1. Properties of Sulfuric Acid Paper Sulfuric acid paper is intertwined with fine plant fibers, free-powdered, sizing, filler-free, paper-making in a wet state, soaked in 72% concentrated sulfuric acid for 2 to 3 seconds, and washed with clean water. Treated with glycerin and dried to form a hard film type material. Sulfuric acid paper is solid, dense and slightly transparent, with strong resistance to grease and water penetration, airtight, and high wet strength, and can be waterproof, moisture-proof, oil-proof, sterilizing and disinfecting.
2. Color reproduction
Sulfuric acid paper is translucent and has strong resistance to penetration of oil and water, poor air permeability, and poor ink adsorption and color reproduction in the printing process.
The color rendering mechanism of the object is as follows: When the white light is irradiated on the surface of the object, part of the light is absorbed by the surface of the object, part of the light is reflected, and part of the light is transmitted; the reflected light is reflected in the human eye as the color of the object. If the white light is all reflected, the object is white; if the white light is all absorbed, the object is black; if the white light is all transmitted, the object is colorless. After the printing of sulfuric acid paper, because of its translucent performance, the three forms of reflection, absorption, and transmission of light exist at the same time, making the actual ink color and the color observed on the sulfate paper vary greatly. A small test showed that under the same printing conditions, the magenta ink was printed on sulfuric acid paper and double gum to measure the solid density, the solid density of sulfate paper was 0.618, and the offset paper was 0.971. Explain that the same ink is printed on sulfate paper at a much lower density. When printing sulfuric acid paper for this purpose, attention should be paid to the adjustment of the ink color and the ink amount. When observing the ink color, it is better to put a stack of white paper under the sulfuric acid paper, which can reduce or avoid the color difference. Sulfuric acid paper has a low smoothness of 100s and is not suitable for fine screen printing. The number of screens should not be too high.
3, adjustment of printing process parameters
1) Water consumption control
Sulfuric acid paper is relatively dry, with a large amount of moisture absorption deformation, and the water used for printing is as small as possible. Otherwise, the overlay accuracy is greatly affected. Take the Heidelberg model as an example, control it within 40%. Such a large amount of deformed paper is not suitable for overprinting four-color prints with a monochrome machine or a two-color machine. It is best to print on four-color printing presses using alcohol dampening or waterless offset printing. When the material is opened, pay attention to the direction of the paper's silk, in many ways to ensure the accuracy of overprinting of the printed product.
2) Adjustment of printing pressure
Due to the poor ink absorption of sulfuric acid paper, the printing pressure is slightly larger than that of other substrates 0.02mm.
3) Selection of printing speed
In order to ensure the smooth running of the paper, to meet the process requirements of overprint accuracy, timely drying of ink and other aspects, the use of low-speed printing (3000 print hours) is better. Printing sulfuric acid paper is relatively dry compared to other types of paper, and it is prone to generate static electricity. It is prone to empty sheets, double sheets and multiple sheets when paper is moved. In order to ensure the smooth running of paper during printing, sulfuric acid paper must be printed before printing, and the temperature and humidity of the printing shop should be appropriate. In addition, because the sulfate paper is firm, the separation of the paper is more difficult than the ordinary paper of the same weight, so the amount of blowing and the amount of suction are slightly increased.