Photocured coatings

Absolute correlations between service performance and electrochemical measurements do not appear frequently in the literature. Based on 300 test systems. Bacon and coworkers (, correlated electrochemical resistance with exposure time. Recently, Mills ( also observed a correlation between salt fog corrosion and electrochemical resistance. We have found open circuit potential measurements to be extremely useful for the routine evaluation of high-nitrile polymer-based photocured coatings. 

BARTOSZEK-LOZA AND BUTLER Characterization of Photocured Coatings... 

Figure 2. Changes in open circuit potential (OPC) and rust rating (RR) with temperature for post-thermally treated Bonderite 40 coated steel (B40) panels and Barex 210/N-vinylpyrrolidone (B210/NVP) photocured coatings on B40 panels.

High nitrile photocured coatings on B40 coated steel panels exhibit corrosion resistance when their open circuit potentials are either more noble or less noble than the B40 coated steel panel (Figure 3). At first, we assumed that enhanced nobility should give rise to enhanced corrosion resistance, i.e. the galvanic series. 

In conclusion, we have shown that a simple, fast, electrochemical measurement, the open circuit potential, can be extremely useful in assessing the effect of diluent for high nitrile photocured coatings. Further work is underway to elucidate the underlying reasons behind the temperature induced changes observed in corrosion performance. 

Photocurable coatings are widely used for metal, plastics wood and paper. Photoinitiated free-radical polymerization, however, can only be applied to vinyl monomers. The studies of Crivello have broadened the scope of monomers. In addition, photoinitiated cationic polymerization is not sensitive toward oxygen (air). Photoinitiated free-radical polymerization sometimes requires working in inert atmosphere in order to avoid the inhibition through oxygen1). 

Carter, R. G., "Formulating Trade-Offs in Developing Low Viscosity Photocurable Coatings for Packaging," Proc. of SME Radiation Curing Conference, FC76-533, (1976). 

The reaction of glycidyl acrylate with a-(2-carboxyethyl)benzoin methyl ether has allowed one to obtain [101] the corresponding acrylic monomer which, upon copolymerization with different amounts of MMA, butyl methacrylate and 2-(V, V-dimethylamino)ethyl methacrylate, gives rise to polymeric photoinitiators, containing side-chain benzoin methylether moieties, for photocurable coatings ... 

Clear or pigmented liquid photocurable coatings can be applied to a flexible substrate (metal, polyethylene or filter paper) and the relative rate of cure or network formation as a function of changes in dynamic mechanical properties versus exposure time can be determined. 

The data at this time is only qualitative but efforts are being made to develop the torsional pen-dulum-UV-curIng techniques and to quantify relationships between relative rigidity, damping, gel-point, vitrification, and irradiation intensity or exposure time for clear as well as pigmented photocurable coatings. ... 

Epoxy resins have been cured using a tris(ethyl acetoacetato) aluminium complex and tris (4-chloro-phenyl) (a-nitrobenzoy-loxy) silane.Resins produced by this catalyst mixture were found to have desirable electrical characteristics. N-vinyl-2-pyrrolidone is claimed to be a much superior resin than several acrylate diluents for photocured coatings... 

Materialsfor Photocurable Coatings andlnks, Union Carbide Corp., New York. 

Ariga (45) disclosed developments with CTBN-modified epoxy acrylates which when prepared with other lower molecular weight dicarboxylic acids and select carboxyl-terminated oligopolyesters serve as novel oligomers for photocurable coatings. These systems have low uncured viscosity. In the cured state they possess excellent scratch and crosshatch adhesion, good direct and reverse impacts (duPont impact tester) and pass bending diameters of 2 mm. 

Since the introduction of photocuring of coatings as a viable industrial process well over a decade ago, the UV curing industry has followed a line of steady growth. This paper deals with the mechanisms and components which characterize photocurable coatings. Free radical and cationic photoinitiated polymerization are discussed in light of key review references from the recent literature. In addition, a section is dedicated to discussion of the lamp sources available for photocuring operations. 

Oligomers As indicated in Table II, functionalized oligomers provide the photocured coating with its basic physical properties. A generalized structure for reactive oligomeric resins or pre-polymers is shown below ... 

The exotherm apparatus (either DSC or thin-foil) is a highly useful tool for evaluation of the efficiency and speed of UV curable systems. It can be applied as a screening mechanism for UV curable formulations or as a highly sophisticated scientific tool. Its use has led, and will no doubt lead in the future, to the development and improvement of photocurable coatings. 

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