Pretreatment sprayed coatings

A low acid polyvinyl butyral-based pretreatment primer ( etch or wash primer are alternative names) is usually advantageous as the first treatment of a metal-sprayed surface before painting. Up to an equal volume of spirit soluble phenolic resin is used as a diluent to the polyvinyl butyral of conventional pretreatment primers. This has an incidental, but particularly valuable effect, in reducing the free acid available to penetrate into the pores of the coating. The modified pretreatment primer is highly water resistant and this helps to avoid damage due to condensation. 

First comes the pretreatment stage. After rust removal and alkaline degreasing, a zinc phosphate formulated pretreatment (see Section 15.2) is applied by dip or spray-dip. Crystalline iron-rich zinc phosphate forms on the metal surface at a coating weight of 0.5-4.5 g/m. ... 

Electrostatic spray Charged particles are sprayed on electronically conductive parts process gives high paint utilization more expensive than conventional spray. Spray gun, high-voltage power supply pumps dryers Pretreating station for parts (coated or preheated to make conductive). 

Our electrochemical work differed drastically from the Groseclose work in that polymer coated metal samples were employed. Furthermore, we found that coatings can have corrosion resistance when their rest potentials are either more noble (B210/NVP) or less noble (B210/GBL) than the uncoated substrate. Leidheiser (22,23) examin zinc phosphate pretreated panels with automotive primer after 10 days exposure to the salt spray. The start and finish rest potentials of the samples with good paint performance were consistently more negative than those samples with poor paint performance ... 

Figures 31.23 and 31.24 show typical scanned images of SO2 and Prohesion salt spray-tested [7B] panels, respectively. Visual observation of these images reveals that the plasma-modified panels of [7B] have outperformed both control panels in the SO2 salt spray test. These plasma film combinations were prepared on deoxidized [7B] surfaces without any plasma cleaning pretreatment. Figure 31.23 also shows an image of a panel that had simply been deoxidized prior to the application of E-coat, which performed excellently in the SO2 salt spray test. Figure 31.25 compares the corrosion width obtained by the two methods. The comparisons shown in Figures 31.19, 31.22, and 31.25 indicates that the results obtained by the two methods do not match, partly due to the different duration of tests, and that samples which show good results in one test do not do as well in the other test.

The coating is two-component and needs mixing on-site prior to application. It can be applied either using conventional airless spray equipment or by brush or roller. A final thickness of 1 mm to 2 mm can be obtained with two coats. Pretreatment of the substrate with an epoxy primer ensures good adhesion. Defects in the concrete or brickwork are sealed with an elastomeric sealant which is resistant to the fluid being stored in the tank. 

A great store of information has been accumulated on the effectiveness of WRPs in protecting exterior wood (J, 117-119, 121, 122, 124-129). The treatments can be applied by vacuum impregnation, by immersion (which is preferred), by brush, or by spray application. They improve the performance of many finishes applied over them and add greatly to the durability of exposed wood. Even chipboard or particleboard, which is very susceptible to moisture, can be protected quite effectively against the effects of outdoor exposure by using a WRP pretreatment followed by a diffusion-resistant coating 126, 130-133). 

Salt-spray data (for nos. 1 and 2 in Table V) indicated that, on zinc-phosphated steel, cathodic ED indeed led to considerably better corrosion resistance. On bare steel, however, both cathodic and anodic coatings failed completely. Further, we prepared a number of different, amine-modified epoxy resin esters containing between 30 and 50 %w of drying fatty acids (e.g. no. 3 in Table V). These could all be deposited cathodically and again attained excellent salt-spray ratings on phosphated steel but performed poorly on bare steel. We concluded that cathodic ED prevents phosphate layer degradation (a well-known phenomenon with anodic ED) and thus leads to superior corrosion resistance on pretreated steel. On bare steel the binders performed too poorly to allow comparison between cathodic and anodic ED. 

Metallic objects are first cleaned to remove impurities and materials associated with metal forming, welding, temporary rust protection, etc. In many instances phosphate and/or chromate treatments are applied. Overall, any electrically conductive surface preparation will impart benefits to electropainted articles similar to the benefits imparted to spray painted or dip-coated articles. The workpieces go from pretreatment to the electrocoating tank either water wet or dried. 

Brown SR, Turner IG, Reiter H (1994) Residual stress measurement in thermal sprayed hydroxylapatite coatings. J Mater Sci Mater in Med 5 756-759 Brown WE, Chow LC (1983) A new calcium phosphate setting cement. J Dent Res 63 672 Browne M, Gregson PJ (2000) Effect of mechanical surface pretreatment on metal ion release. Biomaterials 21 385-392... 

Stoved acrylic resin films are generally applied as single coats which requires careful pretreatment of the metal surfaces by cleaning and phosphating. The paints are applied by electrostatic spraying using rotating bells or disks. 

Spray gun, high-voltage power supply pumps dryers. Pretreating station for parts (coated or preheated to make conductive). 

These two-pack cold-cure solvent-borne coatings have excellent durability and abrasion resistance. They are designed for spray applications on steel, aluminium and light alloy surfaces wMch have been suitably pretreated. Base and hardener are mixed in 3 1 or 5 1 ratios as recommended by the manufacturer and the pot life is around 2 hours under normal working conditions (20 C) and should not be used after the stated time. Polyurethane/acrylic resin combination is also available. Two-pack polyurethanes are widely used in veMcle body repair and can contain isocyanate which is a basic constituent in the production of polyurethane and is the most common cause of industrial asthma and it is also a skin irritant. It should be easily identified by a label on the container which should say contains isocyanates, harmful by inhalation and in contact with skin . Waterborne two-pack polyurethane finishes are available. 

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