In the field of packaging and printing, the printing of corrugated board occupies a large share. With the expansion of the packaging market and the ever-increasing level of printing technology, the quantity and quality of corrugated board printing have been rapidly developed. However, people are increasingly considering environmental protection factors. Therefore, the use of inks for corrugated board printing has become a concern. In corrugated printing, the commonly used inks are mainly solvent-based inks, water-based inks, and UV inks.
1, corrugated paper commonly used printing methods and inks
Because corrugated paperboard has multiple layers of wavy corrugated composites, poor surface smoothness, printing pressure can not be too large, only a few simple patterns can be printed by screen printing, text, printing is relatively difficult, so corrugated board is generally used Flexo printing. This is mainly because: 1 elastic deformation of the flexographic printing plate can compensate for the thickness error and surface unevenness of the corrugated paper in the printing process, so that the printing ink is uniform, thereby improving the quality of the finished product; 2 the flexographic printing pressure is small, even after the printing plate is compressed and deformed. Can be better with the uneven thickness of corrugated board contact, while avoiding the thick part of the paste paste, the thin part of the contact with the phenomenon of imprinting false empty; 3 flexographic printing using anilox roller transfer ink, to facilitate water-based ink delivery, Plates need only light contact with corrugated paper, water-based ink will be almost all absorbed by the corrugated cardboard; 4 flexographic printing press structure is simple, easy to process with other processes, such as indentation, slotting, die cutting, gluing, box making, etc. Machines are combined for online operations.
When using flexo printing corrugated paper, commonly used inks mainly include solvent-based inks, water-based inks and UV inks. With the emphasis on environmental protection factors, the proportion of solvent-based inks has decreased year by year, while water-based inks and UV inks have increased. The more popular. At present, water-based inks have the fastest growth and have a relatively large market share. For example, about 90% of flexographic inks in the United States are water-based. In the case of flexible printing of corrugated cartons, the proportion of water-based inks is greater, because the characters or simple patterns printed on the corrugated boxes need not have a high gloss, and water-based inks can meet the requirements for the quality of printed products; in addition, the corrugated boxes are Fiber loose fabric, there is a strong water absorption, after the printing of water-based ink, the main osmotic drying, no need to set the drying device; and water-based ink is non-toxic, harmless, non-flammable, easy to use and safe, low cost. Therefore, the combination of these factors, corrugated paper is the main printing method is flexo, and the most commonly used ink is water-based ink.
2. Water-based ink in corrugated paper printing
2.1 composition of water-based ink
(1) Connection material
The binders in water-based inks are water-soluble resins and aqueous polymer emulsions. There are many types of water-based resins, such as rosin maleic acid resin, styrene maleic acid resin, acrylic acid copolymer, amino ethyl acrylate, etc., polymer emulsion that is aqueous dispersion resin, vinyl acetate copolymer, acrylic copolymer, polyurethane resin , epoxy resin and so on. At present, water-based acrylic resins are the most commonly used binders in aqueous screen printing inks. The most successful acrylic polymers currently used are mainly alkali-soluble resins, acrylic emulsions, colloidal emulsions and solutions, and special acrylic polymers.
Water-based inks mainly use organic or inorganic pigments that have strong alkali resistance and good dispersibility in aqueous systems. In addition to common powders, these pigments also include pigment filter cakes, aqueous dispersions of pigments, and easily dispersible pigments in water. The pigments in water-based inks must have strong alkali resistance, high hiding power, high color concentration, and easy dispersion.
Since the water's dissolving power and wetting ability are not large, it is necessary to use the corresponding cosolvents, such as ethanol, propanol (positive and negative), ethylene glycol monoacetic acid and the like. By adding a co-solvent, the disadvantages of the ink can be improved and the stability thereof can be improved, the surface tension of the water-based ink can be reduced, the wetting of the plastic can be increased, and the dissolving resin can also be used to increase the drying speed. In addition, the resin is generally insoluble in water, and an appropriate alkaline substance must also be added to promote the dissolution of the resin in water. Generally used amines such as ethanolamine, the amount depends on the pH value.
Many types of additives, such as thinners, dispersants, brighteners, defoamers, diluting agents, electrostatic agents, etc., to improve the printability of the ink.
2.2 Requirements for Water-Based Inks in Corrugated Printing
Corrugated cartons are characterized by rough paper, uneven surface, fast ink penetration, and most of the paper is dark brown, to volatilize the unique ink layer of the flexographic printing, rich layers and rich color printing effect, use High quality water-based ink. In addition to the requirements for ordinary water-based inks, the following points are the key considerations in formulating corrugated paper printing inks.
(1) The basic color should be bright and the coloring power should be strong to ensure that the imprinting has a high hiding power; at the same time, the basic balance of low viscosity and high color concentration can be achieved, so that the printing of the hierarchical printing plate and the dot printing can be clearly distinguished.
(2) It is necessary to maintain a fast penetration drying performance, to adapt to high-speed printing, to avoid back-scratching, but also have good leveling performance, so that the imprint is smooth, smooth, full, vivid color effect, and let the printing plant have A wide range of papers and paperboards were selected for the conditions.
(3) The printing process must have good re-solubility to ensure that the ink-discharging process is smooth and adapts to various printing speeds.
(4) The imprinting has good abrasion resistance and water resistance, and can meet the new performance requirements that are constantly put forward by packaging materials.
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