Processing internal lubricant

The various lubricants formulated into PVC to improve the processing can also enhance the performance of the stabilizet. In pigmented apphcations, calcium soaps, eg, calcium stearate, ate commonly used as internal lubricants to promote PVC fusion and reduce melt viscosity. This additive is also a powerfiil costabilizer for the alkyl tin mercaptide stabilizers at use levels of 0.2 to 0.7 phr. Calcium stearate can significantly improve the eady color and increase the long-term stabiUty at low levels however, as the concentration increases, significant yellowing begins to occur. 

By far the most common lead salt used for PVC stabilization is tribasic lead sulfate. It can be found either alone or combined with another lead salt in almost every lead-stabilized PVC formulation. Many of the combinations are actually coprecipitated hybrid products, ie, basic lead sulfophthalates. Dibasic lead stearate and lead stearate are generally used as costabilizers combined with other primary lead salts, particularly in rigid PVC formulations where they contribute lubrication properties dibasic lead stearate provides internal lubrication and lead stearate is a good external lubricant. Basic lead carbonate is slowly being replaced by tribasic lead sulfate in most appHcations due the relatively low heat stabiHty of the carbonate salt which releases CO2 at about 180°C during PVC processing. 

Additive, slip An additive modifier that acts as an internal lubricant which exudes to the surface of the plastic during and immediately after processing providing the necessary lubricity to reduce or eliminate coefficient of friction in molded parts, film, etc. products. 

Lubricants can be classified as internal or external lubricants. Internal lubricants should be partially miscible with the polymer at processing temperatures (i.e., behave similar to a plasticiser), but phase separate at ordinary temperatures. Whereas plasticisers are completely miscible with the bulk polymer, lubricants have a limited solubility. 

Some of these processing aids are incorporated into the bulk of the material rather than being directly applied to the surface and are known as internal release agents. In the process of migration to the surface they have an inevitable internal lubrication effect. Most internal lubricants also have an external lubricant effect, particularly at higher concentrations because usually some material finds its way to the exterior. 

Removal of the article from the mold is lengthy process because anti-adhesive lubricants have to be sprayed on the on a mold surface before every injection, in an operation that takes up to 25 - 30% of the full cycle. In reactive molding of polyurethane-based compounds, internal lubricants are used in combination with surface coatings. This allows us to remove articles from a mold many times with a single coating treatment. One of the compounds used as an internal lubricant is silicon-organic liquids. 

The next chapter is a review of current practice in lubrication of internal combustion engines and lubricant design. The role of individual lubricant components and their use in mineral and synthetic formulations is covered. This is followed by a discussion of the tribochemical effects of additive interactions. The heart of the manuscript is chapters, "Tribochemical nature of antiwear film , "Surface tribochemistry and activated processes", and "Analytical techniques in lubricating practices". Topics covered include tribofilm formation, organomolybdenum compounds in surface protection, catalytic activity of rubbing surfaces, introduction of some techniques for evaluation of tribofilms composition and analytical techniques for evaluation of lubricant degradation. Examples of the application of basic concepts are introduced, eg., acidity and basicity in the process of lubricant deterioration. 

The characteristics of lubricants, their effects during plastics processing and their influence in the calendering process are discussed in depth. Attention is paid to the different intemal/external behaviour of lubricants, viscosity reduction by internal lubricants, fusion delay by external lubricants, shear liquefaction by lubricants and the suitability of various lubricants for the manufacture of calendered PVC films in relation to melt elasticity, release effect, flow and plate-out. 

Internal lubricants are added as part of the formulation during plastics processing. Depending on their compatibility with the resin they can have a more pronounced internal lubrication effect mainly interacting with the molecules of the polymer melt or they can have a more pronounced external effect, i.e. additionally reduce friction at the interface between processed plastic melt and metallic machinery parts [121, 151-153]. Lubricants in resin systems improve flow characteristics and reduce adhesion in the polymer melt. Added in very small quantities... 

Similarly, fatty alcohols with chain length from C12 to C22, which are industrially produced by hydrogenation of fatty acid methyl esters are efficient internal lubricants and exhibit good compatibility with PVC. However, they also have the disadvantage of high volatility under plastics processing conditions. 

Aidall. [Disco] Internal lubricant for processing elastomeric conq>ds. 

Superaid. [EX. Puskas] Dispersants, processing aids, internal lubricants. 

An unplasticized PVC formulation usually contains at least one other lubricant, which is mainly intended to improve the flow of the melt, i.e., to reduce the apparent melt viscosity. Such materials are known as internal lubricants. Unlike external lubricants they are reasonably compatible with the polymer and are more like plasticizers in their behavior at processing temperatures, whereas at room temperature this effect is negligible. Among materials usually classified as internal lubricants are montan wax derivatives, glyceryl monostearate, and long-chain esters such as cetyl palmitate. 

Rimplast materials from Petrarch are silicone/thermoplastic IPNs that combine the warpage and wear resistance properties of silicone with nylon, thermoplastic polyurethane, or styrene/butadiene block copolymers. The combination of properties these IPNs possess make them suitable for high quality, high tolerance gear and bearing applications that can benefit from the addition of internal lubrication and isotropic shrinkage of silicone to the fatigue endurance and chemical resistance of crystalline resin, while processability still remains the same. 

Processing Aids (external and internal lubricants, and so on) Improving processability ... 

Processing aids are usually based on high molecular weight acrylic copolymers (for PVC). They modify the rheology and processing characteristics of the melt. Lubricants are processing aids that function to ease the process and are of two types either internal lubricants (that influence the viscosity, such as calcium stearates) or external lubricants (such as oxidised polyethylene wax). Lead-stabilised PVC lubricants are a part of the stabiliser system. They are important in PVC foam formulations. 

A special additive used to provide surface lubrication during and immediately following processing of the plastic material. Slip agents act as an internal lubricant which will eventually migrate to the surface. 

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