Polyester resin colourant

For this use, the preferred powders are based on acrylic, epoxy or polyester and epoxy resins. For best colour, epoxy resins are crosslinked with anhydrides of dicarboxylic acids in the straight epoxy coatings, or with saturated polyesters of high acid content in the epoxy-polyester type. Acrylics contain epoxide rings via, for example, glycidyl methacrylate (CH2=C(CH3) —CO—O—CHj—CH —CH2), and these groups crosslink... 

Dyes can be used to obtain transparent colours in polyester resins. Considerable care in their selection needs to be taken as most will quickly fade on the addition of catalyst to the liquid resin or on exposure of the cured resin outdoors. However, certain quinone-type aromatic-soluble dyes in the yellow-red range are extremely lightfast and transparent blues and greens can be satisfactorily produced using small quantities of the corresponding phthalocyanine pigments. 

Although more expensive, saturated polyester resins have better colour retention and water-resistance. Ether linkages are water-sensitive (diethyl ether, C2H3 0 C2H5, is partly soluble in water) and in polyethers they are repeated throughout the polymer chain without the separation by long, water-insensitive hydrocarbon chains which could offset their effect. 

Non-drying short oil polyester in combination with melamine-formaldehyde (MF) resin can also be used as a binder for stoving paint, as it can be cured at a high temperature and possesses a dark colour. A short oil polyester resin based on Mesua ferrea L. seed oil (consisting of monoglyceride of the oil, phthalic and maleic anhydrides) has been successfully used in the preparation of industrial stoving paint in combination with partially n-butylated MF resin. ° The performance characteristics of this paint are comparable with those of industrially used castor oil-based paint with the same formulation and processing conditions. As this oil is much cheaper than industrially used castor oil, the final cost of the test paint is lower than that of the standard paint. 

A good basecoat is important in a COB system. Coloured metallic basecoats use strong, transparent, light fast pigments dispersed in an oil free polyester resin. As the film thickness is thin, relatively high levels of pigment are required to give deep metallic shades. 

The basic difference between the latter type of resins and the alkyds is that they do not contain oil or oil-derived fatty acids which are otherwise an integral part of conventional baking alkyds. The absence of oil imparts a light colour to the resins and eliminates post-embrittlement caused by the oxidation of double bonds present in oils. Also, the elimination of long-chain fatty acids gives improved chemical resistance. A unique hardness-to-flexibility relationship with polyester resins made it possible to attain greater hardness with higher reverse impact than is possible with current systems. 

David s Isopon, being a typical product, consists of a two-part filled polyester resin with catalyst. The tin contains the resin while a tube of catalyst is fitted inside the plastic lid. The recommended mixing proportions for small jobs are to take a golfball size lump of resin with a bead of catalyst as big as a pea. These are mixed together to an even colour on a clean sheet of metal or plastic. It must be applied promptly as initial setting takes place within about five minutes, although some hours are required for it to reach full strength. 

When the resin temperature drops below the boiling point of the reactive diluent (usually styrene) the resin is pumped into a blending tank containing suitability inhibited diluent. It is common practice to employ a mixture of inhibitors in order to obtain a balance of properties in respect of colour, storage stability and gelation rate of catalysed resin. A typical system based on the above polyester fomulation would be ... 

Compared with the phenolics and polyesters the resins have better heat resistance, better chemical resistance, particularly to alkalis, greater hardness and better water resistance. In these respects they are similar to, and often slightly superior to, the epoxide resins. Unlike the epoxides they have a poor adhesion to wood and metal, this being somewhat improved by incorporating plasticisers such as poly(vinyl acetate) and poly(vinyl formal) but with a consequent reduction in chemical resistance. The cured resins are black in colour. 

Organotin compounds such as monobutyltin oxide, the main substance used, accounting for 70% of consumption, dibutyltin oxide, monooctyltin oxide, and dioctyltin oxide are used in certain esterification and transesterification reactions, at concentrations between 0.001% and 0.5% by weight. They are used in the production of substances such as phthalates, polyesters, alkyd resins, fatty acid esters, and adipates and in trans-esterifications. These substances are in turn used as plasticizers, synthetic lubricants, and coatings. Organo-tins are used as catalysts to reduce the formation of unwanted by-products and also provide the required colour properties (ETICA, 2002). 

Decorative laminate is defined in ISO 472 but in common usage has come to mean sheet materials consisting of decorative surface papers impregnated with melamine resin and consolidated under heat and pressure with plies of core paper permeated with phenolic resin. In a wider sense the term can be applied to many associated products—including laminates in solid colour laminates with facings such as metal foils, textiles, or wood veneers polyester laminates direct faced boards and composite boards comprising thin laminates bonded to substrates of various kinds. 

A continuously manufactured sheet consisting of layers of fibrous sheet material (for example, paper) impregnated with phenolic and/or aminoplastic and/or polyester thermosetting resins, assembled and bonded together by means of heat and pressure, the outer layer or layers on one side having decorative colours or designs. 

---