Formable laminate

Abstract

The overcoat agent for an electroconductive coating according to one aspect of the present invention is applied to an electroconductive coating and forms an insulating overcoat, the overcoat agent including a (meth)acrylic copolymer having a tri-block structure formed from a first polymer block and two second polymer blocks that are different from the first polymer block and that are respectively positioned on the two sides of the first polymer block.

Description

[Technical field]

[0001] The present invention relates to an overcoat agent for conductive coating films, an overcoat for conductive coating films, and a coating film structure. This application claims priority based on Japanese Patent Application No. 2021-020154, filed on February 10, 2021, the contents of which are incorporated herein by reference. [Background technology]

[0002] A circuit of a printed circuit board is formed, for example, by applying a conductive paste containing conductive particles and a binder resin onto a board. In the case of printed circuit boards, in order to protect the circuits and prevent short circuits, an overcoat agent is sometimes applied on a conductive coating film formed from a conductive paste to form an insulating overcoat. Patent Document 1 describes the formation of an insulating coating film by applying a paint containing a thermoplastic resin such as epoxy acrylate or unsaturated polyester onto a conductive coating film. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2001-214091 Summary of the Invention [Problem to be solved by the invention]

[0004] However, when a conventional overcoat agent is applied to a conductive coating film, the conductive coating film may have a phenomenon in which the resistance value of the conductive coating film increases or the conductive coating film is deformed. When a printed circuit board is molded in a state where such a phenomenon occurs, the resistance value of the conductive coating film may further increase compared to when the printed circuit board is molded in a state where an overcoat is not formed.

[0005] An object of the present invention is to provide an overcoat agent for conductive coating films, an insulating overcoat for conductive coating films, and a coating film structure which are less likely to increase the resistance value of the conductive coating film. [Means for solving the problem]

[0006] The present invention has the following aspects. [1] An overcoat agent that is applied on a conductive coating to form an insulating overcoat, An overcoat agent for conductive coatings, comprising a (meth)acrylic copolymer having a triblock structure consisting of a first polymer block and two second polymer blocks different from the first polymer block, the second polymer blocks being positioned on both ends of the first polymer block, respectively. [2] The overcoat agent for conductive coatings according to [1] above, wherein the ratio expressed by the total mass of the two second polymer blocks / the mass of the first polymer block is within the range of 10 / 90 to 60 / 40. [3] The overcoating agent for conductive coating films according to [1] or [2] above, wherein the first polymer block has a glass transition temperature of -75 to -35°C. [4] The overcoating agent for conductive coating films according to any one of [1] to [3] above, wherein the two second polymer blocks each have a glass transition temperature of 75° C. or higher. [5] An insulating overcoat for conductive coating film, which is a coating film of the overcoat agent for conductive coating film according to any one of [1] to [4] above. [6] A coating structure comprising a conductive coating and an insulating overcoat for the conductive coating of [5] provided on the conductive coating. Effect of the Invention

[0007] According to the present invention, it is possible to provide an overcoat agent for a conductive coating film, an insulating overcoat for a conductive coating film, and a coating film structure which are less likely to increase the resistance value of the conductive coating film. [Brief description of the drawings]

[0008] [Figure 1] FIG. 2 is a schematic cross-sectional view showing an example of a coating structure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] In the present invention, "electrically conductive" means that the resistivity is less than 1.0×10 Ω·cm. "Insulating" means that the resistivity is 1.0×10 4 This means that the resistance is Ω·cm or more. "(Meth)acrylic" is a general term for acrylic and methacrylic. The same goes for "(meth)acrylic acid ester", "(meth)acrylic acid", and "(meth)acrylonitrile". As used herein, reversible addition-fragmentation chain transfer polymerization is referred to as "RAFT polymerization," and a chain transfer agent used in RAFT polymerization is referred to as a "RAFT agent." In this specification, the number average molecular weight is also referred to as "Mn" and the weight average molecular weight is also referred to as "Mw." Mn and Mw are each values ​​calculated as standard polystyrene measured by gel permeation chromatography (GPC). The "acid value" of a copolymer refers to the number of milligrams of potassium hydroxide required to neutralize the acid contained in 1 gram of copolymer, and is measured in accordance with JIS K 2501:2003. In this specification, the glass transition temperature is also referred to as "Tg." The Tg of the polymer block can be calculated from the Fox formula shown in the following formula (i): The Tg of the copolymer can be calculated in the same manner. 1 / (Tg P +273.15) = Σ[W i / (Tg i +273.15)] …(i) In formula (i), Tg P is the Tg of the polymer block (℃), and W m is the mass fraction of the monomer (hereinafter also referred to as "monomer m") constituting the polymer block, and Tg m is the Tg (°C) of the homopolymer of monomer m. In addition, Tg mis widely known as a characteristic value of homopolymers, and for example, the value given in "POLYMER HANDBOOK, THIRD EDITION" or the value given in the manufacturer's catalog may be used.

[0010] [Overcoat agent for conductive coating film] An overcoating agent for conductive coating films according to one embodiment of the present invention (hereinafter also simply referred to as "overcoating agent") contains a specific copolymer (hereinafter also referred to as "copolymer A"). From the viewpoint of coatability, the overcoat agent preferably contains an organic solvent. The overcoat agent may contain a crosslinking agent, if necessary. The overcoat agent may contain other components than those described above, as necessary, without departing from the spirit of the present invention.

[0011] <Copolymer A> Copolymer A is a (meth)acrylic copolymer having a triblock structure consisting of a first polymer block (hereinafter also referred to as "block (1)") and two second polymer blocks (hereinafter also referred to as "block (2)") located at both ends of block (1). Copolymer A can also be expressed as block (2)-b-block (1)-b-block (2). Each block will be described in detail later.

[0012] The term "(meth)acrylic copolymer" refers to a copolymer in which at least a portion of the monomer units constituting the copolymer are (meth)acrylic monomer units. The term "(meth)acrylic monomer" refers to a compound having a (meth)acryloyl group. Examples of the (meth)acrylic monomer include (meth)acrylic acid esters, (meth)acrylic acid, (meth)acrylamide compounds, and (meth)acrylonitrile. It is preferable that at least a portion of the (meth)acrylic monomer units are (meth)acrylic acid ester units. The proportion of the (meth)acrylic monomer units in all the monomer units constituting the copolymer A is preferably 80% by mass or more, and more preferably 95% by mass or more.

[0013] The ratio expressed as the total mass of the two blocks (2) / the mass of block (1) is preferably within the range of 10 / 90 to 60 / 40. If this ratio is equal to or greater than the lower limit, tackiness tends not to remain on the surface of the coating film of the overcoat agent, whereas if it is equal to or less than the upper limit, the coating film of the overcoat agent has good elongation and tends not to crack when bent or stretched.

[0014] Copolymer A preferably has an acid value. Having an acid value means having an acid group. An example of the acid group is a carboxy group. When the copolymer A has an acid value, the acid value is preferably 5 to 35 mgKOH / g. Price If the acid value is equal to or greater than the lower limit, crosslinking with isocyanate or the like is possible. In particular, if the acid value is equal to or greater than the lower limit, a sufficient crosslinking structure is formed in the coating film of the overcoat agent, and the coating film tends to have excellent strength. If the acid value is equal to or less than the upper limit, the overcoat agent tends to have excellent storage stability.

[0015] The Mw of the copolymer A is preferably from 20,000 to 80,000, and more preferably from 20,000 to 50,000. When the Mw is not less than the lower limit, the coating strength tends to be excellent, and when it is not more than the upper limit, the coating workability tends to be excellent. The molecular weight dispersity (Mw / Mn) of the copolymer A is preferably 2.0 or less, and more preferably 1.2 to 2.0. When the molecular weight dispersity is equal to or less than the above upper limit, coating workability tends to be excellent.

[0016] (Block (1)) Block (1) is located in the central portion of the triblock structure. The block (1) preferably contains at least one selected from the group consisting of (meth)acrylic monomer units and aromatic vinyl compound units. Examples of the (meth)acrylic monomer include (meth)acrylic acid esters, (meth)acrylic acid, (meth)acrylamide, and (meth)acrylonitrile. Examples of the aromatic vinyl compound include styrene, α-methylstyrene, o-, m- or p-methylstyrene, o-, m- or p-chlorostyrene, etc. Among these, styrene is preferred. The block (1) may further contain other monomer units, if necessary.

[0017] Block (1) preferably contains at least one selected from the group consisting of (meth)acrylic acid ester (hereinafter also referred to as "monomer (1)") units having a linear or branched side chain and aromatic vinyl compound units. When block (1) contains monomer (1) units or aromatic vinyl compound units, copolymer A tends to have a microphase-separated structure in the coating film of the overcoat agent.

[0018] Examples of the side chain of the monomer (1) include an alkyl group and an alkoxyalkyl group. The number of carbon atoms in the side chain is preferably 1 to 8, more preferably 2 to 8, and even more preferably 4 to 8. When the number of carbon atoms in the side chain is 1 or more, copolymer A is likely to have a microphase-separated structure in the coating film of the overcoat agent, and when the number is 8 or less, tackiness tends not to remain. From the viewpoint of flexibility, the side chain is preferably linear, and from the viewpoint of coatability, the side chain is preferably branched.

[0019] Specific examples of the monomer (1) include (meth)acrylic acid alkyl esters such as methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate; and (meth)acrylic acid alkoxyalkyl esters such as 2-methoxyethyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate, 2-(n-propoxy)ethyl (meth)acrylate, 2-(n-butoxy)ethyl (meth)acrylate, 3-methoxypropyl (meth)acrylate, 3-ethoxypropyl (meth)acrylate, 2-(n-propoxy)propyl acrylate, and 2-(n-butoxy)propyl (meth)acrylate. These monomers may be used alone or in combination of two or more. For example, a monomer having 1 to 3 carbon atoms in the side chain may be used in combination with a monomer having 4 to 8 carbon atoms in the side chain. A monomer having a linear side chain and a monomer having a branched side chain may be used in combination.

[0020] The block (1) may further contain a monomer unit other than the monomer (1) and the aromatic vinyl compound, if necessary. Examples of the monomer other than the monomer (1) and the aromatic vinyl compound include a cyclic structure-containing monomer and a functional group-containing monomer other than the aromatic vinyl compound. The cyclic structure-containing monomer and the functional group-containing monomer will be described in detail later. These monomers may be used alone or in combination of two or more.

[0021] The total proportion of monomer (1) units and aromatic vinyl compound units to the total (100 mass%) of all monomer units constituting block (1) is preferably 70 mass% or more, more preferably 85 mass% or more, and may be 100 mass%.

[0022] The Tg of block (1) is preferably −75 to −30° C., and more preferably −70 to −40° C. When the Tg of block (1) is equal to or lower than the upper limit, cracks are unlikely to occur when the coating film of the overcoating agent is bent or stretched, and when the Tg is equal to or higher than the lower limit, tack is unlikely to remain on the surface of the coating film of the overcoating agent. The Tg of the block (1) can be adjusted by the type and mass fraction of the monomer that forms the block (1).

[0023] (Block (2)) The two blocks (2) are located at both ends of the triblock structure. Each of the two blocks (2) is different from the block (1). The fact that the block (2) is different from the block (1) means that the composition of the monomer units constituting the block (2) (either one or both of the types and the ratio of the monomer units) is different from the composition of the monomer units constituting the block (1). It is preferable that at least a part of the monomer units constituting the block (2) is different from the monomer units constituting the block (1). The two blocks (2) may be the same or different from each other. A preferred embodiment of one of the blocks (2) will be described below, but the preferred embodiment of the other block (2) is also similar. The block (2) preferably contains a (meth)acrylic monomer unit. Examples of the (meth)acrylic monomer include the same as those mentioned above. The block (2) may further contain a monomer unit other than the (meth)acrylic monomer, if necessary.

[0024] Block (2) preferably contains a cyclic structure-containing monomer unit. When block (2) contains a cyclic structure-containing monomer unit, copolymer A is likely to have a microphase-separated structure in the coating film of the overcoat agent, and the effect of suppressing an increase in the resistance value of the conductive coating film when the overcoat agent is applied to the conductive coating film is easily obtained. Examples of the cyclic structure-containing monomer include cyclic structure-containing (meth)acrylic acid esters and aromatic vinyl compounds. Examples of (meth)acrylic acid esters having a cyclic structure include (meth)acrylic acid esters having an aromatic ring structure, such as benzyl (meth)acrylate and 2-phenoxyethyl (meth)acrylate; and (meth)acrylic acid esters having an alicyclic structure, such as cyclohexyl (meth)acrylate, dicyclopentanyl (meth)acrylate, and isobornyl (meth)acrylate. Examples of the aromatic vinyl compound include the same compounds as those mentioned above. These monomers may be used alone or in combination of two or more. As the cyclic structure-containing monomer, aromatic vinyl compounds are preferred, and styrene is particularly preferred, in that they are capable of easily forming a microphase-separated structure.

[0025] The block (2) preferably contains a functional group-containing monomer unit such as a carboxy group-containing monomer, a hydroxy group-containing monomer, or a glycidyl group-containing monomer. When the block (2) contains a functional group-containing monomer unit, the heat resistance can be improved by providing a crosslinked structure with a crosslinking agent having an isocyanate group, an epoxy group, a carboxy group or a hydroxy group. When block (2) contains a carboxyl group-containing monomer unit as a functional group-containing monomer unit, hydrogen bonding between the carboxyl groups can induce a pseudo-crosslinked structure in the sequence of copolymer A, thereby improving coating workability.

[0026] Examples of the carboxyl group-containing monomer include (meth)acrylic acid, β-carboxyethyl (meth)acrylate, carboxypentyl (meth)acrylate, itaconic acid, crotonic acid, maleic acid, and fumaric acid. These monomers may be used alone or in combination of two or more. Examples of hydroxy group-containing monomers include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 8-hydroxyoctyl (meth)acrylate, 10-hydroxydecyl (meth)acrylate, 12-hydroxylauryl (meth)acrylate, and (4-hydroxymethylcyclohexyl)-methyl acrylate. These monomers may be used alone or in combination of two or more.

[0027] Block (2) may further contain monomer units other than the cyclic structure-containing monomer and the functional group-containing monomer, if necessary. Examples of the monomer other than the cyclic structure-containing monomer and the functional group-containing monomer include the above-mentioned monomer (1).

[0028] When block (2) contains a cyclic structure-containing monomer unit, the ratio of the cyclic structure-containing monomer unit to the total (100 mass%) of all monomer units constituting block (2) is preferably 50 mass% or more, more preferably 80 mass% or more, and may be 100 mass% from the viewpoint of facilitating microphase separation. If the ratio of the cyclic structure-containing monomer unit is 50 mass% or more, block (2) has high hydrophobicity and copolymer A is likely to have a microphase-separated structure. When block (2) contains a cyclic structure-containing monomer unit and a monomer unit other than the cyclic structure-containing monomer unit, the proportion of the cyclic structure-containing monomer unit to the total (100 mass%) of all monomer units constituting block (2) is preferably 99 mass% or less.

[0029] When block (2) contains a functional group-containing monomer unit, the proportion of the functional group-containing monomer unit relative to the total (100 mass%) of all monomer units constituting block (2) is preferably 0.5 to 10.0 mass%, more preferably 0.5 to 5.0 mass%, and even more preferably 1.0 to 5.0 mass%.

[0030] When block (2) contains functional group-containing monomer units, at least a part of which is a carboxyl group-containing monomer unit, the ratio of the carboxyl group-containing monomer units to the total (100% by mass) of all monomer units constituting block (2) is preferably 0.5 to 10.0% by mass, more preferably 0.5 to 3.0% by mass, and even more preferably 1.0 to 3.0% by mass. If the ratio of the carboxyl group-containing monomer units is equal to or more than the lower limit, copolymer A is likely to have a pseudo-crosslinked structure, and if it is equal to or less than the upper limit, the acid value of copolymer A is likely to be equal to or less than the preferred upper limit.

[0031] The Tg of the block (2) is preferably at least 75° C., more preferably at least 80° C. When the Tg of the block (2) is at least the above lower limit, tackiness is less likely to remain on the surface of the coating film of the overcoat agent. The upper limit of the Tg of the block (2) is not particularly limited, but is, for example, 105°C. The Tg of the block (2) can be adjusted by the type and mass fraction of the monomer that forms the block (2).

[0032] Preferred embodiments of the copolymer A include, for example, the following. Copolymer A-1: ​​A copolymer in which the block (1) contains an acrylate alkyl ester unit having an alkyl group having 2 to 8 carbon atoms, and each of the two blocks (2) contains a methyl methacrylate unit. Copolymer A-2: A copolymer in which the block (1) contains an acrylate alkyl ester unit having an alkyl group having 4 to 8 carbon atoms, and each of the two blocks (2) contains an aromatic vinyl compound unit. Copolymer A-3: A copolymer in which the block (1) contains an acrylate alkyl ester unit having an alkyl group having 2 to 8 carbon atoms, and each of the two blocks (2) contains a cyclic structure-containing (meth)acrylate ester unit.

[0033] In the blocks (1) of the copolymers A-1 to A-3, at least a part of the acrylate alkyl ester units having an alkyl group with 2 to 8 carbon atoms is preferably an acrylate alkyl ester unit having an alkyl group with 4 to 8 carbon atoms. The block (1) of each of the copolymers A-1 to A-3 may further contain a monomer unit other than the alkyl acrylate unit having an alkyl group having 2 to 8 carbon atoms.

[0034] The block (2) of the copolymer A-1 may further contain a monomer unit other than the methyl methacrylate unit. As the monomer unit other than the methyl methacrylate unit, a monomer (1) unit other than the methyl methacrylate unit and a functional group-containing monomer unit are preferable.

[0035] Block (2) of copolymer A-2 may further contain a monomer unit other than the aromatic vinyl compound unit. As the monomer unit other than the aromatic vinyl compound unit, a functional group-containing monomer unit is preferable.

[0036] Block (2) of copolymer A-3 may further contain a monomer unit other than the cyclic structure-containing (meth)acrylic acid ester unit. As the monomer unit other than the cyclic structure-containing (meth)acrylic acid ester unit, the monomer (1) unit and the functional group-containing monomer unit are preferable.

[0037] (Production Method of Copolymer A) Copolymer A can be obtained, for example, by living polymerization. Examples of living polymerization include living anionic polymerization and RAFT polymerization, with RAFT polymerization being preferred. In RAFT polymerization, a RAFT agent and a polymerization initiator are used. Examples of RAFT agents include sulfur-based compounds such as dithioesters, dithiocarbamates, trithiocarbonates, xanthates, etc. Specific examples include those described in JP2018-165300A. Examples of the polymerization initiator include an azo-based polymerization initiator and a peroxide-based polymerization initiator. The method of RAFT polymerization is not particularly limited, and any known method can be used, such as solution polymerization, emulsion polymerization, bulk polymerization, and suspension polymerization. The solvent used in the RAFT polymerization is not particularly limited, and any known solvent can be used.

[0038] For example, when a RAFT agent having one reactive site such as a thiocarbonylthio group is used, first, in the presence of a polymerization initiator and a RAFT agent, a monomer mixture forming block (2) (hereinafter also referred to as "monomer mixture (2)") is polymerized to obtain block (2). Next, in the presence of the obtained block (2), a monomer mixture forming block (1) (hereinafter also referred to as "monomer mixture (1)") is polymerized. This results in a copolymer having a diblock structure consisting of block (2) and block (1). Next, in the presence of the obtained copolymer having a diblock structure, the monomer mixture (2) is polymerized. This results in the desired copolymer A having a triblock structure.

[0039] When a RAFT agent having two reactive sites (for example, a compound represented by formula (1) described later) is used, first, monomer mixture (2) is polymerized in the presence of a polymerization initiator and a RAFT agent to obtain block (2). Next, monomer mixture (1) is polymerized in the presence of the obtained block (2). This results in copolymer A having the desired triblock structure. More specifically, when monomer mixture (2) is polymerized in the presence of a RAFT agent with two reactive sites, block (2) is generated with a structure derived from the RAFT agent sandwiched between them. When monomer mixture (1) is then polymerized, block (1) grows between the reactive site and block (2). The two central blocks (1) are linked by a structure derived from a single molecule of the RAFT agent, so they can be considered as one polymer block.

[0040] <Organic solvent> The organic solvent is not particularly limited, but examples thereof include alcohol-based solvents such as 3-methoxy-3-methyl-1-butanol and 1-butanol; glycol-based solvents such as ethylene glycol monobutyl ether; ketone-based solvents such as isophorone and methyl ethyl ketone; and ester-based solvents such as ethyl acetate. The organic solvent is preferably an organic solvent that does not dissolve the conductive coating film to which the overcoat agent is applied, and is preferably an alcohol-based solvent or a glycol-based solvent, more preferably an alcohol-based solvent.

[0041] The content of the organic solvent can be appropriately set in consideration of the coatability of the overcoat agent, and is, for example, about 100 to 300 parts by mass per 100 parts by mass of Copolymer A.

[0042] <Crosslinking agent> Examples of the crosslinking agent (curing agent) include isocyanate-based crosslinking agents such as hexamethylene diisocyanate (HDI), diphenylmethane diisocyanate (MDI), and isophorone diisocyanate (IPDI). When the overcoat agent contains a crosslinking agent, the content of the crosslinking agent per 100 parts by mass of Copolymer A is, for example, about 5.0 to 10.0 parts by mass.

[0043] <Other ingredients> Examples of other components include additives such as surface conditioners. The content of the other components is, for example, about 0 to 10.0 parts by mass relative to 100 parts by mass of Copolymer A.

[0044] The overcoat agent of this embodiment can be produced by producing copolymer A as described above, and blending a liquid medium, a crosslinking agent, and other components as necessary.

[0045] The overcoat agent of this embodiment is applied onto the conductive coating to form an insulating overcoat, which will be described in detail later.

[0046] According to the overcoat agent of this embodiment, when the overcoat agent is applied to the conductive coating film, an increase in the resistance value of the conductive coating film can be suppressed. The reasons for the above effects are considered to be as follows. When a conventional overcoat agent is applied to a conductive coating film, it is believed that some of the resin components of the overcoat agent (epoxy acrylate, unsaturated polyester, etc.) penetrate into the conductive coating film, causing the resistance value of the conductive coating film to increase. In contrast, in the overcoat agent of this embodiment, since copolymer A has the above structure, copolymer A forms a microphase separation structure during coating film formation, and it is considered that the solvent used is less likely to attack the conductive coating film, which makes it difficult for copolymer A to penetrate into the conductive coating film and thus makes it difficult for the resistance value of the conductive coating film to increase. In addition, the insulating overcoat formed from the overcoat agent of this embodiment is excellent in stretchability and moldability. The excellent moldability leads to a good appearance of the overcoat formed.

[0047] [Insulating overcoat for conductive coating] The insulating overcoat for conductive coatings (hereinafter, also simply referred to as "overcoat") according to one embodiment of the present invention is a coating of the above-mentioned overcoat agent and contains copolymer A. The copolymer A in the overcoat typically has a microphase-separated structure and may have a crosslinked structure.

[0048] The thickness of the overcoat is preferably 10 to 40 μm, more preferably 20 to 30 μm. When the thickness of the overcoat is equal to or more than the lower limit, the insulating properties of the conductive coating film tend to be excellent, and when the thickness is equal to or less than the upper limit, the film-forming properties and extensibility of the overcoat tend to be excellent. The thickness of the overcoat is the thickness of the upper surface side of the conductive coating film. Here, the thickness of the upper surface side of the conductive coating film refers to the thickness of the portion laminated on the upper surface of the conductive coating film (the surface opposite to the substrate). As an example, the thickness of the overcoat 13 shown in FIG. 1 is the thickness of the portion laminated on the upper side of the conductive coating film 11 in the figure. The thickness of the overcoat is measured by a constant pressure thickness gauge.

[0049] The overcoat can be formed by applying the above-mentioned overcoat agent onto the conductive coating film, and then heating it as necessary. Examples of a method for applying the overcoat agent include known application methods such as gravure printing, offset printing, screen printing, roll coating, and bar coating. The heating conditions include, for example, conditions of 80 to 130° C. for 3 to 30 minutes.

[0050] [Coating film structure] A coating structure according to one aspect of the present invention includes a conductive coating and the above-described overcoat. The overcoat is provided on the conductive coating. An example of a coating structure is shown in Figure 1. The coating structure 10 of this example includes a conductive coating 11 provided on a substrate 20, and an overcoat 13 provided on the conductive coating 11. The conductive coating 11 is provided on the substrate 20. The overcoat 13 covers the entire surface of the conductive coating 11.

[0051] The coating film structure of this embodiment can be produced by forming an overcoat on the conductive coating film. The method for forming the overcoat is as described above.

[0052] <Conductive coating film> The conductive coating film is not particularly limited and may be a known conductive coating film. An example of a conductive coating film is one that contains conductive particles and a binder resin, the conductive particles being dispersed in the binder resin.

[0053] Examples of conductive particles include silver, nickel, copper, gold, platinum, carbon, and graphite. The conductive particles preferably have an average particle size of 7 μm or less from the viewpoint of coatability when forming a conductive coating film. The lower limit of the average particle size is not particularly limited, but is, for example, 1 μm. The average particle size of conductive particles is the particle size at which the cumulative volume percentage in the volume particle size distribution is 50 volume%. The volume particle size distribution is measured using a method conforming to JIS Z 8825 "Particle size analysis - Laser diffraction and scattering method."

[0054] Examples of binder resins include polyester resins, phenoxy resins, polyamide resins, polyamideimide resins, polyimide resins, polyurethane resins, acrylic resins, polystyrene, styrene-acrylic resins, styrene-butadiene copolymers, epoxy resins, phenolic resins, polyether resins, polycarbonate resins, alkyd resins, polysulfone resins, polyethersulfone resins, vinyl chloride-vinyl acetate copolymer resins, ethylene-vinyl acetate copolymers, silicone resins, fluorine-based resins, etc. These resins may be used alone or in combination of two or more.

[0055] As the binder resin, from the viewpoints of flexibility and thermal processability, a polyester resin or a polyurethane resin is preferable. A polyester resin and a polyurethane resin may be used in combination. The polyurethane resin is obtained by reacting a polyol resin with an isocyanate compound. Examples of the polyol resin include polyester polyol, polyether polyol, polycarbonate polyol, polycaprolactone polyol, etc. The polyol resin may be used alone or in combination of two or more kinds, or may be used in combination with a polyester resin. The polyol resin is preferably a polyester polyol resin, and the hydroxyl value thereof is, for example, 2 to 100 mgKOH / g. The hydroxyl value of the polyester polyol resin is measured by a method conforming to JIS K 0070 "Testing method for acid value, saponification value, ester value, iodine value, hydroxyl value and unsaponifiable matter of chemical products." Examples of the isocyanate compound include hexamethylene diisocyanate (HDI), diphenylmethane diisocyanate (MDI), isophorone diisocyanate (IPDI), etc. Blocked isocyanates in which the isocyanate group of the isocyanate compound is masked with a blocking agent may be used.

[0056] The conductive coating film may contain additives as necessary, such as dispersants, surface conditioners, and thixotropic agents.

[0057] The content of the conductive particles in the conductive coating film is, for example, 40 to 95% by mass relative to the total mass of the conductive coating film. The content of the binder resin is, for example, 5 to 60% by mass with respect to the total mass of the conductive coating film. The conductive coating has a thickness of, for example, 5.0 to 20.0 μm.

[0058] The conductive coating film can be formed, for example, by applying a conductive paste containing conductive particles and a binder resin to the surface of the substrate, and heating it as necessary. The conductive paste may contain additives as necessary.

[0059] The conductive paste may contain an organic solvent as necessary. As the organic solvent, a known organic solvent used in a general conductive paste (containing conductive particles and a binder resin) can be used, such as butyl diglycol acetate, terpineol, isophorone, etc.

[0060] In the conductive paste, the content of the organic solvent is not particularly limited as long as the suitability for application of the conductive paste to a substrate can be ensured. For example, it is preferable to adjust the content of the non-volatile matter (components other than the organic solvent) of the conductive paste to 70 to 90 mass %.

[0061] The substrate may be an insulating substrate, such as a resin substrate made of polyethylene terephthalate (PET), polycarbonate, polyethylene naphthalate (PEN), or thermoplastic polyurethane (TPU). The substrate may be in the form of a film, a plate, or the like.

[0062] Examples of the method for applying the conductive paste include known application methods such as gravure printing, offset printing, screen printing, roll coating, and bar coating. The heating conditions include, for example, conditions of 80 to 130° C. for 3 to 30 minutes.

[0063] By forming an overcoat on the conductive coating film formed on the substrate as described above, a laminate in which the coating film structure of this embodiment is provided on the substrate is obtained. If necessary, the obtained laminate may be subjected to a forming process such as folding or vacuum thermoforming. The obtained laminate can be used for applications such as printed circuit boards and touch sensors. EXAMPLES

[0064] The present invention will be described in detail below with reference to examples, but the present invention is not limited thereto. "Parts" refers to "parts by mass." Examples 12 ~15 is a reference example.

[0065] <Measurement and Evaluation> (Calculation of Tg) The Tg of the polymer block was calculated from the Fox formula shown in the above formula (i).

[0066] (Acid value measurement) The acid value was measured in accordance with JIS K 2501: 2003. Specifically, the acid value was measured by titrating a solution prepared by dissolving potassium hydroxide in methanol to a normality of 0.1.

[0067] (Measurement of electrical resistance) The electrical resistance value of the conductive coating film was measured using a digital multimeter ("6581" manufactured by ADC Corporation).

[0068] (Change in electrical resistance when overcoating agent is applied) The electrical resistance value of the conductive coating film (electrical resistance value of the conductive coating film after application of the overcoat agent) of the obtained evaluation sample was measured using a digital multimeter (ADC Corporation "6581") From the measurement results, the rate of change in electrical resistance value ([electrical resistance value of the conductive coating film after application of the overcoat agent] - [electrical resistance value before application of the overcoat agent]) / [electrical resistance value before application of the overcoat agent] x 100 (%) was calculated.

[0069] (Appearance of conductive coating film and overcoat after overcoat drying) The conductive coating film of the obtained evaluation sample (after drying the overcoat) was visually observed and evaluated according to the following criteria. The overcoat was also evaluated in the same manner. ○: No wrinkles are observed. ×: Wrinkles are observed.

[0070] (Appearance of the overcoat after thermoforming) The obtained evaluation sample was subjected to thermoforming to an elongation rate of 100% using a vacuum forming machine. The overcoat of the evaluation sample after the thermoforming was visually observed and evaluated according to the following criteria. ◯: No cracks were observed in the overcoat, and the surface of the overcoat had no tack. Δ: Fine cracks are observed in the overcoat, or the surface of the overcoat is slightly tacky, but sufficient for practical use. ×: Cracks were observed in the overcoat, or there were obvious tacks on the surface of the overcoat.

[0071] (Appearance after elasticity test) The obtained evaluation sample was stretched 100 times at a stretching speed of 1200 mm / min to change the length of the conductive coating film from 50 mm to 60 mm using a tabletop durability tester. After that, the appearance of the overcoat was visually observed and evaluated according to the following criteria. ◯: No cracks were observed in the overcoat, and the surface of the overcoat had no tack. Δ: Fine cracks are observed in the overcoat, or the surface of the overcoat is slightly tacky, but sufficient for practical use. ×: Cracks were observed in the overcoat, or there were obvious tacks on the surface of the overcoat.

[0072] <Preparation of conductive paste> According to the composition shown in Table 1, the materials were mixed and dispersed to obtain a conductive paste.

[0073] [Table 1]

[0074] The abbreviations in Table 1 represent the following: UE-3400: Polyester resin, "Elitel UE-3400" manufactured by Unitika Ltd., hydroxyl value 4 mg KOH / g. SBN-70D: HDI blocked isocyanate, "Duranate SBN-70D" manufactured by Asahi Kasei Corporation, solid content 70 mass%, NCO 10.0 mass%. SF70: Silver powder, manufactured by Ames Goldsmith, average particle size 2.6 μm.

[0075] <Production of copolymer> (Manufacturing example A-1) [First stage RAFT polymerization] In the examples, first, 29.7 g of MMA (methyl methacrylate), 0.3 g of AA (acrylic acid), 0.60 g of RAFT agent (1) (a compound represented by formula (1) described below), 0.15 g of ABN-E (2,2'-azobis(2-methylbutyronitrile)), and 30 g of ethyl acetate were placed in a two-neck flask, and the temperature was raised to 85°C while replacing the inside with nitrogen gas, and then a polymerization reaction was carried out for 6 hours with stirring. After the polymerization reaction was completed, the content in the two-neck flask was poured into 1,000 g of n-hexane and stirred to reprecipitate the reaction product, which was then filtered and dried under reduced pressure at 70°C to obtain block (2), which was a copolymer of MMA:AA = 99:1 (mass ratio).

[0076] [Second-stage RAFT polymerization] Next, 27.0 g of the above block (2), 13.5 g of BA (n-butyl acrylate), 13.5 g of 2-EHA (2-ethylhexyl acrylate), 0.04 g of ABN-E, and 60.0 g of ethyl acetate were placed in a two-neck flask, and the temperature was raised to 85°C while replacing the inside with nitrogen gas, and then a polymerization reaction was carried out for 6 hours with stirring. After the reaction was completed, the contents in the two-neck flask were poured into 1000 g of n-hexane and stirred to reprecipitate the reactant, which was then filtered and dried under reduced pressure at 70°C to obtain a copolymer having a triblock structure consisting of block (1), a copolymer of BA:2-EHA = 50:50 (mass ratio), and blocks (2) located on both ends of block (1), with a ratio of the total mass of the two blocks (2) to the mass of block (1) (hereinafter also referred to as "block (2) / block (1)") of 60 / 40. The acid value of the obtained copolymer and the Tg of each of blocks (1) and (2) are shown in Tables 2-3. In addition, since the block (2) at one end of the block (1) and the block (2) at the other end are the single block (2) synthesized in the previous stage that has been divided in the middle, these blocks (2) can be considered to be the same block.

[0077] (Manufacturing examples A-2~A-12) Copolymers A-2 to A-12 were obtained in the same manner as in Production Example 1, except that the type and composition (% by mass) of the monomer forming block (1) or block (2) and the block (2) / block (1) were as shown in Tables 2 to 3. The blank spaces in Tables 2 to 3 indicate that the component was not contained. The acid values ​​of the obtained copolymers and the Tg of each of blocks (1) and (2) are shown in Tables 2 to 3.

[0078] [Table 2]

[0079] [Table 3]

[0080] The abbreviations in Tables 2 and 3 are as follows. The Tg in parentheses after each monomer is the Tg of the homopolymer. MMA: methyl methacrylate (Tg: 105°C). St: styrene (Tg: 100°C). CHMA: cyclohexyl methacrylate (Tg: 66°C). n-BMA: n-butyl methacrylate (Tg: 20°C). AA: acrylic acid (Tg: 106°C). EA: Ethyl acrylate (Tg: -22°C). 2-EHA: 2-ethylhexyl acrylate (Tg: -70°C). BA: n-butyl acrylate (Tg: -54°C). ABN-E: 2,2'-azobis(2-methylbutyronitrile). RAFT agent (1): A compound represented by the following formula (1).

[0081] [ka]

[0082] <Examples 1 to 15, Comparative Examples 1 to 2> The obtained conductive paste was applied by screen printing onto a polycarbonate plate in a linear pattern of 1.0 mm wide x 50 mm long, and heated at 120°C for 30 minutes to form a conductive coating film, and the electrical resistance value (electrical resistance value before application of the overcoat agent) was measured.

[0083] Overcoat agents were obtained by mixing the materials according to the formulations shown in Tables 4 and 5. Blank spaces in Tables 4 and 5 indicate that the component was not included. The obtained overcoat agent was applied by screen printing onto the conductive coating film of the polycarbonate plate, and heated at 120° C. for 30 minutes to form an overcoat having a thickness of 20.0 μm. This resulted in an evaluation sample in which the conductive coating film and the overcoat were laminated on the polycarbonate plate. The obtained evaluation samples were subjected to the above evaluations, and the results are shown in Tables 4 and 5.

[0084] [Table 4]

[0085] [Table 5]

[0086] The abbreviations in Tables 4 and 5 represent the following: jER1256: Phenoxy type epoxy resin, manufactured by Mitsubishi Chemical Corporation. UE3510: Polyester resin, "Elitel UE-3510" manufactured by Unitika. SBN-70D: HDI blocked isocyanate, "Duranate SBN-70D" manufactured by Asahi Kasei Corporation, solid content 70 mass%, NCO 10.0 mass%. Solfit: 3-methoxy-3-methyl-1-butanol, manufactured by Kuraray Co., Ltd.

[0087] As shown in the above results, in each of Examples 1 to 15, the increase in the resistance value of the conductive coating film during application of the overcoat agent was suppressed compared to Comparative Examples 1 and 2. In addition, the appearance of the conductive coating film after thermoforming was good. In particular, in Examples 1 to 12, in which the Tg of block (1) was −75 to −35° C., the Tg of block (2) was 75° C. or higher, and the ratio expressed by the mass of block (2) / the mass of block (1) was within the range of 10 / 90 to 60 / 40, the appearance of the overcoat after thermoforming was also excellent. [Industrial Applicability]

[0088] According to the present invention, it is possible to provide an overcoat agent for a conductive coating film, an insulating overcoat for a conductive coating film, and a coating film structure which are less likely to increase the resistance value of the conductive coating film. [Explanation of symbols]

[0089] 10 Paint film structure 11 Conductive coating 13 Overcoat (insulating overcoat for conductive coating) 20 Base material

Claims

1. The present invention includes a resin substrate, a conductive coating film formed on the resin substrate, and an insulating overcoat formed on the conductive coating film, a moldable laminate, wherein the insulating overcoat is a coating of an overcoat agent for conductive coatings, comprising a (meth)acrylic copolymer having a triblock structure consisting of a first polymer block and two second polymer blocks different from the first polymer block, the two second polymer blocks being located on both ends of the first polymer block, respectively; a ratio expressed by a total mass of the two second polymer blocks / a mass of the first polymer block is within a range of 10 / 90 to 60 / 40; the first polymer block has a glass transition temperature of -75 to -35°C, and each of the two second polymer blocks has a glass transition temperature of 75°C or higher; and the second polymer blocks contain functional group-containing monomer units selected from a carboxy group, a hydroxy group, and a glycidyl group.

2. The laminate according to claim 1 , wherein the overcoat agent for the conductive coating contains an organic solvent.

3. The second polymer block comprises a cyclic structure-containing monomer unit, 3. The laminate according to claim 1, wherein the proportion of the cyclic structure-containing monomer unit relative to a total of all monomer units constituting the second polymer block (100% by mass) is 50% by mass or more.

4. The laminate described in claim 3, wherein the cyclic structure-containing monomer unit is an aromatic vinyl compound unit.

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