Release internal agents

Some of these processing aids are incorporated into the bulk of the material rather than being directly applied to the surface and are known as internal release agents. In the process of migration to the surface they have an inevitable internal lubrication effect. Most internal lubricants also have an external lubricant effect, particularly at higher concentrations because usually some material finds its way to the exterior. 

They are often blended into compounds that are developed for injection molding applications. Where such an additive is absent, molded components tend to stick to mold surfaces. To prevent this, mold surfaces must be treated between every cycle, or they can be coated with a range of semipermanent mold release treatments. Inclusion of an internal release agent prevents mold surface build-up, surface charring, and simplifies production. Internal mold release agents may include hydrocarbons, alcohols, carboxylic acids, halogenated compounds, ketones, carboxylic acid esters, amides, metal salts, and silicone compounds. 

This paper will discuss silicone internal mold release as a major contribution towards increased RIM productivity. The value of these internal release agents together with the necessary developmental parameters of such agents will be detailed. The paper also presents details of internal mold release agents developed by Dow Corning for polyurethane RIM. Field trial results including paint aging data will be presented. 

Finally, an update on more-recent commercial and experimental Dow Corning internal release agents, including two stream additives will be given. This paper should enable RIM processors to see how useful internal mold release agents can be in their polyurethane RIM process and the benefits they can realize by incorporating internal release agents into their systems. 

Dow Corning has introduced DOW CORNING Q2-7119 Fluid (hereafter known as Q2-7119) as an IMR agent commercially available to the RIM industry. Field evaluations of Q2-7119 in amine and glycol extended systems demonstrated the ability of this functional silicone fluid to act as an internal release agent. Table I shows results of this material as an internal mold release agent in an amine extended system. 

These are 1) a permanent release coating on the mold, 2) an internal release agent added to the reaction mixture, 3) a combination of a permanent base coat with an occasionally renewable top coat, and 4) a renewable release coat applied every cycle or every few cycles. The options are listed in order of desirability from a production point of view. Option 4 is in fact what nearly everyone uses, by necessity. Once Option 4 is accepted, it is reassuring to know that excellent release agents are available which can provide smooth, automatic production. 

Lubricants (may also be used as internal release agents)... 

Loss of torque against time has been well documented with plastic caps on plastic bottles. This does not necessarily mean that the closure becomes ineffective, but there are occasions when a low torque only needs the vibration effects of transportation to become an unsatisfactory (loose/leaking) closure. Certain tamper-evident/resistant features such as sealed diaphragms and ratchet-type closure systems are likely to overcome such problems. Having the right combination of plastics may also eliminate or reduce this loss of torque. However, there is the converse where the use of the incorrect combination of plastics, or plastics with undesirable constituents such as lubricants, mould release agents, internal release agents, may actually exacerbate the loss of closure torque. This loss may be associated with thread forms, area of thread contacts, cold flow or creep of plastics involved, lubricants, etc. 

Uses Mold release agent lubricant and internal release agent for rubber and plastics textile lubricant metal-forming lubricant rust protective... 

Chem. Descrip. Mercapto-functional methyl alkyl silicone polymer Uses Release agent for molded metal, plastic, rubber parts internal release agent tor rubber and plastics metal forming lubricant corrosion-inhibiting coatings... 

P(5) The use of internal release agents in the moulding material shall be avoided or minimised. When such additives are used the level of the adhesion shall be verified by testing. 

The moulding methods discussed typically require the use of internal release agents. These agents weaken the adhesion and therefore lower the load-bearing capacity of the joint. The use of these agents should be minimised, but can seldom be entirely avoided. 

External release agents are lubricants, liquids, or powders, which coat a mold cavity to facilitate part removal. Internal release agents can accomplish the same purpose. The identity of the release agent is rarely disclosed, but frequently they are fine fluoro-polymer powders called micropowders, silicone resins, or waxes. 

Plastic inserts can, and should, be delivered in clean containers and manufactured from grades that contain little or no internal release agents or process aids. This will allow the inserts to be coated with bonding agents without further treatment (see later). Polyamide grades shonld be selected for their mechanical properties and especially with regard to the temperature at which distortion can occnr. 

Siiicones. Although silicones are used as both external and internal mold release agents, the primary application is as the active ingredient in external release agents. The silicone is in a solution or aqueous dispersion that is sprayed intermittently into the mold cavity between shots. A disadvantage of silicones as internal release agents is their possible interference with painting and contamination of finish surfaces. 

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