In general, paper with a basis weight of 200 g/m2 or more and a thickness of 0.1 mm or more is collectively referred to as cardboard. According to its use, it can be divided into four categories: packaging paperboard, industrial technology paperboard, construction paperboard and decorative paperboard. The coated white paperboard belongs to the category of packaging paperboard. It is a processed paperboard made by coating and finishing after coating the white paper on the raw paperboard, and is mainly used for packaging boxes after one-sided color printing. The performance characteristics of white paperboard: The whiteness of the coated surface is higher, the smoothness, the ink absorption and the printing gloss are all very good, and the cardboard itself has a good stiffness and folding resistance, so that it can perform high quality on it. The color printing, which can meet the requirements of packaging, is a high-quality material for high-end commodity packaging. The coated white paperboard is divided into A, B, and C according to different quality levels. When selecting, several aspects such as variety, specification, and quality grade should be considered. A type white board paper with bleached chemical wood pulp on the surface, sulphate wood pulp, mechanical wood pulp, fine waste paper, etc. on the surface layer and the bottom layer. It has good folding resistance and is used for the production of small paper boxes; type B white paper, The surface uses bleached chemical pulp or finest white paper, the surface layer and bottom layer use waste pulp, and the type C whiteboard paper uses lower grade materials than the type B whiteboard paper, which is no longer produced. In order to meet the needs of the packaging industry, China annually imports large quantities of coated white paperboard. Although domestic self-sufficiency has increased, the amount of imports continues to increase year after year. In recent years, there have been many improvements in domestic products, but there is still a considerable gap between imported products and flatness, color, uniformity, size, and packaging. Most of the domestic products are poorly printable, mainly due to the poor quality of the base paper, inadequately coated pharmaceuticals, and imperfect post-finishing processes. In the physical properties of cardboard, the stiffness of domestic products needs to be improved, and the uniformity of thickness, weight, and strength needs to be improved.
1 Structure of coated white paperboard
The layer structure of the coated white paperboard is as shown in FIG. 1 and consists of a secondary coating layer, a surface layer, a core layer, a bottom layer, and a one-to-second coating layer. Layers 1 and 5 are coating layers, whose role is to increase the whiteness and printing effect of the coated paper; 2 to 4 layers are sulphate wood pulp, mechanical wood pulp, deinked waste newsprint paper pulp, and its role is to maintain the cardboard The intensity and whiteness. The carton is made of cardboard and piled up. The carton is not squashed because of the strength of the carton; the 3rd layer is mixed waste newsprint pulp, waste magazines, waste corrugated cardboard pulp. Its role is to increase the thickness of the board, reduce the cost of the board and improve the ink absorption of the board.
2 Technical requirements for coated white paperboard
1) Strength. The reason why cardboard becomes cardboard is strength first, which is the basic performance of packaging materials. When used as a packaging material, cardboard is usually made into a carton. It is obvious that the performance of the carton differs from that of the paper bag and must have a solid shape and a certain hardness. For example, the folding lid of a medicinal carton breaks at the fold line after frequent opening and closing, which is related to insufficient folding strength.
2) has a good processing performance. In punching and forming machines, the white paperboard is required to have suitable hardness and cushioning properties, and is easy to die-cut and easy to bond. This is in line with the process requirements of the box making.
3) Excellent printability. Adapted to offset and gravure and other printing methods.
4) Because of the proper cushioning and light weight characteristics of white paperboard, it is very beneficial to the protection and transport performance of the package contents.
3 Classification and Technical Specifications of Coated Whiteboard
The classification of coated whiteboard varies from country to country. At present, there are two types of single-coated white cardboard and double-sided coated white paperboard in China. The rations of single-side coated gray paperboard are 200, 220, 250, 270, 300, 350, 400, 450g/m2; the quantification of double-coated white paperboard is 200, 220, 250, 270, 300, 350, 400g/m2. The coated white paperboard is generally based on flat paper, the size of 787mm × 1092mm, 880mm × 1230mm. There are also reeled white paperboards. The technical specifications of single-side coated gray cardboard can refer to the QBl011-91 standard, and the technical specifications of double-sided coated white cardboard can refer to the ZBY32024-90 standard.
4 Printability of coated white paperboard
The printability of coated white paperboard refers to the requirements for the paper to meet the requirements of ink, printing plates, and printing conditions to ensure the smooth operation of the print job and obtain the necessary conditions for high-quality prints. The printability of the coated white paperboard is not a certain fixed property, but is compatible with different printing conditions and different print product characteristics, including two aspects of print job suitability and print quality suitability. The former refers to various properties that the paper can successfully meet for the necessary operations on the printing press, such as the smoothness of the paper; the latter refers to the properties of the paper that play a decisive role in the quality of the print, such as whiteness, gloss, thickness, surface strength, Smoothness, ink absorption, etc. The following is a brief analysis of the main properties of coated white paperboard related to print quality suitability.
4.1 Whiteness The whiteness of paperboard refers to the ability of the board to fully reflect light after being exposed to light, that is, the ratio of reflected light to incident light under certain test conditions. The whiteness of cardboard is one of the important indicators of coated white paperboard. The high whiteness of paperboard can enhance the contrast between ink and paperboard and help to distinguish the graphic and text. Printing a color picture on a cardboard with high whiteness can make the picture bright and beautiful.
4.2 Gloss Cardboard gloss indicates the brightness of the cardboard surface, and the gloss of the cardboard is closely related to printing. High-gloss paperboard can make the color of the prints bright, but cardboard with too much gloss will cause glare to the carton prints, which is not conducive to its display effect. The board is sometimes coated with varnish after printing to increase gloss and protect the ink layer from damage.
4.3 Thickness Thickness refers to the thickness of paper. From the printing point of view, the thickness of each batch of cardboard is generally required to be uniform. If the thickness of the cardboard is not uniform, the printing pressure will be unstable during the printing process, and it will suddenly change. So that the printing ink transfer situation changes, imprinting also different shades, affecting the quality of printed matter.