In the voice of protecting the environment, saving energy, reducing pollution, recycling and safe production. my country’s packaging and printing water-based inks ranked first among other packaging printing inks with 35% of its usage in just a few years. Looking at the packaging printing ink, the more high-end, especially the water-based printing ink, the stronger the printing characteristics and the narrower the application range. From ordinary batter starch, dextrin to shellac, casein, sodium lignin; from rosin-modified maleic acid resin to styrene-acrylic acid copolymer resin and even current polymer emulsion resin with core-shell structure and network structure . All are called water-based inks without exception.
In my country, the number of inks used in packaging and printing products is increasing every year, especially in the form of screen mesh and flexographic printing. However, most of them are paper substrates of absorbent media and use gravure printing. In particular, plastic and aluminum foil substrates used in non-absorbent media have only just realized printing on roll materials using rotary machines in recent years. The advancement of this technology shows that ink and wash have become more and more mature. At present, ink has been recognized as “non-toxic ink” by the American Food and Drug Association.
The development speed of ink and wash makes other inks hard to beat. In the past, the poor gloss of ink on paper, poor water resistance, poor adhesion, difficult overprinting, discoloration and fading, and products that are easy to warp edges and corners have been improved. This is very beneficial to promote the application of water-based inks on cartons and cartons. In addition, ink-wash has the characteristics of non-explosion, no transportation hazard, no pollution, no toxicity, etc. It uses water to adjust the drilling degree and clean the printing equipment, reducing production costs and labor intensity. And it reduces the hidden safety hazards for production, transportation and use units. At present, the use of ink is increasing day by day. Despite the quality, there are still some shortcomings, but the safety has been unanimously recognized by the packaging and printing industry.
For more than ten years, ink and wash have combined the characteristics of various packaging and printing materials in manufacturing experimental printing, production and application, and firmly grasped: ①The film-forming substance in the ink adheres the pigments and fillers to the substrate. And it gives the ink a standing body without sticking; ②It can make the ink have sufficient leveling, spreading and gloss on the printing material; ③Has high-efficiency wetting agent and abrasion resistance: ④Maintain and improve the pigment Dispersion and printability; ⑤ It can have sufficient printing resolubility, but it must have a certain degree of water resistance after drying. It has changed the traditional water-based ink using pure water-soluble polymer compounds (such as casein, shellac, polyvinyl alcohol resin, etc.) as the ink binder, which is not resistant to friction and water due to its attachment to water only. Therefore, for the rotary flexible embossing and gravure printing ink systems, water-based ink binders such as acrylic acid and polyurethane have been used in the past, which have been metabolized to produce harmful substances such as alkoxy acetic acid. The propylene glycol ether series (metabolized to produce almost non-toxic 1,2-propylene glycol. Finally, it is decomposed into carbon dioxide and water, with low toxicity. There is also an initiator-free water-based uv ink that will enter the market) to prepare non-toxic inks. The latter is mostly adopted now.
The relationship between printing conditions and drying speed and gloss
1. Water-soluble ink for printing and packaging paper bags, books, cartons, cartons, cigarette packets, and rotogravure printing webs for more than ten years. Although the gravure paper ink produced with high polymer acrylic resin can meet the printing requirements of high-end products with high printing quality requirements, it is recommended to choose initiator-free water-based UV inks that can truly meet the user’s requirements for gloss and brightness.
2. The temperature and humidity of the printing workshop have a great influence on the drying speed and gloss of the ink film. Temperature is the main factor that affects oxidative polymerization, volatilization, and solid ink film. Therefore, the gloss of the ink after drying and film formation is about 1 times different in summer and winter in the southern coastal and northern plateau areas. When the relative humidity reaches 95% and 65%, the drying time is almost two times different. At the same time, the dry humidity and pH value of the paper and carton itself will directly affect the drying time of the printed products.
3. Acidity can delay the oxidative polymerization of the ink and the formation of a solid ink film by volatilization. If the alkalinity is too large, it will cause the inside to be wet and the outside to dry, which will affect the adhesion of the ink on the surface of the printed product.
4. Because oxygen or air blowing or drying tunnel baking is a factor that promotes oxidative polymerization and volatilization of a strong ink film, the degree of ventilation in the printing workshop and the way the printed parts are stacked are also related to the drying speed of the printed products.
Causes and troubleshooting of ink wash
1. Inaccurate hue. If the ink penetration is too low or the pigment content in the ink system is low or the color purity is deviated, the ink will precipitate and precipitate during printing, resulting in poor transfer. Mix the original ink, adjust the drilling degree to mix the ink evenly before printing, and check whether the printing plate and ink roller are aging.
2. The viscosity is unstable. The ink is thixotropic, foams, and the solvent is volatile. The ink should be evenly stirred and then add an appropriate amount of defoamer (0.2%) and an appropriate amount of solvent to achieve a balance of volatility.
3. Poor dryness. The imprint does not dry or even sticks to the hands within the expected time. The ink has a high degree of penetration and is poorly dried. The base paper or plastic and fabric have poor absorbency. Dilute the ink, adjust the printing pressure to increase the blowing or drying tunnel temperature, or use fast-drying ink. Or adjust the dryness. Change the substrate to replace the light version.
4. The outline is blurred. The high-profile parts of the printed products are blurred. The dots are blurred and the tone is lost. The quality of the printing plate is not high. The contact between the printing plate and the ink roller is too tight. The pad should be evenly and smoothly to adjust the printing pressure. When adjusting the ink penetration, water and alcohol should be mixed to stir the ink reasonably, and the ventilation device should be adjusted. Don’t blow it on [examples, ink rollers. Increase the speed of the machine, scrub with water containing monoethanolamine or add 0.2% dimethyl silicone oil or increase the proportion of coupling agent.
5. Graphics and text squeeze the ink to squeeze out of the graphics and text. The quality of the printing plate is too soft or the pad elasticity is too large. The contact is too tight and the pressure is too large. The ink privacy is too low. The ink mixing is poor. Adjust the printing pressure or manual silk screen squeegee pressure by padding the printing plate, adjusting the drilling degree to high-drilling ink or changing the ink with greater hardness and mixing the ink reasonably.
6. Poor transfer. Insufficient printing pressure. The hardness of the printing plate is too high, the water resistance of paper is too strong, and the ink roller is worn and aged. Increase the printing pressure and use hydrophobic ink to check the wear and aging of the ink roller. Add TM-20. Coupling agent. Replace the worn out metal anilox roller.
7. Difficult to register, multi-color register is not accurate. The printing pressure of the first color ink is too large. The first color ink dries too fast. The second color printing pressure should be increased, and the first color printing pressure should be light. Adding an appropriate amount of TM-200S coupling agent should reduce the privacy of the first color ink and adjust the dryness of the first color ink or print the second color when the ink film is not completely dry (overcoming the surface vitrification) ) The printing plate swells and protrudes and deforms, replace the paper.
8. The ink foams, and the foam overflows after the ink circulates in the ink fountain of the printer. Poor foam inhibitor in the ink system. Insufficient circulation of ink, too much water, too much pump circulation, and pipe leaking. The ink is too thin. Appropriately add defoamer (0.2% is best to mix the internal and external plasticizing defoamers) to reduce the circulation of the pump and replenish the new ink so that it is not excessively diluted. Check the tube to prevent air leakage.
9. Chemical pinhole. Too much defoaming agent is added, the ink is too diluted and the ink with low privacy is too much ink. Note that about 0.2% of defoamer is added. It should be mixed with the original ink and mixed well before printing.
10. The printing plate is worn out. The contact is too tight, the printing pressure is too heavy, or the texture of the printing plate is too hard. Adjust the contact, adjust the printing pressure to replace the printing plate or add a 3mm plastic foam sheet behind the plate.
11. Ink gelation. Use the wrong solvent (some active molecules begin to associate to form colloidal aggregates). Mixed with other types of ink, improper storage, wrong colorant used in the ink, and long-term aging of the ink. Use a solvent with good solubility to add about 2% silica gel or 0.3% TM-200 coupling agent, and store it in a sealed container. Add active auxiliary agents.
12. Paste plate sticking/sucking dirty during printing and stacking dirty after printing. Friction occurred on the transfer rod and the film was peeled and fouled. The ink drying speed is too slow, the printing speed is too fast, and the ink is too soft due to improper ventilation and heat. Replace the harder ink and add a fast-evaporating solvent (ethanol or acetone) to slow down the printing speed and increase the air supply.
13. Ink fade The color of ink fades during printing or stacking. The ink system has too many fillers and the wrong pigments are used (acid is not alkali resistant). The printing carrier is too acidic. Ink pigments are not heat resistant. Use quick-drying ink or use less drier. The pigment in the ink uses heat-resistant and light-resistant stable pigments, and replaces the colorless calcium fillers. Add inorganic mica powder or anti-ultraviolet absorber or antioxidant 0.1% to 0.3%.
14. Striped orange peel. Imprints are not level. The ink leveling is too poor, the plasticizer is too much, and the thixotropy is too large, sometimes the net stains, the paper is not level, the ink is too large, the printing pressure is too large, the ink is too thin, and the water is too large. Replace thicker inks, reduce printing pressure and change inks with good water resistance. Use opaque inks. Replace high-quality substrates with a uniform surface to increase the amount of filling (such as talcum powder can prevent settling and improve leveling). Change the ink with lower viscosity and don’t dilute the color too lightly to reduce static electricity.
15. The blotting falls off (chalking). After the printed product is bound, moved or wiped by hand, the ink color contaminates the printed product and fingers. Due to improper adjustment of the ink, the resin in the printing ink system is reduced or the solubility of the ink system solvent and the binder is unbalanced, and the wettability of pigments and fillers is poor. The surface of the paper is too rough or the surface of aluminum or plastic is too smooth. Increase the resin content and reduce the proportion of water as much as possible to balance the content and solubility.
16. Poor patience. Water resistance, light resistance and abrasion resistance, poor alkali resistance. Use appropriate ink “After the solid ink film is formed, its pH value should be controlled between 7 and 7.5! Replace light-resistant ink or add 0.2% anti-ultraviolet absorber or inorganic mica powder to use softer ink.
17. Blocking the net and the plate. The large f at both ends of the ink roller accumulates like ink residue. The pigments and fillers of the ink system are not resistant to alkaline binders and are neutralized and accumulated, and the ink is mixed with paper scraps, plastic scraps and fabric scraps. Reduce the printing pressure and filter the ink to adjust the ink supply. Choose alkali-resistant pigments and fillers and alkaline active additives, and use the original ink with suitable viscosity to add to the already printed ink for adjustment.
Basic knowledge of ink storage and printing process
1. After printing, the printing machine, ink roller, and printing plate should be thoroughly cleaned. Waste water should be treated. The ink fountain should be sealed to prevent dust from falling. Note that the ink will separate immediately when it encounters acidic water and the iron barrel is rusted.
2. Ink should be kept in a cool place to prevent deterioration. Although it is water-based, because the solvent contains alcohols, it is forbidden to approach the fire source to prevent heat volatilization and deterioration.
3. After opening the barrel (tank box), you should pay attention to storage, do not bring in impurities, and use it as soon as you open it. Prevent the amine and ammonia of the ink system from being in an unstable state after volatilization. Do not use light-transmitting packaging barrels (cans, boxes) to prevent UV rays from causing instability in the oil.
4. If the gloss is not bright, it can be adjusted by adding tung oil or polymer resin plus acrylic resin or adding magnesium salt or TM coupling agent.
5. If the ink is too low and the fluidity is too large, it is easy to deposit or sag when printing. You can add cheap aluminum salt or white carbon black or bentonite in an appropriate amount.
6. The ink drying speed (such as 3-5 seconds for initial drying of gravure printing and 100 seconds for thorough drying) can be determined by the process flow of gravure, embossing and silk-screen printing.
7. For water-soluble printing inks that are difficult to clean, add triethylamine or TM-2005 coupling agent, and finally add a cheap LLJ all-around solvent to improve ink rewetting or increase the true solvent to reduce the proportion of ink. In the case of coarse particles clogging the anilox ink roller, the ink can be re-filtered. The ink stains during the cleaning of the printing press, the printing plate, the ink roller and the cleaning barrel tools can be filtered and purified or introduced into the ground. Avoid its pollution to the environment.