Water-based ink on corrugated paper printing techniques
Date: Oct 19 2023 From: Star Color
Because corrugated cardboard has multiple layers of corrugated composite, the surface flatness is poor, the printing pressure can not be too large, the screen printing method can only print some simple patterns, text, printing difficulty is relatively large, so corrugated cardboard is generally printed with flexography.this is mainly because：
1.The elastic deformation of flexographic plate can make up for the thickness error of corrugated paper and the uneven surface in the printing process, so that the printing ink is uniform, so as to improve the quality of the finished product.
2.lexographic printing pressure is small, even if the printing plate compression deformation can be better contact with the uneven thickness of corrugated cardboard, and avoid the thick part of the imprint paste, thin part of the contact of poor imprint empty and unreal phenomenon.
3.Flexographic printing adopts mesh roller ink transfer, which is convenient for water-based ink transfer. The printing plate only needs to touch the corrugated paper lightly, and the water-based ink will be almost all absorbed by the corrugated board.
4.Flexographic printing machine has a simple structure and is easy to combine with other processes, such as indentation, slotting, die cutting, gluing, box making and other corresponding machinery for online work.
When using flexographic printing corrugated paper, the commonly used inks are mainly solvent-based inks, water-based inks and UV inks, with people's attention to environmental factors, the proportion of solvent-based inks is decreasing year by year, while water-based inks and UV inks are becoming more and more popular.
At present, water-based inks are growing fastest and occupy a larger market share, for example, about 90% of flexo printing inks in the United States are water-based.In the flexible printing of corrugated boxes, water-based ink accounts for a larger proportion, because the text or simple pattern printed on the corrugated box does not need a high gloss, and water-based ink can meet the requirements of print quality；Moreover, the corrugated box is a loose interlace of fibers, and has strong water absorption. After printing water-based ink, it is mainly permeated and dried without setting up a drying device；And water-based ink non-toxic, harmless, non-flammable, easy to use, safe, low cost.Therefore, combining these factors, the most important printing method of corrugated paper is flexo printing, and the most commonly used ink is water-based ink.
Composition of water-based ink
1.Bonding material
2.pigment
Water-based inks mainly use organic or inorganic pigments with strong alkaline resistance and good dispersion in the water system. In addition to ordinary powders, these pigments also include pigment filter cake, pigment water-based dispersion and easily dispersed pigments in water.The pigment in the water-based ink must have strong alkaline resistance, high hiding power, high color concentration and easy dispersion.
3.cosolvent
Due to the small solubility and wetting capacity of water, it is necessary to choose the corresponding co-solvent, such as ethanol, propanol (positive, different), ethylene glycol monoacetic acid, etc.By adding a co-solvent can improve the shortcomings of the ink and improve its stability, can reduce the surface tension of the water-based ink, increase the wetting of the plastic, but also help dissolve the resin to improve the drying speed.In addition, the resin is generally insoluble in water, and appropriate alkaline substances must be added to promote the resin to dissolve in water.Generally choose amines such as ethanolamine, the amount depends on the pH value.
4.Auxiliaries
There are many kinds of additives, such as diluent, dispersant, brightener, defoamer, diluent, electrostatic agent, etc., to improve the printability of ink.
Requirements for water-based inks used in corrugated printing
The biggest characteristic of corrugated cardboard boxes is that the paper is rough, the surface is not flat enough, the ink penetrates quickly, and the surface paper is mostly dark yellow brown. To produce the unique printing effect of flexographic printing, which is characterized by a full ink layer, rich layers, and bright colors, high-quality water-based ink is used.In addition to the requirements of ordinary water-based ink, the following points are important to consider when preparing water-based ink for corrugated printing.
1.The basic color should be bright and the coloring power is strong to ensure that the blot has a high hiding power；At the same time, it can achieve the basic balance of low viscosity and high color concentration, so that the layered plate and dot printing can be clear.
2.The printing process must have good resolubility to ensure that the ink spreading process is smooth and adapt to various printing speeds.
3.Imprinting has good wear resistance and water resistance, which can meet the new performance requirements of packaging materials.
Some problems of using water-based ink in corrugated paper printing
1.Flexographic printing with mesh roller ink, the net hole is small, water-based ink bucket to add a filter to prevent impurities such as damage to the mesh roller.
2.The texture of water-based ink should be fine, the color should be bright, and the viscosity of the ink should match the printing speed.
3.The water-based ink selected for corrugated paper printing is an oil-water miscible system formed by resin and water under the action of surfactant, and the stability of the system is poor.The stability of water-based ink depends on the size of its PH value.When the ph value drops to about 7.8 or lower, the ink begins to be cloudy and thickened, easy to conjunctiva, and hinder the normal transfer of ink.Alkaline is too strong, has an impact on the roller, the general ph value is controlled in 8~9. Water-based ink is alkaline, similar to soap solution, easy to bubble.
4.Before use, stir thoroughly to keep the composition of ink evenly；After opening and using, the ink storage should be immediately covered and sealed to prevent dust from falling off and dry crust；If the remaining ink contains impurities, it should be filtered first and then used together with new ink；During the storage period, please avoid close to high temperature or scorching sun exposure, under normal conditions are stored for one year without deterioration.
5.Reasonable use of ink additives.There are many types of water-based ink additives, to be used correctly according to the instructions and experience, before the formal printing, to comprehensively consider the printing conditions, the surface characteristics of the substrate, environmental temperature and humidity, water-based ink storage time and many other factors to adjust the ink.
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