GB2353038A

GB2353038A - Polyolefin composition comprising non-migrating optical brightener

Info

Publication number: GB2353038A
Application number: GB0018476A
Authority: GB
Inventors: Kenneth W Hyche; Bryan Alan Johnson
Original assignee: Eastman Chemical Co
Current assignee: Eastman Chemical Co
Priority date: 1999-08-12
Filing date: 2000-07-27
Publication date: 2001-02-14
Also published as: GB0018476D0

Abstract

A polymeric composition for photographic paper, extrusion coatings, thermoforming or mouldings comprises a polyolefin, an optical brightener and synthetic silica which prevents exudation of the brightener. The olefin preferably comprises low, linear low or high density polyethylene or homo- or co-polymers of ethylene, propylene, styrene and butylene. The optical brightener preferably comprises 0.001-1% by weight of a stilbene or derivative thereof or 2,2'-(1,2-ethanediyldi-4,1-phenylene) bisbenzoxazole. The silica preferably comprises at least 0.25% fumed silica or silica gel. Additives such as dyes, organic or inorganic pigments, antioxidants, heat stabilizers, antistatic agents, fillers, processing aids, slip agents and lubricants may be added.

Description

2353038 POLYOLEFIN COMPOSITIONS CONTAINING OPTICAL BRIGHTENERS

FIELD OF THE INVENTION

The present invention relates to polyolefins having an optical brightener included therewith, and particularly to a polyethylene having synthetic silica included therein.

BACKGROUND OF THE INVENTION

The use of polyolefins, such as polyethylene, has become quite prevalent. Various polyolefins, including low density polyethylene (LDPE), linear low density polyethylene (LLDPE), high density polyethylene (HDPE), polypropylene (PP), ethylene-vinyl acetate copolymers (EVA), and ethylene-propylene copolymers (EP) are used in a variety of applications including injection molding, extrusion coatings, blow molding, rotational molding, and thermoforming.

Polyolefin coatings can include optical brighteners and whitening agents to make the white areas of the article of manufacture even whiter or brighter. Wbitening agents include organic or inorganic pigments that provide an opaque white appearance to the composition. The optical brightener compensates for the yellow cast produced by light or heat degradation of the polymer over time. 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 brightness. Optical brighteners; mask undesirable tints, such as yellow tint from recycled products, and/or modify the fluorescent nature of certain color imparting pigments.

A particularly useful application of polyolefins is for photographic supports. The photographic support generally includes a paper base material having a polyolefin coating. 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 in the visible region so as to enhance the brightness of the print.

Preferably, the optical brightener has stability to temperatures as high as 2500C 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.

Unfortunately, optical brighteners tend to exude to the surface of polyethylenes. For example, U.S. Patent 3,449,257 discloses 2,5-bis (benzoxazolyl) thiophenes, such as Uvitex OB available from Ciba Specialty Chemicals, Basle, Switzerland, as non-migrating brighteners for hydrophobic polymers, however, this optical brightener was found to undergo bleeding and yellowing from a polyolefin film in U.S. Patent No.

5,173,397. In applications, such as film supports it is desirable that the optical brighteners remain in the polyethylene and not migrate to the surface and exude as a surface film. Such exudation not only gives rise to a non-uniform brightness of the reflection surface, but also readily transfers the optical brightener to any other surface coming in contact with it. The exudation of the optical brighteners results in a yellow crystalline appearance on the surface of the polyethylene part or article of manufacture. For example, an optical brightener may be transferred to the back side of the adjacent support layer when winding the photographic support into a roll, which may adversely affect subsequent coating and finishing operations of the photograph. This can result in the final product having a poor quality and performance.

One specific class of optical brighteners, 2,2'-(1,2- ethenediyidi-4, 1 phenylene) bisbenzoxazole, has experienced solubility problems in polyethylene polymers. For instance, at levels of 50-200 ppm, the above brightener migrates to the surface of LDPE, LLDEPE, and HDPE molded or extruded parts or articles of manufacture. Commercial examples of this type of brightener include Eastobrite OB-10 and Eastobrite OB-30, available from Eastman Chemical Company, Kingsport, Tennessee. Polyethylene products containing Eastobrite OB-10 or Eastobrite OB-30 brightener experience brightener migration to the surface within one to four weeks aging after molding or extrusion. Because of the surface migration problem, Eastobrite OB-I@) and Eastobrite OB-3@ have been excluded from certain markets, such as the photographic paper market. As a result, more expensive and difficult-to-obtain optical brighteners are used with polyethylene in such markets.

The exudation problem of optical brighteners has a wider scope. For instance, the exudation rate depends on the amount of optical brightener present and the brightener used in the composition. Alternative chemical types of optical brighteners to 2,2'-(1,2- ethenediyldi-4, I -phenylene) bisbenzoxazole, naphthotriazolyl counarin and bisbenzoxazolyl-stilbene derivatives, may be more soluble in polyolefins. However, these optical brighteners may still exude from the composition, but the exudation occurs at a slower rate. Furthermore, almost all optical brighteners exude in polyolefins at levels of 1000 ppm and above, especially when certain migrating additives are present, such as mold release aids.

The rate of exudation is further dependent on the type of polyolefin, the part dimensions, part temperature, and other derivatives in the composition. The presence of additives such as fatty acid amides, commonly used as slip agents, can also accelerate the brightener migration. Generally in regard to rates of migration, levels of 10 to 150 PPM optical brightener takL- longer to exude compared to levels of 200 PPM and above.

Many attempts have been made to prevent or reduce the exudation of optical brighteners from polyolefins, especially polyethylene. U.S. Patent Nos. 4,794,071 and 4,859,539 issued to Tomko, et al. 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. Mixtures of optical brighteners include certain fluorescent bis (benzoxazolyl) stilbenes. U.S. Patent No. 4,794,071 teaches that single component optical brighteners exhibit severe exudation when compared to the optical brightener mixture described in U.S. Patent No.

4,794,071.

U.S. Patent Nos. 5,340,854 and 5,198,330 issued to Martic, et al.

address the same problem of optical brightener exudation in polyolefin compositions. The polyolefin composition contains an optical brightener and cyclodextrin to reduce brightener migration. Accordingly, there is a need for the polyolefin formulation containing an optical brightener that will not exude to the surface of polyolefins.

SUMMARY OF THE INVENTION

Unexpectedly, we have found that the addition of effective amounts of synthetic silica to a polyolefin reduces or prevents the optical brightener exudation from the polyolefin and may further result in an increased brightening efficiency of the optical brightener. As used herein, "effective amounts" is defined as the amount of synthetic silica necessary to significantly reduce or prevent exudation of optical brighteners from polyolefins. In particular, it has been discovered that the presence of effective amounts of synthetic silica prevents exudation of optical brighteners in LPIDE, LLIDPE, and HDPE. Furthermore, the use of effective amounts of synthetic silica allows the use of higher levels of brightener in ail types of polyolefin polymers. Primarily, the synthetic silica prevents exudation of normal levels of optical brightener in polyolefin compositions.

Additionally, the synthetic silica permits an increased amount of the optical brightener to be incorporated into the polyolefin without the disadvantages of exudation described above.

The present invention is directed to a polyolefin composition containing a polyolefin, an optical brightener and a synthetic silica in an amount sufficient to significantly reduce or eliminate the exudation of the optical brightener from the polyolefin.

In another embodiment, the present invention is directed to an imaging support paper base material having a polyolefin coating including an optical brightener and synthetic silica in an amount suffi(:ient to significantly reduce or eliminate the exudation of the optical brightener from the polyolefin.

Additional advantages and embodiments of the present invention will be apparent from the following description and appended claims or may be learned by the practice of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Although it is known that the addition of optical brightener into a polyolefin composition improves the brightness of a film made from the polyolefin, it has been recognized that such optical brightening agents generally exude from the polyolefin. Unexpectedly, it has been discovered that the addition of effective amounts of synthetic silica prevents the exudation of the optical brightener from the polyolefin without affecting the optical brightener performance.

Accordingly, the composition of the invention includes a polyolefin having admixed, blended or melt-blended therein an optical brightener and an effective amount of a synthetic silica. Although the examples and experiments created injection molded plaques for the simplicity of preparation and observation, the invention hereafter is described with particular reference as a polyethylene 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. With the improvements of the present invention, the processes of film blowing, coating extrusion, and injection molding can be applied to produce end products such as photographic film (a polyolefin coating for a photographic support), outdoor furniture, recycled products, toilet seat moldings, credit card moldings, road signs, and plastic toys.

Unless otherwise specified, all percents referred to herein are percent by weight of the entire composition.

The polyolefin suitable for use in the invention can be any polyolefinic material known in the polymer art with particula r 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/CM3 to about 0.96 gramS/CM3 being preferred and a density of about 0. 910 graMS/CM3 to about 0.925 graMS/CM3 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 propylene, butylene, hexene, vinyl stearate, vinyl acetate, acrylic acid, methyl acrylate, ethyl acrylate, acrylamide, methacrylic acid, methyl methacrylate, ethyl methacrylate, methacrylamide, butadiene, isoprene, and vinyl chloride.

Commercially available examples include low-density Epolene C-1 7 polyethylene, linear low-density polyethylene, high-density polyethylene H6001 and Tenite@) P4G3Z-039 polypropylene available from Eastman Chemical Company, Kingsport, TN.

The optical brighteners can be any class of materials having an absorption in the range of 280-405 nanometers (nm) and an emission in the visible spectrum of from about 400-450 nanometers. The most useful optical brighteners include stilbenes, substituted stilbenes and stilbene derivatives. Suitable examples of s uch optical brighteners include bis(benzoxazolyl) stilbenes such as those disclosed in U.S. Patent No.

4,794,071, the disclosure of which is incorporated herein by reference.

Preferably, the optical brighteners include the optical brighteners Eastobrite OB-10 or OB-30, stilbenes available from Eastman Chemical Company, described in U.S. Patents 3,260,715 and 3,322,680; HOSTALUX@ KS, a mixture of stilbenes available from Hoechst AG, Frankfurt, Germany described in U.S. Patent U.S. 4,794,071; and Uvitex OB available from Ciba Specialty Chemicals, Basle, Switzerland the entire disclosures of each being incorporated herein by reference.

Other optical brighteners include mono(azol-2-yl)stilbenes, such as, 2-(stilben-4-yl)naphthotriazoles and 2-(4-phenylstilben-4-yl)benzoxazoles; 0 N, CH = CH-0-R2 RI wherein R' is hydrogen or C=-N and R2 is hydrogen or chlorine.

0,a /'-CH = CH (HP3C N -0-0 NMj:D-R3 0 0 O N wherein R 3 is hydrogen or alkyl.

q-CH = CH--aCH = CH C=N N=P Bis(benzoxazol-2-yl) derivatives, such as:

R4 R5--<o R6 -OfN/> N'O wherein R 5 is C21-12 and R 4 and R 6 are independently selected from alkyl or CH3, R5 is -<-O--CH = CH and R 4 and R6 are independently selected from hydrogen and alkyl, R 5 is and R 4 and R 6 are independently selected from hydrogen, alkyl, COO- alkyl, and S02-alkyl, and R5 is 4S- and R 4 and R 6 are independently selected from hydrogen and alkyl, wherein in all cases R5 above represents a conjugated system. Bis(benzimidazol-2-yl) derivatives of:

N>- X - I I R7 wherein "X" is C21-12or --Co" and R 7 and R8 are independently selected from hydrogen, alkyl, hydroxyalkyl, and the like.

The amount of optical brightener that is used depends on several factors, such as the use of the polyolefin coating and the amount of brightness desired. In a preferred embodiment, the amount of optical brightener included in the polyolefin range from about 0.001 to about 1 percent by weight (or 10 to 10,000 ppm) based on the total weight of the polyolefin. More preferably, the amount of optical brightener is from about 0.005 percent to about 0.1 percent by weight (or 50 to 1000 ppm) based on the total weight of the polyolefin. Most preferably, the amount of optical brightener is from about 0.01 to about 0.025 percent by weight (or 100 to 250 ppm). Alternatively, the brightener can be a mixture of one or more of the above identified optical brighteners. I should be noted that high concentrations of the optical brightener are used when preparing a master batch or concentrate.

Silica is an inexpensive additive that has been used in polyolefin compositions to prevent blocking of film surfaces or extrusion coated surfaces. Low levels of silica, such as about 0. 1 percent by weight, are sufficient to prevent blocking. However, these normally used levels are not sufficient to prevent optical brightener exudation.

Synthetic silicas are considered polymers of silicic acid in which the bulk structure is produced by interlinking the Si04 tetrahedra. At the surface, the structure terminates in siloxane groups and one of the several forms of silanol groups. Regardless of the method of preparation, all synthetic silicas are amorphous in nature and have the chemical composition Of Si02.

The polyolefin composi tion of the present invention includes a synthetic, amorphous silica. Three types of synthetic silica include silica gel, fumed silica, and precipitated silica. The synthetic silica can be prepared by methods well known in the art. For example, fumed silica is prepared by a vapor process while gel silica is prepared by a liquid process. The primary particles of fumed silica are formed when silicon tetrachloride is burned in a flame of hydrogen and oxygen. Fumed silicas include hydrophilic silicas, hydrophobic silicas, and mixed oxides. Silica gels, such as xerogels and areogels, may be produced by reacting sodium silicate solution with sulfuric acid under acidic conditions. An example of commercially available silica includes Sylobloc 48 Silica, synthetic amorphous silica made by Davis Chemical Division of W.R. Grace & Company, Spartenburg, South Carolina.

The synthetic silica is present in an amount sufficient to significantly reduce or prevent the exudation of the optical brightener from the polyolefin (also referred to herein as an effective amount). In a preferred embodiment, the silica is present in the polyolefin composition in at least about 0.25 percent by weight, more preferably at least 0.5 percent by weight, and most preferably at least 1 percent by weight. The effective amount of synthetic silica is combined with the optical brightener and the polyolefin by any means known in the art, including admixing, blending and melt blending.

The polyolefin composition may further include colorants such as pigments and dyes which includes blue, violet or magenta pigments described in U.S. Pat. No. 3,501,298, titanium dioxide, zinc oxide or pigments such as barium sulfate, colloidal or amorphous silica, calcium carbonate and the like; antioxidants such as 4,4'-butylidene-bis(6-tert- butylmeta-cresol), di-I auryi-3,3'-th iodi prop ionate, N-butylated-paminophenol, tetra (2,4-d i-tert-butyl phenyl)-4,4'-di phenyl dip henyldiphosphonite, 2,6-di-tert butyl-p--cxesol, 2,6-di-tert-butyl-4-methyl phenol, N,N-disalicylidene-1, 2 diaminopropane, octadecyl 3-(3',5'-di-tert-butyl-4-hydroxyphenyI propionate) and combinations of the above; processing aids, such as higher aliphatic acid metal salts such as sodium stearate, potassium stearate, lithium stearate, magnesium stearate, calcium stearate, zinc stearate, aluminum stearate, calcium palmitate, sodium palmitate, zirconium octylate, sodium laurate, and salts of benzoic acid such as sodium benzoate, calcium benzoate, magnesium benzoate and zinc benzoate; antistatic agents; dispersing agents; ultraviolet stabilizers; coating aids; slip agents; lubricants and the like, as is well known to those skilled in the art.

Commercially available examples of the above mentioned additives include Irganox 1010 Antioxidant, hindered phenol antioxidant made by Ciba-Geigy, Basel, Switzerland, tetra-kis [methylene 3-(3,5-diterbutyl-4 hydroxy phenyl) propionate] methane; Slip-Eze Slip Agent, fatty acid amide made by Ferro Corporation, Cleveland, Ohio; TiPure R-1 00 Ti02, rutile T102 made by DuPont, Wilmington, Delaware; and Tioxide A-PG Ti02, anatase Ti02 made by Tioxide Canada, Inc, London, England.

The polyolefin mixture may be used in any application where the incorporation of an optical brightener in a polyolefin material is important or desired. Besides injection moldings, the polyolefin composition of the invention may be used in the imaging arts and more desirably on imaging paper suitable for thermal, digital, or a photographic support paper base material. The weight and thickness of the support can be varied depending on the intended use. A preferred weight range is from about 20 g/M2 to about 500 g/M2. preferred thicknesses (those corresponding to commercial grade photographic paper) are from about 20 microns to about 500 microns. It is preferred to use a paper base material calendered to a smooth surface. The paper base material can be made from a suitable paper stock preferably comprising pulps made from hard or softwood.

Either bleached or unbleached pulp can be utilized as desired. The paper base material can also be prepared from partially esterified cellulose fibers or from a blend of cellulose and suitable synthetic fibers such as a blend of cellulose and polyethylene fiber.

As is known to those skilled in the art, the paper base material can contain, if desired, agents to increase the strength of the paper such as wet strength resins which includes amino-aldehyde or polyamide epichlorohydrin resins, and dry strength agents, such as starches, including both ordinary search and cationic search of polyacrylamide resins. Other conventional additives include water soluble gums such as cellulose ethers which includes carboxymethyl cellulose, sizing agents, such as a ketene dimer, which includes sodium stearate and the like.

The polyolefin can be coated onto the paper base material by extruding the polyolefin from a hot melt as is known in the art. The paper base material may be treated with a corona discharge to obtain a good adhesion of the extruded polyolefin. The polymer can be extruded over a wide range of temperatures of from about 1500 to about 3250C and more preferably from about 2500 C to about 3000C, and most preferably from about 1900 C to about 2250C. The polyolefin is coated onto the paper base material at a basis weight of about 1 g/M2 to about 100 g/M2 and a thickness of about 1 micron to about 100 microns.

Advantageously, the addition of synthetic silica into the polyolefin, reduces or eliminates the exudation of the optical brightener from the polyolefin material.

The following xamples that further illustrate the novelty and utility of the present invention are not for limiting the scope of the invention described herein.

EXAMPLES

The following test procedures were used in evaluating the fluorescence and exudation of the polyolefinic compositions herein.

Exudation was tested with the use of a relative swatch scale under UV light while wiping the surface of the sample plaque with a paper cloth under UV light tested exudation. The presence of any amount of brightener on the paper cloth indicated exudation of optical brightener. If the cloth was free of brightener (did not glow under UV light), then no exudation occurred.

Fluorescence was obtained by viewing the sample plaques under a UV light. The relative difference in fluorescence was determined by an observer and quantitatively expressed by characterizing the fluorescence as excellent (E), good (G), fair (F) and poor (P).

EXAMPLE1

Polyolefin compositions were prepared using LIDPE (Epolene C-17 polymer available from Eastman Chemical Company), having a 20 melt index. Formulations were compounded on a laboratory Brabender 30 mm twin screw counter rotating extruder. Precipitated amorphous silica was compared to rutile and anatase Ti02 at 2.5 and 10 percent by weight. All compositions contained 0.02 weight percent (or 200 ppm) optical brightener.

After compounding and pelletizing, each composition was injection molded into 4 inch x 4 inch by 1/8inch plaques. Plaques were then tested for degree of fluorescence, and aged for 21 weeks at room temperature to detect brightener exudation. In all the Ti02 containing compounds, optical brightener exuded to the plaque surface within eight weeks. The plaques of the polyolefinic composition containing synthetic amorphous silica showed no sign of brightener exudation after 36 weeks aging. Results for example 1 are reported in Table 1.

Table 1

Properties of LDPEIOB-1 Composites Fluorescence Exudation' LDPE CAdditive % @ 3 @ 8 @ 36 @ -@ -8 @ 36 17% weeks weeks weeks weeks weeks Fw!eeks 99.98 None E E G Yes Yes Yes 89.98 10 Sil E E E No No No 89.98 10AN P P P v.sl Yes Yes 97.48 2.5 R F F F Yes Yes Yes 89-98 10 AN P P P v.sl Yes Yes 97.48 2.5 R P P P Yes Yes Yes 97.48 2.5 Sil E E E No No No 97.48 2.5 AN G G F No V.S1 Yes 89.98 1OR P P P v.sl sl Yee 97.48 2.5 R F F F Yes Yes Yes 89.98 10AN P P P V.S1 sl Sil = synthetic silica; AN = anatase T102; R = rutile T102; v.sI = very slight E = excellent; G = good; F = fair, P = poor EXAMPLE2 A second set of LDPE compounds were prepared which contained Ti02 and synthetic silica plus 2500 pprn of a phenolic antioxidant (Irganox 1010) and 2500 ppm of a fatty acid amide slip agent (Slip-Eze). The compounds that contained synthetic silica exhibit no optical brightener exudation. All compositions contained 0.02 weight percent (200 ppm) Eastobrite OB-1@ optical brightener. Results for example 2 are reported in Table 2. 20 Table 2

Properties of LDPE/OB-1 Composites Fluorescence Exudation LDPE C- Additive % @ 3 @ 8 @ 36 @ 3 @ 8 @ 36 17% weeks weeks weeks weeks weeks weeks 89.73 10 Sil +A G G G No No No 89.73 10 AN +A F F F v.sl Yes Yes 97.23 2.5 AN +A G G G V.S1 Yes Yes 97.23 2.5 Sil + A G G G No No No 89.73 IOR+A P P P Yes Yes Yes 97.23 2.5 R + A G G G No Sl Yes 97.23 2.5 R + S F F P Yes Yes Yes 89.73 10R+S P P P Yes Yes Yes 97.23 2.5 AN + S F F P Yes Yes Yes 97.23 2.5 Sil + S E E E No No No 89.73 10 Sil + S G G G No No No 89.73 10 AN + S P P P Yes Yes Yes 89.48 10 R +A+S F P P Yes Yes Yes 89.48 10 Sil +A+S G G G No No No 96.98 2.5 Sil +A+S G G G No No No 96.98 2.5 AN+A+S F F F Yes Yes Yes 96.98 2.5 R + A+S F F F Yes Yes Yes 89.48 10 AN +A+S F F F Yes Yes Yes Sil = synthetic silica; AN = anatase Ti02; R = rutile T102; A = Irganox 1010 at 0.25%; S = Slip-Eze at 0.25%; v.sl = very slight; sl = slight "E = excellent; G = good; F = fair, P = poor EXAMPLE3

A third set of LDPE compounds were prepared which contained fillers such as BaS04, talc, Zn02, and natural crystalline silica. All compounds except those containing synthetic silica at levels above 0.25 weight percent exhibited optical brightener exudation. For example, the composition of 97.78 % LDPE, 1.5 % Ti02 pigment, 0.5 % synthetic silica, 0. 1 % antioxidant, 0. 1 % Slip-Eze, and 0.02 weight percent (or 200 ppm) OB-1 0 optical brightener yielded no brightener exudation. These results are reported in Table 3. All compositions contained 0.02 weight percent (200 ppm) Eastobrite OB-10.

Table 3

Properties of LDPEIOB-1 Composites Exudation LDPE C- @ 3 @ 36 17% Additive % weeks weeks 97.78+.5Sil No No 1.5 R +.1A +.1S 97.78+.513 Yes Yes 1.5 R +.IA +.1S 97.78+.5z Yes Yes 1.5 R +.1A +.1S 97.78+.5T Yes Yes 1.5 R +.IA +.1S 98.28+ Yes Yes 1.5 R +.IA +.1S I I Sil synthetic silica; AN = anatase Ti02; R = ruble I IU2; AIrganox 1010 at 0.25%; S = Slip-Eze at 0.25%; B = BaS04; Z = Zn02, T = Talc; NatS = natural crystalline silica EXAMPLE 4

A fourth set of LDPE compounds containing Epolene C-17 polyethylene (20 melt index) was prepared on a 30 mm twin screw counter rotating extruder. Plaques were injection molded for color and exudation studies. Synthetic silica was present at a level of 0.25 percent by weight.

Results indicated that levels above 0.25 percent by weight synthetic silica are sufficient to prevent brightener exudation. Synthetic silica was observed to prevent the exudation of various brighteners (OB-2@, 013-40, and HOSTALUX@ KS). The brightener level of the optical brightener was maintained at 0.02 weight percent (200 ppm). Results are reported in Table 4.

Table 4 Properties of LDPE/Optical Brightener Composites Compositions, % By eight Material 1 2 3 4 5 6 Epolene C-17 96.75 96.73 96.73 96.73 96.73 99.23 polyethylene Rutile T102 2.5 2.5 2.5 2.5 2.5 OB-1 % - 0.02 - 0.02 OB-2 % - 0.02 06-4% - 0.02 KS % - - - 0.02 Sylobloc 48 0.25 0.25 0.25 0.25 0.25 0.25 silica Irganox 1010 0.25 0.25 0.25 0.25 0.25 0.25 AO Slip-Eze fatty 0.25 0.25 0.25 0.25 0.25 0.25 acid amide Brightener Exudation Q 3 weeks NA Yes No No No SI @ 36 weeks NA Yes No No No Yes Fluorescence NA G G G G G 21 weeks G= Good EXAMPLE 5

A fifth set of LDPE compounds containing Epolene C-17 was prepared to compare natural silica with synthetic silica. 0.5 weight percent of Sylobl6c 48 synthetic silica was compared to 0.5 weight percent of Ultrasil VN3 natural crystalline silica, United Silicone, Inc. Lancaster, New York. All compositions contained 1.5 percent of TiPure R-100, rutile T102 made by DuPont; 0.02 weight percent (200 ppm) 06-10;.01 percent Irganox 1010; 0. 1 percent Slip-Eze. The results appear in Table 5.

Table 5

Properties of LDPE/OB-1 Composites Exudation LDPE C- @ 3 @ 36 17% Additive % weeks weeks 97.78+.5 Sill No No 1.5 R +.1A + AS 97.78+.5 NatS Yes Yes 1.5 R +.1A +AS 1 Silsynthetic silica; R = rutile Ti02; A = Irganox 1010 at 0.25%; S = Slip-Eze at 0.25%; NatS = natural crystalline silica EXAMPLE6

Similar compounds were made using an 8.0 melt index HDPE with minimal stabilization. Compounds contained rutile or anatase Ti02 or synthetic silica with 2500 ppm each of the phenolic antioxidant and the fatty acid amide slip agent. The synthetic silica level was also reduced down successively. Results indicated that HDPE compounds, which contained no synthetic silica, exhibited exudation of the brightener. Compounds that contained 0.5 percent synthetic silica did not exhibit brightener exudation after 36 weeks aging. All compositions contained 0.02 weight percent (200 ppm) Eastobrite OB-10 optical brighteners. Data are presented in Table 6.

Table 6

Properties of HDPE/OB-1 Composites 5 Additive, % Fluorescence Exudatio HPIDE @ 3 @ 8 @ 36 @ 3 @ 8 @ 36 % weeks weeks weeks weeks weeks weeks99.98 None E E E No sl Yes 97.48 2.5 Si E E E No No No 97.48 2.5 An G F F sl Yes Y.

97.48 2.5 R F F P Yes Yes Yes 97.23 2.5 R +A F F P Yes Yes Yes 97.23 2.5 An + A G F F sl Yes Yes 97.23 2.5 Si + S G G G No No No 97.23 2.5 Si + S G G G No No No 97.23 2.5 An + S F P P sl Yes Yes 97.23 2.5 R + S F P P Yes Yes Yes 96.98 2.5 R + A+S p P P Yes Yes Yes 96.98 2.5 An + A+S F F P sl Yes Yes 96.98 2.5 Si + A+S G G G No No No 94.48 2.5 Si + 2.5 R + F F F No No No A+S 95.48 1.5 Si + 2.5 R + F F F No No No A+S 96.48 0.5 Si + 2.5 R + F F F No No No A+S Si = synthetic silica; AN = anatase T102; R= rutile Ti02; A = Irganox 1010 at 0.25%; S = Slip-Eze at 0.25% 1 G 'sl slight E excellent; G = good; F = fair, P = poor EXAMPLE7 Master batches of the polyolefin composition containing synthetic silica and optical brightener were prepared in 20 melt index LDPE and 8.0 melt index LLDPE using the 30 mm counter rotating twin screw extruder.

Sufficient synthetic silica and optical brightener were included in the master batch to allow letdowns into LDPE, LLDPE, or HDPE. The ratio of synthetic silica to optical brightener was set at a level such that a letdown would provide 0.5 weight percent silica and 0.02 weight percent (200 ppm) brightener in the final processed part. TeniteO Plastics, HDPE H6001, 8 melt index high density polyethylene and LLDPE, 8 melt index are made by Eastman Chemical Company. The results are presented in Tables 7-10. 5 TABLE7

Brightener/Silica Concentrates in LDPE Compositions, % By Weight Material 1 2 3 LDPE (20 melt 90 89.6 59.6 index) Sylobloc 48 silica 10 10 10 Eastobrite OB-1 0 0.4 0.4 brightener R-1 00 TiO2 0 0 30 TABLE 8

HDPE Composites Containing Brightener/Silica Concentrates 15 Compositions, % By Weight Material 1 2 3 4 5 6 HDPE (8 MI) 94.4 94.38 93.63 92.88 93.64 93.34 Conc. (Table 7-1) 5.0 2.5 1.5 Conc. (Table 7-2) 5.0 2.5 Conc. (Table 7-3) 2.5 5.0 2.5 3.5 Irganox 1010 0.1 0.1 0.1 0.1 0.1 0.1 OB-1 level, PPM 0 200 200 200 100 140 Silica level, % 0.5 0.5 0.5 0.5 0.5 0.5 T102, % 0 0 0.75 1.5 0.75 1.05 RESULTS Fluorescence @24 weeks NA G F F P F Exudation @ 3 weeks NA No No No No No @ 24 weeks NA No No No No No NA not applicable G good F fair P poor ppm of OB-I is equivalent to 0.02 weight percent TABLE9

Polyethylene/Brightener/Silica Concentrates Compositions, % By Weight Materials 1 2 LDPE (20 MI) 79 LLDPE (8MI) - 79 Sylobloc 48 silica 20 20 Eastobrite 013-1 0.8 0.8 lrganox 1010 0.2 0.2 TABLE 10

Polyethylene/Brightener Composites Compositions, % By Weight Materials 1 2 3 4 5 LDPE (20 MI) 98.19 96.98 95.77 HDPE (8MI) 96.98 95.98 R-900 T102 1.0 Conc. Table 9-1 1.5 2.5 3.5 Conc. Table 9-2 2.5 2.5 Silica level, % 0.3 0.5 0.5 0.5 0.7 OB-1 level, PPM 120 200 200 200 280- RESULTS Fluorescence @ 24 weeks G G G F G Exudation @ 24 weeks No No No No No ppm is equivalent to 0.012 weight percent 200 ppm is equivalent to 0.02 weight percent EXAMPLEB

In polypropylene, optical brighteners can be used at higher than normal levels when synthetic silica is present at levels of 0.25 to 0.50 percent by weight of the total compounds. Several types of brighteners can be used at much higher levels than is possible without the use of silica.

Possible uses of this discovery where higher levels of optical brightener are needed could include polymer weathering applications, recycling needs, and polymer alloys or blends. Tenite@ Plastic, P4039 polypropylene is made by Eastman Chemical Company. Polyolefin compositions containing polypropylene are shown in Table 11.

TABLE I I

Polypropylene/Optical Brightener Composites Compositions, % By ei ht Material 1 2 3 4 5 P4039 97.98 97.96 97.92 97.9 98.4 polypropylene Eastobrite OB-1 0.02 0.04 0.08 brightener Uvitex OB - - - 0.1 0.1 Sylobioc 48 silica 0.5 0.5 0.5 0.5 R-1 00 Ti02 1.5 1.5 1.5 1.5 1.5 RESULTS Fluorescence @ 8 G G G G G weeks Although the present invention has been shown and described in terms of the presently preferred embodiment(s), it is to be understood that various modifications and substitutions, rearrangements of parts, components and process steps can be made by those skilled in the art without departing from the novel spirit and scope of the invention.

Claims

We claim:

I A polymeric composition comprising a polyolefin, an optical brightener and synthetic silica in an amount sufficient to significantly reduce or prevent exudbtion of said optical brightener from said polyolefin.
2. The polyolefin composition of claim 1 wherein said polyolefin is selected from the group consisting of homopolymers and copolymers of olefins; selected from ethylene, propylene, styrene, butylene, and mixtures thereof.
3. The polyolefin composition of claim 1 wherein said polyolefin is selected from low density polyethylene, linear low-density Polyethylene, and high density polyethylene.
4. The polyolefin composition of claim 1 wherein said synthetic silica is selected from synthetic silica gel and synthetic fumed silica.
5. The polyolefin composition of claim 1 wherein said synthetic silica is present in the polyolefin composition in at least about 0.25 percent by weight of the polyolefin composition.
6. The polyolefin composition of claim 1, wherein said synthetic silica is present in the polyolefin composition in at least about 0.5 percent by weight of the polyolefin composition.
7. The polyolefirt composition of claim 1, wherein said synthetic silica is present in the polyolefin composition in at least about 1 percent by weight of the polyolefin composition.
8. The polyolefin composition of claim 1 wherein said optical brightener absorbs light having a wavelength of 280-405 nm and emits light having a wavelength of about 400-450 nm.
9. The polyolefin composition of claim I wherein said optical brightener is selected from the group consisting of stilbenes, substituted stilbenes, stilbene derivatives and mixtures thereof.
10. The composition of claim 1 wherein said optical brighteners are selected from the group consisting of mono(azol-2-yl)stilbenes, selected from 2-(stilben-4-yl)naphthotriazoles and 2-(4-phenylstilben 4-yl)benzoxazoles of the formula:

(0 N, N-q--CH = CH R2 N / -0- R' wherein R1 is hydrogen or C=N and R2 is hydrogen or chlorine; 0 /,-CH = CH (H3C)3C N 0 0 0 wherein R3 is hydrogen or alkyl; Q-CH = CH--aCH = CH C = N N bis(benzoxazol-2-yl) derivatives, such as:

R4 R6 R5--<o "a -QfNl> N' wherein R5 is C21-12 and R 4 and R 6 are independently selected from alkyi or hydrogen, R 5 is -0-CH=CH-0 and R4 and R6 are independently selected from hydrogen and alkyl, R5 is and R 4 and R6 are independently selected from hydrogen, alkyl, COO-alkyl, and S02-alkyl, and R5 is -TS \ and R4 and R6 are independently selected from hydrogen and alkyl, wherein in all cases R5 above represents a conjugated system; bis(benzimidazol-2-yl) derivatives of 0:: N>- x NJJU I I R7 R8 CH = CH D wherein "X" is C21-12 or -& -(0- and R 7 and R 8 are independently selected from hydrogen, alkyl, hydroxyalkyl, and mixtures thereof.
11. The polyolefin composition of claim 1 wherein the amount of optical brightener added to said polyolefin is from about 0.001 percent to about I percent by weight based on the weight of the polyolefin composition.
12. The polyolefin composition of claim 1 wherein the amount of optical brightener added to said polyolefin is from about 0.01 percent to about 0.05 percent by weight based on the weight of the polyolefin composition.
13. The polyolefin composition of claim I wherein said optical brightener is 2,2'-(1,2-ethenediyldi-4,1-phenylene) bisbenzoxazole.
14. The polyolefin composition of claim 1 further including additional materials selected from the group consisting of colorants, antioxidants, heat stabilizers, antistatic agents, dispersing agents, coating aids, ultraviolet stabilizers, fillers, processing aids, slip agents, lubricants and mixtures thereof.
15. The polyolefin composition of claim 14 wherein said additional materials are selected from the group consisting of pigments; dyes; 4,4'-butylidene-bis(64ert-butyl-meta-cresol); di-lauryl-3,3 thiodipropionate; N-butylated-p-aminophenol; tetra(2,4-di-tert butylphenyl)-4,4'-diphenyidiphenyldiphosphonite; 2,6-di-tert-butyl-p cresol; 2,6-di4ert-butyl-4-methyl phenol; N,N-disalicylidene-1,2 diaminopropane; octadecyl 3-(3',5'-di-tert-butyl-4-hydroxyphenyI propionate); sodium stearate; potassium sterate; lithium sterate; magnesium stearate; calcium stearate; zinc stearate; aluminum stearate; calcium palmitate; sodium palmitate; zirconium octylate; sodium laurate; salts of benzoic acid selected from sodium benzoate, calcium benzoate, magnesium benzoate and zinc benzoate; and mixtures thereof.
16. The polyolefin composition of claim 15 wherein said pigments are selected from organic or inorganic pigments.
17. The polyolefin composition of claim 15 wherein said pigments are present in amounts up to about 1.0 percent by weight.
18. The polyolefin composition of claim 13 wherein said pigments are selected from talc, Ti02, CaC03, BaS04, Zn02, AI(OH)3, and mixtures and derivatives thereof.
19. An imaging support article comprising:

(a) an image support paper base; and (b) a polyolefin coating on the base comprising a polyolefin, an optical brightener, and a synthetic silica in an amount sufficient to reduce the exudation of the optical brightener from the polyolefin.
20. The imaging support of claim 19 wherein said synthetic silica is selected from synthetic silica gel and synthetic fumed silica.
21. The imaging support of claim 19 wherein said polyolefin is selected from the group consisting of homopolymers and copolymers of olefins selected from ethylene, propylene, styrene, butylene, and mixtures thereof.
22. The imaging support of claim 19 wherein said optical brightener is selected from the group consisting of stilbenes, substituted stilbenes, stilbene derivatives and mixtures thereof.
23.The imaging support of claim 19 includes thermal, digital and photographic paper.
24. The composition of claim 19 further applied to photographic art, injection molding, extrusion coatings, blow molding, rotational molding, and thermoforming.