Paper color, which people value, has been used as an important technical indicator of paper appearance quality. Harmonious and uniform color can give paper a good visual effect. If the color difference is obvious, it will not only affect the beauty of the printed matter, but also cause the printing department or manufacturer to suffer certain economic losses. Because once the color difference of the product is caused, it will not only affect the quality of the product and the reputation of the enterprise, but also cause waste of the product. The common method is visual inspection, but the more popular way in reality is to use Spectrophotometer . The measurement of NH Spectrophotometer can objectively evaluate and quantify the depth of color and the size of color difference.
In actual production, the visual evaluation is simple and convenient, and can prevent and control the relatively obvious color difference paper. The correct observation method is:
(1) The illumination of the light source is 45 degrees to the surface of the paper sample, and the observation direction is perpendicular to the surface of the paper sample, indicating 45/0, and the observation distance is 30.40 cm (see Figure 1) light source
Figure 1 The light source illumination is at 45 degrees to the surface of the paper sample
(2) The illumination of the light source is perpendicular to the surface of the paper sample, and the observation direction is 45 degrees from the surface of the sample, indicating 0/45 (see Figure 2)
Figure 2 The illumination of the light source is perpendicular to the surface of the paper sample
However, in addition to the requirements of the environment and light sources, the visual evaluation also requires the evaluation of human vision and color discrimination experience to meet the requirements, and only relying on human vision will be affected by subjective factors and environmental factors. Therefore, it is easy to make the relationship between the manufacturer and the customer disagreements and disputes. The measurement of the instrument can objectively evaluate and quantify the depth of the color and the size of the color difference, so it is a more popular method in the world today.
In order to track and measure the color difference of paper more accurately and meet the needs of the market, we use 3NH Spectrophotometer for detection. For the analysis of color and chromatic aberration, ISO/A02 and AATCC gray cards are mainly used as standards, and the chromaticity of the gray cards is stipulated as follows: the paper
should be neutral gray, and it should be measured by a Spectrophotometer with specular reflection. Chromaticity data is calculated with CIE1964 supplementary standard chromaticity system (100 field of view) and D65 light source. The AATCC gray card is also measured by the CIELAB color difference method, and the color difference comparison of the ISO/A02 gray card levels is listed in the table below: We chose the CS-650 Spectrophotometer for the instrument, and chose the CIEL*a* that matches it b*(ClELAB) color difference calculation formula. Put the paper sample on the CS-650 Spectrophotometer , adopt the CIELAB color difference formula, and the instrument will automatically use the above color difference formula to test.
In the field of paper production, although the color can be evaluated visually, the error is relatively large due to the subjective factors of the Tester and the environment. Using a 3NH Spectrophotometer to detect paper is not only The color difference value can be controlled within the visual range, and the color fastness level evaluation, whiteness measurement, sample color determination, etc. can also be carried out, so as to prevent and control the color difference of the paper, combining experience and Technology works well together.
