Basic knowledge of ink additives (3)

Second, anti-(dry) desiccant

Anti-desiccant (anti-oxidants, antioxidants, anti-skinning agents) function contrary to the desiccant, its role is mainly to prevent (resist) oxidative drying. It is an oxidation inhibitor. It is a negative catalyst.

Sterol, Tocopherol, etc. in dry oil are some natural antioxidants. Their presence will make the dry oil have an induction period before oxygen absorption and drying.

Most macromolecules react with oxygen, leading to degradation or cross-linking. Especially under the effect of heat and light, the speed of oxidation is faster.

The oxidation of the polymer is a free radical chain reaction (ie, a chain reaction). The function of the anti-desiccant is (1) to combine with free radicals to break the chain reaction of oxidation (generally, they do not bind to the free radicals of hydrocarbons); (2) to decompose hydroperoxides It is a stable substance that no longer participates in the chain reaction. It can also be considered that the antioxidant is a substance which can trap active radicals to generate inactive radicals, thereby suspending the chain reaction, or can decompose the hydroperoxide produced by the polymer during oxidation. Non-free radical products are generated, thus interrupting the chain reaction.

There are many types of antioxidants, including amines, phenols, esters, quinones, quinones, and acids, among which amines and phenols are predominant.

According to the mechanism of action, there are two major types of antioxidants, free radical inhibitors and peroxide decomposers. Free radical inhibitors, also known as primary antioxidants, include the two major series of amines and phenols. Amine antioxidants are almost all derivatives of aromatic secondary amines, mainly diaryl secondary amines, p-phenylenediamines, and ketoamines, aldehydes, and the like. Most of them have better antioxidant properties, but the pollution is more serious. Phenolic antioxidants are mainly hindered phenols, and the antioxidant performance is generally worse than that of amines, but the pollution is relatively light.

Peroxide decomposers, also known as auxiliary antioxidants, are mainly thioesters such as thiodilactones and phosphites.

Antioxidants also include copper inhibitors (also known as metal deactivators) and antiozonants, most of which are derivatives of terpenes, terpenoids and aldol condensation products. Some amine antioxidants have excellent ozone resistance.

Among the amine antioxidants, the N-substituted derivatives of the para-isomer work best. The activity of replacing p-phenylenediamine can be summarized as follows:

1. If the N-substituent is a secondary alkyl group, the trisubstituted compound is more potent than the disubstituted compound. If both substituents are secondary alkyl groups, the opposite is true.

2. Substituted alkyls are more active than primary ones.

3. If it is a tri-substituted compound, there is still only one secondary substituted alkyl group having a large effect.

4. The substitution of the aromatic ring will reduce the activity of the di- and tri-substitution compounds.

5. For a disubstitution compound, one substituent per nitrogen atom has a higher activity than two substituents.

6. Substitution of an alkyl group in a disubstituted compound with an aryl group greatly increases the activity. Among phenolic antioxidants, the effect of alkyl substituted phenols is better, and the application has an upward trend.

Alkyl-substituted phenols are characterized by the steric hindrance to hydroxyl groups since both ortho positions can have alkyl substituents. This type of product is mainly derived from the butylation of phenols. For example, isobutylene reacts with cresol to give 2,6-di-tert-butyl-4-methylphenol. Treatment with 2,4-dimethylphenol gives 2,4-dimethyl-6-tert-butylphenol and the like.

The effectiveness of alkyl phenols depends on the position and nature of the substituents. The monohydric substitution on the phenol ring was not significantly more active than phenol. Binary substitution has a greater impact, but the replacement effect at the 2,6 position is better. The ternary substitution is more significant when it is in the position of 2,4,6.

Amine antioxidants are more potent than phenols in overcoming the induction period. Because the research and development of this type of product is indeed very fast. In particular, studies on phenolic antioxidants have become more active and new varieties have emerged one after another. High efficiency, low toxicity, and low cost are the direction of future development of antioxidants.

China's ink industry is currently more common is butylated hydroxytoluene (ie BHT-Butylatedhydroxytoluene, antioxidant 264).

Acetaldoxime is a kind of steroid antioxidant. Among them, butyraldehyde oxime is particularly suitable for the application of phenolic resin dispersed in tung oil.

To prevent the ink from peeling in the tank, in addition to the addition of antioxidants, dispersants can also be added to overcome, such as acidic dispersants (benzoic acid, crotonic acid, etc.), solvent-based dispersants (cyclohexanol, methyl cyclohexane Alcohol, pine oil, dipentene, etc.)

The most effective anti-wrinkling agents are Acetylenic Carboxylie Acids.

Since the desiccant can prevent the desiccant from continuing its function, the durability of the dried film can be increased. The use of antioxidants in the ink prevents wrinkling of the film and reduces its peeling properties in the can and on the machine.

The use of antioxidants can also overcome the discoloration problems caused by metallic dry oils. However, phenols have the disadvantage of iron discoloration.

Their usage is generally less than 2% so as not to affect the degree of drying of the printed product.

When using desiccant, caution should be taken. It is harmful because of improper use. If you use volatile helium and hydrazines, you can worry-free.

The above is a description of chemical antioxidants, such as printing on the machine want to prevent the crust of the ink dry, there is a physical isolation method, that is, in the printing machine on the part of the ink spray - layer filming substances, so that the ink and the air isolation To stop the ink from drying. Obviously, this film-forming material is miscible with the ink.