Ink is an indispensable production material for printing, and its nature greatly influences or determines the printing quality of the product. Correctly understanding the nature of the ink, in the actual production process, according to the printing conditions and characteristics, certain properties of the ink will be adjusted and improved accordingly, will play a positive role in promoting the improvement of production efficiency and product quality.
Ink has its own characteristics, it has a good side, there is no lack of negative impact.
1 Ink viscosity
The characteristics of inks under the influence of external forces (that is, resistance that can hinder their molecular motion) are commonly referred to as ink viscosity.
Process practice shows that the viscosity of the ink is proportional to the consistency (concentration), ie, the greater the ink consistency, the greater the viscosity. The ink has a large consistency and the resistance to internal molecules is relatively large. On the contrary, it is small. Obviously, the viscosity of the ink is an important condition for the transfer performance of the ink, the fastness, penetration, and gloss of the ink layer of the ink. If the ink viscosity is too large or too small, the printing quality will be adversely affected. If the viscosity of the ink is too high, it may cause ink transfer and ink inhomogeneity. It will pull off the paper paper powder to make the layout a batter or make a flower. If the ink viscosity is too small, it will easily lead to a print bar mark caused by the rubber. Poorly applied inks will cause blots, ink emulsification, floating dirty and other undesirable phenomena.
The viscosity of ink is inversely proportional to the temperature, the speed of the printing press, and the number of ink rollers. The temperature is low, the speed of the printer is low, the number of ink rollers used on the printer is small, and the viscosity of the ink is also increased accordingly. This is because the ink has thixotropy, the heat is large, the ink becomes thin, and its viscosity also decreases. The speed of the machine and the number of ink rollers determine the amount of frictional heat during the movement. With a large coefficient of friction, the printing press tends to become thin when the ink is heated and its viscosity decreases. The viscosity of the ink is adjustable, according to the printing conditions to add appropriate additives to the ink, such as No. 0, No. 6 varnish, detackifier, etc., can achieve the purpose of increasing or reducing the viscosity of the ink. It is worth noting that the surface of printing paper is smooth and the paper surface has good strength, and the viscosity of the ink may be appropriately larger. Conversely, for papers with poor surface strength, the ink viscosity should be smaller in order to obtain relatively good printing results.
2 Ink concentration
High density inks are also thick, so the ink concentration determines the hue of the ink. The large ink concentration will darken the printing hue; conversely, the printing hue will be shallow. The amount of ink consumed in printing with a large ink concentration is relatively small, and the ink quality is also relatively good. On the contrary, the ink concentration is relatively small and the amount of ink used during printing is relatively large, and the ink color is also relatively light.
When printing large area plate products, the effect of ink density on the printing effect is particularly significant. Smaller inks are used to print underlays or overlays. The amount of ink on the plate must be increased to obtain the desired print hue. However, it is very easy for the product to suffer from malpractice. Therefore, the inks used in color printing products generally have their hue appropriately deepened, and the concentration is also appropriately increased. The printing effect is relatively good and it is also conducive to the anti-adhesion of printed products.
3 Fineness of the ink
The fineness of the ink refers to the size of the pigment (including the filler) particles in the ink and the uniformity of the pigment particles distributed in the binder.
The inks with poor fineness are prone to quality problems such as uneven ink transfer, poor printing, and poor color rendering during the printing process. The fineness of the ink is relatively good and its concentration is relatively large, and printing is also relatively clear. The fineness of the ink is poor, and the printed dot screen layout is susceptible to hairiness and blistering, and the printing plate has a low printing rate.
4 The proportion of ink
The specific gravity of the ink refers to the weight-to-volume ratio (g/cm3) of the ink at a temperature of 20C.
From the concept of the proportion of ink can be seen. The ink consumption of the major ink is inevitably large. Color printing products with the same hue of the ink, the proportion of ink than the specific gravity of the smaller amount of ink, in order to adjust the same phase of the ink.
In addition, the color printing inks prepared by mixing different inks with different proportions are prone to delamination due to deposition, resulting in color variation or uneven coloration in printing. This is because the more important inks are deposited and the specific gravity is smaller. The ink is floating on the top of the reason, so, before using the ink after deployment, it should be stirred evenly and then poured into the ink fountain, and often stirred in the printing to ensure that the hue of the front and back printing products can be consistent.
The specific gravity of the ink can be measured by the microvolume meter, that is, the ink to be measured is first sucked into the volume meter, and then the weight is weighed, and the result is calculated using the formula d=ab/Ï…. In the formula: d is the specific gravity of the ink, a is the total weight of the ink in the container and inhale, b is the weight of the container, and Ï… is the volume of the inhaled ink.
5 ink coloring power
Coloring power is a reflection of the ink shade.
The coloring power is mainly determined by the degree of dispersion of the pigment, which increases with the increase of the degree of pigment dispersion, and at the same time increases with the increase of the pigment content in the ink. The tinting power of an ink is also related to the selective reflection of the wavelength of the light by the pigment.
When the coloring power is examined, a color ink and a standard white ink may be used to dilute it in a ratio of 1:10 and be scraped off in comparison with a standard sample. A dark color indicates that the coloring power is high, and conversely, the coloring power is low.
6 Heat resistance of ink
The heat resistance of the ink is mainly determined by the nature of the pigment. Some pigments are not heat-resistant, the structure changes under the effect of high temperature, resulting in discoloration, such as poor heat resistance of light blue paste. After the black ink is used to make the printed film, discoloration will occur.
The heat resistance of the ink is generally tested by coating the ink on the printed sheet with a thin film layer and then putting it in a constant temperature oven at a temperature of 100oC, 130oC, and 150oC for a certain period of time to test the dried proofs. Dried ink samples for comparison.
Grasp the heat resistance of the ink, for the correct choice of ink for printing, to ensure product quality is of great significance.
7 Lightfastness of ink
In the role of light under the influence of light, the relative change of color light is called lightfastness of the ink.
In fact, inks that do not change color are not. Under the effect of light, the color of the ink will change more or less. Good light fastness ink, the bright color of the printed product, the layout of the Internet is full and solid, full of three-dimensional, and long-term preservation. In poor light fastness inks, prints tend to fade and discolor.
Ink light resistance test. Generally, the printed sheets are exposed to sunlight or exposed to ultraviolet light in an exposure test machine, and then taken out and compared with the international standard of grade VIII blue color fading to determine the grade. Grade 8 is the best, and the lightfastness of the inks with grades 7 and 8 will hardly discolor and fade. Lightfastness is only one or two grades of ink. It will change color and fade after 2 to 3 hours of exposure to sunlight, and it will fade and discolor when placed indoors. It is worth noting that the light resistance of the ink is also reduced.
8 Acid, alkali and alcohol resistance of ink
Acid-resistant, alkali-resistant, and alcohol-resistant inks, the printed products are brightly colored ink, the layout is clearly structured, and the outlets are clear. On the contrary, the printed products are dark and lacking in ink, and the layout level is not clear. The outlets are not clean.
Printing inks with acid, alkali, and alcohol resistance are basic requirements for the quality of packaged products, such as soaps, sodas, or food packaging prints. The ink used must have good acid and alkali resistance. In addition, because the coating oil contains alcohol solvent, the coating product must use ink with alcohol resistance so as not to cause adverse phenomena.
Ink resistance to acid, alkali, alcohol performance determination, the general use of a certain thickness of the ink sample, one end immersed in acid, alkali or alcohol solution, after soaking for about 1 day, observe the ink layer test sample color change, ie Can determine the ink acid, alkali, alcohol. If the sample appears severe discoloration of a: obvious discoloration of secondary; slightly discolored to three; basically do not change to four; do not change to five, five inks best acid, alkali and alcohol.
In short, the properties of inks are varied, and they affect the quality of printed products to a certain extent. Understand and understand the nature of the ink, help to avoid the blindness of the process operation during printing, prevent the occurrence of quality defects in the printing process, so that the ergonomics and quality of the printing are increased synchronously.