JP6719550B2 - Conductive adhesive and shield film - Google Patents

Description

The present invention relates to a conductive adhesive and a shield film.

As a method of noise reduction in a printed wiring board, a method in which a metal reinforcing plate such as SUS is adhered with a conductive adhesive to maintain the shielding performance is mainly used, and a flexible printed wiring board (FPC) or the like is used. Regarding the bent portion, a method of using a flexible shield film made of a thin metal foil layer and a conductive adhesive is adopted.
Examples of conventional methods relating to this include those described in Patent Documents 1 and 2.

For such a conductive adhesive, a heat cycle test in which the atmosphere temperature is changed from a low temperature (for example, −45° C.) to a high temperature (for example, 125° C.), the temperature is returned to the low temperature again, and then the temperature is changed to the high temperature is repeated. It is required that the material has excellent characteristics when subjected to the above. For example, when used in a mobile phone, it is required that the performance hardly deteriorates even if the heat cycle is repeated 1000 times.

Further, in addition to the above heat cycle property, the conductive composition has been required to have good reflow property and be difficult to peel off from the substrate.

JP, 2003-298285, A Patent No. 5139156

However, conventionally, the conductive adhesive for bonding a metal plate and the conductive adhesive for a shield film have a sufficient shield performance because the resistance value increases due to humidity and temperature during use of an electronic device and the repetition thereof. It has a problem that it does not show. That is, there is a problem that strain is generated between the conductive adhesive and the metal plate due to temperature and humidity and repeated heat treatment, the contact point at the interface is lowered, and the resistance value is increased.

The present inventor has conducted diligent studies to solve the above problems, has excellent heat cycle properties, has good reflow properties, and has found a conductive adhesive that is difficult to peel off from a substrate and a shield film containing the same, and Completed the invention.
The present invention is the following (1) to (5).
(1) A conductive adhesive containing a thermosetting resin and a conductive filler,
After curing,
Tg (TMA method) is 35°C or higher,
Tensile elastic modulus of 1.5 GPa to 4 GPa,
When the linear expansion coefficient is -25°C to 125°C, 250 ppm/°C or more,
The coefficient of humidity expansion is 0.05% or less when increased from 55% to 75% at 20°C, and is 0.15% or less when increased from 55% to 95% at 20°C. Adhesive.
(2) The conductive adhesive according to (1) above, wherein the thermosetting resin contains a urethane resin, a polyester resin, and an epoxy resin.
(3) The conductive adhesive according to (1) or (2) above, wherein the conductive filler is electrolytic copper powder having a silver-plated dendritic crystal structure.
(4) The conductive adhesive according to (3), wherein the content of silver plating in the electrolytic copper powder is 5% by mass or more and the electrolytic copper powder contains 45% by mass or more.
(5) A shield film having a layer made of the conductive adhesive according to any one of (1) to (4) above on one main surface of an insulating layer made of polyimide.

According to the present invention, it is possible to provide a conductive adhesive having excellent heat cycle properties, good reflow properties, and hard to peel off from a substrate, and a shield film containing the same.

It is a schematic sectional drawing of the evaluation board [1] used in the Example.

The present invention will be described.
The present invention is a conductive adhesive containing a thermosetting resin and a conductive filler, which has a Tg (TMA method) of 35°C or higher, a tensile elastic modulus of 1.5 GPa to 4 GPa, and a line after curing. The expansion coefficient is 250 ppm/°C or higher at -25°C to 125°C, and the humidity expansion coefficient is 0.05% or less when increased from 55% to 75% at 20°C, and 55% to 95% at 20°C. It is a conductive adhesive that is 0.15% or less when increased to 0.1%.
Hereinafter, such a conductive adhesive will also be referred to as the “adhesive of the present invention”.

The present inventor has found that such a conductive adhesive has excellent heat cycle characteristics, good reflow characteristics, and is hardly peeled off from the substrate.
The Tg (TMA method), the tensile modulus of elasticity, the coefficient of linear expansion and the coefficient of humidity expansion of the adhesive of the present invention mean the values obtained by measurement by the methods described in Examples described later.

The adhesive of the present invention contains a thermosetting resin and a conductive filler. Here, the total content of the thermosetting resin and the conductive filler is preferably 70% by mass or more. The total content is more preferably 80% by mass or more, further preferably 95% by mass or more.
The adhesive of the present invention may contain additives and the like contained in conventionally known adhesives, in addition to the thermosetting resin and the conductive filler. For example, an additive such as hindered amine-based, hindered phenol-based, phosphorus-based antioxidant, bromine-based, phosphorus-based, nitrogen-based, flame retardant such as metal hydroxide compound, leveling agent, pigment, dye, etc. is appropriately mixed. be able to.

Examples of the thermosetting resin in the adhesive of the present invention include an epoxy resin, a phenol resin, an amino resin, an alkyd resin, a urethane resin, a synthetic rubber, and a UV curable acrylate resin, and one or more of these can be used. ..
The adhesive of the present invention more preferably contains a urethane resin, a polyester resin, and an epoxy resin, and more preferably a resin composition shown below.

The resin composition contains a carboxyl group, has an acid value of 100 equivalents/10 ⁶ g or more and 1000 equivalents/10 ⁶ g or less, and has a number average molecular weight of 5.0×10 ³ or more and 1.0×10 ⁵ or less. And a polyurethane resin (a-1) having a glass transition temperature of 30° C. or higher and 80° C. or lower, a number average molecular weight of 5.0×10 ³ or higher and 1.0×10 ⁵ or lower, and a glass transition temperature of 0° C. or lower. The content ratio of the polyurethane resin (a-1) to the total of the polyurethane resin (a-1) and the polyester resin (a-2), which is composed of the polyester resin (a-2) and the epoxy resin (b). Is 70% by mass or more and 95% by mass or less, and the total content of the epoxy resins contained in the resin composition with respect to the total of the polyurethane resin (a-1) and the polyester resin (a-2) is 5% by mass or more and 30% by mass or more. The content of the epoxy resin (b) is 0.1% by mass or more and 20% by mass or less based on the whole epoxy resin contained in the resin composition.
In the resin composition, the polyurethane resin (a-1) is obtained by reacting a polyester polyol (c), a compound (d) having one carboxylic acid group and two hydroxyl groups, and a polyisocyanate (e). Is preferred.
Further, the resin composition preferably further contains an organic solvent.

The resin composition will be described in detail.
The resin composition comprises a specific polyurethane resin (a-1), a specific polyester resin (a-2) and an epoxy resin (b), and may further contain an organic solvent.

The number average molecular weight of the polyurethane resin (a-1) used in the resin composition is 5.0×10 ³ or more and 1.0×10 ⁵ . When the number average molecular weight of the polyurethane resin (a-1) is less than 5.0×10 ³ , the adhesion immediately after coating is insufficient and the workability deteriorates, and the flexibility decreases and the adhesion decreases. There is a tendency. When the number average molecular weight of the polyurethane resin (a-1) exceeds 1.0×10 ⁵ , the solution viscosity at the time of application is too high, and a uniform coating film may not be obtained. The lower limit of the number average molecular weight of the polyurethane resin (a-1) is preferably 8.0×10 ³ , and more preferably 1.0×10 ⁴ . Moreover, the upper limit of the number average molecular weight of the polyurethane resin (a-1) is preferably 5.0×10 ⁴ , and more preferably 3.5×10 ⁴ .

The acid value of the polyurethane resin (a-1) used in the resin composition is 100 equivalents/10 ⁶ g or more and 1000 equivalents/10 ⁶ g or less. When the acid value of the polyurethane resin (a-1) is less than 100 equivalent/10 ⁶ g, the adhesion to the metal base material tends to be insufficient. In addition, the crosslinking with the epoxy resin is insufficient, and the heat resistance tends to decrease. When the acid value of the polyurethane resin (a-1) exceeds 1000 equivalents/10 ⁶ g, the storage stability of the varnish when dissolved in a solvent decreases, and the crosslinking reaction of the adhesive sheet easily proceeds at room temperature. However, there is a tendency that a stable seat life cannot be obtained. Further, the cross-linking with the epoxy resin becomes too dense, and the adhesiveness tends to decrease. The lower limit of the acid value of the polyurethane resin (a-1) is preferably 150 equivalents/10 ⁶ g, more preferably 200 equivalents/10 ⁶ g, and further preferably 400 equivalents/10 ⁶ g. The upper limit of the acid value of the polyurethane resin (a-1) is preferably 900 equivalents/10 ⁶ g, more preferably 800 equivalents/10 ⁶ g, and further preferably 700 equivalents/10 ⁶ g. Examples of the method of introducing an acid value include a method of copolymerizing a polyester polyol constituting polyurethane with a polyfunctional carboxylic acid having a functionality of 3 or more, and a method of using a diol containing a carboxylic acid as a chain extender.

The polyurethane resin (a-1) used in the resin composition has a glass transition temperature of 30° C. or higher and 80° C. or lower. If the glass transition temperature is less than 30°C, the adhesiveness under high temperature and high humidity tends to be insufficient. When the glass transition temperature exceeds 80° C., the bonding with the substrate becomes insufficient, the elastic modulus at room temperature becomes high, and the adhesiveness at room temperature tends to be insufficient. The lower limit of the glass transition temperature is preferably 35°C, more preferably the lower limit of the glass transition temperature is 40°C. A preferred upper limit is 75°C, and a more preferred upper limit is 70°C.

The polyurethane resin (a-1) used in the resin composition preferably uses a polyester polyol (c), a polyisocyanate (e), and a chain extender as its raw materials.
The number average molecular weight of the polyester polyol (c) is preferably 2000 or more and 50000 or less, and more preferably 6000 or more and 35000 or less. If the number average molecular weight is less than 2000, the number of urethane bonds in the molecule will be too large and the solder heat resistance will be poor, and the adhesiveness will also be reduced. On the other hand, when the number average molecular weight exceeds 50,000, the distance between crosslinking points with the epoxy resin becomes too long and the solder heat resistance becomes poor.

The polyester polyol (c) preferably has an aromatic acid content of 30 mol% or more, more preferably 45 mol %, when the total amount of all the acid components constituting the polyester polyol (c) is 100 mol %. Or more, and more preferably 60 mol% or more. If the aromatic acid content is less than 30 mol %, the cohesive force of the coating film is weak and the adhesive strength to various substrates is reduced.

Examples of aromatic acids include aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, orthophthalic acid, naphthalenedicarboxylic acid, biphenyldicarboxylic acid, diphenic acid and 5-hydroxyisophthalic acid. Further, sulfoterephthalic acid, 5-sulfoisophthalic acid, 4-sulfophthalic acid, 4-sulfonaphthalene-2,7-dicarboxylic acid, 5-(4-sulfophenoxy)isophthalic acid, and their metal salts and ammonium salts. An aromatic dicarboxylic acid having a sulfonic acid group or a sulfonate group, p-hydroxybenzoic acid, p-hydroxyphenylpropionic acid, p-hydroxyphenylacetic acid, 6-hydroxy-2-naphthoic acid, 4,4-bis(p Examples thereof include aromatic hydroxycarboxylic acids such as -hydroxyphenyl)valeric acid. Among these, terephthalic acid, isophthalic acid, and a mixture thereof are particularly preferable in terms of increasing the cohesive force of the coating film.

Incidentally, other acid components include alicyclic dicarboxylic acids such as 1,4-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, and 1,2-cyclohexanedicarboxylic acid, succinic acid, adipic acid, azelaic acid, sebacine. Examples thereof include acids, dodecanedioic acid, and aliphatic dicarboxylic acids such as dimer acid.

On the other hand, the glycol component is preferably an aliphatic glycol, an alicyclic glycol, an aromatic-containing glycol, an ether bond-containing glycol or the like, and examples of the aliphatic glycol include ethylene glycol, 1,2-propylene glycol, 1, 3-propanediol, 1,4-butanediol, 2-methyl-1,3-propanediol, 1,5-pentanediol, neopentyl glycol, 1,6-hexanediol, 3-methyl-1,5-pentane Diol, 1,9-nonanediol, 2-ethyl-2-butyl-1,3-propanediol, hydroxypivalic acid neopentyl glycol ester, dimethylolheptane, 2,2,4-trimethyl-1,3-pentanediol And the like. Examples of the alicyclic glycol include 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, tricyclodecanediol, tricyclodecane dimethylol, spiroglycol, hydrogenated bisphenol A, Examples thereof include an ethylene oxide adduct and a propylene oxide adduct of hydrogenated bisphenol A. Examples of the ether bond-containing glycol include diethylene glycol, triethylene glycol, dipropylene glycol, polyethylene glycol, polypropylene glycol, polytetramethylene glycol, neopentyl glycol ethylene oxide adduct, neopentyl glycol propylene oxide adduct, and the like. be able to. Examples of the aromatic-containing glycol include para-xylene glycol, meta-xylene glycol, ortho-xylene glycol, 1,4-phenylene glycol, 1,4-phenylene glycol ethylene oxide adduct, bisphenol A, bisphenol A ethylene oxide adduct, and Examples thereof include glycols obtained by adding 1 to several moles of ethylene oxide or propylene oxide to two phenolic hydroxyl groups of bisphenol such as propylene oxide adduct.

An oxycarboxylic acid compound having a hydroxyl group and a carboxyl group in its molecular structure can also be used as a polyester raw material, and 5-hydroxyisophthalic acid, p-hydroxybenzoic acid, p-hydroxyphenylpropionic acid, p-hydroxyphenyl. Examples thereof include acetic acid, 6-hydroxy-2-naphthoic acid, and 4,4-bis(p-hydroxyphenyl)valeric acid.

In the polyester polyol (c) used in the resin composition, for the purpose of introducing a branched skeleton, when the total of all acid components or all glycol components constituting the polyester polyol (c) is 100 mol %, 0 It is also possible to copolymerize trifunctional or higher polycarboxylic acids and/or trifunctional or higher polyols within a range of 1 mol% or more and 5 mol% or less. Since the epoxy resin is blended in the resin composition, by introducing a branched skeleton, the number of terminal groups of the resin (a-1), that is, the functional groups capable of reacting with the crosslinking agent, increases, the crosslinking density is high, and the strength is high. A high coating film can be obtained. Examples of trifunctional or higher functional polycarboxylic acids that exhibit such effects include trimellitic acid, trimesic acid, ethylene glycol bis (anhydrotrimellitate), glycerol tris (anhydrotrimellitate), trimellitic anhydride, Pyromellitic dianhydride (PMDA), oxydiphthalic dianhydride (ODPA), 3,3',4,4'-benzophenone tetracarboxylic dianhydride (BTDA), 3,3',4,4'-diphenyltetra Carboxylic dianhydride (BPDA), 3,3′,4,4′-diphenylsulfone tetracarboxylic dianhydride (DSDA), 4,4′-(hexafluoroisopropylidene)diphthalic dianhydride (6FDA) , 2,2′-bis[(dicarboxyphenoxy)phenyl]propane dianhydride (BSAA) and the like, while examples of trifunctional or higher functional polyols include glycerin, trimethylolethane, and trimethylol. Examples thereof include propane and pentaerythritol. When using a trifunctional or higher functional polycarboxylic acid and/or a trifunctional or higher functional polyol, each is 0.1 mol% or more and 5 mol% or less, preferably 0.1 mol% or more, based on the total acid component or total glycol component. Copolymerization is preferable in the range of 3 mol% or less, and if it exceeds 5 mol %, mechanical properties such as elongation at break of the coating film may decrease, and gelation may occur during polymerization. is there.

In the polyester polyol (c) used in the resin composition, acid addition can be carried out within the range of 0.1 mol% or more and 10 mol% or less for the purpose of introducing a carboxyl group if necessary. When a monocarboxylic acid, a dicarboxylic acid, or a polyfunctional carboxylic acid compound is used for acid addition, transesterification causes a decrease in the molecular weight, and therefore it is preferable to use an acid anhydride. Examples of acid anhydrides include succinic anhydride, maleic anhydride, phthalic anhydride, 2,5-norbornene dicarboxylic acid anhydride, tetrahydrophthalic anhydride, trimellitic anhydride, pyromellitic dianhydride (PMDA), and oxydiphthalic dianhydride. (ODPA), 3,3′,4,4′-benzophenonetetracarboxylic dianhydride (BTDA), 3,3′,4,4′-diphenyltetracarboxylic dianhydride (BPDA), 3,3 ',4,4'-Diphenylsulfone tetracarboxylic acid dianhydride (DSDA), 4,4'-(hexafluoroisopropylidene)diphthalic acid dianhydride (6FDA), 2,2'-bis[(dicarboxyphenoxy ) Compounds such as phenyl]propane dianhydride (BSAA) can be used. When the total acid component constituting the polyester polyol (c) used in the present invention is 100 mol %, 10 mol% or more of acid addition may cause gelation, and depolymerization of polyester may occur. The resin molecular weight may be lowered. As the method of acid addition, for example, there are a method of directly carrying out the polycondensation of the polyester in a bulk state and a method of solutionizing and adding the polyester. The reaction in the bulk state is fast, but if a large amount is added, gelation may occur, and the reaction will occur at a high temperature, so care must be taken to block oxygen gas and prevent oxidation. On the other hand, addition in a solution state is slow in reaction, but a large amount of carboxyl groups can be stably introduced.

The polyisocyanate (e) used for producing the polyurethane resin (a-1) used in the resin composition includes diisocyanate, its dimer (uretdione), its trimer (isocyanurate, triol adduct, burette), etc. , Or a mixture of two or more thereof. For example, the diisocyanate component may be 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, 4,4'-diisocyanate diphenyl ether, 1,5-xylylene diisocyanate, 1,3-diisocyanate methylcyclohexane, 1,4 -Diisocyanate-methylcyclohexane, 4,4'-diisocyanate cyclohexane, 4,4'-diisocyanate cyclohexylmethane, isophorone diisocyanate, dimer acid diisocyanate, norbornene diisocyanate and the like, but due to the problem of yellowing, aliphatic/alicyclic Group diisocyanates are preferred. Further, hexamethylene diisocyanate and isophorone diisocyanate are particularly preferable because they are easily available and economical.

In producing the polyurethane resin (a-1) used for the resin composition, a chain extender may be used if necessary. Examples of the chain extender include compounds (d) having one carboxylic acid and two hydroxyl groups such as low molecular weight diols, dimethylolpropionic acid, and dimethylolbutanoic acid which have already been described as constituent components of the polyester polyol (c). To be Of these, dimethylolbutanoic acid is preferred because of its ease of introduction of acid value and solubility in general-purpose solvents. Further, trimethylolpropane is preferably used because it is easy to introduce a hydroxyl group.

As a method for producing the polyurethane resin (a-1) used in the resin composition, the polyester polyol (c) and the polyisocyanate (e), and optionally the chain extender may be charged all at once in a reaction vessel, You may prepare by dividing. In any case, the total of the hydroxyl values of the polyester polyol and the chain extender in the system and the total of the isocyanate groups of the polyisocyanate are reacted at a ratio of isocyanate group/functional group of hydroxyl group of 1 or less. In addition, this reaction can be produced by reacting in the presence or absence of a solvent inert to the isocyanate group. As the solvent, ester solvents (ethyl acetate, butyl acetate, ethyl butyrate, etc.), ether solvents (dioxane, tetrahydrofuran, diethyl ether, etc.), ketone solvents (cyclohexanone, methyl ethyl ketone, methyl isobutyl ketone, etc.), aromatic carbonization Examples of the solvent include hydrogen solvents (benzene, toluene, xylene, etc.) and mixed solvents thereof, and ethyl acetate and methyl ethyl ketone are preferable from the viewpoint of reducing environmental load. The reaction device is not limited to the reaction can equipped with the stirring device, and a mixing and kneading device such as a kneader or a twin-screw extruder can also be used.

Catalysts used in ordinary urethane reactions to accelerate the urethane reaction, such as tin-based catalysts (trimethyltin laurate, dimethyltin dilaurate, trimethyltin dioxide, dimethyltin dihydroxide, stannas octoate), lead-based catalysts (Red oleate, red-2-ethylhexoate, etc.), amine-based catalysts (triethylamine, tributylamine, morpholine, diazabicyclooctane, diazabicycloundecene, etc.) can be used, but they are not harmful. From the viewpoint, amine-based catalysts are preferable.

The number average molecular weight of the polyester resin (a-2) used in the resin composition is preferably 5.0×10 ³ or more and 1.0×10 ⁵ or less. If the number average molecular weight of the polyester resin (a-2) is less than 5.0×10 ³ , the mechanical strength of the adhesive tends to be low, and the heat resistance and adhesiveness tend to be low, and the number average molecular weight is 1.0. When it exceeds ×10 ⁵ , the solution viscosity at the time of coating is too high, and a uniform coating film may not be obtained. The lower limit of the number average molecular weight of the polyester resin (a-2) is preferably 8.0×10 ³ , and more preferably 1.0×10 ⁴ . The upper limit of the number average molecular weight of the polyester resin (a-2) is preferably 5.0×10 ⁴ , and more preferably 3.5×10 ⁴ .

The glass transition temperature of the polyester resin (a-2) used in the resin composition is 0°C or lower. When the glass transition temperature is higher than 0°C, the adhesive sheet tends to be hard and brittle, and the adhesive sheet may be deteriorated in workability for cracking during production. Further, the adhesive tends to be hard and the adhesiveness tends to be insufficient. The glass transition temperature is preferably −5° C. or lower, more preferably −10° C. or lower.

As the acid component and glycol component used for the polyester resin (a-2) in the resin composition, the same compounds as those mentioned as the acid component and glycol component used for the polyester polyol (c) are preferably used. It is possible. As a method of setting the glass transition temperature of the polyester resin (a-2) to 0° C. or lower, a method of copolymerizing an aliphatic dicarboxylic acid, a method of copolymerizing a long chain glycol, a method of copolymerizing a polyalkylene glycol, a lactone And the like.

Examples of the aliphatic carboxylic acid include succinic acid, adipic acid, azelaic acid, sebacic acid, dodecanedioic acid, dimer acid and the like. Examples of long-chain glycols include nonanediol, decanediol, dimer acid diol, and the like. Examples of the polyalkylene glycol include diethylene glycol, triethylene glycol, dipropylene glycol, polyethylene glycol, polypropylene glycol, polytetramethylene glycol, and the like. Examples of lactones include β-propiolactone, γ-butyrolactone, δ-valerolactone, ε-caprolactone and the like. Among the lactones, ε-caprolactone is preferable from the viewpoint of easy availability and economic reasons, and as the copolymerization method, a method in which a lactone monomer is added in a bulk state after polycondensation and the polyester resin is subjected to ring-opening polymerization is preferable.

In the resin composition, the mixing ratio of the polyurethane resin (a-1) and the polyester resin (a-2) is 95/5 to 70/30 by mass ratio, preferably 95/5 to 80/20, and more preferably It is 93/7 to 85/15. If the blending amount of the polyester resin (a-2) is larger than 30% by mass, the adhesiveness at room temperature, high temperature and high temperature and high humidity tends to decrease, and if it is less than 5% by mass, the adhesive sheet becomes hard and brittle. The adhesive sheet tends to crack during production, resulting in a decrease in workability.

The epoxy resin (b) contained in the resin composition is not particularly limited as long as it contains at least two epoxy groups in the molecule.
Novolak type epoxy resin such as bisphenol A type epoxy resin, bisphenol F type epoxy resin, bisphenol S type epoxy resin and other bisphenol type epoxy resin, phenol novolac type epoxy resin, cresol novolac type epoxy resin, bisphenol A novolac type epoxy resin, etc. Cyclic epoxy resin, aliphatic chain epoxy resin, dicyclopentanediene type epoxy resin, trifunctional (or tetrafunctional) glycidyl amine compound, naphthalene diol diglycidyl ether compound, phenol diglycidyl ether compound, Examples thereof include diglycidyl ethers of alcohols, alkyl-substituted products of these, hydrogenated products, and the like. More preferably, a dichloropentanediene type epoxy resin having a dicyclopentadiene skeleton is used.
When a dichloropentanediene type epoxy resin is used, the cured coating film has a very low moisture absorption rate, and the crosslink density of the cured coating film can be lowered, so that the stress at the time of peeling from the substrate can be relaxed. It is possible to obtain the effect of further improving the adhesiveness under high humidity.
As the epoxy resin, one kind may be used alone, or two or more kinds may be mixed and used.
Other epoxy resins further include glycidyl ester type such as hexahydrophthalic acid glycidyl ester and dimer acid glycidyl ester, or alicyclic group such as 3,4-epoxycyclohexylmethyl carboxylate, epoxidized polybutadiene, and epoxidized soybean oil. Alternatively, an aliphatic epoxide may be mentioned.

The total amount of the epoxy resin compounded in the resin composition is 5 parts by mass or more and 30 parts by mass or less based on 100 parts by mass of the total of the polyurethane resin (a-1) and the polyester resin (a-2). When the total amount of the epoxy resin is less than 5 parts by mass with respect to 100 parts by mass of the total of the polyurethane resin (a-1) and the polyester resin (a-2), the crosslinking becomes insufficient and the heat resistance decreases. If the amount exceeds 30 parts by mass, a large amount of unreacted epoxy resin remains, and heat resistance and moisture resistance tend to decrease.

A curing catalyst can be used in the curing reaction of the epoxy resin (b) used in the resin composition. For example, 2-methylimidazole, 1,2-dimethylimidazole, 2-ethyl-4-methylimidazole, 2-phenyl-4-methylimidazole, 1-cyanoethyl-2-ethyl-4-methylimidazole and other imidazole compounds, triethylamine , Triethylenediamine, N'-methyl-N-(2-dimethylaminoethyl)piperazine, 1,8-diazabicyclo(5,4,0)-undecene-7,1,5-diazabicyclo(4,3,0)- Nonene-5,6-dibutylamino-1,8-diazabicyclo(5,4,0)-undecene-7 and other tertiary amines, as well as these tertiary amines with phenol, octylic acid and quaternized tetra Examples thereof include compounds obtained by converting phenyl borate salts into amine salts, cationic catalysts such as triallyl sulfonium hexafluoroantimonate and diallyl iodonium hexafluoroantimonate, and triphenylphosphine. Of these, 1,8-diazabicyclo(5,4,0)-undecene-7,1,5-diazabicyclo(4,3,0)-nonene-5,6-dibutylamino-1,8-diazabicyclo(5,5) 4,0)-undecene-7 and other tertiary amines, and compounds obtained by converting these tertiary amines into amine salts with phenol, octylic acid, quaternized tetraphenylborate salts, etc. It is preferable from the viewpoints of stability, adhesiveness to metal, and storage stability after compounding. The compounding amount at that time is preferably 0.01 part by mass or more and 1.0 part by mass or less with respect to 100 parts by mass of the polyurethane resin (a-1). Within this range, the effect on the reaction between the polyurethane resin (a-1) and the epoxy compound is further increased, and a strong adhesive performance can be obtained.

The adhesive of the present invention is a conductive adhesive containing the above thermosetting resin (preferably the above resin composition) and a conductive filler, and has a specific Tg after curing. (TMA method), specific tensile elastic modulus, specific linear expansion coefficient, specific humidity expansion coefficient.

The conductive filler in the adhesive of the present invention is not particularly limited, and may be copper powder, silver powder, gold powder, and is preferably electrolytic copper powder.

The shape and the like of the conductive filler are not particularly limited, and examples thereof include a columnar shape and a scaly shape, but a dendritic crystal structure (dendritic crystal structure) is preferable.

The conductive filler is more preferably an electrolytic copper powder having a silver-plated dendritic crystal structure (dendritic crystal structure).

The content of the conductive filler contained in the adhesive of the present invention is not particularly limited, but is preferably 10 to 80% by mass. If it exceeds 80% by mass, the adhesiveness tends to decrease, and if it is less than 10% by mass, the conductivity tends to decrease.

The conductive filler is preferably electrolytic copper powder having a silver plating content of 5% by mass or more. It is more preferable that the electrolytic copper powder is contained in an amount of 45% by mass or more.

The present invention includes, in addition to the adhesive of the present invention, a shield film having a layer made of the adhesive of the present invention on one main surface of an insulating layer made of polyimide.
Hereinafter, such a shield film is also referred to as a “film of the present invention”.

Since the layer made of the adhesive of the present invention has a shielding property, it can be used as an electromagnetic wave shielding film for a flexible printed wiring board.

The film of the present invention has a layer made of the adhesive of the present invention on one main surface of an insulating layer made of polyimide.
As the polyimide, a film obtained by coating, drying and cyclizing a general polyamide-imide solution containing an acid anhydride and a diamine is used, but black polyimide is preferably used because of problems in design. The black construction method is not particularly limited, but it is preferable that carbon black is mixed with a polyamideimide solution to form a film.

The film of the present invention may have a layer made of the adhesive of the present invention on one main surface of an insulating layer made of polyimide, and may further have a protective film (release) thereon. In this case, the layer made of the adhesive of the present invention is sandwiched between the protective film (release) and the insulating layer.
Examples of the protective film include a PET film alone, a PET using paper as a base material, and a laminate of OPP. If the adhesive layer is in close contact, a release agent may be applied if necessary.

The film of the present invention can be obtained by applying the adhesive of the present invention to an insulating layer made of polyimide according to a conventional method and drying it. Further, after drying, when a protective film is attached to the layer comprising the adhesive of the present invention, the film can be wound without causing offset to the base material and is excellent in operability, and the layer comprising the adhesive of the present invention. Since it is protected, it has excellent storage stability and is easy to use.

In the film of the present invention, the thickness of the layer comprising the adhesive of the present invention is not particularly limited, but is preferably 1 to 500 μm, more preferably 10 to 300 μm, and further preferably 20 to 100 μm. ..

Examples and comparative examples according to the present invention will be described below.
Polyester urethane resin A, polyester urethane resin B and polyester resin C were obtained by the following synthesis method. Then, each number average molecular weight, glass transition temperature, and acid value were determined. The measuring methods of these measurement evaluation items are described below.

<Acid value>
0.2 g of the sample was dissolved in 20 ml of chloroform, and titrated with 0.1 N potassium hydroxide ethanol solution using phenolphthalein as an indicator to calculate the equivalent per 10 ⁶ g of resin (equivalent/10 ⁶ g). ..

<Glass transition temperature>
10 mg of a measurement sample was placed in an aluminum pan, the lid was pressed and sealed, and a differential scanning calorimeter (DSC) DSC-200 manufactured by Seiko Instruments Inc. was used to measure at a temperature rising rate of 20° C./min, and the temperature was low. The glass transition temperature was defined as the intersection of the straight line extending the side baseline to the high temperature side and the tangent line drawn at the point where the slope of the curve of the stepwise change portion of the glass transition becomes maximum.

<Number average molecular weight>
Tetrahydrofuran was used as a measurement sample by dissolving and/or diluting the sample with tetrahydrofuran so that the resin concentration becomes about 0.5% by mass, and filtering with a membrane filter made of polytetrafluoroethylene having a pore size of 0.5 μm. The molecular weight was measured by gel permeation chromatography using a mobile phase as a detector and a differential refractometer as a detector. The flow rate was 1 mL/min and the column temperature was 30°C. Showa Denko KF-802, 804L, and 806L were used for the column. Monodisperse polystyrene was used as the molecular weight standard.

<Synthesis of polyester urethane resin A>
50 parts by mass of terephthalic acid, 49 parts by mass of isophthalic acid, 1 part by mass of trimellitic anhydride, 83 parts by mass of 2-methyl-1,3-propanediol, in a reaction can equipped with a stirrer, a thermometer, and a cooler for outflow. Parts, 17 parts by mass of 1,4-butanediol were charged, the temperature was gradually raised to 230° C. over 4 hours, and the esterification reaction was performed while removing distilled water out of the system. After the completion of the esterification reaction, the initial polymerization under reduced pressure was carried out to 10 mmHg over 30 minutes, the temperature was raised to 240° C., and the latter polymerization was carried out at 1 mmHg or less for 30 minutes. Then, the pressure was returned to normal pressure with nitrogen, 1 part by mass of trimellitic anhydride was added, and the mixture was reacted at 220° C. for 1 hour to obtain a polyester resin.

650 parts by mass of the polyester resin thus obtained is charged into a reaction vessel equipped with a thermometer, a stirrer, a reflux cooling tube and a distillation tube. Further, 650 parts by mass of toluene is charged and dissolved, and then 413 parts by mass of toluene is distilled. Then, the reaction system was dehydrated by azeotropic distillation with toluene/water. After cooling to 60° C., 22.3 parts by mass of 2,2-dimethylolbutanoic acid (DMBA) and 237 parts by mass of methyl ethyl ketone were added. After DMBA was dissolved, 30.6 parts by mass of hexamethylene diisocyanate, 0.03 parts by mass of diazabicycloundecene (DBU) as a reaction catalyst were further added, and after reacting at 80° C. for 7 hours, 444 parts by mass of methyl ethyl ketone, 148 parts by mass of toluene was added to adjust the solid content concentration to 40% by weight to obtain a solution containing the polyester urethane resin A. The solution containing the polyester urethane resin A was dried at 120° C. for 1 hour to measure the solvent-free film according to the above-described measurement evaluation items.
As a result, the acid value was 360 equivalents/10 ⁶ g, the glass transition temperature was 40° C., and the number average molecular weight was 18,000.

<Synthesis of polyester urethane resin B>
29 parts by mass of terephthalic acid, 70 parts by mass of isophthalic acid, 1 part by mass of trimellitic anhydride, 30 parts by mass of 2-methyl-1,3-propanediol were placed in a reaction can equipped with a stirrer, a thermometer, and an outflow cooler. Part, 70 parts by mass of 1,4-butanediol were charged, the temperature was gradually raised to 230° C. over 4 hours, and the esterification reaction was carried out while removing distilled water out of the system. After the completion of the esterification reaction, the initial polymerization under reduced pressure was carried out to 10 mmHg over 30 minutes, the temperature was raised to 240° C., and the latter polymerization was carried out at 1 mmHg or less for 30 minutes. Then, the pressure was returned to normal pressure with nitrogen, 1 part by mass of trimellitic anhydride was added, and the mixture was reacted at 220° C. for 1 hour to obtain a polyester resin.

650 parts by mass of the polyester resin thus obtained is charged into a reaction vessel equipped with a thermometer, a stirrer, a reflux cooling tube and a distillation tube. Further, 650 parts by mass of toluene is charged and dissolved, and then 413 parts by mass of toluene is distilled. Then, the reaction system was dehydrated by azeotropic distillation with toluene/water. After cooling to 60° C., 22.3 parts by mass of 2,2-dimethylolbutanoic acid (DMBA) and 237 parts by mass of methyl ethyl ketone were added. After DMBA was dissolved, 53.4 parts by mass of hexamethylene diisocyanate, 0.03 parts by mass of diazabicycloundecene (DBU) as a reaction catalyst were further added, and after reacting at 80° C. for 7 hours, 444 parts by mass of methyl ethyl ketone, 148 parts by mass of toluene was added to adjust the solid content concentration to 40% by weight to obtain a solution containing polyester urethane resin B. The solution containing the polyester urethane resin B was dried at 120° C. for 1 hour to measure the solvent-free film according to the above-described measurement evaluation items.
As a result, the acid value was 630 equivalent/10 ⁶ g, the glass transition temperature was 10° C., and the number average molecular weight was 13,000.

<Synthesis of polyester resin C>
49 parts by mass of terephthalic acid, 49 parts by mass of isophthalic acid, 2 parts by mass of trimellitic anhydride, 50 parts by mass of ethylene glycol, 50 parts by mass of neopentyl glycol are placed in a reaction can equipped with a stirrer, a thermometer, and a cooling device for outflow. Was gradually heated to 250° C. over 4 hours, and an esterification reaction was carried out while removing distilled water out of the system. After the completion of the esterification reaction, the initial polymerization under reduced pressure was carried out to 10 mmHg over 30 minutes, the temperature was raised to 250° C., and the latter polymerization was carried out at 1 mmHg or less for 30 minutes. Then, the pressure was returned to normal pressure with nitrogen, 140 parts by mass of ε-caprolactone was added, and the reaction was performed at 200° C. for 1 hour to obtain a polyester resin C. Then, the solution containing the polyester resin C was dried at 120° C. for 1 hour, and the solvent-free film was used to perform the measurement according to the above-described measurement evaluation items.
As a result, the acid value was 40 equivalents/less than 10 ⁶ g, the glass transition temperature was −18° C., and the number average molecular weight was 28,000.

<Epoxy resin D>
As the epoxy resin D, YDCN703 (o-cresol novolac type epoxy resin) manufactured by Tobu Kasei Co., Ltd. was prepared.

<Epoxy resin E>
As the epoxy resin E, HP7200-H (dicyclopentanediene type epoxy resin) manufactured by Dainippon Ink and Chemicals, Inc. was prepared.

<Electrolytic copper powder F>
As the electrolytic copper powder F, 10% silver plated ACAX-2 (manufactured by Mitsui Mining & Smelting Co., Ltd.) was prepared.

<Electrolytic copper powder G>
As the electrolytic copper powder G, ACAX-2 (manufactured by Mitsui Mining & Smelting Co., Ltd.), which is a 7% silver-plated product, was prepared.

<Examples 1 to 5>
The above polyester polyurethane resin A, polyester polyurethane resin B, polyester resin C, epoxy resin D, epoxy resin E, electrolytic copper powder F and electrolytic copper powder G were mixed in the ratio (parts by mass) shown in Table 1 below. Specifically, other than the electrolytic copper powders F and G, methyl ethyl ketone and toluene are mixed at a ratio of 1:1 (mass ratio) and dissolved in a mixed solvent, and then the electrolytic copper powder F or electrolytic copper powder is added to the mixed solvent. Powder G was added and dispersed by stirring to obtain a conductive adhesive solution.

Next, three types of commercially available conductive adhesives were prepared as comparative examples for the conductive adhesive solutions according to Examples 1 to 5 shown in Table 1. And each was made into the electroconductive adhesive agent solution which concerns on the comparative example 1, the comparative example 2, and the comparative example 3. Further, a composition obtained by removing the electrolytic copper powder F from the composition of Example 1, that is, a mixture of the polyester polyurethane resin A, the polyester resin C and the epoxy resin E in a mass ratio of 30:5:5 was prepared. The conductive adhesive solution according to Comparative Example 4 was used.

Next, for each of the conductive adhesive solutions according to Examples 1 to 5 and each of the conductive adhesive solutions according to Comparative Examples 1 to 4 shown in Table 1, the PET films subjected to the one-side release treatment were used. It was coated on one side so that the thickness after drying was 60 μm, and dried to obtain a film for evaluation in which a layer (adhesive layer) made of a conductive adhesive solution was attached to a PET film.
Next, the adhesive layer was peeled from the evaluation film, sandwiched between two Teflon plates, vacuum pressed (2 MPa) at 180° C. for 200 seconds, and subsequently placed in an N ₂ oven at 140° C. It was cured for 4 hours.
The thus-treated adhesive layer thus obtained was subjected to Tg measurement, linear expansion coefficient measurement, tensile elastic modulus measurement, and humidity expansion coefficient measurement by the following methods.

<Tg measurement/linear expansion coefficient measurement>
The glass transition temperature was determined using a thermomechanical analyzer (TMA).
Further, the linear expansion coefficient was measured by fixing the sample length to 15 mm with a constant tensile load of 0.05 N, and raising the temperature from room temperature at a rate of 5° C./min to obtain the linear thermal expansion coefficient (CTE). .. The film measurement was in the TD direction.

<Measurement of tensile modulus>
It was measured according to JIS-K6251. The sample width was 10 mm, the gauge length was 100 mm, and the pulling speed was 50 mm/min.

<Humidity expansion rate>
The sample size was MD200×TD250 mm, and 20-hole measurement was performed using an optical non-contact three-dimensional measuring machine as a measuring device. Here, the drilling was described in accordance with IPC TM650 2,2,4. The humidity control conditions were 20° C. and 55% RH for 24 hours, and the humidification conditions were 20° C. and 75% RH for 24 hours. That is, the humidity was increased from 55% to 75% at 20° C., and the humidity expansion coefficient after 24 hours was measured. The obtained hygroscopic expansion coefficient was designated as "hygroscopic expansion coefficient A".
The hygroscopic expansion coefficient was measured also when the hygroscopic expansion coefficient A was obtained and when the humidifying conditions were changed to 20° C., 95% RH, and 24 hours. That is, the humidity was increased from 55% to 95% at 20° C., and the humidity expansion coefficient after 24 hours was measured. The obtained hygroscopic expansion coefficient was defined as "hygroscopic expansion coefficient B".

Table 2 shows the Tg measurement, the linear expansion coefficient measurement, the tensile elastic modulus measurement, and the humidity expansion coefficient of the treated adhesive layer obtained as described above.

Next, for evaluation, each conductive adhesive solution according to Examples 1 to 5 and each conductive adhesive solution according to Comparative Examples 1 to 4 shown in Table 1 obtained as described above are used. The evaluation board [1] shown in FIG. 1 was prepared from the film. How to create is explained.
First, an evaluation film obtained from each of the conductive adhesive solutions according to Examples 1 to 5 shown in Table 1 and the conductive adhesive solutions according to Comparative Examples 1 to 4 obtained as described above. Then, the adhesive layer 3 was peeled off and placed on the main surface of the Ni-SUS plate 1. Here, the Ni-SUS plate 3 is Ni-plated SUS304 (thickness: 0.12 mm). Then, vacuum pressing (2 MPa) was performed at 100° C. for 10 seconds using a vacuum press machine. The obtained Ni-SUS plate with an adhesive layer is designated as SUS auxiliary material 5.
Next, the SUS auxiliary material 5 and the FPC 13 were bonded by performing vacuum pressing (2 MPa) at 180° C. for 200 seconds using a vacuum press machine. The FPC 13 is formed by forming a circuit 9 made of gold plating on a copper foil 11 and further forming a polyimide cover film 7 covering a part of the circuit 9. The opening area of the portion exposed from the cover film 7 in the circuit 9 made of gold plating is 4 mm ² .
Next, the one obtained by pasting the SUS auxiliary material 5 and the FPC 13 was placed in an N ₂ oven and cured at 140° C. for 4 hours, and subsequently, at a maximum temperature of 260° C. for 10 seconds. Reflow treatment was performed to obtain an evaluation substrate [1] (10) shown in FIG.

With respect to the evaluation substrate [1] thus obtained, the initial resistance value, the resistance value after moisture absorption, the resistance value after heat cycle, and the resistance value after reflow were measured by the following methods.

<Initial resistance value>
The resistance value between the two measurement parts shown in FIG. 1 was measured. The results are shown in Table 2.
In addition, in Table 2, in addition to the initial resistance value, the resistance value after moisture absorption, the resistance value after heat cycle, and the resistance value after reflow are ◎ when the resistance value is less than 100 mΩ, and when the resistance value is 100 mΩ or more and less than 500 mΩ. ◯, when it was 500 mΩ or more, it was shown as x.

<Resistance value after moisture absorption>
After holding the evaluation substrate [1] in an atmosphere of 85° C. and 85% RH for 500 hours, the resistance value was measured by the same method as in the case of the above initial resistance value. The results are shown in Table 2.

<Resistance value after heat cycle>
When the evaluation substrate [1] is held in an atmosphere of −45° C. for 30 minutes, and then held in an atmosphere of 125° C. for 30 minutes, which is set as one cycle, and this cycle is repeated 1000 times. The resistance value was measured by the same method. The results are shown in Table 2.

<Reflow resistance>
After the process of holding the evaluation substrate [1] in the atmosphere having the maximum temperature of 260° C. for 10 seconds was repeated 4 times, the resistance value was measured by the same method as in the case of the above initial resistance value. The results are shown in Table 2.

Next, the shield performance was measured. Specifically,
By using the adhesive layer in Example 1 and Comparative Example 1 described above, the portion of the Ni-SUS plate in the evaluation substrate [1] shown in FIG. 1 was changed to a black polyimide film (a film made of a polyimide containing carbon black). Evaluation substrates [2] were obtained. The evaluation substrate [2] can be manufactured by the same method as the evaluation substrate [1].
Then, the shield performance was measured for each evaluation substrate [2] including the adhesive layer of Example 1 and Comparative Example 1.
For the shielding performance, a device owned by KEC (Kansai Electronics Industry Promotion Center) including a signal transmitter: Anritsu SIGNAL GENERATOR MG3601A, a spectrum analyzer: Agilent E4403B, an amplifier: Anritsu PRE AMPLIFIER MH648A was used.
As a result, there was no difference in the shielding performance between the evaluation substrates [2] including the adhesive layers of Example 1 and Comparative Example 1.

Claims (4)

A conductive adhesive containing a thermosetting resin and a conductive filler,
The thermosetting resin contains a carboxyl group, has an acid value of 100 equivalents/10 ⁶ g or more and 1000 equivalents/10 ⁶ g or less, and has a number average molecular weight of 5.0×10 ³ or more and 1.0×10 ⁵ or more. Polyurethane resin having a glass transition temperature of 30° C. to 80° C., polyester having a number average molecular weight of 5.0×10 ^{3 to} 1.0×10 ⁵ and a glass transition temperature of 0° C. or less A resin, an epoxy resin, and a content of the polyurethane resin with respect to the total of the polyurethane resin and the polyester resin is 70% by mass or more and 95% by mass or less, and a resin composition with respect to the total of the polyurethane resin and the polyester resin The content rate of the whole epoxy resin contained is 5 mass% or more and 30 mass% or less, and the compounding ratio of the epoxy resin is 0.1 mass% or more and 20 mass% or less of the whole epoxy resin contained in the resin composition. ,
After curing,
Tg (TMA method) is 35°C or higher,
Tensile elastic modulus of 1.5 GPa to 4 GPa,
When the linear expansion coefficient is -25°C to 125°C, 250 ppm/°C or more,
The coefficient of humidity expansion is 0.05% or less when increased from 55% to 75% at 20°C, and is 0.15% or less when increased from 55% to 95% at 20°C. Adhesive. The conductive adhesive according to claim 1, wherein the conductive filler is an electrolytic copper powder having a silver-plated dendritic crystal structure. The conductive adhesive according to claim 2 , wherein the content of silver plating in the electrolytic copper powder is 5% by mass or more, and the electrolytic copper powder contains 45% by mass or more. On one main surface of the insulating layer made of polyimide, having a layer of a conductive adhesive according to any one of claims 1 to 3 shielding film.

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