Silicone Internal mold release

Improved RIM Processing with Silicone Internal Mold Release Technology... 

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. 

Although many fluids can be developed to act as IMR for RIM, many would fail as commercial products due to their inability to impart paintability to the resulting molded part. In order to rectify this paintability concern with the use of silicone internal mold release agents, a functional moiety is designed into the silicone. This functionality, when correctly specified, reacts into the urethane matrix once the IMR has migrated to the urethane/mold interface. This reactivity causes the IMR to be immobilized in the urethane matrix, thus allowing paintability. 

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. 

Internal mold release technology is well developed for nylon RIM systems while it is being developed for urethanes. Most urethanes require application of a mold release agent, a wax, a soap or a silicone, after every shot. Many mold releases cannot be added to the urethane reactant streams or the tanks because they react with the urethane chemicals. These reactions have caused problems of build-up in the mold, even with spray-on mold releases, necessitating periodic shutdowns to scrub the mold surfaces. Some newer systems use a third component stream to Introduce mold release at the mix head. Newer Internal mold release systems permit from 0 to 50 urethane shots to be made between applications of external mold release spray to the tool. Monsanto s nylon RIM system contains an internal mold release that is paintable. In certain applications where a high quality smooth show surface is required on a part, a... 

Figure 2 illustrates how the tailor-made silicones function as IMR agents in RIM molding. Due to the known surface tension reduction phenomenon of silicone fluids in urethanes and the differences In surface tension at the urethane/mold interface, internal mold release agents based upon silicone molecules can be developed to selectively migrate at different rates to the urethane/mold interface. There, it will orientate itself to build a protective layer which decreases the ability of the urethane to wet-out the mold surface. The inability of the urethane to wet-out the mold surface will facilitate release. 

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. 

Figure 2. How silicone-organic hybrid fluids function as internal mold release agents.

Uses Interm iate for synthesis of silicone/org. copolymers used in textiles, coatings, detergent-resist, car polishes, lubricants, coating formulations, cosmetic and personal care applies, ind. hair care mold release agent for rubber, plastics, foundry applies. internal mold release Features Good heat stability... 

Chem. Descrip. Amine functional silicone fluid Uses Silicone for prod, of silicone-org. copolymers for use in textiles, rust-inhibitive coatings, detergent-resist, car polishes internal mold release lubricant... 

Chem. Descrip. Amine functional silicone polymer Uses Silicone for prod, of silicone-org. copolymers for use in textiles, rust-inhibitive coatings, detergent-resist, car polishes rubber and plastic mold release internal mold release lubricant Features Compat. with dimethyl silicone fluids, aliphatic and aromatic hydrocarbon soivs. good heat stability high amine-alkyl content Properties Colorless to It. straw, clear to hazy liq. sp.gr. 0.98 dens. 8.0 Ib/gal vise. 450 cSt amine no. 110 flash pt. (PMCC) > 200 F 100%. act. Toxicology Alkaline material prevent contact with skin, eyes Storage Stable indefinitely in closed containers store below 100 F moisture-sensitive keep container tightly closed do not weld or cut drum, even when empty... 

Classification Amino functional silicone Uses Polymer modifier for epoxies and urethanes internal mold release agent for... 

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. 

Witco internal mold release agents are an alternative to spray-on release agents. They provide a consistent, predictable amount of release without the drawbacks of fluorocarbon or silicon spray-on release agents. Kemamlde E Ultra fatty amide is recommended for polyethylenes. Atmul 84, Atmos 150, and Olmul S additives provide a combination of mold release and antistat for polypropylene. Kemamide AS-974, AS-974/1, and AS-989 fatty amines provide a combination mold release and antistat for polyethylenes. 

Croda Polymer Additives IncroMold additives provide internal filler and glass-fiber lubrication and mold release in one case, 0.45% additive in a 30%-glass-fiber, carbon-black-pigmented PP automotive molding reportedly increased output by 20% and eliminated the need for a silicone spray-on mold release [11-24]. 

Chem. Descrip. Methyl all laiyl silicone fluid Uses Release agent for mold metal, plastic, or rubber pads, foundry applies. internal lubricant for rubber, vinyl plastisols die lubricants paint additive... 

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... 

Chem. Descrip. Methyl alkyl dimethyl silicone fluid Uses Surf. tens, reducer for nonaq. solv. and oil systems wetting agent, leveling agent in inks, coatings, plastisols antifoam mold release agent internal release agent for plastics and rubber textile lubricant Properties Straw cl. liq., odorless sol. in aliphatic, aromatic, and chlorinated soivs. sp.gr. 0.94 dens. 7.8 Ib/gal vise. 100 cSt flash pt. (PMCC) > 300 F 100% act. 

A 100% active organo silicone wax copolymer. This unique product is recommended for use as a lubricant, mold release agent and internal lubricant for plastics. 

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