Water-based varnish has the advantages of advanced technology, convenient use, economical application, non-toxic and non-pollution, etc. It has a broad development prospect, especially in food packaging and printing. However, due to the difference in composition and drying method of water-based varnish and other types of varnish, new quality problems have occurred in the process of water-based varnish. For example, after connecting the water and oil, due to some factors, the paper surface after glazing will have a similar "orange peel" phenomenon. The so-called "orange peel" phenomenon is that after the water-based varnish and drying, the smoothness of the varnish film layer is very poor, showing a rough rough surface like the surface of the orange peel.
Before analyzing the cause of this phenomenon, we first need to understand the composition and drying method of the aqueous varnish.
Aqueous varnish is mainly composed of three main categories: main agent, solvent and auxiliary agent.
1. Main agent: The main agent of water-based glazing oil is film-forming resin, usually synthetic resin, which affects and controls various physical properties and glazing qualities of the film, such as gloss, adhesion, and drying.
2. Auxiliary agent: The auxiliary agent can improve the physical and chemical properties and processing characteristics of the water-based polishing agent. The types of additives are: ①curing agent; ② surfactant; ③ defoamer; ④ desiccant; ⑤ adhesion promoter; ⑥ wetting and dispersing agent; ⑦ other plasticizers that can improve the folding resistance.
3. Solvent: The main role of the solvent is to disperse or dissolve synthetic resin and various additives.
The conjunctiva speed of water-based varnish is fast. When the varnish still contains 20% ~ 30% moisture, it can be conjunctival. If no drying method is used, 30% of the moisture in the drying process is evaporated and 70% is absorbed by the material, so the drying is rapid and can be completed in about a few seconds.
The phenomenon of "orange peel" similar to the surface of the printed product after the connection of water and oil is mainly caused by the poor smoothness of the varnish layer after film formation. According to the functions of the ingredients in the water-based varnish and the factors affecting the film formation process, we believe that the main factors that lead to the "orange peel" phenomenon are factors such as paper type, coating amount, and varnish quality.
To solve the "orange peel" fault of water-based varnish, the first thing to consider is whether the fault is caused by poor paper surface performance. If the smoothness of the paper is poor, it may be because the coating amount is too small, so that the varnish film layer cannot fill the "concavo-convex" on the surface of the paper, and eventually the film after the glaze also appears "concave". Increase the amount of coating to solve; if the smoothness of the paper is good, it may also be because the absorption of the paper is too large, so that the glazing oil is excessively absorbed by the paper, which will also lead to the "orange peel" failure. Apply primer or varnish twice to solve the problem; if the first two reasons are eliminated, it is necessary to consider whether the leveling of water and oil on the surface of the printed product is poor due to improper use of surfactants. If the film is not well leveled and unfolded before it is formed, it will also cause the "orange peel" failure. The solution should be to adjust the surfactant to improve the leveling of the varnish. At the same time, the desiccant can also be adjusted to make the drying speed Slow down, provide enough time for the leveling of varnish; if the above problems are eliminated, the "orange peel" failure still occurs, it may be that the film-forming quality of the varnish film-forming substance is not good, and it should be replaced with a higher quality The varnish.
Through the above analysis, the cause of the "orange peel" failure during the connection of water and oil processing is not only the paper performance factor, but also the quality problem of water-based varnish. Therefore, it is very important to choose an aqueous varnish with stable quality, good glazing adaptability and high film-forming quality.
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