Papers by Author: Peter Hope

Abstract: Classical EPD has typically been conducted in organic solvent media. Many suitable solvents are volatile and highly flammable and this limits the industrial application of the technique on the basis of safety alone. Aqueous EPD may be seen as a safer method, but issues relating to electrolysis and surface energy phenomena become prominent and can create interferences and variability unless the substrate type and its preparation are compatible with the aqueous EPD chemistry and its deposition method. As EPD layers become thinner, factors such as substrate surface structure and wettability become more critical. Industrial processes utilising some principles of EPD for applying paint from water-based preparations are well established in the metal finishing sector. Consequently there is a significant body of practical experience available from this sector that can be of use in translating classical EPD from a solvent to an aqueous technique while avoiding interferences inherent in the use of water as the deposition medium. In this paper, substrate selection is discussed in relation to the electrolyte content of the system where phenomena such as dissolution and micro-arcing can occur. The initial wetting of the substrate must be considered prior to applying voltage. Surface preparation techniques and the methods of introducing the substrate into the EPD dispersion all can have an impact on the final result. Note: This paper is based on the authors’ personal and practical experience of industrial electrophoretic painting over more than 40 years. Only metal substrates are discussed because these have been almost exclusive in this sector during that time. Non-metal substrates such as conductive plastics, graphite and carbon fibre have also been coated with electrophoretic paints but this is not yet at any significant scale and so no general principles have been established

Abstract: nvestigating the electrodeposition properties of PEEK from solvents such as ethanol and acetone presents difficulties due to the higher density of the polymer particles relative to that of the solvent. The settling rate in unagitated baths is too rapid to obtain consistent deposits. Whole-bath or bulk agitation aimed at maintaining particle suspension can disturb electrodeposits due to eddies and other turbulent flow effects. To eliminate settling, mixtures of two solvents have been employed, the individual solvents having respectively lower and higher densities than PEEK. The proportions of the mixture are adjusted to be the same density as PEEK so that a colloid-like suspension of PEEK particles is possible. This enables the electrodeposition of PEEK to be studied without any significant gravitation or whole-bath agitation effects. Eliminating mechanical agitation of the suspension enables a study of the influence of target electrode movement alone on the rate and quality of electrodeposition. Note: The origin of this paper is in a project to establish if PEEK could be applied as a controllable conformal thin film onto a specific non-planar substrate geometry by using electrophoretic deposition. The paper describes only the development of a reliable methodology to investigate the feasibility of this project. The details of the project as a whole are outside the scope of the paper.

Abstract: Semi-automatic handguns characterised by the classic Colt 1911 model rely on a reciprocating slide mechanism for loading and ejecting. The moving surfaces require a tight fit to maintain firing accuracy while having ease of movement to avoid misloading or jamming. The electrophoretic painting method is ideal for coating complex geometries where engineering tolerances need to be maintained. The anodically depositable paint system developed for this application incorporates nanosilica for reinforcement of the resin binder and a blend of polytetrafluoroethylene, boron nitride and molybdenum disulphide to provide a self-lubricating anti-corrosive coating. Colourants have been added to provide various appearance attributes. The formulating procedures for producing this type of complex electrophoretic paint are described. This includes considerations of manufacture, shelf life, shipping, application by the customer, and compliance with health and environmental regulations as well as meeting the extreme performance requirements of the end use.

Abstract: Electrophoretic deposition or EPD is a well established method for creating decorative and protective coatings and other structures on various electroconductive substrates. The formation of these coatings and structures can be prejudiced by the presence of oversized or contaminant particles as well as excess or contaminant electrolytes resulting in appearance and performance problems in the final product. Nuisance particles come from diverse sources and are an inevitability in industrial environments. Efficient and effective particle capture strategies are therefore essential. In water-based EPD processes, control over the content electrolytes and other continuous phase materials can be accomplished using tangential or cross-flow filtration where the permeate contains the undesirable materials and can be treated or disposed of outside the system. But for particles and other disperse phase materials, dead-end filtration techniques are required. Here the undesirable materials are captured, concentrated and retained on the filter medium within the system. Disposal only occurs as a result of discarding or treating the filter medium itself. Many types of dead-end filtration media are commercially available. Retention size and materials of construction all have relevance for system compatibility and effectiveness of particle capture. Practical experience shows that selection of the correct type of particle filtration optimises process quality. Using inappropriate filter media can be not just ineffective, but actively detrimental. This paper describes commonly available particle filter systems and how they interact with industrial EPD process.