Conductive plastic products

Abstract

The invention proposes a conductive resin composition capable of producing a cured product with superior bond strength and electrical conductivity even when cured at low temperatures such as around 80°C. The conductive resin composition contains components (A) to (C), where component (C) contains (C-1) and (C-2), and component (A) is epoxy resin, component (B) is a conductive particle, component (C) is a polyamine-based latent curing agent, (C-1) is a polyamine-based latent curing agent with a softening point from 50 to 129°C, and (C-2) is a polyamine-based latent curing agent with a softening point from 130 to 180°C.

Description

Conductive resin composition

[0001] The present invention relates to an electrically conductive resin composition that can be cured at low temperatures to give a cured product having excellent adhesive strength and electrical conductivity.

[0002] Conductive resin compositions have traditionally been used for fixing electrical and electronic components, such as smartphones and mobile electronic devices, and for grounding. In recent years, as electronic components have become smaller, the amount of conductive resin composition applied has decreased, creating a demand for better adhesive strength and conductivity so that even a small amount of resin can perform well. Furthermore, because plastics are often used in electronic components these days, curing at low temperatures, such as around 80°C, is required. Examples of conductive resin compositions that cure at low temperatures include those disclosed in JP 2000-230112 A and JP 2017-214548 A.

[0003] However, when curing at a low temperature such as about 80°C, the thermal energy required for the reaction is insufficient, resulting in insufficient curing and a deterioration in the adhesive strength and electrical conductivity of the cured product.

[0004] The present invention has been made in view of the above circumstances, and aims to provide a conductive resin composition that can be cured at low temperatures and that gives a cured product having excellent adhesive strength and electrical conductivity. The present invention also provides a cured product obtained by curing the conductive resin composition. As a result of extensive research to achieve the above object, the inventors discovered a method for producing a conductive resin composition that has excellent adhesive strength and electrical conductivity when cured at low temperatures, and have completed the present invention.

[0005] The gist of the present invention is described below. [1] A conductive resin composition comprising the following components (A) to (C), wherein component (C) comprises (C-1) and (C-2): Component (A): epoxy resin; Component (B): conductive particles; Component (C): polyamine-based latent curing agent; (C-1): polyamine-based latent curing agent having a softening point of 50 to 129°C; (C-2): polyamine-based latent curing agent having a softening point of 130 to 180°C. [2] The conductive resin composition according to [1] or [2], wherein component (A) comprises a bisphenol-type epoxy resin. [3] The conductive resin composition according to any one of [1] to [3], wherein component (A) comprises (A-1) an epoxy resin having two or more epoxy groups per molecule and (A-2) an epoxy resin having one epoxy group per molecule. [4] The conductive resin composition according to any one of [1] to [4], wherein component (B) comprises (B-1) crystalline conductive particles. [5] The conductive resin composition according to [4], wherein the component (B) comprises (B-1) crystalline conductive particles and (B-2) amorphous conductive particles. [6] The conductive resin composition according to any one of [1] to [5], wherein the component (C) is an aliphatic polyamine-based latent curing agent. [7] The conductive resin composition according to any one of [1] to [6], wherein the component (C) is an adduct-modified polyamine-based latent curing agent. [8] The conductive resin composition according to any one of [1] to [7], wherein the component (C) comprises only (C-1) and (C-2). [9] The conductive resin composition according to any one of [1] to [8], wherein the mass ratio of (C-1) to (C-2) is 10:90 to 90:10.

[10] A cured product obtained by curing the conductive resin composition according to any one of [1] to [9].

[0006] The present invention will be described in detail below. In this specification, "X to Y" is used to mean that the numerical values ​​(X and Y) before and after it are included as the lower and upper limits, respectively, and means "X or more and Y or less." In this specification, the term "(meth)acrylic" means both acrylic and methacrylic. In addition, "A and / or B" means that A and B are included individually and in combination.

[0007] The present invention provides a conductive resin composition comprising the following components (A) to (C), wherein component (C) comprises (C-1) and (C-2): Component (A): epoxy resin Component (B): conductive particles Component (C): polyamine-based latent curing agent (C-1): polyamine-based latent curing agent having a softening point of 50 to 129°C (C-2): polyamine-based latent curing agent having a softening point of 130 to 180°C The conductive resin composition of the present invention having such a configuration can give a cured product having excellent adhesive strength and conductivity when cured at low temperatures.

[0008] <Component (A)> The component (A) used in the present invention is an epoxy resin.

[0009] Component (A) may be either a solid or a liquid epoxy resin having one or more epoxy groups per molecule, and is not particularly limited thereto. However, in terms of excellent curing properties and workability, an epoxy resin having two or more epoxy groups per molecule is preferred, and a liquid epoxy resin is particularly preferred. The upper limit of the number of epoxy groups in an epoxy resin having two or more epoxy groups per molecule is, for example, four or less, or three or less. Specific examples of component (A) include bisphenol-type epoxy resins, hydrogenated bisphenol-type epoxy resins, 1,2-butanediol diglycidyl ether, 1,3-butanediol diglycidyl ether, 1,4-butanediol diglycidyl ether, (poly)ethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, 2,3-butanediol diglycidyl ether, 1,5-pentanediol diglycidyl ether, 1,6-hexanediol diglycidyl ether, and neopentyl glycol diglycidyl. Examples of suitable epoxy resins include alkylene glycol epoxy resins such as ether and 1,4-cyclohexanedimethanol diglycidyl ether, novolac epoxy resins such as phenol novolac epoxy resins and cresol novolac epoxy resins; glycidyl amine compounds such as N,N-diglycidyl-4-glycidyloxyaniline, 4,4'-methylenebis(N,N-diglycidylaniline), tetraglycidyldiaminodiphenylmethane, and tetraglycidyl-m-xylylenediamine; and naphthalene epoxy resins having four glycidyl groups. These may be used alone or in combination of two or more types. However, from the viewpoint of excellent conductivity, it is preferable to include a bisphenol epoxy resin, and it is preferable to include a bisphenol epoxy resin having two or more epoxy groups. Furthermore, the silane coupling agent described below is not treated as component (A) but is treated as an optional component.

[0010] The bisphenol epoxy resin is not particularly limited as long as it is an epoxy resin having a bisphenol skeleton, but examples include bisphenol A epoxy resin, bisphenol F epoxy resin, bisphenol S epoxy resin, bisphenol AD ​​epoxy resin, urethane-modified bisphenol epoxy resin, rubber-modified bisphenol epoxy resin, and polyoxyalkylene-modified bisphenol epoxy resin. These may be used alone or in combination of two or more. However, from the viewpoint of excellent conductivity and workability, it is preferable to use a combination of bisphenol A epoxy resin and bisphenol F epoxy resin, and it is particularly preferable for the mass ratio of bisphenol A epoxy resin to bisphenol F epoxy resin to be 25:75 to 75:25 or 35:65 to 65:35. The mass of the bisphenol A epoxy resin may be the same as the mass of the bisphenol F epoxy resin, or may be greater or less than the mass of the bisphenol F epoxy resin.

[0011] Commercially available epoxy resins include, but are not limited to, jER828, 1001, 801, 806, 807, YX4000, YX8000, and YX8034 (manufactured by Mitsubishi Chemical Corporation), Epicron 830, 850, EXA-830CRP, EXA-830LVP, EXA-850CRP, and EXA-835LV (manufactured by DIC Corporation), ADEKA RESIN EP-4100, EP-4000, EP-4000S, EP-4080, EP-4085, EP-4088, EPU-6, EPU-7N, EPR-4023, EPR-1309, and EP-4920 (manufactured by ADEKA Corporation), and TEPIC (manufactured by Nissan Chemical Industries, Ltd.). Examples of epoxy resin components that can be used include epoxy resin components such as KF-101, KF-1001, KF-105, X-22-163B, and X-22-9002 (manufactured by Shin-Etsu Chemical Co., Ltd.), Denacol EX411, 314, 201, 212, and 252 (manufactured by Nagase ChemteX Corporation), DER-331, 332, 334, 431, and 542 (manufactured by The Dow Chemical Company), YH-434, YH-434L, and ST-3000 (manufactured by Nippon Steel Chemical & Material Co., Ltd.), Rikaresin HBE-100 (manufactured by New Japan Chemical Co., Ltd.), Epolite 4000 (manufactured by Kyoeisha Chemical Co., Ltd.), and Cureduct L-07N (manufactured by Shikoku Chemicals Corporation). These may be used alone or in combination of two or more.

[0012] It is preferable that the component (A) be a combination of (A-1) an epoxy resin having two or more epoxy groups per molecule and (A-2) an epoxy resin having one epoxy group per molecule. Although the reason for this is not clear, the combined use of (A-1) and (A-2) not only makes it possible to adjust the viscosity but also to lower the connection resistance, thereby enabling a conductive resin composition to be obtained that has low viscosity and good conductivity. (A-2) is not particularly limited, but examples thereof include methyl glycidyl ether, ethyl glycidyl ether, butyl glycidyl ether, isobutyl glycidyl ether, phenyl glycidyl ether, 2-ethylhexyl glycidyl ether, decyl glycidyl ether, stearyl glycidyl ether, allyl glycidyl ether, 2-methyloctyl glycidyl ether, methoxypolyethylene glycol monoglycidyl ether, ethoxypolyethylene glycol monoglycidyl ether, butoxypolyethylene glycol monoglycidyl ether, phenoxypolyethylene glycol monoglycidyl ether, p-tert-butylphenyl glycidyl ether, sec-butylphenyl glycidyl ether, n-butylphenyl glycidyl ether, phenylphenol glycidyl ether, cresyl glycidyl ether, dibromocresyl glycidyl ether, and neodecanoic acid glycidyl ester. These may be used alone or in combination of two or more. Furthermore, p-tert-butylphenyl glycidyl ether and / or neodecanoic acid glycidyl ester are preferred due to their superior storage stability and electrical conductivity. In addition, from the viewpoint of suppressing outgassing during heating, it is preferable that the boiling point of (A-2) is 290° C. or higher. The boiling point of (A-2) may be 450° C. or lower, 400° C. or lower, 350° C. or lower, or 300° C. or lower. The boiling point of (A-2) may be 290° C. or higher and 450° C. or lower.

[0013] Commercially available products of (A-2) include ED-509S (manufactured by ADEKA CORPORATION), EPIOL (registered trademark) TB (manufactured by NOF CORPORATION), and CARDURA E10P (manufactured by MOMENTIVE), but are not limited thereto.

[0014] When (A-1) and (A-2) are used in combination, the mass ratio of each is preferably 99:1 to 50:50, more preferably 95:5 to 60:40, and most preferably 90:10 to 70:30. By using a mass ratio in the range of 99:1 to 50:50, a conductive resin composition having excellent storage stability and conductivity can be obtained.

[0015] <Component (B)> The component (B) used in the present invention is a conductive particle. The material and shape of the component (B) are not limited as long as it exhibits conductivity. For example, it can be appropriately selected from metal particles composed of one or more metals selected from gold, silver, copper, nickel, palladium, platinum, tin, bismuth, etc., alloy particles composed of a combination of these metals, or particles coated with a coating layer of the above metals. These may be used alone or in combination. However, from the viewpoints of conductivity and cost, silver particles or particles coated with a silver coating layer are preferred. The shape of the component (B) may be spherical, irregular, flaky, filamentous (needle), or dendritic. These may be used alone or in combination. The component (B) may also be surface-treated with a lubricant. Saturated fatty acids and / or unsaturated fatty acids can be used as the lubricant. Examples include capric acid, undecylic acid, lauric acid, tridecylic acid, myristic acid, pentadecylic acid, palmitic acid, margaric acid, stearic acid, linolenic acid, palmitoleic acid, oleic acid, malonic acid, and hexanoic acid, among which untreated, stearic acid, and oleic acid-treated acids are preferred in terms of excellent adhesive strength and conductivity when cured at low temperatures. These may be used alone or in combination of two or more.

[0016] The component (B) preferably contains (B-1) crystalline conductive particles. Crystalline conductive particles are produced by known production methods, such as the production method disclosed in JP 2014-196527 A, which is generally referred to as a reduction method, in which conductive particles are produced by growing a single crystal. The crystalline conductive particles are thin flake-shaped particles with a polygonal plate shape, such as a triangular plate shape, with a substantially uniform overall flake thickness, and have a generally smooth surface. Silver particles are preferred because of their excellent conductivity when cured at low temperatures.

[0017] The commercially available product of (B-1) is not particularly limited, but examples thereof include N300, M612, M13, M27, and LM1 (manufactured by Tokusen Kogyo Co., Ltd.).

[0018] The (B) component preferably uses a combination of (B-1) crystalline conductive particles and (B-2) amorphous conductive particles. When (B-1) and (B-2) are used together, the weight ratio is preferably 10:90 to 90:10, more preferably 10:90 to 75:25, and most preferably 15:85 to 50:50. By using a ratio in the range of 10:90 to 90:10, a conductive resin composition with excellent conductivity when cured at low temperatures can be obtained. When (B-1) and (B-2) are used together, the weight ratio may be 20:80 to 45:55, or 25:75 to 45:55.

[0019] The shape of (B-2) is not particularly limited, but as mentioned above, examples include spherical, amorphous, flaky (scale-like), filamentous (needle-like), and dendritic shapes. These may be used alone or in combination of two or more types, but it is preferable to include flaky and / or spherical conductive particles in terms of excellent conductivity. As an example, amorphous conductive particles refer to flaky conductive particles obtained in a pulverization process or conductive particles in which the surface of organic or inorganic particles is coated with a conductive metal. In terms of excellent conductivity when cured at low temperatures, (B-2) is preferably silver particles or particles coated with silver.

[0020] The average particle size of component (B) is preferably in the range of 0.01 to 100 μm, more preferably in the range of 0.1 to 50 μm, even more preferably in the range of 0.1 to 30 μm, and most preferably in the range of 0.3 to 10 μm, where the average particle size of component (B) is the particle size at a cumulative volume ratio of 50% (D50) in the particle size distribution determined by laser diffraction scattering.

[0021] The average particle size of (B-1) is preferably in the range of 0.01 to 30 μm, more preferably in the range of 0.1 to 20 μm, and most preferably in the range of 0.3 to 10 μm, from the viewpoint of excellent conductivity. Here, the average particle size of (B-1) is the particle size at a cumulative volume ratio of 50% (D50) in the particle size distribution determined by a laser diffraction scattering method.

[0022] The thickness (average thickness, T) of (B-1) is not particularly limited, but from the viewpoint of achieving superior conductivity of the cured product, it is preferably 1 nm or more and less than 1,000 nm, more preferably 10 to 200 nm, even more preferably 30 to 150 nm, and particularly preferably 60 to 100 nm. The thickness of (B-1) can be confirmed using a scanning electron microscope (SEM). More specifically, the thickness can be obtained by randomly selecting 100 plate-shaped silver particles, measuring the thickness of each, and calculating the average value.

[0023] The average particle size of (B-2) is preferably in the range of 0.1 to 50 μm, more preferably in the range of 0.1 to 30 μm, even more preferably in the range of 0.5 to 20 μm, and most preferably in the range of 0.5 to 10 μm. Each average particle size is the particle size at a cumulative volume ratio of 50% (D50) in the particle size distribution determined by a laser diffraction scattering method.

[0024] The content of the component (B) is preferably 50 to 500 parts by mass, more preferably 100 to 400 parts by mass, and most preferably 150 to 350 parts by mass, per 100 parts by mass of the component (A). When the content is 50 parts by mass or more, a conductive resin composition having excellent conductivity, such as low connection resistance and low volume resistivity, can be obtained, and when the content is 500 parts by mass or less, a conductive resin composition having excellent workability can be obtained.

[0025] The content of component (B) is preferably 40 to 95 mass % of the entire conductive resin adhesive, more preferably 50 to 90 mass %, and most preferably 60 to 85 mass %. By containing component (B) in the above range, a conductive resin adhesive having excellent workability and conductivity when cured at low temperatures can be obtained.

[0026] <Component (C)> The component (C) used in the present invention is a latent curing agent containing (C-1) a polyamine-based latent curing agent having a softening point of 50 to 129°C and (C-2) a polyamine-based latent curing agent having a softening point of 130 to 180°C. The curing agent contained in the conductive resin composition according to the present invention may contain a curing agent other than component (C). However, from the viewpoint of electrical conductivity and adhesive strength, the total amount of (C-1) and (C-2) in the curing agent is preferably 50 mass% or more, more preferably 80 mass% or more, and most preferably contains only (C-1) and (C-2). The softening point in the present invention is a value measured using a measurement method in accordance with the softening point measurement method of JIS K 7234:1986.

[0027] Examples of the latent curing agent include an adduct-modified latent curing agent. The adduct-modified latent curing agent is not particularly limited, and examples thereof include a reaction product (urea adduct-modified latent curing agent) obtained by reacting an amine compound with an isocyanate compound or a urea compound, or a reaction product (epoxyamine adduct-modified latent curing agent) obtained by reacting an amine compound with an epoxy compound. Examples of the polyamine structure include aliphatic polyamines and aromatic polyamines, but aliphatic polyamines are preferred from the viewpoint of curability. In other words, an adduct-modified aliphatic polyamine-based latent curing agent is preferred.

[0028] Component (C) may be either a liquid or a solid, but is preferably a solid from the viewpoint of storage stability, and more preferably a powder from the viewpoint of dispersibility. The average particle size of the powder is preferably in the range of 0.1 to 30 μm, more preferably in the range of 0.5 to 20 μm, and most preferably in the range of 1 to 10 μm. Here, the average particle size of component (C) is the particle size at a cumulative volume ratio of 50% (D50) in the particle size distribution determined by laser diffraction scattering.

[0029] The (C-1) is a polyamine-based latent curing agent having a softening point of 50 to 129° C. The powder (C-1) preferably has a softening point of 125° C. or less in order to have excellent low-temperature curing properties, and preferably has a softening point of 50° C. or higher, more preferably 80° C. or higher in order to have excellent storage properties. In other words, the softening point of (C-1) is preferably 50 to 125° C., more preferably 80 to 125° C.

[0030] The (C-2) is a polyamine-based latent curing agent having a softening point of 130 to 180° C. The powder (C-2) preferably has a softening point of 130° C. or higher because of its excellent electrical conductivity, and preferably has a softening point of 180° C. or lower because of its excellent low-temperature curing property, and more preferably has a softening point of 150° C. or lower. In other words, the softening point of (C-2) is preferably 130 to 180° C., and more preferably 130 to 150° C.

[0031] The commercially available product of the component (C) is not particularly limited, but examples of (C-1) include Fujicure FXE-1000, FXR-1020, FXR-1081, and 1061 (manufactured by T&K TOKA Corporation). Examples of (C-2) include Fujicure FXE-1030 (manufactured by T&K TOKA Corporation). These may be used alone or in combination of two or more.

[0032] The content of the component (C), i.e., the total amount of (C-1) and (C-2), is preferably 1 to 100 parts by mass, more preferably 10 to 50 parts by mass, and most preferably 15 to 40 parts by mass, per 100 parts by mass of the component (A). When the content is 1 part by mass or more, a conductive resin composition having excellent low-temperature curing properties is obtained, and when the content is 100 parts by mass or less, a conductive resin composition having excellent storage stability is obtained.

[0033] The weight ratio of (C-1) to (C-2) is preferably 10:90 to 90:10, more preferably 15:85 to 85:15, even more preferably 20:80 to 80:20, still more preferably 20:80 to 60:40, and most preferably 20:80 to 50:50. A weight ratio of 10:90 to 90:10 allows for the production of a cured product with excellent electrical conductivity and adhesive strength.

[0034] <Other Components> The conductive resin composition of the present invention preferably contains substantially no organic solvent. If the conductive resin composition contains an organic solvent, the organic solvent may dissolve component (C), resulting in a deterioration in storage stability or separation of the organic solvent, which may affect physical properties. "Substantially free of organic solvent" means that the organic solvent is not intentionally included as a compound in the conductive resin composition. Specifically, the content of the organic solvent relative to the entire conductive resin composition is 1% by mass or less, preferably 0.5% by mass or less, and more preferably 0.1% by mass or less. If the content is 1% by mass or less, deterioration in storage stability or separation will not occur.

[0035] Examples of the organic solvent include aromatic organic solvents such as toluene and xylene; aliphatic organic solvents such as n-hexane; alicyclic organic solvents such as cyclohexane, methylcyclohexane, and ethylcyclohexane; ketone organic solvents such as acetone and methyl ethyl ketone; alcohol organic solvents such as methanol and ethanol; ester organic solvents such as ethyl acetate and butyl acetate; and propylene glycol ether organic solvents such as propylene glycol methyl ether, propylene glycol ethyl ether, and propylene glycol t-butyl ether; and fluorine-based solvents.

[0036] In addition to the above components, the conductive resin composition of the present invention may optionally contain various additives as needed, provided that the effects of the present invention are not impaired. Examples of additives include storage stabilizers, rubber particles, silane coupling agents, plasticizers, fillers (excluding component (B)), tackifiers, organic or inorganic pigments, rust inhibitors, antifoaming agents, dispersants, surfactants, viscoelasticity modifiers, thickeners, and organometallic complexes. The conductive resin composition of the present invention may not contain additives other than storage stabilizers and plasticizers.

[0037] The conductive resin composition of the present invention may contain a storage stabilizer. The storage stabilizer is not particularly limited as long as it improves storage stability. Examples of storage stabilizers that may be used include borate ester compounds, phosphoric acid, alkyl phosphate esters, p-toluenesulfonic acid, and methyl p-toluenesulfonate. Examples of borate ester compounds include trimethyl borate, triethyl borate, tri-n-propyl borate, triisopropyl borate, tributyl borate, trihexyl borate, tri-n-octyl borate, tris(2-ethylhexyloxy)borane, triphenylborate, trimethoxyboroxine, and 2,2'-(carbonylbisoxy)bis(1,3,2-dioxaborolane-4,5-dione). Commercially available and / or synthetic products may be used as the storage stabilizer. Examples of commercially available borate ester compounds include the storage stabilizer component of "Cureduct (registered trademark) L-07N" (manufactured by Shikoku Chemicals Corporation). Examples of alkyl phosphate esters that can be used include, but are not limited to, trimethyl phosphate and tributyl phosphate. Storage stabilizers may be used alone or in combination. Considering storage stability, phosphoric acid, borate ester compounds, trimethoxyboroxine, and methyl p-toluenesulfonate are preferred. Storage stabilizers dispersed in epoxy resins or plasticizers may also be used. When adding a storage stabilizer, if a mixture containing the storage stabilizer and an epoxy resin is added, the epoxy resin is preferably a bisphenol-type epoxy resin, and the plasticizer may be a phenolic resin. Commercially available phenolic resins include, for example, the plasticizer component of Cureduct L-07N (manufactured by Shikoku Chemicals Corporation).

[0038] The content of the storage stabilizer is preferably 0.01 to 10 parts by mass, more preferably 0.02 to 7 parts by mass, and even more preferably 0.05 to 5 parts by mass, per 100 parts by mass of component (A). An amount of 0.01 part by mass or more ensures excellent storage stability, while an amount of 10 parts by mass or less does not inhibit curing. The content of the plasticizer is preferably 0.01 to 10 parts by mass, more preferably 0.02 to 7 parts by mass, and even more preferably 0.05 to 5 parts by mass, per 100 parts by mass of component (A).

[0039] The conductive resin composition of the present invention may contain a filler (excluding component (B)). The filler may be an inorganic filler such as alumina powder, calcium carbonate powder, talc powder, silica powder, or fumed silica powder, or an organic filler such as rubber particles. Although the reason for this is unclear, it is preferable to contain rubber particles because this allows for the production of a conductive resin composition with excellent conductivity.

[0040] The rubber particles referred to in the present invention are particles containing a layer exhibiting rubber elasticity. The rubber particles may be particles consisting of only one layer exhibiting rubber elasticity, or may be core-shell particles, which are particles with a multilayer structure exhibiting rubber elasticity. However, core-shell particles are preferred because they have excellent volume resistivity. Rubber particles dispersed in an epoxy resin in advance may also be used. For example, butadiene rubber, acrylic rubber, silicone rubber, butyl rubber, olefin rubber, styrene rubber, NBR, SBR, IR, EPR, etc. may be used. These may be used alone or in combination of two or more.

[0041] The core-shell particles are fine particles whose core (nucleus) and shell (wall) portions are made of polymers with different properties. In producing preferred powder particles for use in the present invention, the core portion is first produced by polymerizing a polymerizable monomer. Examples of the polymerizable monomer include (meth)acrylate monomers such as n-propyl (meth)acrylate, n-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and n-decyl (meth)acrylate; aromatic vinyl compounds such as styrene, vinyltoluene, and α-methylstyrene; vinyl cyanide compounds such as acrylonitrile and methacrylonitrile; vinylidene cyanide; 2-hydroxyethyl (meth)acrylate, 3-hydroxybutyl (meth)acrylate, 2-hydroxyethyl fumarate, hydroxybutyl vinyl ether, monobutyl maleate, and butoxyethyl methacrylate. Further examples include crosslinkable monomers having two or more reactive groups such as ethylene glycol di(meth)acrylate, butylene glycol di(meth)acrylate, trimethylolpropane di(meth)acrylate, trimethylolpropane tri(meth)acrylate, hexanediol di(meth)acrylate, hexanediol tri(meth)acrylate, oligoethylene di(meth)acrylate, oligoethylene tri(meth)acrylate, aromatic divinyl monomers such as divinylbenzene, triallyl trimellitate, triallyl isocyanate, etc., and these can be used alone or in combination of two or more different types. Next, the polymer particles thus obtained are used as cores, and a second polymerization is carried out in which a polymerizable monomer is polymerized to form a shell made of a polymer having a melting point above room temperature. The polymerizable monomer used here can be selected from the same polymerizable monomers as those used to obtain the cores. Preferred examples of the polymerizable monomer used as the shell material include (meth)acrylates having an alkyl group with 1 to 4 carbon atoms, such as ethyl (meth)acrylate, n-butyl acrylate, methyl methacrylate, and butyl methacrylate.

[0042] The core-shell particles may be synthesized as described above, or commercially available products may be used. Examples of commercially available core-shell particles include, but are not limited to, Paraloid EXL-2655 (manufactured by Kureha Chemical Industry Co., Ltd.) made of a butadiene-alkyl methacrylate-styrene copolymer, Stafiloid AC-3355, Stafiloid AC3364, Stafiloid TR-2105, Stafiloid TR-2102, Stafiloid TR-2122, Stafiloid IM-101, and Stafiloid IM-102 made of an acrylic acid ester-methacrylic acid ester copolymer. Examples of suitable compounds that can be used include Staphyloid IM-203, Staphyloid IM-301, Staphyloid IM-401, and Staphyloid IM-406, Staphyloid IM-601 made of an acrylic acid ester-acrylonitrile-styrene copolymer, Zefiac F-351G (manufactured by Aica Kogyo Co., Ltd.) made of a polymethacrylic acid ester polymer, and Paraloid EXL-2314, EXL-2611, and EXL-3387 (manufactured by Dow Chemical Japan Co., Ltd.). These compounds may be used alone or in combination of two or more.

[0043] The particle size of the rubber particles is preferably 0.01 to 10 μm, and particularly preferably 0.05 to 5 μm. By keeping the particle size within this range, an increase in viscosity can be suppressed and a conductive resin composition with excellent conductivity can be obtained.

[0044] The content of the rubber particles is preferably 0.01 to 20 parts by mass, more preferably 0.03 to 10 parts by mass, and most preferably 0.05 to 5 parts by mass, per 100 parts by mass of component (A). By being in this range, a conductive resin composition with excellent conductivity can be obtained.

[0045] Specific examples of rubber particles dispersed in advance in an epoxy resin include rubber particles dispersed in an epoxy resin using a mixing / stirring device such as a hyper or homogenizer, and rubber particles synthesized in an epoxy resin by emulsion polymerization. These may be used alone or in combination of two or more. The epoxy resin in which the rubber particles are dispersed is treated as the aforementioned component (A).

[0046] Commercially available rubber-dispersed epoxy resins include Kane Ace MX-153, MX-136, MX-257, MX-127, and MX-451 (manufactured by Kaneka Corporation), Acryset BPF-307, and BPA-328 (manufactured by Nippon Shokubai Co., Ltd.), etc. These may be used alone or in combination of two or more.

[0047] The conductive resin composition of the present invention may contain a silane coupling agent. Examples of the silane coupling agent include glycidyl group-containing silane coupling agents such as 3-glycidoxypropyltriethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 3-glycidoxypropyltrimethoxysilane, and 3-glycidoxypropylmethyldiethoxysilane; vinyl group-containing silane coupling agents such as vinyltris(β-methoxyethoxy)silane, vinyltriethoxysilane, and vinyltrimethoxysilane; (meth)acrylic group-containing silane coupling agents such as γ-methacryloxypropyltrimethoxysilane; amino group-containing silane coupling agents such as N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane, γ-aminopropyltriethoxysilane, and N-phenyl-γ-aminopropyltrimethoxysilane; γ-mercaptopropyltrimethoxysilane, γ-chloropropyltrimethoxysilane, and oligomers thereof. Among these, glycidyl group-containing silane coupling agents are preferred because of their excellent adhesion. These may be used alone or in combination of two or more.

[0048] Commercially available silane coupling agents include, but are not limited to, KBM-1003, KBE-1003, KBM-303, KBM-403, KBE-403, KBM-502, KBE-502, KBM-503, KBE-503, KBM-5103, KBM-1403, KBM-602, KBM-603, KBM-903, KBE-903 (manufactured by Shin-Etsu Chemical Co., Ltd.), Z-6610, Z-6044, Z-6825, Z-6033, and Z-6062 (manufactured by Dow Corning Toray Co., Ltd.).

[0049] <Curing Method and Cured Product> A cured product obtained by curing the conductive resin composition of the present invention is also an aspect of the invention. Furthermore, the conductive resin composition of the present invention can be cured at low temperatures, allowing it to be used in applications where heat-sensitive plastic members are used. The curing temperature conditions are not particularly limited, but are preferably 25 to 100°C, more preferably 50 to 95°C, and most preferably 70 to 90°C, which is a low temperature for heat curing. The curing time is not particularly limited, but is preferably 10 to 180 minutes, more preferably 30 to 120 minutes, and most preferably 40 to 100 minutes.

[0050] <Applications> The conductive resin composition of the present invention can be cured at low temperatures, and therefore can be suitably used in components that use heat-sensitive plastics, etc. Specific examples include liquid crystal image display elements, organic EL elements, solar cell elements, camera modules, flexible printed circuit boards, wearable devices, and battery packs. Examples of plastics that can be used include polypropylene, polyethylene, polyurethane, ABS, phenolic resin, CFRP (carbon fiber reinforced plastic), GFRP (glass fiber reinforced plastic), 6,6-nylon, PPS, and PBT.

[0051] The conductive resin composition of the present invention is preferably used on an adherend whose outermost surface is nickel. Although the exact reason is not clear, the conductive resin composition of the present invention having the above-described configuration has the advantage that it can reduce the connection resistance, have excellent storage stability, and exhibit excellent handling properties, even on an adherend whose outermost surface is nickel that forms an oxide film. The adherend whose outermost surface is nickel is not particularly limited, and is primarily nickel-plated, for example, SPCC (cold-rolled steel sheet), stainless steel, or copper components that have been electroplated or electroless plated (electric wires, printed circuit boards, etc.).

[0052] [Examples] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. Unless otherwise specified, tests were carried out in an environment of 25°C and 55% RH.

[0053] Examples 1 to 7 and Comparative Examples 1 to 5 The following components were prepared to prepare conductive resin compositions, which will hereinafter also be referred to simply as "compositions."

[0054] Component (A): Epoxy resin (A-1): Epoxy resin having two or more epoxy groups in one molecule Epiclon EXA-835LV (a mixture of bifunctional bisphenol A type epoxy resin and bifunctional bisphenol F type epoxy resin, mass ratio 50:50, manufactured by DIC Corporation) Cureduct L-07N (epoxy resin (bifunctional bisphenol A type epoxy resin: 91 mass%), phenolic resin (phenol novolac resin: 4 mass%), boric acid ester compound (2,2'-(carbonylbisoxy)bis(1,3,2-dioxaborolane-4,5-dione): 5% by mass (mixture of epoxy resin components manufactured by Shikoku Chemical Industry Co., Ltd.); (A-2): Epoxy resin having one epoxy group per molecule: ED-509S (p-tert-butylphenyl glycidyl ether, boiling point: 294°C, manufactured by ADEKA Corporation); CARDURA E10P (neodecanoic acid glycidyl ester, boiling point: 278°C, manufactured by HEXION); (B) component: Conductive particles; (B-1): Crystalline conductive particles; M27 (crystalline silver particles, flake-shaped, surface-treated with stearic acid, average particle size: 4.5 μm, average thickness T: 80 nm, manufactured by Tokusen Kogyo Co., Ltd.); (B-2): Amorphous conductive particles; Silbes TC-770 (amorphous silver particles, flake-shaped, surface-treated with stearic acid, average particle size: 3.5 μm, manufactured by Tokuriki Honten Co., Ltd.); Component (C): Polyamine-based latent curing agent (C-1): Polyamine-based latent curing agent having a softening point of 50 to 129°C Fujicure FXR-1081 (adduct-modified aliphatic polyamine-based latent curing agent, average particle size: 5 μm, softening point: 121°C, manufactured by T&K TOKA Corporation) Fujicure 1061 (adduct-modified aliphatic polyamine-based latent curing agent, average particle size: 5 μm, softening point: 98°C, manufactured by T&K TOKA Corporation) Fujicure FXR-1020 (adduct-modified aliphatic polyamine-based latent curing agent, average particle size: 5 μm, softening point: 124°C, manufactured by T&K TOKA Corporation) (C-2): Polyamine-based latent curing agent having a softening point of 130 to 180°C・Fujicure FXR-1030 (adduct-modified aliphatic polyamine-based latent curing agent, average particle size: 5 μm, softening point: 140°C, manufactured by T&K TOKA Corporation) Component (C'): latent curing agent other than component (C) ・Fujicure FXR-1121 (imidazole-based latent curing agent, average particle size: 5 μm, softening point: 133°C, manufactured by T&K TOKA Corporation) Optional components ・Cureduct L-07N (epoxy resin (bifunctional bisphenol A type epoxy resin: 91% by mass), phenolic resin (phenol novolac resin: 4% by mass), boric acid ester compound (2,2'-(carbonylbisoxy)bis(1,3,2-dioxaborolane-4,and a storage stabilizer component, Cureduct L-07N (a mixture of epoxy resin (difunctional bisphenol A epoxy resin: 91% by mass), phenolic resin (phenol novolac resin: 4% by mass), and boric acid ester compound (2,2'-(carbonylbisoxy)bis(1,3,2-dioxaborolane-4,5-dione): 5% by mass), manufactured by Shikoku Chemical Industry Co., Ltd.), a plasticizer component, manufactured by Shikoku Chemical Industry Co., Ltd. The compositions of Examples 1 to 7 and Comparative Examples 1 to 5 were prepared as follows: Component (A), component (B), and optional components were weighed and stirred for 30 minutes using a planetary mixer. Next, component (C) and component (C') were weighed and added, and the mixture was stirred for an additional 30 minutes using a planetary mixer while being vacuum degassed, to obtain a conductive resin composition.

[0055] <Conductivity> Five 5 mm diameter holes were drilled at 10 mm intervals along the length of a 10 mm wide, 100 μm thick masking tape. The masking tape was attached to an electroless nickel-plated plate measuring 25 mm wide, 100 mm long, and 1.6 mm thick, and a composition was applied to the electroless nickel-plated plate with the masking tape attached using a squeegee. Care was taken to avoid introducing bubbles into the composition when applying the composition using the squeegee. Next, the masking tape was peeled off, and a 2φ×1 mm gold-plated copper chip was placed on the composition. The composition was then cured by heating at 80°C for 60 or 90 minutes in a hot air drying oven to prepare a test piece. After the test piece cooled to room temperature, the needle electrodes of a dual display multimeter were touched to adjacent gold-plated copper chips (two located 10 mm apart) on the composition to measure the resistance, and the obtained resistance value was recorded as the "connection resistance value (Ω)." For stabilizing conductivity, the connection resistance is preferably 3.0Ω or less, more preferably 2.5Ω or less, and particularly preferably 2.0Ω or less (lower limit: 0Ω).

[0056] <Adhesion Strength> Masking tape was applied to an electroless nickel-plated plate measuring 1.6 mm thick, 25 mm wide, and 100 mm long, so that it was 5 mm wide and 50 μm thick. The composition was applied using a squeegee to form a uniform coating, and then the masking tape was removed. A 2φ x 1 mm ceramic tip was dropped vertically onto the coating from 1 cm above the coating to create a test piece (n = 5). The test piece was heated in a hot air drying oven at 80°C for 60 or 90 minutes to cure the composition, and the test piece was then used. After the test piece cooled to room temperature, a digital force gauge with contacts was moved at 50 mm / min with the nickel-plated plate fixed in place, and the contacts pressed the tip perpendicular to the long edge of the test piece to measure the "maximum strength (N)." The "adhesion strength (MPa)" was calculated from the adhesive area and evaluated according to the following evaluation criteria. To prevent the adherend from falling off, a strength of 20 MPa or greater is preferred.

[0057] The compositions of the examples and comparative examples are shown in Table 1. Note that blank spaces in Table 1 indicate that the component is not contained.

[0058]

[0059] It was confirmed that Examples 1 to 7 yielded cured products with excellent conductivity and adhesive strength even when cured at low temperatures such as 80°C. In particular, Examples 1 to 3 confirmed that increasing the proportion of (C-2) in component (C) resulted in excellent conductivity of the cured products. In contrast, Comparative Examples 1 and 4, which are compositions that do not contain (C-2), show poor conductivity of the cured products. Comparative Example 2, which is a composition that does not contain (C-1), shows poor adhesive strength of the cured products. Comparative Examples 3 and 5, in which component (C-1) or (C-2) is replaced with component (C'), show poor conductivity and adhesive strength.

[0060] The conductive paste of the present invention has excellent conductivity and adhesive strength, making it useful for electrical and electronic component applications that have become increasingly miniaturized in recent years, and can particularly reduce resistance to metals that tend to have poor conductivity, such as nickel. These properties allow the present invention to be used in the assembly of a variety of electrical and electronic components, and it has the potential to be expanded to a wide range of applications.

[0061] This application is based on Japanese Patent Application No. 2023-181725, filed on October 23, 2023, the disclosure of which is incorporated herein by reference in its entirety.

Claims

1. A conductive resin composition comprising the following components (A) to (C), with component (C) comprising (C-1) and (C-2): Component (A): epoxy resin Component (B): conductive particles Component (C): polyamine-based latent curing agent (C-1): polyamine-based latent curing agent having a softening point of 50 to 129°C (C-2): polyamine-based latent curing agent having a softening point of 130 to 180°C 2. The conductive resin composition according to claim 1, wherein component (A) comprises a bisphenol type epoxy resin.

3. The conductive resin composition according to claim 1, wherein component (A) comprises (A-1) an epoxy resin having two or more epoxy groups per molecule, and (A-2) an epoxy resin having one epoxy group per molecule.

4. The conductive resin composition according to claim 1, wherein the component (B) comprises (B-1) crystalline conductive particles.

5. The conductive resin composition according to claim 4, wherein the component (B) comprises (B-1) crystalline conductive particles and (B-2) amorphous conductive particles.

6. The conductive resin composition according to claim 1, wherein component (C) is an aliphatic polyamine-based latent curing agent.

7. The conductive resin composition according to claim 1, wherein component (C) is an adduct-modified polyamine-based latent curing agent.

8. The conductive resin composition according to claim 1, wherein the component (C) contains only (C-1) and (C-2).

9. The conductive resin composition according to claim 1, wherein the mass ratio of (C-1) to (C-2) is 10:90 to 90:

10.

10. A cured product obtained by curing the conductive resin composition according to claim 1.