SLIP AGENT

Slip agents are related to antiblocking agents, but instead of decreasing surface contact, they reduce blocking by introducing a thin, low-friction coating between the plastic materials. These additives are usually mixed into the polymer film, but 

Combinations of a slip and an antiblocking agent can improve performance through more rapid development of slip properties and a more efficient use of the antiblock in both cases this is the result of Improved dispersion of the additives. These agents are commonly added to a resin in the form of a multicomponent master batch which also includes other additives. Amounts of the antiblock in the master batch commonly range from 5 to 50%. 

Both Toshiba and General Electric market solid spherical silicone powders that are reported to have combined antiblocking and slip agent properties, distributing evenly on film surfaces and reducing friction between film layers, without detracting from film clarity. 

Slip agents often consist of amide waxes with about 22 carbon atoms, containing a cA-double bond to prevent them from crystallising. Erucamide, oleamide, stearamide and ethylene bis-stearamide are preferred. They do not usually perform very well as antiblocking agents, although a few substances can perform both roles. 

Although some of the additive chemistries covered in this chapter were already mentioned in the previous chapter on molding aids, this chapter will cover processing aids in the context of extrusion, with particular attention on cast and blown films. Some basic questions will be addressed, such as  

Various processing aids serve the needs of cast- and blown-film converters and other extrusion operations, including the following  

Copyright O 2009, Michael Tollnski. Published by Elsevier Inc. All rights reserved 

Many of the processing aids discussed in this channel address more than one of these needs, although some also have negative side effects such as additive buildup or high cost. Thus the most complicated issue is to sort through the products offered by industry to find the right additive solution [12-17]. 

But many fadors determine the right concenttation for a film. If anything, slip agents are often added at too high a concenttation. This causes an excessive 

Due to their high coefficient of friction, poly(olefin) films tend to adhere either mutually or to the production equipment during processing. 

Slip additives act as they modify the surface properties of the pol)mieric materials. They reduce the friction coefficient of any other surfaces with which they come into contact. Thus slip agents (1)  

Facilitate an increased line speed in the manufacturing process, when applied as processing aids, and 

Eventually enhance the performance of the packaging machine by reducing the coefficient of friction. 

Exposed filtn surface area Re-covering of film siirfiice area 

a monolayer is formed on the polymer surface followed by deposition of subsequent layers when new molecules of antislip agent arrive onto the surface. 

Further interest in mechanism requires mformation on fate of exuded slip agent during production and processing operations in which films contact many metal rollers and guides, which may affect distribution of slip agent on the surface. Detailed studies were conducted for emcamide in polyethylene and polyole- 

Rate of migration is an essential factor and it depends, among others, on chemical structure. It was found by XPS spectroscopy that the surfaee eoneentra-tion of oleamide was increasing for 30 days until it become constant. Steara-mide, at this point of time, had 3 times lower concentration on the surface than oleamide. Oleamide undergoes surface oxidation due to the presenee of double bonds in its structure.  

It is noticeable that the above mechanism is based on studies of fatty acid amides while other slip agents are also used for various purposes related with reduction of coefficient of fnction. Fluoropolymer additives, for example, are used to improve film extmsion in which they act in a similar manner during process as amides act in the final film. Fluoropolymer additive is also not compatible with polymer matrix. During extrusion it migrates to the surface of metal and forms film which has pronounced effect on production parameters. It reduces melt fraction, viscosity, shear rate, and gate pressure. This makes production faster and eneigy use lower. Some of these additives are developed in such a manner that they migrate only in a molten state but are immobilized within material after material solidifies. This makes them essentially absent from the film surface which in some post process operation is an important requirement.  

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There are a number of applications for the acid, outlined in Scheme 6.5. The current major use is in the production of erucamide, a slip agent used in the manufacture of polythene bags to make them open more easily. 

Foaming agents Slip agents Lubricants Mould releases Curing agents... 

Plasticisers Lubricants/mould release agents Organic peroxides Slip agents... 

Applications The broad industrial analytical applicability of microwave heating was mentioned before (see Section 3.4.4.2). The chemical industry requires extractions of additives (antioxidants, colorants, and slip agents) from plastic resins or vulcanised products. So far there have been relatively few publications on microwave-assisted solvent extraction from polymers (Table 3.5). As may be seen from Tables 3.27 and 3.28, most MAE work has concerned polyolefins. 

LDPE or HDPE extracts has been determined colorimet-rically at 430 nm by oxidation with H202 in the presence of H2S04 [66]. p-Phenylenediamine derivatives such as Flexzone 3C, used as antiozonants in rubber products, have been determined colorimetrically after oxidation to the corresponding Wurster salts [67]. A wide range of amine AOs in polyolefins has been determined by the p-nitroaniline spectrophotometric procedure [68]. Monoethanolamine (MEA) in a slip agent in PE film has been determined as a salicylaldehyde derivative by spectrophotometric quantification at 385 nm [69]. Table 5.6 contains additional examples of the use of 1JV/VIS spectrophotometry for the determination of additives in polymers. 

The use of the particle-beam interface for introduction of samples into a mass spectrometer (PB-MS), without chromatographic separation, was shown by Bonilla [55] to be a useful method for analysis of semi-volatile and nonvolatile additives in PC and PC/PBT blends. The method uses the full power of mass spectrometry to identify multiple additives in a single matrix. The usefulness, speed and simplicity of this approach were illustrated for AOs, UVAs, FRs, slip agents and other additives. 

See Antiblocking agents, Release agents, Slip agents. 

See Antistatic agents, Foaming agents, Lubricants, Slip agents, Wetting agents. 

Slip agents Minimize coefficient of friction, especially polyolefins ... 

As an example, when automotive catalytic mufflers and converters were introduced many years ago, the automobile industry required the petrochemical industry to eliminate lead from gasoline since lead degraded and reduced the effectiveness of the catalyst and caused the destruction of the gasoline. One set of industrial compounds that can harm catalysts are halogens, a family of compounds that include chlorine, bromine, iodine, and fluorine. Bromine, while not prevalent in industry, is present in chemical plants. Freons are fluorine compounds. Silicone is another compound that is deleterious to catalysts. It is used as a slip agent, or a lubricant, in many industrial processes. Phosphorous, heavy metals (zinc, lead), sulfur compounds, and any particulate can result in shortening the life of the catalyst. It is necessary to estimate the volume or the amount of each of those contaminants, to assess the viability of catalytic technologies for the application. 

In addition, polyester bottles may contain colorants in the form of pigments, dyes or lakes. The colorants may be dispersed or dissolved in the polymer or may be covalently bound to the polymer backbone. Polyester packaging, which may be collected for depolymerization, may include nucleators for enhanced crystallization, anti-slip agents, branching agents, anti-blocking agents and anti-stats. 

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