Organic Silicone Resin Coatings As Protecting Films For Gold And Silver Commemorative Coins

When gold and silver commemorative coins were exposed in the airduring daily use and maintenance, some compounds including oxides,sulfides, carbonates, sulfites and other substances occurred on the coin surfacedue to chemical and physical reactions with oxygen, water vapor, carbondioxide, sulfur dioxide as well as some other organic matters. Subsequently,these compounds came to vulnerate the surface to form some little spots anddark veins and then were further abrased easily to cause a large area of injurybecause of their relative low hardness and poor abrasion resistance. Finally,these processes can destroy the structures of the fine design and gloss of goldand silver commemorative coins. In recent years, a coating film has attractedgreat interest for use to protect the surface of gold commemorative coins andmake them anti-oxidation and wear-resistant.The organic silicone resins can form the films which possessed someexcellent properties, such as high-hardness, scratch-resistance, high or lowtemperature-resistance, solvent-resistance, water-resistance and thetransmittance rate of above90%of visible light due to their high degree oftransparent. And they can improve the anti-moisture, anti-aging, anti-radiationand impact-resistance of the substrate. Thus, they have been widely used asthe coatings of hard wear-resistant on a variety of plastics and rubber products,especially organic glass products. These films can not only undermine thetransparency, but also improve the impact performance of the organic glass.The silicone resin coatings on the surface of cuprum, aluminum, iron, steeland other metals, not only prevented oxidation and maintained the originalmetallic luster, but also enabled the substrate to resist chemical corrosion andatmospheric corrosion.In this thesis, the research progress of organic silicone resins about thestructure, performance and applications was briefly reviewed. The preparation of organic silicone resins and fluorinated silicone resins and their applicationsin the coating industry were subsequently overviewed. Moreover, thecomposition of coatings and test methods of the coating films have also beensummarized.A series of novel transparent polysilicone coatings were preparedthrough the condensation reaction between the alkoxy groups ofmethyltrimethoxy-silane (MTMS) and γ-aminopropyltriethoxysilane(APTES) and hydroxyl groups of hydroxyl terminated silicone oil (HTSO).The coating films were made from these coating solutions on iron fleet, glassfleet and gold commemorative coin substrates. After curing, the structure andproperties of these films were characterized by FT-IR, UV, water contactangle, TG, and SEM. Their mechanical and medium-resistance propertieswere also evaluated. These coating films obtained possessed some goodproperties including high hydrophobicity, high water contact angles, highlight transmittance, good heat-resistance, adhesion, hardness andweatherability. Moreover, the protective films formed on the surface of coinswere uniform, clear, transparent and dense and did not cover the symphonysurface patterns or affect the metallic luster. Thus these polysilicone coatingswere prepared successfully to protect the surfaces of gold commemorativecoins.Transparent polysilicone coatings as protecting films for silvercommemorative coins were prepared by the hydrolysis and condensationpolymerization between methyl trithoxysilane (MTES) and tetraethoxysilane(TEOS) with an acid resin as the catalyst. The effect of different feed ratios onthe hydrophobic and heat-resistance of coating films were further studied. Thestructures and properties of coating films were characterized by FT-IR, watercontact angle, UV, TG, and SEM. Furthermore, the change of coating filmhardness along with the curing time extending and the effect of long-chainalkyl siloxane on the hydrophobic properties were also evaluated. A transparent room-temperature curing organic fluorosilicone coatingwere prepared by condensation reaction between hydroxyl terminatedfluorinated polymethylsiloxane, MTMS, and APTES. The coating films werecharacterized by FT-IR and their transmittances of visible light andheat-resistances were also investigated.