Conductive adhesive tape

Abstract

The present invention provides a conductive adhesive tape which is capable of suppressing an increase in the resistance value in the thickness direction even when subjected to repeated temperature changes, and which has excellent conductivity. The present invention provides a conductive adhesive tape having at least a conductive adhesive layer, the conductive adhesive layer containing an adhesive and conductive particles; among primary particles and agglomerates of the conductive particles present in a 2.5 mm2 region (A) in a plan view of the conductive adhesive layer (excluding the primary particles and agglomerates having a maximum length of 10 [mu] m or less), the number ratio of the primary particles and agglomerates having a maximum length of 60 [mu] m or more is 5% or less. The proportion of the number of the primary particles having a maximum length of less than 50 [mu] m and the aggregate is 85% or more.

Description

Technical Field

[0001] The present invention relates to a conductive adhesive tape (“adhesion” corresponds to “sticking” in Japanese). Background Art

[0002] Conductive adhesive tapes are used in electronic devices and communication devices for the purpose of shielding electromagnetic waves and grounding to prevent static electricity.

[0003] For example, Patent Document 1 discloses a conductive pressure-sensitive adhesive tape having a total thickness of 30 μm or less. The conductive pressure-sensitive adhesive tape includes a conductive substrate and a conductive pressure-sensitive adhesive layer containing conductive particles. Prior art literature Patent Literature

[0004] Patent Document 1: International Publication No. 2015 / 076174 Summary of the invention Technical problem to be solved by the invention

[0005] A conductive adhesive layer containing conductive particles has a problem that, when subjected to repeated temperature changes, the resistance value in the thickness direction increases significantly, thereby reducing the conductivity.

[0006] The present invention has been made in view of the above-mentioned actual situation, and provides a conductive adhesive tape which can suppress an increase in resistance value in the thickness direction even when subjected to repeated temperature changes and has excellent conductivity. Technical solutions for solving technical problems

[0007] The present inventors have found that the conductive particles exist in the conductive adhesive layer as primary particles and / or aggregates, and that the unevenness in the sizes of the primary particles and aggregates affects the conductivity in the thickness direction caused by repeated temperature changes.

[0008] That is, the present invention has the following embodiments. [1] A conductive adhesive tape comprising at least a conductive adhesive layer, wherein the conductive adhesive layer contains an adhesive and conductive particles; and a conductive adhesive layer having a thickness of 2.5 mm2 in a plan view of the conductive adhesive layer. 2 Among the primary particles and agglomerates of the above-mentioned conductive particles in region A (excluding the above-mentioned primary particles and the above-mentioned agglomerates whose maximum length is less than 10 μm), the number ratio of the above-mentioned primary particles and agglomerates whose maximum length is more than 60 μm is less than 5%, and the number ratio of the above-mentioned primary particles and agglomerates whose maximum length is less than 50 μm is more than 85%. [2] The conductive pressure-sensitive adhesive tape according to [1] above, wherein the conductive pressure-sensitive adhesive layer has a thickness of 10 μm or less. [3] The conductive pressure-sensitive adhesive tape according to [1] or [2], wherein the total amount of the conductive particles is in the range of 0.1 to 10 parts by mass based on 100 parts by mass of the pressure-sensitive adhesive. [4] A conductive adhesive tape according to any one of [1] to [3] above, wherein the total number of primary particles and agglomerates of the conductive particles present in the area A in a top view of the conductive adhesive layer (excluding the primary particles and agglomerates having a maximum length of less than 10 μm) is in the range of 20 to 150. [5] The conductive pressure-sensitive adhesive tape according to any one of [1] to [4] above, wherein the average particle size (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 agglomerates are agglomerated primary particles having an average particle size (d50) in the range of 5 μm to 30 μm. [7] The conductive pressure-sensitive adhesive tape according to any one of [1] to [6] above, wherein the conductive particles are metal particles. [8] The conductive pressure-sensitive adhesive tape according to any one of [1] to [7] above, wherein the conductive particles are nickel powder. [9] The conductive pressure-sensitive adhesive tape according to any one of [1] to [8], wherein the conductive pressure-sensitive adhesive layer is provided on one or both surfaces of a substrate.

[10] The conductive pressure-sensitive adhesive tape according to [9] above, wherein the substrate is a metal foil.

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

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

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

[0009] According to the present invention, it is possible to provide a conductive pressure-sensitive adhesive tape which can suppress an increase in resistance in the thickness direction due to repeated temperature changes and has excellent conductivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 These are images showing the appearance state for each criterion of appearance evaluation in Examples and Comparative Examples. DETAILED DESCRIPTION

[0011] I. Conductive adhesive tape The conductive adhesive tape of the present invention (hereinafter sometimes referred to as tape) comprises at least a conductive adhesive layer, wherein the conductive adhesive layer contains an adhesive and conductive particles. The conductive adhesive tape of the present invention has a conductive adhesive layer at 2.5 mm in a top view. 2 Among the primary particles and agglomerates of the above-mentioned conductive particles in region A (excluding the above-mentioned primary particles and the above-mentioned agglomerates whose maximum length is less than 10 μm), the number ratio of the above-mentioned primary particles and the above-mentioned agglomerates whose maximum length is more than 60 μm is less than 5%, and the number ratio of the above-mentioned primary particles and the above-mentioned agglomerates whose maximum length is less than 50 μm is more than 85%.

[0012] In a conductive adhesive tape having an adhesive layer (conductive adhesive layer) containing conductive particles, the conductive particles in the conductive adhesive layer are dispersed in the adhesive. However, the conductive particles are easily condensed, so they are easily present in the conductive adhesive layer in the form of agglomerates. In addition, in the preparation stage of the conductive adhesive, even if the particle size of the primary particles of the conductive particles is adjusted to disperse them in the adhesive, the size of the agglomerates of the conductive particles in the conductive adhesive layer will become uneven. If the adherend to which the conductive adhesive tape containing such a conductive adhesive layer is attached is exposed to an environment with large temperature changes, it is easy for the tape to float and peel off from the adherend. At this time, the conductive contact point cannot be obtained at the part where the tape floats and peels off from the adherend, so the resistivity in the thickness direction rises over time. Here, it is inferred that the floating and peeling of the tape from the adherend is generated starting from the conductive particles present on the bonding surface of the adherend and the conductive adhesive layer. Among them, if there are a large number of large agglomerates and primary particles in the top view of the conductive adhesive tape, the size of the floating and peeling of each tape becomes larger, so the increase in resistivity caused by the reduction in conductive contact points between the adherend and the tape is more significant, making it difficult to maintain good conductivity in the thickness direction over time.

[0013] In contrast, the conductive adhesive tape of the present invention controls the size of the primary particles and aggregates of the conductive particles in the top view of the conductive adhesive layer, and the ratio of their number, so that the initial resistance value is low, and the size of the floating and peeling generated from the aggregates and primary particles can be reduced, so that the increase in the resistance value in the thickness direction caused by repeated temperature changes (hot and cold cycles) can be suppressed. Therefore, the conductive adhesive tape of the present invention has excellent temporal stability of the conductivity in the thickness direction.

[0014] The 2.5 mm thickness in the top view of the conductive adhesive layer is 2The region A refers to arbitrarily selecting 10 small regions a (area: 0.25 mm) having a rectangular shape of 0.5 mm×0.5 mm in the top view observed from the conductive adhesive layer side of the conductive adhesive tape (top view of the conductive adhesive layer) 2 ), set it as the total area composed of 10 small areas a (the set of 10 small areas a).

[0015] When counting the number of conductive particles contained in the small area a, for example, when a part of the conductive particles overflow from the small area a due to being located at the boundary of the small area a, particles in which 80% or more of the top view of the conductive particles are present in the small area a are counted as one object. The maximum length of the conductive particles, etc., is measured based on the portion present in the small area a.

[0016] 1. Conductive adhesive layer The conductive adhesive layer in the present invention contains a binder and conductive particles. Such a conductive adhesive layer is formed of a conductive adhesive containing a binder and conductive particles.

[0017] The thickness of the conductive adhesive layer is preferably 10 μm or less, preferably 1 μm or more and 9 μm or less, more preferably 2 μm or more and 8 μm or less, and further preferably 4 μm or more and 6 μm or less. By setting the thickness of the conductive adhesive layer to the above range, the conductive adhesive layer can exert good adhesive force, and by controlling the size of the primary particles and agglomerates of the conductive particles in the top view of the conductive adhesive layer, and the ratio of the number thereof, the temporal stability of the conductivity in the thickness direction can be exhibited.

[0018] The thickness of the conductive adhesive layer is measured at five locations at intervals of 100 mm in the longitudinal direction using a digital length meter (Nikon MS-11C), and is the average value of the five thicknesses.

[0019] (1) Conductive particles In the above-mentioned conductive adhesive layer, the conductive particles exist in the form of primary particles and / or agglomerates. The above-mentioned conductive adhesive layer may contain at least agglomerates of conductive particles, may contain at least primary particles of conductive particles that have not formed agglomerates, or may contain both agglomerates of conductive particles and primary particles of conductive particles that have not formed agglomerates. Preferably, it contains at least agglomerates of conductive particles. The number of primary particles of conductive particles refers to the number of primary particles that have not formed agglomerates present in the conductive adhesive layer. In the above-mentioned area A, the number of the above-mentioned agglomerates may be more or less than the number of the above-mentioned primary particles, and preferably the number of agglomerates is less than the number of primary particles.

[0020] The agglomerates of the conductive particles may be agglomerates of primary particles of one type of conductive particles, or may be agglomerates of primary particles of two or more types of conductive particles.

[0021] In the top view of the conductive adhesive layer, there is a 2 Among the primary particles and agglomerates of the conductive particles in region A (excluding the primary particles and agglomerates having a maximum length of 10 μm or less), the number ratio of the primary particles and agglomerates having a maximum length of 60 μm or more is 5% or less. Thus, the tape of the present invention can prevent the agglomerates and primary particles from floating or peeling off from the adherend even when subjected to repeated temperature changes, thereby suppressing the decrease in conductivity over time.

[0022] Among the primary particles and aggregates of the conductive particles, primary particles having a maximum length of 60 μm or more may be referred to as primary particles A, and aggregates having a maximum length of 60 μm or more may be referred to as aggregates A.

[0023] Among them, the number ratio of the primary particles and agglomerates with a maximum length of 60 μm or more in the above-mentioned area A of the above-mentioned conductive adhesive layer in the top view (the number ratio of primary particles A and agglomerates A) is preferably 4.5% or less, more preferably 3.5% or less, further preferably 2.5% or less, and particularly preferably 0%, that is, the area A does not contain primary particles and agglomerates with a maximum length of 60 μm or more. By making the number ratio of primary particles A and agglomerates A present in the above-mentioned area A within the above-mentioned range, when the belt of the present invention is subjected to repeated temperature changes (hot and cold cycles), it is possible to effectively suppress not only the increase in the resistance value in the thickness direction, but also the increase in the resistance value in the horizontal direction.

[0024] The number of the primary particles A and the aggregates A present in the region A of the conductive adhesive layer is not particularly limited, but is preferably 3 or less, more preferably 2 or less, further preferably 1 or less, and particularly preferably 0.

[0025] In the plan view of the conductive adhesive layer, the area of ​​the quadrilateral circumscribing the primary particles A and / or the aggregates A is not particularly limited, but is preferably 300 μm. 2 ~2700μm 2 The range is preferably 300 μm. 2 ~2400μm 2 The range is more preferably 300 μm. 2 ~2100μm 2 within the range.

[0026] In the plan view of the conductive adhesive layer, the area occupancy of the primary particles A and the aggregates A in the region A is preferably 10% or less, more preferably 5% or less, further preferably 1% or less, and particularly preferably 0%.

[0027] In the top view of the conductive adhesive layer, among the primary particles and agglomerates of the conductive particles present in the region A of the conductive adhesive layer (excluding the primary particles and agglomerates with a maximum length of less than 10 μm), the number ratio of the primary particles and agglomerates with a maximum length of less than 50 μm is 85% or more. As a result, the tape of the present invention has a low initial resistance value and can exhibit good conductivity. In addition, in the bonding surface between the conductive adhesive layer and the adherend, the size of the floating and peeling starting from the agglomerates and primary particles caused by the cold and hot cycles can be reduced, and the decrease in conductivity over time can be suppressed.

[0028] It should be noted that among the primary particles and aggregates of the conductive particles, primary particles having a maximum length of less than 50 μm may be referred to as primary particles B, and aggregates having a maximum length of less than 50 μm may be referred to as aggregates B. The primary particles B and aggregates B do not include primary particles and aggregates having a maximum length of less than 10 μm.

[0029] The ratio of the number of the primary particles and the aggregates whose maximum length is less than 50 μm in the region A of the conductive adhesive layer (the ratio of the number of the primary particles B and the aggregates B) is preferably in the range of 85% to 100%, more preferably in the range of 90% to 100%, and further preferably in the range of 95% to 100%. By setting the ratio of the number of the primary particles B and the aggregates B in the region A of the conductive adhesive layer to the above range, the belt of the present invention can achieve both high initial conductivity and time-dependent conductivity.

[0030] 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, and may be set to 150 or less, preferably 120 or less, and more preferably 100 or less. In addition, the number is preferably 17 or more, preferably 20 or more, and more preferably 40 or more. More specifically, the number is preferably 40 or more and 100 or less, preferably 47 or more and 95 or less, more preferably 50 or more and 90 or less, and more preferably 60 or more and 80 or less.

[0031] In addition, the area of ​​each of the primary particles B and the aggregates B in the top view of the conductive adhesive layer can be smaller than the area of ​​each of the primary particles A and the aggregates A. As long as the tape can be prevented from floating and peeling and good conductivity is exhibited, the size of the area is not particularly limited. In the top view of the conductive adhesive layer, the area of ​​the quadrilateral circumscribed with the primary particles B and / or the aggregates B is not particularly limited, and is preferably 1 μm. 2 ~250μm 2 , more preferably 5 μm 2 ~200μm 2 The range is more preferably 10 μm 2 ~150μm 2 The method for calculating the area of ​​the quadrilateral circumscribing the primary particle B and / or the aggregate B is the same as the method for calculating the area of ​​the quadrilateral circumscribing the primary particle A and / or the aggregate A described above.

[0032] In the top view of the conductive adhesive layer, the number ratio of the primary particles A and aggregates A having a maximum length of 70 μm or more (sometimes referred to as 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 further preferably 0%. If the number ratio of the primary particles A′ and aggregates A′ present in the region A of the conductive adhesive layer is greater than the above range, the size of each floating or peeling portion on the surface of the conductive adhesive layer becomes larger, and the resistance value caused by the thermal cycle is likely to increase.

[0033] In the top view of the above-mentioned conductive adhesive layer, the number ratio of primary particles and agglomerates with a maximum length of more than 50 μm and less than 60 μm existing in the above-mentioned area A of the conductive adhesive layer is not particularly limited as long as the number ratio of the above-mentioned primary particles A and the above-mentioned agglomerates A and the number ratio of the above-mentioned primary particles B and the above-mentioned aggregates B are within a specific range, for example, it is preferably less than 15%, more preferably less than 10%, and further preferably less than 5%.

[0034] In the top view of the conductive adhesive layer, the ratio of the number of primary particles A and aggregates A of the conductive particles in one small area a is preferably 5% or less, preferably 4.5% or less, more preferably 3.5% or less, further preferably 2.5% or less, and particularly preferably 0%, that is, no primary particles and aggregates with a maximum length of 60 μm or more are included. By making the ratio of the number of primary particles A and aggregates A in one small area a within the above range, when the belt of the present invention is subjected to repeated temperature changes (hot and cold cycles), not only the increase in the resistance value in the thickness direction can be suppressed, but also the increase in the resistance value in the horizontal direction can be suppressed.

[0035] The number of the primary particles A and the agglomerates A present in the above-mentioned small area a is not particularly limited as long as the number of the primary particles A and the agglomerates A present in the above-mentioned area A can be set to the preferred range, for example, it is preferably 3 or less, more preferably 2 or less, further preferably 1 or less, and particularly preferably 0.

[0036] From the perspective of being able to highly balance initial conductivity and temporal conductivity, the ratio of the number of primary particles B and their agglomerates B of the above-mentioned conductive particles present in the above-mentioned small area a is preferably greater than 85%, preferably in the range of 85% to 100%, more preferably in the range of 90% to 100%, and further preferably in the range of 95% to 100%.

[0037] The number of the primary particles B and the agglomerates B present in one small area a is not particularly limited as long as the number of the primary particles B and the agglomerates B present in the area A can be set to a preferred range. For example, it can be set to a range of 1 to 15, preferably a range of 2 to 12, more preferably a range of 4 to 10, further preferably a range of 5 to 9, and particularly preferably a range of 6 to 8.

[0038] The number ratio of primary particles and aggregates (sometimes referred to as primary particles A' and aggregates A') with a maximum length of 70 μm or more in one small area a is preferably 1.5% or less, more preferably 1.0% or less, and further preferably 0%. This is because the size of each floating or peeling portion on the surface of the conductive adhesive layer becomes larger, and the resistance value caused by the thermal cycle is likely to increase.

[0039] The maximum length P1 of the primary particles and agglomerates of the conductive particles in the top view of the conductive adhesive layer refers to the maximum value of the distances between any two points on the contour line in the shape of the primary particles and agglomerates of the conductive particles in the top view of the conductive adhesive layer (also referred to as the top view shape of the primary particles and agglomerates of the conductive particles). The maximum length P1 of the primary particles and agglomerates of the conductive particles is measured by the following method. Using an optical microscope (manufactured by HIROX, RH-2000 digital microscope, ACS rotary zoom lens (Japanese: レボズームレンズ; 30-2500x)), the surface of the conductive adhesive layer side of the conductive adhesive tape (excluding the release liner when the surface has a release liner) is set to the lens side of the optical microscope and placed on the platform, and 10 0.5 mm×0.5 mm squares (0.25 mm 2 ), 10 small areas a are photographed at a magnification of 400 times to obtain photographed images. The black parts in the above photographed images represent primary particles and agglomerates of conductive particles. Using the measurement function of the optical microscope, the straight line distance connecting any two points selected on the outline of the black part of the photographed image of each small area a (the outline of the primary particles and agglomerates of conductive particles in the top view) is measured as the longest distance between the two points, and it is set as the maximum length P1.

[0040] In addition, the ratio of the number of primary particles and agglomerates whose maximum length P1 is within a specific range (for example, the maximum length P1 is greater than N1 μm, the maximum length P1 is less than N2 μm, the maximum length P1 is greater than N3 μm and less than N4 μm. N1 to N4 are specific numerical values ​​within the specified range) existing in the above-mentioned area A of the conductive adhesive layer is determined by the following method. First, in the same manner as the above-mentioned determination method of "the maximum length P1 of the primary particles and agglomerates of the conductive particles", 10 0.5 mm × 0.5 mm squares (0.25 mm 2 ), 10 small areas a are photographed at a magnification of 400 times to obtain photographed images. For each of the above small areas a, the number S1 of black parts whose maximum length P1 in the photographed image is within a specified range (for example, the maximum length P1 is greater than N1μm, the maximum length P1 is less than N2μm, the maximum length P1 is greater than N3μm and less than N4μm) and the total number S2 of black parts in the above photographed image (wherein the black parts whose maximum length P1 is less than 10μm are not counted) are counted. The total number S′1 of black portions whose maximum length P1 is within the specific range included in the 10 small regions a is defined as the number of primary particles and aggregates of conductive particles whose maximum length P1 is within the specific range existing in the region A. In addition, the total number S′2 of black parts contained in the above 10 small areas a is set as the total number of primary particles and agglomerates of conductive particles present in area A. Based on the above S′1 and S′2, the number ratio in area A is calculated by the following formula (1). Number ratio in area A [%] = (S′1 / S′2)×100 Formula (1) It should be noted that the number ratio in the small area a is calculated according to the following formula (2). The number ratio in small area a [%] = (S1 / S2) × 100... Formula (2)

[0041] It should be noted that, in the small region a and the region A, primary particles and aggregates having a maximum length P1 of 10 μm or less in a plan view are not included in the number.

[0042] In the top view of the conductive adhesive layer, the total number of primary particles and agglomerates of the conductive particles present in the region A (excluding the primary particles and agglomerates having a maximum length of less than 10 μm) is preferably in the range of 20 to 150, more preferably in the range of 50 to 120, further preferably in the range of 60 to 110, and particularly preferably in the range of 70 to 100. By setting the total number of primary particles of the conductive particles and their agglomerates present in the total region A to the above range, the tape of the present invention can increase the contact points between the conductive adhesive layer and the adherend, thereby being able to exert good conductive properties. In addition, the tape of the present invention is not prone to floating and peeling caused by hot and cold cycles.

[0043] The conductive particles in the present invention are not particularly limited as long as they are conductive particles, and examples thereof include metal particles, composite particles in which the surface of core particles is coated with metal (metal-coated particles), carbon fillers, etc. The conductive particles may be used alone or in combination of two or more.

[0044] 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.

[0045] Examples of the metal-coated particles include metal-coated resin particles in which a metal is coated on the surface of resin particles such as polymer beads and glass beads, and metal-coated metal powders in which a different type of metal is coated on the surface of a metal powder.

[0046] From the perspective of achieving both conductivity and adhesion of the conductive adhesive layer, the conductive particles are preferably metal particles, and preferably metal particles made of a metal selected from nickel, copper, silver and stainless steel, and more preferably nickel particles from the perspective of excellent conductivity.

[0047] As nickel particles, nickel powder is preferably used. Nickel powder can be manufactured by carbonyl method. As nickel powder manufactured by carbonyl method, there is no particular limitation, and it can be appropriately selected according to the purpose, for example, NI255T (filament) manufactured by Futian Metal Foil Powder Industry Co., Ltd., Ni123 (spherical) manufactured by Vale, Ni255 (filament) manufactured by Vale, N06 (beaded) manufactured by Jinchuan Group Co., Ltd., etc.

[0048] The shape of the conductive particles is not particularly limited, and examples thereof include spherical, spike-shaped (surface needle-like), flake-shaped (scaly), dendritic, fibrous, amorphous (polyhedral), bead-shaped, beaded, etc. Among them, spherical, bead-shaped, or beaded is preferred from the viewpoint of being able to reduce the resistance value of the conductive adhesive tape.

[0049] The average particle size (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 further preferably in the range of 12 μm to 20 μm. In addition, the average particle size (d90) of the primary particles of the conductive particles is preferably in the range of 5 μm to 60 μm, more preferably in the range of 27 μm to 55 μm, further preferably in the range of 30 μm to 50 μm, and particularly preferably in the range of 31 μm to 50 μm. By setting the average particle size d50 and / or d90 of the primary particles of the conductive particles within the above range, the size of the agglomerates and their number ratio in the conductive adhesive layer can be adjusted by using the preparation method of the conductive adhesive described later, and a conductive adhesive layer with good adhesion and conductivity before and after hot and cold cycles can be prepared.

[0050] The average particle size d50 and d90 of the primary particles of the conductive particles refer to the 50% cumulative value and the 90% cumulative value in the particle size distribution, and are values ​​measured by the laser diffraction scattering method. As a measuring device, Microtrac MT3000 II manufactured by Nikkiso Co., Ltd., laser diffraction particle size distribution measuring instrument SALD-3000 manufactured by Shimadzu Corporation, etc. can be used. It should be noted that, in the case of containing two or more conductive particles, the above particle size is calculated based on the distribution of all the conductive particles mixed.

[0051] Examples of a method for adjusting the particle size of the conductive particles include a method of pulverizing the conductive particles using a jet mill and a sieving method using a sieve or the like.

[0052] The ratio of the average particle size d50 of the primary particles of the conductive particles to the thickness of the conductive adhesive layer ([average particle size d50 of the primary particles of the conductive particles / thickness of the conductive adhesive layer]) is preferably 50% to 150%, more preferably 60% to 120%, and further preferably 70% to 100%. In addition, the ratio of the average particle size d90 of the primary particles of the conductive particles to the thickness of the conductive adhesive layer ([average particle size d90 of the primary particles of the conductive particles / thickness of the conductive adhesive layer]) is preferably 80% to 300%, more preferably 100% to 250%, and further 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 to the above ranges, it is possible to achieve both conductivity and adhesion of the conductive adhesive layer.

[0053] The content of the conductive particles in the conductive adhesive layer is not particularly limited as long as it can take into account both conductivity and adhesion. Relative to 100 parts by mass of the adhesive (solid content), the conductive particles are preferably 0.1 to 10 parts by mass, more preferably 0.5 to 5 parts by mass, and further preferably 0.8 to 2 parts by mass. By setting the content of the conductive particles to the above range, the reduction in the adhesive force of the conductive adhesive layer can be suppressed, and the conductivity of the conductive adhesive layer can be ensured by the agglomerates of the conductive particles. The content of the conductive particles in the conductive adhesive layer refers to the total amount of the content of the primary particles and agglomerates in the conductive adhesive layer.

[0054] <Adhesive> As the adhesive included in the above-mentioned conductive adhesive layer, the adhesive used in the usual adhesive sheet can be used. The above-mentioned adhesive is an adhesive that is a polymer (hereinafter sometimes referred to as "base polymer") that becomes the main component of the polymer components included in the adhesives such as acrylic polymers, rubber polymers (natural rubber, synthetic rubber, their mixtures, etc.), polyester polymers, carbamate polymers, polyether polymers, silicone polymers, polyamide polymers, and fluorine polymers. Specifically, (meth) acrylic adhesives, carbamate adhesives, rubber adhesives, polyester adhesives, silicone adhesives, etc. can be cited. Among them, from the viewpoint of bonding performance and heat resistance, (meth) acrylic adhesives are preferably used.

[0055] Hereinafter, the (meth)acrylic adhesive will be mainly described, but the conductive adhesive layer in the present invention is not limited to being composed of the (meth)acrylic adhesive, and may be composed of the other adhesives mentioned above.

[0056] The (meth)acrylic adhesive contains a (meth)acrylic copolymer ((meth)acrylic polymer) as a base polymer, and the (meth)acrylic copolymer contains a single (meth)acrylate or a copolymer of (meth)acrylate and other monomers. The above-mentioned (meth)acrylic adhesive contains at least a base polymer, i.e., a (meth)acrylic copolymer, and may contain a tackifying resin, a cross-linking agent, other additives, etc. as required. It should be noted that "(meth)acrylic acid" generally means "acrylic acid or methacrylic acid", and "(meth)acrylate" generally means "acrylate or methacrylate".

[0057] As the (meth)acrylic acid copolymer, an acrylic acid copolymer having a (meth)acrylic acid ester monomer having an alkyl group with 1 to 18 carbon atoms as a main monomer component is preferred. The alkyl group may be linear or branched. As the (meth)acrylic acid ester monomer having an alkyl group with 1 to 18 carbon atoms, for example, methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, tert-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, etc. can be mentioned. They can be used alone or in combination of two or more. Among them, it is preferred 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 a carbon number in this range, the conductive adhesive layer can exert better adhesion and cohesion.

[0058] The content of the (meth)acrylate monomer in the (meth)acrylic copolymer is preferably in the range of 80% to 99% by mass, more preferably in the range of 90% to 98.5% by mass, of the monomer components constituting the (meth)acrylic copolymer. By setting the content of the (meth)acrylate monomer in the above range, the conductive adhesive layer can exhibit excellent adhesive force and cohesive force.

[0059] The monomer components constituting the above-mentioned (meth) acrylic acid copolymer preferably include a high polarity vinyl monomer in addition to the above-mentioned (meth) acrylate monomer. As the high polarity vinyl monomer, carboxyl-containing vinyl monomers, hydroxyl-containing vinyl monomers, amide-containing vinyl monomers, etc. can be cited. One or more of the high polarity vinyl monomers can be used. Among them, carboxyl-containing vinyl monomers are easy to adjust the adhesion of the conductive adhesive layer to an appropriate range, so it is preferred.

[0060] 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, acrylic acid is preferably used as a copolymerization component.

[0061] The content of the carboxyl-containing vinyl monomer is preferably in the range of 0.2% to 15% by mass, more preferably in the range of 0.4% to 10% by mass, and further preferably in the range of 0.5% to 6% by mass in the monomer components constituting the above-mentioned (meth)acrylic copolymer. By making the monomer components constituting the above-mentioned (meth)acrylic copolymer contain the carboxyl-containing vinyl monomer within this range, it is easy to adjust the adhesion of the conductive adhesive layer to an appropriate range.

[0062] Examples of the hydroxyl group-containing vinyl monomer include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, and 6-hydroxyhexyl (meth)acrylate.

[0063] Examples of the amide group-containing vinyl monomer include N-vinyl pyrrolidone, N-vinyl caprolactam, acryloyl morpholine, acrylamide, and N,N-dimethylacrylamide.

[0064] Examples of highly polar vinyl monomers other than those mentioned above include sulfonic acid group-containing monomers such as vinyl acetate and 2-acrylamide-2-methylpropanesulfonic acid, and terminal alkoxy-modified (meth)acrylates such as 2-methoxyethyl (meth)acrylate and 2-phenoxyethyl (meth)acrylate.

[0065] The total content of the high polarity vinyl monomer in the monomer components constituting the above-mentioned (meth) acrylic copolymer can be set to 20% by mass or less, 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 further preferably in the range of 0.5% by mass to 6% by mass. By making the monomer components constituting the above-mentioned (meth) acrylic copolymer contain the high polarity vinyl monomer within this range, it is easy to adjust the adhesion of the conductive adhesive layer to an appropriate range.

[0066] The weight average molecular weight of the (meth)acrylic acid-based copolymer is not particularly limited, but is preferably in the range of 300,000 to 1,500,000, and more preferably in the range of 500,000 to 1,200,000, from the viewpoint of adhesive performance.

[0067] The weight average molecular weight of the (meth)acrylic copolymer is a converted value measured by gel permeation chromatography (GPC) using polystyrene as a standard sample. The weight average molecular weight by GPC was measured using a GPC device (HLC-8329GPC) manufactured by Tosoh Corporation under the following measurement conditions. [Measurement conditions] Sample concentration: 0.5 mass% (tetrahydrofuran solution) Sample injection volume: 100μL Eluent: THF (tetrahydrofuran) Flow rate: 1.0mL / min ·Measurement temperature: 40℃ Main column: 2 pieces of "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)

[0068] The (meth)acrylic acid-based copolymer can be obtained by polymerizing the monomers by known methods such as solution polymerization, bulk polymerization, suspension polymerization, and emulsion polymerization. Among them, solution polymerization is preferred from the viewpoint of production cost and productivity.

[0069] The conductive adhesive layer (conductive adhesive) may include a tackifier resin as required. By including a tackifier resin in the conductive adhesive layer, the adhesion and surface bonding strength of the conductive adhesive layer to the adherend may be improved. As the tackifier resin, for example, 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, (methyl) acrylate-based tackifier resins, etc. The tackifier resin may be used alone or in combination of two or more.

[0070] The tackifier resin is preferably one or more selected from disproportionated rosin ester tackifier resins, polymerized rosin ester tackifier resins, rosin phenol tackifier resins, hydrogenated rosin ester tackifier resins, (meth)acrylate tackifier resins and terpene phenol tackifier resins.

[0071] The softening point of the tackifier resin is preferably 30° C. to 180° C., more preferably 70° C. to 140° C. By using a tackifier resin having the above softening point, the adhesive performance of the conductive adhesive layer can be further improved. When a (meth)acrylate tackifier resin is used, it is preferred to use a tackifier resin having a glass transition temperature of 30° C. to 200° C., more preferably 50° C. to 160° C.

[0072] The amount of the tackifier resin is preferably 0 to 65 parts by mass, based on 100 parts by mass of the base polymer contained in the adhesive, and preferably 5 to 55 parts by mass in order to further improve the adhesion of the conductive adhesive layer to the adherend.

[0073] <Cross-linking agent> The conductive adhesive layer (conductive adhesive) may contain a crosslinking agent as needed. This is because it can react with the base polymer to form a three-dimensional crosslinked structure in the conductive adhesive layer, which can improve the cohesive force of the conductive adhesive layer. As the crosslinking agent, an isocyanate crosslinking agent, an epoxy crosslinking agent, a metal chelate crosslinking agent, an aziridine crosslinking agent, etc. can be used, and it can be appropriately selected according to the base polymer contained in the adhesive.

[0074] When the base polymer is the (meth)acrylic copolymer, an isocyanate crosslinking agent or an epoxy crosslinking agent having high reactivity with the (meth)acrylic copolymer is preferably used as the crosslinking agent, and an isocyanate crosslinking agent is more preferred due to its higher reactivity.

[0075] As the above-mentioned isocyanate crosslinking agent, for example, toluene diisocyanate, naphthalene-1,5-diisocyanate, hexamethylene diisocyanate, diphenylmethane diisocyanate, xylylene diisocyanate, trimethylolpropane-modified toluene diisocyanate, etc. can be mentioned. Among them, trifunctional polyisocyanate compounds are preferred. As trifunctional isocyanate compounds, for example, toluene diisocyanate or trimethylolpropane adducts thereof, triphenylmethane isocyanate, etc. can be mentioned.

[0076] The content of the crosslinking agent can be an amount that allows 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, further 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. By making the gel fraction of the conductive adhesive layer within the above range, a three-dimensional crosslinked structure is formed in the conductive adhesive layer, which can further improve the cohesive force and improve the peeling resistance.

[0077] The gel fraction of the conductive adhesive layer is the insoluble content when the 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 pressure-sensitive adhesive tape (excluding the release liner) has a substrate, the mass of the conductive pressure-sensitive adhesive layer is calculated by the following formula (4). The mass of the conductive adhesive layer = (the mass of the conductive adhesive tape) - (the mass of the substrate)... (4)

[0078] The conductive adhesive layer may contain additives as required. As the additives, conventional materials in the adhesive field may be cited, such as leveling agents, crosslinking agents, crosslinking aids, plasticizers, softeners, fillers, colorants (pigments, dyes, etc.), antistatic agents, anti-aging agents, ultraviolet absorbers, antioxidants, light stabilizers, etc. The amount of the additives is preferably 1 part by mass or less relative to 100 parts by mass of the base polymer.

[0079] 2. Substrate The conductive adhesive tape of the present invention may have a substrate. The substrate may be a single layer or a multilayer. In particular, from the viewpoint of improving heat resistance and rust resistance, the substrate is preferably a multilayer.

[0080] The substrate is preferably a substrate having conductivity (conductive substrate). The conductive substrate is composed of a conductive material, for example, a metal substrate, a graphite substrate, a conductive resin substrate, a conductive nonwoven fabric, a conductive woven fabric, etc. Among them, from the viewpoint of conductivity, a metal substrate and a conductive nonwoven fabric are preferred.

[0081] The metal substrate may be made of a metal or an alloy, and examples thereof include metal foil and metal film. Among them, metal foil is preferred from the viewpoint of conductivity, processability and cost.

[0082] The material of the metal substrate is not particularly limited, and examples thereof include metals such as gold, silver, copper, aluminum, nickel, iron, tin, and alloys thereof, etc. Among them, aluminum or copper is preferred, and copper is more preferred, from the viewpoints of conductivity, processability, and cost.

[0083] When the metal substrate is a copper foil, examples of the copper foil include electrolytic copper foil and rolled copper foil. Examples of the electrolytic copper foil include CF-T9FZ-HS-12 (thickness 12 μm), CF-T8G-DK-18 (thickness 18 μm), and CF-T8G-DK-35 (thickness 35 μm) manufactured by Fukuda Metal Foil Powder Industry Co., Ltd. In addition, examples of the rolled copper foil include TCU-H-8-RT (thickness 8 μm) manufactured by Nippon Foil Co., Ltd. and TPC (thickness 6 μm) manufactured by JX Nippon Mining & Metals Co., Ltd.

[0084] The 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 the reduction of electrical conductivity and poor appearance caused by corrosion. As the material of the plating layer, for example, tin plating, silver plating, gold plating, zinc plating, etc. can be cited.

[0085] Furthermore, the metal substrate may be subjected to coupling treatment using a silane coupling agent or the like, chromate treatment, or rust-proofing treatment using a benzotriazole or the like on one or both sides.

[0086] The conductive nonwoven fabric is not particularly limited and can be appropriately selected depending on the intended purpose. For example, the conductive nonwoven fabric may be a metal-plated nonwoven fabric obtained by plating a nonwoven fabric with a metal.

[0087] The nonwoven fabric may be made of a material that can be metal-plated, and general-purpose resin nonwoven fabrics, glass nonwoven fabrics, etc. can be used. Specifically, polyester nonwoven fabrics, etc. can be mentioned.

[0088] In addition, the metal plating applied to the nonwoven fabric may be electroplating or electroless plating. Examples of metals used to form the metal plating include copper, nickel, silver, platinum, and aluminum. Among them, copper or nickel is preferred from the viewpoint of conductivity and cost.

[0089] The thickness of the substrate is not particularly limited as long as it can show conductivity, and can be set according to the type of substrate, for example, it can be set to 1 μm or more and 40 μm or less, preferably 3 μm or more and 35 μm or less, more preferably 5 μm or more and 30 μm or less, and more preferably 5 μm or more and 25 μm or less. More specifically, when the substrate is a metal substrate, the thickness of the metal substrate is not particularly limited, and can be appropriately selected according to the purpose, preferably 1 μm or more and 40 μm or less, more preferably 3 μm or more and 35 μm or less, and more preferably 5 μm or more and 25 μm or less. In addition, when the substrate is a conductive non-woven fabric, the thickness of the conductive non-woven fabric is not particularly limited, and can be appropriately selected according to the purpose, preferably 3 μm or more and 50 μm or less, more preferably 5 μm or more and 30 μm or less, and more preferably 8 μm or more and 25 μm or less. By setting the thickness of the substrate to the above range, a thin conductive adhesive tape with excellent conductivity and adhesion can be made.

[0090] The thickness of the substrate is the average value of the thickness at five locations measured at intervals of 100 mm in the longitudinal direction using TH-102 (thickness meter, manufactured by Tester Industries, Ltd.).

[0091] From the viewpoint of further improving electrical characteristics, the thermal conductivity of the substrate is preferably 90 W / m·K or more, more preferably 100 W / m·K or more.

[0092] 3. Release liner The conductive adhesive tape of the present invention may have a release liner on the adhesive surface. The release liner is not particularly limited, and examples thereof include: resin films and papers with a release treatment on the surface, low-adhesion resin films such as polyethylene, polypropylene (OPP, CPP), polyethylene terephthalate, and fluorine-based resins (polytetrafluoroethylene, etc.), laminated paper formed by laminating paper and resin films, resin films and papers with a caulking treatment on the surface using clay, polyvinyl alcohol, etc., and resin films and papers with a release treatment on one or both sides of the caulking treatment. As the release treatment agent used in the release treatment, for example, silicone-based release treatment agents, long-chain alkyl-based release treatment agents, fluorine-based release treatment agents, molybdenum sulfide, etc. can be mentioned.

[0093] When the conductive adhesive tape of the present invention is a tape without a substrate as described below, the release liner may be provided on one side of the conductive adhesive layer or on both sides. In addition, when the conductive adhesive tape of the present invention is a tape with a substrate as described below, the release liner may be provided on the surface of the conductive adhesive layer on one side of the substrate or on the surfaces of the conductive adhesive layers on both sides of the substrate.

[0094] 4. Conductive adhesive tape The conductive adhesive tape of the present invention may be a single-sided adhesive tape having an adhesive surface on one side, or a double-sided adhesive tape having adhesive surfaces on both sides. In addition, the conductive adhesive tape of the present invention may be a tape without a substrate including the conductive adhesive layer of the present invention, or a tape with a substrate having the conductive adhesive layer of the present invention on at least one side of the substrate.

[0095] When the conductive pressure-sensitive adhesive tape of the present invention is a tape without a substrate, the two opposing surfaces of the conductive pressure-sensitive adhesive layer constituting the tape may be respectively used as the adhesive surfaces of the conductive pressure-sensitive adhesive tape, that is, a double-sided adhesive specification.

[0096] In addition, when the conductive adhesive tape of the present invention is the tape with a substrate, the conductive adhesive tape may be a single-sided adhesive tape having the conductive adhesive layer of the present invention on one side of the substrate. When the tape with a substrate is a single-sided adhesive tape, the surface of the conductive adhesive layer may be used as the adhesive surface of the conductive adhesive tape.

[0097] In addition, when the conductive adhesive tape of the present invention is the above-mentioned tape with a substrate, the conductive adhesive tape may be a double-sided tape having adhesive layers on both sides of the substrate. In this case, the adhesive layer on at least one side of the substrate may be the conductive adhesive layer of the present invention, and the adhesive layers on both sides of the substrate may be the conductive adhesive layers of the present invention. When the conductive adhesive tape of the present invention is a double-sided adhesive tape with a substrate, the surfaces of the adhesive layers on both sides of the substrate may be used as the adhesive surface of the conductive adhesive tape.

[0098] The resistance value Rz of the conductive adhesive tape of the present invention in the initial thickness direction (Z direction) is preferably 1Ω or less, preferably 0.5Ω or less, and more preferably 0.2Ω or less. In addition, the resistance value change rate (%) of the conductive adhesive tape of the present invention in the thickness direction before and after the hot and cold cycle test is preferably 200% or less. Among them, the above-mentioned resistance value change rate (%) is preferably 180% or less, more preferably 150% or less, and further preferably 140% or less. By making the resistance value change rate of the tape of the present invention in the thickness direction before and after the hot and cold cycle test within the above-mentioned range, the resistivity of the tape of the present invention can be suppressed from rising even in an environment subjected to repeated temperature changes, and the conductivity over time is good. In other words, this suggests that the floating and peeling of the conductive adhesive tape from the adherend caused by the hot and cold cycle can be suppressed.

[0099] The rate of change in resistance value in the thickness direction of the conductive pressure-sensitive adhesive tape before and after the thermal cycle test can be calculated by the following formula (5). Change rate of the resistance value in the thickness direction of the conductive adhesive tape before and after the hot and cold cycle test (%) = (resistance value R′z (Ω) in the thickness direction of the conductive adhesive tape after the hot and cold cycle test / initial resistance value Rz (Ω) in the thickness direction of the conductive adhesive tape) × 100···(5)

[0100] The initial horizontal direction (XY direction) resistance value Rxy of the conductive adhesive tape of the present invention is preferably 2Ω or less, preferably 1.5Ω or less, and more preferably 0.8Ω or less. In addition, the resistance value change rate (%) of the conductive adhesive tape of the present invention in the horizontal direction before and after the hot and cold cycle test is preferably 300% or less, more preferably 200% or less, and further preferably 100% or less. By making the resistance value change rate of the tape of the present invention in the horizontal direction before and after the hot and cold cycle test within the above range, the tape of the present invention can suppress the increase of the resistivity in the horizontal direction in addition to the thickness direction in an environment subjected to repeated temperature changes, and can exert good conductivity over time in the thickness direction and the horizontal direction.

[0101] The rate of change in resistance value in the horizontal direction of the conductive pressure-sensitive adhesive tape before and after the thermal cycle test can be calculated by the following formula (6). Change rate of resistance value in horizontal direction of conductive adhesive tape before and after hot and cold cycle test (%) = (resistance value R′xy (Ω) in horizontal direction of conductive adhesive tape after hot and cold cycle test / initial resistance value Rxy (Ω) in horizontal direction of conductive adhesive tape) × 100···(6)

[0102] The initial resistance value in the thickness direction and the horizontal direction of the conductive pressure-sensitive adhesive tape, and the resistance value in the thickness direction and the horizontal direction after the thermal cycle test can be measured by the method described in the examples described later.

[0103] 5. Preparation method of conductive adhesive The method for preparing a conductive adhesive disclosed herein is a method for preparing a mixture by dispersing conductive particles in an adhesive, and filtering the mixture to obtain a conductive adhesive. According to the method, the conductive particles in the conductive adhesive are dispersed in the adhesive and then filtered to make the conductive particles in the conductive adhesive uniform in size, so that the size of the aggregates of the conductive particles can be controlled when forming a conductive adhesive layer.

[0104] As a method for dispersing the conductive particles in the above-mentioned adhesive, a known method can be used, for example, a method of dispersing the adhesive, the conductive particles, the solvent, etc. using a dispersing stirrer can be cited. As commercially available dispersing stirrers, for example, dissolvers, butterfly mixers, BDM twin-shaft mixers, and planetary mixers can be cited. Among them, a dissolver or butterfly mixer that has a moderate share of less thickening of the adhesive during stirring is preferred.

[0105] As the dispersion conditions for dispersing the conductive particles in the above-mentioned adhesive, the following conditions are preferred: the primary particles of the conductive particles are fully dispersed in the mixture before the filtration treatment, and the size of the agglomerates formed by the above-mentioned primary particles becomes the desired range (for example, the maximum length is 10 μm or more and less than 60 μm), and becomes the desired distribution. 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 further preferably in the range of 800 r / min to 2000 r / min. In addition, the stirring time is not particularly limited and can be appropriately set, for example, it can be set 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 stirring time to the above-mentioned conditions, the conductive particles can be stirred at a high speed in the above-mentioned adhesive, and the primary particles of the conductive particles can be fully dispersed in the mixture before the filtration treatment. As a result, the size of the agglomerates formed by the above-mentioned primary particles can be set to a specific range (for example, the maximum length is 10 μm or more and less than 60 μm) and set to the desired distribution.

[0106] As a method for filtering a mixture in which conductive particles are dispersed in an adhesive, for example, gravity filtration through a screen, pressure filtration through a filter while pressurizing, sedimentation by centrifugation, etc., cooling and precipitation, etc. can be cited, and these can be used in combination. Among them, the method of filtering using a screen and / or a filter is simple and convenient, and therefore preferred. In addition, the filtration can be once, or it can be repeated twice or more.

[0107] The material of the mesh and the filter is not particularly limited, and a general material used for filtration can be appropriately selected, and examples thereof include metal (wire mesh), glass, and resin.

[0108] The mesh number of the sieve also depends on the size of the mesh, preferably 100 mesh or more, preferably 150 mesh or more, more preferably 200 mesh or more. In addition, the mesh number of the above-mentioned sieve is preferably 400 mesh or less, preferably 300 mesh or less, more preferably 250 mesh or less. In particular, from the perspective of being able to form the desired conductive adhesive layer and thus improving the productivity in the filtration process, the mesh number of the above-mentioned sieve is preferably 100 mesh or more and less than 300 mesh, more preferably 150 mesh or more and 250 mesh or less. In addition, the mesh of the sieve is 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, preferably 30 μm or more, 45 μm or more, 60 μm or more, and as the mesh of the above-mentioned sieve, it is preferably 150 μm or less, 110 μm or less, 80 μm or less.

[0109] The pore size of the filter can be appropriately selected according to the particle size of the primary particles of the conductive particles, and is, for example, preferably in the range of 90 μm to 200 μm, more preferably in the range of 100 μm to 150 μm, and further preferably in the range of 100 μm to 120 μm.

[0110] In the present invention, it is preferred to filter the mixture of conductive particles with an average particle size d50 of primary particles in the range of 5 μm to 30 μm dispersed in the binder using a screen with the above mesh number and mesh opening and / or a filter with the above aperture. Among them, it is preferred to filter the mixture of conductive particles with an average particle size d50 of primary particles in the range of 5 μm to 30 μm dispersed in the binder using a screen with a mesh number less than 300 meshes; when the mesh number of the screen is less than 200 meshes, it is more preferred to further filter using a filter with an aperture range of 90 μm to 200 μm after filtering using the mesh opening.

[0111] 6. Method for manufacturing conductive adhesive tape The conductive adhesive tape of the present invention can be produced by a known method, for example, by applying the conductive adhesive prepared by the method described in "5. Method for preparing conductive adhesive" on a release liner and drying the coated film to form a conductive adhesive layer. As a manufacturing method when the conductive adhesive tape of the present invention has a substrate, for example, there can be mentioned: a method of laminating the above-mentioned conductive adhesive layer formed on a release liner to one side or both sides of a substrate, a method of coating the above-mentioned conductive adhesive on one side or both sides of a substrate and drying the coated film to form a conductive adhesive layer, etc.

[0112] As a coating method for the conductive adhesive, a known coating method can be used. Examples of the coating method include coating machines such as a gravure roll coater, a reverse roll coater, a lick roll coater, a lip coater, a dip roll coater, a rod coater, a knife coater, a spray coater, a comma coater, a direct coater, and a slot jet coater.

[0113] The conductive adhesive layer may be aged to promote the crosslinking reaction. The aging conditions are not particularly limited, but the aging conditions may be, for example, 48 hours or more at a temperature within a range of 20° C. to 50° C.

[0114] When the conductive pressure-sensitive adhesive layer formed on the release liner is attached to the substrate, heat lamination may be performed to improve interlayer adhesion. The temperature of the heat lamination is not particularly limited, but is preferably within a range of 60°C to 150°C, for example.

[0115] 7. Purpose The conductive adhesive tape of the present invention is useful, for example, for shielding electromagnetic waves used in electrical or electronic equipment, shielding harmful electromagnetic waves in space generated by other electrical or electronic equipment, and for grounding and fixing to prevent static electricity. Among them, it can be appropriately applied to portable electronic devices that are being made thinner and have strict volume restrictions in the frame, and is particularly suitable for use as a built-in component attached to a small electronic terminal.

[0116] It should be noted that, in the present specification, the expression "the primary particles and agglomerates of the above-mentioned conductive particles present in the area A of the conductive adhesive layer (excluding the above-mentioned primary particles and the above-mentioned agglomerates with a maximum length of less than 10 μm)" (and similar expressions) means that the primary particles and agglomerates of the conductive particles present in the above-mentioned area A of the conductive adhesive layer may contain primary particles and agglomerates with a maximum length of less than 10 μm, but when calculating the ratio of the number of primary particles and agglomerates of each size, the number of primary particles and agglomerates of the conductive particles as a whole does not include (that is, excludes) the number of primary particles and agglomerates with a maximum length of less than 10 μm. Furthermore, the present invention is not limited to the above-mentioned embodiments. The above-mentioned embodiments are illustrative, and any technical solution having substantially the same structure and exerting the same function and effect as the technical idea described in the claims of the present invention is included in the technical scope of the present invention. Example

[0117] Hereinafter, the present invention will be further described by showing Examples and Comparative Examples.

[0118] [Preparation 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 dissolved in 100 parts by mass of ethyl acetate at the following ratios, 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 parts by mass 2,2′-azobisisobutyronitrile (polymerization initiator): 0.1 parts by mass

[0119] The weight average molecular weight of the acrylic copolymer is a polystyrene-equivalent value measured by a 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 mass% (tetrahydrofuran solution) Sample injection volume: 100μL Eluent: THF (tetrahydrofuran) Flow rate: 1.0mL / min ·Measurement temperature: 40℃ Main column: TSKgel GMHHR-H (20) 2 pieces Guard column: TSKgel HXL-H Detector: Differential refractometer · Standard polystyrene molecular weight: 10,000 to 20,000,000 (manufactured by Tosoh Corporation)

[0120] (Preparation Example of a Mixture of a Binder and Conductive Particles) 100 parts by mass (solid content) of the acrylic copolymer (1), 10 parts by mass of polymerized rosin pentaerythritol ester (Pensel D-135, manufactured by Arakawa Chemical Industries, Ltd., softening point 135° C.), and 10 parts by mass of disproportionated rosin glycerol ester (SuperEster 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 acrylic polymer.

[0121] Next, 100 parts by mass (solid content) of the acrylic adhesive, 1 part by mass of nickel powder (manufactured by Jinchuan Group Co., Ltd., product name: N06, beaded, d50: 19.0 μm, d90: 43.0 μm) as conductive particles, 2 parts by mass of BURNOCK 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 for 10 minutes using a disperser to obtain a mixture.

[0122] (Preparation Example of Conductive Adhesive A) The mixture was stirred at a high speed of 1200 r / min for 60 minutes using a disperser, and then filtered through a 250-mesh metal screen by gravity to obtain a conductive adhesive A.

[0123] (Preparation Example of Conductive Adhesive B) The mixture was stirred at a high speed of 1200 r / min for 60 minutes using a disperser, and then filtered through a 300-mesh metal screen by gravity to obtain a conductive adhesive B.

[0124] (Preparation Example of Conductive Adhesive C) The mixture was stirred at a high speed of 1200 r / min for 60 minutes using a disperser, filtered by gravity through a 200-mesh metal screen, and further filtered under pressure using a metal filter with a mesh size of 100 μm to obtain a conductive adhesive C.

[0125] (Preparation Example of Conductive Adhesive D) The mixture was stirred at a high speed of 1200 r / min for 60 minutes using a disperser, filtered by gravity through a 200-mesh metal screen, and further filtered under pressure using a metal filter with a mesh size of 125 μm to obtain a conductive adhesive D.

[0126] (Preparation Example of Conductive Adhesive E) The mixture was stirred at a high speed of 1200 r / min for 60 minutes using a disperser, and then a conductive adhesive E was obtained without filtering.

[0127] (Preparation Example of Conductive Adhesive F) The mixture was stirred at a low speed of 400 r / min for 60 minutes using a propeller stirrer, and then a conductive adhesive F was obtained without filtering.

[0128] (Preparation Example of Conductive Adhesive G) The mixture was stirred using a disperser at a speed of 1200 r / min for 60 minutes, and then filtered through a 200-mesh metal screen by gravity to obtain a conductive adhesive G.

[0129] The conductive adhesives A to G are shown in the following table. [Table 1]

[0130] (Example 1) The conductive adhesive A was applied to a release film A (PET38×1, A3, manufactured by NIPPA Co., Ltd.) using 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 side of a copper foil A (average thickness 12 μm, surface resistance 0.003 Ω / □) having chrome plating on both sides, and then pressed at a linear pressure of 100 N / cm using a laminator at 40° C., and aged at 40° C. for 48 hours to produce a conductive adhesive tape A.

[0131] (Example 2) A conductive adhesive tape B was produced by the same procedure as in Example 1 except that the conductive adhesive B was used instead of the conductive adhesive A to form the conductive adhesive layer.

[0132] (Example 3) A conductive adhesive tape C was produced by the same procedure as in Example 1 except that the conductive adhesive C was used instead of the conductive adhesive A to form the conductive adhesive layer.

[0133] (Example 4) A conductive adhesive tape D was produced by the same procedure as in Example 1 except that the conductive adhesive D was used instead of the conductive adhesive A to form the conductive adhesive layer.

[0134] (Comparative Example 1) A conductive adhesive tape E was produced by the same procedure as in Example 1 except that the conductive adhesive E was used instead of the conductive adhesive A to form the conductive adhesive layer.

[0135] (Comparative Example 2) A conductive adhesive tape F was produced by the same procedure as in Example 1 except that the conductive adhesive F was used instead of the conductive adhesive A to form the conductive adhesive layer.

[0136] (Comparative Example 3) A conductive adhesive tape G was produced by the same procedure as in Example 1 except that the conductive adhesive G was used instead of the conductive adhesive A to form the conductive adhesive layer.

[0137] [evaluate] The conductive pressure-sensitive adhesive tapes obtained in Examples and Comparative Examples were evaluated as follows.

[0138] <Maximum length P1, number, and ratio of primary particles and aggregates of conductive particles> The maximum length P1 of the primary particles and aggregates of the conductive particles in the top view of the conductive adhesive layer of the obtained conductive adhesive tape, and the number and number ratio of the primary particles and aggregates of the conductive adhesive layer whose maximum length P1 is within the specified range in the above-mentioned area A are measured by the method described in the column "(1) Conductive particles" in the column "1. Conductive adhesive layer" in the column "I. Conductive adhesive tape" above. It should be noted that the primary particles and aggregates whose maximum length P1 in the top view is less than 10 μm are not included in the number.

[0139] <Initial resistance value> <<Resistance in the thickness direction (conductivity in the thickness direction)>> Copper foil (5 mm wide × 5 mm wide) was attached to the conductive adhesive layer of the conductive adhesive tape cut to a size of 100 mm wide × 50 mm wide. Under an environment of 23°C and 50% RH, a load of 1 N was applied from the conductive adhesive tape attachment position of the copper foil, and the copper foil was connected to the conductive adhesive tape, and a current of 100 μA was passed using a milliohmmeter (manufactured by NF Circuit Design Module Co., Ltd.) to measure the resistance value Rz (Ω) in the thickness direction (attachment method).

[0140] <<Horizontal resistance value (conductivity in the plane direction)>> In the length direction of the conductive adhesive tape cut into a size of 100 mm wide (long side) × 50 mm wide (short side), one end of two copper foils (5 mm wide strips) were respectively attached to the surface of the conductive adhesive layer at a position 40 mm away from the short side of the conductive adhesive layer in the length direction, so that the bonding area between the copper foil end and the conductive adhesive layer became 5 mm wide × 5 mm wide; the other ends of the two copper foils (the ends on the side not bonded to the conductive adhesive layer) were respectively connected to the positive and negative electrodes of a milliohmmeter (manufactured by NF Circuit Design Module Co., Ltd.). Under an environment of 23°C and 50% RH, the copper foil was connected to the conductive adhesive tape without applying surface pressure from the bonding position of the copper foil and the conductive adhesive tape, and a current of 100 μA was passed using a milliohmmeter to measure the horizontal resistance value Rxy (Ω).

[0141] <Resistance value after thermal cycle test> The conductive adhesive tape was cut into a size of 100 mm wide × 50 mm wide, and a copper foil (5 mm wide × 5 mm wide) was attached to the conductive adhesive layer of the conductive adhesive tape to obtain a test piece. The test piece was placed in a thermal cycle tester (trade name "SH-242", manufactured by Espec Co., Ltd.) and a thermal cycle test was performed under the following test conditions. Relative humidity in the test machine: no control Thermal cycle test conditions: temperature rise rate 2°C / min, temperature drop rate 2°C / min, -35°C (hold for 30 minutes) → 85°C (hold for 30 minutes) → -35°C as one cycle, performed 100 times. The conductive adhesive tape after the thermal cycle test was used to measure the resistance value R′z (Ω) in the thickness direction and the resistance value R′xy (Ω) in the horizontal direction by the same method as the initial resistivity measurement method. In addition, the resistance value change rates in the thickness direction and the horizontal direction were calculated from the resistance value after the thermal cycle test and the initial resistance value using the following equations (7) and (8). Change rate of the resistance value in the thickness direction of the conductive adhesive tape before and after the hot and cold cycle test (%) = (resistance value R′z (Ω) in the thickness direction of the conductive adhesive tape after the hot and cold cycle test / initial resistance value Rz (Ω) in the thickness direction of the conductive adhesive tape) × 100···(7) Change rate of resistance value in horizontal direction of conductive adhesive tape before and after hot and cold cycle test (%) = (resistance value R′xy (Ω) in horizontal direction of conductive adhesive tape after hot and cold cycle test / initial resistance value Rxy (Ω) in horizontal direction of conductive adhesive tape) × 100···(8)

[0142] <Adhesion> The conductive adhesive tape was cut into a size of 25 mm in width, and the conductive adhesive layer side of the conductive adhesive tape was attached to a stainless steel plate (SUS plate, a stainless steel plate obtained by hairline grinding using 360 water-resistant abrasive paper) under the conditions of an ambient temperature of 23°C and a humidity of 50% RH. A 2 kg roller was reciprocated once on its upper surface to press the conductive adhesive tape against the stainless steel plate, and then the sheet obtained by placing it at room temperature for 1 hour was used as a test piece. The test piece was peeled off at a speed of 300 mm / min using a Tensilon universal tensile tester (manufactured by A&D Co., Ltd., Tensilon RTA-100) under the same temperature and humidity conditions as above, thereby measuring the 180 degree peeling adhesion.

[0143] <Retention capacity> The conductive adhesive tape was cut into 25 mm wide pieces and attached to the surface of a clean and smooth stainless steel plate in an attachment area of ​​25 mm × 25 mm. The sheet obtained by pressing the upper surface with a 2 kg roller by reciprocating once was placed under the conditions of 23°C and 50% RH for 1 hour according to JIS Z-0237, and then a load of 500 g was applied in the shear direction at 70°C, and the tape displacement distance after 24 hours was measured.

[0144] <Appearance> A copper foil was attached to the conductive adhesive layer of the conductive adhesive tape to obtain a test piece. The mixing of bubbles in the test piece was visually confirmed and judged according to the following criteria. Figure 1 (a) is the image when the reference is ○, Figure 1 (b) is the image when the reference is ○△, Figure 1 (c) is the image when the reference is △, Figure 1 (d) is the image when the reference is ×. (Benchmark) ○: Mixing of air bubbles cannot be visually recognized. ○△: A small amount of bubbles can be visually recognized (the outline of the bubbles is not clear) △: The outline of the bubble can be clearly seen ×: The outline of the bubbles is clear, and the mixing of bubbles can be visually recognized in the entire area

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

[0146] [Table 2]

[0147] [Table 3]

[0148] [Table 4]

[0149] [Table 5]

[0150] The conductive adhesive tape of the example has a smaller resistance value change rate [%] before and after the thermal cycle test than the conductive adhesive tape of the comparative example, indicating that the increase in resistance value in the thickness direction due to repeated temperature changes can be suppressed and the conductive adhesive tape has excellent conductivity. Industrial Applicability

[0151] The conductive adhesive tape of the present invention can be appropriately applied to a joint portion that requires conductivity. For example, it is useful for shielding electromagnetic waves used in electrical or electronic equipment, shielding harmful space electromagnetic waves generated by other electrical or electronic equipment, and anti-static grounding and fixing. Among them, it can be appropriately applied to portable electronic devices that are thinned and have strict volume restrictions in the frame, and is particularly suitable for use as a built-in component attached to a small electronic terminal.

Claims

1. A conductive adhesive tape, characterized in that having at least a conductive adhesive layer, The conductive adhesive layer contains an adhesive and conductive particles; In the top view of the conductive adhesive layer, there is a 2.5 mm 2 Of the primary particles and aggregates of the conductive particles in region A, after excluding primary particles and aggregates having a maximum length of 10 μm or less, The ratio of primary particles and agglomerates with a maximum length of 60 μm or more is less than 5%. The number ratio of 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. The conductive adhesive tape according to claim 1 or 2, wherein The total amount of the conductive particles is in the range of 0.1 parts by mass to 10 parts by mass based on 100 parts by mass of the binder.

4. The conductive adhesive tape according to claim 1 or 2, wherein The total number of primary particles and aggregates of the conductive particles present in the region A in a plan view of the conductive adhesive layer, excluding primary particles and aggregates having a maximum length of 10 μm or less, is in the range of 20 to 150.

5. The conductive adhesive tape according to claim 1 or 2, wherein The average particle size d50 of the primary particles is in the 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 or 2, wherein The conductive particles are metal particles.

8. The conductive adhesive tape according to claim 1 or 2, wherein The conductive particles are nickel powder.

9. The conductive adhesive tape according to claim 1 or 2, wherein The conductive adhesive layer is provided on one or both sides of the 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 plating layer on one side or both sides.

12. The conductive adhesive tape according to claim 1 or 2, wherein The resistance value change rate in the thickness direction before and after the thermal cycle test was 200% or less.

Images