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
2000-08-08
2002-08-27
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...
C524S209000, C524S111000, C524S128000, C524S151000, C524S153000
Reexamination Certificate
active
06441071
ABSTRACT:
Polycarbonate resins offer an excellent balance of properties with respect to transparency, toughness, dimensional stability and heat resistance. These properties make polycarbonate an ideal choice for the preparation of many types of molded, shaped or otherwise fabricated articles, especially including sheets or other structures and parts to be used in glazing and other outdoor applications. However, polycarbonates, like most organic polymers, degrade when they are exposed to ultraviolet light. As the polycarbonate absorbs significant amounts of high energy light and begins to degrade, it is known to become yellow and hazy and lose its toughness. Since polycarbonates derive much of their value and utility from their excellent optical properties, i.e. low color and high clarity, protection against UV becomes vital.
The use of various types of UV absorbers in the stabilization of polymers is well known. See for example U.S. Pat. No. 3,215,725 (bis cyano-diphenyl-acrylic acid esters); U.S. Pat. No. 4,812,498 (bis benzotriazoles); U.S. Pat. No. 5,288,778; GB Patent 2,290,745 and EP 825,226 (triazine compounds); U.S. Pat. No. 5,821,380 (multifunctional 2-cyanoacrylic esters); EP 68,327 (cyclic imino esters also referred to benzoxazinones) and EP 110, 221 (benzophenones and benzotriazoles). These stabilizers function by absorbing incident UV radiation and dispersing the absorbed energy in a nondestructive manner. Their overall effectiveness in preventing UV degradation of the polymer depends on numerous factors, including absorptivity, compatibility, stability and distribution within the polymer. Their UV absorption effectiveness is a function of their concentration in the polymer, especially near the surface. Concentration of the UV absorber near the surface of the polymer is very desirable to prevent penetration of UV light is considered to be more efficient and economical than dispersion of the UV absorber throughout the bulk of the polymer.
It is critical, therefore, for effective UV stabilization of polymers to have effective concentrations of UV absorbers present near the surface after processing and during long term. Both chemical and physical losses of the UV absorber will affect the concentration of UV absorbers in polymers. Chemical losses result from the thermal, photo-oxidative and oxidative reactions that inactivate or consume the compounds themselves. Physical loss of the UV-absorber involves the removal of material from the surface by evaporation or dissolution that is not offset by its replacement in the surface layer by diffusion from the bulk polymer
When UV-absorbers are physically lost from polymers, this may lead to undesired effects, such as fuming and plate-out in sheet extrusion or juicing and mould sweat during injection molding. All of these phenomena will result in reduced UV absorber concentrations in the resin and reduced production rates due to frequent, necessary cleaning operations of the equipment. Improved retention of a UV-absorber conversely provides more effective stabilization in the desired end use as well as better processability in terms of reduced fuming, plate-out, mould sweat, juicing, etc.
Various methods have been used to improve the UV-stability of polycarbonate. Common approaches are to use UV-absorbers as additives in the polycarbonate and to apply surface layers or other surface treatments to prepare structures where the UV absorbers can be concentrated in the surface or outer layers to prevent UV radiation from deeper penetration into and degradation of the main thickness of the PC sheet. A number of methods and techniques have been developed to concentrate UV absorbers near or at the surface of polymeric materials. These include surface impregnation (see for example U.S. Pat. Nos. 3,309,220; 3,043,709; 4,861,664 and 4,937,026); coating a plastic article with solutions containing thermoplastic resins and UV absorbers (see for example U.S. Pat. Nos. 4,668,588 and 4,353,965); thermal bonding of film layers (see for example JP 07-9,560); and coextrusion (see for example European Patent Publications EP 110,221, EP 247,480, EP 320,632, EP 338,355 and EP 825,226; GB Patent 2,290,745 and U.S. Pat. Nos. 4,264,680 and 5,108,835). In these and other coextrusion references, there is an emphasis on the use of higher molecular weight and lower volatility compounds if used in higher concentrations in coextruded surface layers.
It is also generally known to incorporate additional stabilizers of various other types into polycarbonate compositions to prevent discoloration of the polymer and the final article during processing and end-use. U.S. Pat. Nos. 4,812,498, 5,288,778 and 5,821,380 and GB Patent 2,290,745 all teach the use of numerous co-stabilizers. The use of phosphite stabilizers in combination with a triazine-type UV absorber has been described in EP 825,226. JP 10-044,356; JP 10-044,357; and JP 10-044,358 teach the use of a combination of triazine-type UV absorber, phosphite and hindered phenolic stabilizers added or applied to polycarbonate resins. JP 04-103,626; JP 04-159,354 and JP 10-138,435 teach the use of a combination of benzotriazole-type UV absorber, phosphite and hindered phenolic stabilizers added or applied to polycarbonate resins. GB Patent 2,322,861 teaches the stabilization of polycarbonates with benzofuran-2-one lactone-type additives optionally employing a wide range of additional co-stabilizers of various different types. However, in the case of polycarbonate formulations and especially co-extrudable compositions, which contain high levels of UV absorbers, it is always desirable to have improved combinations of physical, processing and appearance properties. It is especially desirable to have such improved resins, improved stabilized articles and improved processes where the stabilizers volatilize less and are better maintained in the compositions and articles during and after processing.
It is thus the objective of the present invention to provide improved polycarbonate compositions and improved molded, shaped or otherwise fabricated articles having appropriate UV protection (physical property and appearance stability) for outdoor applications. It is also an objective to provide improved processes for the preparation of these improved molded, shaped or otherwise fabricated articles.
In one embodiment, this invention relates to a polycarbonate resin composition comprising a polycarbonate, a cyanacrylic acid ester compound having a molecular weight of at least 500 g/mol and a phenyl phosphite type stabilizer. In another embodiment, the polycarbonate resin further comprises a hindered phenol type stabilizer and preferably, also a lactone type stabilizer. Preferably such polycarbonate resin compositions comprise from 0.05 to 15 weight percent cyanacrylic acid ester type UV absorber, 20 to 1500 ppm phosphite type stabilizer, from 10 to 750 ppm hindered phenol type stabilizer and from 5 to 400 ppm lactone type stabilizer. Polycarbonate resin composition according to the invention desirably comprise at least about 2 percent by weight cyanacrylic acid ester compound based on weight of polycarbonate and advantageously are used in surface layers or otherwise applied to the surface of articles, preferably polycarbonate articles.
In a preferred, alternative embodiment, the polycarbonate resin compositions comprise a cyanacrylic acid ester compound according to the following formula:
where the R
1
and R
2
substituents are each hydrogen or a radical having an iso- or heterocyclic ring system with at least one iso- or heteroaromatic nucleus, and at least one of the radicals R
1
or R
2
must be different from hydrogen; p has an average value of at least 3; X is the radical of an aliphatic or cycloaliphatic polyol having from about 3 to about 20 carbon atoms and at least p hydroxyl groups, a cycloaliphatic radical optionally containing 1 or 2 hetero atoms, and an aliphatic radical optionally being interrupted by up to 8 non-adjacent oxygen atoms, sulfur atoms, imino or C
1
-C
4
-alkylimino groups.
In another embodiment, this inve
Dow Global Technologies Inc.
Sanders Kriellion A.
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