US 3351470 A
Description (OCR text may contain errors)
United States Patent PRGDUCTS,
This invention is concerned with photography and, more particularly, with photographic elements for use in diffusion transfer processes performed outside of the camera wherein exposure was effected.
U.S. Patent No. 3,080,805, among others, describes film units for forming diffusion transfer images, which film units, after being exposed within a camera, are designed to be removed from the camera to complete the processing. The diffusion transfer process is initiated by the application of a processing composition as the film unit is withdrawn from the camera. Since the photosensitive element remains light sensitive during the processing operation, the photosensitive element and the imagereceiving element have been provided with opaque layers or supports. The use of such opaque elements is generally effective where the imbibition time is relatively short, e.g., about seconds. Where, however, as in the formation of color transfer images by the processes disclosed in US. Patent No. 2,983,606, the imbibition time is relatively long, e.g., from about 50 to 60 seconds, or even longer at relatively low temperatures, the use of opaque bases has been found to be only partially effective in preventing fogging of the developing photosensitive layers. This problem is even greater where the imagereceiving element is relatively thick. Under such conditions, it has been found that sufficient light penetrates through the edges of the sandwich or lamination comprising the photosensitive element, the layer of processing composition, and the image-receiving element, to adversely affect the quality of the transfer image. This invention is concerned with providing an effective solution to this problem.
Accordingly, the principal objects of this invention are to provide photographic materials adapted to prevent transmission of light inwardly from the edges of a film unit, and to provide processes employing such photographic materials.
Other objects of the invention will in part be obvious and will in part appear hereinafter.
The invention accordingly comprises the processes involving the several steps and the relation and order of one or more of such steps with respect to each of the others, and the products processing the features, properties and the relation of elements which are exemplified in the following detailed disclosure, and the scope of the application of which will be indicated in the claims.
For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description.
This invention is particularly concerned with film units of the type intended to be processed outside a camera, e.g., as shown in said US. Patent No. 3,080,805, when said film units embody multicolor negatives of the type described and claimed in the copending application of Edwin H. Land and Howard G. Rogers, Ser. No. 565,135, filed Feb. 13, 1956, and also as described in connection with FIG. 9 of US. Patent No. 2,983,606, issued May 9, 1961 to Howard G. Rogers, and especially where said film units further embody an image-receiving element of the type described and claimed in the copending application of Edwin H. Land, Ser. No. 234,864, filed Nov. 1, 1962. The latter image-receiving elements are substantially thicker than those previously proposed for use in ice color transfer processes, primarily because at least one, and preferably two, additional layers are positioned be tween the support and the image-receiving layer itself. Because of the presence of these additional layers, which generally are relatively thick, and because of the relatively long imbibition times, light may penetrate the edge of one or more of these layers and be transmitted to the developing photosensitive layers, notwithstanding the fact that the image-receiving element may be substantially opaque to light which might otherwise be transmitted transversely through the image-receiving element, e.g., by virtue of the fact that the layers are coated on an opaque support.
It has now been found that this undesired edge light leakage or transmission of light may be controlled by incorporating a white pigment into such layers as are thick enough to have such undesired light transmission. In the preferred embodiments, the pigment is titanium dioxide.
Image-receiving elements of the type herein contemplated comprise at least a layer adapted to receive an image by diffusion transfer, and preferably contain a layer of a polymeric acid positioned between said imagereceiving layer and the support. In the most preferred embodiments, a timing layer of an inert polymer is positioned between said image-receiving layer and said polymeric acid layer in order to provide a time control for the alkalineutralizing action of said polymeric acid. The nature of such image-receiving elements and materials useful in providing said layers are described in detail in the aforementioned copending application of Edwin H. Land, Ser. No. 234,864, and also in the copending application of Leonard C. Farney, Howard G. Rogers and Richard W. Young, Ser. No. 447,100, filed Apr. 9, 1965 as a continuation-in-part of Ser. No. 277,099, filed May 1, 1963 (now abandoned).
The image-receiving element contains a layer, e.g., the support, which is so constituted as to possess sufficient opacity to substantially prevent light being transmitted transversely therethrough to the photosensitive layers. A suitable opaque layer may be formed of dispersed carbon black; the particular composition of this opaque layer is not critical and may be varied among the many available materials capable of providing tle desired opacity. The photosensitive element may be provided with a suitable opaque layer by dispersing carbon black, or some other opacifying material, in the film base at the time it is cast. Opaque pigmented supports of the type used in movie film are particularly useful.
It has been found that unexpectedly small amounts of white pigment are effective to prevent the aforementioned undesired edge leakage of light. In general, the pigment does not exceed 1% 'by weight of the coated layer, and good results have been obtained at concentrations of 0.2 to 0.1%, or even less, by weight of the polymeric layer. Higher concentrations, e.g., 1.5%, have been used but do not appear to offer any advantages. The amount employed naturally will vary with the thickness of the layer in question, but is insufficient to impart any color to the layer, i.e., the layer remains, for all practical purposes, transparent and uncolored notwithstanding the presence of the white pigment. This invisibility is particularly significant when it is remembered that the image dyes are deposited in such a layer.
In diffusion transfer processes employing multilayer is color negatives, the layer of processing composition applied is frequently thicker than that used in silver transfer processes, with the latters relatively thin negatives. Where the thickness of the processing composition layer is great enough to transmit light from the edge of the developing film sandwich to the photosensitive layers, this edge leakage may be controlled by adding small amounts of carbon black to the processing composition. Again, it
has been found that unexpectedly small amounts of carbon black are needed, particularly where the thicker layers of the image-receiving element contain titanium dioxide as described above. In general, the carbon black is added in concentrations of less than 1% by weight of the water in the processing composition. Carbon black concentrations of 0.1% and even less have been found efiective. It has been found that the carbon black does not interfer process and is not deposited on the image-receiving element.
The following examples of the preparation of imagereceiving elements in accordance with this invention are intended to be illustrative only.
EXAMPLE 1 was allowed to cool, du Pont TiPure titanium dioxide (approximately 0.2% by Weight of the polymer) was added, and the resulting coating composition then coated on a cellulose nitrate subcoated baryta paper (which had been back-coated with a carbon black dispersion to provide an opaque base) to give a layer about 0.8 mil thick. An image-receiving layer about 0.3 mil thick of polyvinyl alcohol and poly-4-vinylpyridine (3:1 by weight) was then applied.
EXAMPLE 2 An image-receiving element was prepared as in Example 1, except that the titanium dioxide was added to a 1:3 mixture by weight of cellulose nitrate and the butyl half ester of medium viscosity poly(methyl vinyl ether/ maleic anhydride):
which was then coated to provide the polymeric acid layer.
[The polymeric anhydride is commercially available from General Aniline & Film Corporation, New York, N.Y., under the trade name Gantrez AN139.]
EXAMPLE 3 The procedure described in Example 1 was repeated, except that a layer approximately 0.5 mil thick of polyvinyl alcohol and titanium dioxide was coated between the layer of the partial butyl ester of the ethylene/maleic anhydride copolymer and the image-receiving layer. The polyvinyl alcohol was applied using a solution of 7 parts by Weight polyvinyl alcohol, 100 parts by Weight of water, approximately 0.1% titanium dioxide by weight of the polyvinyl alcohol, and a small amount of wetting agent.
EXAMPLE 4 An image-receiving element similar to that in Example 3 was prepared using a partial butyral of polyvinyl alcohol instead of polyvinyl alcohol to provide the titanium dioxide containing timing interlayer.
EXAMPLE 5 An image-receiving element similar to that in Example 3 was prepared using a mixture of polyvinyl alcohol and a partial butyral of polyvinyl alcohol instead of poly- 4 vinyl alcohol to provide the titanium dioxide containing timing layer.
EXAMPLE 6 Image-receiving elements were prepared as in the preceding examples except that titanium dioxide was added in the image-receiving layer in a concentration of approximately 0.12% by weight of the polyvinyl alcohol, and the titanium dioxide in the polymeric acid layer was present in quantities of approximately 0.1% as well as 0.2%.
EXAMPLE 7 Image-receiving elements were prepared as in Exa-mple 1 to 6, except that the ratio of polyvinyl alcohol to poly-4-vinylpyridine was 2:1 by weight and the imagereceiving layer was approximately 0.4 mil thick.
EXAMPLE 8 The procedures in Examples 1 to 7 were repeated, except that a small amount of l-phenyl-S-mercaptotetrazole was incorporated in the image-receiving layer.
EXAMPLE 9 The procedure described in Example 3 was repeated, except that the image-receiving layer was applied using a solution comprising (a) 20 cc. of aqueous polyvinyl alcohol (10%) solution, (b) 10 cc. of a 50:50 by volume solution of ethanol and water containing 10% of the ptrimethylammonium benzaldehyde p-toluene sulfonate partial acetal of polyvinyl alcohol, (c) 60 cc. of water, (d) 0.25 cc. of l-phenyl-S-mercaptotetrazole, and approximately 0.1% of titanium dioxide by weight of said polyvinyl alcohol. [Use of partial acetals of polyvinyl alcohol with trialkylammonium benzaldehyde quaternary salts as image-receiving layers is disclosed and claimed in the copending application of Howard C. Haas, Ser. No. 71,424, filed November 25, 1960, now US. Patent Nov 3,239,337, issued March 8, 1966.]
EXAMPLE 10 The procedure described in Example 3 was repeated, except that 30% of arbutin (based on solids) was included in the solution employed to apply the layer of the partial butyl ester of the ethylene/maleic anhydride copolymer.
The following examples of processing compositions containing carbon black and useful in processing imagereceiving elements prepared as above are given for purposes of illustration only:
EXAMPLE 11 Water .cc NaOI-I g 5.17 Hydroxyethyl cellulose (high viscosity) [commercially available from Hercules Powder Co., Wilmington 99, Del., under the trade name Natrasol 250] g 4.03 Sodium thiosulfate g 1.15 Benzotriazole g 2.3 N-benzyl-upicolinium bromide g 2.3 Carbon black g 1.0
EXAMPLE 12 G. Water 100 KOH 11.2 Benzotriazole 2.3 N-benZyl-a-picolinium bromide 2.3 Hydroxyethyl cellulose [Natrasol 250] 4.0 Carbon black 1.0
The image-receiving elements prepared as described in Examples 1 to 9 were processed with a multilayer negative of the type employed in commercially available Polaroid Polacolor Film, Type 48 (coated on an opaque base), exposure being made in a camera of the type shown in U.S. Patent No. 3,080,805. Development was effected outside the camera at 75 F., processing having been initiated by applying a layer approximately 0.0045" thick of the processing composition described in Example as the film unit was withdrawn from the camera. After approximately 60 seconds imbibition, the image-receiving elements were separated and were found to contain good quality multicolor images. In comparison experiments performed under substantially the same conditions except that the titanium dioxide Was omitted and no carbon black was present in the processing composition, significant fogging of the negative was observed, particularly where processing was effected in bright light. Good control of edge light leakage also was obtained without the carbon black in the processing composition, particularly where the imbibition was effected in shaded areas, with appreciably thinner layers of processing composition, or at higher temperatures so that the imbibition period was shortened.
The use of white pigments to prevent fogging by edge leakage of light in the image-receiving element is partic ularly unobvious since the white pigment is not being employed in the usual sense of an opacifying agent.
In the preferred embodiments of the invention, titanium dioxide is present in the polymeric acid layer, the inert spacer or timing interlayer, and the image-receiving layer, as illustrated in Example 6.
As in other camera applications of diffusion transfer processes, the image-receiving element includes a suitable mask, e.g., as shown in U. S. Patent No. 2,612,450 issued Sept. 30, 1952 to Edwin H. Land, to provide the final transfer image with a white, i.e., image-free, border. As a result, light penetrating through an edge of the image-receiving element may have to travel about a quarter of an inch or more to reach the photoexposed portion of the photosensitive layers and have a significant fogging effect. It is possible that this fact contributes to the ability to use such small amounts of pigment to prevent fogging by edge light leakage.
As disclosed in the aforementioned copending application Ser. No. 234,864, the layer of polymeric acid is effective to markedly reduce the pH of the surface of the image-receiving layer prior to separation of the imagereceiving element from the photosensitive element. The presence of the titanium dioxide in the various layers of the image-receiving element has not been found to interfere with the desired pH reduction.
The processing compositions employed in diffusion transfer processes of the type contemplated herein usually are highly alkaline, having a pH in excess of 1-2, and frequently have a pH of the order of 14 or even greater hydroxyl ion concentration.
In accordance with the preferred embodiment of the invention, a layer containing an acid-reacting polymer, and particularly a polymer containing free carboxyl groups, is provided between the image-receiving layer [i.e., the layer in which the dye image is formed, and frequently referred to simply as the image layer] and the support. For simplicity, this layer is sometimes referred to herein as the polymeric acid layer" or as acid polymer layer.
The acid polymer layer contains at least sufficient acid groups to effect a reduction in the pH of the image layer from a pH of about 13 to 14 to a pH of at least 11 or lower at the end of the imbibition period, and preferably to a pH of about 5 to 8 within a short time after imbibition. As previously noted, the pH of the processing composition preferably is of the order of at least 13 to 14 It is, of course, necessary that the action of the polymeric acid be so controlled as not to interfere with either development of the negative or image transfer of unoxidized dye developers. For this reason, the pH of the image layer should be kept at a level of pH 12 to 14 until the positive dye image has been formed after which the pH should be reduced very rapidly to at least about pH 11, and preferably about pH 9 to 10, before the positive image is separated and exposed to air. Unoxidized dye developers containing hydroquinonyl developing radicals diffuse from the negative to the positive as the sodium or other alkali salt. The diffusion rate of such dye developers thus is at least partly a function of the alkali concentration, and it is necessary that the pH of the image layer remain on the order of 12 to 14 until transfer of the necessary quantity of dye developer has been accomplished. The subsequent pH reduction, in addition to its desirable effect upon image light stability, serves a highly valuable photographic function by substantially terminating further dye transfer. This processing technique thus effectively minimizes changes in color balance as a result of longer imbibition times in multicolor processes using multilayer negatives.
In order to prevent premature pH reduction evidenced, for example, by an undesired reduction in positive image density, the acid groups are so distributed in the acid polymer layer that the rate of their availability to the alkali is controllable, e.g., as a function of the rate of swelling of the polymer layer which rate in turn has a direct relationship to the diffusion rate of the alkali ions. The desired distribution of the acid groups in the acid polymer layer may be effected by mixing the acid polymer with a polymer free of acid groups, or lower in concentration of acid groups, and compatible therewith, or by using only the acid polymer but selecting one having a relatively lower proportion of acid groups. These embodiments may be illustrated, respectively, by (a) a mixture of cellulose acetate and cellulose acetate hydrogen phthalate and (b) a cellulose acetate hydrogen phthalate poly mer having a much lower percentage of phthalyl groups than the first-mentioned cellulose acetate hydrogen phthalate.
The layer containing the polymeric acid thus may also contain a water-insoluble polymer, preferably a cellulose ester, which acts to control or modulate the rate at which the alkali salt of the polymer acid is formed. As examples of cellulose esters contemplated for such use, mention may be made of cellulose acetate, cellulose acetate butyrate, etc. Such a polymer also may be added to provide increased wet adhesion to prevent separation of the image-receiving layer or other layers of the image-receiving element during processing. The particular polymers and combinations of polymers employed in any given embodiment are, of course, selected so as to have adequate wet and dry strength.
Where necessary or desirable, suitable subcoats may be employed to improve dry and/or wet adhesion and thus help the various polymeric layers adhere to each other during storage and use.
As used herein, the term polymeric acid is intended vto mean polymers which contain acid groups, such as carboxylic acid and sulfonic acid groups, which are capable of forming salts with alkali metals, such as sodium,
potassium, etc., or with organic bases, particularly quaternary ammonium bases, such as tetramethyl ammonium hydroxide, or potentially acid-yielding groups, such as anhydrides or lactones, or other groups which are capable of reacting with bases to capture and retain them. The acid-reacting group is, of course, nondiffusible from the acid polymer layer. In the preferred embodiments, the acid polymer contains free carboxyl groups and the processing composition contains a large concentration of sodium ions. The acid polymers found to be most useful are characterized by containing free carboxyl groups, being insoluble in water in the free acid form, and by forming water-soluble sodium salts. One may employ polymers containing carboxylic acid anhydride groups, at least some of which preferably have been converted to free carboxyl groups prior to imbibition. While the most readily available polymeric acids are derivatives of cellulose or of vinyl polymers, polymeric acids from other classes of polymers may be used. As examples of specific polymeric acids contemplated as being used in this invention, mention may be made of di-basic acid half-ester derivatives of cellulose which derivatives contain free carboxyl groups, e.g., cellulose acetate hydrogen phthalate, cellulose acetate hydrogen glutarate, cellulose acetate hydrogen succinate, ethyl cellulose hydrogen succinate, ethyl cellulose acetate hydro-gen succinate, cellulose acetate hydrogen succinate hydrogen phthalate; ether and ester derivatives of cellulose modified with sulfoanhydrides, e.g., with ortho-sulfobenzoic anhydride; polystyrene sulfonic acid; carboxymethyl cellulose; polyvinyl hydrogen phthalate; polyvinyl acetate hydrogen phth-alate; polyacrylic acid; acetals of polyvinyl alcohol with carboxy or sulfo substituted aldehydes, e. g., o-, m, or pbenzaldehyde sulfonic acid or carboxylic acid; partial esters of ethylene/maleic anhydride copolymers; partial esters of methylvinyl ether/maleic anhydride copolymers; etc.
As noted above, the provision of an inert interlayer between the image layer and the polymeric acid layer substantially improves the control of the pH reduction by the polymeric acid layer. While this spacer layer preferably is composed of a polymer such as polyvinyl alcohol or a partial acetal of polyvinyl alcohol, such as a partial polyvinyl butyral, other polymers, such as gelatin, which are inert of alkali but through which the alkali may diffuse to the polymeric acid layer may be used. The presence of such an interlayer has been found quite effective in evening out the various reaction rates over a wide range of temperatures, e.g., by preventing premature pH reduction when imbibition is effected at temperatures above room temperature, e.g., at 95100 F. By providing an inert interlayer, the rate at which alkali is available for capture in the polymeric acid layer becomes a function of alkali diffusion rates. The pH reduction thus is relatively independent of chemical reaction rates which would show a greater variation over similar wide changes in imbibition temperature.
The inert spacer layer, e.g., the polyvinyl alcohol or partial polyvinyl butyral interl-ayers of the above examples, acts to time control the pH reduction by the polymer acid layer. This timing is a function of the rate at which the alkali diffuses through this inert spacer layer. It has been found that the pH does not drop until the alkali has passed through this spacer layer, i.e., the pH is not reduced to any significant extent by the mere diffusion into the polyvinyl alcohol interlayer, but the pH drops quite rapidly once the alkali diffuses through the polyvinyl alcohol layer.
Although the preferred image-receiving layer is a mixture of polyvinyl alcohol and poly-4-vinylpyridine (such receiving layers are disclosed and claimed in the copending application of Howard C. Haas, Ser. No. 50,848, filed Aug. 22, 1960, now U.S. Patent No. 3,148,061, issued Sept. 8, 1964), the invention is not limited thereto. Other image-receiving layers are known in the art and may be employed. Similarly, While the preferred embodiment effects development in the presence of a quaternary ammonium compound (as disclosed and claimed in the copending application of Milton Green and Howard G. Rogers, Ser. No. 50,851, filed Aug. 22, 1960, now US. Patent No. 3,173,786, issued Mar. 16, 1965), and particularly a quaternary ammonium compound capable of forming an active methylene base in alkali, the invention is not so limited.
In all embodiments of this invention involving a polymeric acid layer, the polymeric acid layer preferably is thicker than the image-receiving layer and has an appreciably higher mg./ft. coverage. The image-receiving layer is preferably about 0.25 to 0.4 mil thick, and the polymeric acid layer is preferably 0.3 to 1.5 mil thick. If an inert spacer layer is present, that layer is preferably about 0.1 to 0.7 mil thick.
Although the invention has been illustrated in connection with dye developers, and the invention is particularly applicable to multicolor diffusion transfer processes employing dye developers, the novel image-receiving elements of this invention may be used in other diffusion transfer processes employing other image-forming reagents wherein processing is effected in an area of light actinic to the photosensitive material.
Since certain changes may be made in the above products, compositions and processes without departing from the scope of the invention herein involved, it is intended that all matter contained in the above description shall be interpreted as illustrative and not in a limiting sense.
What is claimed is:
1. A photographic film unit adapted for performing a diffusion transfer process in a lighted area, said film unit comprising:
(a) a photosensitive element comprising a substantially light-opaque support carrying blue-sensitive, greensensitive and red-sensitive silver halide emulsion layers, said emulsions respectively having associated therewith a yellow dye developer, a magenta dye developer and a cyan dye developer, each of said dye developers being present in a layer behind its respective silver halide emulsion layer, said support layer possessing sufficient opacity to substantially prevent light being transmitted transversely therethrough to said photosensitive layers;
(b) an image-receiving element adapted to be brought into superposed relationship with said photosensitive element, said imagereceiving element including a substantially light-opaque support and an image-receiving layer, said support possessing sufficient opacity to substantially prevent light being transmitted transversely therethrough to the photosensitive layers when said image-receiving element is in superposed relationship with said photosensitive element, said imagereceiving element also including a mask releasably bonded to the outer surface of said image-receiving layer and defining an image area thereon;
(c) said image-receiving element containing at least one polymeric layer capable of transmitting light incident upon the edge of said layer inwardly from said edge by internal reflection a distance greater than the width of said mask so that light entering said edge may be emitted inwardly of said mask when said photosensitive element is in superposed processing relationship with said image-receiving element, said polymeric layer containing titanium dioxide in an amount less than 1%, by weight, of said polymer, said concentration of titanium dioxide being effective to prevent said inward or lateral transmission of light incident on said edge, said concentration of titanium dioxide being insufficient to visibly color said polymeric layer; and
(d) a rupturable container releasably holding a processing composition and so positioned as to be adapted to release said processing composition for distribution between said image-receiving element and said photosensitive element as said elements are brought into superposed relationship, said processing composition comprising water and alkali, a film-forming material eifective to increase the viscosity of said composition, and carbon black in an amount approximately 1% or less, by Weight, of said water, said quantity of carbon black being effective to prevent lateral transmission of light entering an edge of a layer of said processing composition.
2. A photographic film unit as defined in claim 1 wherein said image-receiving element comprises, in turn, said light-opaque support, a layer of a polymeric acid, an alkali permeable spacer layer and said image-receiving layer, each of said layers containing titanium dioxide in an amount less than 1%, by weight, of the polymer in said layer.
3. A photographic film unit as defined in claim 1 wherein at least one polymeric layer of said image-receiving 9 10 clement contains polyvinyl alcohol, each said layer contain- FOREIGN PATENTS ing polyvinyl alcohol also containing about 0.1% of 223,213 4/1960 A t li titanium dioxide, by Weight, of said polyvinyl alcohol. 598,888 5/1961 Belgium.
860,233 2/1961 Great Britain.
References Cited OTHER REFERENCES UN TED STA S PATENTS Abstracts of Photographic Science and Engineering 2 558 857 7/1951 Land 96 29 Literature, vol. 1, p. 220, entry 15555, (1962). 2,563,342 8/1951 Land 29 J. TRAVIS BROWN, Primary Examin r.
2,607,685 8/1952 Land 9629 O NORMAN G. TORCHIN, Examiner.