The application of color steel plate is becoming more and more extensive. Its rich color has become a beautiful scenic spot for all walks of life and all kinds of buildings. So how did the landscape come into being, how did the color steel industry detect the color, and what precautions should be paid attention to in this process? This paper makes some basic introduction.

Basic knowledge of color

Three elements of color

Picture 1 (1) png

1. Brightness (L)

The greater the L value, the whiter the material; For example, l = 100 indicates white; L = 50 indicates gray; If l = 0, the value indicates black;

2. Hue (also known as hue, usually represented by a and b)

Hue refers to the color category of colored light+ A indicates the degree of redness- A indicates the degree of greenness+ B indicates the degree of yellow marking- B indicates the degree of stool blue;

3. Chromaticity (also known as saturation, which refers to the depth of color)

L - > △ L: the difference between the actual brightness of the material and the standard brightness;

A - > △ A: the difference between the actual red and green degree of the material and the quality inspection of the standard value;

B - > △ B: the difference between the actual yellowish blue degree of the material and the quality inspection of the standard value;

△ e: comprehensive difference between actual value and standard value on L / A / b.

Picture 2 (1) png

Light and color

1. Visible light (see the figure below for details): light is a kind of substance in the form of electromagnetic wave. The light that can be seen by human eyes is called visible light. Generally, people can perceive the electromagnetic wave length of 400nm ~ 700nm, and others can perceive the electromagnetic wave between 380nm ~ 780nm;

Picture 3 (2) Png picture 4 (1) png

2. There are two sources of color:

① The color of the illuminant;

② The color presented by the non luminous body through the luminous body, and the color presented by the non luminous body is related to the light source illuminating it;

Principle of three primary colors (r-red; g-green; b-blue)

1. Most colors in nature can be obtained by mixing three primary colors in a certain proportion. On the contrary, colors in nature can be decomposed into three primary colors;

2. Three primary colors are mutually independent colors, and any primary color cannot be produced by mixing the other two primary colors;

3. The mixing ratio between the three primary colors determines the hue and saturation of the mixed color;

4. Chromaticity triangle

Picture 5 png

Definition of color difference

Color difference refers to the difference between two colors, that is, the comprehensive difference of brightness, hue and saturation. At present, the most practical and popular spatial model for measuring object color is L * a * b * hue space, which is the hue space defined by CIE (International Lighting Space Committee).

Color measurement - color difference meter

Classification of color difference meter

According to the performance parameters, accuracy range and application requirements, it can be divided into handheld color difference instrument, portable color difference instrument and desktop color difference instrument.

1. Hand held color difference meter: also known as color difference meter, it can directly read data without connecting to computer and without software. It is easy to use and cheap, but with low precision. It is widely used in general fields of color management, such as ou4600;

Picture 6 (1) png

2. Portable color difference meter: also known as portable spectrophotometer, in addition to directly reading data, it can also be connected to computer and equipped with software. It is small, easy to carry, high precision and moderate price, such as aiseli SP series;

Picture 7 png

3. Desktop color difference meter: also known as desktop spectrophotometer and color matching meter, it has a reading window. When connecting to the computer, it needs to use color measurement and color matching software. It has high-precision color measurement and color matching functions, large volume, stable performance and high price, such as hunter lab, date color, etc.

Picture 9 (1) png

Working principle of color difference meter

The color difference meter is a measuring instrument that simulates the human eye's induction of red, green and blue light. It can analyze the measured object from multiple angles.

The color difference meter can measure and display the color difference between the sample and the standard sample according to the lab and LCH principles of CIE chromaticity space Δ E and Δ L、 Δ a、 Δ B value. Δ E is defined as the total color difference of the sample, Δ The greater the E value, the greater the color difference, but it can not reflect the color difference bias of the sample. The color difference bias of the sample is used Δ L、 Δ a、 Δ B.

The test results of different brands and models of color difference instruments are different. One of the main factors is the difference of measuring optical / geometric structure. At present, there are three common types:

1. Multi angle effect colorimeter, which can measure multi angle color difference;

Picture 10 png

2. The color measuring optical mechanism is 45 / 0, 45 ° annular lighting, 0 ° observation angle and annular lighting system, which eliminates the direction dependence. No matter changing the sample position, tilting the sample or rotating the instrument, it can achieve high accuracy and repeatability, and reduce the impact of grain. Measurement on frosted, textured and structured material surfaces brings great advantages;

Picture 11 png

3. Measuring the geometric structure D / 8, integrating sphere diffuse reflection illumination and 8 ° observation angle. At present, it is an international observation condition;

Picture 12 png

light source

1. Illuminant a (a light source): CIE standard light source represented by incandescent lamp, yellow orange, and the related color temperature is 2856 ° K;

For example, the average color temperature of the light source represented by LNT is 672 ° C, which is related to the standard light source;

3. Illuminant D (d light source): CIE standard light source represented by fluorescent lamp, which is based on the real measurement spectrum of sunlight. The related color temperatures are 6504 ° K, D65 and d75, and D65 light source is commonly used in coating and color steel plate industry;

4. Illuminant f (f light source): CIE standard light source represented by fluorescent lamp, F2 represents cold white fluorescent lamp (4200 ° K), F7 represents broadband fluorescent lamp (6500 ° K), F11 represents narrow-band white fluorescent lamp (4200 ° K).

Specular and diffuse reflection

1. SCI (special component include): it can accept specular reflection and diffuse reflection (including gloss), which is generally used for enterprises or institutions that study the properties of the color itself and do not care about the surface gloss of the sample to which the color is attached;

2. SCE (special component exclude): it does not accept specular reflection light (excluding gloss), which is generally applicable to enterprises or institutions that are directly observed and require measurement results and visual inspection to be very close to the sample;

3. Illuminant D (d light source): CIE standard light source represented by fluorescent lamp, which is based on the real measurement spectrum of sunlight. The related color temperatures are 6504 ° K, D65 and d75, and D65 light source is commonly used in coating and color steel plate industry;

Color difference range (tolerance)

1. 0~0.25  Δ E is very small or not, ideal matching, negligible and difficult to distinguish with the naked eye;

2. 0.25~0.5  Δ E is small, can be matched, can be ignored and difficult to distinguish with the naked eye;

3. 0.5-1.0 Δ E small to medium; It is acceptable in some applications and can be distinguished by people with long-term professional training;

4. 1.0-2.0  Δ E medium, acceptable in specific applications and easy to distinguish;

5. 2.0-4.0  Δ E there is a gap, which is acceptable in specific applications and easy to distinguish;

6. Above 4.0 Δ E is very large and unacceptable in most applications.

Shandong Huijin is generally acceptable according to the specific requirements of different products Δ E 0 ~ 1.5 color difference range.

General precautions for measuring color difference with color difference meter

1. Check whether the equipment status is normal before use;

2. It can be used only after the calibration is qualified. The white board or other standard board used for calibration shall be properly kept to avoid falling dust or discoloration;

3. Select the correct light source (D65);

4. If the measurement method needs to be selected, select SCI;

5. If the measuring port aperture needs to be replaced, it shall be calibrated again after changing the aperture;

6. Select the international universal and popular spatial model: L * a * b * hue space;

7. It cannot be used in special environments such as strong magnetic field, high heat and humidity;

8. If the ambient temperature changes more than 10 ℃, it shall be calibrated again;

Analysis of color difference

1. The color difference of the same sample is detected by multiple parties. The possible reasons are as follows:

① The brand and model of color difference instrument are different;

② Abnormal state of one or more detection equipment;

③ The standards adopted are different;

④ Improper detection operation;

2. Color difference in the production process of color steel plate, common causes:

① Abnormal state of detection equipment;

② Failure to adopt correct standards;

③ Improper detection operation;

④ Improper film thickness;

⑤ Improper plate temperature;

⑥ Color difference of coating;