JPH0929888A - 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 a specifically plated steel plate, further, providing a chromate composition with a specified total Cr deposition amount on the metal film, and finally, forming a specific rust inhibitive pigment layer and a top film. SOLUTION: The 3-50mg/m<2> of a metal film consisting 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. In addition, a chromate composition at a total Cr weight ratio of 10-50% of Cr<3+> and 0.5-2.0 of gas-phase silica with a primary average grain size of 3-5μm is formed on the upper layer of the metal film. In this case, the total Cr deposition amount is 10-150mg/m<2> . Further, the 0.5-10μm of polyester resin primer film consisting of a blend of 10-100 pts.wt. of basic phosphite rust inhibitive pigment with 100 pts.wt. of resin, is formed on the upper layer of the chromate composition. on the top layer, a top film containing 30-90% at the solid weight ratio of a melamine curable polyester resin with a glass transition point of 5-70 deg.C and an average molecular weight of 15000-50000, 1-50% at the solid weight ratio of organic resin particles as an aggregate with a primary average grain size of 2-50μm, and 1-5% at the solid weight ratio of polyethylene wax with a melting point of 80-130 deg.C as a lubricant, is formed.

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 has been a great need for cost reduction of coated steel sheets in the fields of home appliances and automobiles, and while precoating of post-coating has progressed further, resistance to perforation by continuous punching (hereinafter simply referred to as punching resistance) and There is an increasing market demand for guard film-free precoated steel sheets that are compatible with pressure mark resistance.

Particularly, in the case of a precoated steel sheet (hereinafter, simply referred to as a precoat) which is required to have high functionality and which is often used as an outer panel of audio products and cooking products, a front side top coating appearance generated in a product forming process by a customer. In order to prevent the handling flaw of the precoat, on the manufacturing side of the precoat, a cost is high because a guard film having a film thickness of several tens to several hundreds μm is separately attached to the coated surface and provided on the market. At present, there is a growing demand for precoat film to be non-guarded from the viewpoint of global environment in a broad sense, due to incineration of dust as a post-treatment of film.

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 there is an unavoidable situation in which there is a demand for non-guarding.

However, as a product manufacturing technique for satisfying this requirement on the manufacturing side, it is necessary to manufacture this guard film-free precoat under a highly productive line. Are often placed on the floor and stored as coil products, and the problem is that it is also necessary to solve the indentation transfer flaw (pressure mark) on the painted surface due to the coil's own weight during this period. It is imposed on the pre-coated film including the floor-standing method. The same PM resistance can be given to other products besides the primary products on the precoat manufacturing side, and it is essential to maintain the product appearance by the packaging material when the final processed product is transported by the customer. There are strong demands.

In the guard film-free type, depending on the unit weight of the coil, a considerable number of linear or strip-shaped indentation marks are formed in the coating film at the contact portion with the floor in the plate width direction, and these are generated at a constant pitch in the coil longitudinal direction, thus improving productivity. Because it causes a significant decrease in
In this respect, the countermeasure against the pressure-resistant scratches on the coating film (hereinafter, simply referred to as PM resistance) is the largest problem to be solved. Moreover, this P resistance
In the case of a precoat with M property, it is basically required to clear the continuous perforation (punching resistance) by machining without hindering the performance of other coating films. Punching resistance and PM resistance to the coating film are required. It is indispensable to provide compatibility.

The punching resistance means the abrasion resistance of the punching die due to the rubbing with the coating film, and the burrs around the holes of the steel sheet which may be caused by the abrasion resistance or the powdered release coating film. Since it is pressed against the mold and this causes a flaw on the coated surface, it is an important issue to achieve both of these, including coating film adhesion.

In this sense, at present, there is almost no technology disclosed in the prior art, which discloses the precoated steel sheet having both punching resistance and PM resistance, or the manufacturing method thereof.

Further, as an issue related to the regulation of industrial waste, it is about to arrive at an era in which commercialization using raw materials that conflict with such regulations must be avoided in the future, including recycling. Among various surface-treated steel sheets, especially painted steel sheets, Cr
The rust preventive pigments and the like are often used, and there is a risk of violating the waste regulation.

[0010]

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 the market with a guard film-free precoat that has both excellent properties at a low cost.Consequently, from the producer to the final commercialization by customers, processing and handling scratches including punching properties occur. It must be a precoat that does not exist. For that purpose, there are the following technical problems in coating undercoating and coating modification.

It is necessary to improve the adhesion of the underlying chromate film to the base material plate and the adhesion of the coating film (imparting punching resistance) on the side of the coating undercoat treatment. Also,
On the coating side, high corrosion resistance as a coated steel sheet by specifying non-Cr pigments, imparting elasticity and pressure resistance to the coating in response to the storage and transportation environment of processed products (giving PM resistance) It must be a precoat that satisfies all coating performances, such as softening of aggregates in coatings (providing PM resistance) that may shorten the mold life, and not sacrificing other coating performances. I have to.

That is, it is basically required to improve the adhesion of the underlying chromate film to the substrate and to design a coating film which is moderately hard and rich in elasticity. For that purpose, first it is necessary to suppress the adhesion of the release coating film to the punching die by increasing the adhesion of the base chromate film to the base chromate film formed on the surface of the base plating original plate and thereby improving the adhesion of the coating film to the punching die. The 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 referred to as Tg) is controlled within a specific range,
In addition, it is basically necessary to design a coating film that enhances impact resistance and is highly elastic to improve punching resistance, but for that purpose, it is necessary to control the hardness of the aggregate in the coating film. In the invention, it is essential to apply a resin type organic aggregate that hardly dissolves or reacts with the main resin of the binder, and the inorganic crystal aggregate (silica grains) with high crystallinity often used in the prior art is hard. However, it is premised on the exclusion from the coating system.

Further, the more stable P resistance of the front top coating film is obtained.
In order to obtain M property, the present invention is proposed based on the knowledge that the surface state of the back coating film, for example, the appearance gloss of the back coating film needs to be controlled to be equal to or lower than the glossiness of the top coating film. It came to.

[0014]

[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 design of a clear black precoat film which has both punching resistance and PM resistance of a top coating film having a high design property.

In order to improve the adhesion of the base chromate film to the base material and the upper coating film, it is essential to make the chromate film form insoluble, and for that purpose it is necessary to form a specific metal film under the chromate film. . Corrosion resistance is provided by the component system of the non-Cr pigment and its property. 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. Stabilization of 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 film constitution of the steel sheet of the present invention, first, a flash plating film made of a specific element is formed on a front surface and a back surface of a plating original plate in a specific amount in an equal amount, and then a chromate composition in which components are specified in an upper layer is specified in a specific amount. Form by coating.

Next, when forming a coating film on the upper layer thereof, the rust preventive pigment component is non-Cr on the front side (top coating side).
2C2, which has both a punching resistance and a PM resistance, which are formed by specifying the composition of a polymer polyester resin based primer coating specified as a system and a top coating as an upper layer thereof.
It consists of the coating film of B. The surface thereof is a 1C1B coating film having a specified surface gloss.

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, even if the original plate is accompanied by some rust generated in the inventory, the application of the present invention has the advantage of obtaining an effect comparable to that of the original plate that is not in stock. It is added that there is.

As the original plate applied to the present invention,
The zinc-based plated steel sheet may be any obtained by a known plating method, for example, in the electroplating system,
A Zn-based alloy-plated steel sheet may be used in which Zn plating and an alloy element are one or more of Ni, Cr, and Fe.
In addition, in the electrodispersive plating system, Zn-Ni, Zn
SiO ₂ and -Fe based, TiO _2, ZrO _2, Ba
Zn formed by uniformly dispersing and depositing a metal oxide such as CrO ₄
A system dispersion alloy plated steel sheet may be used.

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, on the surface of the original plating plate, Ni, C
³ to 50 mg / m ^{2 of a} metal film made of at least one of o, Fe, Zr, Sb, V, Mo and W is formed, and Cr ³⁺ is 10 to 50% in the total Cr amount ratio in the upper layer, and the primary average The gas phase silica having a particle size of 3 to 50 mμm has a total Cr content ratio of 0.5 to
It is characterized in that the chromate composition consisting of 2.0 forms 10 to 150 mg / m ² as the total Cr deposition amount.

In the upper layer, a basic phosphite type rust preventive pigment whose base is specified as zinc potassium or zinc potassium phosphate is 10 to 10 parts with respect to 100 parts by weight of the resin.
A high molecular polyester resin-based primer coating, which is specifically blended with 0 parts by weight, is formed as a solid coating having a thickness of 0.5 to 10 μm, and then the glass transition point (Tg) of the coating is 5 to the uppermost layer.
Melamine curable high molecular polyester resin having an average molecular weight of 15,000 to 50,000 at 70 ° C. is 30 by weight of solid content.
~ 90%, primary average particle size 2 which hardly fuses with this resin
50 μm organic resin particles as aggregates in 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 is formed to form a top coating film. It is an excellent guard film-free precoated steel sheet.

Further, the surface glossiness of the back side coating film is controlled to at least 50 to 100% of the front side top coating film, which is a guard film free type precoat excellent in punching resistance and PM resistance. It is a steel plate.

That is, the gist of the present invention 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. Achieving insolubility by modifying the morphology of the chromate film. In imparting PM resistance to the coating film, the Tg and the molecular weight of the resin are set in a specific range, whereby 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. Achieve eco-friendly prepainted steel sheet by removing Cr-based pigment from the coating composition.

In the top coating film design of the present invention,
Coloring of the coating film as needed may be done freely without being particular about black color, and there is no particular limitation on imparting design properties as a top coating film such as metallicization and appearance gloss. Let me add that.

[0026]

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 or more, and 3 to 50 as a proper amount of coating.
mg / m ² may be formed. 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.

Further, regarding the effect of the metal coating,
It can be inferred as follows from the state analysis of the chromate film by ESCA and the elution of the chromate film with respect to water. That is, the metal film is bonded to the base original plate in the same metal, and the chromate film is hardly soluble due to the presence of the metal film, and the Cr ⁶⁺ content in the chromate film is reduced to decrease the Cr ³⁺ content. The fact that there is a Cr reduction reaction between the metal film and the chromate film in a wet state in the upper layer is confirmed as a source for inducing the reduction reaction. It is presumed that the metal film serves as a cathode to cause the anode plating of the base plating layer to dissolve, and the transfer of electrons generated at that time reduces Cr ⁶⁺ to change the form of the chromate film to increase the form of Cr ^3+. .

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 proper deposition amount of the metal coating is preferably 3 to 50 mg / m ² , and preferably 5 to 30 mg / m ^2.
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, which is not a good idea because there is a problem with the commercial value and cost as a prepainted steel sheet.

(2) Chromate film In the chromate composition of the present invention, Cr ³⁺ is 1 in the total Cr amount ratio.
A chromate composition having 0 to 50% and a primary average particle diameter of 3 to 50 mμm in a vapor phase silica in a total Cr amount ratio of 0.5 to 2.0 forms 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 cannot be obtained as a prepainted steel sheet, 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 gelation of the treatment bath impairs uniform coating property on the steel sheet by roll coating. , It becomes difficult to control the adhesion amount,
It is not a good idea from the viewpoint of coating film performance and production stability. Therefore, the proper Cr ³⁺ amount is 10 in terms of the total Cr amount ratio.
-50%, preferably 30-40%.

The purpose of using the vapor phase silica is mainly to improve the adhesion of the coating film and to prevent scratches on the back surface coating film. The silica is secondarily aggregated in a chromate solution to several hundred mμm-μm.
There is a characteristic of grain growth on the order, and it is necessary to control the grain growth so that the grain growth falls within a certain range, and this exerts the anchor effect of the coating film as a chromate film. In order to exert this function sufficiently, the average primary particle size of the silica should be 3 to 50 m, preferably 10
-30 mμm is preferable. From the same point of view, the compounding ratio of the silica is also an important control factor, and in the present invention, the total C
The ratio of r is preferably 0.5 to 2.0, and particularly 0.7 to 1.5.
Is preferred.

The range of the proper deposition amount of the chromate composition as the chromate film in the present invention thus formed may be 10 to 150 mg / m ² as the total Cr deposition amount, preferably 30 to 90 mg / m ^2. Good. Total Cr
If the adhesion amount is less than 10 mg / m ² , the coating performance such as corrosion resistance and coating adhesion is not sufficiently satisfied, and the commercial value as a prepainted steel sheet cannot be expected. On the other hand, if it exceeds 150 mg / m ² , peeling of the coating film is likely to occur in the processed part due to the concentration of processing stress, and the punching resistance is lowered, which is not a good measure from the viewpoint of cost.

(3) Primer coating film Proper mixing ratio of rust preventive pigment In maintaining the corrosion resistance of the steel sheet of the present invention, a basic phosphite is used as a rust preventive pigment in the primer coating film, and its base is zinc potassium or Must be specified with zinc potassium phosphate. If the blending ratio of the pigment to 100 parts by weight of the resin is less than 10 parts by weight, the rust preventive property against undercoat corrosion is insufficient and sufficient corrosion resistance cannot be obtained. On the other hand, if the compounding ratio exceeds 100 parts, the elongation workability of the coating film deteriorates and cracks or cracks are likely to occur in the top coating film. Therefore,
A preferable mixing ratio of the rust preventive pigment is 30 to 80 parts with respect to 100 parts of the resin.

The particle size of the rust-preventive pigment is not particularly limited in the present invention, but it is preferable to control the average primary particle size to about 30 m to 1 μm for corrosion resistance as a coated product. It can be said that productivity is higher in terms of processability and smoothness of the coating appearance.

Primer coating film thickness In the present invention, if the coating film thickness of the primer is less than 0.5 μm, not only the corrosion resistance of the coating but also the adhesion of the top coating film to the substrate and the appearance uniformity are impaired, which is not preferable. Also, 1
If it exceeds 0 μm, the product performance is saturated, so it is not a good idea in terms of economy. Therefore, the preferred range of the primer coating film thickness is 1 to 7 μm.

The binder resin system of the anticorrosive pigment for the primer coating film is not particularly limited in the present invention, but is preferably polyester, polyolefin, nylon, polyacryl, polyurethane, polypropylene, epoxy. , Polyamides, phenols, polyethylenes may be used.

(4) Top coating film In order to impart PM resistance to the top coating film in the present invention, the top coating film is first hardened appropriately 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.

When the molecular weight of the resin is less than 15,000, the crosslink density becomes too high and work cracks are likely to occur in the coating film, and peeling of the coating film tends to occur when mechanical impact such as punching is applied. On the other hand, when it is 50000 or more, defects in the appearance of the coating, such as generation of scratched 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.
~ 50,000, especially 20,000 to 30,000
Is preferred.

Appropriate Blending Ratio of High 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.
Also, it becomes difficult to obtain a uniform coating appearance. On the other hand, if it exceeds 90%, it becomes difficult to control the desired coating appearance (coloring, glossiness), and the coating tends to crack due to the deterioration of the elongation workability of the coating, so that the coating performance including appearance can be reduced. There is a big drop and it is not a good idea including the cost. Therefore, the appropriate compounding amount of the resin is 30 to 90%, preferably 40 to 7%.
0% is good.

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 not sufficient, and if the Tg is more than 70 ° C, the PM resistance of the coating film is saturated, but the coating film tends to harden, resulting in work cracking and excellent resistance to corrosion. It is difficult to obtain punching properties, and it is difficult to obtain a scratched surface or cracks, and it is difficult to obtain at least a uniform coating appearance, 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., especially 20
-60 degreeC is preferable.

Proper Particle Size and Proper Amount of 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 improved. 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. Therefore, it is necessary to design the particle size and composition sufficiently.

First, the average particle diameter of the resin particle aggregate is 2 μm.
When the amount is less than the above value, elasticity to the coating film is excessively imparted, so that punching resistance is sufficiently imparted, but the coating film is softened and PM resistance and scratch resistance are conversely decreased to a certain extent. Stabilized and less preferred. In addition, in the appearance of the coating film, the function of adjusting gloss and gloss is deteriorated, 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 a very good measure including productivity. Absent. Therefore, the particle size range of the organic resin particle aggregate is preferably 2 to 50 μm, and particularly 3 to 30 μm.
Is preferred.

Next, when the content of the resin particle aggregate is less than 1% by weight of the solid content, elasticity of the aggregate due to the aggregate is insufficient and good PM resistance is maintained. ,
It is not preferable because it is difficult to achieve both punching resistance, deterioration in scratch resistance, and unstable control of appearance gloss. On the other hand, 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.
% Is good.

In the present invention, polymethyl methacrylate, polypropylene, polyamide, polyacrylonitrile, polyester, alkyl silicone, melamine-formaldehyde, polyurethane and polyvinylidene fluoride may be applied as the resin particle aggregate. , There is no difference in the effect.

Proper 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 flaws due to pressure-bonding of the release coating film. On the other hand, if it exceeds 5%, a water-cooled pattern is noticeable at the time of baking the coating film, and it is difficult to obtain a uniform coating appearance. Therefore, the proper 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 surface of the coating film is not sufficient, so that the scratch resistance is lowered and the important PM resistance, and further, after baking, For example, a water-cooled pattern occurs on the surface of the coating film, reducing the product value.
Not very good. 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, more preferably 100 to 120 ° C.

In the present invention, a silicone type lubricant and a fluorine type lubricant may be used as the lubricant in addition to polyethylene, and there is no difference in the effect.

(5) 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 glossiness of the back coating film is less than 50% of the glossiness of the top coating film, the PM resistance of the top coating film is lowered and the glossiness is 100%.
Even if it exceeds, the PM resistance of the top coating film similarly 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%.

[0051]

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
On both surfaces of the zinc-based or aluminum-plated steel sheet of No. 1, the flash plating specified by Table 1 to Table 10 according to the present invention is first performed by the displacement plating method at the line speed of 70 m / min, and then the base chromate is applied by the roll coating method of the prior art. Perform processing. This chromate film is adjusted so that the chromate composition of the present invention specified in Tables 1 to 10 is a solid film in a specific amount, dried, and immediately subjected to a coating process.

The front side of the base-treated steel sheet is coated with 2C2B and the back side is coated with 1C1B. The coating system used for these is an organic solvent-based melamine-curable polymer polyester resin coating, The paint is baked under the conditions.

On the 2C2B coated surface on the front side, the present invention was roll-coated with a primer coating consisting of the specific pigment shown in Tables 1 to 10 as a solid coating for 5 μm, and then a top coating with functionality added thereto. Table 1 to Table 10
The coating composition whose components are specified by the present invention is used as a solid film.
It is curtain-coated to a thickness of 9 μm, 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 of the present invention, which has the gloss of the coating film adjusted, is specified by Table 1 to Table 10 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 and water-cooled and dried.

The coating film performance of the precoated steel sheet according to the present invention thus produced is also shown in Tables 1 to 10.
The pressure mark resistance (PM resistance) required for a top coating film with high designability, as described below,
And as a precoated steel sheet that has both punching resistance,
The present invention has brought to market an epoch-making pre-coated steel sheet that does not exist in the prior art and that enables stable production of this at low cost.

(1) About the effect of the metal film under 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 adhesiveness of the upper layer film is also increased. Regarding the effect of the metal film for stabilizing the punching resistance at a high level, the embodiment of the present invention is
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 a specific amount in the lower layer of the chromate coating, even a steel plate burr portion cut without impairing other properties of the coating. The sound film adhesion was maintained, and it became possible to achieve both punching resistance and PM resistance (pressure mark resistance) stably 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 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 of the coating by making the chromate film insoluble by the metal film and changing the chromium morphology.

Regarding the effect of the present invention as described above, the proper ratio of Cr ^{3+ in} the examples is No. 3 and No. 3 22
-No. No. 26, and the comparative example is No. 27-No.
28. Further, regarding the proper range of the average primary particle size of the vapor phase silica, No. 3 and No. 3 29-
No. No. 32 shows the comparative example. 33-No. 34.

Further, regarding the compounding ratio of the gas phase silica, No. 3 and No. 3 35-No. 38,
The comparative example is No. 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 apparent from these examples, by using the chromate film specified by the present invention, not only excellent film adhesion but also punching resistance and PM resistance (pressure resistance It has become possible to achieve both high and stable markability.

(3) Primer coating film Regarding the effect of applying the rust-preventive pigment according to the present invention to the primer coating film, the type of pigment and the compounding ratio thereof, the examples of the present invention are described. 3 and No. 3 51-No. No. 58 and the comparative example No. 59-No. 62. Further, regarding the proper primer coating film thickness, No. 3 and N
o. 63-No. 67, and its comparative example No. 68
-No. 69.

As is clear from these examples, by providing a primer coating film in which the rust preventive pigment specified by the present invention is properly blended to a proper film thickness, excellent coating film adhesion,
Punching resistance and PM resistance (pressure mark resistance) can be consistently achieved at a high level without impeding other performances.

(4) Action and effect of main resin Regarding the action and effect of the main resin for imparting PM resistance to the coating film, the examples of the present invention in the proper molecular weight range are given.
3 and No. 3 70-No. No. 75 of the comparative example.
76-No. 77.

Regarding the proper Tg of the main resin, the No. 3 and No. 3 78-No. 81
No. 82-No. 83. Further, regarding the proper blending ratio of the main resin, No. 3 and No. 3 84-No. 87, a comparative example N
o. 88-No. 89.

As is clear from these examples, in order to impart PM resistance to a coating without impairing other properties of the coating, it is necessary to design the Tg of the coating within the range of the present invention. It is important to note that, in addition, in order to stably obtain the uniform appearance and punching resistance of the coating film, it is necessary to properly design the resin molecular weight and the blending amount referred to in the present invention.

(5) Appropriate Blending of Resin Particle Aggregate in Coating Film The resin aggregate is present in the coating film for imparting scratch resistance, but in the present invention, a machine such as punching machine 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 No. 3 90-No. 96
Comparative Example No. 97-No. 98. Further, regarding the proper blending amount, No. 3 and No. 3 99
-No. No. 104, a comparative example. 105-No. 10
6 is shown.

As is clear from these examples, punching resistance and PM resistance without deteriorating the performance of other coating films.
It is understood that it is necessary to control the particle size and the blending amount of the resin particle aggregate within the appropriate range referred to in the present invention in order to make the coating film compatible with the property.

(6) Appropriate Mixing of Polyethylene Lubricant This lubricant is in powder form, and its purpose is to appropriately improve the scratch resistance by imparting sliding property to the coating film, and it is necessary to optimize its mixing. Is. Examples of the lubricant according to the present invention are No. 3 and No. 3 107-No. 111, the comparative example No. 112-No. Shown at 113.

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 especially by imparting PM resistance to the coating film, the guard film free In the steel sheet of the present invention characterized by the above, proper blending of the lubricant is essential. 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 No. 3 and No. 3 114-No.
116, the comparative example No. 117-No. Shown at 118. 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. 3 119-No. 123,
No. 124-No. Shown at 125. 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. 3 126-No. 136. 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.

[0075]

[Table 1]

[0076]

[Table 2]

[0077]

[Table 3]

[0078]

[Table 4]

[0079]

[Table 5]

[0080]

[Table 6]

[0081]

[Table 7]

[0082]

[Table 8]

[0083]

[Table 9]

[0084]

[Table 10]

(Note) The notes in the above tables are as follows. * 1. Plating system EZ: Electric Zn 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 )
Is measured by a chemical analysis method. NS: Ni + Sb, NF:
Ni + Fe, NM: Ni + Mo, NV: Ni + V, N
W: 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.
μm. The unit for displaying the ratio is wt% as a ratio to the total Cr amount. The adhesion amount is displayed as the total Cr amount, and the fluorescence X
According to the line analysis method.

* 4. Primer coating using high molecular polyester resin Anticorrosion pigment ZK: basic potassium potassium phosphite, primary average particle size 10 mμm to 2 μm applied Anticorrosion pigment PK: basic zinc potassium phosphite phosphorous, primary average particle size Applicable in the range of diameter 10m-2m

* 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 On a test piece in which a back side coating film was superposed on the top coating side, a load of 80 kg / cm ² , RH 95%, and a wet atmosphere of 40 ° C. were used for 16 times.
After standing for 8 hrs, the test piece was taken out and the indentation state of the coated surface was visually evaluated. ◎: Initial appearance and no change ○: Very slight indentation transfer when transparent △: Slight indentation transfer seen from the front ×: Clear indentation transfer

* 8. Punching resistance Continuous punching punching device: Continuous punching by electric crank press machine, 4 pieces per second Die: Uses a die with hard surface finish. Four sets of blades with a wall thickness of 1 mm and a 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 occurred ×: Frequent burr occurrence: ◎: None ○: Slightly cracked but no flaw △: Attached to the mold However, the blemishes sporadically x: Adhered to the mold considerably and blemishes frequently occurred

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

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

[0095]

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.
The result is a study on the compatibility of the ()) and punching resistance, and as a result, the plating base plate controlled to a plating surface roughness within the specified range based on the following technical concept is used as the substrate, and a specific metal film as the lower layer film of the chromate film on top of it. The adhesion of the chromate film to the substrate and the change of the chromate film to the insolubilized form of the metal film dramatically improve the film adhesion, which can stabilize the outstanding punching resistance to a high level. In addition, by combining the top coating composition and the gloss control of the back coating, it is possible to obtain a clear black precoated steel sheet of non-guard film type on an industrial level without lowering other coating performance. It has come to be offered to the market.

(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 greatly improved, and at the same time the chromate film is difficult to form due to the formation of the metal film. 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) By using a non-Cr type pigment as the rust preventive pigment in the primer coating film, most of the elution of Cr from the coated product was eliminated. (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 became possible to suppress wear and to stably obtain perforation resistance to the steel sheet (achieve punching resistance by suppressing die wear). (4) Coil is achieved by the compatibility of each coating film component technology such as Tg of top coating film, molecular weight of resin and its blending, melting point of lubricant and blending thereof, and proper control of appearance gloss of back coating. 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 (2)

[Claims] 1. A surface of a zinc-based plated steel sheet or a hot-dip aluminum-plated steel sheet is coated with Ni, Co, Fe, Zr, Sb,
A metal coating consisting of at least one of V, Mo and W is formed in an amount of 3 to 50 mg / m ² and Cr is present in the upper layer in a total Cr content ratio.
Chromate composition in which ³⁺ is 10 to 50% and the primary average particle diameter is ³ to 50 mμm and the vapor phase silica is 0.5 to 2.0 in the total Cr amount ratio, and the total Cr deposition amount is 10 to 150 mg / m ^2. In addition, a basic phosphite-based rust preventive pigment whose base is specified by zinc potassium or zinc potassium phosphate is added to the upper layer in an amount of 10 to 100 parts by weight with respect to 100 parts by weight of the resin.
After forming a high-molecular polyester resin-based primer coating film by weight of 0.5 to 10 μm as a solid coating, a glass transition point (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 excellent in punching resistance and pressure mark resistance of chrome resistant elution type characterized by forming a top coating film containing 1 to 5% by weight of polyethylene wax at ℃ Free type precoated steel sheet. 2. The non-chromium-eluting punching resistance and pressure resistance mark according to claim 1, wherein the surface glossiness of the back surface coating film is controlled to at least 50 to 100% of the front side top coating film. A pre-coated steel sheet with excellent guard film free type.