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This paper aims to disclose the evolution of pendulum hardness of two-component acrylic polyurethane coatings during the cure process and attempts to describe the quantitative relationship between pendulum hardness and curing time. These findings are helpful for the study of fast curing acrylic polyurethane coatings.

The pendulum hardness method was used to monitor the hardness of two-component acrylic polyurethane coatings during curing. The quantitative relationship between pendulum hardness and curing time can be obtained with Avrami equation.

The evolution of coating pendulum hardness can be divided into three stages. By using the Avrami equation that explained the influence of both the acid value and the curing temperature on the drying speed of hydroxyl acrylic resin, the evolution of coating pendulum hardness during curing can also be accurately described.

It should be noted that the physical meaning of the Avrami exponent, n, is not yet clear.

The results are of great significance for the development of fast-curing hydroxyl-functional acrylic resins, with the potential to improve the drying speed of the coatings used in automotive refinish.

It is novel to divide the pendulum hardness into three stages, and, for the first time, the Avrami equation is utilized to describe the evolution of coating pendulum hardness during curing.

The purpose of this paper is to formulate two component polyurethane coatings based on acrylic polyol, to study the effects of variable nanosilica loadings in these coatings on different morphological, optical, mechanical, corrosion resistance and weather resistance properties and to study the intercalation of acrylic polyol molecules into nanosilica crystals by XRD technique.

Two component polyurethane coatings were synthesised using acrylic polyol and isocyanate HDI. The nanosilica was incorporated in polyurethane formulation at the weight ratios of 1%, 3% and 5% based on total weight of polyol and isocyanate. The performance of nanocoatings was compared for variable loads of nanosilica for different properties such as morphological, optical, mechanical, corrosion resistance, weather resistance and were studied for intercalation of acrylic polyol into nanosilica crystals by XRD technique.

Improvement in the properties of polyurethane coatings is achieved with the incorporation of nanosilica. The improvement is the result of inherently high properties of inorganic nanosilica. Tensile strength, scratch hardness, abrasion resistance, corrosion and weathering resistance show significant improvement in performance with the incorporation of nanosilica. Properties are found to deteriorate beyond a certain loading of nanosilica; hence it is important to optimise loading level. The optimal range for high performance was found to be in the range of 1% to 3%. The improvement was a result of synergistic behaviour and good interfacial interaction between polyurethane and nanosilica at optimal levels.

The method used for incorporation of nanosilica into polyurethane was direct incorporation method. The other method of incorporation, i.e. in situ addition and its effect on properties can also be studied.

With the addition of optimal loading level of nanosilica to polyurethane coatings, properties can be enhanced up to the mark. The addition is relatively easy and cost effective.

The paper proves the significance of incorporation of nanosilica on original properties of polyurethane coatings and widens the area of applications of two component polyurethane coatings from acrylic polyol by strengthening them in their properties. The coatings can be applicable in high performance topcoats especially for automotive topcoats.

An important development in the urethane coating area is the use of polyisocyanates, in combination with hydroxylated acrylic resins, to provide room‐temperature‐curing coatings. These new formulations, according to Klein and Elms [Journal of Paint Technology, 43, November (1971) p. 68], demonstrate lightfastness, good outdoor durability and solvent resistance when the acrylic resin is coreacted with an aliphatic polyisocyanate. The acrylic resins are copolymers which contain either the hydroxypropyl or hydroxybutyl ester of acrylic or methacrylic acid as one component. Hydroxypropyl acrylate acetoacetate extends the potlife of this two‐component coating. The authors describe work in which glass transition temperature is used as a means for selecting the correct hydroxylated acrylic resins for use in the system. If the glass transition temperature is between 22 and 54°C, a flexible coating with good impact resistance results, but the system requires baking. At a glass transition temperature of 54° and a hydroxyl value of 26, a composition results which dries rapidly at ambient temperatures and which provides good hardness and mar resistance. The coreactant in this instance is an aliphatic diisocyanate composition based on hexamethylene diisocyanate.

This study aims to extend the pot life without altering the qualities and performance of the coating, which is important to increase when manufacturing polyurethane coatings.

An acrylic polyol from a mixture of different monomers of hydroxypropyl methacrylate, methacrylic acid, 2-ethylhexyl acrylate, methyl methacrylate and n-butyl methacrylate was prepared with different ratios of 2,4-pentanedione as a pot life extender. The reaction takes place in presence of di-tert-butyl peroxide as initiator with samples (T1–T7). The physical properties of prepared acrylic polyol were characterized. Then, coating polyurethane varnish was prepared from the prepared acrylic polyol with an aliphatic polyisocyanate in a 1:1 equivalent ratio of OH:NCO at room temperature, in presence of paint thinner (diluents/solvent) and dibutyltin dilaurate as a catalyst to give samples (T1C–T7C). This coating was evaluated via Fourier-transform infrared spectroscopy, drying time, hardness and gloss, distinctness of image and reflected image quality.

The coating has a prolonged pot life while still maintaining the other qualities, thanks to the greater 2,4-pentanedione content.

It is desired to have a paint which has a satisfactory pot life, short curing time and reduces many drawbacks such as inefficient working and deterioration of the paint before application.

Summarizes the different techniques for the removal of conformal coatings from printed circuit boards and other electronic assemblies. Addresses each of the four techniques for the removal of conformal coating (thermal, mechanical, chemical and abrasive), along with how they work with each type of conformal coating (urethane, acrylic, silicone, epoxy, parylene and UV curable coatings). Also provides summaries for the removal times and clean up for each technique.

The number of new alkyd resin‐based coatings introduced decreases yearly. To be sure, alkyd resins are the most important vehicles used for solvent‐based paints. On the other hand, the technology is mature and the major variations in the products are those which must be made to accommodate needs of the user. For the most part, these do not lead to completely new types of compositions.

Acrylic resins are formulated into protective coatings in several ways. Most important volumewise are waterborne formulations based either on pure acrylics or on acrylic‐vinyl copolymers. Second most important are solvent‐based enamels and lacquers widely used for product finishes particularly in the automotive and appliance industries. An innovation of a decade or so ago is proving popular in this area, namely two component coatings based on hydroxyl‐containing acrylics and di‐ or polyisocyanates. These combine many of the good features of acrylics and urethanes and provide hard thermoset coatings. Yet they cure at temperatures as low as ambient.

The use of fluoropolymer resin within ambient temperature curing exterior paint finishes for use on aircraft are shown to be a practical and beneficial proposition. Comparison with two‐component polyester polyurethanes and with acrylic urethanes clearly indicates superior durability in terms of gloss and colour retention.

The interest in waterborne coatings continues, and this trend is well‐demonstrated by many new proprietary products. For example, a new acrylic latex enamel has been announced which has high gloss and superior colour retention. Associated with the product are the usual properties of easy application, low odour, and water cleanup. The product is available from the O'Brien Corp. [450 E. Grand Ave., So., San Francisco, CA 94080].

Additions for use in polyurethane coatings. Angus Chemie GmbH has announced the introduction of two new additions to its product line for polyurethane coatings. Zoldine RD‐20 Reactive Diluent is designed to replace higher viscosity polyols in high solids polyurethane coatings. Zoldine MS‐Plus Moisture Scavenger eliminates bubbles, pinholes, downglossing and hazing in polyurethane coatings to allow for fast cure times in all types of weather.