US3522047A - Thermographically useful light sensitive image-yielding material containing finely divided sulfur particles - Google Patents

Description

United States Patent .THERMOGRAPHICALLY USEFUL LIGHT SENSI- TIVE IMAGE-YIELDING MATERIAL CONTAIN- ING FINELY DIVIDED SULFUR PARTICLES Toshimi Kishida, Masaaki Yoshioka, and Isamu Fushiki, Tokyo, Japan, assignors to Konishiroku Photo Industry Co., Ltd., Tokyo, Japan No Drawing. Filed Aug. 2, 1966, Ser. No. 569,600 Int. Cl. G03c 5/54 US. C]. 96-29 4 Claims ABSTRACT OF THE DISCLOSURE This invention relates to a thermographically useful image-yielding material comprising a support and a photographic silver image-forming layer coated thereon, said layer or its photographically contiguous layer having finely divided sulfur incorporated therein. The object of the present invention is to provide a new and useful material which, after formation of a photographic image thereon, can be used as a mother sheet for thermographic process to obtain a large number of copies.

For the purpose of obtaining reproductions from such originals as hand-written documents, printed matters, and the like, various methods have conventionally been developed. Of these, the thermographic process which We invented by utilizing the supercooling phenomenon (cf. Japan Printer, vol. 47, No. 4, page 12 (1964)) is a novel process having many characteristics. By the present invention, it is intended to make said process more advantageous by provision of a new and useful image-yielding material. Since the above-mentioned supercooling process is one of the thermographic type, it usually has failed to give clear reproductions of portions less in IR-absorbing nature. In contrast thereto, the image-yielding material of the present invention yields an image by utilization of silver photographic process and hence can provide a clear copy regardless of the color of the original employed, which copy serves as a mother sheet for thermographic process to produce a great number of copies. Further, the supercooling process is useful only in contact printing, whereas use of the material of the present invention makes it possible to obtain, by application of a photographic process, reproductions enlarged or reduced in size. Further, when the material of the present invention is used, any original which is entirely opaque and which is so thick, large or heavy as not to be accepted by a usual copying machine can be reproduced with case.

In accordance with the present invention, there is provided a thermographically useful image-yielding material which comprises a support and a photographic silver image-forming layer coated thereon, said layer or its photographically contiguous layer having finely divided sulfur incorporated therein. In one embodiment of the present invention, fine particles of sulfur may exist in the photographic silver image-forming layer of the imageyielding material. In another embodiment of the present invention, they may exist in a protective layer, for exam- 3,522,047. Patented July 28, 1970 ple, coated on the photographic silver image-forming layer, with or without an inter layer. Thus, it is to be understood that the term, photographically contiguous layer referred to therein to mean a layer adjacent to the photographic silver image-forming layer, regardless of the existence of an interlayer therebetween. Typically the above-referred photographic silver image-formin layer is a light-sensitive photographic silver halide emulsion layer or a silver diffusion transfer-receiving layer. The abovereferred photographic contiguous layer is a protective layer well known in the photographic art.

The invention will be illustrated in more full detail below. As stated before, the material of the present invention has a silver-image yielding layer and if desired, a layer photographically contiguous therewith, either one of these layers having finely divided sulfur incorporated therein, said sulfur being recognized as one of heat-sensitive substances usable in the supercooling process. As heat-sensitive substances in the supercooling process, many substances have been known in addition to sulfur. In the present invention, wherein the silver photographic process is utilized, those giving detrimental effects to light-sensitive emulsions or diffusion transfer imagereceiving materials are not usable. Further, in the present invention which requires such photographic treatments as development and fixation, water-soluble heat-sensitive substances also are not usable because they flow out during the treatments. For example, benzotriazole has been a heat-sensitive material and has frequently been used in the supercooling process. However, said material causes marked desensitization on the light-sensitive photographic emulsions and hence is not suitable for the object of the present invention. Further, p-toluenesulfonamide is so high in water solubility that it flows out of the layer during the photographic treatments and hence is neither suitable as the heat-sensitive substance of the present invention. In contrast thereto, sulfur employed in the present invention, which is entirely insoluble in water, does not flow out during the treatments and it does cause neither fogging nor desensitization of photographic sensitive emulsions. Therefore, it is entirely suitable as a heatsensitive component of the image-yielding material of the present invention. Moreover, sulfur has many such advantages that it is excellent in transferability, is long in supercooled state to make it possible to obtain a stable dustadherable latent image, and can be incorporated in a relatively large amount into the layer, whereby a great number of reproductions can be obtained from a single mother sheet. Commercial availability and cheap price of sulfur are additional advantages. In the art, the existence of sulfur in a photographic emulsion has been considered as causing a serious problem in photographic properties. Taking this into account, the present invention is unexpectedly beyond the prejudice of the prior art.

Any of the conventionally known light-sensitive photographic silver halide emulsions can be successfully used for the preparation of a photographic silver image-forming layer in the present invention. Further, any emulsions which are used to form an image-receiving layer of the silver diffusion transfer process can be used in the present invention, said emulsions being referred to image-receiving emulsions hereinafter. The above-mentioned lightsensitive silver halide emulsions include not only the ordinary light-sensitive emulsions but also the so-called directpositive, light-sensitive emulsions which can directly give positive image by utilizing the solarization phenomenon or Harschel effect. Quick processable emulsions for stabilization method or heat-developable emulsions are also usable. These light-sensitive emulsions may be treated, before use, by color sensitization, noble metal sensitization or reductive sensitization, or by addition of such additives as stabilizers, hardeners and development-controlling agents. The image-receiving emulsion of the silver diffusion transfer process, which is suitable for the purpose of the present invention, is a dispersion of colloidal noble metal or metal sulfide as silver-precipitating nuclei in a layer-forming binder as a protective colloid.

Now, how to use the material of the present invention will be illustrated below with reference to the case Where a light-sensitive direct-positive photographic emulsion is used. In the first place, the material of the present invention is exposed through an image-bearing original at desired magnification and then subjected to photographic treatments such as development and fixation according to the known procedures, whereby a mirror silver image is formed on the material of the present invention. In the second place, the material which is now usable as a mother sheet is placed on a paper as receptor sheet and then the resulting composite is subjected to infrared irradiation, whereby sulfur of the image portion is transferred onto the paper, due to the action of heat of the infrared-absorbing silver image portion, to yield on the paper a latent image of sulfur in a supercooled state. In the third place, the latent image yielded on the paper is developed by sprinkling thereon such a fine coloring powder as is ordinarily used in electrophotographic process (hereinafter referred to as a toner). The developed image can be fixed by application of a solvent vapor, thereby to obtain a copy bearing a right image of the original. The infrared irradiation and image transfer can be effected repeatedly up to a maximum of about 200 times, whereby a large number of reproductions are obtainable from a single mother sheet.

In the present invention, the conventionally known silver halide photographic process is utilized for the formation of images, and therefore it is possible to obtain, according to desired objects, materials having any desired sensitiveness within a markedly wide range. Further, by application of many known techniques, such as color sensitization, direct reversal and the like, imageyielding materials usable for various purposes can be obtained. Further, as the image formed by use of the present material is composed of infrared-absorbing and thermally conductive silver metal particles, heat of the silver particles is well transmitted to heat-sensitive sulfur particles, whereby reproductions bearing clear images can be obtained with high etficiency by application of thermography.

The preparation of the image-yielding material of the present invention can be made as follows: Sulfur is conveniently prepared as a dispersion of fine particles, which dispersion is then mixed with a light-sensitive photographic emulsion or the like. That is, sulfur is added to a solution prepared by first forming a solution of hydrophilic high molecular weight dispersion medium and then adding thereto a suitable surface active agent, and the resulting mixture is subjected to a dispersing machine such as a ball mill to form a dispersion of finely divided sulfur having a particle size of less than 50g, preferably less than g. As the high molecular weight dispersion medium, gelatine is preferred, in general. In addition thereto, gum arabic, polyvinyl alcohol, carboxy-methyl cellulose and sodium alginate also are usable. As the dispersion agent, alkylnaphthalenesulfonic acid, an alkyl phenolethylene oxide polycondensate or saponin may be used. It is of importance that sulfur contains no such impurities as to injure photographic properties, and may be in any form of crystalline sulfur or sublimated sulfur so far as it is pure. The thus obtained sulfur dispersion is mixed with a light-sensitive photographic emulsion or the like, and the mixture is applied onto a suitable support and is then dried to obtain the image-yielding material of the present invention. In this case, if the amount of sulfur incorporated is excessively large, the sensitivity of the light-sensitive emulsion is damaged due to the diffusion of light, whereas if the amount is excessively small, no effect can be attained. Generally, sulfur is preferably used in an amount substantially equal to the weight of silver halide in the light-sensitive emulsion, but the amount may be suitably varied, within the range of from 0.0 5 to 5 parts per part of silver halide. That is, a commercially available photographic paper contains 2 to 3 g. of silver per square meter, and therefore sulfur may be used in an amount within the range of 0.1 to 15 g. As the support, paper is used, in general. The imageyielding material of the present invention is to be subjected later to thermographic process, and therefore the use of a thin paper favorable in infrared transmission is preferred. However, there are some cases where a thin paper is used as a receptor sheet in thermographic process. In such cases, therefore, an ordinary photographic raw paper may be used as the support. In addition to paper, a film base such as cellulose acetate or polyethylene terephthalate may also be used as the support.

The typical applications of the image-yielding material of the present invention will be explained below. The image-yielding material is exposed imagewise by utilizing the conventionally known photographic technique. In this case, the exposure is desirably effected by use of an optical system because, as the most common mode of practice, it is convenient to form a mirror image on the imageyielding material. However, in case a thin paper is used as the receptor sheet and the copy can be seen from the back, such exposure as to give a right image, i.e. contact printing, is acceptable. The exposed image-yielding material is then subjected to treatment by development and fixation, thereby to obtain a silver image. In this case, the material may be subjected to any of a quick treatment utilizing stabilization process, a heat development, or a tanning development followed by washing off of the unexposed portion with hot water. The tanning development is particularly advantageous in that the subsequent thermographic process can be effected simply, because sulfur as a heat-sensitive material does not exist in any other portion than the image portion. All the above-mentioned procedures and operations are the photographic techniques known heretofore, and not much explanation thereof would be necessary.

The material, on which a silver image has been formed in the above manners, is then used as a mother sheet for the thermographic process to obtain a large number of reproductions. The thermographic process is carried out by placing on the mother sheet an ordinary paper as a receptor sheet, subjecting the composite to IR-irradiation by which the sulfur in the image portion is transferred onto the receptor sheet to form a dustable latent image in a supercooled state, developing the latent image with a toner and then fixing the image to obtain a copy. IR- irradiation of the composite of the mother sheet and transfer paper may be effected, by use of a strong infrared ray lamp, the silver image portion on the more readily IR-transmissible side of the composite. The above procedure may be effected by use of a commercial thermographic machine having a transparent quartz infrared ray lamp with an output of 30400 w./cm. Typical of the thermographic machines of this kind are Thermofax Secretary type copying machine (trade name; manufactured by Minnesota Mining & Manufacturing Co., U.S.A.). The mother sheet subjected to tanning development contains no sulfur in any other portion than the image portion, and therefore a composite thereof with a receptor sheet can be passed between hot rolls having a surface temperature of about 0, whereby a dustadhering latent image can be simply formed on the receptor sheet. The dust-adhering, supercooled latent image formed on the receptor sheet in the above manner is then developed by dusting with a toner. The toner is prepared by incorporating a coloring matter in a thermofusible or solvent vapor-soluble resin and finely dividing the mixture. Any toner which is ordinarily employed at present in the electrophotographic process can be used as such.

The-development may be conducted by utilization of any methodemployed in the electrophotographic process, such as magnetic brushing method, cascade method or smoke chambermethod. In this toner is used a coloring matter which is stable by itself, and therefore the resulting copy is markedly stable and does not suffer from fading. Further,- the toner can be incorporated with a coloring matter or any color tone, it is possible to obtain copies bearing not only black colored images but also images colored to optional colors. After completion of the toner development, the receptor sheet is treated by application of heatflor solvent vapor, whereby a copy with the fixed image 'is obtained. In the case of the material of the presentjinvention, a considerably large amount of sulfur as a. heat-sensitive material can be incorporated into the layer, and therefore up to about 200 sheets of clear copies can be obtained from a single mother sheet.

The image-yielding materials of the present invention utilize light-sensitive photographic silver compounds for image formation and hence are variable in sensitivity over a wide range. Further, the present materials can be processed by many known techniques, e.g. direct reversal, tanning development and the like. The present material can therefore be utilized not only in the reproduction of hand-written documents and printed matters but in a varietyof fields for copying and printing. For example, letters .are directly printed on the material by use of a photographic typesetting machine and the material is used as a mother sheet to obtain a great number of copies, or an image of a meteorological radar is directly photographed and a plurality of copiesof the photograph are immediately prepared so that the copies may be delivered to concerned sections. Further, the toners employed may be those having optional color tones, and therefore it is possible to obtain a natural color" copy by preparing 3 mother sheets from a tricoloranalyzed halftone negative, transferring the images of the mother sheets onto one receptor sheet, and developing the images by use of cyan, yellow: and magenta toners, respectively.

following examples illustrate the present invention, but it should be construed that the invention is not limited thereto but various modifications are possible within the scope of the claimed invention. In the examples, all parts are expressed by volume.

EXAMPLE 1 150 g. of sublimated sulfur powder is added to a solution of 5 g. of saponin in 1.1 of 1% aqueous gelatine. The resulted mixture is treated in a porcelain ball mill for 20 hours to form a homogeneous sulfur dispersion, which is then used for the preparation of two samples A and B.

(A) 0.8 part of the sulfur dispersion is mixed with 1 part of a gelatinous silver chlorobromide emulsion (gelatine cone. 3%). The resulting mixture is coated on a thick tracing paper to dry thickness of 5.5,u. and then dried.

(B) To 1 part of a gelatinous silver chlorobromide emulsion (gelatine cone. 3%) is added 0.8 part of 1% gelatine. The mixture is coated on a thick tracing paper to dry thickness of 5.5p. and then dried. On the dried paper, the above-prepared sulfur dispersion is coated as a separate layer to dry thickness .of 2.5;!

(C) To 1 part of a gelatinous silver chlorobromide emulsion (gelatine cone. 3%) is added 0.8 part of 1% gelatine. The mixture is coated on a thick tracing paper to dry thickness of 5.5 1. and dried.

The above samples A and B are the image-yielding materials according to the invention and the sample C is a control. Imagewise exposure is given to these samples which are then developed at 20 C. for one minute. Photographic properties of these samples are measured immediately after their preparation and after their incubation for two days at 55 C. The. results are set forth below:

Specific speed Max. density Fog Incu- Ineu- Incu- Just bated Just bated J 11st bated after for 2 after for 2 after for 2 prepadays at prepadays at prepadays at Sample ration 55 C. ration 55 C. ration 55 C A 93 1. 9 1. 8 0.01 0. 01. B. 94 94 1.6 1. 6 0.01 0.01 C (control)- 99 2. 1 2. 1 0. O1 0. C1

The above data shows that the image-yielding materials are stable during their storage under considerably strict conditions and that their photographic properties are substantially free from the advsere influence of sulfur.

The samples A and B are employed to obtain copies i nthe following manners: A microlm negative bearing an original image is printed at desired magnification onto the sample as an image-yielding material so as to obtain a mother sheet bearing a silver mirror image. On the sensitive side of said motor sheet is placed an ordinary paper as a receptor sheet, and the composite is subjected to infrared irradiation fro mthe back side of said mother sheet by means of a Thermographic copying machine. The receptor sheet is removed from the mother sheet. The latent image thus formed on the receptor sheet is then developed according to the cascade method using Konifax Toner-PP (trade name, manufactured and sold by Konishiroku Photo Industry Co., Ltd.) and thermally fixed by use of Konifax fixing machine (trade name, manufactured and sold by Konishiroku Photo Industry Co., Ltd.) to obtain a clear copy. By repetition of the above thermal transfer dust development and fixing operations in sequence, 200 sheets of clear copies could be obtained from one mother sheet.

EXAMPLE 2 50 mg. of colloidal silver sulfide is suspended in 1 l. of a 3% aqueous gelatine solution. To the suspension is added 30 mg. of phenyl mercaptotetrazole as a color modifier to form a solution for a diffusion transfer imagereceiving layer. The solution is mixed with 0.3 l. of the sulfur dispersion employed in Example 1, and the mixture is coated onto a thin photographic paper to a dry thickness of 2a and is then dried to obtain an image-yielding material of the present invention. This material is employed to obtain copies in the following manners: A negative material for diffusion transfer is brought into contact acording to the ordinary procedure with an original to be reproduced and the composite is exposed by reflection printing. The exposed negative material is placed on the above-mentioned image-yielding material, and the resulting composite is treated according to a diffusion transfer method to form a silver image on the image-yielding material which is now ready for use as a mother sheet. The silver image on said mother sheet is a right image, therefore in the thermal transfer thereof, a thin IR-transmissible transparent paper is used. Application of infrared irradiation is made onto the back side of the transfer paper. Thereafter, the same dust development and thermal fixation as in Example 1 are effected to obtain 100 sheets of copies.

What we claim is:

1. A method of producing thermographically at least one reproduction of photographable material from a master, which comprises the steps of providing a support bearing an emulsion of a light-sensitive silver imageforming layer containing finely divided sulfur of a particle size of less than 50 Ill/L in an amount of 0.05 to 5.0 g. per gram of silver compound in said layer, photographic'ally exposing said image-forming layer and developing and fixing the resultant image, providing a receptor sheet of material and placing said support now bearing said image in contact therewith, subjecting the resultant composite to infrared radiation, whereby sulfur from the image-forming layer is transferred onto said receptor sheet to yield a latent image of sulfur thereon in a supercooled state and then developing and fixing said latent image.

2. A method of producing thermographically at least one reproduction of photographable material from a master which comprises the steps of providing a support bearing an emulsion of a light-sensitive silver imageforming layer and an outer light-transmitting layer containing from 0.5-5.0 g. finely divided sulfur of a particle size of less than 50 mp per gram of silver compound in said layer, photographically exposing said image-forming layer and developing and fixing the resultant image, providing a receptor sheet of material and placing said support now bearing said image in contact therewith, subjecting the resultant composite to infrared radiation, whereby sulfur from the image-forming layer is transferred onto said receptor sheet to yield a latent image of sulfur thereon in a supercooled state and then developing and fixing said latent image.

3. Thermographically useful image-yielding material which comprises a support and a light-sensitive silver 8 image-forming layer coated thereon and a light-transmitting outer layer containing from 0.5-5.0 g. finely divided sulfur of a particle size of less than mp per gram of silver compound in said layer.

4. Thermographically useful image-yielding material which comprises a support and a light-sensitive silver image-forming layer coated thereon, said layer containing from 0.05 to 5.0 g. of finely divided sulfur of a particle size of less than 50 mg per gram of silver compound in said layer.

References Cited UNITED STATES PATENTS 3,158,481 11/1964 Shanefield 96-29 GEORGE F. LESMES, Primary Examiner J. P. BRAMMER, Assistant Examiner US. Cl. X.R. 96-67; 250-