Conductive additive, conductive paste, conductive thin film-coated member, and method for producing conductive thin film-coated 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. The present invention also provides a conductive thin film-coated member which is configured of this conductive paste, and a method for producing this conductive thin film-coated member. A conductive additive 1 contains: metal particles 10, at least the surfaces of which are configured of copper or a copper alloy; a first surface treatment agent 11 that is configured of a molecule having a predetermined structure or a copper complex of the molecule; and a second surface treatment agent 12 having a predetermined structure. 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

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

[0001] This 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.

[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, conductive additives consisting of metal particles are sometimes added to organic polymers. For example, conductive paste is used to form conductive areas, such as conductive paths including patterned circuits, on the surface of an insulating substrate. Conductive thin films can be easily formed by placing conductive paste at predetermined positions on the surface of the substrate using printing methods such as screen printing to form a thin film. As described in Patent Document 1, conductive paste is generally composed of fine particles of metal, such as silver, dispersed in a binder resin.

[0003] Silver has traditionally been used as the metal particle that makes up conductive pastes, but copper can be considered as an alternative because it is inexpensive and less prone to migration. However, copper is a metal that oxidizes easily, and when copper particles are added to a conductive paste, copper oxide, which acts as an insulator, is formed on the surface. If the oxidation of the copper particles progresses while the prepared conductive paste is stored, it may not be possible to ensure sufficient conductivity in the conductive thin film formed using that conductive paste.

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

[0005] Japanese Patent Publication No. 2014-236103, Japanese Patent Publication No. Hei 11-224532, Japanese Patent Publication No. 2018-92864

[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.

[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. Here, R １ and R ２ Each of these is independently hydrogen 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. ４is a hydrogen atom 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. Here, R ５ and R ６ are each independently a hydrogen atom or a hydrocarbon group having 3 or fewer carbon atoms. R ７ is a hydrocarbon group having 8 or more and 30 or fewer carbon atoms, including cases where it has a branched portion.

[0009] The conductive paste of the present disclosure includes the conductive additive and a binder resin, and the conductive additive is dispersed in the binder resin.

[0010] The conductive thin film coated member of the present disclosure has a base material having a surface made of an insulator, and a conductive thin film made of the conductive paste and disposed on the surface of the base material.

[0011] In the method for manufacturing the conductive thin film coated member of the present disclosure, after disposing the conductive paste on the surface of the base material, a step of heating at a temperature of 200°C or lower is included to manufacture the conductive thin film coated member.

[0012] The conductive additive and the conductive paste according to the present disclosure are a conductive additive in which oxidation of copper particles is suppressed, and a conductive paste containing such a conductive additive. Further, the conductive thin film coated member and the method for manufacturing the conductive thin film coated member according to the present disclosure are a conductive thin film coated member composed of such a conductive paste and a method for manufacturing the same.

[0013] FIG. 1 is a cross-sectional view schematically showing the structure of the conductive additive according to an embodiment of the present disclosure. FIG. 2 is a cross-sectional view schematically showing the structure of the conductive thin film coated member according to an embodiment of the present disclosure.

[0014] [Description of Embodiments of the Present Disclosure] First, the embodiments of the present 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 this disclosure has metal particles whose surfaces are surface-treated with a first surface treatment agent having 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 coordinates with the copper atoms on the surface of the metal particles. Furthermore, the second surface treatment agent forms an organic layer containing long-chain hydrocarbon groups 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 from the formation of oxides and their precursors on the surface. Therefore, the conductive additive according to this disclosure has metal particles in which oxidation is suppressed, even though the metal particles contain 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 matrix materials such as binder resins and used suitably in applications requiring conductivity, such as conductive pastes, to exhibit high conductivity. The imparting of oxidation-inhibiting ability to metal particles is achieved not by matrix materials or separately added antioxidants, reducing agents, or other substances independent of the metal particles, but by substances used in the surface treatment of the metal particles that bond to the surface of the metal particles. Therefore, the need to inhibit oxidation of metal particles does not restrict the type of matrix material or other substances used with conductive additives, or the method of using conductive additives.

[0017] [2] In the embodiment of [1] above, it is preferable that the average particle size of the metal particles is 0.1 μm or more and 30 μm or less. This makes it possible to suppress the decrease in conductivity due to contact resistance between metal particles when the conductive additive is dispersed in a matrix material such as a binder resin. In addition, it is possible to maintain a high degree of uniformity of the material, such as surface smoothness.

[0018] [3] In the embodiment 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. In this case, the effect of suppressing oxidation of the metal particles by the first surface treatment agent is particularly high.

[0019] [4] In the embodiment of [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 embodiment 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 of the aspects [5] to [7] above, the content of the conductive additive may be 50% by mass or more and 95% by mass or less in terms of the ratio of the metal particles in the entire conductive paste. Then, high conductivity can be imparted to the conductive paste, and the characteristics of the binder resin such as flexibility can be effectively utilized.

[0024] [9] In any one of the aspects [5] to [8] above, the content of the binder resin may be 5% by mass or more and 30% by mass or less with respect to the entire conductive paste. Then, the fluidity of the conductive paste can be effectively increased, and it becomes easier to ensure high conductivity due to the contact between the particles of the conductive additive.

[0025]

[10] The conductive thin film coating member according to the present disclosure includes a substrate having a surface made of an insulator, and a conductive thin film made of any one of the conductive pastes [5] to [9] above and 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, as the metal particles constituting the conductive paste, at least those containing copper on the surface, migration in the conductive thin film is less likely to occur. Furthermore, since the metal particles are surface-treated with the above first surface treatment agent and second surface treatment agent, a decrease in conductivity due to oxidation, which is a concern in metal particles containing copper, is also less likely to occur, and a conductive thin film having high conductivity can be formed even when using a conductive paste that has undergone long-term storage.

[0026]

[11] In the aspect

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

[0027]

[12] In the method for manufacturing the conductive thin film coating member according to the present disclosure, after disposing the conductive paste on the surface of the base material, a step of heating at a temperature of 200° C. or lower is included to manufacture the conductive thin film coating member of

[10] or

[11] above. When manufacturing the conductive thin film coating member, using a printing method or the like, after disposing the conductive paste at a predetermined location such as a pattern circuit, by heating, volatile components such as a solvent are removed, thereby forming a stable conductive thin film. At this time, if heating is performed at a temperature of 200° C. or lower, decomposition and deterioration of the binder resin in the heating step, and decomposition, deterioration, and state change of the first surface treatment agent and the second surface treatment agent present on the surface of the copper particles can be suppressed.

[0028] [Details of Embodiments of the Present 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 the present disclosure will be described in detail below. An example of a material containing the conductive additive according to the embodiment of the present disclosure becomes the conductive paste according to the embodiment of the present disclosure. Further, using the conductive paste, the conductive thin film coating member according to the embodiment of the present disclosure can be manufactured.

[0029] <Conductive Additive> First, the conductive additive according to an embodiment of the present 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 FIG. 1.

[0030] The conductive additive 1 includes metal particles 10, a first surface treatment agent, and a second surface treatment agent. The conductive additive 1 is obtained by 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 form of FIG. 1, the first surface treatment agent covers the surface of the metal particles 10 to form a first surface treatment layer 11. Further, covering the surface of the first surface treatment layer 11, the second surface treatment agent forms a second surface treatment layer 12. The molecular structures of the first surface treatment agent and the second surface treatment agent will be shown later, but in surface treatment, cases where the carboxyl group contained in the molecule is in an anionic state and / or the amino group is in a cationic state are also included.

[0031] (1) Metal Particles Metal particles are metal particles whose surface is at least 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 using 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 a solid shape 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 may be used.

[0035] (2) The first surface treatment agent for surface-treating the metal particles has a structure represented by the following formula (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 is hydrogen or a hydrocarbon group having 12 or fewer carbon atoms, and includes 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, R is preferred. １ , R ２ , R ４The hydrocarbon groups that make up the R are each independently alkyl groups, ３ The hydrocarbon group constituting it is preferably an alkylene group.

[0036] The first surface treatment agent, as shown in formula (1), contains carboxyl groups 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 molecules and oxygen molecules contained in the surrounding materials, such as the outside air and matrix materials including 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 has a carboxyl group, which is a weakly acidic group, and an amino group, which is a weakly basic 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). As a result, 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 the above formula (1), but R １ , R ２ , R ３ Each of these elements is preferably independent of having 2 or fewer carbon atoms. Also, R ４Preferably, the molecule 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 copper complex beforehand. 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 surface-treats the metal particles treated with the first surface treatment agent, has a structure represented by the following formula (2). Here, R ５ and R ６ Each of these is independently either hydrogen or a hydrocarbon group having 3 or fewer carbon atoms. ７ is a hydrocarbon group having 8 to 30 carbon atoms, and includes cases where it has a branched portion. From the viewpoint of forming a dense surface treatment layer, R is preferred. ５ , R ６ , R ７ The hydrocarbon groups constituting it are each preferably alkyl groups, independently of each other.

[0040] The second surface treatment agent is a long-chain hydrocarbon group (R) as shown in formula (2). ７ It is composed of an amine molecule having a long-chain hydrocarbon group 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. In addition, it exhibits high crystallinity due to having a long-chain hydrocarbon group.

[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. This organic layer makes it less likely for oxidizing substances such as surrounding water molecules and oxygen molecules to come into contact with the metal particles. 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 is insufficient or missing, further surface treatment with the second surface treatment agent coats these areas, resulting in a stable and continuous organic layer covering the metal particle surface. In other words, the second surface treatment agent exhibits sealing ability on the first surface treatment agent layer on the metal particles. This further enhances the oxidation-inhibiting function provided by the first surface treatment agent. In particular, R ７ Having 8 or more carbon atoms provides a high level of effectiveness in forming a thick surface treatment layer and enhancing oxidation suppression. Furthermore, it exhibits high affinity with matrix materials such as binder resins. On the other hand, R ７ Having 30 or fewer carbon atoms makes it easier to keep the contact resistance between metal particles low when forming a conductive thin film 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 surface of the first surface treatment agent and / or 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 electrostatically bonding. 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 the above formula (2), but it is preferably a primary amine or a secondary amine. Also, R ５ , R ６ Each of these elements is preferably independent of having 2 or fewer carbon atoms. ７ It is preferable that the carbon number is 22 or less. As the second surface treatment agent, one type of molecule may be used alone, or two or more types may be used in mixture form.

[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. 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 N,N-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 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] A method for surface-treating metal particles that have undergone appropriate pretreatment with a first surface treatment agent is to dissolve the first surface treatment agent in a suitable solvent such as water, add the metal particles to the solution, and then suspend and stir. 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 the 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 0.02% by mass or more and 10% by mass or less 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 0.01% by mass or more and 5% by mass or less 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, the second surface treatment agent is used for sealing purposes and is not required in large quantities, so 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 added to various resin materials, elastomers, rubbers, etc., as a conductive filler or electromagnetic wave absorber.

[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 the 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 position 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-R ８ (3) Here, R ８ This 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 place the conductive paste at predetermined positions, such as in pattern circuits, by 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. Non-ether-based 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. Examples of 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 use 50 parts by mass or more and 900 parts by mass or less per 100 parts by mass of binder resin. Using 50 parts by mass or more increases the fluidity of the conductive paste, improving convenience in placing the conductive paste in a predetermined position by printing or other methods. Using 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, fungicides, 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. 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 or 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 Member> Next, a conductive thin film coating member according to one embodiment of the present disclosure will be described. Figure 2 schematically shows a cross-section of the conductive thin film coating member 2 according to this embodiment. The conductive thin film coating member 2 has a substrate 20 and a conductive thin film 21. The conductive thin film 21 is made 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 due to heating, as well as 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 that coat the metal particles.

[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. 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. 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 was removed from the copper powder-containing hydrochloric acid aqueous solution by vacuum filtration. Then, the filtered copper powder was added to 60 g of isopropanol and stirred at room temperature for 10 minutes, and then the isopropanol was removed from the copper powder-containing isopropanol 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 the first surface treatment agent. Specifically, the composition and mass of the first surface treatment agent described in the "First Treatment Solution" column of Tables 1 and 2 were added to a solution of the first surface treatment agent, the mass described was added, the mixture was stirred at 50°C for 30 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 obtained the first treatment powder. Here, the presence of a layer of the first surface treatment agent on the surface of the metal particles was confirmed by diffuse reflectance infrared absorption spectroscopy (IR) measurement of the obtained first treatment powder. Note that for samples where the "First Treatment Solution" column in Table 2 is blank, surface treatment with the first surface treatment agent was not performed.

[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 measurement was 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 described 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"). Then, the mixture was degassed in the same machine for 2 minutes to obtain a conductive paste.

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

[0074] (3) Preparation of conductive thin film samples A conductive thin film was prepared on a polyester film (Toray Industries, Ltd. "Lumirror S10") using the conductive paste obtained above. At this time, a pattern with a width of 2 mm, a length of 50 mm, and a thickness of 20 μm was prepared using a screen mask with a screen printing machine (Newlong Precision Industries Co., Ltd. "LS-500"). Then, the polyester film on which the conductive paste pattern was formed was heated in a heating furnace at 125°C for 30 minutes to obtain a conductive thin film sample. Basically, conductive thin film samples were prepared immediately after the preparation of the conductive paste, but for the evaluation of storage stability described below, conductive thin film samples were also prepared using conductive paste that had been stored for a predetermined period.

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

[0076] (1) Evaluation of the state of the conductive thin film In the above-mentioned process for preparing the conductive thin film sample, the conductive thin film was visually observed in the state in which the conductive paste pattern was formed (before heating) and in the state 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 in the longitudinal direction of the formed pattern, and the resistance value was measured using a milliohmmeter (GOM-800, manufactured by XIO Technology). 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 determined that the volume resistivity was sufficiently low (A). On the other hand, if the volume resistivity was 1000 μΩ·cm or more, it was determined that the volume resistivity was high (B). 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 that were evaluated as having a sufficiently low volume resistivity (A) in the test 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 used 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 used 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 the initial conductive thin film and the post-storage conductive thin film in the same manner as in the test 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%, it was evaluated as having high storage stability (A), and if it was 150% or more, it was evaluated as having low storage stability (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 conductive thin film at the beginning)] × 100 (4)

[0079] (4) Evaluation of Flexibility For samples that were evaluated as having a sufficiently low volume resistivity (A) in the test described in (2) above, the flexibility of the conductive thin film was further evaluated using the change in conductivity during stretching as an indicator. Specifically, the lengthwise 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. The resistance value was measured and the volume resistivity was calculated for this stretched thin film sample 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 %". The amount of each material used to prepare the samples is expressed in "g".

[0081]

[0082]

[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, but high in 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, in applications where high flexibility is not required, 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 embodiment of this disclosure has a high oxidation suppression effect itself, 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 using 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, 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 carboxyl groups and amino groups. In samples B4 and B5, the volume resistivity of the conductive thin film is high. Although the first surface treatment agent has polar functional groups and has a complexing effect on copper atoms, it is thought that 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 storage stability of the conductive paste is low. This is because of the hydrocarbon chain R of the second surface treatment agent. ７ This is thought to be because the interval is too short, resulting in low crystallinity of the second surface treatment agent layer, and preventing the formation of an organic layer capable of adequately exhibiting sealing ability. Therefore, it is confirmed that using first and second surface treatment agents having the predetermined structures of formulas (1) and (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.

[0089] 1 Conductive additive 10 Metal particles 11 First surface treatment layer 12 Second surface treatment layer 2 Conductive thin film coating member 20 Substrate 21 Conductive thin film

Claims

1. A conductive additive comprising at least metal particles whose surface is made 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 the 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. Here, R １ and R ２ are each independently hydrogen or a hydrocarbon group having 3 or fewer carbon atoms, including the case where a hydroxyl group is bonded to the hydrocarbon group, and the case where R １ and R ２ are linked to each other by a ring structure. R ３ is a hydrocarbon group having 3 or fewer carbon atoms. R ４ is hydrogen or a hydrocarbon group having 12 or fewer carbon atoms, including the case where an amino group or a hydroxyl group is bonded to the hydrocarbon group. Here, R ５ and R ６ are each independently hydrogen or a hydrocarbon group having 3 or fewer carbon atoms. R ７ is a hydrocarbon group having 8 or more and 30 or fewer carbon atoms, including the case 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 paste comprising a conductive additive according to any one of claims 1 to 4 and a binder resin, wherein 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 conductive thin film coating member comprising a substrate having a surface made of an insulator, and a conductive thin film made 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 according to claim 10, comprising the step of placing the conductive paste on the surface of the substrate and heating it at a temperature of 200°C or lower.

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