Nylon system molds

Third, the gel times of nylon systems are much longer than those of urethanes, typically on cue order of 45 to 120 seconds, versus 5 to 30 seconds for urethanes. There are several reasons for this. First, the polymer is soluble in the monomer until very high molecular weights are attained. Second, the reactants are typically held at temperatures 30 to 90°F lower than the mold temperatures for reasons of energy conservation and product stability. At these temperatures, polymerization rate is low and pot life of the mixed stream is on the order of 5-10 minutes. For optimum physical property generation, part surface quality and release from the tool, nylon RIM molds are normally run at temperatures between 250 and 325°F. At these temperatures, gel times are typically 30 to 60 seconds for parts of about 1/8-inch thickness. Thus, part of the gel time difference is the time reauired for the reactants to rise to mold temperature by conductive heating. 

FIRE RETARDANT FILLERS. The next major fire retardant development resulted from the need for an acceptable fire retardant system for such new thermoplastics as polyethylene, polypropylene and nylon. The plasticizer approach of CP or the use of a reactive monomer were not applicable to these polymers because the crystallinity upon which their desirable properties were dependent were reduced or destroyed in the process of adding the fire retardant. Additionally, most halogen additives, such as CP, were thermally unstable at the high molding temperatures required. The introduction of inert fire retardant fillers in 1965 defined two novel approaches to fire retardant polymers. 

Heat-cleaned fiberglass cloth was treated with 0.5% carboxysilane J (Table 1) and compression-molded into a laminate with nylon 6,6 polymer. Laminates were compared to state-of-the-art silane H. Table 9 shows that silane H provided a significant improvement in flexural strength over the control, expecially after a 2 h water boil, but a carboxysilane/zinc ion ionomer system gave an even better strength improvement. 

These solvent system tipping products provide Nylon tips to Nylon cord with proper heat/mold procedures. 

The successful utilization of Reaction Injection Molding (RIM) to fabricate complex polyurethane shapes In a single step from relatively low viscosity streams has led to a search for other chemical systems which can be fabricated by the RIM process. The rapid polymerization of molten caprolactam by anionic catalysis has been utilized to develop attractive nylon RIM systems. The incorporation of a rubber segment In the polymer chain allows the fabrication of high Impact or even elastomeric nylon parts. The combination of a rubber phase with the high melting (215°C) crystalline nylon phase provides useful properties at low temperatures as well as at elevated temperatures. 

Anionic polymerization of nylon-based polymer systems to produce finished parts directly from monomers or prepolymers can be carried out by several processes e.g., reaction injection molding, low-pressure casting, resin transfer molding, rotational casting. 

Nylon-based RIM systems differ from urethane RIM systems in several important aspects which impact the design of RIM equipment and the molding process conditions. 

First, the monomers found most useful for nylon RIM systems are E-caprolactam and lauryl lactam. Unlike the liquid polyol and isocyanate materials in common use in urethane RIM, these materials have melting points of 158°F and 320°F respectively, making them solids at room temperature. Thus, nylon RIM equipment must have heated tanks, pumps, lines and molds. In commercial practice, this is accomplished by jacketing the equipment with circulating hot oil or water systems, by enclosing the hardware in temperature-controlled ovens or by electrically tracing the equipment with resistance heating hands and tapes. The first two methods are preferred because of their uniformity of control and lack of hot spots. 

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 last major difference between urethane and nylon RIM systems lies in the extent of cure obtained in the mold. Many urethanes are polymerized just far enough in the mold to generate sufficient green-strength for demolding and handling the part. Parts are then oven post-cured to complete the reaction before atmospheric moisture reacts with the residual isocyanate In the part. Nylon RIM parts are fully cured in the mold. 

Molds for nylon RIM systems can be made from a wide variety of materials including steel, aluminum, klrkslte and nickel. Chrome and nickel plating has also been widely used to improve the scratch resistance of molds made of softer materials. At this writing, no epoxy tooling system has been demonstrated that will produce more than a few parts before failing. Development work continues in this area. 

In contrast to urethane casting systems, open-topped molds cannot be used for all parts. Inhibitation of polymerization at the exposed surface of the nylon reaction mix by moisture in the air will produce a tacky surface. If this is to be machined off to produce a finished part, open topped molds may be used. 

Polyurethane RIM systems have been commercial in the United States for about 50 years and a bit longer in Europe. It is still a rapidly growing field of technology. The automotive industries in the United States account for most of the commercial RIM production. A later development for RIM polyurethane, and to a lesser extent RIM nylons, is the application for housings of various instruments and appliances computer housings, business machine housings, TV and radio cabinets, instrument cases, and similar electronic product enclosures. While elastomeric RIM is most commonly used in these applications, some housings are also molded fi-om RIM structural foam. 

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