Printing ink and printing quality (a)

In the pad printing process, ink is often considered to be the most critical factor affecting the print quality. However, the control of other factors is also very important. The printing staff often attribute the printing problems caused by other factors to the ink. Sometimes they can not solve the problem within a few hours, mainly because they ignore other variables such as mechanical settings, Environmental conditions and other factors. Therefore, the printing staff should thoroughly understand the role of the printing process and the ink. When the problem arises, all the factors affecting the quality will be taken into account, rather than simply looking for ink problems.

1 type of printing ink

Special inks for pad printing differ from general solvent-based inks, water-based inks, and UV-curable screen printing inks. Although pad printing inks and screen printing inks have some similar characteristics, they are still quite different. Unlike screen printing inks, pad printing inks dry faster, which is the most prominent feature of pad printing inks. At the same time, pad printing ink is often printed on the film. This application causes the pad printing ink to be easily affected by factors such as temperature, humidity, and static electricity. The inks specially formulated for pad printing include single-component inks, two-component inks, baked-dry, oxidized, and sublimated inks.

1) One-component ink

The drying of single-component inks (also called solvent-evolving inks) is volatilized by solvents, which do not necessarily have to be added to the catalyst. One-component inks are glossy and non-glossy, they are mainly used for the printing of plastic substrates.

2) Two-component ink

Two-component inks are also called chemical reaction inks. Before the printing, the catalyst must be added. The catalyst reacts with the resin in the ink to achieve the purpose of ink drying through the polymerization reaction.

When two-component inks are used in pad printing, it is necessary to add a certain amount of catalyst, usually measured by weight. The addition rate of the catalyst must be strictly controlled, and adding too much will greatly shorten the “adaptation period” of the ink; adding too little may cause the ink to reach the best drying performance when it is dried. In general, if the ink and the catalyst are not properly formulated, the ink may be unevenly adhered and the durability of the printed image may be insufficient.

3) baked dry ink

Dry-type inks are divided into two types: one is the addition of additional catalysts based on standard two-component inks; the other is the ink specially formulated for substrates such as glass, ceramics and metals. As its name suggests, baked dry inks must be warmed and dried at a certain temperature. When using this kind of ink to calculate the drying time, the higher the temperature, the shorter the drying time, but the drying temperature is too high will make the ink film brittle, so the ink can be baked at a temperature to maintain the flexibility of the ink.

4) Oxidation type ink

The oxidized ink absorbs oxygen in the surrounding environment and undergoes a polymerization reaction to form an ink film without the addition of a catalyst. Oxidation inks are typically used for flexible packaging substrates and synthetic substrates such as rubber or keyboards. Oxidation type inks have a limited amount of use due to their slow drying speed and long time.

5) Sublimation ink

Sublimation inks require special processing during use, that is, they are heated after printing to make the substrate porous, so that when the dye comes into contact with the surface of the heated substrate, the dye in the ink becomes gaseous. Then it enters the surface of the substrate, which actually changes the surface color of the substrate. Once the substrate cools, the ink sticks to the surface of the substrate.

The most common applications for sublimation inks are computer keyboard printing and those prints that require high oil resistance and abrasion resistance, which cannot be achieved with two-component inks. A particularly noteworthy problem is that because the sublimation ink actually changes the surface color of the substrate, the matching between the substrate and ink color is more difficult. Therefore, the color of the substrate must be lighter than the color needed for final printing, because sublimation inks tend to have less color change on the darker surface of the substrate.

6) Special inks and additives

Pad printing specialty inks include edible inks, silicone resin inks, lubricating inks, corrosion resistant inks, conductive inks, and UV light curable inks. The ability of these inks to quickly become sticky will determine whether ink can be effectively transferred to the surface of the substrate. . At the same time, in order to adjust the printability and performance of the ink, in addition to the addition of solvents and catalysts, it is also possible to use many additives, such as viscosity inks, antistatic agents, rheological agents, and the like. However, the use of additives will have a great impact on the printing performance of inks, and must be used with caution.