Electroconductive adhesive

Abstract

Provided is an electroconductive adhesive which, even when formed into a thin layer, has sufficiently high adhesion properties and high adhesiveness stability. This electroconductive adhesive is characterized by comprising: an acrylic resin having a weight-average molecular weight of 500,000 to 1,000,000 inclusive and having an epoxy group; a thermosetting resin which has a glass transition temperature of 5°C to 100°C inclusive and a number-average molecular weight of 10,000 to 50,000 inclusive and has a functional group that reacts with an epoxy group; an electroconductive filler; and a titanate coupling agent containing a P atom, the content of the titanate coupling agent in the electroconductive adhesive being 0.2-1.0 wt%.

Description

Conductive Adhesive

[0001] The present invention relates to a conductive adhesive.

[0002] In flexible printed wiring boards, conductive adhesives are widely used. For example, a reinforcing metal plate made of stainless steel is attached to a flexible printed wiring board. By using a conductive adhesive for attaching the metal reinforcing plate, the metal reinforcing plate can function as a shield against electromagnetic waves. In this case, the conductive adhesive is required to firmly bond the insulating layer (coverlay) provided on the surface of the flexible printed wiring board and the metal reinforcing plate.

[0003] Further, the conductive adhesive is embedded in the opening provided in the insulating layer and used for the purpose of conducting the metal reinforcing plate and the ground circuit by contacting the ground circuit exposed from the opening. Therefore, the conductive adhesive is required to have high embedability. Furthermore, the conductive adhesive is required to have high adhesion to the ground circuit. In particular, in recent years, with the miniaturization of electronic devices, the above-mentioned opening has become smaller, so the conductive adhesive is required to achieve both embedability and adhesion.

[0004] As such a conductive adhesive that achieves both embedability and adhesion, Patent Document 1 discloses a conductive adhesive containing an acrylic resin having a weight average molecular weight of 500,000 or more and 1,000,000 or less and having an epoxy group, a thermosetting resin having a glass transition temperature of 5°C or more and 100°C or less, a number average molecular weight of 10,000 or more and 50,000 or less, and having a functional group that reacts with an epoxy group, and a conductive filler, wherein the ratio of the acrylic resin to the total of the acrylic resin and the thermosetting resin is 15% by mass or more and 95% by mass or less, and the thermosetting resin is a urethane-modified polyester resin.

[0005] Japanese Patent No. 6956096

[0006] When using the conductive adhesive described in Patent Document 1 to bond the insulating layer (coverlay) of a flexible printed circuit board to a metal reinforcing plate, the conductive adhesive is arranged in a layer between the insulating layer and the metal reinforcing plate. In recent years, there has been a demand for further miniaturization of electronic devices, and as described above, there is a need to make the layer formed with the conductive adhesive thinner.

[0007] Generally, the thickness of a layer formed with conductive adhesive is proportional to its adhesive strength. For example, simply making the layer formed with conductive adhesive thinner resulted in insufficient adhesion. Furthermore, there was the problem of unstable adhesive strength (the adhesive strength fluctuating with each use).

[0008] This invention was made to solve the above problems, and the object of this invention is to provide a conductive adhesive that has sufficiently high adhesion and high adhesive stability even when a thin layer is formed.

[0009] The present inventors, through diligent research, discovered that the adhesion is improved by adding a titanate-based coupling agent containing P atoms to a conductive adhesive layer, thus completing the present invention. Specifically, the conductive adhesive of the present invention comprises an acrylic resin having epoxy groups with a weight-average molecular weight of 500,000 or more and 1,000,000 or less, a thermosetting resin having a glass transition temperature of 5°C or more and 100°C or less, a number-average molecular weight of 10,000 or more and 50,000 or less, and functional groups that react with epoxy groups, a conductive filler, and a titanate-based coupling agent containing P atoms, characterized in that the content of the titanate-based coupling agent in the conductive adhesive is 0.2 to 1.0 wt%.

[0010] When a conductive adhesive contains a titanate-based coupling agent containing phosphorus atoms, the titanate is thought to improve the compatibility and dispersibility between acrylic resins and thermosetting resins and powders (conductive fillers). Therefore, even when a thin conductive adhesive layer is formed using the conductive adhesive of the present invention, the uniformity of the resin and conductive filler is high, allowing the conductive adhesive layer to cure uniformly. Consequently, the conductive adhesive of the present invention exhibits high adhesive properties. Furthermore, when a thin conductive adhesive layer is formed using the conductive adhesive of the present invention, the high uniformity of the resin and conductive filler makes it less likely for curing to fail in some parts of the conductive adhesive layer. In addition, titanate has the effect of improving the adhesion between resins and metals. Therefore, when using the conductive adhesive of the present invention, the stability of the adhesive strength is improved.

[0011] In the conductive adhesive of the present invention, the content of the titanate-based coupling agent is 0.2 to 1.0 wt%. When the content of the titanate-based coupling agent is in this range, the adhesive properties are improved when the conductive adhesive of the present invention is used. If the content of the titanate-based coupling agent is less than 0.2 wt%, the adhesive properties tend to be low, and the stability of the adhesive strength tends to be low. If the content of the titanate-based coupling agent exceeds 1.0 wt%, the adhesive properties become low, and the temporary fixing properties also decrease.

[0012] In the conductive adhesive of the present invention, the titanate-based coupling agent comprises a titanium compound comprising titanium and a first atomic group containing P atoms bonded to the titanium, wherein the first atomic group preferably comprises the atomic group represented by the following general formula (1). Furthermore, the titanium compound further comprises a second atomic group that does not contain P atoms bonded to the titanium, wherein the second atomic group preferably comprises the atomic group represented by at least one general formula selected from the group consisting of the following general formulas (2), (3), and (4).

[0013] (In general formula (1), R １ (where "●" represents an alkoxy group, and "●" represents a bond.)

[0014] (In general formula (2), "●" represents a combination.)

[0015] (In general formula (3), "●" represents a combination.)

[0016] (In general formula (4), "●" represents a combination.)

[0017] When a titanate-based coupling agent contains the above-mentioned titanium compound, the compatibility of the resin and the dispersibility of the conductive filler are further improved.

[0018] In the conductive adhesive of the present invention, the thermosetting resin is preferably a urethane-modified polyester resin. Adhesion is improved when the thermosetting resin is a urethane-modified polyester resin.

[0019] In the conductive adhesive of the present invention, the thermosetting resin preferably has an acid value of 5 mg KOH / g or more and 50 mg KOH / g or less. When the acid value of the thermosetting resin is within the above range, the heat resistance is improved.

[0020] In the conductive adhesive of the present invention, the acrylic resin preferably has an epoxy equivalent of 1,000 g / eq or more and 10,000 g / eq or less. When the epoxy equivalent of the acrylic resin is within the above range, the heat resistance is improved.

[0021] According to the present invention, even when a thin layer is formed, it is possible to provide a conductive adhesive that has sufficiently high adhesion and high adhesive stability.

[0022] Figure 1 is a schematic cross-sectional view showing an example of a printed circuit board comprising a laminate using the conductive adhesive of the present invention. Figure 2A is a schematic diagram showing, in sequence, an example of a method for manufacturing the printed circuit board shown in Figure 1. Figure 2B is a schematic diagram showing, in sequence, an example of a method for manufacturing the printed circuit board shown in Figure 1. Figure 2C is a schematic diagram showing, in sequence, an example of a method for manufacturing the printed circuit board shown in Figure 1. Figure 2D is a schematic diagram showing, in sequence, an example of a method for manufacturing the printed circuit board shown in Figure 1. Figure 3 is a schematic cross-sectional view showing an example of an electromagnetic wave shielding film using the conductive adhesive of the present invention. Figure 4A is a schematic cross-sectional view showing a test sample in a peel test. Figure 4B is a schematic cross-sectional view showing a method for measuring the peel force of a test sample in a peel test.

[0023] The conductive adhesive, laminate, and electromagnetic shielding film of the present invention will be described in detail below. However, the present invention is not limited to the following embodiments and can be modified and applied as appropriate without altering the gist of the invention.

[0024] (First Embodiment) First, a conductive adhesive which is the first embodiment of the present invention will be described. The conductive adhesive of the present invention comprises an acrylic resin having epoxy groups and a weight-average molecular weight of 500,000 or more and 1,000,000 or less, a thermosetting resin having a glass transition temperature of 5°C or more and 100°C or less and a number-average molecular weight of 10,000 or more and 50,000 or less and functional groups that react with epoxy groups, a conductive filler, and a titanate-based coupling agent containing P atoms, wherein the content of the titanate-based coupling agent in the conductive adhesive is 0.2 to 1.0 wt%.

[0025] When a conductive adhesive contains a titanate-based coupling agent containing phosphorus atoms, the titanate is thought to improve the compatibility and dispersibility between acrylic resins and thermosetting resins and powders (conductive fillers). Therefore, even when a thin conductive adhesive layer is formed using the conductive adhesive of the present invention, the uniformity of the resin and conductive filler is high, allowing the conductive adhesive layer to cure uniformly. As a result, the conductive adhesive of the present invention has high adhesive properties. Furthermore, when a thin conductive adhesive layer is formed using the conductive adhesive of the present invention, the uniformity of the resin and conductive filler is high, making it less likely for curing to fail in some parts of the conductive adhesive layer. In addition, titanate has the effect of improving the adhesion between resins and metals. Therefore, when using the conductive adhesive of the present invention, the stability of the adhesive strength is improved.

[0026] In the conductive adhesive of the present invention, the content of the titanate-based coupling agent is 0.2 to 1.0 wt%. More preferably, the content is 0.25 to 1.0 wt%. When the content of the titanate-based coupling agent is such that it is found, the adhesiveness is improved when the conductive adhesive of the present invention is used. If the content of the titanate-based coupling agent is less than 0.2 wt%, the adhesiveness tends to be low, and the stability of the adhesive strength is also low. If the content of the titanate-based coupling agent exceeds 1.0 wt%, the adhesiveness is low, and the temporary fixing ability is also reduced.

[0027] The components of the conductive adhesive of the present invention will be described below.

[0028] (Titanate-based coupling agent) In the present invention, the titanate-based coupling agent may be a titanium compound comprising titanium and a first atomic group containing P atoms bonded to titanium.

[0029] The above titanium compound has the structure shown in the following general formula (5), and has four R ｘ At least one of these may be a first group of atoms containing a P atom.

[0030]

[0031] In the above titanium compound, the first atomic group may contain an atomic group represented by the following general formula (1).

[0032] (In general formula (1), R １ is an alkoxy group, and "●" is a bond.)

[0033] Further, the first atomic group is preferably an atomic group represented by the following general formula (1-1).

[0034] (In general formula (1-1), "●" is a bond.)

[0035] Further, the above titanium compound may further contain a second atomic group that does not contain a P atom bonded to the above titanium.

[0036] The above second atomic group may contain an atomic group represented by at least one general formula selected from the group consisting of the following general formula (2), general formula (3), and general formula (4).

[0037] (In general formula (2), "●" is a bond.)

[0038] (In general formula (3), "●" is a bond.)

[0039] (In general formula (4), "●" is a bond.)

[0040] In the above titanium compound, the first atomic group is preferably an atomic group represented by the above general formula (1-1), and the second atomic group is preferably an atomic group represented by the above general formula (2).

[0041] When the titanate coupling agent contains the above titanium compound, the compatibility of the resin and the dispersibility of the conductive filler are further improved. As a result, the adhesiveness of the conductive adhesive is improved. In addition, the variation in the adhesiveness of the conductive adhesive between products is reduced.

[0042] The titanate coupling agent preferably has an SP value of 8.0 to 10.5, and more preferably 8.5 to 10.0. When the SP value of the titanate coupling agent is within the above range, the compatibility of the resin and the dispersibility of the conductive filler are further improved.

[0043] Furthermore, the conductive adhesive of the present invention may contain coupling agents other than titanate-based coupling agents, such as aluminate coupling agents.

[0044] (Acrylic Resin) In the present invention, the acrylic resin is a polymer mainly composed of alkyl acrylate or alkyl methacrylate. Hereinafter, acrylate and methacrylate will be collectively referred to as (meth)acrylate. The alkyl (meth)acrylate is not particularly limited, but for example, it can be a (meth)acrylate having a linear or branched alkyl group with about 1 to 18 carbon atoms. Specifically, it can be methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isopropyl (meth)acrylate, isobutyl (meth)acrylate, isodecyl (meth)acrylate, lauryl (meth)acrylate, and stearyl (meth)acrylate, etc. These alkyl (meth)acrylates can be used individually or in combination of two or more types.

[0045] The acrylic resin in this invention has epoxy groups. The epoxy groups are obtained by polymerizing the acrylic resin by adding a polymerizable monomer having epoxy groups to an alkyl (meth)acrylate. The polymerizable monomer having epoxy groups can be, for example, a (meth)acrylate having epoxy groups such as glycidyl (meth)acrylate. Alternatively, it can be obtained by polymerizing the acrylic resin by adding a polymerizable (meth)acrylate oligomer having epoxy groups. It can also be obtained by polymerizing the acrylic resin by adding other polymerizable monomers or oligomers having epoxy groups.

[0046] The acrylic resin in the present invention may contain other monomer components. Other monomer components include, for example, aromatic vinyl compounds, carboxyl group-containing monomers such as (meth)acrylic acid, β-carboxyethyl acrylate, itaconic acid, crotonic acid, maleic acid, fumaric acid, and maleic anhydride; aliphatic ester group-containing monomers other than alkyl groups such as cyclohexyl (meth)acrylate and isobornyl (meth)acrylate; aromatic ester group-containing monomers such as phenyl (meth)acrylate and benzyl (meth)acrylate; 2-hydroxyethyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, chloro-2-hydroxypropyl acrylate, die Examples include hydroxyl group-containing monomers such as ethylene glycol mono(meth)acrylate and allyl alcohol; amino group-containing monomers such as aminomethyl(meth)acrylate and dimethylaminoethyl(meth)acrylate; amide group-containing monomers such as acrylamide, methylol(meth)acrylamide, and methoxyethyl(meth)acrylamide; alkoxy group-containing monomers such as methacryloxypropylmethoxysilane; acetoacetyl group-containing monomers such as acetoacetoxyethyl(meth)acrylate; vinyl monomers other than styrene, such as vinyl acetate and vinyl chloride; and (meth)acrylonitrile. These can be used individually or in combination of two or more.

[0047] In the present invention, the epoxy equivalent of the acrylic resin is preferably 1000 g / eq or more, more preferably 2000 g / eq or more, and even more preferably 3000 g / eq or more. Furthermore, in the present invention, the epoxy equivalent of the acrylic resin is preferably 10000 g / eq or less, more preferably 9000 g / eq or less, and even more preferably 8000 g / eq or less. When the epoxy equivalent of the acrylic resin is within the above range, the heat resistance is improved. The epoxy equivalent of the acrylic resin can be measured in accordance with JIS K7236:2001.

[0048] In this invention, the weight-average molecular weight of the acrylic resin is 500,000 or more and 1,000,000 or less. Preferably, the weight-average molecular weight of the acrylic resin is 700,000 or more, and more preferably 750,000 or more. When the weight-average molecular weight of the acrylic resin is within this range, the embedding properties of the conductive adhesive are improved. Furthermore, in this invention, the weight-average molecular weight of the acrylic resin is preferably 950,000 or less, and more preferably 900,000 or less. When the weight-average molecular weight of the acrylic resin is within this range, the fluidity of the conductive adhesive is improved. The weight-average molecular weight of the acrylic resin can be the styrene-converted value measured by gel permeation chromatography (GPC).

[0049] In the present invention, the glass transition temperature of the acrylic resin is preferably 0°C or higher, more preferably 5°C or higher, and even more preferably 10°C or higher. Furthermore, the glass transition temperature of the acrylic resin is preferably 50°C or lower, more preferably 30°C or lower, and even more preferably 20°C or lower. When the glass transition temperature of the acrylic resin is within the above range, the embedding properties of the conductive adhesive are improved. The glass transition temperature can be measured using a differential scanning calorimetry (DSC).

[0050] The polymerization method for acrylic resins is not particularly limited, and known polymerization methods can be used. For example, by using suspension polymerization, acrylic resins having epoxy groups and a weight-average molecular weight of 500,000 or more and 1,000,000 or less can be easily obtained.

[0051] (Thermosetting Resin) In the present invention, the glass transition temperature of the thermosetting resin is 5°C or higher and 100°C or lower. Furthermore, the glass transition temperature of the thermosetting resin is preferably 10°C or higher, and more preferably 30°C or higher. Furthermore, in the present invention, the glass transition temperature of the thermosetting resin is preferably 90°C or lower, and more preferably 80°C or lower. When the glass transition temperature of the thermosetting resin is within the above range, the embedding properties of the conductive adhesive are improved. The glass transition temperature of the thermosetting resin can be measured using a differential scanning calorimetry (DSC).

[0052] In the present invention, the number-average molecular weight of the thermosetting resin is 10,000 or more and 50,000 or less. Preferably, the number-average molecular weight of the thermosetting resin is 30,000 or less. When the number-average molecular weight of the thermosetting resin is within the above range, the embedding properties of the conductive adhesive are improved. The number-average molecular weight of the thermosetting resin can be the styrene-converted value measured by gel permeation chromatography (GPC).

[0053] In the present invention, the thermosetting resin has a functional group that reacts with epoxy groups. The functional group that reacts with epoxy groups is not particularly limited, but examples include hydroxyl groups, carboxyl groups, epoxy groups, and amino groups. Among these, hydroxyl groups and carboxyl groups are preferred.

[0054] When the thermosetting resin contains carboxyl groups, its acid value is preferably 5 mg KOH / g or more, more preferably 10 mg KOH / g or more, and even more preferably 15 mg KOH / g or more. Furthermore, the acid value is preferably 50 mg KOH / g or less, more preferably 45 mg KOH / g or less, and even more preferably 40 mg KOH / g or less. When the acid value of the thermosetting resin containing carboxyl groups is within the above range, the heat resistance of the conductive adhesive is improved.

[0055] In the present invention, the thermosetting resin is not particularly limited, but is preferably a urethane-modified polyester resin. A urethane-modified polyester resin is a polyester resin containing a urethane resin as a copolymer component. A urethane-modified polyester resin can be obtained, for example, by condensation polymerization of an acid component such as a polycarboxylic acid or its anhydride with a glycol component to obtain a polyester resin, and then by reacting the terminal hydroxyl groups of the polyester resin with an isocyanate component. Alternatively, a urethane-modified polyester resin can also be obtained by simultaneously reacting the acid component, glycol component, and isocyanate component.

[0056] The acid component is not particularly limited, but examples include terephthalic acid, isophthalic acid, orthophthalic acid, 1,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 4,4'-diphenyldicarboxylic acid, 2,2'-diphenyldicarboxylic acid, 4,4'-diphenyletherdicarboxylic acid, adipic acid, azelaic acid, sebacic acid, 1,4-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,2-cyclohexanedicarboxylic acid, 4-methyl-1,2-cyclohexanedicarboxylic acid, dimer acid, trimellitic anhydride, pyromellitic anhydride, 5-(2,5-dioxotetrahydro-3-furanyl)-3-methyl-3-cyclohexene-1,2-dicarboxylic acid anhydride, etc.

[0057] The glycol component is not particularly limited, but examples include ethylene glycol, propylene glycol, 1,3-propanediol, 2-methyl-1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 3-methyl-1,5-pentanediol, neopentyl glycol, diethylene glycol, dipropylene glycol, 2,2,4-trimethyl-1,5-pentanediol, cyclohexanedimethanol, neopentyl hydroxypivalate, and bisphenol A. Dihydric alcohols such as ethylene oxide adducts and propylene oxide adducts, ethylene oxide adducts and propylene oxide adducts of hydrogenated bisphenol A, 1,9-nonanediol, 2-methyloctanediol, 1,10-decanediol, 2-butyl-2-ethyl-1,3-propanediol, tricyclodecanedimethanol, polyethylene glycol, polypropylene glycol, polytetramethylene glycol, etc., and, if necessary, trihydric or higher polyhydric alcohols such as trimethylolpropane, trimethylolethane, and pentaerythritol can be used.

[0058] The isocyanate component is not particularly limited, but examples include 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, p-phenylene diisocyanate, diphenylmethane diisocyanate, m-phenylene diisocyanate, hexamethylene diisocyanate, tetramethylene diisocyanate, 3,3'-dimethoxy-4,4'-biphenylene diisocyanate, 1,5-naphthalene diisocyanate, 2,6-naphthalene diisocyanate, 3,3'-dimethyl-4,4'-diisocyanate, 4,4'-diisocyanate diphenyl ether, 1,5-xylylene diisocyanate, 1,3-diisocyanate methylcyclohexane, 1,4-diisocyanate methylcyclohexane, isophorone diisocyanate, and the like.

[0059] The thermosetting resin is not limited to urethane-modified polyester resin; urethane resin, acid anhydride-modified polyester resin, epoxy resin, and the like can also be used.

[0060] In the conductive adhesive of the present invention, the ratio of the weight of the acrylic resin to the total weight of the acrylic resin and thermosetting resin ([weight of acrylic resin] / ([weight of acrylic resin] + [weight of thermosetting resin])) is preferably 15 or more, more preferably 20 or more, and even more preferably 30 or more. Furthermore, the above ratio is preferably 90 or less, and more preferably 80 or less. With such a ratio, it is possible to achieve a good balance between the embedding properties and adhesive properties of the conductive adhesive.

[0061] (Conductive Filler) The conductive filler included in the conductive adhesive of the present invention is not particularly limited, but for example, metal fillers, metal-coated resin fillers, carbon fillers, and mixtures thereof can be used. Examples of metal fillers include copper powder, silver powder, nickel powder, silver-coated copper powder, gold-coated copper powder, silver-coated nickel powder, and gold-coated nickel powder. These metal powders can be produced by electrolysis, atomization, or reduction. Among these, silver powder, silver-coated copper powder, and copper powder are preferred.

[0062] The average particle size of the conductive filler is preferably 1 μm or more, and more preferably 3 μm or more. Furthermore, the average particle size of the conductive filler is preferably 20 μm or less, and more preferably 10 μm or less. When the average particle size of the conductive filler is within this range, the conductive fillers come into contact with each other more easily, improving the conductivity of the conductive adhesive. Note that conductive fillers with an average particle size of less than 1 μm are difficult to manufacture, and conductive fillers with an average particle size exceeding 20 μm tend to increase the surface resistance of the conductive adhesive.

[0063] The shape of the conductive filler is not particularly limited and may be spherical, flake-shaped, dendritic, fibrous, etc. Among these, a dendritic shape is preferred. When the conductive filler is dendritic, it disperses well and makes it easier to impart isotropic conductivity to the conductive adhesive. In other words, when the conductive filler is dendritic, the conductivity of the conductive adhesive is improved.

[0064] In the conductive adhesive of the present invention, the content of the conductive filler can be appropriately selected depending on the application, but it is preferably 5 wt% or more, and more preferably 10 wt% or more. Furthermore, the content of the conductive filler is preferably 95 wt% or less, and more preferably 90 wt% or less. From the viewpoint of the embedding properties of the conductive adhesive of the present invention, the content of the conductive filler is preferably 70 wt% or less, and more preferably 60 wt% or less. Furthermore, when imparting anisotropic conductivity to a conductive adhesive layer formed using the conductive adhesive of the present invention, the content of the conductive filler is preferably 40 wt% or less, and more preferably 35 wt% or less.

[0065] (Other Components) The conductive adhesive of the present invention may also contain curable resin components other than the acrylic resin having epoxy groups and the thermosetting resin having functional groups that react with epoxy groups as described above. As such curable resin components, epoxy resins that are solid at room temperature or epoxy resins that are liquid at room temperature can be used. With respect to epoxy resins, "solid at room temperature" means that it is in a state where it does not have fluidity in a solvent-free state at 25°C, and "liquid at room temperature" means that it is in a state where it has fluidity under the same conditions.

[0066] Examples of epoxy resins that are solid or liquid at room temperature include bisphenol-type epoxy resins such as bisphenol A type epoxy resin, bisphenol F type epoxy resin, and bisphenol S type epoxy resin; glycidyl ether-type epoxy resins such as spiro-ring type epoxy resin, naphthalene-type epoxy resin, biphenyl-type epoxy resin, terpene-type epoxy resin, tris(glycidyloxyphenyl)methane, and tetrakis(glycidyloxyphenyl)ethane; glycidylamine-type epoxy resins such as tetraglycidyldiaminodiphenylmethane; novolac-type epoxy resins such as tetrabrombisphenol A type epoxy resin, cresol novolac-type epoxy resin, phenol novolac-type epoxy resin, α-naphthol novolac-type epoxy resin, and brominated phenol novolac-type epoxy resin; and rubber-modified epoxy resins. These can be used individually or in combination of two or more types. When adding other curable resin components to the conductive adhesive of the present invention, it is preferable to blend 1.0 to 10.0 parts by weight of the resin component with respect to 100 parts by weight of the total of the acrylic resin having epoxy groups and the thermosetting resin having functional groups that react with epoxy groups.

[0067] The conductive adhesive of the present invention may contain a curable compound for the purpose of promoting the reaction between an acrylic resin having epoxy groups, a thermosetting resin having functional groups that react with epoxy groups, and, if necessary, other curable resin components. Examples of such curable compounds include imidazole-based curing agents, phenol-based curing agents, cationic curing agents, and the like. These can be used individually or in combination of two or more.

[0068] Examples of imidazole-based curing agents include compounds in which an alkyl group, an ethyl cyano group, a hydroxyl group, an azine, etc., is added to the imidazole ring, such as 2-phenyl-4,5-dihydroxymethylimidazole, 2-heptadecylimidazole, 2,4-diamino-6-(2'-undecylimidazolyl)ethyl-S-triazine, 1-cyanoethyl-2-phenylimidazole, 2-phenylimidazole, 5-cyano-2-phenylimidazole, 2,4-diamino-6-[2'methylimidazolyl-(1')]-ethyl-S-triazine isocyanuric acid adduct, 2-phenylimidazole isocyanuric acid adduct, 2-methylimidazole isocyanuric acid adduct, and 1-cyanoethyl-2-phenyl-4,5-di(2-cyanoethoxy)methylimidazole.

[0069] Examples of phenolic curing agents include novolacphenol and naphthol compounds.

[0070] Examples of cationic curing agents include amine salts of boron trifluoride, antimony pentachloride-acetyl chloride complexes, and sulfonium salts having phenethyl or allyl groups.

[0071] The conductive adhesive of the present invention may optionally contain defoaming agents, antioxidants, viscosity modifiers, diluents, settling inhibitors, leveling agents, colorants, flame retardants, etc. Among these, it is preferable to add a flame retardant in order to impart flame retardancy to the conductive adhesive.

[0072] Examples of such flame retardants include nitrogen-based flame retardants such as melamine cyanurate and polyphosphate melamine; metal hydrates such as magnesium hydroxide and aluminum hydroxide; and phosphorus-based flame retardants such as phosphate esters, red phosphorus, and phosphate compounds. Among these, phosphate compounds are preferred.

[0073] When adding a flame retardant to the conductive adhesive of this embodiment, it is preferable to blend 10 to 60 parts by weight of the flame retardant with respect to 100 parts by weight of the total of the acrylic resin having epoxy groups and the thermosetting resin having functional groups that react with epoxy groups (and, if necessary, other curable resin components).

[0074] (Second Embodiment) Next, a laminate using the conductive adhesive of the present invention will be described. Figure 1 is a schematic cross-sectional view showing an example of a printed circuit board comprising a laminate using the conductive adhesive of the present invention.

[0075] The printed circuit board 1 shown in Figure 1 comprises a base film 10, a printed circuit 20 arranged on the base film 10, an insulating layer 30 arranged to cover the printed circuit 20, a conductive adhesive layer 40 arranged on the insulating layer 30, and a metal plate 50 arranged on the conductive adhesive layer 40. The conductive adhesive layer 40 contains the conductive adhesive of the present invention.

[0076] The printed circuit 20 includes a ground circuit 20a. Furthermore, the insulating layer 30 has an opening 30a that exposes the ground circuit 20a.

[0077] The conductive adhesive layer 40 is embedded in the opening 30a and in contact with the ground circuit 20a. As a result, the ground circuit 20a and the metal plate 50 are electrically connected via the conductive adhesive layer 40.

[0078] The conductive adhesive layer 40 contains the conductive adhesive of the present invention, and therefore has high adhesive properties. As a result, the adhesive strength between the insulating layer 30 and the conductive adhesive layer 40, and the adhesive strength between the metal plate 50 and the conductive adhesive layer 40 are sufficiently high.

[0079] Furthermore, the conductive adhesive layer 40 is embedded in the opening 30a. As described above, since the conductive adhesive of the present invention has high embedding properties, the conductive adhesive layer 40 is more likely to come into contact with the ground circuit 20a.

[0080] In the printed circuit board 1, an insulating layer 30, a conductive adhesive layer 40, and a metal plate 50 are stacked in order to form a laminate 60.

[0081] In the printed circuit board 1, the thickness of the conductive adhesive layer 40 is preferably 20 to 65 μm, and more preferably 20 to 60 μm. The conductive adhesive of the present invention has high adhesive properties. Therefore, even if the conductive adhesive layer 40 is this thin, it exhibits sufficient adhesive properties. If the thickness of the conductive adhesive layer is less than 20 μm, it becomes prone to deformation during pressing. If the thickness of the conductive adhesive layer exceeds 65 μm, the entire printed circuit board becomes thicker.

[0082] The function and structure of the metal plate 50 will now be explained. Generally, electronic components are mounted on printed circuit boards, but distortion may occur in the mounting areas of the electronic components. When the metal plate 50 is arranged as in printed circuit board 1, the metal plate 50 functions as a reinforcing member, and even if electronic components are mounted on the printed circuit board 1 at a position opposite the metal plate 50, distortion can be prevented.

[0083] Since the metal plate 50 is conductive, it also functions as a shielding element for electromagnetic waves. Furthermore, because the metal plate 50 is electrically connected to the ground circuit 20a, the shielding performance is good.

[0084] The material of the metal plate 50 may be, for example, stainless steel, nickel, copper, silver, tin, gold, palladium, aluminum, chromium, titanium, and zinc. Among these, stainless steel is preferred because it has high corrosion resistance and strength.

[0085] The thickness of the metal plate 50 is preferably 0.05 mm or more, and more preferably 0.1 mm or more. Furthermore, the thickness of the metal plate 50 is preferably 1.0 mm or less, and more preferably 0.3 mm or less. When the thickness of the metal plate 50 is within the above range, the reinforcing performance is easily exhibited. If the thickness of the metal plate is less than 0.05 mm, it is difficult for it to function as a reinforcing member. If the thickness of the metal plate exceeds 1.0 mm, the flexibility tends to decrease.

[0086] A nickel layer may be formed on the surface of the metal plate 50. The method for forming the nickel layer is not particularly limited, but it can be formed by electroless plating or electrolytic plating, etc. If a nickel layer is formed, the adhesion between the metal plate 50 and the conductive adhesive layer 40 can be improved.

[0087] In the printed circuit board 1, the base film 10 can be, for example, a resin film, and specifically, it can be a film made of a resin such as polypropylene, crosslinked polyethylene, polyester, polybenzimidazole, polyimide, polyimideamide, polyetherimide, or polyphenylene sulfide.

[0088] In the printed circuit board 1, the printed circuit 20 is arranged on the base film 10. The printed circuit 20 may be bonded to the base film 10 via an adhesive, or it may be bonded without using an adhesive, similar to a so-called adhesive-free copper-clad laminate.

[0089] The materials used to construct the printed circuit 20 are not particularly limited, and examples include circuit materials such as copper.

[0090] Furthermore, the printed circuit 20 may have a surface layer made of copper, gold, nickel, silver, tin, or the like.

[0091] In the printed circuit board 1, the insulating layer 30 is not particularly limited, but can be formed from resins such as polyethylene terephthalate, polypropylene, crosslinked polyethylene, polyester, polybenzimidazole, polyimide, polyimideamide, polyetherimide, and polyphenylene sulfide.

[0092] The thickness of the insulating layer 30 is not particularly limited, but is preferably 10 μm to 30 μm.

[0093] Next, the method for manufacturing the printed circuit board described above will be explained. Figures 2A to 2D are schematic diagrams showing, in order, an example of the method for manufacturing the printed circuit board shown in Figure 1.

[0094] First, as shown in Figure 2A, the conductive adhesive of the present invention is coated onto a release substrate (separator film) 71 to form a conductive adhesive film 72 having a conductive adhesive layer 40. Next, as shown in Figures 2A and 2B, the conductive adhesive film 72 and the metal plate 50 are pressed together to form a conductive reinforcing material 73 having a conductive adhesive layer 40.

[0095] Next, as shown in Figure 2C, a printed circuit board 1a is prepared, which includes a base film 10, a printed circuit 20 placed on the base film 10, and an insulating layer 30 placed to cover the printed circuit 20. In the printed circuit board 1a, the printed circuit 20 includes a ground circuit 20a, and the insulating layer 30 has an opening 30a that exposes the ground circuit 20a.

[0096] Next, the release substrate 71 is peeled off from the conductive reinforcing material 73. Then, the printed circuit board 1a and the conductive reinforcing material 73 are laminated together so that the conductive adhesive layer 40 is positioned above the opening 30a.

[0097] Next, as shown in Figure 2D, the metal plate 50 and the printed circuit board 1a are sandwiched from above and below by two heating plates (not shown) heated to a predetermined temperature (e.g., 120°C) and pressed with a predetermined pressure (e.g., 0.5 MPa) for a short time (e.g., 5 seconds). This temporarily fastens the metal plate 50 to the printed circuit board 1a.

[0098] Next, the temperature of the two heating plates is set to a predetermined temperature (e.g., 170°C) that is higher than the temperature used during the temporary fixing process, and pressurized at a predetermined pressure (e.g., 3 MPa) for a predetermined time (e.g., 30 minutes). This allows the metal plate 50 to be fixed to the printed circuit board 1a with the conductive adhesive layer 40 filled into the opening 30a.

[0099] A printed circuit board using the conductive adhesive of the present invention can be manufactured through the above process.

[0100] Next, a solder reflow process is performed for component mounting. During the reflow process, the printed circuit board is exposed to a high temperature of approximately 260°C. The components to be mounted are not particularly limited and can include connectors, integrated circuits, as well as chip components such as resistors and capacitors.

[0101] (Third Embodiment) Next, an electromagnetic wave shielding film using the conductive adhesive of the present invention will be described. Figure 3 is a schematic cross-sectional view showing an example of an electromagnetic wave shielding film using the conductive adhesive of the present invention.

[0102] The electromagnetic wave shielding film 102 shown in Figure 3 is formed by sequentially laminating an insulating layer 180, a shielding layer 190, and a conductive adhesive layer 140. The conductive adhesive layer 140 contains the conductive adhesive of the present invention.

[0103] The electromagnetic shielding film 102 will be attached to the printed circuit board. The conductive adhesive layer 140 contains the conductive adhesive of the present invention, so it has high adhesive properties. Therefore, when the electromagnetic shielding film 102 is attached to the printed circuit board, the adhesive strength will be sufficiently high.

[0104] In the electromagnetic wave shielding film 102, the thickness of the conductive adhesive layer 140 is preferably 20 to 65 μm, and more preferably 20 to 60 μm. The conductive adhesive of the present invention has high adhesive properties. Therefore, even if the conductive adhesive layer 140 is this thin, it exhibits sufficient adhesive properties. If the thickness of the conductive adhesive layer is less than 20 μm, it becomes prone to deformation during pressing. If the thickness of the conductive adhesive layer exceeds 65 μm, the electromagnetic wave shielding film becomes thick.

[0105] In the electromagnetic wave shielding film 102, the insulating layer 180 preferably contains at least one selected from the group consisting of polyimide resin, acrylic resin, epoxy resin, polyester resin, polyamide-imide resin, and urethane resin. Among these, the inclusion of polyimide resin is more preferable. These resins have sufficient insulating properties and are suitable materials for protecting the shielding layer 190 and the conductive adhesive layer 140. Furthermore, when the insulating layer 180 contains these resins, cracks are less likely to occur in the insulating layer 180 when the electromagnetic wave shielding film 102 is bent at a sharp angle.

[0106] In the electromagnetic shielding film 102, the thickness of the insulating layer 180 is preferably 1 to 15 μm, and more preferably 3 to 8 μm. If the thickness of the insulating layer is less than 1 μm, it is too thin, resulting in weak strength and easy damage. If the thickness of the insulating layer exceeds 15 μm, it is too thick, making it difficult to bend the protective layer and making it difficult to place the electromagnetic shielding film on a printed circuit board that is bent at a sharp angle.

[0107] The insulating layer 180 may optionally contain curing accelerators, tackifiers, antioxidants, pigments, dyes, plasticizers, ultraviolet absorbers, defoamers, leveling agents, flame retardants, viscosity modifiers, anti-blocking agents, and the like.

[0108] In the electromagnetic wave shielding film 102, the shielding layer 190 may be made of any material that can shield electromagnetic waves, for example, a metal layer or a conductive resin material. However, it is preferable that the shielding layer 190 be a metal layer.

[0109] The material of the metal layer is not particularly limited, but nickel, copper, silver, tin, gold, palladium, aluminum, chromium, titanium, zinc, and alloys containing two or more of these metals can be used. Among these, copper is preferred.

[0110] Furthermore, the material and thickness of the metal layer can be appropriately selected according to the required electromagnetic shielding effect and resistance to repeated bending and sliding. For example, from the viewpoint of obtaining a sufficient electromagnetic shielding effect, the thickness of the metal layer is preferably 0.1 μm or more. Also, from the viewpoint of productivity and flexibility, it is preferably 8 μm or less.

[0111] The metal layer can be formed by electrolytic plating, electroless plating, sputtering, electron beam deposition, vacuum deposition, CVD, metal organic deposition, etc. Alternatively, the metal layer can be formed from metal foil, metal nanoparticles, flake-like metal particles, etc.

[0112] This specification contains the following information:

[0113] The present disclosure (1) is a conductive adhesive comprising an acrylic resin having an epoxy group and a weight-average molecular weight of 500,000 or more and 1,000,000 or less; a thermosetting resin having a glass transition temperature of 5°C or more and 100°C or less and a number-average molecular weight of 10,000 or more and 50,000 or less and having a functional group that reacts with the epoxy group; a conductive filler; and a titanate-based coupling agent containing a P atom, wherein the content of the titanate-based coupling agent in the conductive adhesive is 0.2 to 1.0 wt%.

[0114] The present disclosure (2) is a conductive adhesive according to the present disclosure (1) in which the titanate coupling agent comprises a titanium compound comprising titanium and a first atomic group including P atoms bonded to the titanium, and the first atomic group comprises the atomic group shown by the following general formula (1).

[0115] (In general formula (1), R １ (where "●" represents an alkoxy group, and "●" represents a bond.)

[0116] Disclosure (3) is a conductive adhesive according to Disclosure (2), wherein the titanium compound further comprises a second atomic group that does not contain P atoms bonded to the titanium, and the second atomic group is represented by at least one general formula selected from the group consisting of general formulas (2), (3), and (4).

[0117] (In general formula (2), "●" represents a combination.)

[0118] (In general formula (3), "●" represents a combination.)

[0119] (In general formula (4), "●" represents a combination.)

[0120] Disclosure (4) is a conductive adhesive according to any one of Disclosures (1) to (3), wherein the thermosetting resin is a urethane-modified polyester resin.

[0121] Disclosure (5) is a conductive adhesive according to any of Disclosures (1) to (4), wherein the thermosetting resin has an acid value of 5 mg KOH / g or more and 50 mg KOH / g or less.

[0122] Disclosure (6) is a conductive adhesive according to any of Disclosures (1) to (5), wherein the acrylic resin has an epoxy equivalent of 1,000 g / eq or more and 10,000 g / eq or less.

[0123] The following are examples that more specifically disclose the conductive adhesive of the present invention. However, the present invention is not limited to the following examples.

[0124] In Examples 1 to 6 and Comparative Examples 1 to 4, conductive adhesives were prepared by mixing and stirring an acrylic resin having epoxy groups, a thermosetting resin having functional groups that react with epoxy groups, a conductive filler, and a titanate coupling agent using a planetary stirring and defoaming apparatus to the weight ratios shown in Table 1. In Table 1, the numerical values ​​for composition represent "parts by weight". In Comparative Example 4, the components did not mix properly, and a conductive adhesive could not be prepared.

[0125]

[0126] In Table 1, the weight-average molecular weight of the acrylic resin containing epoxy groups was 850,000, the epoxy equivalent was 4,800 g / eq, and the glass transition temperature was 12°C.

[0127] In Table 1, the thermosetting resin having a functional group that reacts with epoxy groups was a urethane-modified polyester resin, with a glass transition temperature of 40°C, a weight-average molecular weight of 150,000, and a number-average molecular weight of 18,000.

[0128] In Table 1, titanate coupling agent 1 is a titanate-based coupling agent containing the atomic group shown in the following general formula (1-1) and the atomic group shown in the following general formula (2). The SP value of titanate coupling agent 1 was 9.2.

[0129] (In general formula (1-1), "●" represents a combination.)

[0130] (In general formula (2), "●" represents a combination.)

[0131] Furthermore, titanate coupling agent 2 is a titanate-based coupling agent containing the atomic group shown in the following general formula (2) and the atomic group shown in the following general formula (6). The SP value of titanate coupling agent 2 was 12.0.

[0132] (In general formula (2), "●" represents a combination.)

[0133] (In general formula (6), "●" represents a combination.)

[0134] In Table 1, titanate coupling agent 3 is a titanate-based coupling agent containing the atomic group shown in general formula (2) and the atomic group shown in general formula (7). The SP value of titanate coupling agent 3 was 8.0.

[0135] (In general formula (2), "●" represents a combination.)

[0136] (In general formula (7), "●" represents a combination.)

[0137] (Peel Test) <Preparation of Conductive Reinforcement Material> Conductive adhesive films were prepared by hand-coating the conductive adhesives according to Examples 1 to 6 and Comparative Examples 1 to 3 onto mold-release treated polyethylene terephthalate film (separator film) using a plate-shaped spatula (doctor blade) and drying at 100°C for 3 minutes. At this time, after pressing as described later, the amount of conductive adhesive applied was adjusted so that the thickness of the conductive adhesive layer was 20 μm.

[0138] Next, a conductive adhesive film and a 200 μm thick SUS metal plate were temporarily bonded together to create a conductive reinforcing material in which a conductive adhesive layer was provided on the surface of the metal plate.

[0139] <Preparation of Test Samples> Next, the separator film was peeled off the conductive reinforcing material, and the conductive reinforcing material was placed on a pre-prepared polyimide film so that the conductive adhesive layer was in contact with it. Then, the polyimide film and the conductive reinforcing material were pressed using the press type, pressure, and pressing time shown in Table 1. The pressing temperature was set to 170°C and the preheating time to 60 seconds.

[0140] The press conditions in Table 1 refer to the following press types: SSP: Single Step Press VQ: Vacuum Quick Press

[0141] Afterward, the mixture was heated at 150°C for 60 minutes for after-curing.

[0142] Finally, these laminates were attached to a fixing plate with double-sided tape to prepare a test sample with a width of 10 mm. Figure 4A is a schematic cross-sectional view showing the test sample in the peel test. The test sample 3 shown in Figure 4A consists of a fixing plate 4, a polyimide film as an insulating layer 30, a conductive adhesive layer 40, and a metal plate 50, all laminated in that order.

[0143] Figure 4B is a schematic cross-sectional view illustrating the method for measuring the peel force of a test sample in a peel test. As shown in Figure 4B, with the test sample 3 fixed to the fixing plate 4, the conductive adhesive layer 40 and the metal plate 50 were pulled at a pulling speed of 10 mm / min and a pulling angle of 90° to peel off the insulating layer 30 and the conductive adhesive layer 40, and the average peel force and its standard deviation were measured. The evaluation test was performed five times. The results are shown in Table 1. Note that an adhesive force of 10.0 N / 10 mm or higher is considered sufficiently high.

[0144] As shown in Table 1, the test samples using the conductive adhesives according to each example were found to have high peel strength and high adhesive strength stability. Also, as shown in Table 1, the test samples using the conductive adhesive according to Comparative Example 1 had a high average adhesive strength of 16.1 N / 10 mm, but its standard deviation was 1.6, indicating low adhesive strength stability. In particular, some of the test samples using the conductive adhesive according to Comparative Example 1 had a peel strength of less than 10.0 N / 10 mm. Furthermore, as shown in Table 1, the test samples using the conductive adhesives according to Comparative Examples 2 and 3 had an average adhesive strength of less than 10.0 N / 10 mm, indicating low adhesive strength.

[0145] (Evaluation of heat resistance) The conductive reinforcing material after curing, as described in <Preparation of test samples> above, was visually inspected to evaluate whether or not blistering had occurred. The results are shown in Table 1. In Table 1, a rating of "Good" means that no blistering occurred and the heat resistance is high.

[0146] As shown in Table 1, the conductive adhesives in each example were found to have high heat resistance.

[0147] (Measurement of surface resistance) The separator film is peeled off from the conductive reinforcing material prepared in the above <Preparation of conductive reinforcing material> and a cube-shaped electrode (electrode area: 1 cm²) is used. ２Two electrodes (each side = 1 cm, electrode surface: gold plated) were placed on the surface. The distance between the two electrodes was 10 mm. A load of 4.9 N was applied vertically to each electrode, and the resistance value between each electrode was measured using the two-terminal method. The value obtained 1 minute after the start of measurement was taken as the surface resistance (Ω / □). A surface resistance of 1 Ω / □ or less is considered sufficiently low.

[0148] As shown in Table 1, the conductive adhesive layers using the conductive adhesives according to each embodiment were found to have sufficiently low surface resistance.

[0149] 1, 1a Printed circuit board 3 Test sample 4 Fixing plate 10 Base film 20 Printed circuit 20a Ground circuit 30 Insulating layer 30a Opening 40 Conductive adhesive layer 50 Metal plate 60 Laminate 71 Release substrate 72 Conductive adhesive film 73 Conductive reinforcing material 102 Electromagnetic shielding film 140 Conductive adhesive layer 180 Insulating layer 190 Shielding layer

Claims

1. A conductive adhesive comprising: an acrylic resin having epoxy groups and a weight-average molecular weight of 500,000 or more and 1,000,000 or less; a thermosetting resin having a glass transition temperature of 5°C or more and 100°C or less, a number-average molecular weight of 10,000 or more and 50,000 or less, and functional groups that react with epoxy groups; a conductive filler; and a titanate-based coupling agent containing a P atom, wherein the content of the titanate-based coupling agent in the conductive adhesive is 0.2 to 1.0 wt%.

2. The conductive adhesive according to claim 1, wherein the titanate coupling agent comprises a titanium compound comprising titanium and a first atomic group containing P atoms bonded to the titanium, and the first atomic group comprises the atomic group shown by the following general formula (1). (In general formula (1), R １ (where "●" represents an alkoxy group, and "●" represents a bond.) 3. The conductive adhesive according to claim 2, wherein the titanium compound further comprises a second atomic group that does not contain P atoms bonded to the titanium, and the second atomic group is represented by at least one general formula selected from the group consisting of general formulas (2), (3), and (4). (In general formula (2), "●" represents a combination.) (In general formula (3), "●" represents a combination.) (In general formula (4), "●" represents a combination.) 4. The conductive adhesive according to any one of claims 1 to 3, wherein the thermosetting resin is a urethane-modified polyester resin.

5. The conductive adhesive according to any one of claims 1 to 4, wherein the thermosetting resin has an acid value of 5 mg KOH / g or more and 50 mg KOH / g or less.

6. The conductive adhesive according to any one of claims 1 to 5, wherein the acrylic resin has an epoxy equivalent of 1,000 g / eq or more and 10,000 g / eq or less.

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