Experience in printing ink for color flexo carton
Carton color green Why do ordinary corrugated boxes need to be colored? The first is the needs of the market, consumers are increasingly favoring high-quality printed packaging. High-quality printed packaging gives consumers a sense of pleasure when shopping, and a sense of confidence and trust in the goods. Secondly, the design of corrugated boxes is changing. Designers require packaging to display more product content and beautify commodities. Now more and more corrugated carton design has used high-quality patterns, through the perfect embodiment of the pattern level to better express the creativity and content of the design. Promote the corporate culture, make the goods have affinity for consumers, and stimulate consumers' desire to buy. Third, improve the positioning of commodities in the market through the design of high-quality patterns. High-quality pattern printing is indirectly reflected in high-quality products, which is a foreshadowing of the product positioning of the merchants, and can unify the inner packaging, outer packaging and transportation packaging of the product, and strengthen the awareness of the product market. Fourth, the colorization of corrugated cardboard boxes helps to improve the anti-counterfeiting function of product packaging. The high-quality color corrugated carton produced by the cooperation of professional design companies and professional plate-making companies to produce printing plates and high-level carton printing manufacturers must be scanned by the counterfeiters to obtain plate-making data. The possibility of corrugated box manufacturers printing counterfeit is very small. Domestic fraud is still rampant, causing huge losses to many companies. Most companies make big fuss about the small packages of products to prevent counterfeit and shoddy products. However, most small packages use offset printing or gravure printing, which is more likely to be counterfeited due to technical reasons. If technical measures are also adopted in the printing of outer packaging cartons, it will inevitably increase the difficulty of counterfeiting. The advantages of flexo printing are first of all green and environmental protection. The use of water-based ink printing has no pollution to the working environment and substrates, which is definitely beneficial to on-site operators and end consumers. The carton industry has introduced and developed a large number of high-net-line flexo printing machines, mainly including Bobst, Martin, TCY, Nanhai Dongfang, Jingshan light machine and other brand models. The carton screen printing easily exceeds 50 lines, and the fineness is catching up. offset printing. The carton packaging is mainly based on the logistics transportation function, and the product display function is at least one meter away from the consumer. Flexographic printing can completely replace offset printing to meet the carton colorization. In addition, because flexo printing is generally printed directly on the formed cardboard, the corrugated composite strength of the same quantitative paper distribution is better than the offset printing method, which brings a lot of space for carton cost reduction. The development of flexible ink Regardless of whether white-faced paper or cardboard paper is used as face paper for flexible ink printing, the color effect can be reflected. Cooperating with the ever-changing flexo printing technology, the ink products are based on high-quality water-based ink, and continuously develop UV / EB cured flexible inks with higher technological content, which improves the ink and paperboard ink absorption and diffusion, making the flexo products more dense and saturated , The layers are clear, the beauty is suddenly on the paper. With the continuous development of flexographic printing machines, the packaging and printing industry will be more urgent for water-based inks and various new flexible inks, and the demand will be further increased. At present, there are nearly 1,000 carton flexo printing machines of various types in China, which mainly use water-based ink for printing, with an annual consumption of more than 50,000 tons, accounting for 25% of the total amount of ink. There are two reasons why ink is suitable for carton printing: one is that corrugated cardboard is a loose fiber interwoven fabric, which has strong water absorption. After the water-based ink is transferred to the surface of the cardboard, it is easy to penetrate and dry, and there is no need to install a drying device; second, because the water-based ink is non-toxic , Harmless, non-flammable, safe and convenient to use, low cost. Characteristics of water-based ink The water-based ink is composed of water-based polymer resin and emulsion, organic pigments, water solvent and related additives through physical and chemical processes. It does not contain volatile organic solvents and some toxic and harmful substances in solvent-based inks. The main difference between it and solvent-based ink is that the solvent used is not an organic solvent but water, that is, the binder is composed of resin and water, and its environmental protection is more suitable for products with strict hygiene requirements such as food, beverages, and pharmaceuticals. The composition of water-based ink is as follows: The color material is the coloring substance of the ink, and most of the organic pigments with complete chromatogram, high color concentration and easy to achieve high hiding power are used, such as magenta ink, yellow ink, cyan ink, etc. Generally, organic pigments are used; white ink is mostly titanium dioxide; black Ink is carbon black. Water-soluble or water-dispersible resins are the linking materials for inks and inks, which are important factors affecting the quality of inks. The printing suitability of viscosity, adhesion, gloss, and drying depends on the resin composition. There are many types of water-based ink binders, which can be selected according to different occasions and functions. At present, domestic ink companies mostly focus on the research and development of inks, including polyvinyl alcohol, hydroxyethyl cellulose, and polyvinylpyrrolidone, etc., and water-soluble binders, and the soluble alkali-soluble links of soluble resins. Materials and diffusion bonding materials commonly known as latex containing propylene, ethylene or styrene-butadiene polymers. From a formulation point of view, the ability of domestic ink blending color pastes is poor, only reaching 50%, and the imported resin packaging color pastes can reach 80%. The coarseness of domestic ink is easy to damage the printing anilox roller, and the imported ink has a finer particle size. It has a good affinity with the anilox roller and will not scratch the surface of the printing material and affect the printing effect. The solvent of water-based ink is mainly water, and a very small amount of alcohol, such as ethanol, isopropanol or polypropanol, can be added during use. The addition of alcohol helps to improve the stability of the ink, speed up the drying speed, and reduce the surface temperature. The hub? Thistle grub is more powerful? , The role is to adjust the PH value, eliminate bubbles and adjust the curing and drying time. Colorants and ink blending oils are important raw materials for the manufacture of inks. The inks and inks that we make in China use imported color pastes and ink blending oils. When choosing water-based ink, attention should be paid to the viscosity, concentration, fineness, drying speed, wear resistance, water resistance and stability of the ink. Viscosity Viscosity is the size of the cohesion of the ink, and it is also the most important control index in the application of ink. If the viscosity of the ink is too low, it will cause the disadvantages of light color, large dot expansion, high light spot deformation, and uneven ink transfer; too high viscosity of the ink will affect the ink transfer performance of the anilox roller, the ink color is uneven, and the color is sometimes printed instead. It is not deep, and at the same time it is easy to cause ills such as dirty version, paste version, blistering, and non-drying. ■The influence of temperature on ink viscosity The temperature has a great influence on ink viscosity. The influence of workshop temperature on printing quality is shown in Table 5. Relative humidity is preferably between 60% and 85%. When the temperature difference between winter and summer is large, the viscosity is the most sensitive. When the temperature is high, the moisture evaporates quickly and the drying is fast. When operating, you must pay attention to prolong the drying time or increase the speed of the machine; when the temperature is low, the moisture evaporates slowly and the ink drying is also slow. During operation, the ink drying speed can be increased or increased. Turn on the drying device. In winter, the ink is easy to freeze because it is below 0 ℃. If the ink is frozen, it can be placed in a room with a high temperature to allow it to dissolve naturally. After stirring evenly, it can continue to be used. In actual production, when a printing machine with a doctor blade is used, the ink transfer amount when the temperature is too low is not as stable as when the temperature is slightly higher. Increasing the temperature of the ink will reduce the viscosity. As a result, the density of the printed product will decrease and the ink layer will become thinner. To maintain the consistency of printing quality, it is necessary to maintain the consistency of ink viscosity. The printer must pay close attention to the influence of the temperature of the ink. Before printing, the temperature of the ink should be stabilized at the temperature of the printing workshop. This measure is very important, otherwise the ink density in the printing process will change significantly. ■The effect of thixotropy on ink viscosity The thixotropy refers to the fluidity of the ink increases under the action of external stirring, and the fluidity gradually decreases after stopping the agitation to restore the original performance. After the ink has been left for a long time, some inks with poor stability tend to settle and delaminate. There are also false thick phenomenon. At this time, it can be fully stirred. After a certain period of time, the above problems will naturally disappear. When using fresh ink, be sure to stir in advance before making dilution adjustments. Or it is expected that after a certain amount of ink is applied to the machine, the degree of viscosity decline will be improved due to the water content in the machine and the thixotropy of the ink. When printing is normal, the ink Fountain should be stirred regularly, especially the ink with high white pulp content. PH value of ink ■The effect of PH value on ink viscosity The PH value of another index that needs to be controlled in the application of water ink, its normal range is 8.5 ~ 9.5, at this time, the printing performance of the water-based ink is the best, and the print quality is the most stable. Because ammonia continuously volatilizes during the printing process, the operator will also add new ink and various additives to the ink from time to time, so the PH value of the ink may change at any time. Using a standard PH meter, the pH of the ink can be easily measured. When the PH value is higher than 9.5, the alkalinity is too strong, the viscosity of the water-based ink is reduced, the drying speed becomes slow, the water resistance becomes poor, and paste printing is easy to occur; and when the PH value is lower than 8.5, that is, the alkalinity is too weak, the water The viscosity of the base ink will increase, the ink is easy to dry, clogged on the plate and the anilox roller, causing the plate surface to be dirty and generating bubbles. The influence of PH value on the printability of water-based ink is mainly manifested in the viscosity stability and drying property of the ink and the clarity of the dot. As the pH value increases, the viscosity of the ink drops and the drying speed becomes slower. Application experience Water-based inks often encounter some problems in the cardboard printing process. The reasons for analysis and solutions can be referred to as follows: ◆ The adjustment of printing pressure is critical, it includes the pressure between the printing plate and the substrate and the pressure between the anilox roller and the printing plate. If the ink viscosity is too high and the ink dries too quickly, the solution is to adjust the pressure, dilute the ink, and add a slow drying agent. ◆ The ink is dry on the printing plate, if the printing edge is blurred, it may be that hot air is blowing on the printing plate, and the paper fiber is mixed with the ink to cause static reaction. The way to eliminate is to dilute the ink and gradually increase the speed, cover the ink system, or replace the ink, Install an anti-static device. ◆ Flexo is especially suitable for printing on the spot. If the spot is not solid, the cause may be that the viscosity of the ink is too low and the surface of the substrate is uneven. The solution is to use a high viscosity ink and use a substrate with good surface quality. ◆ Ink accumulates on the printing plate or dots are full, the reasons include too much ink, too much printing pressure, ink drying too fast or too weak ink, etc. The solution is to replace the anilox roller, adjust the pressure, add slow drying agent Or use high color and strong ink. ◆ The reason for poor printing adhesion is that the drying temperature of the ink is too low, the ink has no affinity with the material, and the dyne value of the material surface is too low. Corona treatment is required. The solution is to measure the surface tension, increase the drying temperature, change the ink type or print The surface of the wool printing material.
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