Selection of steel screen printing ink in different environments (2)

Selection of steel screen printing ink in different environments (2)

Second, the adhesion of steel drum screen printing ink

Screen printing of steel drums requires good adhesion of ink, and the problem of adhesion of screen printing inks is also the most prominent problem of ink after screen printing. If the ink does not have adhesion on the steel drum after printing, it means that there is no printing and it will cause a lot of waste. The adhesion problem of the ink relates to the bonding mechanism of the ink and the steel drum. At present, the following reasons are generally considered to affect the adhesion of ink:

1, the impact of resin

Resin is the main component of the ink binder, and 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 surface coating of the steel drum, the ink solvent is not easy to select. If the molecular weight of the resin is too large, in order to achieve the desired viscosity of the screen printing, the solid (resin) content in the ink is too small, resulting in waste of solvent. The molecular weight is high, the melting point is also high, and it is difficult to dissolve in a solvent, which is disadvantageous for 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 molecular weight selection of the ink resin is very important and must be suitable.

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

3 The composition of the resin. The functional groups, the branched structure and the like in the resin molecules directly affect the adhesion effect of the ink on the steel drum. Therefore, the printing ink used for the different coated steel drums is different in the screen printing of the steel drum. For example, the coating on the surface of the steel drum is coated with an amino baking paint and a galvanized coating, a chrome coating and a tin plating coating.

4 Element content of resin monomer. The change in the content of a certain element of the synthetic resin monomer causes the performance of the resin to also change. Therefore, when designing the drum screen printing ink formulation, the synthesis of some special resins will greatly improve the performance of the ink. A change in the content of a certain element of the resin monomer will result in a prominent change in a certain characteristic of the resin.

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

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

2, the influence of solvent

The solvent in which the ink is formulated also affects its adhesion. It is known that the solubility parameters of the resin and solvent used are similar, and the solubility parameters of the steel surface coating are also considered similar.

1 Solubility parameters of resin and solvent are similar, which is good for dissolution.

2 The solvent with a high boiling point is used too much, and the adhesion of the ink is lowered.

3 The solvent is not properly selected, and the adhesion of the ink is poor. The use of the solvent is considered from a plurality of factors, so that the ink solvent often uses three or more mixed solvents.

4 The solvent and the binder (polymer) in the ink are in contact with the surface coating of the steel drum to swell and dissolve the surface coating of the steel drum, so that the coating material in the surface coating of the steel drum and the binder in the ink are mutually diffused. Forming a layer of an unlined intermediate layer, resulting in the disappearance of the interface, forming a firm bond between the ink and the surface coating of the steel drum.

The diffusion process is the process in which the ink solvent dissolves the surface coating of the steel drum, and the dissolution of the steel surface coating is determined by the polarity of the binder and solvent in the ink. Only when the ink and the surface coating of the steel drum are similar in polarity, they can be dissolved to have the adhesion fastness.

The binder in the ink is generally a molecular polymer of a linear structure, and the two ends of the molecule are easily diffused into the surface coating of the steel drum, the short side chain is not conducive to diffusion, and the large branch is favorable for diffusion.

The binder has a large molecular weight and a long chain, and its permeation is slow and diffusion is slow. When the molecular weight is small, the penetration is fast and the adhesion is large, but the cohesive strength itself is small. Therefore, the polymer as a binder needs to have an optimum molecular weight, which is advantageous for both diffusion and cohesive strength.

The binder is sensitive to temperature during the diffusion process to the surface of the steel drum. Increasing the temperature can promote the Brownian motion of the macromolecule, facilitate the speed and ability of diffusion, and also facilitate the bonding fastness of the ink. This is the reason why the drying speed of the ink is fast and the adhesion is good when the surface of the steel drum is printed in the summer, and the drying speed is slow in winter and the adhesion of the 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 greatly improve the hardness, water resistance and drying speed of the ink.

2 coupling agent. The coupling agent promotes the coupling of the resin and the surface coating material of the polymer steel barrel in the ink, thereby improving the adhesion of the ink.

3 plasticizer. 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 steel drum is not wetted, and the ink has dried or solidified, the adhesion is poor.

1 When formulating inks, it is necessary to control the volatilization rate of the solvent, and the presence of a high-boiling solvent is advantageous for leveling.

2 The ink is formulated with a resin of appropriate molecular weight, and 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. Influence of surface quality of steel drum

The surface coating of the steel drum directly affects the adhesion of the screen printing ink. For different coatings (eg steel drums coated with amino baking paint, steel drums coated with alkyd paint, steel drums with galvanized coating surfaces, steel drums with chrome-coated surfaces and steel with tin-coated surfaces) Bucket), special ink should be prepared to improve the adhesion of the ink. In addition, the cleaning of the surface of the steel drum can also improve the adhesion of the ink on the surface of the steel drum. For example, the presence of dust, grease, and dirt on the surface of the steel drum makes the ink difficult to adhere, so it must be removed.

Third, the type of steel screen printing ink

Steel drum screen printing inks can generally be divided into resist inks, anti-electroplating inks and two-liquid (two-component) reactive inks.

1, resist ink

The anti-corrosion inks used in wire mesh screen printing are mainly solvent-based resist inks.

The ink has good corrosion resistance and finally uses a solvent to remove the film. For example: asphalt ink, can be dissolved in gasoline by using No. 5 road asphalt, to achieve a certain viscosity, can be screen printed, low production cost; white thick paint can be added with alkyd varnish, novolac, gasoline, turpentine, etc. Mixed use.

2, anti-electroplating ink

The main components of the anti-electroplating ink are asphalt type, modified polyethylene type, synthetic rubber type and thermosetting epoxy type.

3, two liquid reaction ink

The two-liquid reaction type ink is also called a two-component reaction type ink. The two components which are completely different in chemical properties are sufficiently mixed and uniformly printed before printing, and chemical reaction occurs after printing, and the polymer is combined to dry the conjunctiva.

Fourth, the status of practical inks and problems

The screen printing inks used by many steel drum manufacturers can be summarized into two categories:

One type is a slow drying ink; the other is a fast drying ink. Among them, slow-drying inks use metal offset inks for most steel drum manufacturers. Its main formula is ink + alkyd paint + dry oil, the ratio is 75-80% ink; alkyd paint is 20%; dry oil is 3-5%. The purpose of adding dry oil is mainly to speed up the drying speed of the printed image after silk screen printing. The ink has a strong adhesion after printing. However, its drying speed is slow. Under normal circumstances, it takes 10-30 minutes in summer and longer in winter. Therefore, this ink is not suitable for use in the north in winter. Another type of quick-drying ink is mainly one of two-liquid reactive inks, that is, the ink is composed of two components of A and B. Before printing, component B is added to component A, and the proportion of the ink is added according to the actual production. Depending on the situation and weather conditions. In general, we refer to component B as a slow-drying agent. The amount of slow-drying dose added to the ink directly affects the quality of the screen printing of the steel drum. The more slow dry doses are added, the worse the adhesion of the silkscreen prints. However, if the slow dry dose is added too little, it is easy to seal when printing, which makes the operation difficult.

It can be seen from the above analysis that the performance of the ink directly affects the effect of the screen printing of the steel drum. The steel drum manufacturer should reasonably select the ink that meets the requirements of its own production according to the actual climate change of the production to achieve the best effect of the silk screen printing. .