Publication of optical properties and test standards for printing paper
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In recent years, China's paper industry has developed rapidly. The total output and total consumption of paper and paperboard have ranked second in the world, and a complete standardization system has been formed. Among them, the national standardization law, measurement method and product quality law are the three basic laws that must be followed in the production and sale of paper products.
China's paper industry standards include national standards, light industry standards and corporate standards. As far as the application field is concerned, there are product standards, product performance test method standards and product test environment atmospheric condition standards, as well as paper quality supervision and inspection papermaking special measuring instruments light industry department department metrological verification procedures. According to the papermaking standardization system of China's paper industry, publishing printing paper is divided into two categories: uncoated paper and coated paper. Publishing papers used in large quantities in the printing industry, such as newsprint, offset printing paper, offset printing paper, letterpress printing paper, etc., non-coated printing paper; coated paper, low-quantity coated paper, cast coated paper, etc. class. The optical properties of the paper are based on the optical principle of the test. Whiteness, chromaticity, opacity, etc. are the diffuse reflection characteristics of the paper. Glossiness and printing gloss are the specular reflection characteristics of the paper. This article focuses on the optical properties of whiteness, chromaticity, opacity and other test standards for publishing printing paper.
Optical performance
Whiteness
As is known to all, white paper can truly and objectively reflect the full color of printed graphics, improve the contrast and clarity of the text, make the reproductions bright and colorful, and achieve the effect of illustration and text. The higher the whiteness of the paper, the more pronounced this effect. However, the whiteness should not be too high, otherwise the reflected light is strong, the visual nerve stimulation is too strong, and it is easy to cause visual fatigue. Therefore, the printing paper is not as white as possible. Moreover, the whiteness values of different printing papers are not the same. It is reported that China Children's Publishing House, from the perspective of protecting the visual acuity of children, many textbooks use low whiteness paper, and some books even use beans. Green, light yellow writing paper. Heilongjiang Children's Publishing House also used bean green and light yellow writing paper; Anhui Children's Publishing House also reduced the paper whiteness of teaching assistant books to 76%-85%. According to the Ministry of Education, the whiteness of children's textbooks is 75% to 76%.
Although the printing paper is basically white or nearly white, it has a color cast phenomenon, some are blue and some are reddish. The purpose is to make the visual judgment appear whiter, but it also varies from person to person. In any case, the same batch of paper should be consistent in whiteness, uniform in color, and inconspicuous in color, so as to avoid delamination of the color of the cut of the printed book.
2. Opacity
The opacity value of the printing paper directly affects the print-through of the printed product. The printing paper for various purposes must have sufficient opacity, otherwise the offset failure may occur easily.
3. Gloss
The gloss of the print is closely related to the specular reflection characteristics of the paper. The printing gloss of the paper refers to the solid printing on the paper sample with a predetermined standard bright ink under predetermined conditions, and the gloss of the printed area is measured after drying, expressed as a percentage. Generally, the gloss of the paper is high, the gloss of the printed matter is high, and the printed graphics are vivid and colorful. For example, coated paper gloss and printing gloss are required to be at least 60% and 88%.
Optical performance standards for each paper type
Newsprint
The national standard GB/T1910-1999 divides newsprint products into superior products, first-class products and qualified products.
1 brightness. Brightness is also called whiteness. The standard specifies that the whiteness values of the three grades are not less than 52%, 50% and 48% respectively;
2 tone reference value. It is stipulated that the three grades of products are based on L*≥80.0, a*=-2.0～+2.0 and b*<10.0 as the basis for controlling the color tone of each factory.
3 color difference △ E *. The color difference △E* of the same batch of paper, the superior product and the first-class product should be no more than 2.5 and 3.0 respectively, and the qualified product is not required.
4 opacity value. The opacity value of the finished products of 45g/m2 paper is 86.0%; the paper of 47g/m2 is 88.0%, the first grade and the qualified product is 86.0%; the paper of ≥49g/m2, the superior is 90.0%, First-class products and qualified products were 87.0%.
In addition, in June 2002, the China Newspaper Association's Materials Supply Committee formulated the “National Newsprint (User) Quality Standards”, which refers to the technical indicators of optical performance, in accordance with GB/T1910-1999 and the newsprint factory standards of relevant newsprint manufacturers. It is stipulated that the whiteness of newsprint with a basis weight of 45g/m2 and 48.8g/m2 is ≥56.0%, and the opacity is ≥90.0%.
2. Coated paper
According to the national standard GB/T1033-1995, the coated paper is divided into A, B-I, B-II, C, etc., and the whiteness value is 80.0% except for C and so on, and the other three are 85.0%. The opacity value varies depending on the amount of quantification, 70 to 90 g/m 2 is not less than 85.0%, 90 to 130 g/m 2 is not less than 90.0%, and paper having a diameter of more than 130 g/m 2 is not less than 95.0%. The opacity values are the same for different grades of products. The national standard has no specific requirements on the chroma value of the coated paper, but there should be no significant difference in the color of the same batch of paper.
3. Offset printing paper
The publishing printing industry calls offset printing paper a double-adhesive paper. It is commonly used in the industry as Daolin paper. It is specially used for multi-color offset printing. The light industry standard QB/T1012-1991 divides it into three grades: A, B and C. The specified whiteness values are not less than 87.0%, 82.0%, and 77.0%, respectively, and the opacity varies depending on the amount of quantification, 60 g/m2, 70 g/m2, 80 g/m2, 90 g/m2, 100 g/m2, 120 g/m2, and 150 g/ The opacity value of the offset paper of m2 stipulates that the products such as A are 84.0%, 86.0%, 87.0%, 89.0%, 91.0%, 93.0% and 95.0%, respectively, and the products such as B and C are lower than those of A and the like. There is no specific requirement for chromaticity, only the color of each batch of paper should be consistent, and there should be no obvious difference.
4. Offset book paper
According to the light industry standard QB/T1211-1991, offset printing papers are classified into A, B, and C. The whiteness values are A: 70.0% to 75.0%, B: ≥ 60.0%, and C: ≥ 55.0%. The opacity value of the three grade products is specified, 52g/m2 is not less than 78.0%, 60g/m2 is not less than 80.0%; 70g/m2 paper, A and other products are not less than 82.0%, and B and C grades are not less than 80.0%. The color should be consistent, and there should be no significant difference between each batch of paper.
5. Low basis weight coated paper
Also known as lightweight coated paper, LWC paper, there is no uniform national standard or industry standard, and finished product inspection is generally carried out according to enterprise standards or contract standards. In view of the fact that the paper is suitable for color printing, and the freight rate is low, the printing cost is greatly reduced, and it has been widely used internationally. In addition to meeting domestic demand, some light-coated papers produced by some papermaking enterprises such as Shandong Huatai, Quanlin, Chenming, Luohe Silver Pigeon, Yueyang Paper, and Guangzhou Paper have some exports. It is reported that the new national standards for coated printing paper, which is being developed, will make corresponding regulations and specifications for the performance of low-quantity coated paper.
In the method standards for the publication of optical properties testing of printing paper: national standard GB/T7973 "Determination of diffuse reflectance factor for pulp, paper and cardboard (diffuse/vertical method)", GBT7974" paper and paperboard whiteness determination method "Ejection / Vertical Method", GB/T7975 "Paper and Cardboard Color Measurement Method (Diffuse/Vertical Method)" and GB/T8940.1 "Paper and Paperboard Whiteness Measurement Method (45/0 Directional Reflection Method)" promulgated and implemented It has been more than 10 years. The promulgation and implementation of these method standards is of great significance for the uniform paper performance testing operation, improving the paper optical performance testing technology, popularizing the basic knowledge of colorimetry theory, and guiding production. These standards apply to optical performance testing of published printing papers associated with diffuse reflection factors.