Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2000-05-19
2001-10-02
Sanders, Kriellion A. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C524S100000, C524S186000
Reexamination Certificate
active
06297300
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a carbonate polymer composition which contains low volatile UV absorbers.
BACKGROUND OF THE INVENTION
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 (UV) 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 2,290,745 and EP 825,226 (triazine compounds); U.S. Pat. No. 5,821,380 (multifunctional 2-cyanoacrylic acid 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 and 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 mold 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 an UV absorber conversely provides more effective stabilization in the desired end use as well as better processability in terms of reduced fuming, plate-out, mold sweat, juicing, etc.
Various methods have been used to improve the UV-stability of polycarbonate (PC). Common approaches are to use UV absorbers as additives in the polycarbonate and to apply 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 EP 110,221; 247,480; 320,632; 338,355 and 825,226; GB 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.
However, in the case of polycarbonate formulations and especially coextrudable 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.
SUMMARY OF THE INVENTION
It is thus the objective of the present invention to provide improved carbonate polymer compositions and improved molded, shaped or otherwise fabricated articles having appropriate UV protection (e.g., appearance stability) especially for outdoor applications. It is also an objective to provide an improved process for the preparation of these improved molded, shaped or otherwise fabricated articles.
In one embodiment, this invention relates to improved carbonate polymer compositions comprising one or more UV absorbing compounds selected from two or more of the following groups: a hydroxybenzotriazole derivative, a hydroxyphenyltriazine derivative, or a cyanoacrylic acid ester compound, wherein all UV absorbing compounds have a molecular weight of at least 400 g/mol.
In another embodiment, the present invention is an improved process for preparing a carbonate polymer composition as described hereinabove.
In a further embodiment, the present invention involves a process of extruding or molding (e.g., thermoforming, blow molding, injection molding, etc.) an improved carbonate polymer composition prepared as described hereinabove and extruded or molded into an improved extruded or molded article.
In yet a further embodiment, the invention involves extruded or molded articles of an improved carbonate polymer composition as described hereinabove.
It has been found that the improved carbonate polymer compositions and the improved articles which can be prepared have excellent resistance against UV radiation and provide improved combinations of base color and color stability. It has also been found that the UV absorbers added according to the present invention provide reduced levels of color or yellowing in the final carbonate polymer compositions/articles. This can be particularly noticeable in the resin granules when high levels of UV absorbers are incorporated in a resin to be used as the coextrudable surface layer or when there are multiple thickness of extruded sheet or other article that is stacked or lined up together.
It has also been found that the invention provides improved processes for preparing such articles with reduced levels of plate-out, fuming, mold sweat and/or juicing.
DETAILED DESCRIPTION OF THE INVENTION
All types of carbonate polymers are generally suitable for use in the compositions, articles and processes of the present invention. Many types of suitable carbonate polymers are well known and commercially available. Suitable types of carbonate polymers include linear and branched carbonate polymers as well as blends thereof. As mentioned above, the present invention is directed both to formulations based on carbonate polymers which can be directly used to prepare molded, shaped or otherwise fabricated articles (“bulk stabilized resins”) and to formulations based on carbonate polymers which can be used as a surface or external coating or layer (“capstock resins”) to protect substrate articles or core layers which can be a carbonate polymer of the same or different type or some other polymer resin.
The carbonate p
Sanders Kriellion A.
The Dow Chemical Company
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