Conductive additive, conductive paste, conductive thin film coating member, and method for manufacturing a conductive thin film coating member

Abstract

The present invention provides a conductive additive containing copper particles in which oxidation of the copper particles is suppressed, and a conductive paste containing such a conductive additive. Furthermore, the present invention provides a conductive thin film coating member composed of such a conductive paste and a method for manufacturing the same. [Solution] A conductive additive 1 comprises metal particles 10 whose surface is composed of copper or a copper alloy, a first surface treatment agent 11 composed of a molecule having a predetermined structure or a copper complex of said molecule, and a second surface treatment agent 12 having a predetermined structure, wherein the metal particles 10 are surface-treated with the first surface treatment agent 11 and then surface-treated with the second surface treatment agent 12.

Description

Technical Field

[0001] The present disclosure relates to a conductive additive, a conductive paste, a conductive thin film coating member, and a method for manufacturing a conductive thin film coating member.

Background Art

[0002] In order to utilize the properties of organic polymers such as thermoplasticity and flexibility and the conductivity of metal materials in a single material, a conductive additive composed of metal particles may be added to an organic polymer. For example, a conductive paste is used to form a conductive region such as a pattern circuit on the surface of an insulating substrate. By using a printing method such as screen printing to place the conductive paste at a predetermined position on the surface of the substrate and forming a thin film, a conductive thin film can be easily formed. Generally, as described in Patent Document 1 and the like, a conductive paste is configured as a dispersion of fine particles of a metal such as silver in a binder resin.

[0003] Silver has generally been used as the metal particles constituting the conductive paste, but copper, which is inexpensive and less likely to cause migration, can be cited as a metal to replace silver. However, copper is a metal that easily undergoes oxidation, and when copper particles are added to the conductive paste, copper oxide, which is an insulator, is formed on the surface. If the oxidation of the copper particles progresses while the prepared conductive paste is being stored, there may be a case where sufficient conductivity cannot be ensured in the conductive thin film formed using the conductive paste.

[0004] As one method of preventing the oxidation of copper particles, as in Patent Documents 2 and 3, it has been proposed to use a phenolic resin as the binder resin constituting the conductive paste. Since the phenolic resin has reducing properties, it exhibits a function of suppressing the oxidation of copper particles in the conductive paste.

Prior Art Documents

Patent Documents

[0005] [Patent Document 1] Japanese Patent Publication No. 2014-236103 [Patent Document 2] Japanese Patent Application Publication No. 11-224532 [Patent Document 3] Japanese Patent Publication No. 2018-92864 [Overview of the project] [Problems that the invention aims to solve]

[0006] As described above, when copper particles are used as a conductive additive in conductive pastes, suppressing the oxidation of the copper particle surface is important to ensure high conductivity. However, if the oxidation of copper particles is suppressed by a substance independent of the copper particles, such as the phenolic resin described in Patent Documents 2 and 3, then the substances that can be used together with the copper particles become restricted. For example, if a phenolic resin must be used as the binder resin in a conductive paste, the flexibility of the conductive thin film formed from the conductive paste will be reduced because phenolic resin is a hard resin. This makes it difficult to use conductive pastes in applications requiring flexibility, such as forming patterned circuits on flexible substrates. From the perspective of avoiding the restriction of usable substances, as seen in the phenolic resins described in Patent Documents 2 and 3, it is desirable to be able to suppress the oxidation of copper particles without relying on the effect of a substance independent of the copper particles.

[0007] Therefore, the objective is to provide a conductive additive that contains copper particles while suppressing the oxidation of the copper particles, a conductive paste containing such a conductive additive, and further, a conductive thin film coating member composed of such a conductive paste and a method for manufacturing the same. [Means for solving the problem]

[0008] The conductive additive of this disclosure comprises metal particles whose surface is composed of copper or a copper alloy, a first surface treatment agent composed of a molecule having a structure represented by the following formula (1), or a copper complex of said molecule, and a second surface treatment agent having a structure represented by the following formula (2), wherein the metal particles are surface-treated with the first surface treatment agent and then surface-treated with the second surface treatment agent. [ka] Here, R1 and R2 are independently hydrogen or a hydrocarbon group having 3 or fewer carbon atoms, and this also includes cases where a hydroxyl group is bonded to the hydrocarbon group, and where R1 and R2 are linked to each other by a ring structure. R3 is a hydrocarbon group having 3 or fewer carbon atoms. R4 is hydrogen or a hydrocarbon group having 12 or fewer carbon atoms, and this also includes cases where an amino group or a hydroxyl group is bonded to the hydrocarbon group. [ka] Here, R5 and R6 are independently hydrogen or a hydrocarbon group having 3 or fewer carbon atoms. R7 is a hydrocarbon group having 8 to 30 carbon atoms, including cases where it has a branched portion.

[0009] The conductive paste of this disclosure comprises the conductive additive and a binder resin, wherein the conductive additive is dispersed in the binder resin.

[0010] The conductive thin film coating member of this disclosure comprises a substrate having a surface made of an insulator, and a conductive thin film made of the conductive paste and disposed on the surface of the substrate.

[0011] The method for manufacturing a conductive thin film coated member according to the present disclosure includes the step of placing the conductive paste on the surface of the substrate and then heating it at a temperature of 200°C or lower to manufacture the conductive thin film coated member. [Effects of the Invention]

[0012] The conductive additive and conductive paste according to this disclosure are conductive additives in which oxidation of copper particles is suppressed, and conductive pastes containing such conductive additives. Furthermore, the conductive thin film coated member and method for manufacturing the conductive thin film coated member according to this disclosure are conductive thin film coated members composed of such conductive paste and a method for manufacturing the same. [Brief explanation of the drawing]

[0013] [Figure 1] Figure 1 is a schematic cross-sectional view showing the structure of a conductive additive according to one embodiment of the present disclosure. [Figure 2] Figure 2 is a schematic cross-sectional view showing the structure of a conductive thin-film coated member according to one embodiment of the present disclosure. [Modes for carrying out the invention]

[0014] [Description of Embodiments in this Disclosure] First, embodiments of this disclosure will be listed and described.

[0015] [1] The conductive additive according to the present disclosure comprises metal particles whose surface is at least composed of copper or a copper alloy, a first surface treatment agent composed of a molecule having the structure represented by formula (1) above, or a copper complex of said molecule, and a second surface treatment agent having the structure represented by formula (2) above, wherein the metal particles are surface-treated with the first surface treatment agent and then surface-treated with the second surface treatment agent.

[0016] As described above, the conductive additive according to the present disclosure is such that the surface of the metal particles is surface-treated with a first surface treatment agent containing the structure of formula (1) and further surface-treated with a second surface treatment agent having the structure of formula (2). The first surface treatment agent forms a coordination bond with the copper atoms on the surface of the metal particles. Further, the second surface treatment agent forms an organic layer containing a long-chain hydrocarbon group on the surface of the metal particles surface-treated with the first surface treatment agent. Due to the effects of these first and second surface treatment agents, the metal particles are effectively protected from contact with surrounding oxidizing substances and the formation of oxides and their precursors on the surface. Therefore, the conductive additive according to the present disclosure has a suppressed oxidation state while containing at least copper on the surface, which is inherently prone to oxidation. By suppressing the oxidation of the metal particles, the conductive additive can be added to a matrix material such as a binder resin and suitably used for applications requiring conductivity, such as conductive pastes, to exhibit high conductivity. The imparting of the oxidation suppression ability to the metal particles is achieved not by substances independent of the metal particles, such as the matrix material, separately added antioxidants, reducing agents, etc., but by substances used for the surface treatment of the metal particles and bonded to the surface of the metal particles. Therefore, the necessity for suppressing the oxidation of the metal particles does not limit the type of matrix material and other substances used together with the conductive additive and the method of using the conductive additive.

[0017] [2] In the aspect of [1] above, it is preferable that the average particle diameter of the metal particles is 0.1 μm or more and 30 μm or less. Then, when the conductive additive is dispersed and used in a matrix material such as a binder resin, it is possible to suppress a decrease in conductivity due to the contact resistance between the metal particles. Also, the uniformity of the material, such as the smoothness of the surface, can be maintained at a high level.

[0018] [3] In the aspect of [1] or [2] above, it is preferable that the surface of the metal particles is covered with a layer of the first surface treatment agent. Then, the effect of suppressing the oxidation of the metal particles by the first surface treatment agent can be obtained particularly highly.

[0019] [4] In the embodiment described in [3] above, it is preferable that the surface of the metal particles coated with the layer of the first surface treatment agent is further coated with the layer of the second surface treatment agent. In this case, the effect of suppressing oxidation of the metal particles by the second surface treatment agent is particularly high. Alternatively, at least a portion of the second surface treatment agent may directly coat the surface of the metal particles.

[0020] [5] The conductive paste according to the present disclosure comprises a conductive additive from any of [1] to [4] above and a binder resin, wherein the conductive additive is dispersed in the binder resin. By adding the conductive additive of the present disclosure having the above configuration to a conductive paste, a conductive paste can be obtained that suppresses oxidation of metal particles, even when using metal particles containing copper which are inherently prone to oxidation, thereby maintaining high conductivity over a long period of time. There is no need to limit the type of binder resin constituting the conductive paste or to add large amounts of additive components such as antioxidants or reducing agents in order to suppress oxidation of metal particles.

[0021] [6] In the embodiment of [5] above, the glass transition temperature of the binder resin is preferably 140°C or lower. This results in the binder resin having high flexibility, and the conductive thin film composed of the conductive paste also exhibits high flexibility. Therefore, the conductive paste can be suitably used in applications requiring flexibility, such as forming patterned circuits on a flexible substrate.

[0022] [7] In the embodiments of [5] or [6] above, the conductive paste may further contain an organic solvent. This increases the fluidity of the conductive paste, making it easier to arrange the conductive paste by printing or other methods.

[0023] [8] In any one embodiment of [5] to [7] above, the content of the conductive additive is preferably 50% by mass or more and 95% by mass or less in proportion to the metal particles in the entire conductive paste. This allows for high conductivity to be imparted to the conductive paste and for the properties of the binder resin, such as flexibility, to be effectively utilized.

[0024] [9] In any one embodiment of [5] to [8] above, the content of the binder resin is preferably 5% by mass or more and 30% by mass or less of the total conductive paste. This effectively increases the fluidity of the conductive paste and makes it easier to ensure high conductivity through contact between the conductive additive particles.

[0025]

[10] The conductive thin film coating member according to the present disclosure comprises a substrate having a surface made of an insulator, and a conductive thin film made of any of the conductive pastes described in [5] to [9] above, disposed on the surface of the substrate. By forming a conductive thin film, such as a pattern circuit, using the conductive paste, a conductive region can be provided at a predetermined location on the surface of the insulating substrate. By using metal particles that contain copper on at least the surface as constituting the conductive paste, migration in the conductive thin film is less likely to occur. Furthermore, since the metal particles are surface-treated with the first surface treatment agent and the second surface treatment agent, the decrease in conductivity due to oxidation, which is a concern with copper-containing metal particles, is less likely to occur, and a conductive thin film with high conductivity can be formed even when using conductive paste that has been stored for a long period of time.

[0026]

[11] In the embodiment of

[10] above, the conductive thin film coated member may constitute an in-vehicle component. In in-vehicle components, components equipped with a conductive thin film formed using a conductive paste are frequently used as control circuits for various devices. These components can be suitably configured as the conductive thin film coated member according to the embodiment of the present disclosure.

[0027]

[12] The method for manufacturing a conductive thin film coated member according to the present disclosure includes the step of placing the conductive paste on the surface of the substrate and then heating it at a temperature of 200°C or lower to manufacture the conductive thin film coated member according to

[10] or

[11] . When manufacturing a conductive thin film coated member, a stable conductive thin film can be formed by placing the conductive paste at predetermined locations, such as pattern circuits, using a printing method or the like, and then removing volatile components such as solvents by heating. In this case, by performing the heating at a temperature of 200°C or lower, it is possible to suppress the decomposition and alteration of the binder resin during the heating process, as well as the decomposition, alteration, and change of state of the first surface treatment agent and the second surface treatment agent present on the surface of the copper particles.

[0028] [Details of the embodiments of this disclosure] The conductive additive, conductive paste, conductive thin film coating member, and method for manufacturing the conductive thin film coating member according to the embodiments of this disclosure will be described in detail below. An example of a material containing the conductive additive according to the embodiments of this disclosure is the conductive paste according to the embodiments of this disclosure. Furthermore, the conductive thin film coating member according to the embodiments of this disclosure can be manufactured using this conductive paste.

[0029] <Conductive additives> First, a conductive additive according to one embodiment of this disclosure will be described. An example of the structure of the conductive additive 1 according to this embodiment is schematically shown in the cross-sectional view of Figure 1.

[0030] The conductive additive 1 contains metal particles 10, a first surface treatment agent, and a second surface treatment agent. The conductive additive 1 is formed by first surface-treating the metal particles 10 with the first surface treatment agent, and then surface-treating them with the second surface treatment agent. In the embodiment shown in Figure 1, the first surface treatment agent coats the surface of the metal particles 10 to form a first surface treatment layer 11. Furthermore, the second surface treatment agent coats the surface of the first surface treatment layer 11 to form a second surface treatment layer 12. The molecular structures of the first and second surface treatment agents will be shown later, but this also includes cases where the carboxyl groups and / or amino groups contained within the molecules are in anionic and cationic forms, respectively, during surface treatment.

[0031] (1) Metal particles Metal particles are metal particles whose surface is composed of copper or a copper alloy. Preferably, at least the surface is composed of copper. It is also preferable that the entire metal particle is composed of copper or a copper alloy, but it may also be a core-shell particle in which a shell made of copper or a copper alloy is formed on the outer circumference of a core made of a metal other than copper or a copper alloy. These metal particles having various compositions will be collectively referred to as copper particles below.

[0032] In materials such as conductive pastes, silver particles have generally been used as metal particles to impart conductivity. However, by using copper particles as metal particles, material costs can be reduced compared to using silver particles. Furthermore, when forming fine structures such as fine pattern circuits with conductive pastes using silver particles, migration, or short circuits between parts of the pattern due to ion deposition, is likely to occur. However, by using copper particles, the occurrence of migration can be suppressed.

[0033] Metal particles can take on various shapes, such as spherical, plate-shaped, dendritic, rod-shaped, or fibrous. In particular, when a conductive additive is used in a conductive paste, it is preferable to use plate-shaped metal particles because, when a conductive thin film is formed from the conductive paste, curing shrinkage in the planar direction of the film and the resulting deformation of the thin film are suppressed, and high adhesion to the substrate can be maintained. Metal particles may be solid, hollow, or porous, but solid is preferred from the viewpoint of improving conductivity.

[0034] The particle size of the metal particles is preferably 0.1 μm or more and 30 μm or less, with an average particle size D50. If the metal particles have an anisotropic shape, such as a plate, the average particle size may be defined as the average value of the area circle equivalent diameter in the observation image using an electron microscope or the like. If the average particle size of the metal particles is 0.1 μm or more, in materials in which conductive additive particles are dispersed in a matrix material such as a conductive paste, the number of contact points between the metal particles can be reduced, and the increase in electrical resistance due to contact resistance can be suppressed. An average particle size of 0.5 μm or more, and more preferably 1 μm or more, is more preferable. On the other hand, if the average particle size of the metal particles is 30 μm or less, in materials in which conductive additive particles are dispersed in a matrix material such as a conductive paste, the uniformity of the material structure, such as surface smoothness, is improved. Furthermore, the material can be easily used to form fine structures such as fine pattern circuits. An average particle size of 25 μm or less, and more preferably 20 μm or less, is more preferable. Furthermore, when the metal particles take on an anisotropic shape, such as plate-shaped or rod-shaped particles, the average thickness of the particles should be between 0.1 μm and 5 μm. Also, the aspect ratio (average particle size / average thickness) should be between 2 and 100. The metal particles constituting the conductive additive may consist of only one type of copper particle, or a mixture of multiple types of copper particles differing in at least one of their composition, shape, or particle size.

[0035] (2) First surface treatment agent The first surface treatment agent for surface-treating metal particles has a structure represented by the following formula (1). [ka] Here, R1 and R2 are each independently hydrogen or a hydrocarbon group having 3 or fewer carbon atoms, including cases where a hydroxyl group is bonded to the hydrocarbon group, and cases where R1 and R2 are interconnected by a ring structure. R3 is a hydrocarbon group having 3 or fewer carbon atoms. R4 is hydrogen or a hydrocarbon group having 12 or fewer carbon atoms, including cases where an amino group or a hydroxyl group is bonded to the hydrocarbon group. From the viewpoint of forming a dense surface treatment layer, it is preferable that the hydrocarbon groups constituting R1, R2, and R4 are each independently alkyl groups, and the hydrocarbon group constituting R3 is an alkylene group.

[0036] The first surface treatment agent, as shown in formula (1), contains carboxyl and amino groups, and these functional groups coordinate to the copper atoms on the surface of the metal particles. Through coordination bonds, the surface of the copper particles is coated and protected by organic molecules, making it less likely to come into contact with oxidizing substances such as water and oxygen molecules contained in the surrounding materials, including the ambient air and matrix materials such as binder resin. Since the molecules of the first surface treatment agent are monomers, they tend to strongly bond to the surface of the metal particles one molecule at a time through complex formation, coating the surface of the first surface treatment agent. Furthermore, because the first surface treatment agent possesses a weakly acidic carboxyl group and a weakly basic amino group, and coordinates to the copper atoms through these functional groups, the entire layer of the first surface treatment agent coordinated to the metal particles becomes a weakly acidic to weakly basic layer (generally around pH 5 to 9). Therefore, the activity of the surface of the copper particles to which the first surface treatment agent is coordinated is suppressed, and hydroxyl groups, which are precursors to oxides, are less likely to be generated. Thus, because the first surface treatment agent has metal complexing ability and metal surface coating ability, it can suppress the oxidation of metal particles.

[0037] The first surface treatment agent can take any form on the surface of the metal particles as long as it coordinates with the copper atoms, but it is preferable that it forms a layer that covers the surface of the metal particles 10, as shown in the first surface treatment layer 11 in Figure 1. This is highly effective in suppressing the oxidation of the metal particles. However, if the copper particles are porous, the first surface treatment agent does not necessarily have to take a layered structure, for example, by penetrating into the fine details of the pore structure and coordinating with them.

[0038] The specific molecular structure of the first surface treatment agent is not particularly limited as long as it satisfies formula (1) above, however, it is preferable that R1, R2, and R3 each have 2 or fewer carbon atoms independently. Furthermore, it is preferable that R4 has 5 or fewer carbon atoms. Specific examples of the first surface treatment agent include alanine, glycine, proline, valine, leucine, isoleucine, serine, threonine, lysine, arginine, β-alanine, bicine, etc., or copper complexes thereof. The first surface treatment agent is more likely to coordinate strongly with metal particles when used in the form of an organic molecule that does not constitute a copper complex, but it may also be used as a pre-existing copper complex. The first surface treatment agent may be used as a single molecule or as a mixture of two or more molecules.

[0039] (3) Second surface treatment agent The second surface treatment agent, which further treats the metal particles treated with the first surface treatment agent, has a structure represented by the following formula (2). [ka] Here, R5 and R6 are each independently hydrogen or a hydrocarbon group having 3 or fewer carbon atoms. R7 is a hydrocarbon group having 8 to 30 carbon atoms, and may also have branched portions. From the viewpoint of forming a dense surface treatment layer, it is preferable that the hydrocarbon groups constituting R5, R6, and R7 are each independently alkyl groups.

[0040] The second surface treatment agent, as shown in formula (2), is composed of an amine molecule having a long-chain hydrocarbon group (R7) and exhibits weak basicity. Therefore, it can form electrostatic bonds with carboxyl groups such as carboxylic acids or carboxylate salts derived from the first surface treatment agent, and with surface atoms of metal particles. Furthermore, due to the presence of a long-chain hydrocarbon group, it exhibits high crystallinity.

[0041] By using this second surface treatment agent to further surface-treat metal particles that have been surface-treated with the first surface treatment agent, the second surface treatment agent can form an organic layer of a certain thickness, starting from the electrostatic bonds described above. Due to the effect of this organic layer, contact between the metal particles and surrounding water molecules, oxygen molecules, and other oxidizing substances becomes less likely. Even if there are areas on the surface of the metal particles where the first surface treatment agent layer is thin or where the coating by the first surface treatment agent is insufficient or missing, further surface treatment with the second surface treatment agent coats these areas, resulting in a highly continuous and stable organic layer covering the surface of the metal particles as a whole. In other words, the second surface treatment agent exhibits sealing ability for the first surface treatment agent layer on the metal particles. As a result, the oxidation suppression function provided by the first surface treatment agent is further enhanced by the second surface treatment agent. In particular, the fact that R7 has 8 or more carbon atoms is highly effective in forming a thick surface treatment layer and enhancing the oxidation suppression function. It also shows high affinity with matrix materials such as binder resins. On the other hand, having 30 or fewer carbon atoms in R7 makes it easier to keep the contact resistance between metal particles low when a conductive thin film is formed using a conductive additive.

[0042] The second surface treatment agent can take any form on the surface of the metal particles as long as it is electrostatically bonded to the first surface treatment agent and / or the surface of the metal particles. However, it is preferable that it constitutes a layer that further coats the surface of the metal particles 10 coated by the first surface treatment layer 11, as shown in the second surface treatment layer 12 in Figure 1. This allows the second surface treatment agent, together with the first surface treatment agent, to exhibit a high effect in suppressing the oxidation of the metal particles. However, if the copper particles are porous, the second surface treatment agent does not necessarily have to take a layered structure, for example, by penetrating into the fine details of the pore structure and forming electrostatic bonds. Furthermore, the first and second surface treatment agents do not necessarily have to take a structure in which they are clearly separated into layers and stacked sequentially, as in the first surface treatment layer 11 and the second surface treatment layer 12. For example, at least a part of the second surface treatment agent may be directly bonded to the surface of the metal particles.

[0043] The specific molecular structure of the second surface treatment agent is not particularly limited as long as it satisfies formula (2) above, but it is preferably a primary amine or a secondary amine. In addition, R5 and R6 are each preferably independent of having 2 or fewer carbon atoms. R7 is preferably 22 or fewer carbon atoms. The second surface treatment agent may be used as a single molecule or as a mixture of two or more molecules.

[0044] Specific examples of secondary surface treatment agents include primary amines such as octylamine, nonylamine, decylamine, undecylamine, laurylamine, tridecylamine, myristylamine, pentadecylamine, cetylamine, heptadecylamine, stearylamine, and behenylamine. Examples of secondary amines include N-methyloctylamine, N-ethyloctylamine, N-methylnonylamine, N-ethylnonylamine, N-methyldecylamine, N-ethyldecylamine, N-methylundecylamine, N-ethylundecylamine, N-methyllaurylamine, N-ethyllaurylamine, N-methyltridecylamine, N-ethyltridecylamine, N-methylmyristylamine, N-ethylmyristylamine, N-methylpentadecylamine, N-ethylpentadecylamine, N-methylcetylamine, N-ethylcetylamine, N-methylheptadecylamine, N-ethylheptadecylamine, N-methylstearylamine, N-ethylstearylamine, N-methylbehenylamine, and N-ethylbehenylamine. Examples of tertiary amines include N,N-dimethyloctylamine, N,N-diethyloctylamine, N,N-dimethylnonylamine, N,N-diethylnonylamine, N,N-dimethyldecylamine, N,N-diethyldecylamine, N,N-dimethylundecylamine, N,N-diethylundecylamine, N,N-dimethyllaurylamine, N,N-diethyllaurylamine, N,N-dimethyltridecylamine, N,N-diethyltridecylamine, N,N Examples include dimethylmyristylamine, N,N-diethylmyristylamine, N,N-dimethylpentadecylamine, N,N-diethylpentadecylamine, N,N-dimethylcetylamine, N,N-diethylcetylamine, N,N-dimethylheptadecylamine, N,N-diethylheptadecylamine, N,N-dimethylstearylamine, N,N-diethylstearylamine, N,N-dimethylbehenylamine, and N,N-diethylbehenylamine.

[0045] (4) Method for manufacturing conductive additives The conductive additive according to this embodiment can be manufactured by applying a surface treatment with a first surface treatment agent and then a surface treatment with a second surface treatment agent to metal particles in that order.

[0046] While commercially available metal particles can be used, they often have impurities such as dispersants and copper oxide attached to their surface due to the manufacturing process. Therefore, it is preferable to pre-treat them to remove these impurities. For pre-treatment, the metal particles can be washed with a solvent or solution that can dissolve the impurities. For example, as shown in later examples, they can be sequentially washed with hydrocarbon solvents such as toluene, alcohols such as isopropanol, and acidic aqueous solutions such as hydrochloric acid aqueous solution.

[0047] As a method for surface treatment of metal particles that have been appropriately pre-treated with a first surface treatment agent, the first surface treatment agent is dissolved in a suitable solvent such as water, and the metal particles are suspended and stirred in the solution. Alternatively, the solution of the first surface treatment agent may be placed on the surface of the metal particles by spraying or the like. In these treatments, the amount of the first surface treatment agent used for surface treatment should be between 0.1% by mass and 20% by mass relative to the amount of metal particles. Furthermore, when the manufactured conductive additive is used in the conductive paste described below, the amount should be between 0.05% by mass and 10% by mass relative to the total conductive paste. By setting the amount of the first surface treatment agent above the lower limit above, it becomes easier to ensure sufficient surface treatment of the metal particles. On the other hand, by setting the amount below the upper limit above, it becomes easier to avoid the residue of excess first surface treatment agent on the surface of the metal particles and to ensure conductivity through mutual contact between metal particles. After surface treatment by suspension stirring, spraying, etc., the metal particles surface-treated with the first surface treatment agent can be collected as a powdered substance after appropriate washing, filtration, drying, etc. During cleaning, the amount of the first surface treatment agent remaining on the surface of the metal particles can be adjusted by controlling the amount of cleaning solvent, the cleaning intensity, the cleaning time, etc.

[0048] Furthermore, as a method for surface treatment with the second surface treatment agent, the second surface treatment agent can be dissolved in a suitable solvent such as alcohol, and then the metal particles that have been surface treated with the first surface treatment agent can be further surface-treated using this solution in the same manner as the surface treatment with the first surface treatment agent. In this case, the amount of the second surface treatment agent used for surface treatment should be between 0.02% by mass and 10% by mass relative to the amount of metal particles. Also, when the manufactured conductive additive is used in the conductive paste described below, the amount should be between 0.01% by mass and 5% by mass relative to the total conductive paste. By using an amount of the second surface treatment agent above the lower limit above, sufficient sealing ability of the second surface treatment agent can be utilized. On the other hand, since the second surface treatment agent is used for sealing purposes and is not required in large quantities, it is sufficient to use an amount below the upper limit above. After surface treatment, the metal particles that have been further surface-treated with the second surface treatment agent can be collected as a powdered substance after appropriate washing, filtration, drying, etc. During cleaning, the amount of the secondary surface treatment agent remaining on the surface of the metal particles can be adjusted by controlling the amount of cleaning solvent, the cleaning intensity, the cleaning time, etc.

[0049] The conductive additive according to this embodiment, as described above, is composed of copper particles that are surface-treated with a first surface treatment agent and then with a second surface treatment agent. This effectively suppresses the oxidation of copper particles, even though copper particles are inherently prone to oxidation. Therefore, the conductive additive can be suitably used to impart conductivity to polymer materials by dispersing it in a matrix material such as a binder resin. Suitable examples of materials that can be manufactured using the conductive additive according to this embodiment include conductive pastes, conductive inks, and conductive adhesives, which will be described below. In addition, the conductive additive according to this embodiment can be suitably used as a conductive filler or electromagnetic wave absorber in various resin materials, elastomers, rubbers, etc.

[0050] <Conductive paste> Next, a conductive paste according to one embodiment of the present disclosure will be described. The conductive paste according to this embodiment comprises a conductive additive according to the embodiment of the present disclosure described above and a binder resin. The conductive additive is dispersed in the binder resin.

[0051] In a conductive paste, the first and second surface treatment agents constituting the conductive additive remain on the surface of the metal particles without dissolving, separating, or peeling. However, it is preferable that the first and / or second surface treatment agents have affinity for the binder resin and / or the organic solvent described later. In that case, in the conductive paste, the first and / or second surface treatment agents tend to become semi-dissolved (gel-like) in the binder resin and / or organic solvent.

[0052] The content of conductive additives in conductive paste is preferably 45% by mass or more and 95% by mass or less, in terms of the proportion of metal particles constituting the conductive additives to the total conductive paste. A content of 45% by mass or more ensures high conductivity in the conductive paste. On the other hand, a content of 95% by mass or less maintains the fluidity of the conductive paste, making it easier to place it in predetermined locations by printing or other methods.

[0053] The binder resin constituting the conductive paste is not particularly limited as long as it is an insulating polymer that has fluidity (viscosity) at room temperature (approximately 25°C), but it is preferable that its glass transition temperature (Tg) is 140°C or lower, and more preferably 100°C or lower. This high flexibility of the binder resin results in a highly flexible conductive thin film composed of the conductive paste. Therefore, the conductive paste can be suitably used in applications requiring flexibility, such as forming patterned circuits on flexible substrates. The binder resin may consist of one type of polymer or contain multiple types of polymers, but when containing multiple types of polymers, it is preferable that the Tg of the binder resin as a whole is 140°C or lower. In this case, it is not prohibited to include polymers with a Tg exceeding 140°C, such as phenolic resin, as part of the components, but it is preferable not to include such polymers.

[0054] From the viewpoint of improving the adhesion between the conductive thin film composed of the conductive paste and the substrate, it is preferable that the binder resin contains a substituent represented by the following formula (3). -O-R8(3) Here, R8 is hydrogen or a hydrocarbon group having 3 or fewer carbon atoms, preferably an alkyl group, and may include a branched structure.

[0055] Specific examples of binder resins include polyurethane resin, hydroxypolyurethane resin, phenoxy resin, vinyl chloride-vinyl acetate copolymer, hydroxyvinyl chloride-vinyl acetate copolymer, polyvinyl acetal, hydroxy-modified polyvinyl acetal, polyvinyl alcohol, ethylcellulose, polyhydroxypolyether, polyvinylpyrrolidone, polyester, polyisoprene, polychloroprene, polybutadiene, ethylene-vinyl acetate copolymer, ethylene-vinyl alcohol copolymer, ethylene-isoprene copolymer, ethylene-chloroprene copolymer, and ethylene-butadiene copolymer.

[0056] The binder resin content in the conductive paste is preferably 5% by mass or more and 60% by mass or less relative to the metal particles of the conductive additive. Furthermore, it is preferable that the binder resin content be 5% by mass or more and 20% by mass or less relative to the entire conductive paste. Keeping the binder resin content above these lower limits helps maintain high fluidity in the conductive paste. Conversely, keeping the binder resin content below these upper limits makes it easier to bring the conductive additive particles into contact with each other in the conductive paste, thereby ensuring high conductivity.

[0057] The conductive paste preferably contains an organic solvent in addition to conductive additives and a binder resin. The use of an organic solvent increases the fluidity of the conductive paste, making it easier to position the conductive paste at predetermined locations such as pattern circuits using methods such as printing. The organic solvent preferably dissolves the binder resin. When forming a conductive thin film such as a pattern circuit using the conductive paste, the organic solvent is removed by evaporation. However, from the viewpoint of preventing decomposition and deterioration of the binder resin due to high temperatures, the boiling point of the organic solvent is preferably 250°C or lower, so that evaporation can occur without excessively high temperatures. However, if the volatility is too high, the viscosity of the conductive paste tends to become unstable, making it difficult to form a homogeneous conductive thin film. Therefore, the boiling point of the organic solvent should be 150°C or higher.

[0058] Specific examples of organic solvents include ether-based alcohols such as diethyl ether, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol mono-n-propyl ether, ethylene glycol mono-isopropyl ether, ethylene glycol mono-n-butyl ether, ethylene glycol dimethyl ether, ethylene glycol methyl ethyl ether, ethylene glycol ethyl ether acetate, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, diethylene glycol monomethyl ether acetate, diethylene glycol monoethyl ether acetate, diethylene glycol monobutyl ether acetate, propylene glycol monoethyl ether, propylene glycol monopropyl ether, propylene glycol monobutyl ether, and propylene glycol monomethyl ether. Examples of non-ether alcohols include methyl alcohol, ethyl alcohol, isopropyl alcohol, cyclohexanol, ethylene glycol, propylene glycol, 1,4-butanediol, and triethylene glycol. Examples of esters include ethyl lactate, butyl lactate, methyl acetate, ethyl acetate, butyl acetate, methyl methoxypropionate, ethyl ethoxypropionate, diethyl oxalate, and diethyl malonate. Examples of ketones include acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone. Examples of terpenes include turpentine oil, turpineol, borneol, dihydroterpineol acetate, and α-pinene. Other hydrocarbons include tetrahydrofuran, dichloromethane, 1,2-dichloroethane, 1,4-dichlorobutane, trichloroethane, chlorobenzene, o-dichlorobenzene, hexane, heptane, octane, diacetone alcohol, and propylene carbonate.

[0059] The amount of organic solvent added to the conductive paste is not particularly limited, but it is preferable to add 50 parts by mass or more and 900 parts by mass or less per 100 parts by mass of binder resin. Adding 50 parts by mass or more improves the fluidity of the conductive paste and enhances the convenience of placing the conductive paste in a predetermined position by printing or other methods. Adding 900 parts by mass or less shortens the time required for the organic solvent to evaporate after the conductive paste has been placed, and also reduces the amount of residual organic solvent.

[0060] The conductive paste may consist only of conductive additives, a binder resin, and optionally added organic solvents, but it may also contain additional additives in addition to these components, as long as they do not significantly impair the function of those components. Examples of such additives include preservatives, antifungal agents, antioxidants, dehumidifiers, oxygen absorbers, and colorants. However, as mentioned above, conductive additives themselves have high antioxidant properties, so it is not necessary to add a large amount of antioxidant to prevent oxidation of the copper particles of the conductive additive, and even when antioxidants are used, it is preferable to limit the amount added to, for example, 2% by mass or less of the total conductive paste. Furthermore, it is preferable that the conductive paste does not contain conductive additives that include metal particles other than copper particles surface-treated with the first and second surface treatment agents, such as silver particles. In addition, it is preferable that the conductive paste does not contain strong acid / strong base components that may corrode copper particles, and components (phenol, epoxy, thiol, etc.) that may reduce the flexibility of the conductive thin film through crosslinking reactions.

[0061] To manufacture the conductive paste according to this embodiment, a conductive additive, a binder resin, and any other components, including an organic solvent, should be mixed thoroughly and uniformly. When using an organic solvent, the binder resin should first be mixed with the organic solvent and preferably dissolved. Then, the conductive additive and other additive components should be mixed into this mixture.

[0062] The conductive paste according to this embodiment contains a conductive additive consisting of copper particles surface-treated with a first surface treatment agent and a second surface treatment agent, making the copper particles less susceptible to oxidation. Therefore, even if the conductive paste is stored in the atmosphere, oxidation of the copper particles is suppressed over a long period of time, and it can maintain a state of high conductivity. For this reason, as will be explained below, the conductive paste can be suitably used to produce a conductive thin film for a conductive thin film coating member.

[0063] <Conductive thin film coating material> Next, a conductive thin-film coated member according to one embodiment of the present disclosure will be described. Figure 2 schematically shows a cross-section of the conductive thin-film coated member 2 according to this embodiment. The conductive thin-film coated member 2 comprises a substrate 20 and a conductive thin film 21. The conductive thin film 21 is composed of the conductive paste according to the embodiment of the present disclosure described above and is arranged on the insulating surface of the substrate 20.

[0064] The substrate is composed of an insulator, at least on its surface. Preferably, the entire substrate is composed of an insulator. The conductive thin film is composed of a conductive paste, which gives it conductivity and allows it to form conductive regions, such as conductive paths, on the surface of the insulating substrate. The conductive thin film may cover the entire surface of the substrate or only a part of the surface. A preferred example of the latter is a form in which the conductive thin film forms a pattern structure, such as a pattern circuit. If the conductive paste contains an organic solvent, it is preferable that at least a part, preferably all, of the organic solvent is removed by volatilization in the conductive thin film of the conductive thin film coating member.

[0065] The specific types and applications of the conductive thin-film coating member are not particularly limited, but for example, the conductive thin-film coating member according to this embodiment can be suitably applied as a component of an in-vehicle device. Specific examples of such in-vehicle devices include control units and sensor circuits equipped with pattern circuits for various in-vehicle equipment.

[0066] As for the manufacturing method of the conductive thin film coated member, a conductive paste can be placed at a predetermined position on the surface of the substrate, and then heated as appropriate. The conductive paste can be placed by any method, such as coating or immersion, but when forming a patterned circuit or when forming a conductive thin film in a predetermined pattern on the surface of the substrate, a printing method such as screen printing can be suitably used.

[0067] By placing a conductive paste on the surface of a substrate and then heating (baking) it, a conductive thin film can be formed that stably covers a predetermined area of ​​the substrate surface. If the conductive paste contains an organic solvent, heating can accelerate the removal of the organic solvent. Heating is preferably carried out at a temperature of 200°C or lower, and more preferably at 150°C or lower. By not raising the heating temperature too high, it is possible to suppress the decomposition and alteration of the binder resin in the conductive paste, the decomposition and alteration of the first and second surface treatment agents constituting the conductive additive, and changes in the state of these surface treatment agents coating the metal particles. [Examples]

[0068] Examples are shown below. The present invention is not limited to these examples. Here, conductive additives and conductive pastes according to embodiments of the present disclosure were actually prepared and their properties were evaluated. Unless otherwise specified, the preparation and evaluation of samples were carried out in air at room temperature.

[0069] [Test Method] <Sample preparation> (1) Preparation of metal particles 20 g of copper powder (Mitsui Mining & Smelting Co., Ltd. "1400YP"; average particle size D50: 5.8 μm, average particle thickness: 1.1 μm) was added to 60 g of toluene and refluxed at 50°C for 30 minutes while stirring to disperse the particles. After refluxing, the toluene was removed. The filtered copper particles were added to 60 g of isopropanol and refluxed at 50°C for 30 minutes while stirring to disperse the particles. After refluxing, the isopropanol was removed. The filtered copper powder was added to 60 g of a 2 mol / L hydrochloric acid aqueous solution and stirred at 30°C for 30 minutes. After stirring, the hydrochloric acid aqueous solution containing the copper powder was removed by vacuum filtration. Then, the filtered copper powder was added to 60 g of isopropanol and stirred at room temperature for 10 minutes, and the isopropanol was removed from the isopropanol containing the copper powder by vacuum filtration. This operation washed away the adhering hydrochloric acid. Furthermore, this isopropanol washing was performed again. The filtered copper powder was dried under reduced pressure at room temperature for 18 hours to obtain acid-washed copper powder. The resulting acid-washed copper powder was used as metal particles constituting the conductive additive in subsequent processes.

[0070] (2) Preparation of conductive additives The obtained metal particles were subjected to surface treatment with a first surface treatment agent. Specifically, a solution of the first surface treatment agent with the composition and mass described in the "First Treatment Solution" column of Tables 1 and 2 was mixed with the mass of acid-washed copper powder described, stirred at 50°C for 30 minutes, and then filtered by vacuum filtration. The filtered powder was mixed with 30 g of isopropanol, stirred at room temperature for 5 minutes, filtered by vacuum filtration, and then dried under reduced pressure at room temperature for 18 hours. This yielded the first-treated powder. At this point, diffuse reflectance infrared absorption (IR) spectroscopy was performed on the obtained first-treated powder to confirm the presence of a layer of the first surface treatment agent on the surface of the metal particles. Samples where the "First Treatment Solution" column in Table 2 is blank were not subjected to surface treatment with the first surface treatment agent.

[0071] Furthermore, the obtained first-treated powder was subjected to surface treatment with a second surface treatment agent. Specifically, the entire amount of the first-treated powder prepared above was added to a solution of the second surface treatment agent with the composition and mass listed in the "Second Treatment Solution" column of Tables 1 and 2, stirred at room temperature for 15 minutes, and then filtered by vacuum filtration. The filtered powder was added to 30 g of isopropanol, stirred at room temperature for 5 minutes, filtered by vacuum filtration, and then dried under reduced pressure at room temperature for 18 hours. This yielded a conductive additive. At this point, diffuse reflectance IR measurements were performed on the obtained conductive additive to confirm the presence of a layer of the second surface treatment agent on the surface of the first-treated powder. Note that for samples where the "Second Treatment Solution" column in Table 2 is blank, surface treatment with the second surface treatment agent was not performed.

[0072] (2) Preparation of conductive paste The conductive additive obtained above was mixed with the binder resin solution (binder resin dissolved in an organic solvent) as indicated in the "Binder Resin / Solvent" column of Tables 1 and 2, in the specified mass, and dispersed for 3 minutes using a rotation / revolution type mixer (Sinky Co., Ltd. "AR-100"). After that, the mixture was degassed in the same machine for 2 minutes to obtain a conductive paste.

[0073] The glass transition temperatures of each binder resin used were as follows: Hydroxypolyurethane: 90°C • Polyhydroxypolyether: 92℃ • Polyvinyl acetal: 76℃ • Resol-type phenolic resin: 180~200℃ Furthermore, the boiling points of each organic solvent used were as follows: • Dipropylene glycol monomethyl ether: 188℃ • Diethylene glycol monoethyl ether: 196℃ • Dihydroterpineol acetate: 225℃

[0074] (3) Preparation of conductive thin film samples Using the conductive paste obtained above, a conductive thin film was fabricated on a polyester film (Toray Industries, Ltd.'s "Lumirror S10"). A screen mask was used to create a pattern with a width of 2 mm, a length of 50 mm, and a thickness of 20 μm using a screen printing machine (Newlong Precision Industries Co., Ltd.'s "LS-500"). The polyester film with the conductive paste pattern was then heated in a heating furnace at 125°C for 30 minutes to obtain a conductive thin film sample. While conductive thin film samples were generally prepared immediately after the conductive paste was prepared, for the evaluation of storage stability described below, conductive thin film samples were also prepared using conductive paste after a predetermined storage period.

[0075] <Evaluation Method> The conductive thin film samples obtained above were evaluated as follows.

[0076] (1) Evaluation of the state of conductive thin films In the above-described process for preparing conductive thin film samples, visual inspection was performed on the conductive paste in the state where the pattern was formed (before heating) and on the conductive thin film finally obtained by heating it. If the pattern was formed normally in both states, the conductive thin film was evaluated as being in good condition (A). On the other hand, if blurring or other defects occurred in the pattern in at least one of the states before heating or after heating, and the pattern was not formed normally, the conductive thin film was evaluated as being in poor condition (B).

[0077] (2) Evaluation of volume resistivity For the conductive thin film samples obtained above, a measuring probe was pressed against both ends of the formed pattern in the longitudinal direction, and the resistance value was measured using a milliohmmeter (XIO Technology "GOM-800"). The volume resistivity was calculated from the obtained resistance value and the dimensions of the pattern. If the calculated volume resistivity was less than 1000 μΩ·cm, it was judged that the volume resistivity was sufficiently low (A). On the other hand, if the volume resistivity was 1000 μΩ·cm or more, it was judged that the volume resistivity was high (B). A low volume resistivity of a conductive thin film indicates that the oxidation of the conductive additive has not progressed much.

[0078] (3) Evaluation of storage stability For samples evaluated as having a sufficiently low volume resistivity (A) in the test described in (2) above, further evaluation of storage stability was performed. Specifically, a conductive thin film sample prepared immediately after the preparation of the conductive paste was designated as the initial conductive thin film. Separately, a conductive thin film sample was prepared using a conductive paste that had been stored for a predetermined period, and this was designated as the post-storage conductive thin film. The storage conditions were based on JIS C 60068-2-2, with a temperature of 30°C and a time of 168 hours. The atmosphere was air. The resistance value was measured and the volume resistivity was calculated for both the initial conductive thin film and the post-storage conductive thin film in the same manner as in the test described in (2) above. Furthermore, the ratio of the volume resistivity before and after storage was calculated using the following formula (4), and the storage stability of the conductive paste was evaluated based on this calculated value. In other words, if the obtained ratio was less than 150%, the storage stability was evaluated as high (A), and if it was 150% or more, the storage stability was evaluated as low (B). High storage stability indicates that the conductive additive is less susceptible to oxidation. Volume resistivity ratio (%) = [(Volume resistivity of the conductive thin film after storage) / (Volume resistivity of the initial conductive thin film)] × 100 (4)

[0079] (4) Evaluation of flexibility In the test described in (2) above, for samples evaluated as having a sufficiently low volume resistivity (A), the flexibility of the conductive thin film was further evaluated using the change in conductivity during stretching as an indicator. Specifically, the longitudinal ends of the conductive thin film sample were attached to the gripping parts of an Autograph (Shimadzu Corporation "AGX-V2") at a 50 mm interval, softened in an environment of 150°C, stretched by 5 mm, cooled to room temperature, and then removed from the gripping parts to obtain a stretched thin film sample. For this stretched thin film sample, the resistance value was measured and the volume resistivity was calculated in the same manner as in the test described in (2) above. If the obtained volume resistivity was less than 1000 μΩ·cm, it was evaluated as having high flexibility (A), and if the volume resistivity was 1000 μΩ·cm or more, it was evaluated as having low flexibility (B).

[0080] [Test Results] Tables 1 and 2 below show the materials used to prepare samples A1-A16 and B1-B6, as well as the results of each evaluation. The concentration of each solution used to prepare the samples is expressed in "mass percent". The amount of each material used to prepare the samples is expressed in "grams".

[0081] [Table 1]

[0082] [Table 2]

[0083] According to Table 1, in samples A1 to A16, the conductive additive constituting the conductive paste was metal particles composed of copper particles, which were surface-treated with a first surface treatment agent having the structure of formula (1) above, and then surface-treated with a second surface treatment agent having the structure of formula (2) above. In all of these samples A1 to A16, a conductive thin film in good condition was obtained. Furthermore, as indicated by the sufficiently low volume resistivity and high storage stability of these conductive thin films, the oxidation of the metal particles constituting the conductive additive was sufficiently suppressed.

[0084] Regarding the flexibility of the conductive thin film, it is low in sample A16, while it is high in all samples A1 to A15. This corresponds to the fact that the binder resins used in samples A1 to A15 have lower glass transition temperatures and are more flexible compared to sample A16. When the conductive paste is used in applications requiring high flexibility, it is preferable to use a highly flexible binder resin, as in samples A1 to A15. On the other hand, for applications that do not require high flexibility, a conductive paste using a binder resin with relatively low flexibility, as in sample A16, can also be suitably used. Since the conductive additive according to the embodiments of this disclosure has a high oxidation suppression effect on its own, it is not necessary to consider the suppression of oxidation in the conductive additive when selecting materials used together with the conductive additive, such as binder resins, and a wide range of materials can be used depending on the physical properties required of those materials themselves, such as flexibility.

[0085] In all of the samples B1 to B6 summarized in Table 2, the conductive additive constituting the conductive paste is not made by surface-treating metal particles composed of copper particles with a first surface treatment agent having the structure of formula (1) above, and then surface-treating them with a second surface treatment agent having the structure of formula (2) above. Correspondingly, the oxidation suppression effect of the conductive paste, which is evaluated by volume resistivity and storage stability, is low.

[0086] In sample B1, neither the first nor the second surface treatment agent was used to surface the metal particles, resulting in a high volume resistivity of the conductive thin film. This is thought to be due to oxidation of the copper particles because no surface treatment was performed. In sample B2, a conductive thin film with low volume resistivity was obtained, corresponding to the surface treatment using the first surface treatment agent having the structure of formula (1). However, since no surface treatment with the second surface treatment agent was performed, the storage stability of the conductive paste was low. This suggests that the sealing effect of the second surface treatment agent could not be utilized, and that treatment with the first surface treatment agent alone was insufficient to suppress oxidation of copper particles. In sample B3, no surface treatment with the first surface treatment agent was performed, and only the second surface treatment agent was used. However, similar to sample B1, the volume resistivity of the conductive thin film was high. In other words, the second surface treatment agent alone is not sufficient to suppress the oxidation of copper particles. From a comparison of these results with the results for samples A1 to A16 above, it can be seen that in order to sufficiently suppress the oxidation of metal particles composed of copper particles, it is necessary to perform both surface treatment with a first surface treatment agent having a predetermined structure and surface treatment with a second surface treatment agent.

[0087] In samples B4 to B6, surface treatment was performed using a first surface treatment agent and a second surface treatment agent, but at least one of these surface treatment agents does not have the predetermined structure represented by formulas (1) and (2) above. In samples B4 and B5, the first surface treatment agent does not contain both a carboxyl group and an amino group. In samples B4 and B5, the volume resistivity of the conductive thin film is high. It is thought that the first surface treatment agent has polar functional groups and has a complexing effect on copper atoms, but it cannot form a sufficiently stable film, and therefore has little effect in protecting the metal particles from external oxidizing substances. In sample B6, although a conductive thin film with low volume resistivity is formed, the shelf life of the conductive paste is low. This is thought to be because the hydrocarbon chain R7 of the second surface treatment agent is too short, resulting in low crystallinity of the layer of the second surface treatment agent, and an organic layer that can exert sufficient sealing effect cannot be formed. From the above, it is confirmed that using a first surface treatment agent and a second treatment agent having the predetermined structures of formula (1) and formula (2), respectively, is necessary to effectively suppress the oxidation of copper particles.

[0088] Although embodiments of the present disclosure have been described in detail above, the present invention is not limited in any way to the above embodiments, and various modifications are possible without departing from the spirit of the present invention. [Explanation of Symbols]

[0089] 1. Conductive additives 10 metal particles 11. First surface treatment layer 12 Second surface treatment layer 2. Conductive thin film coated member 20 Base material 21 Conductive Thin Film

Claims

1. Metal particles whose surface is composed of copper or a copper alloy, A first surface treatment agent comprising a molecule having the structure represented by the following formula (1), or a copper complex of said molecule, A second surface treatment agent having the structure represented by the following formula (2) is included, A conductive additive in which the metal particles are surface-treated with the first surface treatment agent and then surface-treated with the second surface treatment agent. 【Chemistry 1】 Here, R １ and R ２ Each of these is independently a hydrogen atom or a hydrocarbon group having 3 or fewer carbon atoms, and when a hydroxyl group is bonded to the hydrocarbon group, and R １ and R ２ This also includes cases where they are interconnected by a ring structure. ３ R is a hydrocarbon group with 3 or fewer carbon atoms. ４ This includes hydrogen or a hydrocarbon group having 12 or fewer carbon atoms, and also includes cases where an amino group or a hydroxyl group is bonded to the hydrocarbon group. 【Chemistry 2】 Here, R ５ and R ６ are each independently hydrogen or a hydrocarbon group having 3 or less carbon atoms. R ７ is a hydrocarbon group having 8 or more and 30 or less carbon atoms, including cases where it has a branched portion.

2. The conductive additive according to claim 1, wherein the average particle size of the metal particles is 0.1 μm or more and 30 μm or less.

3. The conductive additive according to claim 1, wherein the surface of the metal particles is coated with a layer of the first surface treatment agent.

4. The conductive additive according to claim 3, wherein the surface of the metal particles coated with the layer of the first surface treatment agent is further coated with the layer of the second surface treatment agent.

5. A conductive additive according to any one of claims 1 to 4, It contains a binder resin, A conductive paste in which the conductive additive is dispersed in the binder resin.

6. The conductive paste according to claim 5, wherein the glass transition temperature of the binder resin is 140°C or lower.

7. The conductive paste according to claim 5, further comprising an organic solvent.

8. The conductive paste according to claim 5, wherein the content of the conductive additive is 50% by mass or more and 95% by mass or less in proportion to the metal particles in the entire conductive paste.

9. The conductive paste according to claim 5, wherein the content of the binder resin is 5% by mass or more and 30% by mass or less with respect to the entire conductive paste.

10. A substrate having a surface made of an insulator, A conductive thin film coating member comprising a conductive thin film composed of the conductive paste described in claim 5 and disposed on the surface of the substrate.

11. A conductive thin film coating member according to claim 10, which constitutes an in-vehicle component.

12. A method for manufacturing a conductive thin film coated member, comprising the step of placing the conductive paste on the surface of the substrate and then heating it at a temperature of 200°C or lower, to produce the conductive thin film coated member according to claim 10.

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