Coated mold surfaces

The coated mold surface will have low friction so that it basically has no shearing for the surface bubble. Depending what kind of coated layer some of them act as thermo insulator. In this way, the part surface will be soft enough so that even if some surface bubbles appear the injection pressure will repair them. However, this method may leave the flow free front as the possible problem for rough surface in the end of filling unless the injection is fast enough. 

The hand lay-up or spray-up process, used universally for the production of laminar composites incorporating glass fiber reinforcement, is most efficient for the manufacture of large parts, such as boats, bathtubs, tanks, architectural shapes, and recreational accessories. Resins intended for spray-up processes are usually modified with thixotropic additives, such as fumed siHca (1%), to reduce the risk of drainage when appHed over large vertical mold surfaces. Molds are also made from ERP for short-mn products usually surfaced with a tooling gel coat to provide consistent surface quaHty and appearance. 

Gel coats are pigmented polyester coatings appHed to the mold surface and are an integral part of the finished laminate. Gel coats are used widely on hand lay-up and spray-up parts to enhance surface aesthetics and coloration as weU as to provide an abrasion-resistant waterproof surface that protects the underlying glass-reinforced stmcture. 

A special attribute of these processes is the abiHty to pre-position reinforcement, inserts, and core materials for stiffening ribs. Gel coatings can be apphed to the mold surface to eliminate post-mold finishing. Because both surfaces of the part are formed in a mold to close tolerances, accurate assemblies are possible, which is a requirement for many automotive or tmck body appHcations. 

Unsaturated polyester resin powders can provide a colored and finished exterior molded surface or a finish ready for painting. Normally, a primer/sealer must be appHed to molded articles prior to painting. In addition to the unsaturated polyester resin, multifimctional unsaturated monomers such as triaHyl cyanurate (TAC) [101-37-1] or diaHyl phthalate (DAP) [131-17-9] suitable peroxide initiators (qv) or mixtures thereof, and mold release agents (qv) are used to formulate the coating powder (46). 

For RRIM-based composites, the main benefit is the case with which the properties can be varied across a wide range. Decorative finishes can be applied to RRIM molding by painting or, where color matching between components is less important, by self-coloring. However, color coating of the mold surface prior to RIM provides a better finish. 

After cooling, the final part is removed and the mold is recharged with resin. Since the mold surfaces are often complex, processors commonly apply mold release agents to allow the part to demold. Mold release agents are lubricants that coat the metal surface with a waxy material preventing the polymer from adhering to the mold s surface. Examples of mold release agents include silicone sprays or olefin based waxes. 

Electroforming. The reproduction of an object or a pattern by electro deposition (See under Electrochemistry). A mold of the object to be reproduced is made in a soft metal or in wax (by impression). The non-conductor mold surface is made conductive by coating with graphite. Some suitable metal is then deposited electro lyrically on the mold surface. This mold is then (in most cases) a negative of the object to be produced. Most extensive use is in the phonograph record industry Ref GondChemDicc (1961), 434-R... 

Removal of the article from the mold is lengthy process because anti-adhesive lubricants have to be sprayed on the on a mold surface before every injection, in an operation that takes up to 25 - 30% of the full cycle. In reactive molding of polyurethane-based compounds, internal lubricants are used in combination with surface coatings. This allows us to remove articles from a mold many times with a single coating treatment. One of the compounds used as an internal lubricant is silicon-organic liquids. 

Slush Molding. This is the reverse of dip molding. A female mold is used to give any desired surface finish on the product. The mold is preheated, plastisol is pour into it, and gels onto the surface of the mold. The excess liquid plastisol is poured out, and the internally- coated mold is heated to gel, then cooled to solidify the rubbery product, and the product is stripped out of the mold. Typical products are arm rests, head rests, road safety cones, anatomical models, dolls, toys, and auto parts. 

The vinyl acetate content of such materials ranges between 3 and 40%, and the copolymers are more soluble and pliable than poly(vinyl chloride) homopolymer. They can be shaped mechanically at lower temperatures than homopolymers with the same degree of polymerization and are used mainly in surface coatings and products where exceptional flow and reproduction of details of a mold surface are needed. 

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. 

The article, which is usually in the form of an impregnated fabric, is laid-up on a mold or a base plate (Figure 6.65 and 6.66) which defines the surface shape of the article. A release agent is applied to the mold surface to prevent adhesion of the part to the mold. A release film, such as a fluoropol5mier typically a fluorinated ethylene propylene copol5mier or a glass fabric coated with polytetrafluoroethylene is often the next layer. Other films such as nylon or polyester can be used where release is less demanding such as lower cure temperature resins. 

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