Epoxy Varnish Research Articles

Influence of cationic photoinitiator type on properties of coating materials based on cycloaliphatic and glycidyl epoxy resins

Abstract Epoxy binder based on 3,4-epoxycyclohexylmethyl-3′,4′-epoxycyclohexanecarboxylate (EEC) and polytetrahydrofurane diglycidyl ether (PTHDE) was cured using four types of commercial cationic UV-photoinitiators (two iodonium salts and two sulfonium salts) and a medium-pressure mercury lamp. Influence of a type of photoinitiator on thermal, optical, mechanical and barrier features of the varnish coatings was investigated. Moreover, conversion of cycloaliphatic epoxy (CC) and glycidyl (GC) groups was analyzed. Generally, systems containing iodonium or sulfonium hexafluorophosphates exhibited higher GC, gel content, gloss and water-vapor transmission rate as well as lower yellowness and hardness than samples based on SbF6−-type salts. Photoinitiator type did not significantly affect CC parameter, however, application of the iodonium salts mixtures influenced on CC as well as GC, thermal features and gloss of epoxy varnishes and coatings.

Influence of synthetic and bio-based amine curing agents on properties of solventless epoxy varnishes and coatings with carbon nanofillers

Abstract Solventless epoxy varnishes and coatings were prepared using carbon nanotubes (CNT) and/or graphene (GNP) dispersions in a Bisphenol F-type epoxy resin, synthetic hardeners [tetraethylenepentamine, poly(oxyethylene)diamine, isophoronediamine, m-xylylenediamine] or bio-based amine hardener (Cardanol-based phenalkamine, abbreviationabbreviation: PAA). Room temperature cured coatings, containing 0.35 wt.% of CNT predispersed in PAA, showed outstanding combination of optical (i.e. high gloss and transparency, low haze in humid conditions) and electrostatic dissipative properties (surface resistivity ca. 5.5 × 10 7 Ω) in relation to the samples containing carbon nanofiller(s) dispersion in the epoxy resin or a synthetic amine. PAA-based coatings with the carbon nanofillers exhibited increased cupping resistance (+20% for samples with CNT) as well as high hardness and excellent adhesion to a glass substrate. The carbon nanofillers addition influenced on curing process and glass transition temperature (monitored using differential scanning calorimetry technique) of the epoxy varnishes and coatings as well.

Protective properties of paint and lacquer coatings based on a fluorine-containing film-forming material

Paint and lacquer coatings (PLCs) are most commonly used when one needs to impart an aesthetic appeal to metal surfaces and protect them from the effects of the environment. Priming paint and lacquer compositions, which are dispersions of anticorrosion pigments in film-forming materials possessing a high adhesion to the surface that is being coated, are rather widespread among the variety of paint and lacquer corrosion- protection materials. The use of a fluorine-containing film-forming material to produce a PLC is rather promising. In this work, we have studied the protective properties of coatings that are based on epoxy varnish and a fluorine-containing polymer and filled with chromate and chromate-free anticorrosion pigments. The protective properties of PLCs have been evaluated by express tests in a salt spray chamber. The PLC structure has been analyzed by scanning-electron and atomic-force microscopy.

A High Adhesive Epoxy Varnish Coating on Galvanized Steel

Epoxy varnish coatings with different amount of sulfosalicylic acid were prepared on galvanized steel. The adhesion and corrosion performance of the coatings were characterized by means of pull-off adhesion tester and electrochemical impedance spectroscopy (EIS) respectively. While the effect of sulfosalicylic acid on the corrosion resistance of the coatings was also studied in 3.5%NaCl solution. The results show that with the increasing amount of sulfosalicylic acid, the ad- hesive strength of the coatings increases firstly, and then decreases. Among others, the coating with 3% (mass fraction) sulfosalicylic acid exhibits the highest adhesive strength, modules at low fre- quency and pore resistance during the immersion process only except for the initial stage; as well as the highest charge transfer resistance. These results show that the epoxy varnish coatings contain- ing 3% sulfosalicylic acid has the best adhesion and corrosion resistance.

UV-curable epoxy varnishes modified with polyvinyl resins

Abstract Epoxy varnishes based on 3,4-epoxycyclohexylmethyl-3′,4′-epoxycyclohexanecarboxylate (EEC) and polyvinyl components, i.e., two polyvinyl butyral resins (PVB) and one polyvinyl butyral- stat -acetal resin (PVBA) were prepared and cured using a commercial cationic iodonium photoinitiator and medium-pressure mercury lamp. An influence of a type and content of polyvinyl resin (5, 10, and 20 wt.%) on thermal, optical, mechanical, and barrier features of varnish coatings was investigated. Coats containing the highest amount of PVB resins exhibited higher epoxy group conversion, higher gloss, and smoother surface in comparison with EEC/PVBA samples. Moreover, cured coats and films with PVB reached markedly higher barrier features, i.e., limited distilled water absorption and low water vapor transmission rate. An influence of reactivity and UV transmittance value of the photocurable varnishes on coat wrinkling process was presented and discussed.

Evaluation of the corrosion protection of defective polyaniline/epoxy coating by localized electrochemical impedance spectroscopy

Defective epoxy varnish and hydrofluoric acid-doped polyaniline/epoxy (PANI-HF/EP) coatings were coated on the surface of an AZ91D magnesium alloy. The corrosion protection of the defective coatings was evaluated in 0.05 M NaCl by localized electrochemical impedance spectroscopy. Then, the surface of AZ91D magnesium alloy beneath the coating was analyzed by scanning electron microscopyand energy dispersive X-ray spectroscopy. The results indicated that the defective epoxy varnish coating could not protect the magnesium alloy because it only served as an electrolyte barrier. By contrast, the PANI-HF/EP coating served not only as an electrolyte barrier, but also facilitated the formation of a protective layer by redox processes. Therefore, the defective PANI-HF/EP coating could protect magnesium alloy from corrosion.

Investigation of the effect of fraction composition and specific surface of anticorrosive pigments on the protective properties of epoxy coatings

The technological parameters of grinding of anticorrosive pigments are presented. The effect of nanosized particles of anticorrosive pigments on the protective properties of coatings based on epoxy varnish is studied. The structures of varnish-and-paint coatings are investigated by means of electron-scanning microscopy and atomic force microscopy.

Study of the failure mechanism of an epoxy coating system under high hydrostatic pressure

The failure mechanisms of an epoxy varnish coating and an epoxy glass flake coating were investigated under ordinary pressure (1atm) and high hydrostatic pressure (35atm), from electrochemical behavior, water absorption, wet adhesion and mechanical characteristics. The results revealed that mechanical properties were more favorable under 35atm, but pressure changed the electrochemical behavior and deteriorated coating protectiveness by accelerating water absorption, increasing diffusion coefficient and changing diffusion type. More importantly, loss of wet adhesion, induced by blisters and corrosion products on interface, became the main reason for coating failure and thus the key factor controlling coating lifetime.

Research on Corrosion Resistance of AZ91D Magnesium Alloy Coated with Epoxy Resin

The corrosion resistance of a 1~2mm thick AZ91D magnesium alloy die-casting coated with epoxy varnish after phosphatizing was tested. Zinc phosphating solution was used. In the experiment, uniform paint was obtained by dipping method. Scratch test showed that the adhesion force between the coating and matrix is excellent. Within the test range the optimal phosphating temperature and time are 50°C and 1 min tested by dynamic potential scanning method. With the organic coating the corrosion current density decreased 3 orders of magnitude, the polarization resistance increased 3 orders of magnitude. The coated specimens were immersed in10% H2SO4, 10% NaOH and acetone for 10 days, respectively. The results showed that blistering did not occur on the paint films. This work illustrated that the simple zinc phosphating process combined with simple organic coating can meet the corrosion resistance requirements of thin-wall die casting magnesium components that require higher quality appearance.

UV aging characterization of epoxy varnish coated steel upon exposure to artificial weathering environment

Abstract Epoxy varnish coating was exposed to artificial weathering environment produced by fluorescent UV/condensation weathering equipment for different time periods. The degradation process of epoxy varnish coating was studied by electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM) and adhesion test. The results showed that the electrochemical behavior of aged coating was closely related to the formation and development of blisters on the surface due to coating degradation. The coating resistance, Rp, decreased to a lower value after 28 days of exposure, which indicated significant deterioration of barrier properties. Small blisters were observed on coating surface after 21 days of exposure. With increasing aging time, blisters grow up and subsequently broke. The mechanism of blisters formation and subsequent breakage were suggested. The soluble degradation products penetrate into the coating along with water to form osmotic cells leading to the form of blisters on the coating surface under the alternating wet and UV irradiation condition. The spread of degradation areas caused the growth and development of blisters. With the loss of coating material and embrittlement, cracks appear on the surface and the blisters break, which may result in the significant deterioration of bulk properties of the coatings.

Accelerated Evaluation Cycle for Commercial Epoxy Varnish Free of Pigments

not Available.

Studies of water transport behavior and impedance models of epoxy-coated metals in NaCl solution by EIS

Using electrochemical impedance spectroscopy (EIS) technique, the analyses of impedance models and the water uptake processes of epoxy-coated mild steels and LY12 aluminum alloys immersed in 3.5% (weight fraction) NaCl solution were studied. The fitting results using suitable electrical equivalent circuits (EEC) suggested that there were four kinds of impedance models in the course of immersion. In the initial period of immersion, an EEC containing the coating capacitance and the coating resistance was used to fit the EIS data. Along with the immersion time, the number of time-constant of impedance spectra for metal/coating systems increased, indicating that corrosion reaction took place. After a certain time's attacking of metal substrates, the diffusion process towards solution of corrosion products forming at the metal/coating interface might be restrained due to the presence of coating barrier, resulting in the appearance of diffusion elements. This diffusion did not act as an ideal Warburg behavior, leading to a deviation of dispersive number, n, from 0.5. After longer immersion times, the Cl − ions reached the surface of metal through the coating and participated in chemical reactions with corrosion products to form salt film on aluminum alloy surface. The formation of chloride ion-incorporation salt film resulted in the change of impedance spectrum characteristics. The studies revealed that the water transport in epoxy varnish coatings followed the Fickian diffusion law during the initial time of exposure to the testing solution. After immersion for a certain time, the water uptake reached saturation and the coating capacitance tended to a relatively steady value. According to the variation of coating capacitance with time, the water diffusion coefficient was deduced. The experimental results indicated that the water diffusion coefficients in epoxy coatings were slightly dependent on coating thickness and were to some extent influenced by substrate type. The similar surface chemical structures of epoxy coatings on different metals were found from the Fourier transform infrared spectroscopy (FT-IR)–attenuated total reflection (ATR) measurements. The glass transition temperature ( T g) of epoxy coatings prepared on different metal substrates before and after immersion was measured by using differential scanning calorimetry (DSC). Lower diffusion rate of water in Al alloy based epoxy films than that in steel based ones was interpreted by the higher absolute value and smaller decrease of T g of organic coatings painted on the former substrate.

INFLUENCE OF FILM THICKNESS, TEMPERATURE AND INORGANIC FILLERS ON THE VOLUME ELECTRIC RESISTIVITY OF HEAT-CURING EPOXY VARNISH

The dependence of the volume electric resistivity of heat-during epoxy varnish on the film thickness, temperature, and nature of inorganic fillers for films obtained by spraying on steel supports cured for 30 minutes at l60 °C was determined. Film thicknesses ranged between 5 and 56 µm, temperature between 24 °C and l40 °C, and the fillers were rutile type titanium micronizes mica, colloidal aluminium oxide, and aluminium silicate. The experimental data, treated statistically by the Linear regression method, shows a linear dependence of the volume electric resistivity on the film thickness and a hyperbolic one on temperature. The highest volume electric resistivity was obtained for films containing titanium dioxide and the lowest one for those with aluminum silicate. The volume electric resistivity depends on film thickness for films deposited from the solution and can not be considered a material constant.