JP6506461B1 - Conductive adhesive tape - Google Patents

Abstract

The present invention provides a conductive adhesive tape excellent in electromagnetic wave shielding properties and conductivity.
The conductive pressure-sensitive adhesive tape has a conductive substrate and a pressure-sensitive adhesive layer disposed on at least one surface of the conductive substrate, the pressure-sensitive adhesive layer comprising an acrylic copolymer. The electroconductive adhesive tape which contains a metal filler and whose a value calculated by following formula (1) is 0 or more.
a value = (25 * M) + {22 * (d70 / D)}-3 * (d70-d40) -18 (1)
M: Metal amount (volume%) of the metal filler with respect to the volume of the pressure-sensitive adhesive layer
D: Thickness of the pressure-sensitive adhesive layer (μm)
d40: particle diameter (μm) of the metal filler when the cumulative distribution on a volume basis is 40%
d70: particle diameter (μm) of the metal filler when the cumulative distribution on a volume basis is 70%
【Selection chart】 None

Description

The present invention relates to a conductive adhesive tape.

The degree of integration of electronic board components that constitute electronic devices is increasing, and a CPU, a connector, and the like may be disposed in proximity to an antenna portion. In such a case, in order to suppress a malfunction caused by electromagnetic waves (noises) emitted from the CPU, the connector, etc., noise measures are taken such as covering the CPU, the connector, etc. with the electromagnetic wave shielding material or performing grounding. There is.

As an electromagnetic wave shielding material, for example, a conductive pressure-sensitive adhesive tape in which a pressure-sensitive adhesive layer is laminated on a metal foil such as copper foil or aluminum foil is used. Patent Document 1 describes a conductive pressure-sensitive adhesive sheet having a total thickness of 30 μm or less and having a conductive substrate and a conductive pressure-sensitive adhesive layer containing conductive particles, and the conductive pressure-sensitive adhesive sheet It is described that, while being extremely thin, it has good adhesion to the adherend and conductivity.

International Publication No. 2015/076174

As a physical property which shows the performance of a conductive adhesive tape, electroconductivity (resistance value measurement) is used abundantly as a physical property which shows electromagnetic wave shielding property alternatively as it describes also in patent documents 1. FIG.
On the other hand, in addition to the conductivity (resistance value measurement), the present inventors evaluated in detail the actual electromagnetic wave shielding property. As a result, the present inventors have the advantage that the conductive pressure-sensitive adhesive tape can be used by being attached because it has a pressure-sensitive adhesive layer, but when the cross-section of the pressure-sensitive adhesive layer is exposed, the cross-section exhibits electromagnetic waves (noise As a radiation source, it is easy to produce noise radiation, and the problem that electromagnetic wave shielding property is not fully obtained was discovered.

An object of the present invention is to provide a conductive pressure-sensitive adhesive tape excellent in electromagnetic wave shielding properties and conductivity.

The present invention is a conductive pressure-sensitive adhesive tape having a conductive substrate and a pressure-sensitive adhesive layer disposed on at least one surface of the conductive substrate, the pressure-sensitive adhesive layer comprising an acrylic copolymer. It is a conductive adhesive tape which contains a metal filler and whose a value calculated by the following formula (1) is 0 or more.
a value = (25 * M) + {22 * (d70 / D)}-3 * (d70-d40) -18 (1)
M: Metal amount (volume%) of the metal filler with respect to the volume of the pressure-sensitive adhesive layer
D: Thickness of the pressure-sensitive adhesive layer (μm)
d40: particle diameter (μm) of the metal filler when the cumulative distribution on a volume basis is 40%
d70: particle diameter (μm) of the metal filler when the cumulative distribution on a volume basis is 70%
Hereinafter, the present invention will be described in detail.

The present inventors, in a conductive pressure-sensitive adhesive tape having a conductive substrate and a pressure-sensitive adhesive layer disposed on at least one surface of the conductive substrate, an acrylic copolymer and a metal filler in the pressure-sensitive adhesive layer. And controlling the metal amount of the metal filler relative to the volume of the pressure-sensitive adhesive layer, the thickness of the pressure-sensitive adhesive layer, and the particle diameter of the metal filler.
As a result, the present inventors have determined the specific formula from the values of the metal amount of the metal filler relative to the volume of the adhesive layer, the thickness of the adhesive layer, and the particle diameter of the metal filler rather than the individual values. It has been found that there is a high correlation between the value calculated by (hereinafter referred to as “a value” in the present specification) and the electromagnetic wave shielding property. The present inventors have found that by controlling the “a value” to a specific range, noise radiation from the cross section of the pressure-sensitive adhesive layer can be suppressed, and excellent electromagnetic wave shielding properties and conductivity can be realized, and the present invention is completed. It came to

The conductive pressure-sensitive adhesive tape of the present invention has a conductive substrate and a pressure-sensitive adhesive layer disposed on at least one surface of the conductive substrate.
The said electroconductive base material is not specifically limited, For example, metal foil, an electroconductive resin base material, etc. are mentioned. Among them, metal foil is preferably included. The material of the metal foil is not particularly limited, and examples thereof include nickel, silver, copper, aluminum and the like, and may be an alloy of these metals. Among them, silver and copper are preferable and copper is more preferable because the resistance value is stable and the electromagnetic wave shielding property is stable in each frequency band.

The thickness of the conductive substrate is not particularly limited, but the preferable lower limit is 1 μm, and the preferable upper limit is 150 μm. When the conductive base material is 1 μm or more, the strength of the conductive pressure-sensitive adhesive tape is increased, and it is possible to suppress breakage when a strong impact is applied. If the said electroconductive base material is 150 micrometers or less, the floating peeling of the electroconductive adhesive tape by repulsion when a long period passes can be suppressed. From the same viewpoint, the lower limit of the thickness of the conductive substrate is preferably 5 μm, more preferably 40 μm, still more preferably 9 μm, still more preferably 35 μm, still more preferably 10 μm, still more preferably 30 μm. It is.

The pressure-sensitive adhesive layer may be disposed on one side or both sides of the conductive substrate as long as the pressure-sensitive adhesive layer is disposed on at least one surface of the conductive substrate. When the pressure-sensitive adhesive layer is disposed on both sides of the conductive substrate, the pressure-sensitive adhesive layers on both sides may have the same composition or different compositions, and at least one of the pressure-sensitive adhesive layers is described later It suffices to have an a value of

The pressure-sensitive adhesive layer contains an acrylic copolymer and a metal filler.
The above-mentioned acrylic copolymer is preferably a copolymer obtained by copolymerizing a monomer mixture containing butyl acrylate (BA) and 2-ethylhexyl acrylate (2EHA). The content of butyl acrylate and the content of 2-ethylhexyl acrylate in the total monomer mixture are not particularly limited, but the preferable content of butyl acrylate is 50 to 90% by weight, and the preferable content of 2-ethylhexyl acrylate is 10 to 10%. It is 50% by weight.

The above-mentioned monomer mixture may optionally contain other copolymerizable polymerizable monomers other than butyl acrylate and 2-ethylhexyl acrylate.
As the above-mentioned other copolymerizable polymerizable monomers, for example, (meth) acrylic acid alkyl ester having 1 to 3 carbon atoms of alkyl group, (meth) acrylic acid alkyl ester having 13 to 18 carbon atoms of alkyl group, Functional monomers are mentioned. These other copolymerizable polymerizable monomers may be used alone or in combination of two or more.

As the (meth) acrylic acid alkyl ester having 1 to 3 carbon atoms in the alkyl group, for example, methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, (meth) acrylic acid Isopropyl etc. are mentioned.
As a (meth) acrylic-acid alkylester whose carbon number of the said alkyl group is 13-18, a tridecyl methacrylate, a stearyl (meth) acrylate, etc. are mentioned, for example.
Examples of the functional monomer include hydroxyalkyl (meth) acrylate, glycerin dimethacrylate, glycidyl (meth) acrylate, 2-methacryloyloxyethyl isocyanate, (meth) acrylic acid, itaconic acid, maleic anhydride, crotonic acid, Maleic acid, fumaric acid etc. are mentioned.

In order to copolymerize the above-mentioned monomer mixture to obtain the above-mentioned acrylic copolymer, the above-mentioned monomer mixture may be radically reacted in the presence of a polymerization initiator. The method of radically reacting the monomer mixture, that is, the polymerization method may be a conventionally known method, and examples thereof include solution polymerization (boiling point polymerization or constant temperature polymerization), emulsion polymerization, suspension polymerization, bulk polymerization and the like.
The said polymerization initiator is not specifically limited, For example, an organic peroxide, an azo compound, etc. are mentioned. Examples of the organic peroxide include 1,1-bis (t-hexylperoxy) -3,3,5-trimethylcyclohexane, t-hexylperoxypivalate, t-butylperoxypivalate, and 2,5. -Dimethyl-2,5-bis (2-ethylhexanoylperoxy) hexane, t-hexylperoxy-2-ethylhexanoate, t-butylperoxy-2-ethylhexanoate, t-butylperoxy Isobutyrate, t-butylperoxy-3,5,5-trimethylhexanoate, t-butylperoxy laurate and the like can be mentioned. Examples of the azo compound include azobisisobutyronitrile, azobiscyclohexanecarbonitrile and the like. These polymerization initiators may be used alone or in combination of two or more.

Although the weight average molecular weight (Mw) of the said acrylic copolymer is not specifically limited, A preferable lower limit is 400,000 and a preferable upper limit is 1.2 million. If the said weight average molecular weight is 400,000 or more, the cohesion of the said adhesive layer will become high and the adhesion reliability of a conductive adhesive tape will improve. If the said weight average molecular weight is 1.2 million or less, the said adhesive layer will have sufficient level | step difference follow-up property and adhesiveness, without becoming hard too much, and the adhesion reliability of a conductive adhesive tape will improve. The more preferable lower limit of the above weight average molecular weight is 500,000, and the more preferable upper limit is 700,000.
In order to control the weight average molecular weight in the above range, polymerization conditions such as a polymerization initiator, polymerization temperature and the like may be controlled.
In addition, a weight average molecular weight (Mw) is a weight average molecular weight of standard polystyrene conversion by GPC (Gel Permeation Chromatography: gel permeation chromatography).

The metal filler may be a filler consisting only of a metal, or may be a filler in which a core other than a metal (for example, resin particles) is metallized.
Examples of the metal in the metal filler include nickel, silver, copper, gold, aluminum, iron, a tin alloy, titanium and the like. Among them, copper, silver and nickel are preferable. Nickel is more preferable because copper and silver may cause passivation and the like to lower the conductivity.

The shape of the metal filler is not particularly limited, and examples thereof include spheres, ovals, needles, horns, branches, pieces, irregular shapes, teardrops, particles and the like. Among these, from the viewpoint of the dispersibility in the above-mentioned acrylic copolymer and the stability of the resistance value, spherical, elliptical, needle-like or granular is preferable.

In the pressure-sensitive adhesive layer, the a value calculated by the following formula (1) is 0 or more.
a value = (25 * M) + {22 * (d70 / D)}-3 * (d70-d40) -18 (1)
M: Metal amount (volume%) of the metal filler with respect to the volume of the pressure-sensitive adhesive layer
D: Thickness of the above adhesive layer (μm)
d40: particle diameter (μm) of the metal filler when the cumulative distribution on a volume basis is 40%
d70: particle diameter (μm) of the metal filler when the cumulative distribution on a volume basis is 70%

If the a value is 0 or more, noise radiation from the cross section of the pressure-sensitive adhesive layer is suppressed, and the electromagnetic wave shielding properties and the conductivity of the conductive pressure-sensitive adhesive tape are improved. From the viewpoint of further improving the electromagnetic wave shielding properties, the a value is preferably 5 or more, more preferably 7 or more, still more preferably 10 or more, still more preferably 12 or more, and particularly preferably 14 or more.
The upper limit of the a value is not particularly limited, but from the viewpoint of the electromagnetic wave shielding property and conductivity of the conductive pressure-sensitive adhesive tape and the balance of adhesion performance, the preferred upper limit is 200, the more preferred upper limit is 100, and the more preferred upper limit is 50. The particularly preferred upper limit is 30.
The “a value” is the metal content of the metal filler relative to the volume of the pressure-sensitive adhesive layer in Examples and Comparative Examples, the thickness of the pressure-sensitive adhesive layer, and the particle diameter of the metal filler when the cumulative distribution based on volume is 40%. And it is derived by regression analysis from the correlation between the particle size of the metal filler when the cumulative distribution on a volume basis is 70% and the electromagnetic wave shielding property. Under the present circumstances, when the measurement result in 1 GHz was 65 dB or more in evaluation of electromagnetic wave shield property, it was judged that it had sufficient electromagnetic wave shield property. As regression analysis, for example, a commonly performed method such as linear regression or non-linear regression can be adopted.

As a method of controlling the a value in the above range, a method of increasing the metal amount (M) of the metal filler to the volume of the pressure-sensitive adhesive layer, a method of reducing the thickness (D) of the pressure-sensitive adhesive layer, the pressure-sensitive adhesive layer It is preferable to increase the ratio (d70 / D) of the particle diameter (d70) of the metal filler when the cumulative distribution on a volume basis is 70% to the thickness (D) of Also, the difference between the particle diameter (d70) of the metal filler when the cumulative distribution on a volume basis is 70% and the particle diameter (d40) of the metallic filler when the cumulative distribution on a volume basis is 40% Also preferred is a method of reducing d70-d40) (i.e., sharpening the particle size distribution). These methods may be used alone or in combination of two or more.

The preferable lower limit of the metal amount (M) of the metal filler with respect to the volume of the pressure-sensitive adhesive layer is 0.001% by volume, and the preferable upper limit is 10% by volume. When the metal content is 0.001% by volume or more, a conductive path is sufficiently formed in the pressure-sensitive adhesive layer, and the electromagnetic wave shielding properties and the conductivity of the conductive pressure-sensitive adhesive tape are improved. When the amount of metal is 10% by volume or less, the increase in resistance value due to the influence of the contact resistance at the interface of the metal filler can be suppressed. The more preferable lower limit of the metal amount is 0.01% by volume, and the more preferable upper limit is 3.5% by volume.

The preferable lower limit of the thickness (D) of the pressure-sensitive adhesive layer is 1 μm, and the preferable upper limit is 50 μm. When the thickness is 1 μm or more, the pressure-sensitive adhesive layer has sufficient adhesive strength, and the adhesion reliability of the conductive pressure-sensitive adhesive tape is improved. If the said thickness is 50 micrometers or less, the noise radiation from the cross section of the said adhesive layer will be suppressed, and the electromagnetic wave shielding property and electroconductivity of a conductive adhesive tape will improve. The more preferable lower limit of the thickness of the pressure-sensitive adhesive layer is 5 μm, and the more preferable upper limit is 30 μm.

The lower limit of the ratio (d70 / D) of the particle diameter (d70) of the metal filler when the cumulative distribution on a volume basis to the thickness (D) of the pressure-sensitive adhesive layer is 70% is 0.6, and the upper limit is preferably 5 .0. When the ratio (d70 / D) is 0.6 or more, the protrusion of the metal filler from the pressure-sensitive adhesive layer becomes large, and the electromagnetic wave shielding properties and the conductivity of the conductive pressure-sensitive adhesive tape are improved. When the ratio (d70 / D) is 5.0 or less, excessive protrusion of the metal filler from the pressure-sensitive adhesive layer can be suppressed, and sufficient adhesion performance can be maintained. From the same viewpoint, the lower limit of the above ratio (d70 / D) is more preferably 0.7, more preferably 5.0, still more preferably 0.9, more preferably 4.0, still more preferably lower. The upper limit is preferably 1.0, more preferably 3.5, particularly preferably 1.1, and more preferably 3.2.

The difference (d70−) between the particle diameter (d70) of the metal filler when the cumulative distribution on a volume basis is 70% and the particle diameter (d40) of the metallic filler when the cumulative distribution on a volume basis is 40% The preferred lower limit of d40) is 0.01 μm, and the preferred upper limit is 40 μm. When the difference (d70-d40) is 0.01 μm or more, high electromagnetic wave shielding properties can be exhibited even when the ratio (d70 / D) is small. When the difference (d70-d40) is 40 μm or less, the particle size distribution becomes sharp, and the electromagnetic wave shielding property and the conductivity of the conductive adhesive tape can be stably obtained. The more preferable lower limit of the difference (d70-d40) is 1 μm, and the more preferable upper limit is 30 μm.

The particle diameter (d70) of the metal filler when the cumulative distribution on a volume basis is 70% is a preferable lower limit because the a value can be easily controlled within the above range regardless of the thickness (D) of the pressure-sensitive adhesive layer. Is preferably 4.0 μm, preferably 50 μm, more preferably 6.0 μm, and still more preferably 40 μm.
The particle diameter (d40) of the metal filler when the cumulative distribution on a volume basis is 40% has a preferable lower limit of 2.0 μm, a preferable upper limit of 40 μm, a more preferable lower limit of 4.0 μm, and a more preferable upper limit of 30 μm It is.
The particle size (d70 and d40) of the metal filler can be obtained by measuring the particle size distribution with a laser diffraction apparatus (for example, SALD-3000 manufactured by Shimadzu Corporation).

The pressure-sensitive adhesive layer preferably contains a tackifying resin.
As the tackifying resin, for example, rosin ester resin, hydrogenated rosin resin, terpene resin, terpene phenol resin, coumarone indene resin, alicyclic saturated hydrocarbon resin, C5 petroleum resin, C9 resin A petroleum resin, C5-C9 copolymer-based petroleum resin, etc. are mentioned. These tackifying resins may be used alone or in combination of two or more.

The tackifying resin is preferably highly polar from the viewpoint of adhesion improvement and dispersion improvement of the metal filler, and the preferable lower limit of the hydroxyl value is 20, the preferable upper limit is 200, and the more preferable lower limit is 30 More preferable upper limit is 150.

The content of the tackifier resin is not particularly limited, but a preferable lower limit is 5 parts by weight and a preferable upper limit is 40 parts by weight with respect to 100 parts by weight of the acrylic copolymer. When the content is 5 parts by weight or more, the pressure-sensitive adhesive layer has sufficient adhesive strength, and the adhesion reliability of the conductive pressure-sensitive adhesive tape is improved. When the content is 40 parts by weight or less, the pressure-sensitive adhesive layer does not become too hard and has sufficient step followability and adhesive strength, and the adhesion reliability of the conductive pressure-sensitive adhesive tape is improved. From the same viewpoint, a more preferable lower limit of the content is 10 parts by weight, and a more preferable lower limit is 30 parts by weight.

In the pressure-sensitive adhesive layer, a crosslinking structure is formed between the main chains of the resin (the acrylic copolymer and / or the tackifying resin) constituting the pressure-sensitive adhesive layer by the addition of a crosslinking agent. preferable.
The said crosslinking agent is not specifically limited, For example, an isocyanate type crosslinking agent, an aziridine type crosslinking agent, an epoxy type crosslinking agent, a metal chelate type crosslinking agent etc. are mentioned. Among these, isocyanate crosslinking agents are preferred. The addition of an isocyanate-based crosslinking agent to the pressure-sensitive adhesive layer causes the isocyanate group of the isocyanate-based crosslinking agent to react with the alcoholic hydroxyl group in the resin constituting the pressure-sensitive adhesive layer, thereby causing crosslinking of the pressure-sensitive adhesive layer. Become loose. Therefore, since the said adhesive layer can disperse the peeling stress added intermittently, the adhesion reliability of a conductive adhesive tape improves.
The amount of addition of the crosslinking agent is preferably 0.01 to 10 parts by weight, and more preferably 0.1 to 3 parts by weight with respect to 100 parts by weight of the acrylic copolymer.

The pressure-sensitive adhesive layer may contain, if necessary, plasticizers, emulsifiers, softeners, fillers, additives such as pigments and dyes, and other resins such as rosin resins.

The degree of crosslinking of the pressure-sensitive adhesive layer is not particularly limited, but a preferable lower limit is 20% by weight and a preferable upper limit is 45% by weight. When the degree of crosslinking is 20% by weight or more, the cohesion of the pressure-sensitive adhesive layer becomes high, and the adhesion reliability of the conductive pressure-sensitive adhesive tape is improved. When the degree of crosslinking is 45% by weight or less, the pressure-sensitive adhesive layer does not become too hard and has sufficient step followability and adhesiveness, and the adhesion reliability of the conductive pressure-sensitive adhesive tape is improved. The lower limit of the crosslinking degree is preferably 25% by weight, more preferably 40% by weight, still more preferably 30% by weight, and still more preferably 35% by weight.
The degree of crosslinking of the pressure-sensitive adhesive layer was determined by collecting the pressure-sensitive adhesive layer W1 (g), immersing the pressure-sensitive adhesive layer in ethyl acetate at 23 ° C. for 24 hours, and filtering undissolved components with a 200 mesh wire mesh. The residue on the wire mesh is vacuum dried, the weight W2 (g) of the dried residue is measured, and the weight is calculated by the following equation (2).
Degree of crosslinking (% by weight) = 100 × W2 / W1 (2)

Although the total thickness of the electroconductive adhesive tape of this invention is not specifically limited, A preferable minimum is 2 micrometers and a preferable upper limit is 200 micrometers. If the said total thickness is in the said range, the handleability of a conductive adhesive tape will improve. The more preferable lower limit of the total thickness is 10 μm, and the more preferable upper limit is 50 μm.

As a manufacturing method of the electroconductive adhesive tape of this invention, the following methods are mentioned, for example. First, a solvent is added to an acrylic copolymer, a metal filler, a tackifying resin, a crosslinking agent, etc. as required to prepare a solution of adhesive a, and the solution of adhesive a is applied to the surface of a conductive substrate. The solution is applied, and the solvent in the solution is completely removed by drying to form a pressure-sensitive adhesive layer a. Next, a release film is superimposed on the formed pressure-sensitive adhesive layer a with the release-treated surface of the release film facing the pressure-sensitive adhesive layer a.
Then, a release film different from the above release film is prepared, a solution of the adhesive b is applied to the release treated surface of the release film, and the solvent in the solution is completely removed by drying. The laminated film in which the adhesive layer b was formed in the surface of a type | mold film is produced. The resulting laminated film is superimposed on the back surface of the conductive substrate on which the pressure-sensitive adhesive layer a is formed, in a state where the pressure-sensitive adhesive layer b faces the back surface of the conductive substrate, to prepare a laminate. Then, a pressure-sensitive adhesive layer is provided on both sides of the conductive substrate by pressing the above laminate with a rubber roller or the like, and a conductive pressure-sensitive adhesive tape in which the surface of the pressure-sensitive adhesive layer is covered with a release film is obtained. Can.

Also, two sets of laminated films are prepared in the same manner, and these laminated films are laminated on both sides of the conductive substrate in a state where the pressure-sensitive adhesive layer of the laminated film is opposed to the conductive substrate. A body may be produced and this laminate may be pressed by a rubber roller or the like. As a result, a conductive pressure-sensitive adhesive tape may be obtained which has a pressure-sensitive adhesive layer on both sides of a conductive substrate and the surface of the pressure-sensitive adhesive layer is covered with a release film.

The use of the conductive pressure-sensitive adhesive tape of the present invention is not particularly limited, but it is preferably used to cover a CPU, a connector and the like in an electronic substrate component constituting an electronic device because of excellent electromagnetic wave shielding properties and conductivity.
The shape of the conductive pressure-sensitive adhesive tape of the present invention in such a CPU cover (shield cap) application is not particularly limited, and examples thereof include a rectangular shape, a frame shape, a circular shape, an elliptical shape, and a donut shape. Although the sticking area of the electroconductive adhesive tape of this invention in that case is not specifically limited, It is preferable that it is 10000 mm < ² > or less.

ADVANTAGE OF THE INVENTION According to this invention, the electroconductive adhesive tape excellent in electromagnetic wave shielding property and electroconductivity can be provided.

EXAMPLES The present invention will be described in more detail by way of examples, but the present invention is not limited to these examples.

Example 1
Ethyl acetate as a polymerization solvent was added to the reaction vessel, and after bubbling with nitrogen, the reaction vessel was heated while refluxing with nitrogen to start refluxing. Subsequently, a polymerization initiator solution in which 0.1 part by weight of azobisisobutyronitrile was diluted 10-fold with ethyl acetate as a polymerization initiator was charged into the reaction vessel. Subsequently, 30 parts by weight of 2-ethylhexyl acrylate (2-EHA), 60 parts by weight of butyl acrylate (BA), 6.7 parts by weight of cyclohexyl methacrylate (CHMA), 3 parts by weight of acrylic acid (AAC), 4-butyl hydroxyacrylate 0.3 parts by weight of (4-HBA) was added dropwise over 2 hours. After completion of the dropwise addition, a polymerization initiator solution prepared by diluting 0.1 parts by weight of azobisisobutyronitrile as a polymerization initiator by 10 times with ethyl acetate is again introduced into the reaction vessel, and a polymerization reaction is carried out for 4 hours. A combined solution (weight average molecular weight (Mw) of 1,000,000 of the acrylic copolymer) was obtained.

Nickel particles (spherical, d40 = 8.5 μm, d70 = 17.7 μm, specific gravity 8.91 g / cm 3) were stirred and mixed as metal fillers with respect to 100 parts by weight of the acrylic copolymer. Furthermore, 15 parts by weight of a terpene resin (hydroxyl value 130, G-150 manufactured by Yasuhara Chemical Co., Ltd.) as a tackifying resin, 1 part by weight of an isocyanate-based crosslinking agent (Coronate L manufactured by Tosoh Corp.) as a crosslinking agent, ethyl acetate 50 as a solvent The parts by weight were stirred and mixed to prepare a pressure-sensitive adhesive solution.
A 25 μm-thick PET separator was prepared, a pressure-sensitive adhesive solution was applied to the release-treated surface of the separator, and dried at 110 ° C. for 3 minutes to form a pressure-sensitive adhesive layer. The conductive adhesive tape was obtained by bonding this adhesive layer with copper foil with a thickness of 18 micrometers. In addition, the compounding quantity of the metal filler was controlled so that the metal amount of a metal filler might be 1.10 volume% with respect to the volume of the adhesive layer formed. The a value of the obtained pressure-sensitive adhesive layer was calculated by the above-mentioned formula (1).

(Examples 2 to 12 and Comparative Examples 1 to 4)
A conductive pressure-sensitive adhesive tape was obtained in the same manner as in Example 1, except that the thickness of the pressure-sensitive adhesive layer and the metal filler (type, shape, particle diameter and blending amount) were changed as shown in Table 1.

<Evaluation>
The following evaluation was performed about the electroconductive adhesive tape obtained by the Example and the comparative example. The results are shown in Table 1.

(1) An electromagnetic wave shielding conductive adhesive tape was cut into a flat rectangular shape of 41 mm × 50 mm to prepare a test piece. A jig for electric field measurement of a KEC device (manufactured by Techno Science JPA) was prepared, and a 3 mm thick copper plate with a 38 mm × 48 mm hole was placed at the lower jig at the center. The test piece was stuck on a copper plate according to a hole shape so that the pasting width of each side might be 1.5 mm. The upper lid of the jig was put there and tightened sufficiently. The electromagnetic wave shielding property of the test piece was measured at 100 MHz to 8 GHz using a network analyzer (manufactured by KEYSIGHT TECHNOLOGIES, E5071C). In the state where a 3 mm thick copper plate with a 38 mm × 48 mm hole was installed, the value without the test piece was taken as the calibration value. In addition, when the measurement result in 1 GHz was 65 dB or more, it was judged that it had sufficient electromagnetic wave shielding.

(2) The conductive conductive adhesive tape was cut into a rectangular shape of 25 mm × 75 mm to prepare a test piece. The test pieces were attached to two 25 mm wide copper electrodes. The affixing area of the test piece to each electrode was 25 mm × 25 mm. Thereafter, the resistance value was measured in a test room at a temperature of 23 ° C. and a humidity of 50% RH. The lower the resistance value, the better the conductivity. When the measurement limit was exceeded and the resistance value could not be measured, it was indicated as "OL."

ADVANTAGE OF THE INVENTION According to this invention, the electroconductive adhesive tape excellent in electromagnetic wave shielding property and electroconductivity can be provided.

Claims (3)

A conductive pressure-sensitive adhesive tape comprising a conductive substrate and a pressure-sensitive adhesive layer disposed on at least one surface of the conductive substrate,
The pressure-sensitive adhesive layer, an acrylic copolymer, containing a metal filler state, and are a value of 0 or more calculated by the following equation (1),
The ratio (d70 / D) of the particle diameter (d70) of the metal filler when the cumulative distribution on a volume basis is 70% to the thickness (D) of the pressure-sensitive adhesive layer is 0.9 or more Characteristic conductive adhesive tape.
a value = (25 * M) + {22 * (d70 / D)}-3 * (d70-d40) -18 (1)
M: Metal amount (volume%) of the metal filler with respect to the volume of the pressure-sensitive adhesive layer
D: Thickness of the pressure-sensitive adhesive layer (μm)
d40: particle diameter (μm) of the metal filler when the cumulative distribution on a volume basis is 40%
d70: particle diameter (μm) of the metal filler when the cumulative distribution on a volume basis is 70% The thickness of the pressure-sensitive adhesive layer (D) is 30 μm or less, the conductive pressure-sensitive adhesive tape according to claim 1 . The difference (d70-d40) between the particle diameter (d70) of the metal filler when the cumulative distribution on a volume basis is 70% and the particle diameter (d40) of the metallic filler when the cumulative distribution on a volume basis is 40% The conductive pressure-sensitive adhesive tape according to claim 1 or 2, having a thickness of 40 μm or less.