JPH04311577A - Production of thin film organic composite plated sheet excellent in corrosion resistance after electrodeposition coating - Google Patents

Abstract

PURPOSE:To offer a thin film organic composite plated steel sheet free from the elution of harmful substance such as chromium in a surface treating stage and having high corrosion resistance in a consumer to the market. CONSTITUTION:This is method for manufacturing an organic composite plated steel sheet formed in such a manner that a coating chromium compsn. obtd. by incorporating specified amounts of one or more kinds of inorganic inhibitors constituted of the metallic salt, carbonate and silicate of Mo, V, W, Ni, Co, Si, Ti, Zr and Li is formed on the surface of a galvanized steel sheet by 5 to 150mg/m<2> by the total content of chromium, and the upper layer is subjected to 0.3 to 5mum thin film baking/hardening of a coating compsn. constituted of silica powder, hydrophilic polyamide resin, urethane epoxy ester resin and a lubricant. In an organic composite plated steel sheet using coating chromium as a base, chromium eluting resistance properties and corrosion resistance after electrodeposition coating are remarkably improved.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an organic composite plated steel sheet coated with a thin film, and more particularly to a method for producing a highly corrosion resistant organic composite plated steel sheet with excellent chromium elution resistance.

0002

[Prior Art] In recent years, there has been a strong demand for lower costs and higher rust resistance of zinc or zinc alloy coated steel sheets (hereinafter simply referred to as zinc alloy coated steel sheets) for automobiles and home appliances.
Recently, research has been actively conducted to develop new products for this purpose. Among these, there is an organic composite plated steel plate in which chromate treatment is applied to only one side of the zinc-based alloy plated steel plate and a thin film is coated on the upper layer, but the coating base for the plated surface on the opposite side is Due to the demand for improved phosphate treatment properties as a treatment, there is an increasing need in the market for the base chromate treatment for thin film coating to be changed from an electrolytic type to a coating type. In order to meet this demand, it is necessary to develop a hardly soluble coating chromate treatment technology that suppresses the chromium elution resistance of the coating chromate film as much as possible. In the prior art, an example of an attempt to make the chromate film difficult to dissolve is disclosed in Japanese Patent Application Laid-Open No. 50-1
There is No. 58535. This discloses a chromate solution based on chromic anhydride-phosphoric acid-water-soluble or water-dispersible polymer compound, and the hexavalent chromium ion in the treatment solution is reduced by 70% or more with a reducing agent such as ethylene glycol. It is something that However, since the chromate film formed according to this example contains a polymer, it has poor solubility, corrosion resistance,
Although it has excellent paintability, it has the disadvantage of poor weldability. Next, the chromate solution disclosed in Japanese Patent Publication No. 61-58552 is based on chromic acid - chromate reduction product - silica sol. When painting, the problem is that mainly hexavalent chromium in the chromate film tends to be eluted during alkaline cleaning before painting, resulting in a decrease in the corrosion resistance of the film.

[0003] Next, JP-A-58-22383 and JP-A-62-83478 disclose the use of a silane coupling agent to reduce hexavalent chromium ions in a chromate treatment solution. It will be done. Although the films formed by these methods have excellent coating adhesion, the chromate film formed by the former method has poor alkali resistance because it is formed with a chromate treatment solution that does not contain phosphoric acid. bad. Furthermore, in the latter method, the alkali resistance is similarly insufficient. When examining the performance of each component in the conventional technology in the above-mentioned chromate treatment method, it was found that organic polymers and silica tend to improve corrosion resistance but deteriorate alkali resistance, and that silane coupling agents 6 in the chromate treatment solution as it tends to reduce valent chromium ions.
There is a tendency for the valence chromium ion concentration to decrease for a while, making the corrosion resistance of the chromate film unstable. As mentioned above, various methods have been disclosed, but the performance of each method as a coated chromate film strongly depends on the drying conditions of the chromate treatment.

[0004] In addition, an aqueous solution prepared by mixing a water-dispersible emulsion resin with chromic acid or a chromium compound having high anti-corrosion properties was applied to the surface of a zinc-plated or zinc-alloy plated steel sheet to achieve high anti-rust properties. No. 55-51032, JP-A-59-162278, JP-A-61-584, etc. have been proposed, but all of these have high rust prevention properties, but chromium elution has been observed in dew condensation and water-based treatment solutions. is,
There are practical problems. In addition, as a product made by blending a water-dispersible emulsion resin with an organic composite silicate (silica sol, silane coupling agent) and coating it with a thin film, JP-A-6
0-50181, JP-A-60-149786, etc. Although these do not have the above-mentioned problems due to chromium elution, since they contain silica in the form of a stable colloid, alkali, ammonium ions, etc. are present, and therefore there are problems in the physical properties of the coating film, such as water resistance. in this way,
On the other hand, it has higher corrosion resistance than thin-film coated anti-rust steel sheets.
■Coating film formed on the steel plate (especially cationic electrodeposition coating film)
In order to improve the adhesion of the steel sheet and (1) improve the working strength of the steel sheet, it is required to lower the baking sheet temperature (140 to 170° C.). While various coating compositions have been proposed that can be expected to meet these requirements, the present inventors have already proposed Japanese Patent Application Laid-open No. 62-283161, and have also proposed this coating composition. An organic composite steel sheet coated with a thin film is further proposed in JP-A No. 63-035798.

[0005]

[Problems to be Solved by the Invention] Therefore, we have developed an organic composite plated steel sheet that has excellent corrosion resistance due to a thin film coating on a coated chromate base that does not elute harmful substances such as chromium during the surface treatment process at the customer and can be baked at low temperatures. The main purpose of the invention is to provide the market with: In addition, in response to the above market needs, the present inventors have already developed
JP-A-63-03 using the coating composition of No. 3161
No. 5798, an organic composite steel sheet has been proposed, and the present invention is aimed at further improving the corrosion resistance of the organic composite plated steel sheet after electrodeposition coating. This is an improvement. Therefore, the present invention relates to an organic composite steel sheet having the above-mentioned soluble coated chromate film, and in order to achieve even higher corrosion resistance after electrodeposition coating, it is necessary to make the coated chromate film even less soluble. We considered it necessary and conducted the following study. In other words, in order to make the applied chromate film hardly soluble, it is basically necessary to achieve the ionization of soluble Cr6+ ions into hardly soluble Cr3+, and for this purpose, reduction of Cr6+ including uniform reactivity with the underlying plating layer and elution are unavoidable. A trace amount of Cr6
By actively forming a reactive compound with +, the barrier effect of the reaction product blocks corrosion factors,
The purpose was to achieve high corrosion resistance as the thin-film organic composite plated steel sheet, and for this purpose, the following studies were conducted. ■ Optimization of the Cr3+/Cr6+ ratio in the chromate solution with the aim of improving the chromium elution resistance of the applied chromate film and thereby improving the adhesive strength with the upper thin film coating. ■ In order to equalize the adhesion of the chromate film to the plated surface, it is necessary to give it the ability to promote a uniform reaction at the plated interface, and we are investigating the appropriate etching accelerator for this purpose. ■ Examining inorganic inhibitors to provide sufficient barrier effects against corrosion factors. As a result of the above studies, the etching effect of hydrofluoric acid in the chromate solution applied to the plating surface promotes the uniform formation of a chromate film with excellent adhesion by exposing the fresh plating surface. I said W, Mo, V. The chromate film formed by the combined action of an inorganic inhibitor has the effect of blocking corrosion factors and suppressing the elution rate of Cr6+, which is essential for achieving high corrosion resistance, resulting in unprecedented high corrosion resistance according to the amount of chromate deposited. We have discovered that this can be achieved, and have come to propose the present invention.

[0006]

[Means for Solving the Problems] First, the structure of the method for manufacturing an organic composite plated steel sheet according to the present invention will be explained. A coating type chromate film made of the bath composition of [A] below is applied as a first layer on the surface of zinc, zinc-based alloy plating and zinc-based composite alloy-plated steel sheet as a fixed film at a concentration of 5 to 150 mg/m.
2 is formed, and the organic solvent-based coating composition of the following [B] is coated as a second layer on top of the solid film with a thickness of 0.3 to 5 μm. This is a method for producing a corrosion-resistant organic composite plated steel sheet. [A] Coating chromate bath composition ■ Cr6+; 1 to 30 g/l ■ Cr3+; 1 to 30 g/l ■ Cr6+/Cr3+ weight ratio; 0.1 to 2.0 ■
HF; 1 to 10 g/l ■ Mo, V, W, Zr, Si, Ti, Ni, Co,
Inorganic inhibitor consisting of at least one of Li fluorides, oxyacids, carbonates, chromium compounds, and borides; [Cr6+] x 0.1 to 1 g equivalent ■ pH
; 2.0 to 4.0 [B] Organic solvent-based coating composition (a) Urethane epoxy ester resin (
However, number average molecular weight 300-100
,000) 30-90%
(b) Hydrophilic polyamide resin (degree of polymerization 50-1
,000) 5-40% (c) Silica powder (average particle size 1-100 mμ)
5-40% (d) Polyethylene wax (molecular weight 1,000-
10,000)
1
~20%
[Non-volatile content weight %] That is, the gist of the present invention is as follows: (1) The coated chromate layer forming the first layer is basically converted from soluble chromic chromic chromate to sparingly soluble fluoride chromium by employing hydrofluoric acid and an inorganic inhibitor. It is characterized by a compound-dominated structural change, and in addition, by improving the uniform reactivity at the plating interface with hydrofluoric acid, it improves the adhesion of the chromate layer and improves the chromium elution resistance and chromium elution resistance as an organic composite plated steel sheet. It has improved corrosion resistance, especially corrosion resistance after electrodeposition coating. ■The second layer is characterized by a combination of a solid film made of a solvent-based organic polymer resin that is a composite of highly water-resistant epoxy resin, hydrophilic polyamide resin, and fine-grained silica. Therefore, hydrophilic polyamide resin is necessary for the smoothness of the electrodeposited coating (gas pinholes, craters, yuzu skin), adhesion and corrosion resistance will decrease if fine silica is not used together, and hydrophilicity The combination of polyamide resin, fine silica, a flexible resin, and high hardness fine particles gives good results for the lubricity of the film, but the electrodeposition with the electrodeposited film is insufficient, so a highly corrosion-resistant epoxy resin binder is used. This method was developed based on the knowledge that the underlying chromate film must be poorly soluble in order to further improve the water-resistant secondary adhesion of the electrodeposited coating. In addition, as the plating system for the steel sheet applied to the present invention, in the electroplating system, Zn,
Alternatively, a Zn-based plated steel sheet containing at least one alloy element group consisting of Ni, Cr, and Fe may be used. SiO2, TiO2, Al2O
3. A steel plate coated with a dispersion of metal oxides such as ZrO2 and BaCrO4 may be used. Furthermore, in the hot-dip coating system, galvanized iron sheets, alloyed galvanized steel sheets, Zn-
It may be applied to Al alloy plated steel sheets. Zinc-, aluminum- and alloy-plated steel sheets or zinc-based composite alloy-plated steel sheets may be used, all of which are obtained by known methods.

[0007]

[Action] The limits of action on the constituent factors of the present invention will be described below. ■ Regarding the applied chromate film, the applied chromate film used in the present invention is located between the lower plating layer and the upper coating film, and improves the adhesion of the coating film, which provides high corrosion resistance as an organic composite plated steel sheet. It is a very important film in bringing about this. In particular, swelling and elution resistance against water, alkali resistance, and acidic aqueous solutions is essential. To achieve this, the chromate film must be highly insoluble, and the bath composition must be limited as follows. . The present chromate composition [A] uses water as a solvent and contains 1 to 30 g/l of hexavalent chromium ions and 3
Contains 1 to 30 g/l of valent chromium ions as a basic component. Hexavalent chromium ion concentration of less than 1 g/l and 1 g/l
If the trivalent chromium ion concentration is less than 30 g/l, it is difficult to form a chromate film showing satisfactory corrosion resistance;
At a valent chromium ion concentration and a trivalent chromium ion concentration exceeding 30 g/l, the viscosity of the chromate solution increases, and the stability of the chromate solution deteriorates, making it difficult to control the amount of chromium deposited. Therefore, the preferred concentration range is C
R6+5 to 20 g/l and Cr3+5 to 20 g/l are preferable. Also, what is important in the amount of chromium is the content ratio of hexavalent and trivalent chromium ions, and the weight ratio of hexavalent/trivalent chromium ions must be in the range of 0.1 to 2.0. 6
If the weight ratio of valent and trivalent chromium ions is less than 0.1, the chromate composition tends to gel and the corrosion resistance of the chromate film formed decreases. On the other hand, if the weight ratio of hexavalent and trivalent chromium ions exceeds 2.0, the concentration of hexavalent chromium ions will increase accordingly, reducing the water swelling resistance of the chromate film itself, which will affect the adhesion and electrical properties of the upper thin film coating. This leads to a decrease in adhesion after coating. Therefore, preferred Cr6+ and C
The weight ratio of r3+ is preferably 0.5 to 1.5. The chromium ion weight ratio can also be controlled using a known reducing agent such as ethanol, methanol, hydrogen peroxide, starch, or sucrose. As another component, the chromate composition of the present invention needs to contain hydrofluoric acid (HF) at 1 to 10 g/l. When HF is less than 1.0 g/l, the chromium elution resistance of the chromate film decreases, leading to a decrease in corrosion resistance and alkali resistance. Moreover, if the HF exceeds 10.0 g/l, the excessive etching action of the underlying plating layer will have an adverse effect on the bath balance control of the chromate solution, leading to a decline in quality and productivity. Therefore, the concentration of HF is preferably 0.3 to 5 g/l.

Next, the action of inorganic inhibitors will be described. The chromate composition of the present invention requires the use of an inorganic inhibitor to further enhance the barrier effect against corrosion factors. Inorganic inhibitors include Mo,
Consisting of the group of V, W, Zr, Si, Ti, Ni, Co, Li fluorides, oxyacids, carbonates, borides, and chromium compounds, at least one of which is 0.1% of Cr6+
~1 g equivalent is required. Among these compounds, preferred compounds include the following. M
The O compound is phosphomolybdic acid hydrate or lithium molybdate, the V compound is vanadate, the Zr compound is potassium zirconium fluoride or the sodium zirconium hexafluoride, the W compound is silicotungstic acid, and the Si compound is fluorosilicate. Hydrogen acid and Li compounds include lithium carbonate, lithium borate, lithium chromate, etc. Ni compounds include nickel carbonate, and Co compounds include cobalt carbonate. If the amount of these inorganic inhibitors added is less than 0.1 g equivalent of Cr6+, a dense and tight chromate film that is sufficient to block corrosion factors will not be formed. A significant improvement in corrosion resistance in the alkaline corrosive environment under the coating film cannot be expected. On the other hand, if the amount of the inhibitor added exceeds 1.0 g equivalent of Cr6+, the performance level as corrosion resistance is saturated, and on the other hand, the thin coating film as an organic composite plated steel sheet may be partially peeled off during press working etc. It becomes easier to wake up,
This is not very preferable because it causes problems such as spot weldability. The preferred amount of the inhibitor added is 0.3 to
0.7g equivalent is good. Furthermore, the coating chromate composition of the present invention requires pH control of the solution. This p
H maintains uniform dispersion of various additives forming the composition in the liquid, suppresses excessive dissolution of the base plating layer, and efficiently removes metal oxides or hydrates formed on the surface. This is a necessary factor for exposing the active plating surface and improving uniform reactivity at the plating interface. If this pH is less than 1.0, the free acid is too high and the chromate film formed is likely to be redissolved due to excessive etching of the underlying plating layer, and the bath balance of the chromate composition is likely to be lost, leading to a decrease in corrosion resistance and productivity due to the contamination of impurities. causing a decline. On the other hand, pH
If it exceeds 3.0, the bath dispersibility of the inhibitor will be affected, and the etching removal function of metal hydrates etc. generated on the surface of the base plating will be reduced, and the uniform reactivity at the interface of the plating layer will be reduced. This makes it difficult to form a chromate film with good adhesion. Therefore, the preferred pH range is 1.9 to 2.5.

■Amount of chromate deposited The chromate composition [B] of the present invention is applied to the surface of a zinc-plated steel sheet using, for example, a roll coater, and then dried to form a chromate film with a chromium deposition amount of 10 to 150 mg/m2. let The amount of chromium deposited is the total amount of metallic chromium,
If it is less than 10 mg/m2, the corrosion resistance of the film and the corrosion resistance after painting will be insufficient, and if it exceeds 150 mg/m2, it will be difficult to control the amount of chromium deposited in the chromate film, and the corrosion resistance improvement effect will be saturated and no further effect will be obtained. This is difficult to predict and a part of the chromate film is easily removed by external force, which causes a decrease in paint film adhesion and a decrease in weldability. Therefore, the amount of chromium deposited is preferably 20 to 100 mg/m2.

(1) Drying plate temperature after chromate treatment One of the features of the present invention is that the chromate film after coating chromate treatment is dried over a relatively wide range of plate temperatures. In order to increase the chromium elution resistance of the chromate film and improve the corrosion resistance of the thin-film organic composite plated steel sheet using the chromate film as a base, it is necessary not only to use the above-mentioned chromate composition but also to appropriately select the drying conditions after treatment. is necessary. Of course, when selecting the appropriate drying conditions, it is necessary to take into account the material strength of the steel plate, and in particular BH
It is preferable that steel plates requiring high properties can be dried at lower temperatures. Among the drying conditions after the chromate treatment of the present invention, if the final plate temperature at the exit side of the drying oven is less than 50°C, the water film contained in the chromate film remains in the evaporation drying region, and air oxidation, which is necessary for achieving high corrosion resistance, occurs. The polymerization reaction is promoted and a sufficient network structure cannot be expected, and therefore, further improvement in chromium elution resistance and corrosion resistance as a thin-film organic composite plated steel sheet cannot be expected. Furthermore, if the plate temperature exceeds 150°C, even the water content necessary to maintain the stability of the chromate film itself begins to be dehydrated, making it physically brittle to process and impairing adhesion. Therefore, the dry plate temperature after the chromate treatment is 50 to 15
0°C, preferably 60-120°C. Note that under the chromate drying conditions of the present invention, the drying time is not particularly limited, but sufficient performance can be achieved with drying in 1 to 5 seconds or less even in a low temperature range with a final board temperature of 100°C or less. be.

■ Inlet plate temperature in thin film coating process When applying the coating composition of the present invention in a thin film, the uniform coating finish improves the appearance and corrosion resistance and other qualities of the thin film organic composite steel sheet, and increases the commercial value. Sufficient control is necessary to further increase the In the present invention, in order to achieve a uniform appearance of the coating film, it is necessary to control the temperature of the plate at the entrance of the coating process to a low level that can be achieved under air cooling. If the entrance plate temperature exceeds 70°C, the solvent in the paint will evaporate rapidly, causing a drying phenomenon on the coater roll surface and creating a streaky pattern, resulting in poor paint appearance and difficulty in controlling the uniformity of the paint film. As a result, the product value or securing stable manufacturing technology will be impaired. Of course, the lower limit of the entrance plate temperature is not particularly emphasized, but it may be at a room temperature level that changes depending on the seasons. In this case, in order to reduce the temperature to room temperature level, it is necessary to control the humidity in the working environment to prevent condensation, and normally it is essential to maintain the humidity necessary for painting. In addition, in the present invention, there is a method of water cooling as a method of controlling the temperature of the plate after chromate drying in a short time in consideration of productivity, but this method causes the chromate film to elute and change the appearance of the chromate treatment. This may cause unevenness, or the eluted chromium may re-deposit on the back side (plated surface) of the single-sided thin-film coated steel sheet, which corresponds to the outside surface of the car body, and may interfere with the phosphate treatment performed before electrodeposition painting. This is not very desirable as it invites In order to avoid re-deposition of this eluted chromium, it is essential to control the purity of the water if it is used in a circulating manner.Also, it is possible to dispose of the water, but in either case it is not a good idea as it increases the cost.

[0012] Regarding the organic solvent-based coating film, the urethanized epoxy ester resin, which is the binder resin used in forming the organic coating film of the present invention, contains 50% or more of phenol in the molecule as a non-volatile component of the paint. , an epoxy ester resin obtained by reacting the epoxy resin with a dicarboxylic acid in the presence or absence of an amine catalyst, and a urethane obtained by reacting the epoxy ester resin with a partially blocked isocyanate compound. Number average molecular weight 300 to 100,000 selected from the group consisting of chemically modified epoxy ester resins
30 to 90% by weight of the epoxy binder resin is used. When the number average molecular weight is less than 300, adhesion and corrosion resistance deteriorate, and the resin molecular weight that can be dissolved in an organic solvent and used for coating purposes is limited to 100,000. Furthermore, within the range of the number average molecular weight of the epoxy binder resin, if the amount of the epoxy binder resin is less than 30% by weight of the non-volatile content of the paint, the adhesion and processability of the electrodeposited film will deteriorate; If it exceeds 90% by weight, the binder function as a paint will be halved. Next, in the present invention, the hydrophilic polyamide resin used as the second resin component together with the binder resin has a degree of polymerization of 50 to 1000, preferably 50 to 1000.
If the polymerization degree is less than 50, the coating will dissolve during the above-mentioned alkaline degreasing or electrodeposition, and a uniform appearance will not be obtained, and a decrease in acid resistance will be observed. unsuitable for the purpose of the invention. Incorporation of polyamide resin is also desirable in terms of imparting flexibility and high processability to the coating film. Regarding the amount of the polyamide resin to be incorporated into the paint, the amount of the polyamide resin is selected to be 5 to 40% by weight, preferably 5 to 25% by weight of the non-volatile content of the paint. If it is less than 5% by weight, no significant improvement in uniform electrodeposition (gas pin, yuzu skin) can be expected, and if it exceeds 40% by weight, the adhesion of the electrodeposited film will decrease. Next, in the present invention, silica having an average particle size of 1 to 100 mμ is used in an amount of 5 to 40% by weight based on the nonvolatile content of the paint for the purpose of improving corrosion resistance. If the primary particle size of the silica particles is less than 1 mμ, the alkali resistance of the composite coating film will deteriorate, which is undesirable, and if it exceeds 100 mμ, there will be no effect of improving corrosion resistance, and the smoothness of the electrodeposited film will also deteriorate. Therefore, the average particle size of the silica particles should be in the range of 1 to 100 mμ, and preferably in the range of 5 to 50 mμ. Examples of such silica particles include fumed silica, colloidal silica, etc. Among them, fumed silica is preferably used. Colloidal silica contains ammonium ions and alkali metal ions for colloidal stabilization, and these ions tend to reduce membrane anticorrosion ability. In addition, the amount of silica particles blended is 5 to 40% by weight, preferably 10 to 20% by weight, based on the nonvolatile content of the paint.
If it is less than 5% by weight, there is no effect of improving corrosion resistance;
If it exceeds % by weight, a decrease in processability is observed, which is insufficient for the purpose of the invention. As described above, the organic composite coating film of the present invention contains specific amounts of epoxy binder resin, hydrophilic polyamide resin, and particulate silica as nonvolatile components, and the combination of these three components mutually improves electrodeposition coating properties. It is possible to provide a coating film that is highly corrosion resistant, highly workable, has excellent adhesion, and is smooth and can be spot welded. Regarding processability, the coating composition of the present invention contains lubricants such as polyolefins, carboxylic acid esters, carboxylic acid metal salts, polyalkylene glycols, and lubricant powders such as molybdenum disulfide, silicone compounds, and fluorine compounds. 1 to 20% by weight, preferably 1 to 10%
It is preferable to add % by weight to further improve processability. Particularly preferred lubricants have a molecular weight of 1,000 to 10,
000 polyethylene wax. however,
When adding a lubricant, the maximum amount added should be up to 20% by weight, and if it exceeds this, the adhesion of the electrodeposited film will deteriorate, which is undesirable. In addition, in imparting the low-temperature baking function to the coating composition of the present invention as described above, a curing agent such as a melamine resin, a resol type phenol resin, or a polyisocyanate is added to the epoxy resin in a solid content weight ratio of curing agent/epoxy resin. The resin can be contained in a ratio of 0.1/9.9 to 4/6 and thermally cured. Particularly preferable resol type phenolic resins have the formula

[0013]

[ka]

(In the formula, n is 0 to 4; W is -CH2- or -CH2-O
-CH2-;R is CH3, H or -C(CH3)2OH
) is a resol type phenolic resin.

[0014] When the organic composite coating composition of the present invention prepared as described above is applied to the plated steel plate, the coating method may be roll coating, spray coating, shower coating, etc. As for the temperature,
The temperature may be 100 to 250°C. The dry coating thickness is
0.3 to 5 μm, preferably 0.5 to 3 μm, and 0
．． If the thickness is less than 3 μm, a decrease in corrosion resistance, press lubricity, etc. is observed, and if it exceeds 5 μm, stable spot weldability cannot be expected. In the organic composite plated steel sheet of the present invention made as described above, the following various pigments are used in the coating composition constituting the uppermost organic solvent-based coating film in order to further improve the functionality of the coating film. Good too. Rust-inhibiting pigments (chromate pigments - especially low-solubility zinc, lead, barium salts, phosphate pigments, leadate pigments, etc.), extender pigments (carbonate pigments, silicate pigments, etc.), which are added to ordinary paints. Pigments, etc.) Coloring pigments (titanium oxide, carbon), rust inhibitors (amine compounds, phenolic carboxylic acids, etc.), dispersion stabilizers, etc. may be added, but they should be added with sufficient consideration for spot weldability and press workability. It is better to use particles whose average particle diameter is adjusted to 10 mμ or less. Note that the coating film baking conditions after painting of the coating composition used in the present invention are not particularly limited, but the final baking board temperature is 1
It is possible to carry out baking treatment for a short time while maintaining good performance within the range of 00 to 200°C. The coating method may be any known method such as a roll coating method or a curtain flow coating method. The organic composite plated steel sheet of the present invention, which is manufactured as described above, solves the quality problems of conventional organic composite plated steel sheets by greatly improving press workability and spot weldability, and further improves the quality of conventional organic composite plated steel sheets by electro-deposition coating. This is an epoch-making organic composite plated steel sheet that has succeeded in further improving its properties and corrosion resistance, and can fully meet market demands. The present invention will be explained in more detail below by way of Examples.

[0015]

[Example] In a continuous line, a low carbon steel plate with a thickness of 0.8 mm is coated with the specified zinc-based alloy plating or zinc-based dispersion plating shown in Table 1 using a known plating method, and then immediately transferred to a reverse roll coater. A predetermined coating chromate treatment corresponding to the first layer is applied using the method, and the plate is dried to reach the specified maximum plate temperature in 5 seconds. Thereafter, the temperature of the plate at the entrance of the painting process is controlled to a specific plate temperature by air cooling. Next, Table 1
After applying the coating composition specified in (1) to one side by roll coating to a predetermined thickness, the board was immediately baked to reach a maximum temperature of 150° C. in 20 seconds. Table 1 summarizes the performance of the coated steel sheet thus obtained. Incidentally, the blending ratio of the coating composition is expressed in weight % based on the non-volatile content. First, as a base for painting,
Regarding the role of bath composition and coating amount effect on making the applied chromate film difficult to solubilize, Example No. 1 of the present invention. 1~No. 98
Shown below. Among these, as a comparative example, Cr6+/Cr
Regarding the concentration ratio of 3+, No. 22~No. 23.HF
Regarding concentration, No. 32~No. 35, regarding the amount of inorganic inhibitor added. 65~No. No. 66 and pH. 73~No. 74. Furthermore, the amount of chromium deposited is No. 84~No. 85. As a result, it is clear that the chromate film between the paint film and the underlying plating layer needs to be poorly soluble in water in order to improve various properties such as corrosion resistance.
Furthermore, it is preferable to keep the amount of adhesion within the range of the present invention in terms of performance and cost merit. Regarding the appropriate plate temperature after the chromate treatment, Example No. 70 and no. 86~No. 91, and its comparative example is No. 9
2~No. 93. As is clear from this, in order to increase the chromium elution resistance of the chromate film and improve various performances such as corrosion resistance as a thin film organic composite steel sheet, it is necessary to maintain the dry plate temperature range after chromate as defined in the present invention. I understand that it must be done. As described above, the reason why the chromate film of the present invention is appropriately rendered insoluble and this effectively works to improve the corrosion resistance of the thin-film organic composite steel sheet, especially the corrosion resistance after electrodeposition coating, has not yet been fully elucidated. However, in view of the measurement results of ESCA, polarization, etc., the following can be considered. The form of the chromate film produced by ESCA is basically chromic chromate consisting of CrO3 and Cr2O3, and as the amount of Cr3+ increases in the bath or the drying plate temperature increases after chromate,
It is thought that the Cr3+ ratio in the film increased, and the solubilization rate of the chromate film in water decreased accordingly, resulting in the chromate film becoming poorly soluble. This makes the chromate film difficult to dissolve.
Organic composite steel sheets coated with a thin film on the upper layer have corrosion resistance, especially corrosion resistance after electrodeposition coating.Blisters of the electrodeposition coating ( This is considered an essential condition for suppressing paint film blistering and achieving high corrosion resistance. On the other hand, in the present invention, it is necessary to add an appropriate amount of an inorganic inhibitor in order to further strengthen the corrosion-preventing function of such a corrosion-preventing mechanism. This effect is explained by the fact that the inhibitor tends to further promote the passivation phenomenon, especially on the anode polarization side, as seen from the results of polarization measurements.The chromate film makes the surface of the base plating layer more inactive, and this It is presumed that this further improved corrosion resistance.

Next, the effects of the factors constituting the coating film in the organic composite plated steel sheet of the present invention will be described. First, regarding the appropriate molecular weight and blending ratio of the main resin, Example No. 1 of the present invention is shown. 70 and no. 106~No. No. 116, and the comparative example is No. 116. 109~No. 110 and no. 115~No. 116. From this, it is preferable that the average molecular weight of the urethane-modified epoxy resin as the main resin be within the range of the present invention.If the molecular weight is too small, the effectiveness in terms of corrosion resistance and alkali resistance will decrease, and if it is too large, it will become difficult to paint. Problems arise, such as making it difficult to Therefore, the preferred molecular weight is 4000 or less. Further, according to the present invention, the blending ratio of the main resin is 30 to 5.
0% by weight is preferred. Next, regarding the degree of polymerization and blending ratio of the hydrophilic resin used in the coating composition of the present invention, Examples of the present invention are shown in No. 70 and no. 117~N
o. 128. Among these, the comparative example is No. 121~N
o. 122, No. 127~No. 128. If the degree of polymerization of the resin is too low, the flexibility of the coating film will be impaired, leading to a decline in various properties including corrosion resistance. Moreover, if it is too high, the viscosity of the paint increases and it loses its original function as a paint. Therefore, the degree of polymerization is preferably from 100 to 500. In addition, regarding the blending ratio of the hydrophilic resin, in order to increase the wettability of the steel plate to the bath during electrodeposition coating, prevent coating film defects such as gas pins, and obtain a uniform electrodeposition coating appearance. teeth,
A ratio of 5 to 40% based on non-volatile content is good, preferably 10%.
It turns out that ~25 is good.

Furthermore, in order for the organic composite plated steel sheet of the present invention to exhibit high rust prevention properties, it largely depends on the fumed silica in the coating film, and regarding the blending ratio and appropriate particle size, No. 70 and no. 129~No. 1
42. Among these, the comparative example is No. 134~No.
135 and no. 141~No. 142. As fumed silica, fine particles of 100 mμ or less are good;
The blending ratio should also be 40% or less in terms of press workability and weldability, and by blending this within the range of the present invention, the alkali moisture resistance of the coating film can be improved and high corrosion resistance can be achieved. Next, regarding the lubricant in the coating film used in the present invention, polyethylene lubricant was mainly studied, and the appropriate molecular weight range and blending ratio were determined using Example No. 1 of the present invention. 70 and no.
．． 143~No. 154. Among them, the comparative example is No. 146~No. 147 and no. 153~No
．． 154. If the molecular weight of the polyethylene lubricant is too low, the lubricant effect will be halved, and if it is too high, the corrosion resistance will be slightly lowered. In addition, the blending ratio of polyethylene lubricant can be adjusted to improve press workability even if it is not blended at all.
Powdering) is considered to be at a level that poses no practical problem, but it is preferable to mix it within the scope of the present invention in order to reduce the stiffness resistance of the coating film and maintain a passable processing level without mold galling. . Moreover, excessive blending lowers the water swelling resistance of the coating film and leads to deterioration of the corrosion resistance.

Next, regarding the appropriate film thickness of the coating composition of the present invention, Example No. 1 of the present invention will be described. 70 and no. 155~No. 166. Among these, the comparative example is No. 165~No. 166. As is clear from this, it is necessary to apply the coating film thickness within the range referred to in the present invention in terms of corrosion resistance and spot weldability. Regarding the embodiment of the present invention when the base plating system was changed, No. 70 and no. 9
9~No. 105, it can be seen that the method of the present invention can be sufficiently applied to various plating systems. Further, regarding the coater penetration plate temperature when coating the coating composition in a thin film after drying the chromate film on the thin-film organic composite plated steel sheet of the present invention, Examples of the present invention were compared with No. 70 and no.
94~No. 98. Among these, the comparative example is No.
98. As is clear from this, the plate temperature range according to the present invention is preferable as the plate temperature entering the coater so as not to impair the uniformity of the coating appearance, press workability, and corrosion resistance.

[0019]

[Table 1A]

[0020]

[Table 1B]

[0021]

[Table 1C]

[0022]

[Table 1D]

[0023]

[Table 2A]

[0024]

[Table 2B]

[0025]

[Table 2C]

[0026]

[Table 2D]

[0027]

[Table 3A]

[0028]

[Table 3B]

[0029]

[Table 3C]

[0030]

[Table 3D]

[0031]

[Table 4A]

[0032]

[Table 4B]

[0033]

[Table 4C]

[0034]

[Table 4D]

[0035]

[Table 5A]

[0036]

[Table 5B]

[0037]

[Table 5C]

[0038]

[Table 5D]

[0039]

[Table 6A]

[0040]

[Table 6B]

[0041]

[Table 6C]

[0042]

[Table 6D]

[0043]

[Table 7A]

[0044]

[Table 7B]

[0045]

[Table 7C]

[0046]

[Table 7D]

[0047]

[Table 8A]

[0048]

[Table 8B]

[0049]

[Table 8C]

[0050]

[Table 8D]

(Note) *1 Plating adhesion measurement gravimetric method according to JIS H-0401 *2 Names of reagents used as inorganic inhibitors Mo-based salts; phosphomolybdic acid hydrate V-based salts; vanadic anhydride W-based Salt; Zr-based salt of tungstate silicate; Si-based salt of potassium zirconium fluoride; Ti-based salt of hydrofluorosilicic acid; Ni-based salt; Co-based salt; Li-based salt; However, for purity, use a reagent grade 1 or higher. In addition, the p of the treatment bath
H was adjusted with ammonia water. *3 Use a mixture of urethanized epoxy ester resin (manufactured by Nippon Paint) and resol type phenol resin (BKS-316/manufactured by Showa Kobunshi KK) at 8/2. *4 Uses polypropylene glycol modified nylon 6 (manufactured by Toyo Rayon) *5 Aerosil 300 (manufactured by Nippon Silica) *6 Ceridus 3620 (manufactured by Hoechst) molecular weight 3000 *7 Calculated from cross-sectional examination *8 Finished appearance of organic coating film (visual inspection) ) ◎ Smooth and without defects, ○ Slightly matte but without defects, △ Slight linear pattern occurs, × Clear linear pattern occurs on entire surface *9 Alkali-resistant alkaline degreasing of paint film L-4410 (manufactured by Nippon Parkerizing)
2%, 65℃ x 5 minutes immersion, ◎No abnormality, ○Slight whitening, △Partial whitening, ×Partial peeling*
10 Chromium elution resistance L-4410 alkaline degreasing 2%, 65℃ x 2 minutes immersion → P
B3020 chemical conversion treatment (manufactured by Nippon Parkerizing), standard condition treatment, evaluation based on the amount of chromium eluted on the plate ◎ No chromium elution at all, ○ Very slight elution △ Slight elution, × Significant elution *11 Press workability Cylindrical drawing processing (uncoated) Oil) Peel off cellophane tape from the surface of the die side of the post-processing section. ◎No peeling at all, ○Mild mold galling (no peeling), △Very slight powdering, ×Significant powdering and peeling. *12 Spot weldability (continuous dotting ability) Steel electrode tip diameter 6mmφ Rolling force 2000kg・f, Current 8-9KA, Time 10
Cycle ◎ 5000 points or more consecutively, ○ 4000 points or more consecutively, △ 2000 points or more consecutively, × 20 consecutively
Less than 00 points *13 Electrodeposition coating After phosphate treatment (PB3020/Nippon Parkerizing Co., Ltd.), cationic electrodeposition coating Power Top U-100 (Nippon Paint Co., Ltd.) 20μm ■Appearance (gas pins, craters) ◎No defects, ○Very few Gas pins occur, △ gas pins occur (partially), × gas pins occur on the entire surface.■ Adhesion (1 mm goblin after 10 days immersion in 40℃ hot water)
00 pieces, taping) ◎No peeling, ○Very slight peeling, △Partial peeling, ×Significant peeling*14 Corrosion resistant flat plate (with 1/2 cross cut), salt water spray test (JI
SZ-2371) 2000 hours ◎ White rust 10% or less, ○ White rust 30% or less, △ Red rust 5% or less, × Red rust 5% or more

[0052]

Effects of the Invention As described above, a special poorly soluble chromate film is formed as the first layer on a base-plated steel sheet prepared by a known method, and a specified coating composition is applied as a fixed film on the upper layer as the second layer. The organic composite plated steel sheet produced by the method of the present invention, which maintains its thickness, has excellent corrosion resistance, press workability, electrodeposition coating property,
It has dramatically improved chromium elution resistance and spot weldability, and can fully satisfy the conventional demands of customers.

Claims (4)

[Claims] Claim 1: A coated chromate film made of the following bath composition [A] is formed as a first layer on the surface of zinc, zinc-based alloy plating and zinc-based composite alloy-plated steel sheet as a solid film at 5 to 150 mg/m2. , a thin organic film with excellent corrosion resistance after electrodeposition coating, characterized in that the organic solvent-based coating composition of the following [B] is coated as a solid film with a thickness of 0.3 to 5 μm on top of the second layer. Manufacturing method of composite plated steel sheet. [A] Coating chromate bath composition ■ Cr6+; 1 to 30 g/l ■ Cr3+; 1 to 30 g/l ■ Cr6+/Cr3+ weight ratio; 0.1 to 2.0 ■
Mo, V, W, Zr, Co, Ni, Si, Ti, L
Inorganic inhibitor consisting of at least one of fluorides, oxyacids, carbonates, chromium compounds, and borides of i; 0.1 to 1 g equivalent of Cr6+ pH; 1.0 to 3.0 [B] Organic solvent-based coating composition (a) Urethane epoxy ester resin (number average molecular weight 300 to 100,0
00) 30-90%
(b) Hydrophilic polyamide resin (degree of polymerization 50-1,000
) 5-40% (c) Silica powder (
Average particle size 1-100mμ)
5-40% (d) Polyethylene wax (
Molecular weight 1,000~
10,000)
1-20%

[Nonvolatile content weight%] 2. The manufacturing method according to claim 1, wherein the drying after the coating chromate treatment is performed so that the final plate temperature on the exit side of the drying oven is 50 to 150°C. 3. The manufacturing method according to claim 1, wherein the coating is carried out at an entrance side plate temperature of 70° C. or lower in the thin film coating step after drying the coated chromate. 4. The manufacturing method according to claim 2, wherein the baking after the thin film organic coating is performed such that the final plate temperature on the exit side of the baking oven is 140 to 200°C.