Water-based surface treatment agents and laminates

Abstract

This invention provides a surface treatment agent that can achieve excellent adhesion between copper foil and resin film without roughening the surface of copper foil. An aqueous surface treatment agent for surface treatment of metals comprises a nitrogen-containing silane coupling agent and a amide-containing resin, wherein the amide-containing resin has amide groups on its side chains.

Description

Water-based surface treatment agent and laminate The present invention relates to a water-based surface treatment agent and a laminate. Currently, with the widespread adoption of fifth-generation mobile communication systems, devices utilizing high-frequency radio waves are being developed, and the demand for printed wiring boards capable of transmitting high-frequency signals is increasing. Copper foils such as rolled copper foil and electrolytic copper foil are used as materials for such printed wiring boards. Conventionally, copper foils have been used after their surfaces have been roughened in order to improve adhesion with resin films. However, roughening the surface of the copper foil causes a problem in that the electric signal is attenuated and the transmission loss increases during the transmission of high-frequency signals. On the other hand, if the adhesion between the copper foil and the resin film can be ensured without roughening the surface of the copper foil, the transmission loss caused by the roughening treatment can be reduced, and the production steps can be simplified and the cost can be reduced. In contrast, Patent Document 1, for example, discloses a copper surface treatment agent that can smooth the copper surface without roughening it by etching or other means and maintains adhesion between the copper and an insulating material such as a resin. The agent comprises a tin compound, a complexing agent, and a water-soluble polymer or a water-dispersible polymer having at least one functional group selected from the group consisting of an amino group, an epoxy group, a thiol group, a carboxyl group, a sulfonic acid group, a hydroxyl group, a phosphoric acid group, an imine group, and a silanol group. [Prior Art Document] [Patent Document] [Patent Document 1] International Publication No. 2010 / 010716 [Problems to be solved by the invention] However, it was found that there is room for further improvement in the adhesion between the copper foil and the resin film. Therefore, an object of the present invention is to provide a surface treatment agent capable of obtaining excellent adhesion between a copper foil and a resin film without roughening the surface of the copper foil. Another object of the present invention is to provide a laminate having a metal film and a film of a water-based surface treatment agent that can achieve excellent adhesion to a resin film. [Solution to Problem] The water-based surface treatment agent of the present invention is a water-based surface treatment agent for metal surface treatment. The water-based surface treatment agent comprises a nitrogen-containing silane coupling agent and an amide-containing resin having amide groups as side chains. This agent achieves excellent adhesion between copper foil and a resin film without requiring surface roughening of the copper foil. In one embodiment of the aqueous surface treatment agent of the present invention, the amide group is -CO-NH 2. In one embodiment of the water-based surface treatment agent of the present invention, the amide group-containing resin is polyacrylamide. In one embodiment of the water-based surface treatment agent of the present invention, the nitrogen-containing silane coupling agent has at least one selected from the group consisting of an amine group and an imine group. The layered product of the present invention is a layered product comprising a metal and a film of any of the above-mentioned aqueous surface treatment agents in this order. In one embodiment of the laminated body of the present invention, the metal is copper or a copper alloy. In one embodiment of the laminate of the present invention, the laminate includes the metal, the film, and a resin film in this order. In one embodiment of the laminate of the present invention, the laminate is a flexible printed wiring board. [Effects of the Invention] The present invention provides a surface treatment agent capable of achieving excellent adhesion between copper foil and a resin film without roughening the surface of the copper foil. Furthermore, the present invention provides a laminate comprising a metal capable of achieving excellent adhesion to a resin film and a film comprising a water-based surface treatment agent. Hereinafter, embodiments of the present invention will be described. These descriptions are for the purpose of illustrating the present invention and do not limit the present invention in any way. In the present invention, two or more embodiments can be arbitrarily combined. In the present invention, the term "solid content" is a concept including solid content and non-volatile content. Unless otherwise specified, the materials, components, compounds, resins, bases, and solvents described in this specification may be used alone or in combination of two or more. In this specification, unless otherwise specified, numerical ranges are intended to include both the upper and lower limits of the range. For example, 1% by mass to 20% by mass means a range of 1% by mass or more and 20% by mass or less. In this specification, the nitrogen-containing silane coupling agent and the amide group-containing resin may be referred to as component (A) and component (B), respectively. When a compound belongs to both a nitrogen-containing silane coupling agent and an amide group-containing resin, the compound is not treated as an amide group-containing resin but as a nitrogen-containing silane coupling agent. In this specification, "-co-" refers to a copolymer comprising repeating units based on monomers on either side. For example, acrylamide-co-acrylic acid refers to a copolymer comprising repeating units based on acrylamide and repeating units based on acrylic acid. Furthermore, "-co-" indicates that the arrangement of the repeating units in the copolymer is unspecified and can be random, alternating, periodic, or block-like. Aqueous Surface Treatment Agent The aqueous surface treatment agent of the present invention is an aqueous surface treatment agent for metal surface treatment, comprising a nitrogen-containing silane coupling agent and an amide group-containing resin having an amide group in a side chain. Hereinafter, each component of the aqueous surface treatment agent of the present invention will be described with examples. Component (A): Nitrogen-Containing Silane Coupling Agent As the component (A), a known silane coupling agent containing nitrogen can be used. Examples of the nitrogen-containing group contained in the component (A) include an amino group (—NH 2), imine group (=NR, -N(R)-), quaternary ammonium group (-N + R 3) Urea group (-NHCONH 2), isocyanate group (-N=C=O), isocyanurate group, etc. In one embodiment, component (A) has one or more selected from the group consisting of an amine group, an imine group, a quaternary ammonium group, a urea group, an isocyanate group, an isocyanurate group, and a benzotriazole group. In another embodiment, component (A) has one or more selected from the group consisting of an amine group and an imine group. Component (A) may have an aromatic ring containing nitrogen. Component (A) may have, for example, residues of pyrrole, pyrazole, imidazole, triazole, tetrazole, oxazole, oxadiazole, isoxazole, thiazole, isothiazole, furazol, pyridine, pyridazine, pyrimidine, pyrazine, triazine, tetrazine, azobenzene, diazonone, or triazonone; residues of indole, isoindole, indazole, purine, quinoline, isoquinoline, or benzotriazole; residues of carbazole, acridine, β-carboline, acridone, phenazine, phenazine, phenanthidine, phenathiazine, phenoxazine, or phenanthroline; residues of quinoline, quinindoline, or azaindoline. Examples of the component (A) include N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, N-2-(aminoethyl)-3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-triethoxysilyl-N-(1,3-dimethylbutylene)propylamine, N-phenyl-3-aminopropyltrimethoxysilane, hydrochloride of N-(vinylbenzyl)-2-aminoethyl-3-aminopropyltrimethoxysilane, N-2-(aminoethyl)-3-aminopropyltriethoxysilane, 3-triethoxysilyl-N-(1,3-dimethylbutylene)propylamine, trimethoxysilane, bis[3-(trimethoxysilyl)propyl]amine, bis[3-(triethoxysilyl)propyl]amine, N,N'-bis[3-(trimethoxysilyl)propyl]ethylenediamine, and the like. Other examples include X-12-1290 (containing an isocyanurate group), X-12-1214A (containing a benzotriazole group), and X-12-1172ES (containing an imine group) manufactured by Shin-Etsu Chemical Co., Ltd., and VD-5 (containing a triazine ring) manufactured by Shikoku Chemicals Co., Ltd. In a preferred embodiment, component (A) is one or more selected from the group consisting of 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, N-2-(aminoethyl)-3-aminopropyltriethoxysilane, N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, and N-phenyl-3-aminopropyltrimethoxysilane. The content of component (A) in the aqueous surface treatment agent may be adjusted as appropriate. For example, the content of component (A) may be 80% to 99% by mass relative to the total solid content of the aqueous surface treatment agent. In one embodiment, the total concentration of the component (A) and the component (B) relative to the entire aqueous surface treatment agent is 100 ppm to 30,000 ppm. In one embodiment, the mass M of component (A) A Mass M relative to component (B) B The ratio of M A / M B ) is 3 or more. In another embodiment, the ratio M A / M B is 3 or more, 4 or more, 5 or more, 10 or more, 20 or more, 30 or more, 40 or more, 50 or more, 60 or more, 70 or more, 80 or more, 90 or more, 100 or more, 150 or more, 200 or more, or 300 or more. In another embodiment, the ratio M A / M B 500 or less, 400 or less, 300 or less, 200 or less, 150 or less, 100 or less, 90 or less, 80 or less, 70 or less, 60 or less, 50 or less, 40 or less, 30 or less, 20 or less, 10 or less, or 5 or less. In another embodiment, the ratio of M A / M B 3 to 100. Component (B): Amide-containing resin. Component (B) may be a known amide-containing resin having an amide group in a side chain. Examples of component (B) include polyamide having an amide group in a side chain, polyacrylamide having an amide group in a side chain, and polyacrylamide copolymer having an amide group in a side chain. Examples of the polyacrylamide having an amide group in a side chain include cationic polyacrylamide and nonionic polyacrylamide. Examples of the component (B) include polyacrylamide (Sigma-Aldrich catalog number: 535311, hereinafter, the numbers in parentheses in this paragraph represent Sigma-Aldrich catalog numbers), poly(N-isopropylacrylamide), poly(acrylamide-co-acrylic acid) potassium salt (432776), poly(N-isopropylacrylamide) carboxylic acid -thiol terminal (806366), poly (N-isopropylacrylamide) N-hydroxysuccinimide ester terminal (900188), poly (acrylamide-co-acrylic acid) sodium salt (511471), poly (N-isopropylacrylamide) amine terminal (724823), poly (2-acrylamide-2-methyl-1-propanesulfonic acid-co-acrylonitrile) (191981), poly (N-isopropylacrylamide) carboxylic acid terminal ( 724807), Poly(N-isopropylacrylamide-co-methacrylic acid) (724858), Poly(2-acrylamide-2-methyl-1-propanesulfonic acid) (191973), Poly(N,N-dimethylacrylamide) dodecyl trithiocarboxylate terminal (773638), Poly(acrylamide-co-diallyldimethylammonium chloride) (409081), Poly(N-isopropylacrylamide) azide terminal end (747068), poly (ethylene glycol) -block -poly (N-isopropylacrylamide) (747181), poly (N-(2-hydroxypropyl) methacrylamide) (804746), poly (N-isopropylacrylamide-co-butyl acrylate) (762857), poly [(2-ethyldimethylammoniumethyl methacrylate ethyl sulfate) -co-(1-vinylpyrrolidone)] (190888), etc. In addition, commercially available products of the component (B) include, in addition to the above-mentioned substances, "Haricoat G35", "Haricoat G50", "Haricoat G51", "Haricoat GA-1", and "Haricoat 1057" manufactured by Harima Chemical Co., Ltd.; Sigma-Aldrich catalog number: 725668; and "PAS-2141CL", "PAS-J-81L", "PAS-J-81", and "PAS-J-41" manufactured by NITTOBO MEDICAL Co., Ltd. The component (B) may be an amide-modified resin in which an amide group is introduced by modifying a resin having a functional group other than an amide group in a side chain as a starting material. The component (B) may be in the form of a water-soluble substance, an emulsion, or a dispersion. In one embodiment, the amide group of component (B) is -CO-NH 2. In one embodiment, component (B) is polyacrylamide. In another embodiment, component (B) includes one or more selected from the group consisting of cationic polyacrylamide and nonionic polyacrylamide. In another embodiment, component (B) includes one or more selected from the group consisting of cationic polyacrylamide and nonionic polyacrylamide. In yet another embodiment, component (B) includes one or more selected from the group consisting of Sigma-Aldrich catalog numbers 432776, 511471, and 409081, and NITTOBO MEDICAL products under the trade names "PAS-2141CL," "PAS-J-81L," "PAS-J-81," and "PAS-J-41." In another embodiment, component (B) is one or more selected from the group consisting of Sigma-Aldrich catalog numbers 432776, 511471, and 409081, and NITTOBO MEDICAL trade names "PAS-2141CL," "PAS-J-81L," "PAS-J-81," and "PAS-J-41." The content of the component (B) in the aqueous surface treatment agent may be adjusted as appropriate. For example, the content of the component (B) may be 1% to 20% by mass relative to the total solid content of the aqueous surface treatment agent. The aqueous surface treatment agent of the present invention may contain, in addition to component (A) and component (B), components used in known surface treatment agents. For example, the aqueous surface treatment agent may contain a solvent such as water, alcohol, or acetone; a water-soluble polymer, a water-dispersible polymer, a resin, a pH adjuster, a rust inhibitor, condensates of components (A) and condensates of component (A) with other components, and the like. To adjust the solid content concentration or drying rate, the aqueous surface treatment agent of the present invention may further contain an organic solvent miscible with water, as needed. Examples of such organic solvents include ketone-based solvents such as acetone and methyl ethyl ketone; amide-based solvents such as N,N'-dimethylformamide and dimethylacetamide; alcohol-based solvents such as methanol, ethanol, isopropanol, and 1-methoxy-2-propanol; ether-based solvents such as ethylene glycol monobutyl ether and ethylene glycol monohexyl ether; and pyrrolidone-based solvents such as 1-methyl-2-pyrrolidone and 1-ethyl-2-pyrrolidone. As the water, known water can be used, and examples thereof include distilled water, purified water, deionized water, and tap water. The aqueous surface treatment agent of the present embodiment may also contain known acids, bases, surface conditioners, and defoaming agents that have been formulated in conventional aqueous surface treatment agents. The method for preparing a water-based surface treatment agent is not particularly limited, and any method is to mix components (A) and (B). In addition to components (A) and (B), other components such as a solvent may be mixed in any order. Laminate The laminate of the present invention is a laminate having a metal and a film of a water-based surface treatment agent in this order. This allows for excellent adhesion between the metal and the resin film through the film of the water-based surface treatment agent. Metal The metal is not particularly limited as long as it requires adhesion to the resin film, and a known metal can be used. Examples of the metal include copper, nickel, and aluminum. Examples of copper include rolled copper foil and electrolytic copper foil. Furthermore, copper may be alloyed with tin, zinc, nickel, arsenic, silicon, titanium, or chromium. In one embodiment, the metal of the laminate is copper or a copper alloy. In another embodiment, the metal of the laminate is at least one selected from the group consisting of rolled copper foil and electrolytic copper foil. The metal in the laminate of the present invention may be a roughened metal or an unroughened metal. The laminate of the present invention includes a film of the aqueous surface treatment agent of the present invention, and thus, even unroughened metal can achieve excellent adhesion to the resin film. In one embodiment, the metal in the laminate is an unroughened metal. The surface roughness of a single surface of a metal may, for example, have an Rz (ten-point average roughness) of 10 μm or less, 5 μm or less, 3 μm or less, 2 μm or less, 1.5 μm or less, 1.4 μm or less, 1.3 μm or less, 1.2 μm or less, 1.1 μm or less, 1.0 μm or less, 0.9 μm or less, 0.8 μm or less, 0.7 μm or less, 0.6 μm or less, 0.5 μm or less, 0.4 μm or less, 0.3 μm or less, 0.2 μm or less, or 0.1 μm or less. Furthermore, the surface roughness of a single surface of a metal may, for example, have an Rz of 0.1 μm or greater. Rz can be measured in accordance with Japanese Industrial Standards (JIS) B0601 (2013) using a commercially available laser microscope, OPTELICS HYBRID, manufactured by Lasertec. The thickness of the metal can be adjusted as appropriate, for example, from 1 μm to 200 μm. In one embodiment, the thickness of the metal is 1 μm or greater, 5 μm or greater, 10 μm or greater, 20 μm or greater, 30 μm or greater, 40 μm or greater, 50 μm or greater, 100 μm or greater, or 150 μm or greater. In another embodiment, the thickness of the metal is 200 μm or less, 150 μm or less, 100 μm or less, 50 μm or less, 40 μm or less, 30 μm or less, 20 μm or less, or 10 μm or less. • Film of Water-Based Surface Treatment Agent The film of the water-based surface treatment agent is a film formed using the water-based surface treatment agent of the present invention. In the laminate, the metal and the film of the water-based surface treatment agent only need to be arranged in sequence. The metal and the film of the water-based surface treatment agent can be adjacent to each other, that is, directly contacted and laminated, or they can be laminated with other layers or films interposed between them. The film of the aqueous surface treatment agent may be deposited on at least a portion of at least one surface of the metal, and may be deposited on all of one surface or both surfaces (opposite surfaces) of the metal. In one embodiment of the laminate of the present invention, the laminate includes the metal, the film, and a resin film in this order. Resin film: The resin film is not particularly limited, and known resin films can be used. Examples of the resin film include polyimide films, modified polyimide (MPI) films, polyamide films, polyester films (e.g., polyethylene terephthalate films, poly(1,4-cyclohexanedimethylene terephthalate) films, etc.) used for printed wiring boards, liquid crystal polymer films, polycarbonate films, cycloolefin polymer films, and fluororesin films. The thickness of the resin film can be adjusted as appropriate, for example, in the range of 5 μm to 200 μm. In one embodiment, the thickness of the resin film is 5 μm or more, 10 μm or more, 15 μm or more, 20 μm or more, 25 μm or more, 30 μm or more, 35 μm or more, 40 μm or more, 45 μm or more, 50 μm or more, 100 μm or more, or 150 μm or more. In another embodiment, the thickness of the resin film is 200 μm or less, 150 μm or less, 100 μm or less, 50 μm or less, 45 μm or less, 40 μm or less, 35 μm or less, 30 μm or less, 25 μm or less, 20 μm or less, 15 μm or less, or 10 μm or less. Other Layers or Films Examples of layers or films that may be disposed between the metal and the film of the aqueous surface treatment agent include plating layers and chromate films formed by surface treatment of the metal. Examples of the plating layer include Ni plating, Ni—P plating, Ni—Co plating, Ni—Mo plating, Zn plating, Zn—Ni plating, Cu—Zn plating, Cu—Ni plating, and Cu—Ni—Co plating. The application of the laminate of the present invention is not particularly limited, and examples thereof include flexible printed wiring boards, home appliances, information terminals, and building materials. In one embodiment of the laminated body of the present invention, the laminated body is a flexible printed wiring board. The method for manufacturing a laminate is not particularly limited as long as a film having a metal and an aqueous surface treatment agent in this order can be laminated. Known methods for manufacturing flexible printed wiring boards, for example, can be used. Examples of laminate manufacturing methods include the following steps: preparing a metal and an aqueous surface treatment agent; applying the surface treatment agent to at least a portion of at least one side of the metal; and heating or drying the applied surface treatment agent to form a film of the surface treatment agent. The method for applying the surface treatment agent is not particularly limited, and a known coating method can be used. Examples of the coating method include dipping, bar coating, roller coating, shower coating, spraying, and brushing. The heating or drying temperature of the surface treatment agent is not particularly limited, and is, for example, 50°C to 250°C. The heating or drying time of the surface treatment agent is not particularly limited, and is, for example, 2 seconds to 1 hour. The thickness of the film is not particularly limited and may be adjusted appropriately. The thickness of the film is, for example, 1 nm to 10 μm in terms of dry film thickness. As a manufacturing method for a laminate having a structure of a metal / aqueous surface treatment agent film / resin film, for example, the following method can be cited: after forming a laminate of a metal / aqueous surface treatment agent film, a resin film is arranged on the film, and then the metal, the aqueous surface treatment agent film and the resin film are crimped. The temperature during compression bonding is, for example, 100°C to 450°C. The pressure during compression bonding is, for example, 0.1 MPa to 10 MPa. Hereinafter, the present invention will be described in more detail with reference to examples. However, these examples are for the purpose of illustrating the present invention and do not limit the present invention in any way. The materials used in the examples are as follows. (A) Component A1: 3-Aminopropyltrimethoxysilane, trade name "KBM-903" A2: N-2-(Aminoethyl)-3-aminopropyltrimethoxysilane, trade name "KBM-603" A3: 3-Aminopropyltriethoxysilane, trade name "KBE-903" A4: N-(2-Aminoethyl)-3-aminopropyltriethoxysilane, trade name "KBE-603" A5: N-2-(Aminoethyl)-3-aminopropylmethyldimethoxysilane, trade name "KBM-602" A6: N-Phenyl-3-aminopropyltrimethoxysilane, trade name "KBM-573" Comparative Silane Coupling Agents Comparative Silane Coupling Agent 1: Vinyltriethoxysilane, trade name "KBE-1003", described as "CS1" in the table. Comparative Silane Coupling Agent 2: 3-Methacryloxypropyltriethoxysilane, trade name "KBE-503", described as "CS2" in the table. A1 to A6 and CS1 to CS2 are all manufactured by Shin-Etsu Chemical Co., Ltd. · (B) Component B1: Nonionic polyacrylamide having an amide group in the side chain, manufactured by Harima Chemical Co., Ltd., trade name "Haricoat 1057" B2: Anionic polyacrylamide having an amide group in the side chain, manufactured by Harima Chemical Co., Ltd., trade name "Haricoat G-50" B3: NITTOBO MEDICAL Co., Ltd., trade name "PAS-2141CL" B4: Poly(N-isopropylacrylamide) manufactured by Sigma-Aldrich Co., Ltd. · Comparative amide-containing resins: Toray Co., Ltd., trade name "AQ Nylon T-70," a nylon having an amide group in the main chain, indicated as "CA1" in the table The devices and materials used in the examples are as follows. Press: Kodaira Manufacturing Co., Ltd., trade name "PYS-10" Electrolytic copper foil: Chromated electrolytic copper foil with a thickness of 20 μm. This electrolytic copper foil was not roughened. Load measuring device: MinebeaMitsumi, trade name "LTS-200N-S100" Polyimide film: UBE, trade name "upilex (registered trademark)-25VT", thickness 25 μm Examples 1 to 22 and Comparative Examples 1 to 6 Component (A), component (B), and deionized water were mixed to give the concentrations shown in Table 1 to prepare aqueous surface treatment agents. Preparation of a laminate: The electrolytic copper foil that has not been roughened is immersed in the aqueous surface treatment agent of Example 1 for 5 seconds and then pulled up. Subsequently, the electrolytic copper foil is dried at 120°C for 30 seconds to form a film of the aqueous surface treatment agent on the surface of the electrolytic copper foil. Subsequently, an intermediate is arranged on a press with a layer structure of electrolytic copper foil / film of aqueous surface treatment agent / polyimide film. Subsequently, the temperature of the press is raised to 300°C over 1 hour. While maintaining the temperature at 300°C, a pressure of 5.8 MPa is applied to the intermediate from the electrolytic copper foil side and the polyimide film side using the press and maintained for 30 minutes. Subsequently, a laminate with a three-layer structure of electrolytic copper foil / film of aqueous surface treatment agent / polyimide film is obtained. In Examples 2 to 22 and Comparative Examples 1 to 6, the aqueous surface treatment agent was also changed, and a three-layer laminate having an electrolytic copper foil / aqueous surface treatment agent film / polyimide film structure was obtained in the same manner as in Example 1. Evaluation of Adhesion The obtained laminate was subjected to the following peel strength test to evaluate adhesion. The results are shown in Table 1. Peel Strength Test: A 10 mm wide x 60 mm long cut was made in the copper foil from the copper foil side of the laminate. Using a load tester, grip the tip of the copper foil with a clamp and perform a 90° peel test over a 50 mm length at a peel rate of 50 mm / min in accordance with JIS C 6481 to measure the peel strength. [Table 1] The present invention provides a surface treatment agent that can achieve excellent adhesion between copper foil and a resin film without roughening the surface of the copper foil. [Industrial Applicability] The present invention provides a surface treatment agent capable of achieving excellent adhesion between copper foil and a resin film without roughening the surface of the copper foil. Furthermore, the present invention provides a laminate comprising a metal capable of achieving excellent adhesion to a resin film and a film comprising a water-based surface treatment agent. none none

Claims

1. An aqueous surface treatment agent for surface treatment of metals, the aqueous surface treatment agent comprising a nitrogen-containing silane coupling agent and a amide-containing resin, wherein the amide-containing resin has amide groups on its side chains, the mass ratio (MA) of the nitrogen-containing silane coupling agent to the mass ratio (MB) of the amide-containing resin is 3 to 100, wherein the nitrogen-containing silane coupling agent is selected from one or more of the group consisting of amino, imino, quaternary ammonium, urea, isocyanate, isocyanurate, and benzotriazole, and the content of the nitrogen-containing silane coupling agent is 80% to 99% by mass relative to the total solid content of the aqueous surface treatment agent. The amide-containing resin is selected from one or more of the group consisting of polyamides having amide groups in the side chain, polyacrylamides having amide groups in the side chain, or polyacrylamide copolymers having amide groups in the side chain. The content of the amide-containing resin is 1% to 20% by mass relative to the total solids of the aqueous surface treatment agent, and the total concentration of the nitrogen-containing silane coupling agent and the amide-containing resin relative to the aqueous surface treatment agent is 100 ppm to 30,000 ppm.

2. The water-based surface treatment agent as described in claim 1, wherein, The amino group is -CO-NH2.

3. The water-based surface treatment agent as described in claim 1, wherein, The resin containing amide groups is polyacrylamide with amide groups on its side chains.

4. The water-based surface treatment agent as described in claim 1, wherein, The nitrogen-containing silane coupling agent has one or more members selected from the group consisting of amine and imine groups.

5. The water-based surface treatment agent as described in claim 1, wherein, The aqueous surface treatment agent is an aqueous surface treatment agent used for direct surface treatment of the metal.

6. A laminate comprising, in sequence, a metal and a film of an aqueous surface treatment agent as claimed in any one of claims 1 to 5.

7. The stack as described in claim 6, wherein, The metal is copper or a copper alloy.

8. The laminate as claimed in claim 6, comprising the metal, the film, and the resin film in sequence.

9. The stack as described in claim 8, wherein, The stacked body is a flexible printed wiring board.

10. The stack as described in claim 6, wherein, The metal is in direct contact with the membrane.