Paper is an important part of consumables in printing. Its quality determines the stability of the printing process and the quality of the printing quality.
The paper can be divided into three types during printing: the weight of newsprint is about (49-52g / m2), which is mainly used for the printing of newspapers. Because the pulp of newsprint also has a lot of lignin and impurities, the surface of newsprint yellows, and It is not suitable for long-term placement, it is easy to become brittle, and the printing quality is poor. Usually only monochrome printing is performed on newsprint. The offset paper contains less lignin and impurities, so the offset paper has less elasticity, uniform absorption of ink, good smoothness, tight and opaque texture, good whiteness, strong water resistance, high printing quality, suitable for Relatively exquisite printing paper. The usual weight is (50-180g / m2). The basis weight of coated paper is generally (150 ～ 280g / m2), which is mostly used for high-grade and exquisite printed paper. Coated paper is divided into single-sided coated paper, double-sided coated paper, matte coated paper, and cloth coated paper. According to the quality, it is divided into a, b, and c. The main raw materials of coated paper are coated base paper and paint. The requirements for the base paper of the copperplate are uniform thickness, small stretchability, high strength and good water resistance. The paper surface is not allowed to have spots, wrinkles, eye holes and other paper diseases. The coating used for coating is composed of high-quality white pigments (such as kaolin, barium sulfate, etc.), adhesives (such as polyvinyl alcohol, casein, etc.) and auxiliary additives. of. This kind of paint with high fluidity and high solid content is coated thinly and evenly on the base paper by the coating machine, then dried, rolled into a roll on the reel, and sent to the super calender Finishing, final cutting, paper selection and packaging.
Paper is a relatively large proportion of printing costs. As global pulp prices have risen, so have paper prices. Make printing enterprises, printing costs are on the high side. Choosing the right paper to reduce the consumption of paper in the printing process is an efficient way to increase the profits of the printing industry.
When buying paper, some parameters of paper should be considered:
1. Whiteness: refers to the degree of whiteness on the surface of the paper. Magnesium oxide is usually called 100% white, and the whiteness of the paper is relative to this 100% white. In printing, high-whiteness paper is generally used for relatively exquisite prints. The relative spread of high-whiteness prints is large, the prints are rich in layers, and the color reproduction is good. When buying, printing companies should determine the required whiteness range according to the printing effect required by their own printing business. The paper with high whiteness will have a relatively high price because of less internal impurities.
2. Quantitative: refers to the weight of the paper per unit area, also called the gram weight. Different printed materials require different amounts of paper. Generally speaking, newspaper printing generally uses low basis weight paper, and packaging printing generally uses high basis weight paper. The higher the paper weight, the greater the paper tightness and the higher the reproducibility of the printed matter.
3. Smoothness: the time required for a certain volume of air to pass through the gap between the sample surface and the glass surface under a certain pressure under a certain vacuum. Smoothness is an index to evaluate the degree of unevenness of the surface of paper or paperboard. It is very important for printing paper and it affects the uniform transfer of printing ink. The smoothness of paper or paperboard is affected by factors such as fiber morphology, pulp beating degree, weaving method of papermaking nets and felts, wet-pressing pressure and the presence or absence of calendering, filling and coating.
4. Surface tension: also called the pulling strength. It is the strength of separation between the paper coating layer and the inside of the paper. In some papers, due to too many additives, there will be a phenomenon of fluffing and fluffing during printing. This is caused by the low surface tension of the paper. When choosing paper, pay attention to the requirements on the surface tension of the paper.
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