EP0030974A4

EP0030974A4 - Composite photographic structure.

Info

Publication number: EP0030974A4
Application number: EP19800901439
Authority: EP
Inventors: Harry A Loder; Charles A Mathna
Original assignee: Minnesota Mining and Manufacturing Co
Current assignee: 3M Co
Priority date: 1979-06-21
Filing date: 1980-12-30
Publication date: 1982-05-10
Also published as: WO1980002879A1; FR2459498A1; BR8008724A; BE883941A; IT1146088B; EP0030974A1; IT8049031A0

Description

Composite Photographic Structure

Technical Field

This invention relates to composite photographic structures, especially to structures having utility in the transfer of photographic images to substrates.

Background Art

Photographic images may be applied to leather, fabric or other substrates in a variety of ways. For example, a photographic emulsion containing silver halide particles can be brushed or otherwise applied to a canvas backing under controlled light conditions, exposed to imaging radiation through a photographic negative, and the thusexposed emulsion layer subjected to developing solutions to yield a positive image. While this technique can be performed with a single coating to yield a black-and-white image, individual handling procedures greatly increase the cost; further, the preparation of colored images is not practical . The production of colored photographs on a canvas backing offers an attractive way to simulate an expensive portrait done in oil, and various techniques have been employed to achieve this effect. For example, three photographic emulsion layers may be prepared on a conventional backing, each such layer thereafter exposed to imaging radiation through a mask of a different primary color (cyan, magenta or yellow), and the emulsion layers developed and transferred in turn to the desired substrate, making certain that the three imaged layers are in register. 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 a full range of color rendition with photopolymers, but the several stripping layers and adhesive layers also tend to destroy the true color rendition unless each such layer is water-white.

Prior to the present invention, the most popular way of transferring a colored photographic image to a canvas or other substrate involved a process known as photo paper stripping. This process utilizes a curl-resi stant commercially available photographic print paper which has a thin polyethylene foil laminated to each major face, the photographic emulsion layers being coated over one of the foil surfaces. A colored photographic image is developed in the emulsion layers and the opposite surface temporarily adhered to a supporting substrate. Exercising great care, the paper backing is then split as close to the papercontacting face of the emulsion-coated polyethylene foil, the foil and developed image being carefully removed by rolling them around a small cylindrical dowel . The removed polyethylene foil, bearing the developed emulsion layers on one face, is then adhered to the desired substrate and subjected to pressure to conform it intimately thereto. Not only is the splitting process difficult, but the rolled emulsion-bearing polyethylene foil also often resists efforts to make it lie flat. Further, the exposed photographic emulsion layer is subject to injury, both during the process of applying it to a new substrate and when the laminate is handled after the emulsion layer has been transferred.

The Invention

The present invention provides a simple, inexpensive means for applying high quality colored or black-and-white images to canvas or other desired substrates. Use of the product of the invention is simple enough that amateurs should be able to obtain excellent results, even without previous experience. A colored image transferred to a canvas substrate not only closely resembles a portrait, but is also protected from inadvertent abrasion of the photographic emulsion layers.

In its simplest form, the article of the invention is a composite photographic structure comprising a selfsupporting flexible carrier sheet over which is positioned a light-sensitive element including at least one stratum of photographic emulsion containing dispersed silver halide particles. Interposed between the carrier sheet and the light-sensitive element, binding them together, is a lighttransmitting, flexible, stretchable thermoplastic polymeric self-supporting barrier foil. Peel adhesion between the barrier foil and the carrier sheet is substantially less than either the peel adhesion between the barrier foil and the light-sensitive element or the cohesive strength of either the carrier sheet or the barrier foil. At the same time, the peel adhesion between the barrier foil and carrier sheet is sufficiently high to prevent separation during manufacture of the composite and the subsequent handling during imaging, developing and drying of the lightsensitive element.

A photographic image which has been prepared in a composite photographic structure of the type just described is transferred to any desired substrate by applying a layer of adhesive to the surface of the image-bearing lightsensitive element, placing the surface of the adhesive in contact with a substrate and forming an adhesive bond thereto, and stripping away the carrier sheet to leave a photographic image adhered to the substrate and protectively covered by the light-transmitting polymeric barrier foil .

The product resulting from the steps described in the preceding paragraph is thus a photographic reproduction comprising in combination a substrate, an adhesive layer overlying at least a portion of the substrate, an imaged silver halide-containing element overlying the adhesive and bonded thereto, and a self-supporting flexible protective light-transmitting polymeric barrier foil overlying and bonded to the silver halide-containing element. Dra wi n g s

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 depicts the simplest form of composite photographic structure of the invention;

FIGURE 2 is a cross-sectional view of a composite photographic structure of the invention, showing imaged plural layers of photographic emulsions containing dispersed silver halide particles, as is the case where a colored image is sought, with an adhesive layer applied to the exposed silver halide layer;

FIGURE 3 shows the imaged composite color photographic structure of FIGURE 2 in the process of being transferred to a substrate; and

FIGURE 4 shows, in perspective, a portrait-like image transferred to a substrate as shown in FIGURE 3.

Detailed Description Considering the drawing in more detail, composite photographic structure 10 comprises light-sensitive element 11, made up of silver halide particles 11a dispersed in photographic emulsion lib. Element 11 is firmly bonded to transparent polymeric barrier foil 13, which in turn i s removably bonded to carrier sheet 15. The adhesion of light-sensitive element 11 to transparent barrier foil 13 along interface 12. exceeds the adhesion of barrier foil 13 to carrier sheet.15 along interface 14.

In FIGURE 2, a somewhat more sophisticated, and presently preferred, form of composite photographic structure 20 is shown in imaged condition, ready for transfer to a substrate. Light-sensitive element 21 is made up of imagable strata 21a, 21b and 21c adhered to transparent barrier foil 23, primer (or subbing) layer 22 being interposed to enhance adhesion. Barrier foil 23 is removably adhered to photographic carrier sheet 25, release layer 24 optionally being interposed to assure the proper degree of separability. Photographic carrier sheet 25 comprises paper base layer 26, to which is laminated polymeric foil 27, serving to reduce any tendency of sheet 25 to curl, e.g., when paper 26 expands during the development process. (It will be appreciated, of course, that acutance dyes, filters, interlayers, antihalo layers, top coats and similar conventional components and layers may be present to enhance the photographic performance of structure 20.) In structure 20, each of the three imagable strata 21a, 21b and 21c has been exposed to a desired pattern of actinic radiation, respectively resulting in imaged areas 28a, 28b and 28c and unimaged areas 29a, 29b and 29c. One of the three strata 21a, 21b and 21c contains a cyan-forming dye, the other two strata respectively containing a yellowforming dye and a magenta-forming dye. As a result, an observer gains the visual impression of a colored picture. Firmly adhered to the outermost surface of light-sensitive element 21 is adhesive layer 30. FIGURE 3 shows how the imaged and adhesive-coated composite photographic structure 20 of FIGURE 2 is transferred to one face of canvas substrate 40 and carrier sheet

25 stripped away, leaving the combined image of strata 21a, 21b and 21c adhered to substrate 40 but protectively covered by transparent polymeric barrier foil 23. For convenience in processing photographic structure 20 and transferring imaged light-sensitive element 21 without distortion, it has been found that the force required to separate release layer 24 from barrier foil 23 should be more than 1 gm/cm width but less than 25 gm/cm width; preferably, the peel adhesion value lies between 6 and 10 gm/cm width. In most cases, especially where base layer 26 is photographic paper, release layer 24 can be omitted. If, however, base layer 26 is a polymeric foil, release layer 24 will probably be required to reduce the adhesion between the base layer

26 and barrier foil 24 to the desired range. Barrier foil 23 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 structure is applied. It should also have sufficient strength that the separation of base layer 26 from its surface will not cause it to distort or rupture. Among the satisfactory barrier foils are certain A-B-A rubbery block copolymers and substantially unoriented polyolefins, especially low density polyethylene. To provide a combination o f a d e q u a t e strength and protection, while at the same time minimizing the separation of the photographic image in light-sensitive element 21 from the viewer, barrier foil 23 is at least 10 micrometers thick but not more than 100 micrometers thick, preferably, the thickness is in the range of 15-30 micrometers, thereby enabling the foil to conform to the irregularities of the underlying substrate. Layer 30, which may comprise a curable, dryable heatactivated, solvent-activated or normally tacky and pressuresensitive adhesive, may be applied from organic solvents, melts or aqueous solutions and dispersions; alternatively, it may be applied by well-known transfer coating processes. Excellent results have been obtained using polyvinyl acetate emulsion ("white glue"), conventional pressure-sensitive adhesive transfer tapes, aerosol spray adhesives, etc. Application techniques include roll coating, brushing, transfer coating, etc. Adhesive layer 30 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 21, i.e., as in a color photograph. The flexibility and conformability of adhesive layer 30 should also be consistent with the properties of barrier layer 23 and substrate 40.

The presently preferred adhesive system is one which has pressure-sensitive adhesive characteristics at room temperature and 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 20 to remain temporarily in a fixed position, the amount of tack being low enough, however, that structure 20 can be readily removed and repositioned if necessary. After structure 20 has been finally positioned, sufficient heat is applied to surface 27 to activate the hot melt adhesive component of layer 30, causing it to flow sufficiently to conform intimately to the surface irregularities of substrate 40. While a press having a heated platen is preferred for activating the hot melt component of the adhesive layer 30, it has been found that an ordinary pressing iron can be used for this purpose.

It will readily be appreciated that the image visible in exposed and developed light-sensitive element 11 or 21 is reversed when structure 10 or 20 is applied to a substrate. A positive rendition is easily obtained, however, by simply inverting the negative through which lightsensitive element 11 or 21 is exposed to actinic radiation. As a further aid to understanding the invention, attention is directed to the following illustrative but nonlimiting examples, in which all parts are by weight unless otherwise noted .

Example 1 A sheet of biaxially oriented polyethylene terephthal ate foil, approximately 36 micrometers thick and having a silicone release coating on one face, was obtained. A high density polyethylene foil approximately 15 micrometers thick was positioned over the silicone-coated surface of the polyester foil and placed in a dry mounting press set at approximately 150°C for 3 minutes. The resulting laminate was removed from the press and allowed to cool for 5 minutes at room temperature, after which the exposed surface of the polyethylene foil was subjected to corona dis¬

2 charge treatment to a level of 54 dynes/cm and, using a rotogravure roll, coated with a 1 % solids subbing solution containing chrome alum, gelatin and a wetting agent.

To impart more body to the structure just described, there was next obtained an opaque white paper having a polyethylene foil laminated to each face and weighing approximately 125 g/m². On one exposed polyethylene foil surface of the paper there was coated a 25% solids solution of 95.5:4.5 iso-octyl-acrylate:acrylic acid copolymer adhesive, the solvent thereafter being evaporated in a hot air oven maintained at approximately 80°C for 4 minutes to leave a dried adhesive coating weighing approximately 12.5 g/m². To the adhesive-coated surface was then laminated the untreated side of the polyester foil described in the preceding paragraph, after which three strata constituting a full color silver halide photographic emulsion element was coated on the previously subbed surface of the polyethylene foil. Each of the three strata contained a different color-forming chemical, viz., a cyanforming dye, a yellow-forming dye, and a magenta-forming dye. The composite photoemulsion element was then imaged, developed by conventional wet photographic methods, and dried, after which a pre-formed layer of hot melt adhesive containing inherently tacky elastomeric copolymer microspheres (cf. U.S. Patent 4,049,483), carried by a removable liner, was placed in contact with the surface of the developed photo emulsion and the back side of the liner rubbed briskly to ensure adequate bonding. When the liner was removed, the exposed surface of the adhesive was sufficiently tacky to permit the assembly to be mounted in a desired position but readily removed and repositioned.

The tacky adhesive-coated surface of the structure just described was placed in contact with a canvas cloth, having 8 threads/cm in both the warp and fill directions, and placed for one minute in a press having a 2.5-cm foam pad opposed by a platen heated to approximately 80°C, thereby flowing the hot melt adhesive component of the adhesive layer and firmly bonding it to the canvas substrate. The laminate was then removed from the press and allowed to cool for one minute, after which the polyethylene-surfaced photographic paper was doubled back on itself at 180° and peeled away from the photographic layer; the force required for removal at 30.5 cm/minute was found to be 8.7 gm/cm width when measured in accordance with ASTM Test No. D903. There remained on the canvas a photograph which was the mirror image of that which previously appeared on the original photographic composite. The photograph was protected by the high density polyethylene foil, the surface of which displayed an irregular appearance corresponding, to that of the underlying canvas.

Example 2

A white photographic grade base paper having a polyethylene anti-curl foil laminated to one surface was obtained. To the exposed paper face was applied a 5% solids heptane solution of a conventional silicone release agent ("Siloff" 23, commercially available from Dow Chemical Company), after which the solvent was evaporated in an oven and the silicone cured by heating 2 minutes at 93°C, leaving a dry release coating weighing approximately 230 mg/m².

Over the silicone-coated paper surface, a 19-micrometer layer of high density polyethylene (DFD 3300, available from Union Carbide, Inc.) was extruded. The equipment employed was a 4-zone 19-mm. laboratory extruder having a length : diameter ratio of 25:1 and a screw speed of 20 revolutions per minute. The four zones were respectively heated to 244°C, 254°C, 266°C and 271°C, the die temperature being 258°C, and the die pressure 42.8 kg/cm². The extruded polyethylene ribbon, in contact with the silicone-coated surface of the paper, was then passed between a rubber roll and chrome steel chill roll (82°C), the latter contacting the extruded polyethylene. The exposed surface of the extruded polyethylene was then subjected to corona discharge treatment, subbed, and coated with full color photographic emulsion, all substantially as in Example 1.

The emulsion was imaged, developed, dried, provided with a layer of microsphere-containing hot melt adhesive, and transferred to a canvas substrate, again following the procedure of Example 1. The force required to separate the paper carrier from the polyethylene-protected image was 5.4 g/cm width.

Example 3

Example 2 was repeated except that the silicone release agent was omitted. The force to separate the carrier from the polyethylene-protected image was 6.3 g/cm width. Exam pl e 4

Example 3 was repeated except that the high density polyethylene resin was replaced by a low density transparent polyethylene resin ("PolyEth" 4516, commercially available from Gulf Oil Chemical Co.) and a 51-mm extruder having alength:diameter ratio of 28:1 was employed. Satisfactory results were obtained when the extruder operating conditions were as follows: screw-speed -- 70 rpm; extruder zone temperatures -- respectively 246°C, 260°C, 274°C, and 274°C; die temperature -- 274°C; die pressure -- 35.1 kg/cm²; chill roll temperature -- 8°C. The force required to remove the base web from. the polyethylene-protected imaged layer was 6.4 g/cm width.

Although, as indicated, desirable artistic effects can be achieved by transferring imaged photographic emulsion layers to cloth, the images can be transferred to card stock for the preparation of aesthetically appealing packaging material, to clear acrylic sheet material for use in back-illuminated photographic displays, to steel plates for use in the area of automotive graphics, to glass for an inexpensive simulation of stained glass, to enamelpainted panels for use a photographic decal comania, to wooden boards for rustic effects, etc.

Claims

1. A photographic reproduction comprising in combination: a substrate such as cloth, steel, glass, wood, enamel-painted panels or acrylic sheet material,an adhesive system layer overlying at least a portion of the substrate, and an imaged silver-halide containing element overlying the adhesive system layer and bonded thereto, characterized by the feature that a selfsupporting, flexible, light-transmitting barrier foil overlies and is bonded to the silver halide-containing element, thereby protecting the imaged element from abrasion.

2. The photographic reproduction of claim 1, further characterized in that the adhesive system is white and opaque, thereby providing the background necessary for true color balance.

3. The photographic reproduction of claim 2 further characterized in that the adhesive system comprises a heat-activatable hot melt adhesive containing inherently tacky elastomeric copolymer microspheres.

4. The photographic reproduction of claim 1, 2 or 3 further characterized by the feature that the barrier foil is formed of polyethylene.

5. The photographic reproduction of claim 1, 2 or 3 further characterized in that the barrier foil is 15-30 micrometers thick and formed from high density polyethylene

6. The method of making the photographic reproduction of claim 1, characterized by the steps of

6.1 providing a composite photographic structure comprising in combination:

6.11 a light-sensitive element which includes at least one stratum of photographic emulsion containing dispersed silver halide particles, 6.12 a self-supporting flexible carrier sheet, and 6.13 interposed between said light-sensitive element and said carrier sheet, binding them together, a light-transmitting flexible, stretchable thermoplastic polymeric self-supporting barrier foil, the peel adhesion between said barrier foil and said carrier sheet being substantially less than either the peel adhesion between said barrier foil and said light-sensitive element or the cohesive strength of either said carrier or said barrier,

6.2 exposing the light-sensitive element to imageforming radiation,

6.3 developing an image in said light-sensitive element,

6.4 applying a layer of adhesive to the surface of said light-sensitive element, 6.5 placing the surface of the adhesive in contact with a substrate and forming an adhesive bond thereto, and 6.6 stripping away the carrier sheet to leave a photographic image adhered to the substrate and protectively covered by the barrier foil.