For packaging printed products (paper or plastic flexible packaging
1 Ink or varnish, with particular attention to the surface condition of the printing carrier (substrate). The surface roughness, bubbles, internal stress, deformation, cracks, and adhesion of different substrates are different. On the one hand, the printing or finishing technology should be improved. On the other hand, necessary surface measures should be taken to implement treatments such as corona discharge treatment or chemical spray surface treatment.
2. Substrate, especially polyolefin material, generally has a relatively large surface polarity. The substrates with low crystallinity have a strong adhesion to the printing ink or coating oil. For example, the surface of flexible carrier printing carriers such as PE and PP must be specially prepared. The processor can print or polish.
3. The surface concentration of the auxiliary agent in the ink or varnish system, for example, the plasticizer in the flexible packaging substrate carrier tends to migrate to the surface, especially the ink film with a low softening point will migrate and deform when it is compounded or steamed. There is also a release agent for silicones, paraffins, etc. during molding and even storage. This is not conducive to the normal display and adhesion of packaging printing inks or coating oils. Degreasing and cleaning should be performed, but excessive use of stearic acid or silicone oil. It is very difficult to completely remove the place. For example, the surface of a flexible packaging plastic product is in a charged state. As an insulator, the substrate and the ink or coating surface are easily electrostatically generated by friction. Therefore, the surface is easily adsorbed with dust. Before the ink or varnish is produced, it is necessary to carry out a solution to eliminate static electricity.
In order to facilitate a careful analysis of the defects of the package printing and printing carrier, a rough classification of the causes is given below.
1. Factors related to the quality of ink or coating oil include:
A. The surface tension of the ink or varnish after the film formation, the wettability and adhesion of the package printing carrier, and the leveling of the ink film and the oil film surface;
B. Whether the solubility parameters of the solvents and thinners of packaging printing inks or coating oil systems are similar, surface tension and volatilization rate, especially volatilization gradient are balanced;
C. Viscosity, viscosity and rheological properties of ink or varnish. Special attention should be paid to the characterization and characteristics of the viscosity in the process of film formation that tends to follow ink printing, varnish coating methods, and printing and coating environment changes; various additives in inks or varnish systems The rationality and compatibility and tolerance.
2. Factors related to the dilution and stirring dispersion of packaging printing inks or coating oils:
A, mixing of dust and impurities;
C. Dilution is suitable for the ink or coating oil;
D. Adjusting and stabilizing the viscosity of ink printing and gloss grease coating.
3. Factors related to packaging, printing and coating environment:
A. Temperature, humidity, indoor wind direction, air volume, and wind speed during production;
B, printing ink splash, aerosol pollution;
C. Prevention of dust and impurities.
4, open-air production, printing and coating environmental factors:
A, ink printing, varnish time choices one by one, temperature, humidity;
B. Wind direction, air volume, wind speed, etc.;
C. Weather conditions such as cloudy days, clear days, mornings and evenings.
5. Relevant factors of substrate carriers:
A. Whether the full-printing ink is used for full-printing or full-printing of the base oil, in particular, the interval distance, printing speed, thickness of the ink layer, and the thickness of the ink layer between the printing plate and the middle plate;
B, surface treatment, dust blowing and corona treatment;
C. Solvents, chemical reagents, surfactant treatment, cross-linking agent and coupling agent addition promotion;
D, the principle of drying, in addition to electrostatic devices, methods and so on.
6. Factors related to the packaging and printing of inks and the coating and finishing process of varnishes:
A, printing, coating methods (such as manual or mechanical, high-speed or low-speed / offset, gravure, flexo, screen printing or transfer printing and transfer coating);
B. In addition to the quality of ink, varnish, and substrates, the operator's skills (experience and skill) level;
C. Printing, coating angles, speeds, distances, ink film and film thickness, monochromatic printing of a package, or multi-color overprinting of a package, and the number, thickness, and type of coating of base oil, varnish, etc.;
D, air pressure, air volume, light energy, light intensity, curing method and degree of drying and curing;
E. The cycle speed, make-up amount and interval time in the replenishment system for packaging printing ink or varnish, and the viscosity of the diluent.
7, drying methods and placement time factors:
A, drying (drying, air, infrared, ultraviolet, etc.) and open time; B, temperature and heating rate and the length of the temperature; C, environmental ventilation and ventilation speed.
8. Factors related to film formation conditions of inks or coatings include:
A. Drying (chain drying bed) temperature and distribution, heating rate and temperature time;
B. Drying time; C. Ventilation speed and air pollution.
From the above article-by-bar analysis, it is concluded that the printing defects caused by ink printing and varnish coating are various. As long as we are open-minded and clear-cut in terms of clarity, we must propose our own solutions, that is, we must accumulate experience in summing up the lessons learned, and we will not apply the traditional symptomatic treatment. Although some theoretical analysis is ideal, the actual situation is often much more complicated. The combination of theory and practice just can narrow this gap. Sagging:
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