Offset Inks and Gravure Inks

30-11-2022

Offset printing ink must have high viscosity (dynamic viscosity η = 40 ~ 100Pa · s). When offset printing ink spreads on the inking unit rollers or transfers to the substrate, such as printing plates and blankets, the drying components in the ink do not cause the ink to harden. Also, inks used in traditional offset printing (with fountain solution and ink) must be able to "store" a certain amount of fountain solution (in waterless offset printing, the ink is added Silicone oil to ensure that the non-graphic part does not absorb ink). The ink film thickness of the ink in offset printing is extremely thin, and when it is transferred to the substrate, the ink film thickness of the ink is about 0.5-1.5 μm. The main components of offset printing ink are as follows (weight ratio):

a. Binder (grease), mainly includes: hard resin containing a high proportion of rosin (20% to 50%), alkyd resin (0% to 20%), a certain proportion of vegetable oil (0% to 30%), such as Castor oil, soybean oil and wood oil, mineral oil (20% to 40%) and various desiccants (<2%).

b. Pigment: According to the requirements of color, the proportion of pigment is between 10% and 30%.

c. Additives: The proportion of additives can be up to 10%.

offset ink

Additives consist of the following ingredients:

• Dry catalyst (composed of cobalt, manganese and other metals to make),

• Waxes to improve wear resistance and lubricity,

•Prevents premature drying and skinning in ink tanks or fountains Element,

•Silicone oil in waterless offset printing ink.

Due to the various requirements of printing product processing and the different surface characteristics of the substrate, the percentages of the corresponding components contained in various inks are also different. When formulating inks produced by offset printing, the special requirements of offset printing must also be considered. For offset printing inks, important property requirements are:

a. High transparency (offset printing is to overprint ink on the surface of the substrate).

b. Printability and pressroom throughput characteristics such as flow, drying, gloss/brightness, emulsification (interaction between ink and fountain solution), and rub resistance.

c. Absorption of ink by the substrate, ink overprint and its adaptability during wet-on-wet printing.

According to the above requirements, offset printing ink can be divided into the types shown in Table 1.5-7.

gravure ink

gravure ink

Ink viscosity is the most essential difference between gravure ink and offset ink. Gravure printing requires the use of liquid ink that can fill the image cells on the gravure cylinder under high-speed printing (η = 0.05 ~ 0.2Pa·s, in the gravure printing of publications, even as low as 0.01Pa·s).

Of all traditional printing inking units, gravure printing has the shortest inking unit (the shortest path the ink travels from ink fountain to paper). It contains only one chamber that infuses ink directly to the printing plate.

Ink tank and squeegee. This compact structure allows the use of low viscosity inks (see Figure 2.2-14). From a production point of view, the composition and manufacture of gravure printing inks are simpler than offset printing inks, and a wide range of inks can be used. For example, an ink film with an ink thickness of more than 2 μm can be obtained, or inks containing special metallic pigments can be used. Due to the direct transfer of ink, in principle, a large change in the chemical composition of the ink is allowed.

UV Offset Ink