Sulfuric acid paper 1, the properties of sulfuric acid paper
Sulfuric acid paper is a kind of hard film-like material, which is made by interweaving fine plant fibers, beating freely, not sizing, not adding fillers, making in wet state, soaking in 72% concentrated sulfuric acid for 2 ~ 3 s, washing with clean water, treating with glycerol and drying. Sulfuric acid paper is firm, dense and slightly transparent, and has the characteristics of strong oil resistance, waterproof permeability, good air tightness and high wet strength, and can be waterproof, moisture-proof, oil-proof and sterilized.
Main quality indicators related to printing process:
1) Quantization: It is divided into three categories according to two categories, namely, 75g/m2 for Class A, 60g/m2 for Class B and 45g/m2； for Class B; For c;
2) Density: ≥ 0.70 g/cm3;
3) Fracture length (vertical and horizontal average): A ≥5000m, B ≥4500m and C ≥ 4000m;
4) Blast resistance: dry -A ≥270kPa, B ≥250kPa, C ≥ 230 kPa; Wet -A ≥ 130kPa, B ≥ 120kPa, c ≥110kpa;
5) Oil permeability: ≤ 4/100cm2;
6)pH value: 7.01.0;
7) Moisture: 6.0% 1.0%.
2, the use of sulfuric acid paper
Kraft paper, also known as plate-making transfer paper sulfate, is mainly used in printing and plate-making industry. It has the characteristics of pure paper, high strength, good transparency, no deformation, sun resistance, high temperature resistance and aging resistance, and is widely used in manual drawing, pen/ink jet CAD plotter, engineering electrostatic copying, laser printing, art printing, document recording and so on. There are 63gA4, 63gA3, 73gA4, 73gA3, 83gA4, 83gA3, 90gA4, 90gA3 and other specifications.
3. Problems needing attention in printing sulfuric acid paper
1) print feed
Compared with other types of paper, printed sulfuric acid paper is relatively dry and prone to static electricity, and blank paper, double sheets and multiple sheets are easy to appear when moving paper. In order to ensure smooth paper feeding during printing, sulfuric acid paper should be dried before printing, and the temperature and humidity in the printing workshop should be appropriate. In addition, due to the firmness of sulfuric acid paper, the separation of paper is more difficult than that of ordinary paper with the same gram weight, so the air blowing volume and air suction volume should be slightly increased.
2) color recovery
Sulfuric acid paper is translucent, has strong oil and water penetration resistance and poor air permeability, so it has poor ink absorption and color reproduction ability in the printing process.
The coloring mechanism of an object is that when white light shines on the surface of the object, part of the light is absorbed, 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. When all the white light is reflected, the object is white; When all the white light is absorbed, the object is black; When all the white light is transmitted, the object is colorless. After sulfuric acid paper is printed, the actual ink color is very different from that observed on sulfuric acid paper because of its translucent performance of reflecting, absorbing and transmitting light at the same time. A small experiment shows that under the same printing conditions, magenta ink is printed on sulfuric acid paper and double-sided tape paper, and the solid density is measured. The solid density of sulfuric acid paper is 0.6 18, and that of double-sided adhesive paper is 0.97 1. It shows that the density of the same ink printed on sulfuric acid paper is much lower. Therefore, when printing sulfuric acid paper, we should pay attention to the adjustment of ink color and ink quantity. When observing the color of ink, it is best to put a stack of white paper under sulfuric acid paper, which can reduce or avoid color difference. Sulfuric acid paper has low smoothness.
4. Adjustment of printing process parameters
1) Water consumption control
Sulfuric acid paper is relatively dry and has a lot of hygroscopicity and deformability, so water should be used as little as possible when printing, otherwise it will have a great influence on overprinter accuracy. Take the Heidelberg model as an example, and control it within 40%. This kind of deformed paper is not suitable for overprinting four-color printed matter with monochrome machine or two-color machine. It is best to arrange printing on a four-color printing machine with alcohol dampening, or use waterless offset printing. Pay attention to the grain direction of paper when cutting, and ensure the overprinter accuracy of printed matter in many ways.
2) Adjustment of printing pressure
Because of the poor ink absorption of sulfuric acid paper, the printing pressure is slightly higher than other printing materials by about 0.02 mm
3) Selection of printing speed
In order to ensure smooth paper feeding, meet the technical requirements of overprinter accuracy and timely ink drying, it is best to use low-speed printing (3000 sheets/hour).