Composition and Application Technology of Flexo Printing Water Based Ink

From a professional point of view, flexo-based water-based inks are solvent-based inks and the solvent is "water." In the flexographic ink, the main function of "water" is to make the ink have better fluidity, so that the ink can be transferred from the anvil of the anilox roller to the substrate.

There is hardly any kind of printing that can go so fast like today's flexo printing. In a very short period of time, it has evolved from the printing of bags in people's minds to high-quality color printing. This depends on the development of the entire printing industry. Of course, it is inseparable from the efforts of suppliers. The suppliers mentioned here include ink suppliers.

Flexo printing is a printing method with a wide range of applications. Corrugated cartons can be pre-printed and post-printed using old slow-speed machines and new high-speed machines. There are wide ranges for flexible packaging. And a narrow plastic film flexo printing; paper printing including facial paper and napkin printing; there are many different printing materials, such as narrow flexo labels, tickets, gift certificates and the latest development of UV flexo printing carton.

In addition, there are many different water-based inks and solvent-based inks. We can choose various inks and ink systems. Regardless of raw materials or formulas, the flexo-printed water-based ink has its common features. As long as the ink properties meet the requirements, satisfactory prints can be printed with flexo-based water-based inks.
This article on the formula of water-based ink, water-based ink in the end is what? What are the ingredients? What print effects will be analyzed.

First, the composition of printing ink

Printing inks are a chemical mixture, while flexographic printing refers to water-based inks that are low-viscosity and whose viscosity is measured by standard measuring cups. Water-based ink is a combination of four different chemical raw materials. They are: pigments, which give the ink a certain hue, so that we can see the color; resin, after drying, wrap the molecules of the color material to form a smooth layer. Membrane; Additives, it is to improve the physical and chemical properties of ink additives, not much, but the role can not be underestimated; solvent, it is to reduce the viscosity of water-based ink, so that the ink is more easily transferred to the substrate, and then volatile drying. The typical composition of printing ink is: solvent 70%, pigment 10%, additive 5%, resin 15%.

Of course, this is only a rough figure, and the final decision has to be made based on the requirements of ink and print quality. Now, for high-quality flexographic printing, the colorant composition can reach 17%, and the proportion of ingredients can also be adjusted as needed. For printers, the most important thing is to print satisfactory quality at an acceptable cost, while also taking into account environmental protection and health issues.

1. Pigment

In today's printing, the main function of the ink is to express the color and the hue of the print, so the most important part of the ink is the color material. Colorants are divided into dyes and pigments. Dyes are common color agents. Dyes are found in foods and pigments. Although the printing effect of dye ink is not good and it is easy to fade, there are still some paper printing and cardboard printing still being used due to low price.

High-quality flexographic water-based inks are chemically synthesized using pigments. Studies have found that the colors of hundreds of pigments exhibit a color spectrum that covers all visible light. However, in normal use, the typical ink formulation is only about 50 kinds.

The world's famous pigment manufacturers include BASF in Germany. There are also some very small factories. The manufacturing of pigments is batch, but the color system of each factory is slightly different. With the usual four-color inks: blue, magenta, yellow, and black, there is a slight difference in each set of inks, and there is no real standard. In particular, the colors that the Oriental and Western markets place their emphasis on are different. Take the magenta ink as an example. The east prefers the blue one and the western one loves the yellow one.

2. Resin

Another part of the ink formulation is a resin or carrier transfer system. The main function of the resin here is to transfer the pigment to the substrate during the printing process. The first is that the resin is dissolved in the solvent and transferred to the substrate through the printing plate. After the solvent is absorbed or evaporated and dried, the resin will remain to wrap the colorant and keep the color. We have a lot of resins to choose from, but it's not possible to use just one resin. Maybe we will consider using different resins according to different printing requirements, such as: high temperature resistance, acid and alkali resistance, high gloss and so on.

The typical resin for typical aqueous inks is a particulate resin that prevents diffusion of water, a resin that does not dissolve in water, and a resin that dissolves in alkaline water.

3. water

The third element of the water-based ink composition is "water". Its main function is to make the ink more fluid, so that the ink can be carried from the engraved web of the anilox roller to the surface of the substrate. When the resin and the pigment are brought to the substrate At that time, the excess water must be removed, which is more difficult on non-absorbent substrates, so the ink removal rate and drying speed are the key considerations in the printing process.

Water-based inks require limited use of organic solvents, which can affect the drying speed of water and reduce the dissolving power. In water-based inks, water is not added without restriction. The pH, hardness, and softness of the water all affect the dryness of the ink.

4. additive

Additives account for the least proportion of water-based ink formulations. The addition of additives is the chemical substance that best represents or improves the physicochemical properties of the ink. There are also many types of additives, and we must choose their function and be fully integrated with the ink components. Additives include surface lubricants, defoamers, leveling agents, synthetic resins, and waxes.

Lubricants: Ink formulations generally contain lubricants. The lubricant's role is abrasion resistance, preventing dirt on the ink and reducing the vitrification of the ink film layer. The amount of lubricant in the ink composition is related to the printing process and the end use of the print. Lubricants cannot be used in compound inks, as this will affect the adhesion of the compound ink.

The most widely used lubricants in the ink are PE wax, PP wax, silicone resin wax, fluorocarbon resin wax (for example, PTFE wax), and the like. These lubricants vary widely in terms of lubricity, transfer rate, and temperature resistance. PTFE (Polytetrafluoroethylene Wax) gives the ink a very high temperature resistance and abrasion resistance, but the price of this lubricant is relatively higher. In general, experienced ink masters will use the above mentioned lubricants to obtain the best ink lubricity.

Surfactants: Surfactants in additives are often used to improve the printability of inks. These surfactants reduce the surface tension of the ink, increase the latitude of the ink wettability, and improve the printability of the ink on the press. The amount of surfactant is very small, about 0.1% of the ink composition. Use extreme caution when using surfactants because there are surfactants that can cause bubbles in the ink.

Adhesion promoters: Adhesion promoters are used to increase the adhesion energy of inks. They are very reactive materials or low molecular weight solvents. Adhesion promoters give the ink a strong ability to adhere, but its use must be strictly controlled in order to avoid negative effects such as strong ink odors or ink discoloration.

Defoamer: If you are using water-based inks, there must be defoamer ingredients in the ink. Antifoaming agent accounts for about 0.1% of the ink composition. If there is no defoamer in the ink, the flexo printing work may not be performed smoothly.

Bactericides: Most aqueous inks require the addition of bactericides to prevent the growth of bacteria in the ink. The amount of added bactericide is very small. If you want to store water-based inks for a long time, bactericides are indispensable additives.

Oxidizers: There are some binders in water-based inks that can polymerize under the action of oxidants. These water-based inks are often used in applications that require strong alkali resistance, such as soap packaging for printing folding cartons.

Plasticizers: Plasticizers are used to increase the elasticity of the ink film. Common plasticizers are high boiling ester compounds that remain in the ink film even after the ink has dried. When using plasticizers in water-based inks, the plasticizer concentration should be kept as small as possible. Because of the high concentration of plasticizers, some negative effects can be caused, such as lower abrasion resistance of the ink.

In addition to the above-mentioned additives, other additives such as deodorants, UV light absorbers, release agents, buffers, and the like are also used in the flexographic printing aqueous inks.

Second, the viscosity of water-based ink

The basic concept of ink has already been made. We return to the problem of the viscosity of water-based inks. Each of the factors we talked about above will affect the viscosity.
Ink manufacturers often ask you how much viscosity you need, or recommend how much viscosity you want to use. The viscosity of water-based inks is very important. Whether it is transferred from one batch of printing to another, or from one printing press to another, or other situations may require different ink viscosities. It depends on several aspects, different printing presses, doctor blades, anilox rollers and mesh thickness.

The viscosity of the water-based ink is easily measured by the measuring cup, but the measuring cup must pay attention to the temperature change and the cleaning and protection of the measuring cup during use.

Third, the drying of water-based ink

In terms of drying, evaporation of water is a very important factor, especially in non-absorbent materials, where energy can be used to evaporate the solvent. Drying of water-based inks absorbs both substrates and non-absorbing substrates. It is clear that non-absorbing substrates such as plastic films do not absorb water. Even absorbing the substrate can only absorb a considerable amount of water. However, if the water and the resin are not completely absorbed and separated when they are dry, that is, the water capacity of the substrate is saturated, it will not be dry. At this time, if there is any grinding, it will be colored. Transfer.

Fourth, the pH of water-based ink

In aqueous inks, pH is a very important factor. Lack of control or incorrect pH can cause many problems. The pH value is a method for measuring the acidity and the basicity of the solvent. The pH value ranges from 0 to 14, and the pH value affects the viscosity of the aqueous ink. In a typical aqueous ink, it can be seen from the graph that the general pH range should be between 8 and 9. Several simple steps to control the ink: Stir before use, detect the ink viscosity when printing on the machine, adjust the viscosity and reconfirm the viscosity and PH value. (Wen / Wang Liying)