Application of water-based ink in carton and carton printing

In the call for protecting the environment, saving energy, reducing pollution, recycling and safe production. China's packaging and printing water-based inks ranked first among other packaging and printing inks with its 35% dosage in just a few years. In general, the more high-end packaging printing inks, especially water-based printing inks, the stronger its printing characteristics, the narrower the scope of adaptation. From ordinary batter starch, dextrin to shellac, casein, sodium lignin; from rosin modified maleic acid resin to styrene-acrylic copolymer resin and even polymer emulsion resins with core-shell structure and network structure . All are called water-based inks without exception.

In China, the number of inks used in packaging and printing products is increasing every year, especially in the form of screen printing and flexible letterpress, but most of the paper substrates are made of absorbent media and gravure printing is used. In particular, plastic and aluminum foil substrates applied to non-absorbent media have only recently achieved printing on web materials by rotary machines. The advancement of this technology shows that ink painting has gradually matured. At present, ink has been recognized as "non-toxic ink" by the American Food and Drug Association.

The rapid development of ink makes other inks hard to see. In the past, ink has poor gloss on paper, poor water resistance, poor adhesion, difficult overprinting, discoloration and fading, and products that are prone to edge warping and uneven clothing have been improved. This is very advantageous for promoting the application of water-based inks on cartons and cartons. In addition, ink and wash has the characteristics of no explosion, no transportation risk, no pollution, no toxicity, etc. and uses water to adjust the drilling degree and clean the printing equipment, which reduces the production cost and labor intensity. And for the production and transportation and use units to reduce potential safety hazards. The current use of ink is increasing. 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 ink have combined the characteristics of various packaging and printing materials in manufacturing experimental trial printing and production applications, and firmly grasped: ① The film-forming substance in the ink adheres the pigment and filler to the substrate. And give the ink a standing and non-stick body; ② can make the ink have sufficient leveling, spreading and gloss on the printing material; ③ has an efficient wetting agent and wear resistance: ④ maintain and improve the pigment Dispersion and printing suitability; ⑤ Can have sufficient printing resolubility, but must have a certain water resistance after drying. The traditional water-based ink is changed to use a simple water-soluble polymer compound (such as casein, shellac, polyvinyl alcohol resin, etc. as the ink connection material), because it only adheres to water and is not resistant to friction and water. Therefore, water-based ink binders such as acrylic and polynitrogen vinegar are used for the rotary flexographic and gravure ink systems. Glycol ethers (which can be metabolized to produce harmful substances such as alkoxyacetic acid) have been used in the past. Instead, the non-toxic ink is prepared from the propylene glycol ether series (metabolized to produce almost non-toxic 1,2-propylene glycol. It is finally decomposed into carbon dioxide and water, and the toxicity is very low. There is also an initiator-free water-based uv ink that will enter the market). The latter is now mostly adopted.

The relationship between printing conditions and drying speed and gloss

1. Water-based flexographic and rotogravure printing rolls for printing and packaging paper bags, books, magazines, cartons, cartons, cigarette packs, water-based inks for nearly ten years. Although the water ink of gravure paper produced by high polymer acrylic resin can meet the printing requirements of high-end products with high print quality requirements, but it can really meet the user's requirements for gloss and brightness, it is recommended to choose an initiator-free water-based UV ink.

2. The temperature and humidity of the printing workshop have a great influence on the drying speed and gloss of the ink film of the printing. Temperature is the main factor that affects oxidative polymerization, volatilization, and strong ink film. Therefore, the gloss difference between the southern coastal and northern plateau regions in summer and winter after the ink is dried and formed into a film is about 1 times. In the two cases where the relative humidity reaches 95% and 65%, the drying time is almost more than twice different. At the same time, the dry humidity and pH of the paper and the carton itself will directly affect the drying time of the printed products.

3. Acidity can delay the oxidative polymerization of ink and the formation of volatile solid ink film. If the alkalinity is too large, it will lead to internal wetness and external dryness, which will affect the adhesion of the ink on the surface of the printed product.

4. Because oxygen or air blowing or baking in the drying tunnel is a factor that promotes oxidative polymerization and volatilizes the solid ink film, the degree of ventilation in the printing workshop and the stacking method of the printed parts are also related to the drying speed of the printed products.

Causes and troubleshooting of ink and wash

1. Hue is not correct. The degree of ink drilling is too low or the pigment content in the ink system is low or the color purity is deviated. The ink precipitates during printing and is poorly transferred. Mix the original ink, adjust the drilling degree to mix the water ink before printing, and check whether the printing plate and ink roller are aging.

2. Unstable viscosity. The ink is thixotropic, foaming, and the solvent is volatile. The ink should be stirred evenly, and then the appropriate amount of defoamer (0.2%) should be added to add the appropriate amount of solvent to balance the volatilization.

3. Poor drying. In the expected time, the blot should not dry or even stick to your hand. The ink has a high degree of drilling and poor absorption of poorly dried base paper or plastics and fabrics. Dilute the ink, adjust the printing pressure to increase the temperature of the blowing or drying tunnel, or use quick-drying ink. Or adjust the dryness. Replace the substrate and replace the light version.

4. The outline is blurred. The high-profile part of the printed product is blurred. The dots are false 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 drilling of the ink is large and the ink returns to the coarse ink. The drying is too fast and the stirring is poor. The backing plate should be even and even to adjust the printing pressure. When adjusting the ink drilling degree, the water and alcohol should be mixed to reasonably stir the ink and adjust the ventilation device. Don't blow it onto the ink roller or the roller, and increase the speed. Scrub with water containing monoethanolamine or add 0.2% dimethyl silicone oil or increase the proportion of coupling agent.

5. Graphic crushing ink extrudes out of the graphic. The quality f of the printing plate is too soft or the pad elasticity is too large, the contact pressure is too tight, the pressure is too low, the ink privacy is too low, and the ink is poorly stirred. Pad the plate to adjust the height of the printing plate, adjust the printing pressure or the pressure of the manual screen printing squeegee, adjust the drilling degree to water ink with high drilling degree or exchange the ink with greater hardness and stir the ink reasonably.

6. Poor transfer. Insufficient printing pressure The plate hardness is too high, the water resistance of the paper is too strong, and the ink roller wears out. Increase printing pressure. Use water-repellent ink to check ink roller wear and aging. Add TM-20. Coupling agent. Replace the metal anilox roller that blocks wear.

7. Difficult to overprint, multi-color overprint is not allowed. The printing pressure of the first color ink is too high. The first color ink dries too quickly. The second color printing pressure should be increased, and the first color printing pressure should be light. Add the appropriate amount of TM-200S coupling agent. The privacy of the first color ink should be reduced and the dryness of the first color ink should be adjusted or the second color should be printed when the ink film is not completely dry (overcoming the surface vitrification ) The printing plate swells and protrudes out of shape, replace the paper.

8. Ink foaming, the foam overflows after the ink in the ink fountain of the printing machine circulates. Insufficient suds suppressor in the ink system. Insufficient ink circulation, too much water, too much pump circulation, and air leakage in the tube. The ink is too thin. Appropriately add defoamer (0.2% is best to mix the two plastic defoamers inside and outside) to reduce the pump circulation and add new ink so that it does not overly dilute the inspection tube to prevent air leakage.

9. Chemical pinholes. Adding too much defoamer will cause the ink to dilute the excessively low-privacy ink and ink too much. Note that about 0.2% of defoamer is incorporated. It should be mixed with the original ink and mixed before printing.

10. The printing plate is worn. The contact is too tight, the pressure is too heavy, or the texture of the plate is too hard. Adjust the contact, adjust the printing pressure, replace the printing plate or add a 3mm plastic foam sheet on the back of the plate.

11. Ink gelatinization. Use the wrong solvent (some active molecules begin to associate to form colloid-sized aggregates). Mixed with other types of ink, improper storage, wrong colorant used in ink, ink ages over time. Use a solvent with good solubility to add about 2% of silica gel or 0.3% TM-200 coupling agent, seal and store it. Add an auxiliary agent with activity.

12. Paste dirty / sticky and dirty during printing and stacking after printing. Friction occurs on the conveying rod and the film peels off causing fouling. Ink drying speed is too slow, printing speed is too fast, improper ventilation to heat the ink is too soft. Replace the hard ink and add a solvent that evaporates quickly (ethanol or acetone) to slow down the printing speed and increase the air supply.

13. Ink fading Ink color fades during printing or stacking. Ink system fillers have too much color and have wrong pigments (acid is not resistant to alkali). The printing carrier is too acidic. Ink pigments are not heat resistant. Use fast-drying ink or less use of drier ink. The pigment in the ink adopts heat-resistant and light-resistant stable pigments, and replaces non-coloring calcium fillers. Add inorganic mica powder or anti-ultraviolet absorber or antioxidant about 0.1% to 0.3%.

14. Striped orange peel. The imprint is uneven. Ink ink leveling is too poor, too much plasticizer, and thixotropy is too large, sometimes there are stains on the net, the paper is not flat, the ink is too large, the ink is too thin, and the water is too large. Replace thicker ink, reduce printing pressure, and replace water-resistant ink. Use opaque ink. Change the high-quality substrate with a uniform surface to increase the filling amount (such as talcum powder can not only prevent sinking but also improve leveling). Replace the ink with lower viscosity, do not dilute the color too lightly to reduce static electricity.

15. Blotting (pulverization). 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 ink system is reduced or the solubility of the solvent and the binder of the ink system is unbalanced. The wettability of the pigment and filler is poor. The paper surface is too rough or the aluminum and plastic surfaces are too smooth. Increasing the resin content reduces the proportion of water as much as possible to balance the content and solubility.

16. Poor tolerance. Poor water resistance, light resistance, and alkali resistance. Use appropriate ink "The pH value of the strong ink film should be controlled between 7 and 7.5! Replace the light-resistant ink or add 0.2% of the ultraviolet absorber or inorganic mica powder to use soft ink.

17. Block the network and block 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 neutralized and are neutralized and accumulated. The ink is mixed with paper scraps and plastic scraps. Reduce printing pressure, filter ink and adjust the ink supply. Use alkali-resistant fillers and alkaline active additives, add the original viscosity of the appropriate viscosity to the printed ink to adjust.

Basic knowledge of ink storage and printing process

1. After printing, the printing machine, ink roller and printing plate should be thoroughly washed. Waste water should be treated. The ink fountain should be covered and sealed to prevent it from falling into the dust.

2. Ink should be kept in a cool place to prevent deterioration. Although it is water-based, due to the presence of alcohol in the solvent, it is forbidden to approach the fire source to prevent the heat from volatilizing.

3. Care should be taken after opening the barrel (can box), do not bring impurities, and use it as it is opened. To prevent the amine and ammonia of the ink system from volatilizing in an unstable state. Do not use light-transmitting packaging barrels (cans, boxes) to prevent the ultraviolet rays from invading and 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 magnesium salt or TM coupling agent.

5. Ink and ink are too low and the fluidity is too large. Storage is easy to deposit or printing is easy to sag. It can add cheap aluminum salt or white carbon black or bentonite in appropriate amount.

6. Ink and ink drying speed (such as gravure printing for 3-5 seconds and 100 seconds for drying) can be determined by gravure, embossing and screen printing process.

7. For water-soluble printing inks that are difficult to clean, add triethyl thiamine or TM-2005 coupling agent, and finally add an inexpensive LLJ all-around solvent to increase the rewetting of the ink or increase the true solvent to reduce the proportion of ink. For the case where the anilox roller is blocked by coarse particles, the ink can be re-filtered. The ink stains when cleaning the printing machine, printing plate, ink roller and bucket tool are cleaned by filtration or introduced underground. Avoid its pollution to the environment.

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