In the screen printing process, the ink is required to have good printability, and it can be applied as soon as possible by opening the can, and adjustment is not required. However, the printing conditions are quite varied. In order to enable printers to actively adapt to changing printing conditions and use good ink, it is still necessary to produce several inks with specific properties.
The following inks are commonly used.
First, the viscosity reducing agent is also known as a spreading agent. The purpose of the use of a viscosity-reducing agent is to reduce the viscosity of the ink while not affecting the body of the ink as much as possible. The amount is generally 3-5% of the ink. The viscosity-reducing agent used in the earlier period was mainly composed of ink transfer, adding some waxes, or Vaseline as the main body, adding some waxes and oils. The use of these viscosity-reducing agents is not good enough. Mainly used for grease type inks. In recent years, finely floated linseed oil and high-boiling point kerosene have been used as the main components. Synthetic resins, gels, and waxes have been used to make semi-gels for use. This viscosity-reducing agent is used for bright inks and resin inks, which can reduce the viscosity of the base, while maintaining the fixing speed, gloss, and other characteristics of the ink.
The gelling agent used in the spreading agent, aluminum soap, is aluminum stearate for the first two years, with mono-, di-, and tristearate salts.
Second, the role of thinner diluent has two points, one is to reduce the viscosity of the ink. The second is to thin the ink, thereby increasing the flow properties. In the printing process, often due to the ink viscosity is too large, or because of the inferior quality of the paper, it will produce pull paper hair, off edition and other problems, affect the normal printing. In this case, in addition to using a viscosity reducing agent to reduce the viscosity of the ink, it is sometimes necessary to add a small amount of diluent to reduce the consistency of the ink. For thin and sticky inks, it is better to use a viscosity reducer.
Grease-based inks generally use the bottom viscosity of No. 6 varnish oil as the diluent; resin-type inks use the bottom-viscosity vegetable oil, high-point kerosene, and a small amount of rosin-modified phenolic resin to make the resin-type varnish oil as a diluent. Solvent-type gravure ink can use toluene, xylene as a diluent; water type gravure ink can be used as a diluent with water or acetaldehyde.
Third, spread (red) light agent dispersant is also called dilute. The purpose of use is to dilute the color of the ink and reduce the color intensity of the ink without substantially altering the viscosity and other rheological properties of the ink, printing properties, and the like.
Grease-type ink dilute agent is generally transparent oil, transparent oil (commonly known as Weili oil) is made of aluminum hydroxide and dry vegetable oil chain material dispersed rolling paste made of transparent body.
The resin ink diluting agent is a resin type, which is made of resin, vegetable oil, high-boiling point kerosene, gelling agent and wax, etc. It also uses resin oil, colloidal oil and colloidal calcium carbonate to be rolled on a three roll machine. Made. Regardless of the method used to produce the diluting agent, it is required to have a certain body bone, dryness and printability.
Four, driers (desiccant)
Drying agent, also known as desiccant or dry oil, dry oil, etc., is a very important class of additives. It is a catalyst for the oxidative polymerization of dried vegetable oils. It is not only oil-based inks with oxidized conjunctiva as the main dry form. It is a dry type resin ink that combines the infiltration of gelled oxidized conjunctiva, and its thorough drying still depends on it. Since the amount of vegetable oil for the resin type ink is reduced by the resin and the mineral oil, there is still a certain amount of the plasticizer for the ink film serving as the auxiliary agent for the resin in the mineral oil. The oxidative polymerization of this part of vegetable oil still requires driers.
1. Mechanism of the driers The driers are mainly organic acid soaps such as cobalt, manganese, and lead. Their dryers have not yet been fully understood. And each other's function is not the same. Generally considered to have the following three aspects:
1 Shorten the impurities in protein, phospholipids, and vitamin E contained in dry oils during the induction period. They are easily oxidized first to hinder the oxidative polymerization of dry oils. Therefore, they are often referred to as natural antioxidants. Although refined, there is still a small amount of residues. The process of delaying the dry oxidative polymerization of these residual impurities is called the dry induction period. If drying agents are added to the drying oil, the metals in the driers are reduced to low prices, and the impurities in the drying oil are oxidized or precipitated in combination to shorten the induction period of the drying oil. .
2 accelerated oxidation driers can dissociate itself into free radicals, this radical can accept the hydrogen bond on the ortho carbon atom of the double bond in the oil molecule, leaving the oil molecules to form radicals. It is further oxidized to peroxides while generating new free radicals.
3 promote the polymerization driers can promote dry oil double bond open, form free radicals, and further polymerization. During this polymerization, no oxygen is absorbed.
2. The composition of driers The driers are mostly composed of metal and organic acid radicals, which are soaps. The general formula R-COOM can be used to indicate the properties of the driers and determine the metal part. The effect is related to the organic acid radicals. .
The metal with driers performance can be roughly ranked as follows: (decrease)
Cobalt, manganese, lead, antimony, lead, iron, zinc, and calcium Among them, cobalt, manganese, and lead are the most important metals that can be used as the main driers, while others are used as the metal for driers.
The organic acid radicals are derived from organic acids and the organic acids used in the driers must meet the following conditions;
1 The formed metal has good solubility in oils and organic solvents. The organic acid has a carbon chain segment and has a side chain, particularly a side chain adjacent to the hydrogen group adjacent to the carbon, and has good solubility and stability, such as naphthenic acid, 2-ethylhexanoic acid and the like.
The greater the degree of unsaturation of the organic acid, the better the solubility of the metal soap, the solubility of the linolenic soap is good, and the solubility of the stearic acid soap is poor.
2 The solubility in water is small.
3 light color, small odor, less impurities.
4 The source is wide and the price is low.
The commonly used organic acids mainly include naphthenic acid, 2-ethylhexanoic acid, linolenic acid, pine oleic acid, and rosin acid. The properties of 2-ethylhexanoic acid are the most preferred, followed by naphthenic acid and flax After the oleic acid, rosin acid was the worst.
Naphthenic acid, also known as naphthenic acid, is obtained by separation, acidification and purification from petroleum. The n in the formula is 0-8, depending on the source, and the acid value is between 170-250. Naphthenic acid soap is currently the most widely used driers, has good solubility and storage stability, good drying effect, wide source, the only drawback is that some odors. (To be continued)
Ink Additives (I)
January 07 10:09:12, 2024
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