Color flexo printing carton printing ink development

For a long time, the image of many commodities in the international consumer market in our country is "low price, poor quality, and poor packaging." Many traders have benefited from the improvement of packaging in the secondary sales after importing Chinese goods. In order to prevent Chinese goods from entering in large numbers, some European countries have played "packing cards." With a positive attitude to such rules of the game, domestic packaging products should be quality, quality, environmental protection, and gradually move toward internationalization. Corrugated cartons as one of the most commonly used consumer goods packaging, environmentally friendly flexo printing will become the mainstream of the domestic carton manufacturing industry, and flexo printing substrates - color flexo printing cartons is bound to promote the development of ink.

Carton color green

Why do common corrugated boxes need to pursue colorization? The first is the need of the market. Consumers increasingly prefer high-quality printing packaging. High-quality printed packaging gives consumers a sense of pleasure when they shop, and a sense of trust and trust in their products. Second, the design of corrugated boxes is changing. Designers demand that packaging be able to display more of the product's content and beautify the product. Nowadays more and more corrugated boxes have been designed using high-quality patterns, and the design ideas and content are better represented through the perfect representation of the pattern level. This corporate culture is promoted so that the products have affinity with consumers and can stimulate consumers' desire to purchase. Third, improve the positioning of products in the market through the design of high-quality designs. High-quality pattern printing indirectly embodies high-quality products, which is a kind of pave for the product positioning of the merchants, and can organically integrate the inner packaging, outer packaging and transportation packaging of products, and strengthen the recognition of the product market. Fourth, the colorization of corrugated boxes helps to improve the anti-counterfeiting capabilities of product packaging. Through high-quality colored corrugated boxes produced by professional design companies and professional plate-making companies that cooperate with printing plates and high-level carton printing manufacturers, counterfeiters obtain plate-making data by scanning cartons, and then small The possibility of imitation of counterfeit corrugated box manufacturers is very small. Domestic fraud is still very rampant, causing huge losses to many companies. Most companies are making big mistakes in the small packaging of products to prevent counterfeit products. However, most of the small packages use offset or gravure printing, and there is a greater chance of counterfeiting for technical reasons. If technical measures are taken in the printing of packaging cartons, it is bound to increase the difficulty of counterfeiting.

Flexographic advantages are first manifested in green environmental protection. The use of water-based ink printing has no pollution to the working environment and substrates, and it is absolutely beneficial to on-site operators and end consumers. The carton industry has introduced and developed a large number of high-line flexographic presses, mainly Boste, Ma Tin, TCY, Nanhai Dongfang, Jingshan lighter and other brand models, carton screen printing easily over 50 lines, fine pursuit offset printing. The carton packaging is mainly based on the logistics transportation function. The commodity display function is at least one meter away from the consumer. Flexo printing can completely replace the offset printing to meet the carton colorization. In addition, since the flexo printing is generally directly printed on the formed cardboard, the integrated strength of the corrugated paper with the same basis weight is better than the offset printing mode, which brings many room for price reduction to the cost of the cartons.

The development of flexible ink

Flexible ink printing Whether white paper or cardboard is used for facial paper, color effects can be reflected. With the ever-changing flexographic technology, ink products based on high-quality ink, continue to develop more high-tech UV/EB cured flexible ink, improved ink and paperboard ink diffusion, so that the flexo ink product is more concentrated, more saturated , structured, beautiful and vivid. With the continuous development of flexographic printing machines, the demand for water-based inks and various new flexible inks in the packaging and printing industry will be even more urgent, and the demand will further increase.

At present, there are nearly 1,000 sets of various types of carton flexo presses in China, mainly using water-based ink printing. The annual consumption is more than 50,000 tons, accounting for 25% of the total amount of ink and water. There are two reasons why ink is suitable for carton printing: First, because the corrugated paperboard is a loose fabric with high water absorbency, the water-based ink can be easily penetrated and dried after being transferred to the surface of the paperboard, and no drying device is required; second, the water-based ink is nontoxic. , harmless, non-flammable, safe and convenient to use, low cost.

Water-based ink features

Water-based inks are made of a mixture of aqueous polymer resins and emulsions, organic pigments, water solvents and related additives through physical and chemical processes. They contain no volatile organic solvents and do not contain certain toxic or hazardous substances in solvent-based inks. The main difference between it and solvent-based ink is that the solvent used is not organic solvent but water, that is, the binder is composed of resin and water, and its environmental protection is more suitable for foods, beverages, drugs and other sanitary products with strict requirements. The composition of the water-based ink is as follows:

The colorant is the coloring matter of the ink, and organic pigments with complete chromatogram, high color concentration, and high hiding power are widely used. For example, magenta ink, yellow ink, and blue ink generally use organic pigments; white ink uses titanium dioxide; black Ink is carbon black.

Water-soluble or water-dispersible resin is a linking material for ink and is an important factor influencing the quality of the ink. The printing aptitudes such as viscosity, adhesion, gloss, and drying are all determined by the resin composition. There are many kinds of water-based ink binders, which can be selected according to different occasions and functions. At present, the research and development of inks by domestic ink companies are mostly concentrated on the research of linking materials, including water-soluble linking materials such as polyvinyl alcohol, hydroxyethyl cellulose and polyvinyl pyrrolidone, and soluble and saline-soluble links of soluble resins. Materials and diffusion binders commonly referred to as latex containing propylene, ethylene or styrene polymers.

From the formulation point of view, domestic ink-pumping inks have a poor ability to package colorants, which can only reach 50%, and the ability of imported resin packaging colorants to reach 80%. Domestic ink due to coarse particles, easy to damage the printing anilox roller, imported ink particles more fine, with the formation of a good affinity between the anilox roller, will not scratch the surface of the printed 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 when used. The addition of alcohols helps to increase the stability of the ink, speed up drying, and reduce the surface tension. Isopropanol also acts as a defoamer. Water-based ink additives include amine stabilizers, defoamers, slow-drying agents, the role of which is to adjust the PH value, eliminate air bubbles and adjust the curing drying time. Pigments and varnish are important raw materials for ink production. The inks we use in our country are all imported colorants and varnish.

When selecting water-based inks, attention should be paid to the viscosity, concentration, fineness, drying speed, abrasion 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 indicator in ink applications. Ink viscosity is too low, it will cause the color light, dot enlargement, high light spot deformation, uneven ink transfer and other defects; Ink viscosity is too high, will affect the anilox roller transfer ink performance, ink uneven, sometimes color and India Not deep, but at the same time it can easily lead to dirty, dirty, blistering, quit and other ills.

â–  Influence of Temperature on Ink Viscosity Temperature has a great influence on ink viscosity.

The effect of shop temperature on the print quality is shown in Table 5, and the relative humidity is 60%~85%.

The viscosity is most sensitive to the temperature difference between winter and summer. When the temperature is high, the water evaporates quickly and the drying is fast. During operation, it is necessary to pay attention to prolonging the drying time or increasing the speed of the machine. When the temperature is low, the water evaporates slowly and the ink drying is slow. In the operation, the ink drying speed can be increased or increased. Open drying device. When used in winter, the ink will freeze easily below 0°C. If the ink freezes, it can be placed in a room with high temperature, and it can be dissolved naturally. After mixing, it can be used continuously.

In actual production, when a printer with a squeegee is used, the amount of ink transferred when the temperature is too low is not as stable as when the temperature is slightly higher. An increase in the temperature of the ink causes the viscosity to decrease. As a result, the density of the print is reduced and the ink layer is thinned. To maintain consistency in print quality, it is necessary to maintain consistent ink viscosity. The printer must attach great importance to the influence of the ink temperature, and the temperature of the ink to be used before printing should be stabilized at the temperature of the printing shop. This measure is very important, otherwise the ink density in the printing process will have more obvious changes.

Thixotropic effect on ink viscosity

Thixotropy refers to the increase of the fluidity of the ink under stirring by external force, and the ability of the fluid to gradually decrease and resume its original state after ceasing stirring. After the ink has been left for a long time, some poorly stabilized inks tend to precipitate and delaminate. There is a phenomenon of false thickening. At this time, it can be fully stirred, and after a certain period of stirring, the above problems naturally disappear. When using fresh ink, be sure to mix evenly beforehand and make dilution adjustments. Or it is expected that after a certain amount of ink on the machine, the viscosity will decrease, because the thixotropy of water and ink in the machine can improve the fluidity of the ink. When the printing is normal, the ink fountain must also be stirred regularly, especially with a high content of white pulp.

The PH value of the ink

â–  Influence of pH on the viscosity of ink

The pH value of another index that needs to be controlled in the ink-and-wash application has a normal range of 8.5-9.5. At this time, the printing performance of the water-based ink is the best, and the quality of the printing product is the most stable. As ammonia is constantly evaporating during the printing process, the operator will occasionally add new inks and various additives to the ink, so the PH value of the ink may change at any time. Using a standard pH meter, you can easily measure the pH of the ink. When the PH value is higher than 9.5, the alkali is too strong, the viscosity of the water-based ink decreases, the drying speed becomes slower, the water resistance becomes worse, and the paste plate easily occurs. When the PH value is lower than 8.5, the alkalinity is too weak, the water The viscosity of the base ink will increase, and the ink will tend to dry, blocking the plate and the anilox roller, causing the plate to be dirty and causing bubbles. The influence of PH value on the printability of the aqueous ink is mainly manifested in the viscosity stability and dryness of the ink and the dot definition. As the PH value increases, the ink viscosity decreases and the drying speed also slows.

Application experience

Water-based inks often encounter some problems in the printing process of cardboard. Reason analysis and solutions can be referred to as follows:

â—† 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 quickly, the solution is to adjust the pressure, dilute the ink, and add a slow drying agent.

â—† When the ink dries on the printing plate and the printing edge is blurred, hot air may blow onto the printing plate. The paper fiber mixed with the ink causes electrostatic reaction. The elimination method is to dilute the ink and gradually increase the speed, cover the ink system, or replace the ink. Install an electrostatic discharge device.

â—† Flexographic printing is especially suitable for printing in the field. If the actual situation is not true, the cause may be the low viscosity of the ink and the uneven surface of the substrate. The solution is to use a high-viscosity ink and use a substrate with good surface quality.

â—† The ink accumulates on the printing plate or the dots are full. The causes include excessive ink loading, excessive printing pressure, too fast ink drying, or too weak ink. The solution is to change the anilox roller, adjust the pressure, and add slow drying agent. Or use high intensity inks.

â—† The reasons for poor printing adhesion are: ink drying temperature is too low, ink and material have no affinity, corona treatment is required for surface material with too low value, etc. The solution is to measure the surface tension, increase the drying temperature, change the ink type or Mao printing material surface.

Source: China Merchants Logistics Network