Method for producing cured sheet and method for producing composite molded product

Abstract

To provide a method for manufacturing a specific sheet cured product which is excellent in a shelf life of a sheet cured product, and can reduce warpage of the sheet cured product after curing.SOLUTION: There is provided a method for manufacturing a sheet cured product obtained using a resin composition containing an inorganic filler, a thermosetting resin and a thermosetting catalyst, wherein the inorganic filler contains an inorganic aggregation filler, the thermosetting resin contains an epoxy resin, a melting point of the thermosetting catalyst is 120°C or higher, and the method includes the following step (a) and step (b). (a) Step of forming a sheet using a resin composition, and (b) a step of heating the sheet obtained in the step (a) at 95°C or lower, and setting a reaction rate of the sheet at 50% or more.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing a cured sheet and a method for producing a composite molded product, and the cured sheet can be suitably used as a heat dissipation sheet for, for example, a power semiconductor device. [Background technology]

[0002] Power semiconductor devices are used in a variety of fields, including railways, automobiles, and general home appliances. In recent years, power semiconductor devices have been shifting from conventional Si-based power semiconductors to power semiconductors that use SiC, AlN, GaN, etc., in order to achieve further miniaturization, cost reduction, and higher efficiency. Power semiconductor devices are generally used as a power semiconductor module in which a plurality of semiconductor devices are arranged on a common heat sink and packaged.

[0003] Various challenges have been identified for the practical application of such power semiconductor devices, one of which is the problem of dissipating heat generated by the devices. Generally, power semiconductor devices can achieve high output and high density by operating at high temperatures, so insufficient heat dissipation affects the reliability of power semiconductor devices. For example, there is concern that heat generated by device switching may reduce reliability. In particular, in recent years, the density of integrated circuits has been increasing in the electrical and electronic fields, and the heat generated by this increase in density has become an urgent issue.

[0004] One method to solve this problem is to use highly thermally conductive ceramic substrates such as alumina substrates and aluminum nitride substrates as heat dissipation substrates on which power semiconductor devices are mounted. However, ceramic substrates have drawbacks such as being easily cracked by impact and being difficult to make thin and compact.

[0005] As a method for solving the above problems, a thermally conductive resin sheet containing a thermosetting resin such as an epoxy resin and a highly thermally conductive inorganic filler has been proposed (for example, Patent Document 1). Patent Document 1 uses an epoxy resin and a curing agent as binder resin components, and an alumina filler and a BN filler as highly thermally conductive inorganic fillers. In addition, by adjusting the particle size and composition ratio of the highly thermally conductive inorganic filler, peeling between the resin sheet and the conductive layer is made less likely to occur, improving long-term insulation reliability. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] International Publication No. 2018 / 235918 Summary of the Invention [Problem to be solved by the invention]

[0007] However, Patent Document 1 uses a high-melting-point catalyst such as dicyandiamide or 2MZA-PW to improve insulation and adhesion after curing. While the use of a high-melting-point catalyst can maintain shelf life, it cures at high temperatures of 200°C, resulting in significant warpage of the substrate due to cure shrinkage. On the other hand, using a low-melting-point catalyst lowers the curing temperature, reducing substrate warpage but shortening shelf life. Thus, there is a trade-off between shelf life and substrate warpage.

[0008] The present invention provides a method for producing a specific cured sheet product that has an excellent shelf life and can reduce warpage of the cured sheet product after curing, and a method for producing a composite molded product using the same. [Means for solving the problem]

[0009] [1] A method for producing a sheet cured product obtained using a resin composition containing an inorganic filler, a thermosetting resin, and a thermosetting catalyst, comprising: the inorganic filler comprises an agglomerated inorganic filler; the thermosetting resin comprises an epoxy resin; The melting point of the thermosetting catalyst is 120°C or higher, A method for producing a cured sheet, comprising the following steps (a) and (b): (a) forming a sheet using a resin composition (b) a step of heating the sheet obtained in step (a) at 95°C or less to make the reaction rate of the sheet 50% or more; The reaction rate of the sheet is calculated as follows. (Response rate) It is calculated from the calorific value of the exothermic peak obtained by differential scanning calorimetry (DSC) when the temperature is raised from 40°C to 250°C at a rate of 10°C / min, using the following formula. Reaction rate (%) = (1 - (heat generation after step (b) / heat generation after step (a))) x 100 [2] The method for producing a cured sheet according to [1], wherein the resin composition contains the thermosetting catalyst in an amount of 5% by mass or less relative to the resin component. The resin component here refers to the components obtained by excluding the inorganic filler and the solvent, if any, from the resin composition. [3] The method for producing a sheet cured product according to [1] or [2], wherein the thermosetting catalyst contains a compound having a structure derived from imidazole and / or dicyandiamide. [4] The method for producing a cured sheet according to any one of [1] to [3], wherein in the step (b), the heating time for the sheet is 5 hours or less. [5] The method for producing a cured sheet according to any one of [1] to [4], wherein in the step (b), a pressing pressure of 0.1 MPa or more and 1000 MPa or less is applied simultaneously with heating. [6] The method for producing a cured sheet according to any one of [1] to [5], wherein the inorganic filler contains agglomerated particles of boron nitride. [7] A method for producing a composite molded product, which comprises obtaining a composite molded product having a cured product part made of the sheet cured product obtained by the production method according to any one of [1] to [6] and a metal part. [Effects of the Invention]

[0010] The present invention provides a method for producing a cured sheet, in which a resin composition containing an aggregated inorganic filler contains a specific curing catalyst, thereby controlling the reaction rate of the thermosetting resin. Furthermore, by heating a sheet formed using the resin composition at 95°C or less to achieve a specific reaction rate, the shelf life of the sheet is improved and warping of the sheet (cured sheet) after step (b) is suppressed. DETAILED DESCRIPTION OF THE INVENTION

[0011] The following describes in detail the embodiments of the present invention, but the present invention is not limited to the following embodiments and can be practiced in various modified forms within the scope of the gist thereof.

[0012] [mechanism] The following two points are believed to be the reasons why the method for producing a cured sheet of the present invention can improve the shelf life of the sheet and further suppress warping of the sheet (cured sheet) after step (b). 1) The shelf life can be increased by using a curing catalyst with a high melting point and minimizing the amount used. 2) Warping occurs due to hardening shrinkage, which is caused by shrinkage due to hardening and shrinkage due to cooling after hardening. Therefore, hardening at low temperatures can reduce shrinkage during cooling. The resin composition and process satisfy both of the above points, which is thought to improve the shelf life of the sheet and also to suppress warping of the sheet (cured sheet) after step (b).

[0013] [Cured sheet] The cured sheet of the present invention is a cured product obtained using the resin composition described below, and refers to a cured sheet that has undergone steps (a) and (b). The cured sheet is not particularly limited as long as it has a reaction rate of 50% or more, and may also be one that has undergone other steps in addition to steps (a) and (b).

[0014] [Method for producing cured sheet] The method for producing a cured sheet of the present invention includes the following steps (a) and (b). (a) forming a sheet using a resin composition (b) a step of heating the sheet obtained in step (a) at 95°C or less to make the reaction rate of the sheet 50% or more; The reaction rate of the sheet is calculated as follows. (Response rate) It is calculated from the calorific value of the exothermic peak obtained by differential scanning calorimetry (DSC) when the temperature is raised from 40°C to 250°C at a rate of 10°C / min, using the following formula. Reaction rate (%) = (1 - (heat generation after step (b) / heat generation after step (a))) x 100

[0015] In addition to the steps (a) and (b), other steps may be included, such as a pressurizing step and a post-curing step.

[0016] ((a) process) Step (a) is a step of forming a sheet using the resin composition. The method for forming the sheet is not particularly limited and can be appropriately selected depending on the viscosity of the resin composition, the film thickness and size of the sheet to be formed, etc. An example of a method for producing a sheet cured product using a slurry resin composition will be described below. First, a slurry resin composition is applied to the surface of a substrate to form a sheet (coating film; sheet-like resin composition). Specifically, a coating film is formed on the substrate using the slurry resin composition by a dip method, spin coating method, spray coating method, blade method, or any other method. A coating device such as a spin coater, slit coater, die coater, or blade coater can be used to apply the slurry resin composition. By using a coating device, it is possible to form a uniform coating film of any desired thickness on the substrate. As the substrate, copper foil and PET film, which will be described later, are generally used, but there is no particular limitation. Furthermore, when the resin composition of the present invention is in the form of a sheet that has been subjected to processes such as coating and drying, it may contain a solvent.

[0017] In step (a), a sheet formed using the resin composition may be dried at a temperature of typically 10 to 150°C, preferably 25 to 120°C, and more preferably 30 to 110°C to remove solvents, low-molecular-weight components, and the like. If the drying temperature is below the upper limit, curing of the thermosetting resin in the sheet (coating) is suppressed, and the resin in the sheet (coating) tends to flow in the subsequent pressurizing step, making it easier to remove voids. On the other hand, if the drying temperature is above the lower limit, solvents and the like can be effectively removed, tending to improve productivity.

[0018] The drying time is not particularly limited and can be adjusted appropriately depending on the state of the sheet (coating film), the drying environment, etc. When drying at a temperature below 80°C, the drying time is preferably 1 minute or more, more preferably 2 minutes or more, even more preferably 5 minutes or more, even more preferably 10 minutes or more, particularly preferably 20 minutes or more, and most preferably 30 minutes or more. On the other hand, the drying time is preferably 4 hours or less, more preferably 2 hours or less. When drying at 80°C or higher, the drying time is preferably 1 minute or more, preferably 30 minutes or less, more preferably 20 minutes or less, more preferably 15 minutes or less, and more preferably 10 minutes or less. When the drying time is equal to or longer than the lower limit, the solvent and the like can be sufficiently removed, and the residual solvent tends to be prevented from forming voids in the cured sheet. When the drying time is equal to or shorter than the upper limit, productivity tends to be improved, and production costs tend to be reduced.

[0019] ((b) process) In step (b), the sheet obtained in step (a) is heated to 95°C or less to bring the reaction rate of the sheet to 50% or more. This step reduces the cure shrinkage and ultimately the amount of warping. The reactivity of the sheet (cured sheet) is sufficient as long as it is 50% or more, preferably 60% or more, more preferably 70% or more, and even more preferably 80% or more. The reactivity may be 100%. The upper limit of the reactivity can be adjusted appropriately depending on the use form of the cured sheet.

[0020] The heating temperature of the sheet is not particularly limited as long as it is 95° C. or less, but is more preferably 94° C. or less, and even more preferably 93° C. or less. The lower limit is also not particularly limited, but is preferably 10° C. or more, more preferably 20° C. or more, even more preferably 30° C. or more, even more preferably 40° C. or more, and particularly preferably 50° C. or more. When the heating temperature is within the above range, curing shrinkage due to cooling is reduced, warping can be suppressed, and curing tends to proceed.

[0021] The heating time may be adjusted as needed to achieve a reaction rate of 50% or more, preferably 10 hours or less, more preferably 5 hours or less. The lower limit is not particularly limited, but is preferably 1 hour or more, more preferably 2 hours or more. By keeping the heating time within the above range, the production time for the cured sheet can be reduced, which tends to reduce production costs. Furthermore, voids and gaps within the cured sheet can be sufficiently removed, which tends to improve heat transfer performance and voltage resistance.

[0022] In step (b), heating and pressure may be applied simultaneously. By applying pressure in addition to heating, the inorganic fillers are bonded to each other to form heat paths, thereby suppressing voids and gaps in the sheet. The pressing time may be the same as or different from the heating time. The pressing pressure is preferably 0.1 MPa or more, more preferably 0.5 MPa or more, and even more preferably 1 MPa or more, and is preferably 1000 MPa or less, more preferably 700 MPa or less, and even more preferably 500 MPa or less. When the pressing pressure is within this range, the secondary particles of the inorganic filler are not destroyed, and a sheet-like cured sheet having high thermal conductivity can be obtained without voids, etc. Furthermore, when the pressing pressure is equal to or greater than the lower limit, contact between the inorganic fillers is good, making it easier to form thermal conduction paths, and therefore a cured sheet having high thermal conductivity tends to be obtained.

[0023] (Pressure process) A pressurizing step may be performed after step (a) and before step (b). By applying pressure, the inorganic fillers are bonded to each other to form heat paths, thereby suppressing voids and gaps in the sheet. The time for the pressurizing step is not particularly limited. The time for the pressurizing step is preferably 30 seconds or more, more preferably 1 minute or more, even more preferably 3 minutes or more, and particularly preferably 5 minutes or more. The time for the pressurizing step is preferably 1 hour or less, more preferably 30 minutes or less, and even more preferably 20 minutes or less. When the pressing time is equal to or less than the upper limit, the production time for the cured sheet can be reduced, and production costs tend to be reduced. On the other hand, when the pressing time is equal to or more than the lower limit, voids and gaps in the cured sheet can be sufficiently removed, and heat transfer performance and voltage resistance tend to be improved. The pressing pressure is preferably 0.1 MPa or more, more preferably 0.5 MPa or more, and even more preferably 1 MPa or more, and is preferably 1000 MPa or less, more preferably 700 MPa or less, and even more preferably 500 MPa or less. By keeping the pressing pressure within this range, it is possible to sufficiently remove voids and gaps in the cured sheet, which tends to improve the heat transfer performance and voltage resistance characteristics.

[0024] (Post-curing process) A post-curing step may be included after step (b). By carrying out the post-curing, the cured sheet is completely cured, and peeling of the sheet from the substrate during high-temperature storage tends to be suppressed. The means for post-curing are not particularly limited, but examples include heating, pressure, and a combination thereof. The time for the post-curing step is not particularly limited. The time for the post-curing step is preferably 5 minutes or more, more preferably 10 minutes or more, even more preferably 20 minutes or more, and particularly preferably 30 minutes or more. The time for the post-curing step is preferably 5 hours or less, more preferably 4 hours or less, and even more preferably 3.5 hours or less. When the post-curing time is equal to or less than the upper limit, the production time of the cured sheet can be shortened, and production costs tend to be reduced. On the other hand, when the post-curing time is equal to or more than the lower limit, curing of the cured sheet proceeds, and peeling from the substrate during high-temperature storage tends to be suppressed. The heating temperature in the post-curing step is not particularly limited. The heating temperature in the post-curing step is preferably 100°C or higher, more preferably 120°C or higher, even more preferably 140°C or higher, and particularly preferably 160°C or higher. When the heating temperature is equal to or higher than the lower limit, the uncured portions of the resin can be cured, and complete curing tends to prevent peeling of the cured sheet from the substrate during high-temperature storage. The pressure conditions in the post-curing step are not particularly limited, and the pressure in the post-curing step is preferably 30 MPa or less, more preferably 25 MPa or less, even more preferably 20 MPa or less, and particularly preferably 15 MPa or less. When the pressure condition is equal to or less than the upper limit, cracks and the like are less likely to occur in the sheet cured product during the post-curing step.

[0025] The thickness of the cured sheet product obtained after step (b) or step (b) plus a post-curing step is not particularly limited, but is preferably 50 μm or more, more preferably 80 μm or more, and even more preferably 100 μm or more. The thickness of the cured sheet product is preferably 400 μm or less, more preferably 300 μm or less. When the thickness of the cured sheet product is equal to or greater than the lower limit, the voltage resistance characteristics are obtained and the breakdown voltage tends to be improved. When the thickness of the cured sheet product is equal to or less than the upper limit, the device can be made smaller and thinner, and the thermal resistance of the resulting cured sheet product tends to be reduced.

[0026] <Composite molded body> The cured sheet obtained by the present invention can be laminated with a metal part made of metal to produce a composite molded product. The metal part may be provided on only one surface of the cured sheet part made of the cured sheet of the present invention, or on two or more surfaces. For example, the cured sheet may have a metal part on only one surface, or on both surfaces. The metal part may also be patterned.

[0027] Such a composite molded product of the present invention can be produced by using a metal part as the substrate in step (a) and subjecting the substrate, including the metal part, to step (b) and, if necessary, a post-curing step to form a sheet cured product. Alternatively, the composite molded product can be produced by peeling a sheet-like resin composition formed on a substrate other than the metal part in step (a) from the substrate, and then heat-pressing the resin composition onto a metal member that will become the metal part in step (b) and, if necessary, a post-curing step.

[0028] In this case, the sheet-like resin composition of the present invention is formed in the same manner as described above, except that in step (a) it is applied to a substrate such as PET which may be treated with a release agent, and then peeled off from the substrate. This sheet-like resin composition is placed on another metal plate or sandwiched between two metal plates, and then cured in step (b) and, if necessary, a post-curing step to integrate the two.

[0029] In this case, the metal plate may be a metal plate having a thickness of about 10 μm to 10 cm and made of copper, aluminum, nickel-plated metal, etc. The surface of the metal plate may be physically roughened or chemically treated with a surface treatment agent, etc. From the viewpoint of adhesion between the resin composition and the metal plate, it is more preferable that the surface of the metal plate is subjected to such treatment.

[0030] <Semiconductor devices> The semiconductor device of the present invention has the composite molded article of the present invention. The composite molded article of the present invention can be used as a semiconductor device. In particular, it can be useful in power semiconductor devices that can be operated at high temperatures to achieve high output and high density.

[0031] [Resin composition] The resin composition of the present invention refers to a composition that contains an inorganic filler, a thermosetting resin, and a thermosetting catalyst and is subjected to step (a). The thermosetting resin contains an epoxy resin, and the thermosetting catalyst contains a thermosetting catalyst having a melting point of 120°C or higher.

[0032] <<Inorganic filler>> The resin composition of the present invention contains an inorganic filler. The inorganic filler may be a filler composed of particles of at least one type selected from the group consisting of metal carbides, metal oxides, and metal nitrides. Examples of metal carbides include synthetic magnesite, silicon carbide, titanium carbide, tungsten carbide, etc. Examples of metal oxides include aluminum oxide (alumina), magnesium oxide, silicon oxide, calcium oxide, zinc oxide, yttrium oxide, zirconium oxide, cerium oxide, ytterbium oxide, sialon (ceramics composed of silicon, aluminum, oxygen, and nitrogen), etc. Examples of metal nitrides include boron nitride, aluminum nitride, silicon nitride, etc. The shape of the inorganic filler is not limited, and may be particulate, spherical, whisker-like, fibrous, plate-like, or an aggregate thereof, and inorganic fillers of the above types and shapes may be used in combination.

[0033] Among the above, it is preferable to contain a large amount of agglomerated inorganic filler in order to improve the thermal conductivity and control the linear expansion coefficient of the cured sheet of the present invention. By containing agglomerated inorganic filler, the agglomerated inorganic fillers come into contact with each other during the pressurizing process and deform, and the surface contact forms more heat conduction paths, tending to result in high thermal conductivity. The agglomerated morphology of the agglomerated inorganic filler can be confirmed using a scanning electron microscope (SEM).

[0034] <Agglomerated inorganic filler> As the agglomerated inorganic filler, an electrically insulating filler can be used, and examples thereof include the above-mentioned filler composed of at least one type of particles selected from the group consisting of metal carbides, metal oxides, and metal nitrides. For power semiconductor applications, insulation is required, so the aggregated inorganic filler has a volume resistivity of 1×10 13 Ω·cm or more, especially 1×10 14 It is preferable that the filler is an inorganic compound having excellent insulating properties of Ω·cm or more. Among them, oxides and nitrides are preferable because the cured sheet has sufficient electrical insulating properties. More specifically, alumina (Al2O3, volume resistivity 1×10 14 Ω·cm), aluminum nitride (AlN, volume resistivity 1×10 14 Ω·cm), boron nitride (BN, volume resistivity 1×10 14 Ω·cm), silicon nitride (Si3N4, volume resistivity 1×10 14 Ω·cm), silica (SiO2, volume resistivity 1×10 14 Among them, alumina, aluminum nitride, boron nitride, and silica are preferred, and alumina and boron nitride are particularly preferred.

[0035] The aggregated inorganic filler may be surface-treated with a surface treatment agent, and known surface treatment agents can be used.

[0036] These aggregated inorganic fillers may be used singly or in any combination and ratio of two or more. In particular, in the present invention, there are no particular limitations on the method or degree of agglomeration of the agglomerated inorganic filler, but it is preferable to use the following agglomerated boron nitride particles as the agglomerated inorganic filler. Furthermore, a filler of a different shape or type than the agglomerated boron nitride particles may be used in combination.

[0037] <Boron nitride agglomerated particles> Boron nitride has high thermal conductivity, but is scaly, and while it conducts heat in the plane direction, it has high thermal resistance in the direction perpendicular to the plane. For ease of handling, it is preferable to use agglomerated particles in which the scales are gathered and agglomerated into a spherical shape. When boron nitride agglomerated particles are stacked like cabbage, it is preferable to align them in the plane direction, with the diameter of the agglomerated particles being the direction with better thermal conductivity. On the other hand, it is preferable for the boron nitride agglomerated particles to have a house-of-cards structure. The "house-of-cards structure" is described, for example, in Ceramics 43 No. 2 (published by the Ceramic Society of Japan, 2008), and is a structure in which plate-shaped particles are stacked in a complex manner without being oriented. More specifically, boron nitride agglomerated particles having a house-of-card structure are aggregates of boron nitride primary particles, in which the flat surfaces and end surfaces of the primary particles come into contact with each other to form, for example, a T-shaped aggregate. As the boron nitride agglomerated particles used in the present invention, boron nitride agglomerated particles having the above-mentioned house-of-card structure are particularly preferred, and by using boron nitride agglomerated particles having a house-of-card structure, thermal conductivity can be further increased.

[0038] The new Mohs hardness of the boron nitride agglomerated particles is not particularly limited, but is preferably 5 or less, and although there is no particular lower limit, it is, for example, 1 or more. When the new Mohs hardness is 5 or less, the particles dispersed in the resin composition tend to come into surface contact with each other, forming heat conduction paths between the particles and tending to improve the thermal conductivity of the cured sheet. The volume average particle diameter of the boron nitride agglomerated particles is not particularly limited, but is preferably 10 μm or more, more preferably 15 μm or more. Also, it is preferably 100 μm or less, more preferably 90 μm or less. A volume average particle diameter of 10 μm or more results in a relatively small number of particles in the resin composition and in a cured product using the resin composition. In other words, the reduced interparticle interfaces result in a low thermal resistance, which may result in a composite molded product with high thermal conductivity. Furthermore, a volume average particle diameter of not more than the upper limit mentioned above tends to result in a cured product using the resin composition with good surface smoothness.

[0039] Here, the volume-average particle size of boron nitride agglomerated particles refers to the particle size at which the cumulative volume reaches 50% when a cumulative curve is drawn, with the volume of the powder used for measurement being 100%. Measurement methods include wet measurement, in which a sample prepared by dispersing agglomerated particles in a pure water medium containing sodium hexametaphosphate as a dispersion stabilizer is measured using a laser diffraction / scattering particle size analyzer, and dry measurement, in which measurement is performed using a Malvern "Morphologi" analyzer. The same applies to the spherical filler described below.

[0040] <Agglomerated inorganic filler content> The content of the aggregated inorganic filler in the resin composition of the present invention is preferably 30% by mass or more, more preferably 40% by mass or more, and particularly preferably 50% by mass or more, based on 100% by mass of the resin composition, and is preferably 99% by mass or less, more preferably 90% by mass or less, and particularly preferably 80% by mass or less. Furthermore, the combination of the upper and lower limits is not particularly limited, but is preferably 30% by mass or more and 99% by mass or less, more preferably 40% by mass or more and 90% by mass or less, and particularly preferably 50% by mass or more and 80% by mass or less. When the content of the aggregated inorganic filler is equal to or greater than the lower limit, the effect of improving thermal conductivity and the effect of controlling the linear expansion coefficient due to the inclusion of the aggregated inorganic filler tend to be sufficiently obtained, while when the content is equal to or less than the upper limit, the formability of the cured sheet and the interfacial adhesion of the composite molded product tend to be improved.

[0041] When other non-agglomerated inorganic fillers are used in addition to the agglomerated inorganic filler, the content ratio of the agglomerated inorganic filler to the other non-agglomerated inorganic filler in the resin composition is not particularly limited, but is preferably 90:10 to 10:90 in mass ratio, and more preferably 80:20 to 20:80.

[0042] <Breaking strength of agglomerated inorganic filler> The breaking strength of the agglomerated inorganic filler is not particularly limited, but is preferably 300 MPa or less, more preferably 100 MPa or less, even more preferably 50 MPa or less, even more preferably 20 MPa or less, particularly preferably 15 MPa or less, and most preferably 10 MPa or less. When the breaking strength is below the above upper limit, the agglomerated structure of the agglomerated inorganic filler is deformed during press treatment, making it easier for the agglomerated inorganic filler particles to come into surface contact with each other. On the other hand, the lower limit of the breaking strength is not particularly limited, but from the viewpoint of ease of handling, the breaking strength is preferably 2.5 MPa or more, more preferably 3 MPa or more, even more preferably 3.5 MPa or more, and particularly preferably 4 MPa or more.

[0043] <Elastic modulus of aggregated inorganic filler> The elastic modulus of the aggregated inorganic filler is not particularly limited, but is preferably 10 MPa or more, more preferably 20 MPa or more, even more preferably 30 MPa or more, more preferably 50 MPa or more, and even more preferably 55 MPa or more. If the elastic modulus is equal to or greater than the above lower limit, the aggregated inorganic filler tends to undergo plastic deformation in the direction of the pressing pressure, and collapse of the aggregated structure can be suppressed. On the other hand, the upper limit of the elastic modulus is not particularly limited, but from the viewpoint of easily obtaining sufficient deformation, it is preferably 5 GPa or less, more preferably 2 GPa or less, even more preferably 1.5 GPa or less, even more preferably 1 GPa or less, still more preferably 500 MPa or less, particularly preferably 300 MPa or less, and most preferably 150 MPa or less. When the agglomerated inorganic filler has an elastic modulus within the above range, it tends to maintain its spherical shape during press processing. On the other hand, when the breaking strength is within the above range, the contact portions of the agglomerated inorganic filler tend to deform, facilitating surface contact. While maintaining high thermal conductivity within the agglomerated inorganic filler, the contact thermal resistance at the agglomerated inorganic filler interface and at the interface between the metal substrate and the sheet cured product (described later) can be reduced, thereby improving overall thermal conductivity.

[0044] When the agglomerated inorganic filler is present in a cured sheet, the breaking strength and elastic modulus of the agglomerated inorganic filler can be measured after baking the resin of the cured sheet and removing the agglomerated inorganic filler so as not to alter the agglomerated inorganic filler.

[0045] <Spherical filler> A spherical filler may be used as the inorganic filler. The spherical filler of the present invention is not particularly limited, but preferably has a thermal conductivity of 10 W / m·K or more, preferably 15 W / m·K or more, more preferably 20 W / m·K or more, for example, 20 to 30 W / m·K, and a new Mohs hardness of 3.1 or more, for example, 5 to 10. By using such a spherical filler in combination with the above-mentioned agglomerated inorganic filler, the heat dissipation properties of the resulting cured sheet material relative to metal can be further improved.

[0046] Here, "spherical" means anything that is generally recognized as spherical; for example, an average circularity of 0.4 or more may be considered spherical, or an average circularity of 0.6 or more may be considered spherical. Usually, the upper limit of the average circularity is 1. The circularity can be measured by image processing the projected image, and can be measured, for example, with an FPIA series from Sysmex Corporation.

[0047] The spherical filler is preferably at least one selected from the group consisting of alumina, synthetic magnesite, crystalline silica, aluminum nitride, silicon nitride, silicon carbide, zinc oxide, and magnesium oxide. Use of these preferred spherical fillers can further improve the heat dissipation properties of the resulting cured sheet.

[0048] The average particle size of the spherical filler is preferably in the range of 0.5 μm to 40 μm, which makes it easier to maintain the dielectric breakdown properties of the cured sheet.

[0049] <Other fillers> In the present invention, an organic filler may be used in combination with the inorganic filler. In the present invention, the organic filler is a component that does not contain an epoxy group, does not fall under the definition of a thermosetting catalyst, and is solid at room temperature, composed of organic components. Examples of organic fillers include natural products such as wood flour, optionally modified cellulose, starch, various organic pigments, thermoplastic resins, and thermosetting resins, which may be used in combination. Specific examples include acrylic resin particles, nylon resin particles, polyester resin particles, polystyrene resin particles, and silicone resin particles. The inclusion of an organic filler may impart appropriate elongation to the resin composition, alleviate the stress that occurs, and suppress the occurrence of cracks in a temperature cycle test.

[0050] The upper limit of the average particle size of the organic filler is preferably 100 μm or less, more preferably 50 μm or less, and even more preferably 30 μm or less. By keeping the particle size below these upper limits, it is possible to produce cured sheets of various thicknesses without risk of a decrease in thermal conductivity. The particle size of the organic filler is also an average particle size determined from the results of volume-average particle size distribution measurement using a laser diffraction particle size distribution analyzer.

[0051] <<Thermosetting resin>> The thermosetting resin contained in the resin composition of the present invention is not particularly limited as long as it can be cured in the presence of a curing agent or curing catalyst to give a cured product. Specific examples of thermosetting resins include epoxy resins, phenolic resins, polycarbonate resins, unsaturated polyester resins, urethane resins, melamine resins, and urea resins. Among these, epoxy resins are preferred from the viewpoints of viscosity, heat resistance, moisture absorption, and ease of handling. Examples of epoxy resins include epoxy group-containing silicon compounds, aliphatic epoxy resins, bisphenol A or F epoxy resins, novolac epoxy resins, alicyclic epoxy resins, glycidyl ester epoxy resins, multifunctional epoxy resins, and polymeric epoxy resins.

[0052] (epoxy resin) Epoxy resin is a general term for compounds that have one or more oxirane rings (epoxy groups) in the molecule. The oxirane rings (epoxy groups) contained in epoxy resins may be either alicyclic epoxy groups or glycidyl groups, but from the viewpoints of reaction rate and heat resistance, glycidyl groups are more preferable.

[0053] The epoxy resin used in the present invention may be an aromatic oxirane ring (epoxy group)-containing compound. Specific examples thereof include bisphenol-type epoxy resins obtained by glycidylating 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 glycidylating dihydric phenols such as dihydroxynaphthalene and 9,9-bis(4-hydroxyphenyl)fluorene; epoxy resins obtained by glycidylating trisphenols such as 1,1,1-tris(4-hydroxyphenyl)methane; epoxy resins obtained by glycidylating tetrakisphenols such as 1,1,2,2-tetrakis(4-hydroxyphenyl)ethane; and novolac-type epoxy resins obtained by glycidylating novolacs such as phenol novolac, cresol novolac, bisphenol A novolac, and brominated bisphenol A novolac.

[0054] The epoxy resin contained in the resin composition of the present invention is not particularly limited, but is preferably one or more selected from the group consisting of various bisphenol-type epoxy resins obtained by glycidylating bisphenols, such as bisphenol A-type epoxy resins and bisphenol F-type epoxy resins; various biphenyl-type epoxy resins obtained by glycidylating biphenyls; epoxy resins obtained by glycidylating aromatic compounds having two hydroxyl groups, such as dihydroxynaphthalene and 9,9-bis(4-hydroxyphenyl)fluorene; epoxy resins obtained by glycidylating trisphenols, such as 1,1,1-tris(4-hydroxyphenyl)methane; and epoxy resins obtained by glycidylating tetrakisphenols, such as 1,1,2,2-tetrakis(4-hydroxyphenyl)ethane. Novolac-type epoxy resins obtained by glycidylating novolacs, such as phenol novolac, cresol novolac, bisphenol A novolac, and brominated bisphenol A novolac; and silicone-containing epoxy resins.

[0055] The epoxy resin used in the present invention preferably contains a polyfunctional epoxy resin. A multifunctional epoxy resin is an epoxy resin that has three or more oxirane rings (epoxy groups) per molecule.

[0056] To increase the storage modulus of the cured sheet of the present invention, particularly at high temperatures, which is important for devices such as power semiconductors that generate a large amount of heat, epoxy resins having two or more oxirane rings (epoxy groups) per molecule are preferred, epoxy resins having three or more oxirane rings (epoxy groups) per molecule are more preferred, and epoxy resins having four or more glycidyl groups per molecule are even more preferred. Having multiple oxirane rings (epoxy groups), particularly glycidyl groups, per molecule improves the crosslink density of the cured product, resulting in a stronger cured sheet. This prevents the cured sheet from deforming or breaking during a moisture absorption reflow test, thereby maintaining its shape and preventing the formation of voids or other voids within the cured sheet. Furthermore, from the viewpoint of increasing the storage modulus of the cured sheet, the molecular weight of the polyfunctional epoxy resin is preferably 1,000 or less, and more preferably 800 or less. The lower limit is not particularly limited, but is at least 100. Furthermore, from the viewpoint of achieving lower moisture absorption and higher crosslinking, polyfunctional epoxy resins that do not contain nitrogen-containing amine or amide structures are more preferred.

[0057] The addition of a multifunctional epoxy resin makes it possible to introduce highly polar oxirane rings (epoxy groups) at a high density, thereby enhancing the effects of physical interactions such as van der Waals forces and hydrogen bonds, and improving adhesion between the metal and the cured sheet in the composite molded product. The addition of a multifunctional epoxy resin also increases the storage modulus of the cured sheet after thermal curing, which allows the cured resin composition to penetrate into the irregularities of the metal adherend, thereby exerting a strong anchoring effect and improving adhesion between the metal and the cured sheet.

[0058] On the other hand, the introduction of a polyfunctional epoxy resin tends to increase the hygroscopicity of the resin composition, but by improving the reactivity of the oxirane ring (epoxy group), the amount of hydroxyl groups during the reaction can be reduced, thereby suppressing the increase in hygroscopicity. Furthermore, by producing a resin composition by combining the above-mentioned specific epoxy resin and a polyfunctional epoxy resin, it is possible to achieve both high elasticity and low hygroscopicity of the sheet cured product.

[0059] Specifically, the polyfunctional epoxy resin is preferably an epoxy resin having three or more epoxy groups, such as EX321L, DLC301, DLC402 manufactured by Nagase ChemteX Corporation, or BATG or PETG manufactured by Showa Denko KK. These polyfunctional epoxy resins may be used alone or in combination of two or more.

[0060] (Content) The resin composition of the present invention preferably contains 5 to 90 mass %, particularly 10 to 60 mass %, of a thermosetting resin relative to 100 mass % of the resin composition of the present invention excluding the solvent when the resin composition contains a solvent. When the content of the thermosetting resin component is equal to or greater than the lower limit, moldability is improved, and when it is equal to or less than the upper limit, the content of other components can be ensured, resulting in improved thermal conductivity.

[0061] Furthermore, when the resin composition of the present invention contains an inorganic filler, a thermosetting catalyst, and a solvent, the main component excluding the solvent is preferably an epoxy resin. Here, the main component refers to the component that is present in the largest amount. The proportion of the epoxy resin in the resin composition excluding the inorganic filler and the thermosetting catalyst is not particularly limited, but is preferably 20% by mass or more, and more preferably 45% by mass or more. The upper limit is 100 mass %, and the entire composition may be epoxy resin. When the proportion of the epoxy resin is within the above range, low moisture absorption, high elastic modulus, high toughness, and easy reaction control become possible, and the effects of high reflow resistance, high reliability in cycle tests, and high thermal conductivity tend to be exhibited.

[0062] Furthermore, the resin composition of the present invention preferably contains 5% by mass or more, more preferably 10% by mass or more, of the polyfunctional epoxy resin, which is the aforementioned preferred epoxy resin, based on the total epoxy resin content. Furthermore, the content is preferably 50% by mass or less, more preferably 40% by mass or less. When the content of the polyfunctional epoxy resin is equal to or greater than the above-mentioned lower limit, the aforementioned effects of containing the polyfunctional epoxy resin can be effectively achieved. On the other hand, when the content of the polyfunctional epoxy resin is equal to or less than the above-mentioned upper limit, the moisture absorption of the cured product can be suppressed and the strength performance of the cured product can be improved, thereby achieving both of these performances.

[0063] From the viewpoints of film-forming ability, low moisture absorption, and flexibility, the epoxy resin used in the present invention preferably contains a high-molecular-weight epoxy resin. Specifically, the high-molecular-weight epoxy resin is preferably an epoxy resin having a mass-average molecular weight of 10,000 or more, more preferably an epoxy resin having a mass-average molecular weight of 20,000 or more, particularly preferably an epoxy resin having a mass-average molecular weight of 30,000 or more, and even more preferably an epoxy resin having a mass-average molecular weight of 80,000 or less. High molecular weight epoxy resins are preferred because they are more hydrophobic. Specifically, the epoxy equivalent of the epoxy component is preferably greater. Specifically, it is preferably 5,000 g / equivalent or greater, more preferably 7,000 g / equivalent or greater, and more preferably 20,000 g / equivalent or less.

[0064] The mass average molecular weight of the epoxy resin is a value calculated as polystyrene equivalent measured by gel permeation chromatography. The epoxy equivalent is defined as "the mass of the epoxy resin containing one equivalent of epoxy groups" and can be measured in accordance with JIS K7236.

[0065] Such high molecular weight epoxy resins may be used alone or in combination of two or more kinds, and may further be used in combination with other epoxy resins that do not have a high molecular weight.

[0066] <<Thermosetting catalyst>> The resin composition of the present invention contains a thermosetting catalyst having a melting point of 120° C. or higher. By using this thermosetting catalyst, the reaction rate of the thermosetting resin during storage can be reduced, thereby improving the shelf life.

[0067] The thermosetting catalyst is not particularly limited as long as it has a melting point of 120°C or higher. The melting point is preferably 150°C or higher, more preferably 200°C or higher. The upper limit is not particularly limited, but is preferably 300°C or lower. By keeping the temperature within this range, the effect of slowing down the reaction rate of the thermosetting resin during storage tends to be obtained. The thermosetting catalyst contained in the resin composition of the present invention may be one type or multiple types. When multiple types are used, it is sufficient that at least one of them has a melting point of 120°C or higher. When multiple types of thermosetting catalysts are used, their melting points are not particularly limited, but it is preferable that all of them are 120°C or higher. When a thermosetting catalyst having a melting point of less than 120° C. is used in combination, the amount of the thermosetting catalyst is preferably 10 mass % or less of the total amount of the thermosetting catalyst.

[0068] Examples of thermosetting catalysts having a melting point of 120°C or higher include compounds having a structure derived from imidazole, dicyandiamide, linear or cyclic tertiary amines, organophosphorus compounds, quaternary phosphonium salts, diazabicycloalkenes such as organic acid salts, etc. Organometallic compounds, quaternary ammonium salts, metal halides, etc. can also be used. Examples of the organometallic compounds include zinc octoate, tin octoate, and aluminum acetylacetone complex. Among these, compounds having a structure derived from imidazole and / or dicyandiamide are preferred from the viewpoints of storage stability and heat resistance of the cured product. The proportion of the compound having a structure derived from imidazole and dicyandiamide in the thermosetting catalyst is not particularly limited, but is preferably 50% by mass or more, more preferably 60% by mass or more, even more preferably 70% by mass or more, even more preferably 80% by mass or more, and even more preferably 90% by mass or more. There is no particular upper limit, and it may be 100% by mass. When a compound having a structure derived from imidazole and dicyandiamide are used in combination, the ratio between them is not particularly limited.

[0069] Examples of compounds having a structure derived from imidazole and dicyandiamide, which have a melting point of 120°C or higher, include 2,4-diamino-6-[2'-ethyl-4'-methylimidazolyl-(1')]-ethyl-s-triazine, 2-phenyl-4,5-dihydroxymethylimidazole, 2-methylimidazole, 2-phenylimidazole, 2-phenyl-4-methylimidazole, 2,4-diamino-6-[2'-methylimidazolyl-(1')]-ethyl-s-triazine, 2,4-diamino-6-[2'-undecylimidazolyl-(1')]-ethyl-s-triazine, 2,4-diamino-6-[2'-methylimidazolyl-(1')]-ethyl-s-triazine isocyanuric acid adduct, 2-phenyl-4-methyl-5-hydroxymethylimidazole, and dicyandiamide.

[0070] The content of the thermosetting catalyst in the resin composition is preferably 5% by mass or less, more preferably 4.5% by mass or less, and even more preferably 4% by mass or less, based on 100% by mass of the resin component. The lower limit is not particularly limited, but is preferably 0.1% by mass or more, more preferably 0.5% by mass or more. Here, the resin component refers to the components of the resin composition of the present invention excluding the inorganic filler and solvent, if any. By keeping the content of the curing catalyst within the above range, the reaction rate of the thermosetting resin during storage can be reduced, which tends to improve shelf life.

[0071] The average particle size of the thermosetting catalyst is not particularly limited, but the average particle size of at least one thermosetting catalyst is preferably 15 μm or less, more preferably 10 μm or less. It is also preferably 50 nm or more, more preferably 100 nm or more, even more preferably 500 nm or more, and even more preferably 1000 nm or more. Having an average particle size equal to or less than the upper limit of the above range tends to improve the solubility of the thermosetting catalyst in the resin component, thereby improving the reaction rate. It also tends to increase the modulus of elasticity of the cured sheet and the glass transition temperature. It also tends to improve the dispersibility of the thermosetting catalyst and the storage stability. On the other hand, having an average particle size equal to or greater than the lower limit of the above range tends to suppress secondary aggregation of the thermosetting catalyst itself, improve the dispersibility of the thermosetting catalyst, and improve the storage stability of the resin composition. It also tends to improve the handleability during production of the resin composition. The average particle size of the plurality of thermosetting catalysts is not particularly limited, but may be within the above range.

[0072] <<Curing agent>> The resin composition of the present invention may contain a curing agent. The curing agent is not particularly limited, but preferred examples include phenolic resins, acid anhydrides having an aromatic or alicyclic skeleton, or hydrates or modified products of such acid anhydrides. The use of these preferred curing agents tends to produce a cured sheet having an excellent balance of heat resistance, moisture resistance, and electrical properties. Only one curing agent may be used, or two or more may be used in combination.

[0073] The phenolic resin used as the curing agent is not particularly limited. Specific examples of the phenolic resin include phenol novolac, o-cresol novolac, p-cresol novolac, t-butylphenol novolac, dicyclopentadiene cresol, polyparavinylphenol, bisphenol A novolac, xylylene-modified novolac, decalin-modified novolac, poly(di-o-hydroxyphenyl)methane, poly(di-m-hydroxyphenyl)methane, and poly(di-p-hydroxyphenyl)methane. Among these, novolac-type phenolic resins having a rigid main chain skeleton and phenolic resins having a triazine skeleton are preferred for further improving the flexibility and flame retardancy of the resin composition and the mechanical properties and heat resistance of the cured sheet.Furthermore, phenolic resins having an allyl group are preferred for improving the flexibility of the resin composition and the toughness of the cured sheet.

[0074] Commercially available phenolic resins include MEH-8005, MEH-8000H, and NEH-8015 (all manufactured by Meiwa Kasei Co., Ltd.), YLH903 (manufactured by Mitsubishi Chemical Corporation), LA-7052, LA-7054, LA-7751, LA-1356, and LA-3018-50P (all manufactured by Dainippon Ink Co., Ltd.), and PSM6200, PS6313, and PS6492 (manufactured by Gun-ei Chemical Industry Co., Ltd.).

[0075] The acid anhydride having an aromatic skeleton, the water additive of the acid anhydride, or the modified product of the acid anhydride used as the curing agent is not particularly limited. Specific examples include SMA Resin EF30 and SMA Resin EF60 (both manufactured by Sartomer Japan), ODPA-M and PEPA (both manufactured by Manac), Ricadit MTA-10, Ricadit TMTA, Ricadit TMEG-200, Ricadit TMEG-500, Ricadit TMEG-S, Ricadit TH, Ricadit MH-700, Ricadit MT-500, Ricadit DSDA, and Ricadit TDA-100 (all manufactured by New Japan Chemical Co., Ltd.), EPICLON B4400, and EPICLON B570 (all manufactured by Dainippon Ink and Chemicals Co., Ltd.).

[0076] The acid anhydride having an alicyclic skeleton, the hydration product of the acid anhydride, or the modified product of the acid anhydride is preferably an acid anhydride having a polyalicyclic skeleton, the hydration product of the acid anhydride, or the modified product of the acid anhydride, or an acid anhydride having an alicyclic skeleton obtained by the addition reaction of a terpene compound with maleic anhydride, the hydration product of the acid anhydride, or the modified product of the acid anhydride.Specific examples include Ricadit HNA and Ricadit HNA-100 (both manufactured by New Japan Chemical Co., Ltd.), and Epicure YH306 and Epicure YH309 (both manufactured by Mitsubishi Chemical Corporation).

[0077] When a solvent is contained, the curing agent is preferably contained in an amount of 0 to 70% by mass, particularly 0 to 55% by mass, based on 100% by mass of the resin composition of the present invention excluding the solvent and inorganic filler. When the content of the curing agent is equal to or greater than the lower limit, sufficient curing performance can be obtained, and when the content is equal to or less than the upper limit, the reaction proceeds effectively, improving the crosslink density, increasing the strength, and further improving film formability.

[0078] Furthermore, when the thermosetting resin is an epoxy resin, the content of reactive groups in the curing agent is not particularly limited, but may be 0 equivalents, preferably 0.05 equivalents or more, more preferably 0.1 equivalents or more, even more preferably 0.15 equivalents or more, and particularly preferably 0.2 equivalents or more, relative to the amount of epoxy groups in the thermosetting resin. Also, the content of reactive groups in the curing agent is preferably 2 equivalents or less, more preferably 0.9 equivalents or less, even more preferably 0.6 equivalents or less, and particularly preferably 0.4 equivalents or less, relative to the amount of epoxy groups in the thermosetting resin. When the content of reactive groups in the curing agent relative to the amount of epoxy groups in the thermosetting resin is equal to or greater than the lower limit, the curing rate is prevented from decreasing, epoxy groups are less likely to remain, and the strength of the cured sheet and the moisture absorption are likely to be improved. On the other hand, when the content is equal to or less than the upper limit, the elastic modulus of the cured sheet tends to be high.

[0079] (Other ingredients) The resin composition of the present invention may contain other components in addition to those described above, provided that the effects of the present invention are not impaired. Examples of such other components include a surface treatment agent such as a silane coupling agent that improves the interfacial adhesive strength between the resin composition and an inorganic filler that is optionally used when producing a sheet cured product using the resin composition, an insulating carbon component such as a reducing agent, a viscosity modifier, a dispersant, a thixotropy-imparting agent, a flame retardant, a colorant, an organic solvent, and a thermoplastic resin. Among these, the inclusion of a dispersant makes it possible to form a uniform cured sheet, which may improve the thermal conductivity and dielectric breakdown characteristics of the resulting cured sheet. Furthermore, the inclusion of a thermoplastic resin may impart appropriate elongation to the resin composition, alleviate generated stress, and suppress the occurrence of cracks in a temperature cycle test.

[0080] The resin composition according to the present invention may contain an organic solvent, for example, to improve the coatability when the resin composition is subjected to a coating step to form a sheet-like cured product. Examples of organic solvents that may be contained in the resin composition according to the present invention include methyl ethyl ketone, cyclohexanone, propylene glycol monomethyl ether acetate, butyl acetate, isobutyl acetate, propylene glycol monomethyl ether, etc. These organic solvents may be used alone or in combination of two or more.

[0081] When the resin composition according to the present invention contains an organic solvent, the content thereof is appropriately determined depending on the handleability of the resin composition when preparing a sheet cured product, the shape before curing, drying conditions, etc. When the resin composition according to the present invention is in the form of a slurry to be subjected to the coating step described below, the organic solvent is preferably used so that the solids concentration (total of components other than the solvent) in the resin composition according to the present invention or in the resin composition according to the present invention after adding the inorganic filler described below is 10 to 90 mass %, particularly 40 to 80 mass %. Furthermore, when the resin composition of the present invention is in the form of a sheet that has been subjected to processes such as coating and drying, the organic solvent is preferably used so that the solid content (total of components other than the solvent) concentration in the resin composition of the present invention or in the resin composition of the present invention after the addition of an inorganic filler described below is 95 mass % or more, and more preferably 98 mass % or more.

[0082] (Method of producing resin composition) The resin composition of the present invention can be obtained by uniformly mixing the inorganic filler, the thermosetting resin, the thermosetting catalyst, and other components added as needed by stirring or kneading. For mixing, a general kneading device such as a mixer, a kneader, or a single-screw or twin-screw kneader can be used, and heating may be performed during mixing as needed. The order of mixing the various components may also be arbitrary as long as there are no particular problems, such as the occurrence of reactions or precipitates. For example, a method may be used in which a thermosetting resin component is mixed and dissolved in an organic solvent (e.g., methyl ethyl ketone) to prepare a resin liquid, and a sufficiently mixed inorganic filler and other components are added to the obtained resin liquid and mixed, and then an organic solvent is further added to adjust the viscosity, and the mixture is mixed. After that, additives such as a curing agent, a curing accelerator, or a dispersant are further added and mixed. [Example]

[0083] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples. Various conditions and values ​​of evaluation results in the following examples indicate preferred ranges of the present invention, similar to preferred ranges in the embodiments of the present invention, and the preferred ranges of the present invention can be determined by taking into consideration the preferred ranges in the above-mentioned embodiments and the values ​​in the following examples or the ranges indicated by a combination of values ​​between the examples.

[0084] [raw materials] The raw materials used in the examples and comparative examples are as follows.

[0085] <Thermosetting resin> Resin component 1: a bifunctional epoxy resin disclosed in Resin component 1 of JP 2020-63438 A Resin component 2: Biphenyl-type solid epoxy resin manufactured by Mitsubishi Chemical Corporation Resin component 3: Showa Denko multifunctional epoxy resin containing a structure having four or more glycidyl groups per molecule

[0086] <Agglomerated inorganic filler> Inorganic filler 1: boron nitride agglomerated particles having a house-of-cards structure, produced in accordance with the method for producing boron nitride agglomerated particles disclosed in the examples of WO 2015 / 119198 New Mohs hardness: 2 Volume average particle size: 45 μm

[0087] <Other fillers> Inorganic filler 2: Spherical alumina particles manufactured by Admatechs Peak particle size: 15 μm, 0.6 μm

[0088] <Curing agent> Hardener 1: Phenolic resin hardener ("MEH-8000H" manufactured by Meiwa Kasei Co., Ltd.)

[0089] <Thermosetting catalyst component> Thermosetting catalyst 1: 2,4-diamino-6-[2'-ethyl-4'-methylimidazolyl-(1')]-ethyl-s-triazine. This catalyst contains both an imidazole-derived structure and a triazine-derived structure in a single molecule ("Curezol 2E4MZ-A" manufactured by Shikoku Chemical Industries, Ltd.). Molecular weight: 247 Melting point: 215-225°C Heat curing catalyst 2: 2-phenyl-4,5-dihydroxymethylimidazole (Shikoku Chemicals Corporation, "Curezol 2PHZ-PW") Molecular weight: 204 Melting point: 230°C or higher (decomposes at 230°C) Thermosetting catalyst 3: 2-ethyl-4-methylimidazole ("Curesol 2E4MZ" manufactured by Shikoku Chemical Industries, Ltd.) Molecular weight: 110 Melting point: 40℃ Thermosetting catalyst 4: Dicyandiamide ("DICY7" manufactured by Mitsubishi Chemical Corporation) Molecular weight: 84 Melting point: 208℃

[0090] [Sample preparation, measurement, and evaluation] The methods for producing the molded bodies in the examples and comparative examples, as well as the measurement conditions and evaluation methods, are as follows.

[0091] [Example 1] Using a planetary stirring device, resin component 1, resin component 2, resin component 3, curing agent 1, thermosetting catalyst 1, thermosetting catalyst 2, inorganic filler 1, and inorganic filler 2 were mixed to obtain a mixture in the mass ratios shown in Table 1 below. When preparing this mixture, a slurry-like resin composition was prepared using 18% by mass each of methyl ethyl ketone and cyclohexanone so that the mixture would account for 64% by mass (solids concentration) of the coating slurry.

[0092] <(a) Process> The resulting slurry-like resin composition was applied onto a PET film by a doctor blade method, and then dried by heating at 60° C. for 120 minutes. The sheet that had undergone step (a) was pressed at 50°C and 147 MPa for 10 minutes to obtain a sheet with a thickness of 150 μm. The total content of methyl ethyl ketone and cyclohexanone in the sheet was 1 mass% or less (solid content concentration of 99 mass% or more).

[0093] Each sample was prepared by carrying out the step (b) below, and the reactivity, shelf life, and warpage of the sheet and the cured sheet were measured and evaluated. The results are shown in Table 1. <Creating a sample for reaction rate> The sheet that had been subjected to step (a) was cured at 90° C. under a pressure of 9.8 MPa for 4 hours in step (b) to obtain a cured sheet.

[0094] <How to prepare a sample to measure the amount of warpage> After step (a), a 60 mm x 60 mm x 0.1 mm thick copper sheet was laminated on one side of the sheet, and then in step (b), the sheet was cured at 90°C under a pressure of 9.8 MPa for 4 hours. After that, in the post-curing step, the temperature was increased from 60°C to 175°C over 1 hour and 30 minutes without pressure, and held at that temperature for 1 hour to obtain a cured copper-laminated sheet.

[0095] [Measurement method] <Response rate> Differential scanning calorimetry (DSC) was performed on the sheets formed after each of steps (a) and (b) (cured sheets after step (b)). The reaction rate was calculated from the heat release amount at the exothermic peak obtained when the temperature was increased from 40°C to 250°C at a rate of 10°C / min, using the following formula: Reaction rate (B) (%) of step (b) = (1 - Amount of heat generated after step (b) / Amount of heat generated after step (a)) × 100 (b) Processes with a reaction rate of over 85% were marked as ◯.

[0096] <Shelf life of the sheet> After step (a), the sheet was stored at 23°C and 50% RH for 2 days and then subjected to differential scanning calorimetry (DSC). The residual reaction rate after 2 days of storage, as defined by the following formula, was calculated from the heat release amount at the exothermic peak obtained when the temperature was raised from 40°C to 250°C at a rate of 10°C / min. Residual reaction rate after 2 days of storage (%) = ((heat generation amount after 2 days of storage / heat generation amount after step (a))) × 100 The residual reaction rate after 2 days of storage was 90% or more, and was evaluated as ◯.

[0097] <Measurement of warpage> The prepared sample for measuring the amount of warpage (cured copper laminate sheet) was placed on a surface plate with one of the two sides with the largest inward warpage in the recess, and pressed down to make it contact with the surface plate, and the height of the other side from the surface plate was measured with a ruler. A warpage of less than 10 mm was marked with a ◎, 10 to 20 mm with a ○, and more than 20 mm with an ×.

[0098] [Example 2, Example 3, Comparative Example 1] Similar to Example 1, slurry resin compositions were prepared with the compositions shown in Examples 2, 3, and Comparative Example 1 in Table 1, and step (a) was carried out to obtain a sheet having a thickness of 150 μm. The total content of methyl ethyl ketone and cyclohexanone in the sheet was 1% by mass or less (solid content concentration of 99% by mass or more). (b) Samples for reaction rate measurement and samples for warpage measurement were prepared in the same manner as in Example 1, and the reaction rate, shelf life, and warpage of the sheet were measured and evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0099] Comparative Example 2 A slurry resin composition was prepared using the composition shown in Comparative Example 2 in Table 1 in the same manner as in Example 1, and step (a) was carried out to obtain a sheet having a thickness of 150 μm. The total content of methyl ethyl ketone and cyclohexanone in the sheet was 1 mass % or less (solid content concentration of 99 mass % or more). Each sample was prepared by carrying out the following step (b), and the reaction rate of the sheet and the cured sheet, as well as the shelf life and warpage of the sheet were measured and evaluated. The shelf life was measured in the same manner as in Example 1. The results are shown in Table 1. <Creating a sample for reaction rate> In step (b), the sheet that had undergone step (a) was held at 120°C for 30 minutes under a pressure of 9.8 MPa, then heated to 175°C and held there for 30 minutes, and then further heated to 200°C and held there for 30 minutes to obtain a cured sheet.

[0100] <How to prepare a sample to measure the amount of warpage> After step (a), a 60 mm x 60 mm x 0.1 mm thick copper sheet was laminated on one side of the sheet, and then in step (b), the sheet was held at 120°C for 30 minutes under a pressure of 9.8 MPa, then heated to 175°C and held for 30 minutes, and then further heated to 200°C and held for 30 minutes to obtain a cured copper laminated sheet.

[0101] [Table 1]

[0102] Comparison between the Examples and Comparative Examples demonstrates that the present invention is a method for producing a cured sheet product that achieves both a good shelf life and reduced warpage.

Claims

1. A method for producing a cured sheet obtained by using a resin composition containing an inorganic filler, a thermosetting resin, and a thermosetting catalyst, comprising: the inorganic filler comprises an agglomerated inorganic filler; the thermosetting resin comprises an epoxy resin; The melting point of the thermosetting catalyst is 120°C or higher, The method includes the following steps (a) and (b): In the step (b), the sheet is heated and pressed at the same time, the pressing pressure is 0.1 MPa or more and 1000 MPa or less, and the time for heating and pressing the sheet is 2 hours or more and 5 hours or less. Method for producing a cured sheet. (a) Step of forming a sheet using a resin composition (b) a step of heating the sheet obtained in the step (a) at 95°C or less to make the reaction rate of the sheet 50% or more. The reaction rate of the sheet is calculated as follows. (Response rate) It is calculated from the calorific value of the exothermic peak obtained by differential scanning calorimetry (DSC) when the temperature is raised from 40° C. to 250° C. at a rate of 10° C. / min, using the following formula: Reaction rate (%) = (1 - (amount of heat generated after step (b) / amount of heat generated after step (a))) x 100

2. The method for producing a cured sheet according to claim 1 , wherein the resin composition contains the thermosetting catalyst in an amount of 5 mass % or less relative to the resin component of the resin composition. The resin component here refers to the components obtained by excluding the inorganic filler and the solvent, if any, from the resin composition.

3. 3. The method for producing a cured sheet according to claim 1, wherein the thermosetting catalyst comprises a compound having a structure derived from imidazole and / or dicyandiamide.

4. The method for producing a cured sheet according to any one of claims 1 to 3, wherein the inorganic filler comprises agglomerated particles of boron nitride.

5. A method for producing a composite molded product, comprising obtaining a composite molded product having a cured product part made of the sheet cured product obtained by the production method according to any one of claims 1 to 4 and a metal part.

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