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Photochromic Dyes of Enhanced Performance

Photochromic compounds are those that can be reversibly transformed between two states having different absorption spectra, such change being induced in at least one direction by the action of electromagnetic radiation. Organic photochromics exhibit good coloration and, unlike the silver halides, can be incorporated into plastics, widening the fields of possible use. This chapter deals with the properties and synthesis of spiroindolinonaphthoxazines (SINOs) and chromenes, and reviews some of the optical and performance properties. The general method of a SINO synthesis is to condense a 1-nitroso-2-naphthol with a 2-methyleneindoline. Variants of the SINO system can, therefore, be produced by altering the substituents in the nitrosonaphthol, or by varying the nature of the methyleneindoline. In investigating the effect of varying substituents, it became apparent that improvements to the performance of the SINO were possible. The extent of fatigue that a photochromic dye undergoes is directly related to the energy in the form of UV light that it has received. Photochromic dyes have an intrinsic fatigue rate, even when all oxygen, water, and solvents are removed. Fatigue demonstrates itself as a reduction in colorability, loss in IOD, and an increase in yellowness of the bleached state. The performance of the dyes depends on the delivery systems, the pH, nature of the host polymer, and the method of application. Direct casting of photochromics into acrylics, polyurethanes, and polyolefins has been achieved.

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Reactive Trapping of 3,3′-Dichlorobenzidine Decomposition Products in Polyethylene-Based Diarylide Pigment Concentrates

The last 10 years have seen a steady decline in the use of lead and cadmium-based pigments in the coloration of polyethylene and polypropylene packaging materials and durable goods. Concerns over the thermal decomposition products of diarylide pigments in polyethylene matrices have severely limited the use of this versatile and cost-effective pigment family in many colorant applications. Largely as a result of environmental concerns, these relatively inexpensive, highly opaque, lightfast pigments have been replaced with expensive organic alternatives. The replacement pigments are much more expensive, much less strongly colored, less opaque, and they possess poorer light fastness. A strategy for the reactive trapping of 3, 3’-dichlorobenzidine—a potential human carcinogen formed during the high temperature processing of polyethylene concentrates—is discussed is this chapter. Chemical trapping tests made using maleic anhydride modified polymer additives showed favorable reactivity towards 3, 3’-DCB in model systems. The results of laboratory screening trials with Pigment Yellow 13 and Pigment Yellow 83 are also reported. The apparent complexity of the diarylide pigment decomposition reaction in LLDPE at typical processing temperatures (> 200 °C) made isolation, analysis, and quantification of residual 3, 3’-DCB levels extremely difficult.

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A comparative Study of the Use of High Intensity Dispersive Mixers and Co-Rotating Twin Screw Extruders in the Manufacture of High Quality Color Concentrates

Over the past three decades, high intensity dispersive mixing (HIDM) technologies have been adapted for specialized applications in the polyolefin and PVC compounding industries. High intensity dispersive mixers (also referred to as thermokinetic mixers) are unique in their ability to rapidly mix and melt polymer preparations in a single high-speed operation. This chapter provides a direct comparison of commercial-scale HIDM and twin-screw extrusion compounding technologies for the preparation of polyolefin color concentrates. Five commercial concentrate formulations were prepared independently on a 40-liter HIDM and a 60 mm co-rotating twin-screw extruder. A detailed analysis of dispersion quality and color strength is presented. HIDM operational parameters, pigments and fillers, and resin characteristics are also discussed in this chapter. Results indicate that these compounding technologies can provide virtually identical product quality when operating conditions are properly optimized. The results show that both HIDM and twin-screw compounding technologies can provide concentrate products with virtually identical quality when operating conditions are properly optimized. Where differences exist, they appear to be formulation specific. Both technologies offer equivalent ability to disperse organic and inorganic pigments effectively, although the twin-screw extruders provides the capability to increase shear stress, if required.

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Visual Color Matching and the Importance of Controlling External Variables

This chapter attempts to address and offer suggestions to the most critical areas that causes problems when color matching. Considering all technology available regarding color matching, visual color matching is still considered pivotal in quality control acceptance. The function of the light booths is to produce a particular spectrum of light that will reflect the proper colors off the sample. If there are any shifts in the spectral output, the samples mayor may not match. This is due to an effect known as Metamerism. This effect will cause samples to match under one lighting condition, but not under another. There are many items that contribute to shifting spectral outputs. These items include the age of the lamps in the light booth, the color of the inspectors' shirt being worn during the inspection process, ambient light, and sample size, just to name a few. One can expect a higher level of quality in color appearance by controlling these items. The only way to verify that the light booth is producing the correct spectral output is to measure the color temperature and foot-candles of the booth. The color temperature reading must be ± 200 degrees Kelvin and the intensity should be no less than 80-foot candles. If these readings are not within the specifications, proper corrective action should be taken to ensure the correct spectral output. This will greatly reduce color mismatches from master to sample and from light booth to light booth.

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Visual Texture

Surface texture imparted to polymer has a long history of use. These include masking surface imperfections, creating special effects, imitating natural materials such as leather, or help hide scuffmarks and fingerprints. Surface texture is usually controlled by the properties of the surface onto which a part is cast, molded, or embossed. Physical texture can be applied to the surface to change its tactile properties. The control of slip is an important parameter in the design of some products. However, most texturing of polymer surfaces seems to be used to control “visual” effects. Texture creates a pattern of light and dark areas that might be characterized as a shadow-scatter mask. Texturing is primarily accomplished by embossing the surface of the polymer. An alternative technique for creating the visual appearance of texture while maintaining a smooth surface has been developed by creating homogeneous patterns in the polymer melt. This technique optically breaks up the surface appearance, creating a visual texture. Most polymer processes including extrusion and injection molding are amenable to this technique. A method of imparting a visual texture appearance throughout a polymer part has been developed. This effect is available in a variety of foreground and background colors, and domain sizes giving the appearance of a through colored texture. Applications include masking defects, hiding dirt,and simulating natural materials such as stone, marble, and leather.

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Customized Decorating of Plastic Parts with Gray Scale and Multi-Color Images Using Lasers

This chapter discusses the techniques whereby sophisticated graphic images can be manipulated to optimize their appearance in decorative laser marking of polymers. This involves the manipulation of digitized bitmap images to obtain vector images suitable for laser writing, the choice of fill patterns to achieve the desired gray scale image quality, and evaluating the interaction of the laser with the desired polymers. Various examples of grayscale and color decorative images marked on suitable polymers are also presented. Customized decorating with sophisticated graphic images applied using lasers is a new value-adding process applicable to plastic parts. Many of the techniques familiar for printing on paper, such as halftone and dithering, are applicable to polymers using indelible direct-write laser marking technology. Computer-software methods applicable to transfer graphics to a format suitable for laser marking are described and examples of decoration applied to suitable polymers, including color marking, are also presented in the chapter. The most sophisticated laser marking technology, most suitable for decorative marking of graphic images, is the directed beam “laser-writing” scenario, which usually utilizes the solid state Nd:YAG (Neodymium: Yttrium Aluminum Gamet) laser. In this scheme, a PC computer drives two galvanometer-mounted mirrors, which scan the YAG laser beam in a suitable pattern focused on the sample to be marked. Other lasers than the YAG laser can also be used within the laser writing format if that is what is required to mark the polymer in question.

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Multi-Angle Spectrophotometers for Metallic, Pearlescent, and Special Effects Colors

Designers use special effects in new and innovative designs, which force quality engineers to search for more consistent and accurate means of quantifying color in the manufacturing process. When evaluating exterior automotive color differences with instrumentation, there are a number of variables that need to be considered, the most important being instrument geometry. Other areas of focus are color standards, paint technologies, part configuration, part orientation and, of course, visual comparison. Utilizing recent technology, one can now accurately monitor and control automotive colors with the use of a multi-angle spectrophotometer. Multi-angle color measurement is an essential tool in identifying and reducing color variation in processes that use metallic, pearlescent, and special effects color. There are also several options available in using the instrument to reduce the variation amongst standards, the key being to use the multi-angle spectrophotometer and a selected population of standards to quantify the actual target standard. Throughout the paint manufacturing process, several conditions may warrant the development of an offset standard. This too should be a physical and quantifiable target. In many of the processes, several variables relating to processing, application, and curing of color on car bodies and components need to be monitored and related to color measurements. Visual assessment information should be gathered in conjunction with multi-angle measurements so that objective color evaluation and development of meaningful tolerance can be achieved. Success is total assembly color harmony with no color mismatches and continuous, consistent color from front to back, side to side, from top to bottom, and from body to parts.

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Relationship Between the Microstructure and the Properties of Rotationally Molded Plastics

In this chapter, work done on polyethylene and polypropylene rotational moldings is presented to illustrate the influence of a number of factors: molding temperature, grinding and mixing conditions, type of pigment, antioxidant level, mold material, and inner atmosphere. The effects of pigments are investigated as well as the mechanical and thermal processes that plastic powders typically undergo during preparation for roto-molding. In all cases, the mechanical properties of the molded articles have been related to the microstructure. The rotational molding process has characteristic features that make the microstructure of the molded plastic articles unique. The polymer microstructure in the bulk, and also at the inner surface layer, has a major influence on the mechanical properties of the molded material. In rotational molding, polyethylene and polypropylene polymers show different degradation behavior. While the thermo-oxidative degradation causes mainly chain scission in polypropylene, cross-linking dominates in polyethylene. The use of increased amounts of antioxidant in the polymer, or the use of an inert atmosphere, delays the degradation but does not prevent it. It has also been observed that the thermomechanical effects caused by the mixing processes commonly used to add pigments increase the mechanical properties of polyethylene products. Finally, the nucleating activity of the pigment combined with the mixing process, has a major effect on the microstructure and on the mechanical properties of the final products.

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