulting in raised edges. Furthermore, cracks sometimes occurred in the thermosetting resin composition during transport after it had been applied to the substrate sheet in slurry form, dried, and the solvent had been removed.

[0008] Therefore, the present invention relates to a method for producing a thermosetting resin sheet comprising an inorganic filler and a thermosetting resin, and aims to provide a method for producing a thermosetting resin sheet that, when a slurry-like thermosetting resin composition is applied to a base sheet and dried, can improve the wettability of the thermosetting resin composition to the base sheet ("repellency after application and drying"), can suppress large irregularities on the surface of the coating film ("surface irregularities during application"), and can suppress the occurrence of cracks in the thermosetting resin composition after it has been applied to the base sheet and dried ("handling properties"). [Means for solving the problem]

[0009] The method for manufacturing a thermosetting resin sheet proposed by the present invention has the following configuration in order to solve the above problems.

[0010] [1] A first aspect of the present invention involves preparing a slurry-like resin composition comprising an inorganic filler containing boron nitride aggregate particles, a thermosetting resin containing an epoxy resin, a solvent with a boiling point of 100°C or higher, and a solvent with a boiling point of less than 100°C, wherein the solvent with a boiling point of 100°C or higher accounts for 40% by mass or more of the total amount of solvent, and the solid content concentration is 50% by mass or more and 80% by mass or less (also referred to as the "resin composition preparation step"), The slurry-like resin composition is applied to a base sheet having a tape peel strength (a 180-degree peel test in accordance with JIS Z0237:2009 using cellophane adhesive tape conforming to JIS Z1522:2009) of 0.1 N / 10 mm or more and 5 N / 10 mm or less to form a coated sheet (also referred to as the "coating process"), After continuously heating the coated sheet in a temperature range of 40°C or higher and less than 100°C for 60 seconds or more, the solvent is removed by heating in a temperature range of 100°C or higher (also referred to as the "solvent removal step"). This is a method for manufacturing a thermosetting resin sheet, which involves winding the coated sheet into a roll (also referred to as the "winding process").

[0011] [2] A second aspect of the present invention is the manufacturing method of the first aspect, wherein after the winding step, the coated sheet is unwound and the coated sheet is cut into individual sheets (also referred to as the "cutting step") in an environment with a temperature of 10°C to 40°C and a humidity of 30%RH to 70%RH, This is a method for manufacturing a thermosetting resin sheet, comprising laminating a protective film onto a cut sheet of coated material so that it is in contact with the resin composition to form a laminate (also referred to as the "protective film lamination process"). [3] A third aspect of the present invention is a method for manufacturing a thermosetting resin sheet, wherein the laminate is packaged with a resin film (also referred to as the "packing process") in the manufacturing method of the second aspect.

[0012] [4] A fourth aspect of the present invention is a method for manufacturing a thermosetting resin sheet, wherein the laminate is pressurized at a temperature of 0°C to 140°C and a pressure of 10 MPa to 200 MPa (also referred to as the "pressurization step"). [5] A fifth aspect of the present invention is a method for manufacturing a thermosetting resin sheet, wherein the laminate is pressurized at a temperature of 0°C to 140°C and a pressure of 10 MPa to 200 MPa (also referred to as the "pressurization step").

[0013] [6] A sixth aspect of the present invention is a method for manufacturing a thermosetting resin sheet, wherein the laminate is aged at a temperature of 0°C or lower (also referred to as the "aging process") in the manufacturing method of any one of the second to fifth aspects.

[0014] [7] The seventh aspect of the present invention is a method for manufacturing a thermosetting resin sheet in the manufacturing method according to any one of the first to sixth aspects, wherein the boron nitride aggregated particles have a card house structure.

Effects of the Invention

[0015] The present invention relates to a method for manufacturing a thermosetting resin sheet containing an inorganic filler and a thermosetting resin. When preparing a slurry-like resin composition, as a solvent, it includes a solvent with a boiling point of 100 °C or higher and a solvent with a boiling point of less than 100 °C, and the ratio of the solvent with a boiling point of 100 °C or higher is limited, and the solid content concentration is limited. Furthermore, the tape peeling strength of the base material sheet on which the slurry-like resin composition is applied is limited, and the drying conditions when applying and drying the resin composition are limited. By doing so, the wettability of the thermosetting resin composition with respect to the base material sheet can be enhanced (referred to as "bounce after coating and drying"), large irregularities on the coating film surface can be suppressed (referred to as "surface irregularities during coating"), and after applying and drying the thermosetting resin composition on the base material sheet, the occurrence of cracks in the thermosetting resin composition can be suppressed (referred to as "handling property").

Brief Description of the Drawings

[0016] [Figure 1] It is a perspective view schematically showing an example of a cutting method according to an example of an embodiment of the present invention.

Embodiments for Carrying Out the Invention

[0017] Hereinafter, an example of an embodiment of the present invention will be described. However, the present invention is not limited to the embodiments described below.

[0018] <Method for Manufacturing a Thermosetting Resin Sheet> A method for producing a thermosetting resin sheet according to an example of an embodiment of the present invention (referred to as the "production method of the present invention") involves preparing a slurry-like resin composition (also referred to as the "resin composition") containing an inorganic filler containing boron nitride aggregate particles, a thermosetting resin containing epoxy resin, and a solvent (also referred to as the "resin composition preparation step"), applying the resin composition onto a base sheet to form a coated sheet (also referred to as the "coating step"), heating the coated sheet to remove the solvent (also referred to as the "solvent removal step"), and winding the coated sheet into a roll (also referred to as the "winding step") to obtain a thermosetting resin sheet (referred to as the "thermosetting resin sheet of the present invention").

[0019] Here, the "thermosetting resin sheet" of the present invention is any sheet that has curability that leaves room for further curing by heat, and may be a sheet that has already cured (also called "partially cured") in a state where room for further curing remains, or it may be a sheet that has not yet cured at all (also called "uncured"). By curing the "thermosetting resin sheet," its thermal conductivity and insulation properties are enhanced, allowing it to be used as a heat dissipation sheet or insulating sheet. However, its applications are not limited to these uses. In the manufacturing method of the present invention, the "process" may or may not be performed in a series of manufacturing lines, and may be performed intermittently, and in such cases, it may be performed intermittently by taking breaks in time, changing equipment, or changing locations.

[0020] <Composition of this resin composition> The resin composition preferably comprises an inorganic filler containing boron nitride aggregate particles, a thermosetting resin containing epoxy resin, a solvent with a boiling point of 100°C or higher, a solvent with a boiling point of less than 100°C, and, if necessary, other resin components and other components.

[0021] (Inorganic filler) From the viewpoint of thermal conductivity, the inorganic filler is preferably inorganic particles with a thermal conductivity of 10 W / m·K or higher. Examples of such inorganic fillers include electrically insulating inorganic fillers consisting solely of carbon, inorganic fillers consisting of metal carbides or metalloid carbides, metal oxides or metalloid oxides, metal nitrides or metalloid nitrides, etc. These inorganic fillers may be single or in combination of two or more types.

[0022] Examples of electrically insulating inorganic fillers consisting solely of carbon include diamond (thermal conductivity: approximately 2000 W / m·K). Examples of the aforementioned metal carbides or metalloid carbides include silicon carbide (thermal conductivity: approximately 60-270 W / m·K), titanium carbide (thermal conductivity: approximately 21 W / m·K), and tungsten carbide (thermal conductivity: approximately 120 W / m·K). Examples of the aforementioned metal oxides or metalloid oxides include aluminum oxide (thermal conductivity: 29 W / m·K), magnesium oxide (thermal conductivity: approximately 40 W / m·K), zinc oxide (thermal conductivity: approximately 54 W / m·K), yttrium oxide (thermal conductivity: approximately 27 W / m·K), ytterbium oxide (thermal conductivity: approximately 38.5 W / m·K), beryllium oxide (thermal conductivity: approximately 250 W / m·K), and "Sialon" (ceramics composed of silicon, aluminum, oxygen, and nitrogen, thermal conductivity: approximately 21 W / m·K). Examples of the aforementioned metal nitrides or metalloid nitrides include boron nitride (thermal conductivity in the plane direction of plate-like hexagonal boron nitride (h-BN) particles: approximately 200-500 W / m·K), aluminum nitride (thermal conductivity: approximately 160-285 W / m·K), silicon nitride (thermal conductivity: approximately 30-80 W / m·K), and the like.

[0023] (Boron nitride aggregated particles) Among the inorganic fillers mentioned above, those containing boron nitride aggregates (also referred to as "BN"), which are formed by the aggregation of primary boron nitride particles, are particularly preferred because they offer excellent insulating properties, thermal conductivity, solid lubricity, chemical stability, and heat resistance.

[0024] Examples of boron nitride aggregated particles include those formed by the aggregation of plate-like, flake-like, or needle-like primary particles into a spherical shape. Here, "spherical" refers to a particle whose aspect ratio (ratio of major axis to minor axis) is between 1 and 2, preferably between 1 and 1.5. The aspect ratio of boron nitride aggregated particles is determined by arbitrarily selecting 200 or more particles from images taken with a SEM, calculating the ratio of the major axis to the minor axis of each particle, and then calculating the average value.

[0025] Examples of conventionally known boron nitride aggregated particles include forms in which the crystals of primary particles exhibiting a flaky or needle-like shape grow radially from the center to the surface of the aggregated particle, spherical forms formed by the sintering and aggregation of plate-like primary particles, and forms having a cardhouse structure formed by the aggregation of plate-like primary particles. Among these, forms having a cardhouse structure are particularly preferred because they can further increase the thermal conductivity in the thickness direction. Here, "cardhouse structure" refers to a structure in which plate-like particles are stacked in a complex manner without orientation, as described, for example, in Ceramics 43 No. 2 (published by the Ceramic Society of Japan in 2008). More specifically, boron nitride aggregate particles having a cardhouse structure are aggregates of primary boron nitride particles, in which the planar portion and end portion of the primary particles are in contact.

[0026] The average particle size (D50) of the boron nitride aggregate particles is not particularly limited, but is preferably 20 μm or more, more preferably 25 μm or more, and even more preferably 30 μm or more. On the other hand, the D50 of the boron nitride aggregate particles is preferably 150 μm or less, more preferably 130 μm or less, even more preferably 100 μm or less, and particularly preferably 95 μm or less. When the D50 of the boron nitride aggregate particles is above the lower limit, the thermal conductivity of the boron nitride aggregate particles themselves is increased. Furthermore, when it is below the upper limit, the surface smoothness is improved when this resin composition is cured into a sheet, the contact between the sheet-like cured material and the substrate is improved, and the thermal conductivity is enhanced.

[0027] The maximum particle size of the boron nitride aggregate particles is preferably 20 μm or more, more preferably 30 μm or more, and even more preferably 40 μm or more. On the other hand, the upper limit of the maximum particle size is preferably 300 μm or less, more preferably 200 μm or less, and even more preferably 150 μm or less. Regarding the particle size of boron nitride aggregates, increasing the particle size reduces the heat transfer path between inorganic fillers via a thermosetting resin with low thermal conductivity, thereby reducing the increase in thermal resistance in the heat transfer path in the thickness direction. From this viewpoint, it is preferable that the maximum particle size of the boron nitride aggregates is within the above range.

[0028] Here, the average particle diameter (D50) of boron nitride aggregates refers to the particle diameter at which the cumulative volume reaches 50% when a cumulative curve is drawn with the volume of the boron nitride aggregates subjected to measurement set to 100%, and the maximum particle diameter refers to the maximum particle diameter when such a cumulative curve is drawn. The measurement methods include, as a wet measurement method, a method in which boron nitride aggregated particles are dispersed in a pure water medium containing naphthalene sulfonate-formaldehyde condensate as a dispersion stabilizer, and then measured using a laser diffraction / scattering particle size distribution analyzer. As a dry measurement method, a method using MALVERN's "MORPHOLOGI" is used. To measure the D50 or maximum particle size of boron nitride aggregated particles, the resin components may be removed and the fillers separated by washing or calcining the cured material with a solvent, i.e., by washing or ashing treatment, and the D50 or maximum particle size may be measured by laser diffraction or morphology of the fillers contained in the resulting residue, or the D50 or maximum particle size may be calculated by cross-sectional SEM observation of the cured material.

[0029] The boron nitride aggregated particles may also contain other inorganic fillers in combination. In this case, the "other inorganic filler" is preferably one with a thermal conductivity of 10 W / m·K or higher, and examples include particles of flaky boron nitride, aluminum oxide (alumina), aluminum nitride, silica, and magnesium oxide. In particular, from the viewpoint of filling properties, water resistance, and thermal conductivity, it is preferable to include alumina particles, especially spherical alumina particles, together with the boron nitride aggregate particles.

[0030] When the aforementioned "other inorganic fillers" are included, the mass percentage of boron nitride aggregated particles in 100% by mass of the total inorganic filler content (inorganic filler and other inorganic fillers) in the resin composition is preferably 50% by mass or more, more preferably 55% by mass or more, more preferably 60% by mass or more, more preferably 65% ​​by mass or more, and most preferably 70% by mass or more, from the viewpoint of increasing thermal conductivity. On the other hand, regarding the upper limit, from the viewpoint of increasing thermal conductivity, it is sufficient if it is 99% by mass or less, and preferably 98% by mass or less.

[0031] (thermosetting resin) In this resin composition, the thermosetting resin is the matrix resin, that is, the component that forms the continuous phase (master structure) of the thermosetting resin sheet of the present invention. In this invention, "resin" includes compounds, monomers, oligomers, and polymers, regardless of their molecular weight.

[0032] Thermosetting resins can be any compound (including polymers) that has the property of hardening with heat, and examples include epoxy resins, cyanate resins, benzoxazine resins, unsaturated polyester resins, phenolic resins, melamine resins, silicone resins, maleimide resins, acrylic resins, and methacrylic resins. It may be any one of these, or it may contain two or more of these. However, among these, it is preferable to include epoxy resin from the viewpoint of viscosity, heat resistance, hygroscopicity, and ease of handling.

[0033] [Epoxy resin] This resin composition preferably contains an epoxy resin as the thermosetting resin.

[0034] In this resin composition, epoxy resin preferably accounts for 30 to 100% by mass of the thermosetting resin, and more preferably 40% by mass or more, of which 50% by mass or more, of which 60% by mass or more, and of which 70% by mass or more. Furthermore, the epoxy resin used in this context also includes the epoxy polymer described later.

[0035] An epoxy resin used as a thermosetting resin can be any compound that has one or more oxirane rings (epoxy groups) in one molecule.

[0036] The oxirane ring (epoxy group) contained in the epoxy resin can be either an alicyclic epoxy group or a glycidyl group. From the viewpoint of reaction rate or heat resistance, a glycidyl group is more preferable.

[0037] Examples of epoxy resins include epoxy group-containing silicon compounds, aliphatic epoxy resins, bisphenol A or F type epoxy resins, novolac type epoxy resins, aromatic epoxy resins, alicyclic epoxy resins, glycidyl ester type epoxy resins, polyfunctional epoxy resins, and polymeric epoxy resins.

[0038] The epoxy resin may also be a compound containing an aromatic oxirane ring (epoxy group). Specific examples include bisphenol-type epoxy resins obtained by glycidly modifying bisphenols such as bisphenol A, bisphenol F, bisphenol AD, bisphenol S, tetramethylbisphenol A, tetramethylbisphenol F, tetramethylbisphenol AD, tetramethylbisphenol S, and tetrafluorobisphenol A; biphenyl-type epoxy resins; epoxy resins obtained by glycidly modifying divalent phenols such as dihydroxynaphthalene and 9,9-bis(4-hydroxyphenyl)fluorene; epoxy resins obtained by glycidly modifying trisphenols such as 1,1,1-tris(4-hydroxyphenyl)methane; epoxy resins obtained by glycidly modifying tetrakisphenols such as 1,1,2,2-tetrakis(4-hydroxyphenyl)ethane; novolac-type epoxy resins obtained by glycidly modifying novolacs such as phenol novolac, cresol novolac, bisphenol A novolac, and brominated bisphenol A novolac; epoxy resins having a dicyclopentadiene skeleton; and epoxy resins having a naphthalene skeleton. In particular, it is preferable to include an epoxy resin having at least one structure selected from epoxy resins having a biphenyl skeleton, epoxy resins having a dicyclopentadiene skeleton, and epoxy resins having a naphthalene skeleton.

[0039] [Multifunctional epoxy resin] The resin composition preferably contains the following polyfunctional epoxy resin as the thermosetting resin.

[0040] A polyfunctional epoxy resin is an epoxy resin that has three or more oxirane rings (epoxy groups) in a single molecule and has a mass-average molecular weight of less than 5,000. By including such a polyfunctional epoxy resin, it is possible to introduce highly polar oxirane rings (epoxy groups) at high density, thereby increasing the effects of physical interactions such as van der Waals forces and hydrogen bonds, and improving the adhesion between the resin composition and the conductor. Furthermore, by including a polyfunctional epoxy resin, the storage modulus of the resin composition can be increased, which allows the resin composition to penetrate into the irregularities on the surface of the conductor, thereby exhibiting a strong anchoring effect and improving the adhesion between the resin composition and the conductor. Furthermore, by preparing this resin composition by combining the epoxy polymer and polyfunctional epoxy resin described later, it is possible to improve the elasticity of this resin composition while also enhancing its handling properties.

[0041] As for the polyfunctional epoxy resin, any epoxy resin having three or more oxirane rings (epoxy groups) in one molecule is acceptable, from the viewpoint of increasing the storage modulus of the resin composition, especially the storage modulus at high temperatures which is important when generating a lot of heat, such as in power semiconductors. Among these, epoxy resins having four or more oxirane rings (epoxy groups) in one molecule are preferred. Having multiple oxirane rings (epoxy groups), especially glycidyl groups, in one molecule improves the crosslinking density of the resin composition, making the resin composition stronger.

[0042] Furthermore, from the viewpoint of adjusting the flexibility of this resin composition, the molecular weight of the polyfunctional epoxy resin, particularly the polyfunctional epoxy resin having three or more epoxy groups in one molecule, is preferably 800 or less, more preferably 700 or less, more preferably 650 or less, more preferably 100 or more or 630 or less, and more preferably 200 or more or 600 or less. In addition, to improve the handling properties of this resin composition, it is preferable to include a component that is liquid at 25°C. Furthermore, from the viewpoint of achieving higher crosslinking, it is preferable not to include amine-based or amide-based structures that contain nitrogen atoms.

[0043] The epoxy equivalent of a polyfunctional epoxy resin, particularly a polyfunctional epoxy resin having three or more epoxy groups in one molecule, is preferably 50 g / equivalent or more, and more preferably 75 g / equivalent or more. On the other hand, it is preferably 200 g / equivalent or less, more preferably 180 g / equivalent or less, more preferably 160 g / equivalent or less, and more preferably 150 g / equivalent or less.

[0044] As a polyfunctional epoxy resin, for example, EX321L, DLC301, DLC402, etc., manufactured by Nagase ChemteX Corporation can be used. A single type of polyfunctional epoxy resin may be used, or two or more types may be used in combination.

[0045] [Epoxy polymer] This resin composition preferably contains a high molecular weight epoxy resin (also referred to as "epoxy polymer") with a mass-average molecular weight of 5,000 or more as a thermosetting resin, from the viewpoint of ensuring film-forming properties.

[0046] Examples of epoxy polymers include phenoxy resins having at least one skeleton selected from the group consisting of a bisphenol A type skeleton, a bisphenol F type skeleton, a bisphenol A / F mixed type skeleton, a naphthalene skeleton, a fluorene skeleton, a biphenyl skeleton, anthracene skeleton, a pyrene skeleton, a xanthene skeleton, an adamantane skeleton, and a dicyclopentadiene skeleton.

[0047] The mass-average molecular weight of the epoxy polymer is preferably 5,000 or more, more preferably 10,000 or more, more preferably 15,000 or more, more preferably 20,000 or more, and more preferably 25,000 or more. The upper limit can be 100,000 or less. When the mass-average molecular weight of the epoxy polymer is within this range, the film-forming properties and handling properties of the resin composition tend to improve. Furthermore, the improved film-forming properties of the resin composition have the effect of binding the fillers together at the uncured stage, making it less likely for voids to occur in the resin composition.

[0048] The epoxy equivalent of the epoxy polymer is preferably 3,000 g / equivalent or more, more preferably 5,000 g / equivalent or more, and more preferably 7,000 g / equivalent or more, from the viewpoint of ensuring film-forming properties and imparting flexibility. On the other hand, it is preferably 25,000 g / equivalent or less, and more preferably 20,000 g / equivalent or less.

[0049] Note that the mass-average molecular weight is the value converted to polystyrene, measured by gel permeation chromatography. Furthermore, epoxy equivalent is defined as "the mass of epoxy resin containing one equivalent of epoxy groups" and can be measured in accordance with JIS K7236.

[0050] (solvent) The resin composition preferably contains a solvent with a boiling point of 100°C or higher and a solvent with a boiling point of less than 100°C. Using only solvents with a boiling point below 100°C results in a drying rate that is too fast, leading to a large number of voids between inorganic fillers, which may not resolve the issues of surface irregularities and handling difficulties. On the other hand, using only solvents with a boiling point above 100°C results in a drying rate that is too slow, leading to poor productivity. Therefore, it is preferable to include both solvents with a boiling point above 100°C and solvents with a boiling point below 100°C. However, as long as this resin composition contains two types of solvents—one with a boiling point of 100°C or higher and one with a boiling point of less than 100°C—it is optional to include any other solvents. Furthermore, the solvents with a boiling point of 100°C or higher and those with a boiling point of less than 100°C may each consist of one type or two or more types.

[0051] In particular, it is preferable that in this resin composition, solvents with a boiling point of 100°C or higher account for 40% or more by mass of the total amount of solvent. If solvents with a boiling point of 100°C or higher account for 40% or more by mass of the total amount of solvent, handling issues such as cracking of the thermosetting resin composition during transport after the slurry-like thermosetting resin composition has been applied to a substrate sheet and dried to remove the solvent can be resolved. From this viewpoint, it is preferable that the resin composition contains at least 40% by mass of the total amount of solvent, with solvents having a boiling point of 100°C or higher, and more preferably 45% by mass or higher, and more preferably 50% by mass or higher. However, if the proportion of solvents with a boiling point of 100°C or higher is too high, the drying rate will be slow and productivity will decrease. From this viewpoint, it is preferable that the resin composition contains 10% by mass or more of solvents with a boiling point of less than 100°C, and more preferably 15% by mass or more of those, and more preferably 20% by mass or more of those.

[0052] Here, the solvent with a boiling point below 100°C is preferably an organic solvent with a boiling point below 100°C, such as acetone, methyl ethyl ketone, methyl alcohol, ethyl alcohol, isopropyl alcohol, n-hexane, ethyl acetate, petroleum benzine, dichloromethane, and tetrahydrofuran. One or two of these can be selected and used. On the other hand, the solvent with a boiling point of 100°C or higher is preferably an organic solvent with a boiling point of 100°C or higher. Examples include toluene, xylene, butyl alcohol, cyclohexanone, methyl isobutyl ketone, butyl acetate, propylene glycol monomethyl ether acetate, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, propylene glycol monomethyl ether, n-methyl-2-pyrrolidone, and N,N-dimethylformamide. One or two of these can be selected and used.

[0053] (Other resin components) In addition to the inorganic filler, thermosetting resin, and solvent, this resin composition may optionally contain "other resin components." "Other resin components" may be compositions containing polymers, curing agents, curing accelerators, dispersants, surfactants, and other components, and these may be conventionally known compositions, such as those described in International Publication No. 2021 / 085593 and International Publication No. 2023 / 189030.

[0054] [Hardening agent] This resin composition preferably contains a curing agent, if necessary. Examples of curing agents include phenolic resins, compounds having a heterocyclic structure containing nitrogen atoms (referred to as "nitrogen-containing heterocyclic compounds"), acid anhydrides having an aromatic or alicyclic skeleton, aqueous additives of said acid anhydrides or modified products of said acid anhydrides, and active esters. The hardening agent may be used alone or in combination of two or more types. The use of these preferred curing agents makes it possible to obtain a resin composition with an excellent balance of heat resistance, moisture resistance, and electrical properties.

[0055] In particular, when the resin composition uses the above-mentioned epoxy resin as the thermosetting resin, it is preferable to use a curing agent having an active group that can react with epoxy groups in combination with the epoxy resin. For example, it is preferable to use at least one of the following in combination with the epoxy resin: phenol resin, benzoxazine compound, cyanate, maleimide, and active ester. Of these, it is especially preferable to include phenol resin.

[0056] The content of the curing agent in the resin composition is preferably 1% by mass or more and 50% by mass or less based on 100% by mass of the solid content excluding inorganic fillers from the resin composition, and more preferably 3% by mass or more and 40% by mass or less, more preferably 5% by mass or more and 30% by mass or less, and more preferably 10% by mass or more and 25% by mass or less. If the curing agent content is above the lower limit, sufficient curing performance can be obtained. If it is below the upper limit, the reaction proceeds effectively, improving crosslinking density, increasing strength, and further improving film-forming properties.

[0057] [Curing accelerator] This resin composition may contain a thermosetting catalyst as a curing accelerator to adjust the curing speed and the physical properties of the cured product, if necessary.

[0058] It is preferable to select the thermosetting catalyst appropriately depending on the type of thermosetting resin and curing agent. Specific examples of thermosetting catalysts include diazabicycloalkenes such as linear or cyclic tertiary amines, organophosphorus compounds, quaternary phosphonium salts, or organic acid salts, and imidazoles. Organometallic compounds, quaternary ammonium salts, or metal halides can also be used. Examples of the above organometallic compounds include zinc octoate, tin octoate, or aluminum acetylacetone complexes. Furthermore, the nitrogen-containing heterocyclic compounds described above as curing agents also act as thermosetting catalysts, and may therefore be incorporated as thermosetting catalysts.

[0059] Among these, compounds containing imidazole (referred to as "imidazole compounds") are particularly preferred from the viewpoint of storage stability, heat resistance, and curing speed. Preferred imidazole compounds include, for example, 2-ethyl-4-methylimidazole, 2-phenylimidazole, 1-benzyl-2-methylimidazole, 1-benzyl-2-phenylimidazole, 1-cyanoethyl-2-undecylimidazole, 1-cyanoethyl-2-ethyl-4-methylimidazole, 2-phenyl-4-methylimidazole, 1-cyanoethyl-2-phenylimidazolium trimellitate, 2,4-diamino-6-[2'-methylimidazolyl-(1')]-ethyl-s-triazine, 2, Examples include 4-diamino-6-[2'-undecylimidazolyl-(1')]-ethyl-s-triazine, 2,4-diamino-6-[2'-ethyl-4'methylimidazolyl-(1')]-ethyl-s-triazine, 2,4-diamino-6-[2'-methylimidazolyl-(1')]-ethyl-s-triazine isocyanurate adduct, 2-phenylimidazole isocyanurate adduct, 2-phenyl-4,5-dihydroxymethylimidazole, and 2-phenyl-4-methyl-5-hydroxymethylimidazole. In particular, by using imidazole compounds with a melting point of 100°C or higher, and more preferably 200°C or higher, a resin composition with excellent storage stability and adhesion can be obtained. Furthermore, a composition containing nitrogen-containing heterocyclic compounds other than the aforementioned imidazole ring is even more preferable from the viewpoint of adhesion. Furthermore, the thermosetting catalyst may be used alone or in a mixture of two or more types.

[0060] The thermosetting catalyst in this resin composition is preferably contained in a proportion of 0.1% to 15% by mass, and more preferably 0.5% to 10% by mass, per 100% by mass of the solid content of the resin composition excluding inorganic fillers. If the content of the thermosetting catalyst is above the lower limit, the curing reaction can be sufficiently promoted to achieve good curing, and if it is below the upper limit, the curing speed will not be too fast, and therefore the storage stability of the resin composition can be improved.

[0061] [Other ingredients] This resin composition may further contain "other components". Examples of these "other components" include thermoplastic resins, organic fillers, inorganic fillers, additives such as silane coupling agents that improve the interfacial adhesion strength between inorganic fillers and resin components, additives that are expected to enhance the adhesion strength between the resin composition and metal plate-like materials, insulating carbon components such as reducing agents, viscosity modifiers, thixotropic agents, flame retardants, colorants, phosphorus-based, phenol-based and other various antioxidants, phenol acrylate-based and other process stabilizers, heat stabilizers, hindered amine-based radical scavengers (HAAS), impact modifiers, processing aids, metal deactivators, copper damage inhibitors, antistatic agents, and bulking agents. When using these additives, the amount added should generally be within the range used for their respective purposes.

[0062] (solid content concentration) The resin composition preferably has a solid content concentration of 50% by mass or more and 80% by mass or less at the time of application. Furthermore, the "solid content" of this resin composition refers to all components excluding the solvent, i.e., all inorganic fillers (inorganic fillers and other inorganic fillers) and resin components. In this context, "resin components" refers to thermosetting resins and other organic components, and "other organic components" include curing agents, curing accelerators, dispersants, viscosity modifiers, etc. Because resins and solvents are trapped inside and between inorganic fillers, and the liquid content outside the particles decreases, high solid content concentrations can lead to a decrease in the liquid properties of the slurry, potentially failing to resolve the issue of surface irregularities. Therefore, it is preferable to include 20% by mass or more of solvent. In other words, it is preferable to keep the solid content concentration at 80% by mass or less. This tendency is particularly pronounced in boron nitride aggregate particles because they have internal spaces. On the other hand, if there is too much solvent, cracking is more likely to occur after drying, potentially failing to resolve the aforementioned issue of repulsion. Therefore, it is preferable to keep the solid content concentration at 50% by mass or more. From this viewpoint, the resin composition preferably has a solid content concentration of 50% by mass or more at the time of application, more preferably 55% by mass or more, and more preferably 60% by mass or more. On the other hand, it is preferable that it is 80% by mass or less, more preferably 75% by mass or less, and more preferably 70% by mass or less.

[0063] (Ratio of raw materials) The thermosetting resin content in this resin composition is preferably 5% by mass or more and 99% by mass or less, based on 100% by mass of the solids content obtained by subtracting the total inorganic fillers (inorganic fillers and other inorganic fillers) from the total solids content of this resin composition. If the thermosetting resin content is 5% by mass or more relative to 100% by mass of the total solid content of the resin composition excluding all inorganic fillers, it is preferable because it results in good moldability. On the other hand, if it is 99% by mass or less, it is preferable because it allows for the content of other components to be maintained and improves thermal conductivity. From this viewpoint, the content of thermosetting resin in the resin composition is preferably 5% by mass or more, more preferably 10% by mass or more, more preferably 20% by mass or more, more preferably 30% by mass or more, more preferably 40% by mass or more, and more preferably 50% by mass or more, while it is preferably contained in a proportion of 99% by mass or less, and more preferably in a proportion of 98% by mass or less.

[0064] The inorganic filler content in this resin composition is preferably 50% by mass or more based on 100% by mass of the total solids content of this resin composition. Since increasing the proportion of inorganic fillers can improve insulation and thermal conductivity, the inorganic filler content is preferably 50% by mass or more relative to 100% by mass of the total solids content of the resin composition, more preferably 55% by mass or more, and even more preferably 60% by mass or more. On the other hand, from the viewpoint of maintaining good handling properties (brittleness), it is preferable that the amount be 95% by mass or less, more preferably 90% by mass or less, and even more preferably 85% by mass or less.

[0065] When the resin composition contains an epoxy resin as a thermosetting resin and boron nitride aggregate particles as an inorganic filler, the content of the boron nitride aggregate particles in the resin composition is preferably 50% by mass or more and 95% by mass or less, based on 100% by mass of the total solid content of the resin composition, and more preferably 55% by mass or more or 90% by mass or less, and more preferably 60% by mass or more or 85% by mass or less. Furthermore, the epoxy resin content in this resin composition is preferably 30% by mass or more and 100% by mass or less, based on 100% by mass of the total amount of thermosetting resins in this resin composition, and more preferably 40% by mass or more, of which 50% by mass or more, of which 60% by mass or more, and of which 70% by mass or more. In this context, "epoxy resin" includes epoxy resins, polyfunctional epoxy resins, and epoxy polymers.

[0066] When the thermosetting resin includes a polyfunctional epoxy resin having three or more oxirane rings (epoxy groups) in one molecule and a mass-average molecular weight of less than 5,000, it is preferable that the content of the polyfunctional epoxy resin in the resin composition is 5% by mass or more and 80% by mass or less, based on 100% by mass of the solid content of the resin composition excluding inorganic fillers. If the content of the polyfunctional epoxy resin in this resin composition is 5% by mass or more, the resin composition can maintain its curability. On the other hand, if the content is 80% by mass or less, the resin composition can contain other components to maintain its film-forming properties and can suppress performance degradation due to moisture absorption. From this viewpoint, the content of polyfunctional epoxy resin in the present resin composition is preferably 5% by mass or more, more preferably 10% by mass or more, and more preferably 15% by mass or more, based on 100% by mass of the solid content of the present resin composition excluding inorganic fillers. On the other hand, it is preferably 80% by mass or less, more preferably 70% by mass or less, more preferably 60% by mass or less, and more preferably 50% by mass or less.

[0067] When the thermosetting resin contains an epoxy polymer with a mass-average molecular weight of 5,000 or more, the content of the epoxy polymer in the resin composition is preferably 5% by mass or more and 30% by mass or less, based on 100% by mass of the solid content of the resin composition excluding inorganic fillers. If the epoxy polymer content in this resin composition is 5% by mass or more, the film-forming properties of this resin composition can be maintained; on the other hand, if the content is 30% by mass or less, the curability of this resin composition can be maintained. From this viewpoint, the epoxy polymer content in the resin composition is preferably 5% by mass or more, more preferably 10% by mass or more, and more preferably 15% by mass or more, based on 100% by mass of the solid content of the resin composition excluding inorganic fillers. On the other hand, it is preferably 30% by mass or less, more preferably 27% by mass or less, and more preferably 25% by mass or less.

[0068] <Resin composition preparation process> Regarding the method for preparing this resin composition, it is preferable to uniformly mix each raw material by stirring and kneading. For this mixing, general kneading equipment such as a mixer, kneader, three-roll kneader, single-screw or twin-screw kneader, or rotational stirring mixer can be used. During mixing, heating may be applied as needed, and if heat is generated by stirring or kneading, cooling may be applied.

[0069] When preparing the resin composition by adding a solvent, preferably an organic solvent, if preparing a fluid slurry-like coating solution, it is preferable to mix and stir using a general mixing device such as a paint shaker, bead mill, planetary mixer, homomixer, agitated disperser, self-rotating agitator mixer, rotary homogenizer, three-roll mixer, kneader, single-screw or twin-screw kneader, etc., in order to improve the uniformity of the coating solution and remove foam.

[0070] The method of mixing the raw materials is not particularly limited, but for example, a thermosetting resin containing epoxy resin may be mixed with a solvent having a boiling point of 100°C or higher and a solvent having a boiling point of less than 100°C to prepare a mixed solution, and then the remaining components, such as inorganic fillers, curing agents, curing accelerators, dispersants, viscosity modifiers, and other components, may be added to the mixed solution and mixed.

[0071] <Coating process> The resin composition prepared as described above is applied onto a base sheet to form a coated sheet.

[0072] (Base sheet) The base sheet is preferably one with a tape peel strength (180-degree peel test in accordance with JIS Z0237:2009) of 0.1 N / 10 mm or more and 5 N / 10 mm or less. The peel strength of the base sheet is correlated with the surface free energy of the base sheet surface. If the peel strength is too low, the resin composition may repel after coating and drying, potentially causing problems such as bulging or shrinkage at the edges and holes in the coating surface. On the other hand, if the peel strength is too high, it may become difficult to peel the thermosetting resin sheet from the base sheet. From this viewpoint, the tape peel strength of the base sheet (180-degree peel test in accordance with JIS Z0237:2009) is preferably 0.1 N / 10 mm or more, more preferably 0.5 N / 10 mm or more, more preferably 0.6 N / 10 mm or more, and more preferably 1.0 N / 10 mm or more. On the other hand, it is preferable that it is 5 N / 10 mm or less, more preferably 4 N / 10 mm or less, and more preferably 3 N / 10 mm or less. The adhesive tape used for the peel strength test shall be cellophane adhesive tape conforming to JIS Z1522:2009. The upper limit of the adhesive strength of the tape shall normally be 10 N / 10 mm or less, and preferably 7 N / 10 mm or less. The peel strength of the base sheet can be adjusted by the material and surface treatment of the base sheet.

[0073] Examples of base sheets include resin films such as polyethylene, polypropylene, polyethylene terephthalate, polyethylene naphthalate, polycarbonate, polyethersulfone, polyetheretherketone, and polyimide. The surface of the base sheet may have irregularities or be surface-treated, such as having a release agent applied. Examples of release agents include silicone compounds, long-chain alkyl group-containing compounds, waxes, and fluorine compounds.

[0074] (Application method) The application method can include dipping, spray coating, blade application, or any other method of your choice. For example, it is preferable to uniformly form a coating film of a predetermined thickness on a substrate sheet using a coating device or means such as a slit coater, die coater, blade coater, comma coater, screen printing, doctor blade, applicator, spray coating, dispenser, or gravure printing. From this viewpoint, it is preferable to use a slit die.

[0075] <Solvent removal process> In the solvent removal process, it is preferable to heat continuously for 60 seconds or more in a temperature range of 40°C to less than 100°C, and then heat in a temperature range of 100°C or higher to remove the solvent. The temperature in this case is the ambient temperature inside the drying chamber (drying oven).

[0076] If a slurry-like resin composition is applied to a substrate sheet and then dried at a temperature of 100°C or higher from the start, the solvent will dry rapidly, causing pores in the coating where the solvent has escaped, resulting in large irregularities on the surface. Therefore, in the solvent removal process, it is preferable to dry the composition slowly at a relatively low temperature in the initial stages to increase the solid content and viscosity, and then dry it at a relatively high temperature. From this perspective, it is preferable that the initial stage of the process involves continuous heating for 60 seconds or more, more preferably 90 seconds or more, and even more preferably 120 seconds or more, in a temperature range of 40°C or higher but less than 100°C, particularly in a temperature range of 50°C or higher or 80°C or lower. Furthermore, the initial temperature of the solvent removal process is more preferably in the temperature range of -30°C to +10°C above the boiling point of the solvent with a boiling point of less than 100°C, and more preferably in the temperature range of -20°C or above or +5°C or below. Furthermore, the step of continuously heating for 60 seconds or more in a temperature range of 40°C or more but less than 100°C may be performed by continuously heating at a constant temperature of 40°C or more but less than 100°C for 60 seconds or more, or multiple zones with different heating temperatures may be provided, and the temperature may be gradually increased while continuously heating in the temperature range of 40°C or more but less than 100°C for 60 seconds or more.

[0077] As described above, it is preferable to heat continuously for 60 seconds or more in the temperature range of 40°C to less than 100°C, and then heat in the temperature range of 100°C or higher. The temperature at this time is preferably 100°C or higher from the viewpoint of drying speed, more preferably 105°C or higher, and more preferably 110°C or higher. On the other hand, from the viewpoint of suppressing the reaction of the thermosetting resin, the temperature is preferably 150°C or lower, more preferably 140°C or lower, and more preferably 130°C or lower. Furthermore, it is even more preferable that the temperature in this case be in the temperature range of -50°C to +10°C above the boiling point of the solvent with a boiling point of 100°C or higher, and more preferably in the temperature range of -45°C or higher or +5°C or lower, and more preferably in the temperature range of -40°C or higher or +2°C or lower. From the viewpoint of solvent removal, the heating time is preferably 60 seconds or more, more preferably 120 seconds or more, and more preferably 150 seconds or more. On the other hand, from the viewpoint of preventing the thermosetting resin from hardening, the heating time is preferably 600 seconds or less, more preferably 500 seconds or less, and more preferably 400 seconds or less.

[0078] As a heating and drying method, the resin composition may be directly heated using a heating means such as a heater, or it may be dried by flowing hot air into a drying oven. Furthermore, it is preferable to heat and dry by circulating air in the opposite direction to the conveying direction and parallel to the sheet. Alternatively, the food may be directly heated to a constant temperature using an infrared heater or similar device.

[0079] In the solvent removal process, the solvent may be completely removed, but it is not always necessary to remove it completely. For example, before completely removing the solvent, the coated sheet may be rolled up once, unrolled, and then heated and dried again.

[0080] <Winding process> In the winding process, the coated sheet is wound into a roll. In this case, the coated sheet can be wound onto a core such as a paper tube, metal tube, or plastic tube. There are no particular limitations on the roll width or the length of film wound onto the roll.

[0081] Alternatively, the coated sheet after solvent removal may be wound up via a calender roll. A calender roll, that is, a coated sheet placed between two or more rolls and rotated to stretch it, can be used to equalize the unevenness of the sheet surface and improve its smoothness.

[0082] The rolled material, wound in this manner, may be transported in its rolled state and supplied to the next process, or it may be supplied to the next process continuously.

[0083] <Cutting process> As described above, the rolled body can be used, for example, to unwind the coated sheet and cut the coated sheet into individual sheets under a predetermined environment. In this process, working in low temperature and low humidity conditions can make the film brittle and prone to cracking. Conversely, working in an environment with a certain level of humidity allows the film to absorb moisture, making it more flexible and less likely to crack. From this perspective, the environment in which the coated sheet is cut is preferably at a temperature of 5°C to 40°C, and more preferably at 10°C to 30°C. Regarding humidity, it is preferable that it be between 30%RH and 70%RH, and more preferably between 40%RH and 60%RH.

[0084] As an example of a cutting method, as shown in Figure 1, the roll body 10 is unwound, and while conveying the coated sheet 11, which is made by laminating the resin composition 11A on a base sheet 11B, laser blades 12 are positioned appropriately on the inner parts from both ends in the width direction of the coated sheet 11, and the coated sheet is cut in the conveying direction (flow direction) of the coated sheet 11, cutting off the edges (ears) 13 on both sides in the width direction. Next, a shear blade 14 that crosses in the width direction is used to cut the coated sheet 11 in the width direction into individual sheets 15. However, the cutting method is not limited to this.

[0085] When cutting the coated sheet in the conveying direction (flow direction) and cutting the edges (ears) on both sides in the width direction, the tapered blade can cause lateral stress on the sheet, potentially leading to sheet damage or delamination from the base material. If the sheet delaminates from the base material, it becomes a standalone sheet, further increasing the risk of chipping. Therefore, it is preferable to use a single-sided tapered laser blade 12, positioning its vertical surface on the side to be retained as part of the product and the tapered surface on the side to be removed, thereby significantly reducing the risk of chipping on the product side. On the other hand, when cutting a coated sheet into individual sheets by cutting in the width direction, if a double-sided tapered upper blade is used for the shear blade 14, which consists of an upper blade and a lower blade, there is a possibility that the coated film surface will bulge and chip. However, if the upper blade of the shear blade 14 is a single-sided tapered blade, the coated sheet can be cut cleanly and vertically, which is preferable. However, since the sheet on the blade side may bulge, this effect can be reduced by making the blade angle blunter or by slowing down the descent speed during cutting.

[0086] <Protective film lamination process> To protect the resin composition, it is preferable to laminate the cut, single-sheet coated material with a protective film so that it is in contact with the resin composition, forming a laminate consisting of a protective film, the resin composition, and a base sheet. Examples of protective films in this case include polyethylene terephthalate film, polytetrafluoroethylene film, and polyethylene film, all coated with a release agent.

[0087] <Packaging Process> The laminate described above can be supplied as is to the next process, such as the aging process, but it is preferable to package it with a resin film (also referred to as the "packing process"). In this case, since it is best to avoid contact with air to prevent moisture absorption, a water vapor permeability of 5-20 g / m² is appropriate. 2 It is preferable to vacuum pack using a resin film with a 24-hour shelf life. The resin film may be a composite laminate film of aluminum and resin. The number of laminates placed inside the resin film can be one or two or more. For example, two or more laminates can be stacked and packed inside.

[0088] <Pressurization process> The above laminate, preferably a packed laminate, is pressurized as needed at a temperature of 0°C to 140°C and a pressure of 10 MPa to 200 MPa (also referred to as the "pressurization process"). However, the pressurization process is not a mandatory process. For example, if there is a large amount of solvent or inorganic filler, many pores may remain after the solvent has escaped, so it is preferable to perform the pressurization process in such cases. By performing the pressurization process, the voids inside the sheet, especially the connecting pores, can be reduced or made smaller.

[0089] Examples of pressurization methods include flat plate presses, hydrostatic presses, vacuum presses, calender presses, belt presses, roll presses, and servo presses. However, the method is not limited to these.

[0090] The temperature during the pressurization process should preferably be such that the thermosetting resin does not harden. For example, when using epoxy resin as the thermosetting resin, the heating temperature should preferably be less than 140°C, more preferably 100°C or lower, and even more preferably 80°C or lower, from the viewpoint of suppressing the reaction of the epoxy resin. On the other hand, from the viewpoint of the elastic modulus of the resin composition, it is more preferably 0°C or higher, more preferably 10°C or higher, and even more preferably 15°C or higher. For example, when performing a pressurizing process using a flat plate press, the temperature of the flat plate being pressed should be adjusted to the above temperature range.

[0091] In the pressurization process, for example in the case of a flat plate press, it is preferable to apply pressure to the sheet at 1 MPa or more and 250 MPa or less, and more preferably at 5 MPa or more or 200 MPa or less, and more preferably at 7.5 MPa or more or 170 MPa or less. In this case, the pressurization time is preferably 1 second or more and 60 minutes or less, more preferably 10 seconds or more or 45 minutes or less, and more preferably 30 seconds or more or 30 minutes or less.

[0092] Furthermore, in the case of the calender press method, it is preferable to set the linear pressure on the sheet to 20 kgf / cm or more and 200 kgf / cm or less, and more preferably 25 kgf / cm or more or 150 kgf / cm or less, and even more preferably 30 kgf / cm or more or 125 kgf / cm or less. A standard calender roll machine with 1 or more roller sets (number of rollers) for passing the sheet can be used. Note that 1(2) means 1 set and 2 rollers. Due to the characteristics of the calender press method, the pressurizing time is 10 seconds or less.

[0093] <Aging Process> The above-mentioned laminate, preferably a packed laminate, is preferably subjected to low-temperature aging in a temperature environment of 0°C or below. By aging the laminate at low temperatures, the moisture in the resin composition can be frozen and dispersed as tiny ice crystals. Even after returning to room temperature, these trapped moisture chambers are created, preventing the formation of large voids and thus preventing deterioration of insulation properties, while also suppressing cracking when the sheet is bent.

[0094] In low-temperature aging, a lower temperature is preferable because a faster cooling rate results in the formation of minute ice crystals. From this viewpoint, a temperature of 0°C or lower is preferable, and of course -5°C or lower, more preferably -10°C or lower, and more preferably -15°C or lower. On the other hand, if the temperature is too low, it will fall below the glass transition temperature (Tg) of the uncured thermosetting resin, making it prone to cracking. Therefore, a temperature of -50°C or higher is preferable, and if epoxy resin is included, more preferably -40°C or higher, and more preferably -30°C or higher.

[0095] The duration of the low-temperature aging is not particularly limited as long as the resin composition is frozen. Rapid freezing and holding for 10 minutes or more is sufficient, more preferably 30 minutes or more, more preferably 1 hour or more, more preferably 2 hours or more, more preferably 4 hours or more, more preferably 8 hours or more, more preferably 16 hours or more, and more preferably 24 hours or more. On the other hand, since epoxy resins react gradually even at low temperatures, from the viewpoint of avoiding prolonged storage, it is preferable that the aging period be 365 days or less, more preferably 180 days or less, more preferably 90 days or less, more preferably 30 days or less, and more preferably 7 days or less.

[0096] While it is not necessary to apply pressure during low-temperature aging, it is acceptable to apply a small pressure of 0.1 kPa or less above atmospheric pressure.

[0097] <Applications of thermosetting resin sheets> The thermosetting resin sheet of the present invention can be cured by heating and used, for example, as a thermally conductive or insulating component in semiconductor devices. However, its applications are not limited to these.

[0098] The heating temperature for curing the thermosetting resin sheet of the present invention is preferably 30 to 400°C, more preferably 50°C or higher, and more preferably 90°C or higher. On the other hand, it is preferably 300°C or lower, and more preferably 250°C or lower.

[0099] It is also possible to apply pressure and harden the material by applying weight. The load applied in this process is not particularly limited, but it is preferable to apply a load of 0.1 MPa or more to the sheet-like resin composition, more preferably 1.0 MPa or more, more preferably 5.0 MPa or more, and especially preferably 10 MPa or more. Furthermore, the load is preferably 1000 MPa or less, and more preferably 200 MPa or less. By keeping the applied load below the upper limit when pressurizing and curing are performed simultaneously, a sheet-like resin composition with high thermal conductivity and no voids in the sheet can be obtained without damaging the secondary particles of the boron nitride aggregate particles. Furthermore, by keeping the applied load above the lower limit, good contact between inorganic fillers is achieved, making it easier to form heat conduction paths, thus enabling the production of a resin composition with high thermal conductivity.

[0100] The pressurizing time when pressurizing and curing are performed simultaneously is not particularly limited. The pressurizing time is preferably 30 seconds or more, more preferably 1 minute or more, even more preferably 5 minutes or more, and especially preferably 10 minutes or more. Also, the pressurizing time is preferably 4 hours or less, more preferably 3 hours or less, and even more preferably 2 hours or less. When the pressurization time is below the upper limit, the manufacturing time for the sheet-like resin composition can be reduced, and production costs tend to be lowered. When the pressurization time is above the lower limit, voids and air pockets within the sheet-like resin composition can be sufficiently removed, and heat transfer performance and dielectric strength tend to be improved.

[0101] <Explanation of terms and phrases> In this invention, the term "film" includes "sheets," and the term "sheet" includes "film."

[0102] In this invention, when "α~β" (where α and β are arbitrary numbers) is written, unless otherwise specified, it means "α or greater and β or less," and also includes the meaning of "preferably greater than α" or "preferably less than β." Furthermore, when "α or greater" (where α is any number) is written, unless otherwise specified, it includes the meaning of "preferably greater than α," and when "β or less" (where β is any number) is written, unless otherwise specified, it also includes the meaning of "preferably less than β." [Examples]

[0103] The following describes an example of an embodiment of the present invention. However, the present invention is not limited to the embodiment described below.

[0104] <Ingredients> The raw materials used in the examples and comparative examples are as follows:

[0105] (Inorganic filler) • Inorganic filler 1: Spherical boron nitride aggregates having a cardhouse structure formed by the aggregation of plate-like primary particles, manufactured in accordance with the method for producing boron nitride aggregates disclosed in the examples of International Publication No. 2015 / 561028. Maximum particle size: 90μm Average particle size (D50): 45μm

[0106] • Inorganic filler 2: Spherical alumina particles Average particle size (D50): 7~13μm

[0107] The maximum particle diameter and average particle diameter (D50) of the inorganic filler were determined by dispersing the inorganic filler in a pure water medium containing sodium hexametaphosphate as a dispersion stabilizer, measuring the volume-based particle size distribution using a laser diffraction / scattering particle size distribution analyzer LA-300 (manufactured by Horiba, Ltd.), and then obtaining the maximum particle diameter and cumulative volume 50% particle diameter (average particle diameter D50) from the resulting particle size distribution.

[0108] (Epoxy resin) • Epoxy resin 1: Biphenyl-type solid epoxy resin manufactured by Mitsubishi Chemical Corporation, containing two glycidyl groups per molecule. Molecular weight: approx. 400 Epoxy equivalent: 200g / equivalent • Epoxy resin 2: A bifunctional epoxy polymer manufactured by Mitsubishi Chemical Corporation and disclosed as resin component 1 in Japanese Patent Publication No. 2020-63438. Mass-average molecular weight in polystyrene equivalent: 30,000 Epoxy equivalent: 9,000g / equivalent • Epoxy resin 3: A polyfunctional epoxy resin containing a structure with four or more glycidyl groups per molecule, and not containing amine-based or amide-based structures containing nitrogen atoms. Molecular weight: approx. 400 Epoxy equivalent: 100g / equivalent

[0109] (Hardening agent) • Hardener 1: MEH-8000H manufactured by Meiwa Kasei Co., Ltd., phenolic resin-based hardener (allylphenol novolac resin)

[0110] (Thermosetting catalyst) • Thermosetting catalyst 1: 2,4-diamino-6-[2'-ethyl-4'-methylimidazolyl-(1')]-ethyl-s-triazine. It possesses both structures derived from imidazole and structures derived from triazine within a single molecule (Shikoku Chemicals Co., Ltd. "Curezol 2E4MZ-A"). • Thermosetting catalyst 2: 2-phenyl-4,5-dihydroxymethylimidazole (Shikoku Chemicals Co., Ltd. "Curezol 2PHZ-PW")

[0111] (solvent) • Solvent 1: Methyl ethyl ketone (MEK, boiling point 80°C) • Solvent 2: Cyclohexanone (CHN, boiling point 156°C)

[0112] <Examples 1-4 and Comparative Examples 1-5> Each raw material was weighed to achieve the composition (parts by mass) shown in Table 1, mixed using a planetary mixer, and dispersed using a homomixer to prepare a slurry-like resin composition. The obtained slurry-like resin composition was applied to the surface of a PET substrate sheet using a slit die to form a coated sheet. This coated sheet was then supplied into a drying oven and heated and dried while being transported within the oven to remove the solvent. During this process, the drying oven was heated and dried by circulating air at the temperatures shown in Table 1 for each of the three zones (1, 2, and 3). The thickness of this sheet after pressurization was 150 μm. The coated sheets removed from the drying oven were rolled up and collected.

[0113] The wound roll was unwound, and under the temperature and humidity conditions shown in Table 1, the coated sheet was transported while being cut from both ends in the transport direction (flow direction) using a single-sided tapered laser blade so that the width of the coated sheet was 350 mm, cutting off the edges (selvages) on both sides in the width direction. Next, the sheet was cut in the width direction using a shear blade with a single-sided tapered upper blade, resulting in sheets measuring 400 mm x 350 mm.

[0114] Next, a protective film (Mitsubishi Chemical's "MRV38(V04)") was laminated to the cut single-sheet coated material so as to be in contact with the resin composition to form a laminate. This laminate was then placed in a vacuum-sealed bag (Kurilon Chemicals), the air inside the bag was removed, and the opening of the bag was heat-sealed to seal it. The laminate in this vacuum-sealed state was then pressed at 145 MPa at 40°C for 15 minutes, followed by low-temperature aging by storing it in a freezer at -20°C for 48 hours to obtain a thermosetting resin sheet (sample).

[0115] The peel strength (N / 10mm) of the base sheet (PET) shown in Table 1 is the result of a 180-degree peel test conducted in accordance with JIS Z0237:2009, using cellophane adhesive tape (Sekisui Chemical Co., Ltd. "PB-TP2435", 24mm width) conforming to JIS Z1522:2009, and using PET film instead of SUS304 steel plate as the test plate. In the examples and comparative examples other than Example 4 and Comparative Example 4, a PET sheet (film thickness 38μm) with no surface release treatment was used as the base sheet. In Example 4, Lintec Corporation's "PET38X" (film thickness 38μm) was used, and in Comparative Example 4, a PET sheet (film thickness 38μm) with a surface release treatment by silicone coating was used. Furthermore, the water vapor permeability of the vacuum-sealed bags is based on tests conducted in accordance with JIS K 7129.

[0116] <Evaluation of manufacturing methods> The manufacturing methods in Examples 1-4 and Comparative Examples 1-5 were evaluated from the following perspectives.

[0117] (Surface irregularities during application) After applying and drying a slurry-like thermosetting resin composition onto a substrate sheet, the coated surface was visually inspected. If there were no large depressions or protrusions, the surface unevenness during coating was judged as "○ (pass)". If large crater-like depressions or protrusions caused by particle aggregation occurred, the surface unevenness during coating was judged as "× (fail)". As a guideline, the depression depth or protrusion height was considered to be 1 / 5 or more of the film thickness.

[0118] (Repelling after application and drying) After applying and drying a slurry-like thermosetting resin composition onto a substrate sheet, the coated surface was visually inspected. If there were no depressions on the film surface due to repulsion and almost no shrinkage at the edges, the repulsion after drying was judged as "○ (pass)". If depressions occurred on the film surface due to repulsion, or if shrinkage occurred at the coated edges causing them to bulge, the repulsion after drying was judged as "× (fail)".

[0119] (Handling) When the coated sheet was removed from the drying oven, wound into a roll, and then unwound, if no cracks or fissures were visible on the coated surface, the handling performance was judged as "○ (pass)". If cracks or fissures were visible on the coated surface, the handling performance was judged as "× (fail)".

[0120] (cracks during cutting) When the coated sheet was cut, if no cracks, fissures, or chips on the edges were visually observed on the coated surface, the cutting was judged as "○ (pass)". If cracks, fissures, or chips on the edges were visually observed on the coated surface, the cutting was judged as "× (fail)".

[0121] [Table 1]

[0122] Examples 1, 2, 3, and 4 all received a "○ (pass)" rating for "surface unevenness during application," "repellency after application and drying," and "handling ability." Although not directly related to the issues addressed by this invention, regarding "cracking during cutting," Examples 1, 2, and 4 all passed, while Example 3 failed. This is likely because the cutting humidity in the cutting environment was low, resulting in insufficient moisture content in the resin sheet. Comparative Example 1 received a "fail" rating for "handling performance." This is presumed to be because the low proportion of solvent with a boiling point above 100°C resulted in an excessively fast drying rate, leading to many gaps between the fillers. Consequently, cracks and fissures occurred on the coated surface when the roll was unwound. Comparative Example 2 received a "fail" rating for "repellency after coating and drying." This is presumed to be because the low solid content concentration and low viscosity caused shrinkage towards the center of the coating surface, resulting in raised edges. Comparative Example 3 received a "× (fail)" rating for "surface unevenness during application." This is presumed to be because the high solid content concentration resulted in high slurry viscosity and reduced liquid properties, causing aggregated filler clumps to remain on the applied surface without leveling, resulting in significant unevenness. Comparative Example 4 received a "fail" rating for "repellency after coating and drying." This is presumed to be due to the low peel strength of the substrate sheet surface, which caused the slurry to repel and resulted in shrinkage at the coating edges. Comparative Example 5 received a "× (fail)" rating for "surface irregularities during coating." This is presumed to be because, due to high-temperature drying from the initial stages of the drying process, the solvent dried rapidly, causing the particles to aggregate without leveling out, and resulting in depressions in the film where the solvent evaporated, thus creating significant irregularities on the coated surface.

[0123] Based on the results of the above examples and comparative examples, as well as the test results conducted by the present inventors to date, the present inventors have provided a method for producing a thermosetting resin sheet containing an inorganic filler and a thermosetting resin, wherein when preparing the slurry-like resin composition, the solvent includes a solvent with a boiling point of 100°C or higher and a solvent with a boiling point of less than 100°C, and the solvent with a boiling point of 100°C or higher accounts for 40% by mass or more of the total amount of solvent, and the solid content concentration is adjusted to 50% by mass or more and 80% by mass or less, and furthermore, the tape peel strength of the substrate sheet to which the slurry-like resin composition is applied is 0.1 N / 10 mm or more and 5 N / 10 mm By limiting the scope to the following, and further specifying the drying conditions when applying and drying the resin composition to be heated continuously for 60 seconds or more in a temperature range of 40°C to less than 100°C, followed by heating in a temperature range of 100°C or higher to remove the solvent, it was found that the wettability of the thermosetting resin composition to the substrate sheet can be improved ("repellency after application and drying"), large irregularities on the surface of the coating film can be suppressed ("surface irregularities during application"), and cracking of the thermosetting resin composition after it has been applied to the substrate sheet and dried can be suppressed ("handling properties"). [Explanation of symbols]

[0124] 10 rolls 11. Coating sheet 11A This resin composition 11B Base Sheet 12 razor blades 13. Edges (ears) on both sides in the width direction 14 Sharpening blades 15 leaves

Claims

1. A slurry-like resin composition is prepared (also referred to as the "resin composition preparation step"), comprising an inorganic filler containing boron nitride aggregate particles, a thermosetting resin containing epoxy resin, a solvent with a boiling point of 100°C or higher, and a solvent with a boiling point of less than 100°C, wherein the solvent with a boiling point of 100°C or higher accounts for 40% or more of the total amount of solvent, and the solid content concentration is 50% or more by mass and 80% or less by mass. The slurry-like resin composition is applied to a base sheet having a tape peel strength (a 180-degree peel test in accordance with JIS Z0237:2009 using cellophane adhesive tape conforming to JIS Z1522:2009) of 0.1 N / 10 mm or more and 5 N / 10 mm or less to form a coated sheet (also referred to as the "coating process"). After continuously heating the coated sheet in a temperature range of 40°C or higher and less than 100°C for 60 seconds or more, the solvent is removed by heating in a temperature range of 100°C or higher (also referred to as the "solvent removal step"). A method for manufacturing a thermosetting resin sheet, comprising winding the coated sheet into a roll (also referred to as the "winding process").

2. After the winding process, the coated sheet is unwound, Under conditions of a temperature of 10°C to 40°C and a humidity of 30% RH to 70% RH, the coated sheet is cut into individual sheets (also referred to as the "cutting process"), A method for producing a thermosetting resin sheet according to claim 1, comprising laminating a protective film so as to be in contact with the resin composition of a cut sheet of coated material to form a laminate (also referred to as the "protective film lamination step").

3. A method for producing a thermosetting resin sheet according to claim 2, comprising packaging the laminate with a resin film (also referred to as the "packing process").

4. A method for producing a thermosetting resin sheet according to claim 2, comprising pressurizing the laminate at a temperature of 0°C to 140°C and a pressure of 10 MPa to 200 MPa (also referred to as the "pressurization step").

5. A method for producing a thermosetting resin sheet according to claim 3, comprising pressurizing the laminate at a temperature of 0°C to 140°C and a pressure of 10 MPa to 200 MPa (also referred to as the "pressurization step").

6. A method for producing a thermosetting resin sheet according to any one of claims 2 to 5, comprising aging the laminate at a temperature of 0°C or lower (also referred to as the "aging process").

7. A method for producing a thermosetting resin sheet according to claim 1, wherein the boron nitride aggregated particles have a cardhouse structure.

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