Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2000-05-16
2002-11-05
Szekely, Peter (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C524S087000, C524S537000, C524S539000, C524S601000, C524S605000, C524S611000
Reexamination Certificate
active
06476158
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to colored polycarbonate-polyester compositions having improved weathering properties and process for their formation.
BACKGROUND OF THE INVENTION
Polyester resins derived from terephthalic acid and reactive derivatives thereof, such as dimethyl terephthalate, and alkanediols have been known for some time and have become important constituents for moldable compositions. Workpieces molded from such polyester resin compositions, alone, or combined with reinforcements, offer a high degree of surface hardness, solvent resistance, abrasion resistance, and high gloss. More recently, blends of such polyester resins with one or more second resins have become of significant commercial interest because such second resins, carefully selected, can greatly improve impact strength, as well as tensile strength, modulus, dimensional stability and distortion temperature under load in parts molded from such compositions. Such second resins can comprise aromatic polycarbonate resins as described for example, in Kawase et al, U.S. Pat. No. 3,953,539 and related polyester-carbonate and polyarylate resins.
Polyester-Polycarbonate blends, like most other plastics, are typically colored with carbon black and titanium dioxide used alone, in combination or with other colorants to produce a range of resins and articles made color. Both titanium dioxide and carbon black are present in such blends as discrete particles. Such typically colored polycarbonate/polyester blends tend to develop haze and surface roughness when subjected to weathering, i.e. either accelerated artificial weathering or natural outdoor weather. This surface roughness shows up as a loss of gloss and/or a color shift. This loss of appearance poses a serious problem for aesthetic applications which require retention of a high gloss appearance.
Hence, it is desirable to obtain improved weathering properties from such colored resins so a high gloss appearance can be retained.
SUMMARY OF THE INVENTION
The present invention provides a process for identification and preparation of high gloss retention resin molding formulations comprising a polyester resin and a polycarbonate, polyarylate or polyester carbonate resin where the process comprises the steps of selecting a desirable colorant which is stable at molding temperatures in the resin mixture and has desirable color retention properties when subjected to weathering, determining an optimized concentration of the colorant for maximizing gloss retention properties of the selected colorant by performing weathering testing at differing concentrations of the colorant, and optionally determining a suitable gloss retention agent for addition to the formulation.
In a preferred embodiment of the present invention molding compositions will comprise (a) from 10 to 90 weight percent of a polyester resin; (c) from 90 to 10 weight percent of an aromatic polycarbonate, polyarylate, polyester carbonate resin or blend thereof and a colorant or colorants in a sufficient amount to give a desirable coloration with the optional addition of a suitable gloss retention agent or impact modifier.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
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 hundreds of different colorants of many different chemical classes for instance; 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, phthalocyanine and inorganic pigments. Colorants may be organic or inorganic, being dyes and 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 is somewhat arbitrary since it will depend on the polymer matrix, colorant concentration, temperature, crystallinity and other factors.
Despite this huge variety of colorants there exists a problem in finding suitable colorants for thermoplastic polyester- polycarbonate blends, especially blends that will be exposed to direct sunlight and outdoor weathering. The colorant must be stable to polymer processing at high temperature, must not chemically degrade the resin matrix, must provide molded articles that have good initial color tone and high gloss and then, most difficult to achieve, retain the color, gloss and properties under weathering. We have found that surprisingly few specific colorants, that we believe must largely be soluble or very finely dispersed in a specific polyester blend matrix, give shaped articles with good as molded color and gloss and retain a significant portion or those properties when weathered under natural or artificial conditions.
It is desirable to select a colorant that exhibits good color and gloss retention when subjected to weathering test. Color shift and gloss should be desirably measured by a standard test so that comparison data may be generated to select a desirable dye colorant. Color shift measurements may be measured using the CieLAB system using L, a, b values to calculate a color shift: delta E, compared to an unweathered control. Surface gloss, often measured as 60° gloss values using ASTM D523, can also be monitored as a function of exposure time under normal weathering or in an accelerated weathering apparatus (“weatherometer”) to determine resistance of a material to loss of properties due to photo-aging. The weatherometer as referred to in this application was run according to conditions given in the SAE J1960 or ASTM G26 protocols. Details of the weathering tests are discussed in the examples of the invention.
Examples of the invention will have high gloss as molded, that is with a 60° gloss of ≧80%, most preferred with a gloss of ≧90%, and will show greater than or equal to 50% retention of said initial gloss after 1000 hours of accelerated weathering under ASTM G26 or SAE J1060 test conditions. The preferred compositions of the invention will show ≧50% retention of initial gloss after 3000 hours ASTM G26 or SAE J1960 accelerated weathering. The most preferred compositions of the invention will show 50% or greater retention of the initial gloss after 5000 hours of ASTM G26 or SAE J1960 accelerated weathering.
In addition to selecting a colorant that exhibits good color retention when subjected to weathering, it is desirable to independently check the colorant for gloss retention by performing separate weathering test at different concentrations of colorant to find the concentration with the desired optimized gloss retention.
Even further enhanced gloss retention may be desirably achieved with additions of a suitable gloss retention agent such as an UV absorber, for example, benzotriazoles. UV absorbers may be used in any effective concentration with ranges of 0.1-2.0 wt.% (based on the whole composition) being most preferred.
Preferred colorants of the invention having good thermal stability on processing and good retention of gloss during weathering of the compositions of the invention are: solvent green 3, solvent green 28, solvent red 52, solvent red 111, solvent red 135, solvent red 169, solvent red 179, solvent red 207, disperse red 22, vat red 41, solvent orange 60, solvent orange 63, solvent violet 13, solvent violet 14, solvent violet 50, pigment blue 29, amino ketone black (KEYSTONE BLACK AN from Keystone Aniline Co.), disperse blue 73, solvent blue 97, solvent blue 101, solvent blue 104, solvent blue 138, pigment yellow 139, disperse yellow 160, solvent yellow 84, solvent yellow 93, solvent yellow 98, solvent yellow 163 and solvent yellow 160:1.
The most pr
England William P.
Gallucci Robert Russell
Hans Paul Joseph
Hubbard Patricia A.
Whalen David
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