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1. High Whiteness of Coated Paper The whiteness of paper is the ability of the paper to fully reflect light after it is illuminated, as well as the light intensity of the paper. Because the coated paper is made of porcelain clay, calcium carbonate, titanium dioxide, adhesives and dispersants, fluorescent brighteners, plasticizers, PH modifiers and other chemical additives formulated white coating, in a special coating equipment It is coated on the surface of the base paper, dried and pressed to produce a white coated paper. Therefore, the general whiteness of coated paper is above 85%, and the whiteness of other printed paper is only around 50 to 80%. In addition coating paper coating also contains high refractive index, high brightness of fine-grained pigments, so coated paper whiteness and gloss are higher than offset paper and general writing paper. Due to the high whiteness of the coated paper, it can better reflect the full color of the color picture, achieve a colorful, rich layer of copying effect, greatly improving the printing contrast, so that the light and dark levels are more abundant.
2. Smoothness of coated paper surface Smoothness is one of the most important printing performance indicators of paper. Requirements coated paper smoothness to reach 400 to 600 seconds. For example, polishing coating paper with extremely high quality needs to be coated twice. After the wet coating is calendered and heated by the metal roller polished into a mirror surface, a very smooth surface can be obtained with good porosity and ink absorption. Other printed papers were observed under a 10x magnifier to have uneven surfaces. Some of the height differences were as high as about 25 μm (micrometers). However, the microscopic height difference of coated paper, especially advanced coated paper, is generally within 3 to 5 μm. Therefore, the surface of the coated paper is high in smoothness, and the printed ink is glossy and the dots are neat and beautiful. This is due to the fact that a smooth surface can reflect parallel incident beams like a mirror. In particular, the coated paper is used for dot and dot picture printing in shades of light, and its effect is excellent. Small dots are not lost and the edges of the dot are very neat.
Coating paper can not only print products with high gloss, but also have high optical density of ink and even ink. Therefore, the void rate of coated paper is low, only 38 to 40%, while the newsprint void rate can reach 58 to 65%, and the relief paper porosity is also about 50%. The higher the voidage, the stronger the ink absorption, and the paper whose surface absorption capacity is too strong will affect its gloss and optical density. The voidage of the coated paper is lower than that of other printing papers, so its absorption capacity is low, and therefore the gloss and optical density are high.
Especially when the coated paper is printed on the ground, the surface of the paper has a high degree of smoothness, and the ink layer is more flat and solid, and its printing quality is greatly superior to other printed papers.
3. The surface strength of coated paper is high. The paper surface must have high strength, which is an important printability index. Base paper is the basis of coated paper. In order to produce good coated paper, it is not only required that the base paper has a high tensile strength, but also that it has a high surface strength. Due to the high surface strength of coated paper, its surface coating is resistant to moisture and friction. Their binding force between fiber and filler and rubber compound is stronger than that of ink on paper. It is greater than the peeling tension of paper, and is greater than the adhesive force and viscosity of rubber blanket. Therefore, there is little phenomenon of de-powdering and hair loss.
4. Surface efficiency of coated paper is high Paper surface efficiency refers to the effect of paper on the color of the ink, and it is also closely related to the glossiness of the paper. The higher the paper surface efficiency, the higher the gloss, the general surface efficiency of the coated paper is about 46%, the glossiness is about 36%, the surface efficiency of the advanced coating paper is about 58%, and the glossiness is as high as 54%. Paper surface efficiency and hue error and gray scale also have a corresponding relationship. The coated paper with high surface efficiency has relatively small hue error and gray scale, and the color efficiency is relatively high. It is relatively easy to achieve the gray balance when overprinting.
5. The coated paper has a certain pH value. The paper is acidic (PH value <7) or alkaline (PH value> 7). This property is very good for the printing process, the service life of the printing plate, and the drying speed of the ink. Great influence. The paper is acidic ink drying slowly, the paper is alkaline ink drying faster. The coated paper is weakly alkaline, the general PH value between 8 to 9, so the ink drying speed is also faster.
According to the printing process requirements, the pH of the paper is preferably neutral, that is, the pH is about 7 or it is weakly alkaline, and the pH of the coated paper is suitable for the printing process.
6. The moisture content of the coated paper is moderate. The moisture content of the paper is too large, which weakens the tensile strength of the paper, increases the plasticity, is easily deformed, slows down the drying speed of the print, and is prone to defects such as smudging on the back of the printed product.
The moisture content of the paper is too small, and the paper becomes brittle, hard, tearing, and static electricity.
According to the printing process requirements, the moisture content of the paper is about 7%. The coated paper after calendering, the moisture content is generally between 6-8%, is suitable for printing process requirements. Because the moisture content of the paper needs to be controlled during calendering, so that the water content of the raw paper is uniform, so the coated paper has better dimensional stability, and its retractility is also relatively small. If printed in an air-conditioned printing shop, the coated paper is guaranteed to be Printing quality will be more favorable. Because paper's folding resistance, tear resistance, tensile strength, and expansion and contraction are all related to the relative humidity in the surrounding air, the retractability of the paper is especially noticeable. Therefore, after the printing shop is equipped with air-conditioning, the temperature and relative humidity are kept stable to ensure the production of good-quality color prints. (Yu Cunfu) ("China Packaging News")
Printability of coated paper
Printing suitability refers to the necessary properties suitable for printing. Coated paper (also known as coated paper) has a good printability, so most of the embossing and offset printing uses it to print art pictures, inserts, pictorials, albums, and packaging boxes. Bid farewell is a double-sided coating of thin-layer coating paper, which has become the main text of many books and magazines, which will play a decisive role in improving the quality of books and periodicals. The printability of coated paper can be summarized as follows: