JPH0758225B2 - Prediction method of color mixture result - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method of predicting a color mixing result.

[Background technology]

In recent years, with the increase in processing speed of digital computers, when color matching is performed in plastics (resins), paints, inks, dyeings, etc., it is becoming popular to use a computer to predict the color mixture result and obtain a coloring prescription. It is done. Various methods have been known for predicting the color mixing result, a coloring formula can be obtained quickly, and no special skilled worker is required, which contributes to the rationalization of the work.

On the other hand, resin is being used more and more in electronic device cases and automobile bodies. Usually, colored resin is used, so that color matching is frequently performed.

Some colored materials have a small light-shielding property and allow light to pass through from the back side. In this case, the color looks different depending on the object (background) placed behind it, and it is difficult to accurately grasp the color of the colored object.

When the light concealing property is also small in the color sample, the color sample is used by folding it so that there is no see-through. However, the area of the color sample is usually small in many cases, and it may not be possible to fold it depending on the material of the color sample itself, and it is difficult to accurately and promptly predict the color mixture result.

Therefore, place the color sample on the base of different spectral reflectance, measure the spectral reflectance of each, and based on the obtained spectral reflectance, the spectral reflectance when the color sample is made thick enough to show through A method has been proposed in which the ratio is tentatively calculated, and based on this spectral reflectance, the color mixture result can be predicted even when the color sample is thin. However, there is a problem that the predicted value of the color mixture result is far from the actual color if it is simply placed on the base.

[Object of the Invention]

In view of the above circumstances, the present invention provides a method of predicting a color mixture result that can accurately match a color colored based on a coloring prescription obtained by predicting a color mixture result using a computer with a color of a color sample. The purpose is to provide.

[Disclosure of Invention]

In order to achieve the above-mentioned object, the inventor has conducted various studies such as suitability of the type of computer method to be applied in order to investigate the cause of the color mismatch. Finally, the color sample and the base are joined and integrated so that there is no air layer between them, and the spectral reflectance of the color sample is measured, and the color mixing result is predicted based on this measurement result. It has been found that, for example, the results obtained are in good agreement with the actual color of the color sample. In other words, it has been clarified that the color sample has conventionally been simply placed on the base. If the resin plate of the color sample is simply placed on the base, a gap (air layer) will be created between the base and the color sample, and reflection will occur at the interface due to the difference in refractive index between the color sample and air. The reflectance is higher than the true reflectance. This effect is particularly large when the reflectance of the base is low. In order to eliminate this air layer and obtain accurate reflectance, it may be possible to sandwich glycerin, etc., which has the same refractive index as the color sample, but actually it takes a lot of time and effort. Poor performance, so it is not practical. The present invention has been completed based on such knowledge.

Therefore, according to the present invention, a back surface of a color sample is applied with a substrate having a different spectral reflectance, each spectral reflectance is measured, and the obtained spectral reflectance is computer-processed and used for different color samples. In the method of predicting the color mixing result when a colorant is mixed, the measurement of the spectral reflectance is performed in a state where the base is directly adhered to and integrated with a color sample, and the color mixing result is obtained. The method of prediction is as the gist.

Hereinafter, the method of predicting the color mixture result according to the present invention will be described in detail based on an example thereof.

To calculate the color mixture, a coefficient (K; absorption coefficient), which is the optical property of the monochromatic colorants (coloring materials) to be mixed, and a coefficient (S; scattering) It is necessary to calculate the coefficient. In that case, several points of a single color sample for each colorant used for color mixing are prepared, the reflectance thereof is accurately measured, and it is calculated based on the data. According to the present invention, even if these color samples have show-through, more accurate reflectance than before can be obtained, and the color mixing result can be predicted based on this accurate data.

First, the background theory, Kubelker Munk's theory and formulas, and Duncan's formula will be briefly described.

A colored object is a dyed fiber,
Light absorption and scattering occur in the inside and the surface of each of the colored and molded plastic and the coating film depending on the spectral light. When light is incident on the colored material from the outside, the amount of reflected light is determined by the effects of absorption and scattering described above.

In this case, the absorption property is represented by an absorption coefficient K, and the scattering property is represented by a scattering coefficient S. If K and S can be defined, the reflectance R can be defined. This is mathematically represented by the so-called Kubelker Munk's equation (1).

Further, there is an equation (2) as an inverse transformation of the equation (1).

Thus, when the reflectance R is measured, (K / S), that is, the ratio of K and S is known.

The R _∞ used in this theory neglects the error due to the difference in refractive index at the interface between the colorant and air. Therefore, this point must be taken into consideration when using this theory. Therefore, the measurement value of the spectrophotometer is usually corrected by the Saunderson formula, and the corrected reflectance is used.

On the other hand, if the absorption and scattering of the object to be colored are known and the absorption and scattering coefficients of the dye / pigment (colorant) used for coloring are known, the absorption coefficient K of the coloring result by the mixing ratio given by these _m and scattering coefficient S _m of Duncan
It can be predicted by equation (3).

K _m / S _m = (K ₁ · P ₁ + K ₂ · P ₂ ＋ ・ ・ ・ K _i · P _i +) / (S ₁ ·
P ₁ + S ₂ · P ₂ + ... S _i · P _i +) (3) However, P ₁ + P ₂ + ... + P _i = 1.

Here, P _{1 to} P _i are the addition amount (or addition rate) of the colorant. K _{1 to} K _i are absorption coefficients of the colorant, and S _{1 to} S ₁ are scattering coefficients of the colorant.

Next, a more specific example of calculation of the scattering coefficient S and the absorption coefficient K will be described.

A certain white pigment is used as the standard of the scattering coefficient, and S = 1
(Uniform for all wavelengths), and the absorption coefficient and scattering coefficient of other pigments are represented by their relative values. For this purpose, the addition ratio of the pigment to the object to be colored is set to a fixed value such as 1% or 2% in advance, and a colored product to which a colored pigment (of a single type) is added is produced by this addition ratio. Since this represents the color of the pigment itself, it is usually a mass-ton.
e).

Also, a mixture of each pigment and a white pigment in a certain ratio is added at the above-mentioned fixed addition ratio. This is usually referred to as Let-down. Considering accuracy, let down should be made in several stages with a stepwise ratio (for example, 80: 20; 60: 40; 50: 50; 40: 60; 20: 80; 10: 90). .

If these letdowns can be made, the spectral reflectance is measured using a spectrophotometer, but in the present invention, as described below, even if there is show-through in the reddown,
An accurate value can be obtained in the reflectance measurement.

For example, when the let-down is a resin plate (eg, vinyl chloride resin sheet), the resin plate 1 is a base resin plate (eg, chloride) as shown in FIGS. 1 (a) and 1 (b). Vinyl resin sheets 2 and 2'are joined and integrated to be in close contact. Therefore, since no air layer is formed between the resin plates 1 and 1 and the resin plates 2 and 2 ', accurate reflectance can be measured. In order to bring them into close contact, for example, thermocompression bonding may be performed using a hot press.

Resin plate 2 is white (colorant: white manufactured by Sumika Color Co., Ltd.
VM700) and the resin plate 2'is black (colorant: Black VM817 manufactured by Sumika Color Co., Ltd.).

Spectral reflectance R _G1 (λ) of base resin plate 2 and base resin plate 2 ′
The spectral reflectances R _G2 (λ) of are different.

First, the spectral reflectances R ₁ (λ) and R of the resin plate 1 with a white base and the resin plate 1 with a black base, respectively.
₂ Measure (λ). Then, from both spectral reflectances, the spectral reflectance R _∞ (λ) of the color sample when the thickness is increased to such an extent that there is no see-through in the uniform tissue state is calculated by the following equation (4).

However, M = R ₁ (λ) · R _G2 (λ) −R ₂ (λ) · R _G1 (λ) N = [R _G1 (λ) −R _G2 (λ)] ・ [1 + R ₁ (λ) ・R
₂ (λ)]-[R ₁ (λ) -R ₂ (λ)] ・ [1 + R _G1 (λ)
・ R _G2 (λ)] and 1> R _G1 (λ)> R ₁ (λ)> R
₂ (λ)> R _G2 (λ)> 0 After the accurate reflectances of all the color samples are measured in this manner, the (K / S) of each color sample is obtained by the above Kubelker-Munk equation.

First, the white absorption coefficient K _W is obtained (S _W = 1).

K _W = (K / S) _W = (1-R _W ) ² / 2R _W Let (K / S) of the let down be (K / S) _WP , then from the Duncan formula, (K / S) _WP = [C _W・ (K / S) _W ＋ C _P・ K _P ] / [C _W・ 1 ＋ C _P・
S _P ]. Solving for S _P, S _P is determined.

Also, if S _P is known, K _P is of course the mass tone (K / S) _P
Since it is known, it can be obtained from the equation of K _P = S _P · (K / S) _P … (6).

From Equations (5) and (6), the absorption coefficient K and scattering coefficient S of each color sample can be obtained.

The K and S of each colorant to be mixed have been found by the work up to this point.

On the other hand, the (K / S) _mix of the coloring layer when 4 kinds of suitable coloring agents 1 to 4 are mixed, if the concentration of the coloring agent is appropriately selected,
It is predicted and calculated by the Duncan's formula shown above.

Then, using the formula (2) and the like, R _∞ (λ) in the color mixture layer when four kinds of colorants are mixed and colored is predicted and calculated, and based on this R _∞ (λ), Stimulus value (JIS Z8
722, Measuring method of object color in 2 degree field of view) X _mix : Y
_mix : Predict and calculate Z _mix . These are compared with the tristimulus values X _s : Y _s : Z _s of the mixed color sample S, and the concentration formulas of the colorants 1 to 4 when both tristimulus values are the same are the coloring prescription. This method is usually called the metameric match method.

In the method of predicting the color mixing result described above, even if there is show-through in the colored sample (color sample), the sample and the base are joined together and in close contact, so the obtained spectral reflectance is accurate. Has become. Therefore, the prediction of the color mixture result is also accurate. It is particularly effective for a color having low hiding power, for example, yellow. Of course, since the hiding property is high or low depending on the colorant particles and the like, the effectiveness of the present invention is not limited by the type of color.

Next, a method of predicting a color mixing result according to the present invention will be described based on concrete examples and comparative examples.

Color samples A to E of vinyl chloride resin plates colored by mixing three kinds of colorants 1 to 3 at the following concentrations were prepared.

[Examples] Coloring formulations of color samples A to E, that is, colorants 1 to 1
The density of 3 was obtained according to the method of predicting the color mixing result of the example of the present invention described above. The actual concentration of colorants 1-3
The calculated concentration percentages of the colorants 1 to 3 were taken as 100% and are shown in FIG. The numerical values in the table indicate the weight of the colorant added to 100 g of the resin content (therefore, the amount of the colorant added to the resin content is 100% by weight relative to 100% by weight of the resin content. Will be shown in).

The following colorants 1 to 3 were used.

Color sample A Colorant 1 ... Rutile titanium colorant 2 ... Quinacridone red Colorant 3 ... Polyazo yellow, Color sample B Colorant 1 ... Rutile titanium colorant 2 ... Anthraquinone Red Colorant 3 ... Polyazo yellow, Color sample C Colorant 1 ... Rutile titanium colorant 2 ... Perine red Colorant 3 ... Polyazo yellow, color sample D Colorant 1 ... Rutile titanium colorant 2 ... Quinacridone red colorant 3 ... Titanium yellow, Color sample E Colorant 1 ... Rutile-type titanium Colorant 2 ... Quinacridone red Colorant 3 ... Polyazo yellow, [Comparative Example] Color samples A to E, that is, colorants 1 to 1
The density of 3 was calculated in the same manner as in the example except that the color sample was simply placed on the base without being brought into close contact with the base. The actual concentration of colorants 1-3 is 100
The calculated concentration percentages of the coloring agents 1 to 3 are shown as% in FIG.

Obviously, it can be seen that the example of the present invention can match the color of the actual color sample much better than the comparative example.

The present invention is not limited to the above embodiment. For example, a water-based paint (emulsion paint) may be applied to one side of the color sample so that no bubbles are formed on the application surface to form the base. It may be effective to add a defoaming agent to the paint and apply it to improve the adhesion. If there is a risk that the color sample will be damaged by thermocompression bonding, or
It is convenient and useful when there is no hot press nearby.

The isometric match method may be used instead of the metameric match method.

The material of the color sample is not limited to vinyl chloride resin. Polypropylene resin, polystyrene resin, polyethylene resin,
Alternatively, a material other than resin may be used.

Further, the formula for obtaining R _∞ (λ) and the formula given above are not limited.

For example, the following formula can be used.

The Courbeka-Munk equation can also be expressed as equation (7) below.

SX = (1 / b) ・ [Arctgh [(a-R) / b] -Arctgh
[(A−Rg) / b]] (7) where a = (1 / R _∞ + R _∞ ) / 2 b = (1 / R _∞ −R _∞ ) / 2 X: Thickness of color sample Rg: Base The reflectance of is Becomes

Spectral reflectance of two different substrates R _W, usually white substrate),
R _{B is} normally a black background), and the spectral reflectances of the color samples when the respective backgrounds are in close contact are R _WG (for a white background), R
Substituting _BG (for black background) into the above equation and solving them as simultaneous equations gives the following equation.

When the logarithm of both sides of this equation is removed and expanded, the following equation (8) for the spectral reflectance R _∞ is obtained.

A (R _∞ ) ⁴ + B (R _∞ ) ³ + C (R _∞ ) + D = 0 (8)
However, A = R _W · R _{BG −} R _WG · R _B B = − [R _BG + R _W + (R _W · R _B · R _BG ) + (R _W · R _WG · R _BG )
-R _WG -R _B- (R _W / R _B / R _WG )-(R _WG / R _BG / R _B )] C =-[R _B + R _WG + (R _WG / R _BG / R _B ) + ( R _W / R _B / R _WG )
−R _W −R _BG − (R _W · R _BG · R _WG ) − (R _W · R _B · R _BG )] D = R _B · R _WG −R _W · R _BG This equation (8) is applied to the Newton method. Is used to derive a root between 0 and 1 to obtain R _∞ . The method of calculating R _∞ described here was first devised by the inventor. Formula (1) above
The result is almost the same as the result obtained by.

In addition to this, the following formula can also be used.

R _∞ = A '-(A' ² -1) ^1/2 However, A '= 0.5 ・ [R _WG + (R _BG −R _WG + Rg) / R _BG・ R
g] [Effect of the Invention] The present invention has the above-described configuration. According to the method of the present invention, the color mixture result can be predicted based on the accurate spectral reflectance of the color sample, and therefore, the colored color can be matched well with the color sample.

[Brief description of drawings]

FIGS. 1 (a) and 1 (b) are front views showing a color sample and a base used in the method of predicting the color mixture result of the example of the present invention, and FIG.
FIG. 3 is a graph for explaining the accuracy of the color prescription calculated by the method for predicting the color mixture result of one example of the present invention, and FIG. 3 is a graph for explaining the accuracy of the color prescription calculated by the method for predicting the conventional color mixture result. Is a graph of. 1 ... Resin plate, 2 and 2 '... Resin plate

Claims (3)

[Claims] 1. A back surface of a color sample is applied with a base having a different spectral reflectance, each spectral reflectance is measured, and the obtained spectral reflectance is computer-processed to be used for different color samples. In the method of predicting the color mixing result when a colorant is mixed, the measurement of the spectral reflectance is performed in a state in which the base is directly adhered to and integrated with a color sample and the color mixing result is characterized by Prediction method. 2. The color sample and the base are resin sheets, and the base and the color sample are directly intimately adhered to each other and joined together by thermocompression bonding the color sample and the base. Prediction method of color mixture result described in item. 3. The method for predicting a color mixing result according to claim 1, wherein the color sample is a resin sheet, and the base is a paint layer which is adhered and coated on the back surface of the color sample.