Analysis of the Causes of Offset Imprinting Immobilization

First, the paper's performance on ink fixation

Paper is a kind of film-type material formed by finely intertwining plant fibers in a moist state, adding appropriate amounts of fillers, rubber compounds, and color materials, and dehydrating, pressing and drying.

The fixing of paper for ink is relatively good, and the fiber of the paper and the road are related to cellulose, hemicellulose, lignin, and pectin resins. The paper has the following features: ink absorption property is a reflection of fiber properties, interweaving conditions between fibers, fillers, and the nature and content of the rubber compound. Its essence is the adsorption of the pores between fibers on the capillary of the ink binder. I personally think that paper with a high content of woody fibers has good ink-absorbing properties and strong imprints, such as newsprint, letterpress, etc. In addition, when paper is made, paper with less filler and less material absorbs more ink.

Paper absorption of ink is related to the pressure of offset printing and the length of the imprinting time; it is related to the viscosity of the ink and is related to the structure of the paper itself. Absorption of the ink by the paper is too large or too small to affect the fixing fastness of the print.

Coated paper is the most commonly used high-grade trademark, decoration, self-adhesive paper for offset printing. It is coated with a uniform white paste on the base paper and is made of calendered high-grade printing paper. The surface of the paper is smooth. The ink absorption and reception conditions are very good and the surface whiteness is high. It requires a high degree of smoothness in the coated paper, and the paper is not stripped, and the absorption is as small as possible.

Offset paper is composed of 5% bleached chemical pulp mixed with 50% other pulp, such as pulp, pulp, bamboo pulp, rice straw, wheat straw pulp and reed pulp. Offset paper requirements: 1 paper, small scalability, strong water resistance; 2 no pull hair, no off, play close to the texture; 3 ink absorption should not be too high.

After the ink is transferred from the plate or blanket to the paper, some of the ink, especially the binder in the ink, penetrates the paper. At the same time, the solvent in the binder began to evaporate. In addition, the main part of the linking material produces a chemical reaction and a physical reaction, so that the ink film on the surface of the printing plate gradually increases in viscosity and hardness, and finally forms a solid film layer, which is the drying process after ink transfer.

If the paper is too loose. The oil absorption is too strong, combined with the low viscosity of the ink used. The large amount of printing force can also cause the ink to penetrate the back of the paper, forming a print that can be seen from the north side of the print sheet, called "printing."

The paper absorbs ink too strongly, and the mean value of the capillary aperture of the paper is relatively large, which causes some of the pigment particles to infiltrate into the paper together with the binder, affecting the thickness of the ink film layer, the fixing fastness of the ink layer, and the imprinting on the paper surface. Rendering the proper color saturation will also affect the quality of printed products. On the other hand, when the paper is too small in ink absorbency, the dry and conjunctiva is slow when the printing is performed, and the problem of sticking on the back is likely to occur.

Second, the impact of the ink on the imprinting fastness

1, the imprinting is too fast to cause fixation

When multi-color overprinting for offset printing is based on the ink color that has been printed first, the color ink behind does not go up and is not firmly fixed. The main reason is: due to adding too much dry oil in the ink, causing too fast drying, or too long time to stack the semi-finished products, so that the imprinted surface vitrification phenomenon. At the time of imprint, the surface of the blot is very smooth, losing its adsorption capacity, and the latter color cannot be printed on it. Such failures are often found in printing products with large solid areas, and are particularly prone to dryness on yellow ink or lined prints. Too fast vitrification.

Treatment methods: 1 should be based on prevention, try not to make the ink desiccant overdose; 2 for the easy to produce viscous yellow ink in advance to add the appropriate amount of Weili oil, magnesium carbonate powder and other auxiliary materials to make the ink film surface of the conjunctiva Rough or extended drying time, which will have a certain effect on preventing the formation of vitrification; 3 If the phenomenon of vitrification, the latter color can not be printed, when the number is small, you can use a soft cloth magnesium carbonate powder, gently on each surface Rub will have an effect; 4 can also use a soft cloth to wipe the dilute solution of sodium dioxins, will have a certain effect.

2. Causes of Ink Pulverization Causes Instable Warning on Paper and Other Printing Materials

The pulverization of ink refers to the printing of semi-finished products. After the finished products are dried, wipe them by hand. The pigment particles on the surface of the ink will fall off like powder, and the fixation will be very weak. The main reasons are as follows:

The ink is composed of pigment particles and linking materials. The size of the granular pigment particles is also subject to the normal distribution. If the average value of the pigment particles is much larger than the average value of the gap size between the paper fine fibers, the ink is transferred to the paper. Afterwards, the ink is absorbed by capillary action between the fibers, and some of the fine fiber gaps only absorb the binder to form a filtering phenomenon. If the paper absorbs ink too much, the linking material is excessively drawn into the interior of the paper, causing excessive reduction of the oil molecules in the ink layer. Then the pigment particles are suspended on the surface of the paper. After the conjunctiva is dried, the prints lack luster. Even if some marks are rubbed, the paint will peel off. Called “powdering”, it will directly affect the fastness of the prints.

The appearance of imprinted inks is strongly poor, mainly due to ink manufacturing problems, followed by the operator adding oil or kerosene and other unsuitable amounts of auxiliary materials to the ink, resulting in the separation of pigment from the binder in the ink. After printing with this kind of ink, the linking material quickly penetrated into the paper fiber wrap, and the pigment remained on the paper surface, and the powder was pulverized after drying.

Treatment methods: 1 When the operator mixes the ink, the auxiliary material can not be added in excess, generally does not exceed 5%, the auxiliary material in the ink is too much, it will inevitably change its printability; 2 Even in order to increase the ink flow and add the ink , Can not exceed 5% of the ink volume; 3 best not to use oil, kerosene, etc. to the deployment of ink; 4 For the fine products that have been powdered, can be applied to the coating or coating to solve.

(to be continued)