Coatings ultraviolet absorbers

The exterior durabiHty of relatively stable coatings can be enhanced by use of additives. Ultraviolet absorbers reduce the absorption of uv by the resins and hence decrease the rate of photodegradation. Eurther improvements can be gained by also adding free-radical trap antioxidants (qv) such as hindered phenols and especially hindered amine light stabilizers (HALS). A discussion of various types of additives is available (113). 

C.W. Huck, M.R. Buchmeiser and G.K. Bonn, Fast analysis of flavonoids in plant extracts by liquid chromatography-ultraviolet absorbance detection on poly(carboxylic acid)coated silica and electrospray ionization tandem mass spectrometric detection. J. Chromatogr.A 943 (2002) 33-38. 

Figure 48. Ultraviolet absorbance spectrum of IBM s experimental mid UV resist. The resist was coated on quartz and the spectrum was recorded before and after exposure. This figure should be compared to Figure 24 with respect to the extent of bleaching at 313 and 334 nm.

Derivatization is a procedure in which analyte is chemically modified to make it easier to detect or separate. For example, formaldehyde and other aldehydes and ketones in air, breath, or cigarette smoke25 can be trapped and derivatized by passing air through a tiny cartridge containing 0.35 g of silica coated with 0.3 wt% 2,4-dinitrophenylhydrazine. Carbonyls are converted into the 2,4-dinitrophenylhydrazone derivative, which is eluted with 5 mL of acetonitrile and analyzed by HPLC. The products are readily detected by their strong ultraviolet absorbance near 360 nm. 

Detection and Identification Detection and identification of solute bands is done by methods essentially the same as those described in Column Chromatography. However, in TLC an additional method cal led fluorescence quenching is also used. In this procedure, an inorganic phosphor is mixed with the adsorbent before it is coated on the plate. When the developed chromatogram is irradiated with ultraviolet light, the surface of the plate fluoresces with a characteristic color, except in those places where ultraviolet-absorbing solutes are situated. These quench the fluorescence and are detectable as dark spots. 

The amount of radiation required to decompose the PM photoinitiator in a coating 0.2-0.3 mil thick on aluminum was determined spectrophotometrically by changes in the ultraviolet absorbance following exposure to a mercury arc ( ). By this method it was determined that more than 90% of the PM was photo-lyzed during two seconds exposure to the UA-3 arc at a distance of 4.5 inches (see Figure 1). The radiation dose received by the sample under these conditions was 0.70 joule/cm. ... 

Ultraviolet Absorbers, Light Stabilizers, and Antioxidants. Ultraviolet absorbers and light stabilizers can be added to urethane coatings in order to increase their resistance to discoloration and to outdoor weathering. UV absorbers are employed to eliminate the radiation in the region of 334 and 411 um that sensitize the polyurethanes and promote an autoxidation process. Light stabilizers on the other hand do not absorb UV radiations but inhibit or control the degradation by other means. 

Clear organic coatings have been developed to preserve the attractive, bright, as-polished, zinc, zinc alloy, or zinc-coated surfaces. The coatings may be either acrylic or polyurethane lacquers or polyester powders and may be colorless or tinted, usually to simulate brass. They usually incorporate ultraviolet absorbers and a complexing agent for zinc (dithiooxamide). They have only a limited life and, in the atmosphere, usually must be renewed after 3-10 years (depending on the environment) to retain appearance. 

Resistance to ultraviolet radiation is limited. This is because of the strong absorption of ultraviolet by the aromatic species. It can be addressed by coating the PAEK components or to some extent by incorporating ultraviolet absorbers of reflectors. Unfortunately many standard ultraviolet stabilisers are too volatile or lack the thermal stability required to work well in PAEK. 

Coatings may be used as carriers for chemicals that stabilize objects, e.g. corrosion inhibitors and ultraviolet absorbers. 

A potential route to weatherization of plastics Is to coat them with a layer of transparent, ultraviolet absorbing polymer which Is Itself weatherable. A promising candidate Is a copolymer of methylmethacrylate and a vinyl derivative of an ultraviolet absorber chromophore. If the concentration of the chromophore does not exceed 10-15 mole percent, the copolymer Is likely to retain the mechanical and optical properties of FMMA for certain classes of ultraviolet chromophores. Hence, an Investigation of the pho-tostablllty of copolymers of this type was undertaken In order to determine the feasibility of development of UV absorbing transparent coatings. 

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