JP3205207B2 - Guard film-free type clear-cut precoated steel sheet with excellent coating film adhesion, punching resistance and pressure mark resistance - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the use of a guard film free precoated steel sheet having high clarity required for home appliances such as audio products and cooking products, and a hole punching resistance (punching resistance) in a punching machining process. ) Is related to a brilliant precoated steel sheet.

[0002]

2. Description of the Related Art In recent years, there has been a high demand for cost reduction of coated steel sheets in the field of home appliances and automobiles, and as the precoating of post-coats has progressed further, the perforation resistance by continuous punching (hereinafter simply referred to as "punching resistance"). There is a growing market demand for a guard film-free type precoated steel sheet that is compatible with pressure mark resistance (hereinafter, simply referred to as PM resistance) that does not generate indentation transfer flaws. In particular, in the case of prepainted steel sheets with high clarity (hereinafter simply referred to as “precoats”), which are frequently used for the outer panels of audio products and cooking products, the handling of the top coating film, which occurs during the product forming process at the customer, is As a countermeasure for this, on the side of manufacturing the precoat, a guard film having a film thickness of several tens to several hundreds of μm is separately attached to the top painted surface side having high image clarity and provided on the market, resulting in high costs. on the other hand,
The film must be peeled off after the product processing and then subjected to post-treatment such as incineration of garbage, and the demand for non-guarding of the prepainted steel sheet has been intensifying in recent years from the viewpoint of resource utilization and global environmental considerations.

However, when manufacturing this guard film-free type precoated steel sheet under a high productivity line, the manufacturing side may temporarily place the coil product as a coil product on the floor until it becomes a cut plate product. Although there are many problems, there is a risk that indentation transfer flaws (pressure marks) may occur on the painted surface due to the coil's own weight during this period, and this improvement measure is applied to the coating of the pre-coated steel sheet, including the method of placing the coil product on the floor. Imposed. For the same PM resistance, other than the primary product on the pre-coat manufacturing side, the maintenance of the product appearance by the packing material at the time of transport of the final processed product at the customer is an essential condition. There are some persistent requests. With guard film-free, depending on the unit weight of the coil, a considerable amount of linear or band-shaped indentation marks are generated in the coating film at the part in contact with the floor in the width direction of the board, which occur at a constant pitch in the longitudinal direction of the coil. To invite
In this respect, the greatest problem to be solved is to improve the PM resistance of the coating film.

[0004] Further, in the precoat having PM resistance, it is required that the continuous drilling property (punching resistance) by machining is basically cleared without affecting the performance of other coating films. Punching resistance and PM resistance to coating film
It is indispensable to balance the characteristics. Here, the punching resistance is defined. Punching resistance refers to the abrasion resistance of punching dies caused by rubbing with the coating film.Burring occurs at the peripheral edge of the hole in the steel plate due to this, or powdered release coating film generated during punching The term also includes the prevention of dents on the painted surface caused by the adhesion of the mold. Therefore, in order to improve the punching resistance, it is necessary to design a film including an improvement in coating film adhesion. In this sense, there is hardly any conventional technology disclosed in the prior art in a bright precoated steel sheet imparting both punching resistance and PM resistance or a method for producing the same.

[0005]

SUMMARY OF THE INVENTION In the above-mentioned prior art, the present invention provides a guard film-free type sharpness precoat which has both punching resistance including coating film adhesion and PM resistance at a low cost. Therefore, from the producer to the final commercialization by the consumer, the precoat must be excellent in PM resistance and punching resistance. For that purpose, the following technical issues are involved in the undercoating treatment and the coating film modification.
Firstly, it is necessary to control the roughness of the plating surface (to make the appearance of the coating clearer) and to improve the adhesion of the underlayer chromate film to the substrate (coating film adhesion, punching resistance). On the coating film side, on the other hand, the coating film has elasticity and pressure resistance (giving PM resistance) to the coating film corresponding to the storage and transportation environment of the coil product or processed product, and the coating film which may shorten the mold life. These must be precoats that satisfy all coating performances, such as softening of the hard aggregate (providing PM resistance) and without sacrificing other coating performances.

[0006] That is, it is basically required to design a coating film having an adequate hardness and a high elasticity while improving the substrate adhesion of the base chromate film. For that purpose, first, it is necessary to suppress the adhesion of the peeled coating film to the punching die by increasing the adhesion of the chromate film to the base plate and controlling the plating surface roughness (Ra) to a specific range as a substrate. For that purpose, a flash plating film made of a specific metal is effective as a pretreatment of the chromate film, and the glass transition point (hereinafter, simply referred to as Tg) of the coating film is controlled to a specific range, and It is basically necessary to design a coating film with high impact resistance and high elasticity in order to improve punching resistance, but for that purpose, as a softening of the aggregate in the coating film, the main resin of the binder It is essential to use a resin type organic aggregate that hardly dissolves or reacts, and from a coating of hard inorganic aggregate (silica particles) with high crystallinity, which is a factor of deterioration in punching resistance, which is frequently used in the prior art. of Outside exclusion is required. In addition, in order to obtain a stable PM resistance of the front side top coating film, it is particularly necessary to control the surface state of the back coating film, for example, to control the appearance gloss of the back coating film to be equal to or less than the glossiness of the top coating film. Based on the findings described above, the present invention has been proposed.

[0007]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned disadvantages of the prior art and addresses the recent market needs of low cost prepainted steel sheets. The purpose of the present invention is to improve the design of a coating film of a bright precoat having both punching resistance and PM resistance. For the original plate, specify the plating surface roughness (clearness of the coating film appearance), and to improve the adhesion of the base chromate film to the substrate,
In addition to the need to optimize the composition and amount of the chromate film, a specific metal film is especially required under the chromate film (prevention of film peeling during punching). Punching resistance by imparting elasticity to the top film Improving the particle size and blending amount of organic resin aggregates Providing PM resistance to the top coating film Optimizing the molecular weight and blending amount of resin Tg and binder resin, and top coating by controlling the gloss of the back coating film Higher stabilization of the PM resistance of the film.

Hereinafter, the coating composition of the present invention will be described first. In the present invention, first, an original plate whose plating surface roughness is specified is used as a substrate, and a specific amount of a chromium composition whose components are specified on both the front and back sides is applied to the upper layer to form the substrate. Next, in forming a coating film on the upper layer, the front side (top coating film) is an appropriate primer coating film, and 2C2 having both the punching resistance and the PM resistance by specifying the component constitution as the top coating film on the upper layer.
B. The back surface is a 1C1B coating film whose surface gloss is specified.

[0009] The details of these film constitutions will be shown below. In order to obtain the bright coated steel sheet of the present invention, it is essential that a substrate whose plating surface roughness is controlled to 0.5 μm or less in Ra is used as a base plate for plating, and a method for controlling the surface roughness is as follows. It may be in the category of the prior art. The original sheet 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 an electroplating system, Zn plating and an alloy element of any of Ni, Cr and Fe Or Z consisting of one or more
An n-based alloy-plated steel sheet may be used. In the electroplating system, Zn-Ni and Zn-Fe are used as bases.
A Zn-based dispersed alloy plated steel sheet obtained by uniformly dispersing and depositing a metal oxide such as iO ₂ , TiO ₂ , ZrO ₂ , BaCrO ₄ may be used. Furthermore, a hot-dip galvanized steel sheet, a Zn—Al-based alloy-coated steel sheet, and a galvanized steel sheet subjected to alloying treatment by thermal diffusion may be applied in a hot-dip coating system.

[0010] Next, Ni, Co, Fe, Zr, S
A metal film of at least one of b, V, Mo and W is formed at ³ to 50 mg / m ² , and Cr ³⁺ is formed on the upper layer in a total Cr content ratio of 10 to 50% and a primary average particle size is ³ to 50 μm.
Of a gas phase silica having a total Cr content ratio of 0.5 to 2.0 has a total Cr adhesion amount of 10 to 150 mg /
m ^{2 is} formed. In addition, a primer coating film as a solid coating on the upper layer is 1 to 10 μm, and a glass transition point (Tg) of the coating film as a top coating film is 5 to 70 ° C.
Melamine-curable polymer polyester resin having an average molecular weight of 15,000 to 50,000 is 30 to 90 in terms of solid content weight ratio.
%, Primary average particle size 2-50μ which hardly fuses with this resin
m of the organic resin particles as an aggregate is 1 to 50 in terms of solid content weight ratio.
% And a coating composition characterized by containing a polyethylene wax having a melting point of 80 to 130 ° C. as a lubricant in a weight ratio of solid content of 1 to 5%, and forming a coating composition having a constant film thickness. It is a guard film free type sharpness precoated steel sheet with excellent punching resistance and PM resistance of the coating film.

Further, a guard film free type excellent in punching resistance and coating adhesion, characterized in that the surface glossiness of the back coating is controlled to at least 50 to 100% of that of the top coating on the front side. It is a bright black pre-coated steel sheet. The outline is as follows. The surface roughness of the original plate was specified to enhance the sharpness of the paint appearance. In order to maintain the stable punching resistance, the adhesion of the underlayer chromate film to the base material was improved in order to increase the film adhesion around the punch hole edge It is necessary to improve the properties, and as a function, a specific metal film is provided under the chromate film. In order to impart the PM resistance of the coating film, the Tg and the molecular weight of the resin are set in a specific range. The point that appropriate hardness and elasticity were imparted to the resin, the point of applying organic resin particles having a specified average particle size as a coating film aggregate in suppressing mold abrasion and improving the punching resistance, By controlling the surface glossiness at least equal to or less than that of the front side top coating, the PM resistance of the top coating is reduced.
The point to get the stability. In the design of the top coating film of the present invention, the coloring of the coating film as needed is not particularly limited, and may be performed freely, and may also be performed as a top coating film, such as metallicization and appearance gloss. There is no particular limitation on the designability.

[0012]

The following is a description of the limitations on the film constituents of the steel sheet of the present invention. (1) Plating surface roughness of original plate The prepainted steel plate of the present invention has a front-side top painted surface (2C
As long as the sharpness of the coating appearance of (2B coating) is one of the commercial values, a plating base plate having as high a surface smoothness as possible is essential as a substrate. Therefore, it is important to control the plating surface roughness as small as possible, but in the present invention, the average surface roughness Ra is 0.5 μm or less, preferably 0.2 μm or less.

(2) Metal Coating Under Chromate Coating The function of the metal coating in the present invention is to improve the substrate adhesion of the chromate coating under the chromate coating.
This is for improving the adhesion between the chromate film and the upper layer coating 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 film during the continuous punching operation as a prepainted steel sheet and for dramatically improving the punching resistance. Ni, Co, Fe, Zr, S
b, V, Mo, or W, and at least 3 to 50 mg / m ² as an appropriate coating amount of the film. In the present invention, the means for obtaining the metal film may be in the category of a known technique, and a technique such as chemical plating or electroplating may be used.

Regarding the function and effect of the metal film,
From the state analysis of the chromate film by SCA and the elution property of the chromate film to water, it can be inferred as follows.
That is, the metal film is bonded to the base plate by metal, and the presence of the metal film makes the chromate film hardly soluble, and the Cr ⁶⁺ in the chromate film
There is a fact that the content decreases and the Cr3 ⁺ content increases, which confirms that some Cr reduction reaction occurs between the metal film and the chromate film in a wet state on the metal film, As a source of the reduction reaction, the metal film serves as a cathode to cause anodic dissolution of the base plating layer. At that time, the exchange of generated electrons reduces Cr ⁶⁺ and increases the Cr ³⁺ form of a chromate film. It is estimated that the morphology changed.

In other words, an increase in the ratio of Cr ^{3+ in} the chromate film means that the film itself becomes a gel-like insoluble film and the affinity with metals and organic substances increases.
It is considered that this has increased the adhesion of the chromate film itself to the substrate through the metal film, and it is presumed that it also improved the adhesion to the upper layer coating film. From the above points, the proper amount of the metal coating is 3
５０50 mg / m ² , preferably 5-30 mg / m ^2
2 is better. If the amount is less than 3 mg / m ² , the above-mentioned effect cannot be sufficiently exhibited, and if it exceeds 50 mg / m ^2, there is a decrease in corrosion resistance and there is a problem of commercial value and cost as a prepainted steel sheet, so that it is not advisable.

(3) Chromate Coating The chromate composition of the present invention is composed of gas phase silica having a Cr content of 10 to 50% and a primary average particle size of ³ to 50 μm in a total Cr content ratio of 0.5 to 0.5 in a total Cr content ratio. chromate composition comprising at 2.0 is 10-150 mg / m ² is formed as the total Cr deposition amount. When the amount of Cr ^{3+ in the} composition is less than 10% in terms of the total amount of Cr, 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%, the gelling of the treatment bath may hinder uniform roll applicability to the steel sheet, and it will be difficult to control the amount of adhesion. Therefore, the appropriate amount of Cr ³⁺ is 10 to 50%, preferably 30 to 40% in total Cr amount ratio.

The purpose of using fumed silica is mainly to prevent scratches on the backside coating. The silica has a property of secondary agglomeration in a chromate solution to grow grains in the order of several hundreds μm to μm, and it is necessary to control the growth of grains to fall within a certain range. This is to exert the anchor effect. In order to sufficiently exhibit this function, the average primary particle size of the silica is 3 to 50.
mμ, preferably 10 to 30 mμ. Further, from the same point of view, the compounding ratio of the silica is also an important control factor. In the present invention, the total Cr content ratio is preferably 0.5 to 2.0, and more preferably 0.7 to 1.5.

The proper coating weight in the range of the chromate film in the present invention of the chromate composition comprising in this manner may be 10-150 mg / m ² formed as total Cr coating weight, preferably 30~90mg / m ² Is good. If the total amount of Cr is less than 10 mg / m ² , coating performance such as corrosion resistance and coating film adhesion is not sufficiently satisfied, and commercial value as a prepainted steel sheet cannot be expected. Also 150
When the concentration exceeds mg / m ² , the coating stress tends to be peeled off in the processed portion due to the concentration of the processing stress, and the punching resistance is lowered.

(4) Top Coating Appropriate molecular weight of high molecular weight polyester resin as the main resin for the binder In order to impart PM resistance to the top coating in the present invention, the coating is first hardened appropriately. It is premised that the resin can withstand the pressure. For this purpose, it is necessary to specify the molecular weight range of the high-molecular polyester resin as 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 liable to undergo processing cracks,
Further, when a mechanical impact such as punching is received, peeling of the coating film is likely to occur. On the other hand, if it is 50,000 or more, defects in the paint appearance such as the occurrence of cracks and armpits are likely to occur,
Not very good, including cost. Therefore, in the present invention, the molecular weight range of the resin is 15,000 to 500
00, among which 20,000 to 30,000 is preferred.

Appropriate Blending Ratio of High Molecular Weight Polyester Resin In the present invention, the blending amount of the binder resin is preferably 30 to 90% in terms of solids weight ratio. If it is less than 40%, the binder function of the resin with respect to the pigment and the aggregate is reduced, and the extensibility of the coating film is reduced as a whole. There is also a problem, making it difficult to obtain a uniform appearance. On the other hand, if it exceeds 90%, it is difficult to control the desired coating film appearance (color opacity), and the coating film is easily damaged, so that handling scratches are likely to occur. Not a good idea. Therefore, the proper amount of the resin is 30 to 90%, preferably 40 to 70%.

Coating Tg (Glass Transition Point) The coating Tg of the present invention is a basic factor to be particularly controlled in order to obtain more stable PM resistance of the top coating. The Tg
Is less than 5 ° C, sufficient PM resistance cannot be obtained.
Above this, the PM resistance of the coating film is saturated, but on the contrary, the coating film tends to harden, resulting in a coating film with low work elongation, and the coating film is liable to crack, It is easy to cause wrinkles and the like, resulting in a non-uniform coating appearance, which is not very advantageous from the viewpoint of coating film performance and productivity. Therefore, the coating T
g is 5 to 70 ° C. in the present invention, and is preferably 20 to 70 ° C.
60 ° C. is preferred.

Appropriate Particle Size and Appropriate 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 coating film has punching resistance and anti-slip resistance. This is for imparting flaws. In the resin aggregate, resin particles having a function of being insoluble or hardly soluble in a binder resin from the viewpoint of imparting elasticity to the coating film and having a function of sufficiently stably controlling the appearance gloss of the coating film. Must. For that purpose, a sufficient design is required for the particle size and composition. 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, and the punching resistance is sufficiently imparted.
On the contrary, the M property and the scratch resistance are slightly lowered and become unstable, which is not so preferable. In addition, in the appearance of the coating film, the function of adjusting gloss and gloss is reduced, and this is not very advantageous including cost. On the other hand, when the average particle size exceeds 50 μm, the coating film appearance becomes large with protrusions, and stable control of the coating film glossiness becomes difficult, especially,
In addition, there is a decrease in scratch resistance, so that it is not very advantageous including productivity. Therefore, the particle size range of the organic resin particle aggregate is preferably 2 to 50 μm, and particularly preferably 3 to 30 μm.

Next, regarding the compounding amount of the resin particle aggregate,
If the solid content is less than 1% by weight, the elasticity of the aggregate to the coating film is insufficient, and good PM resistance is maintained, but it is difficult to achieve both punching resistance, deterioration of scratch resistance and appearance gloss. This is not preferable because the control may become unstable. On the other hand, if it exceeds 50%, it is difficult to control the gloss of the coating film appearance, even though sufficient PM resistance and punching resistance can be achieved at the same time. Therefore, the amount of the resin particle aggregate is preferably 1 to 50%, and more preferably 3 to 20%. In the present invention, polymethyl methacrylate, polypropylene, polyamide, polyacrylonitrile, polyester, alkyl silicone, melamine-formaldehyde, polyurethane and polyvinylidene fluoride may be used as the resin particle aggregate. There is no difference.

Proper amount of polyethylene lubricant The purpose of the polyethylene lubricant is to improve the scratch resistance of the coating film and the workability in press working. If the lubricant is less than 1% by weight as a solid content, the decrease in the performance of the coating film cannot be avoided,
In addition, there is a flaw due to press-fitting of the release coating, and the punching resistance is not sufficient. On the other hand, if it exceeds 5%, a water-cooled pattern at the time of baking of the coating film is conspicuous, and it is difficult to obtain a uniform coating appearance. Therefore, the proper amount of the lubricant is 1 to 5%, preferably 1.5 to 3%. Next, if 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 reduced, the PM resistance is important, and further, the water-cooled pattern is formed on the coated film surface after baking. Is not so preferable, for example, that the commercial value is lowered due to the occurrence of.

On the other hand, if the melting point of the lubricant exceeds 130 ° C., the uniform dispersibility in the coating material is slightly lacking, so that it is difficult to form a uniform lubricating film on the surface of the coating film, and the unevenness of appearance and scratch resistance It is not preferable because it causes instability. Therefore, in the present invention, the melting point of the lubricant is preferably 80 to 130 ° C., preferably 10 to 130 ° C.
0-120 degreeC is good. In the present invention, silicone-based and fluorine-based lubricants may be used in addition to polyethylene as the lubricant, and there is no difference in the effects.

(5) Surface Gloss of Back Coating In the present invention, the surface gloss of the back coating is a controlling factor for more stably obtaining the PM resistance of the top coating. 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 decreases, and when it exceeds 100%, 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 important to maintain the range of the back surface gloss within the range of the present invention, and preferably 60 to 90%.

[0027]

EXAMPLES Hereinafter, the effects of the present invention will be described in detail based on examples and comparative examples. Plate thickness 0.7 mm, plate width 914 mm of plating surface roughness specified by the present invention in Tables 1 to 9
First, the both sides of the zinc-based or aluminum-plated steel sheet are subjected to a base chromate treatment by a conventional roll coating method at a line speed of 70 m / min. This chromate film is
The chromate composition of the present invention specified in Tables 1 to 9 is adjusted to a specific amount as a solid film, dried, and immediately enters a coating process. The front side of the base-treated steel sheet is 2
The back surface is coated with 1C1B by C2B coating, and all of the coating systems used for these are organic solvent-based melamine-curable high-molecular polyester resin-based coatings, which are coated and baked under predetermined conditions. In the top coating film on the front side, the primer coating system is Nippon Paint's Flexible Coat 600EU primer, which is coated as a solid film to a thickness of 5 μm, baked, water-cooled and dried, and then the upper layer is a coating comprising the component system specified by the present invention. The composition is roll-coated by a known technique so as to have a thickness of 18 μm as a solid film as a black-colored top coating, baked under standard conditions, and water-cooled and dried. At this time, the surface glossiness of the top coating film was controlled to 80%. On the other hand, Nippon Paint's NP0
Using two paints, a known roll coating method is used to control the film thickness to 2 μm as a solid film, bake at a predetermined plate temperature, water-cool, and dry. The coating performance of the precoated steel sheet according to the present invention thus manufactured is shown in Tables 9 to 16 corresponding to Tables 1 to 8.

[0028]

[Table 1]

[0029]

[Table 2]

[0030]

[Table 3]

[0031]

[Table 4]

[0032]

[Table 5]

[0033]

[Table 6]

[0034]

[Table 7]

[0035]

[Table 8]

[0036]

[Table 9]

[0037]

[Table 10]

[0038]

[Table 11]

[0039]

[Table 12]

[0040]

[Table 13]

[0041]

[Table 14]

[0042]

[Table 15]

[0043]

[Table 16]

As described below, the effect can be stably produced as a precoated steel sheet having both the pressure mark resistance (PM resistance) and the punching resistance required for a top coating having high designability. Thus, a revolutionary pre-coated steel sheet not available in the prior art has been offered to the market at low cost. (1) Regarding the effect of controlling the surface roughness of the base plating base plate In the present invention, the plating surface roughness of the base plating base plate is to obtain a smooth and clear image with stable appearance. The embodiment of the present invention is referred to as No. 1 to No. No. 5 and the comparative example is No. 5. 6 is shown. As is evident from these Examples and Comparative Examples, by specifying the plating surface roughness of the original plate within the scope of the present invention, the sharpness of the painted appearance can be stably obtained.

(2) Regarding the effect of the metal film under the chromate film The adhesion between the chromate film and the substrate is increased, and the chromate film is hardly dissolved to increase the adhesiveness of the upper film, thereby improving the resistance as a prepainted steel sheet. Regarding the effect of the metal film for stabilizing the punching property to a high level, the embodiment of the present invention
o. 2, No. 7-No. 13 and No. 16-No.
No. 27, and the comparative example is No. 27. 14-No. FIG. As is clear from these examples, by providing the metal film of the present invention below the chromate film, the punching resistance and the PM resistance (pressure mark resistance) can be achieved without impairing the other properties of the coating film. It is now possible to stabilize both at a high level.

(3) Regarding the effect of the chromate film In the present invention, the role of the chromate film is to suppress the cohesive failure caused by processing, and to adhere to the base material of the chromate film exerted by the synergistic action with the metal film. The improvement of the properties is to suppress the peeling of the coating film during the punching work and to provide the prepainted steel sheet with stable punching resistance. In addition, it is to improve the coating corrosion resistance life by making the chromate film hardly soluble by the metal film and changing its chromium form. Regarding the effect of the present invention, the proper ratio of Cr ^{3+ in} the examples
o. 2 and No. 28-No. No. 32, and the comparative example is No. 32. 33-No. 34. Further, regarding the appropriate range of the average primary particle size of the gas phase silica, the embodiment of the present invention
o. 2 and No. 35-No. 38 shows a comparative example of N
o. 39-No. 40.

Further, with respect to the compounding ratio of the gas phase silica, the examples of the present invention are described in Nos. 2 and No. 41-No. 44,
The comparative example is No. 45-No. Shown at 46. With respect to the range of the amount of chromate adhering specified by the present invention, the examples are referred to as Nos. 2 and No. 47-No. No. 54 shows a comparative example of No. 54. 55-No. 56. As is evident from these examples, the use of the chromate film specified by the present invention stabilizes the punching resistance and the PM resistance (pressure mark resistance) at a high level without impairing the other properties of the coating film. It is now possible to achieve both.

(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 working examples of the present invention are described in Nos. No. 2 including Comparative Examples other than No. 2 57-No. 77. The examples are described as No. 1 for the appropriate range of the resin molecular weight. 2 and No. 57-No.
No. 62, and the comparative example is No. 63-No. 64.
Further, with respect to the appropriate range of the coating film Tg, the examples are referred to as Nos. 2 and No. 65-No. No. 69 is a comparative example. 70-N
o. Shown at 71. In addition, the examples for N
o. 2 and No. 72-No. No. 75 is a comparative example.
76-No. 77. As is evident from these examples, the coating has a P-resistance without impairing the other properties of the coating.
In order to impart M property, it is important to design the Tg of the coating film within the range of the present invention. In addition, in order to stably obtain uniform appearance and punching resistance of the coating film. It can be seen that it is necessary to properly design the resin molecular weight and the compounding amount according to the present invention.

(5) Proper Mixing of Resin Particle Aggregate in Coating Film According to the present invention, the main purpose of the resin aggregate is to suppress mold abrasion in drilling properties in machining such as punching. For this purpose, it is important to control the particle size of the aggregate and the amount of the aggregate within an appropriate range. In the invention of the present application, the examples of the resin aggregates are described as No.
2 and No. 78-No. No. 84 shows a comparative example. 85
To 86. Regarding the proper compounding amount, the examples are No. 2 and No. 87-No. 94 to N
o. 95-No. 96. As is apparent from these examples, in order to achieve both the punching resistance and the PM resistance of the coating film without deteriorating the performance of other coating films, the particle size and the amount of the resin particle aggregate are determined according to the present invention. It is understood that it is important to control the temperature within the appropriate range.

(6) Proper blending of polyethylene lubricant This lubricant is in the form of a powder and its purpose is to appropriately increase the scratch resistance by imparting slipperiness to the coating film. It is. The embodiment according to the present invention is referred to as No. 1. 2 and No. 97-No. 100 to N
o. 101-No. Shown at 102. As is clear from this example, the steel sheet handling flaws in stable press working and the like are eliminated by imparting lubricity to the coating film,
In particular, in the steel sheet of the present invention, which is characterized in that it has a guard film free by imparting PM resistance to a coating film, it is important to properly mix the lubricant. In addition, in the formulation of the lubricant,
It can be seen that a water cooling pattern after baking tends to occur on the coating film appearance outside the upper limit, which is not preferable. Further, regarding the melting point of the lubricant, the examples according to the present invention are described in Nos. 2 and No. 103-No. No. 105 is a comparative example. 10
6-No. Shown at 107. As is clear from this example, when the melting point range of the lubricant of the present invention is out of the proper range, in addition to good scratch resistance, it is possible to stably obtain the PM resistance, which is the gist of the present invention. It can be seen that it becomes difficult and that water-cooled patterns frequently appear on the coating film, which significantly impairs the commercial value in appearance.

(7) Glossiness of Back Coating In the present invention, in order to stably obtain the PM resistance of the top coating, it is preferable to control the gloss of the back coating in an appropriate range. . In this case, the control of the back surface glossiness is performed by comparing the glossiness of the top coating film. Regarding this point, the embodiment of the present invention is referred to as No. 1. 2 and No. 108-No. 111
Nos. And Comparative Examples No. 112-No. 11
3 is shown. As is clear from this, if the present invention deviates from the control range of the back surface glossiness, it becomes difficult to stably maintain the PM resistance on the top coating surface having high commercial value under the high productivity line, and the cost is reduced. It is not very good including it.

(8) Examples of application of various plating systems for base steel sheets Examples of the plating systems for base steel sheets to which the present invention can be applied are described in Nos. 2 and No. 114-No. At 124. As is clear from this example, it is understood that the coating film function of the present invention does not hinder the coating function even if the plating system of the base steel sheet is different.

(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: Electric Zn—Ni—TiO ₂ (Ni; 12%, T
iO ₂ ; 3%) ZNB: Electric Zn—Ni—BaSO ₄ (Ni; 12%,
BaSO ₄ ; 3%) ZFS: Electric Zn—Fe—SiO ₂ (Fe; 10%, S
iO _2; 3%) GZ: molten Zn plating GA: molten Zn-Al plating (Al; 5%) GF: alloyed hot-dip Zn plating (Fe; 8~11%) AL: dip Al plating

The surface roughness of the plated surface of the steel sheet was adjusted by roll rolling on a laboratory scale. * 2. Metal film By a chemical plating method using a known technique. Adhesion amount (mg / m
² ) Measured by chemical analysis method. * 3. Chromate coating The particle size of gas phase silica refers to the primary average particle size, and the display unit is m
μ. The unit of the ratio is indicated by wt% as a ratio to the total amount of chromium. The attached amount is expressed as the total amount of Cr and is determined by a fluorescent X-ray analysis method. * 4. Top coating properties Uses high-molecular polyester resin cured by melamine resin. Tg refers to the glass transition point of the cured coating film and is measured by TMA. All the compounding amounts are in terms of weight ratio to the solid content of the coating film. Organic aggregate refers to resin particle aggregate. Particle size refers to the primary average particle size.

* 5. Glossiness of backside coating This refers to the glossiness of the top side coating by 60 ° specular reflection. * 6. PM resistance evaluation A test piece obtained by superimposing a back coating film on a top coating film surface was allowed to stand in a humid atmosphere of 80 kg / cm ² , RH 95%, and 40 ° C for 168 hrs. Visual evaluation. ◎: No change from initial appearance ：: Very slight indentation transfer when transparent △: Slight indentation transfer when viewed from the front ×: Clear indentation transfer

* 7. Punching resistance Continuous punching hole punching device; continuous punching by electric crank press, 4 pieces per second Die: Use die with surface hardening. Set of 4 blades 1 mm thick x 4.5 mm wide. Drilling resistance evaluation: Visual evaluation of the state of burr generation around the 300,000th punched hole. ◎: no burrs, ○: slight burrs but no burrs, Δ: several burrs, ×: frequent burrs Generating coating powder: ：: none, ○: slight but no burrs, △ : Adhered to the mold and sprinkled. Spread: ×: Adhered considerably to the mold and frequently impressed.

* 8. Paint corrosion resistance Non-painted oiled square cylinder press (50w x 50L x 50H [m
m]) Visual evaluation of the state of swelling of the coating film on the side surface of the processed part. CCT60 cycle (24hrs / cycle) SST6hrs → Lead 1hrs → Dry 70 ° C, RH60%, 4hr
s → Leaving 2 hrs ** → wet 49 ° C, RH 98%, 4hrs → Leaving 2hrs → Cooling -20 ° C, 4hrs → Leaving 1hrs
×: swollen over the entire surface * 9. Coating appearance (discoloration, visual evaluation of coating film defects) ◎: Homogeneous appearance, ○: Very slightly uneven pattern
△: Partially non-uniform, ×: Non-uniform overall

[0058]

As described above, the present invention meets the demand for a guard film free pre-coated steel sheet in the market.
The biggest issue is the resistance to pressure mark resistance of coatings (P resistance).
As a result of examining the compatibility between M-type) and punching resistance, a plating base plate controlled to a specific range of plating surface roughness based on the following technical concept was used as a substrate, and a specific metal By providing the coating, the adhesion of the chromate film to the base material and the change of the chromate film to the insoluble form by the metal film dramatically improve the adhesion of the coating film, which can stabilize the outstanding punching resistance to a high level. In addition, by simultaneously controlling the glossiness of the top coating composition and the back coating composition, the coating quality of non-guard film type prepainted precoated steel sheets at the industrial level without lowering other coating performance. It has been offered to the market. That is,

(1) By forming a specific metal film as a base film of the chromate film, the substrate adhesion of the upper chromate film is greatly improved, and at the same time, the chromate film is hardly soluble due to the formation of the metal film. As a result, the punching resistance of the prepainted steel sheet, which had been a problem, could be stably obtained (when punching by improving the adhesion between the chromate film and the coating film). Prevention of peeling of the coating film). (2) The aggregate in the coating film is limited to the resin particle type aggregate, and the elasticity is imparted to the coating film by specifying the particle size and the amount thereof. Abrasion has been suppressed and hole-penetration resistance to a steel sheet has been stably obtained (achieving punching resistance by suppressing mold wear). (3) The coil of the top coat is adjusted by adjusting the Tg of the top coat, optimizing the molecular weight of the resin and its combination, optimizing the melting point of the lubricant and its mix, and controlling the appearance of the back coat properly. Good pressure mark resistance can be stably obtained regardless of whether the product or the cut plate is loaded (achieving a non-guard film of a coating film by imparting PM resistance).

Continuation of the front page (51) Int.Cl. ⁷ Identification code FI B05D 7/24 302 B05D 7/24 302S 302V 303 303E B32B 15/08 B32B 15/08 GC23C 2/06 C23C 2/06 2/12 2 / 12 2/26 2/26 28/00 28/00 C C25D 15/02 C25D 15/02 G Q (56) References JP-A-4-2779 (JP, A) JP-A 5-169587 (JP, A JP-A-6-316772 (JP, A) JP-A-7-178870 (JP, A) JP-A-62-225569 (JP, A) JP-B 5-38071 (JP, B2) (58) Field (Int.Cl. ⁷ , DB name) B05D 7 / 14,7 / 24 B05D 3 / 10,5 / 00 C23C 2/04-2/12 C23C 2/26 C23C 28/00 C25D 15/02 B32B 15 / 08

Claims (2)

(57) [Claims] 1. The surface of a galvanized steel sheet or a hot-dip aluminum-coated steel sheet whose plating surface roughness is controlled to 0.5 μm in Ra, Ni, Co, Fe, Zr, Sb, V, M
3-5 metal films consisting of at least one of o and W
0 mg / m ² , and the upper layer is ^composed of Cr ³⁺
Is 10 to 50%, and a chromate composition comprising 0.5 to 2.0 of a gas phase silica having a primary average particle size of 3 to 50 μm in a total Cr amount ratio of 0.5 to 2.0 is formed as a total Cr adhesion amount of 10 to 150 mg / m ^2. After further forming a certain primer coating on the upper layer, the uppermost coating has a glass transition point (Tg) of 5 to 70 ° C. and an average molecular weight of 15,000 to 15,000.
50,000 melamine-curable high molecular weight polyester resin is 40 to 90% by solid content weight ratio, and organic resin particles having a primary average particle size of 2 to 50 μm which hardly fuse with this resin are 1 to 50% by solid content weight ratio as aggregate. And a melting point of 80 as a lubricant
Polyethylene wax at ~ 130 ° C is 1
A guard film-free type clarity precoated steel sheet having excellent punching resistance and coating film adhesion, characterized by forming a top coating film characterized by containing up to 5%. 2. A guard excellent in punching resistance and coating adhesion according to claim 1, wherein the surface glossiness of the back coating is controlled to at least 50 to 100% of that of the front top coating. A film-free, clear black pre-coated steel sheet.