EP0060070A2

EP0060070A2 - Fade-resistant and abrasion resistant photographic reproduction, method of preparing and photographic product therefor

Info

Publication number: EP0060070A2
Application number: EP82301048A
Authority: EP
Inventors: Harry A. Loder; Charles A. Mathna
Original assignee: Minnesota Mining and Manufacturing Co
Current assignee: 3M Co
Priority date: 1981-03-12
Filing date: 1982-03-02
Publication date: 1982-09-15
Also published as: BE892457A; IT1148513B; EP0060070A3; IT8247972A0; AU8132082A

Abstract

Color photographic paper in which the backing has a polyolefin foil at the surface coated with the light-sensitive emulsion. The foil can be stripped from the rest of the backing by applying a force of 6-10 grams per centimeter width. The conventional cyan, magenta, and yellow strata of the photoemulsion can be imaged, adhered to any desired substrate, and a portion of the backing stripped cleanly away, leaving a reversed colored image protectively covered by the polyolefin foil. The cyan emulsion layer, normally outermost, is now innermost, where it is protected against UV-induced fading by the UV-absorbing interlayers conventionally interposed between the cyan-magenta and magenta- yellow emulsion strata.

Description

Cross-Reference to Related Applications

This application is a continuation-in-part of application Ser. No. 242,842, filed March 12, 1981, which in turn is a continuation-in-part of Ser. No. 50,686 filed June 21, 1979.

Background of the Invention

This invention relates to the transfer of full-color photographic images to substrates, to adhesive- coated photographic paper especially adapted therefor, and to fade- and abrasion-resistant colored structures made thereby.
It is often desirable to enhance the aesthetic value of photographic works by using special techniques to simulate an oil painting on canvas. Several methods have addressed this problem, albeit with only limited success. For example, a photographic emulsion containing silver halide particles can be knife-coated or otherwise applied to a canvas under controlled light conditions, exposed to imaging radiation through a photographic negative, and the thus-exposed emulsion layer subjected to developing solutions to yield a photographic image. The irregular surface of the canvas substrate tends to cause optical distortion during exposure, and the developing solutions tend to cause shrinkage of the substrate during processing. Further, the thin and fragile emulsion layer remains unprotected, and unreinforced, necessitating the application of a lacquer coating thereover to impart durability. Even more significantly, this procedure is limited to black and white images, primarily because of the extreme difficulty in applying the precisely positioned and proportioned multiple layers of emulsion required to produce a chromatically faithful colored photographic image.
For many years photo resists for platemaking in the printing and graphic arts industry were composed on clear film or glass "flats" by adhering photographic images carried on relatively thin "permanent supports" which had been stripped from relatively thick "temporary supports" after developing; see, e.g., U.S. Patent No. 3,282,643. These "stripping films" were classified as either "wet" or "dry", depending on the technique employed to separate the emulsion-carrying permanent support from the temporary support. U.S. Patent No. 3,359,107 describes a stripping film having a permanent support layer which is preferably (or always) opaque white and relatively thick (25-30 micrometers).
By and large, the physical characteristics deemed essential for a stripping film drastically limit its satisfactory performance in the transfer of a colored photographic image to an irregular substrate. An extremely thin permanent support (which is desired in a stripping film) causes extreme difficulty in handling and consequent distortion, especially when a large sheet is involved. On the other hand, stretchiness (which can not be tolerated in a stripping film, where the stripped film is to be adhered to a smooth surface) is highly desirable where the stripped film is to be conformed to an irregular surface, such as canvas. A thick film minimizes the distortion problem and simplifies handling but it causes optical distortion and edge effects in the composed piece, especially where individual colored emulsion layers are superimposed. In any event, stripping films commonly use high contrast black and white emulsion or photopolymer systems rather than multiple color silver halide emulsion layers.
A currently commercial full color emulsion transfer process utilizes a "wet" stripping film. The several emulsion layers making up a full color silver halide emulsion are coated on a solvent-soluble temporary support, exposed to imaging radiation and developed; the colored emulsion image is then separated by dissolving the temporary support. The extremely delicate and unsupported emulsion image is then carefully transferred to a second surface, to which it is adhered. Since this procedure requires handling an unsupported emulsion, its practical utility is limited to those who specialize in this process.
Because of the limitations inherent in the preceding processes, other techniques have been explored in an attempt to achieve a full-color photograph on a textured- substrate. For example, three photographic emulsion layers (respectively sensitive to blue, green and red), each optionally carried by its own extremely thin individual support film, may be sequentially coated on a conventional backing. The multi-layer emulsion is thereafter exposed to imaging radiation, developed and each emulsion layer in turn (on its support film, if such is present) transferred to the permanent support, making certain that the three imaged layers are in register; see, e.g., U.S. Patent No. 2,182,814. Great care is required in handling the individual emulsion layers, and it is extremely difficult to obtain high quality results, especially if the substrate is irregular or textured.
A somewhat analogous approach is disclosed in U.S. Patent 3,721,557, where individual transparent positive images of different primary colors in a photopolymer carried by a stripping layer are in turn superposed and adhered together in register on a desired substrate. Not only is it impossible to obtain full gray scale contrast or a full range of colors with photopolymers, but the several stripping layers and adhesive layers also tend to shift the color rendition unless each such layer is water-white.
Prior to the present invention, the most popular way of generating a colored photographic image on a canvas or other irregular substrate involved-a process known as "'RC' photo paper stripping". This process utilizes a curl-resistant commercially available photographic print paper of the type where a relatively thick white paper has a thin polyethylene foil laminated to each major face, the multiple photographic emulsion layers being coated over the first foil surface, which normally contains white pigment. A colored photographic image is developed in the emulsion layers, and the exposed surface of the second foil is then adhered to a supporting substrate. Next, exercising great care, the paper backing is split as close to the paper- contacting face of the emulsion-coated first polyethylene foil as possible, the first foil and developed composite image being carefully removed by rolling them around a small cylindrical dowel. The exposed face of the removed polyethylene foil, bearing the developed emulsion layers on the other face, is then adhered to the canvas with a suitable heat-activated or liquid resin and subjected to pressure to conform it intimately thereto.
The results obtained by the splitting process just described are somewhat unpredictable, even though the adhesion of the polyethylene foil to the backing can be controlled; see, e.g., U.S. Patent No. 4,237,206. The removed emulsion-bearing first polyethylene foil can retain a significant and inconsistent amount of paper fiber torn from the original base, often resulting in an irregular caliper; this in turn may impart a distorted and irregular appearance when the curled, fragile, and unsupported foil is thereafter manipulated during the mounting process. Some have addressed the handling problem by bonding a relatively thick transparent heat-activated protective film to the emulsion side of the photo print prior to stripping, the protective film overlying and protecting the imaged surface after the polyethylene supporting foil has been adhered to the canvas substrate. While use of the protective film makes it easier to handle the emulsion layer, an extra processing step is required, increasing the preparation time, and the added thickness of the protective film detracts from the original objective of achieving a true canvas texture in the finished work. As in all prior art colored photographic prints, fading occurs upon extended exposure to light, especially where the wave length is less than about 350 nm.
Others have applied an adhesive layer to the outermost light-sensitive emulsion layer of a photographic paper, bonded the emulsion layer to a substrate, and then dissolved or stripped away the paper backing; see, e.g, U.S. Patent 3,982,940. This procedure yields a transferred image which has no protection against abrasion. In a somewhat related procedure, U.S. Patent 3,933,503 discloses a polyethylene-surfaced carrier coated with a nitrile rubber emulsion over which color photographic emulsion may be applied, imaged and developed; it appears that the imaged emulsion is placed in contact with a substrate and heated, the nitrile rubber acting as binder, and the carrier then stripped away. With very high temperature, the polyethylene is said to melt and merge with the picture.
In summary, prior to the present invention, there has been no simple, convenient way to achieve a faithful color rendition on an irregular substrate. Even in those situations where such a rendition has been achieved, the image was subjected to abrasion, the colors were subject to fading or both. The fading problem has been especially troublesome where the colored reproduction is exposed to direct sunlight, i.e., without the interposition of a window pane which blocks ultraviolet radiation below about 340 nm.

Brief Summary of the Invention

The present invention provides a simple and easy method for attaining the aesthetic qualities of full color photographic images on canvas. The method of the invention expands the practical use of photography to the preparation of large full color murals, and also provides an inexpensive alternative to the use of expensive transparent base prints for backlighted displays. The invention also offers a high quality alternative to four-color lithographic printing where the small number of copies required would otherwise result in prohibitive unit costs. The invention lends itself to the preparation of durable, protected full color renditions for use in package mockup work. As an unexpected advantage, the invention provides products which are far more resistant to fading -- especially when used out-of-doors -- than any prior art products known to the inventors.
In accordance with the invention, there is provided a photographic paper comprising (1) a paper core having a face side and a back side, (2) a first polyolefin (usually polyethylene) foil bonded to the face side but removable therefrom with a force of 6-10 grams per centimeter width, (3) a second polyolefin foil bonded to the back side, and (4) overlying the first foil and bonded thereto a compound full-color light-sensitive element comprising a plurality of superposed strata of photographic emulsions containing disposed silver halide particles, each stratum containing a photographic dye coupler, the outermost stratum containing a cyan dye coupler and the innermost stratum containing a yellow dye coupler; situated between adjacent strata are interlayers containing ultraviolet absorbers. The specified peel adhesion between the barrier foil and the paper core is 6-10 (preferably 6-10) grams per centimeter width, which is substantially less than either (a) the peel adhesion between the barrier foil and the light-sensitive element or (b) the cohesive strength of either the paper carrier sheet or the barrier foil. At the same time, this peel adhesion is sufficiently high to prevent separation during both manufacture and the subsequent handling during imaging, automatic developing, and drying of the light-sensitive element.
It should be pointed out that, except for the low peel adhesion values, and the fact that the first foil is transparent rather than white-pigmented, the product just described is very similar to a conventional reflection print color paper; see, e.g., Neblette's Handbook of Photography and Reprography, Seventh Edition, Van Nostrand Reinhold Company, New York, NY, 1977, pp. 391-393.
A colored photographic image is formed by exposing the compound light-sensitive element through a colored negative to create a latent image which is then developed and fixed. This image is transferred to any desired substrate by applying a uniform layer of adhesive over the outermost stratum, bonding the image-bearing photographic paper to the substrate via the adhesive, and stripping away the paper core and second foil to leave a Cull-colored photographic reproduction bonded to said substrate. Certain portions of the outermost stratum of the previously light-sensitive element now contain yellow dye, which is thus interposed between the light source and the underlying magenta and cyan layers. The absorption spectrum of cyan dye, while peaking at about 650 nm, ranges from 300-750 nm. Because cyan dyes are generally considered the most stable to interior light, they are incorporated in the upper emulsion stratum in standard color photographic paper. For those colors which include cyan dye as a part of the image, the secondary green and blue absorption of such dyes provide some additional protection for the underlying magenta and yellow dyes. Nevertheless, cyan is less stable than yellow in the presence of short wave length UV. The absorption spectrum of yellow, which peaks at about 440 nm and ranges from 340-500 nm, overlaps that of cyan.
Fade resistance of the cyan stratum is obtained by the presence of the interlayers normally present between adjacent color strata. As previously pointed out, such interlayers typically contain a UV absorber effective at wave lengths of 380 nm and less. Thus, in applicants' ultimate photographic reproduction, two UV-absorbing protective interlayers are also positioned between the cyan stratum and the light; in an ordinary-color print, all such UV-absorbing layers lie below the cyan stratum and afford no such protection to the cyan. Where yellow dye is present, it, too, may offer additional protection to underlying colored strata. The first polyethylene foil covers the previously light-sensitive element, whereby the photographic reproduction is protected from abrasion.
The product resulting from the steps described in the preceding paragraph is thus a full color photographic reproduction comprising in combination (a) a substrate, (b) a layer containing a full color image adhesively bonded to said substrate, said layer comprising - a plurality of superposed developed and fixed silver-containing photo emulsion strata, the outermost stratum containing a yellow dye, and (c) overlying and bonded to the outermost stratum a thin polyethylene foil.

Brief Description of the Drawing

Understanding of the invention will be enhanced by referring to the accompanying drawing, in which thickness has been greatly exaggerated in the interest of clarity, like numbers referring to like parts in the several views.

FIGURE 1 is a cross-sectional view of a composite photographic structure of the invention, showing a light-sensitive element comprising imaged plural layers of colored photographic emulsions containing dispersed silver halide particles;
FIGURE 2 is a cross-sectional view of the structure of FIGURE 1, showing the application of a pressure-sensitive adhesive layer to the exposed face of the light-sensitive element;
FIGURE 3 is a cross-sectional view showing the structure of Figure 2 adhered to a canvas substrate, with the original backing being stripped away; and
FIGURE 4 shows, in perspective, a portrait-like image transferred to a canvas substrate as shown in Figure 2.

Detailed Description

Considering the drawing in more detail, attention is directed to FIGURE l, where composite photographic structure 10 is shown in imaged condition, ready for transfer to a substrate. Light-sensitive positive print element 11 is made up of imaged strata lla, llb and llc adhered to transparent polyethylene barrier foil 13, primer (or subbing) layer 12 being interposed to enhance adhesion. Barrier foil 13 is an integral but removable part of photographic carrier sheet 14, which also comprises paper core 15, to the back of which is laminated polymeric foil 16. (It will be appreciated, of course, that acutance dyes, filters, interlayers, antihalo layers, top coats and similar conventional components and layers may be -- and generally are -- present in element 11 to enhance the photographic performance of structure 10. Typically UV-absorbing interlayers 19a and 19b are present between adjacent imaged strata lla-llb and llb-llc.)
In structure 10, each of the three strata lla, llb, and llc has been exposed to a desired pattern of actinic radiation and thereafter developed, respectively resulting in imaged areas 17a, 17b and 17c and unimaged areas 18a, 18b and 18c. Prior to exposure, (which takes place through a color negative) lla, llb and llc contain, respectively, a cyan-forming coupler, a magenta-forming coupler, and a yellow-forming coupler, which correspondingly respond to red, green and blue light. As a result the images in layers lla, llb and llc are additive, and an observer gains the visual impression of a full-colored image.
FIGURE 2 shows the preferred method of providing structure 10 with an adhesive coating. Pressure-sensitive transfer adhesive layer 20 is normally carried on release liner 21. The exposed surface of adhesive layer 20 is placed in contact with the exposed surface of imaged stratum lla, and rolled into uniform contact therewith, after which release liner 21 is removed.
FIGURE 3 shows how the imaged and adhesive- coated composite photographic structure 10 of FIGURE 2 is transferred to one face of canvas substrate 30 and paper core 15 separated from barrier foil 13, leaving the combined image of strata llc, llb and lla adhered to substrate 30 but protectively covered by transparent polyethylene barrier foil 13. For convenience in processing photographic structure 10 and transferring imaged light-sensitive element 11 without distortion, it has been found that the force required to separate paper core 15 from barrier foil 13 should be at least about 6 g/cm width but not more than about 10 g/cm width when measured in accordance with ASTM Test D903.
Polyethylene barrier foil 13 must be sufficiently flexible and extensible to permit the transferred photographic structure to conform to the irregular surface contours of canvas or other substrate to which it is applied. Maximum conformability to irregular substrates is obtained when barrier foil 13 is low density (e.g., 0.924) polyethylene; on the other hand, the high drying temperatures sometimes encountered in processing imaged paper may melt or distort low density polyethylene. Higher density (e.g., 0.946) polyethylene, which has a higher softening point, is generally preferred if a matte finish is to be maintained. Barrier foil 13 should also have sufficient strength that the force required to separate it from the paper fiber interstices at the surface of core 15 will not cause it to distort or rupture, another reason for using the high density polymers. To provide a combination of adequate strength and protection, while at the same time minimizing the separation of the photographic image in light-sensitive element 11 from the viewer, the thickness of barrier foil 13 should be at least about 15 micrometers but not more than about 21 micrometers, thereby enabling structure 10 to conform to the irregularities of substrate 30. After separation from paper core 15, the then-exposed surface of barrier foil 13 has a surprisingly uniform and matte appearance, enabling glare-free viewing of the finished transferred photographic image. It has been determined that the matte surface on barrier foil 13 results from the controlled surface penetration of the polyethylene resin into the fiber interstices at the surface of paper base layer 15 during the manufacturing process.
As previously noted, layer 20 is preferably a pigmented normally tacky and pressure-sensitive adhesive, supplied on a release liner in the form of a transfer tape. Alternatively, layer 20 may comprise a curable, dryable heat-activated adhesive in the form of a solution in organic solvent, a hot melt, an aqueous solution, or a dispersion. Excellent results may be obtained using polyvinyl acetate emulsion ("white glue"), aerosol spray adhesives, etc. Application techniques include roll coating, brushing, transfer coating, etc. Especially where the surface of substrate 30 is not normally white, adhesive layer 20 desirably contains sufficient titanium dioxide or other pigment to render it opaque white, thereby providing the background necessary for true color balance in image-containing layer 11. The flexibility and conformability of adhesive layer 20 should also be consistent with the properties of barrier layer 13 and substrate 30.
The presently preferred adhesive system is an acrylic pressure-sensitive adhesive containing thin-walled, fragile glass micro-balloons. When a solution of the adhesive is coated in a thin layer and dried, the micro- balloons extend above the adhesive surface and allow only partial contact with a substrate to which the exposed surface is applied, permitting repositioning. The application of burnishing pressure ruptures the microballoons, permitting uniform contact and firm adhesion when the desired position has been achieved. Products of this type, containing white pigment, are available from 3M Company under the trade designation "Scotch" Brand No. 569 White Mounting Adhesives.
Another suitable adhesive system comprises a heat-activatable hot melt adhesive containing inherently tacky elastomeric copolymer microspheres, all as described in detail in U.S. Patent No. 4,049,483. An adhesive of this type has sufficient tack to permit structure 10 to remain temporarily in a fixed position on substrate 20, the amount of tack being low enough, however, that structure 10 can be readily removed and repositioned if necessary. After structure 10 has been finally positioned, sufficient heat is applied to the exposed surface of layer 13 to activate the hot melt adhesive component of layer 20, causing it to flow sufficiently to conform intimately to the surface irregularities of substrate 30. A press having a heated platen is preferred for activating the hot melt component of adhesive layer 20.
It will readily be appreciated that the image visible in exposed and developed light-sensitive element 11 is reversed when structure 10 is applied to a substrate. A correct rendition is easily obtained, however, by simply inverting the negative through which light-sensitive element 11 is exposed to actinic radiation.
As has been previously pointed out, light-sensitive stratum lla contains a cyan-forming coupler and is responsive to red light, strata llb and llc containing, respectively, magenta-forming and yellow-forming couplers responding, respectively, to green and blue light. Unfortunately, a finished color print made from photographic paper having this arrangement often fades badly upon exposure to daylight; this problem results from the dual phenomena that (1) cyan has a stronger tendency to fade in the presence of UV light than either magenta or yellow, and (2) losses in optical density in the cyan and magenta strata may be subjectively perceived by the human eye as greater than a loss in optical density in the yellow stratum. Prior to the present invention, no way was known to inhibit this visually apparent color loss other than applying a coating or film containing UV inhibitors over the top of the color print.
An unexpected advantage of the present invention is the fade-resistance of the transferred color prints. In retrospect, it appears that the presence of UV-absorbing interlayers 19a and 19b, both of which are positioned over the cyan layer in the photographic reproduction of the present invention, significantly improves color stability. Thus, the invention provides an unobvious and serendipitous solution to a long-standing problem in the photographic industry. As previously noted, yellow layer llc may also contribute.
As a further aid to understanding the invention, attention is directed to the following illustrative but non-limiting examples, in which all parts are by weight unless otherwise noted.

Example 1

A white photographic base paper having a basis weight of 160 g/m², a thickness of 157.5 micrometers, and a surface smoothness of 30 Sheffield (measured in accordance with TAPPI Useful Method 518) was obtained. Onto one side of the paper (referred to herein as the "back side"), a thin layer of low density polyethylene ("Gulf Polyeth" 4516) was extruded at the rate of about 91 meters/minute. The paper-polyethylene laminate was immediately passed through squeeze rolls comprising a 10.2-cm diameter rubber roll and a 30.5-cm diameter matte finish chrome steel chill roll, the latter contacting the exposed surface of the newly extruded polyethylene at a pressure of 540 g/lineal cm contact. Temperatures and pressures were adjusted to obtain a high degree of adhesion, following well-known procedures; see, e.g., A. Renfrew & Philip Morgan, Polythene -- The Technology and Uses of Ethylene Polymers, 2d ed., Interscience Publishers Inc., New York, 1960. The polyethylene layer was 30.5 micrometers thick and weighed 30 g_/m2_.
Onto the other side of the paper (referred to herein as the "face side") a layer of the same low density polyethylene was then extruded at a rate of about 91 meters/minute and passed between squeeze rolls as in the preceding paragraph. Temperatures, speeds and pressures were carefully controlled to achieve an adhesion of the polyethylene to the face side in the range of 6-10 grams per centimeter of width as measured by ASTM Test D903, indicating an optimum penetration of the face side paper fibers by the polyethylene. The following operating conditions were observed:
All temperatures were maintained + 3°C unless otherwise specified. The resultant laminate had a face side polyethylene foil thickness of 15.2 micrometers and a polyethylene-to-face side adhesion of 6.4 grams/centimeter width.
Following the extrusion-coating process, the exposed surface of the face side polyethylene was subjected to a corona discharge treatment to attain a surface tension level of 54 dynes/cm². Onto the corona-treated surface, a 0.5% solids water-based photographic subbing solution containing gelatine, chrome alum and a wetting agent was air knife coated. Over the subbed polyethylene was then applied a conventional full color light-sensitive 3-stratum silver halide emulsion coating -- yellow, magenta and cyan -- together with the UV-containing interlayers and other components included in conventional photographic papers.
The full color photographic print paper of this example was exposed in a darkroom through a color negative, using a conventional color enlarger, and developed on an automatic roll transport color photographic processor to obtain a print 50 cm x 60 cm. Over the face side of the print was then applied a single layer of "Scotch" No. 569 White Mounting Adhesive, supported on a release liner, manufactured by the 3M Company, St. Paul, Minnesota. The assembly was then passed through a laminator or roller machine to ensure uniform contact of the adhesive with the face of the photographic print, after which the release liner was peeled away, leaving the white adhesive layer adhered to the face side of the photograph.
The exposed face of the tacky adhesive was placed in contact with a canvas cloth, having 8 threads per inch in both the warp and fill directions, and the layup run through the laminator roller machine. The carrier base paper of the photographic print was peeled away, separation occurring cleanly between the face side of the paper and the polyethylene layer, leaving the imaged full color photographic emulsion layer adhered to the canvas and protectively covered by a non-glare clear polyethylene layer. The back side of the canvas was then moistened to assure plasticity of the photographic emulsion layer, and placed in a platen press at l50kPa, the polyethylene in contact with a 2.5-cm thick foam pad and the canvas in contact with an 80°C platen, for one minute. A deeply textured photographic print, corresponding to the underlying canvas pattern, was obtained, the print being protectively covered by a thin, supple polyethylene layer having a non-glare matte surface.
An experiment was conducted to evaluate the relative color stability of (1) the photographic reproduction of the invention, where the protective matte transparent polyethylene layer is on top of the inverted imaged emulsion and (2) an uninverted imaged sheet, as in a normally mounted colored photograph. Specifically, the experiment was conducted as follows:

Sheets of the photographic structure of the invention were exposed through a color-banded test negative and processed according to standard color darkroom procedures. The test prints were then mounted on white paper-faced card stock in the following manner. One portion of the full visible spectrum print was cut and the emulsion side adhered to the card stock with "Scotch" No. 568 unpigmented adhesive, after which the carrier base paper was peeled away, leaving the yellow dye stratum outward and protectively covered by a thin layer of matte polyethylene. The remaining portion of the print was mounted by applying the adhesive to the back side of the carrier base paper and bonding it to the card stock, so that the imaged emulsion side faced outward, the cyan stratum being outermost. A black paper strip was positioned over each of the mounted print portions to shield a part of the entire color spectrum, and two test panels were prepared from each print portion.

One test panel of each print portion was placed in a cylindrical chamber, mounted on a slowly rotating center-shaft, and for 114 hours continuously subjected to radiation from a bank of six 20-watt fluorescent sun lamps located around the circumference of the chamber and spaced an average distance of 7.6 centimeters from the test panel.
The second test panel of each print portion was placed for 306 hours in a light box maintained at 43°C and illuminated by three 275-watt tungsten filament sunlamps spaced 40.6 centimeters apart and 76.2 centimeters above the test panel.
The black paper strips were then removed, and the areas of the prints which had been covered were designated "controls," while the adjacent unprotected areas were designated "irradiated". Visual examination showed the inverted emulsion samples of the invention to be significantly better than the emulsion-side-up samples of the prior art with respect to color loss and shift. To quantify the relative color changes, measurements of the cyan, magenta, yellow, and total density of each reference color band on the test prints were made using a MacBeth Model TR-524 Transmission Reflection Densitometer. Table A shows the values for the 114-hour ultraviolet light- irradiated samples, and Table B shows the values for the 306-hour sunlamp-irradiated samples.

Comparison of the percent changes in the color and density readings in the control and irradiated areas leads to the following general observations:

(1) Overall density loss was significantly lower in the inverted samples of the invention than in the emulsion-side-up samples of the prior art.
(2) Cyan loss was significantly lower in the inverted samples of the invention than in the emulsion-side-up samples of the prior art. Cyan loss in the emulsion-side-up samples was usually accompanied by a yellow gain.
(3) Magenta loss was slightly to moderately higher in the inverted samples of the invention than in the emulsion-side-up samples of the prior art, perhaps because the broad spectrum cyan was no longer interposed between the magenta and the light source.
(4) The general effect of inverting the imaged emulsion layers was a significant improvement in cyan and overall density preservation at some sacrifice to magenta and yellow preservation. Loss of yellow, however, was not readily apparent to the human eye.

It seems clear that the better color and density retention in the inverted samples of the invention is not significantly attributable to the overlying thin matte polyethylene protective foil per se, it being known that the UV-absorbing properties of polyethylene are not significant. Hence, it is believed that the inversion of the emulsion layer was primarily responsible for the improvement. Normal positive color print paper, which is printed from color negatives, is manufactured with the stratum containing the yellow coupler on the bottom (next to the paper), the stratum containing the magenta coupler in the middle, and the stratum containing the cyan coupler on the top. When this order is reversed, as in the application of the photographic structure of this invention to a new surface (e.g., canvas, card stock, etc.), the yellow stratum is above the magenta and cyan. The UV-absorption of the two interlayers inhibit fading in the cyan stratum. A slight additional protection may also result from both the yellow stratum and the light-diffusing properties of the polyethylene barrier foil, especially where it is provided with a matte surface.

Example 2

A product substantially similar to that of Example 1 was prepared using high density polyethylene instead of low density for the first and second foils, the polymer having the commercial identification "du Pont 7250". Extrusion speed was about 150 m/min, the squeeze rolls employing 17-cm, rubber roll and a 62-cm chrome-finish steel roll. Extrusion data included the following:
Resistance to fading and abrasion is comparable to that of Example 1.
The invention lends itself to numerous applications, including some where conformability is not the prime consideration. For example, unpigmented adhesives can be used to transfer photographic images to smooth white surfaces such as card stock, while still retaining color fidelity. Thus, commercial artists can attain desirable artistic effects while saving time in preparing mockup packaging materials, limited copies of full color illustrated brochures, etc. The photographic image can be applied to translucent sheets for use in backlighted displays, to steel panels for use in the area of automotive graphics, to glass for an inexpensive simulation of stained glass, to enamel-painted panels for use as photographic decalcomania, to wooden boards for rustic effects, etc.
Fade resistance can be further enhanced by modifying the photographic paper construction used in the invention either by incorporating a UV-absorber in the first polyethylene foil or the stratum containing the yellow dye coupler, or by providing a UV-absorbing layer between this foil and the stratum containing the yellow dye coupler. This layer could be either the subbing layer itself or an additional layer.
For outdoor use the photographic reproduction can be still further protected by adhering a vinyl foil over the first polyethylene foil, especially if the vinyl foil extends beyond the edges to seal out light and the elements. Additional fade resistance is imparted if the vinyl foil has UV-absorptive properties, either because it is inherent in the polymer (as in the case of polyvinylidene fluoride) or because a UV-absorber is incorporated. It will be recognized that photographic reproductions according to the invention can be made utilizing the principles taught above but employing conventional "RC" color photographic paper, in which both first and second polyethylene foils are firmly bonded to the surfaces of the paper core. Thus, a layer of polyethylene can be extruded onto the surface of the first foil, modifying the conditions of extrusion to obtain a 6-10 g/cm adhesion value. To help provide this fairly low degree of adhesion, certain modifications may be desirable. For example the face side foil of the "RC" paper may have a different chemical composition from that of the subsequently extruded foil; for example, one may be polyethylene and the other polypropylene. It may also be desirable to apply a small amount of adhesion-reducing substance to the surface of the face side foil before the subsequent foil is extruded. In such event, of course, the ultimate photographic reproduction will have a glossy, rather than a matte, appearance.

Claims

1. A.simple and convenient method of preparing a fade-resistant and abrasion-resistant full color photographic reproduction comprising the steps of

a. obtaining a photographic paper comprising

(1) a paper core having a face side and a back side,

(2) a first polyethylene foil bonded to the face side but removable therefrom with a force of 6-10 grams per centimeter width,

(3) a second polyethylene foil bonded to the back side,

(4) overlying the first foil and bonded thereto a full-color light-sensitive element comprising a plurality of superposed strata of photographic emulsions containing disposed siver halide particles, each stratum containing a dye coupler, the outermost stratum containing a cyan coupler and the innermost stratum containing a yellow coupler, adjacent strata being separated by UV-absorbing interlayers,

b. exposing the light-sensitive element through a colored negative to create a latent image and,

c. developing and fixing the latent image,

d. applying a uniform layer of adhesive over the outermost stratum,

e. bonding the image-bearing photographic paper to a desired substrate via said adhesive, and

f. stripping away the paper core and second polyethylene foil to leave a full-colored photograph bonded to said substrate, the outermost stratum of the previously light-sensitive element now ' containing the yellow dye, the cyan stratum being protectively covered by said UV-absorbing interlayers and the yellow stratum, whereby the photographic reproduction is rendered resistant to fading, said first polyethylene foil covering the previously light-sensitive element, whereby the photographic reproduction is protected from abrasion.

2. A photographic reproduction which is resistant to both light-induced fading and mechanical injury, comprising in combination:

a. a substrate,

b. a layer containing a full color image adhesively bonded to said substrate, said layer comprising a plurality of superposed developed and fixed silver-containing photo emulsion strata, adjacent strata being separated by UV-absorbing interlayers, the outermost stratum containing a yellow dye, and

c. overlying and bonded to the outermost stratum a thin polyethylene foil.

3. The photographic reproduction of claim 2 wherein the substrate is canvas.

4. The photographic reproduction of claim 3 wherein the adhesive bonding the image-containing layer is a normally tacky and pressure-sensitive adhesive.

5. The photographic reproduction of claim 4 wherein the adhesive is rendered white and substantially opaque by the incorporation of white pigment.

6. The photographic reproduction of claim 2 wherein the substrate is white card stock.

7. The photographic reproduction of claim 2 wherein a UV-absorbing vinyl film overlies and is bonded to the polyethylene foil.

8. The photographic reproduction of claim 7 wherein the vinyl film is polyvinylidene fluoride.

9. A photographic product for preparing the photographic reproduction of claim 2 comprising in combination:

a. a photographic paper comprising

(1) a paper core having a face side and a back side,

(2) a first polyethylene foil bonded to said face side but removable therefrom with a force of 6-10 grams per centimeter width,

(3) a second polyethylene foil bonded to said back side,

(4) overlying said first foil and bonded thereto, a previously light-sensitive element containing a full-color image, said element comprising a plurality of superposed colored silver-containing emulsion strata, the outermost stratum containing cyan or magenta dye and the innermost stratum containing yellow dye, and

b. overlying and bonded to said outermost emulsion stratum a layer of adhesive.

10. The product of claim 9 wherein a UV- absorbing layer is interposed between the first polyethylene foil and the stratum containing yellow dye.

ll. The product of claim 8 wherein the first polyethylene foil contains a UV absorber.

12. The product of claim 9 wherein the adhesive is a normally tacky and pressure-sensitive adhesive.

13. The product of claim 12 wherein the adhesive contains thin-walled fragile microballoons.

14. The product of claim 12 wherein the adhesive is rendered white and substantially opaque by the incorporation of titanium dioxide pigment.

15. A photographic paper for preparing the photographic reproduction of claim 10 comprising in combination:

a. a paper core having a face side and a back side,

b. a first polyethylene foil bonded to said face side but removable therefrom with a force of 6-10 grams per centimeter width,

c. a second polyethylene foil bonded to said back side,

d. a UV-absorbing layer overlying said first foil and bonded thereto, and

e. overlying said UV-absorbing layer and bonded thereto, a light-sensitive element comprising a plurality of superposed colored silver halide- containing emulsion strata, the outermost stratum containing a cyan dye coupler and the innermost stratum containing a yellow dye coupler.

16. A photographic paper for preparing the photographic reproduction of claim 2 comprising in combination:

a. a paper core having a face side and a back side,

b. a first polyolefin foil bonded to said face side,

c. a second polyolefin foil bonded to said back side,

d. a third polyolefin foil differing in chemical composition from said first foil overlying said first foil, bonded thereto, but removable therefrom with a force of 6-10 grams per centimeter width,

e. overlying said third polyolefin foil and bonded thereto, a light-sensitive element comprising a plurality of superposed colored silver halide- containing emulsion strata, the outermost stratum containing a cyan dye coupler and the innermost stratum containing a yellow dye coupler.

17. The paper of claim 16 wherein the first polyolefin is polyethylene and the third polyolefin is polypropylene.

18. The paper of claim 16 wherein the first polyolefin is polypropylene and the second polyolefin is polyethylene.