Optical properties and test standards of publishing and printing paper

In recent years, with the rapid development of China's paper industry, the total output and consumption of paper and paperboard have ranked second in the world, and a complete set of 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 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 special measuring instruments measurement and verification regulations of Ministry of light industry According to the standardization system 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 newsprint, offset printing paper, offset book and periodical paper, relief printing paper, etc., belongs to the category of uncoated printing paper; copperplate paper, low quantitative coated paper, cast coated paper, etc., belong to the category of coated printing paper According to the optical principle, whiteness, chroma and opacity are diffuse reflection characteristics of paper, while glossiness and printing glossiness are specular reflection characteristics of paper This paper focuses on the optical properties and test standards of whiteness, chroma, opacity and so on As we all know, white paper can truly and objectively reflect all the colors of the printed text, improve the contrast and clarity of the text, make the reproduction colorful, and achieve the effect of both pictures and texts The higher the paper whiteness, the more significant the 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, so the higher the whiteness of printing paper, the better Moreover, the whiteness values of printing paper for different purposes are 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 The Heilongjiang children's Publishing House also uses the bean green and light yellow writing paper; the Anhui children's Publishing House also reduces the whiteness of the paper for teaching auxiliary books to 76% - 85% According to the Ministry of education, the whiteness of children's textbook paper is 75% - 76% Although the paper used for publishing and printing is basically white or nearly white, there are color deviation phenomena, some are blue, some are red, the purpose is to make the visual judgment appear more white, but also different from person to person In any case, the paper supplied in the same batch shall have the same whiteness, uniform color tone and no obvious color difference, so as to avoid layering of the cut color of the printed matter bound into volumes The opacity value of the printing paper directly affects the transparence of the printed matter All kinds of printing paper must have enough opacity, otherwise it is easy to have transparence failure The glossiness of the printed matter is closely related to the specular reflection characteristics of the paper The printing glossiness of paper refers to the field printing on the paper sample with the specified standard glossy ink under the specified conditions, and the glossiness of the printing area is measured after drying, expressed in percentage General paper glossiness is high, the glossiness of printed matter is high, the level of printed matter is bright, and the color is bright For example, the paper glossiness and printing glossiness Zui are lower than 60% and 88% The products of newsprint are divided into three grades: excellent grade, first grade and qualified grade according to GB / t1910-1999 Brightness Brightness is also known as whiteness According to the standard, the whiteness values of the three grades of products shall not be less than 52%, 50% and 48%, respectively It is stipulated that l * ≥ 80.0, a * = - 2.0 ~ + 2.0 and B * < 10.0 are the basis for controlling the color of products in three grades ③ Color difference △ e * The color difference △ e * of the same batch of paper, superior products and first-class products shall be no more than 2.5 and 3.0 respectively, and there is no requirement for qualified products Help ④ opacity value The opacity value of 45g / m2 paper is 86.0%; that of 47g / m2 paper is 88.0% for superior products, 86.0% for first-class products and qualified products; that of ≥ 49G / m2 paper is 90.0% for superior products, 87.0% for first-class products and qualified products In addition, in June 2002, the material supply Committee of China Press Association formulated the "quality standard of domestic newsprint (user)" referring to the delivery standard of newsprint of GB / t1910-1999 and other newsprint manufacturers Among them, the technical indicators related to optical performance are specified, the whiteness and opacity of newsprint of 45g / m2 and 48.8g/m2 are ≥ 56.0% and ≥ 90.0%, respectively According to GB / t1033-1995, the paper is divided into four grades: A, B-I, b-II and C the whiteness value of the other three grades is 85.0% except C grade, which is 80.0% The opacity value varies according to the quantity, 70-90g / m2 shall not be less than 85.0%, 90-130g / m2 shall not be less than 90.0%, and the paper specification of more than 130g / m2 shall not be less than 95.0% The opacity values of the same quantitative products of different grades are the same There is no specific requirement for the chromaticity value of the coated paper in the national standard, but there should be no obvious difference in the color of the same batch of paper Offset printing paper in the publishing and printing industry, offset printing paper is called double offset paper, which is commonly known as forest paper in the commercial field It is specially used for multi-color offset printing 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 The opacity varies with the quantity The opacity values of offset paper of 60g / m2, 70g / m2, 80g / m2, 90g / m2, 100g / m2, 120g / m2 and 150g / m2 are specified The opacity values of Grade A are 84.0%, 86.0%, 87.0%, 89.0%, 91.0%, 93.0% and 95.0%, respectively Grade B and grade C are lower than Grade A There is no specific requirement for the color, only the color of each batch of paper should be the same, there should be no obvious difference According to the light industry standard QB / t1211-1991, offset book paper is divided into a, B and C, with a whiteness value of 70.0% - 75.0%, B: ≥ 60.0% and C: ≥ 55.0% The opacity value of three grades of products is specified, 52g / m2 is not less than 78.0%, 60g / m2 is not less than 80.0%; 70g / m2 paper, Grade A is not less than 82.0%, and grade B and C are not less than 80.0% The color should be consistent, and there should be no significant difference between each batch of paper LWC paper, also known as LWC paper, currently there is no unified national or industrial standard, and the finished product inspection is generally carried out according to the enterprise standard or contract standard This paper has been widely used in the world, because it is suitable for color printing and the freight is low Shandong Huatai, Quanlin, Chenming, Luohe silver pigeon, Yueyang paper industry, Guangzhou Paper and other paper-making enterprises produce light coated paper which not only meets the domestic demand, but also exports part of it It is reported that in the new national standard of coated printing paper that is being formulated, the corresponding regulations and specifications will be made for the performance indicators of low quantitative coated paper Among the methods and standards for testing the optical properties of paper for publication and printing, the national standards GB / t7973, the paper and board diffuse reflectance factor measurement method (diffuse / vertical method), gbt7974, the paper and board whiteness measurement method (diffuse / vertical method), GB / t7975, the paper and board color determination method (diffuse / vertical method) and GB / t8940.1 The paper and board whiteness determination method (45 / 0 directional reflection method) has 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 paper performance testing operation, improve the paper optical performance testing technology, popularize the basic knowledge of chromaticity theory and guide the production These standards are applicable to the measurement of optical properties of printing paper related to diffuse reflection factors.