Polyurethane-acrylic coatings

Polyurethane-acrylic coatings with interpenetrating polymer networks (IPNs) were synthesized from a two-component polyurethane (PU) and an unsaturated urethane-modified acrylic copolymer. The two-component PU was prepared from hydroxyethylacrylate-butylmethacrylate copolymer with or without reacting with c-caprolactonc and cured with an aliphatic polyisocyanate. The unsaturated acrylic copolymer was made from the same hydroxy-functional acrylic copolymer modified with isocyanatoethyl methacrylate. IPNs were prepared simultaneously from the two-polymer systems at various ratios. The IPNs were characterized by their mechanical properties and glass transition temperatures. 

Figure 4. Influence of the reactive diluent on the photopolymerization of a polyurethane-acrylate coating irradiated in the presence of air. [Irgacure 651] = 5% [Diluent] = 47 % Film thickness 24 pm.

There is some interest in water dispersible light curable coatings and binders. Thus, Heischkel et al, reported preparation of a water based radiation curable polyurethane acrylate coating. Some of the water soluble or dispersible monomers are diethylaminoethyl acrylate, butanediol monoacrylate, vinyl caparolactam, and propylene glycol monoacrylate. 

However, polyurethane acrylic coatings have continued to be the subject of toxicological concern over the use of isocyanate compounds, although the commercialisation of higher molecular weight polyisocyanates has minimised the risk of exposure to monomeric isocyanates. These systems are only recommended for use in well ventilated areas with efficient air extraction. In the case of spraying, operators must wear masks with a separate air supply. 

Most dyes, including sulfonated azo dyes, are nonvolatile or thermally unstable, and therefore are not amenable to GC or gas-phase ionisation processes. Therefore, GC-MS techniques cannot be used. GC-MS and TGA were applied for the identification of acrylated polyurethanes in coatings on optical fibres [295]. Although GC-MS is not suited for the analysis of polymers, the technique can be used for the study of the products of pyrolysis in air, e.g. related to smoke behaviour of CPVC/ABS and PVC/ABS blends [263],... 

Butyl benzyl phthalate is a plasticizer added to polymers to give flexibility and softness. It is used extensively in polyvinyl chloride and in cellulose plastics, polyvinyl acetate, polysulfides, and polyurethane. Also used in flexographic inks for food packaging applications and acrylic coatings, profile extrusions, slush moulding, film and sheeting, coated fabrics, floor and wall coverings, vinyl foams and plastisols for car sealants. 

Acrylic polyols represent a special group of amorphous polyols, of molecular weight (MW) of 8000-13000 daltons, obtained by radical copolymerisation of acrylic monomers (ternary or quaternary copolymers), such as acrylic or methacrylic acids and esters. The source of hydroxyl groups in these acrylic polyols is the utilisation in the radical copolymerisation reaction of hydroxyalkyl acrylates or hydroxyalkyl methacrylates [1,2] as comonomers. The acrylic polyols are used in high performance polyurethane (PU) coatings. 

The most common conformal coatings are derived from polyurethanes, acrylics, and epoxies the more special formulations for high-temperature performance are based on silicones, diallyl-phthalate esters, and polyimides. An example of a vapor deposited conformal coating is Parylene. It is obtained by vapor deposition of p-xylylene, which is formed as a transient by dehydrogenation of p-xylene at high temperature, and polymerization on the surface of the object to be coated. Because p-xylylene monomer is not stable, it is advantageous to work with the cyclic dimer, di-p-xylylene (paracyclophane), which, upon heating under reduced pressure, will produce the transient monomer which converts to the polymer at low temperatures. 

For photocured polymer materials, the Persoz hardness was shown to depend mainly on the chemical structure of the prepolymer chain, on the functionality of the reactive diluent, on the photoinitiator system and on the duration of the UV exposure. The hardness of tack-free coatings thus continues to increase with further irradiation, as shown by Figure 6 for polyurethane-acrylates. This slow hardening process is likely to result from some further polymerization of the unreacted acrylic functions since their concentration was found to decrease concomittantly. 

Although two-pack epoxy primers and polyurethane intermediate coats have high solids contents, they still contain significant amounts (20-30 wt%) of organic solvents. In polyurethane topcoats, the VOC is even higher. Anticorrosive, waterborne primers based on aqueous dispersions of two-pack epoxy resins and one-pack acrylic resins have been developed to decrease solvent emission. Waterborne, one-pack acrylic topcoats are also used. All of these waterborne paints contain 2 - 5 % organic cosolvents that are required for film formation. 

Uses Defoamer for water-based systems Ind. polyurethane, acrylate/ polyurethane paints, wood varnishes, furniture paints, pigmented dispersion paints, plastic coatings, inks Properties Colorless to yel. liq. ether-like odor sp.gr. 1.01 g/cc dens. 8.40 Ib/gal flash pt. (Seta) > 100 C ret. index 1.448 > 96% NV Toxicology TSCA fisted... 

Chem. Descrip. Polysiloxane mixt. in dipropylene glycol methyl ether Uses Defoamer for water-based systems ind. polyurethane, acrylate/ polyurethane paints, wood varnishes, furniture varnishes, plastic coatings... 

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. 

Urethane-acrylate. See Urethane-acrylate resin Urethane-acrylate resin Synonyms Polyurethane-acrylic Urethane-acrylate Urethane-acrylic Definition Acrylate-terminated PU prepolymers, producing inks and coatings characterized by toughness and good chem. resist. 

Zhu, S. and Shi, W. Flame retardant mechanism of hyperbranched polyurethane acrylates used for UV curable flame retardant coatings. Polymer Degradation and Stability, 75, 543-547 (2001). 

Adhesives in relation to coated fabrics can be thought of as either the tie-coat to bond the surface coating to the fabric, or the surface coating itself, directly bonded to the fabric. The types of polymers used in coating fabrics are rubbers, PVC, polyurethane, acrylics and silicones the coatings are usually cross-linked to increase durability but some topcoats can be thermoplastic, for example polyurethanes, to facilitate thermal bonding of seams in production of garments or other articles. 

One-pack or two-pack polyurethane surface coatings, which may sometimes be combined with acrylic resin systems. The one-pack system, which has a long shelf life, is an adduct of resin with polyisocyanate dissolved in a moisture-free solvent. When applied to a surface the film cures and hardens, as moisture in the air reacts with the isocyanate groups in the resin. The two-pack system consists of a polyisocyanate (frequently derived from an aliphatic isocyanate monomer) and a polyol as separate components. Once the two components are mixed, the shelf life is very limited. 

Fig. 7. ASTM B-117 salt spray test results of (a) the chromate conlrol on AA 2024-T3 (b) the acrylate-epoxy based system on AA 2024-T3 (c) the novolac epoxy-polyurethane based coating on AA 2024-T3 (d) the polyurethane-based coating on AA 6061 (e) the epoxy-based system on HDG and (f) the chromate control on HDG [30],...

To cure thin coatings in contact with air, it is therefore necessary to work under intense illumination in order to consume rapidly the O2 dissolved in the sample and shorten the exposure time during which atmospheric oxygen diffuses into the coating. This is not a problem anymore in adhesive applications which are performed under oxygen diffusion-free conditions (laminates). After a short induction period during which the dissolved O2 is consumed by the initiator radicals, the polymerisation of the acrylate double bond proceeds as fast in the laminated sample as in an inert atmosphere and much faster than for a coating, as shown in Fig. 2 for a polyurethane-acrylate resin. 

Nowatzki PJ, Koepsel RR, Stoodley P, Min K, Harper A, Murata H, et al. Salicylic acid-releasing polyurethane acrylate polymers as anti-biofilm urological catheter coatings. Acta Biomater 2012 8 1869-80. 

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