Water-based gravure ink and the resolution of common printing problems (I)

Gravure printing has always been characterized by a thick layer of ink and good printing quality. It has a large market share in food, medicine, tobacco and wine packaging, and book publishing. However, with the rapid development of flexo printing, many markets in gravure have been preempted by flexo printing. The reason for this is simple. Flexo printing is of good quality and is eco-friendly. Therefore, it is becoming more and more popular in various packaging printing. Therefore, in order to win back its own market, Gravure must work hard on environmental protection. It is to use water-based environmental protection inks to improve the environmental characteristics of prints.

First, the characteristics of water-based gravure ink

Water-based gravure ink first inherited many advantages of water-based ink, such as low-toxic (or non-toxic), non-irritating odor, while its viscosity and pigment particles and other characteristics of both gravure ink characteristics, so it is very suitable for environmental protection requirements High-grade products and food and medicine packaging printing. In general, the characteristics of water-based gravure inks are as follows:

(1) Non-irritating odor, non-flammable and explosive, conforms to environmental protection requirements, can ensure the health of workers to a certain extent, and contribute to safe production

(2) The printing effect is relatively good, the text is clear, the dot is complete, and the color is strong.

(3) Combination of flat and concave rapid printing, no deduction of rubber, no deduction, no penetration, no spreading, no rubbing, no light ash breaking.

(4) It can meet the requirements of fast printing, create conditions for the development of gravure printing technology, and represent the development direction of gravure ink.

Second, the composition of water-based gravure ink

Water-based gravure ink is mainly composed of water-soluble resin, pigments, various additives and water.

(1) Resin

Resin is a key component in water-based gravure inks, and its types are many, such as alcohol-soluble phenol formaldehyde resin, water-based amino resin, water-based acrylic resin, water-based maleic acid rosin resin, polyvinyl alcohol, casein, carboxyl fiber Vegetarian and latex etc. Because the resin contains a variety of hydrophilic groups - COOH (carboxyl), - OH (hydroxyl), - NH2 (amino), etc., after a certain process, the resin is converted into organic ammonia, completely soluble in water. At present, water-based acrylic resins are the most commonly used binders in water-based gravure inks.

(2) Pigments

Water-based gravure inks use mainly organic or inorganic pigments that have strong alkali resistance and good dispersibility in aqueous systems. Alkaline pigments are prone to condensation reactions.

(3) Solvent

Since the water's dissolving power and wetting ability are not large, it is necessary to use the corresponding cosolvents, such as ethanol, propanol (positive and negative), ethylene glycol monoacetic acid and ethyl cellosolve, butyl cellosolve, etc. The content in the ink is generally about 11%. In addition, the resin is generally insoluble in water, and an appropriate alkaline substance must also be added to promote the dissolution of the resin in water. Generally used amines such as ethanolamine, the amount depends on the pH value.

(4) Additives

Many types of additives, such as thinners, stabilizers, defoamers, dilutants, fast drying agents, slow drying agents, etc., are used to improve the printability of the ink.

Third, common printing failures and solutions

1 Slow drying

(1) Cause of failure

a When the ink viscosity is increased, the water-based ink will have poor drying properties.

b When the aqueous ink is overprinted, the osmotic drying is hindered and the drying speed will be reduced. Generally, the drying time of the fourth color is more than twice that of the first color.

c When printing on completely non-permeable glass plates, aqueous inks will require 5-6 times the drying time of solvent inks.

d The depth of the cell has a great influence on the drying rate. For example, the depth of the 33 μm cell is more than double the drying time of the 18 μm depth. (to be continued)