Introduces the basics of plastic lubricants Guinness
2013-07-03 by wsdchemical
After the molten polymer generally has a high viscosity, in the process, the molten polymer through the slit, when the gate runner, etc., and processing the polymer melt must be mechanical surface friction, some processing of the polymer friction is very unfavorable, these reduced melt flow friction, while the film surface cause severe friction becomes rough, or if the lack of luster rhyolite. To do this, need to be added in order to improve lubricity, reduce friction, for the purpose of reducing the interfacial adhesion additives. This is the lubricant. Lubricants In addition to improving mobility, but also can play a melt accelerator, anti-adhesion and anti-static agent, slip agent effect.
plastic lubricant can be divided into two kinds of external lubricant and lubricant inside and outside lubricant is mainly to improve the polymer melt processing equipment with hot metal surfaces rubbing. Poor compatibility with the polymer which is easy to migrate out from the melt, so that the plastic melt in the interface with the metal to form a thin layer of intenal lubricant. Lubricants and polymers have good compatibility, which serve to reduce the polymer inside the role of cohesion between the polymer molecules, thereby improving the internal friction of the plastic melt heat and melt fluidity. Commonly used lubricants are stearic acid and salts thereof outside; internal lubricant is a low molecular weight polymer. Some other function of the lubricant. Each lubricant has actually can achieve a desired effect, always together internal and external lubrication, except in one respect more prominent. A lubricant in the same or different polymers different processing conditions will exhibit different lubrication, such as high temperature, high pressure, the internal lubricant is squeezed out and become external lubricant.
In plastic film production, we will encounter some of the adhesion phenomena, such as in the production of plastic film, is not easy to separate the two films, which gives high-speed automatic packing difficult. To overcome it, the resin can be increased by adding a small amount of surface lubricity additives to increase the external lubrication, generally referred to as anti-blocking agent, or slip agent. General molecular structure of the lubricant, there will be long chain non-polar group and a polar group in two parts, they are in different compatibility of the polymer is not the same, thus showing the effect of different internal and external lubrication. According to chemical composition, commonly used lubricant can be divided into the following categories: fatty acids and their esters, fatty acid amides, metal soaps, hydrocarbons, silicone compounds and the like.
Lubricant actual processing plastics with a variety of effects, such as the kneading, rolling processing, to prevent adhesion polymer cartridge, inhibition of friction and heat, reduce kneading torque and loads, thus preventing polymer material thermal degradation. In the extrusion molding, to improve mobility, the barrel and the polymeric material to improve adhesion of the mold, to prevent and reduce the retentate. Another film can improve the appearance and luster.
From processing machinery perspective, mixing, rolling, slush molding, etc., the external lubricant has an important role in extrusion, injection molding, lubricants is more effective.
The amount of lubricant is generally 0.5% to 1%, the choice should pay attention to:
1 the flow properties of the polymer molding technology needs have been met, the primary role of lubrication considerations to ensure that internal and external balance;
2 external lubrication is effective, it can be in the molding temperature, the surface layer of the plastic film to form a complete liquid prevail, so the melting point of the lubricant outside the molding temperature should be close, but to a difference of 10 ℃ ~ 30 ℃ order to form a complete film;
3 does not reduce the mechanical strength of the polymer, and other physical properties.
In the production of lubricant selection, should make it meet the following requirements:
4 high performance and long-lasting lubrication;
5 compatibility with the resin medium size, internal and external lubricating balance;
Non-blooming, easy to scale;
6 small surface gravity, viscosity, at the interface scalability, and easy to form the interface layer;
7 is not reduced as much as possible the excellent performance polymers, does not affect the performance of the secondary processing of plastics;
8 itself is excellent in heat resistance and chemical stability, in the processing does not decompose volatile;
9 non-corrosive, does not pollute the film, there is no toxicity.
However, the simple use of a lubricant is often difficult to achieve the purpose, to be used in combination of several lubricants, lubricating composite developed rapidly in recent years, the choice can be viewed from multiple perspectives lubricant.
Commonly used lubricants are stearic acid, butyl stearate, oleamide, ethylene bis stearic acid amide and so on.
Many substances can be used as a lubricant waxes such as natural paraffin, liquid paraffin (mineral oil), microcrystalline wax, etc., but the effect is mixed. Natural wax mostly used external lubrication, the lubricant can be used as a variety of plastic, mold release agents, the general amount 0.2 ~ 1phr, but the compatibility, thermal stability and dispersibility is not good, the amount can not be too large, preferably lubricants and used; while white oil mostly used PVC, PS internal lubricants, lubricating properties, good thermal stability, the general amount 0.5phr. They are no drugs that can be used for food packaging. Another Microcrystalline wax: in Plastics Processing is also used as a lubricant, the amount of 1 ~ 2Phr, thermal stability and lubricity better than normal paraffin.
Low molecular weight polymers are widely used as a lubricant such as polyethylene wax, low molecular weight polypropylene, its internal and external lubrication are better, and non-toxic. PVC and polyethylene wax materials suitable for extrusion, calendering, the dosage is usually 0.1 ~ 1phr, to improve processing efficiency, prevent the film adhesion, improved dispersion of the filler or pigment, compatibility and transparency is not very good; irregular low molecular weight polypropylene can be used as the structure rigid PVC, PE lubricant performance, can improve the dispersibility of other additives, the amount of 0.05 ~ 0.5phr.