Mixed Metal Soaps

The mixed metal soap systems have the advantage of good weatherability, and very fine foam structures can be achieved. European customers used to find that they were less effective than lead as stabilisers xmless used at high dose levels, so the materials costs were higher. As a result. 

OMG has argued that three-metal stabiliser systems (Ca-Ba-Zn carboxylates) offer benefits over two-metal ones in terms of effectiveness and that they also have beneficial effects on plate-out, as well as using a lower heavy metal content than Ba/Zn systems and giving very low volatile 

Ferro has introduced new calcium-zinc stabilisers, Therm-Chek RC 376P and Therm-Chek RC 377P, to replace tribasic lead sulfate in general purpose wire and cable jacketing applications. The company claims that its new additives outperform lead alternatives and that they can be used at lower dose levels. Electrical insulation resistance is also said to be better than with tribasic lead sulphate. 

Very high output rates are required in cable production. Akcros Chemicals offers a calcium-zinc product under the name Interlite 6088/6012, designed to improve initial colour and colour stability, while facilitating high-speed cable extrusion. 

Barium-zinc grades are offered by Ferro as well, with several grades available in liquid form. Applications include flooring topcoats, calendered sheet and extrusion products such as hoses. Some are claimed to give semitransparent products at low cost. 

---

Other stabilisers besides the mixed metal soap types can be assisted by using a co-stabiliser. 

Akcros Chemicals has increased its production of Interlite ZP solid mixed metal soap stabilisers, mostly calcium/zinc based, at its Eccles, Manchester (UK) site. They are for use in sensitive applications such as medical devices and food packaging. The company has withdrawn from making lead stabihsers. 

Ultimately, as the stabilization reactions continue, the metallic salts or soaps are depleted and the by-product metal chlorides result. These metal chlorides are potential Lewis acid catalysts and can greatiy accelerate the undesired dehydrochlorination of PVC. Both zinc chloride and cadmium chloride are particularly strong Lewis acids compared to the weakly acidic organotin chlorides and lead chlorides. This significant complication is effectively dealt with in commercial practice by the co-addition of alkaline-earth soaps or salts, such as calcium stearate or barium stearate, ie, by the use of mixed metal stabilizers. 

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. 

The basic metal salts and soaps tend to be less cosdy than the alkyl tin stabilizers for example, in the United States, the market price in 1993 for calcium stearate was about 1.30— 1.60, zinc stearate was 1.70— 2.00, and barium stearate was 2.40— 2.80/kg. Not all of the coadditives are necessary in every PVC compound. Typically, commercial mixed metal stabilizers contain most of the necessary coadditives and usually an epoxy compound and a phosphite are the only additional products that may be added by the processor. The requited costabilizers, however, significantly add to the stabilization costs. Typical phosphites, used in most flexible PVC formulations, are sold for 4.00— 7.50/kg. Typical antioxidants are bisphenol A, selling at 2.00/kg Nnonylphenol at 1.25/kg and BHT at 3.50/kg, respectively. Pricing for ESO is about 2.00— 2.50/kg. Polyols, such as pentaerythritol, used with the barium—cadmium systems, sells at 2.00, whereas the derivative dipentaerythritol costs over three times as much. The P-diketones and specialized dihydropyridines, which are powerful costabilizers for calcium—zinc and barium—zinc systems, are very cosdy. These additives are 10.00 and 20.00/kg, respectively, contributing significantly to the overall stabilizer costs. Hydrotalcites are sold for about 5.00— 7.00/kg. 

Processing Aids. Stearic acid [57-11-4] or other fatty acids and/or metal soaps of fatty acids are added to reduce shear degradation and mill sticking during mixing. Sorbitan monostearate (ICI s Span 60) is one of the best processing aids to reduce mill sticking. 

Kelbetz Explosives. Expls patented in England in 1896 by an Austrian, Kelbetz. They consisted of AN mixed with oxalates of aromatic amines, such as aniline and toluidine, and sometimes also contained small quantities of charcoal. Other Kelbetz expls contained about 95% AN, fatty acids such as stearic, palmitic, oleic, etc (with or without their metallic soaps, such as Ca), and small quantities of charcoal Ref Daniel (1902), 391... 

Concentration levels of heat stabilizers in various PVC products are in the range 1.5-3.0% for metal soaps and 0.3-2.5 % for organotin stabilizers (Pospfsil, 1990c). Aliphatic (22) or mixed aliphatic/aromatic phosphites (23, 24) are used together with polyols (e.g., pentaerythritol or sorbitol) and acid scavengers as co-stabilizers in PVC (Pospfsil, 1990c). 

Liquid mixed metal heat stabilisers are a blend of the metal soaps or salts in combination with... 

Traditionally metal soaps have been manufactured by reactiOTi of alkali- or alkaline earth oxides or carbonates with natural fats or oils. Both compraients are mixed and at higher temperatures the triglyceride is decomposed yielding metal soap and glycerol. Under such conditions the soap is dispersed in an excess of oil or molten fat, and lubricating greases are yielded that way. 

Ba/Ca Soap + Cd/Zn Soap + Epoxidized Fatty Ester + Organic Phosphite. This synergistic combination has always heen unnecessarily secretive, sold under vague names such as mixed metal, synergistic, and so on. It is universally used for plasticized PVC, because it is soluble, economical, and effective. The metal soap may he phenate, octoate, neodecanoate, naphthenate, benzoate, laurate, myristate, palmitate, or stearate. 

Mixed metal systems can be divided into solid and liquid types. Solid ones are calciiun-zinc combinations and are used to replace lead. The nature of the metal soap determines whether the stabiliser is liquid (as with the naphthenate, phenate and benzoate) or solid (stearate, ricinoleate and laurate). It also determines whether the PVC will be transparent. 

Mixed Metal Salts (or Soaps). These consist of Ba/Cd salts (once the most widely used because of their effectiveness but now declining owing to regulatory pressure), Ba/Zn, and Ca/Zn salts. The efficacy of these mixed metal salts as thermal stabilizers follows that order. Mainly used in flexible or semirigid PVC, they are available in solid and liquid versions. Solids are typically salts of fatty acids such as stearates and laurates while liquid versions are octoate, phenolate, and neodecanoate salts. Mixed metal salts are almost always used in the presence of secondary stabilizers such as organophosphites, epoxies (eg, epoxidized soyabean oil), and j8-diketones. This is particularly the case for the less active Ba and Ca/Zn. The ratio of metal salt to secondary stabilizer is typically 4 1. Mixed metal salts or soaps are available from Akros, Baerlocher, Ferro, and Rohm Haas in North America. 

---