JP2003251743A - Resin coated surface treated steel sheet - Google Patents

Abstract

(57) [Problem] To provide a resin-coated surface-treated steel sheet excellent in corrosion resistance, appearance, blocking resistance, alkali resistance, film adhesion, water resistance, lubricity, and post-paintability. SOLUTION: An acid value of 20 or less and a glass transition temperature of 25 to 55 ° C. comprising a silica-modified acrylic emulsion resin or a mixture of the same and a acrylic emulsion resin on a surface of a zinc-based plated steel sheet or an aluminum-based plated steel sheet.
Emulsion resin, solid lubricant 1-30%, and rust inhibitor 2,5-dimercaptothiadiazole 0.1-10%,
A coating formed from a resin coating composition optionally containing 0.1 to 10% phosphate and / or 0.1 to 10% vanadate as an additional rust inhibitor is applied at a coverage of 0.5 to 8.0 g / m ² ( % Is mass% based on the total solids of the composition).

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention is excellent in corrosion resistance, alkali resistance, film adhesion, water resistance, lubricity, blocking resistance, and post-coatability, and has good workability that allows processing without applying lubricating oil. And a resin-coated surface-treated steel sheet having a good appearance as a base material of a plated steel sheet.

The surface-treated steel sheet of the present invention can be used unpainted or painted, and due to its excellent corrosion resistance and other properties, it is a steel sheet material used especially outdoors, for example, a building material such as a roofing material or a wall material. It is useful as an agricultural material such as an agricultural pipe, an air conditioner outdoor unit, a home appliance material including a vending machine back plate, a soundproof wall, a civil engineering material such as a guardrail, and the like.

[0003]

2. Description of the Related Art In recent years, the demand for surface-treated steel sheets as materials for construction and household appliances has expanded, and their needs have also diversified. Regarding building materials, demand for zinc-aluminum alloy-plated steel sheets has been expanding in place of conventional hot-dip galvanized steel sheets, especially in areas with severe salt damage and industrial areas.

The zinc-aluminum alloy-plated steel sheets that have been put into practical use at present have various Al contents of 3.5 to 55 wt%. Among them, the Zn-55 wt% Al alloy plated steel sheet exhibits high corrosion resistance of 3 to 6 times that of the hot-dip galvanized steel sheet due to the high corrosion resistance of Al and the sacrificial corrosion resistance of Zn. Since the plating surface is silver white and beautiful, it is often used as a clear coat product having a thin transparent organic film formed on the surface from the viewpoint of design.

The performance required for the clear coating of a Zn-55 wt% Al alloy plated steel sheet is as follows. It has roll formability that allows roll forming without applying lubricating oil, and has excellent alkali resistance (Zn-55
The wt% Al alloy-plated steel sheet has the property that it is easily blackened by the elution of alkali from slate, concrete, etc., which is often used in building materials, and in order to prevent this), it is colorless and transparent, and the silver-white design of the plating is good. Does not hurt, excellent corrosion resistance not only in the flat plate part but also in the processed part, and excellent in water resistance (If water resistance is poor, dew condensation is likely to occur, and in the case of roofing materials, the adhesiveness between the backing insulation and glue Becomes worse, and the heat insulating material floats over time).

Further, in consideration of home electric appliances, it may be post-coated, so that it is required to have excellent post-coatability (in particular, adhesion with melamine alkyd paint). From the manufacturer's point of view, it is also required that the resin does not cause blocking when the coils are wound.

To form an industrial clear film on a continuous line, the strip-shaped plated steel sheet of the base material is passed through a coating process of a water-based paint and a baking process in an oven, and then wound into a coil. Done by. Since the length of the furnace is limited, the baking temperature is about 70 to 120 ° C for the final plate temperature (PMT), and the coil is wound at about 40 to 70 ° C after exiting the oven. At this time, blocking is a phenomenon in which the clear films adhere to each other. Once blocking occurs, when the customer opens the coil, a loud noise is heard and the performance as a surface-treated steel sheet becomes insufficient.

Japanese Patent No. 2929957 is a prior art relating to a clear coating applicable to a Zn-55 wt% Al alloy plated steel sheet. This technology applies silica-modified acrylic emulsion resin, and especially improves the corrosion resistance and blocking resistance of the processed part, and also the resin coating surface treatment that has good lubricity, post-coatability, film adhesion, and alkali resistance. It is a steel plate. However, the corrosion resistance performance is not yet sufficient.
If chromic acid is contained in the resin coating film, corrosion resistance can be greatly improved, but harmful hexavalent chromic acid is used, which causes a problem of environmental pollution.

On the other hand, Japanese Unexamined Patent Publication No. 2000-248380 proposes a resin-coated surface-treated steel sheet which can obtain good corrosion resistance without using harmful hexavalent chromium. This technique is a resin-coated surface-treated steel sheet containing a water-soluble resin and at least one of a thiocarbonyl group-containing compound, vanadate and phosphate. In this technique, there is no stipulation regarding the water-soluble resin, but the performance of the processed part and the blocking resistance are insufficient with the commonly used acrylic olefin-based or urethane-based resins.

[0010]

The object of the present invention is to provide excellent corrosion resistance without using harmful hexavalent chromium, which could not be achieved by the above-mentioned prior art, and to further improve the above-mentioned properties (1) to (3). It is intended to provide a resin-coated surface-treated zinc-based or aluminum-based plated steel sheet having a resin coating that can be completely filled.

Specifically, it has excellent lubricity, has roll formability capable of roll forming without applying a lubricating oil, has excellent alkali resistance, does not easily turn black even under alkaline elution conditions, is colorless and transparent, and is harmful. It has excellent corrosion resistance without using hexavalent chromium, has excellent water resistance, has good adhesion to heat insulating materials, good post-coating properties (particularly adhesion to melamine alkyd paints), and blocking resistance. Also excellent,
It is an object of the present invention to provide a resin-coated surface-treated steel sheet.

[0012]

Means for Solving the Problems As a result of intensive investigations aimed at improving the above-mentioned problems, the present inventors have incorporated a cyclic organic compound having a mercapto group into a resin coating film,
It has been found that the corrosion resistance can be remarkably improved without using hexavalent chromium. It was also found that the blocking resistance and the performance of the processed part can be solved by using a silica-modified acrylic emulsion resin mixed with a small amount of colloidal silica at the stage of synthesizing the acrylic emulsion resin.

According to the present invention, an emulsion resin comprising a silica-modified acrylic emulsion resin or a mixture of a silica-modified acrylic emulsion resin and an acrylic emulsion resin on a surface of a zinc-based plated steel sheet or an aluminum-based plated steel sheet, a solid lubricant, And a cyclic organic compound having a mercapto group, which has a film formed from a resin coating composition containing 0.5 to 8.0 g / m ² of the resin coating composition.

In a preferred embodiment, the emulsion resin has an acid value of 20 or less and a glass transition temperature of 25 to 55 ° C.
The content of silica in the film formed from the coating composition is
1 to 10 mass% in terms of SiO ₂ amount, 1 to the content of the solid lubricant
The content of the cyclic organic compound having 30% by mass and the mercapto group is 0.1 to 10% by mass. Further, it is preferable that the resin coating composition further contains one or both of 0.1 to 10% by mass of phosphate and 0.1 to 10% by mass of vanadate, based on the total solid content of the composition.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION The surface-treated steel sheet of the present invention will be described below for each of its constituent elements. The present invention has been completed by examining resin coating of Zn-55wt% Al alloy-plated steel sheet (correctly Zn-55wt% Al-1.6wt% Si alloy) mainly used for building materials or home appliances. Is. However, the base material is not limited to this plated steel sheet, other zinc-aluminum alloy plated steel sheet such as Zn-3.5 to 5.5 wt% Al alloy plated steel sheet, further hot dip galvanized steel sheet, electrogalvanized steel sheet, It can be widely applied to zinc alloy plated steel sheets such as electric zinc-nickel alloy plated steel sheets and alloyed hot dip galvanized steel sheets, as well as hot dip aluminum plated steel sheets and aluminum alloy plated steel sheets with metals other than zinc (e.g. manganese). is there.

That is, the base material-plated steel sheet can be selected from a zinc-based plated steel sheet including a zinc-plated steel sheet and a zinc alloy-plated steel sheet, and an aluminum-based plated steel sheet including an aluminum-plated steel sheet and an aluminum alloy-plated steel sheet.

The emulsion resin used as the base resin for the resin coating in the present invention was developed by the present inventors and is a patent 29
No. 29957, silica-modified acrylic emulsion resin alone or a mixture of this and acrylic emulsion resin. Acrylic emulsion resins have weather resistance, which is an essential condition for building materials, and are also excellent in alkali resistance and acid resistance. Further, as is well known, the acrylic resin film is generally excellent in transparency and is also advantageous in that it does not impair the design of the base material plated steel sheet.

Acrylic emulsion resin is mainly composed of acrylic acid ester and / or methacrylic acid ester, and water obtained by emulsion polymerization of a monomer mixture containing other α, β-ethylenically unsaturated monomer if necessary. It is a dispersible resin. Since various types of monomers can be used in the acrylic emulsion resin as exemplified below, one or more, and usually two or more types of monomers are used depending on the required performance of the film.

Examples of acrylic acid ester and methacrylic acid ester include methyl ester, ethyl ester, butyl ester, 2-ethylhexyl ester of acrylic acid or methacrylic acid.

As the α, β-ethylenically unsaturated monomer copolymerizable with these, acrylic acid, methacrylic acid,
Unsaturated carboxylic acids such as itaconic acid and crotonic acid; vinyl esters of saturated carboxylic acids branched at the α-position; di (meth) acrylate compounds, tri (meth) acrylate compounds, diallyl having two or more polymerizable unsaturated groups Compounds, triallyl compounds, tetraallyl compounds, etc., such as divinyl adipate, ethylene glycol di (meth) acrylate, 1,3-butyl (meth) acrylate,
Examples include triethylene glycol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, diallyl phthalate, triallyl dicyanurate, and tetraallyl ethoxyethane. Aromatic monomers such as styrene and α-methylstyrene can be blended in a small amount.

It is also possible to incorporate a functional monomer in order to introduce a functional group into the resin. As functional monomers, N, N-dimethylaminoethyl (meth) acrylate, 2-hydroxyalkyl acrylate, 2-acetoacetoxyethyl (meth) acrylate, acrylamide,
Examples thereof include glycidyl (meth) acrylate and N-methylol acrylamide.

The resin-coated surface-treated steel sheet according to the present invention is
For building materials such as roofing materials and wall materials, most of them are used unpainted, but for home electric appliances, there are cases where post-painting is performed on outdoor units of air conditioners. In that case, the resin film of the present invention,
Adhesion is not a problem for acrylic paints because they are the same acrylic, but adhesion may be insufficient for melamine alkyd paints. By mixing one or more of the above-mentioned functional monomers, a functional group (eg, β-keto group such as amino group, hydroxyl group, acetoxy group, epoxy group, amide group) can be added to the acrylic emulsion resin. Etc.) is introduced,
The adhesion of the film with the melamine alkyd paint can be improved. In addition, since the functional group also improves the adhesion to the metal, the introduction of the functional group also improves the adhesion between the plated steel sheet of the base material and the film.

The acid value of the acrylic emulsion resin is preferably 20 or less. When the acid value is 20 or less, the formed film has good water resistance, alkali resistance, and acid resistance, the adhesion between the film and the plated steel sheet has no practical problem, and the film has high hydrophobicity and causes dew condensation. Since it is difficult, there is no problem with the adhesiveness of the gluing type heat insulating material which is a problem when dew condensation occurs. On the other hand, when the acid value of the resin exceeds 20, the water resistance, alkali resistance, and acid resistance of the film tend to decrease, and under dew condensation environment, delamination occurs between the film and the adhesive of the heat insulating material. Easier to do.

The acid value of the resin is the number of milligrams of potassium hydroxide required to neutralize 1 g (solid content) of the resin. In the acrylic emulsion resin, the acid value is given by the unsaturated carboxylic acid compounded as a monomer, so the acid value is adjusted by the compounding amount of the unsaturated carboxylic acid. The acid value of the acrylic emulsion resin is more preferably 2
The number is 10 or less.

Further, in order to make the performance of the processed portion of the surface-treated steel sheet of the present invention equal to that of the flat portion, it is necessary to soften the resin film. Therefore, the glass transition temperature (Tg) of the acrylic emulsion resin is preferably within the range of 25 to 55 ° C. The glass transition temperature can be adjusted by selecting the monomer species. When the glass transition temperature of the resin is lower than 25 ° C., the resin film is too soft during coil winding, and blocking is likely to occur. On the other hand, the glass transition temperature of the resin
If it exceeds 55 ° C, the resin film becomes too hard, the number of cracks in the processed part increases, and the performance of the processed part becomes insufficient.
The film formation is also insufficient, and the original performance is difficult to develop.

Emulsion polymerization of an acrylic emulsion resin is generally carried out in the presence of an emulsifier and a radical polymerization initiator. It is known that the emulsifier moves between resin particles during film formation or concentrates at the film-plated steel plate interface, and is therefore preferentially corroded by water and corrosive components, and also reduces the adhesion between the film and plated steel plate. It impairs the original performance of the acrylic resin film. Therefore, the amount of the emulsifier used during the emulsion polymerization is reduced as much as possible, or it is bound to the resin during the emulsion polymerization, a polymerizable reactive emulsifier is used, or a soap-free emulsion polymerization method that does not use the emulsifier is adopted. It is preferable.

However, when the base resin is an acrylic emulsion resin alone, it is difficult to achieve both the blocking resistance and the performance of the processed portion, even if the above-mentioned preferred emulsion polymerization method is adopted. Blocking resistance is improved when the glass transition temperature of the resin is higher than 55 ° C., but the resin film becomes too hard and the performance of the processed part deteriorates. Further, colloidal silica generally added for the purpose of improving the corrosion resistance also improves the blocking resistance, but in order to obtain a sufficient effect, it is necessary to add an amount of 20% by mass or more based on the resin solid content, The addition of multiple colloidal silica deteriorates the alkali resistance of the film and cannot be used.

The present inventors have used a silica-modified acrylic emulsion resin obtained by adding colloidal silica (also referred to as aqueous silica colloid or silica sol) during emulsion polymerization of the acrylic emulsion resin. It has been found that even with a small amount of silica, the blocking resistance is significantly improved. As a result, it is possible to improve the blocking resistance while maintaining the performance of the processed part without lowering the alkali resistance and maintaining the glass transition temperature at 55 ° C or less. It has been found that is possible.

The reason why the use of silica in the form of a silica-modified acrylic emulsion improves the blocking resistance with a small amount as compared with the case where colloidal silica is added to the acrylic emulsion resin is considered as follows. When colloidal silica is added to the acrylic emulsion resin after polymerization, it is difficult to uniformly disperse silica particles, and colloidal silica easily forms clusters,
Since the distribution of silica in the resin film finally obtained becomes non-uniform, it is necessary to add a large amount of silica in order to overcome this non-uniform distribution. On the other hand, when colloidal silica is added during the synthesis of the emulsion resin, silica particles can be uniformly dispersed in the acrylic emulsion resin, and finally a resin film in which silica is extremely uniformly distributed can be obtained. A small amount of silica can prevent blocking.

In the present invention, the silica-modified acrylic emulsion resin alone is used as the base resin,
Alternatively, a silica-modified acrylic emulsion resin is mixed with an acrylic emulsion resin before use. One type or two or more types can be used for both the silica-modified acrylic emulsion resin and the acrylic emulsion resin.
When two or more resins are mixed and used, the acid value and glass transition temperature of the emulsion resin mean the acid value and glass transition temperature of the resin mixture. That is, the acid value of the mixed emulsion resin in which two or more kinds of resins are mixed is 20
Hereinafter, the glass transition temperature is preferably 25 to 55 ° C.

The silica-modified acrylic emulsion resin can be synthesized in the same manner as a usual acrylic emulsion resin except that colloidal silica is added to the emulsion polymerization reaction system during synthesis. The monomers and emulsifiers used are as described above for the acrylic emulsion resin. Colloidal silica is preferably added to the reaction system before the initiation of polymerization. For example, colloidal silica may be added to and dispersed in water used as a reaction medium, and emulsion polymerization of the acrylic emulsion resin may be performed in a dispersion liquid containing the colloidal silica. As the colloidal silica, generally used particles having a particle size of 5 to 100 nm can be used.

The silica-modified acrylic emulsion resin is preferably used so that the silica content in the resin film is in the range of 1 to 10% by mass. If the silica content in the film is less than 1% by mass, the effect of improving the blocking resistance cannot be sufficiently obtained, and if it exceeds 10% by mass, the blocking resistance is good but the alkali resistance decreases. The silica content is more preferably 1.5 to 5% by mass.

When the base resin is only the silica-modified acrylic emulsion resin, the silica content in the coating largely depends on the silica content of the silica-modified resin. The silica content of the silica-modified acrylic emulsion resin itself to be used is adjusted so that the amount of silica relative to the total solid content in the coating composition is within the above range.

On the other hand, when the base resin is a mixture of an acrylic emulsion resin and a silica-modified acrylic emulsion resin, silica having a high silica content (eg, 10 to 30% by mass based on the resin solid content) is used. There is an advantage that the silica content in the formed film can be freely adjusted by synthesizing the modified acrylic emulsion resin and changing the blending amount of the acrylic emulsion resin mixed with the modified acrylic emulsion resin. Even if the acrylic emulsion resin is mixed as described above, once the colloidal silica is in the state of the silica-modified acrylic emulsion resin, the silica-modified resin and the acrylic emulsion resin are uniformly mixed. It can be uniformly dispersed in the emulsion resin after mixing.

The resin film used in the present invention contains a cyclic organic compound having a mercapto group as a component for improving the corrosion resistance. If this compound is not contained, sufficient corrosion resistance cannot be obtained.

The cyclic organic compound having a mercapto group is
It is preferably a nitrogen-containing heterocyclic compound having one or more mercapto groups directly bonded to the ring. A cyclic organic compound that is particularly effective in improving the corrosion resistance is 2,5-dimercaptothiadiazole. When this compound is used, its content in the resin film is preferably within the range of 0.1 to 10% by mass. If it is less than 0.1% by mass, the effect of improving the corrosion resistance is insufficient, and if it exceeds 10% by mass, the corrosion resistance is further improved, but yellow coloring on the surface becomes conspicuous and the commercial value is impaired. In particular, Zn, which has a beautiful silver-white surface appearance
In the case of −55 wt% Al alloy plated steel sheet, from the point of yellow coloring,
The preferable range of the content is 0.1 to 5 mass%. However, if coloring is not a problem depending on the application or the type of base material-plated steel sheet, it may be 10% by mass or more.

The mechanism of improving the corrosion resistance by adding a cyclic organic compound having a mercapto group is not clear, but it is considered as follows. That is, the main mechanism for improving corrosion resistance is the insoluble salt formed by the mercapto group (-SH) of the cyclic organic compound having a mercapto group and the zinc ion when the zinc plating is corroded in the corrosive environment and is eluted as zinc ions. It is considered that this is because the insoluble salt forms a dense precipitate film on the galvanized surface. It is also considered that the mercapto group of the cyclic organic compound having a mercapto group is directly adsorbed on the galvanized surface to form a film, which also contributes to the improvement of corrosion resistance.

The reason why the cyclic organic compound is specified is that when a film is formed by heating and baking, it is stable without being altered by heat. Therefore, it is considered that even after the film is formed, it effectively acts to improve the corrosion resistance. In addition, it is considered that the cyclic organic compound, when forming a precipitation film with an insoluble salt and an adsorption film on the galvanized surface, has a cyclic structure in the compound, which increases the shielding effect, and is considered to be useful for improving corrosion resistance. To be

Examples of the cyclic compound having a mercapto group include the following in addition to 2,5-dimercaptothiadiazole. 3-Methylmercapto-5-mercapto-1,2,4-thiadiazole 2-mercapto-5-methyl-1,3,4-thiadiazole 2-amino-5-mercapto-1,3,4-thiadiazole 3-mercapto- 1,2,4-triazole 3,5-dimercapto-1,2,4-triazole 3-amino-5-mercapto-1,2,4-triazole 3-propyl-4-amino-5-mercapto-1,2 In addition to the above-mentioned components, the coating composition used in the present invention,
A phosphate and / or a vanadate may be further contained as a component for improving the corrosion resistance. The phosphate and / or vanadate show a synergistic effect with the cyclic organic compound having a mercapto group, and by containing one or both of them, the corrosion resistance can be further improved.

The content of the phosphate in the film (that is, the content based on the total solid content of the coating composition) is preferably 0.1 to 10% by mass. If it is 0.1% by mass or less, the effect of improving the corrosion resistance is small, and if it is 10% by mass or more, the effect of improving the corrosion resistance cannot be obtained. The vanadate content is also 0.1-10
It is preferably set to mass%. If it is 0.1% by mass, the effect of improving the corrosion resistance is small, and if it is 10% by mass or more, it becomes difficult to uniformly dissolve it in the coating composition.

As the phosphate, ammonium phosphate,
Sodium phosphate, magnesium phosphate, etc. can be used. Examples of the vanadate include ammonium vanadate, sodium vanadate, and potassium vanadate.

The resin film used in the present invention contains a solid lubricant for the purpose of improving lubricity and imparting roll formability. Preferred solid lubricants include polyolefin waxes, oxidized polyolefin waxes, fluororesins, calcium stearate, calcium laurate, esylamide, and calcium palmitate, and one or more of these may be used. .

Roll forming is mainly performed in the field of building materials, but if the coating does not contain a solid lubricant, the lubricity of the surface is insufficient, the resin coating and the plating layer below it are scraped off by the roll, and black streaks appear. The appearance of the product will be lost, the performance of that part will be impaired, and the commercial value will be reduced. Also,
The scraped film pieces and plated pieces are deposited on the roll, making it difficult to obtain the shape of the molded product.

For general building materials such as roofs and walls,
When the solid lubricant is contained in the coating in an amount of 1 to 7% by mass, the appearance of the roll-formed part is significantly improved. When used as a roofing material, if the amount of the solid lubricant exceeds 7% by mass, the worker may slip off the roof due to excessive sliding, so the solid lubricant is preferably 7% by mass or less.

On the other hand, when it is used for press molding in the field of home electric appliances, etc., where the lubricating oil is omitted, the molding conditions are severe. % Solid lubricant is preferably included. If the content of the solid lubricant exceeds 30% by mass, the ductility of the resin film will decrease and the corrosion resistance will deteriorate.

Therefore, the blending amount of the solid lubricant in the coating is
Within the range of 1 to 30% by mass, it is preferable to select appropriately depending on the application, especially the molding conditions adopted. The above silica-modified acrylic emulsion resin or an emulsion resin composed of a mixture of this and an acrylic emulsion resin is mixed with a solid lubricant, a cyclic organic compound having a mercapto group and, if necessary, a phosphate or a vanadate to obtain a uniform mixture. The coating composition used in the present invention can be obtained by mixing with the above. The solid content concentration of this coating composition is adjusted so as to have a viscosity suitable for coating.

In addition to the above components, the coating composition may contain other additives that can be used in acrylic emulsion resin paints. In the present invention, particularly suitable additives are
A film-forming aid and a surfactant. In addition, color pigments, dyes, etc. may be added depending on the case.

As described above, in the resin coating of the steel plate in the continuous coating line, the baking temperature is often limited to a relatively low temperature of 70 to 120 ° C. as the final reached plate temperature due to the furnace length condition. In such a case, in order to accelerate film formation, a film formation auxiliary can be added to the coating composition, whereby the acrylic emulsion resin coating film can be sufficiently baked within the above temperature range. Becomes As the film-forming aid, it is possible to use hydrophilic ethers such as butyl cellosolve and butyl carbitol, and dibasic acid esters such as dimethyl adipate, dimethyl glutarate and dimethyl succinate. The compounding amount is 1 to the solid content of the emulsion resin.
50% by weight is common.

If the plating surface has irregularities, pinholes may occur. Since pinholes lead to deterioration of corrosion resistance, a surfactant can be added in order to improve the wettability between the paint and the plating surface and prevent pinholes from occurring. An anionic surfactant or a nonionic surfactant can be used as the surfactant. The addition amount of the surfactant is 0 with respect to the solid content of the emulsion resin.
It is preferably in the range of 01 to 0.1% by mass.

The coating of the above-mentioned coating composition can be carried out by any means, but in the case of a continuous coating line, roll coating or spray coating is general. After that, the coating film is dried, but normally, the coating film is dried by baking by heating.
In the continuous coating line, the heating conditions are often 70 to 120 ° C. at the final reached plate temperature due to the furnace length, but the baking conditions are not particularly limited thereto.

The amount of the transparent resin film (clear film) formed by baking is in the range of 0.5 to 8.0 g / m ² . If the coating amount is less than 0.5 g / m ² , corrosion resistance, alkali resistance and lubricity will be insufficient. When it exceeds 8.0 g / m ² , yellow coloring due to the cyclic organic compound having a mercapto group is conspicuous, and cost increase cannot be overlooked. The preferred deposition amount is 1.0 to 5.0 g / m ² .

Next, the present invention will be further illustrated by examples, but the present invention is not limited to these examples. In the examples,% means mass% unless otherwise specified.
Is.

[0053]

[Examples] Base material-plated steel sheet shown in the table.
8 mm) was coated with the coating composition to prepare a sample steel plate. The coating compositions used were all non-volatile (NV)
The content of the volatile matter was 78%, and the content of the volatile matter was 78%.

The coating is carried out by a bar coater, and the baking is carried out under the conditions of a furnace temperature of 350 ° C. and 16 seconds (final ultimate steel plate temperature 90 ° C.)
I went there. Type and amount of each component of coating composition (amount of solid content to total solid content), base emulsion resin (resin mixture when two or more resins are used)
The acid value, the glass transition temperature (Tg), and the coating amount of the film after baking are shown in Table 1.

The meanings of the symbols used in Table 1 are shown below. (Steel plate) AZ: Zn-55% Al-1.6% Si alloy-plated steel plate (80 g / m ^{2 on} one side); EZ: Galvanized steel plate (20 g / m ^{2 on} one side); SZ: Electric Zinc-nickel alloy coated steel sheet (20 g / m ² per side).

(Resin) A: Acrylic emulsion resin (Tg: 50 ° C, acid value 8); B: Acrylic emulsion resin (Tg: 50 ° C, acid value 1); C: Acrylic emulsion resin (Tg: 50) ℃, acid value 23); D: Amide group-containing acrylic emulsion resin (Tg: 85
℃, acid value 8); E: Silica-modified acrylic emulsion resin (SiO ₂ : 20
%, Tg: 10 ° C, acid value 8); F: Silica-modified acrylic emulsion resin (SiO ₂ : 20
%, Tg: 34 ° C., acid value 7).

(Rust preventive agent) A: 2,5-dimercaptothiadiazole; B: ammonium phosphate; C: Ammonium vanadate.

(Lubricant) a: polyethylene oxide wax emulsion (molecular weight 50
00); b: calcium stearate emulsion; c: fluororesin emulsion.

Workability of the obtained resin-coated surface-treated steel sheet,
Workability, alkali resistance, film adhesion, blocking resistance, corrosion resistance, post-coatability and appearance were evaluated according to the following procedures.
The evaluation results are also shown in the table.

(Test conditions) Workability-Evaluated by the following criteria based on the value of the friction coefficient measured by a Bowden tester: ◎: (friction coefficient) 0.20 or less, ○: 0.20 to 0.35, △: 0.35 to 0.45, ×: 0.45 Super.

Alkali resistance-A test piece partially bent by 2T was immersed in a 0.5% NaOH aqueous solution at 20 ° C for 30 minutes, and the blackening rate of the processed part and the flat plate part was visually measured and evaluated according to the following criteria: ⊚: (blackening rate) 0 to 1%, ◯: 1 to 5%, Δ: 5 to 20%, ×: more than 20%.

Adhesion-The peeling rate obtained as the area ratio of the film adhered to the tape after peeling off the cellophane tape (registered trademark) in the 0T adhesion bending portion was evaluated according to the following criteria: ⊚: (Peeling rate) 0 to 2%, ◯: 2-5%, Δ: 5-20%, ×: more than 20%.

Blocking resistance-60 pieces of two test pieces stacked together
Evaluated according to the following criteria depending on the state of separation after pressurizing to 100 kg / cm ² at ℃ for 24 hours: ◎: No adhesion, ○: Light adhesion, △: Adhesion, ×: Hard adhesion.

Corrosion resistance-Evaluation according to the following criteria based on the white rust occurrence rate in a salt spray test (35 ° C., 500 hours) using a test piece press-molded as in the alkali resistance test: ⊚: (white rust occurrence rate) 0 -1%, ◯: 1-5%, Δ: 5-20%, x: more than 20%.

Post-coatability-Melamine alkyd paint 20 μm
With respect to the test piece coated in m thickness, the peeling rate in the cross-cutting test (100 mm cross-cutting Cellotape (registered trademark) peeling) was evaluated according to the following criteria: ◎: (Cross-cut test peeling rate) 0 to 2%, ○ : 2 to 5%, Δ: 5 to 20%, ×: more than 20%.

Water resistance-After immersing the test piece in boiling water for 2 hours, the appearance was visually evaluated according to the following criteria: ⊚: clear film, ◯: lightly colored, Δ: slightly colored, ×: colored.

[0067]

[Table 1]

As can be seen from Table 1, according to the invention,
When a resin film is formed from a resin coating composition in which 2,5-dimercaptothiadiazole (corrosion inhibitor a in Table 1) is added as an anticorrosion agent to an emulsion resin containing at least partially a silica-modified acrylic emulsion resin. , The corrosion resistance is improved as compared with the emulsion resin alone. Further, the combined use of phosphate and vanadate as an additional rust preventive further improves the corrosion resistance. It also has good processability (lubricity), alkali resistance, adhesion, blocking resistance, water resistance, and post-coatability.

[0069]

According to the present invention, a zinc-based plated steel sheet or an aluminum-based plated steel sheet is used as a base material, and a base resin containing a silica-modified acrylic emulsion resin is added with 2,5-dimercaptothiadiazole and a solid lubricant. A resin-coated surface-treated steel sheet excellent in corrosion resistance, appearance, blocking resistance, alkali resistance, film adhesion, water resistance, lubricity, and post-coating property is obtained by applying a mixed coating composition to form a resin film. Obtainable.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) C23C 22/40 C23C 22/40 4K044 28/00 28/00 C E04D 3/35 E04D 3/35 B E04F 13 / 12 E04F 13/12 A (72) Toruyuki Nakagishi, Inventor Toruyuki Nakagishi, 4-1-2, Shigino-nishi, Joto-ku, Osaka-shi, Osaka, Asahi Chemical Industry Co., Ltd. (72) Mamoru Hamasaki, Kazuno, Joto-ku, Osaka-shi, Osaka Nishi 4-chome 1-24 Asahi Kagaku Kogyo Co., Ltd. (72) Inventor Hajime Ashida 4-1-24 Kagino Nishi, Joto-ku, Osaka-shi, Osaka Asahi Kagaku Kogyo Co., Ltd. F-term (reference) 2E108 CC01 CC07 2E110 AA64 AB04 BA03 BB04 GA33W GB02W GB42W 4D075 BB92Z CA08 CA09 CA13 CA32 CA33 CA36 CA38 CA44 CA47 CB06 DA06 DB05 DB07 DC01 DC05 DC15 DC18 EA13 EA37 EA43 EB13 EB14 EB16 EB20 EB14 22 EB53 EB55 EB56 EC01 EC03 EC07 EC15 EC54 4F100 AA04B AB03A AB10A AB18A AH03B AH04B AH04H AJ08B AK01B AK25B AK41 AL05B BA02 CA19 CA30 EH46 E39 A22 A22 A02 JB06A02A02 JB21A02B02B02A02B02B02A02A02 DA02 DA11 4K044 AA02 AB02 BA10 BA11 BA17 BA21 BB03 BC01 BC02 BC04 BC05 CA11 CA16 CA18 CA53

Claims (6)

[Claims] 1. An emulsion resin comprising a silica-modified acrylic emulsion resin or a mixture of a silica-modified acrylic emulsion resin and an acrylic emulsion resin, a solid lubricant, and a mercapto on the surface of a zinc-based plated steel sheet or an aluminum-based plated steel sheet. A resin-coated surface-treated steel sheet having a coating formed from a coating composition containing a cyclic organic compound having a group at an adhesion amount of 0.5 to 8.0 g / m ² . Wherein said coating composition further contains 0.1 to 10 mass% phosphoric acid salt and / or 0.1 to 10 mass% vanadate based on the total solids of the composition, the surface treatment according to claim 1, wherein steel sheet. 3. The content of the solid lubricant in the coating is 1 to
It is 30 mass%, The surface-treated steel plate of Claim 1 or 2. 4. The acid value of the emulsion resin is 20 or less,
The surface-treated steel sheet according to any one of claims 1 to 3, which has a glass transition temperature of 25 to 55 ° C. 5. The surface-treated steel sheet according to claim 1, wherein the silica content in the coating film is 1 to 10 mass% in terms of SiO ₂ . 6. The cyclic compound having a mercapto group is
2,5 a dimercaptothiadiazole, its content in the coating is from 0.1 to 10 mass%, the surface treated steel sheet according to any one of claims 1-5.