Water-based ink is one of the three pillars of contemporary flexo printing. Due to the absence of volatile organics, inks that are considered to be environmentally friendly, safe and hygienic in all types of inks have been considered. Water-based inks are drying much faster than offset and gravure inks, and have good printability and abrasion resistance. They also have better performance in terms of printing density and dot gain. They have also been proved to be more suitable and Cardboard printing, the following brief description of how to make ink printing more beautiful.
Ink transferability The ink absorbability of the substrate has a great influence on the transfer of ink. However, if the paper is too rough, ink absorption is better, which will have a negative effect on the color and the amount of ink used.
Ink transfer is the process of ink penetrating the paper surface by capillary action under the effect of printing pressure. The well-mixed resin is fixed to the surface of the paper by capillary action. The acidity of the paper also plays a role in drying the ink. In order to obtain the best printing effect, the amount of ink used should be minimal under the premise of satisfying the color density and the quality of ink transfer, and is usually expressed in terms of ink holding capacity.
The surface of the paper requires less ink, whereas the rougher surface of the paper consumes more ink. When paper with a rough surface is used, even if the ink is finely regulated and the printed sheet is selected, the dot gain is likely to occur. The dot gain value is related to the type of paper, the surface structure, and the size of the micro-width. In addition, the excessive separation of the binder and the pigment in the ink will cause the anti-friction property of the paper after printing to be reduced, and the powder may be easily generated.
An important factor that determines printability is overprinting, which refers to the overlapping of multiple colors in the same pattern. To obtain a good overprinting effect, the first color ink should be sufficiently dried before the second color ink is superimposed on the first color ink, which is particularly important for the coated paper. Due to the fact that the coated paper surface is smoother than the non-material paper, it is more likely to cause failure. In order to reduce such failures, the color sequence is sometimes adjusted to MYC.
The influence of temperature on the fluidity of the ink changes with temperature, and the viscosity of the ink decreases as the viscosity increases. Therefore, the control of the degree of dryness is very important, and it is preferable to maintain the normal temperature. With the ink supply system of the squeegee system, the ink balance can be maintained only when the temperature is controlled.
In North America and Northern Europe, where the temperature has changed greatly, printers have fully realized that with the change of climate and the season, the temperature of the printing shop will also have great changes. Keep the viscosity of the ink stable and control the amount of diluent. The higher the generality, the less the amount of diluent needed, and the dilution of the ink will reduce the density of the print. The ink thinner is water or a lighter medium.
Drying Properties and Viscosity Control Waterborne inks are adsorbed on the surface of the substrate by evaporation, infiltration, precipitation and related chemical reactions. Evaporation is the removal of volatile organics from the printing surface ink by hot air.
The so-called osmotic drying is under the action of the capillary tube, the ink penetrates into the surface of the printing material. Often refers to the separation of liquid ink and solid phase liquid ink, liquid phase platform into the paper fiber, synthetic resin and solid phase remain on the surface of the paper, the corresponding chemical reaction is conducive to print on the ink layer drying. However, the corrugated post-printing process does not use chemical drying, and most of them use ultraviolet rays, infrared rays, electron beams or microwave drying.
In order to reduce the evaporation of the water-based ink in the ink fountain and the doctoring system, modern corrugated paper printing presses are generally equipped with a closed ink inking device. Most printing press ink tanks are located below the printing press unit and use an ink pump to pump the ink into the ink fountain. Ink through the unit during the cycle of continuous contact with the roller and the ink roller and the air convection solvent evaporation, resulting in increased viscosity, printing color density increased. In this case, it is usually necessary to dilute to make the viscosity meet the requirements. Do not add too much water to water-based inks, or it will be too thin. The water-based ink is too thin. Do not adjust the viscosity of the water-based ink by pouring fresh ink into the thin ink. Experience shows that if a new ink is poured in a thinner water-based ink, a lot of new ink is needed, and effective inks should be gradually added to the new ink.
Water-based ink viscosity control is to ensure its performance and print color, water-based ink is only a small amount of solvent volatilization, easier to adjust than solvent-based ink. As the paper and cardboard printing (7), the î‹„ î‹„   î² î² î² ç³ ç³ ç³ ç³ ç‰§ 牧 [牧 ç »å¬· 牧 ç »å¬· ç »å¬· ç »å¬· æ…· æ…· æ…· ç¨ ç¨ æ°´æ€§ 水性 水性 水性? Health is closely related to the dispersion of resin and water in aqueous ink formulations, and the best balance between drying speed and printability should be found.
Fast-drying inks used in high-speed printing can also quickly dry onto plates or anilox rolls during printing. Therefore, pay special attention to this type of ink.
Additives Additives are added to the ink to improve the performance of the ink. The amount of additives is generally small. To make the additive work, it is first necessary to understand its properties and possible side effects. The ink additives include defoamers, killers, waxes, surface active agents, moisturizers, transfer aids, binders, anti-caking compositions, slip agents, and the like.
Surfactants can reduce the surface tension of water-based inks, contribute to diffusion, increase gloss, and reduce the likelihood of agglomeration of the pigment in the diluted ink.
Defoamers are used to eliminate the trouble caused by the foaming caused by agitation during the printing process and the ink production process. Foams are often difficult to eliminate. Excessive use of defoamers will prevent printing from proceeding properly. Some defoamers contain hydrocarbons that adversely affect flexographic printing plates.
Foam generation is related to the hardness of the water. Silicon-based defoamers need to be diluted with water, and they should be agitated at a constant rate when incorporated into the ink. An undiluted, concentrated silica-based defoamer can cause pinholes or white spots in printed matter. Therefore, defoamers must be used with caution. The amount used should not exceed 1% and should be used after dilution.
The change in the PH value of the pH water-based ink not only affects the ink transfer but also affects the printed color. If the pH is too high, the amino group on the surface is too high and the water-based ink drying speed will slow down. On the contrary, if the PH value is low, the viscosity of the water-based ink tends to fluctuate greatly, and the resin will precipitate in the ink.
The pH value of the water-based ink can be detected with a standard pH meter. The conventional water-based ink is alkaline, the PH value is about 7 or more, and the normal applicable range is 8-9. In addition, the PH values ​​required for different formulations of ink are also different.
In order to obtain good printing quality and meet the requirements of customers, attention should be paid to the entire process from the product design stage to the final product delivery to each household, understand the process requirements of each stage, and try to meet the production requirements, and consider the following factors:
The quality of the original;
Bar code specifications;
Guidelines for optimal number of halftones for multicolor halftones;
Ink type and quality The ink absorption and uniformity of the substrate;
Control element
Anilox roller parameters and scraper type;
Gray balance;
Ink viscosity and pH control;
Ink overprint
The pressure between the anilox roller and the plate roller;
Printing pressure
Loading
Loading system;
Plate type, thickness and quality.
Plates that have a good effect on printing quality can get better printing results. It can reduce the dot gain, make the printed image sharper and the ink transfer better. When printing corrugated board, the best printing effect can be obtained with the minimum pressure. To reduce the dot gain in the corrugated box printing with the post-printing process, the ink transferability in the solid area is good, and generally, 3.18mm or 3.94mm thick can be used. Photoresist flexo, plus PU foam liner. The liner under the plate is compressible and absorbs printing pressure. The printing plate and the foam gasket work together to reduce dot distortion and reduce dot gain. Different types of tape structure, hardness, elasticity, adhesive strength, ink receptivity and ink release, etc., there are differences, and have different effects on the printing quality, should be in accordance with the different image content and adapt to the image of the tape model Used for plate mounting.
The depth of the image after the etching of the printing plate is to be carried out according to different printing machines, printing materials, plates, and printed materials. The company uses a new type of flexographic printing machine to print high quality halftones or fines on coated paper or semi-coated paper. When the graphic is in line, the depth of the graphic highlight should be 1-1.2mm. When using ordinary printing machines to print solid or thick text, the depth of the graphic text should not be too shallow, and the protrusion depth should be 1.5-1.8mm. Corrugated box after printing process should choose thicker photosensitive resin plate thickness of 2.84-3.18mm. If a corrugated red box requires high-quality half-tone printing, with 80 lines/inch images and UPC barcodes, a thicker version should also be used.
Digital version can be used in corrugated box post-printing process. Digital technology-based flexo platemaking is the latest technology in flexo printing today. It enables flexo printing to achieve excellent print quality and achieves and surpasses offset and gravure quality in certain aspects. . Direct Platemaking Process In the process of plate making, oxygen can inhibit the reaction rate of the resin chemical reaction, and can achieve the best balance in the inhibition of oxygen and UVA curing, making the outlets more tax-efficient and effectively suppressing the increase of network points. The use of a hard, compressed gasket material results in excellent screen printing of network images. Compared to conventional flexographic platemaking techniques, the network point reduction can be reduced by 15%-25%.
With the emphasis on environmental protection, the pre-printing process of corrugated cartons has gradually moved from gravure and offset printing to flexo printing, and the digital version is used as the printing plate of the corrugated box pre-printing process, which can also make the flexographic prints colorful and clear.