Stock material or miscellaneous articles – Composite – Of polyamide
Reexamination Certificate
1998-11-25
2001-11-06
Thibodeau, Paul (Department: 1773)
Stock material or miscellaneous articles
Composite
Of polyamide
C428S481000, C428S512000, C428S513000, C430S436000, C524S094000, C524S095000
Reexamination Certificate
active
06312822
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to polymers having an optical brightener included therewith, and particularly to a polyolefin having a polar additive for compatibilizing the polyolefin with the optical brightener. The present invention further relates to a method of incorporating a polar additive into the polyolefin.
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. 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 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 is recognized in the art 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 issued to Tomko, et al. on Dec. 27, 1988, and Aug. 22, 1989, respectively, disclose a mixture of optical brighteners that 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 incorporation of an optical brightener into a non-polar polyolefin that will exhibit the 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 is for a thermoplastic polymer composition having an optical brightener and an effective amount of a polar compatibility additive to reduce the exudation of the optical brightener from the thermoplastic polymer.
Another aspect of the invention is for a method of incorporating into a thermoplastic polymer the polar compatibility additive. Desirably, the polar additive permits an increased amount of the optical brightener to be incorporated into the non-polar polymer without the disadvantages described above.
An advantage of the present invention is that optical brighteners previously not used with a polyolefin due to incompatibility of the materials can now be incorporated into the polyolefin.
It is an object of the present invention to provide a thermoplastic polymer containing at least one optical brightener and a compatibility polar additive.
Another object of the invention is to provide a polyolefin having an optical brightener and a polar compatibility additive which can be incorporated into a pigmented polyolefin layer of a photographic support.
It is another object of the invention to provide a method for incorporating a polar optical brightener into a polyolefin.
It is also an object of the invention to provide a method for incorporating a polar optical brightener into a polyolefin whereby the brightening efficiency of the optical brightener is enhanced.
Unexpectedly, we have found that the addition of a polar additive to a polyolefin improves the level of compatibility of the optical brightener with the polyolefin to thereby reduce or prevent the optical brightener's exudation from the polymer onto the surface of a film made from the polyolefin and may further result in an increased brightening efficiency of the optical brightener.
DETAILED DESCRIPTION OF THE INVENTION
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 having very few polar functional groups, such as an ester, acid or alcohol. This non-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. Unexpectedly, it has been discovered that the addition of a polar compatibility additive 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 includes a non-polar thermoplastic polyolefin having admixed, blended or melt-blended therein an optical brightener and a polar additive for compatibilizing the optical brightener and the polyolefin. Although the invention hereafter is described with particular reference as a polyolefinic coating for a photographic support, one skilled in the art will recognize and understand that other useful applications for such an optically brightened polyolefin may be utilized.
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, propylene, styrene, butylene, 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, acrylamide, met
Farrar Joe L.
Irick, Jr. Gether
Tarazano D. Lawrence
Thibodeau Paul
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