Gel-coat formulations

In addition to electrical uses, epoxy casting resins are utilized in the manufacture of tools, ie, contact and match molds, stretch blocks, vacuum-forrning tools, and foundry patterns, as weU as bench tops and kitchen sinks. Systems consist of a gel-coat formulation designed to form a thin coating over the pattern which provides a perfect reproduction of the pattern detail. This is backed by a heavily filled epoxy system which also incorporates fiber reinforcements to give the tool its strength. For moderate temperature service, a Hquid bisphenol A epoxy resin with an aHphatic amine is used. For higher temperature service, a modified system based on an epoxy phenol novolak and an aromatic diamine hardener may be used. 

The unsaturated polyester resins used to produce gel-coat formulations can be classified into three categories, i.e. orthophthalic-, isophthalic- and neopentyl-glycol-based. The first two types are used in perhaps two thirds of all... 

The traditional precursors for sol-gel reactions have been metal alkoxides. In most of the sol-gel coating formulations, metal alkoxides/organofunctional metal alkoxides are used either alone or in combination with a conventional polymer capable of participating in sol-gel reactions. Sol-gel reactions start with a solution of monomeric metal or metalloid alkoxide precursors M(OR) in an alcohol or other low-molecular-weight organic solvent. Here, M refers to a network-forming element such as Si, Ti, Zr, etc, and R is typically an organic moiety. " ... 

A series of PANI/sol-gel coating formulations have been applied to an AA2024-T3 substrate and evaluated using electrochemical and salt spray tests. Comparison of the corrosion protection performance of these coatings was made with bare and sol-gel only coated samples. 

The weatherabihty and hydrolytic stabiUty of unsaturated polyesters based on neopentyl glycol have made it a popular intermediate for use in formulations exposed to severe conditions, eg, in gel coats for cultured marble and marine appHcations (see Coatings, marine) (13). 

Gel coat Specially formulated polyester resin that is pigmented and contains fillers. Provides a smooth, pore-free surface for the plastic article. 

Gel lacquer formulations used for dip coating. The early catapult propellants were inhibited by dipping in a lacquer consisting of toluene 80p, acetone 20p and a total solids content of 15-18%. The grains were dipped twice and had a cured inhibitor thickness of 20 to 30 mils. As the size of experimental slotted tube catapults increased, coatings of 100 mils were required. This necessitated an increase of the solid content to 25-27%. As this soln was too viscous some methylol was incorporated in solvent formulation. In order to improve the room temp gelling characteristics an aliphatic hydrocarbon was added... 

Taylor, D.J., and Bimie, D.P., 111, Striation prevention by targeted formulation adjustment aluminum titanate sol-gel coatings, Chem. Mater., 14, 1488, 2002. 

Also here the formulator must carefully select what kind of silica should be used. In the reference coating formulation (Table 6) precipitated silicas perform better than silica gels. 

Uses Leveling agent for gel coats based on unsat. polyester resins and in solv.-free epoxy resin systems air release agent in PU resins Properties Colorless clear liq., nonspecific odor insol. In water sp.gr. 0.95 dens. 7.93 Ib/gal vapor pressure 3 mm Hg (20 C) b.p. 160-185 C (solv.) flash pt. (Seta) 45 C ref. index 1.480 51% NV Use Level 0.5-1.5% (on total formulation)... 

Frequently, to provide resistance to weathering, erosion, or chemical attack, a resin-rich surface coat (gel coat) is added. This surface layer is applied first and then allowed to stiffen into a tough layer (not cured) before additional layers are applied. It usually is reinforced with a surface veil using C-glass (rather than the usual E-glass) if chemical resistance is required, or a synthetic fiber veil may be used for resistance to weather, particularly sunlight. The resin may be a special formulation that includes TP to improve the surface appearance. Subsequent layers of mat, fabric, or combinations are then applied. 

This refers to an open mold technique used for the production of many articles where the resin and reinforcement systems can be tailored to meet specific end use requirements. Typical products produced by this method are skis, boat hulls, tubs, and shower stalls. The molded cavity is sprayed with a gel coat to a desired thickness to produce a desired surface finish or color. The reinforcement, which is usually glass fibers, mats, or sheets, is then hand rolled to secure proper wetting of the fibers as well as the required wall thickness. The final curing takes place through the use of a catalyst or hardener reaction. Matched metal molds are often used with hand lay-up formulations in order to achieve high quality surface finishes on both sides of the molded article. 

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