Conductive adhesive tape

Abstract

To provide a conductive adhesive tape suppressed in resistance increase in a thickness direction and excellent in conductivity even when exposed to repeated temperature change and excellent in conductivity.SOLUTION: Provided is a conductive adhesive tape that has at least a conductive adhesive layer, wherein the conductive adhesive layer contains an adhesive and conductive particles, and among the primary particles and aggregates of the conductive particles present in a 2.5 mm2 area A as viewed in plane(except the primary particles and the aggregates with a maximum length of 10 μm or less), a ratio of the number of primary particles and aggregates with a maximum length of 60 μm or more to be 5% or less, and the ratio of the number of primary particles and aggregates with a maximum length of less than 50 μm to be 85% or more.SELECTED DRAWING: None

Description

Technical Field

[0001] The present disclosure relates to a conductive adhesive tape.

Background Art

[0002] In electronic devices and communication devices, conductive adhesive tapes are used for purposes such as electromagnetic wave shielding and grounding for static electricity prevention.

[0003] For example, Patent Document 1 discloses a conductive adhesive tape having a total thickness of 30 μm or less. This conductive adhesive tape includes a conductive base material and a conductive adhesive layer containing conductive particles.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] A conductive adhesive layer containing conductive particles has a problem that when repeatedly subjected to temperature changes, the resistance value in the thickness direction greatly increases, resulting in a decrease in conductivity.

[0006] The present disclosure has been made in view of the above circumstances, and provides a conductive adhesive tape that suppresses an increase in the resistance value in the thickness direction even when repeatedly subjected to temperature changes and has excellent conductivity.

Means for Solving the Problems

[0007] The inventor has found that conductive particles exist as primary particles and / or aggregates in the conductive adhesive layer, and the variation in the size of the primary particles and aggregates affects the conductivity in the thickness direction due to repeated temperature changes.

[0008] That is, the present disclosure has the following embodiments. [1] A conductive adhesive tape having at least a conductive adhesive layer, wherein the conductive adhesive layer contains an adhesive and conductive particles, and in a plan view of the conductive adhesive layer, within a region A of 2.5 mm 2 among the primary particles and aggregates of the conductive particles (excluding the primary particles and aggregates having a maximum length of 10 μm or less) present in the region A, the number ratio of the primary particles and aggregates having a maximum length of 60 μm or more is 5% or less, and the number ratio of the primary particles and aggregates having a maximum length of less than 50 μm is 85% or more. [2] The conductive adhesive tape according to [1] above, wherein the thickness of the conductive adhesive layer is 10 μm or less. [3] The conductive adhesive tape according to [1] or [2] above, wherein the total amount of the conductive particles is in the range of 0.1 part by mass to 10 parts by mass with respect to 100 parts by mass of the adhesive. [4] The conductive adhesive tape according to any one of [1] to [3] above, wherein the total number of the primary particles and aggregates of the conductive particles (excluding the primary particles and aggregates having a maximum length of 10 μm or less) present in the region A in a plan view of the conductive adhesive layer is in the range of 20 to 150. [5] The conductive adhesive tape according to any one of [1] to [4] above, wherein the average particle diameter (d50) of the primary particles is in the range of 5 μm to 30 μm. [6] The conductive adhesive tape according to any one of [1] to [5] above, wherein the aggregates are formed by aggregation of the primary particles having an average particle diameter (d50) in the range of 5 μm to 30 μm. [7] The conductive adhesive tape according to any one of [1] to [6] above, wherein the conductive particles are metal particles. [8] The conductive adhesive tape according to any one of [1] to [7] above, wherein the conductive particles are nickel powder. [9] The conductive adhesive tape according to any one of [1] to [8] above, having the conductive adhesive layer on one side or both sides of a base material.

[10] The conductive adhesive tape according to [9] above, wherein the base material is a metal foil.

[11] The conductive adhesive tape according to [9] above, wherein the base material is a copper foil having a chromium plating layer on one or both sides.

[12] The conductive adhesive tape according to any one of [1] to

[11] above, wherein the change rate of the resistance value in the thickness direction before and after the thermal cycle test is 200% or less.

Effect of the Invention

[0009] According to the present disclosure, it is possible to suppress an increase in the resistance value in the thickness direction due to repeated temperature changes, and to provide a conductive adhesive tape having excellent conductivity.

Mode for Carrying Out the Invention

[0010] I. Conductive Adhesive Tape The conductive adhesive tape of the present disclosure (hereinafter, may be referred to as a tape) has at least a conductive adhesive layer, and the conductive adhesive layer contains an adhesive and conductive particles. In the conductive adhesive tape of the present invention, among the primary particles and aggregates of the conductive particles (excluding the primary particles and aggregates having a maximum length of 10 μm or less) present in a region A of 2.5 mm in a plan view of the conductive adhesive layer, the number ratio of the primary particles and aggregates having a maximum length of 60 μm or more is 5% or less, and the number ratio of the primary particles and aggregates having a maximum length of less than 50 μm is 85% or more. 2

[0011] In a conductive adhesive tape having an adhesive layer containing conductive particles (conductive adhesive layer), the conductive particles in the conductive adhesive layer are dispersed in the adhesive. However, since the conductive particles tend to aggregate, they tend to exist as aggregates in the conductive adhesive layer. Further, even when the particle size of the primary particles of the conductive particles is adjusted and dispersed in the adhesive at the stage of preparing the conductive adhesive, the size of the aggregates of the conductive particles becomes non-uniform in the conductive adhesive layer. When an adherend to which a conductive adhesive tape including such a conductive adhesive layer is attached is exposed to an environment with a large temperature change, the tape is likely to float or peel off from the adherend. At this time, since conduction contacts cannot be established at the floating or peeling portion of the tape from the adherend, the resistivity in the thickness direction increases over time. Here, it is presumed that the floating or peeling of the tape from the adherend occurs starting from the conductive particles present on the bonding surface between the adherend and the conductive adhesive layer. In particular, when there are a large number of aggregates or primary particles having a large size in the plan view of the conductive adhesive tape, the size per peeling or floating portion of the tape becomes large, so that the increase in resistivity due to the decrease in the conduction contacts between the adherend and the tape becomes more prominent, and it becomes difficult to maintain good conductivity in the thickness direction over time.

[0012] On the other hand, according to the conductive adhesive tape of the present disclosure, by controlling the size and the number ratio of the primary particles and aggregates of the conductive particles in the plan view of the conductive adhesive layer, the initial resistance value is low, and also, since the size of the floating or peeling occurring starting from the aggregates or primary particles can be reduced, an increase in the resistance value in the thickness direction due to repeated temperature changes (thermal cycle) is suppressed. Thus, the conductive adhesive tape of the present disclosure is excellent in the temporal stability of the conductivity in the thickness direction.

[0013] The 2.5 mm in the plan view of the conductive adhesive layer 2 The region A refers to a rectangular small region a (area: 0.25 mm 2 ) of 0.5 mm × 0.5 mm is arbitrarily selected 10 times, and the total region (the set of 10 small regions a) composed of the 10 small regions a is defined.

[0014] When counting the number of conductive particles contained in the small region a, for example, when a part of the conductive particle protrudes from the small region a because it is located at the boundary of the small region a, those in which 80% or more of the planar shape of the conductive particle exists within the small region a are counted as one. The maximum length, etc. of the conductive particle is measured in the portion existing in the small region a.

[0015] 1. Conductive Adhesive Layer The conductive adhesive layer in the present disclosure contains an adhesive and conductive particles. Such a conductive adhesive layer is formed from a conductive adhesive containing an adhesive and conductive particles.

[0016] The thickness of the above conductive adhesive layer is preferably 10 μm or less, more preferably 1 μm or more and 9 μm or less, still more preferably 2 μm or more and 8 μm or less, and even more preferably 4 μm or more and 6 μm or less. By setting the thickness of the conductive adhesive layer within the above range, the conductive adhesive layer can exhibit good adhesive strength, and the size and number ratio of the primary particles and aggregates of the conductive particles in the planar view of the conductive adhesive layer can be controlled, thereby expressing the temporal stability of conductivity in the thickness direction.

[0017] The thickness of the above conductive adhesive layer refers to the average value of the thicknesses at five locations at intervals of 100 mm in the length direction using a digital length gauge (MS-11C manufactured by Nikon).

[0018] (1) Conductive Particles In the above conductive adhesive layer, the conductive particles exist as primary particles and / or aggregates. The above conductive adhesive layer may contain at least aggregates of conductive particles, may contain at least primary particles of conductive particles that do not form aggregates, or may contain both aggregates of conductive particles and primary particles of conductive particles that do not form aggregates. It is preferable to contain at least aggregates of conductive particles. The number of primary particles of conductive particles refers to the number of primary particles that do not form aggregates and exist in the conductive adhesive layer. In the above region A, the number of the above aggregates may be more or less than the number of the above primary particles, but it is preferable that the number of aggregates is less than the number of primary particles.

[0019] The aggregate of conductive particles may be an aggregate formed by aggregation of primary particles of one kind of conductive particle, or may be an aggregate formed by aggregation of primary particles of two or more kinds of conductive particles.

[0020] In the plan view of the above conductive adhesive layer, within a region A of 2.5 mm 2 among the primary particles and aggregates of the above conductive particles (excluding the primary particles and the above aggregates with a maximum length of 10 μm or less), the proportion of the number of the primary particles and the above aggregates with a maximum length of 60 μm or more is 5% or less. Thereby, even when the tape of the present disclosure is repeatedly subjected to temperature changes, it is possible to prevent the aggregates and primary particles from floating or peeling off from the adherend, and suppress the decrease in conductivity over time.

[0021] Among the primary particles and aggregates of conductive particles, the primary particle with a maximum length of 60 μm or more may be referred to as primary particle A, and the aggregate with a maximum length of 60 μm or more may be referred to as aggregate A.

[0022] Among them, the number ratio of the primary particles and aggregates (the number ratio of primary particles A and aggregates A) having a maximum length of 60 μm or more and existing in the region A of the conductive adhesive layer in plan view is preferably 4.5% or less, more preferably 3.5% or less, still more preferably 2.5% or less, and particularly preferably 0%, that is, the region A does not contain primary particles and aggregates having a maximum length of 60 μm or more. When the tape of the present disclosure is repeatedly subjected to temperature changes (thermal cycle), the increase in the resistance value in not only the thickness direction but also the horizontal direction can be effectively suppressed by the number ratio of the primary particles A and aggregates A existing in the region A being within the above range.

[0023] The number of the primary particles A and the aggregates A existing in the region A of the conductive adhesive layer is not particularly limited, but is preferably 3 or less, more preferably 2 or less, still more preferably 1 or less, and particularly preferably 0.

[0024] In the plan view of the conductive adhesive layer, the area of the square circumscribing the primary particles A and / or the aggregates A is not particularly limited, but is, for example, 300 μm 2 ~2700 μm 2 within a range is preferable, and 300 μm 2 ~2400 μm 2 within a range is more preferable, and 300 μm 2 ~2100 μm 2 within a range is still more preferable.

[0025] In the plan view of the conductive adhesive layer, the area occupancy ratio of the primary particles A and the aggregates A in the region A is preferably 10% or less, more preferably 5% or less, still more preferably 1% or less, and particularly preferably 0%.

[0026] In the plan view of the conductive adhesive layer, among the primary particles and aggregates of the conductive particles present in the region A of the conductive adhesive layer (excluding the primary particles and aggregates with a maximum length of 10 μm or less), the number ratio of the primary particles and aggregates with a maximum length of less than 50 μm is 85% or more. As a result, the tape of the present disclosure has a low initial resistance value and can exhibit good conductivity. Also, on the bonding surface between the conductive adhesive layer and the adherend, the size of the lifting and peeling starting from the aggregates and primary particles due to thermal cycling can be reduced, and the decrease in conductivity over time can be suppressed.

[0027] Among the primary particles and aggregates of the conductive particles, the primary particles with a maximum length of less than 50 μm may be referred to as primary particles B, and the aggregates with a maximum length of less than 50 μm may be referred to as aggregates B. Also, the primary particles B and the aggregates B do not include the primary particles and aggregates with a maximum length of 10 μm or less.

[0028] Among them, the number ratio (the number ratio of the primary particles B and the aggregates B) of the primary particles and aggregates with a maximum length of less than 50 μm present in the region A of the conductive adhesive layer is preferably in the range of 85% to 100%, more preferably in the range of 90% to 100%, and even more preferably in the range of 95% to 100%. By setting the number ratio of the primary particles B and the aggregates B present in the region A of the conductive adhesive layer within the above range, the tape of the present disclosure can highly balance the initial conductivity and the conductivity over time.

[0029] The number of the primary particles B and the aggregates B present in the region A of the conductive adhesive layer is not particularly limited, but can be 150 or less, preferably 120 or less, and even more preferably 100 or less. Also, the number is preferably 17 or more, preferably 20 or more, and even more preferably 40 or more. More specifically, the number is preferably 40 or more and 100 or less, among which 47 or more and 95 or less is preferable, 50 or more and 90 or less is more preferable, and 60 or more and 80 or less is even more preferable.

[0030] In addition, the area per particle of the primary particles B and the aggregates B in the plan view of the conductive adhesive layer may be smaller than the area per particle of the primary particles A and the aggregates A, and the size of the area is not particularly limited as long as it can prevent the tape from lifting or peeling and can exhibit good conductivity. In the plan view of the conductive adhesive layer, the area of the quadrangle circumscribing the primary particles B and / or the aggregates B is not particularly limited. For example, it is 1 μm 2 ~250 μm 2 is preferable, and 5 μm 2 ~200 μm 2 is more preferable, and 10 μm 2 ~150 μm 2 is even more preferable. The method for calculating the area of the quadrangle circumscribing the primary particles B and / or the aggregates B is the same as the method for calculating the area of the quadrangle circumscribing the primary particles A and / or the aggregates A described above.

[0031] In the plan view of the conductive adhesive layer, the proportion of the number of primary particles and aggregates (which may be referred to as primary particles A' and aggregates A') having a maximum length of 70 μm or more among the primary particles A and aggregates A present in the region A of the conductive adhesive layer is preferably 1.5% or less, more preferably 1.0% or less, and even more preferably 0%. If the proportion of the number of the primary particles A' and aggregates A' present in the region A of the conductive adhesive layer is larger than the above range, on the surface of the conductive adhesive layer, the size per location of lifting or peeling becomes larger, and the resistance value is likely to increase due to thermal cycling.

[0032] In the plan view of the conductive adhesive layer, the proportion of the number of primary particles and aggregates having a maximum length of 50 μm or more and less than 60 μm present in the region A of the conductive adhesive layer is not particularly limited as long as the proportion of the number of the primary particles A and the aggregates A and the proportion of the number of the primary particles B and the aggregates B are within a predetermined range. For example, it is preferably 15% or less, more preferably 10% or less, and even more preferably 5% or less.

[0033] In the plan view of the above conductive adhesive layer, the number ratio of the primary particles A and aggregates A of the above conductive particles present in one small region a is preferably 5% or less, more preferably 4.5% or less, still more preferably 3.5% or less, even more preferably 2.5% or less, and particularly preferably 0%, that is, it does not contain primary particles and aggregates having a maximum length of 60 μm or more. When the number ratio of the primary particles A and aggregates A in one small region a is within the above range, when the tape of the present disclosure is repeatedly subjected to temperature changes (thermal cycling), an increase in the resistance value not only in the thickness direction but also in the horizontal direction can be suppressed.

[0034] The number of the primary particles A and the aggregates A present in the above one small region a is not particularly limited as long as the number of the primary particles A and the aggregates A present in the above region A can be within a preferable range. For example, 3 or less is preferable, 2 or less is more preferable, 1 or less is even more preferable, and 0 is particularly preferable.

[0035] The number ratio of the primary particles B and their aggregates B of the above conductive particles present in the above one small region a is preferably 85% or more from the viewpoint of achieving a high balance between the initial conductivity and the conductivity over time, more preferably in the range of 85% to 100%, still more preferably in the range of 90% to 100%, and even more preferably in the range of 95% to 100%.

[0036] The number of the primary particles B and the aggregates B present in one small region a is not particularly limited as long as the number of the primary particles B and the aggregates B present in the above region A can be within a preferable range. For example, it can be within the range of 1 to 15, preferably within the range of 2 to 12, more preferably within the range of 4 to 10, even more preferably within the range of 5 to 9, and particularly preferably within the range of 6 to 8.

[0037] In a small region a, the proportion of the number of primary particles and aggregates (which may be referred to as primary particle A' and aggregate A') having a maximum length of 70 μm or more is preferably 1.5% or less, more preferably 1.0% or less, and still more preferably 0%. This is because on the surface of the conductive adhesive layer, the size per spot of floating or peeling becomes large, and the resistance value is likely to increase due to thermal cycling.

[0038] In the plan view of the conductive adhesive layer, the maximum length P1 of the primary particles and aggregates of the conductive particles refers to the maximum value among the distances between any two points on the contour line in the shape of the primary particles and aggregates of the conductive particles (also referred to as the plan view shape of the primary particles and aggregates of the conductive particles) of the conductive particles. The maximum length P1 of the primary particles and aggregates of the conductive particles is measured by the following method. Using an optical microscope (manufactured by HIROX, RH-2000 digital microscope, ACS revolver lens (30-2500x)), place the surface on the conductive adhesive layer side of the conductive adhesive tape (excluding the release liner if there is a release liner on the surface) on a flat stage with the lens side of the optical microscope, and on the surface on the conductive adhesive layer side, arbitrarily select 10 small regions a of 0.5 mm × 0.5 mm square (0.25 mm 2 ) and photograph each of the 10 small regions a at a magnification of 400 times to obtain a photographed image. The black portion in the photographed image represents the primary particles and aggregates of the conductive particles. Using the measurement function of the optical microscope, measure the maximum length P1 as the distance between the two points with the longest straight-line distance connecting any two points selected on the contour (the contour in the plan view shape of the primary particles and aggregates of the conductive particles) of the black portion of the photographed image of each small region a.

[0039] In addition, the number ratio of primary particles and aggregates with a maximum length P1 within a predetermined range (for example, the maximum length P1 is N1 μm or more, the maximum length P1 is less than N2 μm, the maximum length P1 is N3 μm or more and less than N4 μm. N1 to N4 are specific numerical values defining the range) present in the region A of the conductive adhesive layer is measured by the following method. First, in the same manner as the measurement method of "the maximum length P1 of the primary particles and aggregates of the conductive particles" described above, on the surface on the side of the conductive adhesive layer, a small region a of 0.5 mm × 0.5 mm square (0.25 mm 2 ) is selected, and 10 small regions a are each photographed at a magnification of 400 times to obtain a photographed image. For each of the small regions a, the number S1 of black portions with a maximum length P1 within a predetermined range (for example, the maximum length P1 is N1 μm or more, the maximum length P1 is less than N2 μm, the maximum length P1 is N3 μm or more and less than N4 μm) present in the photographed image, and the total number S2 of black portions present in the photographed image (however, black portions with a maximum length P1 of 10 μm or less are excluded) are counted. The total number S'1 of black portions with a maximum length P1 within a predetermined range contained in the 10 small regions a is taken as the number of primary particles and aggregates of the conductive particles with a maximum length P1 within a predetermined range present in the region A. In addition, the total number S'2 of black portions contained in the 10 small regions a is taken as the total number of primary particles and aggregates of the conductive particles present in the region A, and from the above S'1 and S'2, the number ratio in the region A is calculated by the following formula (1). Number ratio in region A [%] = (S'1 / S'2) × 100... Formula (1) Note that the number ratio in the small region a is calculated from the following formula (2). Number ratio in small region a [%] = (S1 / S2) × 100... Formula (2)

[0040] Note that in the small region a and the region A, primary particles and aggregates with a maximum length P1 of 10 μm or less in plan view are not included in the count of the number.

[0041] In the plan view of the conductive adhesive layer, the total number of primary particles and aggregates of the conductive particles present in the region A (excluding the primary particles and aggregates having a maximum length of 10 μm or less) is preferably in the range of 20 to 150, more preferably in the range of 50 to 120, still more preferably in the range of 60 to 110, and particularly preferably in the range of 70 to 100. By setting the total number of the primary particles and aggregates of the conductive particles present in the total region A within the above range, the tape of the present disclosure can increase the contact points between the conductive adhesive layer and the adherend, and thus can exhibit good conductive performance. Further, in the tape of the present disclosure, peeling and detachment due to thermal cycling are less likely to occur.

[0042] The conductive particles in the present disclosure are not particularly limited as long as they are particles capable of exhibiting conductivity, and examples thereof include metal particles, composite particles (metal-coated particles) in which the surface of core particles is coated with a metal, carbon fillers, and the like. The conductive particles may be used alone or in combination of two or more.

[0043] The metal constituting the metal film of the metal particles and the metal-coated particles is not particularly limited, and examples thereof include single metals such as nickel, iron, chromium, cobalt, aluminum, antimony, molybdenum, copper, silver, platinum, and gold, and alloys such as solder and stainless steel.

[0044] Examples of the metal-coated particles include metal-coated resin particles in which the surface of resin particles such as polymer beads and glass beads is coated with a metal, and metal-coated metal powders in which the surface of metal powders is coated with a different metal.

[0045] Since it is easy to balance the conductivity and adhesiveness of the conductive adhesive layer, the conductive particles are preferably metal particles. Among them, metal particles composed of a metal selected from the group consisting of nickel, copper, silver, and stainless steel are preferable, and nickel particles are more preferable because of their excellent conductivity.

[0046] As the nickel particles, nickel powder is preferred. Nickel powder can be produced by the carbonyl process. There is no particular limitation on the nickel powder produced by the carbonyl process, and it can be appropriately selected according to the purpose. For example, NI255T (filamentous) manufactured by Fukuda Metal Foil Powder Industry Co., Ltd., Ni123 (spherical) manufactured by Vale, Ni255 (filamentous) manufactured by Vale, N06 (bead-shaped) manufactured by Jinchuan Group Co., LTD, etc. can be mentioned.

[0047] The shape of the conductive particles is not particularly limited, and examples include spherical, spike-shaped (surface needle-shaped), flake-shaped (scaly), dendritic, fibrous, amorphous (polyhedral), bead-shaped, bead-shaped, etc. Among them, spherical, bead-shaped or bead-shaped are preferred from the viewpoint of reducing the resistance value of the conductive adhesive tape.

[0048] The average particle diameter (d50) of the primary particles of the conductive particles is preferably in the range of 5 μm to 30 μm, more preferably in the range of 10 μm to 26 μm, and still more preferably in the range of 12 μm to 20 μm. Further, the average particle diameter (d90) of the primary particles of the conductive particles is preferably in the range of 5 to 60 μm, more preferably in the range of 27 to 55 μm, still more preferably in the range of 30 to 50 μm, and particularly preferably in the range of 31 to 50 μm. By setting the average particle diameters d50 and / or d90 of the primary particles of the conductive particles within the above ranges, the size and the number ratio of the aggregates in the conductive adhesive layer can be adjusted by the method for preparing the conductive adhesive described later, and a conductive adhesive layer having good adhesiveness and conductivity before and after thermal cycling can be obtained.

[0049] The average particle diameters d50 and d90 of the primary particles of the conductive particles refer to the 50% cumulative value and 90% cumulative value in the particle size distribution, and are values measured by the laser diffraction / scattering method. As the measuring device, Microtrac MT3000II manufactured by Nikkiso Co., Ltd., Laser Diffraction Particle Size Distribution Analyzer SALD-3000 manufactured by Shimadzu Corporation, etc. can be used. When two or more kinds of conductive particles are contained, the above particle diameters are calculated from the distribution in which all the conductive particles are mixed.

[0050] As a method for adjusting the particle size of the conductive particles, for example, a method of pulverizing the conductive particles with a jet mill, a sieving method using a sieve or the like can be mentioned.

[0051] The ratio ([average particle size d50 of the primary particles of the conductive particles / thickness of the conductive adhesive layer]) of the average particle size d50 of the primary particles of the conductive particles to the thickness of the above-mentioned conductive adhesive layer is preferably 50% to 150%, more preferably 60% to 120%, and still more preferably 70 to 100%. Further, the ratio ([average particle size d90 of the primary particles of the conductive particles / thickness of the conductive adhesive layer]) of the average particle size d90 of the primary particles of the conductive particles to the thickness of the conductive adhesive layer is preferably 80 to 300%, more preferably 100 to 250%, and still more preferably 120 to 200%. By setting the ratios of the average particle sizes d50 and d90 of the primary particles of the conductive particles to the thickness of the conductive adhesive layer within the above ranges, both the conductivity and adhesiveness of the conductive adhesive layer can be achieved.

[0052] The content of the conductive particles in the above-mentioned conductive adhesive layer is not particularly limited as long as both conductivity and adhesiveness can be achieved, but 0.1 part by mass to 10 parts by mass of the conductive particles is preferably used per 100 parts by mass of the adhesive (solid content), more preferably 0.5 part by mass to 5 parts by mass, and still more preferably 0.8 part by mass to 2 parts by mass. By setting the content of the conductive particles within the above range, it is possible to suppress a decrease in the adhesive strength of the conductive adhesive layer and ensure the conductivity of the conductive adhesive layer by aggregates of the conductive particles. The content of the conductive particles in the conductive adhesive layer means the total amount of the content of the primary particles and aggregates in the conductive adhesive layer.

[0053] <Adhesive> As the adhesive contained in the conductive adhesive layer, an adhesive used for a normal adhesive sheet can be used. The above-mentioned adhesive contains a polymer (hereinafter sometimes referred to as "base polymer") which is the main component among the polymer components contained in adhesives such as acrylic polymers, rubber polymers (natural rubber, synthetic rubber, mixtures thereof, etc.), polyester polymers, urethane polymers, polyether polymers, silicone polymers, polyamide polymers, fluorine polymers, etc. Specifically, (meth)acrylic adhesives, urethane adhesives, rubber adhesives, polyester adhesives, silicone adhesives, etc. can be mentioned. Among them, (meth)acrylic adhesives are preferred from the viewpoints of adhesion performance and heat resistance.

[0054] Hereinafter, the (meth)acrylic adhesive will be mainly described. However, the conductive adhesive layer in the present disclosure is not limited to being composed of a (meth)acrylic adhesive, and may be composed of other adhesives described above.

[0055] (Meth)acrylic adhesives contain a (meth)acrylic copolymer ((meth)acrylic polymer) composed of (meth)acrylate alone or a copolymer of (meth)acrylate and other monomers as a base polymer. The above-mentioned (meth)acrylic adhesive contains at least a (meth)acrylic copolymer which is a base polymer, and may contain, if necessary, an adhesion-imparting resin, a crosslinking agent, other additives, etc. Note that "(meth)acrylic" comprehensively represents "acrylic or methacrylic", and "(meth)acrylate" comprehensively represents "acrylate or methacrylate".

[0056] As the above-mentioned (meth)acrylic copolymer, an acrylic copolymer having a (meth)acrylic acid ester monomer with an alkyl group having 1 to 18 carbon atoms as a main monomer component is preferable. The above-mentioned alkyl group may be linear or branched. Examples of the (meth)acrylic acid ester monomer having an alkyl group with 1 to 18 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-heptyl (meth)acrylate, n-octyl (meth)acrylate, isooctyl (meth)acrylate, n-nonyl (meth)acrylate, isononyl (meth)acrylate, cyclohexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, 1-methylheptyl (meth)acrylate, n-decyl (meth)acrylate, isodecyl (meth)acrylate, n-dodecyl (meth)acrylate, n-lauryl (meth)acrylate, myristyl (meth)acrylate, n-stearyl (meth)acrylate, and the like. These may be used alone or in combination of two or more. Among them, it is preferable to use a (meth)acrylate having an alkyl group with 4 to 12 carbon atoms, more preferably a (meth)acrylate having an alkyl group with 4 to 9 carbon atoms, and particularly preferably at least one of n-butyl acrylate and 2-ethylhexyl acrylate. By using a (meth)acrylate monomer having an alkyl group with the carbon number in the above range, the conductive adhesive layer can exhibit better adhesive force and cohesive force.

[0057] The content of the (meth)acrylic acid ester monomer in the above-mentioned (meth)acrylic copolymer is preferably in the range of 80% by mass to 99% by mass, more preferably in the range of 90% by mass to 98.5% by mass, in the monomer components constituting the above-mentioned (meth)acrylic copolymer. By setting the content of the (meth)acrylic acid ester monomer within the above range, the conductive adhesive layer can exhibit excellent adhesive force and cohesive force.

[0058] In addition to the above (meth)acrylic acid ester monomer, the monomer component constituting the above (meth)acrylic copolymer preferably contains a highly polar vinyl monomer. Examples of the highly polar vinyl monomer include a carboxyl group-containing vinyl monomer, a hydroxyl group-containing vinyl monomer, an amide group-containing vinyl monomer, and the like. One or more highly polar vinyl monomers can be used. Among them, the carboxyl group-containing vinyl monomer is preferable because it is easy to adjust the adhesiveness of the conductive adhesive layer to a suitable range.

[0059] Examples of the carboxyl group-containing vinyl monomer include acrylic acid, methacrylic acid, itaconic acid, maleic acid, (meth)acrylic acid dimer, crotonic acid, and ethylene oxide-modified succinic acid acrylate. Among them, it is preferable to use acrylic acid as a copolymerization component.

[0060] The content of the carboxyl group-containing vinyl monomer is preferably in the range of 0.2% by mass to 15% by mass, more preferably in the range of 0.4% by mass to 10% by mass, and still more preferably in the range of 0.5% by mass to 6% by mass in the monomer component constituting the above (meth)acrylic copolymer. By containing the carboxyl group-containing vinyl monomer in the above range in the monomer component constituting the above (meth)acrylic copolymer, it is easy to adjust the adhesiveness of the conductive adhesive layer to a suitable range.

[0061] Examples of the hydroxyl group-containing vinyl monomer include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, and the like.

[0062] Examples of the amide group-containing vinyl monomer include N-vinylpyrrolidone, N-vinylcaprolactam, acryloylmorpholine, acrylamide, N,N-dimethylacrylamide, and the like.

[0063] Examples of the highly polar vinyl monomer other than those described above include vinyl acetate, sulfonic acid group-containing monomers such as 2-acrylamido-2-methylpropanesulfonic acid, and terminal alkoxy-modified (meth)acrylates such as 2-methoxyethyl (meth)acrylate and 2-phenoxyethyl (meth)acrylate.

[0064] The total content of the highly polar vinyl monomer can be 20% by mass or less in the monomer components constituting the above (meth)acrylic copolymer. Among them, the range of 0.2% by mass to 15% by mass is preferable, the range of 0.4% by mass to 10% by mass is more preferable, and the range of 0.5% by mass to 6% by mass is still more preferable. By containing the highly polar vinyl monomer in the above range in the monomer components constituting the above (meth)acrylic copolymer, it is easy to adjust the adhesiveness of the conductive adhesive layer to a suitable range.

[0065] The weight average molecular weight of the above (meth)acrylic copolymer is not particularly limited, but from the viewpoint of adhesive performance, the range of 300,000 to 1,500,000 is preferable, and among them, the range of 500,000 to 1,200,000 is preferable.

[0066] The weight average molecular weight of the above (meth)acrylic copolymer represents a converted value measured using gel permeation chromatography (GPC) with polystyrene as a standard sample. The measurement of the weight average molecular weight by the GPC method is carried out under the following measurement conditions using a GPC apparatus (HLC-8329GPC) manufactured by Tosoh Corporation. [Measurement Conditions] · Sample concentration: 0.5% by mass (tetrahydrofuran solution) · Sample injection volume: 100 μL · Eluent: THF (tetrahydrofuran) · Flow rate: 1.0 mL / min · Measurement temperature: 40 °C · Main column: Two "TSKgel GMHHR-H(20)" manufactured by Tosoh Corporation · 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)

[0067] The above (meth)acrylic copolymer can be obtained by polymerizing the above-mentioned monomers by known methods such as solution polymerization method, bulk polymerization method, suspension polymerization method, emulsion polymerization method, etc. Among them, the solution polymerization method is preferable from the viewpoints of production cost and productivity.

[0068] The above conductive adhesive layer (conductive adhesive) may contain a tackifier resin as necessary. By including a tackifier resin in the above conductive adhesive layer, the adhesion of the conductive adhesive layer to the adherend and the surface adhesion strength can be improved. Examples of the tackifier resin 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, (meth)acrylate-based tackifier resins, etc. The tackifier resin may be used alone or in combination of two or more.

[0069] Among them, it is preferable that the above tackifier resin is one or more selected from the group consisting of disproportionated rosin ester-based tackifier resins, polymerizable rosin ester-based tackifier resins, rosin phenol-based tackifier resins, hydrogenated rosin ester-based tackifier resins, (meth)acrylate-based tackifier resins, and terpene phenol-based tackifier resins.

[0070] The softening point of the above tackifier resin is preferably 30°C or higher and 180°C or lower, more preferably 70°C or higher and 140°C or lower. By using the tackifier resin having the above softening point, the adhesion performance of the conductive adhesive layer can be further enhanced. When using a (meth)acrylate-based tackifier resin, it is preferable to use one having a glass transition temperature of 30°C or higher and 200°C or lower, more preferably 50°C or higher and 160°C or lower.

[0071] The compounding quantity of the above-mentioned adhesion-imparting resin is preferably 0 to 65 parts by mass, more preferably 5 to 55 parts by mass, based on 100 parts by mass of the base polymer contained in the adhesive, because the adhesion of the conductive adhesive layer to the adherend can be further improved.

[0072] <Crosslinking agent> The above-mentioned conductive adhesive layer (conductive adhesive) may contain a crosslinking agent as necessary. This is because it can react with the base polymer to form a three-dimensional crosslinked structure in the conductive adhesive layer, thereby improving the cohesive force of the conductive adhesive layer. As the above-mentioned crosslinking agent, an isocyanate-based crosslinking agent, an epoxy-based crosslinking agent, a metal chelate-based crosslinking agent, an aziridine-based crosslinking agent, etc. can be used, and they can be appropriately selected according to the base polymer contained in the adhesive.

[0073] When the above-mentioned base polymer is the above-mentioned (meth)acrylic copolymer, it is preferable to use an isocyanate-based crosslinking agent or an epoxy-based crosslinking agent that is highly reactive with the above-mentioned (meth)acrylic copolymer. Among them, the isocyanate-based crosslinking agent is more preferable due to its higher reactivity.

[0074] Examples of the above-mentioned isocyanate-based crosslinking agent include tolylene diisocyanate, naphthylene-1,5-diisocyanate, hexamethylene diisocyanate, diphenylmethane diisocyanate, xylylene diisocyanate, trimethylolpropane-modified tolylene diisocyanate, etc. Among these, trifunctional polyisocyanate-based compounds are preferable. Examples of the trifunctional isocyanate-based compound include tolylene diisocyanate or its trimethylolpropane adducts, triphenylmethane isocyanate, etc.

[0075] The content of the crosslinking agent may be an amount that enables the conductive adhesive layer to have a desired gel fraction, and can be appropriately set according to the gel fraction of the conductive adhesive layer. The gel fraction of the conductive 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, still 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. When the gel fraction of the conductive adhesive layer is within the above range, a three-dimensional crosslinked structure is formed in the conductive adhesive layer, which can further improve the cohesive force and the peel resistance.

[0076] The gel fraction of the conductive adhesive layer is the insoluble content when the above conductive adhesive layer is immersed in toluene for 24 hours, and is calculated by the following formula (3). Gel fraction (mass%) = {(mass of the conductive adhesive layer after immersion in toluene) / (mass of the conductive adhesive layer before immersion in toluene)} × 100 …(3) When the conductive adhesive tape (excluding the release liner) has a base material, the mass of the conductive adhesive layer is calculated by the following formula (4). Mass of the conductive adhesive layer = (mass of the conductive adhesive tape) - (mass of the base material) …(4)

[0077] The above conductive adhesive layer may contain additives as required. Examples of the above additives include common materials in the field of adhesives, such as leveling agents, crosslinking agents, crosslinking aids, plasticizers, softeners, fillers, colorants (pigments, dyes, etc.), antistatic agents, antioxidants, ultraviolet absorbers, antioxidants, light stabilizers, etc. The blending amount of the above additives is preferably 1 part by mass or less per 100 parts by mass of the base polymer.

[0078] 2. Base material The conductive adhesive tape of the present disclosure may have a base material. The above base material may be a single layer or a multilayer. Among them, from the viewpoint of enhancing heat resistance and rust prevention, the above base material is preferably a multilayer.

[0079] The above-mentioned substrate is preferably a conductive substrate (conductive base material). The conductive substrate is composed of a conductive material, and examples thereof include a metal substrate, a graphite substrate, a conductive resin substrate, a conductive non-woven fabric, and a conductive woven fabric. Among them, from the viewpoint of conductivity, a metal substrate and a conductive non-woven fabric are preferable.

[0080] The above-mentioned metal substrate only needs to be formed of a metal or an alloy, and examples thereof include a metal foil and a metal film. Among them, a metal foil is preferable from the viewpoints of conductivity, workability, and cost.

[0081] In addition, the material of the above-mentioned metal substrate is not particularly limited, and examples thereof include metals such as gold, silver, copper, aluminum, nickel, iron, and tin, and alloys thereof. Among them, aluminum or copper is preferable from the viewpoints of conductivity, workability, and cost, and copper is more preferable.

[0082] When the above-mentioned metal substrate is a copper foil, examples of the copper foil include an electrolytic copper foil and a rolled copper foil. As the above-mentioned electrolytic copper foil, for example, CF-T9FZ-HS-12 (thickness 12 μm), CF-T8G-DK-18 (thickness 18 μm), CF-T8G-DK-35 (thickness 35 μm), etc. manufactured by Fukuda Metal Foil & Powder Co., Ltd. can be used. In addition, as the above-mentioned rolled copper foil, for example, TCU-H-8-RT (thickness 8 μm) manufactured by Nippon Foil Mfg. Co., Ltd. or TPC (thickness 6 μm) manufactured by JX Nippon Mining & Metals Co., Ltd. can be used.

[0083] The above-mentioned metal substrate may have a plating layer on one side or both sides. By forming a plating layer on the surface of the metal substrate, it is possible to suppress a decrease in conductivity due to corrosion and appearance defects. Examples of the material of the above-mentioned plating layer include tin plating, silver plating, gold plating, and zinc plating.

[0084] In addition, the above-mentioned metal substrate may be subjected to a coupling treatment using a silane coupling agent or the like, a chromate treatment, or a rust prevention treatment using benzotriazoles or the like on one side or both sides.

[0085] The above conductive nonwoven fabric is not particularly limited and can be appropriately selected according to the purpose. For example, a metallized nonwoven fabric obtained by metallizing a nonwoven fabric can be mentioned.

[0086] The nonwoven fabric only needs to be formed of a material capable of being metallized, and general-purpose resin nonwoven fabrics, glass nonwoven fabrics, etc. can be used. Specifically, polyester nonwoven fabrics and the like can be mentioned.

[0087] In addition, the metallization applied to the nonwoven fabric may be electrolytic plating or electroless plating. Examples of the metal for forming the metallization include copper, nickel, silver, platinum, aluminum, etc. Among these, copper or nickel is preferable from the viewpoints of conductivity and cost.

[0088] The thickness of the above base material is not particularly limited as long as conductivity can be exhibited, and can be set according to the type of the base material. For example, it can be 1 μm or more and 40 μm or less. Among them, 3 μm or more and 35 μm or less is preferable, 5 μm or more and 30 μm or less is more preferable, and 5 μm or more and 25 μm or less is even more preferable. More specifically, when the above base material is a metal base material, the thickness of the above metal base material is not particularly limited and can be appropriately selected according to the purpose, but 1 μm or more and 40 μm or less is preferable, 3 μm or more and 35 μm or less is more preferable, and 5 μm or more and 25 μm or less is even more preferable. Further, when the above base material is a conductive nonwoven fabric, the thickness of the above conductive nonwoven fabric is not particularly limited and can be appropriately selected according to the purpose, 3 μm or more and 50 μm or less is preferable, 5 μm or more and 30 μm or less is more preferable, and 8 μm or more and 25 μm or less is even more preferable. By setting the thickness of the base material within the above range, a conductive adhesive tape having a thin thickness and excellent conductivity and adhesiveness can be obtained.

[0089] The thickness of the base material refers to the average value of the thicknesses at five locations measured at intervals of 100 mm in the length direction using TH-102 (thickness gauge, manufactured by Tester Sangyo Co., Ltd.).

[0090] From the perspective of further enhancing electrical properties, the thermal conductivity of the above-mentioned substrate is preferably 90 W / m·K or more, more preferably 100 W / m·K or more.

[0091] 3. Release Liner The conductive adhesive tape of the present disclosure may have a release liner on the adhesive surface. The release liner is not particularly limited. For example, resin films or papers with a release treatment on the surface, polyethylene, polypropylene (OPP, CPP), polyethylene terephthalate, low-adhesion resin films such as fluororesins (polytetrafluoroethylene, etc.), laminated papers in which papers and resin films are laminated, resin films or papers whose surfaces are sealed with clay, polyvinyl alcohol, etc., resin films or papers whose one or both sides with the above-mentioned sealing treatment are subjected to a release treatment, etc. can be mentioned. Examples of the release treatment agent used for the release treatment include silicone-based release treatment agents, long-chain alkyl-based release treatment agents, fluorine-based release treatment agents, molybdenum sulfide, etc.

[0092] When the conductive adhesive tape of the present disclosure is a tape without a substrate described later, the release liner may be provided on one side of the conductive adhesive layer or on both sides. When the conductive adhesive tape of the present disclosure is a tape with a substrate described later, the release liner may be provided on the surface of the conductive adhesive layer on one side of the substrate, or may be provided on the surfaces of the conductive adhesive layers on both sides of the substrate, respectively.

[0093] 4. Conductive Adhesive Tape The conductive adhesive tape of the present disclosure may be a single-sided adhesive specification having an adhesive surface on one side, or a double-sided adhesive specification having an adhesive surface on both sides. Further, the conductive adhesive tape of the present disclosure may be a tape without a substrate composed of the conductive adhesive layer in the present disclosure, or a tape with a substrate having the conductive adhesive layer in the present disclosure on at least one surface of the substrate.

[0094] When the conductive adhesive tape of the present disclosure is a substrate-free tape, the two opposing surfaces of the conductive adhesive layer constituting the tape can each be a double-sided adhesive specification, which is the adhesive surface of the conductive adhesive tape.

[0095] Further, when the conductive adhesive tape of the present disclosure is a tape with the above-mentioned substrate, the conductive adhesive tape may be a single-sided tape having a conductive adhesive layer in the present disclosure on one side of the substrate. When the tape with the substrate is a single-sided tape, the surface of the conductive adhesive layer can be the adhesive surface of the conductive adhesive tape.

[0096] Further, when the conductive adhesive tape of the present disclosure is a tape with the above-mentioned substrate, the conductive adhesive tape may be a double-sided tape having adhesive layers on both sides of the substrate. At this time, it is sufficient that at least one of the adhesive layers on the substrate is the conductive adhesive layer in the present disclosure, and the adhesive layers on both sides of the substrate may each be the conductive adhesive layer in the present disclosure. When the conductive adhesive tape of the present disclosure is a double-sided adhesive specification tape with a substrate, the surfaces of the adhesive layers respectively provided on both sides of the substrate can be the adhesive surfaces of the conductive adhesive tape.

[0097] The conductive adhesive tape of the present disclosure preferably has a resistance value Rz in the initial thickness direction (Z direction) of 1 Ω or less, more preferably 0.5 Ω or less, and even more preferably 0.2 Ω or less. Further, the conductive adhesive tape of the present disclosure preferably has a resistance value change rate (%) in the thickness direction before and after the thermal cycle test of 200% or less. Among them, the resistance value change rate (%) is preferably 180% or less, more preferably 150% or less, and even more preferably 140% or less. When the resistance value change rate in the thickness direction of the tape of the present disclosure before and after the thermal cycle test is within the above range, even in an environment that undergoes repeated temperature changes, the tape of the present disclosure suppresses the increase in resistivity and has good electrical conductivity over time. In other words, this suggests that the floating and peeling of the conductive adhesive tape from the adherend due to thermal cycling are suppressed.

[0098] The rate of change in the resistance value in the thickness direction of the conductive adhesive tape before and after the thermal cycle test can be calculated by the following formula (5). Rate of change in the resistance value in the thickness direction of the conductive adhesive tape before and after the thermal cycle test (%) = (Resistance value R’z (Ω) in the thickness direction of the conductive adhesive tape after the thermal cycle test / Initial resistance value Rz (Ω) in the thickness direction of the conductive adhesive tape) × 100 …(5)

[0099] The conductive adhesive tape of the present disclosure preferably has an initial resistance value Rxy in the horizontal direction (XY direction) of 2 Ω or less, more preferably 1.5 Ω or less, and even more preferably 0.8 Ω or less. Also, the conductive adhesive tape of the present disclosure preferably has a rate of change in the resistance value in the horizontal direction (%) before and after the thermal cycle test of 300% or less, more preferably 200% or less, and even more preferably 100% or less. By having the rate of change in the resistance value in the horizontal direction of the tape of the present disclosure before and after the thermal cycle test within the above range, the tape of the present disclosure can suppress an increase in the resistivity not only in the thickness direction but also in the horizontal direction in an environment that undergoes repeated temperature changes, and can exhibit good electrical conductivity over time in both the thickness direction and the horizontal direction.

[0100] The rate of change in the resistance value in the horizontal direction of the conductive adhesive tape before and after the thermal cycle test can be calculated by the following formula (6). Rate of change in the resistance value in the horizontal direction of the conductive adhesive tape before and after the thermal cycle test (%) = (Resistance value R’xy (Ω) in the horizontal direction of the conductive adhesive tape after the thermal cycle test / Initial resistance value Rxy (Ω) in the horizontal direction of the conductive adhesive tape) × 100 …(6)

[0101] The initial resistance values in the thickness direction and the horizontal direction of the conductive adhesive tape, and the resistance values in the thickness direction and the horizontal direction after the thermal cycle test are measured by the method described in the examples below.

[0102] 5. Method for preparing a conductive adhesive The method for preparing the conductive adhesive of the present disclosure is a method of dispersing conductive particles in an adhesive to prepare a mixture and subjecting the mixture to a filtration treatment to obtain a conductive adhesive. According to the above method, by filtering after dispersing conductive particles in the adhesive, the sizes of the conductive particles in the conductive adhesive are made uniform, so that the size of the aggregates of the conductive particles can be controlled when forming the conductive adhesive layer.

[0103] As the method of dispersing conductive particles in the above adhesive, known methods can be used. For example, there is a method of dispersing the adhesive, conductive particles, solvent, etc. with a dispersion stirrer. Examples of commercially available dispersion stirrers include a dissolver, a butterfly mixer, a BDM two-shaft mixer, and a planetary mixer. Among them, a dissolver or a butterfly mixer that can apply a medium shear with less thickening of the adhesive during stirring is preferred.

[0104] As the dispersion conditions for dispersing conductive particles in the above adhesive, it is preferable that the primary particles of the conductive particles are sufficiently dispersed in the mixture before the filtration treatment, and the size of the aggregates formed by the primary particles is within a desired range (for example, the maximum length is 10 μm or more and less than 60 μm), and the desired distribution is obtained. For example, the stirring speed is preferably in the range of 500 r / min to 3000 r / min, more preferably in the range of 700 r / min to 2500 r / min, and even more preferably in the range of 800 r / min to 2000 r / min. Also, the stirring time is not particularly limited and can be set as appropriate. For example, it can be in the range of 5 minutes to 120 minutes, and more preferably in the range of 30 minutes to 60 minutes. By setting the stirring speed and the stirring time to the above conditions, the conductive particles can be stirred at a high speed in the above adhesive, and the primary particles of the conductive particles can be sufficiently dispersed in the mixture before the filtration treatment. Thereby, the size of the aggregates formed from the primary particles can be within a predetermined range (for example, the maximum length is 10 μm or more and less than 60 μm) and the desired distribution can be obtained.

[0105] As a method for filtering a mixture in which conductive particles are dispersed in an adhesive, for example, gravity filtration through a mesh, pressure filtration through a filter while applying pressure, sedimentation by centrifugation, cooling precipitation, etc. can be mentioned, and these may be used in combination. Among these, the method of filtering with a mesh and / or a filter is preferable because it is simple. Also, the filtration may be performed once or repeated two or more times.

[0106] The materials of the mesh and the filter are not particularly limited, and general-purpose materials used for filtration can be appropriately selected, for example, metals (wire mesh), glass, resins, etc.

[0107] The mesh count depends on the mesh opening size, but is preferably 100 mesh or more, more preferably 150 mesh or more, and even more preferably 200 mesh or more. Also, the mesh count of the above mesh is preferably 400 mesh or less, more preferably 300 mesh or less, and even more preferably 250 mesh or less. In particular, since a desired conductive adhesive layer can be formed and the productivity in the filtration process is increased, the mesh count of the above mesh is preferably 100 mesh or more and less than 300 mesh, and more preferably 150 mesh or more and 250 mesh or less. Also, the mesh opening only needs to be larger than the average particle size d50 of the primary particles of the conductive particles, and can be appropriately selected according to the average particle size of the primary particles of the conductive particles, but is preferably 30 μm or more, 45 μm or more, 60 μm or more, and the mesh opening of the above mesh is preferably 150 μm or less, 110 μm or less, 80 μm or less.

[0108] The pore size of the filter can be appropriately selected according to the particle size of the primary particles of the conductive particles. For example, the range of 90 μm to 200 μm is preferable, the range of 100 μm to 150 μm is more preferable, and the range of 100 μm to 120 μm is even more preferable.

[0109] In the present disclosure, it is preferable to filter a mixture in which conductive particles having an average particle diameter d50 of the primary particles in the range of 5 μm to 30 μm are dispersed in an adhesive with a mesh having the above-described mesh count and mesh opening and / or a filter having the above-described pore diameter. Among them, it is preferable to filter a mixture in which conductive particles having an average particle diameter d50 of the primary particles in the range of 5 μm to 30 μm are dispersed in an adhesive with a mesh having less than 300 mesh count. When the mesh count of the mesh is 200 mesh or less, it is more preferable to further perform filtration with a filter having a pore diameter in the range of 90 μm to 200 μm after filtration with the mesh.

[0110] 6. Method for manufacturing conductive adhesive tape The conductive adhesive tape of the present disclosure can be manufactured using a known method. For example, a method of manufacturing the conductive adhesive tape can be used in which the conductive adhesive prepared by the method described in the above "5. Method for preparing conductive adhesive" is applied onto a release liner and the coating film is dried to form a conductive adhesive layer. As a method for manufacturing the conductive adhesive tape of the present disclosure when it has a base material, for example, a method of bonding the above-described conductive adhesive layer formed on a release liner to one side or both sides of the base material, a method of applying the above-described conductive adhesive to one side or both sides of the base material and drying the coating film to form a conductive adhesive layer, etc. can be mentioned.

[0111] As the method for applying the above-described conductive adhesive, a known coating method can be used. Examples of the coating method include coaters such as a gravure roll coater, a reverse roll coater, a kiss roll coater, a lip coater, a dip roll coater, a bar coater, a knife coater, a spray coater, a comma coater, a direct coater, and a slot die coater.

[0112] The above-described conductive adhesive layer may be cured to promote the crosslinking reaction. The curing conditions are not particularly limited, and for example, it can be 48 hours or more within the range of 20°C to 50°C.

[0113] When bonding the conductive adhesive layer formed on the release liner to the substrate, heat lamination may be performed to enhance the interlayer adhesion. The temperature of the heat lamination is not particularly limited, but for example, a range of 60°C to 150°C is preferred.

[0114] 7. Applications The conductive adhesive tape of the present disclosure is useful, for example, for shielding electromagnetic waves used in electric or electronic devices, for shielding harmful spatial electromagnetic waves generated from other electric and electronic devices, and for grounding for preventing electrostatic charging. Among them, it can be suitably applied to portable electronic device applications where thinning is progressing and volume limitation inside the housing is severe, and in particular, it is suitable for attaching to built-in components of small electronic terminals for use.

[0115] In addition, in this specification, the expression "primary particles and aggregates of the conductive particles present in the region A of the conductive adhesive layer (excluding the primary particles and aggregates having a maximum length of 10 μm or less)" (and similar expressions) means that the primary particles and aggregates of the conductive particles present in the region A of the conductive adhesive layer may contain those having a maximum length of 10 μm or less, but when calculating the respective number ratios of the primary particles and aggregates of each size, the number of the primary particles and aggregates having a maximum length of 10 μm or less is not added as the total number of the primary particles and aggregates of the conductive particles, that is, it means that they are excluded. Further, the present disclosure is not limited to the above embodiments. The above embodiments are examples, and any configuration having substantially the same configuration as the technical idea described in the claims of the present disclosure and exhibiting the same operational effects is included in the technical scope of the present disclosure.

Examples

[0116] Hereinafter, examples and comparative examples will be shown to further explain the present disclosure.

[0117] [Adjustment Example] (Synthesis Example 1 of Acrylic Copolymer) In a reaction vessel equipped with a stirrer, a cooler, a thermometer, and a dropping funnel, the following materials were each dissolved in 100 parts by mass of ethyl acetate in the following formulation, and after nitrogen substitution, polymerization was carried out at 80 °C for 12 hours to obtain an ethyl acetate solution of an acrylic copolymer (1) having a weight average molecular weight of 600,000. · n-Butyl acrylate: 75.0 parts by mass · 2-Ethylhexyl acrylate: 19.0 parts by mass · Vinyl acetate: 3.9 parts by mass · Acrylic acid: 2.0 parts by mass · 2-Hydroxyethyl acrylate: 0.1 part by mass · 2,2’-Azobisisobutyronitrile (polymerization initiator): 0.1 part by mass

[0118] The weight average molecular weight of the acrylic copolymer is a polystyrene equivalent value measured by the GPC method, and is a value measured under the following measurement conditions using a GPC apparatus (HLC-8329GPC) manufactured by Tosoh Corporation. [Measurement conditions] · Sample concentration: 0.5% by mass (tetrahydrofuran solution) · Sample injection volume: 100 μL · Eluent: THF (tetrahydrofuran) · Flow rate: 1.0 mL / min · Measurement temperature: 40 °C · This column: 2 pieces of TSKgel GMHHR-H(20) · Guard column: TSKgel HXL-H · Detector: Differential refractometer · Standard polystyrene molecular weight: 10,000 to 20,000,000 (manufactured by Tosoh Corporation)

[0119] (Preparation example of a mixture of an adhesive and conductive particles) 100 parts by mass (solid content) of the above acrylic copolymer (1), 10 parts by mass of a polymerized rosin pentaerythritol ester (Pencil D-135, manufactured by Arakawa Chemical Industries, Ltd., softening point 135 °C), and 10 parts by mass of a disproportionated rosin glycerol ester (Super Ester A-100, manufactured by Arakawa Chemical Industries, Ltd.) were mixed and stirred, and then ethyl acetate was added to obtain an acrylic adhesive having a solid content of 40% by mass of the acrylic polymer.

[0120] Next, 100 parts by mass (solid content) of the above acrylic adhesive, 1 part by mass of nickel powder (manufactured by Jinchuan Group Co., LTD, product name: N06, bead-shaped, d50: 19.0 μm, d90: 43.0 μm) as conductive particles, 2 parts by mass of Barnock NC-40 (manufactured by DIC Corporation, solid content 40% by mass) as a crosslinking agent, and 70 parts by mass of ethyl acetate were mixed with a dispersion stirrer for 10 minutes to obtain a mixture.

[0121] (Preparation Example of Conductive Adhesive A) The above mixture was stirred at a high speed using a disper mixer at a speed of 1200 r / min for 60 minutes, and then filtered by gravity through a 250-mesh wire mesh to obtain conductive adhesive A.

[0122] (Preparation Example of Conductive Adhesive B) The above mixture was stirred at a high speed using a disper mixer at a speed of 1200 r / min for 60 minutes, and then filtered by gravity through a 300-mesh wire mesh to obtain conductive adhesive B.

[0123] (Preparation Example of Conductive Adhesive C) The above mixture was stirred at a high speed using a disper mixer at a speed of 1200 r / min for 60 minutes, and then filtered by gravity through a 200-mesh wire mesh, and then further filtered under pressure through a metal filter with an opening of 100 μm to obtain conductive adhesive C.

[0124] (Preparation Example of Conductive Adhesive D) The above mixture was rapidly stirred at a speed of 1200 r / min for 60 minutes using a disperser, then filtered by gravity through a 200-mesh wire netting, and further pressure-filtered through a metal filter with an aperture of 125 μm to obtain the conductive adhesive D.

[0125] (Preparation Example of Conductive Adhesive E) The above mixture was rapidly stirred at a speed of 1200 r / min for 60 minutes using a disperser, and then the conductive adhesive E was obtained without performing a filtration treatment.

[0126] (Preparation Example of Conductive Adhesive F) The above mixture was slowly stirred at a speed of 400 r / min for 60 minutes using a propeller stirrer, and then the conductive adhesive F was obtained without performing a filtration treatment.

[0127] (Preparation Example of Conductive Adhesive G) The above mixture was stirred at a speed of 1200 r / min for 60 minutes using a disperser, and then filtered by gravity through a 200-mesh wire netting to obtain the conductive adhesive G.

[0128] The conductive adhesives A to G are shown in the following table.

[0129]

Table 1

[0130] (Example 1) The above conductive adhesive A was coated on the release film A (PET 38×1, A3, manufactured by Nipper Co., Ltd.) with a comma coater so that the average thickness after drying was 5 μm, and dried in a dryer at 80°C for 2 minutes to form a conductive adhesive layer. Next, the formed conductive adhesive layer was bonded to one surface of a copper foil A (average thickness 12 μm, surface resistance value 0.003 Ω / square) having a chromium plating layer on both surfaces, and then pressed at 40°C with a linear pressure of 100 N / cm using a laminator, and cured at 40°C for 48 hours to produce a conductive adhesive tape A.

[0131] (Example 2) A conductive adhesive tape B was produced in the same procedure as in Example 1, except that a conductive adhesive layer was formed using a conductive adhesive B instead of the above conductive adhesive A.

[0132] (Example 3) A conductive adhesive tape C was produced in the same procedure as in Example 1, except that a conductive adhesive layer was formed using a conductive adhesive C instead of the above conductive adhesive A.

[0133] (Example 4) A conductive adhesive tape D was produced in the same procedure as in Example 1, except that a conductive adhesive layer was formed using a conductive adhesive D instead of the above conductive adhesive A.

[0134] (Comparative Example 1) A conductive adhesive tape E was produced in the same procedure as in Example 1, except that a conductive adhesive layer was formed using a conductive adhesive E instead of the above conductive adhesive A.

[0135] (Comparative Example 2) A conductive adhesive tape F was produced in the same procedure as in Example 1, except that a conductive adhesive layer was formed using a conductive adhesive F instead of the above conductive adhesive A.

[0136] (Comparative Example 3) A conductive adhesive tape G was produced in the same procedure as in Example 1, except that a conductive adhesive layer was formed using a conductive adhesive G instead of the above conductive adhesive A.

[0137] [Evaluation] The following evaluations were performed on the conductive adhesive tapes obtained in the examples and comparative examples.

[0138] <The maximum length P1, number, and number ratio of primary particles and aggregates of conductive particles> The maximum length P1 of the primary particles and aggregates of the conductive particles and the number and percentage of the primary particles and aggregates with the maximum length P1 present in the region A of the conductive adhesive layer in the plan view of the conductive adhesive layer of the obtained conductive adhesive tape are within a predetermined range, and are measured by the method described in the item "(1) Conductive particles" in the item "1. Conductive adhesive layer" in the item "I. Conductive adhesive tape". Note that primary particles and aggregates with a maximum length P1 of 10 μm or less in the plan view are not included in the number.

[0139] <Initial resistance value> <<Resistance value in the thickness direction (conductivity in the thickness direction)>> A copper foil (5 mm width × 5 mm width) was attached to the conductive adhesive layer of the conductive adhesive tape cut to a size of 100 mm width × 50 mm width. In an environment of 23°C and 50% RH, with a load of 1 N of surface pressure applied from the position where the copper foil is attached to the conductive adhesive tape, the copper foil and the conductive adhesive tape were connected, and a current of 100 μA was passed using a milliohm meter (manufactured by NF Circuit Design Block Co., Ltd.) to measure the resistance value Rz (Ω) in the thickness direction (attachment method).

[0140] <<Resistance value in the horizontal direction (conductivity in the surface direction)>> In the longitudinal direction of the conductive adhesive tape cut to a size of 100 mm width (long side) × 50 mm width (short side), one end of each of the two copper foils (long strip with a width of 5 mm) was placed at a position 40 mm in the longitudinal direction from the short side of the conductive adhesive layer on the surface of the conductive adhesive layer so that the bonding area between the copper foil end and the conductive adhesive layer was 5 mm width × 5 mm width, and the other ends of the two copper foils (the ends on the side not bonded to the conductive adhesive layer) were connected to the positive and negative electrodes of a milliohm meter (manufactured by NF Circuit Design Block Co., Ltd.), respectively. In an environment of 23°C and 50% RH, with no surface pressure applied from the attachment position of the copper foil to the conductive adhesive tape, the copper foil and the conductive adhesive tape were connected, and a current of 100 μA was passed using a milliohm meter to measure the resistance value Rxy (Ω) in the horizontal direction.

[0141] <Resistance value after the thermal cycle test> The conductive adhesive tape was cut into a size of 100 mm in width × 50 mm in width, and a copper foil (5 mm in width × 5 mm in width) was attached to the conductive adhesive layer of the above conductive adhesive tape to obtain a test piece. The above test piece was placed in a thermal cycle tester (trade name: "SH-242", manufactured by Espec Corporation), and a thermal cycle test was conducted under the following test conditions. · Relative humidity inside the tester: Without control · Thermal cycle test conditions: With a heating rate of 2°C / min and a cooling rate of 2°C / min, the cycle of -35°C (held for 30 minutes) → 85°C (held for 30 minutes) → -35°C was carried out 100 times as one cycle. Using the conductive adhesive tape after the thermal cycle test, the resistance value Rz (Ω) in the thickness direction and the resistance value R'xy (Ω) in the horizontal direction were measured respectively by the same method as the measurement method of the initial resistivity. Also, from the resistance values after the thermal cycle test and the initial resistance values, the change rates of the respective resistance values in the thickness direction and the horizontal direction were calculated by the following formulas (7) and (8). Change rate of resistance value in the thickness direction of the conductive adhesive tape before and after the thermal cycle test (%) = (Resistance value R'z (Ω) in the thickness direction of the conductive adhesive tape after the thermal cycle test / Initial resistance value Rz (Ω) in the thickness direction of the conductive adhesive tape) × 100 …(7) Change rate of resistance value in the horizontal direction of the conductive adhesive tape before and after the thermal cycle test (%) = (Resistance value R'xy (Ω) in the horizontal direction of the conductive adhesive tape after the thermal cycle test / Initial resistance value Rxy (Ω) in the horizontal direction of the conductive adhesive tape) × 100 …(8)

[0142] <Adhesive force> The conductive adhesive tape was cut into a size of 25 mm in width, and under the conditions of an environmental temperature of 23°C and a humidity of 50% RH, the surface on the side of the conductive adhesive layer of the conductive adhesive tape was attached to a stainless steel plate (SUS plate, a stainless steel plate subjected to hairline polishing treatment using No. 360 waterproof abrasive paper), and the upper surface was reciprocated once with a 2-kg roller to crimp the conductive adhesive tape and the stainless steel plate. Then, the one left standing at room temperature for 1 hour was used as a test piece. The 180-degree peel adhesion was measured by peeling the above test piece at a speed of 300 mm / min under the same temperature and humidity conditions as above using a tensilon universal tensile testing machine (manufactured by A&D Company, Limited, Tensilon RTA-100).

[0143] <Retention force> The conductive adhesive tape was cut into 25-mm width and attached to the surface of a clean and smooth stainless steel plate so as to have an attachment area of 25 mm × 25 mm. The one pressurized by reciprocating once with a 2-kg roller on its upper surface was left standing for 1 hour under the conditions of 23°C and 50% RH according to JIS Z-0237, and then a load of 500 g was applied in the shear direction in an atmosphere of 70°C, and the displacement distance of the tape after 24 hours was measured.

[0144] <Appearance> A copper foil was attached onto the conductive adhesive layer of the conductive adhesive tape to obtain a test piece. The degree of air bubble entrapment in the test piece was visually confirmed and judged according to the following criteria. (Criteria) 〇: No air bubble entrapment can be visually confirmed 〇△: Slight air bubble entrapment can be visually confirmed (the contour of the air bubbles is unclear) △: The contour of the air bubbles can be clearly visually confirmed ×: The contour of the air bubbles is clear, and air bubble entrapment can be visually confirmed over the entire area

[0145] The evaluation results are shown in a table.

[0146]

Table 2

[0147]

Table 3

[0148]

Table 4

[0149]

Table 5

[0150] Compared with the conductive adhesive tape of the comparative example, the conductive adhesive tape of the example has a small change rate of resistance value [%] before and after the thermal cycle test, can suppress the increase in the resistance value in the thickness direction due to repeated temperature changes, and is suggested to have excellent conductivity.

Industrial Applicability

[0151] The conductive adhesive tape of the present disclosure can be suitably used for a bonding site where conductivity is required. For example, it is useful for shielding electromagnetic waves used in electric or electronic devices, etc., shielding harmful spatial electromagnetic waves generated from other electric and electronic devices, and grounding for preventing electrostatic charging. Among them, it can be suitably applied to portable electronic device applications where thinning is progressing and volume limitation inside the housing is severe, and in particular, it is suitable for being attached to built-in components of small electronic terminals for use.

Claims

1. A conductive adhesive tape having at least a conductive adhesive layer, The conductive pressure-sensitive adhesive layer contains a pressure-sensitive adhesive and conductive particles, 2.5 mm in plan view of the conductive adhesive layer ２ Among the primary particles and agglomerates of the conductive particles present in the region A, the primary particles and agglomerates having a maximum length of 10 μm or less are removed, The number ratio of the primary particles and aggregates having a maximum length of 60 μm or more is 5% or less, A conductive pressure-sensitive adhesive tape, wherein the proportion of the primary particles and aggregates having a maximum length of less than 50 μm is 85% or more.

2. The conductive adhesive tape according to claim 1 , wherein the conductive adhesive layer has a thickness of 10 μm or less.

3. 3. The conductive adhesive tape according to claim 1, wherein the total amount of the conductive particles is within a range of 0.1 parts by mass to 10 parts by mass per 100 parts by mass of the adhesive.

4. 3. The conductive adhesive tape according to claim 1, wherein a total number of primary particles and agglomerates of the conductive particles present in the region A in a planar view of the conductive adhesive layer is within a range of 20 to 150 after excluding the primary particles and agglomerates having a maximum length of 10 μm or less.

5. The conductive adhesive tape according to claim 1 or 2, wherein the average particle diameter (d50) of the primary particles is within a range of 5 μm to 30 μm.

6. The conductive adhesive tape according to claim 1 or 2, wherein the agglomerates are formed by agglomerating the primary particles having an average particle diameter (d50) in the range of 5 μm to 30 μm.

7. The conductive adhesive tape according to claim 1 , wherein the conductive particles are metal particles.

8. The conductive adhesive tape according to claim 1 , wherein the conductive particles are nickel powder.

9. The conductive adhesive tape according to claim 1 or 2, comprising the conductive adhesive layer on one or both sides of a substrate.

10. The conductive adhesive tape according to claim 9 , wherein the substrate is a metal foil.

11. The conductive adhesive tape according to claim 9 , wherein the substrate is a copper foil having a chrome-plated layer on one or both sides.

12. 3. The conductive pressure-sensitive adhesive tape according to claim 1, wherein a rate of change in resistance in the thickness direction before and after a thermal cycle test is 200% or less.

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