JP2780657B2 - Quantitative measurement method for blank paper and printed paper surface - 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 quantitatively measuring the surface unevenness due to white unevenness and printing unevenness of paper and coated paper.

[0002]

2. Description of the Related Art Recently, in the production and printing of paper, it has become important to evaluate the appearance due to white unevenness and uneven printing on the paper from the viewpoint of improving their quality. Paper surface feel is a measure of the quality of visual evaluation of unevenness and non-uniformity such as surface gloss based on unevenness and smoothness of the paper surface, and this is based on aesthetics based on visual perception. It was a very delicate evaluation method. Therefore, in the past, it was mostly done by human eyes,
It was not a quantitative evaluation method and was poor in reliability.
In addition, with respect to printing unevenness, evaluation of non-uniformity of the ink density on the halftone printing surface is also visually evaluated. From such a point, it has been recently emphasized to obtain a quantitative measurement method of the surface unevenness due to white unevenness and printing unevenness of paper and coated paper, and various methods for this have been proposed.

One of the methods is a method using an image analysis device. (Refer to page 60 of the 60th Annual Paper and Pulp Research Conference Paper and Pulp Technology Association June 8, 1993) This is to quantify gloss unevenness due to reflected light by focusing on the size of bright and dark areas. Is what you do. The measuring method is as follows. As shown in the schematic diagram of FIG. 6, a white-visible parallel light polarized from a light source 11 is irradiated on a paper surface through a polarizing filter 13 at an incident angle of 25 degrees with respect to a normal to the surface of the coated paper 12. , Coated paper 12
The reflected light having a reflection angle of 25 degrees is detected as an original image by the CCD camera 15 through the polarization filter 14 having the same phase. The photographing area per pixel is 40 × 40 μm
The measurement area of one screen is 10 × 10 mm, and the arithmetic value of the four screens is used as the measurement value. The brightness of each pixel is converted into a digitized gradation by the A / D converter 16 and stored in the storage circuit 17. And computer 1
In step 8, the gradation of each pixel is divided into 256 equal parts from black to white.

Then, the original image is subjected to a two-dimensional Fourier transform by the image analyzer 19 and further subjected to an inverse transform. The resulting image is multiplied by an enhancement coefficient in a specific wavelength range recognizable by the naked eye, thereby enhancing the brightness unevenness of the original image. 0 in the gradation of the emphasized image
After determining the area of each of the black portion and the white portion, with the range of １1 as a black portion and the range of 254 to 255 as a white portion,
This standard deviation is calculated and obtained.

For this reason, a large amount of measurement data must be processed, and high-performance computers and image analyzers are required. Further, measurement must be performed by irradiating a uniform light source with a beam. In order to eliminate external factors, there is a disadvantage that the light source device is necessarily increased in size.

[0006] The above example shows the case where 25 degrees incidence -2 on the coated paper.
This is to quantify the surface feeling from the uneven gloss due to the oblique reflection light reflected at 5 degrees. From the viewpoint of white unevenness, it is possible to analyze the color difference measurement values under the optical conditions of 45 degrees to 0 degrees, but in the above paper, the white paper surface due to the white unevenness only at the oblique angle of 25 degrees incidence-25 degrees reflection is considered. Only a measurement example is described.

It is considered that this is because the gradation division of the color difference of the original image depends on the performance of the CCD camera, and it is difficult to perform the gradation division at the level of the color difference value conforming to JIS-8722 or the like. For this reason, as described above, 25 degrees incidence-2
For example, a method of quantifying the surface feeling from the gloss unevenness due to the reflected light only at the fifth reflection is adopted.

[0008] When actually discussing the feeling of a blank page, there are cases in which the face is directly viewed from above and the appearance is determined based on white unevenness.
There is a case where the surface is judged as gloss unevenness when observing the paper from oblique directions.The method of quantifying gloss unevenness from oblique directions is based on the numerical analysis based on the distribution of reflected light intensity, in addition to the method using image analysis described above. There is a law. (Abstracts of the 57th Paper and Pulp Research Conference, Japan Pulp and Paper Technology Association, June 7, 1990
This is 75 mm incident on a 0.4 mm square -75.
It measures and analyzes the intensity of the reflected light in the degree reflection.

[0009] In these methods, the surface feeling due to the gloss unevenness is mainly used, and the evaluation is actually different from the surface feeling due to the white unevenness of the white paper, and the hue unevenness of printing cannot be evaluated. That is, when viewing the paper surface at a position perpendicular to the paper surface (direct direction), the hue unevenness is a criterion for determining the quality of the paper surface. On the other hand, when viewing the paper surface from a position oblique to the paper surface, This is because unevenness of the surface and unevenness of the gloss are criteria for determining the quality of the paper surface.

[0010] As described above, the conventional method is a method for measuring the surface texture based on the gloss unevenness from the oblique direction, and the method for quantifying the white unevenness and the hue unevenness when directly viewing the paper surface from above has not been described. Did not. Further, as described above, the conventional apparatus has many problems, such as a complicated apparatus configuration, and much time is required for measurement and analysis.

[0011] The present invention has been made in view of such a point, and is a simple method for detecting white unevenness and printing unevenness of white paper and printing paper without using an indirect measurement. It is an object of the present invention to provide a novel method of measuring a sense of appearance that can be made to substantially match.

[0012]

According to the present invention, white unevenness and hue unevenness are measured by directly looking at the surface of the paper from above, and an analysis is performed based on the measurement results. Use a small color difference photometer that can measure the color in the above. Then, an XY stage with a variable pitch is installed on the micro color difference photometer so that continuous multi-point measurement can be performed, and the light source device is adjusted to adjust the continuous multi-point within a microscopic range of 0.3 to 3.0 mmφ. The colorimetry of the points is performed, and the obtained data is subjected to arithmetic processing using a computer having statistical analysis software. The tristimulus values XYZ in the CIE color system, the Lab values in the Hunter color system, and the white color based on the blue reflectance. A WB value, which is a degree, is calculated for each continuous multipoint, and a standard deviation, an average, and a coefficient of variation are obtained. Then, the spectral curve is graphed, and the appearance is measured from the standard deviation, the average, the variation coefficient, and the variation width of the spectral curve. Therefore, it is possible to quantify white unevenness and print unevenness due to a difference in whiteness, which is difficult with an image analyzer using a CCD camera.

[0013]

According to the present invention, there is provided a light source device in which a minute color difference photometer is installed on an XY stage so as to be directly viewed from above the paper surface, a beam can be adjusted to millimeters or less, and an irradiation angle can be selected. The XY stage is installed diagonally above, the XY stage is configured to be movable at a plurality of pitches by a stepping motor, and the paper placed on the XY stage is subjected to continuous multipoint spectral photometry. The tristimulus value XY of the CIE colorimetric system is output by a computer having software for performing statistical analysis processing on the output of the micro color difference photometer.
Z, the Lab value of the Hunter color system and the WB value, which is the whiteness based on the blue reflectance, are calculated for each continuous multipoint, the standard deviation, the average, and the coefficient of variation are determined.
A method for quantitatively measuring white paper and printed paper surface characteristics, in which each spectral distribution measurement value measured at 16 points at 20 nm intervals in a range of 00 nm is graphed to measure the surface appearance due to white unevenness and printing unevenness. is there.

[0014]

[Function] Continuous multi-point spectrophotometry at millimeters or less can be easily performed, and white unevenness and hue unevenness when viewing the paper at a position perpendicular to the paper are spectrally measured and analyzed. By doing so, it is possible to obtain a surface feeling that matches the sensory surface feeling, and it is possible to reliably determine the quality of blank paper and printed paper.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of a method for quantitatively measuring the feeling of blank paper and printed paper according to the present invention will be described with reference to the drawings. FIG. 1 is a schematic diagram showing the configuration of the measuring device. That is, the sample 2 for measuring the surface feeling is placed on the XY stage 1 that can move at an automatic pitch. The XY stage 1 is
The movement pitch can be selected from 0.5 mm, 1.0 mm, and 2.0 mm, and 130 mm in the X direction and 13 mm in the Y direction.
By controlling each stepping motor within the range of 0 mm, X
The position within the measurement range can be selected in a matrix in the directions of the axis and the Y axis. In addition, manual measurement is possible by installing an arbitrary scale.
It is also possible to select a measurement range at an arbitrary position on an arbitrary scale within 50 mm in each of the axis and the Y-axis direction.

The sample 2 placed horizontally on the XY stage 1 has a halogen light projecting unit 3 for irradiating illumination light whose incident angle can be adjusted within a range of 45 ° to 0 °. The sample 2 can be irradiated with a beam having a measurement area of 0.1 to 3.0 mmφ. This sample 2
Color difference photometer 4 composed of a high-speed response type silicon photocell for vertically receiving reflected light from the XY stage 1
It is installed on the top and receives reflected light over a continuous multipoint in the measurement area on the sample 2. The output of the small color difference photometer 4 is connected to a computer 5 having software for performing a statistical analysis process, and is output from the computer 5 to a CRT 6 and a printer 7 for display or recording.

Next, a method of quantitatively measuring a texture based on continuous multi-point color difference light measurement of the present invention will be described. First, the sample 2 is placed horizontally on the XY stage 1 and
-Specify the pitch of the Y stage 1. Next, the beam from the halogen light projecting unit 3 is set to a desired value within the range of 0.1 mm to 3.0 mmφ, and then the angle within the range of 45 ° incidence to 0 ° reflection is set to a desired value. And make it work. Then, the sample 2 is irradiated with a beam, and the measurement wavelength range 400 to
The spectral measurement is performed by the minute color difference photometer 4 in the range of 700 nm at intervals of 20 nm for each of 16 points.

The output data of the small color difference photometer 4 is input to the computer 5, and the tristimulus value XYZ of the CIE color system is first calculated by the statistical analysis processing software. The standard light spectral distribution is S (λ), and the spectral reflectance of the object is R
(Λ), the color matching functions are x (λ), y (λ), z (λ), and the constant given by 1 / ∫S (λ) y (λ) dλ is K
X = K∫S (λ) x (λ) dλ Y = K∫S (λ) y (λ) dλ Z = K∫S (λ) z (λ) dλ . Next, the Lab value of the Hunter color system is calculated by the following equation: L = 10Y ^1/2 a = 17.5 (1.02 XY) / Y ^1/2 b = 7.0 (Y−0.842Z) Y Calculate from ^1/2 . Then, the whiteness based on the blue reflectance is obtained from the equation W (B) = 0.847Z, traced on the XY stage, and the Lab value obtained by the above calculation and the whiteness WB based on the blue reflectance are obtained.
Create a three-dimensional transition graph by value. The standard deviation, the average, and the coefficient of variation are determined based on the three-dimensional transition graph. Further, at this time, a variation graph of a spectral distribution curve measured in the measurement wavelength range of 400 to 700 nm at intervals of 20 nm is formed.

An example of a spectrophotometric graph of the results of measurement of eight types of samples A to H press-coated on commercially available white paperboard and six types of varnished samples A to F with the above-described measuring device and a conventional microgloss meter. Are shown in FIGS. That is, FIGS. 2A and 2B show a beam diameter of 0.6 m by a small color difference photometer of the samples C and D which were press-coated.
FIG. 3A is a spectrophotometric graph showing the result of measuring and processing white unevenness at m φ, a measurement area of 15 mm, and 15 points.
(B) shows a beam diameter of 0.6 mmφ and a measurement area 1 of the varnished samples C and D similarly measured by a micro color difference photometer.
It is a graph of the result of having measured and processed the white unevenness at 5 mm and 45 points.

On the other hand, FIGS. 4A and 4B show a conventional micro-gloss meter with a beam diameter of 0.4 mm square and a measurement area of 18 m.
The graph of white unevenness of Samples C and D among eight kinds of Samples A to H press-coated on a commercially available white paperboard measuring m and 45 points is shown. Similarly, among the six kinds of varnished samples A to F, which were measured at a beam diameter of 0.4 mm square, a measurement area of 18 mm, and 45 points using a conventional microgloss meter, the samples C and D exhibited white unevenness. Fig. 5 shows a photometric graph.
(A) and (b) show.

The X direction obtained by the method of the present invention,
In the WB value transition diagram, there is a considerable difference in the tendency between the variation between the press-coated sample and the varnished sample and the variation in the gloss value measured by the fine gloss meter. [FIGS. 2 (a) and 2 (b), FIGS. 3 (a) and 3 (b),
4 (a), (b), 5 (a), (b))

There is a difference in the tendency between the measurement results of the conventional microgloss meter of the varnished sample and the press-coated sample and the measurement results of the microcolor difference photometer of the present invention. That is, according to the whiteness value measured by the fine color difference photometer of the present invention, when samples C and D are press-coated and varnished, (a) is more white than (b) as shown in FIGS. The degree of variation is increasing. However, in the glossiness measured by the conventional microglossmeter, when samples C and D were press-coated and varnished, as shown in FIGS. 4 and 5, (b) showed a variation in glossiness compared to (a). More
The quality difference between (a) and (b) is reversed by the two measurement methods. For this reason, when evaluating the surface feeling due to white unevenness or printing unevenness, the evaluation using a conventional microgloss meter will give different evaluations. In the case of performing the evaluation of surface appearance due to such white unevenness or printing unevenness, it is necessary to measure a variation by a color difference measurement in a minute area according to the present invention.

Further, when the hues of the printed portions in the samples A to H are evaluated from the fluctuation width of the continuous multipoint spectral curve by the micro color difference photometer of the present invention, FIG.
As shown in (b), the fluctuation width of (a) is larger than that of (b) in the wavelength range around 520 nm. In other words, this indicates that printing unevenness occurs frequently in the green printing portion in FIG. This corresponds to the appearance seen from above.

[0023]

[Table 1]

[0024]

As described above, according to the present invention,
According to the quantitative measurement method of the printing paper surface feeling, the measurement is easier than the conventional measuring method, and it is possible to measure the surface feeling almost coincident with the sensual surface feeling. Therefore, it is possible to easily perform measurements such as quantification of blank surface appearance, quantification of printing surface appearance, quantification of printing defects and mottling, quantification of microscopic color difference values, and performance evaluation of color printers such as ink jet printers. It will be possible, and will greatly contribute to improving the quality of the technical field.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a schematic configuration of a measuring device,

FIGS. 2 (a) and (b) are spectrophotometric graphs of the results of the press-coated samples C and D measured by the measurement method of the present invention;

FIGS. 3A and 3B show varnished sample C,
D is a spectrophotometric graph of the result measured by the measuring method of the present invention,

4 (a) and 4 (b) are spectrophotometric graphs of the results of measurement of press-coated samples C and D by a conventional measurement method,

5 (a) and (b) show varnished sample C,
A spectrophotometric graph of the result measured by the conventional measuring method of D,

FIG. 6 is a schematic diagram showing a schematic configuration of a measuring device applied to a conventional measuring method,

FIGS. 7A and 7B are graphs showing a variation range of a reflectance in a 520 nm wavelength region.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 XY stage 2 Sample 3 Halogen light projection part 4 Micro color difference photometer 5 Computer 6 CRT 7 Printer

Continuation of the front page (56) References JP-A-1-141326 (JP, A) JP-A-2-51032 (JP, A) JP-A-1-201125 (JP, A) Suga Nagaichi "Weatherproof light and color" Suga Test Machine Co., Ltd. (Showa 63-2-20) 253−255 (58) Field surveyed (Int.Cl. ⁶ , DB name) G01J 3/46-3/52

Claims (1)

(57) [Claims] 1. A light source device capable of adjusting a beam within a range of millimeters or less and varying an irradiation angle by mounting a micro color difference optical meter on an XY stage so as to be directly viewed from above the paper surface. The XY stage is configured to be movable at a plurality of pitches by a stepping motor, and continuous multi-point spectrophotometry on the paper placed on the XY stage is performed. A computer having software for performing statistical analysis processing of the output of the meter calculates tristimulus values XYZ of the CIE color system, Lab values of the Hunter color system, and WB values of whiteness based on blue reflectance for each continuous multipoint. , The standard deviation obtained from it,
A method for quantitatively measuring the appearance of blank paper and printed paper, wherein the appearance due to white unevenness and printing unevenness is measured from the average and the variation coefficient and the variation width between the spectral curves at each continuous multipoint.