Paint temperature

Ultimately, sufficient resistance to sag and distortion at on-line paint temperatures to allow on-line painting with the part mounted on the auto. At present shooting for 163 C, but future paint cure temperatures will come down. For initial fenders, automotive is willing to paint off-line. 

The volatility and dissolution properties of the solvent mixture should be adjusted [14.187] so that its parameters move from the solubility boundary to the solubility center of the binder during evaporation. It must, however, be borne in mind that the solids concentration increases during evaporation of the solvent and that the paint temperature increases or decreases, thus altering the solubility range of the binders. Numerous studies have been published on the evaporation of solvent mixtures from paint films [14.188]. 

PC/PBT blends have their fit either in the unpainted grades meeting the retouch oven paint temperatures or in off-line painted applications. PBT/PC blends occasionally will meet the top coat online painted requirement when those do not exceed 14u C. In the years to come one expects that this chart will get more and laore crowded especially in the high ductility, upto 160 C heat area which will be sufficient as car industries develop the all plastic body car no longer requiring the -coat treatment. More new materials based on the here described polymer blends concept are obviously under development. 

Solid, rubbery silicones likewise retain their plasticity at low temperatures and are resistant to many forms of chemical attack they are now incorporated in paints for resisting damp and for waterproofing. Silicones are also used in moulds to avoid sticking of the casting to the mould. 

Chemical bleaching is never used on oils intended for edible use because it oxidizes unsaturated fatty acids to cause off-flavors. However, it does find wide usage for specialty linseed oil, for the paint industry, and fatty chemicals such as sorbitan esters of fatty acids and sodium stearoyl lactylate. Residual peroxide is destroyed by heating above its decomposition temperature. 

A varnish is often appHed on top of the paint layers. A varnish serves two purposes as a protective coating and also for an optical effect that enriches the colors of the painting. A traditional varnish consists of a natural plant resin dissolved or fused in a Hquid for appHcation to the surface (see Resins, natural). There are two types of varnish resins hard ones, the most important of which is copal, and soft ones, notably dammar and mastic. The hard resins are fossil, and to convert these to a fluid state, they are fused in oil at high temperature. The soft resins dissolve in organic solvents, eg, turpentine. The natural resin varnishes discolor over time and also become less soluble, making removal in case of failure more difficult (see Paint and FINNISH removers). Thus the use of more stable synthetic resins, such as certain methacrylates and cycHc ketone resins, has become quite common, especially in conservation practice. 

Wax lining, however, often causes a darkening of the painting, and the adhesive, if it penetrates through the paint layers, is almost impossible to remove. Consequently, much effort has been placed on the development of synthetic adhesives which can be used at lower temperatures and pressures, and use of these materials is commonly accepted as an alternative to wax lining (see Adhesives). 

Cuprous iodomercurate [13876-85-2] Cu2Hgl4, is a bright red water-insoluble compound prepared by precipitation from a solution of K Hgl with cuprous chloride. It is used in temperature-indicating paints because it reversibly changes color to brown at 70°C (see Chromogenic materials). 

Zinc arc spraying is an inexpensive process in terms of equipment and raw materials. Only 55—110 g/m is required for a standard 0.05—0.10 mm Zn thickness. It is more labor intensive, however. Grit blasting is a slow process, at a rate of 4.5 m /h. AppHcation of an adhesive paint layer is much quicker, 24 m /h, although the painted part must be baked or allowed to air dry. Arc sprayed 2inc is appHed at a rate of 9—36 m /h to maintain the plastic temperature below 65°C. The actual price of the product depends on part complexity, number of parts, and part size. A typical price in 1994 was in the range of 10—32/m. ... 

Evaporation Retardants. Small molecule solvents that make up the most effective paint removers also have high vapor pressure and evaporate easily, sometimes before the remover has time to penetrate the finish. Low vapor pressure cosolvents are added to help reduce evaporation. The best approach has been to add a low melting point paraffin wax (mp = 46-57° C) to the paint remover formulation. When evaporation occurs the solvent is chilled and the wax is shocked-out forming a film on the surface of the remover that acts as a barrier to evaporation (5,6). The addition of certain esters enhances the effectiveness of the wax film. It is important not to break the wax film with excessive bmshing or scraping until the remover has penetrated and lifted the finish from the substrate. Likewise, it is important that the remover be used at warm temperatures, since at cool temperatures the wax film may not form, or if it does it will be brittle and fracture. Rapid evaporation occurs when the wax film is absent or broken. 

Because the heat distortion temperature of cured epoxy resins (qv) increases with the functionality of the curing agents, pyromellitic dianhydride is used to cross-link epoxy resins for elevated temperature service. The dianhydride may be added as a dispersion of micropulverized powder in liquid epoxy resin or as a glycol adduct (158). Such epoxies may be used as an insulating layer in printed circuit boards to improve heat resistance (159). Other uses include inhibition of corrosion (160,161), hot melt traffic paints (162), azo pigments (163), adhesives (164), and photoresist compounds (165). 

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