Development of the processing technology of the ho

Development of processing technology of silicone anti stick paper (peel paper) (VI)

2.4 several technical problems needing attention in the production of anti stick paper

2.4.1 coating method of anti stick paper coater

on the surface of anti stick paper, the silicone coating layer is very thin. In other words, the dry coating amount of silicone is very small. In general, regardless of the coating process (solvent, water emulsion or solvent-free), the total coating amount (dry) of silicone, crosslinking agent and curing agent will not exceed 2g/m2. Because the dry coating amount is very small, and the coating amount is required to be very accurate, so for the solvent coating process, the best coating method is the gravure roller coating method. The mesh number of gravure roll lines is preferably within the range of 80 ~ 120 mesh (the specific number depends on the concentration of anti sticking coating). For the emulsion coating process, the gravure roller coating method is also a good form. If the concentration of water emulsion silicone coating is large, air scraper can also be used for coating. As for the solvent-free coating process, we need to use a special coating head to strictly and accurately coat (about the special coating head, we will talk about it later).

2.4.2 the "trough life" of the coating

the trough life of the coating refers to the preparation of the coating of silicone anti adhesion agent (the maximum air force, yield strength, tensile strength, compressive strength, arbitrary point elongation strength, arbitrary point load elongation, elongation, etc. are automatically calculated after the end of the test of anti adhesion agent, cross-linking agent, curing agent, etc. and other additives are mixed together to form a liquid according to the formula requirements), It is put into the trough of the coater and coated. After the start-up coating, the coating has not been used up, and it begins to solidify in the trough. Its performance is that the coating begins to thicken, the viscosity increases, the color turns white, and it is difficult to apply. Then, the paint soon lumped in the paint tank, which made it impossible to use at all. The service life of siloxane coating trough is calculated from the moment when the coating is prepared to the time when the coating begins to thicken and become sticky and cannot be used. Therefore, the service time of the coating should be longer than the service life of the tank of the coating. In other words, silicone coating must be used before the service life of the coating trough, otherwise it will cause great waste. The solution is to control the amount of curing agent. Because the amount of curing agent in the coating is large, the cross-linking and curing of silicone anti adhesion layer is faster, the production speed can be improved, but the service life of the trough is shortened. If the amount of curing agent in the coating is small, the service life of the trough will be extended, but the cross-linking and curing of the anti sticking layer will be slow, and the production efficiency will be affected. Another way is to prepare silicone anti stick coating without adding curing agent first. When to use this batch of paint and when to add curing agent. In other words, the curing agent should be used and added now. Paint should be dispensed less and more times

2.4.3 curing curve of silicone anti stick coating

this is an important problem. The so-called curing curve is the relationship between the curing temperature and curing time of the anti stick coating

in general, the higher the curing temperature, the shorter the curing time. Therefore, when we prepare a batch of anti stick paint and prepare it for use, we should find out the curing curve of this batch of anti stick paint through the laboratory. If the curing curve does not meet the requirements of the factory's process, adjust the formula (for example, increase or decrease the amount of curing agent, etc.) until the curing curve can meet the conditions of process equipment.

2.4.4 inspection of the curing degree of the anti sticking layer in the production process of silicone anti sticking paper

generally speaking, the finished anti sticking paper mainly needs to check two indicators. First, peeling force. It refers to the force when the pressure-sensitive adhesive tape is peeled off from the anti sticking paper with the "peeling force tester" after being pressed and stuck on the anti sticking paper for a certain time under a certain pressure. We call it "180 ° peel force value" of anti sticking paper. The second is to test the percentage of the loss of the bonding strength of the pressure-sensitive adhesive tape by pressing and sticking it to the anti sticking paper, and then peeling it off from the anti sticking paper (this is mainly to check whether the anti sticking layer of the anti sticking paper has transferred and the degree of transfer). The smaller the peeling force, the better the anti sticking performance of the anti sticking paper. The smaller the adhesive strength loss of the pressure-sensitive adhesive tape, the smaller the transfer degree of the anti adhesion layer, and the better the anti adhesion performance. How to test and check is not detailed here.

what we want to put forward here is the inspection of the curing degree of the anti sticking layer in the production process of the anti sticking paper, even for the appearance parts that need metal texture. This is very important. Because, if the anti sticking layer is not cured completely in the coater (either because the coating speed is too fast, or because the drying temperature is low, or because the amount of curing agent in the coating is not enough, etc.), it will bring many problems. For example, due to incomplete curing, the silicone film formed is not firm and strong, and the adhesion with the base paper or isolation layer is very small. In this way, when the anti sticking paper is taken off the machine, the silicone film is easy to be damaged, or fall off, or crack, or empty, or adhere to the back of the base paper, resulting in the paper coated with silicone can not be used and become waste paper; For another example, due to incomplete curing, the stripping force of the silicone film formed cannot meet the requirements, and the anti adhesion performance is poor and unqualified; For another example, due to incomplete curing, it is necessary to extend the post curing time of the anti sticking paper, which is much longer than 3 ~ 5 days, and may take 5 ~ 7 days or more. In this way, the production order will be disrupted, resulting in turnover failure

in the production process, after the above preliminary accuracy alignment of the experimental machine, there are generally two methods to check the curing degree of the anti sticking layer: one is the "finger tapping method", that is, tear off a small piece of paper at the coiling part of the coater, and tap the silicone film coated on the paper with the middle finger. If there are milky finger prints on the silicone film after knocking, or the silicone film is broken, or the silicone film is taken up by fingers, these indicate that the solvent in the silicone coating has not evaporated completely or the silicone film has just begun to cure, which is far from complete curing. If the above-mentioned situations do not appear when tapping with fingers, the second method, namely "hand rubbing method", can be used. Rub the silicone film back and forth with your thumb, or rub the silicone film back and forth with a towel. If the film is rubbed down in the shape of noodles, it indicates that the silicone film has been cured, but the curing is insufficient and incomplete; If nothing can be rubbed down, it means that the silicone film has been completely cured and can be taken off the machine. After getting off the machine, you can take samples to test the stripping force. In general, we should pay attention to the inspection of the curing degree of the anti sticking layer in the production process. Although the method used is "soil", it can solve the problem

2.4.5 pay attention to the problem of "poisoning" of curing agent when using addition reactive silicone anti adhesion agent

when adding reactive silicone is crosslinked with crosslinking agent methyl hydrogen polysiloxane, the curing agent used is the complex of precious metals, such as platinum or rhodium. Although their curing effect is strong, which can promote the quick crosslinking of silicone and crosslinking agent, they are also quite delicate and easy to be "poisoned". The so-called "poisoning" refers to that these precious metal complexes are very easy to be polluted by lead, copper or iron ions and lose their curing ability, which is called poisoning. After poisoning, the cross-linking reaction is greatly reduced, or even cross-linking is not possible. Therefore, in order to avoid this problem, when using these precious metal curing agents, we must clean the coater, especially the coating tank of the coater and various rollers in the coater that contact the paper, and wipe the coater, batching equipment and the surrounding environment regularly. (end)