Polyurethane coatings, curing

Thermosetting epoxy and polyurethane chemically-cured liquid resins can provide, among other characteristics, superior abrasion resistance coatings. Solvent-free formulation applied by hot spray techniques can achieve film thicknesses of up to 5 mm. 

With a minimum of analytical measurements, the effect of several parameters on the curing of polyurethane coatings can be studied using the presented model. 

The addition of small amounts of fluorinated polyols to conventional aqueous polyurethane coatings can improve their water resistance and mechanical properties considerably 47 FEVE resins can be applied as water-based coatings and cured at 160°C (320°F) for 25 min to produce coatings with high gloss and good water and weather resistance.48 They may also be cured with water-based hardeners.49... 

The compound (NP[0(CH2)20C(0)C(Me)=CH2]2 3 has been used as UV-curing agent for a polyurethane coating system. Numerous patents cover the... 

Pitch-polyurethane coatings are two-component materials containing polyol as the base resin and an isocyanate curing agent. They cure satisfactorily at temperatures as low as 0°C (BSC, undated). 

This reaction has great significance in the preparation of polyurethane products as it causes chain extension and branching, provides the carbon dioxide necessary for foaming and forms the basis of air curing of polyurethane coatings. 

Moisture-Cured Polyurethanes. Some polyurethane coatings form their protective cured film by reaction with the moisture from the air. The properties of the resulting film are different from two-component polyurethanes, but contain a basic urethane side group that classifies them as polyurethanes. 

Polyurethane coatings are used wherever applications require toughness, abrasion resistance, skin flexibility, fast curing, good adhesion, and chemical resistance. Use include metal finishes in chemical plants, wood finishes for boats and sports equipment, finishes for rubber goods, and rainerosion resistant coatings for aircraft. 

Aircraft coatings normally consist of two coats. The topcoat used for civil aircraft is a high-gloss two-pack polyurethane product, cured with aliphatic isocyanates. Single-coat systems based on thermoplastic acrylic resins have been used for military aircraft, but are being replaced by polyurethane topcoats [11.10]. 

Interfacial aspects and adhesion of polysulfides have been studied extensively and reported by us [3,17]. The epoxy-modified poly sulfide has improved adhesion due to chemical reactions that increase electronic attraction forces. Water has been found to be the most potent debonding agent in cured polysulfides. Formation of thiourethane is responsible for excellent adhesion of polysulfide onto polyurethane coatings. 

In this example radiation euring is eompared with several other eoating teehnologies, sueh as solvent-based two-eomponent polyurethane, acid curing, nitrocellulose and water-based coatings. In the application discussed here, a specific customer use was defined as performance application of 1,000 wooden front doors. 

Chem. Descrip. Fluorosilicone-contg. defoamer in cyclohexanone soiv. Uses Defoamer for spray and brush applies, of soiv.-borne wood coatings (polyurethane coatings, acid-curing coatings, NC lacquers) Properties Colorless clear Iiq. dens. 0.94-0.96 cm (20 C) flash pf. 42 C ref. index 1.445-1.455... 

TABLE 6.2 Residual Internal Stresses In Polyurethane Coatings Based on TMP-TDI and THF-PO (NCO OH = 2 1) Containing Modified Filler, 48 h after Curing at 353 K... 

Types of liquid coatings used include, among others, acrylics, epoxies, PVC plastisols, polyesters and polyurethanes. Coatings must be easy to apply, have a very short cure time and be flexible enough to enable the coated metal to be bent or formed without cracking or suffering loss of adhesion of the paint film. 

Phenolic compounds react with isocyanates to form phenylurethanes (equation 24). This reaction is important in fast curing foundry resins [94], in single component polyurethane coatings, and in polyester powder coatings crosslinked by phenylurethanes. Phenylurethanes dissociate into the isocyanate and the phenolic compound at temperatures higherthan 180°C [95,%]. 

Polyurethane coatings are cured by reaction with isocyanate or copolymerized with alkyds and then cured by atmospheric oxygen. 

Uses. Acrylics, both lacquers and enamels, were the topcoats of choice for the automotive industry from the early 1960s to the middle 1980s. Thermosetting acrylics are still used by the major appliance industry. Acrylics are used in electrodeposition and have largely replaced alkyds. The chemistry of acrylic-based resins allows them to be used in radiation curing applications alone or as monomeric modifiers for other resins. Acrylic-modified polyurethane coatings have excellent exterior durability. 

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