Stock material or miscellaneous articles – Composite – Of addition polymer from unsaturated monomers
Reexamination Certificate
2000-10-12
2002-12-10
Tarazano, D. Lawrence (Department: 1773)
Stock material or miscellaneous articles
Composite
Of addition polymer from unsaturated monomers
C428S512000, C428S523000, C524S084000, C524S094000, C524S095000
Reexamination Certificate
active
06492032
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a mixture of optical brighteners that are useful for brightening polyolefin films. Another aspect of the present invention is for compositions having the mixture of particular optical brighteners included therewith, and particularly to polyolefins having a blend of three (3) optical brighteners wherein two of the optical brighteners are bis-benzoxazolyl stilbenes and the third optical brightener is selected from at least one bis(benzoxazolyl)naphthalene based brightener, bis(benzoxazolyl)thiophene based brightener, a coumarin based brightener and a pyrazoline based brightener. The polyolefin-brightener blend is particularly useful as a resin coating for a photographic support.
2. Background of the Invention
Polyolefins are widely used in extrusion and molding applications, and in the making of films for varied applications. For example, polyethylene compositions are used in cast or tubular blown films, thin films, extrusion coated paper, paperboard, photographic paper, digital and thermal imaging papers, diaper backing, plastic substrates, injection or compression molded objects, packaging applications (such as coatings on soap boxes, milk cartons, fruit juice cartons, etc.), and the like. In these applications, the polymer is generally processed at high temperatures.
The present invention has particular utility in the field of extruded films for imaging and photographic support applications, such as, extrusion coated paper, paperboard, photographic paper, digital paper and thermal imaging papers. With respect to a photographic support, generally a paper base material is coated with a thin polyolefin film. 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.
To improve image quality, the polyolefin coating usually includes an optical brightener, such as a fluorescent whitening agent, to make the white areas of the support even brighter. 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 includes three specific fluorescent bis(benzoxazolyl)stilbenes. U.S. Pat. No. 4,794,071 teaches that single component optical brighteners of the mixture exhibit severe exudation when compared to the optical brightener mixture described in U.S. Pat. No. 4,794,071.
U.S. Pat. No. 5,817,448 issued to Hayashi et al. on Oct. 6, 1998 discloses a silver halide photographic material having a support material with at least one light-sensitive silver halide emulsion layer provided thereon. The support material includes a resin coated paper having a titanium dioxide pigment coated with a silane coupling agent, and at least one brightening agent selected from a bis-(benzoxazolyl)naphthalene based brightening agent, a bis-(benzoxazolyl)thiophene based brightening agent, a coumarin based brightening agent and a pyrazoline based brightening agent.
The patent further discloses a silver halide photographic material having a support material with three kinds of light-sensitive silver halide emulsion layers, with each layer having different light-sensitive wavelength regions. The support material includes a resin coated paper having a titanium dioxide pigment coated with a silane coupling agent, and at least one bis-(benzoxazolyl)stilbene based brightening agent. However, the patent is silent as to using a combination of at least three optical brighteners where two are bis-(benzoxazolyl)stilbene based brightening agents and the third brightening agent is selected from a bis-(benzoxazolyl)naphthalene based brightening agent, a bis-(benzoxazolyl)thiophene based brightening agent, a coumarin based brightening agent and a pyrazoline based brightening agent.
U.S. Pat. No. 4,416,795 discloses a mixture of optical brighteners having from 1 to 99 weight % of a bis-benzoxazolylstyrene and from 99 to 1 weight % of one or more secondary compounds.
U.S. Pat. No. 5,106,989 discloses a photographic support having a polyolefin resin coating wherein the resin includes a titanium dioxide pigment and an alkyl-substituted 2,2-(1,4-naphthalenediyl)dibenzoxazole optical brightener.
U.S. Pat. No. 4,363,744 discloses a mixture of optical brighteners wherein a bis-benzoxazolyl or bis-benzothiazolyl-stilbene is mixed with a second mixture of optical brighteners having formulae I and II disclosed therein.
U.S. Pat. No. 4,169,810 discloses a mixture of optical brighteners having from 0.05 to 0.95 part by weight of a benzoxazolyl- or a benzothiazolyl-stilbene compound and from 0.95 to 0.05 part by weight of a bis-benzoxazolyl- or bis-benzothiazolyl-stilbene compound or a benzoxazolyl- or benzothiazolyl-stilbene oxazolo[5,4-6]pyridinyl or oxazolo[2,3-b]pyridinyl compound.
U.S. Pat. No. 4,129,412 discloses a mixture of optical brighteners having 0.05 to 1% of a 4-benzoxazolystilbene derivative and 1 to 0.05% of a 1,1-bis-benzoxazolyl or bis-benxthiazolyl-naphthalene derivative that are useful for brightening textile material of linear polyesters, polyamides and acetyl cellulose.
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.
SUMMARY OF THE INVENTION
Broadly, the present invention is a mixture of optical brighteners that show an enhanced degree of whiteness when admixed with a polyolefin and particularly when admixed with polyethylene to make a film, as compared to the same amount of the constituents in the polyolefin as single components. The optical brightener mixture of the present invention includes (a) of from about 45 to 95 weight % of a mixture of benzoxazolyl stilbenes and (b) of from about 55 to about 5 weight % of at least one bis(benzoxazolyl)naphthalene based brightener, bis(benzoxazolyl)thiophene based brightener, a coumarin based brightener and a pyrazoline based brightener, wh
Daily Jeffrey Dan
Irick, Jr. Gether
Boshears Betty J.
Eastman Chemical Company
Graves, Jr. Bernard J.
Tarazano D. Lawrence
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