JPH0929889A - Guard film-free precoated steel plate which hardly elutes chromium and is highly punching-and pressure mark-proof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain punching - and pressure mark-proof properties by providing a specific metal film on the surface of steel plate with specific plating, forming a chromate composition with a specified Cr deposition amount on the metal film, and further, forming a top film on a top layer or specific rust inhibitive pigment and co-pigment. SOLUTION: A metal film of at least, one type of element selected from among Ni, Co, Fe, Zr, Sb, V, Mo and W is formed on the surface of a galvanized or fused Al-plated steel plate, and a chromate composition at a total Cr weight ratio of 10-50% of Cr<3+> and 0.5-2.0 of gas-phase silica having a primary average grain size of 3-50μm, is formed on the upper layer or the metal film. In this case, the total or deposition amount is 10-150mg/m<2> . In addition, a polyester resin-primer film consisting of 10-100 pts.wt. of a basic phosphite rust inhibitive pigment for 100 pts.wt. of resin and the weight ratio of 0.02-0.5 of organic phosphonate as co-pigment for the rust inhibitor, is formed on the upper layer of the chromate composition. In addition, a top film containing 30-90% it the solid weight ratio of melamine curable-type polyester resin with a glass transition point of 5-70 deg.C and an average molecular weight of 15000-50000 and 1-50% at the solid weight ratio of organic particles as an aggregate with a primary grain size of 2-50μm, and 1-5% at the solid weight ratio of polyethylene wax as lubricant with a melting point of 0-130 deg.C, is formed on the top layer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a protective film free of chromium-free precoated steel sheet which is required for home electric appliances such as audio products and cooking products and has high image clarity, and has a hole resistance in punching machining. The present invention relates to a precoated steel sheet having both openability (punching resistance).

[0002]

2. Description of the Related Art In recent years, there is a strong need for cost reduction of coated steel sheets in the fields of home appliances and automobiles, and while precoating of postcoats is progressing further, resistance to perforation by continuous punching processing (hereinafter simply referred to as punching resistance). In addition, there is an increasing market demand for guard film-free precoated steel sheets that have both pressure resistance and pressure mark resistance. Especially for pre-coated steel sheets (hereinafter simply referred to as "pre-coat") that are required to have high functionality and are often used as outer panels for audio products and cooking products, it is difficult to handle the appearance of the top coating on the front side that occurs during the product forming process at the customer's end. To prevent this, on the manufacturing side of the precoat, the coating surface has a film thickness of several tens to several 1
The cost is high because a guard film of about 00 μm is attached separately to the market and it is expensive. On the other hand, from the incineration of dust as a post-treatment of this film, the precoat film is non-guarded from a global environmental perspective in a broad sense. It is the current situation that the demand for is increasing.

In this situation, at the final product stage for consumers, there is a strong demand for cost reduction of the precoat including labor saving of the film peeling work. It is no exaggeration to say that the demand for non-guarding is inevitable. However, as a product manufacturing technology to meet this requirement on the manufacturing side, it is necessary to manufacture this guard film free type precoat under a high productivity line, but until it becomes a cut plate product, it is a coil product. In many cases, it is necessary to solve the indentation transfer flaw (pressure mark) on the painted surface due to the coil's own weight during this period. Is included in the precoat coating film.

In addition to the primary product on the precoat manufacturing side, it is essential to maintain the product appearance by the packaging material when the final processed product is transported by the customer, in order to impart the same PM resistance. There is a strong demand for imparting PM properties. With the guard film free, depending on the unit weight of the coil, not a few linear or strip-shaped indentation marks are generated in the coating film in the plate width direction depending on the unit weight of the coil, and this occurs at a constant pitch in the coil longitudinal direction, greatly reducing productivity. In this respect, a countermeasure against pressure-resistant scratches on the coating film (hereinafter, simply referred to as PM resistance) is the largest problem to be solved.

Furthermore, in the precoat imparted with PM resistance, it is required that the continuous perforation (punching resistance) by machining is basically cleared without hindering the performance of other coating films. Punching resistance and PM resistance to coating film
It is indispensable to provide compatibility. What is this punching resistance?
The abrasion resistance of the punching die due to rubbing with the coating film and the resulting burrs around the holes of the steel sheet, or the powdered release coating is pressed onto the die and pressed against the coated surface. Since flaws occur, it is an important issue to achieve both of these, including coating film adhesion.

[0006] In this sense, in the present situation, there is almost no technology disclosed in the prior art, in which the punching resistance and the PM resistance are imparted at the same time, or the manufacturing method thereof. In addition, as an issue related to the regulation of industrial waste, the era in which commercialization using raw materials that conflict with this, including its recycling, must be avoided in the future is about to arrive. Among various surface-treated steel sheets, especially coated steel sheets, C
R-type rust preventive pigments are often used, and there is a risk of violating the waste regulations.

[0007]

In the prior art as described above, the present invention employs a non-Cr type anticorrosive pigment for the primer coating film, and has punching resistance and PM resistance including coating film adhesion.
The goal is to provide a guard film-free precoat that offers both properties at a low cost on the market, and consistently from the producer to the final commercialization by the consumer, processing scratches including punching properties do not occur. It must be a precoat, and for that purpose, there are the following technical problems in coating undercoating and coating modification.

On the side of the coating base treatment, it is necessary to improve the adhesion of the base chromate film to the base material plate and the adhesion of the coating film (imparting punching resistance). On the coating side, high corrosion resistance as a coated steel sheet is achieved by specifying non-Cr pigments, and elasticity and pressure resistance are imparted to the coating in response to the storage and transportation environment of processed products (giving PM resistance). The softening of the aggregate in the coating film (which imparts PM resistance), which may shorten the mold life, does not sacrifice the performance of other coating films, etc. must be a precoat that satisfies all coating film performance. I have to. That is, basically, it is required to improve the adhesion of the underlying chromate film to the base material, and to design a coating film that is reasonably hard and highly elastic.

For that purpose, first, it is necessary to suppress the adhesion of the release coating film to the punching die by making the underlying chromate film formed on the surface of the underlying plating original plate difficult to dissolve and improving the adhesion of the coating film to the base. For that purpose, a flash plating film made of a specific metal is effective as a pretreatment for the chromate film, and the glass transition point of the coating film (hereinafter,
Simply called Tg. ) Is controlled in a specific range, and it is basically necessary to design a coating film with high elasticity by enhancing impact resistance in order to improve punching resistance. It is necessary to control the hardness, and in the present invention, it is essential to apply a resin-type organic aggregate that hardly dissolves or reacts with the main resin of the binder, and an inorganic aggregate with high crystallinity that is often used in the prior art. Since (silica particles) and the like are hard, they must be excluded from the coating film. In order to obtain stable PM resistance of the front side top coating film, in particular, the surface condition of the back surface coating film,
For example, the present invention has been proposed based on the finding that it is necessary to control the appearance gloss of the back surface coating film to be less than the glossiness of the top coating film.

[0010]

[Means for Solving the Problems] The present invention has the following technical concept as a product which solves the above-mentioned drawbacks of the conventional technique and responds to the recent market needs for cost reduction of prepainted steel sheets. Based on the above, the present invention aims to optimize the coating design of a clear image-defining black precoat which has both the punching resistance and the PM resistance of the top coating film having a high design property. In order to improve the adhesion of the underlying chromate film to the base material and the upper coating film, it is essential to make the chromate film form difficult to dissolve. For that purpose, it is necessary to form a specific metal film under the chromate film. The anticorrosion pigment in the primer coating is made of a non-Cr type to provide corrosion resistance by specifying its component system and its properties. Provides punching resistance by giving elasticity to the top coating film. Optimization of particle size and amount of organic resin aggregate. Addition of PM resistance to the top coating film. Optimize resin Tg, binder resin molecular weight and blending amount. Stabilize the PM resistance of the top coating by controlling the gloss of the back coating.

The coating composition of the steel sheet of the present invention will be described below. As an outline of the coating composition of the steel sheet of the present invention, first, a flash plating film made of a specific element is formed in a specific amount on a front surface and a back surface of an original plating plate in a specific amount, and then a chromate composition in which a component is specified is specified in an upper layer as a specific amount. Form by coating. Next, when forming a coating film on the upper layer, on the front side (top coating side), a polymer polyester resin-based primer coating film in which the component of the rust preventive pigment is specified as a non-Cr system and a top coating film on the upper layer It is a 2C2B coating film having both punching resistance and PM resistance, which are obtained by specifying the composition of the composition. For the back side, the surface glossiness was specified 1
It is a C1B coating film.

The details of these coating structures will be described below. As the surface condition of the plated original plate used as the original plate of the coated steel sheet of the present invention, it is usually preferable not to put a long period after the production. However, depending on the case, if the indoor inventory is about several years, there is an advantage that even if the original plate is accompanied by some rust generated in the inventory, the application of the present invention can obtain an effect comparable to that of the original plate that does not remain in inventory. Is added.
The original plate applied to the present invention may be any one obtained by a known plating method as a zinc-based plated steel sheet. For example, in the electroplating system, Zn plating and any of the alloy elements Ni, Cr and Fe are used. Or Z consisting of one or more
An n-based alloy plated steel sheet may be used. Further, in the electric dispersion plating system, a Zn-based dispersion alloy plated steel sheet obtained by uniformly dispersing and depositing metal oxides such as SiO ₂ , TiO ₂ , ZrO ₂ , and BaCrO ₄ on the basis of Zn-Ni and Zn-Fe is used. You may be taken.

Further, hot-dip galvanized steel sheets, Zn-Al alloy-plated steel sheets, galvanized steel sheets alloyed by thermal diffusion thereof, and hot-dip Al-plated steel sheets may be applied in the hot-dip galvanizing system. Next, Ni, Co, Fe, Zr, Sb, V, M is formed on the surface of the original plating plate.
3-5 metal coating consisting of at least one of o and W
0 mg / m ^{2 is} formed, and Cr ^{3+ is} formed on the upper layer in a total Cr amount ratio.
Of 10 to 50% and a primary average particle diameter of 3 to 50 m [mu] is a chromate composition having a total Cr amount ratio of 0.5 to 2.0 and a total Cr deposition amount of 10 to 150 mg / m < ² >. It is characterized by

In the upper layer, a basic phosphite-based rust preventive pigment whose base is zinc potassium or zinc potassium phosphate is used as a main pigment, and the main pigment is 10 to 100 parts by weight based on 100 parts by weight of the resin. Part, and further, after forming a polymer polyester resin-based primer coating film in which an organic phosphonate having an alkyl group as an auxiliary pigment is specifically blended with the main pigment, a glass transition point of the coating film on the uppermost layer ( T
g) 5 to 70 ° C., average molecular weight 15000 to 5000
Melamine curable high molecular weight polyester resin of 0 is 30 to 90% by weight of solid content, and organic resin particles having a primary average particle diameter of 2 to 50 μm which is hardly fused with this resin are 1 to 50% by weight of solid content as aggregate. And a melting point of 80 to 130 as a lubricant
Guard film free type with excellent punching resistance and PM resistance, characterized by forming a top coating film characterized by containing 1 to 5% by weight of polyethylene wax at a solid content. It is a pre-coated steel sheet. Furthermore, a guard film-free precoated steel sheet excellent in punching resistance and PM resistance, characterized in that the surface glossiness of the back surface coating film is controlled to at least 50 to 100% of the front side top coating film. .

The outline is as follows. In order to maintain stable punching resistance, it is necessary to improve the adhesion of the underlying chromate film to the base material in order to improve the adhesion of the coating film around the edges of the punch holes. For that purpose, a specific metal film is provided under the chromate film. Achievement of insolubility by modifying the morphology of the chromate film due to the above. When imparting PM resistance to the coating film, the Tg and molecular weight of the resin are set within specific ranges, and thereby appropriate hardness and elasticity are imparted to the coating film. . In order to suppress die wear and improve punching resistance, organic resin particles having a specified average particle size are applied as coating film aggregates. By controlling the surface glossiness of the back side coating film to be at least equal to or lower than that of the front side top coating film, PM resistance of the top coating film is improved.
The point to get the sex stable. Achievement of eco-friendly prepainted steel sheet by excluding Cr-based pigment from the coating composition from outside the system In addition, in the top coating film design of the present invention, particular attention should be paid to black coloration of the coating film if necessary. It should be noted that it may be freely performed, and that the addition of design properties such as metallicization and appearance gloss as a top coating film is not particularly limited.

[0016]

The action limits of the steel sheet of the present invention with respect to the film constituent factors will be described below. (1) Metal film under the chromate film The function of the metal in the present invention is to improve the adhesion of the chromate film to the base material under the chromate film and the adhesion of the chromate film to the upper film. In particular, the improvement of the adhesion of the chromate film to the substrate is an essential film for suppressing the peeling of the coating film during the continuous punching work as a prepainted steel sheet and dramatically improving the punching resistance. As a metal system that exhibits this function, N
i, Co, Fe, Zr, Sb, V, Mo, W, at least one kind or more, and an appropriate adhesion amount of the film is 3 to 50.
It may be formed in mg / m ² . In the present invention, means for obtaining the metal coating may be within the range of known techniques, and methods such as chemical plating and electroplating may be used.

Regarding the effect of the metal coating, E
It can be inferred as follows from the state analysis of the chromate film by SCA and the elution of the chromate film with respect to water.
That is, the metal film is bonded to the base original plate by the same metal, and the chromate film becomes insoluble due to the presence of the metal film, and Cr ⁶⁺ in the chromate film is present.
There is a fact that the amount of Cr is reduced and the amount of Cr ³⁺ is increased, which confirms that some Cr reduction reaction is occurring between the metal film and the chromate film in a wet state on the upper layer, As a source for inducing the reduction reaction, the metal film serves as a cathode to cause anodic dissolution of the base plating layer, and the transfer of electrons generated at that time reduces Cr ⁶⁺ to increase the Cr ³⁺ morphology. It is presumed that the shape has changed.

That is, the increase in the ratio of Cr ^{3+ in} the chromate film means that the film itself becomes a gel-like hardly soluble film and the affinity with metals and organic substances is increased.
It is considered that this increased the adhesion of the chromate film itself to the substrate through the metal film, and at the same time, it is presumed that the adhesion to the upper coating film was also improved. From the above points, the appropriate adhesion amount of the metal film is 3
~ 50 mg / m ^{2 is} good, preferably 5-30 mg / m
² is better. If it is less than 3 mg / m ² , the effect of the above-mentioned purpose cannot be exhibited so much, and if it exceeds 50 mg / m ^2, there is a decrease in corrosion resistance, and there is a problem in terms of commercial value and cost as a prepainted steel sheet, which is not a good idea.

(2) Chromate film In the chromate composition of the present invention, Cr ³⁺ is 1 in the total Cr amount ratio.
A chromate composition in which the vapor phase silica having a primary average particle diameter of 3 to 50 mμ is 0 to 50% and the total Cr content ratio is 0.5 to 2.0 is formed in a total Cr deposition amount of 10 to 150 mg / m ² . When the Cr ³⁺ amount in the composition is less than 10% in terms of the total Cr amount ratio, sufficient coating film adhesion as a prepainted steel sheet cannot be obtained and it is difficult to obtain stable punching resistance. On the other hand, if it exceeds 50%, Cr ³⁺ in the chromate film rises too much, which leads to a decrease in corrosion resistance, and the gelation of the treatment bath impairs the uniform coating property on the steel sheet by roll coating. It is not a good idea from the viewpoint of coating film performance and production stability, such as difficulty in controlling the amount of adhesion. Therefore,
The suitable Cr ³⁺ amount is 10 to 50%, preferably 30 to 40% in terms of the total Cr amount ratio.

The purpose of using the vapor phase silica is mainly to improve the adhesion of the coating film and to prevent the back coating film from being scratched. The silica has a characteristic of secondary aggregation in a chromate solution and grain growth in the order of several hundreds μm to μ, and it is necessary to control the grain growth so that it falls within a certain range. The anchor effect of is demonstrated. In order to exert this function sufficiently, the average primary particle diameter of the silica is preferably 3 to 50 mμ, and preferably 10 to 30.
mμ is good. From the same point of view, the compounding ratio of the silica is also an important control element, and in the present invention, the total Cr content ratio is preferably 0.5 to 2.0, and particularly preferably 0.7 to 1.5.

The suitable deposition amount of the chromate composition as a chromate film in the present invention thus formed is 10 to 150 mg / m ² as the total Cr deposition amount, preferably 30 to 90 mg / m ^2. .
If the total amount of Cr deposited is less than 10 mg / m ² , the coating performance such as corrosion resistance and coating adhesion cannot be sufficiently satisfied, and commercial value as a prepainted steel sheet cannot be expected. Also 150 mg
If it exceeds / m ² , the coating film is likely to be peeled off in the processed part due to the concentration of the processing stress, and the punching resistance is lowered, which is not a good measure in terms of cost.

(3) Anticorrosion Pigment in Primer Coating In order to maintain the corrosion resistance of the steel sheet of the present invention, a basic phosphorus compound whose base is specified as zinc potassium or zinc potassium phosphate is used as an anticorrosion pigment in the primer coating. Mainly acid salts,
An organic phosphonate having an alkyl group is used together therewith in an appropriate ratio. As the alkyl group of the organic phosphonic acid,
Any of trimethyl type, triethyl type, triisopropyl type and triphenyl type may be used. When the weight ratio of the basic phosphite of the main pigment to 100 parts by weight of the resin is less than 10 parts, sufficient corrosion resistance cannot be obtained even in the aptitude ratio with the organic phosphonate of the auxiliary pigment. The anticorrosion effect is saturated, and it is difficult to obtain sufficient coating film adhesion. From the above, the suitable mixing ratio of the basic phosphite of the main pigment is preferably 30 to 70 parts by weight with respect to 100 parts of the resin.

Further, if the weight ratio of the main pigment consisting of the basic phosphite to the organic phosphonate used together with the main phosphite is less than 0.02, the rust preventive property against undercoat corrosion is insufficient. However, sufficient corrosion resistance cannot be obtained. On the other hand, if the ratio exceeds 0.5, the rust preventive property is saturated, but the paint life is short, which is a bad idea including the paintability. Therefore, the suitable mixing ratio of the basic phosphite of the main pigment and the organic phosphonate of the auxiliary pigment used in combination is 0.02 to 0.5, preferably 0.3 to 0.3. Is good.

The particle size of the rust-preventive pigment is not particularly limited in the present invention, but it is preferable to control the primary average particle size to about 30 μm to 1 μm for corrosion resistance and processing as a coated product. It can be said that the productivity is higher in terms of maintainability and smoothness of the coating appearance. The binder resin system of the anticorrosive pigment for primer coating is not particularly limited in the present invention, but is preferably polyester, polyolefin, nylon, polyacryl, polyurethane, polypropylene, epoxy, polyamide, phenol, Polyethylene may be used.

(4) Top coating film Suitable molecular weight of polymer polyester resin as main resin for binder In the present invention, in order to impart PM resistance to the top coating film, first, the coating film is appropriately hardened and added. It is necessary to withstand pressure, and for that purpose, it is necessary to specify the molecular weight range of the polymer polyester resin of the binder resin. If the molecular weight of the resin is less than 15,000, the crosslink density becomes too high and the coating film is apt to be cracked during processing, and the coating film is liable to be peeled off when a mechanical impact such as punching is applied. On the other hand, if it is 50,000 or more, defects in the appearance of the coating, such as the generation of cracked skin and cracks, are likely to occur, which is not a good measure including cost. Therefore, in the present invention, the molecular weight range of the resin is 15,000 to 50,000.
Of these, 20,000 to 30,000 are particularly preferable.

Appropriate Blending Ratio of Polymer Polyester Resin In the present invention, the blending amount of the binder resin is preferably 30 to 90% as a solid content weight ratio. If it is less than 30%, the strength of the coating film is lowered and the scratch resistance and workability of the coating film are deteriorated.
It also becomes difficult to obtain a uniform coating appearance. On the other hand, if it exceeds 90%, it becomes difficult to control the desired appearance (coloring, glossiness) of the coating film, and the coating film becomes liable to crack due to the deterioration of the elongation workability of the coating film. There is a big decrease, and it is not a good idea including the cost. Therefore, the suitable blending amount of the resin is 30 to 90%, preferably 40 to 70%.

Coating Film Tg (Glass Transition Point) The coating film Tg of the present invention is a basic factor to be controlled especially in order to obtain more stable PM resistance of the top coating film. If the Tg is less than 5 ° C, the PM resistance is insufficient, and if the Tg exceeds 70 ° C, the PM resistance of the coating film is saturated, but the coating film easily hardens, resulting in work cracking and excellent punching resistance. Is difficult to obtain, and it is difficult to obtain at least a uniform coating appearance due to the occurrence of scratched skin and cracks, which is not a good idea in terms of yield and cost. Therefore, the coating film Tg in the present invention is preferably 5 to 70 ° C, and particularly 20 to 60 ° C.
Is preferred.

Appropriate particle size and suitable blending amount of the organic resin particle aggregate In the present invention, the organic resin aggregate imparts appropriate hardness and elasticity to the coating film, and the punching resistance and the slip resistance of the coating film are imparted. It is for imparting flaws. Resin particle properties of the resin aggregate, which are insoluble or sparingly soluble in the binder resin from the viewpoint of imparting elasticity to the coating film and have a function of sufficiently controlling the appearance gloss of the coating film. Must. For that purpose, it is necessary to design the particle size and composition sufficiently.

First, when the average particle diameter of the resin particle aggregate is less than 2 μm, the elasticity of the coating film is excessively imparted, so that the punching resistance is sufficiently imparted, but the coating film is softened. On the contrary, PM resistance and scratch resistance are rather lowered and become unstable, which is not preferable. In addition, the appearance of the coating film is poor in the function of adjusting gloss and gloss, which is not a good idea including cost. On the other hand, if the average particle size exceeds 50 μm, the appearance of the coating film will be large, and it will be difficult to control the glossiness of the coating film in particular, and the scratch resistance will decrease, which is not a good idea including productivity. . Therefore, the particle size range of the organic resin particle aggregate is preferably 2 to 50 μm, and more preferably 3 to 30 μm.

Next, regarding the compounding amount of the resin particle aggregate,
If the solid content weight ratio is less than 1%, the elasticity of the coating film due to the aggregate is insufficient, and although good PM resistance is maintained, it is difficult to achieve punching resistance at the same time, and deterioration of scratch resistance and appearance gloss are observed. It is not preferable because the control of (1) becomes unstable. Further, if it exceeds 50%, sufficient PM resistance and punching resistance can be achieved at the same time, but it becomes difficult to control the gloss of the coating film appearance, which is not preferable. Therefore, the content of the resin particle aggregate is preferably 1 to 50%, more preferably 3 to 20%. Incidentally, in the present invention, polymethylmethacrylate, polypropylene, polyamide, polyacrylonitrile, polyester, alkyl silicone, melamine-formaldehyde, polyurethane and polyvinylidene fluoride may be applied as the resin particle aggregate, and the effect is obtained. There is no difference in.

Appropriate Amount of Polyethylene Lubricant The polyethylene lubricant is intended to improve the scratch resistance of the coating film and the workability in press working. If the lubricant is less than 1% by weight of the solid content, the deterioration of the coating film performance cannot be avoided.
In addition, punching resistance is not sufficient due to the occurrence of pressing flaws due to pressure-bonding of the release coating film. On the other hand, if it exceeds 5%, a water-cooled pattern at the time of baking the coating film becomes conspicuous, and it is difficult to obtain a uniform coating appearance. Therefore, the suitable blending amount of the lubricant is 1 to 5%, preferably 1.5 to 3%.

Next, when the melting point of the lubricant is less than 80 ° C., the strength of the lubricating film formed on the coating film surface is not sufficient, so that the scratch resistance is deteriorated and the important PM resistance, and further, the coating film surface after baking. It is not so desirable because it causes a water-cooled pattern on the product and reduces the commercial value. On the other hand, when the melting point of the lubricant exceeds 130 ° C., the uniform dispersibility in the coating is slightly lacking, making it difficult to form a uniform lubricating film on the surface of the coating film, resulting in uneven appearance and instability of scratch resistance. Is not preferred. Therefore, in the present invention, the melting point of the lubricant is preferably 80 to 130 ° C, preferably 10
0-120 degreeC is good. In the present invention, silicone-based and fluorine-based lubricants may be used as the lubricant in addition to polyethylene, and there is no difference in the effect.

(4) Surface Glossiness of Back Coating Film In the present invention, the surface glossiness of the back coating film is a control factor for obtaining more stable PM resistance of the top coating film. When the gloss of the back coating is less than 50% of the gloss of the top coating, the PM resistance of the top coating decreases, and when it exceeds 100%, the PM resistance of the top coating also decreases. . That is, in order to stably obtain the PM resistance of the top coating film, it is essential to maintain the range of the present invention as the back surface glossiness, preferably 60 to 90%.

[0034]

EXAMPLES The effects of the present invention will be described in more detail below with reference to examples and comparative examples. Board thickness 0.7 mm, board width 914
mm of zinc-based or aluminum-plated steel sheet is subjected to flash plating as specified in Tables 1 to 5 according to the present invention by a displacement plating method at a line speed of 70 m / min, and then a base by a roll coating method of the prior art. Perform chromate treatment. The chromate film is adjusted so that the chromate composition of the present invention specified in Tables 1 to 5 is a solid film in a specific amount, dried, and immediately subjected to a coating process. The front side of the base-treated steel plate is coated with 2C2B and the back side is 1C
1B is applied, and the coating system used for these is any organic solvent-based melamine-curable high-molecular polyester resin-based coating, which is baked under predetermined conditions. 2 on the front
On the C2B coated surface, the present invention was roll-coated with a polymer polyester resin-based primer coating film containing the specific pigment shown in Tables 1 to 5 as a solid film of 5 μm. Tables 1 to 5 as coating films
The coating composition whose components are specified by the present invention is used as a solid film.
Curtain coating is performed to a thickness of 9 μm, and each is baked under standard conditions and dried in water. The surface glossiness of the top coating film at this time was controlled to 80%.

On the other hand, for coating the back surface of the steel sheet, the coating composition having the glossiness of the coating film specified by the present invention specified in Table 1 to Table 5 was applied by a known roll coating method to give a coating film thickness of 1 μm as a solid film. The coating is controlled so that it will be baked at a predetermined plate temperature, washed with water and dried. The coating film performance of the precoated steel sheet according to the present invention produced in this manner is summarized in Tables 6 to 10 corresponding to Tables 1 to 5, but the effects thereof are as shown below. An unprecedented precoat that enables stable production as a chromium-free eluting type precoated steel sheet that achieves both pressure mark resistance (PM resistance) and punching resistance required for high top coatings. It has come to provide a steel sheet to the market at a low cost.

(1) Effect of the metal film of the lower layer of the chromate film The adhesion between the chromate film and the base is increased, and the chromate film is made difficult to dissolve so that the adhesion of the upper coating film is also increased to improve the resistance as a prepainted steel sheet. With respect to the effect of the metal coating for stabilizing the punching property at a high level, the embodiment of the present invention is applied.
o. 1 to No. 7 and No. 7 10-No. 21,
The comparative example is No. 8 to No. 9 shows. As is clear from these examples, by providing the metal coating of the present invention in the lower layer of the chromate coating in a specific amount, a coating which is sound even in the steel plate burr portion cut without inhibiting other performance of the coating. Adhesion is maintained, and punching resistance and PM resistance (pressure mark resistance) can be consistently achieved at a high level.

(2) Effect of Chromate Coating In the present invention, the role of the chromate coating is to suppress the cohesive failure of itself due to processing, and also the adhesion of the chromate coating to the substrate, which is exhibited by the synergistic action with the metal coating. The improvement of the property is to suppress the peeling of the coating film during punching work and to impart stable punching resistance to the prepainted steel sheet. In addition, it is to improve the corrosion resistance life of the coating by making the chromate film insoluble by the metal film and changing the chromium morphology. Regarding the effects of the present invention as described above, the No. ³ regarding the suitability ratio of Cr ^{3+ in} the examples. 3
And No. 22-No. 26, and the comparative example is N
o. 27-No. 28. Further, regarding the suitability range of the average primary particle size of the vapor phase silica, no. 3
And No. 29-No. No. 32 shows the comparative example. 3
3 to No. 34.

Further, regarding the compounding ratio of the vapor phase silica, No. 3 and No. 3 35-No. No. 38 shows the comparative example. 39-No. 40. Further, regarding the range of the chromate adhesion amount specified by the present invention, No. 3 and No. 3 41-No. No. 48 shows the comparative example. 49-No. 50. As is clear from these examples, by using the chromate film specified by the present invention, not only excellent coating film adhesion, but also punching resistance and PM resistance (pressure mark resistance) without impairing other performances. ), It is now possible to achieve both high and stable compatibility.

(3) Primer coating film Regarding the effect of applying the rust-preventive pigment according to the present invention to the primer coating film, the pigments and the compounding ratio thereof, the examples of the present invention were used. 3 and No. 3 51-No. No. 58 of the comparative example. 59-No. 62. In addition, the effects of the combined use of the organic phosphonate of the rust preventive auxiliary pigment of the present invention are described in Examples
o. 3, No. 63-No. 67 and no. 70-N
o. 72, the comparative example No. 68-No. 69. As is clear from these examples, by appropriately using the rust preventive pigment and the rust preventive auxiliary pigment specified by the present invention in combination with excellent coating film adhesion and punching resistance without hindering other properties. It is possible to achieve both PM resistance (pressure mark resistance) stably at a high level.

(4) Regarding the effect of the main resin Regarding the effect of the main resin for imparting PM resistance to the coating film, the examples of the present invention in the suitable molecular weight range are given.
3 and No. 3 73-No. 77, the comparative example is No.
78-No. Shown in 79. Further, regarding the proper Tg of the main resin, No. 3 and No. 3 80 ~
No. No. 83 shows the comparative example. 84-No. Shown at 85. Further, regarding the proper mixing ratio of the main resin, No. 3 and No. 3 86-No. 89, the comparative example No. 90-No. Shown at 91. As is clear from these examples, it is important to design the Tg of the coating within the range of the present invention in order to impart PM resistance to the coating without impairing other properties of the coating. In addition, it can be seen that proper designing with the resin molecular weight and the blending amount referred to in the present invention is necessary in order to stably obtain the uniform appearance and punching resistance of the coating film.

(5) Appropriate Mixing of Resin Particle Aggregate in Coating Film The resin aggregate is present in the coating film to impart scratch resistance, but in the present invention, a machine such as punching is used. In terms of punching property during processing, the main purpose is to suppress die wear, and for that purpose, it is important to control the particle size of the aggregate and the compounding amount thereof within an appropriate range. In the present invention, No. 3 and N
o. 92-No. No. 98, a comparative example. 99-No.
100 is shown. Further, regarding the proper blending amount, No. 3 and No. 3 101-No. No. 107 for the comparative example. 108-No. Shown at 109. As is clear from these examples, in order to make the coating film have both punching resistance and PM resistance without deteriorating other coating film performance, the particle size and blending amount of the resin particle aggregate are set to the present invention. It turns out that it is necessary to control within the appropriate range.

(6) Appropriate Blending of Polyethylene Lubricant This lubricant is in powder form, and its purpose is to appropriately improve the scratch resistance by imparting slip property to the coating film, and it is necessary to optimize the blending. Is. Examples of the lubricant according to the present invention are No. 3 and No. 3 110-No. 114, the comparative example No. 115-No. Shown at 116. As is clear from this example, by imparting lubricity to the coating film, steel plate handling flaws in stable press working and the like are eliminated, and in particular, by imparting PM resistance to the coating film, it is characterized by guard film free. In the steel sheet of the present invention, it is essential to properly mix the lubricant. Further, it is understood that when the content of the lubricant is out of the upper limit, a water-cooled pattern after baking is likely to occur on the appearance of the coating film, which is not preferable. Further, regarding the melting point of the lubricant, the examples according to the present invention are
3 and No. 3 117-No. 119, the comparative example No.
120-No. Shown at 121. As is clear from this example, when the melting point range of the lubricant of the present invention is out of the proper range, if it is less than the lower limit, not only good scratch resistance but also stable PM resistance which is the object of the present invention. It can be seen that it is difficult to obtain, and if the upper limit is exceeded, a water-cooled pattern is generated on the coating film, which greatly impairs the commercial value in appearance.

(7) Glossiness of Backside Coating In the present invention, it is preferable to control the glossiness of the backside coating within an appropriate range in order to obtain stable PM resistance of the top coating. . In this case, the back surface glossiness is controlled by comparing the glossiness of the top coating film. In this regard, the embodiment of the present invention is No. 3 and No. 3 122-No. To 125,
No. 126-No. 127. As is clear from this, if the back surface glossiness control range of the present invention is deviated, it becomes difficult to stably maintain the PM resistance to the top coating surface having a high commercial value under the high productivity line, and the cost is reduced. It is not a good idea to include it.

(8) Application Examples of Various Plating Systems for Base Steel Sheets No. 3 and No. 3 128-No. 138.
As is apparent from this example, it is understood that the present invention does not hinder the coating film function even if the plating system of the base steel sheet is different.

[0045]

[Table 1]

[0046]

[Table 2]

[0047]

[Table 3]

[0048]

[Table 4]

[0049]

[Table 5]

[0050]

[Table 6]

[0051]

[Table 7]

[0052]

[Table 8]

[0053]

[Table 9]

[0054]

[Table 10]

(Note) * 1. Plating EZ: Electric zinc plating ZN: Electric Zn-Ni alloy plating (Ni; 11.5
%) EC: Electric Zn-Cr-Ni alloy plating (Cr; 10%)
%, Ni; 2%) EF : Electrical Zn-Fe alloy plating (Fe; 15%) ZNS: Electrical _{Zn-Ni-SiO 2 (Ni} ; 12%, S
iO _2; 3%) ZNT: Electrical _{Zn-Ni-TiO 2 (Ni} ; 12%, T
iO _2; 3%) ZNB: Electrical _{Zn-Ni-BaSO 4 (Ni} ; 12%,
BaSO ₄ ; 3%) ZFS: Electric Zn—Fe—SiO ₂ (Fe; 10%, S
iO ₂ ; 3%) GZ: hot-dip Zn plating GA: hot-dip Zn-Al plating (Al; 5%) GF: alloyed hot-dip Zn plating (Fe; 8-11%) AL: hot-dip Al plating

* 2. Metal coating By a chemical plating method known in the art. Adhesion amount (mg / m
² ) Measured by chemical analysis method. NS: Ni + Sb, N
F: Ni + Fe, NM: Ni + Mo, NV: Ni + V,
NW: indicates that the alloy system is Ni + W. * 3. Chromate film The particle size of vapor phase silica refers to the average primary particle size, and the display unit is m.
μ. The unit for displaying the ratio is wt% as a ratio to the total chromium amount. The adhered amount is displayed as the total Cr amount and is determined by the fluorescent X-ray analysis method.

* 4. Primer coating using high molecular polyester resin, anti-corrosion pigment ZK: basic potassium potassium phosphite, applied in the range of primary average particle size 10 mμ to 2 μm Anti-corrosion pigment PK: basic zinc potassium phosphite phosphorous, primary average Applicable in the range of particle size 10 mμ to 2 μm P1: Triphenyl type organic phosphonic acid P2: Triisopropyl type organic phosphonic acid P3: Trimethyl type organic phosphonic acid P4: Triethyl type organic phosphonic acid

* 5. Top coating properties Polymer polyester resin is used by curing melamine resin. Tg refers to the glass transition point of the cured coating film, measured by TMA. All the blending amounts are expressed by weight ratio with respect to coating film solid content. Organic aggregate refers to resin particle aggregate. Particle size refers to the primary average particle size. * 6. Glossiness of the back side coating It means the glossiness contrast of the top side coating by 60 degree specular reflection.

* 7. PM resistance evaluation After leaving the test piece on which the back coating film was superposed on the top coating film surface for 168 hrs in a humid atmosphere of load 80 kg / cm ² , RH 95%, 40 ° C., the test piece was taken out and the impression state of the coated surface was taken out. Visual evaluation. ◎: Initial appearance and no change 〇: Very slight indentation transfer when transparent △: Slight indentation transfer when viewed from the front ×: Clear indentation transfer

* 8. Punching resistance Continuous punching punching device; continuous punching by electric crank press, 4 pieces per second Die: Uses a die with hard surface finish. Four sets of blades with a wall thickness of 1 mm x width of 4.5 mm are set. Drilling resistance evaluation: For the 300,000th punching hole, the state of burrs around the hole is visually evaluated. ◎: No burr ○: Slightly flawed but no burr △: Several burrs occur ×: Frequent burr

Occurrence of coating powder: ⊚: None ∘: Slightly generated but no blemishes △: Die attached to the mold and scattered blemishes ×: Adhered considerably to the die and frequent blemishes

* 9. Paint corrosion resistance Oil-free square cylinder press (50w x 50L x 50H [m
m]) Visual evaluation of occurrence of coating film swelling on the side surface of the processed part. CCT 60 cycles (24 hrs / cycle) SST 6 hrs → Left 1 hrs → Dry 70 ° C, RH 60%, 4 hr
s → Left 2hrs ** → Wet 49 ℃, RH98%, 4hrs → Left 2hrs → Cooling -20 ℃, 4hrs → Left 1hrs ◎: No swelling ○: Slight swelling △: Small partial swelling ×: Swelling on the entire surface

* 10. Appearance of coating film (discoloration, visual evaluation of coating defects) ◎: Appearance homogeneity ◯: Very slightly uneven pattern through watermark △: Partially nonuniform ×: Nonuniform overall

[0064]

INDUSTRIAL APPLICABILITY As described above, the present invention is the most important subject to meet the demand for free guard film of precoated steel sheet in the market.
Of the chromate film by placing a specific metal film by displacement plating as the lower layer film of the chromate film on the base plate of the plating base plate based on the following technical concept. By improving the adhesion of the base material and the chromate film by the metal film to a poorly soluble form, the adhesion of the coating film was dramatically improved, which stabilized the outstanding punching resistance at a high level.
In addition, by providing corrosion resistance by specifying a non-Cr type anticorrosive pigment to the primer coating film, and by controlling the glossiness of the top coating film structure and the back surface coating film at the same time, it is possible to reduce the deterioration of other coating performances. At the industrial level, it has reached the market offer of non-guard film type chromium-free eluting pre-coated steel sheets.

That is, (1) by forming a specific metal film as the base film of the chromate film, the adhesion of the upper chromate film to the substrate is significantly improved, and at the same time, the formation of the metal film makes the chromate film difficult. By changing the shape to a molten type and stabilizing the adhesion of the coating film at a high level, it became possible to stably obtain punching resistance as a prepainted steel sheet, which was a problem (adhesion of chromate film and coating film). Achievement of prevention of coating film peeling during punching due to improvement). (2) Elimination of Cr elution from coated products by identifying the non-Cr pigment as the rust preventive pigment in the primer coating film. (3) The aggregate in the coating film is limited to the resin particle type aggregate, and elasticity is imparted to the coating film by specifying the particle size and the blending amount, whereby a die for mechanical processing such as punching. It has become possible to suppress abrasion and to stably obtain perforation resistance to the steel sheet (achieve punching resistance by suppressing die wear). (4) Coil is achieved by combining each coating film component technology such as Tg of top coating film, molecular weight of resin and its blending ratio, melting point of lubricant and blending ratio, and appropriate control of appearance gloss of back coating film. Good pressure mark resistance can be stably obtained regardless of whether the product or the cut plate product is loaded (achievement of non-guard film of coating film by imparting PM resistance).

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Ryoji Nishioka 20-1 Shintomi, Futtsu-shi, Chiba Nippon Steel Corporation Corporate Technology Development Division

Claims (3)

[Claims] 1. Ni, Co, Fe, Zr, Sb, on the surface of a zinc-based plated steel sheet or a hot-dip aluminized steel sheet,
A metal coating composed of at least one of V, Mo and W is formed in an amount of ³ to 50 mg / m ² and Cr ³⁺ is 10 to 50% in the total Cr amount ratio in the upper layer, and a gas having a primary average particle diameter of ³ to 50 mμ is formed. The chromate composition in which the phase silica has a total Cr amount ratio of 0.5 to 2.0 has a total Cr deposition amount of 10 to 150 mg / m ^2.
10 to 100 parts by weight of a basic phosphite-based rust preventive pigment whose upper layer is specified by zinc potassium or zinc potassium phosphate as an upper layer. The weight ratio and the ratio of the organic phosphonate of the auxiliary pigment to the anticorrosive pigment are 0.02 to 200 by weight.
After forming a polymer polyester resin-based primer coating film characterized by being 0.5, the glass transition point (Tg) of the coating film is 5 to 70 ° C. as a top coating film on the uppermost layer.
Melamine curable high molecular weight polyester resin having an average molecular weight of 15,000 to 50,000 has a solid content weight ratio of 30 to 90.
%, Primary average particle diameter of 2 to 50 μ, which is hardly fused with this resin
The organic resin particles of m as an aggregate have a solid content weight ratio of 1 to 50.
%, And a polyethylene wax having a melting point of 80 to 130 ° C. as a lubricant in an amount of 1 to 5% by weight of solid content, forming a top coating film. Guard film-free precoated steel sheet with excellent punching resistance and pressure mark resistance. 2. An anti-chromium elution type according to claim 1, wherein the organic phosphonate of the rust preventive pigment used together in the primer coating film is any one of trimethyl, triethyl, triisopropyl and triphenyl. Guard film-free precoated steel sheet with excellent punching resistance and coating adhesion. 3. The surface resistance of the back surface coating film is controlled to be at least 50% to 100% of that of the front surface top coating film. Excellent pre-coated steel sheet free of guard film.