JP2963056B2 - Image forming method - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming method, and more particularly to a method for obtaining an image having a large density range using a thermal transfer sheet. 2. Description of the Related Art In order to obtain an image in accordance with image information using a thermal head, conventionally, thermosensitive coloring paper has been mainly used. In these thermosensitive coloring papers, a colorless image or a colorless or pale-colored leuco dye and a developer (for example, bisphenol A) provided on a base paper come into contact with each other when heated to produce a colored image. [0003] However, the thermosensitive coloring paper described above has fatal drawbacks in that when the obtained image is stored for a long period of time, the image is erased or the non-image portion is colored. Further, color printing is limited to two colors, and it is impossible to obtain a color image having continuous gradation. On the other hand, as a recording method for improving the above-mentioned drawbacks, a binder contains a heat transfer sheet or a heat transfer dye in which a sheet-like substrate is provided with a heat-meltable wax layer in which a pigment or dye is dispersed. In recent years, a heat sublimation transfer sheet provided with a heat sublimation transfer layer has been used. [0005] When the hot-melt transfer sheet and the transfer-receiving sheet are superimposed on each other and heating printing is performed from the back side of the heat-transfer sheet, the heat-fusible wax layer containing pigment or dye is transferred onto the heat-transfer-receiving sheet. An image is obtained. According to such a printing method, an image more durable than the thermosensitive coloring sheet can be obtained, and a multicolor image can be obtained by sequentially printing a thermal transfer sheet containing pigments or dyes of three primary colors. On the other hand, a thermal sublimation transfer sheet is formed by providing a binder layer containing a heat transferable dye on a sheet-like substrate, and laminating the obtained thermal transfer sheet and a transfer-receiving sheet to form a thermal transfer sheet. When heating printing is performed from the back surface of the sheet, only the dye in the binder layer thermally sublimates and migrates onto the transfer receiving sheet to obtain an image. According to this printing method, a multicolor image can be obtained by sequentially printing the thermal sublimation transfer sheet containing the heat transfer dyes of the three primary colors. In recent years, there has been an increasing demand for obtaining an image having continuous gradation such as a color photograph directly from an electric signal, and various attempts have been made. As one of these attempts, there is a method of obtaining a silver halide color photograph directly on a CRT screen. This method has drawbacks such as an increase in running cost and, in the case of a 35 mm film, a development process after photographing, which is not immediate. As another method, an impact ribbon method or an ink jet method has been proposed.
There is a drawback that the image quality is poor, image processing is required, and an image such as a photograph cannot be easily obtained. In order to solve such a drawback, attempts have been made to perform recording using the above-described thermal sublimation transfer sheet. The method using the thermal sublimation transfer sheet has a feature that the heat transferable dye in the thermal sublimation transfer layer transfers to the transfer receiving sheet in accordance with the amount of heat energy applied to the thermal transfer sheet. Image is obtained, and is very excellent in that image information can be recorded from television signals by simple and quick processing,
On the other hand, it has the following problems. That is, there is a problem that an image obtained by a conventional method using a thermal transfer sheet has a relatively small optical density range. For example, the optical density of a normal color photograph is in the range of 0 to about 4.0, but the thermal transfer image density range obtained by the conventional method is 0 to about 4.0.
Therefore, when an image pattern is obtained by a conventional method, a portion having a density of 2.0 to 4.0 is compressed to narrow the range. SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems associated with the prior art, and has as its object to provide a method for obtaining a thermal transfer image having a large density range. I have. [0013] In order to achieve the above object, an image forming method according to the present invention comprises a heat transfer sheet comprising a base sheet having a heat transfer layer containing a dye which melts or sublimates upon heating; and a dye image receiving layer. A method in which an image is formed on the transfer sheet by superposing a transfer sheet formed on another base sheet and heating means, wherein the same image is formed on the dye image receiving layer of the transfer sheet. An image having a large density range is obtained by superimposing and transferring an image having the same density range at least twice as an image pattern. Further, in another embodiment of the present invention, a thermal transfer sheet comprising a heat transfer layer containing a dye which melts or sublimates upon heating formed on a base sheet, and a dye transfer layer comprising a dye image receiving layer formed of another base sheet. A method of forming an image on the transfer sheet by superposing the transfer sheet formed thereon on the transfer sheet, wherein the image pattern to be transferred to the dye image receiving layer of the transfer sheet is It is characterized in that the image is partially overlapped and transferred at least twice in only the high density region. Further, the present invention provides a thermal transfer sheet in which a thermal transfer layer containing a dye which melts or sublimates upon heating is formed on a substrate sheet, and a dye image receiving layer is formed on another substrate sheet. A method of forming an image on a transfer sheet by superimposing a transfer sheet on the transfer sheet by heating means, wherein an image pattern of a high density area among image patterns to be transferred to the dye image receiving layer of the transfer sheet. An image is formed only at a certain density at a certain density, and then a second image transfer is performed including other image pattern portions. Further, another aspect of the present invention is characterized in that the transfer is performed a plurality of times by printing so that the dots of the thermal head at least partially overlap. Further, in another embodiment of the present invention, a thermal transfer sheet comprising a substrate and a thermal transfer layer containing a dye which melts or sublimates upon heating, and a dye image receiving layer comprising another substrate sheet A method of forming an image on a transfer sheet by heating means by superimposing a transfer sheet formed thereon, wherein at least two or more heat transfer sheets transferred in the same image pattern are stacked. It is characterized by being integrated. Further, in another embodiment of the present invention, a thermal transfer sheet comprising a substrate and a thermal transfer layer containing a dye which melts or sublimates upon heating, and a dye image-receiving layer comprising another substrate sheet A method in which an image is formed on a transfer sheet by superimposing a transfer sheet formed on the transfer sheet, and the transfer image is overlapped on both sides of one transfer sheet by heating means. It is characterized by transferring the same image pattern. Further, in another embodiment of the present invention, a thermal transfer sheet comprising a base sheet having a thermal transfer layer containing a dye which melts or sublimates upon heating;
A method of forming an image on a transfer sheet by superimposing a transfer sheet on which a dye image receiving layer is formed on another base sheet, and heating the dye image on the transfer sheet by heating means. At least two image patterns in the receiving layer
The second thermal transfer is performed with lower thermal energy than the first thermal transfer. Hereinafter, the present invention will be described in detail with reference to preferred embodiments. As shown in FIG. 1, generally, when an image is formed by thermal transfer, a thermal transfer sheet 1 in which a thermal transfer layer 3 is formed on a base sheet 2;
The heat transfer sheet having the receiving layer 5 formed on the base sheet 4 is overlapped as shown in the figure, and thermal energy according to the image information is applied to the interface between the thermal transfer layer 3 and the receiving layer 5 so that the heat transfer The image is formed by transferring the dye to the receiving layer. As a heat source for applying heat energy, a contact-type point heating means such as a thermal head 7 is preferably used. In this case, by modulating the voltage or pulse width applied to the thermal head, the applied heat energy can be changed continuously or in multiple steps. Before starting the description of the image forming method, the thermal transfer sheet and the transfer sheet used in the present invention will be described first. Thermal transfer sheet The base sheet 2 constituting the thermal transfer sheet includes a condenser paper, a polyester film, a polyethylene naphthalate film, a polystyrene film, a polysulfone film, a polyimide film, a polyvinyl alcohol film, a cellophane, and an aramid (aromatic polyamide) film. And the like, a thickness of 2 to 50 μm, preferably 2 to 12 μm
m. These plastic films are preferable because they have a smooth surface and high mechanical strength. Among them, polyester films and aramid films are preferable. The thermal transfer layer 3 is basically made of a dye and a binder which are transferred by melting or sublimation by heating. The dye is preferably a sublimable disperse dye, a sublimable oil-soluble dye or a sublimable basic dye, and has a molecular weight of 150 to 800, preferably 350 to 70.
0. These dyes are selected in consideration of the sublimation temperature, hue, weather resistance, solubility in the ink or the binder resin, and the like. C. I. Dispersion Yellow 51, 3, 54, 79, 60, 23, 7, 141, C.I.
I. Disperse Blue 24, 56, 14, 14
1, 334, 165, 19, 72, 87, 287, 154, 26, C.I. I. Disperse thread 135, 146, 59, 1, 73, 60
167, C.I. I. Disperse Violet 4, 1
3, 36, 56, 31, C.I. I. Solvent Violet 13, C.I. I. Solvent Black 3, C.I.
I. Solvent Green 3, C.I. I. Solvent Yellow 56, 14, 14, 16, 29, C.I. I. Solvent Blue 70, 35, 63, 36, 50, 4
9, 111, 105, 97, 11, C.I. I. Solvent Red 135, 81, 18, 25, 1
9, 23, 24, 143, 146, 182. Examples of the binder for the thermal transfer layer include cellulose resins such as ethyl cellulose, hydroxyethyl cellulose, ethyl hydroxyethyl cellulose, hydroxypropyl cellulose, methyl cellulose, cellulose acetate, and cellulose acetate butyrate, polyvinyl alcohol, polyvinyl acetal, polyvinyl butyral, polyvinyl pyrrolidone, and polyester. And vinyl resins such as vinyl chloride-vinyl acetate copolymer, polyvinyl acetate and polyacrylamide. As a more preferred example of the binder, a binder having a molecular weight of 6 instead of the above-mentioned ordinary vinyl butyral resin is used.
000 to 200,000, the weight percent of the vinyl alcohol portion is 10 to 40%, preferably 15 to 30% in the polyvinyl butyral resin, and the glass transition point is 60 ° C to 110.
C., preferably 70 ° C. to 110 ° C., special polyvinyl butyral resin. If the glass transition point is lower than 60 ° C., a phenomenon occurs in which the dye is aggregated or precipitated with time,
On the other hand, when the temperature exceeds 110 ° C., the dye does not sufficiently sublimate, which is not preferable. If the molecular weight is less than 60,000, the binding power as a binder is insufficient, and
If it exceeds 000, the viscosity at the time of application becomes too high, and there is a problem in application. If the vinyl alcohol content is less than 10%, the temporal stability of the thermal transfer layer is insufficient, so that aggregation, precipitation and bleeding of the dye on the surface cannot be avoided. Conversely, if it exceeds 40%, the sublimation of the dye is hindered due to the affinity of the polyvinyl alcohol portion for the dye, and the print density is reduced. The weight ratio of the dye to the binder in the thermal transfer layer is preferably such that the ratio of the dye to the binder is 0.3 or more.
If it is less than 0.3, the print density and thermal sensitivity are insufficient. On the other hand, when the ratio of the dye / binder exceeds 3.0, the retention of the dye in the binder becomes insufficient, and the storage stability of the thermal transfer sheet decreases. Therefore, the dye / binder is 0.3 to
It is preferably 3.0, more preferably 0.55
２．５2.5. More preferably, 0.55 to 0.15
It is. It is desirable that the dye is dissolved in the binder of the thermal transfer layer. In the conventional sublimation transfer paper for fabric, the dye is dispersed in the binder, so that sublimation of the dye requires the energy to overcome the interaction between the dye molecules and the interaction between the dye molecule and the binder. Need, and necessarily high energy, resulting in reduced thermal sensitivity. In this regard, the fact that the dye is dissolved in the binder is advantageous in terms of heat sensitivity. As shown in FIG. 2, a dye is selected for the thermal transfer layer so that a desired hue can be transferred when printed.
If necessary, two or more thermal transfer layers having different dyes may be formed side by side on one thermal transfer sheet. For example,
When an image such as a natural color photograph is formed by repeating printing of each color according to a color separation signal, the hue at the time of printing must be cyan (3a), magenta (3b), and yellow (3c). Preferably, three thermal transfer layers containing a dye providing such a hue are arranged. Alternatively, a thermal transfer layer containing a dye giving a black hue in addition to cyan, magenta and yellow may be added. It is preferable to provide a mark for position detection at the same time as forming any of the thermal transfer layers at the time of forming these thermal transfer layers, because it does not require ink or a printing step different from the thermal transfer layer formation. For the purpose of preventing sticking and improving running performance, it is preferable to provide a heat-resistant layer or a heat-resistant slip layer on the surface of the base sheet on which the heat transfer layer is not provided. Such a configuration is described in, for example, Japanese Patent Application No. 61-104189 of the present applicant. Further, additional layers such as an antistatic layer may be provided. Transferred Sheet As shown in FIG. 1, a transferred sheet 6 used in the method of the present invention comprises a base sheet 4 and a receiving layer 5 formed thereon. As the base sheet 4, synthetic paper (polyolefin, polystyrene, etc.), high quality paper, art paper, coated paper, cast coated paper, wallpaper, backing paper,
Synthetic resin or emulsion impregnated paper, synthetic rubber latex impregnated paper, synthetic resin internal paper, paperboard, etc., cellulose fiber paper,
Various plastic films or sheets such as polyolefin, polyvinyl chloride, polyethylene terephthalate, polystyrene, methacrylate, and polycarbonate can be used. Of these, synthetic paper has
It is preferable because it has a microvoid layer having a low thermal conductivity (in other words, a high heat insulating property). Further, a laminate formed by any combination of the above-mentioned to (1) can also be used. As an example of a typical laminate, cellulose fiber and synthetic paper, or
Examples include a laminate of cellulose fiber paper and a plastic film or sheet. Among these, the laminate of cellulose fiber paper and synthetic paper has high printing thermal sensitivity due to the low thermal conductivity of synthetic paper, which does not compensate for the thermal instability (such as expansion and contraction) of synthetic paper. In order to balance the front and back of the laminate in this combination, it is preferable to use a three-layer laminate of synthetic paper, cellulose fiber paper, and synthetic paper, so that curling due to printing can be reduced. As the synthetic paper used for the laminate as described above, any synthetic paper can be used as long as it can be generally used as a synthetic paper base material of a sheet to be heat-transferred. Synthetic paper provided with a layer (for example, commercially available synthetic paper Yubo: manufactured by Oji Yuka synthetic paper) is desirable. The fine holes in the paper-like layer can be formed, for example, by stretching a synthetic resin in a state containing a fine filler. A heat transfer sheet formed using synthetic paper provided with a paper-like layer containing the fine pores has an effect that, when an image is formed by thermal transfer, the image density is high and the image does not vary. This is because the fine pores have a heat insulating effect, and the thermal energy efficiency is good, and the good cushioning property due to the fine pores is provided on the synthetic paper and is considered to contribute to the receiving layer on which an image is formed. It is. or,
It is also possible to directly provide the paper-like layer containing the fine pores on the surface of a core material such as cellulose paper fiber. A plastic film other than the cellulose fiber paper in the laminate may be used.
What laminated | stacked the said cellulose fiber paper and a plastic film can also be used. Examples of the method of attaching the synthetic paper to the cellulose fiber paper include, for example, attaching using a conventionally known adhesive, attaching using an extrusion laminating method, attaching using heat bonding, and the like. Examples of a method for attaching the synthetic paper and the plastic film include a lamination method and a calendar method which simultaneously form the plastic film. The sticking means is appropriately selected according to the material of the thing to be stuck to the synthetic paper. Specific examples of the adhesive include an ethylene-vinyl acetate copolymer, an emulsion adhesive such as polyvinyl acetate, a water-soluble adhesive such as a polyester containing a carboxyl group, and the like. And an adhesive of an organic solvent solution type such as polyurethane, acrylic or the like. The base sheet may be transparent or opaque. In the case of transparency, it can be used as a transparent original for OHP, for example. The receiving layer 5 can be made of, for example, a mixed resin of a saturated polyester and a vinyl chloride-vinyl acetate copolymer, or a copolymer of polystyrene and / or styrene with other monomers. Further, a white pigment such as titanium oxide may be added to the receiving layer in order to improve the whiteness and enhance the sharpness of the transferred image. Further, in order to enhance the light fastness of the transferred image, an ultraviolet absorber and / or a light stabilizer can be added. Furthermore, in order to improve the releasability from the thermal transfer sheet after the transfer, a releasing agent such as a polyethylene wax, a surfactant, and silicone oil may be contained in the receiving layer. As another embodiment described above, an intermediate layer for improving image quality can be provided between the substrate sheet and the receiving layer. A prevention layer can be provided. For details of the configuration of each of these layers, see, for example, Japanese Patent Application No.
Nos. 9934 and 60-192620. Image Forming Method In the present invention, when the above-described thermal transfer sheet and the transfer-receiving sheet are overlapped and an image is formed on the transfer-receiving sheet by heating and printing means, the same image pattern is formed on the transfer-receiving sheet. Is transferred at least twice and an image with a large density range is obtained. Therefore, the image forming method of the present invention can take the following modes. In the present invention, the “density” is based on the logarithm of the ratio of the intensity of the light projected on the image and the light reflected from or transmitted through the image, and the density range is defined as the maximum density and the minimum density. Means the difference. (A) A method in which images having the same image pattern and in the same density range are transferred at least twice. According to this method, for example, an image pattern having a density range of 0 to 2.0 is superimposed twice so that a density range of 0 to 4.
0 transfer image can be obtained. (B) A method in which a plurality of image patterns are partially transferred only in a high-density region of an image pattern to be transferred. According to this method, for example, an image having a large density range as a whole can be quickly formed by transferring a plurality of portions only requiring a high density of 2.0 or more. (C) A method including a step of transferring only an image pattern portion of a high density region in an image pattern to be transferred with an image pattern of a constant density. According to this method, for example, only a portion having a density of 2.0 or more such as an outline or a shadow portion in an image is once transferred at a fixed density (for example, 2.0), and other portions are also included. An image having a density range of 0 to 4.0 can be formed by transferring an image pattern having a density range of 0 to 2.0 again. This method is also advantageous in speeding up image formation, as in the method (b). (D) A method of performing transfer a plurality of times by printing the dots of the thermal head at least partially overlap. (E) A method in which at least two or more transfer sheets transferred in the same image pattern are integrated. (F) A method in which the same image pattern is transferred onto both surfaces of one transfer sheet so that the transfer images overlap. An image having a wide density range can be obtained by using the above method. Further, by using a thermal transfer sheet as shown in FIG. 2, a color photographic color transfer image can be obtained. That is, when applying the method of the present invention, a thermal transfer sheet having areas previously formed by applying different colors to each other as shown in FIG.
First, the yellow color separation image is thermally transferred using the yellow area, then the red color area of the heat transfer sheet is used, and thereafter, the color separation of yellow, red, indigo and, if necessary, black is performed by repeating in order. Adopting the method of thermally transferring an image has the advantage that it is not necessary to replace the thermal transfer sheet. The quality of the obtained image can be improved by appropriately adjusting the size of the heat source used for applying the heat energy, the adhesion between the heat transfer sheet and the heat transfer sheet, and the heat energy. By combining the thermal transfer sheet and the heat transfer sheet as described above, printing using various types of thermal printing printers, facsimile or magnetic recording printing, photograph printing, and television screen printing Can be used for such. For example, one screen of the received television is transferred to a storage medium such as a magnetic tape or a magnetic disk.
It is stored as a signal of each color separation pattern of yellow, red, indigo and, if necessary, black, a signal of each stored color separation pattern is output, and heat energy corresponding to this signal is transferred to a thermal head or the like. When the heat transfer is applied to the superimposed body of the heat transfer sheet and the heat transfer sheet by the heat source and the thermal transfer is sequentially performed for each color, the screen of the television can be quickly reproduced as a sheet-like print. When a combination of a heat transfer sheet and a heat transfer sheet is used for printing out such a television screen, the heat transfer sheet usually has a white receiving layer alone or a colorless and transparent receiving layer. Those lined with a base material such as
Alternatively, it is convenient to obtain a reflection image by using a material in which a white receiving layer is backed with a base material such as paper. The same operations as described above can be performed when a combination of characters, graphics, symbols, colors, etc., and a graphic pattern formed on a CRT screen by operation of a computer are used as an original image. Are fixed images such as paintings, photographs, printed matter or people, still life,
When the object is an actual object such as a landscape, the same operation can be performed by using an appropriate means such as a video camera as a medium. Further, in producing signals of each color separation pattern from the original image, an electronic plate making machine (color scanner) used for photomechanical printing may be used. Further, as the thermal transfer sheet used in the method of the present invention, a thermal transfer sheet having a thermal transfer layer having a different dye concentration for each color may be used. In transferring the same image a plurality of times,
In the second transfer, the dye already transferred in the first transfer may be detached from the receiving layer. Therefore, in order to prevent such detachment of the dye, it is preferable to perform the second thermal transfer with lower thermal energy than the first thermal transfer. As the thermal transfer sheet used for performing such thermal transfer, it is preferable to use a sheet provided with a thermal transfer layer containing a dye having a different sublimation temperature for each color. Further, in the thermal transfer sheet used in the present invention, a sheet in which the sectional area of each color is appropriately changed according to the transfer method can be used. According to the method of the present invention, the following effects can be obtained in addition to the expansion of the image density range. (A) By performing the transfer a plurality of times, the uncolored dye in the first transfer image can be completely dyed by the second transfer, so that an image that is clear and excellent in fading resistance can be obtained. Obtainable. (B) The quality of the black image is further improved.
That is, normally, black is formed by a mixture of three primary colors of red, blue and yellow. However, it is generally difficult to adjust the black as the density range is widened. For example, there is a case where the density of red becomes too high. is there. According to the method of the present invention, by forming the same black image pattern by transferring a plurality of times, it is possible to adjust the combination of the three primary colors as described above to an optimum state, and thus obtain a clear and uniform black color. Can be. Applications Since the present invention has the above-described functions and effects, it is particularly suitable for the following uses. (B) When it is desired to obtain a diagnostic image such as a thermograph or a CT scan in the medical field, it is particularly required to improve the accuracy of the image information. Therefore, it is suitable for such use. (B) Calibration of printing (color proof) can be performed on the transferred image. Normally, in color proofing, a proofing image in the same density range as a print image is required, and conventionally, plate making for this proof printing was necessary. A calibration image having a large density range (for example, 0 to 4) can be obtained quickly and easily without a step. (C) It is also suitable for transparent originals for OHP and the like. Such a transparent original is required to have a higher print density than a normal transfer image, but according to the method of the present invention, a transparent original having a large density (transmission density) range can be obtained.

[Brief description of the drawings] FIG. 1 is a cross-sectional view illustrating an image forming method of the present invention. FIG. 2 is a perspective view of a thermal transfer sheet used in the present invention. [Explanation of symbols] 2 Base sheet 4 Base sheet 3 Thermal transfer layer 5 Reception layer

Claims (1)

(57) [Claims] A thermal transfer sheet formed by forming a thermal transfer layer containing a dye that melts or sublimates by heating on a base sheet,
A method of forming an image on a transfer sheet by superimposing a transfer sheet on which a dye image receiving layer is formed on another base sheet, and heating the dye image on the transfer sheet by heating means. An image forming method, wherein the image is partially overlapped and transferred at least twice with respect to only a high density region in an image pattern to be transferred to a receiving layer. 2. A thermal transfer sheet formed by forming a thermal transfer layer containing a dye that melts or sublimates by heating on a base sheet,
A method of forming an image on a transfer sheet by superimposing a transfer sheet on which a dye image receiving layer is formed on another base sheet, and heating the dye image on the transfer sheet by heating means. Forming an image at a constant density on only an image pattern portion in a high density region of an image pattern to be transferred on a receiving layer, and then performing a second image transfer including other image pattern portions; Method. 3. The image forming method according to claim 1, wherein the transfer is performed a plurality of times by performing printing so that dots of the thermal head overlap at least partially. 4. A thermal transfer sheet formed by forming a thermal transfer layer containing a dye that melts or sublimates by heating on a base sheet,
A method in which a dye image receiving layer is superimposed on a transfer sheet formed on another base sheet, and an image is formed on the transfer sheet by heating means. An image forming method, wherein at least two or more heat transfer sheets are stacked and integrated. 5. A thermal transfer sheet formed by forming a thermal transfer layer containing a dye that melts or sublimates by heating on a base sheet,
A method in which a dye image receiving layer is superimposed on a transfer sheet formed on another base sheet, and an image is formed on the transfer sheet by heating means, wherein one transfer sheet An image forming method, wherein the same image pattern is transferred onto both sides such that the transferred images overlap. 6. A thermal transfer sheet formed by forming a thermal transfer layer containing a dye that melts or sublimates by heating on a base sheet,
A method of forming an image on a transfer sheet by superimposing a transfer sheet on which a dye image receiving layer is formed on another base sheet, and heating the dye image on the transfer sheet by heating means. At least two image patterns in the receiving layer
An image forming method, wherein the image is repeatedly transferred and the second thermal transfer is performed with lower thermal energy than the first thermal transfer.