JPH1134512A - Image forming method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming method wherein a black image having a high concentration and a favorable image storing property can be obtained in a short period of time by a sublimate type heat-transfer. SOLUTION: An ink sheet 1 containing at least two kinds or more of sublimate dyes, and a permeable image receiving sheet 4 having a protective layer 7 and an image receiving layer 6, are superposed, and by a heating means, the same image pattern is transferred to the same part on the permeable image receiving sheet 4 at least twice, and an image is formed by this method, and the content of the sublimate dyes in the ink sheet 1 is 50 wt.% or more of the compositions contained in the ink sheet 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming method, and more particularly to an image forming method capable of significantly increasing the density of a black image formed by sublimation type thermal transfer.

[0002]

2. Description of the Related Art As a method of obtaining a color hard copy, a color recording technique such as an ink-jet method, an electrophotographic method, and a thermal transfer method has been studied. Downsizing,
It has advantages such as low cost and low running cost. In the thermal transfer method, a transfer sheet having a heat-fusible ink layer on a support (hereinafter, referred to as a transfer sheet) is used.
A thermal transfer recording material, which is heated by a thermal head to melt-transfer ink from a heat-fusible ink layer onto an image-receiving sheet for thermal transfer recording; and a heat-diffusing dye (sublimation There is a thermal diffusion transfer method (sublimation transfer method) in which a transfer sheet having an ink layer containing a dye is heated by a thermal head to transfer a thermal diffusible dye from the ink layer to an image receiving sheet. In the method, the gradation of the image can be controlled by changing the transfer amount of the dye in accordance with the change in the thermal energy of the thermal head. Can be obtained.

However, the above method is suitable for obtaining a reflection image having a narrow optical density range, but has a problem that a desired density cannot be obtained when a transmission image having a wider optical density range is to be obtained. JP-A-63-176182 and JP-A-2-587 disclose a method of obtaining a high-density image using the above-mentioned method, that is, a method of forming a heat transfer sheet having a heat transfer layer containing a dye which melts or sublimes on the surface of a support. There is described a technique in which the dye image is transferred imagewise onto an image receiving sheet a plurality of times to increase the density of the transferred image.

However, in order to obtain a high-density black image by this method, it is necessary to print the yellow, magenta, and cyan ink sheets by superimposing three colors continuously, and to repeat this process, which requires a considerable amount of time. I will. Also, in this method, since the dye density is high in the image receiving layer to which the dye has been transferred once, particularly in the surface portion of the image receiving layer in the high density part, the transferability after the second time is reduced, and a sufficient high density image can be obtained efficiently. There is also a problem that it cannot be done. Further, the formed high-density image has a disadvantage that the stability of the obtained image, that is, the light fastness and the fixability are not good because the dye ratio in the image receiving layer is high.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an image capable of giving a black image with high density and good image storability in a short time by sublimation type thermal transfer. It is to provide a forming method.

[0006]

The above object of the present invention has been attained by the following constitutions.

(1) An ink sheet containing at least two or more kinds of sublimable dyes and a transmissive image receiving sheet having a protective layer and an image receiving layer are overlaid, and the same portion on the transparent image receiving sheet is heated by heating means. Transferring the image pattern at least twice to form an image, wherein the content of the sublimable dye in the ink sheet is 50% by weight or more of the composition contained in the ink sheet. Image forming method.

(2) An ink sheet containing at least two or more kinds of sublimable dyes is superimposed on a transparent image receiving sheet having a protective layer and an image receiving layer, and the same portion on the transparent image receiving sheet is heated by heating means. Transferring the image pattern at least twice to form an image, wherein the protective layer of the transmissive image-receiving sheet is dye-permeable and has lower dye-dyeability than the image-receiving layer. Method.

(3) An ink sheet containing at least two or more kinds of sublimable dyes is superimposed on a transparent image receiving sheet having a protective layer and an image receiving layer, and the same portion on the transparent image receiving sheet is heated by heating means. Forming an image by transferring the image pattern at least twice, wherein the image receiving layer of the transmissive image receiving sheet contains a metal ion supply compound capable of chelating with the sublimable dye. Method.

In a preferred embodiment, the metal ion-supplying compound has a concentration gradient, and at least one of the transparent image-receiving sheets is provided before or after transferring an image pattern.
Heating twice and transferring the image pattern two or more times include printing only the portion where the density has not reached in one printing.

That is, the present inventors have conducted intensive studies to solve the above-mentioned problems in a thermal transfer method, particularly a sublimation type thermal transfer method for forming an image by transferring the same image pattern at least twice to the same portion. The content of the sublimable dye in the sheet is specified (focusing on the ink sheet), a substance capable of chelating with the sublimable dye is included in the image receiving layer of the transparent image receiving sheet (focusing on the image receiving layer), or the dye permeability is determined. By forming a protective layer having a lower dye-dyeing property than the image receiving layer (focusing on the protective layer), the transferred image can be efficiently and sufficiently concentrated, and excellent image stability can be obtained. The present invention has been made based on the finding that the maintenance of sex can be achieved.

Hereinafter, the present invention will be described in detail.

First, a preferred embodiment of the present invention will be described in detail with reference to the drawings. As shown in FIG. 1, the image formation in the present invention is performed by an ink sheet 1 having an ink layer 3 containing at least two or more sublimable dyes on a support 2 and an image receiving layer 6 on a transparent support 5. The image receiving sheet 4 having the protective layer 7 and the image receiving sheet 4 is faced as shown in the figure, and the step of imagewise heating with a heating means, for example, a thermal head 8, from the back surface of the support 2 is repeated twice or more. In this case, the applied thermal energy can be changed continuously or in multiple steps by modulating the voltage or pulse width applied to the thermal head.

The materials (ink sheet, transparent image receiving sheet) used in the present invention will be described below.

[1] Transparent image receiving sheet The transparent image receiving sheet comprises at least a transparent support, an image receiving layer and a protective layer. By providing the protective layer on the image receiving layer, in the second and subsequent printings, the reverse transfer of the dye transferred first to the ink layer is suppressed, and more efficient image recording is performed.

According to a second aspect of the present invention, there is provided the transparent image-receiving sheet according to the first aspect, wherein the protective layer is dye-permeable and has a lower dye-dyeing property than the image-receiving layer (type 1). The image-receiving sheet is characterized in that the image-receiving layer contains a metal ion supplying compound capable of chelating with a sublimable dye (type 2), and any of the best image-receiving layers can hold the sublimable dye. It is an aspect. Hereinafter, the transparent support, the image receiving layer and the protective layer will be described in this order.

(Permeable support) As the permeable support,
Acrylic esters, methacrylic esters, polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polycarbonate, polyarylate, polyvinyl chloride, polyethylene, polypropylene, polystyrene, nylon, aromatic polyamide, polyetheretherketone, polysulfone, polyethersulfone And resin films of polyimide, polyetherimide, and the like, and resin films obtained by laminating two or more layers of the resin.

In the present invention, the permeable support is preferably stretched into a film and heat-set, from the viewpoint of dimensional stability.
Fillers such as zinc oxide, barium sulfate and calcium carbonate may be added. Further, the permeable support may be appropriately dyed and used. Examples of the dyeing method include a method of adding a dye at the time of producing a plastic film. As the amount of the dye to be added, a transmission density of 0.001 to 0.
It is desirable to adjust the additive concentration so as to be in the range of 5. The thickness of the permeable support is about 10 to 500 μm, preferably 25 to 250 μm.

(Image Receiving Layer) The image receiving layer can be used without any particular limitation as long as it can receive a sublimable dye diffused by heating from an ink layer in an ink sheet described later. An image receiving layer suitable for such a heat-sensitive transfer recording material can be formed by using a binder resin and, if necessary, various additives.

The type 2 image receiving layer is characterized in that it contains a metal ion supply compound capable of chelating with a sublimable dye in consideration of the stability of the formed image.
The metal ion supplying compound is disclosed in Japanese Patent Application No. 4-23829.
Compound represented by general formula (1) described in No. 8 General formula (1) M ²⁺ (X ⁻ ) ₂ can be used.

In the formula, M ²⁺ represents a divalent transition metal ion. X represents a coordination compound represented by the following general formula (2) capable of forming a divalent metal ion complex.

[0022]

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In the formula, Z represents an alkyl group, an aryl group, an aryloxycarbonyl group, an alkoxy group, an alkoxycarbonyl group, a halogen atom and a hydrogen atom. R and R 'represent an alkyl group and an aryl group, which may be the same or different, and R and Z or R' and Z may be bonded or may be bonded to each other. And R 'are not both methyl groups.

In the compound represented by the general formula (1),
M ²⁺ represents a divalent transition metal ion, and among them, nickel and zinc are preferable in view of the color of the metal ion supply compound itself and the color tone of the chelated dye. X represents a coordination compound represented by the following general formula (2) capable of forming a divalent metal ion complex. Further, a neutral ligand may be provided depending on the central metal, and typical ligands include H ₂ O and NH ₃ .

In the coordination compound represented by the general formula (2), Z represents an alkyl group, an aryl group, an aryloxycarbonyl group, an alkoxy group, an alkoxycarbonyl group, a halogen atom and a hydrogen atom. When Z is an aryloxycarbonyl group, an alkoxycarbonyl group, or a halogen atom, an electron-withdrawing group is preferable for stabilizing the metal ion-supplying compound. Among these, the aryloxycarbonyl group and the alkoxycarbonyl group are more preferable in view of solubility. preferable. Examples of the aryloxycarbonyl group include a phenoxycarbonyl group, and examples of the alkoxycarbonyl group include methoxycarbonyl, ethoxycarbonyl,
Those having a straight or branched chain having 1 to 20 carbon atoms, such as pentyloxycarbonyl and 2-ethylhexyloxycarbonyl groups, are preferred. These alkoxycarbonyl groups may be substituted with a halogen atom, an aryl group, an alkoxy group, or the like.

R and R 'represent an alkyl group or an aryl group, which may be the same or different, and R and Z or R'
And Z may be bonded or a ring may be bonded, but when Z is a hydrogen atom, R and R 'are not both methyl groups.
Examples of the alkyl group represented by R, Z and R ′ include methyl, ethyl, propyl, isopropyl, butyl, s
ec-butyl, t-butyl, hexyl, octyl, 2-
Examples thereof include a linear or branched alkyl group having 1 to 20 carbon atoms such as an ethylhexyl group, and these alkyl groups may be substituted with a halogen atom, an aryl group or an alkoxy group. The aryl group represented by R, Z and R 'includes a phenyl and naphthyl group, and may have a substituent. Examples of the alkoxy group represented by Z include straight-chain or branched alkoxy groups having 1 to 20 carbon atoms such as methoxy, ethoxy, and butoxy. The halogen atom represented by Z is preferably a chlorine atom. The following are examples of compounds, but the present invention is not limited thereto.

[0027]

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[0028]

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[0029]

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[0030]

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[0031]

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[0032]

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The content of the metal ion supplying compound in the type 2 image receiving layer is preferably 0.5 to 20 g / m ² ,
1-15 g / m < ² > is more preferable. These compounds can be synthesized according to the method described in Chelate Chemistry (5) Complex Chemistry Experimental Method [1] (edited by Nankodo).

The image receiving layer is used for the purpose of improving fixability and sensitivity.
It may be composed of more than two layers, in which case the layer closer to the support (hereinafter, lower layer) preferably has a higher sublimation dye receptivity than the layer farther away (hereinafter, upper layer). . The lower layer and the outermost layer are made of a resin having different glass transition point (Tg), or the amount of a high-boiling solvent or a thermal solvent described in JP-A-3-256795 is changed so as to stabilize the image after transfer. Properties (for example, retransfer) can be improved. When the above-mentioned metal ion supplying compound is added, it is preferable to give a concentration gradient such that the concentration increases as approaching the support. In order to have such a concentration gradient, for example, when using a coating method, there is also a method of increasing the concentration of the metal ion supply compound on the support side by electrophoresis or ion electromotive before the solvent is sufficiently dried, An upper layer having a lower concentration of a metal ion-supplying compound than the metal ion-supplying compound in the lower layer is formed by applying a lower layer-forming coating solution preferably containing a metal ion-supplying compound at a certain concentration on a support to form a lower layer The forming coating liquid is applied to the upper surface of the lower layer to form the upper layer. It is preferable to employ a method in which the operation of forming an image receiving layer with an image receiving layer forming coating solution having sequentially different concentrations of the metal ion supplying compound is repeated an arbitrary number of times. In this case, after the lower layer is coated on the support and dried sufficiently, and then the upper layer is coated on the lower layer surface, the image receiving layer has two layers in which the concentration of the metal ion supply compound is different from each other at the layer interface. Can be structured. Also, if the upper layer is coated before the lower layer coated on the support is sufficiently dried, the components forming the coating liquid at the interface between the lower layer and the upper layer cause mutual diffusion, and as a result, between the lower layer and the upper layer. In the image receiving layer formed by the lower layer and the upper layer, the concentration of the metal ion supply compound increases toward the support. Alternatively, when the lower layer applied on the support is sufficiently dried, and then the upper layer containing a solvent that dissolves the lower layer is applied, dissolution and diffusion of the lower layer forming composition occurs at the interface, and as a result, the lower layer and the upper layer In the image receiving layer formed by the lower layer and the upper layer, the concentration of the metal ion supply compound increases toward the support. In this case, the image receiving layer is not limited to the two-layer structure as described above, and may have a structure of three or more layers.

As the binder resin, known resins conventionally used for an image receiving layer of a dye image receiving material can be used. For example, polyester resins, polyvinyl acetal resins, urethane resins, amide resins, cellulose resins Olefin resins, vinyl chloride resins, copolymer resins of vinyl chloride and other monomers (such as vinyl acetate, etc.), acrylic resins, styrene resins, polycarbonate, polyvinyl alcohol, polyvinyl pyrrolidone,
Examples thereof include polysulfone, polycaprolactone resin, polyacrylonitrile resin, urea resin, epoxy resin, and phenoxy resin. These resins may be used alone or in combination of two or more. Is also good. Among these polymers, more preferred are polycarbonates containing a plasticizer described in JP-A-60-19138 and polyvinyl acetal-based polymers, particularly polyvinyl butyrals described in JP-A-61-11293. The amount of the binder used is as follows:
m ² per 0.1g~50g is preferable.

The image receiving layer may contain a release agent, an antioxidant, an ultraviolet absorber, a light stabilizer, a filler (inorganic fine particles, organic resin particles), a pigment, and an antistatic agent. Further, a plasticizer, a thermal solvent or the like may be added as a sensitizer. When forming an image by thermal transfer, the image receiving layer preferably contains a release agent for the purpose of preventing fusion with the ink sheet. Such release agents include silicone oils, silicone resins, solid waxes, surfactants, and polyolefin-based resins. In order to improve compatibility with the binder, modified silicone oil and / or modified silicone resin is used. It is preferably used. The amount of the release agent to be added cannot be determined uniformly because it may vary depending on the type of the release agent. However, generally, the amount of the release agent is usually 0.01 to 30% by weight in the composition for forming an image receiving layer. Yes, preferably 0.1 to
20% by weight.

(Protective Layer) The protective layer preferably has a dye-diffusing property and a dye-dyeing property lower than that of the image receiving layer. In particular, the protective layer of the transmissive image-receiving sheet according to claim 2 is characterized in that it has a dye-permeability and has a lower dye-dyeing property than the image-receiving layer. The protective layer is not particularly limited as long as the protective layer is provided on the image receiving layer and can more efficiently receive the sublimable dye diffused from the ink sheet by heating and can quickly diffuse into the image receiving layer. From the viewpoint of sensitivity and image storability, it is preferable that the protective layer contains substantially no metal ion-supplying compound or contains the metal ion-supplying compound in an amount smaller than that of the image receiving layer.

In the present invention, the dye permeability means a property in which the dye is transferred to the lower layer via the protective layer during the thermal transfer, and preferably, the dye does not remain in the protective layer itself. , Or in a state substantially not contained.
Here, "substantially not contained" means that the amount remaining in the protective layer is very small and most of the amount is transferred to the image receiving layer and does not have or exhibit image density. Dye-dyeability refers to a property in which a transferred dye stays without diffusion and is retained in a layer, and the transfer density of a sublimable dye diffused from an ink sheet is measured and compared. Is evaluated in. Since the type 1 protective layer has a lower dye-dyeing property than the image receiving layer, it is essential that (dye transfer density of image receiving layer / dye transfer density of protective layer)> 1.0, preferably 1.2.
Is greater.

The protective layer is formed of a heat-fusible compound or the binder resin of the image-receiving layer. If necessary, a known release agent can be added to facilitate release from the ink sheet.

As the heat-meltable compound, 65 to 150 ° C.
A colorless or white compound that melts at a temperature of but can be separated from the ink layer when it is cold is preferably used. For example, vegetable waxes such as carnauba wax, wood wax, ouriculi wax and espar wax; beeswax, insect wax, shellac wax and spermaceti wax Petroleum waxes such as paraffin wax, microcrystal wax, polyethylene wax, ester wax and acid wax; and waxes such as montan wax, ozokerite and ceresin, etc., polyester wax, polyurethane wax,
A wax chloride and the like can be mentioned, and a latex dispersion or a solvent dispersion of a polyethylene wax or a polypropylene wax which is preferably peeled off from the ink layer at the time of cooling is more preferable. Further, these protective layers may contain a polymer such as polyvinylpyrrolidone, polyvinylbutyral, polyester, and vinyl acetate. In this protective layer, the additives described in the section of the image receiving layer can be added in a range of 0.1 to 30% by weight. It is extremely important to select a type that does not degrade the adhesion to the image protective layer and the amount of addition.
The protective layer is preferably selected in a range of usually 0.01 to 10 μm, preferably 0.1 to 5 μm.

In the type 1, when selecting the components and materials of the image receiving layer and the protective layer, it is necessary that the protective layer is dye-permeable and has a lower dye-dyeing property than the image receiving layer.
That is, it is essential to select components or materials for forming the protective layer and the image receiving layer so that the image receiving layer becomes larger than the degree of retention of the sublimable dye in the protective layer. If the image receiving layer has a higher sublimation dye retention property than the protective layer, the transferred image of the sublimable dye transferred to the protective layer quickly diffuses and moves to the image receiving layer, and an image having good fixability is formed. Because.

In the present invention, an intermediate layer may be provided between the image receiving layer and the support for the purpose of imparting properties such as heat insulating properties and cushioning properties. Examples of the resin forming the intermediate layer include polyurethane resin, polyester resin, polybutadiene resin, poly (meth) acrylate resin, epoxy resin, polyamide resin, rosin-modified phenol resin, terpene phenol resin, ethylene-vinyl acetate copolymer, and polyolefin. Resin, cellulose resin, gelatin, casein and the like. In order to impart cushioning properties, the intermediate layer may be formed of a layer containing microbubbles. The intermediate layer is preferably selected in a range of usually 1 to 50 μm, preferably 3 to 30 μm.
The intermediate layer may be a single layer or, if necessary, may be provided as a multilayer structure of two or more layers having the same composition or different compositions to separate the functions.

In the present invention, a backing layer is provided on the surface of the support opposite to the image receiving layer for the purpose of preventing static charge, preventing multiple sheets from being supplied, imparting slipperiness, preventing adhesion to other image receiving layers, preventing curling, and the like. It may be provided. For the purpose of antistatic, cationic surfactants, anionic surfactants, nonionic surfactants, polymer antistatic agents, conductive fine particles and the like, as well as “11290 chemical products”, Chemical Daily, p. . 875
~ P. 876 and the like can also be suitably used. It is preferable to add the above-mentioned antistatic agent and / or a filler or a pigment in order to prevent a plurality of sheets from being supplied, to impart a slipperiness, and to prevent adhesion to another image receiving layer. To prevent curl,
It is preferable to use a heat-resistant resin with little thermal deformation or a resin cured by heat or ionizing radiation after forming the backing layer. Examples of the heat-resistant resin include cellulose resins such as methylcellulose and nitrocellulose, styrene resins such as polystyrene and styrene-acrylonitrile copolymer, acrylic resins such as polymethyl methacrylate and polyacrylic acid, and polyester resins such as polyethylene terephthalate. Resin, polycarbonate, polyarylate, polyacetal, polysulfone, polyethersulfone, polyethernitrile, polyetheretherketone, modified polyphenylene oxide, polyoxybenzylene, polyimide, polyetherimide, polyamideimide, polyphenylene sulfide, polyparabanic acid resin, etc. Can be mentioned.

When the above-mentioned backing layers are provided, the thickness of each of them is preferably selected in the range of usually 0.01 to 10 μm, and the backing layer may be a single layer or may have the same composition as necessary. Alternatively, functions may be separated by providing a different multilayer structure of two or more layers. As a method of forming the image receiving layer on the surface of the support, a coating solution for an image receiving layer is prepared by dispersing or dissolving the components for forming the image receiving layer in a solvent, and the coating solution for the image receiving layer is coated on the support. Or a coating method in which the mixture having the components for forming the image receiving layer is melt-extruded and then laminated on the surface of the support. The thickness of the image receiving layer formed on the surface of the support is generally 1 to 50 μm,
Preferably it is about 2 to 20 μm. Other, protective layer,
The intermediate layer and the backing layer can be provided in the same manner as the image receiving layer. In the present invention, when the adhesive strength of the intermediate layer or the image receiving layer laminated on the support is insufficient (for example, when the difference in the wetting angle (contact angle) between the laminated resins is large, particularly 5 deg or more) In this case, it is preferable to apply a treatment to the surface to be laminated before providing the layer to be laminated. Examples of the surface treatment include corona discharge treatment, flame treatment, ozone treatment, ultraviolet treatment, and radiation treatment. , Surface roughening treatment, chemical treatment, low temperature plasma treatment,
A known resin surface modification technique such as a grafting treatment can be applied as it is. Specifically, the methods described in “Chemical Doujinshi, Chapter 2 and / or“ Handbook of New Polymer Materials ”, Chapter 8, Mar. 8, etc.,“ Basics and Application of Polymer Surfaces (2) ”, can be used as one or two kinds of them. The above may be used in combination.

[2] Ink sheet The ink sheet according to claim 1, wherein the content of the sublimable dye is 50% by weight or more of the composition contained in the ink sheet. In the present invention, the “composition contained in the ink sheet” refers to a member of the ink sheet excluding the solvent.

The ink sheet comprises a support and an ink layer containing at least two or more sublimable dyes. As the support for the ink sheet, any material can be used as long as it has good dimensional stability and can withstand heating of a thermal head or the like during recording.
Thin paper such as condenser paper and glassine paper, and heat-resistant plastic films such as polyethylene terephthalate, polyamide and polycarbonate are preferably used. The thickness of the support is preferably 2 to 30 μm, and the support is provided with an undercoat layer made of a polymer selected for the purpose of improving adhesiveness with a binder, transferring a dye to the support, and preventing dyeing. It is preferred to have. Further, a slipping layer may be provided on the back surface of the support (the side opposite to the thermal transfer layer) for the purpose of preventing the head from sticking to the support.

The sublimable dye used in the present invention is obtained by mixing two or more kinds of heat diffusible dyes from cyan, magenta, yellow and black dyes so as to obtain a desired color tone. Examples of the cyan dye include JP-A-59-78896, JP-A-59-227948 and JP-A-59-227948.
No.-24966, No.60-53563, No.60-13
No. 0735, No. 60-131292, No. 60-239
No. 289, No. 61-19396, No. 61-22993
Nos. 61-31292, 61-31467, 61-35994, 61-49893, 61-
148269, 62-191191, 63-9
No. 1288, No. 63-91287, No. 63-2907
Examples include naphthoquinone dyes, anthraquinone dyes, and azomethine dyes described in No. 93 and the like.

The magenta dye is described in JP-A-59-1984.
No. 78896, JP-A-60-30392, JP-A-60-60
-30394, JP-A-60-253595, JP-A-61-262190, JP-A-63-5992, JP-A-63-205288, JP-A-64-159, JP-A-64-63194 And azomethine dyes, and the like.

As the yellow dye, JP-A-59-78 can be used.
896, JP-A-60-27594, JP-A-60-3
No. 1560, JP-A-60-53565, JP-A-61-61
And methine dyes, azo dyes, quinophthalone dyes and anthrisothiazole dyes described in JP-A No. 12394 and JP-A-63-122594.

When the image receiving layer contains a metal ion supplying compound, it is preferable to use a dye capable of chelating with the compound. As chelateable dyes,
For example, as a yellow dye, JP-A-4-82786
Nos. 4-164688, 4-164689, 4-164690, 4-176686, and 4-2
No. 35093, No. 4-292988, No. 4-3208
No. 93, 4-34893, and 5-177958. Examples of magenta dyes include JP-A-4-62092 and JP-A-4-65294.
Nos. 4-73191, 4-82784, 4-
No. 94974, No. 4-97894, No. 4-23278
No. 5, 4-269589, 4-339694,
Nos. 5-16545, 5-185751, 5-3
No. 01470 and the like. Examples of cyan dyes include JP-A-4-62094 and JP-A-4-6.
No. 5293, No. 4-78584, No. 4-82784
Nos. 4-82785, 4-82787, 4-
Nos. 89288, 4-89289, 4-15809
No. 2, No. 4-212888, No. 4-241994,
And dyes exemplified in JP-A-4-261895 and JP-A-4-267194.

Dyes for forming a black dye image include dyes described in JP-A-4-97895, JP-A-7-331773, JP-A-8-310628 and JP-A-8-330905. Is mentioned.

In the present invention, the amount of the sublimable dye used is 0.1 to 20 g, preferably 0.5 to 5 g per 1 m ² of the support of the ink sheet.

As the binder for the ink layer, for example, cellulose-based resins such as cellulose-added compounds, cellulose esters, cellulose ethers, etc .; polyvinyl acetal resins such as polyvinyl alcohol, polyvinyl formal, polyvinyl acetoacetal and polyvinyl butyral; polyvinyl pyrrolidone; polyvinyl acetate , Polyacrylamide, styrene resin, poly (meth) acrylic acid ester, poly (meth) acrylic acid, vinyl resin such as (meth) acrylic acid copolymer, rubber resin, ionomer resin, olefin resin, polyester Resins and the like can be mentioned. Among these resins, polyvinyl butyral, polyvinyl acetoacetal, or cellulosic resins having excellent storage stability are preferable. One of these binders can be used alone, or two or more of them can be used in combination. The weight ratio of the binder to the sublimable dye is preferably 5: 5 to 2: 8.
Range.

Various additives described in the image receiving layer can be appropriately added to the ink layer.

The ink liquid is prepared by dissolving the sublimable dye in a solvent together with a binder, or by dispersing the ink in a fine particle form in the solvent, and providing the ink liquid on a support using the same method as the image receiving layer. Can be. The thickness of the ink layer is usually from 0.2 to 10 μm, preferably from 0.5 to 5 μm, as a dry film thickness.

In order to protect the formed image, it is possible to transfer the resin layer only like a transfer foil after image formation, or to laminate the resin film to use the image protection layer appropriately according to the application. it can. When a resin film is used as an image protection layer, this is one in which an adhesive resin layer is provided on a base material. As the substrate used here, a support that can be used in the image receiving sheet can be appropriately selected and used, but a substrate having a transmittance of 70% or more is preferably used, and the thickness is usually 6 to 100 μm, and furthermore, Is 10
Preferably it is 50 μm. Further, the adhesive resin layer has an adhesive property at normal temperature, such as a binder resin used in an image receiving layer, a substance which exhibits adhesive property by applying pressure, or an adhesive property which is applied by applying heat. Those that express can be appropriately selected and used. The thickness of the adhesive layer is usually 0.1 to 20 μm, and preferably 0.3 to 10 μm. On the other hand, when a transfer foil is used, a surface layer and an adhesive layer are laminated on the substrate in this order, and a release layer and the like are provided as necessary to control the adhesive force between the substrate and the surface layer. May be. Incidentally, the thickness of the substrate is usually 6 to 100 μm, more preferably 10 to 50 μm, the thickness of the release layer, the surface layer and the adhesive layer is usually 0.01 to 20 μm, more preferably 0.1 to 10 μm It is preferred that The transfer of the transfer foil for image protection onto the image receiving layer by the transfer sheet is usually performed using a means capable of applying pressure while heating such as a thermal head, a heat roller, or a hot stamp machine. Among them, a thermal head and a heat roller are particularly preferred for the purpose of the present invention.

[3] Image Forming Method The image forming method of the present invention will be described below. In the present invention, the above-described ink layer of the ink sheet and the protective layer on the image receiving layer of the transmissive image receiving sheet are overlapped, and thermal energy is applied imagewise to the interface between the ink layer and the image receiving layer. The sublimable dye in the ink layer is melted, vaporized or sublimated by an amount corresponding to the applied thermal energy, transferred to the image receiving layer side and received, thereby forming an image on the image receiving layer.

As the heat source for giving the thermal energy,
A thermal head is generally used. In addition, a conventionally known one such as a laser beam, an infrared flash, and a hot pen can be used. The thermal energy may be applied from the ink sheet side, from the image receiving sheet support side, or from both sides, but if priority is given to the effective use of thermal energy, it is preferable to apply from the ink sheet side. desirable. The present invention provides a method for obtaining an image having high density and good image storability in a short time by repeating the transfer of an ink sheet of the same color tone to the same portion of an image receiving layer twice or more times using the above image forming method. Features. In this case, the number of thermal heads may be one or more. In the case of a single thermal head, the image receiving sheet is repeated and printing is performed on the same portion of the image receiving layer a plurality of times. Print sequentially on the same part. Also, the printing energy may be changed for each printing,
For example, when an image including a high-density portion is formed, an image may be formed by applying energy only to a portion where the density has not reached in the first printing after the second printing. The ink sheet may be printed a plurality of times using the same portion as long as the dye is present, but it is desirable to use an unprinted portion of the ink layer for each printing from the viewpoint of sensitivity and reverse transfer.

When a sublimable dye and a chelating metal ion-supplying compound are used in the image receiving layer (type 2), the surface of the image receiving sheet may be subjected to heat treatment before or after image formation in order to further promote chelation. It is preferable in terms of fixability and color tone of the dye image. The heat treatment method in this case is not particularly limited as long as heat is uniformly and sufficiently applied.

As the heat treatment means, a thermal head,
Examples thereof include a heat roller, a hot press using a metal plate and heat-resistant silicone rubber, and a hot stamping method. Among them, it is preferable to use a thermal head and a heat roller in view of the size and simplicity of the apparatus.
When a thermal head is used as the heating means, the area of the heating resistor element of the thermal head used when forming a sublimation-type thermal transfer image is larger than that of the thermal head in terms of smoothing the image surface, energy efficiency to be applied, and heat treatment speed. It is very effective to use a thermal head having an element area. The heating temperature when using a heat roll is usually 6
The temperature is in the range of 0 to 200 ° C, preferably 80 to 180 ° C, the transport speed is usually 0.1 to 100 mm / sec, preferably 0.5 to 50 mm / sec, and the pressure is usually 0.1 to 20 kg.
/ Cm, preferably 0.5 to 10 kg / cm. Furthermore, when using a hot stamp, the heating temperature is usually 6
The pressure is usually in the range of 0 to 200 ° C., preferably 80 to 180 ° C., and the pressure is usually 0.05 to 10 kg / cm ² , preferably 0.5 to 5 kg / cm ² , and the heating time is usually 0.1 to 10 kg / cm ² .
It is 1 to 300 seconds, preferably 0.5 to 100 seconds.
When the image protective layer is provided, the post-heating treatment and the step of transferring the image protective layer may be performed more efficiently at the same time.

[0061]

EXAMPLES The present invention will be described below in detail with reference to examples, but embodiments of the present invention are not limited thereto. The following “parts” indicate “parts by weight”.

Example 1 (Claim 1) <Preparation of Ink Sheet for Thermal Transfer Recording> The following composition was formed on the back of a heat-resistant protective layer of a 6 μm-thick polyethylene terephthalate film (Lumirror 6CF531 manufactured by Toray Industries, Inc.) as a support. The coating liquid for forming an ink layer was applied by a wire bar coating method so that the thickness after drying was 2 μm, and dried to obtain an ink sheet 1 for thermal transfer recording (hereinafter, ink sheet).

(Coating Liquid for Forming Ink Layer) Dye-1 (exemplary compound) 2.94 parts Dye-2 (exemplary compound) 1.26 parts Dye-3 (exemplary compound) 2.80 parts polyvinyl acetoacetal resin ( KY-24, manufactured by Denki Kagaku Kogyo) 2.40 parts Styrene-acrylic resin (RESODA GP200 manufactured by Toagosei Co., Ltd.) 0.6 parts Silicone-modified urethane resin (SP2105 manufactured by Dainichi Seika Co., Ltd.) 08 parts Methyl ethyl ketone 50 parts Toluene 30 parts Cyclohexanone 10 parts In the same manner as described above, ink sheets 2 to 5 shown in Table 1 were prepared. The composition of the binder of the ink sheet 5 was changed as follows.

Polyvinyl acetoacetal resin (KY-24, manufactured by Denki Kagaku Kogyo) 5.6 parts Styrene-acrylic resin (RESODA GP200, manufactured by Toagosei Co., Ltd.) 1.4 parts

[0065]

Embedded image

<Preparation of Image Receiving Sheet> Next, a corona-treated surface of a 175 μm-thick colored transparent support (175 μm-thick polyethylene terephthalate colored blue with an anthraquinone-based dye to a concentration of 0.170) as a support was prepared. A coating solution for forming an anchor layer, a coating solution for forming an image receiving layer, and a coating solution for forming a protective layer having the following compositions are sequentially coated and dried by a wire bar coating method, and an anchor layer having a thickness of 0.2 μm and an image receiving layer having a thickness of 3 μm are obtained. An image receiving sheet 1 comprising a layer and a protective layer having a thickness of 2 μm was obtained.

(Coating Solution for Forming Anchor Layer) Polyvinylacetoacetal (Eslec BL-1 manufactured by Sekisui Chemical Co., Ltd.) 9 parts Isocyanate (manufactured by Nippon Polyurethane Industry Co., Ltd., Coronate HX) 1 part Methyl ethyl ketone 80 parts Cyclohexanone 10 parts (Coating solution for forming image receiving layer) Polyvinyl butyral resin (Eslec BL-1 manufactured by Sekisui Chemical Co., Ltd.) 7 parts Metal ion supply compound (exemplified compound No. 19) 3 parts Polyester modified silicon (Shin-Etsu Chemical Co., Ltd.) 0.2 parts Dioctyl phthalate 0.2 parts Methyl ethyl ketone 79.6 parts Cyclohexanone 10 parts (Coating liquid for forming protective layer) Polyethylene wax emulsion (35% solid content) 20 parts (Toho Chemical Co., Ltd.) Industrial Co., Ltd., Hitec E1000) Water 80 parts <Thermal transfer recording> The obtained ink sheets 1 to 5 and the image receiving sheet 1 are superimposed, a thermal head is applied from the back of the ink sheet, printing is performed once by a thermal printer, and then superimposed on the same place and printing is performed twice. Thus, images 1 to 5 having gradation were obtained.

(Recording conditions) Recording density in main scanning and sub-scanning: 8 dots / mm Recording power: 0.075 W / dot Application time: 0 to 10 msec <Evaluation> After recording, the maximum density of an image and image storability are as follows. Was evaluated according to

(Maximum Density) The maximum transmission density of the vis region (usually, the portion where the application time was the maximum) was measured by X-write 310TR status A.

(Image preservability) The obtained image was irradiated with light for 5 days using a xenon fade meter, and the light resistance was evaluated. Incidentally, D dye residual ratio to density before light irradiation D _0, the density after light irradiation as D /
Expressed as D ₀ × 100.

The results obtained are shown in Table 1 below.

[0072]

[Table 1]

*: Ratio to the composition contained in the ink sheet (% by weight) As is clear from Table 1, the content of the sublimable dye is 50% by weight or more of the composition contained in the ink sheet. It can be seen that the images 1 to 4 obtained by using show high density even in a short time and have good image storability.

Example 2 (Claim 2) The dye-dyeability and dye-permeability of the protective layer and the image-receiving layer of the image-receiving sheet 1 obtained in Example 1 were measured under the following conditions, and the results are shown. .

<Dye Dyeing Property> The resins used for the protective layer and the image receiving layer are each coated on a separate support so as to have a thickness of 2 μm, and a commercially available ink sheet for thermal sublimation type thermal transfer recording is prepared. Thermal printing. Shows the concentration and dyeability at that time. For dyeing properties, apply a commercially available tape to the dye transfer part,
Evaluation was made by the ratio of the density after peeling to the original density.

Print density Dyeing property Polyethylene wax emulsion (protective layer): 1.14 73% Polyvinyl butyral resin (image receiving layer): 1.38 91% <Dye permeability> Obtained in Example 1 The protective layer on the image receiving layer of the obtained image receiving sheet 1 is changed as follows to obtain the image receiving sheet 1a.
To 1c were formed, and thermal printing was performed using the ink sheet 1 of Example 1 under the same conditions. The concentration at that time is shown.

Image receiving sheet 1a Image receiving layer Using polyvinyl butyral resin Protective layer None Image receiving sheet 1b Image receiving layer Using polyvinyl butyral resin Protective layer Using polyethylene wax emulsion Image receiving sheet 1c Image receiving layer Using polyvinyl butyral resin Protective layer Using polyvinyl butyral resin Use (KW-1 manufactured by Sekisui Chemical Co., Ltd.) The print density was 1.48 for 1a, 2.10 for 1b,
1c was 1.32.

As is evident from the results obtained, when the protective layer of the image receiving sheet has excellent dye permeability and is less dyeable than the image receiving layer, a sufficient print density can be obtained. I understand.

Example 3 (Claim 3) Using the ink sheet 1 and the image receiving sheet 1 produced in Example 1, a black image was produced in the same manner.
Image receiving sheets 2 to 5 were obtained in the same manner as in Example 1 except that the metal ion supplying compound of image receiving sheet 1 was changed to the following. Also, an image receiving sheet 6 was obtained in the same manner except that the metal ion supply compound of the image receiving sheet 1 was removed, and an image receiving sheet 7 was obtained in the same manner except that the protective layer of the image receiving sheet 1 was removed.

Further, the image receiving sheet 8 was formed in the same manner as in Example 1 except that the image receiving sheet was replaced with the following composition, and the image receiving sheet 9 was formed in the same manner except that the metal ion supply compound of the image receiving sheet 8 was removed. Image receiving sheet 10 was obtained in the same manner except that the protective layer of sheet 8 was removed. Using the obtained image receiving sheet and ink sheet 1, a black image was similarly produced.

<Preparation of Image Receiving Sheet> (Coating Solution for Forming Image Receiving Layer) 7.0 parts of vinyl chloride-isobutyl vinyl ether copolymer (manufactured by BASF, Laroflex MP25) Metal ion supply compound (Exemplary Compound No. 19) 3.0 parts Methyl ethyl ketone 80 parts Cyclohexanone 10 parts (Coating liquid for forming protective layer) Polyvinyl chloride (TK600, manufactured by Shin-Etsu Chemical Co., Ltd.) 9.5 parts Polyester modified silicon (supra) 0.5 part Methyl ethyl ketone 80 Part Cyclohexanone 10 parts <Thermal transfer recording> Ink sheet 1 and image receiving sheets 1 to 10
Then, a thermal head is applied from the back of the ink sheet under the same conditions as in Example 1, printing is performed once by a thermal printer, and then printing is performed twice by overlapping on the same portion. I got The evaluation was performed under the same conditions as in Example 1.

The results obtained are shown in Table 2 below.

[0083]

[Table 2]

*: Metal ion-supplying compound As is clear from Table 2, images 1 to 5 and 8 obtained by using an image-receiving sheet whose image-receiving layer contains a metal ion-supplying compound capable of chelating with a sublimable dye are shown in FIG. It can be seen that high density is exhibited even in a short time and image storability is good. In addition, even if it contains a metal ion supplying compound, an image receiving sheet having no protective layer causes a problem in image storability, which is not preferable in use.

Example 4 (Comparative Example) Each of Dye-1 to Dye-3 used in the ink sheet of Example 1 was separately prepared, coated on separate supports and dried to obtain yellow, magenta and cyan inks. A sheet was prepared. Then, the process of continuously superimposing three colors on the image receiving sheet 1 under the same recording conditions as in Example 1 was repeated twice to produce a black image having a maximum transmission density of 2.8. The recording time at this time required three times as long as the application time of Examples 1 to 3.

[0086]

According to the image forming method of the present invention, a remarkably excellent effect that an image having high density and good image storability can be obtained in a short time can be obtained.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating an image forming method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Ink sheet 2 Support 3 Ink layer 4 Image receiving sheet 5 Transmissive support 6 Image receiving layer 7 Protective layer 8 Thermal head

Claims (6)

[Claims] 1. An ink sheet containing at least two or more kinds of sublimable dyes and a transmissive image receiving sheet having a protective layer and an image receiving layer are superimposed on each other, and the same portion on the transparent image receiving sheet is heated by heating means. A method for forming an image by transferring an image pattern at least twice, wherein the content of the sublimable dye in the ink sheet is 50% by weight or more of the composition contained in the ink sheet. Forming method. 2. An ink sheet containing at least two or more kinds of sublimable dyes and a transmissive image receiving sheet having a protective layer and an image receiving layer are overlapped, and the same portion on the transparent image receiving sheet is heated by heating means. A method for forming an image by transferring an image pattern at least twice, wherein the protective layer of the transmissive image-receiving sheet is dye-permeable and has lower dye-dyeability than the image-receiving layer. . 3. An ink sheet containing at least two or more kinds of sublimable dyes and a transmissive image receiving sheet having a protective layer and an image receiving layer are superimposed on each other, and the same portion on the transparent image receiving sheet is heated by heating means. A method for forming an image by transferring an image pattern at least twice, wherein the image-receiving layer of the transparent image-receiving sheet contains a metal ion supply compound capable of chelating with the sublimable dye. . 4. The image forming method according to claim 3, wherein the metal ion supply compound has a concentration gradient. 5. The image forming method according to claim 1, wherein the transparent image receiving sheet is heated at least once before or after the transfer of the image pattern. 6. The image forming method according to claim 1, wherein in the transfer of the image pattern after the second time, only a portion where the density is not reached is printed by one printing. .