Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
2000-06-22
2002-03-12
Sanders, Kriellion A. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
active
06355723
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to thermoplastic molding compositions. In particular, the invention relates to colored thermoplastic compositions and articles molded therefrom.
Lighting reflectors, especially for automotive applications, require materials that can withstand the high heat produced by light sources, that have excellent dimensional stability to focus the light in a tight pattern at long distances, and that can be easily processed into complex shapes. These reflectors are usually coated with a metal, such as aluminum, to provide a highly reflective surface. To achieve this high degree of reflectivity with low haze, a very smooth pre-coated surface is required. In order to consistently achieve such a smooth pre-coated surface, it has typically been necessary to base coat the molded reflector with a primer prior to coating the reflector with metal. Efforts to simplify production of these metalized plastic articles by coating metal directly onto the molded reflector have resulted in intolerable waste because of difficulty identifying defective molded articles before the metal coating has been applied. The defective articles have surface blemishes that become noticeable only after a metal coating is applied, causing the parts to be discarded and creating an inefficient use of the coating equipment as well as loss of the thermoplastic resin. Direct metalization of molded parts is also challenging because it introduces the additional requirements of good adhesion of the metal to the molded part and a very smooth surface of the part as molded.
There is therefore a need for molded reflectors satisfying the simultaneous requirements of high temperature stability, high surface smoothness, good adhesion to metal coatings, and ready detectability of surface defects in the reflectors as molded, as well as high reflectivity, low haze, and low diffuse reflectivity after metalization.
BRIEF SUMMARY OF THE INVENTION
High temperature stability, high surface smoothness, good adhesion to metal coatings, and ready detectability of surface defects are provided by an article comprising: (a) a single phase amorphous thermoplastic resin or resin blend having a glass transition temperature (T
g
) not less than about 170° C.; and (b) at least one colorant; wherein a surface of the article exhibits a CIE lightness value (L*) not greater than about 50, and a 20° gloss value per ASTM D523 not less than about 100.
DETAILED DESCRIPTION OF THE INVENTION
Molded articles suitable for direct metalization comprise: (a) a single phase amorphous thermoplastic resin or resin blend having a glass transition temperature (T
g
) not less than about 170° C.; and (b) at least one colorant; wherein a surface of the article exhibits a CIE lightness value (L*) not greater than about 50, and a 20° gloss value per ASTM D523 not less than about 100. After metalization, a surface of the article exhibits a haze value not greater than about 1%, and a diffuse reflectivity not greater than about 1%.
We have discovered that to obtain a directly metalized article with high dimensional stability, a high degree of reflectivity, low diffuse reflectivity, and low haze, it is important that the article comprise a single phase amorphous polymeric resin or resin blend and be substantially free of solid particles and particle aggregates that can detract from the above properties. The use of single phase amorphous resins, rather than crystalline resins, improves the dimensional stability of the molded articles. Limiting the amounts of solid particles and particle aggregates is preferred to ensure high gloss in the article as molded, and low haze and low diffuse reflectivity after the article is metalized. While an unfilled, uncolored resin, like polyetherimide resin, can be directly metalized to give a low haze, high gloss surface that can withstand high heat, it is often difficult to detect blemishes on such transparent articles and discard blemished articles prior to metalization and coating operations. We have found that articles molded from dark thermoplastic resin compositions make surface blemishes, such as splay and shark skin, more noticeable in visual inspections. Thus, the use of dark compositions facilitates visual identification of blemishes prior to metalization, thereby reducing waste and expense. In addition, a partially metalized article may have transparent portions that allow some light to escape. This escaped light may interfere with focusing the light from such a lamp; for instance an unmetalized ring of transparent resin surrounding the bulb opening can create an undesired halo around the bulb. The dark compositions of the invention prevent this problem. We have also found that known opacifying techniques, such as the addition of standard colorants, like titanium dioxide or carbon black, and the addition of non-miscible polymers (such as polyolefins or polycarbonates), cause unacceptable losses of surface smoothness and gloss, and increased haze and diffuse reflectivity of the articles once metalized.
Single phase amorphous thermoplastic resins suitable for use in the articles include polyetherimides, polyarylethers, polyethersulfones, polysulfones, polycarbonates, polyestercarbonates, polyarylates, polyamides, polyesters, and single phase blends comprising at least one of the foregoing resins. The use of polyetherimides and single phase blends comprising polyetherimides, such as polyester polyetherimide blends, is presently preferred. The thermoplastic resin or resin blend has a glass transition temperature, T
g
, greater than about 170° C., preferably greater than about 185° C., more preferably greater than about 200° C. The thermoplastic resins above are generally commercially available, and methods for their synthesis and blending are well known in the art.
While the proportion of thermoplastic resin or resin blend in the article may vary considerably, it is generally at least 80% by weight of the article. In a preferred embodiment, the thermoplastic resin or resin blend is present at about 90 to 99.99 weight percent, preferably about 95 to 99.99 weight percent, more preferably about 97 to 99.99 weight percent.
Synthetic colorants are typically derived from coal tar or petroleum intermediates. Colorants of many distinct types are available for use in plastics and coatings. The Color Index names many different chemical classes of colorants, including, for example, nitroso, nitro, mono azo, diazo, triazo, polyazo, azoic, stilbene, carotenoid, diphenylmethane, triarylmethane, xanthene, quinoline, acridine, methine, thiazole, indamine, indophenol, azine, oxazine, thiazine, sulfur, lactone, aminoketone, hydroxyketone, anthraquinone, indigloid, and phthalocyanine, as well as inorganic pigments. Colorants may be organic or inorganic, dyes or pigments.
Dyes are colorants that do not normally scatter light but absorb light at some visible wavelength. Dyes are often soluble, at some concentration, in the polymer matrix of a colored article. Pigments are organic or inorganic colorants that are usually present in a matrix as discrete particles insoluble in the matrix. The designation of a given colorant as pigment or dye will depend on the polymer matrix, colorant concentration and crystallinity, temperature, and other factors. Preferred colorants are soluble in the matrix resins at the concentrations employed to color the article.
Colorants suitable for use in the articles also generally exhibit high extinction coefficients and high thermal stability. High thermal stability is defined as the absence of significant color shift or thermal degradation when processed at temperatures of 250-350° C. required to form the articles of the invention from the resins indicated above. In addition, the colorants should not attack or degrade the resin resulting in an unacceptable loss of mechanical properties or generation of gaseous by-products during molding.
Suitable colorants having good thermal stability include those known under their Color Index numbers as solvent green 3, solvent green 28, solvent
Bu Jenny Z.
Codella Peter J.
Gallucci Robert R.
Kopp Dennis A.
Lindway Martin J.
General Electric Co.
Sanders Kriellion A.
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