Surface-treated stainless steel material and joint

Abstract

The present invention provides a surface-treated stainless steel material that is suitable for adhesive bonding and can further improve the adhesive durability with other components, and a bonded body containing this surface-treated stainless steel material. [Solution] A surface-treated stainless steel material is provided in which a silane film is provided on at least a portion of the surface of a stainless steel substrate. When the elemental distribution is measured by glow discharge emission spectroscopy in the outermost region R1 and region R2 at a depth of 10 nm from region R1, the atomic concentration of silicon in region R1 is 4.0 atomic% or more and 30.0 atomic% or less. Furthermore, the rate of decrease M of silicon concentration, calculated by the following formula (1) based on the atomic concentration of silicon A1 in region R1 and the atomic concentration of silicon A2 in region R2, is 55% or more. M = ((A1 - A2) / A1) × 100 ... (1)

Description

Technical Field

[0001] The present invention relates to a surface-treated stainless steel material and a bonded body including the surface-treated stainless steel material.

Background Art

[0002] In the field of transportation equipment such as automobiles, ships, and aircraft, from the viewpoint of weight reduction, adhesive bonding is used as a joining technology between different materials such as steel materials and lightweight materials (aluminum alloys, titanium alloys, carbon fibers, etc.). Also, in response to on-site problems such as a shortage of successors to welding workers, technology transfer, and improvement of the working environment, adhesive bonding has attracted attention as a welding alternative technology from the viewpoint of improving productivity and workability.

[0003] On the other hand, adhesive bonding has problems with strength reliability during long-term use, and it is known that strength reduction is likely to occur in an environment where stresses such as high temperature, high humidity environment, fatigue, or creep act in combination, as compared with welding or bolt tightening. In adhesive bonding, the adhesion between the adhesive and the adherent metal is important. If the adhesion between the metal material surface and the adhesive is insufficient, water penetrates into the interface between the metal and the resin. As a result, corrosion of the metal surface progresses, peeling occurs from the interface between the two, and the adhesive strength is significantly reduced. Therefore, it is necessary to prevent water from penetrating into the adhesive interface by enhancing the adhesion between the metal and the adhesive resin, and to modify the surface of the metal material so that the metal surface does not easily change its state even if water penetrates, and to adjust it to a surface state suitable for adhesion.

[0004] To solve the above problems, various surface treatment technologies have been proposed conventionally. For example, Patent Document 1 discloses an aqueous composition containing a tetraalkyl silicate or its hydrolyzed product in monomeric or oligomeric form and a hydrated oxide sol such as silica sol. By treating metal materials such as aluminum materials, steel materials, and titanium materials with the above aqueous composition, the initial adhesion and long-term stability of adhesion of a coating film such as an adhesive formed thereon can be improved.

Prior Art Documents

Patent Documents

[0005] [Patent Document 1] Special Publication No. 10-510307 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] However, even when using the surface treatment technology described in Patent Document 1, long-term wet degradation tests result in a significant decrease in adhesive strength with resins such as adhesives. Therefore, the required adhesive durability cannot be obtained.

[0007] The present invention has been made in view of the above problems, and aims to provide a surface-treated stainless steel material that has excellent adhesive strength with resins such as adhesives, and can further improve the adhesive durability with resins, and a joint including this surface-treated stainless steel material. [Means for solving the problem]

[0008] The above objective of the present invention is achieved by the following configuration [1] relating to a surface-treated stainless steel material.

[0009] [1] A surface-treated stainless steel material having a silane coating on at least a portion of the surface of a stainless steel base material, When the elemental distribution is measured by glow discharge emission spectroscopy in the outermost surface region R1 and region R2 at a depth of 10 nm from region R1 within the region where the silane film is provided, The atomic concentration of silicon in the region R1 is 4.0 atomic% or more and 30.0 atomic% or less. A surface-treated stainless steel material characterized in that the rate of decrease M of silicon concentration, calculated by the following formula (1) based on the atomic concentration A1 of silicon in the region R1 and the atomic concentration A2 of silicon in the region R2, is 55% or more. M = ((A1 - A2) / A1) × 100 ... (1)

[0010] Furthermore, a preferred embodiment of the present invention relating to surface-treated stainless steel materials is described in the following [2].

[0011] [2] The surface-treated stainless steel material according to [1], having an adhesive resin layer on the surface of the silane film.

[0012] The above objective of the present invention is achieved by the configuration of the joint shown in [3] below.

[0013] [3] A joint comprising the surface-treated stainless steel material described in [1] or [2], The first member and the second member are joined together via an adhesive resin layer. At least one of the first member and the second member is the surface-treated stainless steel material, A jointed body characterized in that the silane coating of the surface-treated stainless steel material and the adhesive resin layer are bonded together. [Effects of the Invention]

[0014] According to the present invention, it is possible to provide a surface-treated stainless steel material that has excellent adhesive strength with resins such as adhesives, and can further improve the adhesive durability with resins, as well as a joined body including this surface-treated stainless steel material. [Brief explanation of the drawing]

[0015] [Figure 1] Figure 1 is a graph showing the silicon concentration distribution for Invention Example No. 1 and Comparative Examples No. 1-2, with the vertical axis representing the atomic concentration of silicon and the horizontal axis representing the measurement depth. [Figure 2A] Figure 2A is a side view showing the shape of the jointed test specimen. [Figure 2B] Figure 2B is a plan view showing the shape of the jointed test specimen. [Modes for carrying out the invention]

[0016] The inventors of the present invention have conducted intensive research on stainless steel materials that can enhance the adhesive strength and adhesive durability with resins. As a result, it has been found that in a stainless steel material having a silane film on the surface of a substrate made of stainless steel, when the ratio of silicon on the surface is appropriately controlled, the above problems can be solved. Hereinafter, the surface-treated stainless steel material according to the embodiment of the present invention will be described in detail.

[0017] [Surface-treated stainless steel material] The surface-treated stainless steel material according to the present embodiment is one in which a silane film is formed on at least a part of the surface of the substrate. Hereinafter, the substrate and the silane film will be described in more detail.

[0018] [Substrate] As the substrate, one made of stainless steel is used. As the stainless steel, for example, known ones such as austenitic stainless steel, ferritic stainless steel, martensitic stainless steel, and duplex stainless steel can be used.

[0019] [Silane film] The silane film is provided on at least a part of the surface of the above substrate, and specifically, it is a surface-treated film containing an organic silane compound. The silane film containing a silane compound is excellent in the bonding property with an adhesive and has excellent corrosion resistance. Therefore, due to the provision of the silane film, when adhesively joined to other members, excellent adhesive strength can be maintained.

[0020] The silane film can be formed, for example, by applying an aqueous solution containing silicon oxide to the surface of the substrate. The silicon oxide is activated by being made into an aqueous solution and can self-polymerize by a sol-gel reaction. In addition, a natural oxide film is formed on the substrate made of stainless steel. Therefore, by applying the silicon oxide aqueous solution on the oxide film on the substrate surface, the oxide film on the stainless steel surface reacts with the silicon oxide, and the silicon oxides also polymerize with each other, so that a silane film with excellent bonding force to the substrate can be formed in a desired region on the surface of the substrate.

[0021] Furthermore, the silane coating exhibits high mutual solubility with machine oils such as machining oils and press oils, as well as organic compounds such as adhesives, resulting in excellent bonding properties with adhesives. In addition, the silane coating can mitigate the effects of machine oils such as machining oils and press oils, thus preventing a decrease in adhesive durability due to oiling and achieving excellent corrosion resistance.

[0022] In this embodiment, the silicon concentration on the surface is defined as an indicator of whether a silane film capable of fully exhibiting the above-mentioned effects has been formed. That is, the elemental composition of any region R1 on the outermost surface of the region where the silane film is provided must contain a certain amount of silicon and oxygen atoms.

[0023] (Atomic concentration of silicon in region R1: 4.0 atomic% or more and 30.0 atomic% or less) Here, if region R1 is entirely covered with a silane film, and this silane film is entirely SiO2, then the composition of region R1 becomes SiO2, and the atomic concentration of silicon among the elements constituting region R1 is theoretically at its maximum of (number of Si atoms) / (number of Si atoms + number of O atoms) = 1 / (1 + 2) = 0.33. For example, if the concentration of the silane compound in the metal treatment solution becomes high, the silane compounds will react with each other, and the atomic concentration of silicon A1 in region R1 will be higher than the theoretical maximum value mentioned above. However, even if the atomic concentration of silicon A1 is higher than this, it does not contribute to the adhesive durability, so in this embodiment, the upper limit of the atomic concentration of silicon A1 is set based on the above maximum value. However, since the above maximum value is a theoretical value, in reality, the film also contains some base metal elements. Therefore, considering the effect of the base metal, the upper limit of the atomic concentration of silicon in region R1 will be less than 33 atomic percent. Therefore, in this embodiment, the atomic concentration of silicon in region R1 is preferably 30.0 atomic% or less, preferably 26.0 atomic% or less, and more preferably 22.0 atomic% or less.

[0024] On the other hand, the minimum silicon concentration required to improve adhesive durability is, for example, about 1 / 10 of the above upper limit. Specifically, if the atomic concentration of silicon in the outermost surface region R1 is less than 4.0 atomic%, the desired silane film may not be formed, and sufficient adhesive durability cannot be obtained. Therefore, the atomic concentration of silicon in region R1 should be 4.0 atomic% or more, preferably 8.0 atomic% or more, more preferably 10.0 atomic% or more, even more preferably 12.0 atomic% or more, and particularly preferably 15.0 atomic% or more.

[0025] In this embodiment, the atomic concentration of silicon is obtained by measuring the elemental distribution using glow discharge optical emission spectrometry (GD-OES). GD-OES allows for the measurement of elemental distribution in the depth direction over a predetermined region. The elements measured are based on the elements that make up stainless steel, including silicon and oxygen, which are the main components of the coating; iron, which is the main component of the substrate; and copper, manganese, nickel, chromium, etc., which are alloy components. Hydrogen, carbon, nitrogen, etc., which are included as organic contaminants, are not included in the calculation of the silicon atomic concentration.

[0026] (Decrease in silicon atomic concentration M: 55% or more) In elemental analysis in the depth direction using GD-OES, the decrease in silicon concentration with increasing depth indicates that the silicon concentration on the surface is higher than that of the base material, meaning that a silane film is formed in the outermost surface region R1. If the silane film is too thin, the effect of improving adhesive durability cannot be obtained, but if the silane film is too thick, the film becomes brittle, leading to a decrease in adhesive strength. Therefore, in this embodiment, the thickness of the silane film is defined by the atomic concentration of silicon in the depth direction.

[0027] If a silane film is formed in favorable conditions in the outermost region R1, the silicon content will be highest at the outermost surface and will decrease as the measurement depth increases. If the silane film is too thick, the silicon content will not decrease even at deeper measurement depths, resulting in high values.

[0028] Typically, the thickness of the oxide film on a metal is about 5 nm, and a silane film is formed on top of it. Therefore, when analyzing the elemental distribution in the depth direction, it is desirable to measure the atomic concentration of silicon at a depth that is the thickness of the oxide film plus the thickness of the silane film to be formed (5 nm). However, if the thickness of the silane film is too thick, the thickness will be unevenly distributed, and accurate depth information will not be reflected. For this reason, the atomic concentration of silicon A2 is measured at a depth of about twice the thickness of the oxide film (10 nm) from the outermost surface, and the determination is made based on the rate of decrease from the atomic concentration of silicon A1 at the outermost surface.

[0029] In a surface-treated stainless steel material, if the atomic concentration of silicon in the outermost region R1 of the region where a silane film is formed is denoted as A1, and the atomic concentration of silicon in region R2 at a depth of 10 nm from region R1 is denoted as A2, the rate of decrease in silicon concentration M can be calculated using the following formula (1). M = ((A1 - A2) / A1) × 100 ... (1)

[0030] If the silicon concentration reduction rate M calculated by the above formula (1) is less than 55%, it can be determined that the silane coating is too thick and a brittle coating has been formed. Therefore, the silicon concentration reduction rate M should be 55% or more, more preferably 60% or more, and even more preferably 70% or more.

[0031] As described above, the surface-treated stainless steel material according to this embodiment has a silane film provided on at least a portion of the surface of a stainless steel substrate, and the atomic concentration of silicon in the surface region and the rate of decrease in the atomic concentration of silicon at a predetermined depth are defined. Therefore, it has a silane film with excellent bonding properties and durability with adhesives, and the adhesive bonding properties with similar surface-treated stainless steel materials and other components can be improved.

[0032] (Adhesive resin layer) The surface-treated stainless steel material according to this embodiment may further have an adhesive resin layer on the surface of the silane film. As described above, by having an adhesive resin layer on the surface of the silane film, which has excellent bonding properties and durability with adhesives, the process of adhesively joining the surface-treated stainless steel material according to this embodiment to similar surface-treated stainless steel materials or other components can be simplified.

[0033] The method for forming an adhesive resin layer on at least a portion of the surface of the silane film is not particularly limited, but for example, an adhesive sheet made in advance from an adhesive resin material may be attached to the surface of the silane film, or the adhesive resin material may be sprayed or coated onto the surface of the silane film.

[0034] In the present invention, the resin constituting the adhesive resin layer is not particularly limited, and adhesive resins that have been conventionally used when joining stainless steel materials, such as epoxy resins, urethane resins, nitrile resins, nylon resins, and acrylic resins, can be used. Furthermore, the thickness of the adhesive resin layer is not particularly limited, but from the viewpoint of improving adhesive strength, it is preferably 10 to 500 μm, and more preferably 50 to 400 μm.

[0035] [Manufacturing method for surface-treated stainless steel materials] The surface-treated stainless steel material according to the above embodiment can be manufactured, for example, as follows. First, before applying the metal treatment solution to the surface of the substrate, the surface of the substrate is pre-treated by known methods such as etching or blasting. Etching methods include treatment with an acidic solution (acid pickling) and treatment with an alkaline solution (alkaline cleaning, alkaline degreasing).

[0036] Pretreatment such as etching or blasting cleans the surface of the substrate from contamination, making it easier for a silane film to form. Examples of blasting treatments include wet blasting and dry blasting, but the method of blasting is not particularly limited in this invention. However, when wet blasting is used, the rate of decrease M of silicon concentration tends to be higher. This is thought to be because, compared to wet blasting, dry blasting allows blast particles to penetrate the substrate surface more easily, and the metal treatment solution can easily penetrate between the embedded blast particles and the substrate surface. As a result, when dry blasting is used, silicon derived from the metal treatment solution tends to influence the detection of a higher atomic concentration A2 of silicon in region R2. Therefore, from the viewpoint of adhesive durability, it is more preferable to apply wet blasting to the surface of the substrate as a pretreatment.

[0037] Next, a metal treatment solution is applied to the area of ​​the substrate where the silane film is to be formed. As the metal treatment solution, an aqueous solution containing a silane compound can be used. The method of applying the metal treatment solution to the substrate is not particularly limited; it is sufficient to apply it so that the main component, which is mainly a silane compound, is present on the surface of the substrate. Examples include spraying, showering, roll coating, brushing, and immersion treatment.

[0038] Subsequently, the solvent is evaporated from the metal treatment solution applied to the surface of the substrate to dry the substrate surface and promote the reaction between the silane compound and the oxide film, as well as the polymerization of the silane compounds. By blowing away excess liquid with air during drying, the thickness of the silane film can be controlled so that the silicon concentration reduction rate M falls within an optimal range. The drying temperature is not particularly limited, but for example, 50 to 100°C is preferable as it provides a good balance between productivity and energy consumption. In order to improve the integrity of the silane film and maximize the adhesion effect between the substrate and the silane film, the steps of applying the metal treatment solution to the surface of the substrate and drying the surface of the substrate may be repeated 2 to 3 times.

[0039] (Metal treatment solution) Any solution containing a silane compound can be used as the metal treatment solution. For example, a solvent containing 50-99.99% by mass of water and 0-50% by mass of an organic solvent can be used. It is more preferable that the mass of water relative to the total mass of the solution be 50-99.95% by mass. Furthermore, from the viewpoint of reducing volatile organic compounds (VOCs) and lowering the risk of explosion, it is preferable that the main component of the solvent be water.

[0040] When using organic solvents, various water-soluble solvents can be used, such as various alcohols and polyethers, including methanol, ethanol, propyl alcohol, and butanol (including isomers), glycol-based solvents, and their ethers.

[0041] Specifically, the metal treatment solution can be one containing 0.005% to 0.3% by mass of an alkyl silicate or its oligomer and 0.005% to 0.3% by mass of an organic silane compound, with a pH of 2 to 7. When the above metal treatment solution is applied to at least a portion of the surface of the substrate, the alkyl silicate or its oligomer is introduced to the surface of the substrate, forming a composite oxide film of the stainless steel surface oxide film and the silicon compound. In the subsequent drying process, the organic silane compound and the composite oxide film are chemically bonded to form a silane film made of the organic silane compound. The surface-treated stainless steel material obtained in this way has excellent bonding properties with adhesives, excellent corrosion resistance, and excellent adhesive durability, with little decrease in adhesive strength even when exposed to high-temperature and humid environments. Furthermore, by using the above-mentioned metal treatment solution, surface treatment with alkyl silicates or their oligomers and surface treatment with organosilane compounds can be performed in a single step. This allows for the production of surface-treated metal materials with excellent adhesive durability through a simplified process, thereby reducing equipment investment costs and manufacturing costs.

[0042] The pH of the metal treatment solution is preferably between 2 and 7. A pH higher than 7 is undesirable because it can lead to excessive polymerization of the alkyl silicate or its oligomer, potentially reducing the storage stability of the solution. Furthermore, as polymerization of the alkyl silicate or its oligomer progresses, the resulting film becomes thicker, and under stress, fracture occurs within the silane film, preventing the achievement of high adhesive strength. On the other hand, if the pH of the metal treatment solution is lower than 2, the surface of the substrate dissolves rapidly, resulting in an uneven film and making it difficult to achieve stable adhesive performance. Therefore, the pH of the metal treatment solution is preferably within the range of 2 to 7. Considering the reactivity with the metal oxide film, the pH of the metal treatment solution is preferably 3 or higher. Also, from the viewpoint of the stability of the alkyl silicate, the pH of the metal treatment solution is preferably 6 or lower. The pH of the metal treatment solution can be appropriately adjusted by adding acids such as hydrochloric acid, sulfuric acid, nitric acid, or acetic acid.

[0043] The concentration of alkyl silicate or its oligomer in the metal treatment solution is preferably 0.005% by mass or more and 0.3% by mass or less. If the concentration of alkyl silicate or its oligomer in the metal treatment solution exceeds 0.3% by mass, the resulting film may become thicker, potentially reducing its strength. On the other hand, if the concentration of alkyl silicate or its oligomer in the metal treatment solution is less than 0.005% by mass, the concentration of alkyl silicate or its oligomer is too low, making it impossible to sufficiently form a composite oxide film between the oxide film on the stainless steel surface and the silicon compound, potentially resulting in insufficient adhesive durability. The concentration of alkyl silicate or its oligomer in the metal treatment solution is preferably 0.005% by mass or more, more preferably 0.01% by mass or more, and even more preferably 0.02% by mass or more. Furthermore, the concentration of alkyl silicate or its oligomer in the metal treatment solution is preferably 0.3% by mass or less, more preferably 0.2% by mass or less, and even more preferably 0.15% by mass or less.

[0044] Furthermore, the concentration of the organic silane compound in the metal treatment solution is preferably 0.005% by mass or more and 0.3% by mass or less. If the concentration of the organic silane compound in the metal treatment solution exceeds 0.3% by mass, the resulting film may become thicker, potentially reducing its strength. This is also undesirable because it reduces the stability of the solution. On the other hand, if the concentration of the organic silane compound in the metal treatment solution is less than 0.005% by mass, the concentration of the organic silane compound is too low, making it impossible to sufficiently form a film containing the organic silane compound, and thus insufficient adhesive durability cannot be obtained. The concentration of the organic silane compound in the metal treatment solution is preferably 0.005% by mass or more, more preferably 0.01% by mass or more, and even more preferably 0.02% by mass or more. Furthermore, the concentration of the organic silane compound in the metal treatment solution is preferably 0.3% by mass or less, more preferably 0.2% by mass or less, and even more preferably 0.15% by mass or less.

[0045] Furthermore, the Si atom concentration A1 in region R1, the Si atom concentration A2 in region R2, and the rate of decrease in Si concentration M are affected not only by the type and amount of silane compound contained in the metal treatment solution, but also by the presence or absence of pretreatment, the type of blast treatment, and the drying method of the metal treatment solution. Therefore, by performing appropriate pretreatment, controlling the concentration of the silane compound, and appropriately selecting the film formation method, it is possible to control the Si atom concentration A1, Si atom concentration A2, and the rate of decrease in Si concentration M, thereby obtaining excellent adhesive durability.

[0046] The type of alkyl silicate or its oligomer contained in the metal treatment solution is not particularly limited, but tetraalkyl silicates or their oligomers that do not produce by-products that cause corrosion of the coating or deterioration of the adhesive resin after the reaction are preferred. From this viewpoint, tetraalkyl silicates or their oligomers such as tetramethyl orthosilicate, tetraethyl orthosilicate (TEOS), and tetraisopropyl orthosilicate are preferred, and among these, tetraethyl orthosilicate (TEOS) or its oligomer is preferred from the viewpoint of economy and safety. The polymer includes oligomers, etc. Here, one type of alkyl silicate or its oligomer may be used alone, or two or more types may be used in combination.

[0047] The type of organic silane compound contained in the metal treatment solution is not particularly limited, but the organic silane compound may include a silane compound having multiple hydrolyzable trialkoxyl groups in its molecule, its hydrolysate, or its polymer. Silane compounds having multiple hydrolyzable trialkoxyl groups in their molecule not only form dense siloxane bonds through self-polymerization, but also have high reactivity with metal oxides and form chemically stable bonds, thus further enhancing the durability of the silane film. Furthermore, the silane film has high mutual solubility with machine oils such as processing oils and press oils, and organic compounds such as adhesives, and can mitigate the effects of machine oils such as processing oils and press oils adhering to the film, thus playing a role in preventing a decrease in adhesive durability due to oiling. The type of silane compound is not particularly limited, but from an economic standpoint, a silane compound having two hydrolyzable trialkoxysilyl groups in the molecule (bissilane compound) is preferred. For example, bistrialkoxysilylethane, bistrialkoxysilylbenzene, bistrialkoxysilylhexane, bistrialkoxysilylpropylamine, and bistrialkoxysilylpropyltetrasulfide can be used. In particular, from the viewpoint of versatility and economic efficiency, bistriethoxysilylethane (BTSE) is preferred. Here, as the organic silane compound, one type may be used alone, or two or more types may be used in combination.

[0048] Furthermore, the organosilane compound may include a silane coupling agent having a reactive functional group capable of chemically bonding with an organic resin component, its hydrolysate, or its polymer. For example, by using a silane coupling agent having a reactive functional group such as an amino group, epoxy group, methacrylic group, vinyl group, or mercapto group alone, or in combination with a silane compound, a chemical bond can be formed between the film and the resin, further enhancing adhesive durability. The functional groups of the silane coupling agent are not limited to those mentioned above, and silane coupling agents having various functional groups can be appropriately selected and used depending on the adhesive resin used. Suitable specific examples of silane coupling agents include, for example, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-(N-aminoethyl)-aminopropyltrimethoxysilane, 3-(N-aminoethyl)-aminopropyltriethoxysilane, 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane, 3-methacryloxypropyltrimethoxysilane, and 3-methacryloxypropyltriethoxysilane. Here, the silane coupling agent may be used alone or in combination of two or more.

[0049] In this embodiment, if the metal treatment solution contains particulate inorganic compounds with a diameter of 10 nm or more (hereinafter also simply referred to as "particulate inorganic compounds"), the formed film may become thicker, potentially reducing adhesive strength and durability. Therefore, it is preferable that the metal treatment solution substantially does not contain particulate inorganic compounds. It should be noted that "substantially free of particulate inorganic compounds" does not mean completely free of particulate inorganic compounds; the presence of particulate inorganic compounds at an impurity level is permissible. Specifically, it is permissible for particulate inorganic compounds to be present up to 0.05% by mass or less of the total amount of the metal treatment solution. Examples of particulate inorganic compounds include sols of inorganic oxides such as silica and alumina. The diameter of the particulate inorganic compounds is determined by observation of the solid content after drying the treatment solution using a transmission electron microscope (TEM) or by measurement of the diluted treatment solution using a liquid particle counter.

[0050] Furthermore, in addition to the alkyl silicate or its oligomer and organosilane compound mentioned above, the metal treatment solution may optionally contain one or more stabilizers, auxiliary agents, etc. For example, the stabilizer may include organic compounds such as carboxylic acids having 1 to 4 carbon atoms, such as formic acid and acetic acid, or alcohols having 1 to 4 carbon atoms, such as methanol and ethanol.

[0051] The following is one example of a method for preparing a metal treatment solution, but it is not limited to this method. First, an organic silane compound and a small amount of acetic acid as a catalyst are added to a mixture of alcohol such as ethanol and water, and the organic silane compound is thoroughly hydrolyzed to obtain an aqueous solution of the organic silane compound. Next, an aqueous solution of alkyl silicate or its oligomer is prepared by the same method, and after mixing these two solutions, the metal treatment solution is prepared by diluting it with water to a predetermined silane compound concentration. Furthermore, since alkyl silicates or their oligomers are basic and easily polymerized, when using a basic compound as the organic silane compound, it is preferable to neutralize the organic silane solution with acetic acid or the like beforehand to avoid excessive polymerization of the alkyl silicate or its oligomer when the solutions are mixed, before preparing the solution.

[0052] The concentration of the silane compound in the metal treatment solution is preferably adjusted based on the amount of solution to be applied to the surface of the substrate and the desired silicon concentration on the surface of the surface-treated stainless steel material as defined in this invention. Specifically, the concentration of the silane compound relative to the total mass of the metal treatment solution is preferably 0.01% by mass or more and 0.5% by mass or less. The above-mentioned organic solvent may be included in order to lower the surface tension of the metal treatment solution, thereby improving wettability and coating properties, and to improve the drying speed.

[0053] [zygote] The joint according to this embodiment includes the surface-treated stainless steel material described above. Specifically, the joint comprises a first member and a second member joined together via an adhesive resin layer. At least one of the first member and the second member is the surface-treated stainless steel material, and the silane coating of the surface-treated stainless steel material is bonded to the adhesive resin layer.

[0054] The joint according to this embodiment, configured as described above, is less prone to a decrease in adhesive strength even when exposed to a high-temperature, humid environment, and exhibits excellent adhesive durability. As described above, either one of the first and second members may be the surface-treated stainless steel material according to the present invention, or both may be the surface-treated stainless steel material according to the present invention. When only one of the members (the first member) is the surface-treated stainless steel material, the other member (the second member) may be a surface-treated metal material with another metal material as the base material, an untreated metal material, an untreated resin molded body, etc. As the surface-treated metal material with another metal material as the base material, any metal material other than aluminum or aluminum alloy and stainless steel can be used. As the untreated metal material, various metal materials can be used in addition to titanium or titanium alloy, aluminum or aluminum alloy, and stainless steel.

[0055] Furthermore, as the resin molded body, fiber-reinforced plastic molded bodies formed from various fiber-reinforced plastics such as glass fiber reinforced plastic (GFRP), carbon fiber reinforced plastic (CFRP), boron fiber reinforced plastic (BFRP), aramid fiber reinforced plastic (AFRP, KFRP), polyethylene fiber reinforced plastic (DFRP), and Zylon fiber reinforced plastic (ZFRP) can be used. By using these fiber-reinforced plastic molded bodies, it is possible to reduce the weight of the joint while maintaining a certain level of strength.

[0056] In addition to the fiber-reinforced plastics mentioned above, non-fiber-reinforced engineering plastics such as polypropylene (PP), acrylic-butadiene-styrene copolymer (ABS) resin, polyurethane (PU), polyethylene (PE), polyvinyl chloride (PVC), nylon 6, nylon 6,6, polystyrene (PS), polyethylene terephthalate (PET), polyamide (PA), polyphenylene sulfide (PPS), polybutylene terephthalate (PBT), and polyphthalamide (PPA) can also be used for the resin molded articles.

[0057] [Method for manufacturing a jointed body] The bonded body according to this embodiment can be manufactured by conventionally known methods. For example, an adhesive resin layer can be formed in the region where the silane film is formed by a known method, and other members can be joined so as to be in contact with this adhesive resin layer. The method for forming the adhesive resin layer is not particularly limited, but as described above, an adhesive sheet made of adhesive resin material may be used, or a method of spraying or coating the adhesive resin material onto the surface of the silane film may be used.

[0058] In the embodiments described above, an example of a surface-treated metal material having an adhesive resin layer formed for manufacturing a joint was shown. However, the present invention is not limited to the above example, and may also be a surface-treated metal in which a coating film of paint is formed on at least a part of the surface of the silane film. In a surface-treated metal material with a coating film formed thereon, the adhesion between the stainless steel substrate and the silane film is excellent, as is the bonding between the silane film and the paint, so the effect of preventing paint peeling can be obtained. [Examples]

[0059] The present invention will be described in more detail below with reference to examples and comparative examples. However, the present invention is not limited to these examples, and modifications can be made to the extent that they are in line with the spirit of the present invention, and all such modifications are included within the technical scope of the present invention. Furthermore, the following various manufacturing conditions are merely examples, and this embodiment is not limited to these conditions.

[0060] [Manufacturing of stainless steel test specimens] <Preparation of base material> First, two base materials were prepared for each test condition by cutting stainless steel plates, as shown below, to a length of 100 mm in the longitudinal direction and a width of 25 mm. The symbols and thicknesses of each plate are shown below. • Stainless steel (JIS standard SUS304): 1mm thick

[0061] Next, the evaluation range for the substrate was set to 10 mm from the longitudinal end and 25 mm in the width direction. The substrates of Invention Example No. 1, Comparative Example No. 1, and Comparative Example No. 2 were subjected to wet blasting in the above evaluation range, and then rinsed with water for 1 minute. The wet blasting treatment conditions were as follows.

[0062] (Wet blasting treatment conditions) • Wet blasting equipment: BABY BlastII (Model: MBBII-25) manufactured by Makoh Co., Ltd. • Abrasive material for Invention Example No. 1 and Comparative Example No. 1: Abrasive grain white molandum manufactured by Showa Denko Corporation: WA#320 • Abrasive material for Comparative Example No. 2: Showa Denko Corporation, Abrasive grain white molandum: WA#180 • Air pressure: 0.12 MPa • Gun movement speed: 10mm / sec

[0063] Furthermore, the substrates of Invention Example No. 3, Invention Example No. 4, and Comparative Example No. 3 were subjected to dry blasting treatment. The dry blasting treatment conditions were as follows.

[0064] (Dry blasting treatment conditions) • Dry blasting device: Shot blasting device (NAB-3K) manufactured by Nissanki Co., Ltd. • Abrasive material: TOSA EMERY EXTRA #60 manufactured by Uji Denki Kagaku Kogyo Co., Ltd. • Blast pressure: 0.7 (MPa)

[0065] For the substrate of Invention Example No. 2, which was not subjected to blast treatment, degreasing and pickling were carried out in that order. The conditions for degreasing and pickling were as follows.

[0066] (Degreasing) • Degreasing agent: Surf Cleaner EC370 (manufactured by Nippon Paint Surf Chemicals Co., Ltd.) (Degreasing conditions) The substrate was immersed for 5 seconds in a degreasing solution with a degreasing agent concentration of 1% by mass and a temperature of 70°C. (Pickling conditions) The substrate was immersed for 2 seconds in a solution of nitric acid with a concentration of 15% by mass and a temperature of 60°C.

[0067] <Formation of silane film> Subsequently, the substrates of Invention Examples No. 1 to 4 and Comparative Examples No. 1 to 3 were immersed for 10 seconds at room temperature in a metal treatment solution containing silane compound 1 and silane compound 2 at various concentrations, as shown below, and then removed. A silane film was then prepared by drying in a forced-air drying oven at a temperature of 100°C for 60 seconds, thereby obtaining stainless steel test materials (surface-treated stainless steel materials).

[0068] (Metal treatment solution) • Silane compound 1 (organosilane compound): Bistriethoxysilylethane (BTSE) • Silane compound 2 (alkyl silicate): Tetraethyl orthosilicate (TEOS) Ethanol 2.0g • Acetic acid 0.001g ·Water 97.8g

[0069] In the above metal treatment solution, the concentrations of silane compound 1 and silane compound 2 were changed while keeping the ratio of ethanol, acetic acid, and water unchanged. The type of pretreatment, the type and concentration of silane compounds in the metal treatment solution, and the presence or absence of a silane coating are shown in Table 1 below.

[0070] [Measurement of elemental distribution in stainless steel test specimens] From the evaluation range of the obtained stainless steel test material, the elemental distribution of oxygen, silicon, iron, manganese, nickel, and chromium was measured using a high-frequency glow discharge emission spectrometer (Horiba Jobin Yvon JY-5000RF) in an arbitrary region R1 on the outermost surface and a region R2 at a depth of 10 nm from region R1. The atomic concentration A1 of silicon in region R1 and the atomic concentration A2 of silicon in region R2 were then calculated. Furthermore, based on the atomic concentrations A1 and A2, the rate of decrease M of silicon concentration was calculated using the following formula (1). M = ((A1 - A2) / A1) × 100 ... (1)

[0071] Furthermore, the silicon concentration distribution with respect to measurement depth was observed for Invention Examples No. 1 to 4 and Comparative Examples No. 1 to 3. Figure 1 is a graph showing the silicon concentration distribution of the Invention Examples and Comparative Examples, with the vertical axis representing the atomic concentration of silicon and the horizontal axis representing the measurement depth. As shown in Figure 1, for example, Invention Examples No. 1 to 3 use a metal treatment solution containing organic silane compounds and alkyl silicates in a more preferable range, and a silane film is formed on the surface of the substrate. Specifically, in Invention Example No. 1, the atomic concentration of silicon A1 in the outermost region R1 shows a high value of approximately 18 atomic percent or more. Also, as the measurement depth increases, the atomic concentration of silicon decreases, and in region R2, which is 10 nm deep, the atomic concentration of silicon A2 becomes approximately 3 atomic percent. As indicated by the arrows in Figure 1, the rate of decrease M of silicon concentration calculated based on atomic concentrations A1 and A2 was approximately 83%.

[0072] Similarly, in Invention Example No. 2, the atomic concentration of silicon A1 in the outermost surface region R1 was high, at approximately 30 atomic percent or more, while in region R2, which is 10 nm deep, the atomic concentration of silicon A2 was approximately 3.3 atomic percent. In Invention Example No. 3, the atomic concentration of silicon A1 in region R1 was approximately 21 atomic percent or more, and the atomic concentration of silicon A2 in region R2 was approximately 5.8 atomic percent. In Invention Example No. 4, compared to Invention Examples No. 1 to 3, the concentration of organosilane compounds and alkyl silicates in the metal treatment solution was lower, resulting in a decrease in the atomic concentration of silicon A1 in region R1 to 7.5 atomic percent. However, in all of the invention examples, the decrease in silicon concentration was 55% or more.

[0073] On the other hand, in Comparative Example No. 1, the concentrations of the organic silane compound and alkyl silicate in the metal treatment solution were lower than in Invention Example No. 4, resulting in an atomic silicon concentration of less than 4.0 atomic percent in the outermost surface region R1. In Comparative Example No. 2, the concentrations of the organic silane compound and alkyl silicate in the metal treatment solution were higher than in Invention Examples No. 1 to 3, resulting in an atomic silicon concentration of more than 30 atomic percent in the outermost surface region R1. In Comparative Example No. 3, the combination of the blast treatment type and the concentrations of the organic silane compound and alkyl silicate in the metal treatment solution was not appropriately controlled, resulting in a silicon concentration reduction rate M of less than 55%.

[0074] As shown in Figure 1, for Invention Example No. 2 and Comparative Example No. 1, the atomic concentration of silicon in the region deeper than 20 nm was approximately 2%, whereas in Invention Example No. 3, the atomic concentration of silicon was approximately 5%. The reason for this is that in Invention Example No. 2, the pretreatment method was degreasing and pickling, which is thought to have resulted in a lower atomic concentration of silicon in the deeper regions. In Comparative Example No. 1, it is thought that the low concentration of the silane compound in the metal treatment solution used prevented silicon from reaching the deeper regions.

[0075] In contrast, when blast treatment is used as a pretreatment, depressions are formed to a certain depth from the substrate surface, and a Si film is formed on the valley side surface of these depressions. As a result, Si can be detected even in regions where the measurement depth is 20 nm or more. However, in regions where the measurement depth is, for example, greater than 2 μm, the atomic concentrations of silicon in all the inventive examples and comparative examples are almost identical.

[0076] [Manufacturing of bonded test specimens] Subsequently, two stainless steel test specimens were joined together with an adhesive to obtain a jointed test specimen (joint). Figure 2A is a side view showing the shape of the jointed test specimen, and Figure 2B is a plan view thereof. As shown in Figures 2A and 2B, an adhesive resin layer 35 was formed on the surface of the test specimen 31b (second member) in the evaluation area, and a test specimen 31a (first member) having the same configuration as the test specimen 31b was placed on top of this adhesive resin layer 35. At this time, the specimens were placed with the adhesive resin layer 35 in between so that the 10 mm × 25 mm areas on which the silane film was formed faced each other. The overlap length was set to 10 mm, and the specimens were placed so that only the areas from the ends of the test specimens 31a and 31b overlapped by 10 mm.

[0077] A structural thermosetting epoxy adhesive was used as the material for the adhesive resin layer. Furthermore, a small amount of glass beads (particle size 250 μm) were added to the adhesive resin material to adjust the thickness of the adhesive resin layer 35 to 250 μm. After stacking and arranging the materials as described above, they were dried at room temperature for 30 minutes, and then heated at 180°C for another 30 minutes to perform a thermosetting treatment. Afterward, the materials were left to stand at room temperature for 24 hours to prepare a bonded test specimen (jointed body).

[0078] [Evaluation of bonded test specimens] <Degradation Test> To evaluate the adhesive durability of the obtained bonded specimens, a degradation test was conducted. The degradation test involved immersing the bonded specimens in a 5% NaCl solution at 40°C for 20 days.

[0079] <Tensile Test> Tensile tests were conducted on the bonded specimens after degradation testing to evaluate their adhesive durability. Under tensile conditions, both ends of the bonded specimen were pulled at a tensile speed of 50 mm / min in the tensile direction indicated by the arrows in Figure 2A, causing fracture. Subsequently, the fracture surfaces of specimen 31a (first member) and specimen 31b (second member) were observed, and the area of ​​the region where interfacial delamination occurred between the first member and the adhesive resin layer (interfacial delamination area of ​​the first member) and the area of ​​the contact surface between the first member and the adhesive resin layer (adhesion area of ​​the first member) were measured. Similarly, the area of ​​the region where interfacial delamination occurred between the second member and the adhesive resin layer (interfacial delamination area of ​​the second member) and the area of ​​the contact surface between the second member and the adhesive resin layer (adhesion area of ​​the second member) were measured. The cohesive failure rate was then calculated using the following formula (2).

[0080] Cohesive failure rate (%) = 100 - {(Interface delamination area of ​​the first component / Adhesion area of ​​the first component) × 100 + (Interface delamination area of ​​the second component / Adhesion area of ​​the second component) × 100} ... (2)

[0081] Table 2 below shows the calculation results for the atomic concentration of silicon, the silicon concentration reduction rate M, and the aggregation breakdown rate for each example of the invention and comparative example.

[0082] [Table 1]

[0083] [Table 2]

[0084] As shown in Figures 1 and 2 and Table 2 above, Invention Examples No. 1 to 4 achieved excellent adhesive durability because the atomic concentration A1 of silicon and the rate of decrease M of silicon concentration in the outermost surface region R1 were within the range defined in this invention. In particular, Invention Example No. 1 had a cohesive failure rate of 100%, demonstrating remarkably excellent adhesive durability.

[0085] On the other hand, in Comparative Example No. 1, although a silane film was formed, the atomic concentration of silicon A1 and the rate of decrease in silicon concentration M in the outermost surface region R1 were below the lower limit specified in the present invention. This is thought to be because the concentration of the silane compound in the metal treatment solution was lower compared to Invention Example No. 1. Consequently, the cohesive breakdown rate was low.

[0086] In Comparative Example No. 2, a silane film was formed, but the atomic concentration of silicon A1 in the outermost region R1 exceeded the upper limit specified in the present invention. This is thought to be because the concentration of the silane compound in the metal treatment solution was significantly higher compared to Invention Example No. 1. Consequently, the cohesive failure rate was low. In addition, for Comparative Example No. 2, the atomic concentration of silicon A1 in the outermost region R1 was 34.6%, which is higher than the theoretical maximum value when region R1 is entirely covered with a silane film consisting of SiO2. This is thought to be because the total concentration (1.0%) of silane compounds in the metal treatment solution of Comparative Example No. 2 was high. Specifically, it is thought that after the hydrolysis of the silane compounds TEOS and BTSE, the hydrolyzed silane compounds underwent reactions such as condensation polymerization, resulting in a Si content higher than the theoretical maximum value mentioned above, and thus generating silane products in the outermost region R1 that do not contribute to adhesive durability.

[0087] Comparative Example No. 3 had a silane film formed, but the rate of decrease in silicon concentration M was below the lower limit specified in the present invention, resulting in a low cohesive failure rate. It is believed that for Comparative Example No. 3, for example, by performing a wet blasting treatment as a pretreatment or by adjusting the concentration of the silane compound, the atomic concentration A1, atomic concentration A2, and the rate of decrease in silicon concentration M can be controlled within the range specified in the present invention. As detailed above, the bonded test specimens of these comparative examples exhibited low adhesive durability. [Explanation of Symbols]

[0088] 31a Test material (first component) 31b Test material (second component) 35 Adhesive resin layer

Claims

1. A surface-treated stainless steel material having a silane coating provided on at least a portion of the surface of a stainless steel base material, When the elemental distribution is measured by glow discharge emission spectroscopy in the outermost surface region R1 and region R2 at a depth of 10 nm from region R1 within the region where the silane film is provided, The atomic concentration of silicon in the region R1 is 4.0 atomic percent or more and 30.0 atomic percent or less. A surface-treated stainless steel material characterized in that the rate of decrease M of silicon concentration, calculated by the following formula (1) based on the atomic concentration A1 of silicon in the region R1 and the atomic concentration A2 of silicon in the region R2, is 55% or more. M=((A1-A2) / A1)×100...(1)

2. The surface-treated stainless steel material according to claim 1, further comprising an adhesive resin layer on the surface of the silane film.

3. A joint comprising a surface-treated stainless steel material according to claim 1 or 2, The first member and the second member are joined together via an adhesive resin layer. At least one of the first member and the second member is the surface-treated stainless steel material, A jointed body characterized in that the silane coating of the surface-treated stainless steel material and the adhesive resin layer are bonded together.

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