JP2915192B2 - Evaluation method for thin coating metal plate and thin coating metal plate with excellent sharpness of thin coating film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for evaluating a metal sheet for thin coating for evaluating the sharpness of a coated film after thin coating on the surface of the metal sheet, and to the sharpness of a thin coated film. Method for accurately evaluating the coating sharpness of a metal plate after thin coating when the number of coatings is 2 or less or the total coating thickness is less than 80 μm, and the thin coating excellent in the thin coating coating sharpness described above It relates to a metal plate for use.

[0002]

2. Description of the Related Art Conventionally, a cold-rolled steel sheet as a representative example of a metal sheet for coating used for an automobile body and household electric appliances is:
Usually, it is manufactured by performing degreasing and washing after cold rolling, and further performing temper rolling after annealing. One of the purposes of this temper rolling is to give a moderate surface roughness to the steel sheet surface by performing light rolling using a finishing roll having a dull surface.

[0003] As described above, as a method of dulling the surface of a finishing roll, there have conventionally been known a method of shot blasting in which a shot is projected on the roll surface to perform dulling, and a method of discharging the roll surface by discharging in a working fluid. And a method by electric discharge machining in which a predetermined dull surface is obtained by melting and scattering the molten metal. In the case of dull finishing of finishing rolls by these methods, an irregular roughness profile unique to each dulling method is formed on the roll surface, so that the steel sheet surface after rolling is composed of irregular peaks and valleys. You. If such a steel plate is pressed, lubricating oil is stored in the valley to reduce the frictional force between the press die and the steel plate, facilitating the press work, and at the same time, by the frictional force with the die Press formability can be improved, for example, thin metal powder can be trapped in the valley to prevent seizure. On the other hand, the coating film and the steel plate can be firmly fixed to each other by causing an anchor effect of the coating film on the slopes of the peaks and valleys.

[0004] In recent years, the quality of the overall quality after painting can be directly and visually appealed to customers, not only for passenger cars but also for mini cars, wagons and trucks. Is an extremely important quality control item. By the way, there are various evaluation items for the painted surface. Among them, it is particularly important that the irregular reflection of the painted surface is low and the gloss is excellent, and that the mapping distortion is small, that is, that the image clarity is excellent.In general, these gloss and image clarity are generally combined. This is referred to as “coating film sharpness”. As a method of evaluating the sharpness of the coating film on the painted surface, conventionally, for example, JP-A-63-117206,
JP-A-61-217708, JP-A-62-10354
No. 4, JP-A-62-233712 has been proposed.

[0005] The type of coating and the coating method also have an effect on the sharpness of the coating film on the coated surface, but the surface roughness of a metal plate for coating as a base for coating also has a strong effect. In particular, when the coating film thickness is thin, specifically, when the number of coating times is 1 or 2 times, and when the total coating film thickness is less than 80 μm, the form of the surface of the metal plate for coating as a coating base is a sharpness of the coating film. Has a significant effect. That is, if the proportion of the flat portion of the metal plate surface occupies a small portion and the unevenness component having a large wavelength and amplitude increases, the unevenness increases even on the painted surface, and as a result, irregular reflection of light occurs and the glossiness is impaired, The distortion of the image is caused, thereby deteriorating the sharpness of the coating film. Therefore, when such a thin coating is actually performed, a middle sharpening of the coating film surface is required after the first coating, and there has been a problem that the cost increases in the actual coating process.

Therefore, it is necessary to evaluate the sharpness of the coating film from the microscopic morphology of the surface of the metal plate before coating.
It was evaluated by the method described in JISB-0601 (1982). In this method, among the microscopic forms on the surface of the metal plate, “filtering center line undulation (W _CA )” specified in JISB-0601 is used as an index for evaluating the sharpness of the coating film, and this value is small. The better the sharpness of the coating film, the better.

On the other hand, a steel sheet rolled by a finishing roll processed by shot blasting (hereinafter, referred to as a shot dull steel sheet) or a steel sheet rolled by a finishing roll subjected to electric discharge machining (hereinafter, referred to as a discharge dull steel sheet). In order to improve the sharpness of the coating film, the applicant of the present application has previously described Japanese Patent Publication No. 3-38.
923 has been developed and proposed a metal plate for coating described. This coating metal plate is obtained by dividing a high-density beam energy source such as a laser into short-pitch laser beam pulses by a chopper, and converting the laser beam pulse to a finishing roll A used for rotating temper rolling or the like.
Irradiated on the surface of the surface while moving it in parallel with the rotation axis of the finishing roll at a vertical angle or a close angle to the surface, a micro-shaped microconcavity consisting of a regular circular concave portion B and an annular convex portion C around it as shown in FIG. The craters F are regularly arranged at a predetermined arrangement pitch P, and the shape of the micro craters F is transferred to the surface of the steel plate D at the time of finishing press as shown in FIG. The annular groove is called a dull groove E (FIG. 8).

[0008] The laser dull steel sheet obtained in this way is, as compared with the conventional discharge dull steel sheet and shot dull steel sheet,
Asperity component on the steel sheet surface that deteriorates coating film sharpness, that is, a long wavelength (for example, 0.8 to 8.0 mm or 1.0 to 6.0 m)
m), the "surface roughness component" of the short wavelength (for example, 0 to 0.8 mm or 0 to 1.0 mm) is large while the "surface roughness component" is large. Since the shape of the groove can be arbitrarily set, and the number of the dovetail grooves per unit area which affects the surface waviness component or the flatness can be arbitrarily set, the press lubricity (press workability) can be improved. ) Has the advantage that the sharpness of the coating film can be improved while enhancing the anchor effect of the coating film.

On the other hand, each of the dull steel plates is replaced with the above-mentioned JISB-06.
When evaluated by the method specified in 01, since the long wavelength component and the short wavelength component cannot be cut by 100%, the value of “filtering center line undulation” is replaced by the short wavelength component, that is, “surface roughness component”.
In comparison with the shot dull steel plate and the discharge dull steel plate, the laser dull steel plate has a higher value of the "filtration centerline waviness" and is evaluated as having poor coating film sharpness. It was not possible to accurately compare and evaluate the sharpness of the coating film of a good metal sheet for dull coating.

[0010] For this reason, the present applicant has previously disclosed in Japanese Patent Application Laid-Open No. 3-23 / 1991.
No. 4301 proposes a method for accurately evaluating the coating film sharpness of various coating metal plates having different dulling methods, and a coating film excellent in coating film sharpness accurately evaluated by this evaluation method. A metal plate is proposed. This evaluation method detects a cross-sectional curve of the surface of the metal plate for coating, obtains a frequency analysis curve by Fourier-transforming the cross-sectional curve, and impairs the sharpness of the coating film that impairs the sharpness of the coated steel sheet. The wavelength range is set within the range of 1.0 to 6.0 mm in the wavelength in the frequency analysis curve, and the sum of the power spectra within the sharpness-inhibiting wavelength range is obtained, whereby the coating film sharpness of the coating metal plate is obtained. Is evaluated. Further, by limiting the sum of the power spectra to 0.5 μm ² or less, a metal plate for coating excellent in the sharpness of the coating film is obtained.

[0011]

According to the method for evaluating the sharpness of a coating film of a metal sheet for coating, according to the conventional coating method of three times or more or a total coating thickness of 80 μm or more,
The coating film clarity can be appropriately evaluated, and the coating metal plate thus properly evaluated is a coating metal plate which exhibits excellent coating film clarity at least in normal coating.

However, in the field of using a metal plate for coating, there is a demand for a reduction in the number of coatings and a reduction in the thickness of a thin coating film in order to reduce costs with the improvement of coating technology and coating film performance. However, even in the case of a coating metal plate that is evaluated to be good by the above-described evaluation method based on the power spectrum sum of the coating image sharpness inhibiting wavelength region, for example, a laser dull steel plate, the number of coating times is 2 times or less or the total coating film thickness. If the thickness is less than 80 μm (for example, a standard coating thickness of 30 μm or more and less than 80 μm), the influence of the microscopic morphology caused by the dull finish of the undercoating treatment of the coating metal plate appears on the painted surface. There is a problem in that traces of the dovetail groove appear on the surface of the coating film, which may impair the sharpness of the coating film.

Therefore, the present applicant has previously described Japanese Patent Application Laid-Open No. 3-161.
Oite No. 103, to regulate the form of micro-craters F during Rezadaru processing finishing rolls, thereby has been proposed a coated metal plate which regulates the shape of the dull eyes grooves, painted metal produced by this method Because the means for industrial measurement of the surface of the plate and the method for evaluating it have not been established,
There was a problem that sufficient quality evaluation could not be performed.

The present invention has been developed in order to solve the above-mentioned problems, and provides a quality evaluation index capable of appropriately measuring and controlling the surface shape of a coating metal plate by an industrial or practical measuring means. By determining, especially in a metal sheet for thin coating provided for thin coating with a coating number of 2 times or less or a total coating thickness of less than 80 μm, a thin coating metal sheet for accurately and appropriately evaluating the coating film sharpness An object of the present invention is to provide a thin coating metal sheet excellent in sharpness of a thin coating film, which is appropriately evaluated by the evaluation method and the above evaluation method.

[0015]

Means for Solving the Problems The present inventor has achieved the above-mentioned object, and has achieved a standard coating method, for example, a double coating method having a total coating thickness of 30 μm or more and less than 80 μm. A method for evaluating the sharpness of the coating film of a metal plate for thin coating and an excellent method in order to make the sharpness superior to or higher than the three-time coating which is a normal coating (coating with a total coating thickness of 80 μm or more). The frequency analysis obtained from the cross-sectional curves of the surface of the metal plate before painting and the surface of the thin painted film after painting as a result of intensive studies on the conditions that should be met by the thin painted metal plate showing the sharpness of the thin painted film We paid attention to the distribution of peak values appearing in the curve.
In particular, in a metal plate for thin coating in which microscopic uneven patterns are regularly arranged at a predetermined arrangement pitch, such as a laser dull steel plate, a large peak value of the frequency analysis curve is close to the arrangement pitch. It has been found that the groove diameter of the laser dull groove and a small peak value appear randomly up to around twice the arrangement pitch. Of these, the peak value of the frequency analysis curve appearing near the arrangement pitch is easily understood, but the peak value of the frequency analysis curve appearing near twice the arrangement pitch requires various evaluation experiments. did. As a result, for example, the grooves in the laser dull steel plate are often arranged in a staggered arrangement. Therefore, when a cross-sectional curve is detected in the staggered arrangement direction, the peak value of the cross-sectional curve itself is twice the arrangement pitch. It appeared every neighborhood, and it was perceived that the peak value of the above-mentioned frequency analysis curve appeared near the double value of the arrangement pitch under this influence. Therefore, as described above, at least in the sharpness of a thin coating film which is easily affected by the “surface roughness component”, the upper limit of the sharpness inhibition wavelength region is set to a value near twice the arrangement pitch. As a result, it has been found that the sharpness of the thin coating film can be evaluated. On the other hand, the “surface roughness component” of the cross-sectional curve falling within less than 200 μm of the frequency analysis curve is sufficiently smoothed by a thin coating film at least to such an extent that it cannot be visually distinguished by humans. It has also been found that it is sufficient to set the lower limit value of the wavelength range of the thin coating film sharpness inhibition. Further, a number of experiments were conducted on the correlation between the sum of the power spectrum in the wavelength range where the thin coating film sharpness was inhibited and various industrial evaluation values for the sharpness of the coating film. Power spectrum sum in the wavelength region of
If the thickness is set to not more than μm ² , in all of the thin coating specifications in which the experiment was conducted, no decrease in the sharpness of the coating film due to the trace of the dull groove occurs. It has been developed based on these findings of the present invention.

That is, according to the method for evaluating a metal sheet for thin coating according to the first aspect of the present invention, fine irregularities are regularly arranged at a predetermined arrangement pitch on the surface of the metal sheet for thin coating. No more than 2 coatings or a total coating thickness of 80 on the metal plate surface
In the method for evaluating a thin-painted metal plate used by applying a thin coating of less than μm, a cross-sectional curve of the surface of the thin-coated metal plate is detected, and the cross-sectional curve is subjected to Fourier transform to obtain a frequency analysis curve. The wavelength range in the frequency analysis curve is equal to or greater than a predetermined lower limit and the upper limit in the vicinity of a double value of the disposition pitch is defined as a thin coating film sharpness inhibiting wavelength range that inhibits the sharpness of the metal plate after the thin coating. By setting the range below the value, and by calculating the sum of the power spectrum of this thin coating sharpness inhibition wavelength range,
The present invention is characterized in that the sharpness of a coating film of the metal sheet for thin coating is evaluated.

In the method for evaluating a metal sheet for thin coating according to claim 2 of the present invention, the total coating thickness of the thin coating is preferably 30%.
When the thickness is not less than μm and less than 80 μm, the lower limit value of the wavelength range for inhibiting the sharpness of the thin coated coating film is set to 200 μm. In the present invention, the metal plate for thin coating excellent in sharpness of the thin coating film according to claim 3 has fine irregularities regularly arranged on the surface of the metal plate at a predetermined arrangement pitch, A thin coating metal plate used by applying a thin coating having a coating number of 2 times or less or a total coating thickness of less than 80 μm on at least the surface of the metal plate, and obtained by performing a Fourier transform on a cross-sectional curve of the surface of the metal plate. The thin paint coating which inhibits the sharpness of the metal plate after the thin coating, wherein the wavelength in the frequency analysis curve is set within a range of not less than a lower limit value of 200 μm and not more than an upper limit value near twice the arrangement pitch. The sum of the power spectra in the wavelength range of inhibition of film sharpness is 1.0 μm ² or less.

[0018]

As the metal sheet for thin coating used in the method for evaluating a metal sheet for thin coating of the present invention, for example, a laser dull steel sheet is preferable. This laser dull steel plate is temper-rolled by finishing rolls in which micro craters F are regularly arranged in a square arrangement or a staggered arrangement on the surface at a predetermined arrangement pitch by a high-density beam energy source such as a laser. The form of F is transferred to the surface as the ridge groove E. Accordingly, the arrangement pitch P and the diameter D of the dull groove E mainly affect the wavelength of the cross-sectional curve of the steel sheet surface, and the depth H of the dull groove E mainly affects the amplitude of the cross-sectional curve of the steel sheet surface. give.

The thin coating in the method for evaluating a metal sheet for thin coating according to the present invention is defined as a coating having a total coating thickness of 2 times or less or a total coating thickness of less than 80 μm. 30 μm or more and less than 80 μm. In the method for evaluating a metal sheet for thin coating according to the present invention, first, an input signal indicating an irregular random waveform of the surface shape of the metal sheet for thin coating such as the laser dull steel plate, that is, a random variation with respect to the time axis. A Fourier transform is performed to decompose the signal into amplitude levels for each frequency, and a frequency analysis curve obtained by displaying this is created as a power spectrum diagram showing a waveform of unevenness formed on the surface of the metal plate.

Next, the wavelength range of the thin coating paint film sharpness inhibition wavelength region which inhibits the paint film sharpness of the metal plate after the thin coating is determined by setting the wavelength in the above-mentioned frequency analysis curve (power spectrum diagram) to a lower limit of 200 μm or more. In addition, it is set in a range not more than a predetermined upper limit value in the vicinity of twice the arrangement pitch P. Then, the power spectrum in the wavelength region where the thin coating film sharpness is impaired is integrated to obtain a power spectrum sum.

This thin coating film has a wavelength range in which sharpness is impaired, ie, 2
The sum of the power spectra in the wavelength range of not less than 00 μm and not more than about twice the arrangement pitch becomes smaller as the amount of the surface roughness component of the metal plate for thin coating decreases. However, on the other hand, since this surface roughness component is also a component for improving press workability, it is preferable that a certain degree of surface roughness component be present. This means that in the wavelength range of the thin coating paint film sharpness inhibition, there is a surface roughness component of a specific wavelength that is a press workability improving component, but if the presence of these components is too large, after thin coating. This means that a mixture of microscopic irregularities on the surface of the metal plate remains on the coating film surface, which impairs the sharpness of the coating film.

Accordingly, the smaller the sum of the power spectra in the wavelength region where the thin coating film sharpness is inhibited, the better the sharpness of the coating film after thin coating. It is possible to accurately compare and evaluate the sharpness of the thin coating film. In the present invention, since the power spectrum sum is obtained from the integrated value of the power spectrum diagram, 100% of the power spectrum within the thin coating paint film sharpness inhibition wavelength region is taken in, and conversely, the power spectrum within the other wavelength region is taken. Since a certain power spectrum can be completely removed, only the above-mentioned thin paint film sharpness inhibitory component is added to the sum of the power spectra, so that the paint sharpness after thin paint is accurately determined for each metal plate. Can be evaluated.

The reason why the lower limit of the thin coating film sharpness inhibition wavelength range is set to 200 μm in the power spectrum diagram is that even if a peak value exists in the power spectrum diagram below this range, the current value is not changed. This is because, after the thin coating, the uneven surface which hinders the sharpness of the coating film cannot be perceived almost as human vision. In the metal sheet for thin coating excellent in sharpness of the thin coating film of the present invention, the power spectrum sum of the thin coating film sharpness inhibiting wavelength region needs to be 1.0 μm ² or less. . This power spectrum sum is 1.0
If it exceeds μm ² , many irregularities are present in the wavelength range of the thin coated film sharpness inhibition on the surface of the metal plate before thin coating, and these improve the press workability, but the sharpness of the coated film in thin coating is improved. Is to inhibit

[0024]

FIG. 1 shows the configuration of an apparatus for evaluating a metal sheet for thin coating according to the present invention. In this example, a laser dull steel plate is used as a thin coating metal plate sample to be evaluated. This laser dull steel plate is obtained by, for example, subjecting a cold rolled thin steel plate D to a bright finish, and then performing a skin pass rolling treatment using a laser dull finish roll A having a roll surface as shown in FIG. A dull groove E having a predetermined diameter D is regularly arranged in a staggered arrangement at a predetermined arrangement pitch P in the background, and the top G of the hill surrounded by the dull groove E is also substantially flat.

The finishing roll has a regular roughness profile roll surface in which micro-craters F having a predetermined diameter and a predetermined depth as shown in FIG. 6 are provided in a staggered arrangement at a predetermined pitch P. Such dulling of the finishing roll is performed by irradiating the surface of the rotating finishing roll with a laser beam pulse cut by a chopper while moving in the axial direction of the finishing roll at an angle close to or perpendicular to the finishing roll. This is accomplished by fusing the surface of the roll to form microcraters of a predetermined pitch, depth, and diameter.

For this reason, at the time of laser dulling on the finishing roll, by controlling dulling conditions such as a laser beam pulse interval and beam energy, the arrangement pitch, depth, and depth of the micro crater F formed on the surface of the finishing roll are controlled.
And the diameter can be controlled, so that it is possible to control the wavelength and amplitude of the cross-sectional curve of the surface of the laser dull steel sheet using the finishing rolls in which these are adjusted.

In general, a laser dull steel sheet has less irregularities on the surface of a steel sheet which deteriorates the sharpness of the coating film of a normal coating than a conventional discharge dull steel sheet or a shot dull steel sheet, but has a better press formability improving component. However, this component for improving press formability can also be a component for inhibiting the sharpness of a thin coating film. Therefore, in the evaluation method of the present invention for collecting the cross-sectional curve of the surface of the metal plate for thin coating, the laser dull steel plate D capable of controlling the arrangement pitch P and the diameter D of the dull groove E is to be evaluated. It can be said that it is preferable. In this embodiment, as shown in FIG. 8, the arrangement pitch P of the grooves D is set to 290 μm, and they are shifted from each other by ピ ッ チ pitch for each row to form a staggered arrangement.

In FIG. 1, a metal plate sample 10 for coating made of the laser dull steel plate D is placed on a metal plate sample fixing stand 11 of a stylus type roughness meter 1 or the like. The stylus 12 of the stylus-type roughness meter 1 comes in contact with the metal plate sample 10 and includes a dull groove E formed on the surface of the sample 10.
By scanning the surface, a random waveform corresponding to the cross-sectional curve of the surface of the metal plate sample 10 is output.

This random waveform is input to the three-dimensional surface shape measuring device 2 and is converted into a voltage signal. This voltage signal is subjected to fast Fourier transform by the frequency analyzer 3 to create a frequency analysis curve composed of a power spectrum diagram.
The power spectrum diagram is decomposed and quantified by the microcomputer 4 into an integrated value between wavelength ranges according to the purpose, that is, a power spectrum sum, and the result is displayed on the display device 5.

The stylus 12 is configured to be movable with respect to the sample fixing table 11, and as shown in FIG.
After scanning the stylus 12 in the (axis) direction, the X
The stylus is moved in the horizontal axis (Y-axis) direction orthogonal to the axis, and this is repeated, thereby scanning the dovetail groove E formed on the sample surface.

Therefore, the frequency analysis device 3
An irregular waveform of the surface shape obtained by the two-dimensional surface shape measuring device 2, that is, an input signal showing a random fluctuation with respect to the time axis is decomposed into an amplitude level for each frequency by a fast Fourier transform and displayed, and the power is calculated. A spectral diagram will be obtained. This power spectrum diagram is obtained by mathematically converting a time axis signal into a frequency axis, and the vertical axis is a power spectrum in which the amplitude is displayed in a level with respect to the frequency axis from a random waveform. Therefore, this power spectrum diagram can capture 100% of the amplitude level in the target wavelength range.

According to the present invention, a predetermined storage area in the memory of the microcomputer 4 has a thin paint film sharpness inhibiting wavelength which impairs the thin paint film sharpness as shown in FIG. The lower limit value L _{U is} equal to or more than the lower limit value L _L = 200 μm and is about twice the arrangement pitch P of the dull groove E.
It is set in the following range. In the case of a coating metal plate in which the ridges E are staggered like the laser dull steel plate D of this embodiment, when the cross-sectional curve of the surface of the laser dull steel plate D is collected, the scanning direction is, for example, the X-axis in FIG. Or, when it is parallel to the Y-axis direction, that is, the direction in which the
It is preferable to perform several parallel scans in a range of at least twice the arrangement pitch of the dovetail groove E and use a cross-sectional curve crossing the dovetail groove. This means that at least the unevenness profile of the laser dull steel plate has been detected in all directions, and therefore the upper limit of the thin coating paint film sharpness inhibition wavelength region, which is the main feature of the present invention, is set to be close to twice the arrangement pitch. The set effect is exhibited. That is, what the upper limit L _U wavelength twice value near the arranged pitch, since the upper limit of the peak value in the power spectrum diagram of the surface roughness components, power spectral line below the upper limit L _U In order to obtain the figure, it is necessary to detect the uneven profile in all directions as described above. Since in this embodiment the arrangement pitch P is 290 [mu] m, the upper limit L _U 585
It is set to μm. On the other hand, 200 [mu] of the thin coating paint film distinctness of image inhibitory wavelength band power spectrum diagram the lower limit L _L of
The reason for setting m is that even if there is a peak value in the power spectrum diagram below this, it is not possible to perceive the unevenness trace that hinders the sharpness of the coating film almost as a human eye after thin coating. It is. Therefore, the wavelength range for inhibiting the sharpness of the thin coated coating film is set in the range of 200 μm or more and 585 μm or less.

The microcomputer 4 calculates and outputs the power spectrum sum of the power spectrum diagram in the wavelength range of the thin coating film sharpness inhibition. The sum of the power spectra thus obtained does not include the undulation component on the steel sheet surface which usually impairs the sharpness of the coating film of the coating and the component which is almost disappeared by the thin coating of less than 200 μm. Here, an example of a power spectrum diagram and an example of a power spectrum sum calculation unit performed in the evaluation apparatus will be described.
This will be described based on the flowchart shown in FIG. For example, when the measuring direction is set in the X-axis direction shown in FIG. 8, 60 cross-sectional curves having a length of 40.96 mm in the X-axis measuring direction are collected at a pitch of 50 μm in the Y-axis direction. Next, for example, in step 1, the data pitch in the X-axis measurement direction is read as digital data of 4096 points per cross-sectional curve, and then the process proceeds to step S2, where the minimum value is added to the cross-sectional curve represented by this digital data. The slope correction is performed by the square method, and the two-dimensional average amplitude spectrum distribution of the 60 cross-sectional curves is obtained by linear addition. Next, the process proceeds to step S3, and a power spectrum diagram as shown in FIG. 3 can be obtained by obtaining a sum of squares of power for each wavelength (each frequency) in the amplitude spectrum distribution.
Here, since each frequency component of the amplitude spectrum is composed of a real part and an imaginary part, it is necessary to calculate each sum of squares in order to obtain the sum of squares of the power of each component. The real part of X _k is R _e (X _k ), and the imaginary part is _{Im
Assuming that} (X _k ), the k-th power spectrum P _k is represented by P _k = | X _k | ² = { _Re (X _k )} ² + {I _m (X _k )} ² .

Then, the process proceeds to step S4, and the power spectrum sum is obtained from the power spectrum diagram by using the sum of the respective wavelength components in the wavelength range of the thin coating film sharpness obstruction as an integral value. That is, by dividing the data of the cross-sectional curve as described above, the frequency component X _k (k of the amplitude spectrum falling within the range L _L = 200 μm to _{L U} = 585 μm of the thin coating film sharpness inhibition wavelength range. = 0, 1, 2, ...
.. N) are given as discrete values, so that the power spectrum P _k is also given as discrete values, so that the power spectrum sum PS in this range is Given by

Incidentally, the amplitude spectrum X has a frequency
When given as a continuous function X = f (λ) with respect to λ
Has the power spectrum P as a continuous function P = | f
(Λ) | ^TwoGiven as
Power in the range of 200-585 μm
The spectral sum PS isGiven by

Then, the process shifts to step S5 to output these calculation results to the display device 5 and ends the program. As described above, the range of 200 μm to 585 μm of the thin coating paint film sharpness inhibition wavelength range is a normal surface roughness component, and at the same time, a trace of a concavo-convex profile that can be grasped as human vision without being buried even by a thin coating. Represents
And since it is a wavelength range of a concavo-convex profile which cannot be forcibly applied even by press working and corresponds to a normal surface waviness component, if the power spectrum sum PS in this range is somewhat small, the coating film sharpness becomes good. . Therefore, the range of the wavelength range of the thin coating film sharpness inhibition 200 μm to 58 μm
By using the power spectrum sum PS at 5 μm, the sharpness of a thin coating film can be properly evaluated.

In the metal plate for thin coating of the present invention having excellent thin coating film sharpness, the power spectrum sum PS in the range of 200 μm to 585 μm of the thin coating film sharpness inhibiting wavelength range is 1. The condition is set to 0 μm ² or less. The reason will be described with reference to a preferred embodiment. First, a cross-sectional curve of the original surface of a laser dull steel plate having various uneven profiles is obtained as described above, and the laser dull steel plate is subjected to normal thin coating and normal coating by various coating methods, and the coated film surface after coating is obtained. Are obtained in the same manner as described above, and these cross-sectional curves are obtained as described above by using (a) frequency range 3150 μm to 585
μm, (b) frequency range 585 μm to 200 μm, (c)
The frequency band was divided into three wavelength ranges of 200 μm to 25.6 μm, power spectrum diagrams were obtained, and the respective power spectrum sums PS were calculated. FIG. 4 shows the results. Each division number corresponds to the wavelength range. In addition,
The left and right sides of the center line in these figures show that the measurement of laser dull steel plates of fundamentally different plate materials was performed.

As is apparent from these figures, in the wavelength ranges (a) and (c), the sum of the power spectrum on the surface of the original plate and the sum of the power spectra on the surface of the coating film after thin coating and after normal coating are obtained. It is recognized that there is a correlation between the power spectrum sums of the original plate surface, for example, above and below a predetermined boundary value of the sum of the power spectra of the original plate, and a clear difference in the sum of the power spectra of the coating surface after both coatings. Absent. On the other hand, in the wavelength range (b), it is not recognized that there is still a correlation between the power spectrum sum of the surface of the original plate and the power spectrum sum of the surface of the coating film after the normal coating. Between the sum of the spectra and the sum of the power spectra of the coating surface after thin coating, the sum of the power spectra of the coating surfaces after both coatings is clearly above and below a certain boundary value of the power spectrum sum of the original plate surface. It is recognized that there is a clear correlation that significant differences occur.

This is because, for example, in the wavelength range (a), since the frequency range is twice or more the arrangement pitch of the dull grooves, the surface of the laser dull steel plate is rather flat. It can be said that this is because the undulating component has a greater effect, and therefore does not affect the sharpness of the coating film after the thin coating or after the normal coating. In addition, the undulation component may be smoothed by press working, and from such a meaning, it can be said that there is no influence on the sharpness of the coating film.
On the other hand, in the wavelength range (c), the frequency range is a range in which the surface roughness is considerably small even among the surface roughness components. It can be said that the unevenness profile caused by the surface roughness is buried and dumped depending on the film thickness.

Therefore, the wavelength range of (b), that is, the wavelength range of 200 μm in this example, which is the wavelength range in which the thinness of the coating film sharpness is inhibited.
In order to quantitatively evaluate the sharpness of the coating film after thin coating at 通常 585 μm, the following four sharpness evaluation methods were used for the sum of the power spectra obtained from the cross-sectional curves of the thin coating film surface. The respective evaluation values are shown in FIG. Among them, the one shown in FIG. 5a is a NSIC-type image sharpness measuring instrument (manufactured by Nippon Paint Co., Ltd. and Suga Test Instruments Co., Ltd.).
Values (evaluation index for smoothness) and * NSIC (evaluation index for glossiness).
Measure the light intensity distribution of the rectangular wave pattern imaged through the reflection from the sample surface, analyze it by Fourier spectrum analysis,
This is an index for evaluating the degree of “deviation from the rectangular wave” of the imaging pattern as sharpness. Also, what is shown in FIG.
This is a DOI value measured by a DORIGON clarity gloss meter (manufactured by Hunter Associates Laboratories, USA). The DOI value is incident on the sample surface at an incident angle of 30 °, and the specular reflected light intensity R _e And ± 0.
The scattered light intensity R _0.3 at 3 °, an evaluation index of image clarity represented by the DOI value (%) = 100 × (R e -R 0.3) / R e. The one shown in FIG. 5c is a PGD meter (PORTABLE G
5 shows the PGD value obtained by the LOSS AND DISTINCTION METER).

As is apparent from these figures, the results obtained by any of the measurement methods usually show that the power spectrum sum of the power spectrum diagram obtained from the cross-sectional curve of the coating surface after thin coating is 0.004 μm ² or less. , NSIC value about 70
Above, * NSIC value about 50 or more, DOI value about 85 or more,
The PGD value is about 0.9 or more, indicating good coating film sharpness. However, when the power spectrum sum PS is larger than 0.004 μm ² , the DOI value, NSIC value, * NSIC value, P
It can be seen that all the GD values sharply decrease, and the sharpness of the coating film deteriorates.

Accordingly, in FIG. 4B, (b) the boundary value of the sharpness of the coating film after the normal thin coating in the wavelength region is set to the power spectrum sum PS = 0.004 μm ² , and the normal thin coating separated above and below the boundary is set. When the boundary value of the power spectrum sum PS obtained from the cross-sectional curve of the previous original plate surface is obtained, it is recognized that the boundary value of the power spectrum sum PS obtained from the cross-sectional curve of the original plate surface is 1.0 μm ^2. If the power spectrum sum PS obtained from the cross-sectional curve of the original plate surface is 1.0 μm ² or less, the power spectrum sum P obtained from the cross-sectional curve of the coating film surface after the ordinary thin coating is obtained.
It is recognized that S is also 0.004 μm ² or less.

For the above reasons, in the metal sheet for thin coating of the present invention having excellent sharpness of the thin coating film, the sum of the power spectrum in the wavelength region where the thin coating film sharpness is inhibited is 1.0 μm.
Set to ² or less. Therefore, when the laser dull steel plate is manufactured, the specifications such as the form and shape of the micro crater on the surface of the finishing roll are controlled. A change also occurs in the shape of the groove. However, according to the present invention, by evaluating the sharpness of the coating film after thin coating from the surface shape of the laser dull steel sheet, or by managing the laser dull steel sheet that satisfies the evaluation value, the use limit of the finishing roll can be reduced. It is possible to suitably manage and prevent occurrence of defective products in advance.

In the above embodiment, the stylus-type roughness meter was used as the data collecting means of the three-dimensional surface profile measuring device.
As this data collection means, for example, a non-contact laser reflection type roughness meter which can irradiate a laser to the surface of the metal plate and obtain a cross-sectional curve of the surface from the reflected light can be used. If this is the case, it is possible to obtain a more accurate and quick cross-sectional curve. Therefore, the evaluation method of the present invention can be easily carried out, and a metal sheet for thin coating satisfying the evaluation method can be easily produced.

[0045]

As described above in detail, according to the method for evaluating a thin metal plate for coating according to the present invention, the wavelength of the wavelength in the frequency analysis curve obtained by Fourier transforming the cross-sectional curve of the surface of the metal plate for coating is determined. By setting the range of the lower limit value of 200 μm or more and the upper limit value near the double value of the arrangement pitch of the concavo-convex pattern to the upper limit value of the thin coating film sharpness inhibition wavelength region, by using the power spectrum sum of the wavelength region, It is possible to accurately evaluate the sharpness of the coating film after the thin coating.

According to the metal sheet for thin coating of the present invention having excellent thin coating film sharpness, the sum of the power spectrum of the thin coating film sharpness inhibiting wavelength region is set to 1.0 μm ² or less. This makes it possible to quantitatively measure the sharpness of the coating film after the thin coating, thereby facilitating product management. In particular, in the laser dull steel plate, when the roll finishing roll surface for the temper rolling process is subjected to laser dull processing, micro-rolls formed on the roll surface by controlling processing conditions such as laser beam pulse intervals and laser beam energy. Since the form and shape of the crater can be easily controlled,
It is possible to control the power spectrum sum in the thin coating paint film sharpness inhibition wavelength region, and to stabilize a constant and high quality coating metal plate by managing the finishing roll on which the micro crater is formed. Can be supplied.

[Brief description of the drawings]

FIG. 1 is a configuration diagram illustrating an example of an evaluation apparatus that implements a method for evaluating a metal sheet for thin coating according to the present invention.

FIG. 2 is a flowchart showing a program processed by the evaluation device of FIG. 1;

3 is an explanatory diagram of a frequency analysis curve obtained by the program of FIG. 2 and a power spectrum sum thereof.

4 is an explanatory diagram showing a distribution state of a power spectrum sum obtained from the frequency analysis curve in FIG. 3 in each frequency range of the curve.

FIG. 5 is an explanatory diagram showing evaluation indexes of coating film sharpness after thin coating in a wavelength range of 200 to 585 μm in FIG. 4;

6A and 6B show a micro crater formed on the surface of a finishing roll, wherein FIG. 6A is a longitudinal sectional view and FIG. 6B is a bottom view.

FIG. 7 is a longitudinal sectional view showing a state where the micro crater of FIG. 6 is transferred to a steel plate.

8A and 8B show a laser dull steel plate in which the micro craters of FIG. 6 are transferred as dull grooves, wherein FIG. 8A is a plan view and FIG. 8B is a longitudinal sectional view.

[Explanation of symbols]

 1 is a stylus type roughness meter 2 is a three-dimensional surface shape measuring device 3 is a frequency analyzer 4 is a microcomputer 5 is a display device 10 is a metal plate sample for thin coating A is a finishing roll B is a circular concave C is an annular convex Part D is steel plate E is dull groove F is micro crater

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification symbol FI // B23K 26/00 B23K 26/00 J

Claims (3)

(57) [Claims] 1. A thin metal plate for thin coating, wherein fine irregularities are regularly arranged at a predetermined arrangement pitch on the surface of the metal plate for thin coating, and at least two coatings or less of a total coating thickness of less than 80 μm on the surface of the metal plate. In the method for evaluating a thin-painted metal plate used by applying a coating, a cross-sectional curve of the surface of the thin-coated metal plate is detected, and the cross-sectional curve is subjected to a Fourier transform to obtain a frequency analysis curve. The wavelength range in the frequency analysis curve is equal to or more than a predetermined lower limit and equal to or less than an upper limit in the vicinity of a double value of the arrangement pitch, in a thin coating film sharpness inhibiting wavelength range that inhibits the sharpness of the metal plate. By determining the power spectrum sum of this thin coating sharpness inhibition wavelength region, the method for evaluating a thin coating metal plate is characterized by evaluating the coating film sharpness of the thin coating metal plate. . 2. The method according to claim 1, wherein when the total coating thickness of the thin coating is 30 μm or more and less than 80 μm, the lower limit of the wavelength range of the thin coating coating sharpness inhibition is set to 200 μm. 3. The method for evaluating a metal sheet for thin coating described in 1. 3. A fine unevenness is regularly arranged on a surface of a metal plate at a predetermined arrangement pitch, and at least the metal plate surface is subjected to a thin coating less than twice or less than 80 μm in total coating thickness. A thin metal plate used for thin coating, wherein the wavelength in a frequency analysis curve obtained by Fourier transforming a cross-sectional curve of the surface of the metal plate is not less than a lower limit value of 200 μm and an upper limit value in the vicinity of twice the arrangement pitch. The power spectrum sum of the wavelength range of the lightness of the thin coating paint film that inhibits the sharpness of the metal plate after the thin coating, which is set within the range of the value or less, is 1.0 μm.
A thin coating metal sheet excellent in sharpness of a thin coating film characterized by being ² or less.