JP7796583B2 - Curable resin compositions, dry films, prepregs, cured products, laminates, and electronic components - Google Patents

Description

The present invention relates to a curable resin composition, a dry film, a prepreg, a cured product, a laminate, and an electronic component.

In recent years, mobile communication devices compatible with the fifth generation mobile communication system (5G) have appeared, and
Development has begun with an eye on the next generation. Mobile communication devices and other devices are increasingly using high-frequency (GHz order) electrical signals to transmit and process large volumes of information at high speed. High-frequency signals are prone to attenuation, so materials used are required to be designed to reduce transmission loss.

Against this background, development is underway on materials with low dielectric constants and low dielectric dissipation factors that can reduce transmission loss.

Epoxy resins have traditionally been used as materials with low dielectric constants and low dielectric tangents, but Patent Document 1, for example, proposes a resin material using episulfide resin. The resin material in Patent Document 1 contains episulfide resin, a curing agent, and an inorganic filler, and the curing agent is an active ester compound or a cyanate ester compound.

JP 2013-60553 A

However, the resin material in Patent Document 1 requires an active ester compound or a cyanate ester compound, as well as an inorganic filler, and there is still a need for a resin material that does not require these elements and that achieves a low dielectric constant and low dielectric dissipation factor when cured to a high degree.

The present invention aims to provide a resin material whose cured product has a low dielectric constant and a low dielectric loss tangent.

The present inventors have found that a curable resin composition comprising an episulfide resin in combination with one or more curing agents selected from the group consisting of maleimide compounds, benzoxazine compounds, and carbodiimide compounds can provide a cured product having a low dielectric constant and a low dielectric loss tangent, and have completed the present invention.
In these resin compositions, for example, the thiirane group and the maleimide group form a carbon-sulfur bond in a curing reaction, thereby providing flexibility (elongation), and an excellent cured product with a low dielectric constant can be obtained; the thiirane group and the benzoxazine group form a cured product with excellent low thermal expansion, due to the promotion of ring-opening of the benzoxazine group by the acidity of the thiol generated by the ring-opening of the thiirane group, and the promotion of ring-opening of the thiirane group by the hydroxyl group generated by the ring-opening of the benzoxazine group; and the thiirane group and the carbodiimide group form an imidazolidinethione ring bond in a curing reaction, resulting in a cured product with excellent low thermal expansion and heat resistance.

The gist of the present invention is as follows.
[1] A curable resin composition comprising an episulfide resin and one or more curing agents selected from the group consisting of maleimide compounds, benzoxazine compounds, and carbodiimide compounds.
[2] The curable resin composition according to [1], wherein the ratio of the number of moles of functional groups in the curing agent to the number of moles of thiirane groups contained in the episulfide resin is 0.1 or more and 1.5 or less.
[3] The curable resin composition according to [1] or [2], further comprising an inorganic filler.
[4] A dry film comprising a substrate and a resin layer formed on the substrate, the resin layer being made of the curable resin composition according to any one of [1] to [3].
[5] A prepreg obtained by impregnating a substrate with the curable resin composition according to any one of [1] to [3].
[6] A cured product obtained by curing the curable resin composition of any one of [1] to [3], the curable resin composition in the resin layer of the dry film of [4], or the curable resin composition in the prepreg of [5].
[7] A laminate comprising the cured product of [6].
[8] An electronic component comprising the cured product of [6].

The curable resin composition of the present invention can provide a cured product with a low dielectric constant and a low dielectric loss tangent.

<Curable resin composition>
The curable resin composition of the present invention contains an episulfide resin and one or more curing agents selected from the group consisting of maleimide compounds, benzoxazine compounds, and carbodiimide compounds.

[Episulfide resin]
The episulfide resin is not particularly limited, and a resin having one or more thiirane groups can be used. From the viewpoints of good curability and mechanical strength of the cured product, the number of thiirane groups is preferably two or more, and more preferably two to four.

Examples of episulfide resins having two or more thiirane groups include bisphenol A episulfide resins, bisphenol F episulfide resins, bisphenol S episulfide resins, hydrogenated bisphenol A episulfide resins, hydrogenated bisphenol F episulfide resins, hydrogenated bisphenol S episulfide resins, dicyclopentadiene episulfide resins, biphenol episulfide resins, fluorene episulfide resins, episulfide resins having a triazine nucleus in the skeleton, naphthalene episulfide resins, anthracene episulfide resins, and naphthol aralkyl episulfide resins.
Polyfunctional episulfide resins such as phenol novolac episulfide resins, biphenyl novolac episulfide resins, and phenol aralkyl episulfide resins may also be used.
Aliphatic episulfide resins such as episulfide resins having a tricyclodecane skeleton and episulfide resins having an adamantane skeleton may also be used.

Preferred episulfide resins include bisphenol A, bisphenol F, and biphenyl episulfide resins, as well as episulfide resins with a hydrogenated (alicyclic) structure, with episulfide resins with a hydrogenated (alicyclic) structure being more preferred due to their ability to achieve lower dielectric properties.

Episulfide resins may be used alone or in combination of two or more types in any ratio.

The molecular weight of the episulfide resin can be from 200 to 2,000, and is preferably 350 or more from the viewpoint of safety, and is preferably 1,000 or less from the viewpoint of handling properties such as fluidity of the composition.
Unless otherwise specified, the molecular weight in this specification means the number average molecular weight.

The episulfide equivalent weight (mass of resin per equivalent of episulfide group) of the episulfide resin can be 100 or more and 1,000 or less. A value of 500 or less is preferred, as this provides good reactivity.

Episulfide resins can be easily obtained by converting the epoxy groups of epoxy resins into thiirane groups using a sulfurizing agent. Examples of sulfurizing agents include thiourea and potassium thiocyanate. To suppress the polymerization reaction caused by ring-opening of the thiirane groups, the reaction temperature is preferably 70°C or lower. However, from the perspective of reaction efficiency, the reaction temperature can be set to 40°C or higher.

[Curing agent]
The curing agent is selected from the group consisting of maleimide compounds, benzoxazine compounds, and carbodiimide compounds, and may be any one of maleimide compounds, benzoxazine compounds, and carbodiimide compounds, or a combination of two or all of these compounds in any ratio.
Among these, maleimide compounds are preferred because they have excellent mechanical properties and a low dielectric constant, benzoxazine compounds are preferred because they provide good thermal dimensional stability, and carbodiimide compounds are preferred because they provide good thermal dimensional stability and high heat resistance.

(Maleimide compounds)
The maleimide compound is not particularly limited, and a compound having one or more maleimide groups can be used. From the viewpoints of good curability and toughness of the cured product, the number of maleimide groups is preferably two or more, and more preferably two to four.

Examples of maleimide compounds include polyfunctional aliphatic maleimides and polyfunctional aromatic maleimides. Polyfunctional aliphatic maleimides include maleimides containing an alicyclic structure, and the aromatic ring in polyfunctional aromatic maleimides may be a carbon ring or a heterocyclic ring.

Examples of polyfunctional aliphatic maleimides include isocyanurate-based maleimide ester compounds obtained by dehydration esterification of tris(hydroxyethyl)isocyanurate and aliphatic maleimide carboxylic acid; isocyanurate-based polymaleimides such as isocyanurate-based maleimide urethane compounds obtained by urethanization of tris(carbamatehexyl)isocyanurate and aliphatic maleimide alcohol; aliphatic polymaleimide ester compounds obtained by dehydration esterification of aliphatic maleimide carboxylic acid and various aliphatic polyols, or by transesterification of aliphatic maleimide carboxylic acid esters and various aliphatic polyols; aliphatic polymaleimide ester compounds obtained by the ether ring-opening reaction of aliphatic maleimide carboxylic acid and various aliphatic polyepoxides; and aliphatic polymaleimide urethane compounds obtained by the urethanization reaction of aliphatic maleimide alcohol and various aliphatic polyisocyanates.

Examples of polyfunctional aromatic maleimides include aromatic polymaleimide ester compounds obtained by dehydration esterification of maleimide carboxylic acid with various aromatic polyols or transesterification of maleimide carboxylic acid esters with various aromatic polyols; aromatic polymaleimide ester compounds obtained by the ether ring-opening reaction of maleimide carboxylic acid with various aromatic polyepoxides; and aromatic polymaleimide urethane compounds obtained by the urethanization reaction of maleimide alcohol with various aromatic polyisocyanates.

Polyfunctional aliphatic maleimides and polyfunctional aromatic maleimides can include heterocycles. Specific examples include maleimide group-containing imide compounds obtained by polymerizing a tetracarboxylic acid dianhydride (e.g., alicyclic tetracarboxylic acid, aromatic tetracarboxylic acid dianhydride, etc.) with a diamine (e.g., a diamine having an aliphatic chain structure, aromatic diamine, etc.) and capping the terminal amine with maleic anhydride; and maleimide group-containing benzoxazole compounds obtained by polymerizing a dicarboxylic acid derivative with bis(o-aminophenol) and capping the terminal amine with maleic anhydride.

From the viewpoint of improving the low dielectric properties of the cured product, maleimide compounds containing an alicyclic structure in the skeleton are preferred; from the viewpoint of increasing the toughness of the cured product, maleimide compounds containing an aliphatic chain in the skeleton are preferred; and from the viewpoint of increasing the rigidity of the cured product, maleimide compounds containing an aromatic ring, heterocyclic ring, or a structure in which these are condensed in the skeleton are preferred.

The molecular weight of the maleimide compound can be 300 or more and 8,000 or less. From the viewpoint of flexibility of the cured product, a molecular weight of 1,000 or more is preferable.

The maleimide equivalent of the maleimide compound (mass of compound per equivalent of maleimide group) can be 150 or more and 4,000 or less. From the viewpoint of toughness of the cured product, the maleimide equivalent is preferably 1,000 or more.

These maleimide compounds may be synthesized by known methods, or commercially available products may be used.
Commercially available products include, for example, BMI, BMI-70, and BMI-80 (manufactured by KI Chemical Industry Co., Ltd.), BMI-1000, BMI-1000H, BMI-1000S, BMI-1100, BMI-1100H, BMI-2000, BMI-2300, BMI-3000, BMI-3000H, BMI-4000, BMI-5100, BMI-7000, BMI-7000H, and BMI-TMH (manufactured by Daiwa Chemical Industry Co., Ltd.), MIA-200 (manufactured by DIC Corporation), BMI-2500, BMI-3000J, BMI-6000, and BMI-6100 (Designer Examples of suitable ion exchangers include SLK-2600 (manufactured by Shin-Etsu Chemical Co., Ltd.), SLK-2600 (manufactured by Shin-Etsu Chemical Co., Ltd.), and MIR-3000-70MT (manufactured by Nippon Kayaku Co., Ltd.).

(Benzoxazine compounds)
The benzoxazine compound is not particularly limited, and a compound having one or more benzoxazine rings can be used. From the viewpoints of good curability and brittleness of the cured product, the number of benzoxazine rings is preferably two or more, and more preferably two to four.

The benzoxazine compound may be any known benzoxazine compound, such as a P-d benzoxazine compound, an F-a benzoxazine compound, an ALP-d benzoxazine compound, or a T-ala benzoxazine compound.

The benzoxazine compounds may be used alone or in combination of two or more in any ratio.

The molecular weight of the benzoxazine compound can be 300 or more and 2,000 or less, and preferably 300 or more and 1,000 or less.

The benzoxazine equivalent weight (mass of compound per equivalent of benzoxazine ring) of the benzoxazine compound can be 150 or more and 1,000 or less. The benzoxazine equivalent weight is preferably 500 or less, and more preferably 300 or less.

(Carbodiimide compounds)
The carbodiimide compound is not particularly limited, and a compound containing two or more carbodiimide groups (—N═C═N—) can be used. From the viewpoint of good curability, the number of carbodiimide groups is preferably two or more, and more preferably two to ten.

Carbodiimide compounds can be synthesized using known methods (see, for example, JP 2019-38960 A). Specifically, they can be synthesized by condensation polymerization of diisocyanate.

Diisocyanates used in the synthesis of carbodiimide compounds include aromatic diisocyanates, aliphatic diisocyanates, and alicyclic diisocyanates. Specific examples include aromatic diisocyanates such as 1,5-naphthylene diisocyanate, 2,4'-diphenylmethane diisocyanate, 4,4'-diphenylmethane diisocyanate, 4,4'-diphenyldimethylmethane diisocyanate, 1,3-phenylene diisocyanate, 1,4-phenylene diisocyanate, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, o-xylylene diisocyanate, m-xylylene diisocyanate, and tetramethylxylylene diisocyanate; Examples of the diisocyanate include aliphatic diisocyanates such as tetramethylene diisocyanate, hexamethylene diisocyanate, and trimethylhexamethylene diisocyanate; and alicyclic diisocyanates such as cyclohexane-1,4-diisocyanate, isophorone diisocyanate, dicyclohexylmethane-4,4'-diisocyanate, methylcyclohexane diisocyanate, 2,5-bis(isocyanatomethyl)bicyclo[2.2.1]heptane, and 2,6-bis(isocyanatomethyl)bicyclo[2.2.1]heptane.
These diisocyanates may be used alone or in combination of two or more. Aromatic diisocyanates may be used as appropriate from the viewpoint of reactivity and heat resistance as a cured product, while aliphatic diisocyanates and alicyclic diisocyanates may be used as appropriate from the viewpoint of solubility in organic solvents, flexibility as a cured product, and low dielectric properties.
In particular, the carbodiimide compound used in the present invention is preferably a compound obtained by condensation polymerization of 2,4'-diphenylmethane diisocyanate and 4,4'-diphenylmethane diisocyanate in combination, since this compound achieves a good balance of properties such as solubility in organic solvents, storage stability, reactivity, and heat resistance of the cured product.

The terminal isocyanate groups of the carbodiimide compound obtained in this manner are preferably capped with a compound having one functional group reactive with an isocyanate group. Examples of compounds reactive with an isocyanate group include monoisocyanates, monoalcohols, monoamines, and acid anhydrides.

Examples of monoisocyanates include lower alkyl isocyanates such as methyl isocyanate, ethyl isocyanate, propyl isocyanate, n-, sec-, or tert-butyl isocyanate, alicyclic aliphatic isocyanates such as cyclohexyl isocyanate, and aromatic isocyanates such as phenyl isocyanate, tolyl isocyanate, dimethylphenyl isocyanate, and 2,6-diisopropylphenyl isocyanate.
Examples of the monoalcohol include methanol, ethanol, cyclohexanol, polyethylene glycol monomethyl ether, and polypropylene glycol monomethyl ether.
Examples of the monoamine include primary amines such as butylamine and cyclohexylamine, and secondary amines such as diethylamine, dibutylamine and dicyclohexylamine.
Examples of acid anhydrides include phthalic anhydride, acetic anhydride, succinic anhydride, maleic anhydride, and benzoic anhydride.
These may be used alone or in combination of two or more. Among these, from the viewpoint of reactivity, phenyl isocyanate and tolyl isocyanate are preferred, and phenyl isocyanate is more preferred.

The carbodiimide compounds may be used alone or in combination of two or more in any ratio.

The molecular weight of the carbodiimide compound can be 500 or more and 8,000 or less. From the viewpoint of good film-forming properties, it is preferably 1,000 or more, more preferably 1,400 or more. From the viewpoint of compatibility in the composition, it is preferably 5,000 or less, more preferably 3,500 or less.

The carbodiimide equivalent weight of the carbodiimide compound (mass of compound per equivalent of carbodiimide group) can be 50 or more and 4,000 or less. From the viewpoint of toughness of the cured product, it is preferably 100 or more, more preferably 130 or more. From the viewpoint of good curability, it is preferably 1,000 or less, more preferably 500 or less, and even more preferably 260 or less.

[Amount]
In the curable resin composition of the present invention, the ratio of the number of moles of functional groups in the curing agent to the number of moles of thiirane groups in the episulfide resin is preferably 0.1 or more and 1.5 or less. Within this range, the thiirane groups react with the functional groups in the curing agent in just the right amount, making it possible to simultaneously achieve excellent low dielectric properties, mechanical properties, and thermal properties.
Here, the functional group of the curing agent is a maleimide group for a maleimide compound, a benzoxazine ring for a benzoxazine compound, or a carbodiimide group for a carbodiimide compound.
Specifically, the ratio of the number of moles of maleimide groups in the maleimide compound to the number of moles of thiirane groups in the episulfide resin is more preferably 0.1 or more and 0.5 or less, since a cured product having excellent mechanical properties can be obtained; the ratio of the number of moles of benzoxazine rings in the benzoxazine compound to the number of moles of thiirane groups in the episulfide resin is more preferably 0.1 or more and 1.5 or less, since a cured product having excellent thermal properties can be obtained; and the ratio of the number of moles of carbodiimide groups in the carbodiimide compound to the number of moles of thiirane groups in the episulfide resin is more preferably 0.8 or more and 1.5 or less, since a cured product having excellent thermal properties can be obtained.

In the curable resin composition of the present invention, the total proportion of the episulfide resin and one or more curing agents selected from the group consisting of maleimide compounds, benzoxazine compounds, and carbodiimide compounds in the non-volatile components is preferably 30% by mass or more, and more preferably 40% by mass or more.

[Optional ingredients]
The curable resin composition of the present invention can contain optional components in addition to the episulfide resin and one or more curing agents selected from the group consisting of maleimide compounds, benzoxazine compounds, and carbodiimide compounds, within a range that does not impair the effects of the present invention.

(inorganic filler)
In order to improve the thermal dimensional stability of the cured product, it is preferable to blend an inorganic filler. The inorganic filler is not particularly limited, and examples thereof include silica (fused silica, amorphous silica, crystalline silica, etc.), talc, barium sulfate, barium titanate, clay, magnesium carbonate, calcium carbonate, aluminum oxide, aluminum hydroxide, alumina, silicon nitride, boron nitride, and aluminum nitride. Among these, silica is preferable in terms of low thermal expansion and low dielectric loss tangent.

The average particle size of the inorganic filler can be 0.1 μm or more and 1.0 μm or less, and from the viewpoint of reducing the dielectric constant, a value of 0.3 μm or more is preferable. Here, the average particle size is a value measured using a laser analysis particle size distribution analyzer.

The inorganic filler may be surface-treated with a coupling agent. Examples of coupling agents include silane coupling agents and titanate coupling agents.

The content of the inorganic filler is not particularly limited, but in order to obtain a sufficient effect of the blending, it is preferably 40% by mass or more, more preferably 50% by mass or more, of the non-volatile components of the curable resin composition of the present invention, and is preferably 80% by mass or less, more preferably 75% by mass or less.
When an inorganic filler is used, the inorganic filler may be used alone or in combination of two or more kinds in any ratio.

(Curing accelerator)
From the viewpoint of controlling the curing rate and the crosslinked structure of the cured product, it is preferable to add a curing accelerator. The curing accelerator is not particularly limited, and examples thereof include imidazole compounds, amine compounds, phosphorus compounds, organometallic complexes, and organometallic salts.
Examples of the imidazole compound include imidazole, 2-methylimidazole, 2-ethylimidazole, 2-ethyl-4-methylimidazole, 2-phenylimidazole, 4-phenylimidazole, 1-cyanoethyl-2-phenylimidazole, and 1-(2-cyanoethyl)-2-ethyl-4-methylimidazole.
Examples of the amine compound include dicyandiamide, benzyldimethylamine, 4-(dimethylamino)-N,N-dimethylbenzylamine, 4-methoxy-N,N-dimethylbenzylamine, and 4-methyl-N,N-dimethylbenzylamine.
Examples of phosphorus compounds include triphenylphosphine.
Examples of organometallic complexes or salts include acetylacetonate complexes of cobalt, copper, zinc, iron, nickel, manganese, etc.

The content of the curing accelerator is not particularly limited, but in order to obtain a sufficient effect of the addition, it is preferably 0.05% by mass or more, more preferably 0.1% by mass or more, and is preferably 1% by mass or less, more preferably 0.6% by mass or less, based on the solid content of the curable resin composition of the present invention.
When a curing accelerator is used, the inorganic filler may be used alone or in combination of two or more kinds in any ratio.

(thermoplastic resin)
The curable resin composition of the present invention may contain a thermoplastic resin for the purposes of film-forming properties, flexibility, adhesion, etc. Examples of the thermoplastic resin include a phenoxy resin, a polyvinyl acetal resin, and a thermoplastic elastomer.
When a thermoplastic resin is used, the inorganic filler may be used alone or in combination of two or more kinds in any ratio.

(solvent)
The curable resin composition of the present invention may contain a solvent to adjust the viscosity during application, etc. The solvent is not particularly limited, and an organic solvent is preferred. For example, ketones such as acetone, methyl ethyl ketone, and cyclohexanone; aromatic hydrocarbons such as toluene, xylene, and tetramethylbenzene; glycol ethers such as cellosolve, methyl cellosolve, butyl cellosolve, carbitol, methyl carbitol, butyl carbitol, propylene glycol monomethyl ether, dipropylene glycol monomethyl ether, dipropylene glycol diethyl ether, and triethylene glycol monoethyl ether; ethyl acetate, butyl acetate, diethylene glycol ethyl ether acetate, and dipropylene glycol Examples of suitable solvents include esters such as methyl ether acetate, propylene glycol methyl ether acetate, propylene glycol ethyl ether acetate, and propylene glycol butyl ether acetate; alcohols such as ethanol, propanol, ethylene glycol, and propylene glycol; aliphatic hydrocarbons such as octane and decane; petroleum solvents such as petroleum ether, petroleum naphtha, hydrogenated petroleum naphtha, and solvent naphtha; and aprotic polar solvents such as N-methylpyrrolidone, dimethylformamide, dimethylacetamide, dimethyl sulfoxide, and acetonitrile. Ketones and esters are preferred in terms of solubility and volatility during curing.
The solvent may be used alone or in combination of two or more kinds in any ratio.

(Other ingredients)
The curable resin composition of the present invention may contain other components within a range that does not impair the effects of the present invention, such as conductive particles, colorants, wetting and dispersing agents, ultraviolet absorbers, silane coupling agents, plasticizers, flame retardants, antistatic agents, antioxidants, antioxidants, antibacterial and antifungal agents, antifoaming agents, leveling agents, thickeners, adhesion-imparting agents, thixotropy-imparting agents, release agents, surface treatment agents, dispersants, dispersion aids, surface modifiers, stabilizers, and phosphors.

The curable resin composition of the present invention is thermosetting, but may be made photosensitive or photocurable by incorporating various components (e.g., compounds having an ethylenically unsaturated group such as photopolymerizable monomers and photopolymerizable oligomers; photosensitizers such as photopolymerization initiators, photoacid generators, and photobase generators; photoinitiator assistants; sensitizers, etc.).

The curable resin composition of the present invention may contain, but preferably does not contain, a thermosetting resin other than an episulfide resin (e.g., an epoxy resin, an oxetane resin, etc.). It may also contain, but preferably does not contain, a curing agent other than a maleimide compound, a benzoxazine compound, or a carbodiimide compound (e.g., an active ester compound, a cyanate ester compound, etc.).

[Manufacturing method]
The curable resin composition of the present invention can be prepared by mixing an episulfide resin, one or more curing agents selected from the group consisting of maleimide compounds, benzoxazine compounds, and carbodiimide compounds, and optional components. From the viewpoint of coatability, the viscosity of the composition is preferably 100 mPa·s or more and 100,000 mPa·s or less. The viscosity can be adjusted by adding a solvent, which can be added in any amount from the viewpoints of compatibility with the components in the composition, coatability, and drying properties of the composition.

<Dry film>
The curable resin composition of the present invention can be applied to a substrate and dried to form a resin layer, thereby forming a dry film.
Examples of the substrate include metal foil (for example, copper foil), carrier film, and the like.
The carrier film is not particularly limited, and examples of films that can be used include polyester films such as polyethylene terephthalate and polyethylene naphthalate, polyimide films, polyamideimide films, polyethylene films, polytetrafluoroethylene films, polypropylene films, and polystyrene films.
The methods for application and drying are not particularly limited, and known methods can be used.
A protective film may be laminated on the surface of the resin layer of the dry film, and examples of the protective film include polyester film, polyethylene film, and polypropylene film.

<Prepreg>
The curable resin composition of the present invention can be impregnated into a substrate to form a prepreg. Examples of the substrate include glass cloth, glass nonwoven fabric, and aramid nonwoven fabric. After the substrate is impregnated with the curable resin composition, the substrate may be dried to form a semi-cured product.

<Cured product>
A cured product can be obtained by curing the curable resin composition of the present invention, the resin layer of the dry film of the present invention, or the curable resin composition in the prepreg of the present invention. When using the curable resin composition of the present invention, a cured product can be obtained by applying the composition to a desired object, drying it, and heating it at a temperature of 160°C or higher and 280°C or lower. The heating time can be set appropriately, for example, 30 minutes or higher and 120 minutes or lower. When using the dry film of the present invention, a cured product of the resin layer can be obtained by laminating the dry film to a desired object and heating it at a temperature of 160°C or higher and 280°C or lower. The heating time can be set appropriately, for example, 40 minutes or higher and 90 minutes or lower.

<Laminate>
The present invention also relates to a laminate comprising the cured product of the present invention. The laminate of the present invention can be produced using the prepreg of the present invention. For example, by stacking one or more prepregs of the present invention, and then stacking a metal foil such as copper foil on both sides or one side of the prepreg, and then heat-pressuring the laminate, a laminate having a metal foil on both sides or one side of the laminate and a cured product of the curable resin composition can be obtained.

<Electronic Components>
The present invention further relates to an electronic component comprising the cured product of the present invention. Examples of electronic components include printed wiring boards and inductors. Electronic components comprising the cured product of the present invention are preferably used as a cured film for solder resist, interlayer insulating material, coverlay, etc., or as a hole filler for through holes, via holes, etc.

The present invention will be described in detail below using examples, but the present invention is not limited to these examples.

The following ingredients were used:
<Episulfide resin>
Episulfide resin 1: TBIS-AHSP manufactured by Taoka Chemical Co., Ltd. Hydrogenated bisphenol A episulfide resin, episulfide equivalent weight 214 g/eq
Episulfide resin 2: A bisphenol A type episulfide resin in which the epoxy groups of the following epoxy resin 2 have been converted to thiirane groups as follows. Episulfide equivalent: approximately 207 g/eq
A solution of 2.1 g of thiourea dissolved in 42 mL of methanol in a 50 mL vial was added dropwise over 6 minutes at room temperature (approximately 25°C) to a 120 mL vial containing a solution of 2.9 g of epoxy resin 2 dissolved in 18 mL of tetrahydrofuran (THF), and the mixture was then heated to 50°C and maintained at that temperature for 2.5 hours. The mixture was then cooled to room temperature and allowed to stand for 24 hours.
The resulting reaction solution was transferred to a 200 mL flask using 10 mL of methanol and concentrated using an evaporator, after which 29 mL of distilled water was added, followed by extraction with 32 mL of ethyl acetate (AcOEt) and further extraction with 16 mL of AcOEt. The extract was washed with 30 mL of brine, dried over magnesium sulfate, filtered, and the solvent was removed by distillation to obtain 3.7 g of bisphenol A episulfide resin as a residue.

<Other resins>
Epoxy resin 1: YX-8034 manufactured by Mitsubishi Chemical Corporation. Hydrogenated bisphenol A epoxy resin, epoxy equivalent 270 g/eq
Epoxy resin 2: JER828 manufactured by Mitsubishi Chemical Corporation. Bisphenol A type epoxy resin, epoxy equivalent weight 185 g/eq
Thiol compound: SS32 manufactured by Kawaguchi Chemical Industry Co., Ltd. Trifunctional thiol compound, molecular weight 532. Thiol equivalent 177.3 g/eq

<Curing agent>
Maleimide compound: Designer Molecules BMI-6000, terminal bismaleimide resin, number average molecular weight 6626, weight average molecular weight 21733, maleimide equivalent 3313 g/eq
Benzoxazine compound: Pd-type benzoxazine compound manufactured by Shikoku Chemical Industry Co., Ltd., molecular weight 435, benzoxazine equivalent 217.5 g/eq
Carbodiimide compound: a compound prepared as follows. Number average molecular weight: 2997, weight average molecular weight: 17193, carbodiimide group equivalent: 205 g/eq
A reaction vessel equipped with a reflux condenser and a stirrer was charged with a mixture of 54 parts by mass of 2,4'-diphenylmethane diisocyanate and 46 parts by mass of 4,4'-diphenylmethane diisocyanate (manufactured by Tosoh Corporation, Monomeric MDI; Millionate NM) as the diisocyanate, 10 parts by mass of phenyl isocyanate as a compound having one functional group reactive with an isocyanate group, and 0.6 parts by mass of 3-methyl-1-phenyl-2-phospholene-1-oxide as a carbodiimide catalyst, and the mixture was stirred at 100°C for 2 hours under a nitrogen stream. Infrared absorption (IR) spectroscopy confirmed that the absorption peak due to the isocyanate group at a wavelength of around 2270 ^cm had almost disappeared, yielding a carbodiimide compound.
Active ester compound: HPC-8000-65T manufactured by DIC Corporation, non-volatile component 65% by weight, active ester group equivalent weight 223 g/eq
Cyanate compound: BA-230S manufactured by Lonza Japan, non-volatile content 75% by weight, cyanate ester group equivalent 235 g/eq

<Other ingredients>
Inorganic filler: silica filler (spherical, average particle size 0.5 μm)
Solvent 1: Cyclohexanone Solvent 2: Methyl ethyl ketone

The various measurements were carried out as follows.
<Preparation of Resin Composition>
The components in the amounts shown in Table 1 (in Table 1, the amount of each component is expressed in parts by mass) were stirred at 2000 rpm for 5 minutes and degassed at 2200 rpm for 2 minutes using a revolutionary rotation stirring and degassing apparatus (Kakuhunter SK-300S, manufactured by Shashin Kagaku Co., Ltd.), to prepare compositions of the Examples and Comparative Examples.

<Preparation of cured film>
The compositions of the Examples and Comparative Examples were applied to copper foil with an applicator and dried in a box drying oven at 90°C for 10 minutes. The copper foil with the dried coating film was then placed in a drying oven with an internal temperature of room temperature (approximately 25°C), heated over 30 minutes to the temperature shown in Table 1, and then maintained at that temperature for 1 hour for heat treatment. The copper foil with the cured coating film was removed from the drying oven, the copper foil was removed with an etching solution, and washed with water to obtain a cured film with a thickness of approximately 30 µm.

<Dielectric properties>
The cured film prepared by the above method was dried in a box drying oven at 120° C. for 10 minutes, and the dielectric constant and dielectric loss tangent at 10 GHz were measured using the SPDR method.

<Mechanical properties>
Film samples made of the cured products of each composition prepared in the same manner as above were cut into 5 mm wide x 70 mm long specimens.
Tensile tests were carried out five times on this test piece using an EZ-SX made by Shimadzu Corporation, with a gripping distance of 30 mm and a tensile speed of 3 mm/min.
The modulus of elasticity was measured at a tensile strength of 5 to 10 MPa, and the average value was taken as the modulus of elasticity (GPa). The stress until the test piece broke was measured, and the average value of the maximum values was taken as the maximum point stress (MPa). The elongation until the test piece broke was measured, and the maximum value was taken as the tensile elongation at break (%).

<Thermal properties>
The cured film prepared by the above method was cut into a piece of 3 mm width x 30 mm length, and the thermal expansion coefficient and glass transition temperature were measured using a TMA "Q400-1330" manufactured by TA Instruments, under conditions of a temperature rise rate of 10°C/min and a measurement temperature range of 30 to 300°C.

As shown in Table 1, the cured products of the examples have low dielectric constants and low dielectric dissipation factors, and are improved over the comparative examples in which an epoxy resin or a thiol compound was used in combination, particularly in terms of low dielectric dissipation factor.
In particular, Examples 1 and 2, which used a maleimide compound as a curing agent, showed significant improvements in maximum stress and elongation at break.
Moreover, Example 4, which uses a carbodiimide compound as a curing agent, has an improved thermal expansion coefficient and a high glass transition temperature.

The resin compositions of the Examples and Comparative Examples were prepared using the components in the amounts shown in Table 2 (the amounts of each component are expressed in parts by mass). Cured films were prepared in the same manner as above, and various properties were measured. The resin compositions shown in Table 2 contain an inorganic filler.

As shown in Table 2, even when an inorganic filler was used, the cured products of the examples had low dielectric constants and low dielectric dissipation factors, and were improved over the comparative examples in which an epoxy resin was used in combination, particularly in terms of low dielectric dissipation factor.
In particular, Example 5, which used a maleimide compound as the curing agent, showed significant improvements in maximum stress and elongation at break.
Furthermore, Example 7, which uses a carbodiimide compound as a curing agent, has an improved thermal expansion coefficient and a high glass transition temperature.
On the other hand, it can be seen that Comparative Examples 6 and 7, which used an active ester compound or a cyanate compound as a curing agent, had inferior induction properties to those of the Examples.

The curable resin composition of the present invention is highly useful industrially because it can provide a cured product having a low dielectric constant and a low dielectric loss tangent.

Claims (8)

A curable resin composition comprising an episulfide resin and at least one curing agent selected from the group consisting of a maleimide compound and a benzoxazine compound. The curable resin composition according to claim 1, wherein the ratio of the number of moles of functional groups in the curing agent to the number of moles of thiirane groups contained in the episulfide resin is 0.1 or more and 1.5 or less. The curable resin composition of claim 1, further comprising an inorganic filler. A dry film comprising a substrate and a resin layer formed on the substrate, the resin layer comprising the curable resin composition according to any one of claims 1 to 3. A prepreg obtained by impregnating a substrate with the curable resin composition according to any one of claims 1 to 3. A cured product obtained by curing the curable resin composition according to any one of claims 1 to 3. A laminate comprising the cured product of claim 6. An electronic component comprising the cured product according to claim 6.