Melamine-phenolic molding compound

Figure 14.17 Granules of a melamine-phenolic molding compound.

Glass flber-relnforced thermosets based on unsaturated polyester (UP resins), phenol-formaldehyde molding compounds and laminates (PF), and melamine-formaldehyde molding compounds and laminates (MF) are not attacked by termites [32]. 

The most common and widely used thermoset molding compounds are classified as follows (a) alkyd, (b) allylic (diallyl phthalate), (c) amino (melamine and urea), (d) epoxy, (e) phenolic, (f) polyester, and (g) silicone. There may be other specialty thermoset resin materials used on specific applications. 

Straight melamine-formaldehyde resins are used primarily in the preparation of molding compounds, laminates, and textile finishes. Nearly 90% of these molding powders are used to make dinnerware. Melamine dinnerware can be made very decorative for popularity. This resin has better physical properties than phenolics and it can be very easily colored, which phenolics cannot. Methylolmelamine also is used as a synthetic tanning agent for white leather. 

Phenolic molding scrap is accepted back by some producers for re-use as filler in new compounds. Similarly, amino plastics (urea and melamine) present no problems in disposal or re-use when ground up. Molders have reused as much as 20 AVt% ground scrap with virgin molding compounds in injection molding and those who have adopted the technique have foimd it an effective method for recycling in-house scrap, but for sub-surface parts only. 

The most important resin types used in production of curable molding compounds are phenolic, urea, melamine, unsaturated polyester, epoxide and diallyl phthalate resins. Curable molding compounds built up with these bonding agents are described in DIN 7708" (Phenoplasts and Aminoplasts), DIN 16911 and 169132 (Polyester Molding Compounds and Polyester Resin Mats), and DIN 16912 (Epoxy resin Molding Compounds). There is as yet no standard for diallyl phthalate masses, for the test method see ISO 1385 - 1.02.1977. 

When processing (CM, injection molding, extrusion, ICM, etc.) from uncrosslinked (A state) or crosslinked (B state) duroplastic molding compounds, the shearing forces applied upon injection through dies impose orientations upon the macromolecules and, if any are present, upon the reinforcing fibers as well. Because of the low viscosities of uncrosslinked masses such as phenolic, melamine, UP and epoxy resins and the hot mold wall, relaxation of the molecular orientations sets in quickly. As a rule, duroplastics show little or no orientation. Crosslinking fixes this state. 

Melamines. Melamine was isolated in 1834 and it wasn t until 1933 that Palmer Griffith produced dicyanamide and found that it contained melamine. The addition of formaldehyde produced a resin which could be compounded into a desirable molding compound. This new compound had a number of desirable quahties superior to phenolics and ureas of that time. The colorability and surface hardness led to its use in molded dinnerware along with some very important military and electrical applications. 

Note Combinations of phenolic and melamine resins in molding compounds have produced materials with excellent color stability, ease of moldability, and good heat resistance. Their usage is in appliance components such as pot or pan handles. 

Phenol formaldehyde, PF urea formaldehyde, UF melamine formaldehyde, MF. Applications molded pieces, granulated molding compounds (GMCs), bulk molding compounds, dough molding compounds... 

Phenolic resin (PF) is the technically most important representative of the class of condensafion resins, ft is created in several process steps from the monomer base materials carbolic acid and formaldehyde. Here, we distinguish between resols and novolacs. Phenolic resins are often processed in the form of free-flowing molding compounds under pressure at elevated temperatures individual cases of liquid processing are also known. Melamine resins, urea resins, and furan resins are also condensation resins created from formaldehyde. 

Bulk Molding Compoimd, BMC, (Dough Molding Compound in Europe) is produced by first mixing pre-catalyzed liquid resin with fillers, mainly calcium carbonate and talc, in a heavy duty low speed sigma blade mixer. This is compression molded at 500 psi and 300 to 400°F. The resin most commonly used is unsaturated styrene-diluted polyester. Other BMC resins are alkyds, phenolics, urea, melamine, diallyl phthallate, silicones and epoxy. All are highly filled with calcium carbonate, talc, mica or alumina to improve mechanical properties and reduce shrinkage. 

Fillers in Thermosets. Sixty-five years ago, in a paper presented before the American Chemical Society, L. H. Baekeland (55) discussed the usefulness of phenol-formaldehyde resins that, when compounded with wood flour, could be molded. Wood flour, ground nut shells, a-cellulose, or paper add bulk to phenolics, melamine, or urea-formaldehyde resins and make them easier to fabricate and less expensive. 

Spiral flow (test and mold). There are two types of spiral flow molds— one for the very soft flow encapsulation compound generally associated with the encapsulation grades of the epoxy family of compounds and a spiral flow mold, which is used when testing the high-pressure phenolic, DAP, melamine, urea, epoxy, and thermoset polyester com-poimds. 

The applications of UFs include sanitary wares such as toilet seats, and knobs, closures, buttons, electrical accessories like housings and switches, laminates, and so on. Compounds of UFs use different additives, fillers, and reinforcements to provide different characteristics and permit processing in different equipment, principally by compression, transfer, and injection molding. Like many other TSs, such as the phenolics and melamines, they are easily preformed and preheated, either by RF preheaters or with screw... 

---