JP7574534B2 - 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 having a metal filler dispersed in an adhesive substance on a conductive substrate (see, for example, Patent Document 1).
In addition, a conductive adhesive tape has been proposed having an adhesive layer containing large-diameter conductive particles consisting of a group of particles with a particle size range of 15 μm or more and 50 μm or less, and small-diameter conductive particles consisting of a group of particles with a particle size range of 1 μm or more and 12 μm or less (see, for example, Patent Document 2).

JP 2018-53102 A Patent No. 6106148

However, the pressure-sensitive adhesive sheet described in Patent Document 1 has problems in that, because metal filler is added as conductive particles, peeling occurs easily over time, and the number of contact points decreases, resulting in a decrease in conductivity over time.
In addition, since the conductive adhesive tape described in Patent Document 2 uses only two types of spherical conductive fillers, in order to achieve a low resistance value, it is necessary to increase the amount of conductive filler to be mixed, which results in a problem of reduced adhesive strength.
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 a first conductive filler, a second conductive filler, and a pressure-sensitive adhesive;
The first conductive filler has a scale-like shape,
the first conductive filler and the second conductive filler have different shapes;
The conductive adhesive sheet is characterized in that the content of the first conductive filler is 55 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 the first conductive filler is at least one of scaly metal particles, graphite, and scaly particles formed by coating a scaly substrate with a metal.
<3> The conductive adhesive sheet according to any one of <1> to <2>, wherein the second conductive filler is spherical or filamentary metal particles.
<4> The conductive adhesive sheet according to any one of <1> to <3>, wherein a mass ratio (A/B) of a content A of the first conductive filler in the pressure-sensitive adhesive layer to a content B of the second conductive filler in the pressure-sensitive adhesive layer is 1/1 or more and 1/5 or less.
<5> The conductive adhesive sheet according to any one of <1> to <4>, wherein the content of the first conductive filler is 5 parts by mass or more and 50 parts by mass or less per 100 parts by mass of a solid content of the adhesive.
<6> The conductive adhesive sheet according to any one of <1> to <5>, wherein the content of the second conductive filler is 5 parts by mass or more and 50 parts by mass or less per 100 parts by mass of a solid content of the adhesive.
<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>, further comprising a conductive substrate.
<9> The conductive adhesive sheet according to any one of <1> to <8>, 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 250% or less.
<10> The conductive 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 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 a first conductive filler, a second conductive filler, 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 have conducted extensive research into means for suppressing the increase in electrical resistance over time when metal particles are added to an adhesive layer, and as a result have discovered that by using a combination of a first conductive filler in a scale-like shape in the adhesive layer and a second conductive filler having a different shape from the first conductive filler, the two types of conductive fillers (having different shapes) work synergistically, and since less conductive filler appears on the surface of the adhesive layer, the high adhesive strength is not lost, and since the two types of conductive fillers come into contact with each other in large amounts inside the adhesive layer, the decrease in contact points over time can be suppressed, resulting in a conductive adhesive sheet with excellent conductivity both initially and over time, which has led to 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, a first conductive filler 3 and a second conductive filler 4 contained in the adhesive layer 2 are shown in schematic form. Although not shown, it is preferable that the surface of the adhesive layer 2 has a release liner in FIGS. 1 to 3.

<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 a first conductive filler, a second conductive filler, and a pressure-sensitive adhesive, and may further contain other components as necessary.

<<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 viewpoint of high adhesive strength.

- (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, holding power, 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, 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, as necessary.

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 measured by gel permeation chromatography (GPC) in terms of standard polystyrene.

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 conditions]
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 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 is applied to a release liner 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 samples. Next, the mass (G1) of the 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 mass (G3) of the first and second conductive fillers 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) x 100

<First Conductive Filler>
The first conductive filler is flaky, and examples thereof include flaky metal particles, graphite, and flaky particles formed by coating a flaky base material with a metal.

The scaly particles are also called thin plate-like particles, flat particles, flake-like particles, and the like.
In the present invention, the term "scaly particles" refers to particles having a substantially flat surface and a substantially uniform thickness in the direction perpendicular to the substantially flat surface. The term "scaly particles" refers to particles having a shape in which the thickness is very thin and the length of the substantially flat surface is very long. The length of the substantially flat surface is the diameter of a circle having the same projected area as the projected area of the scale-like particle.
The shape of the substantially flat surface is not particularly limited and can be appropriately selected depending on the purpose, and examples thereof include polygons such as a rectangle, a square, a substantially circle, a substantially ellipse, a substantially triangle, a substantially square, a substantially pentagon, a substantially hexagon, a substantially heptagon, a substantially octagon, etc., and random, indefinite shapes, etc. Among these, a substantially circle or a substantially ellipse is preferable.

Examples of flake-like metal particles include flake-like metal particles made of 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.

Examples of 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 mechanical strength. 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 scaly substrate in the scaly particles formed by coating a scaly substrate with a metal include glass, silica, alumina, mica, and zirconia.
The content of the substrate in the scaly particles in which the scaly substrate is metal-coated is preferably 50% by mass or more, more preferably 65% by mass or more, and even more preferably 80% by mass or more.
Examples of methods for coating a scaly substrate with a metal include metal plating. Examples of metals used for metal plating include silver, gold, platinum, palladium, nickel, copper, and aluminum. The content of the metal plating in the scaly particles formed by coating a scaly substrate with a metal is preferably 10% by mass or more and 50% by mass or less, and more preferably 15% by mass or more and 30% by mass or less.

In the scaly first conductive filler, when the surface with the largest area is taken as the main surface, the average thickness of the main surface is preferably 0.5 μm or more and 6.0 μm or less, and more preferably 1.0 μm or more and 4.0 μm or less.
The average particle size of the main surface of the scaly first conductive filler is not particularly limited and can be appropriately selected depending on the purpose. For example, it is preferably 10 μm or more and 200 μm or less, and more preferably 20 μm or more and 100 μm or less.
The average particle size refers to the 50% cumulative volume particle size in a volume-based particle size distribution, and is a value measured by a laser diffraction scattering method, such as a Microtrac MT300II manufactured by Nikkiso Co., Ltd. or a laser diffraction type particle size distribution analyzer SALD-3000 manufactured by Shimadzu Corporation.
The ratio of the average particle diameter of the main surface of the first conductive filler to the average thickness of the main surface is preferably 10 or more and 100 or less, and more preferably 20 or more and 80 or less.
By satisfying the above ranges of the average thickness and average particle diameter of the main surface, and the ratio of the average particle diameter of the main surface to the average thickness of the main surface, a conductive adhesive sheet can be obtained that has excellent conductivity in the thickness direction of the adhesive sheet (Z-axis direction) as well as in the planar direction (XY direction).

The content of the first conductive filler is 55 parts by mass or less, preferably 5 parts by mass or more and 50 parts by mass or less, more preferably 10 parts by mass or more and 40 parts by mass or less, and even more preferably 15 parts by mass or more and 40 parts by mass or less, per 100 parts by mass of the solid content of the adhesive. By setting the content of the first conductive filler within the above numerical range, it is possible to achieve both high adhesive strength and excellent conductivity both initially and over time.

<Second Conductive Filler>
The second conductive filler is not particularly limited as long as it has a different shape from the above-mentioned scaly first conductive filler and has conductivity, 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, solder, and alloys such as 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 may be appropriately selected depending on the purpose, and examples thereof include spherical, filamentary (bead-like) , spike (chestnut-shaped), etc. Among these, from the viewpoints of ensuring adhesive strength and facilitating the formation of conductive paths by the metal particles in the adhesive layer, spherical or filamentary shapes are preferred.

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 through a sieve.

The content of the second conductive filler is preferably 5 parts by mass or more and 50 parts by mass or less, more preferably 10 parts by mass or more and 45 parts by mass or less, and even more preferably 15 parts by mass or more and 40 parts by mass or less, relative to 100 parts by mass of the solid content of the adhesive. By setting the content of the second conductive filler within the above range, it is possible to achieve both high adhesive strength and excellent initial and aging conductivity.

In the present invention, the mass ratio (A/B) of the content A of the first conductive filler in the pressure-sensitive adhesive layer to the content B of the second conductive filler in the pressure-sensitive adhesive layer is preferably 1/1 or more and 1/5 or less, more preferably 1/1 or more and 1/3 or less, and even more preferably 1/1 or more and 1/2 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 first and second conductive fillers in the adhesive layer, for example, a method of dispersing the (meth)acrylic polymer, the first and second conductive fillers, a solvent, an additive, etc., using a dispersion stirrer can be mentioned. Examples of commercially available dispersion stirrers include the dissolver, butterfly mixer, BDM two-shaft mixer, and planetary mixer manufactured by Inoue Seisakusho Co., Ltd. Among these, the dissolver and butterfly mixer, which 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 crosslinking agents, 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 250% or less, more preferably 200% or less, and even more preferably 150% or less.
When the rate of change in resistance is 250% 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 electric or electronic devices, for shielding harmful spatial electromagnetic waves generated by other electric 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.

The following describes examples of the present invention, but the present invention is not limited to these examples.

(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.

The weight average molecular weight is a weight average molecular weight measured by gel permeation chromatography (GPC) in terms of standard polystyrene, and was measured by the following method.
The molecular weight can be measured by the GPC method using a GPC apparatus (HLC-8329GPC) manufactured by Tosoh Corporation, and is calculated as a polystyrene equivalent value under the following GPC measurement conditions.
[Measurement conditions]
Sample concentration: 0.5% by mass (tetrahydrofuran solution)
Sample injection volume: 100 μL
Eluent: tetrahydrofuran (THF)
Flow rate: 1.0 mL/min Column temperature (measurement temperature): 40° C.
Main column: 2 TSKgel GMHHR-H (20) Guard column: "TSKgel HXL-H" manufactured by Tosoh Corporation
Detector: Differential refractometer Standard polystyrene molecular weight: 10,000 to 20,000,000 (manufactured by Tosoh Corporation)

(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.

Example 1
<Production of conductive adhesive composition A>
A first conductive filler (conductive particles obtained by plating glass flake powder with 20% by weight of silver, scale-like, average thickness of the main surface of 2 μm, average particle diameter of the main surface of 25 μm) of 30 parts by weight, a second conductive filler (nickel, Ni255, manufactured by Vale, filament-like, particle diameter d40=17.2 nm, particle diameter d70=35.4 nm) of 30 parts by weight, and Burnock D-40 (manufactured by DIC Corporation, trimethylolpropane adduct of tolylene diisocyanate, isocyanate group content of 7% by weight, non-volatile content of 40% by weight) of 2 parts by weight were blended relative to 100 parts by weight (solid content) of the pressure-sensitive adhesive A, and the solid content concentration was adjusted to 40% by weight 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 conductive substrate (electrolytic copper foil, average thickness 12 μm) using a comma coater so that the average thickness after drying would be 25 μm, and the coating was dried in a dryer at 80° C. for 2 minutes and then aged at 40° C. for 48 hours to produce the conductive adhesive sheet of Example 1.

Example 2
<Production of conductive adhesive composition B>
20 parts by mass of a first conductive filler (conductive particles obtained by plating 20% by mass of silver on glass flake powder, scale-like, average thickness of the main surface of 2 μm, average particle diameter of the main surface of 25 μm), 40 parts by mass of a second conductive filler (nickel, Ni255, manufactured by Vale, filament-like, particle diameter d40 = 17.2 nm, particle diameter 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% by mass, non-volatile content 40% by mass) were blended with respect to 100 parts by mass (solid content) of the pressure-sensitive adhesive A, and 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 B.

<Preparation of conductive adhesive sheet>
The obtained conductive adhesive composition B was coated on a conductive substrate (electrolytic copper foil, average thickness 12 μm) using a comma coater so that the average thickness after drying would be 25 μm, and the coated substrate was dried in a dryer at 80° C. for 2 minutes and then aged at 40° C. for 48 hours to produce a conductive adhesive sheet of Example 2.

Example 3
<Production of conductive adhesive composition C>
A conductive adhesive composition C was prepared by blending 10 parts by mass of a first conductive filler (conductive particles obtained by plating glass flake powder with 20% by mass of silver, scale-like, average thickness of the main surface of 2 μm, average particle diameter of the main surface of 25 μm), 50 parts by mass of a second conductive filler (nickel, Ni255, manufactured by Vale, filament-like, particle diameter d40 = 17.2 nm, particle diameter 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% by mass, non-volatile content 40% by mass) with 100 parts by mass of the adhesive A (solid content). 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 adhesive composition C.

<Preparation of conductive adhesive sheet>
The obtained conductive adhesive composition C was coated on a conductive substrate (electrolytic copper foil, average thickness 12 μm) using a comma coater so that the average thickness after drying would be 25 μm, and the coated substrate was dried in a dryer at 80° C. for 2 minutes and then aged at 40° C. for 48 hours to produce the conductive adhesive sheet of Example 3.

Example 4
<Production of conductive adhesive composition D>
A first conductive filler (conductive particles obtained by plating glass flake powder with 20% by weight of silver, scale-like, average thickness of the main surface of 2 μm, average particle diameter of the main surface of 25 μm) of 45 parts by weight, a second conductive filler (nickel, Ni255, manufactured by Vale, filament-like, particle diameter d40 = 17.2 nm, particle diameter d70 = 35.4 nm) of 45 parts by weight, and Burnock D-40 (manufactured by DIC Corporation, trimethylolpropane adduct of tolylene diisocyanate, isocyanate group content of 7% by weight, non-volatile content of 40% by weight) of 2 parts by weight were blended relative to 100 parts by weight (solid content) of the pressure-sensitive adhesive A, and the solid content concentration was adjusted to 40% by weight with ethyl acetate, and the mixture was mixed with a dispersion stirrer to prepare a conductive pressure-sensitive adhesive composition D.

<Preparation of conductive adhesive sheet>
The obtained conductive adhesive composition D was coated on a conductive substrate (electrolytic copper foil, average thickness 12 μm) using a comma coater so that the average thickness after drying would be 25 μm, and the coated film was dried in a dryer at 80° C. for 2 minutes and then aged at 40° C. for 48 hours to produce a conductive adhesive sheet of Example 4.

Example 5
<Production of conductive adhesive composition E>
A conductive adhesive composition E was prepared by blending 15 parts by mass of a first conductive filler (conductive particles obtained by plating glass flake powder with 20% by mass of silver, scale-like, average thickness of the main surface of 2 μm, average particle diameter of the main surface of 25 μm), 15 parts by mass of a second conductive filler (nickel, Ni255, manufactured by Vale, filament-like, particle diameter d40 = 17.2 nm, particle diameter 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% by mass, non-volatile content 40% by mass) with 100 parts by mass of the adhesive A (solid content). 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 adhesive composition E.

<Preparation of conductive adhesive sheet>
The obtained conductive adhesive composition E was coated on a conductive substrate (electrolytic copper foil, average thickness 12 μm) using a comma coater so that the average thickness after drying would be 25 μm, and the coated substrate was dried in a dryer at 80° C. for 2 minutes and then aged at 40° C. for 48 hours to produce a conductive adhesive sheet of Example 5.

Example 6
<Production of conductive adhesive composition F>
A first conductive filler (nickel flake powder, HCA-1, manufactured by Vale, scale-like, average thickness of the main surface of 2 μm, average particle diameter of the main surface of 12.5 μm) of 30 parts by mass, a second conductive filler (nickel, Ni255, manufactured by Vale, filament-like, particle diameter d40 = 17.2 nm, particle diameter d70 = 35.4 nm) of 30 parts by mass, and Burnock D-40 (manufactured by DIC Corporation, trimethylolpropane adduct of tolylene diisocyanate, isocyanate group content of 7 mass%, non-volatile content of 40 mass%) of 2 parts by mass were blended with respect 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 conductive substrate (electrolytic copper foil, average thickness 12 μm) using a comma coater so that the average thickness after drying would be 25 μm, and the coated film was dried in a dryer at 80° C. for 2 minutes and then aged at 40° C. for 48 hours to produce the conductive adhesive sheet of Example 6.

(Example 7)
<Production of conductive adhesive composition G>
A first conductive filler (conductive particles obtained by plating glass flake powder with 20% by weight of silver, scale-like, average thickness of the main surface of 2 μm, average particle diameter of the main surface of 25 μm) of 30 parts by weight, a second conductive filler (nickel, Ni123, manufactured by Vale, filament-like, particle diameter d40 = 8.2 nm, particle diameter d70 = 16.6 nm) of 30 parts by weight, and Burnock D-40 (manufactured by DIC Corporation, trimethylolpropane adduct of tolylene diisocyanate, isocyanate group content of 7% by weight, non-volatile content of 40% by weight) of 2 parts by weight were blended with respect to 100 parts by weight (solid content) of the pressure-sensitive adhesive A, and the solid content concentration was adjusted to 40% by weight 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 conductive substrate (electrolytic copper foil, average thickness 12 μm) using a comma coater so that the average thickness after drying would be 25 μm, and the coating was dried in a dryer at 80° C. for 2 minutes and then aged at 40° C. for 48 hours to produce the conductive adhesive sheet of Example 7.

(Example 8)
<Production of conductive adhesive composition H>
A first conductive filler (nickel flake powder, HCA-1, manufactured by Vale, scale-like, average thickness of the main surface of 2 μm, average particle diameter of the main surface of 12.5 μm) of 30 parts by mass, a second conductive filler (nickel, Ni123, manufactured by Vale, filament-like, particle diameter d40 = 8.2 nm, particle diameter d70 = 16.6 nm) of 30 parts by mass, and Burnock D-40 (manufactured by DIC Corporation, trimethylolpropane adduct of tolylene diisocyanate, isocyanate group content of 7 mass%, non-volatile content of 40 mass%) of 2 parts by mass were blended with respect 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 conductive substrate (electrolytic copper foil, average thickness 12 μm) using a comma coater so that the average thickness after drying would be 25 μm, and the coating was dried in a dryer at 80° C. for 2 minutes and then aged at 40° C. for 48 hours to produce the conductive adhesive sheet of Example 8.

(Example 9)
<Production of conductive adhesive composition I>
A conductive adhesive composition I was prepared by blending 10 parts by mass of a first conductive filler (conductive particles obtained by plating 20% by mass of silver on glass flake powder, scale-like, average thickness of the main surface of 2 μm, average particle diameter of the main surface of 25 μm), 10 parts by mass of a second conductive filler (nickel, Ni255, manufactured by Vale, filament-like, particle diameter d40 = 17.2 nm, particle diameter 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% by mass, non-volatile content 40% by mass) with 100 parts by mass of the adhesive A (solid content). 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 adhesive composition I.

<Preparation of conductive adhesive sheet>
The obtained conductive adhesive composition I was coated on a conductive substrate (electrolytic copper foil, average thickness 12 μm) using a comma coater so that the average thickness after drying would be 25 μm, and the coating was dried in a dryer at 80° C. for 2 minutes and then aged at 40° C. for 48 hours to produce a conductive adhesive sheet of Example 9.

(Comparative Example 1)
<Production of conductive adhesive composition J>
A conductive adhesive composition J was prepared by blending 30 parts by mass of a second conductive filler (nickel, Ni255, manufactured by Vale, filamentous, particle diameter d40 = 17.2 nm, particle diameter 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%) with 100 parts by mass of the pressure-sensitive 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 J was coated on a conductive substrate (electrolytic copper foil, average thickness 12 μm) using a comma coater so that the average thickness after drying would be 25 μm, and the coated substrate was dried in a dryer at 80° C. for 2 minutes and then aged at 40° C. for 48 hours to produce a conductive adhesive sheet of Comparative Example 1.

(Comparative Example 2)
<Production of conductive adhesive composition K>
A conductive adhesive composition K was prepared by blending 30 parts by mass of a first conductive filler (conductive particles formed by plating glass flake powder with 20% by mass of silver, scale-like, average thickness of the main surface of 2 μm, average particle diameter of the main surface of 25 μm) and 2 parts by mass of Burnock D-40 (manufactured by DIC Corporation, trimethylolpropane adduct of tolylene diisocyanate, isocyanate group content of 7% by mass, non-volatile content of 40% by mass) with 100 parts by mass (solid content) of the adhesive A, adjusting the solid content concentration to 40% by mass with ethyl acetate, and mixing with a dispersion stirrer.

<Preparation of conductive adhesive sheet>
The obtained conductive adhesive composition K was coated on a conductive substrate (electrolytic copper foil, average thickness 12 μm) using a comma coater so that the average thickness after drying would be 25 μm, and the coated substrate was dried in a dryer at 80° C. for 2 minutes and then 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 L>
A first conductive filler (conductive particles obtained by plating glass flake powder with 20% by weight of silver, scale-like, average thickness of the main surface of 2 μm, average particle diameter of the main surface of 25 μm) was mixed with 60 parts by weight of a second conductive filler (nickel, Ni255, manufactured by Vale, filament-like, particle diameter d40 = 17.2 nm, particle diameter d70 = 35.4 nm), and 2 parts by weight of Burnock D-40 (manufactured by DIC Corporation, trimethylolpropane adduct of tolylene diisocyanate, isocyanate group content 7% by weight, non-volatile content 40% by weight) was mixed with 100 parts by weight (solid content) of the pressure-sensitive adhesive A, and the solid content concentration was adjusted to 40% by weight with ethyl acetate, and 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 coated on a conductive substrate (electrolytic copper foil, average thickness 12 μm) using a comma coater so that the average thickness after drying would be 25 μm, and the coated substrate was dried in a dryer at 80° C. for 2 minutes and then aged at 40° C. for 48 hours to produce a conductive adhesive sheet of Comparative Example 3.

Next, the properties of the obtained conductive adhesive sheets of Examples 1 to 9 and Comparative Examples 1 to 3 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 conductive adhesive sheet at five locations at 100 mm intervals in the longitudinal direction using a dial thickness gauge Type G manufactured by Ozaki Seisakusho Co., Ltd., and averaging the measured thickness.

<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 left at 23° C. for 168 hours, and then the resistance value was measured in the same manner as above. A test piece was evaluated as having excellent conductivity when the resistance value after 168 hours was 100 mΩ or less and the rate of change in resistance value (resistance value after being left at 168 hours/initial resistance value)×100 was 250% or less.

REFERENCE SIGNS LIST 1 Conductive substrate 2 Pressure-sensitive adhesive layer 3 First conductive filler 4 Second conductive filler 10 Conductive pressure-sensitive adhesive sheet

Claims (10)

A conductive adhesive sheet having an adhesive layer,
the pressure-sensitive adhesive layer contains a first conductive filler, a second conductive filler, and a pressure-sensitive adhesive;
The first conductive filler has a scale-like shape,
the second conductive filler is a metal or alloy having a shape other than a scale shape,
The content of the first conductive filler is 55 parts by mass or less relative to 100 parts by mass of a solid content of the pressure-sensitive adhesive;
The content of the second conductive filler is 5 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 pressure-sensitive adhesive ,
The first conductive filler has an average particle size of 10 μm or more and 200 μm or less,
The particle diameter d40 of the second conductive filler is 5 μm or more and 30 μm or less, and the particle diameter d70 of the second conductive filler is 10 μm or more and 50 μm or less,
The conductive adhesive sheet, characterized in that the adhesive contains a (meth)acrylic polymer, a tackifier resin, and a crosslinking agent . The conductive adhesive sheet according to claim 1, wherein the first conductive filler is at least one of scaly metal particles, graphite, and scaly particles formed by coating a scaly substrate with a metal. The conductive adhesive sheet according to any one of claims 1 to 2, wherein the second conductive filler is a spherical, filament-like, or spike-like metal or alloy particle. The conductive adhesive sheet according to any one of claims 1 to 3, wherein the mass ratio (A/B) of the content A of the first conductive filler in the adhesive layer to the content B of the second conductive filler in the adhesive layer is 1/1 or more and 1/5 or less. The conductive adhesive sheet according to any one of claims 1 to 4, wherein the content of the first conductive filler is 5 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 5, wherein the ratio of the average particle diameter of the first conductive filler on the main surface to the average thickness of the main surface is 10 or more and 100 or less. The conductive adhesive sheet according to any one of claims 1 to 6, wherein the adhesive is an acrylic adhesive containing a (meth)acrylic polymer. The conductive adhesive sheet according to any one of claims 1 to 7, which has a conductive substrate. A conductive adhesive sheet according to any one of claims 1 to 8, 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 adhesive layer on the other side of the conductive adhesive sheet so that each has an adhesion area of 15 mm x 15 mm. The rate of change in resistance [(resistance after 168 hours/initial resistance) x 100] is calculated from the measured initial resistance value and the resistance value measured after leaving the test piece at 23°C for 168 hours, and is 250% or less. The conductive adhesive sheet according to any one of claims 1 to 9, which is used for at least one of electromagnetic shielding and grounding inside and outside an electric or electronic device.

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