JP6710924B2 - Surface-treated steel sheet and coated parts - Google Patents

Description

The present invention relates to a surface-treated steel plate and a coated member.

For example, many automobile body members are made of a metal plate such as a steel plate, and for example, (1) a blanking step of cutting the metal plate into a predetermined size, (2) an oil wash for cleaning the blank metal plate with oil. Step, (3) step of press forming a blank metal plate, (4) joining step of assembling a forming material into a member having a desired shape by spot welding, adhesion, etc. (5) degreasing and cleaning of press oil on the surface of the joined members Manufacturing process, (6) chemical conversion treatment process, and (7) electrodeposition coating process. Further, a member for an automobile body used as an outer plate is generally further subjected to a coating process such as (8) intermediate coating process and (9) top coating process. Therefore, in the automobile industry, there is a strong need for cost reduction by omitting and simplifying the manufacturing process, particularly the chemical conversion treatment process and the painting process.

In addition, the corrosion resistance of automobile body members is often ensured by a chemical conversion treatment film by a chemical conversion treatment step and an electrodeposition coating film by a subsequent electrodeposition coating step. However, there may be a part where the chemical conversion treatment film and the electrodeposition coating film do not wrap around at the joint part (plate-to-plate part) of the molding material, especially at the plate-to-plate part and the bent hem part on the inner surface of the bag-shaped member. In that case, the joint portion of the molding material is likely to be exposed to the corrosive environment in a bare state. Therefore, rust-preventive auxiliary materials such as body sealers, undercoats, adhesives, and bag waxes are used to supplement the corrosion resistance of the joint portion of the molding material. These rust-preventive auxiliary materials are not only a factor for increasing automobile manufacturing costs, but also a factor for decreasing productivity and increasing vehicle body weight. Therefore, there is a great need for a member for an automobile body that can ensure corrosion resistance even if these rust-preventive auxiliary materials are reduced.

In response to these needs, research and development of surface-treated steel sheets that can simultaneously achieve the omission of chemical conversion treatment process during automobile manufacturing, omission and simplification of electrodeposition coating process, and omission and reduction of auxiliary materials have been actively conducted. It was Such a surface-treated steel sheet is, for example, press-formed, assembled into a desired shape by spot welding or the like, and thereafter, electrodeposition coating is performed, and when electrodeposition coating is omitted, intermediate coating is performed. Therefore, it is necessary to enhance the press formability, make the coating film conductive so that resistance welding or electrodeposition coating can be performed, and impart corrosion resistance.

For example, Patent Document 1 describes an alloyed zinc-plated steel sheet having a resin-based conductive coating film containing zinc powder, which has high corrosion resistance and can be welded. Patent Document 1 describes that zinc powder is preferably contained in the coating film in an amount of 30 to 90% by mass, and the coating film thickness is preferably 2 to 30 μm.

Further, in Patent Document 2, an organic resin coating film containing 3 to 59% by volume of conductive powder and a rust preventive pigment is formed on the rust preventive treatment layer mainly containing a chromium compound in a thickness of 0.5 to 20 μm. A coated organic composite plated steel sheet, which is excellent in corrosion resistance and capable of resistance welding, is described. In the example of Patent Document 2, it is described that iron phosphide, Fe-Si alloy, Fe-Co alloy and the like are used as the conductive powder, and it is also described that they are excellent in corrosion resistance and spot weldability.

Further, in Patent Document 3, an organic resin layer containing 25 to 45% by mass of a conductive pigment containing iron phosphide as a main component and a rust preventive pigment on a chromate base treatment for improving corrosion resistance and coating adhesion. Which is a Ni-containing electrogalvanized steel sheet having a thickness of 2 to 8 μm and is excellent in corrosion resistance, resistance weldability, etc. for automobile repair parts. The examples of Patent Document 3 exemplify both water-based and solvent-based coating resins, and describe that the coating composition for forming the resin coating layer may be either water-based or solvent-based.

Further, in Patent Document 4, an aqueous system containing 10 to 30% by mass of a specific organic binder and 30 to 60% by mass of a conductive powder as a metal surface coating agent having conductivity and capable of forming a weldable corrosion resistant film. The coating agent is listed. Patent Document 4 describes zinc, aluminum, graphite, carbon black, molybdenum sulfide, and iron phosphide as examples of conductive powders suitable for preparing an aqueous coating agent.

In addition, in Patent Document 5 and Patent Document 6, a conductive pigment and rust-prevention are added to the surface of a zinc-based plated steel sheet or an aluminum-based plated steel sheet through a first layer coating that enhances adhesion with a plating layer. There is described an organic coated steel sheet for automobiles which has excellent corrosion resistance and weldability at the same time by coating a resin-based second layer film containing a chemical agent. Patent Documents 5 and 6 exemplify an aqueous system as a coating composition for forming a first layer film, and exemplify both an aqueous system and a solvent system as a coating composition for forming a second layer film. Further, Patent Documents 5 and 6 describe that the second layer film having a film thickness of 1 to 30 μm contains a conductive pigment in an amount of 5 to 70% by volume. Suitable conductive pigments include metals, alloys, and conductive materials. Examples are natural carbon, iron phosphide, carbides, and semiconductor oxides.

Further, Patent Document 7 discloses a coated metal material having a conductive coating film containing alloy particles or compound particles of metal and metalloid elements as conductive particles and a specific urethane resin, and having high corrosion resistance and welding. Possible coated metal materials are listed. Patent Document 7 describes that the conductive particles are preferably alloys or compounds containing 50 mass% or more of Si, and more preferably ferrosilicon containing 70 mass% or more of Si.

Here, among the conductive particles other than the metal particles, as a technique of using the conductive ceramic particles, for example, in Patent Document 8, a core metal is coated with a clad layer made of a corrosion-resistant metal, and further, a conductive material is used. And a corrosion-resistant metal material coated with a conductive material, which is coated with a surface treatment layer made of any resin that binds these, and which is excellent in corrosion resistance and conductivity. Patent Document 8 describes a corrosion-resistant metal selected from titanium, zirconium, tantalum, niobium, or an alloy thereof as a corrosion-resistant metal, and at least one selected from a carbon material, a conductive ceramics, and a metal powder as a conductive material. The above conductive materials are described.

Patent Document 9 discloses a conductive and weldable anticorrosion composition for application to a metal surface, based on the composition as a whole, (a) (aa) at least one epoxy resin (ab) cyanoguanidine At least one curing agent selected from benzoguanamine and plasticized urea resin (ac) 5 to 40% by mass of an organic binder containing at least one amine adduct selected from polyoxyalkylene triamine and epoxy resin/amine adduct, (b) Anticorrosion pigment 0 to 15% by mass, (c) 40 to 70% by mass of powdered zinc, aluminum, graphite, molybdenum sulfide, carbon black and iron phosphide, and (d) 0 to 45% by mass of solvent. , And, if desired, up to 50% by weight of other active or auxiliary substances, the proportion of these components totaling 100% by weight is described.

Patent Document 10 discloses a silane compound (A) having a hydrolyzable group, which is obtained from a silane coupling agent (a1) having a glycidyl group, a tetraalkoxysilane (a2), and a chelating agent (a3), and zirconium carbonate. A zinc-based plated steel sheet containing a compound (B), a vanadate compound (C), a nitric acid compound (D), and water, which is surface-treated with a surface treatment liquid having a pH of 8 to 10, is described. There is.

Patent Document 11 discloses that on at least one surface of a steel strip having a surface roughness of 0.2 to 3 μmRa, a thickness of an organic resin consisting essentially of C, H or C, H, O or C, H, O, N is 0.1. The total amount of the organic resin film is (a) at least 2 to 50% by mass of at least one coupling agent, and (b) at least 2 to 80% by mass of SiO ₂ , Fe ₃ O _4. , characterized in that it contains one or both of _{Fe 2 O 3, Ni-O} , Zr-O, at least one metal oxide selected from _Cr 2 _{O 3} and _Al 2 _{O 3,,} an inner magnetic shield The material is listed.

In patent document 12, Mg:1-10 mass%, Al:2-19 mass%, Si:0.01-2 mass% is contained in the surface of a steel plate, and Mg and Al contain the following formula Mg (mass). %)+Al (mass %)≦20 mass %, the balance has a Zn alloy plating layer consisting of Zn and unavoidable impurities, and further has a zirconium compound of 10 to 30 mass% and a vanadyl compound of zirconium on its surface layer. Described is a chromate-free hot-dip zinc-aluminum alloy-plated steel sheet having excellent weldability and corrosion resistance, which has a coating containing 5 to 20 mass% of vanadium on at least one surface of 200 to 1200 mg/m ^{2 as} an adhesion amount. Has been done.

In Patent Document 13, (α) silica, (β) phosphoric acid and/or a phosphoric acid compound, and (γ)Mg, Mn are used as a first layer coating on the surface of a zinc-based plated steel sheet or an aluminum-based plated steel sheet. , A surface-treated steel sheet containing at least one metal selected from Al (including the case where it is contained as a compound and/or a complex compound) and a (σ) tetravalent vanadium compound is described. There is.

In Patent Document 14, in order from the steel sheet side, a metal tin layer, a tin oxide layer having an electric quantity of 0.3 to 2.5 mC/cm ² required for reduction, Sn, Fe, Al, Mg, Ca, Ti, Ni, Co. , Zn one or more phosphates or polymetaphosphates of Zn at least as a P content in a chemical conversion treatment layer having 0.1 to 5 mg/m ² is described. ..

Patent Document 15, are formed on the upper layer of the chemical conversion layer, Zr film of 1-500 mg / ^{m 2} of metal Zr content, a P content 0.1-100 mg / ^{m 2} phosphate film, the C amount 0.1 A steel sheet for containers having a Zr-containing coating layer containing two or more of the phenol resin coatings of 100 mg/m ² is described.

Patent Document 16 discloses a main resin, a curing agent, and one or more single metal powders selected from the group consisting of Ni, Co, Mn, Fe, Ti, Cu, Al, Zn, Sn, and Fe ₂ P. Alternatively, a precoated steel sheet coated with a resin metal composition for coating containing these alloy powders is described.

JP-A-55-17508 JP, 9-276788, A JP, 2000-70842, A Japanese Patent Publication No. 2003-513141 JP 2005-288730 A JP, 2005-325427, A JP, 2004-42622, A JP, 2003-268567, A Japanese Patent Publication No. 2003-532778 JP, 2013-60647, A JP 2004-83922 A JP, 2003-55777, A JP, 2005-154812, A JP, 2007-239004, A JP, 2009-249691, A Japanese Patent Publication No. 2013-515854

Surface-treated steel sheets, which are widely used for automobile parts, machine parts, home appliances parts, building materials, etc., need to have high adhesion with the electrodeposition coating film after electrodeposition coating in order to improve the corrosion resistance after coating. is there. On the other hand, weldability is also required.
However, regarding the adhesion and weldability with the electrodeposition coating film, although research and development have been carried out in the techniques described in the above-mentioned respective documents, further improvement is desired with the recent increase in the required level. Is the current situation.

Therefore, an object of the present invention is to provide a surface-treated steel sheet having excellent adhesion and weldability with an electrodeposition coating film after electrodeposition coating, and a coated member using the surface-treated steel sheet.

<1> At least one surface selected from the group consisting of a binder resin, conductive particles, an anticorrosive pigment, zirconia particles, titania particles, nickel oxide particles, and tin (IV) oxide particles on at least one surface of the plated steel sheet. 1 type, and containing the oxide particles having an average particle size of 5 to 200 nm, the content of the conductive particles is 5 to 30 mass% with respect to the coating film, the content of the oxide particles is A surface-treated steel sheet having a coating film having a coating amount of 1 to 10% by mass with respect to the coating film and an adhesion amount of ² to 20 g/m ² .

<2> The surface-treated steel sheet according to <1>, wherein the binder resin is a water-soluble or water-dispersible water-based resin.

<3> The surface according to <1> or <2>, wherein the conductive particles are at least one kind of conductive particles selected from the group consisting of non-oxide ceramic particles, iron alloy particles, and stainless particles. Treated steel plate.

<4> The conductive particles are two or more kinds of conductive particles of non-oxide ceramic particles, iron alloy particles, and at least one kind selected from the group consisting of stainless particles,
Mass ratio of the non-oxide ceramic particles and at least one selected from the group consisting of the iron alloy particles and the stainless particles (consisting of the non-oxide ceramic particles/the iron alloy particles and the stainless particles). The surface-treated steel sheet according to any one of <1> to <3>, wherein at least one selected from the group is 1/9 to 8/2.

<5> The <3> or <4>, wherein the non-oxide ceramic particles are at least one selected from the group consisting of non-oxide ceramic particles containing Ti and non-oxide ceramic particles containing Zr. Surface treated steel sheet.

<6> The anticorrosion pigment is aluminum tripolyphosphate, Zn, Mg, Al, Ti, Zr and Ce salts of phosphoric acid and phosphorous acid, a hydrocalumite-treated phosphate compound, Ca ion-exchanged silica, and <1> to <which is at least one rust preventive pigment selected from the group consisting of amorphous silica having an oil absorption of 100 to 1000 ml/100 g, a specific surface area of 200 to 1000 m ² /g, and an average particle diameter of 2 to 30 μm. 5> The surface-treated steel sheet according to any one of 5>.

<7> The surface-treated steel sheet according to any one of <1> to <6>, wherein the plated steel sheet is a zinc-based plated steel sheet or an aluminum-based plated steel sheet.

<8> A molding material obtained by molding the surface-treated steel sheet according to any one of <1> to <7>,
On the coating film of the molding material, an electrodeposition coating film formed by electrodeposition coating treatment,
Coating member having.

According to the present invention, it is possible to provide a surface-treated steel sheet having excellent adhesion and weldability with an electrodeposition coating film after electrodeposition coating, and a coated member using the surface-treated steel sheet.

FIG. 1A is a schematic diagram for explaining an estimated effect of improving the adhesion with the electrodeposition coating film in the surface-treated steel sheet according to the present embodiment. FIG. 1B is a schematic diagram for explaining an estimated effect of improving the adhesion with the electrodeposition coating film in the surface-treated steel sheet according to the present embodiment.

Hereinafter, an embodiment that is an example of the present invention will be described.

<Surface-treated steel sheet>
Surface-treated steel sheet according to the present embodiment, on at least one surface of the plated steel sheet, binder resin, conductive particles, rust-preventive pigment, zirconia particles, titania particles, nickel oxide particles, and tin oxide (IV) particles from At least one selected from the group consisting of, and the oxide particles having an average particle size of 5 to 200 nm, and the content of the conductive particles is 5 to 30 mass% with respect to the coating film, A surface-treated steel sheet having a coating film (hereinafter, also referred to as "resin coating film") in which the content of oxide particles is 1 to 10 mass% with respect to the coating film, and the adhesion amount is ² to 20 g/m2.

The surface-treated steel sheet according to the present embodiment is excellent in both the adhesion to the electrodeposition coating film after electrodeposition coating and the weldability due to the above configuration. The reason is presumed as follows.

Prior to performing electrodeposition coating on the surface-treated steel sheet, a chemical conversion treatment (for example, a phosphate treatment, a fluorine-free (FF) chemical conversion treatment, etc.) is often performed to form a chemical conversion treatment film. However, the chemical conversion treatment property on the resin coating film is poor and it is difficult to form a chemical conversion treatment film.
On the other hand, in the resin coating film of the surface-treated steel sheet, when the oxide particles having the above-mentioned average particle diameter are included in the above-mentioned predetermined content, the oxide particles are dispersed also on the surface layer side of the resin coating film, and a part of the resin is used. It exists in an exposed state on the surface of the coating film (see FIG. 1A).

Then, when electrodeposition coating is applied on the resin coating film in which the oxide particles are exposed on the surface, an electrodeposition coating film is formed on the resin coating film in a state of being in contact with the oxide particles (see FIG. 1B). ).
When at least one selected from the group consisting of zirconia particles, titania particles, nickel oxide particles, and tin (IV) oxide particles is applied as the oxide particles exposed on the surface of such a resin coating film, electrodeposition coating is performed. It is considered that when this is done, it has some influence on the cohesive precipitation of the electrodeposition coating film, and the oxide particles and the electrodeposition coating film are firmly adhered. Therefore, even if the amount of the chemical conversion coating adhered is not sufficient, the oxide particles provide strong adhesion between the resin coating film and the electrodeposition coating film (especially the secondary adhesion after the hot salt water test). Is considered to be expressed.

In addition, the resin coating film has excellent weldability because the adhesion amount is within the above range and the conductive particles are included within the above range to increase the conductivity, and the oxide particles hardly inhibit the conductivity.

From the above, it is presumed that the surface-treated steel sheet according to the present embodiment is excellent in both the adhesiveness with the electrodeposition coating film after electrodeposition coating and the weldability due to the above configuration.
1A and 1B, 10 represents a resin coating film, 12 represents oxide particles, and 14 represents an electrodeposition coating film.

In the surface-treated steel sheet according to the present embodiment, the resin coating film may be formed on both sides of the plated steel sheet, or may be formed on only one side of the plated steel sheet, depending on the application. Further, the resin coating film may be formed on a part of the surface of the plated steel sheet, or may cover the entire surface of the plated steel sheet. The portion of the plated steel sheet on which the resin coating film is formed has excellent adhesion with the electrodeposition coating film and resistance weldability. It also has excellent corrosion resistance and moldability.

Hereinafter, the surface-treated steel sheet according to this embodiment will be described in detail.

[Plated steel sheet]
Examples of the plated steel sheet include well-known plated steel sheets such as zinc-based plated steel sheet and aluminum-based plated steel sheet. The steel plate may be a normal steel plate or a steel plate containing an additive element such as chromium. However, in the case of press forming, the steel sheet is preferably a steel sheet in which the type and amount of addition elements and the metallographic structure are appropriately controlled so as to have desired followability for forming processing.

Examples of the zinc-based plating layer of the zinc-based plated steel sheet include a plating layer made of zinc and an alloy plating layer of zinc and at least one of aluminum, cobalt, tin, nickel, iron, chromium, titanium, magnesium, and manganese. Various zinc-based alloy plating layers containing further other metal elements or non-metal elements (for example, quaternary alloy plating layers with zinc, aluminum, magnesium, and silicon) can be mentioned. However, alloy components other than zinc are not particularly limited in the zinc-based plating layer.
Incidentally, in these zinc-based plating layers, further, as a small amount of different metal elements or impurities, cobalt, molybdenum, tungsten, nickel, titanium, chromium, aluminum, manganese, iron, magnesium, lead, bismuth, antimony, tin, It may contain copper, cadmium, arsenic or the like, or may contain an inorganic substance such as silica, alumina or titania.

Examples of the aluminum-based plating layer of the aluminum-based plated steel sheet include a plating layer made of aluminum, an alloy plating layer of aluminum and at least one of silicon, zinc, and magnesium (for example, an alloy plating layer of aluminum and silicon, aluminum Examples thereof include an alloy plating layer of zinc, a ternary alloy plating layer of aluminum, silicon and magnesium).

Zinc-based plated steel sheets and aluminum-based plated steel sheets are multi-layer plated steel sheets combined with other types of plating layers (for example, iron plating layers, iron-phosphorus alloy plating layers, nickel plating layers, cobalt plating layers, etc.). Good.

The method for forming the plating layer of the plated steel sheet is not particularly limited. For example, the plating layer is formed by using electroplating, electroless plating, hot dipping, vapor deposition plating, dispersion plating, or the like. The plating layer may be formed by either a continuous method or a batch method. Further, after the plating layer is formed, a zero spangle treatment that is a uniform appearance treatment, an annealing treatment that is a modification treatment of the plating layer, a temper rolling for adjusting a surface state or a material may be performed.

[Resin coating]
The resin coating film contains a binder resin, conductive particles, a rust preventive pigment, and oxide particles. The resin coating film may contain other additives as needed.

(Oxide particles)
The oxide particles are at least one selected from the group consisting of zirconia particles, titania particles, nickel oxide particles, and tin (IV) oxide particles.
Among these, the oxide particles are preferably at least one selected from the group consisting of zirconia particles and titania particles from the viewpoint of further improving the adhesion between the resin coating film and the electrodeposition coating film. ..

Here, these oxide particles do not exist in a state of being dissolved in a composition for forming a resin coating film (for example, in the case of titanium oxide, a state of titanium chelate or the like), but as a primary particle having a particle size of several nm or more. It means a substance mainly composed of an oxide of each metal (zirconium, titanium, nickel, or tin (IV)) which is present in a solid state and dispersed in the composition.
It should be noted that these oxide particles can not only enhance the adhesion to the electrodeposition coating film, but also enhance the durability in an environment immersed in salt water.

The average particle diameter of the oxide particles is 5 to 200 nm. When the average particle size of the oxide particles is less than 5 nm, it is difficult to obtain and the cost is disadvantageous. When the average particle size of the oxide particles exceeds 200 nm, the abundance ratio of the oxide particles occupying the surface of the coating film decreases, so that it becomes difficult to obtain adhesion between the resin coating film and the electrodeposition coating film.
The average particle size of the oxide particles is preferably 10 to 200 nm from the viewpoint of further improving the adhesion between the resin coating film and the electrodeposition coating film.

The “average particle size” of the oxide particles refers to the average primary particle size when the oxide particles present in the resin coating film are present alone, and agglomerates when the oxide particles are present in agglomerated form. It means the average secondary particle size representing the particle size of the oxide particles at that time, and is preferably obtained by the following measuring method. First, the surface-treated steel sheet on which the resin coating film is formed is cut to expose its cross section, and the cross section is further polished. The cross section thus obtained is observed with an electron microscope to obtain an observation image of the cross section in the resin coating film. Select several oxide particles present in the field of view of the observed image, measure the long side length and short side length of each oxide particle, the average value of these long side length and the average of the short side length The value is calculated, and these are averaged to calculate the average particle size.
The numerical value of the average particle size varies slightly depending on the measuring method. For example, when a particle size distribution meter is used, it may vary depending on the measurement principle, and in the case of image analysis, it may vary depending on the image processing method. However, the range of the particle size of the oxide particles defined in the present specification takes such variations into consideration, and the particle size obtained by any method is within the range specified in the present specification. If so, the desired effect can be stably achieved.

The commercially available products that can be used as the oxide particles are as follows.
Examples of commercially available zirconia particles include nano-use zirconia sol manufactured by Nissan Chemical Industries, Ltd.
Examples of commercially available titania particles include TKS (registered trademark) series titania sol manufactured by Teika Co., Ltd.
Examples of commercially available nickel oxide particles include nickel oxide particles manufactured by Ioritech Co., Ltd.
Examples of commercially available tin (IV) oxide particles include ceramase tin (IV) oxide sol manufactured by Taki Chemical Co., Ltd.

The content of the oxide particles is 1 to 10 mass% with respect to the resin coating film (total solid content of the coating film).
When the content of the oxide particles is less than 1% by mass, the oxide particles are hard to be exposed on the surface of the resin coating film, and the adhesion between the resin coating film and the electrodeposition coating film is hard to be obtained. On the other hand, when the content of the oxide particles exceeds 10% by mass, the ratio of the rust-preventive pigment having other functions and the ratio of the binder resin are relatively decreased, so that the weldability and the corrosion resistance are compatible while ensuring the adhesion. It becomes difficult to do.
The content of the oxide particles is preferably 2.5 to 7.5 mass% from the viewpoint of further improving the adhesion between the resin coating film and the electrodeposition coating film.

(Binder resin)
The binder resin may be either a water-soluble or water-dispersible water-based resin that is dissolved or dispersed in water, and a solvent-based resin that is dissolved or dispersed in an organic solvent, but in terms of manufacturing costs and environmental suitability, the water-based resin is preferable.

Examples of the water-based resin include water-soluble or water-dispersible resins such as polyester resins, urethane resins, polyolefin resins, acrylic resins, epoxy resins, phenol resins, and mixed resins of two or more kinds of these resins. When using a polyester resin, the molecular weight is preferably 10,000 to 30,000. When the molecular weight is less than 10,000, it may be difficult to secure sufficient workability. On the other hand, when the molecular weight exceeds 30,000, the binding site of the resin itself is lowered, and it may be difficult to secure excellent adhesion with the coating film. Further, when crosslinking is performed using a curing agent such as melamine, the crosslinking reaction may not be sufficiently performed and the performance as a resin coating film may be deteriorated. When a urethane resin is used, the preferred form of the urethane resin is an emulsion having an emulsion particle size of 10 to 100 nm (preferably 20 to 60 nm). If the emulsion particle size is too small, the cost may increase. On the other hand, when the emulsion particle size is excessively large, the gap between the emulsions becomes large when formed into a coating film, and the barrier properties as a resin coating film may deteriorate. Examples of the urethane resin type include ether type, polycarbonate type, ester type, and acrylic graphite type. These may be used alone or in combination.

On the other hand, examples of the solvent-based resin include polyester resin, urethane resin, epoxy resin, acrylic resin, and mixed resin of two or more kinds of these resins.

Here, the binder resin may be a cross-linked resin having a cross-linked structure or a non-cross-linked resin having no cross-linked structure, but from the viewpoint of low temperature film formation of the resin coating film, the non-cross-linked resin Be good.
A water-soluble crosslinking agent is preferable as the crosslinking agent (curing agent) that imparts a crosslinked structure to the binder resin. Specific examples of the cross-linking agent include melamine, isocyanate, silane compounds, zirconium compounds and titanium compounds. The addition amount of the crosslinking agent is preferably 5 parts by mass to 30 parts by mass with respect to 100 parts by mass of the resin solid content. If the addition amount of the cross-linking agent is less than 5 parts by mass, the cross-linking reaction with the resin may be deteriorated and the performance as a coating film may be insufficient. On the other hand, when the addition amount of the cross-linking agent is more than 30 parts by mass, the cross-linking reaction proceeds too much, the resin coating film becomes excessively hard, and the processability is deteriorated. Paint stability may decrease.

The content of the binder resin is preferably 20 to 80 mass% with respect to the resin coating film (total solid content of the coating film).
When the content of the binder resin is less than 20% by mass, the function as a binder is not exhibited, the cohesive force of the resin coating film is reduced, and the inside of the coating film is broken when an adhesion test or a molding process is performed. (Cohesive failure of coating film) may easily occur. When the content of the binder resin exceeds 80% by mass, the ratio of the pigment component contained in the resin coating film becomes small, and it may be difficult to achieve both weldability, corrosion resistance and adhesion after coating.
The content of the binder resin is 25 to 70 relative to the resin coating film (total solid content of the coating film) from the viewpoint of exhibiting a binder function and achieving both weldability, corrosion resistance, and adhesion with the electrodeposition coating film. Mass% is more preferable, and 30-60 mass% is still more preferable.

Here, in the resin coating film, in order to improve the weldability and corrosion resistance, the content ratio of the conductive particles and the rust preventive pigment is increased, and the content ratio of the binder resin contributing to the adhesion with the electrodeposition coating film is reduced. Even (for example, even if the volume ratio of the binder resin is reduced to less than 50% by volume with respect to the resin coating film), the oxide particles can enhance the adhesion between the resin coating film and the electrodeposition coating film. For this reason, it becomes easy to realize a surface-treated steel sheet having excellent adhesion to the electrodeposition coating film, weldability, and corrosion resistance. However, the volume ratio of the binder resin to the resin coating film is preferably 40% by volume or more from the viewpoint of ensuring the cohesive force of the coating film itself.
As for the volume ratio of the binder resin to the resin coating film, when the components of the resin coating film and their specific gravities are recognized, the volume ratio of the binder resin component can be calculated from the content and specific gravity of each component. .. If the components and specific gravity of the resin coating cannot be recognized, or if the resin coating has already been formed, first, the surface-treated steel sheet on which the resin coating is formed is cut to expose its cross section, Polish. The cross section thus obtained is observed with an electron microscope, and the area ratio of the binder resin component is determined by image analysis. It is possible to carry out this operation with 10 different visual fields and average the area ratios to obtain the values.

(Conductive particles)
Examples of the conductive particles include known conductive particles such as non-oxide ceramic particles, iron alloy particles, stainless particles, particles other than iron alloys (metal particles, metal alloy particles, etc.).
Among these, the conductive particles are preferably at least one selected from the group consisting of non-oxide ceramic particles, iron alloy particles, and stainless particles.

Even when the composition for forming a resin coating film is an aqueous composition, the non-oxide ceramic particles and the stainless particles are less likely to deteriorate in the composition and can retain high conductivity. This makes it possible to maintain the excellent weldability of the surface-treated steel sheet for a long period of time.
Iron alloy particles, when the composition for forming a resin coating film is an aqueous composition, inferior in stability in an alkaline aqueous composition, but in an acidic aqueous composition containing a part of polyester resin, etc. , Stability is excellent to some extent. Therefore, when the composition for forming a resin coating film is an acidic aqueous composition, it becomes possible to maintain the excellent weldability of the surface-treated steel sheet for a long period of time.

The non-oxide ceramic particles will be described.
The non-oxide ceramics constituting the non-oxide ceramics particles are non-oxides having an electric resistivity (volume resistivity, specific resistance) at 25° C. of 0.1×10 ^{−6 to} 185×10 ⁻⁶ Ωcm. Ceramics (boride ceramics, carbide ceramics, nitride ceramics, silicide ceramics, etc.) are preferable.

Here, the non-oxide ceramics are ceramics composed of an element or compound that does not contain oxygen. The boride ceramics, the carbide ceramics, the nitride ceramics, and the silicide ceramics are non-oxide ceramics containing boron B, carbon C, nitrogen N, and silicon Si as main non-metal constituent elements, respectively. .. These are all non-oxide ceramics having an electrical resistivity of less than 0.1×10 ⁻⁶ Ωcm at 25° C.

Since the non-oxide ceramic particles have high conductivity, the content thereof for imparting sufficient conductivity to the resin coating film may be smaller. As a result, the adverse effect on the corrosion resistance and formability of the surface-treated steel sheet is further reduced. For reference, the electric resistivity of pure metal is in the range of 1.6×10 ⁻⁶ Ωcm (Ag simple substance) to 185×10 ⁻⁶ Ωcm (Mn simple substance), and the electric resistivity is 0.1×10 6. ^It can be seen that the non-oxide ceramics in the range of ^{−6 to} 185×10 ⁻⁶ Ωcm has excellent conductivity comparable to that of pure metal.

However, since the non-oxide ceramic particles have high hardness, the content of the non-oxide ceramic particles is preferably 0.5 to 20% by mass, more preferably 1 to 10% by mass, based on the resin coating film. If the content of the non-oxide ceramic particles is less than 0.5% by mass, it may be difficult to maintain weldability even when used in combination with other conductive particles. When the content of the non-oxide ceramic particles exceeds 20% by mass, the conductive particles are likely to stick to the electrode when resistance welding is continuously performed, and welding defects may occur during continuous welding.

Here, examples of the non-oxide ceramic particles are as follows.
Examples of the boride ceramic particles include transition metals of group IV (Ti, Zr, Hf), group V (V, Nb, Ta), group VI (Cr, Mo, W), Mn of the periodic table. Examples thereof include boride ceramic particles of group II (Ca, Sr, Ba) other than Fe, Co, Ni, rare earth elements, or Be and Mg.
In addition, among the bo boride ceramic particles of Be, ceramic particles (for example, Be ₂ B, BeB ₆ etc.) particles having an electrical resistivity at 25° C. of more than 185×10 ⁻⁶ Ωcm have low conductivity and weldability. May decrease. Further, the boride ceramics particles of Mg (Mg ₃ B ₂ , MgB ₂ etc.) particles have low stability against water or acid, and the weldability may deteriorate.

Examples of the carbide ceramic particles include transition metals of group IV (Ti, Zr, Hf), group V (V, Nb, Ta), group VI (Cr, Mo, W) of the periodic table, or Mn, Examples include carbide ceramic particles of Fe, Co, and Ni. The rare earth element and Group II carbide ceramics (for example, YC ₂ , LaC ₂ , CeC ₂ , PrC ₂ , Be ₂ C, Mg ₂ C ₃ , and SrC ₂ ) particles are easily hydrolyzed in a wet atmosphere. , Weldability may be reduced.

As the nitride ceramic particles, each of transition metals of group IV (Ti, Zr, Hf), group V (V, Nb, Ta), group VI (Cr, Mo, W) of the periodic table, or Examples include nitride ceramic particles of Mn, Fe, Co, and Ni. Note that the rare earth element and Group II nitride (eg, LaN, Mg ₃ N ₂ , Ca ₃ N _2, etc.) particles are easily hydrolyzed in a wet atmosphere, and the weldability may be deteriorated.

The silicide ceramic particles include transition metals of group IV (Ti, Zr, Hf), group V (V, Nb, Ta), group VI (Cr, Mo, W) of the periodic table, or Mn, Fe. , Co, and Ni silicide particles are exemplified. Rare earth elements and Group II silicides (for example, LaSi, Mg ₂ Si, SrSi ₂ , BaSi ₂ etc.) particles easily react with water in a wet atmosphere to generate hydrogen, and the weldability is deteriorated. There is.

In addition, as non-oxide ceramic particles, particles of a mixture of two or more kinds selected from the group consisting of these boride ceramics, carbide ceramics, nitride ceramics, and silicide ceramics, and these ceramics as a metal binder. Examples include cermet particles that are mixed and sintered.

When the resin coating film is prepared from an aqueous composition, the standard electrode potential of the metal forming a part of the cermet particles is −0.3 V or more, and the standard electrode potential of the metal forming a part of the cermet particles is water resistant. It is preferably degradable. When the standard electrode potential of the metal that constitutes a part of the cermet particles is less than -0.3 V, if the cermet particles are present in the aqueous composition for a long period of time, a rust layer or a thick oxide insulating layer is likely to occur on the surface of the particles. This is because the conductivity of the particles may be lost. The water degradation resistance of cermet particles, WC-12Co, WC-12Ni , TiC-20TiN-15WC-10Mo 2 C-5Ni the like. The standard electrode potentials of Co and Ni are -0.28 V and -0.25 V, respectively, which are nobler than -0.3 V, and both metals are resistant to water deterioration.

Here, among the non-oxide ceramics, Cr-based ceramics (CrB, CrB ₂ , Cr ₃ C ₂ , Cr ₂ N, CrSi, etc.) are concerned about environmental load, and Hf-based ceramics (HfB ₂ , HfC, HfN, etc.) and many rare earth element-based ceramics on the heavy rare earth side of Tb are high in price and not available in the market. Therefore, non-oxide ceramic particles excluding these ceramics, or these ceramics are excluded. Particles of a mixture of two or more of non-oxide ceramics are preferred.

Further, as the non-oxide ceramic particles, non-oxide ceramics exemplified below are more preferable from the viewpoints of the presence or absence of industrial products, stable distribution in domestic and overseas markets, price, electric resistivity and the like. That is, the non-oxide ceramic particles are BaB ₆ (electrical resistivity 77×10 ⁻⁶ Ωcm), CeB ₆ (the same 30×10 ⁻⁶ Ωcm), Co ₂ B (the same 33×10 ⁻⁶ Ωcm), CoB(the same). Same 76×10 ⁻⁶ Ωcm), FeB (same 80×10 ⁻⁶ Ωcm), GdB ₄ (same 31×10 ⁻⁶ Ωcm), GdB ₆ (same 45×10 ⁻⁶ Ωcm), LaB ₄ (same 12×). 10 ^-6 Ωcm), LaB ₆ (same _{^{15 × 10 -6 Ωcm), Mo}} 2 B ( the ^{40 × 10 -6 Ωcm), MoB} ( the ^{35 × 10 -6 Ωcm), MoB} 2 ( same 45 × 10 ^{- 6} Ωcm), Mo ₂ B ₅ (the same 26×10 ⁻⁶ Ωcm), Nb ₃ B ₂ (the same 45×10 ⁻⁶ Ωcm), NbB (the same 6.5×10 ⁻⁶ Ωcm), Nb ₃ B ₄ (the same). The same 34×10 ⁻⁶ Ωcm), NbB ₂ (the same 10×10 ⁻⁶ Ωcm), NdB ₄ (the same 39×10 ⁻⁶ Ωcm), NdB ₆ (the same 20×10 ⁻⁶ Ωcm), PrB ₄ (the same 40). ×10 ⁻⁶ Ωcm), PrB ₆ (same 20×10 ⁻⁶ Ωcm), SrB ₆ (same 77×10 ⁻⁶ Ωcm), TaB (same 100×10 ⁻⁶ Ωcm), TaB ₂ (same 100×10 −10 ^{−). 6} Ωcm), TiB (the same 40×10 ⁻⁶ Ωcm), TiB ₂ (the same 28×10 ⁻⁶ Ωcm), VB (the same 35×10 ⁻⁶ Ωcm), VB ₂ (the same 150×10 ⁻⁶ Ωcm), W ₂ B ₅ (same 80×10 ⁻⁶ Ωcm), YB ₄ (same 29×10 ⁻⁶ Ωcm), YB ₆ (same 40×10 ⁻⁶ Ωcm), YB ₁₂ (same 95×10 ⁻⁶ Ωcm), ZrB ₂ (same 60×10 ⁻⁶ Ωcm), MoC (same 97×10 ⁻⁶ Ωcm), Mo ₂ C (same 100×10 ⁻⁶ Ωcm), Nb ₂ C (same 144×10 ⁻⁶ Ωcm), NbC. (Same 74×10 ⁻⁶ Ωcm), Ta ₂ C (same 49×10 ⁻⁶ Ωcm), TaC (same 30×10 ⁻⁶ Ωcm), TiC (same 180×10 ⁻⁶ Ωcm), V ₂ C (same). 140×10 ⁻⁶ Ωcm), VC (150×10 ⁻⁶ Ωcm), WC (80×10 ⁻⁶ Ωcm), W ₂ C (80×10 ⁻⁶ Ωcm), ZrC (70×10 ^{−). 6} Ωcm), Mo ₂ N (same 20×10 ⁻⁶ Ωcm) ), Nb ₂ N (same 142×10 ⁻⁶ Ωcm), NbN (same 54×10 ⁻⁶ Ωcm), ScN (same 25×10 ⁻⁶ Ωcm), Ta ₂ N (same 135×10 ⁻⁶ Ωcm), TiN (same 22×10 ⁻⁶ Ωcm), ZrN (same 14×10 ⁻⁶ Ωcm), CoSi ₂ (same 18×10 ⁻⁶ Ωcm), Mo ₃ Si (same 22×10 ⁻⁶ Ωcm), Mo ₅ Si. ₃ (46×10 ⁻⁶ Ωcm), MoSi ₂ (22×10 ⁻⁶ Ωcm), NbSi ₂ (6.3×10 ⁻⁶ Ωcm), Ni ₂ Si (20×10 ⁻⁶ Ωcm), Ta ₂ Si (same as 124×10 ⁻⁶ Ωcm), TaSi ₂ (same as 8.5×10 ⁻⁶ Ωcm), TiSi (same as 63×10 ⁻⁶ Ωcm), TiSi ₂ (same as 123×10 ⁻⁶ Ωcm), V ₅ Si ₃ (same 115×10 ⁻⁶ Ωcm), VSi ₂ (same 9.5×10 ⁻⁶ Ωcm), W ₃ Si (same 93×10 ⁻⁶ Ωcm), WSi ₂ (same 33×10 ⁻⁶ Ωcm). Ωcm), ZrSi (49×10 ⁻⁶ Ωcm) and ZrSi ₂ (76×10 ⁻⁶ Ωcm), and particles of a mixture of two or more selected from these are more preferable.

Among these, non-oxide ceramic particles having an electric resistivity at 25° C. in the range of 0.1×10 ^{−6 to} 100×10 ⁻⁶ Ωcm are particularly preferable. Because these have higher conductivity than the non-oxide ceramic particles having an electric resistivity at 25° C. of more than 100×10 ⁻⁶ Ωcm to 185×10 ⁻⁶ Ωcm, they are sufficient for resin coating. This is because the content of non-oxide ceramic particles for imparting excellent conductivity can be reduced. By reducing the content of the non-oxide ceramic particles, it is possible to suppress the formation of a conductive path for a corrosion current that penetrates the resin coating film, and to suppress the deterioration of corrosion resistance. In addition to this, peeling or galling of the resin coating film during press molding is suppressed, and deterioration of moldability is suppressed.

Among the non-oxide ceramic particles, most preferable are non-oxide ceramic particles containing Ti (for example, particles of TiB, TiB ₂ , TiC, TiN, TiSi, TiSi _{2 and the} like) and non-oxidation containing Zr. It is at least one selected from the group consisting of material ceramic particles (for example, particles such as ZrB ₂ , ZrC, ZrN, ZrSi, and ZrSi ₂ ).
These non-oxide ceramic particles have excellent conductivity, when performing arc welding, or laser welding, the non-oxide ceramic particles are oxidized near the bead toe with a large heat input, A part of the Ti-containing system (non-oxide ceramic particles containing Ti) is TiO ₂ , and a part of the Zr-containing system (non-oxide ceramic particles containing Zr) is ZrO ₂ , so that the vicinity of the bead toe It is possible to suppress a decrease in adhesion after coating.

In addition, the electrical resistivity shown in parentheses of the exemplified non-oxide ceramics is a representative value (reference value) of those sold and used as industrial materials. These electrical resistivities increase and decrease depending on the type and amount of the impurity element that has entered the crystal lattice of the non-oxide ceramics. For this reason, for example, a four-terminal four-probe method using a resistivity meter Loresta EP (MCP-T360 type) manufactured by Mitsubishi Chemical Analytech Co., Ltd. and an ESP probe (diameter of the flat head of the terminal is 2 mm) is used. It is advisable to measure the electrical resistivity at 25° C. according to JIS K7194 by a current application method and confirm that it is in the range of 0.1×10 ^{−6 to} 185×10 ⁻⁶ Ωcm before using. ..

The iron alloy particles will be described.
The iron alloy particles are alloy particles of iron with at least one alloy selected from the group consisting of Si, V, Mn, W, Mo, Ti, Ni and Nb. Examples of the iron alloy powder include ferrosilicon, ferrovanadium, ferromanganese, ferrotungsten, ferromolybdenum, ferrotitanium, ferronickel, ferroboron, and ferroniob.
Among these, ferrosilicon and ferromanganese are preferable as the iron alloy particles from the viewpoint of corrosion resistance in addition to weldability.

The stainless particles will be described.
The stainless particles are alloy particles in which Cr is contained in Fe in an amount of 10.5% by mass or more (however, the content of C is 1.2% by mass or less).

The characteristics of the conductive particles will be described.
The particle shape of the conductive particles may be spherical, pseudo-spherical (eg, ellipsoidal, egg, rugby ball, etc.), or polyhedral (eg, soccer ball, dice, brilliant cut of various gems, etc.). A shape close to a sphere is preferable. The conductive particles having a shape close to a sphere are uniformly dispersed in the resin coating film, and it becomes easy to form an effective current-carrying path that penetrates the resin coating film in the thickness direction, and the bondability is further improved. On the other hand, elongated (eg rod-shaped, needle-shaped, fibrous, etc.) or planar (eg flake-shaped, flat-plate-shaped, flaky-shaped, etc.) conductive particles are parallel to the coating surface during the resin coating formation process. By arranging them or depositing them near the interface between the plated steel sheet (the surface treatment layer if the surface of the plated steel sheet has a surface treatment) and the resin coating film, an effective current path that penetrates through the thickness of the resin coating film is formed. It may be difficult to do so, and the bondability may decrease.

The average particle diameter of the conductive particles is not particularly limited, but is preferably 0.2 to 5 μm, more preferably 0.5 to 2.5 μm. When the average particle diameter of the conductive particles is in the range of 0.2 to 5 μm, it becomes easy to form an effective current-carrying path that penetrates the resin coating film in the thickness direction, and the bondability is further improved. The term "means the average primary particle diameter when the conductive particles present in the resin coating film are present alone, and the particle diameter of the conductive particles at the time of aggregation when the conductive particles agglomerate. Means the average secondary particle size, and is preferably obtained by the following measuring method. First, the surface-treated steel sheet on which the resin coating film is formed is cut to expose its cross section, and the cross section is further polished. The cross section thus obtained is observed with an electron microscope to obtain an observation image of the cross section in the resin coating film. Select several pigments present in the field of view of the observation image, measure the long side length and the short side length of each conductive particle, the average value of these long side length and the average value of the short side length The average particle diameter is calculated by averaging these values.

A suitable aspect of the conductive particles will be described.
The conductive particles are preferably two or more kinds of conductive particles of non-oxide ceramic particles and at least one kind selected from the group consisting of iron alloy particles and stainless particles. Then, the mass ratio of the non-oxide ceramic particles and at least one selected from the group consisting of iron alloy particles and stainless particles (selected from the group consisting of non-oxide ceramic particles/iron alloy particles and stainless particles). 1) to 9/2 is preferable, 1/9 to 7/3 is more preferable, and 2/8 to 6/4 is further preferable.
When the non-oxide ceramic particles as the conductive particles are used together with at least one selected from the group consisting of iron alloy particles and stainless particles in the ratio in the above range, the conductivity of the resin coating film is increased and the weldability is improved. Is further improved. It is possible to reduce the content of hard non-oxide particles. Then, it is possible to suppress the occurrence of the phenomenon that the conductive particles are stuck into the electrode when the resistance welding is continuously performed, and to suppress the occurrence of welding defects and the like during the continuous welding.

The content of the conductive particles will be described.
The content of the conductive particles is 5 to 30 mass% with respect to the resin coating film (total solid content of the coating film).
When the content of the conductive particles is less than 5 mass %, sufficient weldability cannot be obtained. When the content of the conductive particles exceeds 30% by mass, the adhesiveness is reduced due to the decrease in the cohesive force of the coating film.
The content of the conductive particles is more preferably 10 to 20% by mass with respect to the resin coating film (total solid content of the coating film) from the viewpoint of weldability, coating film adhesion and the like.

(Rust preventive pigment)
The anticorrosive pigment is not particularly limited, but may include aluminum tripolyphosphate, Zn, Mg, Al, Ti, Zr and Ce salts of phosphoric acid and phosphorous acid, and a hydrocalumite-treated phosphate compound (for example, zinc phosphate. EXPERT NP-530 N5) produced by Toho Pigment Co., which is a hydrocalumite treatment, and Ca ion-exchanged silica, and an oil absorption amount of 100 to 1000 ml/100 g, a specific surface area of 200 to 1000 m ² /g, and an amorphous particle size of 2 to 30 μm At least one rust preventive pigment selected from the group consisting of high quality silica is preferable.

Among these, preferred rust-preventive pigments are phosphate-based rust-preventive pigments (aluminum tripolyphosphate, hydrocalumite-treated phosphate compounds, etc.), silica-based It is a rust pigment or a combination of both. Particularly preferred rust preventive pigments include aluminum tripolyphosphate, hydrocalumite-treated phosphoric acid compound, Ca-exchanged silica, oil absorption of 100 to 1000 ml/100 g, specific surface area of 200 to 1000 m ² /g, and average particle diameter of 2 to 30 μm. It is at least one selected from the group consisting of amorphous silica.

The oil absorption of silica can be measured according to JIS K 5101-13-2. The specific surface area of silica can be measured by the BET method. The average particle size of silica can be measured by the same method as the average particle size of conductive particles.

The content of the rust preventive pigment is preferably 5 to 40% by mass with respect to the resin coating film (total solid content of the coating film).
When the content of the rust preventive pigment is less than 5% by mass, sufficient corrosion resistance may not be obtained. If the content of the anticorrosive pigment exceeds 40% by mass, the processability of the coating film and the cohesive force may decrease.
From the viewpoint of corrosion resistance and workability, the content of the rust preventive pigment is more preferably 7.5 to 35% by mass, and further preferably 10 to 30% by mass based on the resin coating film (total solid content of the coating film).

(Other additives)
The resin coating film may contain other additives. Other additives include well-known additives such as extender pigments, solid lubricants, rust preventives and leveling agents.

Examples of extender pigments include silica (including colloidal silica) and titania.

As the solid lubricant, it is possible to impart excellent lubricity to the resin coating film and improve the powdering resistance. Examples of the solid lubricant include the following solid lubricants (1) and (2).
(1) Polyolefin wax, paraffin wax: for example, polyethylene wax, synthetic paraffin, natural paraffin, microwax, chlorinated hydrocarbon, etc. (2) Fluororesin wax: for example, polyfluoroethylene resin (polytetrafluoroethylene resin, etc.), Polyvinyl fluoride resin, polyvinylidene fluoride resin, etc.

The average particle size of the solid lubricant is preferably 0.05 to 25 μm. When the average particle diameter of the solid lubricant is less than 0.05 μm, the surface area of the resin coating film tends to occupy a large amount of the lubricant due to the surface concentration of the lubricant, and thus the resin coating film and the electrodeposition coating film Adhesion may decrease. On the other hand, when the average particle size of the solid lubricant exceeds 25 μm, the lubricant is likely to fall off from the resin coating film, it is difficult to obtain the predetermined lubricity, and the corrosion resistance may decrease. The average particle size of the solid lubricant is more preferably 1 to 15 μm, further preferably 3 to 10 μm, from the viewpoint of obtaining excellent paint adhesion, corrosion resistance, lubricity, and powdering resistance.

100 degreeC-135 degreeC is preferable and, as for the softening point of a solid lubricant, 110-130 degreeC is more preferable. When the softening point of the solid lubricant is 100° C. to 135° C., lubricity and powdering resistance are further improved.

The content of the solid lubricant is preferably 0.1 to 10 mass% with respect to the resin coating film (total solid content of the coating film). When the content of the solid lubricant is less than 0.1% by mass, sufficient lubricity may not be obtained. When the content of the solid lubricant exceeds 10% by mass, the adhesion between the resin coating film and the electrodeposition coating film and the corrosion resistance may decrease.
The content of the solid lubricant is 0.5 to 5 mass% with respect to the resin coating film (total solid content of the coating film) from the viewpoint of adhesion between the resin coating film and the electrodeposition coating film, lubricity, and corrosion resistance. Is more preferable, and 0.5 to 2.5 mass% is even more preferable.

Examples of the rust preventive agent include inorganic rust preventive agents and organic rust preventive agents.
Examples of the inorganic rust preventive agent include water-soluble phosphoric acid compounds. When the phosphoric acid compound is contained in the resin coating film, a phosphate film is formed on the surface of the metal substrate to improve the rust preventive property, as in the case of the phosphoric acid rust preventive pigment. Examples of the water-soluble phosphoric acid compounds include phosphoric acids such as orthophosphoric acid, metaphosphoric acid, pyrophosphoric acid, triphosphoric acid, tetraphosphoric acid and salts thereof, and phosphonic acid and salts thereof.
Examples of the organic rust preventives include guanidino group-containing compounds, piguanidino group-containing compounds, and thiocarbonyl group-containing compounds. These are easily adsorbed on the metal surface and are effective in suppressing white rust on zinc steel plates and the like.

The content of the rust preventive agent is preferably 0.5 to 5 mass% with respect to the resin coating film (total solid content of the coating film). When the content of the rust preventive agent is less than 0.5% by mass, a sufficient effect of improving the corrosion resistance may not be obtained. When the content of the rust preventive agent exceeds 5% by mass, it may be difficult to form a coating due to the deterioration of liquid stability.
From the viewpoint of corrosion resistance and paint stability, the content of the rust preventive agent is more preferably 1 to 3% by mass based on the resin coating film (total solid content of the coating film).

(Amount of resin coating)
The adhesion amount of the resin coating film (the adhesion amount of the total solid content of the resin coating film) is ² to ²⁰ g/m ² . When the adhesion amount of the resin coating film is less than 1 g/m ² , sufficient adhesion and corrosion resistance between the resin coating film and the coating film cannot be obtained. When the adhesion amount of the resin coating film exceeds 20 g/m ² , the cohesive force of the coating film is reduced and the weldability cannot be sufficiently obtained.
The adhesion amount of the resin coating film is preferably ² to 15 g/m ² from the viewpoint of adhesion between the resin coating film and the coating film, weldability, and corrosion resistance.

(Formation of resin coating film)
Formation of the resin coating film is not particularly limited, and a known method can be used. For example, a composition for forming a resin coating film is obtained by mixing a binder resin, conductive particles, a rust preventive pigment, oxide particles and, if necessary, other additives with a solvent. The solvent may be water or an organic solvent, but water is preferable from the viewpoint of production cost and environmental suitability. That is, the composition for forming the resin coating film may be an aqueous composition. Then, the resin coating film-forming composition is applied to at least one surface of the plated steel sheet, dried, and heated to form a resin coating film.

(Other aspects of surface-treated steel sheet)
The surface-treated steel sheet may have a well-known functional film such as a base treatment film for further improving the adhesion of the resin coating film to the plated steel sheet and the corrosion resistance between the plated steel sheet and the resin coating film.
As the undercoating film, there is not a chromate-treated film but an undercoating film that does not substantially contain chromium (chromate-free film). Representative examples of chromate-free treatment liquids include liquid-phase silica, vapor-phase silica, silica-based treatment liquids containing silicon compounds such as silicates as main coating components, and zircon-based treatment liquids containing zircon compounds as main coating components. Be done. These treatment liquids may be treatment liquids in which an organic resin coexists with the main film component. The chromate-free treatment liquid is not limited to the silica treatment liquid and the zircon treatment liquid. As chromate-free treatment liquids, in addition to silica-based treatment liquids and zircon-based treatment liquids, various chromium-free treatment liquids have been proposed for use in coating surface treatment, and are expected to be proposed in the future. To be done. It is also possible to use such a chromium-free processing liquid.
The adhesion amount of the base treatment film may be selected as appropriate depending on the treatment liquid used. For example, in the case of a base treatment film made of a silica type treatment liquid, the usual amount of adhesion is preferably in the range of 1 to 20 mg/m 2 in terms of Si.

<Painted parts>
The coating member according to the present embodiment has a molding material obtained by molding the surface-treated steel sheet according to the present embodiment, and an electrodeposition coating film formed by an electrodeposition coating treatment on the resin coating film of the molding material. ..

The coated member according to the present embodiment is manufactured, for example, as follows. First, for example, a well-known forming technique such as cutting and press forming is used to form a surface-treated steel sheet to obtain a formed body having a desired shape. The formed material may be assembled into a desired shape by welding (spot welding or the like), if necessary.

Next, the resin coating film of the molding material is subjected to electrodeposition coating treatment. As a result, an electrodeposition coating film is formed on the resin coating film. The electrodeposition coating treatment may be either anion electrodeposition coating or cation electrodeposition coating, but from the viewpoint of corrosion resistance, cation electrodeposition coating is preferable.
In particular, a resin [for example, an aqueous resin having a hydrophilic group such as a carboxyl group, a hydroxyl group, a methylol group, an amino group, a sulfonic acid group, or a polyoxyethylene bond and a functional group such as a hydroxyl group that reacts with a curing agent (acrylic resin, Known aqueous resins such as polyester resins, alkyd resins, epoxy resins, polyurethane resins, etc.)], curing agents (melamine resins, block polyisocyanates, etc.), and other additives (coloring pigments, light interference pigments, extender pigments, Cationic electrodeposition coating treatment using an aqueous paint containing a dispersant, an anti-settling agent, a reaction accelerator, a defoaming agent, a thickener, a rust preventive, an ultraviolet absorber, a surface modifier, etc.) Thus, when the electrodeposition coating film is formed, the adhesion between the resin coating film and the electrodeposition coating film is easily improved.

After that, another coating film such as an intermediate coating film and a top coating film may be formed on the electrodeposition coating film of the molding material, if necessary.

The coated member according to the present embodiment is manufactured through these steps.

In addition, before electrodeposition coating, after degreasing and surface conditioning the resin coating film on the molding material on which the resin coating film is formed, chemical conversion treatment (for example, phosphate treatment, fluorine-free (FF) chemical conversion treatment, etc.) ) May be given. By chemical conversion treatment, it is difficult to form a chemical conversion treatment film on the resin coating film, but the chemical conversion treatment film is formed on the required area other than the resin coating film, and the entire molding material (painting member) is electrodeposition coated. The adhesion of the film can be improved.

The coating member according to the present embodiment is widely used for applications such as automobile members (automobile body, underbody members, etc.), mechanical members (housings, etc.), household appliances (housings, etc.), building materials (roofs, walls, etc.), etc. To be done.

Hereinafter, the present invention will be described more specifically with reference to examples. However, each of these examples does not limit the present invention.

[Manufacture of surface-treated steel sheet]
1. Preparation of galvanized steel sheet The following four types of galvanized steel sheet were prepared, and the surface was immersed for 2 minutes in a 2.5 mass% aqueous 40% aqueous solution of an aqueous alkaline degreasing agent (FC-301 manufactured by Nippon Parkerizing Co., Ltd.). After degreasing, it was washed with water and dried to obtain a plated steel sheet for painting.
・EG: Electrogalvanized steel plate (plate thickness 0.8 mm, coating weight 40 g/m ² ).
-ZL: Electric Zn-10 mass% Ni alloy-plated steel plate (plate thickness 0.8 mm, coating amount 40 g/m ² ).
・GI: Hot-dip galvanized steel sheet (plate thickness 0.8 mm, coating weight 60 g/m ² ).
GA: hot-dip galvanized steel sheet (sheet thickness 0.8 mm, 10 mass% Fe, coating weight 45 g/m ² ).

2. Formation of undercoating film Next, the following two types of undercoating film forming compositions were prepared, and the composition was bar-coated on a plated steel sheet to a film thickness of 0.08 μm, which was then heated in a hot-blast stove. At 70° C., the temperature reached to the metal surface was dried and air-dried to form an undercoat on the surface of the plated steel sheet.
-P1: water-based coating composition comprising Zr compound, silane coupling agent, silica fine particles-p2: water-based coating composition comprising polyester resin, silica fine particles, silane coupling agent

3. Formation of resin coating film Next, in order to form a resin coating film having the composition shown in Tables 2 to 4, the respective components are mixed so as to have the same solid content concentration as in Tables 2 to 4, and the resin is formed. An aqueous composition for forming a coating film was prepared. According to Table 5 to Table 8, the obtained water-based composition was applied onto a plated steel sheet with a bar coater, and dried using an oven under the condition that the highest temperature reached was 140° C. for 8 seconds to obtain a resin coating film. Formed. The adhesion amount of the resin coating film was adjusted by the dilution of the water-based composition and the bar coater count so that the total adhesion amount of the solid content (nonvolatile content) in the water-based composition would be the values shown in Tables 5 to 8. ..
In Tables 2 to 4, the solid content concentration of each component is the ratio (unit: mass%, value per one side) of the solid content (nonvolatile content) of each component to the solid content (nonvolatile content) of the entire aqueous composition. .).

Details of each component (symbol) in Tables 2 to 4 are as follows.

(A) Conductive particles/VC: Vanadium carbide particles (average particle size 1 to 3 μm)
MoB2: Molybdenum diboride particles (average particle size 1 to 3 μm)
MoSi2: Molybdenum disilicide particles (average particle size 1 to 3 μm)
ZS: Zirconium disilicide particles (average particle size 1 to 3 μm)
・ZN: Zirconium nitride particles (average particle size 1 to 3 μm)
・TN: Titanium nitride particles TiN particles (average particle size 1 to 3 μm)
・FeV: Ferrovanadium particles (average particle size 3 to 7 μm)
FeSi: Ferrosilicon particles (average particle size 3 to 7 μm)
・SUS: SUS particles (average particle size 3 to 7 μm)

(B) Anticorrosion pigment/PA: Aluminum tripolyphosphate (average particle size 1 to 2 μm)
・PM: Magnesium phosphate (average particle size 1 to 2 μm)
・SC: Calcium ion-exchanged silica (average particle size 1-2 μm)
Si: Silica (oil absorption 100 to 1000 ml/100 g, specific surface area 200 to 1000 m ² /g, amorphous silica having an average particle diameter of 1 to 30 μm) (Fuji Silysia silo mask 02)
HP: Hydrocalumite-treated zinc phosphate (EXPERT NP-530 N5 manufactured by Toho Pigment Co., Ltd.) (average particle size 1 to 2 μm)

(C) Binder resin/U: Urethane resin emulsion (Daiichi Kogyo Seiyaku Co., Ltd. Superflex (registered trademark) E-2000)
P: Polyester resin emulsion (Toyobo Co., Ltd. Bayronal (registered trademark) MD1985)
-O: Polyolefin resin emulsion (Unitika Ltd. Arrowace (registered trademark) SB-1010)
-YP: Solvent-based polyester resin (Toyobo Co., Ltd. Byron (registered trademark) GA2310)

(D) Crosslinking agent/Me: imino group-type melamine resin (Cymel (registered trademark) 325 manufactured by Cytex)
-Z: ammonium zirconium carbonate-T: dibutoxybis(triethanolaminat) titanium-S: γ-glycidoxypropyltrimethoxysilane

(E) Oxide particles/ZrO2: Zirconia sol (Nano Youth (registered trademark) ZR-30AL), particle size 70 to 110 nm (catalog value)
-TiO2: Titanium oxide sol (TK-202 manufactured by Teika Co., Ltd., average particle size of about 6 nm)
-SnO2: tin oxide (IV) sol (Ceramece C-10, Taki Chemical Co., Ltd.), average particle size 10 nm
・NiO: Nickel oxide (Ioritec Co., Ltd. nickel oxide), average particle size 20 nm

(F) Other additives-wax: Polyethylene wax-T: Titania particles (Titanium oxide R-930 manufactured by Ishihara Sangyo) Particle size 250 nm
・CS: Colloidal silica (manufactured by Nissan Chemical Co., Ltd. silica sol ST-O)
-P: Phosphoric acid-O1: Diethylthiourea-O2: Sodium dimethyldithiocarbamate

5. Manufacture of surface-treated steel sheet According to the description of Tables 2 to 8 and the above-mentioned respective operating methods, a base treatment film and a resin coating film were formed on the plated steel sheet, and each sample No. The surface-treated steel sheet of was manufactured.

[Chemical conversion treatment evaluation test]
-Phosphate conversion treatment-
Sample No. Using the surface conditioning treatment agent PREPAREN X (trade name) manufactured by Nihon Parkerizing Co., Ltd., the surface treatment of the surface-treated steel sheet was performed at room temperature for 20 seconds. Furthermore, a phosphate treatment was performed using a chemical conversion treatment liquid (zinc phosphate treatment liquid) "Palbond 3020 (trade name)" manufactured by Nippon Parkerizing Co., Ltd. The temperature of the chemical conversion treatment liquid was 43° C., and the surface-treated steel sheet was immersed in the chemical conversion treatment liquid for 120 seconds, washed with water and dried.

-FF formation treatment-
Sample No. An aqueous solution containing Zr ions and/or Ti ions and fluorine, and 100 to 1000 ppm of free fluorine ions in place of the zinc phosphate treatment for some of the surface-treated steel sheets (see below). , FF chemical conversion treatment liquid).
In order to obtain the FF chemical conversion treatment liquid, H ₂ ZrF ₆ (hexafluorozirconic acid) and H ₂ TiF ₆ (hexafluorotitanic acid) were placed in a container so as to have a predetermined metal concentration and diluted with ion-exchanged water. Then, the hydrofluoric acid and the sodium hydroxide aqueous solution were put into a container, and the fluorine concentration and the free fluorine concentration in the solution were adjusted to predetermined values. The free fluorine concentration was measured using a commercially available concentration measuring instrument. After the adjustment, the container was made to have a constant volume with ion-exchanged water to obtain a FF chemical conversion treatment liquid (see Table 1 for specific composition).
Then, the FF formation treatment was carried out as follows. First, as a pretreatment, immersion degreasing was performed at 45° C. for 2 minutes using an alkaline degreasing agent (EC90 manufactured by Nippon Paint Co., Ltd.). Then, the chemical conversion treatment was carried out by immersing the FF chemical conversion treatment liquid shown in Table 1 below at 40° C. for 120 seconds. After the chemical conversion treatment, the surface-treated steel sheet was washed with water and dried.

[Coating film adhesion evaluation test]
After performing phosphate treatment or FF chemical conversion treatment as the chemical conversion treatment, the surface treated steel sheet (some surface treated steel sheet subjected to FF chemical treatment) is a cationic electrodeposition manufactured by Nippon Paint Co., Ltd. The paint was electrodeposited by applying a voltage of 160 V to the slope and further baked at a baking temperature of 170° C. for 20 minutes. The average film thickness of the coating film after electrodeposition coating was 10 μm in all test numbers.
After carrying out the electrodeposition coating, with a cutter knife (load 500 gf, 1 gf is about 9.8×10 ⁻³ N) for the coating film of the surface-treated steel sheet, put 100 squares of 1 mm squares, A polyester tape was attached to the grid. After that, the tape was peeled off. The number of crosses peeled off by peeling off the tape was determined, and the coating film peeling rate (%) was determined based on the following formula.
-Formula: Coating film peeling rate = (number of peeled grids/100) x 100

"X" in the "paint adhesion" column in Tables 5 to 8 means that the coating film peeling rate was 10.0% or more. “Δ” means that the content was 5.0% or more and less than 10.0%. “◯” means that the coating film peeling rate was less than 5.0% and 1.0% or more. "A" means that the coating film peeling rate was less than 1.0%. In the evaluation of coating film adhesion, when it was “◯” or “⊚”, it was judged that the coating film adhesion was excellent.

[SDT resistance evaluation test]
After the above electrodeposition coating, the surface-treated steel sheet was immersed in a 5% NaCl aqueous solution having a temperature of 50° C. for 500 hours. After the immersion, a polyester tape was attached to the entire surface of the test surface of 60 mm×120 mm (area A10=60 mm×120 mm=7200 mm ² ). After that, the tape was peeled off. The area A2 (mm ² ) of the coating film peeled off by peeling off the tape was obtained, and the coating film peeling rate (%) was obtained based on the following formula.
-Formula: Paint film peeling rate = (A2/A10) x 100

"X" in the "SDT resistance" column in Tables 5 to 8 means that the coating film peeling rate was 30.0% or more. “Δ” means that it was 10.0% or more and less than 30.0%. “◯” means that the coating film peeling rate was less than 10.0% and 5.0% or more. "A" means that the coating film peeling rate was less than 5.0%. In the SDT resistance evaluation, when it was “◯” or “⊚”, it was judged that the SDT resistance was excellent.

[Welding test]
Using the CF type Cr-Cu electrode with a tip diameter of 5 mm and R40, the surface-treated steel sheet before the above chemical conversion treatment is continuously spot-welded at a pressing force of 1.96 kN, a welding current of 8 kA, and an energizing time of 12 cycles/50 Hz. A hitting property test was conducted to find the number of hitting points immediately before the nugget diameter fell below 3√t (t is the plate thickness). The superiority or inferiority of spot weldability was evaluated using the following evaluation points.
⊚: 1000 points or more ○: 200 points or more and less than 1000 points Δ: Less than 200 points ×: Nugget is not formed and no point can be welded In such a weldability test, when “○” or “◎” It was judged that the weldability was excellent.

[Cycle corrosion (corrosion resistance) test]
After the above electrodeposition coating was carried out, the coating film of the surface-treated steel sheet was cut with a cutter knife (load 500 gf, 1 gf is about 9.8×10 ⁻³ N) to make a cycle corrosion under the following cycle conditions. The test was conducted for 180 cycles.

-Cycle conditions-
Salt spray (SST, 5% NaCl, 35° C. atmosphere) for 2 hr, dry×dry (60° C.) for 2 hr, and wet (50° C., 98% RH) for 4 hr were performed as one cycle.
Then, the presence or absence of swelling of the coating film generated in a region having a width of about 1 cm from the cut portion was observed.

"X" in the column "Cycle corrosion resistance (corrosion resistance) test" in Tables 5 to 8 means that the coating film swelled more than 3 mm. “Δ” means that there was a swelling of the coating film of 1 mm or more and less than 3 mm. “◯” means that there was a minute coating film swell of less than 1 mm. “⊚” means that the coating film did not swell. In such a cycle corrosion resistance (corrosion resistance) test, it was judged that the cycle corrosion (corrosion resistance) was excellent when it was “◯” or “⊚”.

[SDT resistance test after simulated arc welding]
The surface-treated steel sheet before the above chemical conversion treatment was irradiated with an arc to prepare a simulated arc-welded steel sheet having a bead in the central portion of the steel sheet.
Then, the above-mentioned simulated arc welded steel sheet was subjected to the above-mentioned phosphate chemical conversion treatment and electrodeposition coating. Then, the steel sheet was immersed in a 5% NaCl aqueous solution having a temperature of 50° C. for 500 hours. After the immersion, a polyester tape was attached to the entire surface including the toe of the bead (25 mm×120 mm=3000 mm ² ). After that, the tape was peeled off. The area A2 (mm ² ) of the coating film peeled off by peeling off the tape was obtained, and the coating film peeling rate (%) was obtained based on the following formula.
-Formula: Paint film peeling rate = (A2/A10) x 100

In Table 5, "x" in the "SDT resistance after simulated arc welding" column means that the paint film peeling rate was 30.0% or more. “Δ” means that it was 10.0% or more and less than 30.0%. “◯” means that the coating film peeling rate was less than 10.0% and 5.0% or more. "A" means that the coating film peeling rate was less than 5.0%. In the SDT resistance evaluation, when it was “◯” or “⊚”, it was judged that the SDT resistance was excellent.

Details of the examples are shown in Tables 2 to 8 below. Samples with blank "Remarks" columns in Tables 5 to 8 correspond to the examples. In the column of binder resin in Table 4, “U+O” of “variety” indicates that both the grade U and the grade O are included in the aqueous composition, and the numerical value above the “concentration (mass %)” is The total amount of resin is shown, and the numerical value in the parentheses at the bottom shows the mass ratio (product U: product O).

From the above results, the sample No. of the surface-treated steel sheet corresponding to the example was obtained. 1-5, 8-23, 25-27, 29-31, 33-46, 49-58, 60-64 are sample No. of the surface treatment steel plate corresponding to a comparative example. It can be seen that both the coating film adhesion (primary adhesion) and the SDT resistance (secondary adhesion) after coating after the phosphate treatment are higher than those of Nos. 6 and 7. In addition, the sample No. of the surface-treated steel sheet corresponding to the example. As shown by 1 to 3 and 49 to 54, it is understood that both the coating film adhesion (primary adhesion) and the SDT resistance (secondary adhesion) after coating after FF chemical conversion treatment are high. And it turns out that the corrosion resistance is also excellent.
In addition, the sample No. of the surface-treated steel sheet corresponding to the example is shown. 1-5, 8-23, 25-27, 29-31, 33-46, 49-58, 60-64 are sample No. of the surface treatment steel plate corresponding to a comparative example. It can be seen that the weldability is superior to those of Nos. 24, 28, and 32.
On the other hand, the sample No. of the surface-treated steel sheet corresponding to the comparative example. In Nos. 47 to 48, since the resin coating film does not contain a rust preventive pigment, it can be seen that the corrosion resistance is deteriorated. Sample No. of the surface-treated steel sheet corresponding to the comparative example. It can be seen that 59 has poor SDT resistance (secondary adhesion) and corrosion resistance because the amount of the resin coating film deposited is too small. Sample No. of the surface-treated steel sheet corresponding to the comparative example. In No. 66, the adhesion of the resin coating film is too large, so that the weldability is deteriorated.
Further, in the SDT resistance test after the simulated arc welding, sample No. containing non-oxidized ceramic particles (conductive pigment) containing Ti or Zr. Sample Nos. 8 and 11 to 12 each include non-oxidized ceramic particles (conductive pigment) containing no Ti or Zr. It can be seen that the coating film adhesion is excellent as compared with 9 to 10 and 13.

10 Resin coating film 12 Oxide particles 14 Electrodeposition coating film

Claims (7)

At least one selected from the group consisting of a binder resin, conductive particles, an anticorrosive pigment, zirconia particles, titania particles, nickel oxide particles, and tin (IV) particles on at least one surface of the plated steel sheet. And including oxide particles having an average particle size of 5 to 200 nm,
The conductive particles are two or more conductive particles of non-oxide ceramic particles, iron alloy particles, and at least one selected from the group consisting of stainless particles,
Mass ratio of the non-oxide ceramic particles and at least one selected from the group consisting of the iron alloy particles and the stainless particles (consisting of the non-oxide ceramic particles/the iron alloy particles and the stainless particles). At least one selected from the group) is 1/9 to 8/2,
The content of the conductive particles is 5 to 30 mass% with respect to the coating film,
The content of the oxide particles is 1 to 7.5 mass% with respect to the coating film,
A surface-treated steel sheet having a coating film having an adhesion amount of ² to 20 g/m ² . The surface-treated steel sheet according to claim 1, wherein the binder resin is a water-soluble or water-dispersible water-based resin. The surface-treated steel sheet according to claim 1 or 2, wherein the conductive particles are at least one kind of conductive particles selected from the group consisting of non-oxide ceramic particles, iron alloy particles, and stainless particles. Wherein the non-oxide ceramic particles, to any one of claims 1 to 3 which is a non-oxide ceramics at least one selected from the group consisting of non-oxide ceramic particles comprising particles and Zr containing Ti The surface-treated steel sheet described. The rust-preventive pigment is aluminum tripolyphosphate, Zn, Mg, Al, Ti, Zr and Ce salts of phosphoric acid and phosphorous acid, a hydrocalumite-treated phosphoric acid compound, Ca ion exchange silica, and an oil absorption of 100. ~1000ml / 100g, a specific surface area 200~1000m ² / g, both the average particle size is at least one anticorrosive pigment is selected from the group consisting of amorphous silica 2~30μm of claims 1 to 4 The surface-treated steel sheet according to item 1. The surface-treated steel sheet according to any one of claims 1 to 5 , wherein the plated steel sheet is a zinc-based plated steel sheet or an aluminum-based plated steel sheet. A molded material formed by molding the surface-treated steel sheet according to any one of claims 1 to 6 ,
On the coating film of the molding material, an electrodeposition coating film formed by electrodeposition coating treatment,
Coating member having.