Light stability colourant

The process of post-chlorinating PVC was carried out during World War II in order to obtain polymers soluble in low-cost solvents and which could therefore be used for fibres and lacquers. The derivate was generally prepared by passing chlorine through a solution of PVC in tetrachloroethane at between 50°C and 100°C. Solvents for the product included methylene dichloride, butyl acetate and acetone. These materials were of limited value because of their poor colour, poor light stability, shock brittleness and comparatively low softening point. 

The first synthetic polymers to be used as paint varnishes were acrylic and vinylic resins. Poly(vinyl acetate) (PVAc), commercialized under the name Mowilith by Hoechst and Vinylite by Union Carbide, has been used in conservation as an adhesive since 1932 and in 1937 it was proposed as a picture varnish by Stout and Cross [63]. PVAc was soon rejected as a varnish because, despite its light stability and good solubility in organic solvents, it demonstrated poor optical properties in terms of colour saturation and the tendency to pick up dirt due to its low glass transition temperature. 

Metal phthalocyanines are extremely important materials in a variety of fields ont-side their traditional nse as dyes and pigments (Chapter 2, sections 2.3.1.6 and 2.4.1.4), inclnding electrochromism. The properties of metallophthalocyanines make them attractive as potential electrochromic materials, e.g. high light stability, high molar absorption coefficients, stable and sublimable at high temperatures, and the possibility of multi-colours within one structure. 

One of the features of consumer properties of chemical fibres and goods on their basis is light stability of polymer itself and its colour and also colour resistance to the action of wet treatment. 

Photosensitized degradations of substrates (PC or PMMA) by colourants in optical disc have to be considered, as some dyes and pigments having an absorption band in the visible region have a destabilizing effect on the light stability of polymer (39). However, no systematic investigations of that problem has been published yet, as far as we know. 

Compared with acrylic glass, polystyrene has a lower light stability and resistance to ultraviolet radiation. The slight degradation when exposed to ultraviolet radiation is a disadvantage that occurs with all optical plastics. The higher refractive index of polystyrene permits its use in conjunction with acrylic lenses for the design of colour-... 

It is necessary to use fully saturated intermediates in making transparent PUs with good light stability as they do not discolour when oxidized, unlike the unsaturated materials. For this reason aliphatic diisocyanates are preferred and also because they avoid the molecular resonance effects produced by the benzenoid rings of the aromatic diisocyanates which can also lead to colouration. 

The demands made by a coatings specialist on microbicides are tough they must have a low toxicity, good light stability and good compatibility with the other components in a formulation they must also be non-volatile, colour-fast, odourless, insoluble in water (and thus non-leaching) and economical. As microbicides which satisfy all these requirements are not available, one has to find compromises. 

In respect of colour shade, cochineal can substitute the synthetic colours and it possesses a far better light stability (Ohlen and Bertelsen, 1989). According to Danish food legislation, cochineal is permitted at levels up to 100 ppm when calculated as the active component carmine acid (Positivlisten, 1988). 

A special blend of polymers available in standard primary colours that can enhance colour and light stability, chemical resistance, and the component surface impact resistance. 

A special blend of polyester polymers of excellent clarity, colour and light stability which can be spray applied, alone or added to gelcoat for repairs or to upgrade a tooling gel coat. 

It is also recommended to use Sodium Pyrithion for the dry film protection of paints and adhesives. However in such applications one has to bear in mind in particular the colouration risk, the limited light stability and the leachability of the the active compound. 

---