Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2001-06-27
2003-09-02
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...
C524S099000, C524S102000, C524S139000, C428S480000
Reexamination Certificate
active
06613819
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to light stable articles, including light stable polymeric articles and light stable optical bodies. More particularly, the present invention relates to articles comprised of at least one layer of a polymer film.
BACKGROUND OF THE INVENTION
Polymeric films are widely used and widely useful in a broad range of industrial and consumer applications. Such films, for example, can be employed as transparent or tinted barrier films to protect myriad underlying substrates. Polymeric films, and particularly polymeric films made of a polyester material, offer many characteristics desirable in a barrier film. Among other properties, they exhibit clarity, durability, toughness, pliability, formability and affordability.
Use of some of the most desirable polymeric films, however, can be severely limited for outdoor applications and other applications where the films are exposed to a source of light. For example, many polymeric films degrade when subjected to prolonged exposure to ultraviolet radiation (which occurs naturally during outdoor use or by exposure to fluorescent light or other UV-emitting light source).
There remains, therefore, a desire for articles containing at least one layer of a polymeric film that exhibit improved light stability.
SUMMARY OF THE INVENTION
Briefly, in one aspect, the present invention provides a light stable article that comprises at least one single or multiple layer polyester film and an effective amount of a light absorbing composition comprising an ultraviolet light absorbing compound and a hindered amine light stabilizer (HALS) composition, wherein the weight ratio of the light absorbing compound to the HALS composition is at least, and preferably greater than, about 2:1.
In another aspect, the invention provides a light stable article comprising at least one single or multiple layer polyester film and an effective amount each of a phosphonate stabilizing compound and a light absorbing composition comprising a hydroxy-functional tris-aryl triazine compound.
In yet another aspect, the present invention provides a light stable article comprising at least one single or multiple layer polyester film and an effective amount of a light absorbing composition consisting essentially of a hydroxy-functional tris-aryl triazine compound having the formula:
wherein each R
1
is the same or different and is selected from the group consisting of hydrogen and substituted or unsubstituted, branched or unbranched alkyl, aryl, or alkaryl groups having from 1 to about 18 carbon atoms. Preferably, the carbon chains of any such alkyl, aryl, or alkaryl group is free of interruption by one or more oxygen atoms and is not substituted by a hydroxy substituent.
In still other respects, the present invention provides various composite articles and constructions made utilizing the above light stable articles.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
The articles of the invention generally comprise at least one single or multilayer polyester (i.e., polyester-containing) film and an effective amount of at least one light stabilizing composition. The light stabilizing composition can comprise an ultraviolet absorbing compound alone or in combination with one or more hindered amine light stabilizing (“HALS”) compounds. The polyester film can be oriented and/or can be part of a multilayer optical film construction. The polyester film can also incorporate one or more phosphonate stabilizing compositions to aid in melt stability and/or weather resistance.
The polyester films of the invention can incorporate any polyester-containing polymer. Useful polyester polymers include, for example, polymers having terephthalate, isophthalate, and/or naphthalate comonomer units, e.g., polyethylene naphthalate (PEN), polyethylene terephthalate (PET) and copolymers and blends thereof. Examples of other suitable polyester copolymers are provided in published patent application WO 99/36262 and in WO 99/36248, both of which are incorporated herein by reference. Other suitable polyester materials include polycarbonates, polyarylates, and other naphthalate and terephthalate-containing polymers, such as, for example, polybutylene naphthalate (PBN), polypropylene naphthalate (PPN), polybutylene terephthalate (PBT), polypropylene terephthalate (PPT), and blends and copolymers of any of the above with each other, with other polyesters, or with non-polyester polymers. In a generally preferred embodiment, the light stabilizing compositions are incorporated directly into the polyester resin (e.g., a PET or PEN-based resin). This presents a relatively simple method of effectively, and maximally, protecting standard polyester films from the deterioration upon exposure to sources of ultraviolet radiation. The polymer films can contain multiple layers of the same or different polyester materials, or can be comprised of one or more non-polyester layers.
Most commercially available UV-protected polyester films are made either by applying a UV-protective coating to a polyester substrate, by preparing a multilayered film (as by coextrusion) in which a non-polyester layer contains the UV-protecting agent, or by imbibing a UV-protecting agent into a polyester film after film formation. The current invention can have a significant advantage over such films in that the light stabilizing compositions may be extruded directly in the polyester resin, thus providing simplicity of manufacture, cost reduction, permanence of the light stabilizing additive(s), and uniformity of protection throughout the polyester layer into which the compositions are incorporated.
Polyester films of the invention can be monolayer, bilayer, trilayer or any other non-alternating layered construction. The films can comprise alternating or repeating multi-layer structures, or can include combinations of both. The manufacture of polyester films is well-known in the art, and any of the known methods for forming such films are appropriate to forming the light stabilized articles of this invention. The articles, thus made, can be useful in all applications requiring weatherability, including signing and outdoor protective applications.
Additionally, the polyester films can include or be comprised of a multi-layer optical film. Generally speaking, multi-layer optical films are used to create optical interference filters that reflect light via designed constructive interferences between a multiplicity of layers with alternating low and high indices of refraction. Such films can be composed of either isotropic or birefringement layers, or both. Birefringent optical films are constructed in multi-layer “stacks” for which the Brewster angle (the angle at which reflectance of p-polarized light goes to zero) is controlled to a desired value by control of the relative values of the various indices of refraction in the layers. This property allows for the construction of multilayer mirrors and polarizers whose reflectivity for p-polarized light decreases slowly with angle of incidence, are independent of angle of incidence, or that increases with angle of incidence away from the normal. As a result, multilayer films having high reflectivity (for both s- and p-polarized light for any incident direction in the case of mirrors, and for the selected polarization in the case of polarizers) over a wide bandwidth, can be achieved.
Useful multilayer constructions are disclosed, for example, in the following published patent applications, all of whose descriptions are incorporated herein by reference: WO 95/17303, WO 96/19347, and WO 97/01440. Among the most useful films are multi-layer constructions made of alternating thin layers of PEN and a copolymer of PEN, for example a 70-naphthalate/30-terephthalate co-polyester (co-PEN), or other polymers having a lower refractive index than PEN.
Often, the ability to achieve properties desired in a single or multi-layer polymeric body is influenced by the processing conditions used to prepare it. The polymeric optical body, for example, can be formed by a casting process
Bailey Terry R.
Frank John W.
Johnson Stephen A.
McGurran Daniel J.
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