Experimental study on mechanical property and stone-chip resistance of automotive coatings

The damage of automotive coatings caused by stone impact is a problem that has attracted great attention from automotive companies and users. In this work, experiments were conducted to investigate the dynamic tensile properties and stone-chip resistance of automotive coatings. Four kinds of paint films and three typical coatings (single-layer electrocoat coating, single-layer primer coating, and multilayered coating) were used. Under dynamic tensile load using split Hopkinson tension bar (SHTB), the engineering stress-strain curves of the paint films at medium and high strain rates (from 50 to 600 s-1) were obtained. Results indicated that the mechanical properties of the paint films exhibited strong nonlinearity and strain-rate correlation. A modified anti-impact tester was used to complete repeatable single impact tests. The effects of some key parameters, i.e., impact velocity, impact angle, and paint film thickness, on the stone-chip resistance of coatings were systematically investigated. The influence of contact type under high-speed impact conditions was investigated as well. The surface morphologies of the coatings after impact were examined by scanning electron microscopy (SEM), and the failure mechanism of the coatings under normal/oblique impact was discussed. In all experiments, the paint films showed brittle fracture behavior.

Study on Manufacturing Environmentally Friendly Alkyd Paint

The article presents results of studying and manufacturing environmentally friendly alkyd paint. By producing a polysaccharide intermediate emulsion (LPR), about 20% of water to total paint volume was added. Mechanical properties (impact resistance, flexural strength, adhesion) of paint films were studied. In addition, the paper presents results of thermal stability, 10-cycle UV-thermo-humidity complex stability of paint film. Ability of films to withstand 03-cycle heat shocking of films at temperatures of + 50 oC and -50 oC was investigated. The properties of studying paint were compared with those of an alkyd paint of Hanoi Synthetic Paint Company. Results show that the environmentally friendly alkyd paint has less volatile organic compounds (VOC), uses a smaller amount of toxic solvents, while its properties are comparable to common alkyd paint.

Preliminary Investigations into the Alteration of Cadmium Orange Restoration Paint on an Ancient Greek Terracotta Krater

In preparation for exhibition, an ancient Greek terracotta krater received treatment which included selective in-painting with cadmium orange (CdSSe). After one year on display the object displayed disfiguring alteration in select areas of restoration. Cross-section analysis of samples taken from the object revealed that alteration only occurred in areas where the paint was in direct contact with darkened and abraded areas of the terracotta surface, in which analysis found the presence of chlorine. The alteration was recreated in mock-ups for more in-depth analysis. Using Raman spectroscopy and scanning electron microscopy with energy-dispersive X-rays (SEM-EDS) it was discovered that selenium-rich structures were forming throughout the paint films. The observed alteration is the result of degradation of the CdSSe pigment which occurs in the presence of chlorine and light. This research highlights the need for careful selection of restoration materials when dealing with objects suspected to contain residual chloride ions if desalination cannot be undertaken.

Evolution of the viscoelastic properties of painting stratigraphies: a moisture weathering and nanoindentation approach

In this investigation on the mechanical behaviour of paint films, we use a new ferrule-top nanoindentation protocol developed for cultural heritage studies to examine the impact of repeated relative humidity variations on the viscoelastic behaviour of paint films and their mechanical properties in different paint stratigraphies through the changes in their storage and loss moduli. We show that the moisture weathering impact on the micromechanics varies for each of these pigment-oil systems. Data from the nanoindentation protocol provide new insights into the evolution of the viscoelastic properties dsue to the impact of moisture weathering on paint films.

Easy-to-Make Polymer Hydrogels by UV-Curing for the Cleaning of Acrylic Emulsion Paint Films

The cleaning of acrylic emulsion paint surfaces poses a great challenge in the conservation field, due to their high water sensitivity. In this article, we present easy-to-make polymer hydrogels, made by UV-photopolymerization, that show excellent cleaning properties. The formulation of hydrogels obtained by UV-curing and their performance as dry cleaners for acrylic paints was investigated. First, different hydrogel formulations based on functional acrylic monomers were used to formulate a series of UV cross-linked hydrogels by fast UV photopolymerization. Their effectiveness on surface dirt removal was investigated by SEM microscopy and colorimetry. The hydrogels showed excellent cleaning properties and controlled water release, and they still performed satisfactorily after several cleaning uses. The obtained UV-hydrogels were compared to the well-known agar gels, showing benefits in terms of reducing excess water. This article shows that easy-to-make UV-cured hydrogels are an efficient tool for the cleaning of surface dirt from water-sensitive paintings, overcoming the limits of traditional cleaning methods.

A pilot study of solvent-based cleaning of yellow ochre oil paint: effect on mechanical properties

Nanoindentation and dynamic mechanical analysis were used to measure changes in the surface and bulk mechanical properties of Winsor & Newton Yellow Ochre oil paint films following exposure to deionized water, aliphatic mineral spirits (Shellsol D40™), and D5 silicone solvent (decamethylcyclopentasiloxane). Yellow ochre paint films were exposed to the selected solvents by 24-h immersion, and sponge-cleaning. 24-h immersion in deionised water and Shellsol D40 caused measurable changes to bulk and surface mechanical properties. However, there were no measurable changes to the bulk or surface mechanical properties following sponge cleaning.