JP7363864B2 - Conductive adhesive sheets and portable electronic devices - Google Patents

Description

The present invention relates to a conductive adhesive sheet having a conductive base material and a conductive adhesive layer containing conductive particles, and a portable electronic device equipped with the same.

Due to its ease of handling, conductive adhesive sheets are useful for shielding unnecessary leakage electromagnetic waves radiated from electrical and electronic equipment, for shielding harmful spatial electromagnetic waves generated from electrical and electronic equipment, and for grounding to prevent static electricity. It is used for such things. In recent years, as electric and electronic devices have become smaller and thinner, conductive adhesive sheets used in these devices are also required to be thinner.

A thin conductive adhesive sheet with suitable conductivity and adhesiveness has an adhesive layer on a conductive base material made of a conductive adhesive in which a conductive filler is dispersed in an adhesive substance. Adhesive sheets are known (see Patent Documents 1 and 2).

However, as electrical and electronic devices have become smaller and thinner in recent years, there has been a demand for the conductive adhesive sheet to be thinner. Further, there was also a problem that the adhesiveness of the conductive pressure-sensitive adhesive sheet decreased over time, resulting in a decrease in conductivity. However, a thin conductive pressure-sensitive adhesive sheet that has excellent conductivity, stability over time, and adhesiveness has not yet been found.

Japanese Patent Application Publication No. 2004-263030 JP2009-79127A

The problem to be solved by the present invention is to provide a conductive adhesive sheet that has good adhesiveness and conductivity even if it is thin, and whose conductivity does not easily deteriorate over time, and a portable electronic device equipped with the same. There is a particular thing.

The present inventors have found that the above problem can be solved by combining the total thickness of the adhesive sheet, the content of conductive particles in the conductive adhesive layer, and the thickness of the conductive adhesive layer within a specific range. I found it.

That is, the present invention is a conductive adhesive sheet having a total thickness of 50 μm or less, which has a conductive base material and two conductive adhesive layers provided on both sides of the conductive base material, and has a total thickness of 50 μm or less. Each layer of the conductive adhesive layer contains 0.01% to 10% by mass of at least one type of conductive particle, and the conductive particle has a particle size d50 of 12 μm to 30 μm, and the conductive adhesive layer The present invention relates to a conductive adhesive sheet in which each layer has a thickness of 1 μm to 12 μm. Furthermore, the present invention relates to a portable electronic device equipped with the conductive adhesive sheet.

Although the conductive adhesive sheet of the present invention is extremely thin, it has good adhesion to adherends and conductivity, so it has conductivity that is stable over time, and can be used for electrical and electronic equipment, etc. It is useful for shielding electromagnetic waves used in electronic equipment, for shielding harmful spatial electromagnetic waves generated by electrical and electronic equipment, and for grounding and fixing to prevent static electricity. In particular, it can be suitably applied to portable electronic devices that are becoming thinner and have severe volume restrictions within the housing.

This is a preferred example of the conductive adhesive sheet of the present invention. This is a preferred example of the conductive adhesive sheet of the present invention. FIG. 2 is an electron micrograph of bead-shaped conductive particles suitably used in the conductive pressure-sensitive adhesive sheet of the present invention.

The conductive adhesive sheet of the present invention is a conductive adhesive sheet having a total thickness of 50 μm or less, which has a conductive base material and one or more types of conductive adhesive layers, and has a total thickness of 50 μm or less. Each layer contains 0.01% to 10% by mass of at least one type of conductive particle, and each layer of the conductive adhesive layer has a thickness of 1 μm to 12 μm. .

Below, the conductive pressure-sensitive adhesive sheet of the present invention will be explained in more detail based on its constituent elements. Note that the "sheet" in the present invention refers to a form in which a thin adhesive layer formed using at least one conductive adhesive is provided on a conductive base material or on a release sheet, for example, Includes all product forms such as leaves, rolls, thin sheets, and strips (tape).

(Conductive adhesive layer)
The conductive adhesive sheet of the present invention has one or more conductive adhesive layers. The conductive adhesive layer contains specific conductive particles and an adhesive component. The thickness of each layer of the conductive adhesive layer is 1 μm to 12 μm, preferably 2.5 μm to 10 μm, and preferably 4 μm to 8 μm. The conductive adhesive layer can have both excellent conductivity and excellent adhesiveness even if it is thin as described above.

The conductive thin pressure-sensitive adhesive sheet of the present invention can achieve both excellent conductivity, excellent adhesiveness, and stability of conductivity over time, even if it is extremely thin as described above.
The conductive adhesive layer can be formed by using a pressure-sensitive adhesive composition containing the conductive particles and an adhesive component.

(conductive particles)
The conductive adhesive layer contains at least one type of conductive particle. The conductive particles used have a particle diameter d50 in the range of 10 μm to 30 μm. Thereby, it is possible to obtain a conductive thin pressure-sensitive adhesive sheet that has both excellent conductivity, adhesiveness, and stability of conductivity over time.

The particle diameter d50 of the conductive particles is preferably in the range of 12 μm to 30 μm, more preferably in the range of 10 μm to 26 μm.
Note that the particle diameter d50 refers to the 50% cumulative value in the particle size distribution, and is a value measured by laser analysis/scattering method. Examples of the measuring device include Microtrac MT3000II manufactured by Nikkiso Co., Ltd. and SALD-3000 laser diffraction particle size distribution analyzer manufactured by Shimadzu Corporation.
Examples of methods for adjusting the particle diameter d50 within the above range include a method of pulverizing conductive particles with a jet mill and a method of sieving with a sieve.

The particle diameter d50 of the conductive particles is preferably 100% to 500%, preferably 150% to 470%, of the thickness of the conductive adhesive layer contained in the particles. It is more preferable that the ratio is 200% to 450% in order to achieve both better conductivity, adhesiveness, and stability over time of conductivity.

The conductive particles include metal powder particles such as gold, silver, copper, nickel, and aluminum, conductive resin particles such as carbon and graphite, and metal coatings on the surfaces of the resin particles, solid glass beads, and hollow glass beads. It is possible to use particles having the following properties. Among these, it is more preferable to use nickel powder particles, copper powder particles, or silver powder particles as the conductive particles in order to achieve both even better conductivity and adhesiveness. Nickel particles with an acicular shape on the surface of the particles, those that are made into spherical particles by smoothing (processing (pulverization)) the acicular particles on the surface, and nickel particles manufactured using ultra-high pressure swirling water atomization method. It is particularly preferable to use copper powder, silver powder, etc.

Examples of the shape of the conductive particles include a spherical shape, a spike shape, a flake shape, and a bead shape in which a large number of conductive particles are connected by forming bonds as shown in FIG. It is preferable from the viewpoint of achieving both excellent conductivity, adhesion, and stability of conductivity over time.

The conductive particles are contained in an amount of 0.01% to 10% by mass, more preferably 0.1% to 8% by mass, based on the total mass of the conductive adhesive layer that the particles contain. Preferably, it is particularly preferred to contain 0.5% by mass to 5% by mass in order to obtain a conductive thin pressure-sensitive adhesive sheet with even better conductivity, adhesiveness, and stability over time of conductivity.

(adhesive component)
As the adhesive composition used for forming the conductive adhesive layer, one containing an adhesive component together with the conductive particles can be used.

Examples of the adhesive composition include (meth)acrylic adhesives, urethane adhesive compositions, synthetic rubber adhesive compositions, natural rubber adhesive compositions, silicone adhesive compositions, etc. An acrylic pressure-sensitive adhesive that can contain conductive particles, has a acrylic polymer as a base polymer, and contains the conductive fine particles and, if necessary, additives such as a tackifying resin and a crosslinking agent. It is preferable to use the composition in order to form a conductive adhesive layer with excellent weather resistance and heat resistance.

As the acrylic polymer, for example, an acrylic polymer obtained by polymerizing a monomer component containing a (meth)acrylate monomer having an alkyl group having 1 to 14 carbon atoms can be suitably used. .

Examples of (meth)acrylates having an alkyl group having 1 to 14 carbon atoms include methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, and t-butyl (meth)acrylate. One or more of meth)acrylate, n-hexyl(meth)acrylate, n-octyl(meth)acrylate, isooctyl(meth)acrylate, isononyl(meth)acrylate, cyclohexyl(meth)acrylate, 2-ethylhexyl(meth)acrylate, etc. Two or more types can be used in combination.

Among them, as the (meth)acrylate having an alkyl group having 1 to 14 carbon atoms, it is preferable to use a (meth)acrylate having an alkyl group having 4 to 12 carbon atoms; It is more preferable to use a (meth)acrylate having an alkyl group having a linear or branched structure of 9 to 9, and it is even more preferable to use n-butyl acrylate and 2-ethylhexyl acrylate alone or in combination.

The content of the (meth)acrylate having an alkyl group having 1 to 14 carbon atoms based on the total amount of the monomer components used for producing the acrylic polymer is in the range of 80% by mass to 98.5% by mass. It is preferably in the range of 90% by mass to 98.5% by mass.

As monomer components that can be used for producing the acrylic polymer, in addition to those mentioned above, it is preferable to use a highly polar vinyl monomer as necessary.

As the highly polar vinyl monomer, a vinyl monomer having a carboxyl group, a vinyl monomer having a hydroxyl group, a vinyl monomer having an amide group, etc. can be used alone or in combination of two or more. Among these, it is preferable to use a vinyl monomer having a carboxyl group as the highly polar vinyl monomer because it is easy to adjust the adhesiveness of the conductive pressure-sensitive adhesive layer to a suitable range.

Examples of the vinyl monomer having a carboxyl group include acrylic acid, methacrylic acid, itaconic acid, maleic acid, (meth)acrylic acid dimer, crotonic acid, and ethylene oxide-modified succinic acid acrylate. Preference is given to using acids.

When using a vinyl monomer having a carboxyl group, its content is preferably 0.2% by mass to 15% by mass based on the total amount of monomer components used for producing the acrylic polymer. , more preferably from 0.4% by mass to 10% by mass, and even more preferably from 0.5% by mass to 6% by mass, since the adhesiveness of the pressure-sensitive adhesive can be easily adjusted to a suitable range.

As the vinyl monomer having a hydroxyl group, for example, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, etc. are used. can do.

As the vinyl monomer having an amide group, for example, N-vinylpyrrolidone, N-vinylcaprolactam, acryloylmorpholine, acrylamide, N,N-dimethylacrylamide, etc. can be used.

Examples of other highly polar vinyl monomers include vinyl acetate, ethylene oxide-modified succinic acid acrylate, sulfonic acid group-containing monomers such as 2-acrylamido-2-methylpropanesulfonic acid, 2-methoxyethyl (meth)acrylate, - Terminal alkoxy-modified (meth)acrylates such as phenoxyethyl (meth)acrylate and the like can be used.

The content of the highly polar vinyl monomer is preferably 0.2% by mass to 15% by mass, and 0.4% by mass based on the total amount of monomer components used for producing the acrylic polymer. It is more preferably from 10% by mass, and even more preferably from 0.5% to 6% by mass because it is easy to adjust the adhesiveness of the pressure-sensitive adhesive to a suitable range.

The acrylic polymer can be produced by polymerizing the monomer components described above by a known method such as a solution polymerization method, a bulk polymerization method, a suspension polymerization method, or an emulsion polymerization method. Among these, it is preferable to employ the solution polymerization method in order to improve production costs and productivity.

As the acrylic polymer obtained by the above method, it is preferable to use one having a weight average molecular weight in the range of 300,000 to 1,500,000, and use one having a weight average molecular weight in the range of 500,000 to 1,200,000. It is more preferable to do so.

As the adhesive composition that can be used to form the conductive adhesive layer, one containing various additives can be used as required.

As the additive, for example, one containing a tackifying resin can be used in order to further improve the adhesive force of the conductive adhesive layer.

As the tackifier resin, rosin resin, terpene resin, petroleum resin such as aliphatic (C5 type) or aromatic (C9 type) resin, styrene resin, phenolic resin, xylene resin, methacrylic resin, etc. are used. It is preferable to use a rosin-based resin, and it is more preferable to use a polymerized rosin-based resin.

The tackifier resin is preferably used in an amount of 10 parts by mass to 50 parts by mass based on 100 parts by mass of the acrylic polymer.

As the additives, in addition to those mentioned above, dispersants, anti-settling agents, plasticizers, softeners, metal deactivators, antioxidants, pigments, dyes, etc. can be used as required.

The dispersant and anti-settling agent are preferably used to prevent the conductive particles contained in the adhesive composition from settling over time.

As the antisettling agent, it is preferable to use, for example, a fatty acid amide resin, a urethane resin, or the like.

The anti-settling agent is preferably used in an amount of 0.5% to 10% by weight, more preferably 1% to 6% by weight, based on the solid content of the adhesive component. It is more preferable to use it in a range of 1.5% by mass to 3% by mass.

As the adhesive composition that can be used to form the conductive adhesive layer, one containing a crosslinking agent can be used as required.

As the crosslinking agent, for example, isocyanate crosslinking agents, epoxy crosslinking agents, chelate crosslinking agents, aziridine crosslinking agents, etc. can be used.

The type and amount of the crosslinking agent used are preferably selected appropriately depending on the type and amount of functional groups that the adhesive component such as the acrylic polymer has.

The crosslinking agent can be adjusted and used as appropriate so that the gel fraction of the conductive adhesive layer is in the range of 25% by mass to 60% by mass.

(Gel fraction of conductive adhesive layer)
The conductive adhesive layer preferably forms a three-dimensional crosslinked structure in order to exhibit even better cohesive force. As an indicator of the formation of a crosslinked structure, for example, the gel fraction representing the insoluble matter when the conductive adhesive layer is immersed in toluene, which is a good solvent for (meth)acrylic adhesives, for 24 hours can be mentioned. The gel fraction of the conductive adhesive layer is preferably 10% by mass to 40% by mass, and preferably 15% by mass to 30% by mass, which further improves the cohesive force in the shear direction and improves peeling resistance. This is more preferable because it can improve the properties.

The gel fraction is calculated using the following formula.
Gel fraction (mass%) = {(mass of conductive adhesive layer after immersion in toluene)/(mass of conductive adhesive layer before immersion in toluene)}×100
Mass of conductive adhesive layer = (mass of conductive thin adhesive sheet) - (mass of conductive base material)

An adhesive composition that can be used to form the conductive adhesive layer can be produced, for example, by mixing a composition containing the acrylic polymer and the conductive particles.

Examples of the mixing method include a method of mixing and dispersing a composition containing the acrylic polymer, conductive particles, and optionally additives using a dispersion stirrer or the like. . Examples of the dispersion agitator include a dissolver manufactured by Inoue Seisakusho, a butterfly mixer, a BDM twin-shaft mixer, and a planetary mixer. A dissolver or a butterfly mixer is used because it is easy to uniformly disperse conductive particles such as metal powder without increasing the viscosity. It is preferable.

As the adhesive composition that can be used to form the conductive adhesive layer, it is preferable to use one having a viscosity in the range of 100 mPa·s to 8000 mPa·s, and preferably in the range of 200 mPa·s to 4000 mPa·s. It is more preferable to use a material having a viscosity, and using a material having a viscosity in the range of 200 Pa·s to 1000 mPa·s prevents sedimentation of the conductive particles over time, and the pressure-sensitive adhesive composition This is preferable in terms of preventing coating streaks from occurring when coating.

Examples of methods for adjusting the viscosity of the adhesive composition within the above range include methods of adjusting the type and amount of solvent used, the type of adhesive substance such as acrylic polymer, and its molecular weight, etc. It is preferable to adjust the amount used.

The nonvolatile content of the adhesive composition is not particularly limited, but is preferably in the range of 10% by mass to 35% by mass, more preferably in the range of 10% by mass to 30% by mass. , more preferably in the range of 10% by mass to 20% by mass.

(Conductive base material)
Examples of the conductive base material used for manufacturing the conductive thin pressure-sensitive adhesive sheet of the present invention include metal base materials and graphite base materials.

As the metal base material, for example, a base material made of gold, silver, copper, aluminum, nickel, iron, tin, or an alloy thereof can be used, and a base material made of aluminum or copper can be used. It is preferable because it has excellent processability of the conductive base material and is relatively low cost.
As the base material made of copper, for example, a base material made of electrolytic copper, a base material made of rolled copper, etc. can be used.

The base material made of electrolytic copper includes CF-T9FZ-HS-12 (thickness 12 μm), CF-T8G-DK-18 (thickness 18 μm), and CF-T8G-DK manufactured by Fukuda Metal Foil and Powder Industries Co., Ltd. -35 (thickness: 35 μm), etc. can be used.

As the rolled copper foil, TCU-H-8-RT (thickness: 8 μm) manufactured by Nippon Foil Co., Ltd., TPC (thickness: 6 μm) manufactured by JX Nippon Mining & Metals Co., Ltd., etc. can be used.

The conductive base material preferably has a thickness of 1 μm to 30 μm, more preferably 3 μm to 25 μm, and it is preferable to use metal foil or the like with a thickness of 5 μm to 20 μm. , is more preferable for obtaining a conductive thin pressure-sensitive adhesive sheet with excellent processability.

(Release liner)
If necessary, a release liner may be laminated on the surface of the conductive adhesive layer constituting the conductive thin adhesive sheet of the present invention.

The release liner is not particularly limited, and includes, for example, papers such as kraft paper, glassine paper, and high-quality paper, resin films such as polyethylene, polypropylene (OPP, CPP), and polyethylene terephthalate, and laminations of the above-mentioned papers and resin films. Conventionally known laminated paper, such as paper whose surface has been sealed with clay, polyvinyl alcohol, etc., and paper whose one or both sides of the sealed paper have been peeled off with silicone resin, etc. can be used.

The conductive thin pressure-sensitive adhesive sheet of the present invention can be produced, for example, by coating the pressure-sensitive adhesive composition containing conductive particles on one or both sides of the conductive substrate and drying it (so-called direct coating method).

Further, the conductive thin adhesive sheet of the present invention is prepared by coating the adhesive composition containing the conductive particles on the surface of a release liner in advance and drying it to form a conductive adhesive layer. Next, the conductive adhesive layer can also be manufactured by a method of transferring it to one or both sides of the conductive base material (so-called transfer method).

The conductive thin adhesive sheet produced by any of the methods described above is preferably cured for 48 hours or more at a temperature of 20° C. to 50° C. in order to promote the crosslinking reaction of the conductive adhesive layer.

The method of applying the conductive adhesive composition to the release liner or conductive substrate includes, for example, a method of applying using a comma coater, a method of applying using a gravure coater, a method of applying using a lip coater. For example, a method of coating with Among these, as the coating method, it is preferable to adopt a coating method using a gravure coater or a coating method using a lip coater, and it is preferable to adopt a coating method using a microgravure coater. The thickness of the conductive pressure-sensitive adhesive layer can be formed with high precision, which is more preferable in that it achieves both better conductivity and adhesiveness.

Examples of preferred configurations of the conductive thin pressure-sensitive adhesive sheet of the present invention are shown in FIGS. 1 and 2. FIG. 1 shows a single-sided adhesive sheet in which a conductive adhesive layer 2 is laminated on a conductive base material 1. Further, FIG. 2 shows a double-sided adhesive sheet in which conductive adhesive layers 2 are laminated on both sides of a conductive base material 1. In these configurations, a configuration in which a release liner is provided on the surface of the adhesive layer 2 can be preferably used.

Examples will be specifically described below, but the present invention is not limited to these examples.

(Preparation of acrylic adhesive composition 1)
Into a reaction vessel equipped with a cooling tube, a stirrer, a thermometer, and a dropping funnel were added 75.0 parts by mass of n-butyl acrylate, 19.0 parts by mass of 2-ethylhexyl acrylate, 3.9 parts by mass of vinyl acetate, and 2.0 parts by mass of acrylic acid. Part by mass, 0.1 part by mass of 2-hydroxyethyl acrylate, and 0.1 part by mass of 2,2'-azobisisobutylnitrile as a polymerization initiator were dissolved in 100 parts by mass of ethyl acetate, and the mixture was replaced with nitrogen. By polymerizing at 80° C. for 12 hours, an ethyl acetate solution of an acrylic polymer having a weight average molecular weight of 600,000 was obtained.

Per 100 parts by mass of the solid content of the ethyl acetate solution of the acrylic polymer, 10 parts by mass of Pencel D-135 (manufactured by Arakawa Chemical Co., Ltd., polymerized rosin pentaerythritol ester, softening point 135 ° C.), Superester A-100. (Manufactured by Arakawa Chemical Co., Ltd., disproportionated rosin glycerin ester, softening point 100°C) was blended with 10 parts by mass, and the solid concentration of the acrylic polymer was adjusted to 40% by mass using ethyl acetate. Acrylic adhesive composition 1 was obtained.

[Preparation of conductive adhesive composition]
(Preparation of conductive adhesive composition A)
100 parts by mass of the acrylic adhesive composition 1, 0.4 parts by mass of nickel powder NI255T (d50: 26.0 μm) manufactured by Fukuda Metal Foil and Powder Industries Co., Ltd. as bead-shaped conductive particles, and Burnock NC40 (DIC) as a crosslinking agent. Conductive adhesive composition A was prepared by mixing 2 parts by mass of an isocyanate-based crosslinking agent (solid content 40% by mass) manufactured by Co., Ltd. and 70 parts by mass of ethyl acetate as a diluting solvent for 10 minutes using a dispersion stirrer. was prepared.

(Preparation of conductive adhesive composition B)
100 parts by mass of the acrylic adhesive composition 1, 2.0 parts by mass of nickel powder NI255T (d50: 26.0 μm) manufactured by Fukuda Metal Foil and Powder Industries Co., Ltd. as bead-shaped conductive particles, and Burnock NC40 (DIC) as a crosslinking agent. Conductive adhesive composition B was prepared by mixing 2 parts by mass of an isocyanate-based crosslinking agent (solid content 40% by mass) manufactured by Co., Ltd. and 70 parts by mass of ethyl acetate as a diluting solvent for 10 minutes using a dispersion stirrer. was prepared.

(Preparation of conductive adhesive composition C)
100 parts by mass of the acrylic adhesive composition 1, 0.4 parts by mass of nickel powder NI255T-280 (d50: 15.0 μm) manufactured by Fukuda Metal Foil and Powder Industries Co., Ltd. as bead-shaped conductive particles, and Burnock NC40 as a crosslinking agent. (Isocyanate crosslinking agent manufactured by DIC Corporation, solid content 40% by mass) and 70 parts by mass of ethyl acetate as a diluting solvent were mixed for 10 minutes using a dispersion stirrer to form a conductive adhesive. Product C was prepared.

(Preparation of conductive adhesive composition D)
100 parts by mass of the acrylic adhesive composition 1, 0.4 parts by mass of nickel powder NI255T-350 (d50: 13.0 μm) manufactured by Fukuda Metal Foil and Powder Industries Co., Ltd. as bead-shaped conductive particles, and Burnock NC40 as a crosslinking agent. (Isocyanate crosslinking agent manufactured by DIC Corporation, solid content 40% by mass) and 70 parts by mass of ethyl acetate as a diluting solvent were mixed for 10 minutes using a dispersion stirrer to form a conductive adhesive. Product D was prepared.

(Preparation of conductive adhesive composition E)
100 parts by mass of the acrylic adhesive composition 1, 4.0 parts by mass of nickel powder NI123 (d50: 12.0 μm) manufactured by Fukuda Metal Foil and Powder Industries Co., Ltd. as spherical conductive particles, and Burnock NC40 (DIC stock) as a crosslinking agent. Conductive adhesive composition E was prepared by mixing 2 parts by mass of an isocyanate-based crosslinking agent (solid content 40% by mass) manufactured by the company with 70 parts by mass of ethyl acetate as a diluting solvent for 10 minutes using a dispersion stirrer. was prepared.

(Preparation of conductive adhesive composition F)
100 parts by mass of the acrylic adhesive composition 1, 6.0 parts by mass of nickel powder NI255T (d50: 26.0 μm) manufactured by Fukuda Metal Foil & Powder Industry Co., Ltd., and Burnock NC40 (isocyanate-based manufactured by DIC Corporation) as a crosslinking agent. Conductive adhesive composition E was prepared by mixing 2 parts by mass of crosslinking agent (solid content 40% by mass) and 70 parts by mass of ethyl acetate as a diluting solvent for 10 minutes using a dispersion stirrer.

(Preparation of conductive adhesive composition G)
100 parts by mass of the acrylic adhesive composition 1, 6.0 parts by mass of nickel powder NI123 (d50: 12.0 μm) manufactured by Fukuda Metal Foil and Powder Industries Co., Ltd. as spherical conductive particles, and Burnock NC40 (DIC stock) as a crosslinking agent. Conductive adhesive composition G was prepared by mixing 2 parts by mass of an isocyanate-based crosslinking agent (solid content 40% by mass) manufactured by the company and 70 parts by mass of ethyl acetate as a diluting solvent for 10 minutes using a dispersion stirrer. Prepared.

(Preparation of conductive adhesive composition H)
100 parts by mass of the acrylic pressure-sensitive adhesive composition 1, 0.02 parts by mass of nickel powder NI255T (d50: 26.0 μm) manufactured by Fukuda Metal Foil & Powder Industry Co., Ltd., and Burnock NC40 (isocyanate-based manufactured by DIC Corporation) as a crosslinking agent. Conductive adhesive composition H was prepared by mixing 2 parts by mass of crosslinking agent (solid content 40% by mass) and 70 parts by mass of ethyl acetate as a diluting solvent for 10 minutes using a dispersion stirrer.

(Example 1)
[Preparation of conductive thin adhesive sheet]
Conductive adhesive composition A was coated on a release film "PET38x1 A3" manufactured by Nipper Co., Ltd. using a comma coater so that the thickness of the conductive adhesive layer after drying was 6 μm. After drying in a dryer at 80°C for 2 minutes, it was pasted on both sides of a 12 μm thick electrolytic copper foil (CF-T9FZ-HS-12, manufactured by Fukuda Metal Foil and Powder Industries Co., Ltd.), and then A conductive thin pressure-sensitive adhesive sheet was obtained by curing at ℃ for 48 hours.

(Example 2)
A conductive thin pressure-sensitive adhesive sheet was obtained in the same manner as in Example 1, except that conductive pressure-sensitive adhesive composition B was used instead of conductive pressure-sensitive adhesive composition A.

(Example 3)
A conductive thin adhesive sheet was obtained in the same manner as in Example 1, except that conductive adhesive composition C was used instead of conductive adhesive composition A.

(Example 4)
A conductive thin pressure-sensitive adhesive sheet was obtained in the same manner as in Example 1, except that conductive pressure-sensitive adhesive composition D was used instead of conductive pressure-sensitive adhesive composition A.

(Example 5)
A conductive thin adhesive sheet was obtained in the same manner as in Example 1, except that the thickness of the conductive adhesive layer after drying was 10 μm.

(Example 6)
A conductive thin adhesive sheet was obtained in the same manner as in Example 1, except that conductive adhesive composition E was used instead of conductive adhesive composition A.

(Example 7)
The electrolytic copper foil to be bonded was CF-T8G-DK-18 (thickness 18 μm) manufactured by Fukuda Metal Foil and Powder Industries Co., Ltd. instead of CF-T9FZ-HS-12 manufactured by Fukuda Metal Foil and Powder Industries Co., Ltd., and the surface to be bonded was A conductive thin adhesive sheet was obtained in the same manner as in Example 1 except that the sheet was changed to only one side.

(Comparative example 1)
A conductive thin adhesive sheet was obtained in the same manner as in Example 1, except that conductive adhesive composition F was used instead of conductive adhesive composition A.

(Comparative example 3)
A conductive thin pressure-sensitive adhesive sheet was obtained in the same manner as in Example 1, except that conductive pressure-sensitive adhesive composition G was used instead of conductive pressure-sensitive adhesive composition A.

(Comparative example 4)
A conductive thin film was prepared in the same manner as in Example 1, except that conductive adhesive composition E was used instead of conductive adhesive composition A, and the thickness of the conductive adhesive layer after drying was 15 μm. An adhesive sheet was obtained.

(Comparative example 5)
The same method as in Example 1 was used, except that conductive adhesive composition H was used instead of conductive adhesive composition A, and the copper foil to be bonded was TPC (thickness: 6 μm) manufactured by JX Nippon Mining & Metals Corporation. A conductive thin adhesive sheet was obtained.

(Comparative example 6)
A conductive thin adhesive sheet was obtained in the same manner as in Example 1 except that the thickness of the conductive adhesive layer after drying was 0.5 μm.

(evaluation)
The conductive pressure-sensitive adhesive sheets obtained in Examples and Comparative Examples were evaluated for their total thickness, conductivity, and adhesive strength.

[Total thickness of conductive adhesive sheet]
The total thickness of the conductive adhesive sheet was measured using a thickness gauge "TH-102" (manufactured by Tester Sangyo Co., Ltd.).

[Thickness of adhesive layer]
A part of the conductive adhesive layer formed on the surface of the release liner used in producing the conductive adhesive sheet in the above Examples and Comparative Examples was extracted, and one side of it was coated with S25 (manufactured by Unitika Co., Ltd.). , polyethylene terephthalate film, thickness 25 μm).

The release liner was peeled off from the sample, its thickness was measured using a thickness meter "TH-102" (manufactured by Tester Sangyo Co., Ltd.), and the value obtained by subtracting the thickness of S25 was calculated as the conductive adhesive layer. with a thickness of

[Conductivity evaluation method (resistance measurement)]
A brass electrode measuring 10 mm long x 10 mm wide was attached to one side of the conductive adhesive layer of a 10 mm wide x 10 mm wide conductive adhesive sheet.

A copper foil (thickness: 35 μm) measuring 7.5 mm in length×7.5 mm in width was attached to the other surface of the conductive adhesive sheet.

In an environment of 23°C and 50% RH, the terminals were connected to the brass electrode and copper foil with a load of 20N applied to the upper surface of the brass electrode, and a milliohmmeter (NF Circuit Design Co., Ltd.) was used. A current of 10 .mu.A was passed through the wire using a block (manufactured by BLOCK), and the resistance value was measured. A case where the resistance value was 40 mΩ or less was evaluated as having excellent conductivity. Moreover, the resistance value was measured again after 30 days had passed. A case where the resistance value was 120 mΩ or less was evaluated as having excellent electrical conductivity stability over time.

(Adhesion evaluation method)
A 20 mm wide conductive adhesive sheet was applied to the surface of a stainless steel plate (hereinafter referred to as "stainless steel plate") that had been hairline polished using No. 360 water-resistant abrasive paper under an environment of 23°C and 60% RH using a 2.0 kg roller. It was attached by applying pressure one time back and forth.

After the patch was left at room temperature for 1 hour, the 180 degree peel adhesive strength was measured at room temperature at a tensile rate of 300 mm/min using a tensile tester (Tensilon RTA-100, manufactured by A&D Co., Ltd.). In addition, when using a double-sided adhesive sheet as the conductive adhesive sheet, the conductive adhesive layer on the opposite side of the surface attached to the stainless steel plate is lined with S25 (manufactured by Unitika Co., Ltd., polyethylene terephthalate film, thickness 25 μm). did.
(Evaluation criteria for adhesive strength)
◎: 7N/20mm or more ○: 5N/20mm or more, less than 7N/20mm ×: Less than 4N/20mm

1 Conductive base material 2 Conductive adhesive layer

Claims (5)

A conductive adhesive sheet having a total thickness of 50 μm or less, comprising a conductive base material and two conductive adhesive layers provided on both sides of the conductive base material,
Each layer of the conductive adhesive layer contains 0.1 % to 10% by mass of at least one type of conductive particle,
The conductive particles have a particle size d50 of 12 μm to 30 μm,
The thickness of each layer of the conductive adhesive layer is 1 μm to 12 μm,
A conductive adhesive sheet, wherein the conductive particles have a particle diameter d50 of 100% to 500% of the thickness of the conductive adhesive layer containing the particles. The conductive pressure-sensitive adhesive sheet according to claim 1, wherein the conductive particles have a bead-like shape. The conductive adhesive sheet according to claim 1 or 2, wherein the conductive base material is a metal base material. The conductive adhesive sheet according to any one of claims 1 to 3 , wherein the conductive adhesive layer is an adhesive layer formed using an acrylic adhesive composition containing an acrylic polymer. A portable electronic device comprising the conductive adhesive sheet according to any one of claims 1 to 4 .

Images