With the continuous application of new technologies and the increasing awareness of environmental protection, benzene-based gravure inks have gradually faded out of sight. Instead, ester-soluble, alcohol-soluble inks, especially water-based inks, have been superior in recent years. The environmental protection has been stirred up by the industry. Below, the author summarizes his understanding of water-based inks as follows, hoping to play a certain role in promoting its promotion and application.
The main advantages of water-based inks
(1) The solvent of the aqueous ink is mainly water and a small amount of alcohol, such as ethanol, butanol, isopropanol, etc. The role of the alcohol is to assist the water to enhance the ability to dissolve the resin, improve the dispersion properties of the pigment, and accelerate the penetration and inhibition. Foaming. The content of volatile organic solvents in water-based inks is very low, which greatly reduces the emission of VOCs, reduces air pollution, improves the working environment of printing operators, and is beneficial to the safety and health of employees.
(2) Although the original ink cost of the aqueous ink is slightly higher than that of the solvent type ink, the price of the main solvent used for water, water, is very low, and the practical application cost is comparable to that of the solvent type ink, even lower than the solvent type ink.
(3) At present, the manufacturing technology of domestic water-based inks has become mature (except metal inks), and the application technology is also constantly improving. In the traditional sense, water-based inks have the disadvantages of slow drying, poor gloss, water resistance, and imprinting. It has also been significantly improved, so the current water-based inks are more suitable for packaging and printing products with strict hygiene and quality requirements such as tobacco, wine, food, and medicine.
(4) Water-based inks can reduce the risk of fire and hidden dangers caused by static electricity and flammable solvents.
The main problem with water-based inks
(1) The key technology of water-based inks is resin amination, and the price of organic amines required for the amination process is relatively high. To reduce costs, ink manufacturers often add ammonia to replace or partially replace them, but the irritating smell of ammonia is very high. Large, not only affects the working environment, but also remains on the printed matter.
(2) Compared with solvent-based inks, aqueous inks have a slower drying speed, especially for large-area solid color patches, and when printing on non-absorbent substrates (transfer paper, etc.), the drying speed is faster than solvent-based inks. Several times slower. In order to completely dry the ink layer, it is often necessary to increase the drying temperature; when the drying temperature cannot be increased, it is necessary to adopt a method of lowering the printing speed and sacrificing the printing efficiency.
(3) Water-based inks are prone to virtual shadows when printing fine lines and small characters; when the image is rich in the tone of the screen, the dots tend to increase deformation.
(4) At present, the quality of domestic water-based metal inks and water-based pearlescent inks is generally not good. There are also water-based gold, silver and pearlescent inks with good quality and high gloss, but the prices are very expensive and mostly rely on imports.
(5) The moisture in the water-based ink has a certain rusting effect on the ink tank, the tool holder, the plate roller, the oven and the like of the gravure printing device.
(6) Compared with solvent-based inks, the safe storage period of aqueous inks is relatively short, generally 6 months. If it is more than 6 months, precipitation and delamination may occur, and it is difficult to reuse even if it is stirred again. In addition, care should be taken to prevent high temperature exposure and low temperature freezing during storage of aqueous inks.
Water-based ink application notes
(1) Plate making requirements
The plate should be electronically engraved with gravure or laser engraved gravure, and the depth of the cell should be between 15 and 25 μm. If the plate hole is too deep, it will not only affect the drying of the ink layer, but also print defects such as water ripples on the edge of the printed image.
(2) Solvent selection and ink viscosity control
Preference is given to pure water (or distilled water) as the main solvent. If tap water is selected as the main solvent, it is necessary to perform hardness test on tap water, because the use of tap water with high hardness to dilute the ink produces bubbles (of course, defoaming agent can be added for defoaming, but the amount of defoaming agent is limited).
According to the actual production situation, a small amount of solvent such as ethanol or isopropyl alcohol may be added in the solvent ratio, but if the ratio is too high, the resolubility of the resin may be lowered, and printing failure such as blocking may occur.
The viscosity of the ink is controlled by adding a solvent such as water to 15 to 25 s (coating 3 cups), and the specific viscosity should be determined according to the printing conditions, the depth of the printing plate cavity, and the printing process.
Before the official printing, adjust the ink viscosity according to the depth of the printing plate. Do not add water to the ink during the printing process. Just add new ink to ensure the color and color consistency of the printed product before and after.
(3) Reasonable use of various additives to improve the printability of water-based inks
The printability of water-based inks is also related to the thixotropy, fluidity, viscosity, and drying properties of the ink. In order to improve the performance of water-based inks, it is often necessary to add auxiliaries, and commonly used auxiliaries include defoamers, stabilizers, diluents, slow-drying agents, quick-drying agents, thickeners, and the like.
1 antifoaming agent: used to eliminate foam in water-based ink, the dosage is generally 1% to 2%. Generally speaking, when the viscosity of the aqueous ink is too high, the pH is too low, or the printing speed is fast, and the hardness of the main solvent water added is high, bubbles are easily generated, and excessive bubbles may cause the printed matter to leak and splash. Ink and ink color uneven printing defects.
2 Stabilizer: Also known as pH stabilizer, the main component is organic amines. The stabilizer is mainly used to adjust and control the pH value of the aqueous ink to stabilize it at 8.0 to 9.5, and the printing suitability of the aqueous ink is good. When the pH of the aqueous ink is higher than 9.5, that is, the alkalinity is too strong, the viscosity of the aqueous ink will decrease, the drying speed will be slow, and the water resistance will be deteriorated; when the pH of the aqueous ink is lower than 8.0, the alkalinity is too weak. The viscosity of the water-based ink will increase, and the ink will be easy to dry and accumulate on the printing plate, causing the layout to be dirty, blocking the plate, foaming, and water resistance. In general, during the printing process, an appropriate amount of stabilizer should be added at regular intervals to stabilize the pH of the aqueous ink, while also adjusting the viscosity of the aqueous ink and diluting the ink.
3 thinner: mainly used to reduce the viscosity of water-based ink, the dosage should be controlled within 3%, the color of the water-repellent ink becomes lighter, and the pH value of the water-based ink can be kept unchanged. The diluent should be added slowly while stirring to make the water-repellent ink too low.
4 slow drying agent: slow drying agent can inhibit and slow the drying speed of water-based ink, prevent water-based ink from drying in the printing grid, and reduce the occurrence of printing failures such as blocking and paste. The dosage is generally controlled at 1% to 2%. If the amount is too much, the ink layer is not dried thoroughly, and the printed product may have a sticky or odor on the back.
5 quick-drying agent: used to accelerate the drying speed of water-based ink, the dosage is 0-3%.
6 thickener: used to increase the viscosity of water-based ink, the dosage is 0.5% to 1%.
7 Other additives: such as dispersant, preservative, leveling agent, slip agent, cross-linking agent, etc., generally do not need to be added on site by the operator. If necessary, consult the ink manufacturer and add it according to the actual situation.
By using the above-mentioned additives scientifically, other weaknesses of the aqueous ink are improved to achieve optimum printability. At the same time, the drying speed of the aqueous ink is reasonably controlled so that the ink layer of the ink is sufficiently dried before entering the next printing color group, rewinding or stacking, but it cannot be dried on the printing plate.
(4) According to the characteristics of the printed product, a printing method combining water-based ink and solvent-based ink can be considered. For example, alcohol-soluble, ester-soluble or UV inks are used to print mesh and fine line plates, and water-based inks are used to print color blocks and thick line plates.
(5) In case of abnormal shutdown or temporary shutdown during the printing process, the plate should be kept at a low speed as much as possible, because the water-based ink is easy to dry and block the plate during the shutdown state (the main reason is the poor affinity between the water and the binder, water It is easier to precipitate, and it is difficult to re-dissolve water after the conjunctiva is connected. When a water-based ink dry-blocking plate occurs, the plate may be infiltrated with an aqueous ink cleaning agent, and then the plate is brushed with a glass fiber. The main components of the aqueous ink cleaning agent are about 3% of sodium silicate, about 1% of sodium hydroxide, and one of organic compounds such as polyethanolamine, triethanolamine, diethylaminoethanol, dimethylethanolamine, and aminomethylethanol. Approximately 2%, about 10% of the alkali-resistant penetrant OEP-70, and about 80% of water.
In short, the performance of water-based inks is not yet "to the most beautiful", but with the continuous efforts of the industry and the in-depth development of water-based ink research and promotion work, water-based inks will be "exclusive" in the gravure ink market.
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