Stock material or miscellaneous articles – Composite – Of addition polymer from unsaturated monomers
Reexamination Certificate
1999-11-12
2003-05-20
Thibodeau, Paul (Department: 1773)
Stock material or miscellaneous articles
Composite
Of addition polymer from unsaturated monomers
C428S511000, C428S512000, C428S513000, C524S094000, C264S464000, C430S531000, C430S536000, C430S538000
Reexamination Certificate
active
06565987
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the field of polymer chemistry. In particular, this invention relates to blends of optical brightening compounds and polyolefins.
BACKGROUND OF THE INVENTION
The use of polyolefins, such as polyethylene, has become quite prevalent. A particularly useful application of polyolefins has been for a class of photographic supports. The photographic support generally includes a paper base material having a polyolefin coating on one or both sides of the paper. The polyolefin coating provides a very smooth surface when thin layers of a silver halide emulsion, are desired to be coated on the photographic paper.
The polyolefin coating can include an optical brightener and typically, a fluorescent whitening agent to make the white areas of the support even brighter. The optical brightener compensates for the yellow cast produced by the absorption of short-wavelength light such as violet to blue by the polyolefin. Typical optical brighteners fluoresce upon irradiation with ultraviolet light emitting visible light, typically bluish in hue, replacing the light that would have been lost and thereby enhancing the brightness of the support. Optical brighteners for use in such fields as photographic printing materials must absorb ultraviolet light, especially in the region from 280 to 405 nanometers (nm), and re-emit such light so as to enhance the brightness of the print. Desirably, the optical brightener has stability to temperatures as high as 310° C. to 330° C., so that it may be incorporated into the polyolefin during an extrusion process or film forming process and in extruding the polyolefin onto the paper based material.
It is also desirable that the optical brightener be non-migrating so that it remains in the polyolefin coating and does not exude as a surface film on the polyolefin. Such exudation not only gives rise to a non-uniform brightness of the reflection surface, but also readily transfers to any other surface coming in contact with it. For example, a brightener transferred to the back side of the adjacent support layer when wound in roll can adversely affect subsequent coating and finishing operations of the photograph. This can result in the final product having a poor quality and performance.
It has been recognized that the addition of optical brighteners to polyolefins has been less than satisfactory. For example, U.S. Pat. No. 3,449,257 describes 2,5-bis(benzoxazolyl)thiophenes, such as Uvitex OB™ available from Ciba Specialty Chemicals, as non-migrating brighteners for hydrophobic polymers, but were found to undergo bleeding and yellowing from a polyolefin film in U.S. Pat. No. 5,173,397.
In an effort to improve the compatibility between hydrophobic or non-polar polyolefins and optical brighteners, U.S. Pat. Nos. 4,794,071 and 4,859,539 disclose a mixture of optical brighteners which when incorporated into a pigmented polyolefin layer of a photographic support minimizes exudation of the brightener at the polyolefin surface. The mixture of optical brighteners include certain fluorescent bis (benzoxazolyl)stilbenes. U.S. Pat. No. 4,794,071 teaches that single component optical brighteners exhibit severe exudation when compared to the optical brightener mixture described in U.S. Pat. No. 4,794,071.
Accordingly, there is a need for the ability to incorporate an optical brightener into a non-polar polyolefin that will exhibit good compatibility with the polyolefin and not exude as a surface film on the polyolefin.
Additionally, there is a need for a method of incorporating optical brighteners into hydrophobic or non-polar polyolefins which will enhance their brightening efficiency.
SUMMARY OF THE INVENTION
The present invention provides a composition comprising a polyolefin, an optical brightening compound, and a compatibilizing amount of a non-polar polyolefin polymer having alkyl groups of from 1 to 22 carbons pendant from the polymer backbone. In the practice of the invention, the components are blended at a temperature sufficient to induce softening of the polyethylene polymer, and may be extruded, injection molded, etc., into useful articles. The optical brightener is retained in these articles in these end-use applications to a much greater extent than they would have been in the absence of the non-polar polyolefin additive.
DETAILED DESCRIPTION OF THE INVENTION
The present invention provides a thermoplastic composition comprising a non-polar thermoplastic polymer, an optical brightener and a non-polar polyolefin additive in an amount effective to reduce exudation of said optical brightener from said non-polar thermoplastic polymer, wherein said non-polar polyolefin additive is a polyalkylene polymer having pendant alkyl substituents.
Although it is known that the addition of optical brightener into a non-polar thermoplastic such as a polyolefin will improve the brightness of a film made from the polyolefin, it has been recognized that such optical brightening agents are generally incompatible. Polyolefins are typically non-polar compositions and in general applications, such compositions possess very few if any polar functional groups, such as esters, acids or alcohols. This lack of polarity generally prevents polar materials such as, optical brighteners, from being satisfactorily incorporated into or bonded with the polyolefin. The non-compatibility contributes to the optical brightener exuding from the polyolefin. The present invention, as described herein shows that the addition of a non-polar polyolefin aditive to the polyolefin will substantially improve the incorporation of and reduce the exudation of the optical brightener from the polyolefin without affecting the optical brightener performance. Accordingly, the composition of the invention comprises a non-polar thermoplastic polyolefin having admixed, blended or melt-blended therein an optical brightener and a non-polar polyolefin additive for compatibilizing the optical brightener and the polyolefin. Although the invention hereafter is described with particular reference as a polyolefinic coating for an imaging (i.e., photographic) support, one skilled in the art will recognize and understand that other useful applications for such an optically brightened polyolefin may be utilized. These may include, but are not limited to fibers, adhesives, packaging and shipping containers, cartons, bottles, signs, re-processed polymer, coated paper for non-photographic applications (e.g., thermal, digital, and other imaging applications, and coatings for materials other than paper.
The thermoplastic polyolefin suitable for use in the invention can be any polyolefinic material known in the polymer art with particular relevance to the photographic art. Representative materials include homopolymers and copolymers of olefinic monomers such as ethylene, &agr;-methyl styrene C
3
-C
8
&agr;-olefins, styrene, and mixtures thereof. Preferred polyolefins include linear low density, low density, medium and high density polyethylene. Polyethylene having a density in the range from about 0.90 grams/cm
3
to about 0.96 grams/cm
3
being preferred and a density of about 0.910 grams/cm
3
to about 0.925 grams/cm
3
being particularly preferred. The olefinic monomer can be copolymerized with one or more additional monomer moieties such as esters, carboxylic acids, amides, alcohols and other olefins. Specific examples of copolymerizable monomers include vinyl stearate, vinyl acetate, acrylic acid, methyl acrylate, ethyl acrylate, butyl acrylate, acrylamide, methacrylic acid, methyl methacrylate, ethyl methacrylate, methacrylamide, butadiene, isoprene, and vinyl chloride. The polyethylenes may contain other materials commonly used as processing aids, or materials used to make the finished product perform better in a particular end-use. Such materials are set forth in copending application U.S. Ser. No. 08/986,539 and WO 98/0025998.
The optical brighteners useful in the practice of the invention can be any class of materials having an absorption in the range of about 280-405 nanometers (nm) an
Eastman Chemical Company
Graves, Jr. Bernard J.
Jackson Monique R.
Thibodeau Paul
Wood Jonathan D.
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