Method for producing a cured product of a thermosetting maleimide resin composition

Abstract

To provide a method for producing a cured product of a thermosetting maleimide resin composition that does not cause curing failure or resulting poor appearance.SOLUTION: There is provided a method for producing a cured product of a thermosetting maleimide resin composition containing a maleimide compound (A) having one or more hydrocarbon groups derived from a dimer acid skeleton in one molecule, and a radical polymerization initiator (B). The method for producing a cured product of a thermosetting maleimide resin composition comprises: a lamination step of laminating a release sheet, a resin layer made of the thermosetting maleimide resin composition, and a base material in this order to obtain a laminate; and a curing step of heating the laminate to a temperature at which the thermosetting maleimide resin composition of the resin layer is cured without peeling off the release sheet of the laminate.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for producing a cured product of a thermosetting maleimide resin composition. [Background technology]

[0002] In recent years, the next-generation communication system known as 5G has become popular, and development has begun on the next-generation communication system known as 6G, which goes beyond the millimeter wave range and aims to achieve even faster speeds, larger capacity, and lower latency than current systems. To realize these communication systems, materials for high-frequency bands are required, and reducing transmission loss as a noise countermeasure is essential. Transmission loss is the sum of conductor loss and dielectric loss, and reducing conductor loss requires reducing the surface roughness of the metal foil used. On the other hand, since dielectric loss is proportional to the product of the square root of the relative permittivity and the dielectric loss tangent, there is a demand for the development of insulating materials with excellent dielectric properties (low relative permittivity and low dielectric loss tangent).

[0003] Among these, insulating materials with excellent dielectric properties are in demand for circuit board applications. Reactive polyphenylene ether resin (PPE) is being used for rigid circuit boards, while liquid crystal polymers (LCP) and modified polyimides (MPI) with improved properties are being used for flexible printed circuit boards (FPCs).

[0004] In response to this, it has been reported that maleimide compounds (special maleimide compounds) that essentially have a dimer diamine skeleton are used as resins for substrates (Patent Documents 1 to 4). Contrary to the properties of general maleimide resins, special maleimide compounds have a low glass transition temperature (Tg) and a high coefficient of thermal expansion (CTE), but also have many advantages, such as excellent dielectric properties, flexibility, excellent adhesion to metals, and the possibility of (high) multi-layering because they are thermosetting resins, and are therefore being researched and developed extensively.

[0005] Furthermore, depending on the application, flexibility is considered more important than the dielectric properties of special maleimide compounds, and they are being studied as protective materials for wafers with little warpage (Patent Document 5). These compositions are cured by a thermal radical reaction, but radical reactions are generally inhibited by oxygen (Non-Patent Document 1), and an environment that removes oxygen, such as a nitrogen atmosphere, must be created for curing. However, it is difficult to easily create a high-temperature atmosphere free of oxygen, which can lead to problems such as poor curing and resulting poor appearance. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-131243 [Patent Document 2] Japanese Patent Application Laid-Open No. 2016-131244 [Patent Document 3] International Publication No. 2016 / 114287 [Patent Document 4] Japanese Patent Application Publication No. 2018-201024 [Patent Document 5] Japanese Patent Application Laid-Open No. 2013-211348 [Non-patent literature]

[0007] [Non-Patent Document 1] "Metal Surface Technology" 1977, No.4, Vol28, 196-201 Summary of the Invention [Problem to be solved by the invention]

[0008] Therefore, an object of the present invention is to provide a method for producing a cured product of a thermosetting maleimide resin composition containing a special maleimide compound and a radical polymerization initiator, which does not cause poor curing and the resulting poor appearance. [Means for solving the problem]

[0009] As a result of extensive research to solve the above problems, the present inventors have found that the above object can be achieved by the following method for producing a cured product of a thermosetting maleimide resin composition, and have thus completed the present invention.

[0010] <1> (A) A maleimide compound having one or more hydrocarbon groups derived from a dimer acid skeleton in one molecule. and (B) Radical polymerization initiator A method for producing a cured product of a thermosetting maleimide resin composition comprising: a lamination step of laminating a release sheet, a resin layer made of the thermosetting maleimide resin composition, and a substrate in this order to obtain a laminate; a curing step of heating the laminate to a temperature at which the thermosetting maleimide resin composition of the resin layer is cured without removing the release sheet from the laminate. and a method for producing a cured product of the thermosetting maleimide resin composition. <2> the laminating step is a step of placing another release sheet on the surface of the substrate that is not in contact with the resin layer, to obtain a laminate having at least four layers, namely, the release sheet, the resin layer made of the thermosetting maleimide resin composition, the substrate, and the release sheet; <1> 2. A method for producing a cured product of the thermosetting maleimide resin composition according to claim 1. <3> The component (A) is a maleimide compound represented by the following formula (1) and / or (2): <1> or <2> 2. A method for producing a cured product of the thermosetting maleimide resin composition according to claim 1. [ka] (In formula (1), A's are independently tetravalent organic groups having a cyclic structure; B's are independently divalent alicyclic hydrocarbon groups having 6 to 60 carbon atoms; D's are independently divalent hydrocarbon groups having 6 to 200 carbon atoms, at least one of which is a hydrocarbon group derived from a dimer acid skeleton; m is 1 to 100; and l is 1 to 200. The order of the repeating units bracketed by m and l is not limited, and the bonding pattern may be alternating, block, or random.) [ka] (In formula (2), A's are independently tetravalent organic groups having a cyclic structure, D's are independently divalent hydrocarbon groups having 6 to 200 carbon atoms, and at least one D is a hydrocarbon group derived from a dimer acid skeleton. n is 0 to 100.) <4> A in formula (1) and formula (2) is any of the tetravalent organic groups represented by the following structural formulas: <3> 2. A method for producing a cured product of the thermosetting maleimide resin composition according to claim 1. [ka] <5> The radical polymerization initiator of component (B) is an organic peroxide. <1> ~ <4> 1. A method for producing a cured product of the thermosetting maleimide resin composition according to any one of claims 1 to 9. <6> The release sheet is a plastic film whose surface in contact with the resin layer made of a thermosetting maleimide resin composition is release-treated. <1> ~ <5> 1. A method for producing a cured product of the thermosetting maleimide resin composition according to any one of claims 1 to 9. <7> The substrate is at least one selected from the group consisting of a metal foil, a silicon wafer, a SiC wafer, a sapphire wafer, a compound semiconductor wafer, an organic substrate, and a ceramic substrate. <1> ~ <6> 1. A method for producing a cured product of the thermosetting maleimide resin composition according to any one of claims 1 to 9. <8> The resin layer is 1 to 300 μm thick. <1> ~ <7> 1. A method for producing a cured product of the thermosetting maleimide resin composition according to any one of claims 1 to 9. [Effects of the Invention]

[0011] The method for producing a cured product of the thermosetting maleimide resin composition of the present invention containing the special maleimide compound and a radical polymerization initiator does not cause poor curing of the cured product or the associated poor appearance, and a cured product without poor curing or poor appearance can be obtained by a relatively simple method without necessarily requiring a high-temperature atmosphere free of oxygen, such as a nitrogen atmosphere. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a schematic diagram illustrating an example of a method for producing a cured product of the present invention. FIG. [Figure 2] FIG. 2 is a schematic diagram showing an example of a laminate A. [Figure 3] FIG. 2 is a schematic diagram showing a laminate before and after a lamination step in an embodiment having two release sheets. DETAILED DESCRIPTION OF THE INVENTION

[0013] The present invention will be described in more detail below.

[0014] The method for producing a cured product of the thermosetting maleimide resin composition of the present invention includes the steps of: a lamination step of laminating a release sheet, a resin layer made of a thermosetting maleimide resin composition containing components (A) and (B) described below, and a substrate in this order to obtain a laminate; a curing step of heating the laminate to a temperature at which the thermosetting maleimide resin composition of the resin layer is cured without removing the release sheet from the laminate. It has the following. The thermosetting maleimide resin composition before curing, which is a cured product obtained by the production method of the present invention, and each component contained in the composition will be described in detail below.

[0015] <Thermosetting maleimide resin composition> [(A) Maleimide compound having one or more hydrocarbon groups derived from a dimer acid skeleton per molecule] Component (A) is a maleimide compound that has one or more hydrocarbon groups derived from a dimer acid skeleton per molecule. The hydrocarbon groups derived from the dimer acid skeleton are effective in providing excellent dielectric properties, low stress, and high adhesion.

[0016] The dimer acid referred to here is a liquid dibasic acid primarily composed of a 36-carbon dicarboxylic acid, produced by dimerization of an 18-carbon unsaturated fatty acid derived from natural sources such as vegetable oils. Dimer acids do not have a single skeleton but have multiple structures, resulting in several isomers. Representative dimer acids are classified as linear (a), monocyclic (b), aromatic (c), and polycyclic (d). In this specification, the dimer acid skeleton refers to a group derived from a dimer diamine having a structure in which the carboxy groups of such a dimer acid are substituted with primary aminomethyl groups. That is, the dimer acid skeleton of component (A) can be exemplified by the dimer acids shown below in (a) to (d), in which two carboxy groups are substituted with methylene groups, but is not limited thereto. Furthermore, from the viewpoint of the heat resistance and reliability of the cured product, it is more preferable that the hydrocarbon group derived from the dimer acid skeleton in the maleimide compound of component (A) has a structure in which the carbon-carbon double bond in the hydrocarbon group derived from the dimer acid skeleton is reduced by a hydrogenation reaction.

[0017] [ka]

[0018] Among these, the component (A) is preferably a maleimide compound represented by the following formula (1) and / or a maleimide compound represented by the following formula (2). [ka] (In formula (1), A's are independently tetravalent organic groups having a cyclic structure; B's are independently divalent alicyclic hydrocarbon groups having 6 to 60 carbon atoms; D's are independently divalent hydrocarbon groups having 6 to 200 carbon atoms, at least one of which is a hydrocarbon group derived from a dimer acid skeleton; m is 1 to 100; and l is 1 to 200. The order of the repeating units bracketed by m and l is not limited, and the bonding pattern may be alternating, block, or random.) [ka] (In formula (2), A's are independently tetravalent organic groups having a cyclic structure, as in formula (1), D's are independently divalent hydrocarbon groups having 6 to 200 carbon atoms, as in formula (1), and at least one D is a hydrocarbon group derived from a dimer acid skeleton. n is 0 to 100.)

[0019] Although compositions containing the maleimide compound represented by formula (1) have a high melt viscosity before curing, the resulting cured products not only have better dielectric properties than those containing common maleimide compounds containing many aromatic groups, but also have high adhesion to metal foils such as copper foil, and are less susceptible to moisture absorption than common thermosetting resins such as epoxy resins. Furthermore, the cured products of compositions containing the maleimide compound represented by formula (1) have a higher Tg and are more reliable than those of compositions containing the maleimide compound represented by formula (2).

[0020] In the formula (1), A independently represents a tetravalent organic group having a cyclic structure, and is preferably any of the tetravalent organic groups represented by the following structural formulas. [ka] (The bond not bonded to a substituent in the above structural formula is bonded to the carbonyl carbon that forms the cyclic imide structure in formula (1).)

[0021] In addition, in the formula (1), D's are independently divalent hydrocarbon groups having 6 to 200 carbon atoms, preferably 8 to 100 carbon atoms, and more preferably 10 to 50 carbon atoms. Among these, branched divalent hydrocarbon groups in which one or more hydrogen atoms in the divalent hydrocarbon group are substituted with alkyl or alkenyl groups having 6 to 200 carbon atoms, preferably 8 to 100 carbon atoms, and more preferably 10 to 50 carbon atoms, are preferred. The branched divalent hydrocarbon group may be either a saturated aliphatic hydrocarbon group or an unsaturated hydrocarbon group, and may have an alicyclic structure or an aromatic ring structure in the middle of the molecular chain. Specific examples of the branched divalent hydrocarbon group include divalent hydrocarbon groups derived from diamines at both ends, called dimer diamines. Therefore, D is particularly preferably a group in which the two carboxy groups in each of the dimer acids (a) to (d) above are each substituted with a methylene group, and at least one hydrocarbon group derived from this dimer acid skeleton is contained in one molecule.

[0022] In addition, in the formula (1), each B is independently a divalent alicyclic hydrocarbon group having 6 to 60 carbon atoms, preferably a divalent aliphatic hydrocarbon group, and more preferably a divalent aliphatic hydrocarbon group having 6 to 30 carbon atoms. The aliphatic hydrocarbon group preferably has a cyclohexane skeleton, and the embodiment having the cyclohexane skeleton may be, for example, one having one cyclohexane ring, as represented by the following formula (3), or may be a polycyclic group having a plurality of cyclohexane rings bonded via an alkylene group or a bridged structure. [ka] (In formula (3), R 1 are independently a hydrogen atom or an alkyl group having 1 to 5 carbon atoms, and x1 and x2 are each independently a number from 0 to 4.

[0023] where R 1 Specific examples of R include a hydrogen atom, a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, and a t-butyl group. Among these, a hydrogen atom and a methyl group are preferred. 1 may be the same or different. Furthermore, the x1 and x2 each independently represent a number from 0 to 4, and preferably a number from 0 to 2. Note that x1 and x2 may be the same or different.

[0024] Specific examples of B include divalent alicyclic hydrocarbon groups represented by the following structural formulas. [ka] (The bond not bonded to a substituent in the above structural formula is bonded to the nitrogen atom that forms the cyclic imide structure in formula (1).)

[0025] In the formula (1), m is 1 to 100, preferably 1 to 60, and more preferably 2 to 50, and l is 1 to 200, preferably 1 to 50, and more preferably 3 to 40. If m or l is too large, the flowability may decrease, and moldability may be poor. The order of the repeating units enclosed by m and l is not limited, and the bonding pattern may be alternating, block, or random, but block is preferred from the viewpoint of facilitating a high Tg.

[0026] Compositions containing the maleimide compound represented by formula (2) have superior dielectric properties compared to compositions containing other common maleimide compounds containing many aromatic groups, and provide cured products with superior dielectric properties, especially in the high frequency band. Furthermore, compositions containing the maleimide compound represented by formula (2) have even stronger adhesion to copper foil than compositions containing the maleimide compound represented by formula (1).

[0027] In the formula (2), A is the same as A in the formula (1), and independently represents a tetravalent organic group having a cyclic structure, and the preferred ones are also the same, and are any of the tetravalent organic groups represented by the following structural formulas. [ka] (The bond not bonded to a substituent in the above structural formula is bonded to the carbonyl carbon that forms the cyclic imide structure in formula (2).)

[0028] Similarly to D in formula (1), D in formula (2) is independently a divalent hydrocarbon group having 6 to 200 carbon atoms, preferably 8 to 100 carbon atoms, and more preferably 10 to 50 carbon atoms. Similar to D in formula (1), D in formula (2) is preferably a branched divalent hydrocarbon group in which one or more hydrogen atoms in the divalent hydrocarbon group are substituted with an alkyl or alkenyl group having 6 to 200 carbon atoms, preferably 8 to 100 carbon atoms, and more preferably 10 to 50 carbon atoms. The branched divalent hydrocarbon group may be either a saturated aliphatic hydrocarbon group or an unsaturated hydrocarbon group, and may have an alicyclic structure or an aromatic ring structure in the middle of the molecular chain. Specific examples of the branched divalent hydrocarbon group include divalent hydrocarbon groups derived from diamines at both ends, called dimer diamines. Therefore, D is particularly preferably a group in which the two carboxy groups in each of the dimer acids (a) to (d) above are each substituted with a methylene group, and at least one hydrocarbon group derived from this dimer acid skeleton is contained in one molecule.

[0029] In the formula (2), n is 0 to 100, preferably 0 to 60, and more preferably 0 to 50. If n is too large, the solubility and flowability may decrease, and moldability may be poor.

[0030] The number average molecular weight of the maleimide compound of component (A) is not particularly limited, but from the viewpoint of the handleability of the composition, it is preferably 800 to 50,000, more preferably 900 to 30,000. Furthermore, component (A) may contain not only the maleimide compounds represented by formula (1) and / or (2) above, but also other maleimide compounds having one or more hydrocarbon groups derived from a dimer acid skeleton per molecule, and may use one type alone or multiple types in combination. The number average molecular weight referred to in the present invention refers to the number average molecular weight measured by gel permeation chromatography (GPC) under the following conditions using polystyrene as a standard substance.

[0031] [Measurement conditions] Developing solvent: tetrahydrofuran (THF) Flow rate: 0.35mL / min Detector: Refractive index detector (RI) Column: TSK Guardcolumn SuperH-L TSKgel SuperHZ4000(4.6mmI.D.×15cm×1) TSKgel SuperHZ3000(4.6mmI.D.×15cm×1) TSKgel SuperHZ2000(4.6mmI.D.×15cm×2) (All manufactured by Tosoh Corporation) Column temperature: 40℃ Sample injection volume: 5 μL (0.2% by mass THF solution)

[0032] [(B) Radical polymerization initiator] The radical polymerization initiator (B) is added to promote the crosslinking reaction of the maleimide compound (A) and the radical polymerization reaction between the maleimide group in component (A) and a reactive group that can react with the maleimide group. The method for producing a cured product of the present invention is highly effective, particularly for thermal radical polymerization. The component (B) is not particularly limited as long as it promotes a radical polymerization reaction, and examples thereof include organic peroxides such as diallyl peroxide, dialkyl peroxide, peroxide carbonate, and hydroperoxide; and azo compounds such as azoisobutyronitrile and 1,1'-azobis(cyclohexanecarbonitrile). From the viewpoint of post-curing properties and ease of reaction control, however, organic peroxides are preferably used. Examples of organic peroxides include dicumyl peroxide, t-butyl peroxybenzoate, t-amyl peroxybenzoate, dibenzoyl peroxide, diuraloyl peroxide, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, 1,1-di(t-butylperoxy)cyclohexane, di-t-butyl peroxide, and dibenzoyl peroxide.

[0033] The radical polymerization initiator is preferably blended in an amount of 0.05 to 10 parts by mass, more preferably 0.1 to 5 parts by mass, per 100 parts by mass of component (A). Furthermore, when other thermosetting resins described below are blended in the composition, the amount is preferably blended in an amount of 0.05 to 10 parts by mass, particularly 0.1 to 5 parts by mass, per 100 parts by mass of the total of component (A) and other thermosetting resin components. This range is preferable because it prevents the maleimide resin composition from curing too slowly or too quickly during molding. Furthermore, the resulting cured product has a good balance between heat resistance and moisture resistance. The radical polymerization initiator of component (B) may be used alone or in combination of two or more. In addition, other reaction initiators (reaction accelerators) described below may also be used in combination within the range that does not impair the effects of component (B).

[0034] In the thermosetting maleimide resin composition used in the method for producing a cured product of the present invention, the content of component (A) is preferably 30 to 99 mass %, and more preferably 40 to 99 mass %, based on the total amount of the composition.

[0035] [Other additives] The thermosetting maleimide resin composition used in the method for producing a cured product of the present invention may further contain various additives as needed, provided that the effects of the present invention are not impaired. Examples of other additives are listed below.

[0036] [Inorganic filler] Inorganic fillers can be blended into the thermosetting maleimide resin composition used in the method for producing a cured product of the present invention for the purposes of increasing the strength and rigidity of the cured product, or adjusting the thermal expansion coefficient and dimensional stability of the cured product. As inorganic fillers, those typically blended into epoxy resin compositions or silicone resin compositions can be used, but silica particles such as spherical silica, fused silica, and crystalline silica, or boron nitride are preferred in order to avoid increasing the dielectric constant of the cured product. Inorganic particles such as alumina, talc, magnesium hydroxide, and zinc oxide are often undesirable because they have a low dielectric loss tangent but a high dielectric constant, or many have high dielectric constants and both.

[0037] The average particle size and shape of the inorganic filler are not particularly limited, but when molding a film or substrate, a spherical filler with an average particle size of 0.5 to 5 μm is preferably used, and spherical silica with an average particle size of 0.5 to 5 μm is particularly preferably used. The average particle size is determined by the mass average particle size D 50 (or median diameter).

[0038] Furthermore, in order to improve the properties of the inorganic filler, it is preferable that the surface of the filler is treated with a silane coupling agent having an organic group capable of reacting with a maleimide group, such as an epoxy group-containing alkoxysilane, an amino group-containing alkoxysilane, a (meth)acrylic group-containing alkoxysilane, or an alkenyl group-containing alkoxysilane. As the silane coupling agent, a (meth)acrylic group- and / or amino group-containing alkoxysilane is preferably used, and specific examples thereof include 3-methacryloxypropyltrimethoxysilane, 3-acryloxypropyltrimethoxysilane, N-phenyl-3-aminopropyltrimethoxysilane, N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, and 3-aminopropyltrimethoxysilane.

[0039] [Thermosetting resin having a reactive group capable of reacting with a maleimide group] The thermosetting maleimide resin composition used in the method for producing a cured product of the present invention may further contain a thermosetting resin having a reactive group capable of reacting with a maleimide group. Thermosetting resins are not limited to specific types, and examples include various resins other than component (A), such as epoxy resins, phenolic resins, melamine resins, silicone resins, cyclic imide resins including maleimide compounds other than component (A), urea resins, thermosetting polyimide resins, modified polyphenylene ether resins, thermosetting acrylic resins, and epoxy-silicone hybrid resins. Reactive groups that can react with maleimide groups include epoxy groups, maleimide groups, hydroxyl groups, acid anhydride groups, alkenyl groups such as allyl and vinyl groups, (meth)acrylic groups, and thiol groups. However, reactive groups that can react with maleimide groups also include those, such as epoxy groups, that react with imidazole to form active species, which then react with the maleimide group to undergo anionic polymerization.

[0040] From the viewpoint of reactivity, the reactive group of the thermosetting resin is preferably selected from an epoxy group, a maleimide group, a hydroxyl group, and an alkenyl group, and from the viewpoint of dielectric properties, an alkenyl group or a (meth)acrylic group is more preferable. However, the amount of the thermosetting resin having a reactive group capable of reacting with a maleimide group is 0 to 60 mass % of the total amount of the thermosetting resin.

[0041] [Reaction initiator / reaction accelerator] The thermosetting maleimide resin composition used in the method for producing a cured product of the present invention may further contain a reaction initiator or accelerator other than component (B). These accelerators are used to initiate or accelerate reactions other than radical polymerization, such as reactions between maleimide groups and between maleimide groups and double bonds in a thermosetting resin having a reactive group reactive with the maleimide group. For example, when a compound having an epoxy group is used as the thermosetting resin having a reactive group reactive with the maleimide group, adding imidazole as a reaction initiator or accelerator allows the imidazole group to react with the epoxy group to generate active species, which then react with the maleimide group to initiate anionic polymerization. Examples of reaction initiators and accelerators suitable for such reactions include imidazole, organophosphorus compounds, and amine compounds. Other examples of reaction initiators and accelerators include organometallic compounds such as aluminum chelate and zinc stearate.

[0042] [others] In addition to the above, non-functional silicone oil, reactive diluent, thermoplastic resin, organic rubber, thermoplastic elastomer, organic filler, photosensitizer, light stabilizer, polymerization inhibitor, flame retardant, pigment, dye, adhesion aid, ion trapping material, etc. may be blended. Furthermore, the silane coupling agents used for surface treatment of the inorganic fillers described above, such as epoxy group-containing alkoxysilanes, amino group-containing alkoxysilanes, (meth)acrylic group-containing alkoxysilanes, and alkenyl group-containing alkoxysilanes, may be separately blended into the thermosetting maleimide resin composition used in the method for producing a cured product of the present invention, and specific examples thereof include those similar to those described above.

[0043] The thermosetting maleimide resin composition used in the present invention can be prepared by appropriately mixing the above-mentioned components, and, if necessary, using a kneading device such as a three-roll mill, a ball mill, a bead mill, or a sand mill, or a stirring device such as a high-speed rotary mixer, a super mixer, or a planetary mixer.

[0044] The thermosetting maleimide resin composition used in the present invention can also be dissolved in an organic solvent and treated as a varnish. Forming the composition into a varnish facilitates film formation and facilitates application and impregnation of glass cloth made of E-glass, low-dielectric glass, quartz glass, and other materials. Any organic solvent can be used as long as it dissolves the thermosetting resins (A) and (B) and other additives containing reactive groups capable of reacting with maleimide groups. Examples include anisole, tetralin, mesitylene, xylene, toluene, tetrahydrofuran (THF), dimethylformamide (DMF), dimethyl sulfoxide (DMSO), and acetonitrile. Among these, aromatic organic solvents such as anisole, tetralin, mesitylene, xylene, and toluene are preferred. Ketone-based solvents such as methyl ethyl ketone (MEK) and methyl isobutyl ketone (MIBK) are also commonly used to form varnishes, but the maleimide compound (A) used in the present invention has low solubility in these ketone-based solvents, making their use less desirable. These organic solvents may be used alone or in combination of two or more. From the viewpoint of workability, it is preferable to adjust the ratio of the thermosetting maleimide resin composition to the organic solvent in the varnish so that the thermosetting maleimide resin composition accounts for 30 to 70 mass %.

[0045] Next, the members and the like used in the method for producing a cured product of the present invention will be described in detail.

[0046] <Release sheet> In the method for producing a cured product of the thermosetting maleimide resin composition of the present invention, the release sheet is used without being removed until the curing step, and is peeled off after the thermosetting maleimide resin composition has cured in the curing step. The release sheet used in the present invention is not particularly limited as long as it is a thin film typically used as a release sheet in this field, but plastic films and metal foils are preferred, and plastic films are particularly preferred. Examples of materials for plastic films include polyolefin resins such as polyethylene (PE) resin, polypropylene (PP) resin, and polystyrene (PS) resin; polyester resins such as polyethylene terephthalate (PET) resin, polybutylene terephthalate (PBT) resin, and polycarbonate (PC) resin; and fluorinated resins. Of these, films made of PET resin are preferred due to their ease of availability. The thickness of the release sheet is preferably 10 to 150 μm, more preferably 20 to 70 μm, from the perspective of workability. The surface roughness (Ra) of the release sheet is preferably 100 nm or less, more preferably 50 nm or less, to improve the appearance of the resulting cured product and the formation of fine wiring. In particular, when the release sheet is a metal foil, its thickness is set within the above range to prevent surface cracks. Furthermore, from the viewpoint of preventing leakage of the resin layer and preventing oxygen from entering during the curing process, the size of the release sheet is preferably larger than the area of ​​the resin layer in a plan view, and more preferably 5% or more larger than the area of ​​the resin layer in a plan view.

[0047]

[0033] From the viewpoint of removing the release sheet after curing the thermosetting maleimide resin composition, the release sheet is preferably release-treated, and at least the surface of the release sheet that comes into contact with the resin layer made of the thermosetting maleimide resin composition is preferably release-treated. The release treatment agent used for the release treatment is not particularly limited, and examples that can be used include silicone-based release agents, fluorine-based release agents, and alkyd resin-based release agents.

[0048] <Base material> The substrate used in the present invention may be selected from the group consisting of metal foil, silicon wafer, SiC wafer, sapphire wafer, compound semiconductor wafer, organic substrate and ceramic substrate.

[0049] Examples of metal foils include copper foil and aluminum foil. Examples of compound semiconductor wafers include gallium nitride wafers, indium phosphide wafers, gallium arsenide wafers, and gallium phosphide wafers. Examples of organic substrates include glass epoxy substrates, polyester substrates, polyimide substrates, BT substrates, and other substrates made of a thermosetting resin composition and glass cloth, regardless of whether they have a patterned (circuit-formed) conductor layer.

[0050] <Method of manufacturing the cured product> The method for producing the cured product of the present invention comprises: a lamination step of laminating a release sheet, a resin layer made of the thermosetting maleimide resin composition, and a substrate in this order to obtain a laminate; a curing step of heating the laminate to a temperature at which the thermosetting maleimide resin composition of the resin layer is cured without removing the release sheet from the laminate. It should be noted that "in this order" refers to a positional order, not a chronological order. Other steps may be added as long as the effects of the present invention are not impaired.

[0051] [Lamination process] 1(A) shows a schematic diagram (cutaway end view) of a laminate of a resin layer 2 made of a thermosetting maleimide resin composition and a release sheet 1. The laminate of the resin layer 2 made of a thermosetting maleimide resin composition and the release sheet 1 is referred to as "laminate A" 10, and the release sheet in contact with the resin layer 2 made of a thermosetting maleimide resin composition is sometimes referred to as "release sheet a" to distinguish it from other release sheets described below. This laminate A10 can be obtained, for example, by applying a varnish of the above-mentioned thermosetting maleimide resin composition to one surface of the release sheet 1 and then volatilizing the organic solvent. For example, a varnish of a thermosetting maleimide resin composition dissolved in an organic solvent is applied to one side of the release sheet 1, and then the organic solvent is removed by heating for 0.5 to 30 minutes at a temperature of typically 70°C or higher, preferably 80°C or higher, to form a resin layer 2 with highly uniform properties on one side of the release sheet 1. Methods for applying the varnish include, but are not limited to, spin coaters, slit coaters, sprayers, dip coaters, bar coaters, and the like. The thickness of the coating layer is also not particularly limited, but is preferably 1 to 300 μm, and more preferably 1 to 200 μm.

[0052] Alternatively, the components of the thermosetting maleimide resin composition may be premixed in advance and extruded into a sheet or film using a melt kneader, and the extruded product may be placed on one side of the release sheet 1, or the thermosetting maleimide resin composition may be pulverized into tablets or granules, which may be stretched by a heat press into a sheet or film, and the resulting product may be placed on one side of the release sheet 1. A single layer of the sheet- or film-like thermosetting maleimide resin composition thus formed (a sheet or film of the thermosetting maleimide resin composition) may be placed on one side of the release sheet 1, or multiple sheets or films may be used to form a multi-layer structure and placed on one side of the release sheet 1. Furthermore, as the resin layer 2 of the thermosetting maleimide resin composition, a prepreg in which a fiber substrate is impregnated with the thermosetting maleimide resin composition, preferably a varnish of the thermosetting maleimide resin composition, may be placed on one side of the release sheet 1.

[0053] A cover film 6 may be applied to the resin layer 2 side of the laminate A10 to protect the resin layer 2 (a cross-sectional view is shown in FIG. 2 ), but this cover film 6 must be removed when the laminate is used in the process of laminating the laminate with the substrate 3, which will be described later. The cover film 6 is used as a protective film and is removed when laminating the laminate with the substrate; it is different from a release sheet. Examples of materials for the cover film 6 include polyolefin resins such as polyethylene (PE) resin, polypropylene (PP) resin, and polystyrene (PS) resin, and polyester resins such as polyethylene terephthalate (PET) resin, polybutylene terephthalate (PBT) resin, and polycarbonate (PC) resin. The cover film 6 has an adhesive layer on its surface (the surface in contact with the resin layer 2). The thickness of the cover film 6 is preferably 3 to 100 μm, and more preferably 3 to 50 μm.

[0054] Next, laminate A10 and substrate 3 are laminated together so as to contact the surface of resin layer 2 of laminate A, thereby obtaining a laminate in which release sheet 1, resin layer 2 made of the thermosetting maleimide resin composition, and substrate 3 are laminated in this order. This laminate having three layers, namely release sheet 1, resin layer 2 made of the thermosetting maleimide resin composition, and substrate 3, is sometimes referred to as "laminate B" 11 to distinguish it from other laminates. Specifically, it is preferable to invert the laminate A10 of FIG. 1(A) and place it on a substrate 3 as shown in FIG. 1(B) for lamination. As the lamination step, a method of pressing the laminate B using a roll or press pressure is preferred from the viewpoint of easily obtaining a uniform contact state and good workability. Among these, a vacuum lamination method is preferably used. The lamination method may be a batch method or a continuous method.

[0055] As the vacuum laminator, a commercially available vacuum laminator can be used. A schematic diagram of an example of a lamination process using a vacuum laminator is shown in Figure 1(B). First, the laminate A is placed on the substrate 3 so that the surface of the resin layer 2 is in contact with the substrate 3, and is set in the laminator 20. Next, when the pressure inside the laminator 20 is reduced, the upper rubber plate 4 moves downward, and the release sheet 1 and the resin layer 2 come into contact with the substrate 3. The resin layer 2 is softened by heating with the plate 5 equipped with a heater (not shown) of the laminator 20, and the release sheet 1 and the resin layer 2 are pressed against the substrate 3 by the pressure of the upper plate 5. At this time, the heating by the plate 5 of the laminator 20 is carried out for a short time so that the resin layer 2 is softened, for example, 5 minutes or less, and preferably 15 seconds to 5 minutes, and during this time, the resin layer 2 is not hardened. Finally, the reduced pressure in the system is released, yielding a laminate B11. The heating temperature is preferably 40 to 160°C, and within this range, the thermosetting maleimide resin composition softens but does not flow out, making it easy to press-bond it to the substrate 3. The temperature settings at this time may be different for the upper plate 5 and the lower plate 5. The pressing pressure is preferably in the range of 0.1 to 1.5 MPa, and within this range, the resin composition can be pressed onto the substrate 3 without flowing out. Lamination is preferably performed under reduced air pressure of 30 hPa or less.

[0056] In the lamination step, in addition to the release sheet a, another release sheet b may be disposed. That is, when setting in laminator 20, for example, substrate 3 may be disposed on release sheet 1b, and laminate A10 may be disposed so that the surface of resin layer 2 of laminate A10 is in contact with substrate 3, followed by lamination to form a laminate having at least four layers: release sheet 1a, resin layer 2 made of the thermosetting maleimide resin composition, substrate 3, and release sheet 1b. FIG. 3(A) is a schematic diagram (cross-sectional end view) showing the laminated state of this embodiment, and FIG. 3(B) is a schematic diagram (cross-sectional end view) of the laminate obtained after the lamination step. The embodiment having the release sheet b is preferable because it can prevent leakage of the resin layer 2 when a vacuum laminator is used in the lamination step, and can better prevent oxygen from entering in the curing step described below. The two release sheets a and b used here may be of the same type or different types.

[0057] [Curing process] In the curing step, the laminate B11 is heated to a temperature at which the thermosetting maleimide resin composition of the resin layer 2 cures, without removing the release sheet 1 from the laminate B11, thereby curing the thermosetting maleimide resin composition of the resin layer 2. The curing conditions vary depending on the type of component (B) used, but are generally a curing temperature of 120 to 200°C and a curing time of 15 to 600 minutes. If the release sheet 1 is removed before curing, the curing will be insufficient, even if curing is performed in a nitrogen atmosphere, and strong tackiness may occur on the surface of the resin layer 2, particularly when heated, and poor appearance may occur. In the curing step, pressure may be applied, but is not necessarily required. For example, as shown in Figures 1(B) to (C), the laminate B11 obtained in the lamination step can be placed in an oven 30 set at a curing temperature without peeling off the release sheet 1, and thermally cured.

[0058] After the curing step, the release sheet 1 can be removed from the resulting laminate B12 (FIG. 1(D)) having the cured resin layer 2' as needed before use (FIG. 1(E)). The release sheet 1 is generally removed by mechanical peeling, either manually or using an automatic peeling device. From this perspective, it is preferable that at least the surface of the release sheet 1 that comes into contact with the resin layer 2 is release-treated. When a metal foil is used as the release sheet 1, it can also be removed by etching.

[0059] The cured product (cured film) of the thermosetting maleimide resin composition obtained by the method for producing a cured product of the present invention has excellent heat resistance, mechanical properties, electrical properties, adhesion to substrates, and solvent resistance, as well as a low dielectric constant. Therefore, it can be used in, for example, rigid / flexible printed wiring boards and semiconductor devices, specifically, solder resists and coverlay films, passivation films and protective films on the surfaces of semiconductor elements, junction protective films for junctions of diodes, transistors, etc., alpha-ray shielding films for VLSIs, interlayer insulating films, ion implantation masks, etc., as well as conformal coatings for printed circuit boards, alignment films for liquid crystal surface elements, protective films for glass fibers, and surface protective films for solar cells. [Example]

[0060] EXAMPLES The present invention will be specifically explained below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0061] [Preparation of Laminate A1 Having a Resin Layer Made of Thermosetting Maleimide Resin Composition] Into a 500 mL four-neck flask equipped with a Dimroth condenser and a stirrer, 100 parts of a hydrocarbon group-containing bismaleimide compound derived from a dimer acid skeleton and represented by the following formula (4) (trade name: SLK-3000, manufactured by Shin-Etsu Chemical Co., Ltd., number average molecular weight: 5500), 1 part of di-t-butyl peroxide (trade name: Trigonox B, manufactured by Kayaku Nouryon Co., Ltd.), and 85 parts of toluene were placed, and the mixture was heated to melt with stirring at 50°C for 1 hour to prepare a varnish. The varnish was applied to a 50 μm-thick release-treated PET film (product name: TNT-010, manufactured by Toyobo STC) using a die coater, and the film was heated in a hot air drying oven at 100°C for 5 minutes to remove the solvent, yielding a laminate A1 having a resin layer made of a thermosetting maleimide resin composition as shown in Figure 1(A). The resin layer had a thickness of 50 μm. [ka] -C 36 H 70 - indicates a structure derived from a dimer acid skeleton. n≒5 (average value)

[0062] [Preparation of Laminate A2 Having a Resin Layer Made of Thermosetting Maleimide Resin Composition] Into a 500 mL four-neck flask equipped with a Dimroth condenser and a stirrer, 100 parts of a hydrocarbon group-containing bismaleimide compound derived from a dimer acid skeleton and represented by the following formula (5) (trade name: BMI-2500, manufactured by Designer Molecules Inc., number average molecular weight: 6000), 1 part of di-t-butyl peroxide (trade name: Trigonox B, manufactured by Kayaku Nouryon Co., Ltd.), and 85 parts of toluene were placed, and the mixture was heated to melt with stirring at 50°C for 1 hour to prepare a varnish. The varnish was applied to a 50 μm-thick release-treated PET film (product name: TNT-010, manufactured by Toyobo STC) using a die coater, and the film was heated in a hot air drying oven at 100°C for 5 minutes to remove the solvent, yielding a laminate A2 having a resin layer made of a thermosetting maleimide resin composition as shown in Figure 1(A). The resin layer had a thickness of 50 μm. [ka] -C 36 H 70 - indicates a structure derived from a dimer acid skeleton. l≒5 (average value), m≒1 (average value)

[0063] [Lamination process] An 8-inch silicone wafer was placed on a release-treated PET film (product name: TNT-010, manufactured by Toyobo STC) as a substrate. The resin layer of the laminate A1 or A2 prepared above was then placed on the silicone wafer so that it was in contact with the silicone wafer. The four layers (release sheet (PET film) - silicone wafer - resin layer - release sheet (PET film)) were then laminated and pressed together using a batch-type vacuum laminator (manufactured by Nikko Materials Co., Ltd.) to obtain a laminate. The lamination conditions were: depressurization for 20 seconds to confirm that the air pressure was 10 hPa or less, followed by 30 seconds of pressure bonding at 90°C and 0.4 MPa. When placing the laminate in the vacuum laminator, both release sheets a and b were at least 8% larger than the area of ​​the resin layer of laminate A1 or A2 in plan view, as shown in Figure 3(A). This resulted in the laminate shown in Figure 3(B).

[0064] [Curing process] As shown in Table 1 below, in Examples 1 to 3, the laminate was placed in an inert oven DN411I manufactured by Yamato Scientific Co., Ltd. without removing both release sheets on the outermost surfaces of the laminate, and heated at 180°C for 90 minutes to cure the thermosetting maleimide resin composition of the resin layer. After curing, both release sheets on the outermost surfaces of the laminate were peeled off by hand. On the other hand, in Comparative Examples 1 to 4, both outermost release sheets were first peeled off from the laminate, and then curing was carried out under the same conditions as in Examples 1 to 4. The atmosphere in the oven (curing atmosphere) is shown in Table 1.

[0065] [External inspection] After curing under the above curing conditions, the cured product was removed from the oven and visually inspected. Appearance was evaluated with a rating of ◯ for those with no wrinkles or wrinkles in the resin layer and x for those with wrinkles or wrinkles.

[0066] [Cureability confirmation] After curing, both release sheets were peeled off and the silicone wafer with the resin layer was placed on a hot plate at 120°C. When the surface was poked with a spatula, if the resin layer was not scratched and there was no tack, it was rated as ◯, and if it was easily scratched or had tack and the resin stuck to the spatula, it was rated as ×. [Table 1]

[0067] In Examples 1 to 3, the appearance and curability of the resulting cured products were good whether the curing atmosphere was a nitrogen atmosphere or an air atmosphere. On the other hand, in Comparative Examples 1 to 3, regardless of the curing atmosphere, numerous wrinkles and wrinkles appeared on the exterior due to the hot air emitted in the oven, and in Comparative Example 4, the appearance was good, probably because the radical reaction on the surface progressed slightly in the nitrogen atmosphere. However, in all Comparative Examples, the curability was insufficient, and the resin was significantly deformed or scratched by external forces when heated. [Explanation of symbols]

[0068] 1 Release sheet 1a Release sheet a 1b Release sheet b 2 Thermosetting maleimide resin composition (resin layer) 2' Cured product of thermosetting maleimide resin composition (cured resin layer) 3 Base material 4 rubber plates 5 plates 6 Cover film 10 Laminate A 11 Laminate B 12 Laminate B having a cured resin layer 20 Laminator 30 Oven

Claims

1. (A) A maleimide compound having one or more hydrocarbon groups derived from a dimer acid skeleton in one molecule and (B) Radical polymerization initiator A method for producing a cured product of a thermosetting maleimide resin composition comprising: a lamination step of laminating a release sheet, a resin layer made of the thermosetting maleimide resin composition, and a substrate in this order to obtain a laminate; a curing step of heating the laminate to a temperature at which the thermosetting maleimide resin composition of the resin layer is cured without removing the release sheet from the laminate. and the laminating step is a step of placing another release sheet on the surface of the substrate that is not in contact with the resin layer, to obtain a laminate having at least four layers, namely, the release sheet, the resin layer made of the thermosetting maleimide resin composition, the substrate, and the release sheet; A method for producing a cured product of a thermosetting maleimide resin composition.

2. 2. A method for producing a cured product of the thermosetting maleimide resin composition according to claim 1, wherein component (A) is a maleimide compound represented by the following formula (1) and / or (2): 【Chemical 1】 (In formula (1), A's are independently tetravalent organic groups having a cyclic structure; B's are independently divalent alicyclic hydrocarbon groups having 6 to 60 carbon atoms; D's are independently divalent hydrocarbon groups having 6 to 200 carbon atoms, at least one of which is a hydrocarbon group derived from a dimer acid skeleton; m is 1 to 100; and l is 1 to 200. The order of the repeating units bracketed by m and l is not limited, and the bonding pattern may be alternating, block, or random.) 【Chemistry 2】 (In formula (2), A's are independently tetravalent organic groups having a cyclic structure, D's are independently divalent hydrocarbon groups having 6 to 200 carbon atoms, and at least one D is a hydrocarbon group derived from a dimer acid skeleton. n is 0 to 100.)

3. 3. A method for producing a cured product of the thermosetting maleimide resin composition according to claim 2, wherein A in formula (1) and formula (2) is any of the tetravalent organic groups represented by the following structural formulas: 【Chemistry 3】

4. 2. The method for producing a cured product of the thermosetting maleimide resin composition according to claim 1, wherein the radical polymerization initiator of component (B) is an organic peroxide.

5. 5. The method for producing a cured product of a thermosetting maleimide resin composition according to claim 1, wherein the release sheet is a plastic film whose surface in contact with the resin layer made of the thermosetting maleimide resin composition has been treated with a release agent.

6. 5. The method for producing a cured product of the thermosetting maleimide resin composition according to any one of claims 1 to 4, wherein the substrate is at least one selected from the group consisting of a metal foil, a silicone wafer, a SiC wafer, a sapphire wafer, a compound semiconductor wafer, an organic substrate, and a ceramic substrate.

7. The method for producing a cured product of the thermosetting maleimide resin composition according to any one of claims 1 to 4, wherein the resin layer has a thickness of 1 to 300 µm.

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