How to Comment and Select Ink Correctly in Lithography (Part 2)

Fourth, ink technical indicators

At present, the inspection method of ink finished products is still not perfect, and there are still many unscientific and unpractical. The so-called unscientific, that is to say there are many things to judge and evaluate on the basis of experience and sense organs. The so-called impracticality means that the results of the measurement cannot fully represent the needs of practical applications. In addition, some of the results of the measurement of the project are more error. Therefore, there are many test methods and data can only be used as a relative comparison, that is to say the test of ink is relative. In spite of this, the technical indicators of ink are still instructive for printing. The following describes several technical indicators that are closely related to printing.

1. The concentration of ink. Ink concentration is an indicator of its pigment content. Pigments generally account for about 2% of the total ink. When printing, the ink concentration is high, and the same amount of ink is used, the color of the printed matter is thick; on the contrary, the color of the printed matter is light. With high ink concentration and low ink consumption in printing, the ink layer is thin and relatively dry. In particular, the effect of the ink concentration on the printing quality is particularly significant when printing large areas on the ground, because printing with high-concentration inks is not necessary. The fast fixing of the ink layer can reduce the stickiness of the printed product, and the color balance of various colors can also be easily adjusted. Printing workers have a small amount of experience in the printing of ink and water, the greater the difference between India and India, the smaller the ink, the smaller the better, the experience is in fact based on the concept of concentration, the ink industry to determine the ink concentration by testing the coloring force. the size of. The method is: the standard ink is diluted with white ink, and the sample ink is added with white ink to dilute the amount of the white ink of the sample to make the color shades of the two on the scraping paper consistent. The ratio of the amount of white ink in the sample to the amount of white ink in the standard is expressed as a percentage, which is the coloring power.

Where: S = percentage of coloring power (100% in standard ink) A = standard dilutes the amount of ink used in the white ink B = the amount of ink in the white ink used by the sample dilutes

2. The viscosity of the ink. The ink stickiness meter is manufactured on the principle of a printing press. The viscosity of the ink was measured with an ink stickiness meter. The viscosity value of the ink refers to the magnitude of the force separating the ink film between the two rollers of the sticky meter. The viscosity of the ink has a greater relationship with the ambient temperature and the speed of the printing press. The viscosity of the ink increases with the increase of the operating speed of the copper roller and decreases with the increase of the ambient temperature. The viscosity of the ink is an important index in the printing, and affects the ink transferability of the printing, the ink layer thickness of the printing product, and the penetration. Quantity and gloss size. Too much or too little ink viscosity can affect the quality of printing. When the viscosity of the ink is too large, problems such as poor ink transfer, poor transferability, poor paper-drawing, and poor overprinting may easily occur. If the viscosity is too small, it is easy to cause excessive transmission of ink, flying ink, dot expansion, ink emulsification, floating dirty and other defects, at a certain temperature, the viscosity of the ink is not too large when the printing speed is fast, and vice versa. In addition, the relative viscosity of each color ink is selected according to the printing sequence. Under normal conditions, there is no need to adjust the viscosity of the ink, and adjustments may be made according to its viscosity. Consistency situation selection additive. When the viscosity is large and the consistency is suitable, the viscosity can be adjusted without decreasing viscosity. In general, when the viscosity is large and the consistency is large, it is possible to use additives that both reduce viscosity and reduce viscosity.

3. The dryness of the ink. The drying process of the lithographic ink on the paper is a process in which the ink changes from a non-polar, non-polar colloidal fluid to a fixed state. Measuring the lithographic ink dry ink industry is divided into two indicators; First, the fixing speed, it refers to the ink from the natural flow into a semi-solid state that is printed on a certain height does not stick dirty, printing is called dry, The initial dryness of the ink is determined by the resin structure chosen for the design. The initial drying time is very short, but it is not completely dry. The second is the dryness of the oxidized conjunctiva, which is exactly what is said in printing. The drying time is longer, and it is generally more than 8 hours. It is completely dry. The dryness of the ink is determined by the kind and amount of the desiccant, and can be adjusted within a certain range. The current lithographic inks are all resin type, and the fixation speed is faster. In theory, the initial dryness is faster as possible. However, if the initial dryness is too fast, the gloss of the printed matter will be affected. The level of gloss and the speed of fixation are generally contradictory and should be balanced. People always hope that the ink will be printed on the paper soon, but it will not dry in the ink fountain. Currently, about 80% of the ink conjunctiva drying time on the market is between 16-30 hours. If the conjunctival drying time is too short, it is easy to cause On the crust-holding roller, you can choose the non-skinning ink when printing ordinary coated paper and long-lived printing. Specifically, it is the ink with longer conjunctiva drying time. It is not always skinless. Non-skinning inks are not suitable for printing short runs with high-grade, poor-permeability coated paper (binder-bound prints for about 12 hours) or printing with cardboard, which suggests using fast-drying inks.

4. The gloss of the ink. The gloss of the ink is the ratio of the amount of light reflected by a specific light source at a certain angle of illumination to the amount of light reflected by the standard panel, expressed as a percentage. The brightness of prints gives a direct sensory impression.

In general, the higher the gloss, the better the printing effect. Although the gloss of prints is related to the absorption of the potions and paper used in prints, it is mainly determined by the ink. This form of ink depends on the binder and the pigment in the ink. The link materials and pigments in the ink must have good leveling properties, as well as good printability, and the gloss of the resin itself should be high. Such inks have a high gloss when printed on paper. Glossy inks tend to dry at a slightly slower rate. When overprinting on a stand-alone machine, the ink with high gloss must be well controlled for overprinting time. Otherwise, the crystallization phenomenon of the printed matter is likely to occur.

5. The fineness of the ink. The fineness of the ink indicates the pigment in the ink, the filler particle size, and the uniformity of distribution in the binder. Ink fineness and pigment

The nature of the (solid) material is directly related to the particle size. The looseness of the particles and the wettability of the linking material are easy to study, and the finer the ink properties, the more stable. When the fineness of the ink is poor, the printing plate tends to suffer from the disadvantages of low printing plate or ink pile, voids in the printing plate, expansion and unsmoothness of the dots, etc. The fine ink of fine ink should be selected to select the finer ink. Fine, the more full and effective the network, the same color content when the coloring power, but the production costs for the production plant.

6. Lightfastness of ink. Ink under the effect of sunlight, the color of the light to maintain the same performance you are the lightfastness of the ink. In fact, the absolute lightfast color tone ink is not available. Under the effect of sunlight, the color of the ink print has a varying degree of change, and the lightfastness of the ink is mainly determined by the lightfastness of the pigment in the ink. If you have special requirements for the lightfastness of the print, you should advance to the ink production unit in advance. put forward. Printed with a light-fast ink, the print is bright and long-lasting. The use of light-tolerant ink prints is prone to discoloration and discoloration.

Can not be long-term table village. Printed posters, slogans, advertisements, and other long-term exposure to the sun, should choose good ink fastness.

The lightfastness of the ink was measured by walking the ink on paper and measuring the dryness with a color exposure machine. The light fastness was measured according to the blue standard of the sun-fastness grade 8. The grade 1 faded badly, the surface light-fastness was the worst, and the grade 8 was not easy to fade, indicating that the lightfastness is best. The lithographic four-color inks should have a lightfastness of 7-8 for blue inks and 3-5 inks for red and yellow inks. Lightfastness inks with low light levels should pay attention to color matching and diluting. In short, the variety of inks varies and their nature varies.

The easiest way to determine whether the lithographic ink is good or bad is three-high one-speed, high light, high concentration, high printability, fast drying speed, and inks that generally meet this standard are good inks. Of course, some prints also require good lightfastness.

Understanding and mastering the basic knowledge and technical indicators of inks is of great help in choosing the correct ink for printing. When printing, you must select the ink and the quality of the printed matter can be guaranteed.

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