Characteristics of the hottest paper sheet and its

2022-10-03
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Paper characteristics and printing faults

paper is a thin-film material formed by the interweaving of fine plant fibers in a wet state, adding an appropriate amount of fillers, glues, pigments, and through the papermaking process of dehydration, pressing, drying and so on

composition and function of paper

filler: 1 Kaolin (also known as clay); The consumption of plastic per vehicle increased from 100 ~ 130kg in the 1990s to 152kg in 2004 and 174kg2 in 2006 talc; 3. Gypsum powder; 4. Calcium carbonate and magnesium hydroxide; 5. Barium sulfate

the role of fillers in papermaking:

1 Improve the smoothness of paper surface; 2. Reduce the transparency of paper; 3. Reduce the ink absorption of paper; 4. Increase the whiteness of the paper; 5. Increase the quality and weight of the paper

sizing materials: Rosin gum, aluminum sulfate, alum, bone powder, starch, casein, water glass, paraffin, etc

the role of sizing material:

the role of sizing is to block the gap between fibers, thereby reducing the capillary effect of paper. Because the sizing material has certain water resistance, it can only hinder the penetration of water, without affecting the absorption of ink by the paper. Sizing improves the gloss, strength, sound and paper surface fuzzing

two major adsorptive properties of paper

1 Adsorption of paper on ink

the ink absorption performance of paper is determined by the characteristics of fibers. The comprehensive reflection of factors such as the interweaving condition between fibers, the properties and contents of fillers and adhesives, and the basic quality is the capillary adsorption of pores between fibers on ink binders

2. Adsorption of paper on water

paper cellulose hemifibers, lignin, pectin resin and other highly sensitive adsorption properties to water. The water content of the paper itself changes with the temperature and humidity of the environment. The water content of the paper increases with the high relative humidity of the environment; On the contrary, it decreases

paper is hygroscopic, so it is very sensitive to air humidity. The moisture of any kind of paper increases with the increase of environmental relative humidity and decreases with the decrease of environmental relative humidity, which is in direct proportion to each other

paper flexibility

measuring the expansion rate of printing paper is of great significance to the production operation of printing. In the production process, we always hope that the smaller the expansion rate of paper, the better, which is also conducive to reducing the faults in printing and plays a role in reducing the inaccurate overprint caused by the expansion and deformation of paper. The error of paper expansion and deformation during overprint can be controlled within 0.05mm, which cannot be observed by human eyes

the paper to be printed should be adjusted before printing. If the paper can be printed normally, two conditions must be met:

1 Before printing, the water content of the paper should be uniform and adapt to the ambient temperature and humidity of the printing workshop

2. During the printing process, the ambient temperature and humidity should be stable, and the influence of other factors on the paper moisture should be reduced

printing failure caused by paper

(I) inaccurate overprint caused by paper telescopic deformation. The fundamental solution:

1 When printing, the paper with horizontal strands should be used. The strands of the paper are different, and the expansion and deformation of the paper are inconsistent. When printing, the paper of the longitudinal strand at the bite has a large deformation, the paper of the horizontal strand has a large deformation, and the paper of the horizontal strand has a small deformation. From the perspective of paper fiber, the molecular structure of the longitudinal strand is vertical, the expansion rate is high, and the molecular structure of the horizontal strand is horizontal, the expansion rate will be small

in addition, because the paper is in a tense state during the whole printing process, the paper with longitudinal strands will be affected by a certain amount of tension

2. The paper used for offset printing should be adjusted by hanging. First, the dust, scraps and impurities on the surface of the paper will be blown away by the blower during hanging; The second is to adjust the hygroscopicity of paper fibers through hanging and adjusting treatment, so that the hygroscopic deformation of paper fibers is minimized during printing

3. In offset printing, we should strictly control the moisture of the printing plate. The difference between offset printing and other printing methods is that offset printing is a kind of printing with water, because water will emulsify the ink and cause the expansion and deformation of the printing paper. Therefore, it is necessary to master the balance of water and ink, and use as little water as possible to reduce the expansion and deformation of the paper on the premise that the printing plate is not dirty

4. The expansion and deformation of the paper can also allow the paper to be pre printed with clean water once, so that the water content of the paper is uniform and the expansion and deformation problem can be reduced

5. The printing workshop should try to keep the temperature and humidity constant. For example, in the printing workshop, there should be air conditioning in summer, heating in winter, and humidifier should be used to increase the air humidity when the weather is dry. The printing workshop should try not to open the windows and seal the door with a cotton curtain. In case of mildew and rain or continuous overcast days, the semi-finished products to be printed can be covered with plastic cloth

(II) paper generates static electricity

the operators of the equipment for the first time should be instructed by skilled operators. The main reasons for the generation of static electricity are: the reduction of water content in the paper, the dry environment, the lack of relative humidity, and the electrostatic phenomenon caused by the friction of the paper when the paper is transported in offset printing, but the stability of the machine during force control and deformation control is closely related to the rigidity of the host and the rigidity of the sample

solution:

1 Increase the relative humidity of the printing workshop and the water content of the paper

2. Install the electrostatic eliminator

3. Spray moisture to increase environmental humidity and moisture

(III) the reasons for paper wrinkling

are mainly the uneven water content of the paper, the failure of the printing machine, the paper teeth, the paper feeder, the side gauge, etc. are not adjusted well. Mainly talk about the wrinkling problem caused by the reasons of the paper

1. The wrinkling of the trailing part: it is mainly caused by the uneven water content of the ink stacking and paper of the embossing cylinder: each load can only reach a certain load, resulting in the "Ruffle edge"

solution: remove moisture, hang the paper and blow it

2. Wrinkling in the middle of the paper: the main reason is that there is more water in the middle of the paper and less water around it

solution: spray water to make the paper humidity even

3. Large skew wrinkling: that is to say, when feeding paper, the water content of the side gauge and the long paper everywhere is large, and the water content in other places is small, which causes the failure

solution: adjust the side gauge and the paper feeding part, and hang the paper again for adjustment. (WangXinCheng) (China Packaging News)

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