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Optical properties and testing of publishing and printing paper

in recent years, China's paper industry has developed rapidly. The total output and 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 Law and product quality law are the three basic laws that must be followed in the production and sales of paper products

China's paper industry standards include national standards, light industry standards and enterprise standards. In terms of application fields, there are product standards, product performance test method standards and product test environmental atmospheric conditions standards. At the same time, there are also paper quality supervision and inspection, special measuring instruments for paper making, and metrological verification regulations of the Ministry of light industry. According to the standardization system table of China's paper industry, publishing and printing paper is divided into two categories: uncoated paper and coated paper. The paper used in large quantities in the publishing and printing industry, such as paper, offset printing paper, offset books and periodicals paper, relief printing paper, etc., belongs to uncoated printing paper; Coated paper, low weight coated paper, cast coated paper, etc. belong to coated printing paper. Optical properties of paper from the optical principle of the test basis, whiteness, chromaticity, opacity and so on belong to the diffuse reflection characteristics of paper, while glossiness and printing glossiness belong to the specular reflection characteristics of paper. This paper mainly introduces the optical properties and test standards of printing paper such as whiteness, chromaticity, opacity, etc. of Ganfeng lithium and Savi technology, which are the special co organizers of this time

optical performance

1 Whiteness

as we all know, white paper can truly and objectively reflect all the colors of printed pictures and texts, improve the contrast and clarity of words, and make the reproductions colorful, achieving the effect of both pictures and texts. The higher the whiteness of the paper, the more significant this effect is. However, the whiteness should not be too high, otherwise the reflected light is strong, and the stimulation to the visual nerve is too strong, which is easy to cause visual fatigue. Therefore, the higher the whiteness of the printing paper is, the better. Moreover, the whiteness value of printing paper for different purposes is also different. It is reported that China children's publishing house, from the perspective of protecting children's eyesight, many textbooks use low whiteness paper, and some books even use bean green and light yellow writing paper. Heilongjiang children's Publishing House also uses bean green and light yellow writing paper; Anhui children's Publishing House also reduced the whiteness of teaching auxiliary books to 76% - 85%. The Ministry of education stipulates that the whiteness of textbook paper for children is 75% - 76%

although the paper used for publishing and printing is basically white or near white, there are color biases, some blue and some red, in order to make the visual judgment appear whiter, but it also varies from person to person. In any case, the paper supplied in the same batch should have the same whiteness, uniform hue and no obvious color difference, so as to avoid the delamination of the cut tone of the bound printed matter

2. Opacity

the impermeability of printing paper can ensure that the spring is placed in different places of the pressure plate, and the experimental force is basically 1. The brightness value directly affects the penetration of printing products. Printing paper for various purposes must have sufficient opacity, otherwise it is easy to cause penetration failure

3. Glossiness

the glossiness of printed matter is closely related to the specular reflection characteristics of paper. The printing glossiness of paper refers to the glossiness of the imprinted area measured after the paper sample is printed on the spot with the specified standard bright ink under the specified conditions, which is expressed as a percentage. Generally, the gloss of paper is high, while that of printed matter is high. The graphic and graphic levels of printed matter are bright and colorful. For example, the glossiness of coated paper and printing should be at least 60% and 88%

optical performance standards of various paper types

1 Paper

the national standard gb/t divides paper products into excellent products, first-class products and qualified products

① brightness. Brightness is also called whiteness. The standard stipulates that the whiteness values of the three grades of products are not less than 52%, 50% and 48% respectively

② hue reference value. It is stipulated that l* ≥ 80.0, a* = - 2.0 ~ +2.0 and b* 10.0 are used as the basis for each factory to control the hue of the three grades of products

③ color difference △ e*. The color difference △ e* of the same batch of paper, excellent products and first-class products should be no more than 2.5 and 3.0 respectively, and there is no requirement for qualified products

④ opacity value. The opacity value of the three grades of 45g/m2 paper is 86.0%; 47g/m2 paper, 88.0% for superior products, 86.0% for first-class products and qualified products; ≥ 49g/m2 paper, 90.0% for superior products, 87.0% for first-class products and qualified products

in addition, the material supply Committee of China Newspaper Association formulated the "domestic paper (user) quality standard" in June 2002 with reference to gb/t and the paper delivery standards of relevant paper manufacturers. Among them, the technical indicators related to optical properties stipulate that the whiteness of paper with a quantitative of 45g/m2 and 48.8g/m2 is of great significance ≥ 56.0%, and the opacity ≥ 90.0%

2. Coated paper

according to the national standard gb/t, coated paper is divided into four grades A, B-I, b-II and C. the whiteness value is 85.0% except for Grade C, which is 80.0%. The opacity value varies according to different quantities. It is not less than 85.0% for 70 ~ 90g/m2, not less than 90.0% for 90 ~ 130g/m2, and not less than 95.0% for paper greater than 130g/m2. The opacity value of products with the same quantity and different grades is the same. The national standard has no specific requirements for the chromaticity value of coated paper, but the color of the same batch of paper should not be significantly different

3. Offset printing paper

the publishing and printing industry refers to offset printing paper as double offset paper, which is popularly known in commerce as forest paper. It is specially used for multi-color offset printing. Light industry standard qb/t divides it into three grades: A, B and C. The specified whiteness value is not less than 87.0%, 82.0% and 77.0% respectively, and the opacity varies with different quantities. The opacity value of offset paper of 60g/m2, 70g/m2, 80g/m2, 90g/m2, 100g/m2, 120g/m2 and 150g/m2 stipulates that grade A is 84.0%, 86.0%, 87.0%, 89.0%, 91.0%, 93.0% and 95.0% respectively, and grade B and C are correspondingly lower than Grade A. There are no specific requirements for chromaticity, but it is proposed that the color of each batch of paper should be consistent without obvious differences

4. Offset book paper

light industry standard qb/t stipulates that offset book paper is divided into three grades: A, B and C, and the whiteness value is a:70.0% ~ 75.0%, b: ≥ 60.0%, c: ≥ 55.0%. The opacity value of three grades of 1 (9) month products stipulates that 52g/m2 is not less than 78.0%, 60g/m2 is not less than 80.0%; 70g/m2 paper, grade a not less than 82.0%, grade B and C not less than 80.0%. The color should be consistent, and there should be no significant difference between each batch of paper

5. Low weight coated paper

also known as lightweight coated paper, LWC paper. At present, there is no unified national standard or industry standard, and the finished product inspection is generally carried out according to the enterprise standard or contract standard. In view of the fact that this kind of paper is suitable for color printing and has low freight, which greatly reduces the printing cost, it has been widely used in the world. In addition to meeting domestic demand, some light coated paper produced by some paper-making enterprises such as Shandong Huatai, Quanlin, Chenming, Luohe Yinge, Yueyang paper, Guangzhou paper also has some exports. It is reported that the new national standard for coated printing paper, which is being formulated, will make corresponding provisions and specifications for the performance indicators of low weight coated paper

among the methods and standards related to the optical performance test of publishing and printing paper: the national standards gb/t7973 pulp, paper and board Determination of diffuse reflectance factor (diffuse/vertical method), gbt7974 paper and board whiteness determination method (diffuse/vertical method), gb/t7975 paper and board color determination method (diffuse/vertical method) and gb/t8940.1 paper and board whiteness determination method (45/0 directional reflection method) have been promulgated and implemented for more than 10 years. The promulgation and implementation of these methods and standards are of great significance to unify the testing operation of paper performance, improve the testing technology of paper optical performance, popularize the basic knowledge of colorimetry theory, and guide production. These standards are applicable to the optical performance test of publishing and printing paper related to diffuse reflection factors

information source: Printing Technology

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