JP2025078033A - Conductive adhesive tape - Google Patents

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

This disclosure relates to a conductive adhesive tape.

Conductive adhesive tape is used in electronic devices and communication devices for purposes such as shielding electromagnetic waves and grounding to prevent static electricity.

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 substrate and a conductive adhesive layer containing conductive particles.

International Publication No. 2015/076174

Conductive adhesive layers containing conductive particles have the problem that when they are repeatedly subjected to temperature changes, the resistance value in the thickness direction increases significantly, causing a decrease in conductivity.

This disclosure has been made in consideration of the above-mentioned circumstances, and provides a conductive adhesive tape with excellent conductivity that suppresses increases in resistance in the thickness direction even when subjected to repeated temperature changes.

The inventors discovered that the conductive particles exist as primary particles and/or aggregates in the conductive adhesive layer, and that variations in the size of the primary particles and aggregates affect the conductivity in the thickness direction due to repeated temperature changes.

That is, the present disclosure has the following embodiments.
[1] A conductive adhesive tape having at least a conductive adhesive layer, the conductive adhesive layer containing an adhesive and conductive particles, wherein, among primary particles and agglomerates of the conductive particles (excluding the primary particles and agglomerates having a maximum length of 10 μm or less) present within an area A of 2.5 ^mm2 in a planar view of the conductive adhesive layer, a number ratio of the primary particles and agglomerates having a maximum length of 60 μm or more is 5% or less, and a number ratio of the primary particles and agglomerates having a maximum length of less than 50 μm is 85% or more.
[2] The conductive adhesive tape according to the above-mentioned [1], wherein the conductive adhesive layer has a thickness of 10 μm or less.
[3] The conductive adhesive tape according to [1] or [2], wherein the total amount of the conductive particles is within the range of 0.1 parts by mass to 10 parts by mass per 100 parts by mass of the adhesive.
[4] The conductive adhesive tape according to any one of [1] to [3] above, wherein a total number of primary particles and agglomerates of the conductive particles (excluding the primary particles and agglomerates having a maximum length of 10 μm or less) present in the region A in a planar view of the conductive adhesive layer is within a range of 20 to 150.
[5] The conductive adhesive tape according to any one of [1] to [4], wherein the average particle diameter (d50) of the primary particles is within the range of 5 μm to 30 μm.
[6] The conductive adhesive tape according to any one of [1] to [5], wherein the aggregate is 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 any one of the above [1] to [6], 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 the above [1] to [8], having the conductive adhesive layer on one or both sides of a substrate.
[10] The conductive 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 chrome-plated layer on one or both sides.
[12] The conductive pressure-sensitive adhesive tape according to any one of the above [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.

According to the present disclosure, it is possible to provide a conductive adhesive tape with excellent conductivity that can suppress the increase in resistance value in the thickness direction due to repeated temperature changes.

I. Conductive adhesive tape The conductive adhesive tape (hereinafter, sometimes referred to as tape) of the present disclosure 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 within an area A of 2.5 ^mm2 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.

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 prone to agglomeration, and therefore tend to exist as agglomerates in the conductive adhesive layer. In addition, even if the particle size of the primary particles of the conductive particles is adjusted and dispersed in the adhesive during the preparation stage of the conductive adhesive, the size of the agglomerates of the conductive particles becomes uneven in the conductive adhesive layer. When an adherend to which a conductive adhesive tape containing such a conductive adhesive layer is attached is exposed to an environment with large temperature changes, the tape is likely to float or peel off from the adherend. At this time, the conductive contact cannot be obtained at the floating or peeling part of the tape from the adherend, and 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, if there are many large aggregates or primary particles in the conductive adhesive tape when viewed in a plane, the size of each point of lifting or peeling of the tape will increase, making the increase in resistivity due to the reduction in conductive contact points between the adherend and the tape more pronounced, making it difficult to maintain good conductivity in the thickness direction over time.

In contrast, the conductive adhesive tape of the present disclosure has a low initial resistance value and reduces the size of lifting and peeling that occurs from aggregates and primary particles by controlling the size and number ratio of the primary particles and aggregates of the conductive particles in a planar view of the conductive adhesive layer, thereby suppressing an increase in resistance value in the thickness direction due to repeated temperature changes (cooling and heating cycles). In this way, the conductive adhesive tape of the present disclosure has excellent stability of conductivity over time in the thickness direction.

The 2.5 ^mm2 region A in a planar view of the conductive adhesive layer refers to a total region (a collection of 10 small regions a) consisting of 10 small regions a, each of which is 0.5 mm x 0.5 mm in area and 0.25 ^mm2 in size, selected arbitrarily in a planar view from the conductive adhesive layer side of the conductive adhesive tape (planar view of the conductive adhesive layer).

When counting the number of conductive particles contained in small region a, if a part of the conductive particle protrudes from small region a because it is located on the boundary of small region a, then a conductive particle with 80% or more of its planar shape present within small region a is counted as one particle. The maximum length, etc. of the conductive particle is measured for the part present in small region a.

1. Conductive Pressure-Sensitive Adhesive Layer The conductive pressure-sensitive adhesive layer in the present disclosure contains a pressure-sensitive adhesive and conductive particles. Such a conductive pressure-sensitive adhesive layer is formed from a conductive pressure-sensitive adhesive containing a pressure-sensitive adhesive and conductive particles.

The thickness of the conductive adhesive layer is preferably 10 μm or less, more preferably 1 μm to 9 μm, more preferably 2 μm to 8 μm, and even more preferably 4 μm to 6 μm. By setting the thickness of the conductive adhesive layer within the above range, the conductive adhesive layer can exhibit good adhesive strength, and the conductive layer can exhibit stability over time in the thickness direction by controlling the size of the primary particles and aggregates of the conductive particles in a planar view of the conductive adhesive layer and the proportion of their numbers.

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

(1) Conductive Particles In the conductive pressure-sensitive adhesive layer, the conductive particles are present as primary particles and/or aggregates. The conductive pressure-sensitive adhesive layer may contain at least an aggregate 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 are present in the conductive pressure-sensitive adhesive layer. In the region A, the number of the aggregates may be more or less than the number of the primary particles, but it is preferable that the number of aggregates is less than the number of primary particles.

The conductive particle agglomerate may be an agglomerate formed by agglomerating primary particles of one type of conductive particle, or an agglomerate formed by agglomerating primary particles of two or more types of conductive particles.

In a plan view of the conductive pressure-sensitive adhesive layer, of the primary particles and agglomerates of the conductive particles (excluding the primary particles and agglomerates having a maximum length of 10 μm or less) present within an area A of 2.5 ^mm2 , the number ratio of the primary particles and agglomerates having a maximum length of 60 μm or more is 5% or less. This makes it possible for the tape of the present disclosure to be prevented from floating or peeling off from the adherend starting from the agglomerates or primary particles, even when repeatedly subjected to temperature changes, and to suppress a decrease in conductivity over time.

Of the primary particles and agglomerates of conductive particles, primary particles with a maximum length of 60 μm or more are sometimes referred to as primary particles A, and agglomerates with a maximum length of 60 μm or more are sometimes referred to as agglomerates A.

In particular, the number ratio of the primary particles and aggregates (number ratio of primary particles A and aggregates A) present in the region A of the conductive adhesive layer in a plan view and having a maximum length of 60 μm or more is preferably 4.5% or less, more preferably 3.5% or less, even more preferably 2.5% or less, and particularly preferably 0%, i.e., region A does not contain primary particles and aggregates having a maximum length of 60 μm or more. By having the number ratio of primary particles A and aggregates A present in the region A within the above range, an increase in resistance value can be effectively suppressed not only in the thickness direction but also in the horizontal direction when the tape of the present disclosure is subjected to repeated temperature changes (cooling and heating cycles).

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, even more preferably 1 or less, and particularly preferably 0.

In a plan view of the conductive adhesive layer, the area of the rectangle circumscribing the primary particles A and/or the aggregates A is not particularly limited, but is preferably, for example, in the range of 300 μm ² to 2700 μm ² , more preferably in the range of 300 μm ² to 2400 μm ² , and even more preferably in the range of 300 μm ² to 2100 μm ² .

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

In a plan view of the conductive adhesive layer, the proportion of the primary particles and aggregates of the conductive particles (excluding the primary particles and aggregates with a maximum length of 10 μm or less) present in the region A of the conductive adhesive layer that have a maximum length of less than 50 μm is 85% or more. This allows the tape of the present disclosure to exhibit low initial resistance and good conductivity, and also reduces the size of lifting and peeling caused by the aggregates and primary particles due to cooling and heating cycles at the bonding surface between the conductive adhesive layer and the adherend, thereby suppressing a decrease in conductivity over time.

Of the primary particles and agglomerates of conductive particles, primary particles with a maximum length of less than 50 μm may be referred to as primary particles B, and agglomerates with a maximum length of less than 50 μm may be referred to as agglomerates B. Furthermore, the primary particles B and agglomerates B do not include the primary particles and agglomerates with a maximum length of 10 μm or less.

In particular, the number ratio of the primary particles and aggregates (the number ratio of the primary particles B and the aggregates B) that are present in the region A of the conductive adhesive layer and have a maximum length of less than 50 μm is preferably within the range of 85% to 100%, more preferably within the range of 90% to 100%, and even more preferably within the range of 95% to 100%. By setting the number ratio of the primary particles B and the aggregates B that are present in the region A of the conductive adhesive layer within the above range, the tape of the present disclosure can achieve a high degree of both initial conductivity and conductivity over time.

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 more preferably 100 or less. The number is preferably 17 or more, preferably 20 or more, and more preferably 40 or more. More specifically, the number is preferably 40 to 100, and more preferably 47 to 95, more preferably 50 to 90, and even more preferably 60 to 80.

In addition, the area per one of the primary particles B and the aggregate B in a plan view of the conductive pressure-sensitive adhesive layer may be smaller than the area per one of the primary particles A and the aggregate A, and the size of the area is not particularly limited as long as it is possible to prevent lifting or peeling of the tape and to exhibit good conductivity. In a plan view of the conductive pressure-sensitive adhesive layer, the area of a rectangle circumscribing the primary particles B and/or the aggregate B is not particularly limited, but is preferably, for example, 1 μm ² to 250 μm ² , more preferably in the range of 5 μm ² to 200 μm ² , and even more preferably in the range of 10 μm ² to 150 μm ^2. The method for calculating the area of the rectangle circumscribing the primary particles B and/or the aggregate B is the same as the method for calculating the area of the rectangle circumscribing the primary particles A and/or the aggregate A described above.

In a plan view of the conductive adhesive layer, the proportion of primary particles and aggregates (sometimes referred to as primary particles A' and aggregates A') with 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 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 lift or peeling on the surface of the conductive adhesive layer becomes large, and the resistance value due to thermal cycles is likely to increase.

In a plan view of the conductive adhesive layer, the number ratio 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 number ratio of the primary particles A and the aggregates A and the number ratio of the primary particles B and the aggregates B are within a predetermined range, but is preferably 15% or less, more preferably 10% or less, and even more preferably 5% or less.

In a plan view of the conductive adhesive layer, the proportion of the number of primary particles A and aggregates A of the conductive particles present in one small region a is preferably 5% or less, more preferably 4.5% or less, more preferably 3.5% or less, even more preferably 2.5% or less, and particularly preferably 0%, i.e., no primary particles or aggregates with a maximum length of 60 μm or more. When the proportion of primary particles A and aggregates A in one small region a is within the above range, an increase in resistance value can be suppressed not only in the thickness direction but also in the horizontal direction when the tape of the present disclosure is subjected to repeated temperature changes (cooling and heating cycles).

The number of the primary particles A and the aggregates A present in one small region a is not particularly limited as long as it is possible to set the number of the primary particles A and the aggregates A present in the region A within a preferred range, but 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.

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

The number of the primary particles B and the aggregates B present in one small region a is not particularly limited as long as it is possible to set the number of the primary particles B and the aggregates B present in the region A within a preferred range, but can be, for example, 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.

In one small region a, the percentage of primary particles and aggregates (sometimes referred to as primary particles A' and aggregates A') with a maximum length of 70 μm or more is preferably 1.5% or less, more preferably 1.0% or less, and even more preferably 0%. This is because the size of each lift or peeling point on the surface of the conductive adhesive layer becomes large, making it easier for the resistance value to increase due to thermal cycles.

The maximum length P1 of the primary particles and aggregates of the conductive particles in a planar view of the conductive adhesive layer refers to the maximum value of the distance between any two points on the contour of the shape of the primary particles and aggregates of the conductive particles in a planar view of the conductive adhesive layer (also referred to as the planar view shape of the primary particles and aggregates 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 revo zoom lens (30-2500x)), the conductive adhesive tape is placed on a flat table with the surface of the conductive adhesive layer side (excluding the release liner if the surface has a release liner) facing the lens of the optical microscope, and 10 small areas a of 0.5 mm x 0.5 mm square (0.25 mm ² ) are arbitrarily selected on the surface of the conductive adhesive layer side, and each of the 10 small areas a is photographed at a magnification of 400 times to obtain a photographed image. The black parts in the photographed image represent the primary particles and aggregates of the conductive particles. Using the surveying function of an optical microscope, the longest straight-line distance connecting any two points selected on the outline of the black part of the captured image of each small area a (the outline of the planar shape of the primary particles and agglomerates of conductive particles) is measured and determined as the maximum length P1.

The proportion of primary particles and aggregates in the region A of the conductive adhesive layer and having a maximum length P1 within a predetermined range (for example, maximum length P1 is N1 μm or more, maximum length P1 is less than N2 μm, maximum length P1 is N3 μm or more and less than N4 μm; N1 to N4 are specific values defining the range) is measured by the following method. First, in the same manner as in the measurement method for the "maximum length P1 of primary particles and aggregates of conductive particles", ten small regions a of 0.5 mm × 0.5 mm square (0.25 mm ² ) are selected on the surface on the conductive adhesive layer side, and each of the ten small regions a is photographed at a magnification of 400 times to obtain a photographed image. For each small region a, the number S1 of black portions present in the captured image whose maximum length P1 is within a predetermined range (for example, maximum length P1 is N1 μm or more, maximum length P1 is less than N2 μm, maximum length P1 is N3 μm or more and less than N4 μm), and the total number S2 of black portions present in the captured image (excluding black portions whose maximum length P1 is 10 μm or less) are counted.
The total number S'1 of black portions whose maximum length P1 falls within a specified range and are contained in the above 10 small regions a is defined as the number of primary particles and agglomerates of conductive particles whose maximum length P1 falls within a specified range and are present in region A.
In addition, the total number S'2 of black portions contained in the above 10 small regions a is defined as the total number of primary particles and agglomerates of conductive particles present in region A, and the number ratio in region A is calculated from S'1 and S'2 using the following formula (1).
Proportion of number in region A [%] = (S'1/S'2) x 100 ... formula (1)
The number ratio in the small region a is calculated from the following formula (2).
Number ratio in small region a [%] = (S1/S2) × 100 ... Equation (2)

In addition, in small region a and region A, primary particles and aggregates whose maximum length P1 in a plan view is 10 μm or less are not included in the number.

In a plan view of the conductive adhesive layer, the total number of the 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, even 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 to the above range, the tape of the present disclosure can increase the number of contact points between the conductive adhesive layer and the adherend, thereby exhibiting good conductive performance. In addition, the tape of the present disclosure is less likely to lift or peel off due to thermal cycles.

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 in which the surface of a core particle is coated with a metal (metal-coated particles), carbon fillers, and the like. The conductive particles may be used alone or in combination of two or more types.

The metals constituting the metal particles and the metal coating of the metal-coated particles are not particularly limited, but examples include single metals such as nickel, iron, chromium, cobalt, aluminum, antimony, molybdenum, copper, silver, platinum, and gold, as well as alloys such as solder and stainless steel.

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

The conductive particles are preferably metal particles, since it is easy to achieve both the electrical conductivity and adhesiveness of the conductive adhesive layer. Among these, metal particles made of a metal selected from the group consisting of nickel, copper, silver, and stainless steel are preferred, and nickel particles are even more preferred because of their excellent electrical conductivity.

Nickel powder is preferred as the nickel particles. Nickel powder can be produced by the carbonyl method. There are no particular limitations on the nickel powder produced by the carbonyl method, and it can be appropriately selected depending on the purpose. Examples include NI255T (filament-shaped) manufactured by Fukuda Metal Foil and Powder Co., Ltd., Ni123 (spherical) manufactured by Vale, Ni255 (filament-shaped) manufactured by Vale, and N06 (bead-shaped) manufactured by Jinchuan Group Co., Ltd.

The shape of the conductive particles is not particularly limited, but examples include spherical, spike-like (needle-like surface), flake-like (scale-like), dendritic, fibrous, amorphous (polyhedral), bead-like, and skewer-like shapes. Among these, spherical, bead-like, and skewer-like shapes are preferred from the viewpoint of reducing the resistance value of the conductive adhesive tape.

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 even more preferably in the range of 12 μm to 20 μm. The average particle size (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, even 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 size d50 and/or d90 of the primary particles of the conductive particles within the above range, the size and number ratio of aggregates in the conductive adhesive layer can be adjusted by the method for preparing the conductive adhesive described below, and a conductive adhesive layer with good adhesion and conductivity before and after thermal cycling can be obtained.

The average particle diameters d50 and d90 of the primary particles of the conductive particles refer to the 50% and 90% cumulative values in the particle size distribution, and are values measured by the laser diffraction/scattering method. Measurement devices that can be used include the Nikkiso Microtrac MT3000II and Shimadzu Laser Diffraction Particle Size Distribution Meter SALD-3000. When two or more types of conductive particles are included, the above particle diameters are calculated from the distribution of all the conductive particles mixed together.

Methods for adjusting the particle size of conductive particles include, for example, grinding the conductive particles with a jet mill, or sieving the conductive particles using a sieve.

The ratio of the average particle diameter d50 of the primary particles of the conductive particles to the thickness of the conductive adhesive layer ([average particle diameter 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 even more preferably 70 to 100%. The ratio of the average particle diameter d90 of the primary particles of the conductive particles to the thickness of the conductive adhesive layer ([average particle diameter 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 even more preferably 120 to 200%. By setting the ratios of the average particle diameters d50 and d90 of the primary particles of the conductive particles to the thickness of the conductive adhesive layer within the above ranges, respectively, the conductivity and adhesiveness of the conductive adhesive layer can be achieved at the same time.

The content of the conductive particles in the conductive adhesive layer is not particularly limited as long as both conductivity and adhesiveness are achieved, but 0.1 to 10 parts by mass of conductive particles per 100 parts by mass of adhesive (solid content) is preferably 0.5 to 5 parts by mass, and more preferably 0.8 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 it is possible to ensure the conductivity of the conductive adhesive layer by the agglomerates of the conductive particles. The content of the conductive particles in the conductive adhesive layer refers to the total content of the primary particles and agglomerates in the conductive adhesive layer.

<Adhesive>
The adhesive contained in the conductive adhesive layer may be an adhesive used in a normal adhesive sheet. The adhesive contains a polymer (hereinafter sometimes referred to as "base polymer") that is the main component of the polymer components contained in the adhesive, such as acrylic polymer, rubber polymer (natural rubber, synthetic rubber, a mixture thereof, etc.), polyester polymer, urethane polymer, polyether polymer, silicone polymer, polyamide polymer, fluorine polymer, etc., and specifically includes (meth)acrylic adhesive, urethane adhesive, rubber adhesive, polyester adhesive, silicone adhesive, etc. Among them, (meth)acrylic adhesive is preferred from the viewpoint of adhesion performance and heat resistance.

The following mainly describes (meth)acrylic adhesives, but the conductive adhesive layer in this disclosure is not limited to being made of (meth)acrylic adhesives, and may be made of other adhesives as described above.

The (meth)acrylic adhesive contains a (meth)acrylic copolymer ((meth)acrylic polymer) consisting of (meth)acrylate alone or a copolymer of (meth)acrylate and other monomers as the base polymer. The (meth)acrylic adhesive contains at least a (meth)acrylic copolymer as the base polymer, and may contain a tackifier resin, a crosslinking agent, other additives, etc. as necessary. Note that "(meth)acrylic" collectively refers to "acrylic or methacrylic", and "(meth)acrylate" collectively refers to "acrylate or methacrylate".

The (meth)acrylic copolymer is preferably an acrylic copolymer whose main monomer component is a (meth)acrylic acid ester monomer having an alkyl group with a carbon number of 1 to 18. The alkyl group may be linear or branched. Examples of (meth)acrylic acid ester monomers 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, and n-stearyl (meth)acrylate. 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 preferable to use a (meth)acrylate having an alkyl group with 4 to 9 carbon atoms, and particularly preferable to use 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 within this range, the conductive adhesive layer can exhibit even better adhesive strength and cohesive strength.

The content of the (meth)acrylic acid ester monomer in the (meth)acrylic copolymer is preferably within a range of 80% by mass to 99% by mass, and more preferably within a range of 90% by mass to 98.5% by mass, of the monomer components constituting the (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 strength and cohesive strength.

The monomer components constituting the (meth)acrylic copolymer preferably contain a highly polar vinyl monomer in addition to the (meth)acrylic acid ester monomer. Examples of the highly polar vinyl monomer include a carboxyl group-containing vinyl monomer, a hydroxyl group-containing vinyl monomer, and an amide group-containing vinyl monomer. One or more types of highly polar vinyl monomers can be used. Among them, a carboxyl group-containing vinyl monomer is preferred because it is easy to adjust the adhesiveness of the conductive adhesive layer to a suitable range.

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

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

Examples of hydroxyl group-containing vinyl monomers include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, and 6-hydroxyhexyl (meth)acrylate.

Examples of amide group-containing vinyl monomers include N-vinylpyrrolidone, N-vinylcaprolactam, acryloylmorpholine, acrylamide, and N,N-dimethylacrylamide.

Other highly polar vinyl monomers include, for example, 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.

The total content of the highly polar vinyl monomers in the monomer components constituting the (meth)acrylic copolymer can be 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 even more preferably in the range of 0.5% by mass to 6% by mass. By containing the highly polar vinyl monomers in this range in the monomer components constituting the (meth)acrylic copolymer, it is easy to adjust the adhesiveness of the conductive adhesive layer to a suitable range.

The weight average molecular weight of the (meth)acrylic copolymer is not particularly limited, but from the viewpoint of adhesive performance, it 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.

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 is measured by the GPC method using a GPC device (HLC-8329GPC) manufactured by Tosoh Corporation under the following measurement conditions.
[Measurement conditions]
Sample concentration: 0.5% by mass (tetrahydrofuran solution)
Sample injection volume: 100 μL
Eluent: THF (tetrahydrofuran)
・Flow rate: 1.0mL/min ・Measurement temperature: 40℃
Main column: 2 "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)

The (meth)acrylic copolymer can be obtained by polymerizing the above-mentioned monomers by known methods such as solution polymerization, bulk polymerization, suspension polymerization, and emulsion polymerization. Among these, the solution polymerization method is preferred in terms of production cost and productivity.

The conductive adhesive layer (conductive adhesive) may contain a tackifier resin as necessary. When the conductive adhesive layer contains a tackifier resin, the adhesiveness and surface adhesion strength of the conductive adhesive layer to the adherend can be improved. Examples of tackifier resins include rosin-based tackifier resins, polymerizable rosin-based tackifier resins, polymerizable rosin ester-based tackifier resins, rosin phenol-based tackifier resins, stabilized rosin ester-based tackifier resins, disproportionated rosin ester-based tackifier resins, hydrogenated rosin ester-based tackifier resins, terpene-based tackifier resins, terpene phenol-based tackifier resins, petroleum resin-based tackifier resins, and (meth)acrylate-based tackifier resins. The tackifier resins may be used alone or in combination of two or more.

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

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

The amount of the tackifier resin is preferably 0 parts by weight or more and 65 parts by weight or less per 100 parts by weight of the base polymer contained in the adhesive, and more preferably 5 parts by weight or more and 55 parts by weight or less, in order to further improve the adhesion of the conductive adhesive layer to the adherend.

<Crosslinking Agent>
The conductive adhesive layer (conductive adhesive) may contain a crosslinking agent as necessary. This is because a crosslinking agent 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 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 can be appropriately selected depending on the base polymer contained in the adhesive.

When the base polymer is the (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 (meth)acrylic copolymer as the crosslinking agent, and an isocyanate-based crosslinking agent is more preferable due to its higher reactivity.

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

The content of the crosslinking agent may be any amount that allows the conductive adhesive layer to have the desired gel fraction, and can be set appropriately according to the gel fraction of the conductive adhesive layer. The gel fraction of the conductive adhesive layer is preferably 10% by mass to 70% by mass, more preferably 25% by mass to 65% by mass, even more preferably 35% by mass to 60% by mass, and particularly preferably 40% by mass to 55% by mass. 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 further improves the cohesive force and peel resistance.

The gel fraction of the conductive pressure-sensitive adhesive layer is the insoluble portion when the conductive pressure-sensitive adhesive layer is immersed in toluene for 24 hours, and is calculated by the following formula (3).
Gel fraction (mass%)={(mass of the conductive pressure-sensitive adhesive layer after immersion in toluene)/(mass of the conductive pressure-sensitive 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).
Mass of conductive adhesive layer=(mass of conductive adhesive tape)−(mass of substrate) (4)

The conductive adhesive layer may contain additives as necessary. Examples of the additives include materials commonly used in the field of adhesives, such as leveling agents, crosslinking agents, crosslinking assistants, plasticizers, softeners, fillers, colorants (pigments, dyes, etc.), antistatic agents, antiaging agents, UV absorbers, antioxidants, light stabilizers, etc. The amount of the additives is preferably 1 part by mass or less per 100 parts by mass of the base polymer.

2. Substrate The conductive pressure-sensitive adhesive tape of the present disclosure 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.

The substrate is preferably a substrate having electrical conductivity (conductive substrate). The conductive substrate is made of a conductive material, and examples of the conductive substrate include a metal substrate, a graphite substrate, a conductive resin substrate, a conductive nonwoven fabric, and a conductive woven fabric. Among these, a metal substrate and a conductive nonwoven fabric are preferred from the viewpoint of electrical conductivity.

The metal substrate may be made of a metal or an alloy, and examples of the metal substrate include metal foil and metal film. Among these, metal foil is preferred in terms of electrical conductivity, workability, and cost.

The material of the metal substrate is not particularly limited, and examples include metals such as gold, silver, copper, aluminum, nickel, iron, and tin, as well as alloys of these metals. Among these, aluminum or copper is preferred from the standpoints of electrical conductivity, workability, and cost, and copper is more preferred.

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 that can be used 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 and Powder Co., Ltd. Examples of the rolled copper foil that can be used 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 Corporation.

The metal substrate may have a plating layer on one or both sides. By forming a plating layer on the surface of the metal substrate, it is possible to suppress a decrease in conductivity and poor appearance due to corrosion. Examples of materials for the plating layer include tin plating, silver plating, gold plating, and zinc plating.

The metal substrate may be subjected to a coupling treatment using a silane coupling agent or a chromate treatment on one or both sides, or a rust prevention treatment using benzotriazoles or the like.

There are no particular limitations on the conductive nonwoven fabric, and it can be selected appropriately depending on the purpose. For example, a metal-plated nonwoven fabric in which a nonwoven fabric is plated with a metal can be used.

The nonwoven fabric may be made of any material that can be metal plated, and may be a general-purpose resin nonwoven fabric or glass nonwoven fabric. Specific examples include polyester nonwoven fabric.

The metal plating applied to the nonwoven fabric may be electrolytic plating or electroless plating. Examples of metals that form the metal plating include copper, nickel, silver, platinum, and aluminum. Among these, copper or nickel is preferred from the standpoint of electrical conductivity and cost.

The thickness of the substrate is not particularly limited as long as it can exhibit conductivity, and can be set depending on the type of substrate. For example, the thickness can be 1 μm to 40 μm, and is preferably 3 μm to 35 μm, more preferably 5 μm to 30 μm, and even more preferably 5 μm to 25 μm. More specifically, when the substrate is a metal substrate, the thickness of the metal substrate is not particularly limited and can be appropriately selected depending on the purpose, and is preferably 1 μm to 40 μm, more preferably 3 μm to 35 μm, and even more preferably 5 μm to 25 μm. In addition, when the substrate is a conductive nonwoven fabric, the thickness of the conductive nonwoven fabric is not particularly limited and can be appropriately selected depending on the purpose, and is preferably 3 μm to 50 μm, more preferably 5 μm to 30 μm, and even more preferably 8 μm to 25 μm. By setting the thickness of the substrate within the above range, a conductive adhesive tape that is thin and has excellent conductivity and adhesiveness can be obtained.

The thickness of the substrate is measured at five locations at 100 mm intervals along the length using a TH-102 (thickness meter, manufactured by Tester Sangyo Co., Ltd.), and the average value of the thicknesses at these five locations is taken.

The thermal conductivity of the above substrate is preferably 90 W/m·K or more, and more preferably 100 W/m·K or more, from the viewpoint of further improving electrical properties.

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, but 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 in which paper and resin film are laminated, resin films and papers whose surfaces are sealed with clay or polyvinyl alcohol, and resin films and papers whose one or both sides are sealed and released. 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, and molybdenum sulfide.

When the conductive adhesive tape of the present disclosure is a substrate-less tape described below, the release liner may be provided on one side or both sides of the conductive adhesive layer. When the conductive adhesive tape of the present disclosure is a substrate-attached tape described below, the release liner may be provided on the surface of the conductive adhesive layer on one side of the substrate, or on each of the surfaces of the conductive adhesive layer on both sides of the substrate.

4. Conductive Adhesive Tape The conductive adhesive tape of the present disclosure 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. The conductive adhesive tape of the present disclosure may be a substrate-less tape made of the conductive adhesive layer of the present disclosure, or a substrate-attached tape having the conductive adhesive layer of the present disclosure on at least one side of the substrate.

When the conductive adhesive tape of the present disclosure is a substrate-less tape, the two opposing surfaces of the conductive adhesive layer constituting the tape can each be a double-sided adhesive that is the adhesive surface of the conductive adhesive tape.

In addition, 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 the conductive adhesive layer of the present disclosure on one side of the substrate. When the tape with the above-mentioned substrate is a single-sided tape, the surface of the conductive adhesive layer can be the adhesive surface of the conductive adhesive tape.

In addition, 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. In this case, the adhesive layer on at least one side of the substrate may be the conductive adhesive layer of the present disclosure, and the adhesive layers on both sides of the substrate may each be the conductive adhesive layer of the present disclosure. When the conductive adhesive tape of the present disclosure is a double-sided adhesive tape with a substrate, the surfaces of the adhesive layers on both sides of the substrate may be the adhesive surfaces of the conductive adhesive tape.

The conductive adhesive tape of the present disclosure preferably has an initial resistance value Rz in the thickness direction (Z direction) of 1 Ω or less, more preferably 0.5 Ω or less, and more preferably 0.2 Ω or less. The conductive adhesive tape of the present disclosure also preferably has a resistance value change rate (%) in the thickness direction before and after a thermal cycle test of 200% or less. In particular, the resistance value change rate (%) is preferably 180% or less, more preferably 150% or less, and even more preferably 140% or less. Since the resistance value change rate in the thickness direction of the tape of the present disclosure before and after a thermal cycle test is within the above range, the tape of the present disclosure has good electrical conductivity over time, even in an environment where it is subjected to repeated temperature changes. In other words, this suggests that the floating or peeling of the conductive adhesive tape from the adherend due to thermal cycles is suppressed.

The rate of change in 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 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)

The conductive adhesive tape of the present disclosure preferably has an initial horizontal (XY) resistance Rxy of 2Ω or less, more preferably 1.5Ω or less, and more preferably 0.8Ω or less. The conductive adhesive tape of the present disclosure also preferably has a horizontal resistance change rate (%) of 300% or less before and after a thermal cycle test, more preferably 200% or less, and even more preferably 100% or less. By having the horizontal resistance change rate of the tape of the present disclosure before and after a thermal cycle test within the above range, the tape of the present disclosure can suppress an increase in resistivity in the thickness direction as well as in the horizontal direction in an environment where it is subjected to repeated temperature changes, and can exhibit good electrical conductivity over time in the thickness direction and horizontal directions.

The rate of change in horizontal resistance value of the conductive adhesive tape before and after the thermal cycle test can be calculated by the following formula (6).
Rate of change in horizontal resistance value of conductive adhesive tape before and after thermal cycle test (%)=(horizontal resistance value of conductive adhesive tape after thermal cycle test R′xy (Ω)/initial horizontal resistance value of conductive adhesive tape Rxy (Ω))×100 (6)

The initial resistance value of the conductive adhesive tape in the thickness direction and horizontal direction, as well as the resistance value in the thickness direction and horizontal direction after the thermal cycle test, are measured using the method described in the examples below.

5. Method for preparing conductive adhesive The method for preparing a conductive adhesive of the present disclosure is a method for dispersing conductive particles in an adhesive to prepare a mixture, 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, so that the size of the conductive particles in the conductive adhesive is uniform, and the size of the conductive particle aggregates can be controlled when forming a conductive adhesive layer.

The conductive particles can be dispersed in the adhesive by any known method, such as dispersing the adhesive, conductive particles, solvent, etc., using a dispersion mixer. Commercially available dispersion mixers include dissolvers, butterfly mixers, BDM twin-shaft mixers, and planetary mixers. Of these, dissolvers or butterfly mixers are preferred, as they can apply a moderate shear that causes little thickening of the adhesive during stirring.

The dispersion conditions for dispersing the conductive particles in the adhesive are preferably such that the primary particles of the conductive particles are sufficiently dispersed in the mixture before the filtration process, and the size of the aggregates formed by the primary particles is within the 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 within the range of 500 r/min to 3000 r/min, more preferably within the range of 700 r/min to 2500 r/min, and even more preferably within the range of 800 r/min to 2000 r/min. The stirring time is not particularly limited and can be set appropriately, but can be, for example, within the range of 5 minutes to 120 minutes, and more preferably within the range of 30 minutes to 60 minutes. By setting the stirring speed and stirring time under the above conditions, the conductive particles can be stirred at high speed in the adhesive, and the primary particles of the conductive particles can be sufficiently dispersed in the mixture before the filtration process. As a result, 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.

Methods for filtering the mixture of conductive particles dispersed in the adhesive include, for example, gravity filtration, which is filtering through a mesh; pressure filtration, which is filtering through a filter while applying pressure; sedimentation by centrifugation or the like; and cooling precipitation, and these may be used in combination. Among these, filtering through a mesh and/or filter is preferred because it is simple. Filtering may be performed once or may be repeated two or more times.

The material of the mesh and filter is not particularly limited, and can be selected from general-purpose materials used for filtration, such as metal (wire mesh), glass, resin, etc.

The number of meshes depends on the size of the opening, but is preferably 100 or more, more preferably 150 or more, and more preferably 200 or more. The number of meshes is preferably 400 or less, more preferably 300 or less, and more preferably 250 or less. In particular, the desired conductive adhesive layer can be formed, and the productivity of the filtration process is increased, so the number of meshes is preferably 100 or more and less than 300, and more preferably 150 or more and 250 or less. The opening of the mesh may be larger than the average particle diameter d50 of the primary particles of the conductive particles, and can be appropriately selected according to the average particle diameter of the primary particles of the conductive particles, but is preferably 30 μm or more, 45 μm or more, or 60 μm or more. The opening of the mesh is preferably 150 μm or less, 110 μm or less, or 80 μm or less.

The pore size of the filter can be appropriately selected depending on the particle size of the primary particles of the conductive particles, but is preferably within the range of 90 μm to 200 μm, more preferably within the range of 100 μm to 150 μm, and even more preferably within the range of 100 μm to 120 μm.

In the present disclosure, it is preferable to filter a mixture in which conductive particles having an average primary particle diameter d50 in the range of 5 μm to 30 μm are dispersed in an adhesive with a mesh having the above-mentioned mesh number and mesh opening and/or a filter having the above-mentioned pore size. In particular, it is preferable to filter a mixture in which conductive particles having an average primary particle diameter d50 in the range of 5 μm to 30 μm are dispersed in an adhesive with a mesh having a mesh number of less than 300, and when the mesh number is 200 or less, it is more preferable to further filter the mixture through a filter having a pore size in the range of 90 μm to 200 μm after filtering through the mesh.

6. Manufacturing Method of the Conductive Adhesive Tape The conductive adhesive tape of the present disclosure can be manufactured using a known method, for example, a method 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 is dried to form a conductive adhesive layer.
When the conductive adhesive tape of the present disclosure has a substrate, examples of the manufacturing method include a method in which the conductive adhesive layer formed on a release liner is attached to one or both sides of the substrate, and a method in which the conductive adhesive is applied to one or both sides of the substrate and the coating is dried to form a conductive adhesive layer.

A known coating method can be used to apply the conductive adhesive. Examples of the coating method include a gravure roll coater, reverse roll coater, kiss roll coater, lip coater, dip roll coater, bar coater, knife coater, spray coater, comma coater, direct coater, and slot die coater.

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

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

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 by other electric or electronic devices, and for fixing to earth to prevent static electricity. In particular, it is suitable for use in portable electronic devices that are becoming thinner and have strict volume restrictions within the housing, and is particularly suitable for use by attaching it to built-in components of small electronic terminals.

In this specification, the expression "primary particles and agglomerates of the conductive particles present in the region A of the conductive adhesive layer (excluding the primary particles and agglomerates having a maximum length of 10 μm or less)" (and similar expressions) means that the primary particles and agglomerates of the conductive particles present in the region A of the conductive adhesive layer may include those having a maximum length of 10 μm or less, but when calculating the respective number proportions of primary particles and agglomerates of each size, the number of primary particles and agglomerates having a maximum length of 10 μm or less is not added to the total number of primary particles and agglomerates of the conductive particles, i.e., they are excluded.
Furthermore, the present disclosure is not limited to the above-described embodiments. The above-described embodiments are merely examples, and anything that has substantially the same configuration as the technical idea described in the claims of the present disclosure and exhibits similar effects is included in the technical scope of the present disclosure.

The following examples and comparative examples will further explain this disclosure.

[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 dissolved in 100 parts by mass of ethyl acetate in the following proportions, and after nitrogen substitution, the mixture was polymerized at 80°C for 12 hours to obtain an ethyl acetate solution of 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'-Azobisisobutylnitrile (polymerization initiator): 0.1 parts by mass

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: 1.0mL/min ・Measurement temperature: 40℃
Main column: TSKgel GMHHR-H (20) x 2 Guard column: TSKgel HXL-H
Detector: Differential refractometer Standard polystyrene molecular weight: 10,000 to 20,000,000 (manufactured by Tosoh Corporation)

(Preparation Example of Mixture of Adhesive 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 glycerin ester (SUPER ESTER A-100, manufactured by Arakawa Chemical Industries, Ltd.) were mixed and stirred, and then ethyl acetate was added thereto to obtain an acrylic pressure-sensitive adhesive having an acrylic polymer solid content of 40% by mass.

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, bead-shaped, 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 in a dispersion stirrer for 10 minutes to obtain a mixture.

(Preparation Example of Conductive Adhesive A)
The mixture was stirred at high speed using a disper mixer at a speed of 1200 rpm for a stirring time of 60 minutes, and then filtered by gravity through a 250 mesh wire screen to obtain a conductive adhesive A.

(Preparation Example of Conductive Adhesive B)
The mixture was stirred at high speed using a disper mixer at a speed of 1200 rpm for a stirring time of 60 minutes, and then filtered by gravity through a 300 mesh wire screen to obtain a conductive adhesive B.

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

(Preparation Example of Conductive Adhesive D)
The above mixture was stirred at high speed using a disper mixer at a speed of 1200 r/min for a stirring time of 60 minutes, then filtered by gravity through a 200 mesh wire screen, and further filtered under pressure through a metal filter with 125 μm openings to obtain conductive adhesive D.

(Preparation Example of Conductive Adhesive E)
The mixture was stirred at high speed using a disper mixer at a speed of 1200 rpm for a stirring time of 60 minutes, and then a conductive adhesive E was obtained without performing a filtration treatment.

(Preparation Example of Conductive Adhesive F)
The mixture was stirred at a low speed of 400 rpm for 60 minutes using a propeller stirrer, and then a conductive adhesive F was obtained without filtration.

(Preparation Example of Conductive Adhesive G)
The mixture was stirred using a disper mixer at a speed of 1200 rpm for 60 minutes, and then filtered by gravity through a 200 mesh wire screen to obtain a conductive adhesive G.

The conductive adhesives A to G are shown in the table below.

Example 1
The conductive adhesive A was applied to a release film A (PET38x1, A3, manufactured by Nippa Corporation) using a comma coater so that the average thickness after drying was 5 μm, and the coated film was dried in a dryer at 80° C. for 2 minutes to form a conductive adhesive layer. Next, the conductive adhesive layer thus formed was attached to one side of a copper foil A (average thickness 12 μm, surface resistance value 0.003 Ω/□) having chrome plating layers on both sides, and then the conductive adhesive tape A was produced by applying pressure of 100 N/cm at 40° C. using a laminator and curing the laminate at 40° C. for 48 hours.

Example 2
A conductive adhesive tape B was produced in the same manner as in Example 1, except that the conductive adhesive layer was formed using the conductive adhesive B instead of the conductive adhesive A.

Example 3
A conductive adhesive tape C was produced in the same manner as in Example 1, except that the conductive adhesive layer was formed using the conductive adhesive C instead of the conductive adhesive A.

Example 4
A conductive adhesive tape D was produced in the same manner as in Example 1, except that the conductive adhesive layer was formed using conductive adhesive D instead of conductive adhesive A.

(Comparative Example 1)
A conductive adhesive tape E was produced in the same manner as in Example 1, except that the conductive adhesive layer was formed using conductive adhesive E instead of conductive adhesive A.

(Comparative Example 2)
A conductive adhesive tape F was produced in the same manner as in Example 1, except that the conductive adhesive layer was formed using conductive adhesive F instead of conductive adhesive A.

(Comparative Example 3)
A conductive adhesive tape G was produced in the same manner as in Example 1, except that the conductive adhesive layer was formed using conductive adhesive G instead of conductive adhesive A.

[evaluation]
The conductive adhesive tapes obtained in the examples and comparative examples were evaluated as follows.

<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 in a plan view of the conductive adhesive layer of the obtained conductive adhesive tape, and the number and number ratio of the primary particles and aggregates whose maximum length P1 in the above-mentioned region A of the conductive adhesive layer is within a predetermined range were measured by the method explained in the above item "(1) Conductive particles" in the item "1. Conductive adhesive layer" in the item "I. Conductive adhesive tape". Note that primary particles and aggregates whose maximum length P1 in a plan view is 10 μm or less were not included in the number.

<Initial resistance value>
<<Resistance value in the thickness direction (conductivity in the thickness direction)>>
A copper foil (5 mm wide x 5 mm wide) was attached to the conductive adhesive layer of a conductive adhesive tape cut to a size of 100 mm wide x 50 mm wide. In an environment of 23°C and 50% RH, the copper foil and the conductive adhesive tape were connected in a state where a surface pressure of 1 N was applied from the conductive adhesive tape attachment position of the copper foil, and a current of 100 μA was passed using a milliohmmeter (manufactured by NF Corporation), and the resistance value Rz (Ω) in the thickness direction was measured (attachment method).

<<Horizontal resistance value (surface direction conductivity)>>
In the longitudinal direction of the conductive adhesive tape cut to a size of 100 mm wide (long side) x 50 mm wide (short side), one end of two copper foils (5 mm wide long strips) was attached to 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 wide x 5 mm wide, and the other ends of the two copper foils (ends on the side not bonded to the conductive adhesive layer) were connected to the positive and negative electrodes of a milliohmmeter (manufactured by NF Corporation). In an environment of 23°C and 50% RH, the copper foil and the conductive adhesive tape were connected without applying surface pressure from the bonding position of the copper foil and the conductive adhesive tape, and a milliohmmeter was used to pass a current of 100 μA and measure the horizontal resistance value Rxy (Ω).

<Resistance value after thermal cycle test>
The conductive adhesive tape was cut into a size of 100 mm wide x 50 mm wide, and a copper foil (5 mm wide x 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 (product name "SH-242", manufactured by Espec Corporation) and subjected to a thermal cycle test under the following test conditions.
Relative humidity inside the tester: not controlled. Heat cycle test conditions: heating rate 2°C/min, cooling rate 2°C/min, -35°C (held for 30 minutes) → 85°C (held for 30 minutes) → -35°C was repeated 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 in the same manner as in the measurement of the initial resistivity.
In addition, the resistance 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 according to the following formulas (7) and (8).
Rate of change in 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)
Rate of change in horizontal resistance value of conductive adhesive tape before and after thermal cycle test (%)=(horizontal resistance value of conductive adhesive tape after thermal cycle test R′xy (Ω)/initial horizontal resistance value of conductive adhesive tape Rxy (Ω))×100 (8)

<Adhesive strength>
The conductive adhesive tape was cut to a width of 25 mm, and the conductive adhesive layer side of the conductive adhesive tape was attached to a stainless steel plate (SUS plate, stainless steel plate that was hairline polished using No. 360 waterproof abrasive paper) under conditions of an environmental temperature of 23°C and a humidity of 50% RH, and the upper surface was pressed against the conductive adhesive tape and the stainless steel plate by rolling it back and forth once with a 2 kg roller, and then left at room temperature for 1 hour to prepare a test piece. The test piece was peeled off at a speed of 300 mm/min using a Tensilon universal tensile tester (Tensilon RTA-100, manufactured by A&D Co., Ltd.) under the same temperature and humidity conditions as above, to measure the 180° peel adhesion strength.

<Holding power>
The conductive adhesive tape was cut to a width of 25 mm and applied to the surface of a clean, smooth stainless steel plate so that the applied area was 25 mm x 25 mm. The upper surface of the tape was pressed by rolling it back and forth once using a 2 kg roller, and the tape was left for 1 hour under conditions of 23°C and 50% RH in accordance with JIS Z-0237. After that, 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.

<Appearance>
A copper foil was attached onto the conductive adhesive layer of the conductive adhesive tape to obtain a test piece. The test piece was visually inspected for the presence of air bubbles and was judged according to the following criteria.
(standard)
〇: No visible air bubbles 〇△: A small amount of air bubbles can be seen (the outline of the air bubbles is unclear)
△: The outline of the air bubbles is clearly visible. ×: The outline of the air bubbles is clearly visible, and air bubbles are visible throughout the entire area.

The evaluation results are shown in the table.

Compared to the conductive adhesive tape of the comparative example, the conductive adhesive tape of the embodiment had a smaller resistance change rate [%] before and after the thermal cycle test, suggesting that the increase in resistance in the thickness direction caused by repeated temperature changes can be suppressed and that the tape has excellent conductivity.

The conductive adhesive tape of the present disclosure can be suitably used for joining parts that require electrical conductivity. For example, it is useful for shielding electromagnetic waves used in electrical or electronic devices, shielding harmful spatial electromagnetic waves generated by other electrical or electronic devices, and fixing to earth to prevent static electricity. In particular, it is suitable for use in portable electronic devices that are becoming thinner and have strict volume restrictions within the housing, and is particularly suitable for use by attaching it to built-in components of small electronic terminals.

Claims (12)

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,
Among the primary particles and agglomerates of the conductive particles present within an area A of 2.5 ^mm2 in a plan view of the conductive pressure-sensitive adhesive layer, 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. The conductive adhesive tape according to claim 1, wherein the thickness of the conductive adhesive layer is 10 μm or less. The conductive adhesive tape according to claim 1 or 2, wherein the total amount of the conductive particles is within the range of 0.1 parts by mass to 10 parts by mass per 100 parts by mass of the adhesive. The conductive adhesive tape according to claim 1 or 2, wherein the total number of primary particles and agglomerates of the conductive particles present in the region A in a plan 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. The conductive adhesive tape according to claim 1 or 2, wherein the average particle diameter (d50) of the primary particles is within the range of 5 μm to 30 μm. The conductive adhesive tape according to claim 1 or 2, wherein the aggregate is formed by agglomeration of the primary particles having an average particle diameter (d50) in the range of 5 μm to 30 μm. The conductive adhesive tape according to claim 1 or 2, wherein the conductive particles are metal particles. The conductive adhesive tape according to claim 1 or 2, wherein the conductive particles are nickel powder. The conductive adhesive tape according to claim 1 or 2, which has the conductive adhesive layer on one or both sides of the substrate. The conductive adhesive tape according to claim 9, wherein the substrate is a metal foil. 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.
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.