Of urethane coating

Fig. 5. Cross-sectional view of urethane-coated fabric with coagulated polyurethane layer.

The production of coated fabrics including vinyl- and urethane-coated in the early 1980s is shown in Table 3 (4). Only production in the Far East showed an increase. The increase of urethane-coated fabrics mainly supports this tendency (Table 4). 

RNA and DNA, and to study the effects of phosphorylation state and charge on the results. " In the polymer field. Berry et al. used BDE calculations for model alkyl urethanes to identify vulnerable sites to radical attack, and to examine the effect of branching on the photostability of urethane coatings. ... 

Other Urethane Coating Components Types of Urethane Coatings... 

An important application of urethane coatings is in the fabric coatings field. The terra "wet look" was very fashionable for some time and was applied to highly glossy urethane coatings and was later succeeded by the "suede look." These types of coatings were applied to apparel but were also employed in furniture fabrics. 

Indications are that both oxidation and ultraviolet radiant energy may be involved in the processes responsible for yellowing of urethane coatings based on aromatic isocyanates. 

Isocyanate-Terminated Adducts and Polymers. Monomeric diisocyanates such as TDI, MDI, or Hi2MDI, because of their irritant characteristics, are seldom used in an unreacted form for the compounding of urethane coatings. They are normally converted into isocyanate-terminated polymers or adducts of polyols such as hydroxyl-terminated polyesters and polyethers, castor oil, etc. 

Pi- and Polyhydroxy Components. By far the most important active hydrogen-containing components of urethane coatings are di- and polyhydroxy compounds, often referred to briefly as polyols. 

Polyesters derived from e-caprolactone and ethylene glycol and triols, such as trimethylolpropane, have been employed for the preparation of different types of urethane coatings, including nonyellowing systems (88. 89). These types of polyesters exhibit improved hydrolytic stability and low-temperature properties as compared to adipate polyester based urethanes. 

A variety of urethane coating systems has been introduced based on hydroxyl-containing acrylic and methacrylic ester copolymers that contain hydroxyethyl acrylates or methacrylates and that are generally cured with aliphatic di- or polyisocyanates. Depending upon the type and relative amounts, acrylate or other saturated esters, for example, adipate-isophthalic esters, are also used in combination with aliphatic polyisocyanates. 

Castor Oil and Transesterification Derivatives of Castor Oil and Other Oils. Castor oil, consisting mainly of a triglyceride of ricinoleic (12-hydroxyoleic) acid (90% ricinoleic acid, 10% nonhydroxy acids, largely oleic and linoleic acids), is a frequent hydroxyl component of urethane coatings. On the basis of the hydroxyl number, castor oil is 70% trifunctional and 30% difunctional. The presence of castor oil in urethane polymers... 

There are two specific groups in this series of products (a) neutral urethane polyethers (112) that have to be activated with catalysts when used as second components in urethane coatings, which can be easily transformed into isocyanate-terminated polymers when reacted with additional isocyanate (b) basic urethane polyethers (113. 114) having hydroxyls activated by tertiary amine nitrogen present in the chemical chain of the product and that are very reactive second components of urethane coatings. They can also be converted into isocyanate-terminated polymers, but their stability is very limited (12-24 h). They are stable when immediately blocked by means of phenol, alcohols, or other suitable blocking agents. 

In addition to the five groups of urethane coatings described here, other coating systems have been developed that are described as follows. 

Toluene diisocyanate (TDI), methylene diisocyanate (MDI), and related chemicals are industrial components in the poiymerization of urethane coatings and insulation materiais. Most two-part urethane products contain some amount of one of these chemicais, and iesser amounts may oontaminate one-part systems. Methyl isocyanate (the toxin reieased in the Bhopal, India, tragedy) is a carbamate insecticide precursor it is not used in urethanes, has actions different from those of the TDI group of chemicals, and is not discussed here (see Table IV-4, p 593). 

One major automobile manufacturer was concerned about the use of urethane coatings with regard to solvent safety and emissions regulations. The cost and size of the complex coating supply and solvent evaporation equipment were other issues. Also, a 2 hr oven time limited the type of board it could coat and presented a severe handicap to short-run production and just-in-time delivery systems. 

Urethane resins are synthesized from isocyanates and chemical compounds with hydroxyl or urethane groups (—N—C—O—) including water, polyesters, epoxies, and acrylics [8,9]. The chemical structure of urethane coating is shown in Fig. 13.4. Polyester and epoxy have better barrier resistance to moisture and chemical attack than the acrylic polyol. Ahphatic isocyanate-based coatings are resistant to UV hght and have excellent gloss and color retention. 

The largest volume of urethane coatings is two package (2K) coatings that are mixed just before application. One package contains the polyol (or other... 

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