Paint-and-Varnish Coats

Certain difficulties are connected with the realization of the above idea. Being surfactants or oxidizers in their essence, Cl are able to interact with film-forming substances and lose their protective properties, forming undesirable side products that are hostile to the metal substrate, can initiate gelation and so on. This is why, for optimum matching of each Cl-paint composition pair, the choice is made on a case-study basis, taking account of technical and economic criteria and is usually at the level of know-how. For modification of paint coats water and oil-soluble Cl are commonly employed. 

Water-soluble Cl significantly improve the protective ability of oil, alkyd, alkyd-styrene and alkyd-nitrocellulose coatings (Fig. 3.41), for example, 3wt% of water-soluble potassium chromate guanidine. Cl has been introduced into the lacquer base, after which a 20-pm-thick single-layer coat has been applied on a plate of low-carbon steel (St 2). The time until the appearance of corrosion traces under the coating has been recorded on exposure to atmosphere at 100% humidity and a temperature of T = 18-25°C. The results presented in Fig. 3.38 prove that the introduction of this Cl has perceptibly improved the anticorrosion properties of lacquer coatings [1]. 

The electrode potential of the steel plate coated by the inhibited lacquer is seen to shift to the positive side by 300-500mV (Fig. 3.42). This strong shift in the potential, accompanied by the corrosion rate reduction, is evidence that potassium chromate guanidine hampers anodic reactions of metal ionization. 

The comparison of IR absorption spectra of the films of natural drying oil and that modified by potassium chromate guanidine has shown that the amount of hexavalent chromium (800-900 cm ) diminishes in the inhibited film. This gives grounds for the supposition that chromium forms complex compounds with carbonyl, carboxyl and oxide groups of the dr3ung 

An important characteristic of coatings containing water-soluble Cl is washing out of the inhibitors. Coatings of alkyd-nitrocellulose lacquer are preferable in this respect to those of alkyd lacquer. About 70% of the chromate ions are washed out of the alkyd coatings per day, in contrast to the alkyd-nitrocellulose coatings, in which the chromate ions remain practically unwashed during the first five days and then are washed out but very weakly. 

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Other Derivatives and Applications. Copolymerization of DCPD with other unsaturated substances has received wide attention, and several useful appHcations have been developed. With drying oils (qv) thermal copolymerization leads to the production of resinous products, the so-called bodied oils, that give improved drying and result in paint and varnish coatings of greater resistance to weathering. 

Formation and protective mechanisms of antimicrobial polymer coatings are in principal the same as in inhibited paint-and-varnish coats [97],... 

Paint-and-varnish coatings for temporal protection of metal ware are subdivided into wipe-off and detachable. 

A.D. Yakovlev. Chemistry and Technology of Paint and Varnish Coatings Handbook for Higher Educational Institutions, Leningrad, Khimiya, 1989. 

Paints and varnishes (coatings) have two primary functions protection and decoration. Other objectives include information, identification, safety, insulation, vapor barrier, nonskid surface, and control of temperature, light, and dust. A range of product categories with a wide variety of application is therefore available ... 

BS EN 1062-3 (1997). Paints and Varnishes - Coating Materials and Coating Systems for Exterior Masonry and Concrete. Part 3 Capillary Absorption and Permeability to water, British Standards Institute, London. 

Features of Adhesion of Particles to Paint and Varnish Coatings... 

The relationships found for the adhesion of particles to surfaces in air and in hquid media (see Chapters IV-Vl) are valid in the case of particle adhesion to painted surfaces. The distribution of particles of different shapes adhering to paint and varnish coatings likewise follows a log-normal law [194]. 

A lower adhesion of particles to painted surfaces in a liquid medium in comparison with adhesion in air has also been observed for irregularly shaped particles. In air, the median force of adhesion for irregular particles with an equivalent diameter of 70-110 jum was found to vary from 1.3 10 to 3.8 10 dyn in an aqueous medium, the median force for these same particles varied from 1.6 10 to 4.8 10" dyn. The adhesion of particles to paint and varnish coatings in the aqueous medium was 2 orders of magnitude less than in air i.e., the general relationships found previously for adhesive interaction (see Sections 20 and 30) are manifested under these conditions also. 

Properties of Paint and Varnish Coatings Affecting Particle Adhesion. Any... 

In order to solve problems of dust retention, we must determine which properties of paint and varnish coatings determine the adhesion of dust particles. Among these properties we should mention the following roughness, moisture resistance, elasticity, physicochemical properties (hydrophobicity or hydrophil-icity, tackiness), and electrical properties. In view of the variety of forces responsible for adhesion and the differing properties of paint coatings and particle... 

The substrate roughness, which determines the true contact area of dust particles, affects the forces of adhesion in a manner that has been discussed in detail in Chapter V. In order to reduce the forces of particle adhesion, paint and varnish coatings should be rough on a microscopic scale, without any macroscopic asperities. We will now consider the main classes of paint and varnish coatings (on the basis of external appearance) and the possible roughness and the expected adhesion of dust particles to these coatings (Table VIII. 1). 

In some cases, data are available from which we can obtain a relative characterization of particle adhesion to paint and varnish coatings. Such a relative characterization was given in [213] the deposition and removal of the contaminants were performed under identical conditions. The coatings were ranked in decreasing order of adhesion number as follows melamine-alkyd enamel ML-12-18 (98%) penta-phthalate white enamel PF-115 (94%) red alkyd-nitro-enamel EP-51 (64%) grey chlorinated PVC enamel KhV-113 (57%). It will be noted that the chlorinated PVC enamel KhV-113 gave the least retention of contaminants. 

Many paint and varnish coatings, such as chlorinated PVC, polyurethane, and nitrocellulose enamels, have wetting angles somewhere within the limits indicated above. 

Thus we see that hydrophobization of paint and varnish coatings reduces the... 

Methods for Hydrophobization of Paint and Varnish Coatings. All methods for hydrophobizing paint and varnish coatings may be divided into two groups surface and bulk hydrophobization techniques. In either case, the hydrophobization is accomplished by modifying the coating. 

Bulk modification of paint and varnish coatings is achieved by the incorporation of various additives in the paint or varnish. In particle adhesion tests on certain coatings modified by this method, simultaneous measurements of wetting angle were made. The results obtained on chlorovinyl KhV-124 and penta-phthalic PF-115 coatings are listed in Table VIII.3, and those on chlorinated PVC coatings in Table VIII.4. 

The data that we have reviewed illustrate the fact that hydrophobization of paint and varnish coatings reduces the degree of adhesive interaction. The properties of paint and varnish coatings may be changed by either surface or depth (bulk) modification of the coating. 

Changes in Adhesion to Paint and Varnish Coatings because of Electrical Forces. By changing the electrical component of adhesive force, considerable reductions can be achieved in the adhesion of dust to surfaces, in some cases even complete elimination of dust accumulation. Previously (see Section 15) we examined the possibilities of changing the electrical component of particle adhesive force by modifying the properties of the surface. Adhesive forces can... 

Influence of Electrical Resistance of Paint and Varnish Coatings on Adhesion to Coating. Paint and varnish coatings may be either dust repellent or dust retaining, depending on their ability to conduct an electric current, i.e., on the magnitude of their electrical resistance. 

If all Other conditions are the same, we may expect that the forces of dust adhesion from an air stream on the penta-phthalic lacquer will be greater than on the epoxy enamel. Naturally, the hardness of the coating is not constant it changes depending on the ambient air temperature (particularly at excessively high temperatures) and also changes with the time elapsed from the moment of application. These data, however, can be used for a preliminary estimate of the forces of particle adhesion to paint and varnish coatings. 

In evaluating the adhesive properties of paint and varnish coatings, the hardness index must be used along with other indices characterizing the physicochemical properties of the coating material. Such a correlative index is the contact (wetting) angle. 

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