JPH06103225B2 - Color measurement method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for measuring the color of an object.

(Prior art) In recent years, due to demands for improvement of quality control technology and automation of manufacturing process, there has been a movement to grasp quantitatively or objectively the phenomenon that was conventionally qualitatively or sensory. It is becoming active in each field. The same applies to the problem of color, for example, the color of paper, fiber, cloth, plastic film, emulsion, pulp dispersion, cream, suspension, salt, sugar, crystalline chemicals, various powders, paints, etc. When doing so, color determination is usually performed using an optical colorimeter or color difference meter.

By the way, in a pulp and paper factory, for example, as a colorimeter or color difference meter, conventionally, a Hunter colorimetric glossmeter based on JIS Z8722 of the Japanese Industrial Standards is used, and each reflection when using a blue, green and amber filter is used. The reflectance has been measured, and from the obtained reflectance, the whiteness of paper and coated paper and the color such as hue have been measured for many years. For example, when measuring the reflectance value (H _B ) of the whiteness of the blue filter, a blue filter having a main wavelength of 457 nm is used and the value is obtained. In addition, with the rapid progress of color measurement technology, which has been rarely seen in recent years, a spectral reflectance curve is drawn from the above-mentioned color difference meter of the blue filter type using a spectrophotometer, and the Z value of the tristimulus value is calculated from this curve. There is a technology shift to a color difference meter of the type that does. However, the following problems occur in this method.

(Problems to be Solved by the Invention) That is, in the spectrophotometer method, it is necessary to use the measured Z value to calculate the reflectance value (H _B ) obtained by the filter method of the hunter. The relational expression between the filter method and the spectrophotometer method is a linear relational expression as shown in the equation (1).

Therefore, in order to confirm whether the above relational expression is highly accurate, the inventor of the present application deals with various data cases,
An attempt was made to introduce a linear approximation formula such as the formula (2) and to see the correlation between the two by calculation.

H _B = a ₁ × Z + a ₂ (2) (However, a ₁ and a ₂ are constants.) However, the correlation between them is as low as 0.961 and the standard deviation is as bad as 1.063. It was found that there is a risk of problems in color quality control. Therefore, under the present circumstances, there is a long-awaited demand for the development of a colorimetric method capable of obtaining an extremely high correlation between the two.

The present invention uses a color difference meter spectrophotometer method, very correlated with the values obtained with those of the conventional filter method is high H _B
It is intended to provide a colorimetric method that can obtain a value.

(Means for Solving the Problem) According to the present invention, an equation in which the Y value of tristimulus values and the x and y values of color coordinate values of the International Commission on Illumination are used as variables in advance in the colorimetric operation unit
H _B = C ₁ × Y + C ₂ × x + C ₃ × y + C ₄ (where C _{1 to} C ₄ are constants) is set, and when the color of the object is obtained by the spectrocolorimetric method, The Y value, x value,
By inputting the y value in the above setting formula, the main wavelength is 457 nm.
The colorimetric method is characterized in that the reflectance value (H _B ) of the object obtained by the blue filter of is calculated.

(Operation) The method of the present invention will be described in more detail with reference to the drawings.
FIG. 1 is a diagram schematically showing an apparatus used in the colorimetric method according to the present invention.

When the object to be measured (1) is a sheet and the reflectance value, which is its whiteness, is measured by the light reflection type colorimeter (2), the light from the halogen light source (3) is used as a monitor for reference. The light (4) is branched into the light (4) and the sample light (5) for irradiating the sheet, and the sample light is emitted from the head portion (7) to the sheet surface via the illumination light fiber (6). The light is reflected by the sheet surface to become reflected light, enters the light receiving optical fiber (8), and reaches the switch (9) via the light.

The switching device (9) switches between the sample light and the monitor light that have passed through each optical fiber as described above according to the sequence signal sent from the control unit (10), and sends the sample light to the next spectrophotometer (11). . In the spectrophotometer, the sample light and the monitor light are separated into wavelengths, for example, every 5 nm, and the tristimulus values X, Y, and Z are obtained by obtaining the distribution of the spectral reflectance for each wavelength band. Hereinafter, x and y which are chromaticity coordinate values (hereinafter referred to as CIE) are calculated, and these values are sent to the colorimetric calculation section (12).

The colorimetric calculation unit (12) sets various calculation expressions in advance so that Lab color system, L ^* a ^* b ^* can be calculated using the above tristimulus values and CIE chromaticity coordinate values ^. A color difference is obtained with a color such as a color system, but in the case of the present invention, when x and y of CIE chromaticity coordinate values and Y values of tristimulus values are variable,
It was found that the correlation between these values and the reflectance measurement value (H _B ) on the blue filter was high, and when the H _B value was calculated by setting an arithmetic expression of a very special form as shown below, the correlation coefficient High values ranging from 0.995 to 0.999 with a standard deviation of 0.414
It was found that there is a very good correlation with

H _B = C ₁ × Y + C ₂ × x + C ₃ × y + C ₄ (3) (However, C _{1 to} C ₄ are constants.) The result obtained by the calculation is displayed on the display unit (13).

In the light reflection type colorimeter of the present invention, the measurement result is considerably affected by fluctuations in the light source, mechanical system, electrical system, etc., or dust adhesion. It is a preferred embodiment of the present invention that the light source light itself is measured at every measurement interval and that calibration is performed using a white plate whose reflectance is known as a reference. That is, as shown in FIG. 1, a cylinder device (14) for retracting the head portion (7) so as to separate in the direction perpendicular to the seat surface,
Cylinder device (17) for moving the standard white plate (16) fixed to the fixing base (15) in the direction parallel to the seat surface toward the tip of the head is placed, and the head is moved during calibration. After retreating, move the standard white plate between the head part and the sheet, reflect the light on the standard white plate surface and use the value obtained by calculation as the reference value, and perform calibration based on the following formula. , More accurate measurement becomes possible.

When the light reflectance from the object for each wavelength is ηλ, (Example) Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited thereto. Also,
Unless otherwise specified, parts and% in the examples are parts by weight, respectively.
Indicates.

A coating liquid having the following composition was prepared with a Choles disperser.

Kaolin (manufactured by EMC, UW-90) 80 parts Heavy calcium carbonate (manufactured by Bihoku Powder Co., Ltd., Softon 220)
0) 20 parts Styrene-butadiene copolymer latex (Sumitomo Nogatac Co., SN-307) 10 parts Oxidation modified starch (Oji Corn Starch Co., Ace A) 5
The solid content of the parts sodium polyacrylate 0.3 parts coated liquid was prepared in 60% coater speed 600m by the blade coater so that the coated amount after drying of 40 g / m ² base paper of basis weight 80 g / m ² 120g / sq.m.
A m ² coated paper was obtained.

The resulting coated paper was smoothed with a super calendar.

As an example, as shown in FIG. 1, heads (7) of a light reflection type colorimetric apparatus (2) according to the method of the present invention were prepared from 78 kinds of coated papers obtained by smoothing treatment. The colorimetric calculation unit (12) has 0.959 for C ₁ of each constant of formula (3), −2727 for C ₂ and 1076 for C ₃ After setting the value of 517.5 to ₄ , the H _B value was calculated. The H _B value of the present invention thus obtained is taken on the horizontal axis, and the H _B value measured by a colorimetric gloss meter with a conventional blue filter using the same sample paper is taken on the vertical axis. A diagram of the correlation is shown in FIG.

As is clear from FIG. 2, the correlation between the two is as high as 0.994 and the standard deviation is 0.414, indicating a very good correlation.

On the other hand, as a comparative example, the first-order approximation formula of the formula (2) is set in the colorimetric calculation section when the constants a ₁ is 0.978 and a ₂ is −4.938, and H _{The B} value was calculated.

The result obtained by the first-order approximation formula of formula (2) is plotted on the horizontal axis,
FIG. 3 shows the result of plotting the H _B value measured by the conventional colorimetric gloss meter on the vertical axis. As shown in FIG. 3, it is clear that the correlation between the two is as low as 0.961 and the standard deviation is 1.063, which is very poor.

(Effect) When the light reflection type colorimetric device according to the method of the present invention is used,
The reflectance value of an object can always be obtained with a very high correlation with the value obtained by a conventional filter type color difference meter.

Therefore, the quality control is not affected at all, the non-quality products are not shipped, and the number of claims is drastically reduced.

[Brief description of drawings]

FIG. 1 is a schematic explanatory diagram when the colorimetric method according to the present invention is applied to the measurement of the reflectance value of a sheet. FIG. 2 is a diagram showing the correlation between the case where the reflectance value of the sheet is measured by the conventional filter type color difference meter and the case where the special arithmetic expression of the present invention is set and measured. FIG. 3 is a diagram showing the correlation between the case where the reflectance of the sheet is measured by the conventional filter type color difference meter and the case where the conventional linear relational expression is set and measured. (1): object to be measured (sheet), (2): light reflection type colorimeter (3): halogen light source, (4): monitor light (5): sample light, (6): optical fiber for illumination (7) ): Head part, (8): Optical fiber for receiving light, (9): Switch, (10): Control part (11): Spectrophotometer, (12): Colorimetric calculation part (13): Display part, (14) ): Cylinder device (15): Fixed stand, (16): Standard white board (17): Cylinder device

Claims (1)

[Claims] 1. An expression H _B = C ₁ × Y + C ₂ × x + C ₃ × in which a Y value of tristimulus values and x and y values of color coordinate values of the International Commission on Illumination are used as variables in a colorimetric operation unit in advance. y + C ₄ (where C _{1 to} C ₄ are constants) is set in advance, and when the color of the object is obtained by the spectrocolorimetric method, the Y value obtained from the spectral spectrum, x
By inputting the value and y value into the above setting formula, the dominant wavelength 45
A colorimetric method characterized by calculating a reflectance value (H _B ) of an object obtained by a 7 nm blue filter.