Ink ribbon and image forming method using the same

Abstract: Disclosed are an ink ribbon containing an amphiphilic acid dye or basic dye, which has an excellent thermal transfer sensitivity and which may form an image with high fixation comparable to that of silver salt photographic images, and an image forming method using the ink ribbon. The method comprises bringing the ink ribbon containing an amphiphilic acid dye or basic dye into contact with a photographic paper containing a precipitating agent capable of laking by salt formation with an acid dye or basic dye so that the acid dye or basic dye is transferred and fixed from the ink ribbon to the photographic paper by thermal stimulation.

Description: The present invention relates to an ink ribbon suitable to use, for example, in color video printers of thermal transfer system and also relates to an image forming method using it. An image forming method by thermal transfer system has been attempted, for example, for printing out an image as taken with an electronic still camera or the like, to a photographic paper like silver salt photography. In accordance with the thermal transfer system of the type, an ink ribbon containing dyes is brought into contact with a photographic paper having an image-receiving layer as formed thereon and the ink ribbon is heated with a thermal head or the like so that the dyes in the ink ribbon are transferred to the image-receiving layer of the paper. As the image-receiving layer of a photographic paper, used is a polyester; and as the dyes to be in an ink ribbon, used are disperse dyes. Various reformations and modifications have heretofore been applied to disperse ayes which are generally used in the system of the kind, for example, those disclosed in JP-A 1-259989 and I-275096 (the term "JP-A" as used herein means an "unexamined published Japanese patent application"). However, after transferred to an image-receiving layer, they are retained therein by mere interaction between the transferred dyes and the layer, for example, by van der Waals force of the former to the high polymer substance of the latter, interamphoteric force or hydrogen bond therebetween or the like. Therefore, where the layer to which dyes have been transferred is brought into contact with a resin or solvent having a higher affinity to the dyes or where heat energy enough to dismiss the interaction is imparted to the layer, migration or dissolution of the transferred dyes would thereby be induced or the image formed would become blurred, disadvantageously. Under the situation, other means based on formation of chemical bond between transferred dyes and an image-receiving layer have been proposed, for example, in JP-A 59-78893, 60-2398, 60-110494, 60-220785, 60-260381 and 60-260391. The methods disclosed in the laid-open specifications are a method of incorporating a compound having epoxy groups or isocyanate groups into an image-receiving layer to which dyes having groups capable of reacting with the epoxy or isocyanate groups are applied; a method of incorporating a compound having active hydrogens to an image-receiving layer to which dyes having acryloyl groups or methacryloyl groups are applied; a method of incorporating a metal compound into an image-receiving layer to which dyes capable of forming metal complexes with the metal compound are applied; and a method of subliming and transferring a low molecular compound having an active methyl group (or methylene group) to an image-receiving layer followed by reacting the compound with an aldehyde (nitroso) compound to form a dye in the layer. However, the means based on formation of chemical bond have various drawbacks that the reactivity of the dyes and the image-receiving layer is too high so that the storage stability of them is poor, that the reaction is not finished in a short period of time and therefore a long time is needed for forming a stable image, and that preparation of the dyes is difficult and the kind of usable dyes is limited. In addition, even by the means, fixation of the transferred dyes could hardly be said to be sufficient. As mentioned above, the conventional thermal transfer system has a serious problem of migration of the transferred dyes due to insufficiency of the fixability of them on the image-receiving layer, which is a bar to practical operation of the system. Therefore, improvement of the point is desired. EP-A-0 506 034 and EP-A-0 498 267 which belong to the prior art in the sense of Article 54 (3) and (4) EPC disclose an ink ribbon and a method of forming an image by using a cationic dye wherein an inorganic counterion is substituted with an organic anion. US-A-5 045 524 discloses the use of a basic dye prepared by substituting inorganic ions by a p-toluene sulphonate for thermal dye transfer. JP-A-61-154 995 discloses the use of a basic dye prepared by substituting inorganic ions by organic sulphonic acid for a thermal transfer recording medium. JP-A-61-143 184 discloses the use of a receiving sheet which comprises a polycationic high molecular weight electrolyte in a thermal transfer type recording medium. JP-A-1-72 896 discloses an image-receiving sheet having an image-receiving layer comprising a multivalant metal salt of a salicylic acid derivative for sublimation transfer type thermal recording. Under the situation, the present invention has been proposed for the purpose of overcoming the problems in the prior art, and one object thereof is to provide an ink ribbon having an excellent thermal transferring sensitivity and having a fixability of the transferred dyes therefrom to be able to form an image comparable to silver salt photographic images. Another object of the present invention is to provide an image forming method using the ink ribbon. An image forming material for fixation type thermal transfer system as disclosed in Japanese Patent Application No. 3-89592 has a fixation effect in a complete hydrophobic system (or a medium system with a low dielectric constant) by salt formation. As opposed to this, the same fixation effect by salt formation has been attained by the present invention even in a hydrophilic system (or a system with a high dielectric constant), which is still another object of the present invention. Specifically, there is provided in accordance with the present invention an ink ribbon having a dye layer as formed on a support, in which the dye layer contains an amphiphilic acid dye prepared by substituting inorganic ions of an acid dye by organic cations, wherein the organic cation for amphiphilicating the acidic dye is at least one selected from tetra-n-hexylammonium bromide, tetra-n-butylammonium borofluoride, tetra-n-butylammonium perchlorate, cetyltrimethylammonium bromide, dioctadecyldimethylammonium chloride, myrityldimethylbenzylammonium chloride, benzyldimethyl-[2-[2-(p-1,1,3,3-tetramethylbutylphenoxy)ethoxy]-ethyl]ammonium chloride, alkylpyridinium salts and imidazolinium salts. There is also provided in accordance with the present invention a method of forming an image, in which an ink ribbon as described above is brought into contact with a photographic paper having an image-receiving layer which contains a precipitation agent capable of laking by salt formation with an acid dye, and the acid dye is transferred and fixed from the ink ribbon to the photographic paper by thermal stimulation to form an image on the paper. In accordance with the present invention, an ink ribbon containing an amphiphilic acid dye is brought into contact with a photographic paper containing a precipitating agent capable of laking due to salt formation with the acid dye, whereby the acid dye is transferred and fixed onto the photographic paper from the ink ribbon by thermal stimulation. Accordingly, the fixation of the transferred dye on the photgraphic paper may noticeably be improved to be able to yield on the paper an image having a fixability comparable to that of silver salt photographic images. Fig. 1 shows a line work view of showing one embodiment of an ink ribbon of the present invention, in which 1 is a dye layer, 2 is a support and 3 is a heat-resistant lubricant layer. One embodiment of the ink ribbon of the present invention as well as that of an image forming method of using it will be explained hereunder. A method of preparing the ink ribbon of the present invention will be explained with reference to Fig. 1. Preparation of Dyes: Preparation of Acid Dye: 1000 cm 3 of an aqueous solution of 10 g of sodium copper phthalocyanine-tetrasulfonate (produced by Kodak) was prepared. The solution was dropwise added to 2000 cm 3 of a water/ethanol (1/1, by volume) solution containing 19.57 g of tetra-n-hexylammonium bromide as dissolved therein. A part of the mixture was taken out, to which the same amount of chloroform was added and shaken. After it was statically left as it was, the dye was partitioned also into the oily phase with a partition ratio of about 0.3/1 (oil/water). In the same extraction experiment, the starting material was not almost partitioned into the oily phase. Thus, it is obvious that the dye was made amphiphilic by the treatment. Next, much water was added to the mixture, whereupon a dark blue precipitate formed. The precipitate was taken out by filtration, washed with hexane and dried at room temperature under reduced pressure to give about 30 g of a solid. Although the starting dye was insoluble in ethanol, the solid (dye) obtained by the treatment was soluble in a mixed solvent of water/ethanol. For purification, about 30 g of the dye formed was dissolved in 200 g of a mixed solvent of water/ethanol, 2 g of acidic terra alba was added thereto and ultrasonically stirred for 5 minutes, then the precipitate formed was taken out by filtration. The filtrate was dried with an evaporator under reduced pressure to give a dye of almost the same amount of the starting material. Formation of Ink Ribbons: Formation of Ink Ribbon Containing Acid Dye: Using the acid dye prepared above, an ink ribbon was formed. Precisely, the phthalocyanine dyes obtained above was dissolved in MEK (methyl ethyl ketone) together with a polyester resin as a binder polymer to form a coating solution. Composition parts by weight Polyester 1 Dye 1 MEK 20 The solution was coated over a PET film having a heat-resistant lubricant backing layer on the back surface thereof, with a wire bar and dried with a hot air of 120°C for 2 minutes to obtain a ribbon having a transparent color layer with a dry thickness of about 1 µm. Next, one embodiment of an image forming method using these ink ribbons is mentioned below. Confirmation of Dye Fixed Effect on Photographic Paper: Ribbon with Acid Dye: Preparation of Photographic Paper: An aqueous solution containing barium chloride and a modified vinyl acetate in a weight ratio mentioned below was prepared and was coated over a neutral paper having a thickness of about 200 µm with to form an image-receiving layer having a wet thickness of 100 µm, which was then dried at 120°C for one hour under reduced pressure. Next, the photographic paper having the white image-receiving layer was passed through pressure rollers heated at 100°C to make it glossy. Composition of Coating Solution parts by weight Barium Chloride 1 Modified Vinyl Acetate 5 Silicone Oil 5 Water/methanol (1/9 by volume) 50 Printing Experiment: Using the ink ribbon and the photographic paper thus formed, formation of an image on the paper was effected in a practical manner. Precisely, the ribbon was set in a ribbon cassette of a Sony's color video printer CVP-G500 Model, and the photographic paper in a photographic paper cassette thereof. Using the printer, gradation printing was effected to yield a cyan tone glossy image rich in gradation. Next, water was sprayed over the image and the paper with the image was passed through a hot-pressure (100°C) rollers at a feeding rate of 5 mm/sec. The migration resistance of the image formed was evaluated in the manner mentioned below. A film having a dry thickness of 100 µm was formed from a coating solution having the composition mentioned below with a wire bar. This was used as a film to which the dye of the image will migrate. This was adhesive at room temperature and may easily adhere to and peel off from an image-receiving layer of a photographic paper. Composition of Coating Solution parts by weight Butyral Resin 1 Ethanol (solvent) 50 The adhesive film was attached to the image formed on the photographic paper and left as it was for 30 seconds at 100°C. Then, this was peeled off from the paper. The same migration resistance test was effected, using a conventional photographic paper containing no precipitating agent (in which the other components and compositions were same as those in Example 1). As a result, the image formed in accordance with the present invention retained almost 100 % image density, while the image formed on the conventional photographic paper retained only about 10 % image density (or that is, 90 % of the image density migrated to the adhesive film). From the result, the fixation effect of the present invention is obvious. Table 1 below shows the uppermost limit, lowermost limit and preferred range of each of the dye concentration in an ink and the precipitating agent concentration in an image-receiving layer, when an acid dye is used. The uppermost limit of the dye concentration in an ink of being 100 % by weight is for the case of using a dye having a film-forming property. Where a dye not having a film-forming property is used, a binder resin is needed. If the dye concentration in an ink is lower than 5 % by weight, sufficient coloration could not be attained. Where the precipitating agent concentration in an image-receiving layer is more than 90 % by weight, film-forming would be impossible since the precipitating agent itself has no film-forming property. If, on the contrary, it is less than 5 % by weight, sufficient fixation of dyes onto a photographic paper could not be attained. Range of Concentration of Dye and Precipitating Agent Uppermost limit Lowermost limit Preferred range Dye concentration in ink (wt.%) 100 5 80 to 20 Precipitating agent concentration in image-receiving layer (wt.%) 90 5 80 to 10 The image-receiving layer may contain any other auxiliary compounds (e.g., brightening agent, plasticizer, or moisture absorbing agent), provided that they do not interfere with the interionic salt formation reaction in the layer. The binder resin to be in the layer may not always be a water-swelling one but may be one capable of giving a dielectric constant sufficient for inducing salt formation reaction by itself or may also be a mixture with the corresponding low molecular compound. In the case, water dipping operation is unnecessary. Next, in order to confirm the behavior of dyes in an image-receiving layer of a photographic paper, simulation of fixation and movement of dyes in the layer was effected. Acid Dye: As an acid dye used was sodium copper phthalocyanine tetrasulfonate (produced by Kodak). One part by weight of the dye was dissolved in 1000 parts by weight of ethanol, and 10 parts by weight of an aqueous 1 wt.% barium chloride solution was dropwise added thereto to immediately give a dark blue precipitate and an almost colorless supernatant. The precipitate was recovered by filtration, washed with a large amount of water and then washed with acetone, ethyl acetate and toluene in order, whereupon no dye dissolved out. Accordingly, the dye was confirmed to be pigmented. From the results, it is clarified that a dye as amphiphilicated with a solvent having a high dielectric constant such as ethanol is pigmented by salt formation. This means that when a dye is substituted by organic cations having a lower ion-bonding force than the cations of a laking agent (precipitating agent) and the thus substituted dye is used in forming an ink ribbon, then the dye may easily be ion-exchanged in a high dielectric constant medium of high ion-dissociation ability. In the same manner as above, other anionic dyes may be amphiphilicated. Organic cations for the purpose may be selected from commercial surfactants, ammonium salts and phosphonium salts as defined above, and they are preferably such that the partition coefficient of the dye salts to be formed therewith in a water/chloroform system is from 0.05 to 10. For laking general acid dyes, typical combinations of dye and precipitating agent are shown in Table 2 below. Examples of Combination of Acid Dye and Precipitating Agent Acid Dye Precipitating Agent (Laking Agent) Nitro Compounds Naphthol Yellow S Barium chloride Aluminium chloride Azo Compounds Naphthol type Lake Scarlet 2R (Alkaline earth metal salts, manganese salts) Orange 2 Lake Red C, D Brilliant Carmine 6B Watching Red Pyrazolone type Tartrazine O Fastlight Yellow 3 Aminonaphthol type Anthocyan B Anthocyan 3B Triphenylmethane type Erygrosine A (Sodium salts) Acid Green B Alkali Blue Metal Chelate Dyes Nitroso-β-naphthol Iron Salt In accordance with the present invention as supported by the above-mentioned example, the fixability of the dye may noticeably be improved and an image having a high fixation comparable to that of silver salt photographic images can be formed. In addition, not only the fixability but also other necessary characteristics such as light-fastness, color tone and sensitivity are also improved by the present invention. Further, since the method of forming the ink ribbon of the present invention follows the techniques of the related conventional methods, any and every apparatus for the conventional methods may directly be applied to the method of the present invention.

Claims: An ink ribbon having a dye layer as formed on a support, in which the dye layer contains an amphiphilic acid dye prepared by substituting inorganic ions of an acid dye by organic cations, wherein the organic cation for amphiphilicating the acidic dye is at least one selected from tetra-n-hexylammonium bromide, tetra-n-butylammonium borofluoride, tetra-n-butylammonium perchlorate, cetyltrimethylammonium bromide, dioctadecyldimethylammonium chloride, myrityldimethylbenzylammonium chloride, benzyldimethyl-[2-[2-(p-1,1,3,3-tetramethylbutylphenoxy)ethoxy]ethyl]ammonium chloride, alkylpyridinium salts and imidazolinium salts. The ink ribbon as claimed in claim 1, in which the amphiphilic acid dye has a partition coefficient in a water/chloroform system (1/1, by weight) of from 0.05 to 10. The ink ribbon as claimed in claim 1, in which the dye concentration in the ink is from 5 to 100 % by weight. A method of forming an image, in which an ink ribbon according to any of claims 1-3 is brought into contact with a photographic paper having an image-receiving layer which contains a precipitation agent capable of laking by salt formation with an acid dye, and the acid dye is transferred and fixed from the ink ribbon to the photographic paper by thermal stimulation to form an image on the paper. The method as claimed in claim 4, in which the concentration of the precipitating agent in the image-receiving layer is from 5 to 90 % by weight.

Inventors: HIDEKI HIRANO, KENGO ITO, HIDEKI, HIRANO, KENGO, ITO, Hideki, Hirano, c/o Sony Corporation, KENGO, ITO, C/O SONY CORPORATION
Applicants: SONY CORP, SONY CORPORATION
Application year: 1992
Main classification: B41M5
IPC codes: B41M5