Sulfuric acid paper, also known as plate-making sulfuric acid transfer paper, is mainly used in the printing and plate-making industry. It has the characteristics of pure paper, high strength, good transparency, no deformation, light resistance, high temperature resistance, anti-aging, etc. It is widely used for manual drawing and pen writing / Inkjet CAD plotter, engineering xerography, laser printing, art printing, file recording, etc. There are various specifications such as 63gA4, 63gA3, 73gA4, 73gA3, 83gA4, 83gA3, 90gA4, 90gA3 and so on.
1. The nature of sulfuric acid paper
Sulphuric acid paper is composed of fine plant fibers interweaving each other, freely beating, sizing, no fillers, papermaking in wet state, soaked in 72% concentrated sulfuric acid for 2 ~ 3s, washed with water and treated with glycerin, dried A hard film-like substance formed. Sulfuric acid paper is solid, dense and slightly transparent, has the characteristics of strong resistance to penetration of grease and water, airtight, and high wet strength, and can be waterproof, moisture-proof, oil-proof, sterilizing and disinfecting.
The main quality indicators related to the printing process:
1) Quantitative: Divided into three grades according to grade 2, Grade A 75g / m2, Grade B 60g / m2, Grade C 45g / m2;
2) Tightness: ≥0.70g / cm3;
3) Cracking length (average of vertical and horizontal): A equal ≥5000m, B equal ≥4500m, C equal ≥4000m;
4) Breaking resistance: dry-A etc. ≥270kPa, B etc. ≥250kPa, C etc. ≥230kPa; wet-A etc. ≥130kPa, B etc. ≥120kPa, C etc. ≥110kPa;
5) Oil permeability: ≤4pcs / 100cm2;
6) pH value: 7.0 ± 1.0;
7) Moisture: 6.0% ± 1.0%.
2. Problems that should be paid attention to when printing sulfuric acid paper
1) Printing paper
Compared with other types of paper, printing sulfuric acid paper is relatively dry, and it is easy to produce static electricity. It is easy to appear empty sheets, double sheets and multiple sheets when feeding paper. In order to ensure the smoothness of the paper during printing, the sulfuric acid paper should be dried before printing, and the temperature and humidity of the printing workshop should be appropriate. In addition, due to the strength of sulfuric acid paper, the separation of paper is more difficult than that of ordinary paper of the same gram weight, so the amount of air blowing and air suction are slightly increased.
2) Color reproduction
Sulfuric acid paper is semi-transparent, and has strong resistance to penetration of grease and water, poor permeability, poor absorption of ink and color reproducibility during printing.
The color rendering mechanism of an object is as follows: When white light is irradiated to 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 reflects the color of the object in the human eye. When all white light is reflected, the object is white; when all white light is absorbed, the object is black; when all white light is transmitted, the object is colorless. After printing on 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 greatly different from the color observed on sulfuric acid paper. A small test showed that under the same printing conditions, the magenta ink was printed on sulfuric acid paper and double glue to measure the solid density, the solid density of the sulfuric acid paper was 0.618, and the double adhesive paper was 0.971. It shows that the density of the same ink printed on sulfuric acid paper is much lower. Therefore, when printing sulfuric acid paper, pay attention to the adjustment of ink color and ink volume. When observing the ink color, it is best to pad a stack of white paper under the sulfuric acid paper, so that the color difference can be reduced or avoided. The smoothness of sulfuric acid paper is low <100s, which is not suitable for fine dot printing, and the number of screen lines should not be too high.
3. Adjustment of printing process parameters
1) Water consumption control
Sulfuric acid paper is relatively dry and has a large amount of moisture absorption and deformation. Use as little water as possible during printing, otherwise it will greatly affect the accuracy of overprinting. Take the Heidelberg model as an example, the control is within 40%. This kind of paper with a large amount of deformation is not suitable for overprinting four-color prints with a single-color machine or a two-color machine. It is best to arrange for printing on a four-color press that uses alcohol dampening, or to use waterless offset printing. When opening the material, pay attention to the thread direction of the paper, and ensure the accuracy of the overprint of the printed products in many ways.
2) Adjustment of printing pressure
Due to the poor ink absorption of sulfuric acid paper, the printing pressure is slightly larger than other printing materials by about 0.02mm.
3) Selection of printing speed
In order to ensure the smooth running of the paper, and meet the process requirements of many aspects such as overprint accuracy and timely drying of ink, it is better to use low-speed printing (3000 prints / hour).
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