RELEASE AGENT

Release agents function by either lessening intermolecular interactions between the two surfaces in contact or preventing such close contact. Thus, they can be low surface-tension materials based on aliphatic hydrocarbon, fluorocarbon groups, or particulate solids. The principal categories of material used are waxes, fatty acid metal soaps, other long-chain alkyl derivatives, polymers, and fluorinated compounds. 

Suppliers of release agents vary from large, basic polymer producers to small, regional formulators and distributors. Examples from among the hundreds of such suppliers include the following  

American Cyanamid Chemical Products Division Bareco Division, Petrolite Chem-Trend, Inc. 

Emery Industries Th. Goldschmidt AG C. P. Hall Company Kluber Chemie KG 

Many more suppliers and information about their product line can be obtained from compilations such as the Modem Plastics Tngclopedia (1) and the Thomas Register of American Manufacturers (2). The choice of a release agent depends on the process conditions involved and the nature of the contacting substrates (3). Apart from the obvious ease of release, other important requirements are minimal buildup of residues on mold substrate, minimal effect on the molded article, adequate film-forming ability, compatibility with secondary operations and other processing parameters, health and safety requirements, and cost. 

Mould release agents are substances which help to separate the moulding, i.e. the product, from its mould when it has been made. The choice of release agent depends on the size and complexity of the moulding operation, and on the quality of the surface finish required. 

Considerations should be given not only to the effectiveness of a release agent but also its cost, the health and safety aspects, the effects on other properties, and the ease of use. In this last respect, physical form is important. The stearates are dusty powders, but alkyl phosphates are also available, and have the advantage of being liquid. 

The remainder of this entry is concerned with external mould release agents for use with thermosetting resins, mainly in open mould and low throughput operations. In the case of large fibre glass polyester or epoxy 

Hydrocarbon waxes can be used, subject to temperature limitations. High grade, silicone-free Carnuba wax is effective. Hard, medium and soft waxes are available. Several thin coats (up to about six) are applied and polished. Wax can also be used in an emulsion form. 

Poly(vinyl alcohol) is also frequently used. It is available in coloured solutions, and can be sprayed or brushed. One problem with poly (vinyl alcohol) is the low viscosity of the solution. This means that it drains down slopes and collects in recesses or sharp corners. It may then take a long time to dry, and will not offer protection in these local areas. The use of water/methanol solvent mixtures gives a faster evaporation of solvent after application than water alone. A slow rate of evaporation can result in a long delay before it is safe to proceed to the next step, e.g. the application of a gelcoat which must be applied to a dry surface for satisfactory cure. 

In order to make selection of suitable release agent, the reasons for adhesion must be known. Adhesion is caused by four mechanisms, including  

In compliance with these mechanisms of adhesion it is essential that release agent has these properties 

The above points show that in spite of the fact that release properties are seemingly easy to understand, the multiplicity of causes demands complex set of properties from a suitable release agent. Also, mechanism is described by a variety of influences falling into four categories listed in the beginning of this section. 

In summary, the original surface quality of a mold, its resistance to wear, and potential for modification of the mold surface by release agent, may affect effectiveness of release agent and quality of products manufactured. 

The interdifiusion in three-layers system (mold-release-molded part) that may affect adhesion of molded part would be rather rare and unexpected development. Only absorption of release agent into the molded part may be considered here and if the timing of this process is not suitable then performance of release agent may suffer. 

In rotational molding, release agent is necessary to aid part removal. Release agents are either polymeric or oligomeric. Polysiloxanes are used widely as mold release agents for polyolefins, polystyrene, polyacetal, nylon, and ABS.copolymers. 

Release agents reduce the coefficient of friction between polymer and surface and prevent sticking. They play a vital role in preventing products sticking during processing. When used in extrusion, they are called slip agents. 

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Analgesic tablets are ground into a fine powder, dissolved in HCl, and analyzed for calcium by atomic absorption. A releasing agent of La + is used to prevent an interference due to the formation of calcium pyrophosphate. 

ALCOHOLS,HIGHERALIPHATIC - SURVEY AND NATURALALCOHOLSMANUFACTURE] (Voll) -as release agents [RELEASE AGENTS] (Vol 21)... 

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