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来源:http://www.jingmeisuliao.com/ 日期:2023-11-13

White spot bubbles: ① Insufficient drying
②上胶量不足:督办、复溶性差、转移率下降。。  薄膜太厚
② Insufficient glue application: poor supervision, poor solubility, and decreased transfer rate.. Thin film too thick
③ After compounding, the glue is not leveled: the molecular weight of the glue is large, the aging is not enough, the temperature of the compounding hot roller is too low, and the temperature is too low, making the preheating roller useless
1、 Aluminum coated composite printing substrate, if bubbles are generated, appears as white dots in the light colored part of the printing film. The two layers of substrate in the bubble part are not closely attached, and may not be bulging. But the bubbles formed by severe poor drying are bulging, large like sesame seeds. Some of the reasons for producing such bubbles are due to incomplete drying of the adhesive, while others are due to insufficient drying of the ink solvent, often appearing in large areas of drop printing. Some small printing machines still use infrared drying boxes. Mild dryness, although not accompanied by large bubbles, is only minor enough to release solvents through certain thin films. Under the same process conditions, PET composite aluminum foil has bubbles, while BOPP composite aluminum foil will disappear after heating.
2、 There is not much difference between the small bubbles formed by poor drying and the bubbles generated by insufficient glue application when observed with a magnifying glass. Therefore, rational analysis is necessary. Any surface that looks very smooth is uneven when viewed with a magnifying glass. The adhesive needs a certain thickness to smooth the surface - that is, the amount of adhesive applied. Low viscosity adhesive for ordinary transparent composite films. Printing film coating should be thicker, such as white film, and the thickness of the white film under the color block is even greater. The resin content of inner printed composite ink is less than that of surface printed white film, so the surface of composite white ink is relatively rough. Rough benzene is an advantage of composite white ink, which is beneficial for the penetration of adhesive to produce sufficient peel strength, but in turn requires a higher amount of adhesive application. In order to ensure sufficient adhesive thickness for the ink part, the adhesive amount needs to be 3-3.5G, which is also insufficient. It is easy to understand that insufficient glue application is caused by blocking the plate. There are two types of blocking: temporary and sudden, caused by poor paint re solubility and continuous decrease in transfer rate during operation. If the cause of this type of blockage is not identified and eliminated in a timely manner, relying solely on parking and wiping the plate can only maintain it for a while. Another type of blocking is a gradient type, strictly speaking, it cannot be considered a malfunction because it is impossible to completely clean the residual glue in the anilox roller after each composite, and the residual glue accumulates and solidifies at the bottom of the mesh hole day after day. The amount of glue gradually decreases, and small bubbles gradually emerge, increasing from less to more, and from small to large. Eventually, due to the production of demanding products and thick composite films one day, small bubbles became intolerable. At this point, a specialized plate washing solution needs to be used. The problem is solved, but it is not a good production habit because a large number of products were previously produced between qualified and unqualified. We advocate regularly measuring the amount of glue applied and cleaning when the amount of glue decreases to a predetermined value.
3、 Sometimes the drying is sufficient, and the amount of glue applied is also considerable. The composite film just removed from the machine still has bubbles. In fact, it is impossible for a newly compounded product to have no bubbles at all. Small bubbles can be eliminated by aging, as polyurethane adhesives that do not contain solvents but do not fully cure have a certain degree of fluidity. The higher the temperature, the greater the flow, the larger the molecular weight, and the smaller the fluidity. The essence of solidification is the process of continuously increasing molecular weight. The composite film in the curing chamber is slowly flattened by the adhesive under the action of temperature, with large bubbles shrinking and small bubbles disappearing until the molecular weight of the adhesive increases to the point where the adhesive cannot flow. Experienced operators can see how large white spots can disappear. If unsure, it is best to first place the sample in an 80 degree oven for 30 minutes and check if bubbles are removed. Bubbles of the same size can be eliminated with low viscosity glue, while high viscosity glue may not be effective because 50% of high viscosity glue has a large molecular weight and poor leveling performance.