Classifications

• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03C—PHOTOSENSITIVE MATERIALS FOR PHOTOGRAPHIC PURPOSES; PHOTOGRAPHIC PROCESSES, e.g. CINE, X-RAY, COLOUR, STEREO-PHOTOGRAPHIC PROCESSES; AUXILIARY PROCESSES IN PHOTOGRAPHY
  • G03C1/00—Photosensitive materials
  • G03C1/76—Photosensitive materials characterised by the base or auxiliary layers
  • G03C1/95—Photosensitive materials characterised by the base or auxiliary layers rendered opaque or writable, e.g. with inert particulate additives
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10S430/00—Radiation imagery chemistry: process, composition, or product thereof
  • Y10S430/151—Matting or other surface reflectivity altering material

Definitions

• a photographic composition especially a layer of a photographic element, comprising a colloid binder containing silver halide and a combination of solid, water insoluble, discrete particles of at least two different matting agents, one of which is a soft matting agent and the other hard, provides improved resistance to abrasion and other advantages.
• a mixture of polymethylmethacrylate precedeles as a soft matting agent and silica as a hard matting agent is especially suitable in a layer of a photographic element.
• This invention relates to improved photographic compositions and their process of preparation. More particularly, this invention relates to photographic elements which have a delustered or matte surface. In a specific aspect, this invention relates to photographic elements containing a combination of matting agents and a process for preparing such elements.
• matting agents discrete particles of inorganic or organic materials, called matting agents, can be applied to photographic materials to provide matte surfaces and sufficient tooth for retouching, which characteristics are often desirable in the photographic art.
• matting agents are often added to high contrast copy films which are used to make master negatives of drawings. Corrections are frequently made in a processed negative by retouching with a pencil or by removing silver densities with a chemical etching solution.
• retouching characteristics, as well as other properties such as resistance to abrasion and fingerprint marks in the unprocessed film, have not been wholly satisfactory in prior art products containing matting agents.
• Another object of this invention is to provide photographic elements having matte surfaces that contain finely divided particles of matting agents.
• Another object of this invention is to provide photographic elements that exhibit improved retouching characteristics as Well as improved resistance to abrasion and fingerprint marks.
• Still another object of this invention is to provide a method for preparing such improved photographic materials.
• Another significant feature of this invention is that a particularly outstanding high contrast copy film can be prepared as described herein.
• this copy film shows an improved draw-down in a vacuum printing frame at the time of exposure. It is necessary, during exposure, to have the closest possible contact between a contact film and a negative or positive to be copied. This is generally obtained by exposing in a vacuum printing frame which draws the negative or positive down on the film by means of a vacuum.
• the contact film prepared according to the instant invention enables the negative or positive to be drawn down completely over it in a shorter time than necessary with contact films available heretofore.
• the photographic compositions prepared according to this invention contain a mixture or blend of matting agents.
• particles of at least two matting agents which differ from one another in both hardness and particle size.
• One matting agent is relatively soft and has a large particle size while the other matting agent is, in comparison, both harder and smaller in size.
• the soft matting agents have a Moh Hardness up to about 4, generally in the range of about 1 to about 4, while the hard matting agents generally have a Moh Hardness of at least about 5, and most often in the range of about 5 to about 9.
• the Moh Hardness Scale is a system in which solid substances are classified in order of increasing hardness so that the hardness of any particular substance will be expressed by a number.
• the numbers of this system have been established by assigning the integers from 1 to 10 to arbitrarily chosen substances of increasing hard ness ranging from talc, which is given the number 1, to diamond, which is given the number 10.
• the hardness of any substance not On the scale is determined by the scratch test, i.e., by comparing its hardness with that of the various substances in the standard scale utilizing the principle that the harder of the two substances Will scratch the softer one and will not be scratched by it. When a substance is found to have a hardness between two of the standard substances of the scale, this fact is expressed by use of a decimal notation.
• the Moh Hardness Scale referred to herein can be found in Langes Handbook of Chemistry, 8th edition, Handbook Publishers, Inc., at p. 132.
• the hard matting agents are most often inorganic compounds although some inorganic matting agents such as barium sulfate have a Moh Hardness of only about 2.5 to 3.5.
• the organic matting agents particularly those which are polymers such as poly methyl methacrylate, generally have Moh Hardnesses of less than 4. Any combination of two or more matting agents can be employed in the practice of this invention as long as at least two of the matting agents have the combination of hardness and particle size described herein.
• the matting agents employed in the practice of this invention have a required particle size.
• at least about and preferably by Weight, of all of the particles of matting agent in the photographic composition have a diameter of at least about 1 micron, but not in excess of about 9 or even 8 microns.
• the remainder of matting agent particles, if any are larger than 9 microns, should not exceed about 20 microns.
• the particles of the soft matting agent have a diameter in excess of about 4 microns while no more than about by weight, of the particles of the hard matting agent have a diameter in excess of about 4 microns.
• at least 50%, by weight, of the particles of the soft matting agent have a diameter in excess of about 4 microns and no more than about 20%, by weight, of the particles of the hard matting agent have a diameter in excess of about 4 microns.
• the size of the particles can be readily determined by conventional procedures employed in the prior art for this purpose.
• the matting agents employed in the practice of this invention include any of the water insoluble particulate compounds which can be used to provide a photographic material with a dull, lusterless surface.
• suitable matting agents which have a hard Moh Hardness of at least about 5 as described, include silica, titanium dioxide, magnesium oxide, and aluminum oxide.
• suitable soft matting agents which have a Mob Hardness up to 4, as described, include starch, barium sulfate, calcium carbonate, cellulose esters such as cellulose acetate propionate, cellulose ethers such as ethyl cellulose, synthetic resins such as polymeric esters of acrylic and methacrylic acid, as exemplified by poly methyl methacrylate, polyvinyl resins, such as polyvinyl acetate and polyvinyl alcohol, polycarbonates, homo and copolymers of styrene, hardened gelatin grains, calcium sulfate, barium carbonate and the like.
• the particles of matting agent can be incorporated into one or more layers of a photographic element, preferably in both the silver halide emulsion layer and a layer adjacent to it, using any method which will achieve uniform dispersion of the particles in the layer or layers.
• the matting agent particles are not light sensitive and therefore can be dispersed directly in a photographic silver halide coating solution or they can be dispersed in an aqueous solution or dispersion of the silver halide binding agent, which solution is mixed with a photographic silver halide emulsion prior to coating the latter to form a light sensitive layer.
• a gelatin layer or layer of other silver halide binding agent containing the particles of matting agent can be coated as a protective layer over the silver halide emulsion layer and/or as a backing layer at the rear of the support.
• a backing layer it can contain only a single matting agent of the type defined herein, provided the required mixture of matting agents is incorporated into the photographic element on the silver halide emulsion side of the support.
• Photographic elements which contain matting agents in a protective layer which is outermost from the support generally exhibit especially good resistance to abrasion.
• the presence of matting agent particles in such a protective layer sometimes causes sufficient turbidity to cause a processed silver image to appear gray. This situation can be corrected by incorporating a small concentration of the photographic silver halide used in the photographic element into the protective layer.
• the presence of some silver halide in a protective layer adjacent to the emulsion layer results in the formation of sharp black processed silver images.
• the coverage of hard and soft matting agent per side of support is subject to wide variation.
• the particles of hard matting agent can be coated in the photographic element on the light sensitive side of the support at a total coverage in the range of about 75 to about 150 mg. per square foot of support.
• the particles of soft matting agent can be coated in the photographic element at a total coverage per side in the range of about to about 120 mg., preferably about 80 to about 120 mg. per square foot.
• the silver halide binding agent in the protective layer preferably gelatin
• the silver halide binding agent in the protective layer can be coated at a coverage of about to about 150 mg. per square foot of support.
• photographic silver halide is incorporated into the protective overcoat, it has been found that about .01 to about .1 of the total silver coverage in this layer gives satisfactory results.
• the coverage of hard matting agent in a protective overcoat, if any, is generally in the range of about 10 to about 30 mg. per square foot of support.
• the coverage of soft matting agent, in a protective overcoat, if any can be in the range of about 5 to about 50 mg. per square foot of support.
• the concentration of hard matting agent in this layer can be in the range of about to about 150 mg. per square foot of support while the concentration of soft matting agent can be in the range of about 30 to about mg. per square foot of support.
• the matting agents are often incorporated into other layers such as protective layers, so the concentration of matting agents in the silver halide emulsion layer will often be less than the stated range.
• the silver halide emulsion layer can be coated at a coverage of about 300 mg. to about 400 mg. of silver per square foot of support.
• the binding agent preferably gelatin, can be coated in the emulsion layer at a coverage of about 300 mg. to about 450 mg. per square foot of support.
• a backing layer is employed in the photographic elements of this invention, it is preferably a gelatin backing layer, although other photographic colloids can be used to form such a layer.
• the coverage of colloid or binding agent, preferably gelatin is in the range of about 300 mg. to about 500 mg. per square foot of support.
• the hard matting agent can be employed in the backing layer, if any, at a concentration of about 75 mg. to about 250 mg.
• colloids can be used as the binding agents for the silver halide grains and the matting agents employed in the practice of this invention.
• binding agents include gelatin, or other colloidal materials such as colloidal albumin, cellulose derivatives, synthetic resins such as polyvinyl compounds, acrylamide polymers or the like.
• combinations of binding agents are mixtures of gelatin with aqueous dispersions of polymerized ethylenically unsaturated compounds with added amphoteric or anion dispersing agents and polyoxyethylene compounds. Suitable combinations are disclosed in British Patents 955,197 and 961,490.
• the silver halide employed in the preparation of the light sensitive coatings described herein include any of the photographic silver halides as exemplified by silver bromide, silver iodide, silver chloride or mixed silver halides such as silver chlorobromide or silver bromoiodide.
• Typical supports include those generally employed for photographic elements such as cellulose nitrate film, cellulose acetate film, polyvinyl acetal film, polystyrene film, polyethylene terephthalate film and related films or resinous materials as well as glass, paper, wood and the like.
• Supports such as paper which are coated with a-olefin polymers, particularly polymers of oc-olefins containing 2-10 carbon atoms as exemplified by polyethylene, polypropylene, ethylene butene copolymers and the like, can also be employed.
• the emulsion can also contain additional additives, particularly those known to be beneficial in photographic emulsions, including for example, stabilizers or antifoggants, particularly the water soluble inorganic acid salts of cadmium, cobalt, manganese and zinc as disclosed in US. Patent 2,839,405, the substituted triazaindolizines as disclosed in US. Patents 2,444,605 and 2,444,607, speed increasing materials, gelatin hardeners, plasticizers and the like.
• SensitiZers which give particularly good results in the photographic compositions disclosed herein are the alkylene oxide polymers which can be employed alone or in combination with other materials, such as quaternary ammonium salts, as disclosed in US. Patent 2,886,437 as with mercury compounds and nitrogen containing compounds, as disclosed in US. Patent 2,751,299.
• Example 1 The incorporation of particles of at least two matting agents, as described herein, in at least one layer of a photographic element, results in a product which not only has a matte surface but also a product which combines good resistance to abrasion and fingerprint marks with good retouching characteristics.
• a control photographic element is prepared by coating a photographic silver chlorobromide gelatin emulsion containing silicon dioxide particles over a conventional polyethylene terephthalate film base as the support.
• the silver coverage is 370 mg. of silver per square foot of support.
• the gelatin coverage is 410 mg. of gelatin per square foot of support and the silicon dioxide coverage is 220 mg. per square foot of support.
• a gelatin backing layer containing silicon dioxide particles is also applied to the rear of the support at a coverage of gelatin of 454 mg. per square foot of support and a silicon dioxide coverage of 220 mg. per square foot of support.
• the silicon dioxide employed in the above run has a Moh Hardness of 7; 80%, by weight, of the silicon dioxide particles have a diameter in the range of 1 to 4 microns, and less than by weight, of the silicon dioxide particles have a diameter which is outside of the range of 1 to 9 microns.
• the film Prior to processing, the film has very poor abrasion characteristics and is very susceptible to fingerprint marking.
• the film is exposed to a line image, developed for one minute in Kodak D-72 Developer at 68 F., fixed, washed and dried in the conventional manner. Upon retouching, the processed fihn exhibits low pencil line density and high shine after erasures are made.
• poly methyl methacrylate particles having a Mob Hardness of 2 are incorporated into the light sensitive layer with the silicon dioxide particles.
• the poly methyl methacrylate particles are coated at a coverage of 118 mg. per square foot of support and the silicon dioxide particles are coated at a coverage of 170 mg. per square foot of support.
• 50%, by Weight, of the poly methyl methacrylate particles have a diameter larger than 4 microns and less than 4%, by weight, are larger than 9 microns.
• this coating shows significantly improved resistance to abrasion. Fewer than one-half of the number of abrasion marks present in the control coating can be observed. The resistance to finger print markings is also very much improved in comparison with the control. After processing, the coating gives a high pencil line density, whereas the control gives only low pencil line density. Furthermore, the coating obtained in this run exhibits less shine after erasures are made than the control coating.
• the soft matting agent i.e., the poly methyl methacrylate particles
• other soft matting agents such as barium sulfate (Moh Hardness 2.5-3.5), calcium carbonate (Moh Hardness 3.5-4), barium carbonate (Moh Hardness 33.75), calcium sulfate (Moh Hardness 3-3.5) or other soft polymeric matting agents such as starch, ethyl cellulose or polyvinyl acetate which have Moh Hardnesses below 4.
• the preferred soft matting agents are the vinyl polymers such as poly methyl methacrylate which are prepared by emulsion polymerization procedures, usually in the form of particles, sometimes called beads, having smooth surfaces.
• Example 2 The processed image in the photographic coatings prepared according to this invention can be further improved by the incorporation of a small concentration of photographic silver halide into a layer adjacent to the silver halide emulsion layer.
• a silver chlorobromide gelatin emulsion containing particles of poly methyl methacrylate and silicon dioxide is coated over a conventional polyethylene terephthalate film base as the support.
• the silver coverage in the emulsion layer is 330 mg. of silver per square foot of support.
• the gelatin coverage is 360 mg. of gelatin per square foot of support.
• the poly methyl methacrylate coverage is 46 mg. per square foot of support and the silicon dioxide coverage is 92 mg. per square foot of support.
• a gelatin layer containing silver chlorobromide, poly methyl methacrylate particles and silicon dioxide particles is coated adjacent to the emulsion layer.
• the gelatin coverage is 91 mg. per square foot of support.
• the silver coverage is 12 mg. per square foot of support.
• the poly methyl methacrylate coverage is 11 mg. per square foot and the silicon dioxide coverage is 21 mg. per square foot of support.
• a gelatin backing layer containing silicon dioxide and poly methyl methacrylate particles, is coated on the rear of the support.
• the gelatin coverage is 454 mg. per square foot of support, the poly methyl methacrylate coverage is 54 mg. per square foot of support and the silicon dioxide coverage is mg. per square foot of support.
• Example 1 The size and hardness of the particles of silicon dioxide and poly methyl methacrylate are the same as in Example 1.
• the resulting coating has the excellent combination of characteristics of the product described in Example 1.
• the processed image obtained from the photographic element of this run has a blacker tone and silver line images can be more quickly eradicated with chemical etching solutions.
• Example 3 The concentrations of silver halide and matting agent in the layer coated over the silver halide emulsion layer can be varied widely. To illustrate, three separate coatings are prepared; in one run Example 2 is repeated except that the silver chlorobromide in the gelatin layer is increased to 24 mg. of silver per square foot of support; in the second coating, Example 2 is repeated except that the poly methyl methacrylate particles or beads are coated at a concentration of 44 mg. per square foot of support and in the third run, the poly methyl methacrylate particle coverage is reduced to 22 mg. per square foot of support.
• each of these coatings exhibits good resistance to abrasion and fingerprint marks. After processing, as in Example 1, the coatings show high pencil line density upon retouching.
• Example 4 As already indicated the mixed matting agents employed in the practice of this invention must have the relative size and hardness values described herein. To illustrate, Example 1 is repeated with poly methyl methacrylate particles, 40%, by weight, of which have a diameter larger than 8 microns and 30%, by Weight, of which are larger than 9 microns. Upon exposure and processing, as described in Example 1, the film exhibits poor pencil line image characteristics, i.e., the pencil lines are discontinuous in nature.
• Example 1 When Example 1 is repeated using poly methyl methacrylate particles, only 30%, by weight, of which have a diameter larger than 4 microns, there is obtained a coating which exhibits poor pencil retouching characteristics. Thus, in this case, the pencil retouching lines are much too light to be acceptable.
• Example 1 is repeated except that the average size of the poly methyl methacrylate particles is 1-4 microns and the average size of the silicon dioxide particles is 5 to 9 microns.
• this coating is exposed and processed as in Example 1, there is obtained pencil retouching lines which are distinctly less sharp than those exhibited by the coating of Example 1.
• pencil wear upon retouching, there is a substantial increase in pencil wear which blunts the point of the pencil and results in wide lines having an increased tendency to smudge.
• a photographic element comprising a photographic silver halide layer, and, incorporated in at least one colloid binder containing layer of said photographic element, solid, water insoluble, discrete particles of a soft matting agent having a Moh Hardness up to about 4 and of a hard matting agent having a Moh Hardness of at least about 5, at least about 90%, by Weight, of said particles having a diameter of at least about 1 micron but not in excess of about 9 microns, at least about 40%, by weight, of the particles of said soft matting agent having a diameter in excess of about 4 microns and no more than about 25 by weight, of the particles of said hard matting agent having a diameter in excess of about 4 microns.
• a photographic element comprising a photographic silver halide layer and, incorporated in at least one colloid binder containing layer of said photographic element, solid, water insoluble, discrete particles of a soft matting agent having a Moh Hardness in the range of about 1 to about 4 and a hard matting agent having a Moh Hardness in the range of about 5 to about 9, at least about 90%, by weight, of said particles having a diameter of at least about 1 micron and not in excess of about 9 microns, at least about 40%, by weight, of the particles of said soft matting agent having a diameter in excess of about 4 microns and not more than about 25 by weight, of the particles of said hard matting agent having a diameter in excess of about 4 microns.
• a photographic element comprising a photographic silver halide layer and, incorporated in at least one colloid binder containing layer of said photographic element, solid, water insoluble, discrete particles of a soft matting agent being a vinyl polymer prepared by emulsion polymerization and having a Moh Hardness in the range of about 1 to about 4, and of a hard inorganic matting agent having a Moh Hardness in the range of about 5 to about 9, at least about 95%, by weight, of said particles having a diameter of at least about 1 micron but not in excess of about 8 microns, at least about 50%, by weight, of the particles of said soft matting agent having a diameter in excess of about 4 microns and no more than about 20%, by weight, of the particles of said hard matting agent havinga diameter in excess of about 4 microns.
• a photographic composition comprising a colloid binder containing silver halide and solid, water insoluble, discrete particles of a soft matting agent having a Moh Hardness up to about 4 and of a hard matting agent having a Moh Hardness of at least about 5, at least about by weight, of said particles having a diameter of at least about 1 micron but not in excess of about 9 microns, at least about 40%, by weight, of the particles of said soft matting agent having a diameter in excess of about 4 microns and no more than about 25%, by weight, of the particles of said hard matting agent having a diameter in excess of about 4 microns.
• a photographic composition comprising a colloid binder containing silver halide and solid, water insoluble, discrete particles of a soft matting agent having a Mob Hardness in the range of about 1 to about 4 and of a hard matting agent having a Moh Hardness in the range of about 5 to about 9, at least about 90%, by weight, of said particles having a diameter of at least about 1 micron but not in excess of about 9 microns, at least about 40%, by weight, of the particles of said soft matting agent having a diameter in excess of about 4 microns and no more than about 25%, by weight, of the particles of said hard matting agent having a diameter in excess of about 4 microns.
• a photographic composition comprising a colloid binder containing silver halide and solid, water insoluble, discrete particles of a soft matting agent having a Moh Hardness in the range of about 1 to about 4 and of a hard matting agent having a Moh Hardness in the range of about 5 to about 9, at least about by weight, of said particles having a diameter of at least about 1 micron but not in excess of about 9 microns, at least about 50%, by weight, of the particles of said soft matting agent having a diameter in excess of about 4 microns and no more than about 20%, by weight, of the particles of said hard matting agent having a diameter in excess of about 4 microns.
• the photographic element comprising a photographic silver halide layer containing a colloid binder and, incorporated in said photographic sliver halide layer and in a colloid binder containing a layer adjacent to said silver halide layer, solid, water insoluble, discrete particles of a soft matting agent having a Moh Hardness in the range of about 1 to about 4 and of a hard matting agent having a Moh Hardness in the range of about 5 to about 9, at least about 90%, by Weight, of said particles having a diameter of at least about 1 micron and not in excess of about 9 microns, at least about 40%, by weight, of the particles of said soft matting agent having a diameter in excess of about 4 microns and no more than about 25%, by weight, of the particles of said hard matting agent having a diameter in excess of about 4 microns.
• a photographic element comprising a photographic silver halide layer containing a colloid binder and, incorporated in said silver halide layer and in a colloid binder containing layer adjacent to said photographic silver halide layer, a small concentration of silver halide and solid, water insoluble, discrete particles of a soft matting agent having a Moh Hardness in the range of about 1 to about 4 and of a hard matting agent having a Moh Hardness in the range of about 5 to about 9, at least about 90%, by weight, of said particles having a diameter of at least about 1 micron and not in excess of about 9 microns, at least about 40%, by weight, of the particles of said soft matting agent having a diameter in excess of about 4 microns and no more than about 25 by weight, of the particles of said hard matting agent having a diameter in excess of about 4 microns.
• concentration of silver halide in the adjacent layer is about 0.01 to about 0.1 of the concentration of the silver halide in the photographic silver halide layer.
• the photographic element of claim 9 containing a backing layer and, incorporated in said backinglayer, a colloid binder and solid particles of a matting agent having a Moh Hardness in the range of about to about 9, at least about 90%, by weight, of said particles having a diameter of at least 1 micron but not in excess of about 9 microns and no more than 25%, by weight, of said particles having a diameter in excess of about 4 microns.
• the method which comprises incorporating into a photographic silver halide composition containing a colloid binder solid, water insoluble, discrete particles of a soft matting agent having a Moh Hardness up to about 4 and of a hard matting agent having a Moh Hardness of at least about 5, at least about 90%, by weight, of said particles having a diameter of at least about 1 micron but not in excess of about 9 microns, at least about 40%, by weight, of the particles of said soft matting agent having a diameter in excess of about 4 microns, and no more than about 25 by weight, of the particles of said hard matting agent having a diameter in excess of about 4 microns.
• the method which comprises incorporating into a photographic element comprising a photographic sliver halide layer containing a colloid binder, solid, water insoluble, discrete particles of a soft matting agent having a Moh Hardness up to about 4 and of a hard matting agent having a Moh Hardness of at least about 5, at least about 90%, by weight, of said particles having a diameter of at least about 1 micron but not in excess of about 9 microns, at least about 40%, by weight, of the particles of said soft matting agent having a diameter in excess of about 4 microns and no more than about 25%, by
• the method which comprises incorporating into a photographic element comprising a photographic silver halide layer containing a colloid binder, solid, water insoluble, discrete particles of a soft matting agent having a Moh Hardness in the range of about 1 to about 4 and of a hard matting agent having a Moh Hardness in the range of about 5 to about 9, at least about 95%, by weight, of said particles having a diameter of at least about 1 micron but not in excess of about 8 microns, at least about by weight, of the particles of said soft matting agent having a diameter in excess of about 4 microns and no more than about 20%, by weight, of the particles of said hard matting agent having a diameter in excess of about 4 microns.

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• Chemical & Material Sciences (AREA)
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• Materials Engineering (AREA)
• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Compositions Of Macromolecular Compounds (AREA)
• Laminated Bodies (AREA)
• Silver Salt Photography Or Processing Solution Therefor (AREA)

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Cited By (34)

Citations (4)

• 1965
  • 1965-03-04 US US437272A patent/US3411907A/en not_active Expired - Lifetime
• 1966
  • 1966-03-01 DE DE19661547667 patent/DE1547667A1/de not_active Withdrawn
  • 1966-03-02 BE BE677278D patent/BE677278A/xx unknown
  • 1966-03-04 GB GB9501/66A patent/GB1131091A/en not_active Expired

Patent Citations (4)

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