With the development of social economy and the improvement of people's living standards, the status of gravure printing in various printing methods has become more prominent. The study of gravure printing technology has very important practical significance. Here is a brief discussion on the printability of gravure ink. Please correct your mistakes with your colleagues.
As with other printing inks, the main components of gravure inks are colored substances (pigments) and binders. Among them, the color material plays a role of coloration, and contrasts with the color of the substrate. Images appear on the substrate. Only the proportion of the components of the ink is well-distributed to achieve the proper printability and performance of the ink, so that the printing ink can be properly matched with the printing plate, the printing press, and the printing material, so that the printing process can proceed smoothly.
First, the raw material gravure ink is mostly volatile solvent type ink, composed of pigment, solid resin, volatile solvent, filler and additive.
1. pigment. Pigments are divided into two kinds of inorganic pigments and organic pigments. Inorganic pigments are mostly hard and dense crystal materials. These crystals are difficult to grind into fine particles without special treatment and can not be well dispersed into the binder, so the inorganic pigments are made of The printability of the ink is often not ideal, and it is easy to abrade the plate. The organic pigments can be mostly artificially modified and easily dispersed in the binder. The resulting inks have greater advantages in printability, but the prices are often higher. The pigment composition of the gravure ink is mostly organic pigments, which is determined by the gravure printing characteristics and the quality requirements of the prints.
The influence of the pigment on the printability in the oil is mainly determined by the nature of the pigment, such as the degree of dispersion, hiding power, specific volume, resistance, and the like.
1 Dispersion refers to the size of pigment particles. The pigment particles in the ink must be completely immersed in the binder in the ink film. The size of the pigment particles should not exceed the thickness of the ink film, generally about 5 μm, otherwise the gloss of the printed matter will be affected, and the smaller the particles, the higher the dispersion. The more saturated the hue of the ink is. Gravure printing is a web transfer printing and requires a high degree of pigment dispersion.
2 Coloring power refers to the ability of a pigment to affect the color of a mixed pigment after it is mixed with other pigments. Any pigment that is easily blended with a white substance and tends to lighten will have poor coloring power. The ink used for ink formulation should be pigmented with strong coloring power. It can be used to print inks with less ink and faster drying. This is critical for high-speed gravure printing that requires high ink dryness.
3 hiding power refers to the ability of pigments to cover the background. Whether the ink has hiding power depends on the ratio of the refractive index of the pigment to the refractive index of the binder. When this ratio is 1, the pigment is transparent; when the ratio is greater than 1, the pigment is opaque, ie has hiding power. Different printing products have different requirements for the hiding power of pigments. For example, printing inks require strong hiding power of pigments to prevent the exposure of the background color, and four-color overprinting inks require high transparency of the pigments to make them overlap. The ink achieves a good color reduction effect.
4 The visual volume refers to the volume per gram of pigment, expressed in cubic centimeters. The same pigment with different particles, the apparent volume is different. The larger the visible passengers of the pigment, the smaller the specific gravity of the pigment and the less likely to precipitate in the binder, and the stability of the ink is good.
2. Link material. The binder is a dispersion medium in the ink and is a carrier of pigment particles. The printability of the ink is very close to that of the binder. The composition of the linking material is relatively complex, mainly including the oil type linking material, the resin type linking material, and the organic solvent.
1 Oil type linking material is prepared by heating vegetable oil to a certain temperature and keeping it warm at this temperature. Dry vegetable oil is a mixture of unsaturated fatty acid glycerides, and polymerization occurs upon heating to generate dimer and Trimer, the longer the heating and holding time, the greater the viscosity. The oil-based vehicle contains trace amounts of free fatty acids that act as surfactants, facilitating the mixing of pigments and binders. Oily binders have good adhesion and a certain degree of water resistance, and can form a relatively glossy ink film. However, the fixing speed is slow and the drying time is long.
2 Resin type binder is made by dissolving synthetic resin or modified resin in mineral oil, vegetable oil or volatile solvent, and can be divided into four types of resin: dissolved, dispersed, colloid and volatile. material. Commonly used synthetic resins include pentaerythritol rosin ester, alkyd resin, rosin modified phenol awake resin, polyacrylic resin, maleic acid resin, petroleum, and asphalt.
3 Organic solvents are also the main components in the ink binder. It makes the ink have a certain degree of fluidity. When the ink is transferred to the paper, the volatile solvent quickly evaporates. The solvent with low volatility penetrates into the paper by capillary action, which fixes the resin binder left on the surface of the paper. Paper surface and dry. Commonly used solvents include ethyl acetate, butyl acetate, isopropyl alcohol and the like. (To be continued)