JPH08174007A - Steel sheet excellent in image clarity after coating and manufacture thereof - Google Patents

Abstract

PURPOSE: To improve the image clarity of a steel sheet subjected to thin coating specified in the thickness of a coating film. CONSTITUTION: In the surface properties of the steel sheet, filtered center line waviness (the cutoff value of a low-pass filter is 0.8mm and the cutoff value of a high-pass filter is 2.5mm.) Wca is <=0.65, the number PC1 of peaks of >=1.0μm in height per inch of the filtered waviness curve (the cutoff value of the low-pass filter is 0.8mm.) is <=3 and the number PC2 of valleys of >=1.0μm in depth per inch is <=3. This steel sheet is manufactured by executing temper rolling of the steel sheet which is <=8 in the number PC2' of the valleys of >=2μm in the depth of the filtered waviness curve with the rolls whose filtered center line waviness Wca is <=1.5μm and which is <=8 in the number PC1* of peaks of >=2.5μm in height per inch and <=8 in the number PC2* of the valleys of >=2.5μm in depth per inch in the filtered waviness curve.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steel sheet for painting, which is used for outer panels of automobiles, home electric appliances and the like and has an excellent clearness on the surface of a coating film after painting, and a method for producing the same.

[0002]

2. Description of the Related Art In recent years, in fields such as automobiles and home electric appliances, in order to further stimulate consumers' willingness to purchase and differentiate from products of other companies, the coating surface after coating has a corrosion resistance or the like. In addition to performance, it has become important to manufacture products that satisfy consumers'"vividness" that can be directly visually appealed. In addition, "excellent image clarity" means that the diffused reflection on the coating film surface is small and the glossiness is excellent, and the image distortion is not generated on the coating film surface and the image clarity is excellent.

The image clarity is of course affected by the type of paint and the coating conditions, but is also greatly affected by the surface properties of the coating film. For example, if the degree of unevenness of the coating base is large, the coating film also has large unevenness, and as a result, not only the glossiness is impaired due to irregular reflection of light, but also distortion of the image is generated. If a surface smoothing treatment (for example, blasting) is applied in the process before painting, a product with far superior image clarity can be obtained compared to a dull-finished steel plate. Since it is rare and processed and used in most cases, such a surface smoothing treatment has a drawback that seizure occurs due to deterioration of oil retaining property and increase of contact area during processing.

Therefore, it is required to establish a method for treating the surface of a steel sheet and a method for evaluating the surface properties thereof in order to manufacture a steel sheet which retains a certain degree of workability and is excellent in the image clarity after coating.
In general, the surface roughness of a steel sheet was evaluated by the centerline average roughness Ra, but recently, “filtered centerline waviness: Wca (centerline average value of filtered waviness curve: JIS B 061
It is often evaluated as “0)”, and it is said that the larger Wca is, the more the amplitude after painting cannot be attenuated, and the sharpness is deteriorated.

For example, in Japanese Unexamined Patent Publication (Kokai) No. 62-230402, as a result of investigating the influence of the undulation wavelength component on the image clarity, it was found that a wave having a wavelength of less than 400 μm was not involved, and a roughness curve of the steel plate surface Wavelength included in
The swell component above should be minimized, but 400μ
It has been proposed to set the filter center line waviness, which is an index indicating the intensity of a wavelength component of m or more, to Wca ≦ 0.7 μm. Further, in JP-A-63-132728, the average roughness Ra ≦ 0.8 μm and the filtered center line waviness Wca ≦
It has been proposed to apply a predetermined amount of solid lubricant to the surface of the steel sheet after making it 0.7 μm, but in the case of thin film (less than 70 μm) coating in which the surface properties of the steel sheet as the coating base greatly affect Even after satisfying the above condition, the image clarity after coating was still insufficient, and it was not possible to properly evaluate the image clarity after coating from the value of Wca in thin film coating.

Due to the demand for cost reduction, it is currently particularly required to manufacture a steel sheet which retains a certain degree of workability even in the case of thin film coating and has excellent image clarity after coating. Therefore, based on the development of a steel sheet with a surface texture that can have excellent post-painting image clarity even in the case of thin film coating with a thickness of less than 70 μm, and the simple measurement of the surface texture of the steel sheet under actual operation in a factory. Establishment of quality evaluation index that can be evaluated by

As a quality evaluation index for thin film coating,
In Japanese Unexamined Patent Publication No. 4-37404, a three-dimensional roughness meter is used to detect a cross-section curve of the surface of a coating steel sheet, and the cross-section curve is Fourier transformed to obtain a frequency analysis curve. If the sum of the power spectra of the two wavelength regions of the image clarity wavelength region and the thin coating film sharpness wavelength region is calculated and this is small, the sharpness of the coated surface will be good not only for ordinary coating but also for thin coating steel sheets. It is taught that it can be evaluated as good.

However, the three-dimensional roughness meter has a long measuring time and is not suitable for actually being used as a quality evaluation index in a factory.

[0009]

SUMMARY OF THE INVENTION Therefore, the object of the present invention is to find a value which can be a proper quality evaluation index, especially in thin film coating, from the values obtained by the measurement which is simple and takes a short time. And

It is another object of the present invention to provide a steel sheet that satisfies the above-mentioned appropriate quality evaluation index and a method for manufacturing the steel sheet.

A further object of the present invention is to provide a steel sheet which can have a satisfactory post-painting image clarity even when a thin film is coated by using a paint and a coating method which have been conventionally used.

[0012]

As a result of earnest research, the inventor has found that, in addition to Wca, the number of peaks with a height of 1.0 μm or more per inch: PC1 and 1 of valleys with a depth of 1.0 μm or more. Number per inch: By introducing a new index that can be measured with two two-dimensional roughness gauges such as PC2, we obtained the knowledge that the image clarity after painting including thin film painting can be properly evaluated, and new The present invention has been completed by establishing a quality assurance index.

According to the present invention, the surface texture of the steel sheet is such that the filter center line waviness (the cutoff value of the low-pass filter is 0.
8mm, high-pass filter cutoff value 2.5mm):
Wca ≦ 0.65 Filtered waviness curve (cutoff value of low-pass filter 0.8
mm), the number of peaks with a height of 1.0 μm or more per inch: PC1
≦ 3 Number of valleys with a depth of 1.0 μm or more per inch: PC2
Provided is a steel sheet having excellent image clarity after coating, which is ≦ 3. This steel plate ensures good post-painting clarity even if it is a thin film coating having a film thickness of less than 70 μm.

The reason for limiting the numerical value of each index will be described below.

Wca: 0.65 μm or less. 0.6
This is because when the thickness exceeds 5 μm, satisfactory sharpness cannot be obtained no matter how the values of the other indexes are adjusted within the specified range, as shown in FIG.

PC1 and PC2 of the wave profile curve (cutoff value of the low-pass filter: 0.8 mm) were both set to 3 or less. When both exceed 3, as shown in FIG.
However, the number of valleys on the surface correlates with the leveling of the coating, and in the case of thick film coating, the valleys are not the paint. Although the influence of the buried valley portion is small, it is presumed that in the case of a thin film, the valley portion is not filled with the paint and the valley portion affects the surface after coating. It is presumed that the mountain portion remains on the surface after coating regardless of the coating film thickness and has a great influence on the image clarity.

The steel sheet according to the present invention has a depth of the waviness curve 2
The number of valleys (μm or more) per inch (PC2 ′) is 8 or less, and the center line waviness Wca of the filtered wave is 1.5 μm or less, and the height of the waviness curve is 2.5 μm or more per inch. It can be manufactured by temper rolling with a roll having a number (PC1 *) of 8 or less and a number of valleys having a depth of 2.5 μm or more per inch (PC2 *) of 8 or less.

The surface of the steel sheet before temper rolling must have PC2 'of 8 or less. When considering the transfer rate of the dull work roll roughness to the steel sheet by rolling at a light reduction, the valley of the waviness curve that can be filled (that is, suppressed) by the local plastic flow caused by rolling This is because the number is limited, and if PC 'exceeds 8, even if rolled, the valleys of the waviness curve remarkably remain on the surface of the steel sheet and the sharpness deteriorates.

The method of dull machining the work roll is not limited to a specific one, and various machining such as those using a high-density energy beam such as laser, plasma, electron beam in addition to shot blasting and electric discharge machining. Any method can be used, and a steel sheet having excellent image clarity after painting can be manufactured if the above-mentioned index is satisfied no matter which processing method is used to work with a work roll having a dull weight.

Further, in the present invention, regardless of whether the film thickness is less than 70 μm or more, the type and coating method of the paint which has been conventionally adopted for thick film coating having a film thickness of more than 70 μm is used as it is. it can.

[0021]

The following examples are merely illustrative and do not limit the scope of the invention.

1 of a valley with a depth of 2 μm or more in the wave profile
The number of peaks per inch (PC2 ') is 12 or less, and the height of the waviness curve is 2.5 µm or more and the number of peaks per inch (PC
1 *) is 12 or less and the number of troughs with a depth of 2.5 μm or more (PC2 *) is 11 or less and the thickness is 0.8 mm. Steel plate for automobiles (ordinary steel plate (CR), electricity) The plated steel sheet (SZ) and the hot-dip galvanized steel sheet (GA) were temper-rolled at a rolling reduction of 1.0% or more. Then, the quality assurance index (Wca, PC1, PC2) of the obtained steel sheet was measured. Then, the surface of the steel sheet was subjected to phosphate treatment, electrodeposition coating, and top coating. The total film thickness was 60 μm and 100 μm. Then, the obtained steel plate was measured with a mapping sharpness meter to obtain an NSIC value. In addition, NSIC (60) represents the image clarity after coating when the coating film thickness is 60 μm.
SIC (100) represents the image clarity after coating when the coating film thickness is 100 μm. For the NSIC value, the light intensity distribution of a rectangular wave pattern formed by reflection on the surface of a steel plate was measured, the spectrum was analyzed by Fourier analysis, and the sharpness was evaluated as the degree of "deviation from the rectangular wave" of the imaged pattern. Those having a value of 80 or more were passed (◯).

[0023]

[Table 1]

[0024]

EFFECTS OF THE INVENTION Not only ordinary coating but also thin film coating of less than 70 μm is excellent in sharpness as long as the surface properties of the steel sheet before coating satisfy all the above-mentioned indexes. It is easy and easy to measure whether or not the steel plate satisfies the above-mentioned index in a short time. Therefore, quality control under actual operation in a factory becomes easy.

[Brief description of drawings]

FIG. 1 shows a relationship between a quality index, particularly Wca, and image clarity.

FIG. 2 shows a relationship between a quality index, in particular, PC1 and PC2, and image clarity.

Claims (3)

[Claims] 1. The surface texture of a steel sheet is such that a filter center line waviness (cutoff value of a low-pass filter of 0.
8mm, high-pass filter cutoff value 2.5mm):
Wca ≦ 0.65 Filtered waviness curve (cutoff value of low-pass filter 0.8
mm), the number of peaks with a height of 1.0 μm or more per inch: PC1
≦ 3 Number of valleys with a depth of 1.0 μm or more per inch: PC2
A steel sheet having excellent image clarity after coating, which is ≦ 3. 2. The steel sheet having excellent post-painting image clarity according to claim 1, which is for a thinly coated steel sheet having a coating film thickness of less than 70 μm. 3. A steel plate in which the number of valleys (PC2 ′) per inch (PC2 ′) having a depth of a wave profile of 2 μm or more is 8 or less, a wave center line waviness Wca is 1.5 μm or less, and a height of the wave profile is high. Number of peaks of 2.5 μm or more per inch (P
The post-painting image reflection according to claim 1, wherein the C1 *) is 8 or less and the number of troughs having a depth of 2.5 μm or more (PC2 *) is 8 or less. A method of manufacturing a steel sheet with excellent properties.