Screen printing ink 1000 ask (137-143)

137. Which inks can be used for paper screen printing?

A: There are many types of ink available for screen printing paper substrates (paper, paperboard). The most common ones are various offset inks and plastic inks.

138. What is the basic composition and content of offset ink?

A: Offset inks are mainly composed of pigments, binders, gum oils, resin oils, auxiliary agents, and small amounts of fillers. According to the different binders, they can be divided into many types. The range of content of various components in different types of inks is:

Pigments 10% to 25%

Gel oil 10% to 25%

Resin oil 40% to 60%

Adjuvant 1%～10%

Filler 0%～20%

139. What formula does offset ink use?

A: Offset-type bright inks are mostly used for large-format color advertising and packaging for screen printing. The conventional formula is:

Formula A

Chain material (solid resin type) 22%

Material (liquid resin type) 42%

Gel oil 10%

Ink oil (distillation range 250～290°C) 2%

Pink original 24%

Cobalt naphthalate 0.4%

Formula B

Chain material (solid resin type) 22%

Material (liquid resin type) 39%

Gel oil 25%

Ink oil (distillation range 250～290°C) 2%

Benzidine Yellow G 12%

Cobalt naphthalate 6% 0.1%

140. What is the effect of paper absorption on ink drying?

A: There are many pores between the fibers on the surface of the paper and on the surface of the coating. These pores have the characteristics of capillaries. When the ink is printed on paper, the pores will absorb the binder in the ink (especially thinned from the resin). Components) The process of absorbing the ink binder material in this paper is the process of ink penetration and the beginning of ink fixation. In general, paper with rough surface, loose structure, and low degree of sizing is advantageous for ink drying. At the same time, the affinity of the paper facing the ink also has an effect on the penetration, and the better the affinity of the paper for the ink (the smaller the wetting angle), the faster the ink permeates and the faster the fixation.

141. What is the effect of paper pH on ink drying?

A: The dryness of the ink is related to the pH value of the paper. Acidic paper will hinder the drying of the ink. Neutral or alkaline paper is beneficial to the drying of the ink. The reason is that the inorganic acid present on the surface of the paper reacts with the alkaline driers in the ink under the catalysis of water or water vapor, weakening the activity of the driers.

142. How does the moisture content of the paper affect the drying of the ink?

A: When the moisture content of the paper is high, the fiber or coating on the surface of the paper is loose, the attraction between the molecules is reduced, and the pores are blocked by the water film. This not only hinders the absorption of the ink binder by the paper, but also reduces the oxygen Absorption capacity, and thus the ink drying rate also decreased.

143. How to solve the problem of poor ink fixation?

Answer: Since the screen printing ink layer is thicker than the general printing ink layer, malfunctions of the ink fixing failure are more likely to occur, causing the ink layer to peel off. There are several ways to eliminate fixation failures:

1) Use quick-drying ink;

2) Add a small amount of desiccant;

3) The use of dusting method to isolate the printed sheets;

4) Reduce stacking height of printed products;

5) Reduce the relative humidity of the printing shop and increase the drying temperature;

6) Reduce the squeegee force;

7) Reduce ink volume.

144. Bad ink drying, ink film powder breakdown how to rule out?

A: There are the following exclusion methods:

1) Add appropriate amount of desiccant;

2) If the moisture content of the paper is too large, the paper must be dampened;

3) If the paper pH is too low, it should be strengthened;

4) If the paper temperature is too low, increase the temperature before unpacking or use infrared lamp heating on the paper table;

5) If the paper absorbs oil too much, add pigment glue or varnish to the ink to control the penetration of the resin;

6) If the actual printing area is large, ventilation should be strengthened after printing;

7) For the printing of defective products, you can use a varnish to re-brush once.

145. What are the measures to prevent the vitrification of the printing ink film?

Answer: The surface of the ink film vitrification film is crystallized. The prevention measures include:

1) After the first color printing ink layer is completely dried, the next color printing is performed;

2) In the former color printing, cobalt drying oil should be avoided;

3) If the surface of the ink film is vitrified, try wiping and rubbing with a soft cloth on the ink film surface to remove the crystal layer and increase the adhesion to the ink of the next color. When severely crystallized, it is also possible to try Viley oil or a mixture of zero offset oil and silicone oil overprinting, and then print the second color. (to be continued)