Drum screen printing ink performance requirements two

Second, steel drum screen printing ink adhesion

Drum screen printing requires the ink to have good adhesion, and the problem of adhesion of the screen printing ink is also the most prominent problem of the ink after the drum screen printing. If there is no adhesion of the ink on the steel drum after the printing of the steel drum, it means that there is no printing, and it also causes great waste. The problem of ink adhesion involves the adhesion mechanism of ink and steel drums. At present, it is generally believed that the following factors affect ink adhesion:

1, the impact of resin

Resin constitutes the main component of the ink binder. The adhesion of the ink is closely related to the resin properties.

1 Molecular weight. If the molecular weight of the resin is too close to the molecular weight of the drum coating, the ink solvent is not easy to choose. If the molecular weight of the resin is too large, in order for the ink to reach the required viscosity for screen printing, the solid (resin) content in the ink is too little, resulting in a waste of solvent. It has a high molecular weight, a high melting point, and is difficult to dissolve in solvents, which is detrimental to the adhesion effect. If the molecular weight of the resin is too small, the cohesive force and compatibility are poor, and the adhesion effect is poor. The choice of the molecular weight of the ink distribution resin is very important and must be appropriate.

2 Glass transition temperature. The polymer segment movement only has a significant diffusion rate above the glass transition temperature. The whole chain movement can only be carried out at high temperatures. The glass transition temperature of the resin for room-temperature curing inks should be very low, which is obviously advantageous for adhesion.

3 resin components. The functional groups and branching structures in the resin molecules directly affect the adhesion of the ink on the steel drum. Therefore, the printing inks used for the steel drums with different coatings in the steel drum screen printing are also different. For example, the coating on the surface of steel drums is coated with amino baking varnish and galvanized coating, chrome-plated coating and tin-plated coating.

4 Elemental content of resin monomer. Changes in the content of a certain element of the synthetic resin monomer, so that the performance of the resin will also change. Therefore, when designing a drum screen printing ink formula, synthesizing some special resins will greatly improve the ink performance. Changes in the content of a certain element of the resin monomer will lead to a prominent change in a certain characteristic of the resin.

5 The polarity and crystallinity of the resin. The presence of polarity facilitates the adhesion of the ink, but the highly polar linear polymer also has high crystallinity, and copolymerization and grafting can be used to modify the resin to destroy the crystallinity and maintain polarity.

Practice has proved that epoxy resin can produce chemical bonds on steel drum surface coatings. Therefore, drum screen printing inks are often formulated with epoxy resin in order to achieve the desired adhesion effect.

2, the influence of the solvent

The ink formulation solvent also affects its ability to adhere. As we all know, the solubility parameters of the resin and the solvent used are similar, and the solubility parameters of the steel drum surface coatings must be considered at the same time.

1 The solubility parameters of resin and solvent are similar, which is conducive to dissolution.

2 Excessive use of high-boiling solvents can reduce the adhesion of the ink.

3 The improper choice of solvent, ink adhesion is poor. The use of solvents must be considered from a variety of factors, so ink solvents often use more than three mixed solvents.

4 The solvent and the binder (high molecular polymer) in the ink are in contact with the coating material on the surface of the steel drum to swell and dissolve the coating material on the surface of the steel drum, so that the binder in the coating material and ink of the steel drum surface are mutually dispersed. The formation of a layer of mixed, unbounded intermediate layers leads to the disappearance of the interface and the formation of a strong bond between the ink and the surface coating of the drum.

The diffusion process is the process of the ink solvent dissolving the paint coating on the surface of the drum, and the dissolution of the paint coating on the steel drum depends on the polarity of the binder and the solvent in the ink. Only when the polarity of the ink and steel drum surface coatings are similar, can they be dissolved and have adhesive fastness.

The binder in the ink is generally a molecular polymer having a linear structure, and the molecular ends thereof are easily diffused into the paint coating on the surface of the steel drum. The short side chains are not conducive to diffusion, and the large branch chains are conducive to diffusion.

The linking material has a large molecular weight and a long chain length, and has slow penetration and slow diffusion. When the molecular weight is small, the permeation is quick and the binding force is large, but the cohesive strength is small in itself. Therefore, the high-molecular polymer as a linking material needs to have an optimum molecular weight, which facilitates diffusion and has a certain cohesive strength.

The binder material is sensitive to temperature during the diffusion process of the coating on the surface of the steel drum. Increasing the temperature can promote the Brownian motion of the macromolecule, which is beneficial to the speed and capability of diffusion, and is also favorable to the fastness of the ink. This is also the reason why the drying speed of ink and adhesion is good when printing graphics on the surface of steel drums in summer, and the reason is that the drying speed is slow in winter and the adhesion of ink is poor.

3, the impact of additives

A wide variety of additives will greatly improve the performance of the ink. Additives that have an effect on adhesion are:

1 Crosslinker. The cross-linking agent can not only improve the adhesion of the ink, but also can greatly improve the ink's hardness, water resistance and drying speed.

2 coupling agent. The coupling agent promotes coupling of resin and the surface coating material of the polymer drum in the ink, and can improve the adhesion of the ink.

3 Plasticizers. The plasticizer improves the softness of the ink film and also improves the adhesion.

4, the impact of ink performance

The wettability of the ink is good, and its adhesion is favorable. If the surface of the drum has not yet been wetted, the ink has dried or cured and the adhesion is poor.

1 When preparing the ink, it is necessary to control the volatilization rate of the solvent, and the presence of the high boiling point solvent is favorable for leveling.

2 Use an appropriate molecular weight of resin to formulate the ink. The higher the viscosity of the resin, the more unfavorable the leveling of the ink.

3 Add an appropriate leveling agent to the ink.

5, the impact of the surface quality of the drum

The drum surface coating directly affects the adhesion of the screen printing ink. For different coatings (such as amino-baked steel drums, alkyd-baked steel drums, galvanized steel drums, chrome-plated steel drums, and tin-coated steel surfaces Barrels) Special inks should be formulated to increase ink adhesion. In addition, cleaning the surface of the drum can also increase the adhesion of the ink on the drum surface. For example, the presence of dust, grease, and dirt on the surface of the drum will make it difficult for the ink to adhere and must be removed. (to be continued)