The role of dry oil in ink

When printing high-grade coated paper, offset paper, textured paper, white paperboard, copperplate paperboard, etc., due to the high smoothness of the paper and the low ink absorption, it is easy to happen when the image area is large, the amount of ink is large, and the actual situation is large. The phenomenon of slow drying of the imprinted ink is very likely to cause the back surface to be dirty. At this time, it is necessary to add a desiccant in the ink—dry oil. Under normal circumstances, dry red oil, dry white oil two. Red, white dry oil can promote the ink layer to dry, for the dry vegetable oil oxygen, polymerization can play a similar catalyst to promote, it is also called driers.

Desiccants include red and dry oils are all composed of metal salts. Metal salts consist of organic acids (groups) and metals. Organic acids include: acetic acid, linoleic acid, rosin acid, naphthoic acid, etc.; metals include cobalt, manganese, lead, zinc, iron, calcium, barium and other metal elements.

Cobalt and manganese drying agents are mainly to promote the oxidation of dry vegetable oils. In this regard, cobalt promotes faster oxidation than manganese. Normally oxygen in the air will first act on the surface of the ink, so the surface layer is first oxidized and polymerized into an ink film, which explains why the use of cobalt and manganese desiccants always acts from top to bottom or from Surface to interior.

The main role of lead metal desiccant is to promote the polymerization of dry oil, its poor oxidation, so the role of lead desiccant slower, but it can make the entire ink film can play a role.

Since various metal desiccants have different roles, and the drying of the ink must go through two processes of oxidation and polymerization, cobalt, manganese, and lead are usually mixed in different proportions for use as a desiccant. This is commonly used as white. Dry oil. Some cobalt and lead are also used as a mixture; others are also used as a mixture of manganese and lead. For the sole use of only cobalt metal, such as commonly used red dry oil is only cobalt metal and organic salts of organic acid cobalt soap as a driers.

White dry oil composition: lead borate Pb3 (BO3) 2, manganese borate Mn3 (BO3) 2, special dry oil (Tung oil, oxidized linseed oil), cobalt naphthalate and white spirit oil. The main raw materials of white dry oil are lead and manganese salts, which are in the form of milky white paste, and have no effect on discoloration of light-color inks. Some of the lighter colors use white dry oil as a desiccant. Its dry form is mainly oxidized conjunctiva, and the surface of the ink and the bottom layer are simultaneously dried. Under normal circumstances (at temperatures of 14 to 18°C), 5% to 10% of dry white oil may be added to the ink for the purpose of drying; in special cases, fast drying is required, and the maximum amount should not exceed 20 %. Adding too much dry white oil in the ink not only does not work to accelerate the drying but will make the print sticky.

Red dry oil composition: Refined linseed oil, premium Chinese rosin, cobalt acetate. The main raw material of red oil is cobalt salt, brownish, translucent liquid, and it is also a good drier for printing ink. Since brownish cobalt has a certain discoloration effect on light-colored inks, it should not be used in lighter inks. However, it is suitable for dark color inks (such as black ink, royal blue, blue lotus, and blue light). Its dry form is also dominated by oxidized conjunctiva. The ink film gradually dries from the surface to the inside and is susceptible to air oxidation. Therefore, red oil is a dry substance with a very dry surface. It is mixed with white dry oil, white and red dry oil account for 50% each, and can achieve good results with less dosage, quicker drying and fewer side effects. Red dry oil has the effect of enhancing the ink fastness of aluminum paper products. Under normal circumstances, the amount of red dry oil can be about 3%, the maximum amount should not exceed 5%.

The application of various dry oil dosages on different printing products is inconsistent. Even if the application on the same printing product is not exactly the same, it is necessary to use dry oil flexibly according to different conditions and circumstances, and determine the amount of dry oil in the ink transfer work.

According to the following four conditions to control and grasp the amount of dry oil: 1 the ink itself, the degree of drying; 2 paper's ability to absorb ink; 3 the impact of climate; 4 product printing color number and the number of prints, multi-color, print less The product requires a little quicker drying; the less color printing and the higher number of prints may not necessarily require quick drying.

To test the dryness properties of dry oil: to make the dry oil that is considered satisfactory in normal production as the standard, and then take the newly purchased dry oil as a comparative test. After the two dry oils are thoroughly mixed, they are scraped onto the surface of the paper and observed. Drying speed to determine their drying performance. It is better to check the dryness of dry oil if you use an ink drying tester.

The reason why the dry vegetable oil and resin-based binder in the ink can be converted from a liquid state to a solid state is due to the process of oxidation and polymerization. The ink is a non-polar molecule, the oil molecules are linked to each other, and the linear structure is converted into a net. Solid structure of the sake of reason.

1, dry oil in the ink layer has a strong squeezing effect. The metal itself is reduced to a low price, so that the antioxidant can be oxidized or precipitated by binding with an antioxidant, thereby shortening the induction period before the ink is oxidized.

2. The desiccant can accelerate the destruction of the hydroperoxide after the ink film is oxygen-absorbed, form a more stable oxygen bond, or promote the partial oxidation of the ink, and the other unsaturated bonds of the oil are directly polymerized, thus reducing the ink. The amount of oxygen required for membrane oxidation.

3, dry oil in the ink can directly absorb the oxygen in the air, the formation of new oxides, and then with the oil molecules of the double bond, and then release oxygen to give oil molecules, so that it becomes the oxygen film drying oxygen transporter , thereby reducing the ink film oxygen difficulties.

4, dry oil to enhance the condensation of oil molecules, dry oil most of the strong polar compounds, so when the dry oil in the presence of oil, can strongly promote the orientation of the oil molecules, resulting in bonding and curing phenomenon Early formation. In the final stage of drying of the ink, the oil molecules are arranged perpendicular to the film surface.

Source: China Ink Technology Network