Surface slip additives

Antiblock additives are often incorporated into packaging films to prevent them sticking together. Their effectiveness relates directly to the roughness they impart on a film surface while minimising loss in optical properties. They are often used in association with slip additives such as erucamide. Common antiblock additives include crystalline silica, diatomaceous earth and talc (magnesium silicate). 

IR internal reflection spectroscopy can be used to distinguish the relative differences in the concentration of the slip additive at film surfaces. 

Slip additives act at the surface of a polymer film or article to reduce the friction between it and another surface. In a variety of plastics, such as polyolefins, polystyrene, and polyvinyl chloride, fatty-acid amides are applied as slip additives. Fatty-acid amides, such as oleamide, stearamide, erucamide, and oleyl palmitamide, are added to plastic formulations where they gradually tend to bloom to the surface, imparting useful properties including lubrication, prevention of films sticking together, and reduction of static charge. 

A reason for the use of multilayer films is to minimize the use of additives. Surface-active additives like slip, antiblock or antifog agents are used only in the outer layers of a multilayer film. The migration of the organic additives and their solubility in the polymers has to be considered. 

Three theories were proposed to explain wall-slip (a) adhesive failure at the wall, (b) cohesive failure within the material as a result of disentanglement of chains in the bulk and chains absorbed on the wall, and (c) the creation of a lubricating surface layer at the wall either by a stress-induced transition, or by a lubricating additive. If the polymer contains low molecular weight components or slip-additives, their diffusion to the wall will create a thin lubricating layer at the wall, generating apparent slip. 

Figure 83 Comparison of coefficients of friction of the surfaces of treated and untreated films at different concentrations of slip additive...

The polyester type polyols used in polyurethane laminating adhesives are produced by the direct esterification of polyfunctional carboxylic acids and glycols. Polyester polyols provide the soft segment in polyurethane products giving the adhesive flexibility. Ester groups of the polyol also contribute to adhesion. Polyester polyols provide limited wetting and adhesion of olefinic surfaces with amide slip additives (in contrast to polyether polyols). Typical examples include adipic acid, caprolactone, maleic acid and isophthalic based polyester polyols. 

Plastic additivation (vapor permeability, surface effects), additive for slip agents and (cooler) lubricants... 

Removal of surface acting substances from plastics, e.g. lubricants, slip additives, such as stearamide, stearates, anti-static agents. 

Other surface active ingredients which may be found in plastic materials and suffer loss into product by solution, surface abrasion, etc. include anti-static additives, slip additives, mould release agents, etc. 

In the real world, the COF of a film freshly unwound from a roll is typically higher than that which would be measured 15 to 30 minutes later, due to blooming of the slip additive in the film. Blooming refers to the migration of the additive from the bulk of the film to the surface, and may not occur fully in the roll form. Therefore,... 

Given the low surface friction characteristics they impart, mold-release additives are related to slip additives used in extrusion, discussed in the next chapter. Some overlap with the migratory flow-enhancing lubricants mentioned above. Mold-release agents are typically based on one or more of the following chemistries ... 

Uses Surf, additive, slip agent, wetting agent, scratch and mar resistance aid for paints, printing inks Features Increases surface slip, substrate wetting Properties Colorless to bmsh. liq. mild ether-like odor sp.gr. 1.03 dens. 8.57 Ib/gal Hash pt. (Seta) 65 C ref. index 1.447 > 97% NV Toxicology TSCAIist ... 

An external antistat is applied via a carrier medium to the surface of the plastic part. The same considerations and limitations apply as with nonmigrating slip additives. Conductive filler is incorporated into the organic substrates and builds up a conductive network on a molecular level. While both approaches are used in organic substrates, they are not the most common. 

An internal antistat is compounded into the organic substrate and migrates to the plastic part surface. The same principle considerations apply as for migrating slip additives (Figure 1.19). 

Slip agents. Slip agents or slip additives are the terms used by industry for those modifiers that impart a reduced coefficient of friction to the surface of finished products. Slip agents can significantly improve the handling qualities of polyolefins and, to a lesser extent, PVC, in film and bag applications. They help speed up film production and... 

Slip additives are incorporated directly into the polymer during the extrusion process. They work by migrating to the surface as the polymer cools, forming a solid lubricating layer at the surface, lowering the friction or reducing adhesion between contacting polymer surfaces and the polymer and other materials. 

Slip additives are used with packaging plastics such as polyolefins, polystyrene and PVC to impart lubrication, prevent films (such as cling-film) from sticking together and to reduce static charges. They are usually surfactants such as fatty add amides which have the desired rate of blooming to the polymer surface where their action is needed. 

Areas in which X-ray photoelectron spectroscopy might be expected to perform best are the detection of surface effects (e.g. blooming), surface active additives (e.g. release and slip agents, lubricants, surfactants, etc.), rapidly migrating additives (e.g. plasticisers), or thin-film contaminants. XPS detection limits for additives (0.5 vol.%) are unfavourable for... 

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