JP7528433B2 - Conductive adhesive sheet - Google Patents

Description

The present invention relates to a conductive adhesive sheet.

Because of their ease of handling, conductive adhesive sheets are used to shield unwanted leakage electromagnetic waves radiated from electrical or electronic devices, to shield harmful spatial electromagnetic waves generated by other electrical or electronic devices, and for grounding to prevent static electricity. As electrical or electronic devices have become smaller and thinner in recent years, there is a demand for the conductive adhesive sheets used in these devices to also be thinner and smaller.

As the conductive adhesive sheet, for example, an adhesive sheet has been proposed that has an adhesive layer made of a conductive adhesive in which a metal filler is dispersed in an adhesive substance on a conductive base material (see, for example, Patent Document 1). Also, a conductive adhesive sheet has been proposed that has an adhesive layer that contains an adhesive resin and a carbon-based filler (see, for example, Patent Document 2).

JP 2018-53102 A International Publication No. 2016/051829

However, the pressure-sensitive adhesive sheet described in Patent Document 1 has a problem that it is prone to peeling over time because metal fillers are added as conductive particles, and the electrical conductivity decreases over time due to a decrease in contact points. Also, the conductive pressure-sensitive adhesive sheet described in Patent Document 2 has a problem that it does not obtain electrical conductivity that is sufficiently satisfactory for the demand for low resistance associated with the recent trend toward smaller surface area because carbon-based fillers are added as conductive particles.
An object of the present invention is to provide a conductive pressure-sensitive adhesive sheet that has excellent electrical conductivity both initially and over time while retaining high adhesive strength.

The means for solving the above problems are as follows.
<1> A conductive adhesive sheet having an adhesive layer,
The pressure-sensitive adhesive layer contains carbon particles, metal particles, and a pressure-sensitive adhesive,
The content of the carbon particles is 75 parts by mass or less relative to 100 parts by mass of a solid content of the adhesive,
The conductive adhesive sheet is characterized in that the content of the metal particles is 145 parts by mass or less per 100 parts by mass of a solid content of the adhesive.
<2> The conductive adhesive sheet according to <1>, wherein a mass ratio (A/B) of a content A of the carbon particles in the adhesive layer to a content B of the metal particles in the adhesive layer is 1/10 or more and 7/10 or less.
<3> The conductive adhesive sheet according to any one of <1> and <2>, wherein the content of the carbon particles is 3 parts by mass or more and 50 parts by mass or less with respect to 100 parts by mass of a solid content of the adhesive.
<4> The conductive adhesive sheet according to any one of <1> to <3>, wherein a content of the metal particles is 10 parts by mass or more and 120 parts by mass or less with respect to 100 parts by mass of a solid content of the adhesive.
<5> The conductive adhesive sheet according to any one of <1> to <4>, wherein the metal particles are spherical or filament-shaped.
<6> The conductive adhesive sheet according to any one of <1> to <5>, wherein the carbon particles have an average particle size of 100 nm or less.
<7> The conductive adhesive sheet according to any one of <1> to <6>, wherein the adhesive is an acrylic adhesive containing a (meth)acrylic polymer.
<8> The conductive adhesive sheet according to any one of <1> to <7>, wherein a test piece is prepared by attaching copper foil to one side of a conductive adhesive sheet, cutting the sheet to a size of 15 mm width x 100 mm width, and attaching two tin-plated plates to the other adhesive layer of the conductive adhesive sheet so that each has an attachment area of 15 mm x 15 mm. The test piece is prepared by measuring an initial resistance value and measuring the resistance value of the test piece after leaving it at 23°C for 168 hours. The rate of change in resistance value [(resistance value after leaving it for 168 hours/initial resistance value) x 100] is 300% or less.
<9> The conductive adhesive sheet according to any one of <1> to <8>, further comprising a conductive substrate.
<10> The conductive pressure-sensitive adhesive sheet according to any one of <1> to <9>, which is used for at least one of electromagnetic shielding and earthing inside and outside an electric or electronic device.

The present invention provides a conductive adhesive sheet that maintains high adhesive strength while having excellent electrical conductivity both initially and over time.

FIG. 1 is a schematic cross-sectional view showing an example of the conductive adhesive sheet of the present invention. FIG. 2 is a schematic cross-sectional view showing another example of the conductive adhesive sheet of the present invention. FIG. 3 is a schematic cross-sectional view showing another example of the conductive adhesive sheet of the present invention.

(Conductive adhesive sheet)
The conductive adhesive sheet of the present invention has an adhesive layer, and the adhesive layer contains carbon particles, metal particles, and an adhesive.
The conductive adhesive sheet preferably has a conductive substrate and a release liner in addition to the adhesive layer, and may have other layers such as an intermediate layer and an undercoat layer as long as the object of the present invention is not impaired.

The inventors of the present invention conducted extensive research into means for suppressing the increase in electrical resistance over time when metal particles are added to an adhesive layer, and discovered that by combining metal particles and carbon particles in a specified content in the adhesive layer, two types of conductive particles (metal particles and carbon particles) with different properties work synergistically to suppress the decrease in contact points over time without compromising high adhesive strength, resulting in a conductive adhesive sheet with excellent conductivity both initially and over time, which led to the creation of the present invention.

The "sheet" in the conductive adhesive sheet of the present invention means a form consisting of only an adhesive layer, or a form having at least one adhesive layer on a conductive substrate or a release liner, and includes all product forms such as individual leaves, rolls, thin plates, or strips (tapes).
The "conductive adhesive sheet" may also be referred to as a "conductive adhesive tape" or a "conductive adhesive film", but in the following description, it will be referred to as a "conductive adhesive sheet". Note that the surface of the adhesive layer in the conductive adhesive sheet may be referred to as the "adhesive surface".

The conductive adhesive sheet of the present invention may be a double-sided adhesive type in which both sides of the sheet are adhesive, or a single-sided adhesive type in which only one side of the sheet is adhesive.

The double-sided adhesive conductive adhesive sheet may be a so-called substrate-less conductive double-sided adhesive sheet that does not have a conductive substrate such as metal foil, or may be a so-called substrate-attached conductive double-sided adhesive sheet that has the conductive substrate.

An example of the substrate-less conductive double-sided pressure-sensitive adhesive sheet is a conductive pressure-sensitive adhesive sheet 10 consisting of only a pressure-sensitive adhesive layer 2, as shown in FIG.
An example of the substrate-attached conductive double-sided pressure-sensitive adhesive sheet is a conductive pressure-sensitive adhesive sheet 10 in which pressure-sensitive adhesive layers 2 are formed on both sides of a conductive substrate 1, as shown in FIG.

As an example of a single-sided adhesive conductive adhesive sheet, as shown in FIG. 3, there is a conductive adhesive sheet 10 in which an adhesive layer 2 is formed on one side of a conductive substrate 1 such as a metal foil. In FIGS. 1 to 3, carbon particles 3 and metal particles 4 contained in the adhesive layer 2 are shown diagrammatically. Although not shown, it is preferable that the surface of the adhesive layer 2 in FIGS. 1 to 3 has a release liner.

<Adhesive Layer>
The pressure-sensitive adhesive layer is a layer that provides an adhesive surface of the conductive pressure-sensitive adhesive sheet and has electrical conductivity (electrical conductivity). When the adhesive surface of the pressure-sensitive adhesive layer is attached to an adherend, electrical conduction is ensured between the adherend, such as a conductor, and the pressure-sensitive adhesive layer.
The pressure-sensitive adhesive layer contains carbon particles, metal particles, and a pressure-sensitive adhesive, and may further contain other components as required.

<<Adhesive>>
Examples of the adhesive constituting the adhesive layer include (meth)acrylic adhesives, urethane adhesives, polyester adhesives, synthetic rubber adhesives, natural rubber adhesives, silicone adhesives, etc. Among these, (meth)acrylic adhesives are preferred from the viewpoints of high adhesion, low cost, and high durability.

- (Meth)acrylic adhesive -
The (meth)acrylic pressure-sensitive adhesive contains a (meth)acrylic polymer, and preferably contains a tackifier resin and a crosslinking agent, and further contains other components as necessary.

-(Meth)acrylic polymer-
Suitable examples of the (meth)acrylic polymer include acrylic copolymers containing, as a main monomer component, a (meth)acrylate monomer having 1 to 14 carbon atoms.
Examples of the (meth)acrylate having 1 to 14 carbon atoms include methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, t-butyl (meth)acrylate, n-hexyl (meth)acrylate, n-octyl (meth)acrylate, isooctyl (meth)acrylate, isononyl (meth)acrylate, cyclohexyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate. These may be used alone or in combination of two or more. Among these, (meth)acrylates having an alkyl group with 4 to 12 carbon atoms are preferred, (meth)acrylates having a linear or branched structure with 4 to 9 carbon atoms are more preferred, and n-butyl acrylate and 2-ethylhexyl acrylate are even more preferred because they provide a conductive adhesive sheet with high adhesive strength.

The content of (meth)acrylates having 1 to 14 carbon atoms in the (meth)acrylic polymer is preferably 70% by mass or more and 95% by mass or less, and more preferably 80% by mass or more and 95% by mass or less, of the monomer components constituting the (meth)acrylic polymer.

As the monomers usable in the production of the acrylic polymer, in addition to the above-mentioned ones, highly polar vinyl monomers can be used as necessary.
Examples of the highly polar vinyl monomer include (meth)acrylic monomers having a hydroxyl group, (meth)acrylic monomers having a carboxyl group, and (meth)acrylic monomers having an amide group. These may be used alone or in combination of two or more.

Examples of vinyl monomers having a hydroxyl group include (meth)acrylic monomers such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, and 6-hydroxyhexyl (meth)acrylate.

Examples of vinyl monomers having a carboxyl group include (meth)acrylic monomers such as acrylic acid, methacrylic acid, itaconic acid, maleic acid, (meth)acrylic acid dimer, crotonic acid, and ethylene oxide-modified succinic acid acrylate. Of these, it is preferable to use acrylic acid.

Examples of vinyls having an amide group include (meth)acrylic monomers such as N-vinylpyrrolidone, N-vinylcaprolactam, acryloylmorpholine, acrylamide, and N,N-dimethylacrylamide.

In addition to the above, the highly polar vinyl monomer may be vinyl acetate, ethylene oxide modified succinic acid acrylate, 2-acrylamido-2-methylpropanesulfonic acid, or other sulfonic acid group-containing monomers.

The highly polar vinyl monomer is preferably used in the range of 1.5% by mass to 20% by mass, more preferably 1.5% by mass to 10% by mass, based on the total amount of monomers used in the production of the acrylic polymer, and even more preferably 2% by mass to 8% by mass, since this allows the formation of a pressure-sensitive adhesive layer that is well-balanced in terms of cohesive strength, retention, and adhesiveness.

Among the highly polar vinyl monomers, the vinyl monomer having a hydroxyl group is preferably used when the pressure-sensitive adhesive contains an isocyanate-based crosslinking agent.Specific examples of the vinyl monomer having a hydroxyl group include 2-hydroxyethyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, and 6-hydroxyhexyl (meth)acrylate.
The vinyl monomer having a hydroxyl group is preferably used in an amount of 0.01% by mass or more and 1.0% by mass or less, and more preferably 0.03% by mass or more and 0.3% by mass or less, based on the total amount of monomers used in the production of the acrylic polymer.

The acrylic polymer can be produced by polymerizing the monomers by a known polymerization method such as a solution polymerization method, a bulk polymerization method, a suspension polymerization method, or an emulsion polymerization method. Among these, the solution polymerization method or the bulk polymerization method is preferable.
In the polymerization, if necessary, a peroxide-based thermal polymerization initiator such as benzoyl peroxide or lauroyl peroxide, an azo thermal polymerization initiator such as azobisisobutylnitrile, an acetophenone-based photopolymerization initiator, a benzoin ether-based photopolymerization initiator, a benzyl ketal-based photopolymerization initiator, an acylphosphine oxide-based photopolymerization initiator, a benzoin-based photopolymerization initiator, a benzophenone-based photopolymerization initiator, or the like can be used.

The (meth)acrylic polymer obtained by the above method preferably has a weight average molecular weight (Mw) of 500,000 or more and 2,500,000 or less, more preferably 700,000 or more and 2,000,000 or less, and even more preferably 900,000 or more and 1,800,000 or less.
The weight average molecular weight is a weight average molecular weight calculated as standard polystyrene, measured by gel permeation chromatography (GPC).

The molecular weight is measured by the GPC method using a GPC apparatus (HLC-8329GPC) manufactured by Tosoh Corporation under the following measurement conditions, and is expressed as a standard polystyrene equivalent value.
[Measurement condition]
Sample concentration: 0.5% by mass (tetrahydrofuran solution)
Sample injection volume: 100 μL
Eluent: THF (tetrahydrofuran)
・Flow rate: 1.0mL/min ・Measurement temperature: 40℃
Main column: TSKgel GMHHR-H (20) x 2 Guard column: TSKgel HXL-H
Detector: Differential refractometer Standard polystyrene molecular weight: 10,000 to 20,000,000 (manufactured by Tosoh Corporation)

- Tackifying resin -
As the (meth)acrylic pressure-sensitive adhesive, it is preferable to use one that contains a tackifier resin in order to improve the adhesion to the adherend and the surface adhesive strength.
Examples of the tackifier resin that can be used include rosin-based tackifier resins, polymerizable rosin-based tackifier resins, polymerizable rosin ester-based tackifier resins, rosin phenol-based tackifier resins, stabilized rosin ester-based tackifier resins, disproportionated rosin ester-based tackifier resins, hydrogenated rosin ester-based tackifier resins, terpene-based tackifier resins, terpene phenol-based tackifier resins, petroleum resin-based tackifier resins, and (meth)acrylate-based tackifier resins.

Among these, it is preferable to use disproportionated rosin ester tackifying resins, polymerizable rosin ester tackifying resins, rosin phenol tackifying resins, hydrogenated rosin ester tackifying resins, (meth)acrylate resins, and terpene phenol resins, either alone or in combination.

The tackifier resin preferably has a softening point of 30°C or more and 180°C or less, and more preferably has a softening point of 70°C or more and 140°C or less in order to form an adhesive layer with high adhesive performance. When using a (meth)acrylate tackifier resin, it is preferable to use one with a glass transition temperature of 30°C or more and 200°C or less, and more preferably to use one with a glass transition temperature of 50°C or more and 160°C or less.

The tackifier resin is preferably used in an amount of 5 to 65 parts by weight per 100 parts by weight of the (meth)acrylic polymer, and more preferably in an amount of 8 to 55 parts by weight, since this makes it easier to ensure adhesion to the adherend.

- Crosslinking agent -
The (meth)acrylic adhesive preferably contains a crosslinking agent in order to further improve the cohesive strength of the adhesive layer. The crosslinking agent may be an isocyanate crosslinking agent, an epoxy crosslinking agent, a metal chelate crosslinking agent, an aziridine crosslinking agent, etc. Among them, the crosslinking agent is preferably a type of crosslinking agent that is mixed with the acrylic polymer after production to promote a crosslinking reaction, and is preferably an isocyanate crosslinking agent or an epoxy crosslinking agent that is highly reactive with the acrylic polymer.

Examples of the isocyanate crosslinking agent include tolylene diisocyanate, naphthylene-1,5-diisocyanate, hexamethylene diisocyanate, diphenylmethane diisocyanate, xylylene diisocyanate, and trimethylolpropane-modified tolylene diisocyanate. Among these, trifunctional polyisocyanate compounds are preferred. Examples of trifunctional isocyanate compounds include tolylene diisocyanate or its trimethylolpropane adduct, and triphenylmethane isocyanate.

As an index of the degree of crosslinking, the gel fraction value obtained by measuring the insoluble portion after immersing the pressure-sensitive adhesive layer in toluene for 24 hours is used. The gel fraction of the pressure-sensitive adhesive layer is preferably 10% by mass or more and 70% by mass or less, more preferably 25% by mass or more and 65% by mass or less, even more preferably 35% by mass or more and 60% by mass or less, and particularly preferably 40% by mass or more and 55% by mass or less.

The gel fraction refers to a value measured by the following method. The adhesive composition is coated on a release sheet so that the thickness after drying is 50 μm, dried at 100 ° C for 3 minutes, and aged at 40 ° C for 2 days, and cut into 50 mm squares to be used as a sample. Next, the mass (G1) of the above sample before immersion in toluene is measured in advance, and the toluene-insoluble portion of the sample after immersion in a toluene solution at 23 ° C for 24 hours is separated by filtering with a 300 mesh wire net, and the mass (G2) of the residue after drying at 110 ° C for 1 hour is measured, and the gel fraction is calculated according to the following formula. The weight (G3) of the conductive particles (carbon particles + metal particles) in the sample is calculated from the mass (G1) of the sample and the composition of the adhesive.
Gel fraction (mass%)=(G2−G3)/(G1−G3)×100

<Carbon particles>
The carbon particles are not particularly limited and can be appropriately selected depending on the purpose, and examples thereof include carbon black, glassy carbon, graphite, graphene, fullerene, carbon nanotubes, carbon fibers, etc. These may be used alone or in combination of two or more kinds.
The shape of the carbon particles is not particularly limited and can be appropriately selected depending on the purpose. Examples of the shape include spherical, elliptical, columnar, cylindrical, and fibrous shapes.

Examples of carbon black include furnace black, channel black, acetylene black, thermal black, and lamp black.

Examples of the graphite include natural graphite, kish graphite, and artificial graphite. The artificial graphite may be anisotropic graphite, isotropic graphite, or a mixture of these, but isotropic graphite is preferable from the viewpoint of the mechanical strength of the carbon particles. The graphite may be crystalline or amorphous, or a mixture of these. The graphite may be a carbon fiber-reinforced carbon composite material (C/C composite) in which graphite is reinforced with carbon fibers.

Examples of the fullerene include _C60 , _C70 , _C80 , _C84 , and _C96 .

The carbon nanotube is a cylindrical carbon polyhedron having a cylindrically closed graphite sheet with a carbon six-membered ring structure as the main structure. Carbon nanotubes include single-walled carbon nanotubes having a cylindrically closed structure of one graphite sheet, double-walled carbon nanotubes having a cylindrically closed structure of two graphite sheets, and multi-walled carbon nanotubes having a multi-layer structure of three or more graphite sheets closed in a concentric cylinder, and any of these can be used.

The average particle size of the carbon particles is preferably 100 nm or less, more preferably 50 nm or less, and even more preferably 30 nm or less. When the average particle size of the carbon particles is 100 nm or less, both high adhesive strength and excellent initial and aging conductivity can be achieved.
The average particle size of the carbon particles is a volume-based average particle size, and examples of a measuring device therefor include Microtrac MT3000II manufactured by Nikkiso Co., Ltd. and a laser diffraction type particle size distribution measuring instrument SALD-3000 manufactured by Shimadzu Corporation.

The content of the carbon particles is 75 parts by mass or less, preferably 3 parts by mass or more and 50 parts by mass or less, more preferably 5 parts by mass or more and 30 parts by mass or less, and even more preferably 10 parts by mass or more and 20 parts by mass or less, relative to 100 parts by mass of the solid content of the adhesive. When the content of the carbon particles is within the above content range, it is possible to achieve both high adhesive strength and excellent electrical conductivity both initially and over time.

<Metal Particles>
The metal particles are not particularly limited as long as they are conductive particles such as metal powder, and can be appropriately selected depending on the purpose, and examples thereof include metals such as nickel, iron, chromium, cobalt, aluminum, antimony, molybdenum, copper, silver, platinum, and gold, as well as alloys such as solder and stainless steel, etc. These may be used alone or in combination of two or more kinds.
Among these, nickel, copper and silver are preferred, and nickel powder produced by the carbonyl method is more preferred.
Examples of nickel powder produced by the carbonyl method include Ni123 (spherical) manufactured by Vale and Ni255 (filamentary) manufactured by Vale.

The shape of the metal particles is not particularly limited and can be appropriately selected depending on the purpose. Examples include spherical, filamentous (bead-like), flake-like (thin piece), and spike-like (chestnut-shaped). Of these, spherical or filamentous shapes are preferred from the viewpoints of ensuring adhesive strength and facilitating the formation of conductive paths by the metal particles in the adhesive layer.

The particle diameter of the metal particles is not particularly limited and can be appropriately selected depending on the purpose, but the particle diameter d40 is preferably 5 μm or more and 30 μm or less, and more preferably 10 μm or more and 20 μm or less.
The particle diameter d70 is preferably 10 μm or more and 50 μm or less, and more preferably 20 μm or more and 40 μm or less.
The particle diameter d40 refers to the 40% cumulative volume particle diameter in the volume particle size distribution, and the particle diameter d70 refers to the 70% cumulative volume particle diameter in the volume particle size distribution, and is a value measured by a laser analysis scattering method. Examples of the measuring device include Microtrac MT3000II manufactured by Nikkiso Co., Ltd. and a laser diffraction type particle size distribution measuring instrument SALD-3000 manufactured by Shimadzu Corporation.

Methods for adjusting the particle diameters d40 and d70 to the above numerical ranges include, for example, grinding the metal particles with a jet mill or sieving them using a sieve.

The content of the metal particles is 145 parts by mass or less, preferably 10 parts by mass or more and 120 parts by mass or less, and more preferably 20 parts by mass or more and 80 parts by mass or less, per 100 parts by mass of the solid content of the adhesive. By setting the content of the metal particles within the above range, it is possible to achieve both high adhesive strength and excellent electrical conductivity both initially and over time.

In the present invention, the mass ratio (A/B) of the content A of the carbon particles in the adhesive layer to the content B of the metal particles in the adhesive layer is preferably 1/10 or more and 7/10 or less, more preferably 2/10 or more and 5/10 or less, and even more preferably 2.5/10 or more and 4/10 or less.
By setting the mass ratio (A/B) within the above range, it is possible to achieve both high adhesive strength and excellent electrical conductivity both initially and over time.

As a method for dispersing the metal particles and the carbon particles in the adhesive layer, for example, a method of dispersing a (meth)acrylic polymer, metal particles, carbon particles, a solvent, additives, etc., using a dispersion stirrer can be mentioned. Commercially available dispersion stirrers include dissolvers, butterfly mixers, BDM two-shaft mixers, planetary mixers, etc. manufactured by Inoue Seisakusho Co., Ltd. Among these, dissolvers and butterfly mixers that can apply a moderate shear with little thickening of the adhesive during stirring are preferred.

<Other ingredients>
Other components in the pressure-sensitive adhesive layer include, for example, additives such as antioxidants, ultraviolet absorbers, fillers, polymerization inhibitors, surface conditioners, antistatic agents, defoamers, viscosity modifiers, light stabilizers, weather stabilizers, heat stabilizers, antioxidants, leveling agents, organic pigments, inorganic pigments, pigment dispersants, plasticizers, softeners, flame retardants, metal deactivators, silica beads, organic beads, etc.; inorganic fillers such as silicon oxide, aluminum oxide, titanium oxide, zirconia, antimony pentoxide, etc.

The conductive adhesive tape of the present invention can be produced, for example, by applying the adhesive to a release liner or a conductive substrate using a roll coater, a die coater, or the like, and drying the applied adhesive. Alternatively, the conductive adhesive tape can be produced by a transfer method in which an adhesive layer formed on a release liner is laminated to a conductive substrate.
The double-sided pressure-sensitive adhesive tape can be produced by a transfer method in which the pressure-sensitive adhesive is applied to the surface of a release liner using a roll coater or the like, and then dried to form a pressure-sensitive adhesive layer, and then the pressure-sensitive adhesive layer is bonded to both sides of a conductive substrate.

When bonding the adhesive layer formed on the release liner to the conductive substrate, it is preferable to perform thermal lamination from the viewpoint of imparting excellent adhesion between the conductive substrate and the adhesive layer. The temperature for thermal lamination is preferably 60°C or higher and 150°C or lower, more preferably 70°C or higher and 130°C or lower, and even more preferably 80°C or higher and 110°C or lower in terms of adhesion and suppressing shrinkage of the conductive substrate.

-Release liner-
The release liner is not particularly limited and can be appropriately selected depending on the purpose. Examples of the release liner include papers such as kraft paper, glassine paper, and wood-free paper; resin films such as polyethylene, polypropylene (OPP, CPP), and polyethylene terephthalate; laminated paper in which the above-mentioned papers and resin films are laminated together; and papers that have been sealed with clay, polyvinyl alcohol, or the like and then treated with a release agent such as a silicone-based resin on one or both sides.

- Conductive substrate -
Examples of conductive substrates that can be used in the conductive pressure-sensitive adhesive sheet of the present invention include metal foil substrates and conductive substrates in which a wet-type polyester nonwoven fabric substrate is plated.
Examples of the material of the metal foil include gold, silver, copper, aluminum, nickel, iron, tin, and alloys thereof. Among these, a conductive base material containing copper is preferred, and copper foil is more preferred from the viewpoints of conductivity, processability, and cost.

It is preferable to apply an anti-rust treatment to the copper foil. Types of anti-rust treatment include organic and inorganic anti-rust treatments, with inorganic anti-rust treatment being the most preferable. Commercially available electrolytic copper foils include CF-T9FZ-HS-12 (12 μm: chromate treatment) and CF-T9FZ-HS-9 (9 μm: chromate treatment) manufactured by Fukuda Metal Foil and Powder Co., Ltd. Commercially available rolled copper foils include TCU-H-8-RT (8 μm: organic anti-rust treatment) manufactured by Nippon Foil Co., Ltd. and BAY-64T-DT (35 μm: chromate treatment) manufactured by JX Nippon Mining & Metals Corporation.

The conductive substrate obtained by plating the wet polyester nonwoven substrate is one in which electroless metal plating is used. Examples of metals to be plated include copper, nickel, silver, platinum, and aluminum. Among these, copper or nickel is preferred from the standpoint of conductivity and cost.

The thickness of the conductive substrate is preferably 1 μm or more and 40 μm or less, more preferably 3 μm or more and 35 μm or less, and even more preferably 6 μm or more and 25 μm or less. The thickness in the above numerical range is preferable because it can be made thin and has excellent processability.

The conductive adhesive sheet of the present invention may be a so-called substrate-less conductive adhesive sheet that does not have a conductive substrate, or may be a so-called substrate-attached conductive adhesive sheet that has a conductive substrate.

The substrate-less conductive adhesive sheet is composed only of an adhesive layer, and the average thickness of the adhesive layer is the total thickness of the conductive adhesive sheet. The substrate-less conductive adhesive sheet is formed on a release liner, and is covered with the release liner until use.
The average thickness of the substrateless conductive adhesive sheet (average thickness of the adhesive layer) is preferably 30 μm or less, more preferably 5 μm or more and 25 μm or less, and even more preferably 10 μm or more and 20 μm or less. When it is within the above numerical range, it is possible to achieve both excellent adhesiveness and conductivity and a thin shape.

The total thickness of the conductive adhesive sheet with substrate is preferably 100 μm or less, more preferably 65 μm or less, and even more preferably 50 μm or less. By being in the above range, it is possible to make the conductive adhesive sheet thinner while ensuring adhesion and conductivity, which can contribute to making portable electronic devices thinner. Note that the total thickness of the conductive adhesive sheet is the thickness of the conductive adhesive sheet itself, not including the release liner.

The conductive adhesive sheet of the present invention is preferably such that the 180 degree peel adhesion strength at 300 mm/min after the conductive adhesive sheet is pressed against a stainless steel plate (SUS plate) in an environment of a temperature of 23°C and a humidity of 50% RH with a 2 kg roller in one back and forth motion and left to stand for 1 hour is 5 N/25 mm or more.
When the thickness is within the above range, peeling is easily suppressed, and the conductive adhesive sheet can be peeled off in defective products during the manufacturing process.

The conductive adhesive sheet of the present invention is prepared by attaching copper foil to one side of the conductive adhesive sheet, cutting the sheet to a size of 15 mm wide x 100 mm wide, and attaching two tin-plated plates to the other adhesive layer of the conductive adhesive sheet so that each has an adhesion area of 15 mm x 15 mm. The resistance change rate [(resistance after 168 hours/initial resistance) x 100] of the test piece, calculated from the measured initial resistance value and the resistance value measured after leaving the test piece at 23°C for 168 hours, is preferably 300% or less, more preferably 200% or less, and even more preferably 150% or less.
When the rate of change in resistance is 300% or less, excellent electrical conductivity can be achieved both initially and over time.

<Applications>
The conductive adhesive sheet of the present invention can achieve both high adhesive strength and excellent initial and aging conductivity, and is therefore useful, for example, for shielding electromagnetic waves used in electrical or electronic devices, for shielding harmful spatial electromagnetic waves generated by other electrical or electronic devices, and for fixing to earth to prevent static electricity. Among these, it is suitable for use in portable electronic devices that are becoming thinner and have strict volume restrictions within the housing, and is particularly suitable for use by attaching it to the built-in components of small electronic terminals.

Examples of the present invention will be described below, but the present invention is not limited to these examples in any way.
The weight average molecular weight of the acrylic copolymer, the average particle size of the carbon particles, and the particle size d40 and particle size d70 of the metal particles used in the following Examples and Comparative Examples were measured by the following methods.

<Weight average molecular weight of acrylic copolymer>
The molecular weight of the acrylic copolymer is measured by the GPC method using a GPC apparatus (HLC-8329GPC) manufactured by Tosoh Corporation under the following measurement conditions, and is expressed as a standard polystyrene equivalent value.
[Measurement condition]
Sample concentration: 0.5% by mass (tetrahydrofuran solution)
Sample injection volume: 100 μL
Eluent: THF (tetrahydrofuran)
・Flow rate: 1.0mL/min ・Measurement temperature: 40℃
Main column: TSKgel GMHHR-H (20) x 2 Guard column: TSKgel HXL-H
Detector: Differential refractometer Standard polystyrene molecular weight: 10,000 to 20,000,000 (manufactured by Tosoh Corporation)

<Average particle size of carbon particles>
The average particle size of the carbon particles is a volume average particle size, and is a value measured using a laser diffraction particle size distribution analyzer SALD-3100 manufactured by Shimadzu Corporation, using isopropanol as a dispersion medium.

<Particle diameter d40 and particle diameter d70 of metal particles>
The particle diameters d40 and d70 of the metal particles are the cumulative 40% particle diameter and cumulative 70% particle diameter on a volume basis, and are values measured using a laser diffraction particle size distribution analyzer SALD-3100 manufactured by Shimadzu Corporation, using isopropanol as a dispersion medium.

(Synthesis Example 1 of Acrylic Copolymer)
<Acrylic Copolymer (1)>
In a reaction vessel equipped with a stirrer, a reflux condenser, a thermometer, a dropping funnel, and a nitrogen gas inlet, 92 parts by mass of n-butyl acrylate, 6 parts by mass of acrylic acid, 2 parts by mass of 2-hydroxyethyl acrylate, and 0.2 parts by mass of 2,2'-azobisisobutylnitrile as a polymerization initiator were dissolved in 100 parts by mass of ethyl acetate, and after nitrogen replacement, polymerization was carried out at 80°C for 8 hours to obtain an acrylic copolymer (1) having a weight average molecular weight of 700,000.

(Synthesis Example 2 of Acrylic Copolymer)
<Acrylic Copolymer (2)>
In a reaction vessel equipped with a stirrer, a reflux condenser, a thermometer, a dropping funnel, and a nitrogen gas inlet, 92 parts by mass of n-butyl acrylate, 6 parts by mass of acrylic acid, 2 parts by mass of 2-hydroxyethyl acrylate, and 0.1 parts by mass of 2,2'-azobisisobutylnitrile as a polymerization initiator were dissolved in 100 parts by mass of ethyl acetate, and after nitrogen replacement, polymerization was carried out at 80°C for 8 hours to obtain an acrylic copolymer (2) having a weight average molecular weight of 1,400,000.

(Synthesis Example 3 of Acrylic Copolymer)
<Acrylic Copolymer (3)>
In a reaction vessel equipped with a stirrer, a reflux condenser, a thermometer, a dropping funnel, and a nitrogen gas inlet, 70 parts by mass of n-butyl acrylate, 22 parts by mass of 2-ethylhexyl acrylate, 6 parts by mass of acrylic acid, 2 parts by mass of 2-hydroxyethyl acrylate, and 0.2 parts by mass of 2,2'-azobisisobutylnitrile as a polymerization initiator were dissolved in 100 parts by mass of ethyl acetate, and after nitrogen replacement, polymerization was carried out at 80°C for 8 hours to obtain an acrylic copolymer (3) having a weight average molecular weight of 700,000.

(Preparation Example 1 of Pressure-Sensitive Adhesive)
--Preparation of Adhesive A--
100 parts by mass of the acrylic copolymer (1) was mixed with 5 parts by mass of a polymerizable rosin ester-based tackifier resin (D-125, manufactured by Arakawa Chemical Industries, Ltd.) and 15 parts by mass of a petroleum-based tackifier resin (FTR6125, manufactured by Mitsui Chemicals, Inc.), and the mixture was stirred, and then ethyl acetate was added thereto to obtain a pressure-sensitive adhesive A having a solid content of 40% by mass.

(Preparation Example 2 of Pressure-Sensitive Adhesive)
--Preparation of Adhesive B--
100 parts by mass of the acrylic copolymer (2) was mixed with 5 parts by mass of a polymerizable rosin ester-based tackifier resin (D-125, manufactured by Arakawa Chemical Industries, Ltd.) and 15 parts by mass of a petroleum-based tackifier resin (FTR6125, manufactured by Mitsui Chemicals, Inc.), and the mixture was stirred, and then ethyl acetate was added thereto to obtain a pressure-sensitive adhesive B having a solid content of 40% by mass.

(Preparation Example 3 of Pressure-Sensitive Adhesive)
--Preparation of Adhesive C--
100 parts by mass of the acrylic copolymer (3) was mixed with 5 parts by mass of a polymerizable rosin ester-based tackifier resin (D-125, manufactured by Arakawa Chemical Industries, Ltd.) and 15 parts by mass of a petroleum-based tackifier resin (FTR6125, manufactured by Mitsui Chemicals, Inc.), and the mixture was stirred, and then ethyl acetate was added thereto to obtain a pressure-sensitive adhesive C having a solid content of 40% by mass.

(Preparation Example 4 of Pressure-Sensitive Adhesive)
--Preparation of Adhesive D--
Ethyl acetate was added to a polyester resin (NP-110S50EO, manufactured by Mitsubishi Chemical Corporation) to obtain a pressure-sensitive adhesive D having a solid content of 40% by mass.

Example 1
<Production of conductive adhesive composition A>
20 parts by mass of carbon particles (VULCAN XC72, manufactured by Cabot Corporation, average particle size 30 μm, furnace method), 80 parts by mass of metal particles (nickel, Ni123, manufactured by Vale Corporation, spherical, particle size d40 = 8.2 nm, particle size d70 = 16.6 nm), and 2 parts by mass of Burnock D-40 (manufactured by DIC Corporation, trimethylolpropane adduct of tolylene diisocyanate, isocyanate group content 7 mass%, non-volatile content 40 mass%) were blended relative to 100 parts by mass (solid content) of the pressure-sensitive adhesive A, and the solid content concentration was adjusted to 40 mass% with ethyl acetate, and the mixture was mixed with a dispersion stirrer to prepare a conductive pressure-sensitive adhesive composition A.

<Preparation of conductive adhesive sheet>
The obtained conductive adhesive composition A was coated on a release liner (PET38x1, A3, manufactured by Nippa Corporation) using a comma coater so that the average thickness after drying was 20 μm, and then dried for 2 minutes in a dryer at 80° C. Next, the conductive adhesive sheet of Example 1 was produced by laminating the sheet to a release liner (PET38x1, A3, manufactured by Nippa Corporation) and curing the sheet at 40° C. for 48 hours.

Example 2
<Production of conductive adhesive composition B>
20 parts by mass of carbon particles (Ketjen Black EC, manufactured by Lion Specialty Co., Ltd., average particle size 30 μm, gasification method), 80 parts by mass of metal particles (nickel, Ni123, manufactured by Vale, spherical, particle size d40 = 8.2 nm, particle size d70 = 16.6 nm), and 2 parts by mass of Burnock D-40 (manufactured by DIC Corporation, trimethylolpropane adduct of tolylene diisocyanate, isocyanate group content 7 mass%, non-volatile content 40 mass%) were blended relative to 100 parts by mass (solid content) of the adhesive A, and the solid content concentration was adjusted to 40 mass% with ethyl acetate, and the mixture was mixed with a dispersion stirrer to prepare a conductive adhesive composition B.

<Preparation of conductive adhesive sheet>
The obtained conductive adhesive composition B was coated on a release liner (PET38x1, A3, manufactured by Nippa Corporation) using a comma coater so that the average thickness after drying was 20 μm, and dried for 2 minutes in a dryer at 80° C. Next, the conductive adhesive sheet of Example 2 was produced by laminating the sheet to a release liner (PET38x1, A3, manufactured by Nippa Corporation) and curing the sheet at 40° C. for 48 hours.

Example 3
<Production of conductive adhesive composition C>
20 parts by mass of carbon particles (Denka Black FX-35, manufactured by Denki Kagaku Kogyo Co., Ltd., average particle size 23 μm, acetylene method), 80 parts by mass of metal particles (nickel, Ni123, manufactured by Vale, spherical, particle size d40 = 8.2 nm, particle size d70 = 16.6 nm), and 2 parts by mass of Burnock D-40 (manufactured by DIC Corporation, trimethylolpropane adduct of tolylene diisocyanate, isocyanate group content 7 mass%, non-volatile content 40 mass%) were blended relative to 100 parts by mass (solid content) of the adhesive A, and the solid content concentration was adjusted to 40 mass% with ethyl acetate, and the mixture was mixed with a dispersion stirrer to prepare a conductive adhesive composition C.

<Preparation of conductive adhesive sheet>
The obtained conductive adhesive composition C was coated on a release liner (PET38x1, A3, manufactured by Nippa Corporation) using a comma coater so that the average thickness after drying was 20 μm, and then dried for 2 minutes in a dryer at 80° C. Next, the conductive adhesive sheet of Example 3 was produced by laminating the sheet to a release liner (PET38x1, A3, manufactured by Nippa Corporation) and curing the sheet at 40° C. for 48 hours.

Example 4
<Production of conductive adhesive composition D>
A conductive adhesive composition D was prepared by blending 7 parts by mass of carbon particles (VULCAN XC72, manufactured by Cabot Corporation, average particle size 30 μm, furnace method), 80 parts by mass of metal particles (nickel, Ni123, manufactured by Vale Corporation, spherical, particle size d40 = 8.2 nm, particle size d70 = 16.6 nm), and 2 parts by mass of Burnock D-40 (manufactured by DIC Corporation, trimethylolpropane adduct of tolylene diisocyanate, isocyanate group content 7 mass%, non-volatile content 40 mass%) with 100 parts by mass of the adhesive A (solid content), adjusting the solid content concentration to 40 mass% with ethyl acetate, and mixing with a dispersion stirrer.

<Preparation of conductive adhesive sheet>
The obtained conductive adhesive composition D was coated on a release liner (PET38×1, A3, manufactured by Nippa Corporation) using a comma coater so that the average thickness after drying was 20 μm, and dried for 2 minutes in a dryer at 80° C. Next, the conductive adhesive sheet of Example 4 was produced by laminating the sheet to a release liner (PET38×1, A3, manufactured by Nippa Corporation) and curing the sheet at 40° C. for 48 hours.

Example 5
<Production of conductive adhesive composition E>
A conductive adhesive composition E was prepared by blending 40 parts by mass of carbon particles (VULCAN XC72, manufactured by Cabot Corporation, average particle size 30 μm, furnace method), 80 parts by mass of metal particles (nickel, Ni123, manufactured by Vale Corporation, spherical, particle size d40 = 8.2 nm, particle size d70 = 16.6 nm), and 2 parts by mass of Burnock D-40 (manufactured by DIC Corporation, trimethylolpropane adduct of tolylene diisocyanate, isocyanate group content 7 mass%, non-volatile content 40 mass%) with 100 parts by mass of the adhesive A (solid content), adjusting the solid content concentration to 40 mass% with ethyl acetate, and mixing with a dispersion stirrer.

<Preparation of conductive adhesive sheet>
The obtained conductive adhesive composition E was coated on a release liner (PET38×1, A3, manufactured by Nippa Corporation) using a comma coater so that the average thickness after drying was 20 μm, and then dried for 2 minutes in a dryer at 80° C. Next, the conductive adhesive sheet of Example 5 was produced by laminating the sheet to a release liner (PET38×1, A3, manufactured by Nippa Corporation) and curing the sheet at 40° C. for 48 hours.

Example 6
<Production of conductive adhesive composition F>
20 parts by mass of carbon particles (VULCAN XC72, manufactured by Cabot Corporation, average particle size 30 μm, furnace method), 80 parts by mass of metal particles (nickel, Ni255, manufactured by Vale Corporation, filamentous, particle size d40 = 17.2 nm, particle size d70 = 35.4 nm), and 2 parts by mass of Burnock D-40 (manufactured by DIC Corporation, trimethylolpropane adduct of tolylene diisocyanate, isocyanate group content 7 mass%, non-volatile content 40 mass%) were blended relative to 100 parts by mass (solid content) of the pressure-sensitive adhesive A, and the solid content concentration was adjusted to 40 mass% with ethyl acetate, and the mixture was mixed with a dispersion stirrer to prepare a conductive pressure-sensitive adhesive composition F.

<Preparation of conductive adhesive sheet>
The obtained conductive adhesive composition F was coated on a release liner (PET38x1, A3, manufactured by Nippa Corporation) using a comma coater so that the average thickness after drying was 20 μm, and then dried for 2 minutes in a dryer at 80° C. Next, the conductive adhesive sheet of Example 6 was produced by laminating the sheet to a release liner (PET38x1, A3, manufactured by Nippa Corporation) and curing the sheet at 40° C. for 48 hours.

(Example 7)
<Production of conductive adhesive composition G>
20 parts by mass of carbon particles (VULCAN XC72, manufactured by Cabot Corporation, average particle size 30 μm, furnace method), 40 parts by mass of metal particles (nickel, Ni255, manufactured by Vale Corporation, filamentous, particle size d40 = 17.2 nm, particle size d70 = 35.4 nm), and 2 parts by mass of Burnock D-40 (manufactured by DIC Corporation, trimethylolpropane adduct of tolylene diisocyanate, isocyanate group content 7 mass%, non-volatile content 40 mass%) were blended relative to 100 parts by mass (solid content) of the pressure-sensitive adhesive A, and the solid content concentration was adjusted to 40 mass% with ethyl acetate, and the mixture was mixed with a dispersion stirrer to prepare a conductive pressure-sensitive adhesive composition G.

<Preparation of conductive adhesive sheet>
The obtained conductive adhesive composition G was coated on a release liner (PET38x1, A3, manufactured by Nippa Corporation) using a comma coater so that the average thickness after drying was 20 μm, and then dried for 2 minutes in a dryer at 80° C. Next, the conductive adhesive sheet of Example 7 was produced by laminating the sheet to a release liner (PET38x1, A3, manufactured by Nippa Corporation) and curing the sheet at 40° C. for 48 hours.

(Example 8)
<Production of conductive adhesive composition H>
20 parts by mass of carbon particles (VULCAN XC72, manufactured by Cabot Corporation, average particle size 30 μm, furnace method), 100 parts by mass of metal particles (nickel, Ni255, manufactured by Vale Corporation, filamentous, particle size d40 = 17.2 nm, particle size d70 = 35.4 nm), and 2 parts by mass of Burnock D-40 (manufactured by DIC Corporation, trimethylolpropane adduct of tolylene diisocyanate, isocyanate group content 7 mass%, non-volatile content 40 mass%) were blended relative to 100 parts by mass (solid content) of the pressure-sensitive adhesive A, and the solid content concentration was adjusted to 40 mass% with ethyl acetate, and the mixture was mixed with a dispersion stirrer to prepare a conductive pressure-sensitive adhesive composition H.

<Preparation of conductive adhesive sheet>
The obtained conductive adhesive composition H was coated on a release liner (PET38×1, A3, manufactured by Nippa Corporation) using a comma coater so that the average thickness after drying was 20 μm, and then dried for 2 minutes in a dryer at 80° C. Next, the conductive adhesive sheet of Example 8 was produced by laminating the sheet to a release liner (PET38×1, A3, manufactured by Nippa Corporation) and curing the sheet at 40° C. for 48 hours.

Example 9
<Production of conductive adhesive composition I>
20 parts by mass of carbon particles (VULCAN XC72, manufactured by Cabot Corporation, average particle size 30 μm, furnace method), 80 parts by mass of metal particles (nickel, Ni123, manufactured by Vale Corporation, spherical, particle size d40 = 8.2 nm, particle size d70 = 16.6 nm), and 2 parts by mass of Burnock D-40 (manufactured by DIC Corporation, trimethylolpropane adduct of tolylene diisocyanate, isocyanate group content 7 mass%, non-volatile content 40 mass%) were blended relative to 100 parts by mass (solid content) of the pressure-sensitive adhesive B, and the solid content concentration was adjusted to 40 mass% with ethyl acetate, and the mixture was mixed with a dispersion stirrer to prepare a conductive pressure-sensitive adhesive composition I.

<Preparation of conductive adhesive sheet>
The obtained conductive adhesive composition I was coated on a release liner (PET38x1, A3, manufactured by Nippa Corporation) using a comma coater so that the average thickness after drying was 20 μm, and dried for 2 minutes in a dryer at 80° C. Next, the conductive adhesive sheet of Example 9 was produced by laminating the sheet to a release liner (PET38x1, A3, manufactured by Nippa Corporation) and curing the sheet at 40° C. for 48 hours.

Example 10
<Production of conductive adhesive composition J>
20 parts by mass of carbon particles (VULCAN XC72, manufactured by Cabot Corporation, average particle size 30 μm, furnace method), 80 parts by mass of metal particles (nickel, Ni123, manufactured by Vale Corporation, spherical, particle size d40 = 8.2 nm, particle size d70 = 16.6 nm), and 2 parts by mass of Burnock D-40 (manufactured by DIC Corporation, trimethylolpropane adduct of tolylene diisocyanate, isocyanate group content 7 mass%, non-volatile content 40 mass%) were blended relative to 100 parts by mass (solid content) of the pressure-sensitive adhesive C, and the solid content concentration was adjusted to 40 mass% with ethyl acetate, and the mixture was mixed with a dispersion stirrer to prepare a conductive pressure-sensitive adhesive composition J.

<Preparation of conductive adhesive sheet>
The obtained conductive adhesive composition J was coated on a release liner (PET38×1, A3, manufactured by Nippa Corporation) using a comma coater so that the average thickness after drying was 20 μm, and then dried for 2 minutes in a dryer at 80° C. Next, the conductive adhesive sheet of Example 10 was produced by laminating the sheet to a release liner (PET38×1, A3, manufactured by Nippa Corporation) and curing the sheet at 40° C. for 48 hours.

(Example 11)
<Production of conductive adhesive composition K>
9 parts by mass of carbon particles (VULCAN XC72, manufactured by Cabot Corporation, average particle size 30 μm, furnace method), 20 parts by mass of metal particles (nickel, Ni123, manufactured by Vale Corporation, spherical, particle size d40 = 8.2 nm, particle size d70 = 16.6 nm), and 2 parts by mass of Burnock D-40 (manufactured by DIC Corporation, trimethylolpropane adduct of tolylene diisocyanate, isocyanate group content 7 mass%, non-volatile content 40 mass%) were blended relative to 100 parts by mass (solid content) of the pressure-sensitive adhesive D, and the solid content concentration was adjusted to 40 mass% with ethyl acetate, and the mixture was mixed with a dispersion stirrer to prepare a conductive pressure-sensitive adhesive composition K.

<Preparation of conductive adhesive sheet>
The obtained conductive adhesive composition K was applied to a release liner (PET38×1, A3, manufactured by Nippa Corporation) using a comma coater so that the average thickness after drying was 20 μm, and then dried for 2 minutes in a dryer at 80° C. Next, the conductive adhesive sheet of Example 11 was produced by laminating the sheet to a release liner (PET38×1, A3, manufactured by Nippa Corporation) and curing the sheet at 40° C. for 48 hours.

(Comparative Example 1)
<Production of conductive adhesive composition L>
80 parts by mass of metal particles (nickel, Ni123, manufactured by Vale, spherical, particle diameter d40 = 8.2 nm, particle diameter d70 = 16.6 nm) and 2 parts by mass of Burnock D-40 (manufactured by DIC Corporation, trimethylolpropane adduct of tolylene diisocyanate, isocyanate group content 7 mass%, non-volatile content 40 mass%) were blended relative to 100 parts by mass (solid content) of the pressure-sensitive adhesive A, and the solid content concentration was adjusted to 40 mass% with ethyl acetate. The mixture was mixed with a dispersion stirrer to prepare a conductive pressure-sensitive adhesive composition L.

<Preparation of conductive adhesive sheet>
The obtained conductive adhesive composition L was applied to a release liner (PET38x1, A3, manufactured by Nippa Corporation) using a comma coater so that the average thickness after drying was 20 μm, and then dried for 2 minutes in a dryer at 80° C. Next, the conductive adhesive composition L was attached to a release liner (PET38x1, A3, manufactured by Nippa Corporation) and aged at 40° C. for 48 hours to prepare a conductive adhesive sheet of Comparative Example 1.

(Comparative Example 2)
<Production of conductive adhesive composition M>
20 parts by mass of carbon particles (VULCAN XC72, manufactured by Cabot Corporation, average particle size 30 μm, furnace method) and 2 parts by mass of Burnock D-40 (manufactured by DIC Corporation, trimethylolpropane adduct of tolylene diisocyanate, isocyanate group content 7% by mass, non-volatile content 40% by mass) were blended relative to 100 parts by mass (solid content) of the pressure-sensitive adhesive A, the solid content concentration was adjusted to 40% by mass with ethyl acetate, and the mixture was mixed with a dispersion stirrer to prepare a conductive pressure-sensitive adhesive composition M.

<Preparation of conductive adhesive sheet>
The obtained conductive adhesive composition M was coated on a release liner (PET38x1, A3, manufactured by Nippa Corporation) using a comma coater so that the average thickness after drying was 20 μm, and dried for 2 minutes in a dryer at 80° C. Next, after bonding to a release liner (PET38x1, A3, manufactured by Nippa Corporation), it was aged at 40° C. for 48 hours to produce a conductive adhesive sheet of Comparative Example 2.

(Comparative Example 3)
<Production of conductive adhesive composition N>
20 parts by mass of carbon particles (VULCAN XC72, manufactured by Cabot Corporation, average particle size 30 μm, furnace method), 150 parts by mass of metal particles (nickel, Ni123, manufactured by Vale Corporation, spherical, particle size d40 = 8.2 nm, particle size d70 = 16.6 nm), and 2 parts by mass of Burnock D-40 (manufactured by DIC Corporation, trimethylolpropane adduct of tolylene diisocyanate, isocyanate group content 7 mass%, non-volatile content 40 mass%) were blended relative to 100 parts by mass (solid content) of the pressure-sensitive adhesive A, and the solid content concentration was adjusted to 40 mass% with ethyl acetate, and the mixture was mixed with a dispersion stirrer to prepare a conductive pressure-sensitive adhesive composition N.

<Preparation of conductive adhesive sheet>
The obtained conductive adhesive composition N was coated on a release liner (PET38x1, A3, manufactured by Nippa) using a comma coater so that the average thickness after drying was 20 μm, and dried for 2 minutes in a dryer at 80° C. Next, after bonding to a release liner (PET38x1, A3, manufactured by Nippa), it was aged at 40° C. for 48 hours to prepare a conductive adhesive sheet of Comparative Example 3.

(Comparative Example 4)
<Production of conductive adhesive composition O>
80 parts by mass of carbon particles (VULCAN XC72, manufactured by Cabot Corporation, average particle size 30 μm, furnace method), 80 parts by mass of metal particles (nickel, Ni123, manufactured by Vale Corporation, spherical, particle size d40 = 8.2 nm, particle size d70 = 16.6 nm), and 2 parts by mass of Burnock D-40 (manufactured by DIC Corporation, trimethylolpropane adduct of tolylene diisocyanate, isocyanate group content 7 mass%, non-volatile content 40 mass%) were blended relative to 100 parts by mass (solid content) of the pressure-sensitive adhesive A, and the solid content concentration was adjusted to 40 mass% with ethyl acetate, and the mixture was mixed with a dispersion stirrer to prepare a conductive pressure-sensitive adhesive composition O.

<Preparation of conductive adhesive sheet>
The obtained conductive adhesive composition O was coated on a release liner (PET38x1, A3, manufactured by Nippa Corporation) using a comma coater so that the average thickness after drying was 20 μm, and dried for 2 minutes in a dryer at 80° C. Next, the conductive adhesive composition O was attached to a release liner (PET38x1, A3, manufactured by Nippa Corporation) and aged at 40° C. for 48 hours to produce a conductive adhesive sheet of Comparative Example 4.

Next, the properties of the obtained conductive adhesive sheets of Examples 1 to 11 and Comparative Examples 1 to 4 were evaluated as follows. The results are shown in Tables 1 to 3.

<Measurement of the average thickness of the conductive adhesive sheet>
The average thickness of each conductive adhesive sheet was determined by measuring the thickness of the sheet (only the adhesive layer) after removing the release liner at five locations along the length at intervals of 100 mm using a dial thickness gauge Type G manufactured by Ozaki Seisakusho Co., Ltd.

<Method for evaluating adhesive strength>
The adhesive strength of the conductive adhesive sheet was determined according to the following procedure in accordance with the 180 degree peel adhesion test method of JIS-Z0237 (2000).
The conductive adhesive sheets obtained in the examples and comparative examples were cut to a size with a width of 25 mm.
Next, the adhesive layer on one side of the conductive adhesive sheet was backed with a polyester film having a thickness of 25 μm.
Next, under conditions of an environmental temperature of 23°C and a humidity of 50% RH, the backed conductive adhesive sheet was attached to a stainless steel plate (SUS plate), and the upper surface was pressed against the plate by rolling it back and forth once with a 2 kg roller, and then the plate was left to stand at the above temperature for 1 hour to prepare a test specimen.
The test piece was peeled off at a speed of 300 mm/min under the same temperature and humidity conditions as above using a Tensilon universal tensile tester (RTA100, manufactured by Orientec Co., Ltd.) to measure the 180-degree peel adhesive strength. When the adhesive strength was 5 N/25 mm or more, it was evaluated as having excellent adhesiveness.

<Conductivity evaluation method>
Copper foil (thickness 12 μm) was attached to one side of the conductive adhesive sheet. The conductive adhesive sheet was cut to a size of 15 mm width × 100 mm width. The other adhesive layer of the cut conductive adhesive sheet was attached to two tin-plated plates so that the attachment area was 15 mm × 15 mm, respectively, to prepare a test piece. In an environment of 23 ° C. and 50% RH, a terminal was connected to a position about 100 mm away from the conductive adhesive sheet attachment position on the tin-plated surface, and a current of 10 μA was applied using a resistivity meter (Loresta-GP MCP-T600, manufactured by Mitsubishi Chemical Corporation) to measure the initial resistance value.
The prepared test piece was allowed to stand at 23° C. for 168 hours, and then the resistance value was measured in the same manner as above, and the rate of change in resistance value [(resistance value after standing for 168 hours/initial resistance value)×100] was calculated.
In addition, when the resistance value after 168 hours was 100 mΩ or less and the rate of change in resistance value was 300% or less, the electrical conductivity was evaluated as excellent.

REFERENCE SIGNS LIST 1 conductive substrate 2 adhesive layer 3 carbon particles 4 metal particles 10 conductive adhesive sheet

Claims (8)

A conductive adhesive sheet having an adhesive layer,
The pressure-sensitive adhesive layer contains carbon particles, metal particles, and a pressure-sensitive adhesive,
The carbon particles have an average particle size of 100 nm or less,
The content of the carbon particles is 75 parts by mass or less relative to 100 parts by mass of a solid content of the adhesive,
The content of the metal particles is 145 parts by mass or less per 100 parts by mass of the solid content of the pressure-sensitive adhesive,
A conductive adhesive sheet, characterized in that the mass ratio (A/B) of the content A of the carbon particles in the adhesive layer to the content B of the metal particles in the adhesive layer is 2/10 or more and 7/10 or less. The conductive adhesive sheet according to claim 1, wherein the content of the carbon particles is 3 parts by mass or more and 50 parts by mass or less per 100 parts by mass of the solid content of the adhesive. The conductive adhesive sheet according to any one of claims 1 to 2, wherein the content of the metal particles is 10 parts by mass or more and 120 parts by mass or less per 100 parts by mass of the solid content of the adhesive. The conductive adhesive sheet according to any one of claims 1 to 3, wherein the metal particles are spherical or filament-shaped. The conductive adhesive sheet according to claim 1 , wherein the adhesive is an acrylic adhesive containing a (meth)acrylic polymer. A conductive adhesive sheet according to any one of claims 1 to 5, wherein a test piece is prepared by attaching copper foil to one side of a conductive adhesive sheet, cutting the sheet to a size of 15 mm wide x 100 mm wide, and attaching two tin-plated plates to the other adhesive layer of the conductive adhesive sheet so that each has an adhesion area of 15 mm x 15 mm. The test piece has an initial resistance value measured and a resistance value measured after leaving the test piece at 23°C for 168 hours, and the rate of change in resistance value [(resistance value after leaving for 168 hours/initial resistance value) x 100] is 300% or less. The conductive adhesive sheet according to claim 1 , which comprises a conductive substrate. The conductive adhesive sheet according to claim 1 , which is used for at least one of electromagnetic shielding and earthing inside and outside of electric or electronic equipment.

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