External mold release, application

Productivity factors are shown 1n Table IIWith today s technology, 1t 1s possible to operate both SMC and Injection molding clamps during an entire shift. However, because RIM requires frequent application of an external mold release, approximately one hour per shift 1s required to perform both major and minor cleaning of the tool. Thus for RIM, only an 87.51 process efficiency was assumed. 

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... 

Thus, to eliminate or minimize chemical adhesion the metal mold surfaces must be protected from polar materials such as polyurethanes by an interface which not only avoids the physical problems of adhesion, but those which are of a reactive chemical nature as well, i.e., a non-wetable, non-polar, non-reactive boundry layer or film. In terms of releasibility, therefore, such a boundry between the metal mold surface and the polyurethane must be present. It makes no difference whether this is achieved by the application of an external mold release (EMR) agent, or though the incorporation of an internal mold release (IMR) agent. 

The external mold release agents must be applied at regular intervals, and during the time of their application, the mold is unavailable for production. Fine grooves etched into the mold gradually become covered with residues of mold... 

Antistats function to either dissipate or promote the decay of static electricity. Secondary benefits of antistat incorporation into polymer systems include improved processability and mold release, as well as better internal and external lubrication. Therefore, in certain applications, antistatic agents can also function as lubricants, slip agents, and mold release agents. 

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. 

There are numerous suppliers of lubricants and mold release agents as a result of the variety of chemistries that perform the function of internal and external lubrication. The suppliers are generally large specialty chemical companies that sell the particular chemistry to a wide variety of end-use applications. The amount of material sold to fimc-tion as a lubricant or mold release agent for plastics is typically small in comparison to each company s total sales. Table 4.19 shows the major global suppliers of lubricants and mold release agents by type. 

Metallic soaps and salts of stearic acid and other organic acids are used both as lubricants and as auxiliary heat stabilizers. Metallic stearates are the most widely used lubricants. They are predominantly used in PVC, but also find use in polyolefins, ABS, polyesters, and phenolics. The primary disadvantage of metallic stearates is their lack of clarity. Calcium stearate, the most common metallic stearate, is primarily used as an internal lubricant, but in PVC applications it provides external lubrication and mold-release characteristics while also acting as a heat stabilizer. In addition to PVC, the calcium sterarates go into polypropylene, polystyrene, and ABS. Zinc stearates are used in crystal and impact polystyrene, ABS, and phenolics. 

There are numerous suppliers of mold release agents as a result of the variety of chemistries that perform the function of internal and external release. The suppliers are generally large specialty chemical companies that see the particular chemistry to a wide variety of end use applications. 

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