JP3271237B2 - Weldable automotive pre-primed steel sheet with excellent corrosion resistance and workability - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a pre-primed steel sheet used for an automobile body or a part (including a replacement repair part, etc.). The present invention relates to a pre-primed steel sheet for automobiles which is used after being subjected to intermediate coating and overcoating or only overcoating, or used by applying clear coating on the surface of the overcoating.

[0002]

2. Description of the Related Art Conventionally, in the field of building materials, painted steel sheets such as colored zinc iron sheets and curler steel sheets have been used for roofing materials and wall materials. In addition, in the home appliance industry, where strict performance is required for the design of products, the adoption of pre-coated steel sheets (PCM) in refrigerators by US home appliance manufacturers has triggered the increasing use of pre-coated steel sheets in Japan. I have.
Pre-coating is a method in which the surface of a steel sheet (strip) is previously coated by roll coating, powder coating, etc., and then processed and assembled. In contrast to the conventional post-coating method, in which a steel sheet is processed and then coated, In order to reduce costs due to elimination of pre-treatment and painting processes by users and to prevent pollution caused by painting, they are used for outer panels of home appliances and interior equipment.

On the other hand, in the field of automobiles, corrosion of automobile bodies caused by salts for preventing road freezing sprayed in winter in cold regions such as North America and Northern Europe is a major social problem. Rust measures have been strengthened. Against this background, surface-treated steel sheets for automobiles have been actively developed as one of measures against rust of automobile bodies. Conventionally, as a surface-treated steel sheet for automobiles,
A rust-proof coated steel sheet (zinc metal) in which a zinc powder-containing coating film as disclosed in Japanese Patent Publication No. 230 and JP-B-47-6882 is formed as a thick film having a thickness of 10 to 20 μm has been used. However, this zinc powder-containing coating film undergoes remarkable film peeling at the time of press molding, and this not only causes deposition on the mold and causes defects such as star eyes scratches and press cracking, but also
There was a problem that the corrosion resistance of the part where the rust-preventive film was peeled was deteriorated.

With respect to such a rust-prevention coated steel sheet, an organic composite coated steel sheet as disclosed in Japanese Patent Publication No. 4-48348 and Japanese Patent Application Laid-Open No. H2-15177 has been known. These surface-treated steel sheets have a chromate film as a first layer and a thin resin film as a second layer on the first layer based on a galvanized steel sheet. Each of the above-mentioned zinc metal and organic composite coated steel sheet is pressed and assembled by an automobile manufacturer, then subjected to electrodeposition coating, and then to intermediate coating and top coating.

Recently, automobile manufacturers have been studying coated steel sheets for automobiles aiming at omitting the chemical conversion treatment and the electrodeposition coating process, mainly in Europe and the United States. For example, in the United States in 1988, NCCA began studying the application of pre-primed steel sheets for automobiles to vehicle bodies ("A Manufacturing Engineering Studyfor
Fabrication with Coated Coil ", NCCA (1988). This pre-primed steel sheet is a steel sheet in which a primer has been formed on the surface of the steel sheet in advance with the aim of omitting chemical conversion treatment and electrodeposition coating at an automobile manufacturer.

[0006] When manufacturing an automobile body using a conventional automobile steel sheet (cold-rolled steel sheet, surface-treated steel sheet) as a material, an automobile maker proposes "blanking → press forming → assembly / joining → chemical conversion treatment → electrodeposition coating → medium / A “top coat” process is required. On the other hand, in the case of a pre-primed steel sheet, the chemical conversion treatment and the electrodeposition coating process can be omitted, and the process of “blanking → press forming → assembly / joining → middle / top coating (or only top coating)” Since the structure becomes possible, the coating cost can be reduced. In addition, with pre-primed steel sheets, excellent corrosion resistance can be imparted to the closed structure such as the hem part of the door, which is difficult to paint with conventional electrodeposition coating. Can also be expected. Therefore, there are high expectations for pre-primed steel sheets for automobiles.

[0007]

However, at present, pre-primed steel sheets for automobiles have not yet been put into practical use due to various problems, although they have the above-mentioned advantages. Therefore, the present inventors conducted detailed studies on the technical problems with the aim of commercializing pre-primed steel sheets for automobiles, and as a result, in order to commercialize pre-primed steel sheets, It turns out that there is a problem to be solved.

That is, since the pre-primed steel sheet is used without using the conventional electrodeposition coating having a film thickness of about 20 to 25 μm, in order to apply it to the outer surface of the vehicle body, it is necessary to improve the corrosion resistance after coating. It is necessary to increase the thickness of the primer film (organic resin film) in order to ensure sufficient image sharpness after painting. However, when the thickness of the organic resin film is increased (for example, 20 to 25 μm), there is a problem that peeling (powdering or flaking) occurs during press molding. In particular, conventional body press forming was premised on press forming under oiling conditions such as lubricating oil, rust-preventive oil, and cleaning oil. Since the "alkali degreasing → chemical conversion treatment → electrodeposition coating" process of the line is omitted, if such a degreasing process is assumed to be omitted, the powdering resistance when performing press molding under oilless conditions will be improved. This is an important issue.

In the assembly and joining process of a steel sheet for an automobile, most of the joining is performed by resistance welding. However, when the organic resin film of the pre-primed steel sheet is a thick film, the electrical insulation becomes high, so that the resistance is increased. Welding becomes impossible, so the use of the steel sheet is limited to a very small number of parts that do not require welding, and versatility is lost. In addition, steel plates coated with Zn powder content on the inner surface side, such as zinc metal,
Due to poor powdering and bare corrosion resistance after pressing,
Not applicable to pre-primed steel sheets. As described above, there are various problems to be solved in order to put the pre-primed steel sheet for vehicles into practical use.

[0010]

Means for Solving the Problems The present inventors have repeatedly studied to solve the above-mentioned problems particularly with respect to a pre-primed steel sheet for automobiles, and as a result, have found that the weldability, press formability, inner surface suitability (unpainted) We have invented a pre-prime steel sheet for automobiles with excellent functions on the inner side and outer side as shown below, which is excellent in perforation corrosion resistance) and aptitude after painting (corrosion resistance, sharpness, paint adhesion) on the outer side. . That is, the features of the automotive pre-primed steel sheet of the present invention are as follows.

(1) A zinc-based plated steel sheet has a chromate film having a coating weight of 1 to 500 mg / m ² in terms of metallic chromium on both surfaces, and a volume resistivity value is formed on the chromate film on one side of the steel sheet. There 0.001 ohm · cm or less, the coefficient of dynamic friction under no oil coating conditions 0.03-0.30, pencil hardness 3B～5H, film thickness has a conductive organic resin film of 2.0~30μm , On the other side of the chromate film on the other side of the steel sheet, a volume specific resistance value of more than 1 Ω · cm , under oil-free conditions.
The coefficient of dynamic friction is 0.03-0.30, and the film thickness is 0.1-3 .
A weldable automotive pre-primed steel sheet having an organic resin film of 0 μm and excellent in corrosion resistance and workability.

(2) In the pre-primed steel sheet for an automobile according to the above (1),
The volume specific resistance of the conductive organic resin film formed on one side of the steel sheet is 0.001 Ω · cm or less and the film thickness is 3.0 to 10
A weldable automotive pre-primed steel sheet with excellent corrosion resistance and workability characterized by having a thickness of μm. (3) In the above-mentioned (1) or (2) , in the automotive pre-primed steel sheet, the conductive organic resin film formed on one side of the steel sheet is a metal or alloy powder, conductive carbon, iron phosphide, carbide,
A weldable automotive pre-primed steel sheet having excellent corrosion resistance and workability, characterized by containing one or more conductive fine powders selected from nitrides and semiconductor oxides.

(4) In the pre-primed steel sheet for an automobile according to the above (1) or (2) , the conductive organic resin film formed on one side of the steel sheet is made of metal or alloy powder, conductive carbon, iron phosphide, carbide A weldable pre-primed steel sheet for automobiles excellent in corrosion resistance and workability, characterized by containing one or more kinds of conductive fine powders selected from nitrides, nitrides and semiconductor oxides, and polyethylene wax.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The automotive pre-primed steel sheet of the present invention imparts corrosion resistance and adhesion by forming a chromate film having a predetermined adhesion amount on both sides of a galvanized steel sheet, and has one side ( The surface to be the outer surface side of the vehicle body or parts, which is hereinafter referred to as the “outer surface”) has a volume resistivity of 0.001Ω · c on the upper layer of the chromate film.
m to form a conductive organic resin film with a film thickness of 2.0 to 30 μm, which imparts weldability, outer surface rust resistance, paint adhesion, and post-painting sharpness, while the other side of the steel sheet (The surface to be the inner surface side of the vehicle body or parts, hereinafter referred to as the “inner surface side”) The upper layer of the chromate film has a volume resistivity value of more than 1 Ω · cm and a film thickness of 0.1 to 3.0 μm. This is one in which perforated corrosion resistance is imparted by forming an insulating organic resin film. FIG. 1 shows a schematic film cross-sectional structure of such a preprimed steel sheet of the present invention.

With respect to press formability, press forming under oiling conditions such as lubricating oil, rust-preventive oil, and cleaning oil has been premised in conventional body press forming, but in the case of pre-primed steel sheets for automobiles. The conventional "alkaline degreasing → chemical conversion treatment → electrodeposition coating" process of the automotive coating line is omitted, so if press molding is performed under oiling conditions, new degreasing is performed before intermediate coating. A process is required, which increases costs. Therefore, in order to omit the degreasing step, it is necessary to preform press forming without oiling in pre-primed steel sheets for automobiles. In this case, it is important to improve the powdering resistance under oilless conditions. Issues. Until now, in the field of painted steel sheets (pre-coated steel sheets) for home appliances and building materials,
Since the forming process was mainly bending, mild overhanging / drawing, or roll forming, examination of powdering resistance was conducted under the premise of severe press working under oilless conditions such as in the case of automobile bodies. Little has been done. Numerous studies have been conducted on the press workability of surface treated steel sheets for automobiles such as plated steel sheets and organic composite coated steel sheets.However, examination of the powdering resistance of pre-primed steel sheets with a thick resin coating has been conducted. Has not been done.

On the other hand, in the present invention, the dynamic friction coefficient and the film hardness of a thick organic resin film (2.0 to 30 μm) formed on the outer surface side of a pre-primed steel sheet for an automobile under oilless conditions are measured. By setting both to be in the specific ranges, excellent powdering resistance can be obtained, and specifically, a thick film (2.0 to 30) formed on the outer surface side of the preprimed steel sheet.
μm), the coefficient of kinetic friction under oil-free conditions of the organic resin film is 0.03-0.30, and the pencil hardness of the film is 3B-
It has been found that excellent powdering resistance can be obtained by setting to 5H. Also, as for the resin film of the thin film (0.1 to 3.0 μm) on the inner surface side of the pre-primed steel sheet, the dynamic friction coefficient of the resin film is 0.03 to 0, assuming press molding under oilless conditions. .30,
It has been found that the powdering resistance of the thick organic resin film on the outer surface side of the steel sheet can be further improved.

By forming the organic resin films having different structures on the outer surface side and the inner surface side of the steel sheet as described above, it is weldable, has excellent workability and powdering resistance, and has a suitable inner surface (perforated corrosion resistance). Pre-primed steel sheet with good outer surface suitability (outer surface rust resistance, paint adhesion, clearness after painting) is obtained, and press forming → welding and assembly by automobile manufacturers, etc., then chemical conversion treatment and electrodeposition coating (In some cases, chemical treatment, electrodeposition coating, intermediate coating) can be omitted, and the outer surface can be subjected to intermediate coating, top coating, or only top coating, and the inner surface can be provided to the vehicle body or its parts without painting. it can.

The details of the present invention and the reasons for the limitation will be described below. As the base zinc-coated steel sheet, a zinc-coated steel sheet, a Zn-Ni alloy-coated steel sheet, a Zn-Fe alloy-coated steel sheet, a Zn-Mn alloy-coated steel sheet, a Zn-Al alloy-coated steel sheet, a Zn-Cr alloy-coated steel sheet, Zn -Co
-Cr alloy-plated steel sheet, Zn-Cr-Ni alloy-plated steel sheet, Zn-Cr-Fe alloy-plated steel sheet, and zinc-based composite plated steel sheet obtained by dispersing and plating metal oxide, hardly soluble chromate, polymer, etc. For example, Zn-SiO
₂ Dispersion plated steel sheet, Zn-BaCrO ₄ dispersion plated steel sheet)
And the like. Further, it may be a multi-layer plated steel sheet obtained by plating two or more layers of the same kind or different kinds of the above plating. Plating methods include electrolysis,
Any of the feasible methods out of a melting method and a gas phase method can be adopted.

Since the present invention is a pre-primed steel plate which is used without electrodeposition coating, it is not expected that the electrodeposition coating near the end face has a rustproof effect. In automotive applications, particularly severe end face corrosion resistance is required for drain holes of door parts and exposed portions of lower end faces of fender parts, so in such applications, the sacrificial anticorrosion effect on the end face among the various platings is large and Thick pure zinc plating (for example, when the coating weight is 4
It is preferable to use hot-dip galvanizing of 5 to 60 g / m ² ), thick alloyed hot-dip galvanizing, or Zn-Cr alloy plating that is thin and has excellent end face corrosion resistance.

The chromate film formed on at least one side of the galvanized steel sheet suppresses corrosion of the galvanized steel sheet by a self-repairing action by chromate ions of hexavalent chromium. If the amount of the chromate film adhered is less than 1 mg / m ^{2 in} terms of metallic chromium, sufficient corrosion resistance cannot be expected, while if it exceeds 500 mg / m ² , the adhesion will be degraded. For this reason, the amount of the chromate film deposited is 1 to 500 mg / m ^{2 in} terms of chromium metal. Further, in order to satisfy even higher corrosion resistance and adhesion, the content is preferably in the range of 10 to ²⁰⁰ mg / m ^{2 in} terms of chromium metal. As a chromate treatment for forming the chromate film, any of a reaction type, an electrolytic type, and a coating type can be applied. From the viewpoint of corrosion resistance, a coating type containing a large amount of hexavalent chromium chromate ions in the chromate film is preferable.

[0021] The coating type chromate treatment comprises a treatment solution containing a partially reduced aqueous solution of chromic acid as a main component and, if necessary, one or more of the following components added thereto. And dried without washing. Water-soluble or water-dispersible organic resins such as acrylic resins and polyester resins Colloids and / or powders of oxides such as silica, alumina, titania, zirconia, and zinc oxide Acids such as molybdic acid, tungstic acid, and vanadic acid Or salts thereof Phosphoric acids such as phosphoric acid and polyphosphoric acid Zirconium fluoride, silicide fluoride, fluorides such as titanium fluoride Metal ions such as zinc ions Conductive fine powders such as iron phosphide and antimony-doped tin oxide Hydrogen fluoride silane Coupling agent

In the coating type chromate treatment, the treatment liquid is usually applied by a roll coater method. However, after applying by a dipping method or a spray method, it is also possible to adjust the amount of application by an air knife method or a roll drawing method. In the coating type chromate treatment, the ratio of trivalent Cr: hexavalent Cr in the treatment liquid is preferably 1: 1 to 1: 3, and the pH is preferably 1.5 to 4.0 (more preferably, 2 to 3). . Trivalent Cr: Hexavalent Cr
Is adjusted using a general organic reducing agent (for example, sugars, alcohols, etc.) or an inorganic reducing agent. On the other hand, in the electrolytic type chromate treatment, a cathodic electrolysis treatment is performed in a bath containing chromic anhydride and one or more anions such as sulfuric acid, phosphoric acid fluoride, or halogen oxyacid, and the film is washed with water and dried. Is formed.

An organic resin film is formed as an upper layer on the chromate film. The feature of the present invention is that an organic resin film having a different volume resistivity and a different film thickness range is formed on the outer surface and the inner surface of the steel sheet. That is, a conductive organic resin film having a volume resistivity of 0.001 Ω · cm or less and a thickness of 2.0 to 30 μm is formed on a surface used on the outer surface of an automobile body or the like. An insulating organic resin film having a volume specific resistance value of more than 1 Ω · cm and a film thickness of 0.1 to 3.0 μm is formed on the surface used. By forming films having different volume resistivity values and film thicknesses on the outer surface side and inner surface side of the steel sheet in this manner, weldability and peeling resistance of the film during pressing (powdering resistance or flaking resistance) are obtained. Thus, it is possible to obtain a pre-primed steel sheet for an automobile which satisfies all of the unpainted corrosion resistance on the inner side, the sharpness after painting and the corrosion resistance after painting on the outer side.

First, the structure of the conductive organic resin film on the outer surface side of the steel sheet and the reason for limiting the structure will be described. If the volume resistivity of the organic resin film on the outer surface of the steel sheet exceeds 1 Ω · cm, resistance welding of the steel sheet is difficult , but particularly good weldability is obtained.
Therefore, the specific volume resistance is set to 0.001Ω · cm or less. FIG. 2 shows the volume specific resistance value of the conductive organic resin film (a pre-primed steel sheet having a thickness of 0.1 to 2.0 μm of the organic resin film on the inner surface side of the steel plate) and the weldability (the evaluation criteria for the weldability are as follows). (See the example).

In order to reduce the volume resistivity of the conductive organic resin film on the outer surface of the steel sheet to 0.001 Ω · cm or less, fine conductive powder may be added to the resin film. Examples of the conductive fine powder include powders of metals such as zinc, nickel, iron, aluminum, cobalt, manganese, chromium, molybdenum, tungsten, copper, lead, tin, and alloy powders thereof;
Conductive carbon powder such as conductive carbon and graphite powder; carbide powder; nitride powder; iron phosphide powder; semiconductors such as aluminum-doped zinc oxide powder, tin oxide-titanium oxide, tin oxide-barium sulfate, and nickel oxide-aluminum. Oxide powder and the like. These conductive fine powders can be used alone or in combination of two or more. By appropriately adjusting the blending amount in the organic resin film according to the type of the conductive fine powder, the volume specific resistance value of the film is reduced to 0.0
It can be set to 01 Ω · cm or less.

The conductive organic resin film has a thickness of 2.0
If it is less than μm, the sharpness after painting is insufficient and cannot be applied to the outer surface of the vehicle body. In addition, the swelling generated from the scratched part when it is damaged after painting is remarkable, and the corrosion resistance after painting is insufficient. FIG. 3 shows the relationship between the thickness of the conductive organic resin film and the sharpness after painting (see the evaluation criteria for sharpness after painting described in Examples). On the other hand, if the film thickness exceeds 30 μm, the peeling resistance (powdering resistance or flaking resistance) of the film at the time of press molding decreases. FIG. 4 shows the organic resin film (the coefficient of kinetic friction under oil-free conditions of the organic resin film on the outer surface side of the steel sheet is 0.03 to 0.14, and the pencil hardness is B to 3).
H, Film thickness of the organic resin film on the inner surface side of the steel sheet and the film thickness of the pre-primed steel sheet having a dynamic friction coefficient of 0.03 to 0.14 under oilless conditions) and the amount of film peeling during press forming (powdering resistance)
The relationship is shown. For the above reasons, the thickness of the conductive organic resin film on the outer surface side of the steel sheet is 2.0 to 30 μm, preferably 3.0 to 20 μm, and particularly preferably 4.0 to 10 μm.
0 μm.

In order to ensure particularly excellent powdering resistance, the conductive organic resin film should have a dynamic friction coefficient under oil-free conditions of 0.03 to 0.30 and a pencil hardness of 3B to 5H. Is preferred. If the coefficient of kinetic friction of the conductive organic resin film under oil-free conditions exceeds 0.30, the powdering resistance is remarkably inferior, and proper pressing cannot be performed. FIG. 5 shows the coefficient of kinetic friction of the conductive organic resin film (the organic resin film on the outer surface of the steel sheet has a thickness of 2.0 to 10 μm, the pencil hardness is B to 3H, and the organic resin film on the inner surface of the steel sheet has no oil coating. Shows the relationship between the kinetic friction coefficient of a pre-primed steel sheet having a thickness of 0.03 to 0.14) and the amount of film peeling (powdering resistance) during press forming under oil-free conditions. On the other hand, if the coefficient of kinetic friction is less than 0.03, there is no problem in powdering resistance, but when the steel sheets are carried one by one into the pressing process, the surface of the steel sheets slips too much, hindering handling and wrinkles during press forming. This causes a problem such as occurrence of the problem, which is not preferable. For the above reasons, the coefficient of dynamic friction of the conductive organic resin film under oil-free conditions is 0.03 to 0.30, more preferably 0.03 to 0.20, and particularly preferably 0.03 to 0.20.
It is desirable to set it to 14.

In order to set the dynamic friction coefficient of the conductive organic resin film under oil-free conditions to 0.03 to 0.30, for example, a solid lubricant is blended in the organic resin film, and the kind and amount of the lubricant are mixed. You just have to select As the solid lubricant, for example, the following can be used. -Hydrocarbon lubricants: for example, natural paraffin, synthetic paraffin, microwax, polyethylene wax, chlorinated hydrocarbons, etc.-Fluororesin fine powder: for example, polyvinyl fluoride resin,
Polytetrafluoroethylene resin, polyvinylidene fluoride resin, etc. Fatty acid amide-based lubricant: For example, stearic acid amide,
Palmitic acid amide, methylene bis stearamide, ethylene bis stearamide, oleic acid amide, esyl amide, alkylene bis fatty acid amide, etc. Metallic soaps: for example, calcium stearate, lead stearate, calcium laurate, calcium palmitate, etc. -Metal sulfides: molybdenum disulfide, tungsten disulfide Among these, polyethylene wax and / or fluororesin fine powder (in order to improve the powdering resistance of a thick resin film under oil-free conditions) Particularly, it is preferable to use fine powder of ethylene tetrafluoride resin).

If the pencil hardness of the conductive organic resin film is less than 3B or more than 5H, the powdering resistance is poor. FIG. 6 shows a conductive organic resin film (the thickness of the organic resin film on the outer surface side of the steel sheet is 2.0 to 10 μm, the coefficient of kinetic friction under oil-free conditions is 0.03 to 0.14, and the organic resin film on the inner surface side of the steel sheet). It shows the relationship between the pencil hardness of a pre-primed steel sheet having a dynamic friction coefficient of 0.03 to 0.14 under the condition of no oil coating of the film and the amount of film peeling (powdering resistance) during press forming. From the results shown in the figure, the pencil hardness of the film is 3B to 5H, more preferably B
~ 3H is desirable. The pencil hardness of the conductive organic resin film can be adjusted by appropriately selecting the type of base resin, additives (for example, conductive fine powder, rust preventive pigment, etc.), film thickness, and the like. By doing so, the pencil hardness of the film is adjusted to 3B to 5H.

As the organic resin of the conductive organic resin film on the outer surface side of the steel sheet, a known coating resin, that is, an epoxy resin,
A polyester resin, urethane resin, acrylic resin, or the like can be used. For example, an epoxy resin, a polyester resin, an acrylic resin, or the like having a functional group (for example, a hydroxyl group, a carboxyl group, an epoxy group, etc.) reactive with an amino resin or a polyisocyanate compound as a curing agent component is blended, and this is mixed with an organic solvent. Dissolve or functional group in resin skeleton (hydroxyl group, carboxyl group, amino group, etc.)
And then neutralized with an acid or an alkali to make it water-soluble or water-dispersible.

Examples of the epoxy resin include straight epoxy resins such as epichlorohydrin type and glycidyl ether type, fatty acid-modified epoxy resins, polybasic acid-modified epoxy resins, acrylic-modified epoxy resins, alkyd (or polyester) -modified epoxy resins, and polybutadiene-modified epoxy resins. Resins, phenol-modified epoxy resins, amine or polyamine-modified epoxy resins, urethane-modified epoxy resins, and the like can be used. As the polyester resin, a known resin obtained by a usual synthesis method including an alkyd resin can be used. For example, oil-modified alkyd resin, rosin-modified alkyd resin, phenol-modified alkyd resin, styrenated alkyd resin, silicone-modified alkyd resin, acryl-modified alkyd resin, oil-free alkyd resin (polyester resin) and the like can be mentioned.

The acrylic resin is a resin synthesized by a solution polymerization method, an emulsion polymerization method, a suspension polymerization method, or the like using an ordinary unsaturated ethylenic monomer, and is a methacrylate monomer, Hard monomers such as acrylonitrile, styrene, acrylic acid, acrylamide, and vinyltoluene are essential components, and other unsaturated vinyl monomers are added as appropriate for the purpose of imparting resin hardness, flexibility, and crosslinkability. By doing so, the desired resin is obtained. The acrylic resin may be modified with another resin such as an alkyd resin, an epoxy resin, and a phenol resin. As a curing agent, an amino resin such as a melamine resin or a urea resin, a blocked isocyanate compound, an amine compound, or a phenol resin can be used. Among these, a blocked isocyanate compound excellent in workability and corrosion resistance is most preferred.

A rust preventive additive can be added to the conductive organic resin film on the outer surface side of the steel sheet. As the rust preventive additive, silica and a sparingly soluble chromate are particularly preferable. Silica incorporated in the resin film has the effect of promoting the formation of basic zinc chloride, which is effective in suppressing corrosion among the corrosion products of galvanized steel sheets. It is presumed that silicate ions function as a film-forming corrosion inhibitor, thereby exhibiting an anticorrosion effect.

The silica used in the present invention includes dry silica (for example, AEROS manufactured by Nippon Aerosil Co., Ltd.).
IL 130, AEROSIL 200, AEROSIL
300, AEROSIL 380, AEROSIL R
972, AEROSIL R811, AEROSIL R
805, etc.), and organosilica sols (for example, MA-ST, IPA-ST, NBA-S manufactured by Nissan Chemical Industries, Ltd.)
T, IBA-ST, EG-ST, XBA-ST, ETC
-ST, DMAC-ST, etc.), sedimentation wet silica (for example, T-32 (S), K-41, F- manufactured by Tokuyama Soda Co., Ltd.)
80), gel wet silica (for example, Syloid 244, Syloid 150, Syloid 72, Syloid 65, SHIELDEX, etc., manufactured by Fuji Devison Chemical Co., Ltd.)
And the like. Further, two or more kinds of the above-mentioned silicas can be used as a mixture.

The hardly soluble chromates include barium chromate (BaCrO ₄ ), strontium chromate (SrCrO ₄ ), and calcium chromate (CaCrO ₄ ).
O _4), chromic acid zinc (ZnCrO ₄ · 4Zn (O
H) ₂ ), potassium zinc chromate (K ₂ O.4ZnO.4)
Fine powders such as CrO ₃ .3H ₂ O) and lead chromate (PbCrO ₄ ) can be used. It is also possible to use a mixture of two or more of the hardly soluble chromates described above. Chromium compounds other than these have poor compatibility with the base resin, or have problems such as poor coating adhesion because they contain a large amount of soluble hexavalent Cr, although an anticorrosion effect is observed, Not suitable for the present invention.

Further, the pre-primed steel sheet of the present invention does not require pretreatment such as degreasing, surface conditioning, and phosphate treatment performed by an automobile manufacturer as performed on a conventional organic composite coated steel sheet for automobiles. Therefore, strict chromium elution resistance is not required, but it is 10
Considering exposure to rainfall or the like for up to 20 years, it is preferable that the amount of eluted Cr be small. Therefore, the poorly soluble chromate compounded in the base resin has a low chromium elution property and can greatly contribute to corrosion resistance.
O ₄ or SrCrO ₄ is particularly preferred. When these rust preventive additives are added, the compounding amount [B] is expressed as [A] / (A) / solid weight ratio with respect to the compounding amount [A] of the base resin [A] (including the curing agent). [B] = 99/1 to 50/50 is preferable. When the weight ratio exceeds 99/1, the effect of improving corrosion resistance is small. On the other hand, if the weight ratio is less than 50/50, the powdering resistance of a thick film is reduced.

Since the pre-primed steel sheet of the present invention is used without being subjected to electrodeposition coating, it is preferable to color the organic resin film itself instead of the conventional coloring by electrodeposition coating. For this reason, organic pigments such as white pigments such as titanium oxide, black pigments such as carbon black, condensed polycyclic organic pigments, and phthalocyanine-based organic pigments as colorants on the organic resin film (at least the organic resin film on the outer surface side of the steel sheet); Alternatively, a chromatic dye such as an azo metal complex dye or a black dye is preferably added. Of these colorants, titanium oxide, azo-based metal complex dyes, and organic pigments are particularly effective for preventing the corrosion resistance of the organic resin film from being impaired. However, when a gray or black achromatic color is used for the pre-primed steel sheet as an alternative to electrodeposition coating, it is preferable to add titanium oxide, carbon black, or a black azo metal complex dye.

When a black azo metal complex dye soluble in an organic solvent is used among the dyes, the resin film exhibits the most excellent light fastness and corrosion resistance. This organic solvent-soluble black azo metal complex dye is referred to as “COLOR INDEX
Among the organic solvent-soluble black dyes classified in the "CIGeneric Name", azo dyes and chromium,
It is a complex compound with a trivalent metal such as copper and cobalt.
Representative examples of "CIGeneric Name" of "OLOUR INDEX" include CISolvent Black 6, 22, 23,
25, 28, 29, 30, 34, 35, 36, 37, 3
8, 39, 40, 41, 42, 43, 45, 47, 4
8, 49, etc., and others are not registered.

This dye is characterized in that it has no hydrophilic group in the molecular structure of the dye and thus is soluble in a solvent. For structural reasons considered to be (type metal complex salts), the stability to light (light fastness) is superior to other black dyes. Examples of the metal capable of forming a complex salt with a dye include Cr, Co, Cu, Fe, and Al.
There are many complex salts mainly with Cr. Commercial products include, for example, ORASOL BLACK RL and ORASOL B manufactured by Ciba Geigy.
LACKRLP (above, CI Solvent Black 29), ORASOL BLA
CK CN (CI Solvent Black 28), ORASOL BLACK BA (
CI Solvent Black 6), ZAPON BlackX 51 manufactured by BASF
(CI Solvent Black 27), manufactured by Hodogaya Chemical Co., Ltd.
Aizen Spilon Black RLH Special (CISolvent Blac
k 42). In addition, "COLOURINDEX (THI
RD EDITION) ", for example, Aizen Spilon Black MH Speci manufactured by Hodogaya Chemical Industry Co., Ltd.
al, Kayaset Black KR manufactured by Nippon Kayaku Co., Ltd.
In each case, a black resin film having excellent blackness can be obtained.

In addition, by using a black azo-based chromium complex dye as the black azo-based metal complex dye, extremely excellent corrosion resistance, which is presumed to be a synergistic effect between the trivalent Cr ion and the base chromate, can be obtained. This is trivalent C
This is presumably because the black azo-based metal complex dye containing r is stably present as a passive film and the barrier effect is further improved. For these reasons, the most preferred black azo metal complex salt dye is one in which the metal forming the complex salt is trivalent Cr ion. Further, as other organic solvent-soluble black dyes, azo dyes and azine dyes which are not metal complex salts such as monoazo dyes and disazo dyes, and blue phthalocyanine dyes can also be used. However, blackness, light fastness, and powdering resistance,
From the viewpoint of corrosion resistance after processing and the like, the above-mentioned azo metal complex salt dye is most preferable. The mixing amount of the colorant is 1 to 5 with respect to 100 parts by weight of [base resin [A] + rust inhibitor [B]].
It is preferably 0 parts by weight. If the amount of the coloring agent is less than 1 part by weight, a sufficient coloring effect cannot be obtained, while if it exceeds 50 parts by weight, powdering resistance and corrosion resistance deteriorate.

Next, the structure of the organic resin film on the inner surface side of the steel sheet and the reason for limiting the structure will be described. Since the inner surface of the steel sheet is applied to the vehicle body without being coated, excellent unpainted corrosion resistance (perforated corrosion resistance) is required, and at the same time, good weldability is also required. If the volume resistivity of the organic resin film on the inner surface side of the steel sheet is 1 Ω · cm or less, the movement of electrons and ions in the film becomes easy, and microcells are formed, resulting in insufficient corrosion resistance (perforated corrosion resistance). is there. For this reason, the volume resistivity value of the organic resin film on the inner side of the steel sheet exceeds 1 Ω · cm,
Preferably 10 ⁵ Ω · cm or more, more preferably 10 ¹⁰
Ω · cm or more, particularly preferably 10 ¹⁵ Ω · cm or more. FIG. 7 shows the relationship between the specific volume resistance value of the organic resin film on the inner surface side of the steel sheet and the perforated corrosion resistance (see the evaluation criteria for the perforated corrosion resistance described in Examples). The volume resistivity of the organic resin film can also be adjusted by selecting the type and blending amount of the base resin and the curing agent, and by appropriately selecting these, the volume resistivity of the film can be adjusted to 1Ω ·
cm. In addition, an additive having conductivity (for example, a solid lubricant such as graphite) may be added for the purpose of imparting lubricity to the film, but even in this case, the volume specific resistance of the film exceeds 1 Ω · cm. Need to be managed.

If the thickness of the organic resin film on the inner surface side of the steel sheet is less than 0.1 μm, the unpainted corrosion resistance is insufficient. On the other hand, since the organic resin film on the inner surface side of the steel sheet is insulative, it is necessary to secure conductivity by breaking the film when the electrode presses the film during resistance welding. When the film thickness exceeds 3.0 μm, the conductivity is low. Poor weldability due to insufficient securing. FIG. 8 shows the thickness and weldability of the organic resin film on the inner surface side of the steel sheet (a pre-primed steel sheet having a volume resistivity of 0.001 Ω · cm or less of the organic resin film on the outer surface side of the steel sheet). (See those described in Examples). For the above reasons, the thickness of the organic resin film on the inner side of the steel sheet is 0.1
To 3.0 μm, preferably 0.3 to 2.5 μm, particularly preferably 0.3 to 2.0 μm.

When oil-free molding is assumed,
By setting the kinetic friction coefficient of the organic resin film on the inner surface of the steel sheet under oil-free conditions to 0.03 to 0.30, the powder resistance of the thick organic resin film (2.0 to 30 μm) on the outer surface of the steel sheet is reduced. Ring characteristics can be further improved. If the coefficient of kinetic friction exceeds 0.30, the powdering resistance on the outer surface of the steel sheet is insufficient. On the other hand, if the coefficient of kinetic friction is less than 0.03, there is no problem with the powdering resistance, but the steel sheet slides too much and the handling property is poor. Is unsuitable. FIG. 9 shows an organic resin film on the inner surface side of the steel sheet (the thickness of the organic resin film on the outer surface side of the steel sheet is 2.0 to 10 μm).
m, the coefficient of dynamic friction under oil-free conditions is 0.03 to 0.1
4, the relationship between the coefficient of kinetic friction under oil-free conditions of a pre-primed steel plate having a pencil hardness of B to 3H) and the amount of film peeling during press molding are shown. For the above reasons, the coefficient of kinetic friction under oil-free conditions on the inner surface of the steel sheet is 0.03 to 0.30,
More preferably, it is preferably 0.03 to 0.20, and particularly preferably 0.03 to 0.14.

In order to set the dynamic friction coefficient of the organic resin film on the inner surface side of the steel sheet under oil-free conditions to 0.03 to 0.30, for example, a solid lubricant is blended in the organic resin film, What is necessary is just to select the compounding quantity. As the solid lubricant, those mentioned above with respect to the organic resin film on the outer surface of the steel sheet can be used.In particular, in order to improve the powdering resistance, it is preferable to use polyethylene wax or polytetrafluoroethylene resin fine powder. It is also effective to use both in combination. As the organic resin used for the insulating organic film on the inner surface side of the steel sheet, known coating resins, that is, epoxy resin, polyester resin, urethane resin, acrylic resin, and the like can be used, but particularly severe unpainted corrosion resistance (perforation resistance) When corrosion resistance is required, a resin film composed of an amine-modified epoxy resin and a blocked isocyanate as a curing agent is most preferable.

It is preferable to add an anticorrosive additive to the organic resin film on the inner surface side of the steel sheet in order to secure unpainted corrosion resistance. As the anticorrosive additive, silica and a sparingly soluble chromate are preferred. Particularly, by using silica and a sparingly soluble chromate in combination, excellent corrosion resistance can be expected. silica,
As the hardly soluble chromate, those mentioned above for the organic resin film on the outer surface side of the steel sheet can be used. Usually, the coating composition for forming the above-mentioned organic resin film is applied to a steel sheet surface (upper layer of the chromate film) by a roll coater method, but after being applied by a dipping method or a spray method, an air knife method or a roll drawing method is used. It is also possible to adjust the coating amount by the method. In addition, a hot blast furnace, a high-frequency induction heating furnace, an infrared furnace, or the like can be used for the heat treatment after the coating composition is applied. Heat treatment is 80-300 at ultimate plate temperature
C., preferably in the range of 150 to 250.degree.

[0046]

EXAMPLE As a pre-primed steel sheet for an automobile body,
Various zinc-based plated steel sheets shown in Table 1 were alkali-degreased, washed with water and dried, subjected to a chromate treatment, and then a conductive coating composition for the outer surface of the steel sheet and an insulating coating composition for the inner surface of the steel sheet were respectively coated with a roll coater. It was applied to the front and back surfaces of a galvanized steel sheet and baked. Each of the obtained pre-primed steel sheets was evaluated for powdering resistance, weldability, outer surface suitability (outer surface rust resistance, paint adhesion, clearness after painting), and inner surface suitability (perforated corrosion resistance). went. Table 2 shows the results.
To Table 13. The manufacturing conditions of this example are as follows. (1) Galvanized steel sheet 0.8 mm thick, surface roughness (Ra) 0.5-2.0 μm
Each of the cold-rolled steel sheets was subjected to various types of zinc-based plating, and used as a treated base sheet. (See Table 1)

(2) Chromate treatment Coating type chromate treatment A chromate treatment solution having the following composition was applied by a roll coater and dried without washing with water. The amount of the chromate layer deposited was adjusted by changing the solid content concentration of the treatment liquid and the peripheral speed of the roll coater. Chromic anhydride: 20 g / l Phosphate ion: 4 g / l Zirconium fluoride ion: 1 g / l Zinc ion: 1 g / l Hexavalent chromic acid / zirconium fluoride ion: 20/1
(Weight ratio)

Electrolytic chromate treatment Chromic anhydride 30 g / l, sulfuric acid 0.2 g / l, bath temperature 40
A cathodic electrolytic treatment was performed on a zinc-based plated steel sheet at a current density of 10 A / dm ² using a treatment liquid at a temperature of 10 ° C., followed by washing with water and drying. The adhesion amount of the chromate film was adjusted by controlling the amount of electricity supplied in the cathodic electrolytic treatment. Reaction type chromate treatment Chromic anhydride 30 g / l, phosphoric acid 10 g / l, NaF
Using a treatment liquid of 0.5 g / l, K ₂ TiF ₆ 4 g / l, and a bath temperature of 60 ° C., the zinc-plated steel sheet was spray-treated, washed with water and dried. The adhesion amount of the chromate film was adjusted by changing the treatment time.

(3) Example of preparing a coating composition for a conductive organic resin film applied to the outer surface of a steel sheet A coating composition for a resin film on the outer surface of a steel sheet (1) Amine-modified epoxy resin and blocked isocyanate (manufactured by Asahi Kasei Corporation) A coating composition containing 100 parts by weight (solid content) of a base resin composed of "Duranate MF-B") and 40 parts by weight of strontium chromate was mixed with metallic Ni powder (average particle size: 1 μm) and polyethylene wax ("Seridust 3620" manufactured by Hoechst). )), And the solid content was adjusted with a solvent as necessary. The volume resistivity of the dried organic resin film is adjusted by the amount of metallic Ni powder added to the coating composition, and the coefficient of kinetic friction of the dried organic resin film is adjusted by the amount of polyethylene wax added to the coating composition. It was adjusted.

Paint composition for resin coating on outer surface of steel sheet (2) Base resin 100 made of block urethane-modified epoxy resin (“Epokey 834” manufactured by Mitsui Toatsu Chemicals, Inc.)
To a coating composition containing 40 parts by weight of strontium chromate and 1 part by weight of carbon black, powdered iron phosphide (average particle size: 3 μm) and polyethylene wax (“Seridust 3620” manufactured by Hoechst) are blended. Then, the solid content was adjusted with a solvent as needed. The volume resistivity of the organic resin film after drying is adjusted by the amount of iron phosphide powder added to the coating composition, and the kinetic friction coefficient of the organic resin film after drying is adjusted by the amount of polyethylene wax added to the coating composition. It was adjusted.

Paint composition for resin coating on outer surface of steel plate (3) Epoxy resin (“Epicoat 1007” manufactured by Yuka Shell Epoxy Co., Ltd. dissolved in xylene / methyl ethyl ketone) and blocked isocyanate (Dainippon Ink & Chemicals, Inc.) Co., Ltd. “Barnock B7-887-60”)
Base resin consisting of 100 parts by weight (solid content), strontium chromate 40 parts by weight and black azo metal complex dye 1
A stainless steel powder (average particle size: 5 μm) and a polytetrafluoroethylene resin fine powder (“Fluon Lubricant L155J” manufactured by Asahi ICI Fluoropolymers Co., Ltd.) are added to a coating composition containing 0 parts by weight, if necessary. The solid content was adjusted with a solvent. The volume resistivity of the dried organic resin film is adjusted by the amount of the metal stainless steel powder added to the coating composition, and the kinetic friction coefficient of the dried organic resin film is determined by the fineness of the polytetrafluoroethylene resin in the coating composition. It was adjusted by the amount of powder added.

Paint composition for resin coating on outer surface of steel sheet (4) Polyester resin (“Super Beckolite M-6803-30” manufactured by Dainippon Ink and Chemicals, Inc.) and melamine resin (Dainippon Ink and Chemicals, Inc.) A coating composition containing 100 parts by weight (solid content) of a base resin made of “Super Beckamine L-110” and 40 parts by weight of strontium chromate was mixed with titanium nitride (average particle size 1 μm) and polyethylene wax (Hoechst Co., Ltd.). "Seridust 3620")
And the solid content was adjusted with a solvent as needed.
The volume resistivity of the dried organic resin film is adjusted by the amount of titanium nitride in the coating composition, and the kinetic friction coefficient of the dried organic resin film is adjusted by the amount of polyethylene wax added in the coating composition. did.

(4) Example of preparing a coating composition for an insulating organic resin film applied to the inner surface of a steel sheet A coating composition for a resin film on the inner surface of a steel sheet (1) Amine-modified epoxy resin and blocked isocyanate (manufactured by Asahi Kasei Corporation) Duranate MF-B "), 100 parts by weight (solid content) of base resin, 30 parts by weight of dry silica (" R811 "manufactured by Nippon Aerosil Co., Ltd.), 30 parts by weight of barium chromate, and 30 parts by weight of black azo-based metal complex dye A polyethylene wax (“Ceridust 3620” manufactured by Hoechst) was blended with the coating composition containing the parts, and the solid content was adjusted with a solvent as needed. The volume resistivity value of the dried organic resin film is adjusted by the amount of the blocked isocyanate in the coating composition, and the kinetic friction coefficient of the dried organic resin film is adjusted by the amount of the polyethylene wax in the coating composition. did.

A coating composition for a resin film on the inner surface side of a steel sheet (2) A base resin 100 composed of a block urethane-modified epoxy resin (“EPOKEY 834” manufactured by Mitsui Toatsu Chemicals, Inc.)
Parts by weight (solid content), fumed silica (Nippon Aerosil Co., Ltd.)
(R811), 30 parts by weight of barium chromate, and 30 parts by weight of barium chromate, were mixed with fine powder of polytetrafluoroethylene resin ("Fluonlubricant L155J", manufactured by Asahi IC Fluoropolymers Co., Ltd.). The solid content was adjusted with a solvent according to the above. The volume resistivity value of the dried organic resin film is adjusted by the amount of the blocked isocyanate in the coating composition, and the coefficient of kinetic friction of the dried organic resin film is determined by the fine powder of the polytetrafluoroethylene resin in the coating composition. Was adjusted by the amount of addition.

Paint composition for resin coating on steel sheet inner side (3) Epoxy resin (“Epicoat 1007” manufactured by Yuka Shell Epoxy Co., Ltd. dissolved in xylene / methyl ethyl ketone) and blocked isocyanate (Takeda Pharmaceutical Co., Ltd.) 100 parts by weight (solid content) made of "Takenate B-870N" manufactured by Nissan Chemical Industries, Ltd .; 10 parts by weight (solid content) of silica sol ("Organosilica Sol NPC-ST" manufactured by Nissan Chemical Industries, Ltd.); and 20 weight parts of strontium chromate. The polytetrafluoroethylene resin fine powder (“Fluonlubricant L155J” manufactured by Asahi IC Fluoropolymers Co., Ltd.) was blended with the coating composition containing the above parts, and the solid content was adjusted with a solvent as needed. The volume resistivity of the dried organic resin film is adjusted by the amount of the blocked isocyanate added in the coating composition, and the kinetic friction coefficient of the dried film is determined by the amount of the polytetrafluoroethylene resin fine powder in the coating composition. Adjusted by

Paint Composition for Resin Coating on Inner Surface of Steel Sheet (4) Acrylic resin (“Acridic A-405” manufactured by Dainippon Ink and Chemicals, Inc.) and graphite (“Coat Height” manufactured by Nippon Graphite Industries, Ltd.) Was prepared. Coating composition for resin coating on inner surface of steel sheet (5) Polyester resin ("Super Beckolite M-6803-30" manufactured by Dainippon Ink and Chemicals, Inc.) and melamine resin ("Super" manufactured by Dainippon Ink and Chemicals, Inc.) A coating composition containing 100 parts by weight (solid content) of a base resin composed of Becamine L-110 ") and 40 parts by weight of strontium chromate was mixed with titanium nitride (average particle size: 1 μm) and polyethylene wax (" Seridust "manufactured by Hoechst). 3620 ")
And the solid content was adjusted with a solvent as needed.
The volume resistivity of the dried organic resin film is adjusted by the amount of titanium nitride in the coating composition, and the kinetic friction coefficient of the dried organic resin film is adjusted by the amount of polyethylene wax added in the coating composition. did.

(5) Formation of Organic Resin Coating Each of the coating compositions for the outer surface side and the inner surface side of the steel sheet is coated on each target surface of the steel sheet by a roll coater, and baked at an ultimate temperature of 140 to 250 ° C. A film having a predetermined thickness was obtained. The dynamic friction coefficient of the obtained organic resin film was measured under the following conditions. Tool shape: 3 × 10 mm Pressure: 400 kgf (surface pressure: 13.3 kg / mm ² ) Oil-free Oil pencil hardness was measured according to JIS K5400.

(6) Evaluation method of each characteristic The evaluation method of each characteristic in the present embodiment is as follows. (A) Powdering resistance A test bead was subjected to a draw bead test under the conditions of a bead tip diameter of 0.5 mmR, a bead height of 4 mm, a drawing speed of 200 mm / min, and a pressure of 500 kgf, and an adhesive tape was applied to the sliding portion. The weight difference between the test pieces before and after the test after peeling was measured, and the difference was converted into a unit area to obtain a film peeling amount, which was evaluated as follows. ◎: decapsulation weight 5 g / m ² or less ○ +: decapsulation weight 5 g / m ² ultra ~10g / m ² ○: film peeling amount 10 g / m ² ultra ~15g / m ² ×: film peeling amount 15 g / m ² Super

(B) Weldability CF type electrode, pressurizing force: 200 kgf, energizing time: 10 cycles / 50 Hz, welding current of 10 kA, a continuous hitting test was carried out, and when a nugget diameter of 3.5 mm or more was accepted. The evaluation was based on the number of continuous hit points. The evaluation criteria are as follows. ◎: 2000 points or more ○ +: 1500 points or more and less than 2000 points ○: 1000 points or more and less than 1500 points ○-: 500 points or more and less than 1000 points ×: Less than 500 points or no current

(C) Suitability for outer surface (c-1) Rust resistance to outer surface Intermediate paint K manufactured by Kansai Paint Co., Ltd. on the outer surface of the test piece
Apply intermediate coating (film thickness 40 μm) directly with PX-36,
Next, Luuga Bake B-531 manufactured by Kansai Paint Co., Ltd.
Was applied to form a top coat (film thickness: 40 μm). After cross-cutting the test piece with a cutter knife, complex corrosion with one cycle of [salt spray test / 10 minutes → drying ・ 155 minutes → wetting test ・ 75 minutes → drying ・ 160 minutes → wetting test 80 minutes] The test was performed for 300 cycles, and the external rust resistance was evaluated based on the swollen width of the corrosion from the cross cut portion. The evaluation criteria are as follows. ◎: less than 2 mm ：: 2 mm or more and less than 4 mm Δ: 4 mm or more, less than 6 mm ×: 6 mm or more

(C-2) Coating Adhesion The test piece was subjected to the same intermediate coating and top coating as in (c-1) above, and the test piece was immersed in ion-exchanged water at 40 ° C. for 240 hours. After that, remove the test piece,
Leave at room temperature. The test piece was cut into 100 grids at intervals of 2 mm on the coating film, and an adhesive tape was attached and peeled off, and the peeling rate of the coating film was evaluated. The evaluation criteria are as follows. ◎: no peeling ○: peeling rate less than 3% △: peeling rate 3% or more and less than 10% ×: peeling rate 10% or more

(C-3) Visibility after coating The outer surface of the test piece was subjected to the same intermediate coating and top coating as in (c-1) above, and an image clarity measuring device (manufactured by Suga Test Instruments Co., Ltd.) (ICM-2DP) and the image clarity C when a 0.5 mm slit was used was evaluated. The evaluation criteria are as follows. ◎: 75 or more ○ +: 70 or more, but less than 75 ○: 65 or more, less than 70 △: 60 or more, less than 65 ×: less than 60

(D) Corrosion resistance to perforation (internal suitability)
After tape sealing the edge and the outer surface, [Salt spray 4
Time → drying 2 hours → wetting test 4 hours] as one cycle, and 200 cycles were performed to evaluate the progress of corrosion. The evaluation criteria are as follows. ◎: No red rust occurred ○ +: Red rust area ratio less than 5% ○: Red rust area ratio 5% or more and less than 10% ○-: Red rust area ratio 10% or more and less than 20% ×: Red rust area ratio 20% or more

[0064]

[Table 1]

[0065]

[Table 2]

[0066]

[Table 3]

[0067]

[Table 4]

[0068]

[Table 5]

[0069]

[Table 6]

[0070]

[Table 7]

[0071]

[Table 8]

[0072]

[Table 9]

[0073]

[Table 10]

[0074]

[Table 11]

[0075]

[Table 12]

[0076]

[Table 13]

[0077]

The pre-primed steel sheet of the present invention described above has excellent powdering resistance and weldability, and also has an intermediate coating, a top coating, or an outer coating when directly coated without applying an electrodeposition coating. Pre-prime for automotive bodies that require particularly strict characteristics because they have excellent paint adhesion on the side, excellent rust resistance on the outer surface, and excellent clarity after painting, and also excellent resistance to perforated corrosion on the inner surface of the steel plate. It is extremely useful as a steel plate.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing a schematic film cross-sectional structure of a pre-primed steel sheet of the present invention.

FIG. 2 is a graph showing a relationship between a volume specific resistance value of a conductive organic resin film on an outer surface side of a steel sheet and weldability.

FIG. 3 is a graph showing the relationship between the thickness of a conductive organic resin film on the outer surface side of a steel sheet and the sharpness after painting.

FIG. 4 is a graph showing the relationship between the thickness of a conductive organic resin film on the outer surface of a steel sheet and the amount of film peeling (powdering resistance) during press forming.

FIG. 5 is a graph showing the relationship between the coefficient of kinetic friction of a conductive organic resin film on the outer surface of a steel sheet under oilless conditions and the amount of film peeling (powdering resistance) during press forming.

FIG. 6 is a graph showing the relationship between the pencil hardness of the conductive organic resin film on the outer surface side of the steel sheet and the amount of film peeling (powdering resistance) during press molding.

FIG. 7 is a graph showing the relationship between the volume resistivity of the organic resin film on the inner surface side of the steel sheet and the corrosion resistance to perforation.

FIG. 8 is a graph showing the relationship between the thickness of an organic resin film on the inner surface side of a steel sheet and weldability.

FIG. 9 is a graph showing the relationship between the coefficient of kinetic friction of an organic resin film on the inner surface side of a steel sheet under oilless conditions and the amount of film peeling (powdering resistance) during press forming.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-8-267656 (JP, A) JP-A-3-270932 (JP, A) JP-A-8-196991 (JP, A) 99546 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) B32B 15/00-15/20

Claims (4)

(57) [Claims] 1. A galvanized steel sheet having a chromate film having a coating weight of 1 to 500 mg / m ² in terms of chromium metal on both surfaces thereof,
Volume specific resistance value is 0.001Ω · cm or less , dynamic friction coefficient under oil-free condition is 0.03-0.30, pencil hardness is 3
B to 5H, having a conductive organic resin film having a thickness of 2.0 to 30 μm, on the chromate film on the other side of the steel sheet,
Volumetric resistivity exceeding 1 Ω · cm , friction under oil-free condition
The coefficient of friction is 0.03-0.30, and the film thickness is 0.1-3.0μ.
A weldable automotive pre-primed steel sheet having excellent corrosion resistance and workability, characterized by having an organic resin film of m. 2. The conductive organic resin film formed on one side of a steel sheet has a volume specific resistance of 0.001 Ω · cm or less and a film thickness of 3.0 to 10 μm. Weldable automotive pre-primed steel sheet with excellent corrosion resistance and workability. 3. The conductive organic resin film formed on one side of a steel sheet has at least one conductive material selected from metal or alloy powder, conductive carbon, iron phosphide, carbide, nitride and semiconductor oxide. Claims characterized by containing fine powder
3. A weldable automotive pre-primed steel sheet having excellent corrosion resistance and workability according to 1 or 2 . 4. A conductive organic resin film formed on one side of a steel sheet, wherein the conductive organic resin film is at least one selected from the group consisting of metal or alloy powder, conductive carbon, iron phosphide, carbide, nitride and semiconductor oxide. The weldable pre-primed steel sheet for automobiles having excellent corrosion resistance and workability according to claim 1 or 2, comprising a fine powder and a polyethylene wax.