US3443948A - Photosensitive silver halide microcapsules - Google Patents

Description

United States Patent 3,443,948 PHOTOSENSITIVE SILVER HALIDE MICROCAPSULES Thomas Toplica Bryan, White Bear Lake, Minn., assignor to Minnesota Mining and Manufacturing Company, St. Paul, Minn., a corporation of Delaware No Drawing. Filed July 12, 1965, Ser. No. 471,421

Int. Cl. G03c 3/00; G03 1/52 U.S. Cl. 9667 5 Claims ABSTRACT OF THE DISCLOSURE This invention relates to light sensitive microcapsules, the capsule wall comprising gelatin, silver halide and a water soluble color coupler or a bleachable dyestutf and having water immiscible materials encapsulated within.

This invention relates to novel light sensitive microcapsules, their preparation and use. In one aspect this invention relates to filled microcapsules having a light sensitive shell.

The preparation of microcapsules having a shell of a gelled hydrophilic colloidal material has been described in U.S. Patents Nos. 2,800,457 and 2,800,458 and Belgian Patent No. 628,650. Oil-containing microcapsules may be produced by dispersing the oil in an aqueous solution of gelling hydrophilic colloidal material capable of coacervation. By addition of a coacervating agent a colloidal film can be produced around each oil droplet, and the colloidal film can then be gelled by cooling. In one technique, a gelatin derivative with pH-dependent solubility may be used as the gelling hydrophilic colloidal material, coacervation being achieved by acidification of the emulsion. Microcapsules having gelatin shells may be treated with dichromate solution to impart photosensitivity, such microcapsules having a lesser ability to swell in water after light exposure, as set forth in U.S. Patent No. 3,001,873.

It is an object of this invention to provide a novel light sensitive microcapsule.

Still another object of this invention is to provide a light sensitive microcapsule which can be processed by known photographic techniques without rupturing the microcapsule wall.

A further object of this invention is to provide methods for preparing photosensitive microcapsules.

Yet another object of this invention is to provide useful light sensitive constructions incorporating photosensitive microcapsules.

Other objects and advantages will be apparent from the following description and examples.

In accordance with this invention it has been found that light sensitive silver halide may be incorporated into an aqueous system containing a gellable hydrophilic material capable of serving as a carrier for silver halide in a photographic construction and useful in the preparation of microcapsules and that microcapsules may be prepared therefrom. The resulting microcapsules are thereby rendered photosensitive by virtue of the silver halide contained in the gelable hydrophilic material forming the water permeable microcapsule wall. It has also been found that any of the various techniques for preparing microcapsules from gelable hydrophilic materials, such as gelatin, gelatin derivatives, etc., can be used for purposes of this invention. In general, the preferred techniques involve coagulation or coacervation of the gelable hydrophilic material from an aqueous continuous phase about the water immiscible droplets of the discontinuous phase and the recovery of the microencapsulated water immiscible droplets. Preferred microcapsules normally have a diameter no greater than about 10 microns, usually from 1 to 10 microns. It is often desirable that the aqueous phase additionally contain sensitizers, stabilizers, dyestuffs, color couplers, and other substances advantageously used in silver halide emulsions forphotographic purposes, thereby including such materials into the microcapsule wall. The amount of siliver halide incorporated into the microcapsule wall is controlled by the concentration of silver halide in the aqueous system containing gelable hydrophilic material, the ratio of silver halide to gelable hydrophilic material being determined by the desired use of the resulting microcapsules.

In Belgian Patent No. 628,650 microcapsules are prepared from any gelatin derivative which can be coagulated in an acid medium and which can be formed through reaction of gelatin with an aromatic or aliphatic compound having a group which can react with gelatin. Such a gelatin derivative with pH dependent solubility is defined as a gelatin derivative which is soluble in aqueous alkaline media but which can be deposited from such solutions by acidification to a pH below 5. Examples of such acid-coagulatable gelatin derivatives include the products of the reaction of gelatin with aromatic and aliphatic acid anhydrides (e.g., phthalic acid anhydride, trimellitic acid anhydride, pyromellitic acid anhydride, maleic acid anhydride, succinic acid anhydride, etc.), with compounds containing reactive halogen atoms (e.g., benzene sulphochloride, p-chlorobenzene sulphochloride, mchlorosulphonyl benzoic acid, p-aminobenzene sulphofluoride, m-fluorosulphonyl benzoylacetamide, benzoyl chloride, p-brornocarbonyl benzoic acid, p-bromomethyl benzoic acid, methoxyethyl chloroformate, mucochloric acid, etc.), with isocyanates (e.g., phenyl isocyanate, pbromophenyl isocyanate, naphthyl isocyanate, etc.) and with N-aryl vinyl sulphonamides (e.g., N-vinyl sulphonic acid anilide, N-vinyl sulphonic acid-N-methyl anilide, etc.).

The photosensitive microcapsules of this invention are further characterized by the presence of water insoluble or water immiscible contents, either in solid or liquid form. When the contents is an oil soluble coupler, the microcapsules may be exposed to light to generate silver nuclei which can then serve to actuate or catalyze a development or a color coupling reaction either in the water permeable microcapsule wall or at the interface between the microcapsule wall and the encapsulated contents, i.e., selective color formation. Developers and other reactants, such as those required for a color coupling reaction, may be introduced by diffusion into the microcapsule wall, using the well known techniques of silver halide photography. If the contents of the microcapsule are colored (e.g., colored glass beads, oil soluble dyestuffs (Helo Oil Red R), carbon, titanium dioxide, etc.), selective masking of the encapsulated material can be obtained by photographic development to provide a dense silver deposit or color development in the microcapsule walls. If a colored material capsule of selective decomposition or color conversion in a reaction conducted in the presence of silver nuclei (e.g., bleachable dyestuffs used in the silver dye bleach process) is incorporated in water insoluble form as the microcapsule contents or in water soluble form into the microcapsule wall, the light exposed microcapsules can be developed by treatment with suitable materials which can diffuse into the microcapsule wall to initiate the desired reaction. In all such reactions the water permeable gel microcapsule wall permits diffusion of water soluble reactants into the wall, where a reaction may be made to occur with materials contained in the wall or with the water immiscible contents at the Wallcontents interface. Using the various mechanisms of color forming, color alteration, color destruction and color masking, copysheets having the microcapsules of this invention coated thereon, preferably in conjunction with a water permeable binder such as gelatin, or incorporated therein can be used to record visible images without requin'ng rupture or migration of the mircocapsules.

EXAMPLE 1 In U.S. Patent No. 2,800,457 the coacervation of gelatin is caused by dilution and/or by adjusting the pH of a mixture of two colloids of differing charge. Using silver halide in this procedure photosensitive microcapsules can be prepared, starting with the following two colloids.

The silver halide emulsion was prepared according to the procedures described in Photographic Chemistry, P. Glafkides, vol. I, pages 341-353. The two colloids A and B were mixed, the pH being adjusted to 6.8 by adding 10 percent NaOH. The resulting mixture was then diluted with 30 cc. water. At a tempenature of 50 C. slow addition of 10 percent acetic acid was made until the pH reached 4.0, at which point the silver halide emulsion coagulated around the finely dispersed oil droplets to form microcapsules. The microcapsules were washed several times with water by decantation.

The above procedure was repeated, using a 10 percent color coupler solution in tricresylphosphate as the dispersed oil phase, the color coupler being l-(2',4',6'-trichlorophenyl) 3 [3"-(2,4'-di-tertiary amylphenoxyacetamido)benzamido]-5-pyrazolone, shown as Compound 7 in U.S. Patent No. 2,600,788. The coating mixture was prepared by dispersing the microcapsules in water containing 10 weight percent polyvinyl alcohol as hinder, the concentration of microcapsules in the mixture controlling the density in the final sheet. These microcapsules were coated onto opaque paper and transparent film base with a reverse roll coater, the water permeable binder (e.g., polyvinyl alcohol, gelatin and the various materials described in U.S. 3,189,453) being employed to provide adhesion to the substrate. After air drying the coated sheets were exposed to light through a continuous tone wedge and developed by the same techniques employed with color couplers in conventional silver halide photography, thereby producing a color rendition of the wedge pattern. The color coupling development technique using primary aromatic amino silver halide developer is shown in U.S. Patent No. 2,600,788.

EXAMPLE 2 In U.S. Patent No. 2,800,458 gelatin microcapsules have been prepared by a salt-coacervation technique. The process of flocculating silver halide by the use of ammonium sulfate is described in U.S. 2,618,556. This method was modified to prepare photosensitive microcapsules by the following procedure.

37 weight percent aqueous solution of formaldehyde r 25 Water liters 3 A and B were homogenized at 50 C. to provide an intimate dispersion of the oil droplets in the aqueous phase. The ammonium sulfate solution C was then added slowly with stirring and cooling. The silver halide emulsion deposited around each oil droplet to form photosensitive microcapsules having an oblong shape.

EXAMPLE 3 Anionic soap coagulation of silver halide emulsion for Washing water soluble residues from the emulsion is described in U.S. Patents Nos. 2,489,341 and 2,527,260. The addition of small amounts of anionic compounds to gelatin emulsions will cause separation of a proteinanionic soap complex. This technique has now been employed to encapsulate oil particles with silver halide emulsions.

Water cc 1,000 Silver halide emulsion (as in Example 1) grams 67 Tricressylphosphate cc 20 Anionic surfactant (a secondary sodium alkyl sulfate, Teepol 610) cc 15 Water cc 30 To mixture A, acidified to pH 2.3 with 0.01 normal sulfuric acid, mixture B was added slowly with stirring. A heavy silver halide gelatin shell formed around the tricresylphosphate oil droplets, forming photosensitive microcapsules.

EXAMPLE 4 Gelatin derivatives can also be coagulated by changing pH, as is described in U.S. Patent Nos. 2,481,650; 2,614,- 928; 2,614,929; 2,728,662; 2,787,545; 2,956,880; 3,132,- 945 and 3,138,461. The use of such coagulation techniques for the production of microcapsules from modified gelatin or gelatin derivatives is shown in Belgian Patent No. 628,650.

60 cc. of tricressylphosphate was mixed with 67 grams of silver halide emulsion (as in Example 1 with the substitution of phthalated gelatin, Rousselot Gel 14382, for the unmodified gelatin), and 300 cc. of water at 30 C. was added with cautions stirring. About 20 cc. of 1 percent sulfuric acid was then added slowly until the pH reached 3.5. The coagulated material was then cooled to room temperature, and photosensitive microcapsules were separated by decantation.

EXAMPLE 5 60 cc. of oil (tricresylphosphate) was mixed with 300 cc. of water at 38 C. and grams of the silver halide emulsion of Example 1 to produce an oil dispersion. To this dispersion was slowly added 66 cc. of a 3 percent aqueous solution of dodecyldiphenyl ether ton $0.11

the ether being an anionic surfactant. Because the gelatin is positively charged, the anionic surfactant serves as a satisfactory coagulant. The addition of a few drops of 10 percent sulfuric acid caused the gelatin emulsion to coagulate about the minute oil droplets at a pH of 3.7 and provide a coagulate of somewhat oblong shaped microcapsules. By raising the pH to 4.6 with 10 percent sodium hydroxide the microcapsules assumed a more spherical shape. When the pH was raised to 4.8 by further addition of sodium hydroxide the gelatin coagulant redissolved, only to reform about the oil droplets as the pH was again lowered to 4.0 with the introduction of more sulfuric acid.

EXAMPLE 6 60 cc. of tricresylphosphate was mixed with 100 cc. of silver halide emulsion (as in Example 1) and 300 cc. of water at 38 C. to form an oil-in-water emulsion. To the emulsion was slowly added 38 cc. of 2.5 weight percent aqueous solution of the water soluble copolymer of methyl vinyl ether and maleic anhydride having a specific viscosity of l.0l.4 in solution of 1 gram per 100 milliliters of methyl ethyl ketone at 25 C. (Gantrez AN 139, General Aniline and Film Corporation), a gelatin coagulant, the pH being lowered to 4.3 by addition of diluted sulfuric acid. A gelatin-silver halide deposit formed around the oil droplets, producing photosensitive microcapsules. This example illustrates the use of a polymeric polyelcctrolyte as the gelatin coagulant in photosensitive microcapsule preparation.

EXAMPLE 7 This example will illustrate the incorporation of a water soluble color coupler into the photosensitive microcapsule shell wall.

Dibutyl phthalate cc 60 The silver halide emulsion of Example -1 cc 100 Water cc 300 Color coupler solution containing 20 cc. methyl alcohol, 150 cc. Water, 2 mols/mol coupler of 2 N NaOH cc 20 Magenta color coupler of the formula grams 110 i CH3(CH2)IFCHCNH(|CH2 SO H N 0:0

The color coupler solution was prepared from grams of this color coupler compound. Other suitable couplers are described in US. 2,425,503; 2,768,894 and 2,829,575. Parts A and B were admixed, and 40 cc. of 2.5 weight percent solution of the water soluble copolymer of methyl vinyl ether and maleic anhydride (specific viscosity of 1.0-1.4 in solution of 1 gram per 100 milliliters of methyl ethyl ketone at 25 C.). The pH was adjusted to 4.3 with dilute sulfuric acid, causing coagulation of the gelatin and formation of photosensitive microcapsules containing the color in the capsule shell. When coated onto suitable sheets these microcapsules were exposed to a light image and developed to form a color reproduction, as described in Example 1.

EXAMPLE 8 This example illustrates the encapsulation of hydroquinone, a common photographic developer, in the photosensitive microcapsules of this invention.

Silver halide emulsion (as in Example 1) cc 67 Water cc 1000 10 percent by weight of hydroquinone in tricresylphosphate cc 60 Anionic surfactant (a secondary sodium alkyl sulfate, Tee-pol 6-10) cc 15 Water cc 30 The silver halide emulsion A was acidified with 0.01 N sulfuric acid to a pH of 2.3. Solutions A and B were mixed and homogenized, and solution C was added sloW- ly with stirring. A gelatino-silver halide coagulate formed about the droplets of the tricresylphosphate-hydroquinone oil phase, producing photosensitive microcapsules which could be recovered and coated onto sheets as described in Example 1. The sheets coated with microcapsules were exposed to a light image and developed with a 10 weight percent sodium carbonate solution to form black silver images.

EXAMPLE 9 This example illustrates the incorporation of a colored bleachable azo dye in the photosensitive microcapsule Following the mixing and coagulating techniques of Example '1 photosensitive microcapsules were produced. To this dispersion of microcapsules was added 50 grams of gelatin in 250 cc. of water to form a coating composition, which was then coated onto polystyrene film base. After exposing the sheet to light and developing by the conventional silver dye bleach process, the cyan microcapsules were selectively decolorized in the light exposed areas.

EXAMPLE '10 This example illustrates the incorporation of a colored bleachable azo dye in the photosensitive microcapsule wall and an oil soluble color coupler as the microcapsule contents.

Gum arabic gramsn 10 Water cc 10 weight percent tricresylphosphate solution of the color coupler of Example 1 -cc 40 Silver halide emulsion (as in Example 1) grams 67 2 Weight percent aqueous solution the cyan bleachable azo dyestuif of Example 9 cc 30 Following the same technique as in Example 9 photosensitive microcapsules were produced and then coated in a gelatin binder onto a sheet. After exposure to a light image the sheet was developed by conventional photographic techniques to form at the inner wall interface a col-or from the color coupler contents in the light struck microcapsules and then by silver dye bleach technique to bleach the cyan azo dye in the light exposed microcapsule walls.

EXAMPLE 11 This example illustrates the encapsulation of solids in the photosensitive microcapsules of this invention.

Colored glass geads having a particle size of 10 to 30 microns (1.85-1.95 index of refracti-on) grarns 10 Silver halide emulsion (as in Example '1) cc 100 Water cc 300 After parts A and B were prepared and admixed 3 8 cc. of a 2 weight percent solution of the Water soluble copolymer of methyl vinyl ether and maleic anhydride of Example 6, the pH being lowered with dilute sulfuric acid to 4.3 to etfect coagulation of the gelatin about the dispersed colored glass beads. When the resulting photosensitive microcapsules were coated in a gelatin binder onto a sheet, as in Example 9, exposed to a light image and developed with conventional silver developer, the black silver masked the color of the beads in the image areas, forming a visible reproduction of the light image.

Various other embodiments of the present invention will be apparent to those skilled in the art without departing from the scope thereof.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows.

I claim:

1. A photosensitive microcapsule having a wall comprising gelatin, photosensitive silver halide, and an organic compound capable of eifecting a color change in a reaction conducted in the presence of silver nuclei and having water immiscible contents encapsulated therein.

2. A photosensitive microcapsule having a wall comprising gelatin, photosensitive silver halide and a water soluble color coupler and having water immiscible contents encapsulated therein.

3. A photosensitive microcapsule having a wall comprising gelatin, photosensitive silver halide, and a colored bleachable azo dye and having Water immiscible contents encapsulated therein.

4. The photosensitive capsule of claim 3 in which said water immiscible contents comprises a color coupler.

5. The photosensitive microcapsule of claim 3 in which said colored hleachable azo dye is a water soluble bleachable dyestuit of the type useful in the silver dye bleach process.

References Qited UNITED STATES PATENTS 2,800,457 7/1957 Green et a1. 117-164 2,953,454 9/1960 Berman 11734 3,001,873 9/1961 Foris 9675 3,276,869 10/1966 McCune 9697 3,306,747 2/1967 Haas 96-29 3,369,900 2/ 1968 Taylor 96-76 NORMAN S. TORCHIN, Primary Examiner.

M. F. KELLEY, Assistant Examiner.

US. Cl. X.R. 9697 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Date: May 13 1969 Patent No. 3 4 43 9 Thomas Toplica Bryan It is certified that error appears in the aboveidentified patent and that said Letters Patent are hereby corrected as shown below:

Column 6, line 23, for "10" read 8O and line 7 4, for "geads" read beads SIGNED AND SEALED FEB 2 41970 J Most:

MEFlewhcrJr. WILLIAM E- W, JR.

Dominion of Patents Attosfing Officer