JP7552114B2 - Resin composition and conductive substrate - Google Patents

Description

The present invention relates to a resin composition and a conductive substrate.

The speed and capacity of signals used in electronic devices such as mobile phones, their base station equipment, network infrastructure equipment such as servers and routers, and large computers are increasing year by year. As a result, the printed wiring boards installed in these electronic devices must be able to handle higher frequencies, and there is a demand for board materials with low dielectric constants and low dielectric tangents that can reduce transmission losses. In recent years, in addition to the electronic devices mentioned above, new systems that handle high-frequency wireless signals in the ITS field (related to automobiles and transportation systems) and in the field of indoor short-range communications have been put into practical use and are planned to be put into practical use as applications that handle such high-frequency signals. It is expected that in the future, there will be an even greater demand for low-transmission-loss board materials for the printed wiring boards installed in these devices.

Materials for printed wiring boards are required to be flame retardant. In light of recent environmental issues, environmentally friendly halogen-free flame retardant laminates for printed wiring boards have been considered (see, for example, Patent Documents 1 and 2).

JP 2008-184591 A JP 2019-123769 A

Printed wiring boards require the use of halogen-free resin materials with improved flame retardancy compared to conventional materials. Therefore, the present invention aims to provide a novel halogen-free, flame-retardant resin composition, and a conductor substrate having a resin layer formed from the resin composition.

One aspect of the present disclosure relates to a resin composition that contains a rubber component, a cross-linking component having an epoxy group, a curing agent, polyphenylene ether, a phosphorus-based flame retardant, a melamine-based flame retardant, and a hindered amine.

Another aspect of the present disclosure relates to a conductive substrate having a resin layer and a conductive foil provided on at least one surface of the resin layer opposite the substrate film, the resin layer including a cured product of the above-mentioned resin composition.

The present invention provides a novel halogen-free, flame-retardant resin composition and a conductive substrate having a resin layer formed from the resin composition.

Several embodiments of the present invention are described in detail below. However, the present invention is not limited to the following embodiments.

[Resin composition]
The resin composition according to the present embodiment contains a rubber component, a crosslinking component having an epoxy group, a curing agent, polyphenylene ether, a phosphorus-based flame retardant, a melamine-based flame retardant, and a hindered amine. Even if the resin composition is halogen-free, it can form a cured product having excellent flame retardancy.

(Rubber component)
The rubber component may contain at least one rubber selected from the group consisting of, for example, acrylic rubber, isoprene rubber, butyl rubber, styrene butadiene rubber, butadiene rubber, acrylonitrile butadiene rubber, silicone rubber, urethane rubber, chloroprene rubber, ethylene propylene rubber, fluororubber, vulcanized rubber, epichlorohydrin rubber, and chlorinated butyl rubber. From the viewpoint of protecting the wiring from damage caused by moisture absorption, etc., a rubber component with low gas permeability may be used. From this viewpoint, the rubber component may contain at least one rubber selected from styrene butadiene rubber, butadiene rubber, and butyl rubber. By using styrene butadiene rubber, the resistance of the resin layer to various chemicals used in the plating process is improved, and the wiring board can be manufactured with a good yield.

Examples of commercially available acrylic rubbers include the "Nipol AR Series" from Nippon Zeon Co., Ltd. and the "Clarity Series" from Kuraray Co., Ltd. Examples of commercially available isoprene rubbers include the "Nipol IR Series" from Nippon Zeon Co., Ltd. Examples of commercially available butyl rubbers include the "BUTYL Series" from JSR Corporation Examples of commercially available styrene butadiene rubbers include the "Dynaron SEBS Series" and "Dynaron HSBR Series" from JSR Corporation, the "Craton D Polymer Series" from Clayton Polymer Japan Co., Ltd., and the "AR Series" from Aronkasei Co., Ltd. Examples of commercially available butadiene rubbers include the "Nipol BR Series" from Nippon Zeon Co., Ltd. Examples of commercially available acrylonitrile butadiene rubbers include the "JSR NBR Series" from JSR Corporation. Examples of commercially available silicone rubbers include the "KMP Series" from Shin-Etsu Silicone Co., Ltd. Commercially available ethylene propylene rubber products include, for example, the "JSR EP Series" from JSR Corporation. Commercially available fluororubber products include, for example, the "Dai-El Series" from Daikin Corporation. Commercially available epichlorohydrin rubber products include, for example, the "Hydrin Series" from Zeon Corporation.

Rubber components can also be produced synthetically. For example, acrylic rubber is obtained by reacting (meth)acrylic acid, (meth)acrylic acid esters, aromatic vinyl compounds, vinyl cyanide compounds, etc.

The rubber component may contain a rubber having a crosslinking group. The use of a rubber having a crosslinking group tends to improve the heat resistance of the elastic resin layer. The crosslinking group may be a reactive group that can promote a reaction that crosslinks the molecular chains of the rubber component. Examples of such a group include reactive groups possessed by crosslinking components having epoxy groups, which will be described later, acid anhydride groups, amino groups, hydroxyl groups, epoxy groups, and carboxyl groups.

The rubber component may contain a rubber having at least one of the crosslinking groups of an acid anhydride group or a carboxyl group. An example of a rubber having an acid anhydride group is a rubber partially modified with maleic anhydride. The rubber partially modified with maleic anhydride is a polymer containing structural units derived from maleic anhydride. An example of a commercially available product of rubber partially modified with maleic anhydride is the styrene-based elastomer "Tufprene 912" manufactured by Asahi Kasei Corporation.

The rubber partially modified with maleic anhydride may be a hydrogenated styrene-based elastomer partially modified with maleic anhydride. Hydrogenated styrene-based elastomers are also expected to have effects such as improved weather resistance. Hydrogenated styrene-based elastomers are elastomers obtained by adding hydrogen to the unsaturated double bonds of a styrene-based elastomer having a soft segment containing an unsaturated double bond. Commercially available hydrogenated styrene-based elastomers partially modified with maleic anhydride include "FG1901" and "FG1924" from Kraton Polymer Japan Co., Ltd., and "Tuftec M1911", "Tuftec M1913", and "Tuftec M1943" from Asahi Kasei Corporation.

The weight average molecular weight (Mw) of the rubber component may be 20,000 to 200,000, 30,000 to 150,000, or 50,000 to 125,000 from the viewpoint of coating properties. Mw here refers to the standard polystyrene equivalent value determined by gel permeation chromatography (GPC).

In the resin composition, the content of the rubber component is preferably 60 to 95% by mass, more preferably 65 to 90% by mass, and even more preferably 70 to 85% by mass, based on the total amount of the rubber component, the cross-linking component having an epoxy group, and the curing agent. When the content of the rubber component is 60% by mass or more, more sufficient elasticity is easily obtained, and the rubber component and the cross-linking component tend to mix well. When the content of the rubber component is 95% by mass or less, the resin layer tends to have particularly excellent properties in terms of adhesion, insulation reliability, and heat resistance. The content of the rubber component in the resin layer may be within the above range based on the mass of the resin layer.

(Cross-linking component having an epoxy group)
A crosslinking component having an epoxy group (hereinafter, sometimes simply referred to as "crosslinking component") is a component that crosslinks during a curing reaction to form a crosslinked polymer. The crosslinking component is not particularly limited as long as it has an epoxy group in the molecule, and can be, for example, a general epoxy resin. The epoxy resin may be monofunctional, bifunctional, or polyfunctional, and is not particularly limited, but a bifunctional or polyfunctional epoxy resin may be used to obtain sufficient curability.

Epoxy resins include bisphenol A type, bisphenol F type, phenol novolac type, naphthalene type, dicyclopentadiene type, cresol novolac type, and other epoxy resins. Epoxy resins modified with an aliphatic chain can impart flexibility. An example of a commercially available aliphatic chain modified epoxy resin is EXA-4816 manufactured by DIC Corporation. From the viewpoints of curability, low tackiness, and heat resistance, phenol novolac type, cresol novolac type, naphthalene type, or dicyclopentadiene type epoxy resins may be selected. These epoxy resins may be used alone or in combination of two or more types.

The combination of a rubber having a maleic anhydride group or a carboxyl group with a compound having an epoxy group (epoxy resin) provides particularly excellent effects in terms of the heat resistance and low moisture permeability of the elastic resin layer, adhesion between the elastic resin layer and the conductive layer, and low tack of the elastic resin layer. Improved heat resistance of the elastic resin layer can suppress deterioration of the elastic resin layer during a heating process such as nitrogen reflow. Low tack of the elastic resin layer allows for easy handling of the conductor board or wiring board.

The resin composition may contain other crosslinking components other than the crosslinking component having an epoxy group, as long as the effect of the present invention is not significantly impaired. From the viewpoint of more sufficiently reducing the dielectric tangent of the elastic resin layer, the content of the other crosslinking components is preferably less than 10 parts by mass per 100 parts by mass of the crosslinking component having an epoxy group.

(Hardening agent)
The curing agent is a compound that itself participates in the curing reaction, and can reduce the dielectric tangent while improving the heat resistance of the resin layer.

The curing agent is not particularly limited, but from the viewpoint of more fully obtaining the effect of improving heat resistance and the effect of reducing the dielectric tangent, an ester-based curing agent can be used. Examples of ester-based curing agents include compounds having one or more highly reactive ester groups in one molecule, such as phenol esters, thiophenol esters, N-hydroxyamine esters, and esters of heterocyclic hydroxy compounds. Examples of commercially available ester-based curing agents include "EPICLON HPC8000-65T", "EPICLON HPC8000-L-65MT", and "EPICLON HPC8150-60T" (all trade names manufactured by DIC Corporation). These can be used alone or in combination of two or more.

During the curing reaction, the ester-based curing agent is thought to react with the crosslinking component as shown in the following formula (I). In the reaction between such an ester-based curing agent and the crosslinking component, no hydroxyl groups are produced, and even if a side reaction occurs, hydroxyl groups are unlikely to be produced. As a result, it is thought that a low dielectric tangent can be achieved.

式中、Ｒ^１、Ｒ^２及びＲ^３はそれぞれ独立に、１価の有機基を示すが、本発明の効果がより十分に得られることから、芳香環を有する１価の有機基であってもよい。

In the formula, R ¹ , R ² and R ³ each independently represent a monovalent organic group, but may be a monovalent organic group having an aromatic ring, since this allows the effects of the present invention to be more fully obtained.

In the resin composition, the total content of the crosslinking component and the curing agent is preferably 5 to 40 mass %, more preferably 10 to 35 mass %, and even more preferably 15 to 30 mass %, based on the total amount of the rubber component, the crosslinking component, and the curing agent. When the total content of the crosslinking component and the curing agent is 5 mass % or more, more sufficient curing is easily obtained, and the resin layer tends to have particularly excellent properties in terms of adhesion, insulation reliability, and heat resistance. When the total content of the crosslinking component and the curing agent is 40 mass % or less, more sufficient elasticity is easily obtained, and the rubber component and the crosslinking component tend to mix well.

In the resin composition, the content ratio of the crosslinking component to the curing agent is preferably in the range of 4:5 to 5:4, in terms of the equivalent ratio of the epoxy groups in the epoxy resin to the ester bonds in the ester-based curing agent. By having the content ratio within the above range, more sufficient curing is easily achieved, and the elastic resin layer tends to have particularly excellent properties in terms of adhesion, insulation reliability, and heat resistance.

(Polyphenylene ether)
Since polyphenylene ether has a structure that is easily carbonized, it can improve the flame retardancy of the resin composition. As the polyphenylene ether, modified polyphenylene ether or a polyphenylene ether derivative may be used. Examples of commercially available polyphenylene ether products include ZYLON S201A and S202A (trade names, manufactured by Asahi Kasei Corporation).

From the viewpoint of the balance between flame retardancy and flexibility, the content of polyphenylene ether may be 1 to 30 parts by mass, 2 to 25 parts by mass, or 4 to 20 parts by mass per 100 parts by mass of the total amount of the rubber component, the cross-linking component, and the curing agent.

(Phosphorus-based flame retardant)
The resin composition contains a phosphorus-based flame retardant, and thus can form a cured product having self-extinguishing properties and excellent flame retardancy. The phosphorus-based flame retardant may be used alone or in combination of two or more kinds.

Examples of phosphorus-based flame retardants include aromatic phosphate esters such as triphenyl phosphate, tricresyl phosphate, trixylenyl phosphate, cresyl diphenyl phosphate, cresyl di-2,6-xylenyl phosphate, and resorcinol bis(diphenyl phosphate); phosphonate esters such as divinyl phenylphosphonate, diallyl phenylphosphonate, and bis(1-butenyl) phenylphosphonate; phosphinate esters such as phenyl diphenylphosphinate, methyl diphenylphosphinate, and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide derivatives; phosphazene compounds such as bis(2-allylphenoxy)phosphazene and dicresylphosphazene; and phosphorus-based flame retardants such as melamine phosphate, melamine pyrophosphate, melamine polyphosphate, melam polyphosphate, ammonium polyphosphate, phosphorus-containing vinylbenzyl compounds, and red phosphorus.

To further enhance the flame retardancy of the resin composition, a metal phosphinate or an aromatic condensed phosphate ester may be used as the phosphorus-based flame retardant. Commercially available phosphorus-based flame retardants include, for example, OP930, OP935, OP945 (trade names, manufactured by Clariant Chemicals Co., Ltd.) and PX-200 (trade name, manufactured by Daihachi Chemical Industry Co., Ltd.).

From the viewpoint of the balance between flame retardancy and flexibility, the content of the phosphorus-based flame retardant may be 1 to 30 parts by mass, 2 to 25 parts by mass, or 4 to 20 parts by mass per 100 parts by mass of the total amount of the rubber component, the cross-linking component, and the curing agent.

(Melamine-based flame retardants)
The melamine-based flame retardant generates an inert gas containing nitrogen, thereby enhancing the flame retardancy of the cured product. The melamine-based flame retardant preferably has a 6-membered ring structure containing nitrogen. As the melamine-based flame retardant, for example, melamine cyanurate, which is a compound of melamine and isocyanuric acid, can be used. Examples of commercially available melamine cyanurate products include MC-4000, MC4500, MC6000 (product names, manufactured by Nissan Chemical Industries Co., Ltd.), and STABIACE MC-20S, MC-5F, MC2010N (product names, manufactured by Sakai Chemical Industry Co., Ltd.).

From the viewpoint of the balance between flame retardancy and flexibility, the content of the melamine-based flame retardant may be 1 to 20 parts by mass, 2 to 18 parts by mass, or 4 to 16 parts by mass per 100 parts by mass of the total amount of the rubber component, the cross-linking component, and the curing agent.

(Hindered amine)
The hindered amine is preferably a compound having an NOR (alkoxyimino) group, and may be a compound having a triazine skeleton or a compound having a piperidine skeleton. Examples of commercially available hindered amines include TINUVIN NOR371, TINUVIN XT850FF, TINUVIN XT855FF, TINUVIN PA123, Flamestab NOR 116FF (manufactured by BASF Japan Ltd., product name), and LA-81 (manufactured by ADEKA Corporation, product name).

From the viewpoint of the balance between flame retardancy and flexibility, the content of the hindered amine may be 1 to 10 parts by mass, 2 to 8 parts by mass, or 4 to 6 parts by mass per 100 parts by mass of the total amount of the rubber component, the crosslinking component, and the curing agent.

(Cure Accelerator)
The resin composition may further contain a curing accelerator. The curing accelerator is a compound that functions as a catalyst for the curing reaction. The curing accelerator may be selected from tertiary amines, imidazoles, organic acid metal salts, phosphorus compounds, Lewis acids, amine complex salts, and phosphines. Among these, imidazole may be used from the viewpoint of storage stability and curing properties of the varnish of the resin composition. When the rubber component contains a rubber partially modified with maleic anhydride, an imidazole compatible with the rubber may be selected.

In the resin composition, the content of the curing accelerator may be 0.1 to 10 parts by mass relative to 100 parts by mass of the total amount of the rubber component, the cross-linking component, and the curing agent. When the content of the curing accelerator is 0.1 parts by mass or more, more sufficient curing tends to be obtained. When the content of the curing accelerator is 10 parts by mass or less, more sufficient heat resistance tends to be obtained. From the above viewpoints, the content of the curing accelerator may be 0.3 to 7 parts by mass, or 0.5 to 5 parts by mass.

In addition to the above components, the resin composition may further contain antioxidants, anti-yellowing agents, ultraviolet absorbers, visible light absorbers, colorants, plasticizers, stabilizers, fillers, leveling agents, etc., as necessary, to the extent that the effects of the present invention are not significantly impaired.

[Conductor substrate]
The conductive substrate according to one embodiment includes a resin layer and a conductive foil provided on at least one surface of the resin layer. The resin layer includes a cured product of the resin composition according to the present embodiment.

(Conductor foil)
The elastic modulus of the conductor foil may be 40 to 300 GPa. When the elastic modulus of the conductor foil is 40 to 300 GPa, the conductor foil is less likely to break due to elongation of the wiring board. From the same viewpoint, the elastic modulus of the conductor foil may be 50 GPa or more or 60 GPa or more, and may be 280 GPa or less or 250 GPa or less. The elastic modulus of the conductor foil here may be a value measured by a resonance method.

The conductor foil can be a metal foil. Examples of the metal foil include copper foil, titanium foil, stainless steel foil, nickel foil, permalloy foil, 42 alloy foil, kovar foil, nichrome foil, beryllium copper foil, phosphor bronze foil, brass foil, nickel silver foil, aluminum foil, tin foil, lead foil, zinc foil, solder foil, iron foil, tantalum foil, niobium foil, molybdenum foil, zirconium foil, gold foil, silver foil, palladium foil, Monel foil, Inconel foil, and Hastelloy foil. From the viewpoint of appropriate elastic modulus, the conductor foil may be selected from copper foil, gold foil, nickel foil, and iron foil. From the viewpoint of wiring formability, the conductor foil may be copper foil. The copper foil can be easily formed into a wiring pattern by photolithography without impairing the properties of the elastic resin layer. From this viewpoint, the conductor foil in this embodiment may form a wiring pattern.

The copper foil is not particularly limited, and for example, electrolytic copper foil and rolled copper foil used for copper-clad laminates and flexible wiring boards can be used. Commercially available electrolytic copper foils include, for example, F0-WS-18 (manufactured by Furukawa Electric Co., Ltd., product name), NC-WS-20 (manufactured by Furukawa Electric Co., Ltd., product name), YGP-12 (manufactured by Nippon Denkai Co., Ltd., product name), GTS-18 (manufactured by Furukawa Electric Co., Ltd., product name), and F2-WS-12 (manufactured by Furukawa Electric Co., Ltd., product name). Rolled copper foils include, for example, TPC foil (manufactured by JX Metals Corporation, product name), HA foil (manufactured by JX Metals Corporation, product name), HA-V2 foil (manufactured by JX Metals Corporation, product name), and C1100R (manufactured by Mitsui Sumitomo Metal Mining Co., Ltd., product name). From the viewpoint of adhesion with the elastic resin layer, copper foil that has been subjected to a roughening treatment may be used. From the viewpoint of folding resistance, rolled copper foil may be used.

The metal foil may have a roughened surface formed by a roughening treatment. In this case, the metal foil is usually provided on the stretchable resin layer with the roughened surface facing the stretchable resin layer. From the viewpoint of adhesion between the stretchable resin layer and the metal foil, the surface roughness Ra of the roughened surface may be 0.1 to 3 μm, or 0.2 to 2.0 μm. To easily form fine wiring, the surface roughness Ra of the roughened surface may be 0.3 to 1.5 μm.

The surface roughness Ra can be measured, for example, using a surface profiler Wyko NT9100 (manufactured by Veeco) under the following conditions.
Measurement conditions: Internal lens: 1x External lens: 50x Measurement range: 0.120 x 0.095 mm
Measurement depth: 10 μm
Measurement method: Vertical scanning interferometry (VSI)

The thickness of the conductor foil is not particularly limited, but may be 1 to 50 μm. When the thickness of the conductor foil is 1 μm or more, the wiring pattern can be formed more easily. When the thickness of the conductor foil is 50 μm or less, etching and handling are particularly easy.

The conductor foil is provided on one or both sides of the resin layer. By providing the conductor foil on both sides of the resin layer, warping due to heating for curing, etc. can be suppressed.

There are no particular limitations on the method for providing the conductor foil, but examples include a method in which a resin composition for forming a resin layer is directly applied to a metal foil, and a method in which a resin layer and a conductor foil are laminated in a laminate film.

(Resin Layer)
The resin layer can be produced by a method including, for example, dissolving or dispersing a rubber component, a crosslinking compound having an epoxy group, a curing agent, polyphenylene ether, a phosphorus-based flame retardant, a melamine-based flame retardant, a hindered amine, and, if necessary, other components, in an organic solvent to obtain a resin varnish, and forming the resin varnish onto a conductor foil or a carrier film by a method described below.

The organic solvent is not particularly limited, but examples thereof include aromatic hydrocarbons such as toluene, xylene, mesitylene, cumene, and p-cymene; cyclic ethers such as tetrahydrofuran and 1,4-dioxane; ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, and 4-hydroxy-4-methyl-2-pentanone; esters such as methyl acetate, ethyl acetate, butyl acetate, methyl lactate, ethyl lactate, and γ-butyrolactone; carbonates such as ethylene carbonate and propylene carbonate; and amides such as N,N-dimethylformamide, N,N-dimethylacetamide, and N-methylpyrrolidone. From the viewpoint of solubility and boiling point, toluene or N,N-dimethylacetamide may be used. These organic solvents may be used alone or in combination of two or more kinds. The solid content (components other than the organic solvent) concentration in the resin varnish may be 20 to 80% by mass.

The carrier film is not particularly limited, but examples thereof include polyesters such as polyethylene terephthalate (PET), polybutylene terephthalate, and polyethylene naphthalate; polyolefins such as polyethylene and polypropylene; and films of polycarbonate, polyamide, polyimide, polyamideimide, polyetherimide, polyethersulfide, polyethersulfone, polyetherketone, polyphenylene ether, polyphenylene sulfide, polyarylate, polysulfone, and liquid crystal polymers. Among these, from the viewpoint of flexibility and toughness, films of polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polypropylene, polycarbonate, polyamide, polyimide, polyamideimide, polyphenylene ether, polyphenylene sulfide, polyarylate, or polysulfone may be used as the carrier film.

The thickness of the carrier film is not particularly limited, but may be 3 to 250 μm. If the thickness of the carrier film is 3 μm or more, the film strength is sufficient, and if the thickness of the carrier film is 250 μm or less, sufficient flexibility is obtained. From the above viewpoints, the thickness may be 5 to 200 μm, or 7 to 150 μm. From the viewpoint of improving the peelability from the resin layer, a film in which the carrier film has been subjected to a release treatment using a silicone-based compound, a fluorine-containing compound, or the like may be used as necessary.

If necessary, a protective film may be attached onto the resin layer to form a three-layer resin film consisting of a carrier film, a resin layer, and a protective film.

The protective film is not particularly limited, and examples thereof include films of polyesters such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate; and polyolefins such as polyethylene and polypropylene. Among these, from the viewpoint of flexibility and toughness, films of polyesters such as polyethylene terephthalate, and polyolefins such as polyethylene and polypropylene may be used as the protective film. From the viewpoint of improving the peelability from the elastic resin layer, the protective film may be subjected to a release treatment using a silicone-based compound, a fluorine-containing compound, or the like.

The thickness of the protective film may be varied as appropriate depending on the desired flexibility, but may be 10 to 250 μm. A thickness of 10 μm or more tends to provide sufficient film strength, while a thickness of 250 μm or less tends to provide sufficient flexibility. From the above standpoint, the thickness may be 15 to 200 μm, or 20 to 150 μm.

Any method may be used to obtain a laminate (conductor substrate) having a resin layer and conductor foil, including a method of applying a varnish of a resin composition to form a resin layer onto the conductor foil, and a method of laminating a conductor foil onto a resin layer formed on a carrier film using a vacuum press, laminator, or the like. The resin layer can be formed by heating the resin composition to promote a crosslinking reaction (curing reaction) of the crosslinking component.

The resin layer on the carrier film may be laminated onto the conductor foil by any method, including a roll laminator, vacuum laminator, vacuum press, etc. From the viewpoint of production efficiency, molding may be performed using a roll laminator or vacuum laminator.

The thickness of the resin layer is not particularly limited, but may be 5 to 1000 μm, 10 to 500 μm, 20 to 200 μm, or 30 to 100 μm, from the viewpoint of the balance between the flame retardancy and flexibility of the resin film.

The elastic modulus (tensile elastic modulus) of the resin layer may be 0.1 MPa or more and 1000 MPa or less. When the elastic modulus is 0.1 MPa or more and 1000 MPa or less, the handleability and flexibility as a substrate tend to be particularly excellent. From this viewpoint, the elastic modulus may be 0.3 MPa or more and 100 MPa or less, or 0.5 MPa or more and 50 MPa or less.

The breaking elongation of the resin layer may be 100% or more. When the breaking elongation is 100% or more, sufficient elasticity tends to be easily obtained. From this viewpoint, the breaking elongation may be 150% or more, 200% or more, 300% or more, or 500% or more. The upper limit of the breaking elongation is not particularly limited, but is usually about 1000% or less.

The dielectric loss tangent (Df) of the resin layer may be 0.004 or less, 0.0035 or less, 0.003 or less, or 0.0025 or less, from the viewpoint of sufficiently reducing the transmission loss of the wiring pattern provided on the resin layer. The lower limit of the dielectric loss tangent is not particularly limited, but is usually about 0.0005 or more.

The dielectric constant (Dk) of the resin layer may be 3.0 or less, 2.8 or less, or 2.5 or less, from the viewpoint of sufficiently reducing the transmission loss of the wiring pattern provided on the resin layer.

The above describes preferred embodiments of the present disclosure, but these are merely examples for the purpose of explaining the present invention, and are not intended to limit the scope of the present invention to these embodiments alone. The present invention can be implemented in various forms different from the above embodiments without departing from the spirit of the present invention.

The present invention will be described in more detail with reference to the following examples. However, the present invention is not limited to these examples.

[Example 1]
To a polyvinyl chloride bottle, 80 parts by mass (non-volatile content) of maleic anhydride modified hydrogenated styrene ethylene butadiene rubber (manufactured by KRATON Corporation, product name "FG1924", styrene ratio: 1.3%), 10.9 parts by mass (non-volatile content) of dicyclopentadiene type epoxy resin (manufactured by DIC Corporation, product name "EPICLON HP7200H"), 9.1 parts by mass (non-volatile content) of an ester-based curing agent (manufactured by DIC Corporation, product name "HPC-8150"), and 400 parts by mass of toluene were added and mixed to obtain a base resin with a non-volatile content of 25% by mass. Next, 15 parts by mass of polyphenylene ether (PPE, manufactured by Asahi Kasei Corporation, trade name "S202A"), 20 parts by mass of a phosphorus-based flame retardant (manufactured by Clariant Chemicals Co., Ltd., trade name "OP935"), 20 parts by mass of a melamine-based flame retardant (melamine cyanurate, manufactured by Sakai Chemical Industry Co., Ltd., trade name "STABIACE MC-20S"), 5 parts by mass of a hindered amine (manufactured by BASF Japan Ltd., trade name "Flamestab NOR 116FF"), and 3 parts by mass of 1-benzyl-2-methylimidazole (manufactured by Shikoku Chemical Industry Co., Ltd., trade name "1B2MZ") were added to the base resin and mixed using a planetary centrifugal mixer (manufactured by Thinky Corporation, AR-100) to prepare a resin varnish.

[Comparative Examples 1 to 8]
Resin varnishes were prepared in the same manner as in Example 1, except that the amounts of PPE, phosphorus-based flame retardant, melamine-based flame retardant, and hindered amine added were changed to the amounts (parts by mass) shown in Table 1.

[evaluation]
(Preparation of resin film)
A release-treated polyethylene terephthalate (PET) film (manufactured by Teijin Film Solutions Co., Ltd., product name "Purex A31", thickness 25 μm) was prepared as a carrier film. The above-mentioned resin varnish was applied to the release-treated surface of this PET film using a knife coater (manufactured by Yasui Seiki Co., Ltd., product name "SNC-350"). The coating film was dried by heating at 80 ° C. for 20 minutes in a dryer (manufactured by Futaba Scientific Co., Ltd., product name "MSO-80TPS") to form a resin layer having a thickness of 80 μm. A release-treated PET film identical to the carrier film was attached to the formed resin layer as a protective film with the release-treated surface facing the resin layer side, to obtain a resin film.

(Combustion test)
After peeling off the carrier film and the protective film from the resin film, the resin layer was cured by heating at 180°C for 60 minutes in a dryer (manufactured by Futaba Scientific Co., Ltd., product name "MSO-80TPS") to prepare a sample for a combustion test. The sample for the combustion test was subjected to a UL94V test. The results are shown in Table 1.

Claims (5)

The rubber composition contains a rubber component, a cross-linking component having an epoxy group, an ester-based curing agent, a polyphenylene ether, a phosphorus-based flame retardant, a melamine-based flame retardant, and a hindered amine,
a content of the polyphenylene ether is 1 to 30 parts by mass, a content of the phosphorus-based flame retardant is 1 to 30 parts by mass, a content of the melamine-based flame retardant is 1 to 20 parts by mass, and a content of the hindered amine is 1 to 10 parts by mass, relative to 100 parts by mass of a total amount of the rubber component, the crosslinking component , and the curing agent. The resin composition according to claim 1, wherein the phosphorus-based flame retardant comprises a metal phosphinate or an aromatic condensed phosphate ester. The resin composition according to claim 1 or 2, wherein the melamine-based flame retardant includes melamine cyanurate. The resin composition according to any one of claims 1 to 3, wherein the rubber component contains at least one rubber selected from the group consisting of acrylic rubber, isoprene rubber, butyl rubber, styrene butadiene rubber, butadiene rubber, acrylonitrile butadiene rubber, silicone rubber, urethane rubber, chloroprene rubber, ethylene propylene rubber, fluororubber, vulcanized rubber, epichlorohydrin rubber, and chlorinated butyl rubber. A resin layer and a conductor foil provided on the resin layer,
A conductive substrate, wherein the resin layer comprises a cured product of the resin composition according to any one of claims 1 to 4.