The complexity of lubricant balance design---how to clean acrylic lens

The design of lubrication and balance can be said to be the most critical part of PVC formulation design. Lubricants and lubricating effects currently have no real theory and rules. For general PVC-U formulation design, relevant senior people believe that the difficulty and main content of formulation design are the choice of internal and external lubricant types and their ratios. Add total design. The total amount of lubricant added should be appropriate, and the ratio of internal and external lubricants is more important. Although the total amount is sufficient, if the proportion is out of balance, qualified products will not be continuously produced.　However, for the lubrication system that is crucial to the PVC-U processing process, there is no theory that can be called a theory at present, and there is even no law that can effectively guide the formulation experiment. The only so-called law is to learn from the law of 'similar compatibility' in general chemistry, that is, the more similar the polarity of the lubricant and the polarity of PVC resin, the better its compatibility, and therefore the better its internal lubrication effect; The lubrication effect is strong, but this law is also very limited in guiding the formulation design. Because the basis for judging the polarity of a lubricant is the chemical structure of the lubricant, that is, the type, number and length of the hydroxyl, ester, carboxyl, amide, ether, ketone and other polar functional groups contained in the lubricant molecule. The ratio of chain alkyl groups. Due to the complex and diverse chemical structure of the lubricant, and the mutual influence of adjacent functional groups, it is more difficult to judge the polarity of the lubricant. The difference between the lubricating effects of lubricants is far beyond people's imagination. The complexity of the variability of lubrication is more important. The compatibility of lubricants and resins (that is, lubrication) is also affected by other conditions, especially other lubricants and plasticizers and other additives. Obviously, this change can even make the internal lubricant become the external lubricant. That is to say, the lubricating effect of the same lubricant will vary with the amount of addition, with the composition of other additives in the formula, and with the processing The conditions vary. The reference ratio of internal and external lubrication of commonly used lubricants is as follows: Lubricant internal lubrication ratio,% external lubrication ratio,% fatty alcohol 1000 fatty acid ester 1000CaSt1000PbSt5050 ethylene bisstearamide 8020 stearic acid 2080 coal acid ester 5050 paraffin wax 0100PE wax (light Degree of oxidation) 3070PE wax (unoxidized) 2080 lubricants are more varieties. Usually two or more lubricants are used to form a PVC lubricating system to reduce its ability to migrate to the surface of the product; improve the dispersion of lubricants and balance the effects of internal and external lubricants. Diversity of internal and external lubrication balance. In fact, different types of processing equipment, such as twin-screw and single-screw extrusion, injection molding, and calendering equipment, require their own different lubrication balance. Strictly speaking, similar equipment, products from different manufacturers, or even the same equipment, old and new equipment, have different requirements for lubrication balance. Different types of products, such as pipes, sheets, films, and profiles, must have their own different lubrication balances. For example, profiles with complex cross-sections, extruded sheets, injection molded products, hollow products, blown films and highly transparent products require a higher degree of plasticization and better melt fluidity, so internal and external lubricants are required , Especially the amount of internal lubricant added is more, while the pipe material has relatively low requirements for melt viscosity and fluidity, and the plasticization degree is preferably 60% to 70%, so the external lubricant can be relatively better than the internal lubricant Used slightly more. However, injection molding products require as few non-polar external lubricants as possible in order to minimize the influence of external lubricants on the weld line strength.　　 The above contents all illustrate the diversity of lubrication balance. This makes it more difficult to study the theory of lubrication, and in the actual formulation design, it also greatly increases the difficulty of lubricant formulation design.　Most professionals believe that for general PVC-U, the key to formula design is the design of the type, proportion and total amount of internal and external lubricants, which is the design of lubrication balance. Less internal lubrication and more external lubrication. It takes a long time for plasticization, the fluidity of molten material is poor, the plasticizing torque is large, and the mechanical properties of the product decrease, become brittle, and segregation may appear. In severe cases, there may be oil samples by hand. a feeling of. More internal lubrication and less external lubrication show that the plasticization time is shorter, there is heavier adhesion phenomenon, the surface gloss of the product is poor, and the thermal stability may be deteriorated. In short, if the amount of external lubricant is insufficient, adhesion will occur and the plasticization time will be short; if the amount of external lubricant is excessive, the mechanical properties will decrease, and precipitation may occur. If the amount of lubricant in pvc is insufficient, the plasticizing torque will be larger and the plasticizing time will be longer; if the amount of lubricant in pvc is insufficient, the plasticizing time will be shorter, the plasticizing torque will be smaller, the thermal stability time will be shorter, there will be thermal decomposition, and the inner wall of the product will not be smooth. . The lubrication balance can be judged by the plasticization of the material in the extruder. The plasticization time of the lubrication balance system on the torque rheological curve corresponds to about 2/3 of the extruder, that is, the plasticization section of the corresponding extruder will end. The position where the homogenization segment will start. If it is not a lubricating balance system, the plasticizing time corresponding to the position of the extruder will change. When the plasticizing time corresponds to the position of the extruder less than 2/3, it will be over-plasticized. For PVC-U, it may be thermally decomposed and the material will turn yellow; when the plasticizing time corresponds to the position of the extruder greater than 2/3, The degree of plasticization is insufficient, and the product is rough and brittle. How to clean acrylic lenses