Lubricants calcium stearate

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. 

Typically, soHd stabilizers utilize natural saturated fatty acid ligands with chain lengths of Cg—C g. Ziac stearate [557-05-1/, ziac neodecanoate [27253-29-8] calcium stearate [1592-23-0] barium stearate [6865-35-6] and cadmium laurate [2605-44-9] are some examples. To complete the package, the soHd products also contain other soHd additives such as polyols, antioxidants, and lubricants. Liquid stabilizers can make use of metal soaps of oleic acid, tall oil acids, 2-ethyl-hexanoic acid, octylphenol, and nonylphenol. Barium bis(nonylphenate) [41157-58-8] ziac 2-ethyIhexanoate [136-53-8], cadmium 2-ethyIhexanoate [2420-98-6], and overbased barium tallate [68855-79-8] are normally used ia the Hquid formulations along with solubilizers such as plasticizers, phosphites, and/or epoxidized oils. The majority of the Hquid barium—cadmium formulations rely on barium nonylphenate as the source of that metal. There are even some mixed metal stabilizers suppHed as pastes. The U.S. FDA approved calcium—zinc stabilizers are good examples because they contain a mixture of calcium stearate and ziac stearate suspended ia epoxidized soya oil. Table 4 shows examples of typical mixed metal stabilizers. 

Rigid Applications. The use of the lead stabilizers is very limited in the United States but, they are stiU used in several rigid PVC appHcations in Europe and Asia. The highest use of lead stabilizers in rigid PVC is for pipe and conduit appHcations. Tribasic lead sulfate is the primary heat stabilizer with lead stearates included to provide lubrication. The lead products are typically fully formulated, usually including lubricants and pigments for pipe extmsion appHcations. These lead one-packs, when used at about 1.8—2.5 phr, provide all of the stabilizer and lubrication needed to process the polymer. A lead one-pack contains tribasic lead sulfate, dibasic lead stearate calcium stearate, polyethylene wax, paraffin wax, ester wax, and pigments. 

Dry lubricants are usually added to the powder in order to decrease the friction effects. The more common lubricants include zinc stearate [557-05-17, lithium stearate [4485-12-5] calcium stearate [1592-23-0] stearic acid [57-11-4] paraffin, graphite, and molybdenum disulfide [1317-33-5]. Lubricants are generally added to the powder in a dry state in amounts of 0.25—1.0 wt % of the metal powder. Some lubricants are added by drying and screening a slurry of powder and lubricant. In some instances, lubricants are appHed in Hquid form to the die wall. 

Fig. 10. A model of PVC lubrication mechanism showing (a) PVC adhesion to metal without lubricant (b) surface activity of calcium stearate (c) nonmetal releasing character of paraffin only and (d) synergy between calcium stearate and paraffin (62).

In Britain calcium stearate has been most commonly used with nontransparent products and stearic acid with transparent compounds. In the United States normal lead stearate, which melts during processing and lubricates like wax, is commonly employed. Dibasic lead stearate, which does not melt, lubricates like graphite and improves flow properties, is also used. 

Stearic acid and metal stearates such as calcium stearate are generally used as lubricants at a rate of about 1-3% on the total compound. Waxes such as camauba and ceresin or oils such as castor oil may also be used for this purpose. 

Lubricants. Lubricants such as wax or calcium stearate reduce the viscosity of the molten plastic and improve forming characteristics. 

Many plastics because they are organic are flammable incorporate flame-retardants. Additives that contain chlorine, bromine, phosphorous, metallic salts, and so forth reduce the likelihood that combustion will occur or spread. Lubricants like wax or calcium stearate reduce the viscosity of molten plastic... 

Metallic soaps such as zinc stearate or calcium stearate are used as lubricant, which reduces the friction coefficient of the surface of the thermosensitive layer resulting in smooth running on recording machines. 

Typical additive packages for engineering thermoplastics have been described by Titzschkau [9], such as processing aids for PA, PP, or PET/PBT, three-component additive packages for polyamides and polyesters (nucleating agent, lubricant and process heat stabiliser) and coated copper stabilisers for polyamides. Additive packages or combinations of up to five or more additives are quite common. A typical white window PVC profile formulation comprises an acrylic impact modifier, TiC>2, CaCC>3, calcium stearate, a... 

The most effective lubricants are the hydrophobic stearates, such as magnesium stearate, calcium stearate, and stearic acid. Magnesium stearate is the most widely used lubricant [117,118]. Lubricants proposed as being less hydrophobic such as hydrogenated vegetable oils, polyethylene glycols, and sodium stearyl fumarate are less effective in this application [118]. 

Lubricants and slip Erucamide, oleamide, calcium stearate, zinc... 

One very common beneficial interaction involving an excipient is the interaction between magnesium stearate and the metal of tablet punches and dies, or the equivalent parts on a powder encapsulation machine. Magnesium stearate is an example of a boundary lubricant. As such it has a polar head and a fatty acid tail. It is believed that the polar head of the magnesium stearate is oriented toward the die wall or tablet punch face. In these ways it is able to reduce the ejection force (the force required to eject the tablet from the die after compaction) and prevent sticking to the punch faces. The other boundary lubricants, e.g., calcium stearate and sodium stearyl fumarate, will also function in a similar manner. However, the so-called liquid film lubricants function in a very different manner (19). 

Alternatively, a stiff paste of ceramic and binder solution can be forced through a wire mesh and granules of the required size extracted from the dried product by sieving. The flow of the granules can be enhanced and die-wall friction reduced by tumbling with a small quantity of a powdered lubricant such as calcium stearate. 

Typical strongly external lubricants are paraffin wax, polyethylene wax, oxidised polyethylene wax and stearic acid. Typical strongly internal lubricants are glycerol esters and fatty acids. Calcium stearate functions somewhere between internal and external, depending on addition level. It also acts as an acid scavenger. 

Calcium stearate (Ca(OOC(CH2)i6CHi)2) is sometimes used as a lubricant in the processing of poly(vinyl chloride). A sample of PVC compound containing 2 wt% calcium stearate was found to have A/n =25,(X)0. What is Mn of the balance of the PVC compound ... 

Colloid mills are used to grind and disperse solids in hquids and to prepare emulsions. They operate on the principle of high-speed fluid shear to grind the feed material. Another application is in the manufacture of lubricating greases by dispersion of calcium stearate in hydrocarbon oils. In the paint industry, colloid mills are used to incorporate pigments in liquid vehicles. In the food industry, the mills are used to make purees, sauces, ointments, creams, lotions, and other products. 

Metal stearates, such as magnesium or calcium stearate that serve as lubricants in conventional tablets, are seldom used as intrinsic lubricants in connection with effervescent tablets due to their insolubility in water. Use of stearates results in an undissolved, foamy, soapy-tasting layer on the surface of the cloudy solution. In addition, normal lubricant concentrations of metal stearates make the tablets hydrophobic, which entails a slow dissolution of the effervescent tablet in the water. However, very low concentrations of metal stearates can be used to improve the rate of solution of effervescent tablets as the tablet will remain immersed in the water during dissolution and not float to the surface the way a tablet without metal stearate would. A floating tablet presents a smaller surface area to the water than a tablet immersed in the liquid. 

Fig. 14 The effect of lubricant concentration (% w/w) on the measured adhesion (kPa) of hydroxypropyl methyl-cellulose films (A) Pharmacoat 606 (B) Methocel 60HG viscosity 50 ( ) stearic acid ( ) magnesium stearate ( ) calcium stearate. (From Ref. l)...

The excipients used are fillers, but the most important are lubricants, such as magnesium stearate, PEG 6000, calcium stearate, glycerol palmito stearate, and calcium behenate, which increase the flowability but at the same time modify the hydrophobic characteristics of powders. Their choice depends on compatibility with active ingredient and the flow properties of powders. The characteristics of the excipient have been described previously. 

Fig. 17 Lubricants. Magnesium stearate (A), calcium arachinate (B), and talc (C).

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