External Mold Releases

This problem was approached from the material side, through a search for suitable internal releases, and through the development of improved external mold release compounds. From the equipment side, the development of automatic molds was required if the RIM process was to compete with classical injection molding with respect to mold cycle times and efficient production. 

Staff Written, "Special Report - Chemicals and Additives -External Mold Release," Modern Plastics, 69(9) 94-96 (September 1991). 

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. 

External mold release 1s a raw material consideration for only PU-RRIM and 1s estimated to contribute 0.20 to the overall part cost. 

Examination of the economic data Indicates several specific areas where PU-RRIM 1s penalized, among them are long cycle time, process Inefficiency (down time for mold clean), scrap, and the need for external mold release. These factors result in higher labor, unit capital and tooling costs for PU-RRIM when compared to Injection molding. This situation provides a challange to make PU-RRIM more economically viable. 

Such RIM IMR technology has been developed by Dow and 1s 1n the final stages of production qualification at major RIM molders. While the details of this technology are beyond the scope of this paper, the impact of an effective IMR on RIM economics can be addressed. This data 1s shown on "Table X", where one can see cycle times reduced from 120 seconds to 90 seconds the elimination of nonproductive mold cleaning time and the elimination of scrap resulting from external mold release buildup. The reduction in part cost 1s significant the unit cost for the body panel is reduced from 11.72 to 9.55 for an 18.5% production cost reduction. 

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... 

The problems surrounding part quality, while not always identified in a quantitive way, are certainly inherent in the use of external mold release sprays. A self-releasing system, made possible by the incorporation of an internal mold release agent in polyurethane chemicals offers a possible way of eliminating, or at least, minimizing the problems akin to external release methods. 

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. 

Table IV. Relationship of the Average Cycle Time for n Consecutive Releases ta, and the Number of Releases Between External Mold Release...

Figure 2. Averaged cycle time for n consecutive releases obtained as a result of eliminating the time necessary to apply external mold release spray.

External mold release was still necessary, but only every so often - as little as once every 300 cycles or so, or as often as once every 25 cycles. All In all, not often enough to be a factor In cycle efficiency. For this series, productivity Improvements ranged from a worst case of 33% to a best case of 140%, with the range 50% to 75% being typical. The values are significant. 

Moldwiz [Axel], TM for external mold release agents that are advanced polymeric formulations. 

External mold releases, sprayed onto the mold and not added to the compound itself, can still be valuable tools. These solutions are water- or solvent-based, and when applied condense into a semi-durable, heat-resistant film on the hot mold that may allow dozens of part releases or more before having to be reapplied. However, if an external agent has to be used repeatedly during a production run, it can interfere with productivity, making a mold-rdease lubricant added to the resin itself the more cost-effective approach [11-3,11-13],... 

Thermoplastics internal external mold releases, supplier product guide. Axel Plastics Research Laboratories, Inc. 

Chem. Descrip. Proprietary resin in aliphatic hydrocarbon solv. blend Uses External mold release for polyester, vinyl ester, and epoxies for open molding, cast polymers, cultured marble, and parts requiring exc. finishes... 

Aqualift, Water-based external mold releases, FranMynn Industries... 

Part release Once the resin is cured and the part is solidified, the part is removed from the mold with the aid of ejector pins. Then, the part is cooled down outside the mold, while the mold surfaces are cleaned, and an external mold release agent is applied to the mold surfaces for the next molding cycle. 

After removal from the press, the mold or picture frame sandwich is allowed to cool before opening (using brass implements). It is, therefore, useful to have several picture frame molds of comparable dimensions. The best precision in physical property measurement is obtained by allowing the molded sheet to relax at room temperature for a set period of time, often 24 hours. After opening the mold, the sample should be observed for evidence of surface bleed from excess external lubricant. (With compounds intended for metal adhesion, it may be necessary to use an external mold release coating. Those based on FIFE are effective with vinyl compounds and tend not to interfere with subsequent testing. Silicone-based mold releases, if used, should be of the type that is heat-cured to the mold, rather than migratory.)... 

Features Eliminates need for external mold release Regulatory FDA approved for food contact... 

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