Wen/COF Packaging Yongfu Container (Harbin) Co., Ltd. Deputy Director of Printing Shop Yu Tong
In the tinplate printing industry, white magnetic coating is a very common The process, due to this process coated layout full effect, bright color, favored by many customers. However, there are sometimes black spots on the upper edge or both corners of the white magnetic plate. Sometimes it is even reversed to the back of the tinplate, which seriously affects the quality of the product, and even leads to many scraps of tinplate, causing great economic losses. Actually, this Production defects are often encountered in the coating process. We call it white magnetic sag or white reverse. So how does white magnetic sagging come about? Let's look at the following sketch of the coating work:
The transfer roller B and the feed roller A rotate in the opposite direction to ensure that a sufficient amount of coating is applied The material is conducted to the surface of the rubber roller C, the rubber roller C and the transfer roller B, and the embossing roller D are under appropriate pressure. The tinplate is conveyed by the conveyor belt to between C and D, since C is the elastic roller D is The rigid roller, under pressure, elastically deforms the contact area between the rubber roller C and the tinplate. The C/D rotates in the opposite direction at the same linear velocity, and white magnet (coating material) is evenly coated on the tinplate under pressure rolling.
Since the white magnetic plate surface is required to have a lateral groove, when it is coated, the pressure Under the action of the force, the rubber roller C is elastically deformed. Between the deformation point of the rubber roller and the contact part of the tinplate, a small amount of coating deposits are generated simultaneously with the coating roller, and the roller and the printing roller rotate toward each other. The tinplate advances synchronously, and a small amount of accumulated paint is squeezed backward by the rubber roller. When the rubber roller is rotated to the next slot, the accumulated paint cannot advance and it stays on the top edge of the plate. After the tinplate is put into the drying room and lifted up by the flower iron frame, the accumulated paint flows down slightly, but As the temperature rises, the coating surface begins to cure and the leveling stops. In this way, a height difference between the upper edge and the two corners and the normal layout is formed on the layout, and then the position on the edge higher than the normal layout is the white magnetic sag. As long as the coating process does not change, the height difference on this layout will theoretically always exist, and the greater the height difference, the more serious the quality problems will be. All we have to do is let this height difference be infinitely reduced, so that the harm caused by the appearance of white magnetic sacs will be negligible and reach a completely controllable range. The accumulated amount of paint squeezed out by the relative motion between the rubber roller and the tinplate, the more its volume, the greater the height difference between the plate and the layout, and vice versa, the smaller the actual operation after years of discovery, the problem with the following Related factors:
The greater the pressure between the rubber roller and the embossing roller, the heavier the sag The greater the pressure between the rubber roller and the embossing roller, the greater the pressure acting on the tinplate, the greater the elastic deformation of the rubber roller, and the greater the amount of paint that is squeezed out. The resulting sagging is very great. Serious, so in the white magnetic coating to reduce the pressure as much as possible (in order to not appear on the layout of the dot coating), not only can control the sag, you can also control the expansion due to the expansion of the roller caused by the increase in layout, color printing two Side exposed white edge quality defects.
The thicker the coating on the layout, the more obvious the sag
When the coated tinplate coating is very thick (usually greater than 20 g/m2), the amount of paint squeezed out after the elastic deformation of the rubber roller will be relatively increased, the more obvious the sag traces, but if the limit is reduced When the scale is thinned, the whiteness of the white magnetic plate will also decrease, (whiteness test is less than 70) and even the bottom will not reach the customer's requirements. How can we find a balance point? It is a test. One of the captain's operating levels, my little experience is to control the coating thickness at 14 g/m2 - g/m2 The effect will be better. Because the standards required by customers vary, if you do not meet the requirements, you may consider double-coating.
Effect of paint viscosity on sag
This seems to be a bit controversial. Some people think that the viscosity is large and the flow can be Can reduce, if the rubber roller is very good, the pressure, coating and other adjustments are very good circumstances, may reduce the sag, but some conditions are difficult to control, if the control is not good, not only will not reduce, but will Increases sagging and causes the edges and corners of the layout to be darkened and even reversed to the back of the tinplate. If the pressure, coating, etc., are not adjusted properly, the amount of paint extruded by the rubber roller is relatively large, and the viscosity of the paint is large, and it cannot be leveled in time after entering the drying room. In this way, the difference in height between the plate and the plate becomes larger. The sagging hazard, so from the perspective of operational safety, or to reduce the viscosity of the paint, take the lower limit of the normal value, coated with 4 cups of measurement, in 130s-140s is appropriate, if it is double coated, you can also reduce some. In addition, a large white magnetic viscosity, it is easy to produce orange peel on the coated surface.
The effect of the groove shape of the rubber roller on the sag
The horizontal groove angle of the rubber roller is not the same, and the rubber roller is soft and hard and swelling The coefficient of expansion is different, and the sagging patterns produced during coating are also different. There are basically two types of slots, V-type and Ladder-type. According to each operator's experience and operating habits, the above conditions are different. Impact has its own perception.
In short, the above four factors, for the production of white magnetic sag, are There are certain influences. In the actual production, all kinds of temporary and unforeseeable problems will also be encountered frequently. If they can be reasonably well-targeted and reasonably operated, the above four main factors will be controlled. Must be able to control in a small range, so as to minimize the harm to the quality, and lay a good foundation for subsequent color printing and can making processes.
(From << Metal Packaging "2017 fourth period)
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