This invention relates to resin coated photographic print materials and more particularly to photographic papers and paper-like materials.

Polyolefin coated papers suffer from a disadvantage in that when exposed to light, photodegradation occurs resulting in embrittlement of the polyolefin layer due to a loss in molecular weight. When a photographic print is exposed to variations in temperature and/or humidity, it is believed that differential forces are created due to the mismatch of the respective thermal and humidity expansion properties of adjacent layers. Since these forces are relatively small, the polyethylene layer in a relatively new print can resist them. However, as aging occurs, the polyethylene layer becomes more brittle and as a result of these forces, microcracks commonly called crazes form in the resin layer. Once crazing occurs, the image quality deteriorates and eventually, once the crazing is severe enough, the print is destroyed.

This degradation of polyolefin layers is accelerated by the presence of Tiθ2 which is necessary to provide the opacity and reflectance required for photographic prints. TiC>2 is unique amongst white pigments for this purpose because its refractive index permits its use in smaller quantities than others. Higher concentration of pigments result in dispersion problems as well as economic disadvantages.

De_.f-ri-.tion of Related Art

U.S. Patents 4,562,145 and 4,582,785 disclose certain hindered amine light stabilizers (HALS) in the polyolefin layer of a resin coated photographic paper to prolong the life of a photographic print in an uncracked form. The polyolefin layer may also contain

conventional additives including pigments, dyestuff, optical brighteners and the like. Summary of the Invention

This invention provides a resin coated photographic print material including a paper-like substrate coated with a layer of a polyolefin resin wherein the polyolefin resin layer contains from about 5 to 25 percent by weight of titanium dioxide pigment, at least 0.01 percent by weight of a hindered amine light stabilizer and from about 0.5 to about 4 percent by weight of zinc oxide. It was surprisingly found that the combination of small quantities of hindered amine light stabilizer compounds and zinc oxide added to polyolefin resins coated onto a paper like support improved the stability of the polyolefin coated support by a factor of at least 3 and usually by a factor of 5 or 6 times comparable polyolefin coated substrate containing only a hindered amine light stabilizer as the sole stabilizing agent. Detailed Description of the Invention

Throughout this application the following terms have the meanings assigned hereto:

Paper-like - this terms includes paper materials which have widespread use in the photographic industry as print materials in addition to substrates such as microvoided matrix materials described in U.S. Patents 4,994,312 and 4,770,931, each of which is incorporated wholly herein by reference. A particularly applicable material of this type is one having a matrix material of polyethylene terephalate containing crosslinked microbeads, the material which when oriented in both the machine and transverse direction results in a microvoided sheet material having a white appearance similar to paper. Hindered amine light stabilizers compounds containing a 2,2,6,6-tetramethyl-piperidine moiety and include, for example, bis (2,2,6,6-tetramethyl-4- piperidinyl)sebacate, bis (1,2,2,6,6,-pentamethyl-4-

piperidinyDsebacate, n-butyl-(3,5-di-tert-butyl-4- hydroxybenzyl)bis- (1,2,2,6,6-pentamethyl-4- piperidinyl)malonate, dimethyl succinate polymer with 4-hydroxy-2,2,6,6-tetramethyl-l-piperidine ethanol, N- N'-bis (2,2,6,6-tetramethyl-4-piperidinyl)-l,6- hexanediamine polymer with 2,4,6-trichloro-l,3,5- triazine and 2,4,4-trimethyl-l,2-pentanamine, poly(6- morpholino-s-triazine-2,4-diyl) [ (2,2,6,6-tetra-methyl- 4-piperi yl)iminohexa-Iι.ethyle e_ (2,2, 6,6-tetra-methyl- 4-piperidyl)imino]] . These materials are available under the tradenames Tinuvin 770, Tinuvin 765, Tinuvin 144, Tinuvin 622LD, Chimassorb 944FL and HALS 1, respectively, available from Ciba-Geigy. The HALS should be present in the polyolefin layer in an amount of at least about 0.01 percent by weight, preferably from 0.01 to about 2 percent by weight and most preferably in an amount of from about 0.05 about 0.5 percent by weight. The upper limit is set solely from an economic view as a point is reached where additional amount of the HALS does not increase the stability.

The resin coated photographic print material in accordance with this invention is prepared by blending the various ingredients, including the polyolefin polymer, titanium dioxide in an amount of from about 5 to about 25 percent by weight preferably from about 8 to about 18 percent by weight and most preferably from about 9 to about 15 percent by weight based on the total weight of the formulation for the olefin layer, the hindered amine light stabilizing agent and from about 0.5 to 4 percent by weight, zinc oxide, preferably from about 0.5 to about 3.5 percent by weight plus other optional addenda and melt extruding the polyolefin containing composition onto the surface of a photographic paper or paper like substrate in accordance with procedures well known in the photographic paper forming industry. The substrate may be coated on one or both sides but preferably is coated on both sides thereof. Generally, the substrate

is coated on the emulsion side with a pigmented polyolefin and on the other side with a clear or unfilled polyolefin. The polyolefin layer on the emulsion side serves two functions, to prevent wetting of the paper during film processing and to provide the necessary opacity and reflectance properties.

In a preferred method of making the resin coated paper in accordance with this invention, the masterbatch technique is employed wherein high concentrations of appropriate ingredients, such as

Ti(_>2, ZnO, hindered amine light stabilizer and the like are compounded into the polyolefin in a suitable apparatus, such as, a twin screw extruder. The master batch is then blended with virgin polyolefin to which various addenda are added to achieve the desired final composition. This composition is then extrusion coated by known methods unto the paper like substrate in the coverage desired.

Any suitable polyolefin resin generally used in the preparation of photographic print material may be employed in accordance with this invention such as for example, polyethylene, polypropylene, including mixtures thereof as well as such polymers having different densities such as, low density polyethylene, high density polyethylene, and the like. Pigments other than titanium dioxide may be employed in minor amounts in order to provide the desired opacity to the polyolefin layer as well as to provide the necessary reflectance properties to display the image resulting from the light sensitive layers that are built onto the photographic print material in accordance with this invention, however, TiC>2 as the sole white pigment is preferred. Other white pigments include material barium sulphate, antimony trioxide, and the like. Additional addenda may be incorporated into the polyolefin layer including optical brightening agents, colored pigments, dyestuffs, antistatic agents and the like.

The various layers to convert the paper support into a light reflecting photographic print material, such as silver halide emulsion layers/ subbing layers, interlayers and overcoat layers are provided on to the polyolefin coated paper support. The silver halide emulsions employed in the present invention preferably comprise silver chloride grains which are at least 80 mole percent silver chloride and the remainder silver bromide. The silver chloride is preferably present in an amount of at least 90 mole percent and most preferably in an amount of at least 95 mole percent because of the improved speed in processing of the print material.

The silver halide emulsions comprise vehicles conventional in the art. Preferred vehicles are hydrophilic colloids which can be employed alone or in combination with hydrophobic materials. Preferred hydrophilic colloids are gelatin, for example, alkali- treated gelatin or acid-treated gelatin, and gelatin derivatives such as acetylated gelatin and phthalated gelatin.

The silver halide emulsions can be chemically and spectrally sensitized as in common in the art. The emulsions, or other layers of the material, can contain stabilizers, antifoggants, and other components intended to prolong the useful life of the material prior to exposure or of the ^* photographic image obtained after development.

The material will commonly contain one or more dye-forming couplers which will provide the final viewable image. However, other means of forming a viewable image can be employed.

The material will typically contain additional layers, such as subbing layers to improve adhesion to the support and interlayers and overcoat layers to separate and protect the sensitive layers and to carry stabilizers, filter dyes and the like.

Further details of the components of the photographic reflection print material, the way they are prepared, and how they are processed to obtain a viewable image are provided in Research Disclosure, Nov. 1979, Item No. 18716, published by Kenneth Mason Publications, Ltd., The Hold Harbouraster's, 8 North Street, Emsworth, Hampshire P010 7DD, England and from Atwell U.S. Patent No. 4,269,927, issued May 26, 1981. Print materials in accordance with this invention as well as the control materials were subjected to accelerated aging conditions by incubation over a period of time with samples being taken periodically in order to measure the molecular weight of the polyolefin as a determination of the degree of degradation resulting in the polymer. Both controls containing hindered amine light stabilizing agent as the sole stabilizing agent and with zinc oxide as the sole stabilizing agent were conducted in order to provide a standard from which the improvement can be observed. Specific formulations together with the precise test conditions are set forth in the following examples in which parts and percentages are by weight unless otherwise indicated. Example 1 .Comparison) A medium density polyethylene resin was extrusion coated onto photographic paper at a thickness of 5.6 lbs/1000 ft**-'. The opposite side of the paper was coated with polyethylene at a coverage of 6.0 lbs/1000 f _t 2. Example 2 (Comparison

A masterbatch of 36 weight percent anatase Tiθ2 was melt compounded with polyethylene using a twin extruder, extruded through an annular die, quenched into a waterbath and pelletized. This masterbatch resin was then blended at a ratio of 1 part masterbatch resin to 2 parts pure polyethylene and then extrusion coated onto photographic paper at a coverage of 5.6

lbs/1000 ft-2. The opposite side of the paper was coated similar to Example 1.

Examples 3 - 5

Masterbatches were prepared in a similar manner as described in Example 2, with the exception that various other, additives as well as the Tiθ2 were included; these formulations are shown in Table 1. The masterbatch resins in Examples 3 - 5 were blended and extrusion coated in a similar manner as Example 2, as well as extrusion coated on the opposite side of the paper as Example 1.

Table 1 Formulation (wt%)

Example No. Anatase Ti0 ₂ ZnO Chimassort. 944

0 0.10 0.10

A sample of the pigmented resin layer each of Examples 1 - 5 were measured for weight average molecular weight by gel permeation chromotography.

Samples of each of Examples 1 - 5 were exposed to a 100 footcandle light in an oven controlled to 80°C and 50% RH for 7, 14 and 28 days. Weight average molecular weight was remeasured of the pigmented resin layer on these aged samples. The loss of molecular weight of the polyethylene is an indication of its stability and thus related to crazing propensity. The results are shown in Table 2.

-8-

Table 2.

Molecular Weight After Light Exposure

(Weight Average Mol Wt. X 1000)

Example No Oda s 7da s 14da s 28days

Table 2 shows that when pure polyethylene is exposed to light, it gradually decreases in molecular weight (Example 1) . After Tiθ2 is added (Example 2), light stability of the polyethylene is dramatically reduced. The addition of Tiθ2 also increases L* and causes a shift in b* when measured for color properties using a

Pacific Scientific Spectrogard, a spectrophotometer type colorimeter to measure 1976 CIE values for lightness (L*) and yellowness/blueness (b*) . When ZnO and Tiθ2 are added (Example 3), an improvement in light stability of polyethylene is observed compared to pure polyethylene, but there is essentially no change in the color properties of the sheet. An improvement in polyethylene light stability is also found when a HALS is used with Tiθ2 (Example 4) . However, when a HALS and ZnO are used in combination with Tiθ2 (Example 5) , in accordance with the invention, a very significant improvement in light stability is seen; in fact, essentially no degradation in molecular weight after 28 days at these severe conditions is observed.

Examples 6 - IP

A masterbatch of 1 weight percent Chimassorb 944 was compounded into polyethylene using a twin screw ^' extruder as described in Example 2. Also compounded in the same manner was a second masterbatch containing 15 weight percent ZnO and a third masterbatch containing 45 weight percent anatase Tiθ2. Examples 6 - 10 were

-9- made by using various blend ratios of these three masterbatches and pure polyethylene to extrusion coat onto photographic paper. The formulations for Examples 6 - 10 are shown in Table 3.

Two sets of samples from Examples 6 - 10 were exposed to the same accelerated aging conditions as Examples 1 - 5; however, these sets were cycled to room temperature twice weekly for examination, thus also exposing them to a temperature and humidity cycle. For the first set of samples, the number of days required at the aging conditions to produce crazing of the pigmented polyethylene coated layer was measured. For the second set of samples, during their room temperature cycle they were wrapped around a 3/4 inch mandrel, and then examined for crazing. The number of days required to produce crazing after the mandrel wrapping were thus measured. All of these results are listed in Table 3.

Table3

Table 3 again shows that both a HALS and ZnO can be used separately to improve the light stability (up to 3 times improvement in days to craze) of the resin coated layer. However, when a HALS and ZnO are used in- combination, a much greater degree of light stability (a 7 to 12 times improvement in days to craze) is found.

Examples 6 - 10 were also measured for color properties regarding the 1976 CIE values for lightness (L*) and yellowness/blueness (b*) with the UV filter in the incident light. These values are recorded in Table 4.

Table4

CIELAB Values (UVO)

Example No. L* b*

6 95.41 1.64

7 95.53 1.48

8 95.49 1.81

9 95.54 1.70

10 95.47 1.68

Comparison of Example 6, with only Tiθ2- and Examples 7 and 10 (both with 3% ZnO, Example 10 being the object of this invention) shows that the addition of the ZnO to the formulation has no impact on the color properties of the extrusion coated paper.

Examples 11 - 18

The masterbatches described in Examples 6 - 10 were used to produce extrusion coated paper containing various levels of Chimassorb 944, with all other components constant (3 weight percent ZnO and 12.2 weight percent anatase Tiθ2).

Examples 11 - 18 were exposed to the same conditions as Examples 6 - 10, and measured for the number of days to craze, both with and without the mandrel wrapping. The results are shown in Table 5.

Table 5

Table 5 shows that as little as 0.01 weight percent of a HALS, when used in combination with 3% ZnO, gives a significant improvement in light stability ( a 2 time improvement over ZnO alone) of the polyethylene resin coated layer of photographic paper.

Example 19

To the pigmented layer of the support of Example 5 is coated, in order with the following layers, layer 1 being adjacent to the support to form a light sensitive element: Slue sensitive layer:

Chemically and blue spectrally sensitized monodisperse silver cloride negative emulsion (0.34 g

AG/m ² ) and yellow-dye forming coupler Y (1.08 g/m ² ) in di-n-butyl phthalate coupler solvent (0, .27 g/m ² ), gelatin (1.51 g/m ² )

2_. Interlayer: Gelatin (0.76 g/m ² )

_L. Green sensitive laver:

Chemically and green spectrally sensitized - monodisperse silver chloride negative emulsion (0.27 g

Ag/m ² ) and magenta-dye forming coupler M (0.42 g/m ² ) in di-n-butyl phthalate coupler solvent (0.22 g/m ² ), gelatin (1.24 g/m ² )

4. UV absorbing laver:

A mixture of hydroxyphenylbenzortriazoles (0.38 g/m ² ), gelatin (0.74 g/m ² ) ϋ_ Red sensitive laver: Chemically and red spectrally sensitized monodisperse silver chloride negative emulsion (0.18 g Ag/m ² ) and cyan-dye forming coupler C (0.42 g/m ² ) in di-n-butyl phthalate coupler solvent (0.24 g/m ² ), gelatin (1.08 g/m ² ) 6. UV absorbing laver:

A mixture of hydroxyphenylbenzotriazoles (0.38 g/m ² ), gelatin (0.74 g/m ² ) 7 : Overcoat layer:

Gelatin (1.35 g/m ² ) The layers 1 to 7 were hardened with bis(vinylsulfonyl)methyl ether at 1.8% of the total gelatin weight. Coupler identifications are:

C = Cyan dye forming coupler: 2- (cc-2,4-di-tert- __ιπylphenoxy)butyr__mido) -4, 6-dichloro-5-ethyl phenol M = Magenta dye forming coupler: 1- (2,4,6- trichlorophenyl)-3- (2-chloro-5(α- (4-hydroxy-3-tert- butylphenoxy)-tetradecanoa ido)anilino)-5-pyrazolone Y = Yellow dye forming coupler: α-(4-(4- benzyloxyphenyl-sulfonyl)phenoxy)-α- (pivalyl)-2- chloro-5- (Y- (2,4-di-t- amylphenoxy)butyramido)acetanilide. The light sensitive element is kept at 120°F and 50% relative humidity for various periods of time and then exposed and processed at 35°C in a three-step process of colored development (45 seconds) , bleach-fix (45 seconds) , and stabilization (90 seconds) followed by drying (60 seconds) at 60°C.

The formulations for the above processing solutions are as follows:

(1) Color developers:

Lithium salt of sulfonated polystyrene 0.25π_L

(30% by wt)

Triethanolamine 11.0 mL

N,N diethylhydroxylamine (85% by wt) 6.0 mL

Potassium sulfite (45% by wt) 0.5 mL

Color developing agent 4 (N-ethyl N-2 5.0 g meth_mesulfonyl__minoethyl) 2 methyl phenylenedi-iminesesquisulfate monohydrate

Kodak Ektaprint 2 Stain-Reducing Agent (a 2.3 g stilbene material commercially available from Eastman Kodak Co.)

Lithium sulfate 2.7 g

Potassium chloride 2.5 g

Potassium bromide 0.025 g

Kodak And Cal No. 5 (an organic phosphonic 0.8 mL acid material commercially available from Eastman Kodak Co.)

Potassium carbonate 25.0 g

Water to total of 1 liter, pH adjusted to 10.12

(2 ) Bleach-fix:

Ammonium thiosulfate 58.0 g

Sodium sulfite 8.7 g

Ethylenedianiinetetraacetic acid ferric ammonium 40.0 g salt

Acetic acid 9.0 mL

Water to total 1 liter, pH adjusted to 6.2

(3 ) Stabilizer :

Sodium citrate 1.0 g

Dearside (a biocide produced by Rohm and Haas) 45.0 ppm

Water to total 1 liter, pH adjusted to 7.2

The developed element exhibits excellent resistance crazing.