JPH07103741A - Method for quantifying roughness of gloss surface - Google Patents

Abstract

PURPOSE:To obtain an objective evaluation value matched to man's senses without constituting an apparatus strictly, by photographing a sample surface from vertically above while illuminating the sample surface by means of a light slantwise, and processing an obtained signal of a bright-and-dark distribution through a frequency analysis. CONSTITUTION:A surface of a sample S set on a sample stage 2 is irradiated through a slit 5 by a light from a light source 3 passing through an optical fiber flux 4. The sample surface is illuminated slantwise by a lower half of the luminous flux. A dark-and-bright image along a line on the sample surface parallel to the slit 5 is photographed by a camera 6 from vertically above at a position slightly retreated from a position where a lower side of the luminous flux crosses the sample surface. An output of the camera 6 is stored in a memory 7 and also displayed at a monitor screen 8. A data-processing device 9 obtains data of a spectral distribution of frequencies of the dark-and-bright image by Fourier-transforming a video signal. When a ratio of an area of a high frequency region on the spectrum to that, of an intermediate frequency region is obtained, a quantitative result with good reproducibility not influenced by a change of the illuminating direction or photographing position is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a so-called "pimple" of glossy paper or the like, that is, a method for quantifying the degree of irregular and gentle macroscopic unevenness of the glossy surface or the local inclination of the surface.

[0002]

2. Description of the Related Art Tack paper is a glossy paper in which a glossy sheet is attached to the paper surface, but irregular fine waviness is observed. Since it is ideal that the surface of glossy paper be smooth like a mirror, various efforts have been made to reduce the waviness as described above, but it is important to properly evaluate the effect to improve the manufacturing process and quality. It is also important for management. However, conventionally, the evaluation of the corrugated unevenness has been performed only by ranking by visual inspection.

[0003]

SUMMARY OF THE INVENTION The present invention is intended to quantify and display the degree of unevenness or local inclination of a glossy surface of glossy paper or the like. At this time, the result of the quantification should be consistent with the conventional visual judgment.

[0004]

[Means for Solving the Problems] A sample surface is irradiated with light from an oblique direction, the irradiated sample surface is imaged from a vertical direction, and the obtained distribution signal of brightness and darkness is subjected to frequency analysis to determine the frequency and the amplitude of the brightness and darkness. Relationship, that is, light and dark spectrum data, and in this spectrum, the quantitative value of the unevenness of the sample surface is determined by the ratio of the area of the constant frequency range of the high frequency range to the area of the other constant frequency range of the intermediate frequency range. .

[0005]

By obliquely irradiating the sample surface, the light and dark due to the unevenness of the sample surface is emphasized, and it becomes easy to obtain data in which the unevenness is converted into light and dark. The unevenness of the sample surface is distributed from low frequency to high frequency, but the frequency that human eyes perceive as unevenness is in the middle range, and the low light-dark cycle is felt as the bending of the sample surface, and it is against the high frequency light and dark. Does not feel unevenness. Therefore, in the light-dark spectrum obtained by frequency-analyzing the light-dark signal, it seems that the light-dark amplitude in the intermediate frequency range may be used as the quantitative value of the unevenness, but since the oblique irradiation is performed, the light-dark amplitude is the irradiation angle. Change sensitively depending on the change in the image, and also change depending on the imaging position such as along which line on the sample surface the image is picked up. Therefore, the absolute value of the light and dark amplitude in the intermediate frequency range cannot express the absolute value of unevenness. . However, since the high frequency region and the intermediate frequency region are affected by the irradiation direction and the imaging position in the same manner, by taking the area ratio of the high frequency region and the intermediate frequency region on the spectrum, Therefore, quantitative results with good reproducibility that are not affected by changes can be obtained.

[0006]

FIG. 1 shows an example of an apparatus for carrying out the method of the present invention. A sample stage 1 freely moves the sample table in the x and y2 directions. The sample S is placed on the sample table 2. Reference numeral 3 is a lamp of a light source, and the light is guided to an irradiation slit 5 through an optical fiber bundle 4 and emitted from the slit 5 to the sample surface. The light emitted from the slit 5 is a light beam whose central ray is parallel to the sample surface and spreads up and down in the range of 30 °, and the sample surface is obliquely illuminated by the lower half part of this light beam, as shown in FIG. 1B. As described above, at the position where the lower side of this light flux is retracted by 1 to 2 cm from the position where the lower side of the sample surface is cut, a bright-dark image along the line on the sample surface parallel to the slit 5 is captured by the camera 6 vertically above the sample surface. The image pickup device set in the camera 6 is a one-dimensional image sensor, and the output thereof is stored in the image memory 7. The stored one-dimensional video signal is displayed on the monitor screen 8. A data processing device 9 performs data processing on the video signal stored in the image memory 7 and displays the result.

The data processing device performs data processing as described below. The image memory stores bright and dark video signals along one line on the sample surface. This is shown in Figure 2A. In this figure, the light-dark distribution is moderately high because the illuminance of the irradiation light is low near both edges of the sample. Figure 2A
By performing Fourier transform on the video signal shown in (1), light-dark frequency distribution data, that is, light-dark frequency spectrum distribution data is obtained. This spectrum is shown in FIG. 2B. Looking at this spectrum on various papers, the light and dark amplitudes at low frequencies are large, and the high frequency range (3 mm in terms of wavelength)
In the above), it has been found that the same tendency that the amplitude distribution becomes constant is shown. Then, it was found that the difference between the bright and dark amplitudes in the intermediate frequency range (6 to 3 mm wavelength range) was large between the one having a large number of irregularities and the one having a small number of irregularities. Therefore, in the spectrum shown in FIG.
The ratio of the area D in the wavelength range of 6 to 3 mm to the area H in the 0.6 mm range is calculated and displayed as the degree of unevenness. That is, the degree of unevenness = D / H.

The correspondence between the degree of unevenness obtained as described above and the rank classification of the same sample by visual judgment is shown below. The sample is cast paper, and the degree of unevenness in visual observation increases from A to D. As a control, the results for high-quality paper (no gloss treatment, visual rank A) are also shown. Visual evaluation DH D / HA A 24899 32125 0.775 B 36845 29567 1.25 C 46912 28165 1.66 D 47105 26232 1.8 Fine quality 100231 158352 0.633 From this result, the evaluation value by the method of the present invention is human sense. It turns out that it agrees well with the physical evaluation.

[0009]

According to the present invention, by taking the ratio of the area of the high frequency region of the spectrum and the area of the intermediate frequency region, it is possible to obtain stable results without the need to make the device structure strict. Since the method is easy to carry out and the measurement results are in good agreement with the visual evaluation, it is possible to obtain an evaluation value that is stable and objective with respect to the unevenness of the glossy surface and that matches the human sense.

[Brief description of drawings]

FIG. 1 is a perspective view of an example of an apparatus for carrying out the method of the present invention.

FIG. 2 is a graph of measurement results obtained by the above device

[Explanation of symbols]

 1 sample stage 2 sample stage S sample 3 light source 4 optical fiber bundle 5 slit 6 camera 7 image memory 8 monitor screen 9 data processing device

Claims (1)

[Claims] 1. A sample surface is irradiated with light from an oblique direction, the irradiated sample surface is imaged from above vertically, and the obtained light-dark distribution signal is frequency-analyzed to obtain light-dark spectrum data.
In this spectrum, a method for quantifying unevenness of a glossy surface, wherein the unevenness degree is defined as a ratio of an area of a constant frequency range of a high frequency range to an area of another constant frequency range of an intermediate frequency range.