JP2013010312A - Image forming method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming method by which a printed matter with high color developing sensitivity is formed while preventing secret information from being recognized from a thermal transfer sheet that is subjected to thermal transfer and then is ejected.SOLUTION: The image forming method includes: a preparation step of preparing the thermal transfer sheet provided with a base material and a thermosensitive coloring layer which is provided on one surface of the base material, and which includes a leuco dye and a color developer and is peeled in a pixel shape when heating of the pixel shape is performed by a heating means on the other surface of the base material; a first heating step of lapping a first medium on a thermosensitive coloring layer side of the thermal transfer sheet, performing heating of the pixel shape by a first heating means on the other surface of the base material of the thermal transfer sheet and transferring the thermosensitive coloring layer peeled in the pixel shape from the base material onto the first medium; and a second heating step of forming a second medium by a second heating means on the thermosensitive coloring layer of the pixel shape transferred on the first medium.

Description

  The present invention relates to an image forming method for forming a printed matter, and in particular, relates to an image forming method capable of forming a printed matter having high coloring sensitivity, in which secret information is hardly recognized from a thermal transfer sheet discharged during image formation. .

  Currently, a thermal transfer method is widely used as a simple printing method. Since the thermal transfer method can easily form various images, it can be used in printed materials that require a relatively small number of copies, such as ID card creation, business photographs, personal computer printers, video printers, etc. It's being used.

  In this thermal transfer system, a heat-melting type ink ribbon or a sublimation type ink ribbon generally called a thermal transfer sheet is used (for example, Patent Document 1). The heat melting type ink ribbon is an ink ribbon provided with a heat melting colored layer. By heating the ink ribbon by a heating means such as a thermal head, the heat melting colored layer is melted and softened, and the transferred object is transferred. Transcribed above. On the other hand, a sublimation type ink ribbon is an ink ribbon provided with a color material layer. By heating the ink ribbon by a heating means such as a thermal head, the dye in the color material layer is sublimated and the dye is transferred. Transcribed above.

  As described above, since the thermal transfer method forms an image on the transfer target using a dedicated ink ribbon, after the image formation is performed on the transfer target, there is an ink ribbon that has a portion printed out. Will be discharged. When creating an ID card for identification, etc., the portion of the ink ribbon that is ejected may contain personal information that you want to keep secret, and personal information is easily known from the ejected ink ribbon. There was a risk that it would end up.

JP-A-7-314918

  However, at present, when an ink ribbon as described above is used in image formation by the thermal transfer method, it is not possible to prevent leakage of secret information. The present invention has been made in view of such a situation, and provides an image forming method capable of forming a printed matter with high coloring sensitivity, in which secret information is hardly recognized from a thermal transfer sheet discharged during image formation. This is the main issue.

  The present invention for solving the above problems is an image forming method, comprising a base material and one side of the base material, comprising a leuco dye and a developer, and on the other side of the base material A preparatory step of preparing a thermal transfer sheet provided with a thermal coloring layer that is peeled into pixels when the pixel is heated by heating means, and a first medium is superimposed on the thermal coloring layer side of the thermal transfer sheet In addition, a pixel-like heating is performed by a first heating unit on the other surface of the base material of the thermal transfer sheet, and the heat-sensitive color developing layer peeled off in a pixel shape from the base material is transferred onto the first medium. A heating step; and a second heating step of forming a second medium on the pixel-like thermosensitive coloring layer transferred onto the first medium by a second heating means. .

  Further, the first medium is an intermediate transfer medium, and the second heating step heats a surface of the intermediate transfer medium that is different from the surface onto which the thermosensitive coloring layer is transferred, by a second heating unit, It may be a step of re-transferring the pixel-like thermosensitive coloring layer transferred onto the intermediate transfer medium onto the second medium.

  Further, in the image forming method of the present invention, the second medium is a transparent protective layer, and the second heating step includes a pixel-like thermosensitive coloring layer and a transparent protective layer transferred onto the first medium. And the surface of the transparent protective layer that does not overlap with the thermosensitive coloring layer is heated by a second heating means to form a transparent protective layer on the thermosensitive coloring layer transferred onto the first medium. It may be a process.

  According to the image forming method of the present invention, it is possible to form a printed matter with high color development sensitivity while preventing secret information from being recognized from the thermal transfer sheet discharged after thermal transfer.

It is a typical sectional view showing the thermal transfer sheet concerning an embodiment of the invention. It is a typical sectional view showing the thermal transfer sheet concerning an embodiment of the invention. It is a figure for demonstrating a 1st heating process. It is a figure for demonstrating 1st Embodiment of a 2nd heating process. It is a figure for demonstrating 2nd Embodiment of a 2nd heating process.

  The image forming method of the present invention includes a base material and a leuco dye and a developer which are provided on one side of the base material, and are heated in a pixel-like manner by heating means from the other side of the base material. A thermal transfer sheet provided with a thermal coloring layer that is peeled in a pixel form when the thermal transfer sheet is prepared; a first medium is superimposed on the thermal coloring layer side of the thermal transfer sheet; The first heating step of heating the pixel-like shape by the first heating means from above and transferring the thermosensitive coloring layer peeled off from the base material to the pixel shape onto the first medium, and the second heating means And a second heating step of forming a second medium on the pixel-like thermosensitive coloring layer transferred onto the first medium. Hereinafter, each step of the image forming method of the present invention will be specifically described.

<Preparation process>
The preparatory step is provided on a base material and one side of the base material, and includes a leuco dye and a developer, and the pixel is heated by heating means from the other side of the base material. This is a step of preparing a thermal transfer sheet provided with a heat-sensitive color-developing layer that is peeled into a shape.

  As shown in FIG. 1, the thermal transfer sheet 1 prepared in this step includes a base material 2, a release layer 3 provided on one surface of the base material 2, and a heat sensitive provided on the release layer 3. And a coloring layer 4. The substrate 2 and the thermosensitive coloring layer 4 are essential components in the thermal transfer sheet 1, and the release layer 3 is an arbitrary component in the thermal transfer sheet 1.

  The thermosensitive coloring layer 4 contains a leuco dye and a developer, and is peeled into pixels when the pixel is heated from the other surface of the substrate by heating means.

(Base material)
The substrate 2 used for the thermal transfer sheet 1 is not particularly limited as long as it has a certain degree of heat resistance and strength, and a conventionally known material can be appropriately selected and used. Examples of the substrate 2 include a polyethylene terephthalate film, a 1,4-polycyclohexylenedimethylene terephthalate film, a polyethylene naphthalate film, and a polyphenylene sulfide having a thickness of about 0.5 to 50 μm, preferably about 1 to 10 μm. Film, polystyrene film, polypropylene film, polysulfone film, aramid film, polycarbonate film, polyvinyl alcohol film, cellophane, cellulose derivatives such as cellulose acetate, polyethylene film, polyvinyl chloride film, nylon film, polyimide film, ionomer film, etc. . Furthermore, each of these materials can be used alone, but may be used as a laminate in combination with other materials.

  Further, the base material 2 is preferably the same color or substantially the same color as the thermosensitive coloring layer 4, and when the thermosensitive coloring layer 4 is colorless, it is preferable to use a transparent film. On the other hand, when the thermosensitive coloring layer 4 is white opaque, for example, a white opaque film formed by adding a white pigment, a filler, or the like is used, or a back layer or a release layer described later is white. It is preferably opaque.

(Easy adhesion treatment)
Moreover, when providing the mold release layer 3 on the base material 2 as arbitrary structures, it is good also as performing an easily bonding process on the surface of the base material 2. FIG. The easy adhesion process is a process of forming an easy adhesion layer (not shown) between the substrate 2 and the release layer 3. As such an easy-adhesion layer, for example, those composed of aqueous acrylic, aqueous polyester and aqueous epoxy compound are preferable. The water-based acrylic is a water-soluble or water-dispersible acrylic resin, preferably having an alkyl acrylate or alkyl methacrylate as a main component, and the component is 30 to 90 mol% and copolymerized. Is preferred. The water-based polyester is a water-soluble or water-dispersible polyester resin, and examples of components constituting the polyester resin include polyvalent carboxylic acids and polyvalent hydroxy compounds. An aqueous epoxy compound is a compound containing an epoxy group that is water-soluble or water-dispersible, preferably water-soluble, and contains at least one, preferably two or more epoxy groups in the molecule. is there. Examples of such aqueous epoxy compounds include glycols, polyethers, glycidyl ethers of polyols, glycidyl esters of carboxylic acids, glycidyl-substituted amines, and the like, but glycidyl ethers are preferred. For the easy adhesion treatment, a method of forming an easily adhesive coating film on the surface of the substrate 2 is preferably used.

(Thermosensitive coloring layer)
On one surface of the substrate 2, a thermosensitive coloring layer 4 containing a leuco dye and a developer is provided directly or indirectly. The heat-sensitive color developing layer 4 is colorless or white opaque before transfer, and the leuco dye and the developer undergo a chemical reaction by heating during transfer, and the heated portion develops color. In the present invention, the heat-sensitive color developing layer 4 is peeled off from the base material 2 in a pixel shape and transferred onto the first medium 21 when the pixel-like heating is performed from above the base material 2 by heating means. The In the present invention, the term “pixel shape” means a shape corresponding to the print information of a finally produced printed material, and the shape is not limited in any way.

"Leuco dye"
The leuco dye contained in the thermosensitive coloring layer 4 is not particularly limited, and a conventionally known colorless or light leuco dye can be appropriately selected and used. For example,
(1) 3,3-bis (p-dimethylaminophenyl) -6-dimethylaminophthalide, 3- (p-dimethylaminophenyl) -3- (2-phenyl-3-indolyl) phthalide, 3- (p -Dimethylaminophenyl) -3- (1,2-dimethyl-3-indolyl) phthalide, 3,3-bis (9-ethyl-3-carbazolyl) -5-dimethylaminophthalide, 3,3-bis (2 -Triarylmethane compounds such as -phenyl-3-indolyl) -5-dimethylaminophthalide;
(2) Diphenylmethane compounds such as 4,4-bis (dimethylamino) benzhydrin benzyl ether and N-2,4,5-trichlorophenylleucooramine;
(3) 3-dibutylamino-6-methyl-7-bromofluorane, rhodamine-β-anilinolactam, 3- (N-methyl-N-cyclohexylamino) -6-methyl-7-anilinofluorane, 3-diethylamino-7-octylaminofluorane, 3-diethylamino-7- (2-chloroanilino) fluorane, 3-diethylamino-6-methyl-7-anilinofluorane, 3-diethylamino-6-methyl-7- ( 2,4-dimethylanilino) fluorane, 3-diethylamino-7-dibenzylaminofluorane, 3-diethylamino-6-chloro-7- (β-ethoxyethylamino) fluorane, 3-diethylamino-6-chloro-7 -(Γ-chloropropylamino) fluorane, 3- (N-ethyl-N-isoamylamino) -6-methyl Ru-7-anilinofluorane, 3- (N-ethyl-N-ethoxyethylamino) -6-methyl-7-anilinofluorane, 3- (N-ethyl-N-tetrahydrofurfurylamino) -6 -Methyl-7-anilinofluorane, 3- (N-ethyl-N-tolylamino) -6-methyl-7-anilinofluorane, 3-dibutylamino-6-methyl-7-anilinofluorane, 3 -Dibutylamino-7- (2-chloroanilino) fluorane, 3-dipentylamino-6-methyl-7-anilinofluorane, 3-piperidino-6-methyl-7-anilinofluorane, 3- (4-anilino) ) Xanthene compounds such as anilino-6-methyl-7-chlorofluorane;
(4) thiazine compounds such as benzoylleucomethylene blue and p-nitrobenzoylleucomethylene blue;
(5) Spiro compounds such as 3-methylspirodinaphthopyran, 3-ethylspirodinaphthopyran, 3-benzylspirodinaphthopyran, 3-methylnaphtho- (3-methoxybenzo) spiropyran;
(6) 3,5 ′, 6-tris (dimethylamino) -spiro [9H-fluorene-9,1 ′ (3′H) -isobenzofuran] -3′-one, 1,1-bis [2 -(4-Dimethylaminophenyl) -2- (4-methoxyphenyl) ethenyl] -4,5,6,7-tetrachloro (3H) isobenzofuran-3-one, etc. Or 2 or more types can be mixed and used.

  Although there is no limitation in particular about content of a leuco dye, about 10-35 mass% is common with respect to the solid content total amount of the thermosensitive coloring layer 4. FIG.

"Developer"
The developer is not particularly limited, and examples thereof include p-octylphenol, p-tert-butylphenol, p-phenylphenol, p-hydroxyacetophenone, α-naphthol, β-naphthol, p-tert-octylcatechol, 2,2′-dihydroxybiphenyl, bisphenol-A, 1,1-bis (p-hydroxyphenyl) butane, 2,2-bis (4-hydroxyphenyl) heptane, 2,2-bis- (3-methyl-4 -Hydroxyphenyl) propane, 2,2-bis (3,5-dimethyl-4-hydroxyphenyl) propane, 2,2-bis (3,5-dichloro-4-hydroxyphenyl) propane, bis (4-hydroxyphenyl) ) Sulfone, bis (3-allyl-4-hydroxyphenyl) sulfone, bis (3,4-dihydroxyphene) ) Sulfone, 2,4′-dihydroxyphenylsulfone, 1,1-bis (4-hydroxyphenyl) cyclohexane, bis (4-hydroxyphenyl) ether, bis [2- (4-hydroxyphenylthio) ethoxy] methane, Phenols such as 4- (4-isopropoxybenzenesulfonyl) phenol, dimethyl 4-hydroxyphthalate, butyl bis (4-hydroxyphenyl) acetate, benzyl p-hydroxybenzoate, 3,5-ditert-butylsalicylic acid Developers such as organic carboxylic acid systems such as benzoic acid; metal systems such as zinc salicylate; and anilide derivative systems such as 2,4-dihydroxy-N-2′-methoxybenzanilide. An agent can be used 1 type or in mixture of 2 or more types.

  Although there is no limitation in particular about the compounding ratio of a leuco dye and a color developer, about 1-10 mass parts of color developers are common with respect to 1 mass part of leuco dyes.

"Adhesive resin"
In the present invention, the heat-sensitive color developing layer 4 that is colored in a pixel shape is peeled off from the base material 2 in a pixel shape in the first heating step and transferred onto the first medium 21. Therefore, in the case where the thermosensitive coloring layer is provided on the uppermost surface of the thermal transfer sheet, good adhesion between the thermosensitive coloring layer 4 and the first medium 21 is required. Therefore, when no separate layer for improving the adhesiveness between the heat-sensitive color forming layer 4 peeled in a pixel shape and the first medium 21 is provided on the heat-sensitive color developing layer 4, it adheres to the heat sensitive color developing layer 4. It is preferable that a functional resin is contained.

  Examples of the adhesive resin include resins such as acrylic resins, vinyl chloride resins, vinyl acetate resins, vinyl chloride-vinyl acetate copolymer resins, styrene-acrylic copolymer resins, polyester resins, polyamide resins, and the like. It is done.

  When an adhesive resin is included in the thermosensitive coloring layer, the adhesive resin is preferably contained within a range of 10 to 50% by mass with respect to the total solid content of the thermosensitive coloring layer. By setting the content of the adhesive resin within the above range, the thermal coloring layer 4 is transferred onto the first medium 21 or re-transferred to the second medium 22 described later without reducing the coloring sensitivity of the thermal coloring layer. Adhesion during transfer can be ensured.

  In the present invention, a heat seal layer is provided directly on the heat-sensitive color developing layer 4 or indirectly through another layer without imparting adhesiveness to the heat-sensitive color developing layer 4. Adhesiveness between the medium 21 and the thermosensitive coloring layer 4 peeled in a pixel shape can be ensured. The heat seal layer will be described later.

"Other materials"
Moreover, you may add a sensitizer and a storage stabilizer to the thermosensitive coloring layer 4 as needed. Examples of the sensitizer include zinc acetate, zinc octylate, zinc laurate, zinc stearate, zinc oleate, zinc behenate, zinc benzoate, salicylic acid dodecyl ester zinc salt, calcium stearate, magnesium stearate, stearic acid. Metal salts of organic acids such as aluminum; amide compounds such as stearamide, stearic acid methylolamide, stearoyl urea, acetanilide, acetoluidide, benzoic acid stearylamide, ethylenebisstearic acid amide, hexamethylene bisoctylic acid amide; -Bis (3,4-dimethylphenyl) ethane, m-terphenyl, 1,2-diphenoxyethane, 1,2-bis (3-methylphenoxy) ethane, p-benzylbiphenyl, p-benzyloxybiphenyl, di Phenyl carbonate, bis (4-methylphenyl) carbonate, dibenzyl oxalate, bis (4-methylbenzyl) oxalate, bis (4-chlorobenzyl) oxalate, phenyl 1-hydroxy-2-naphthalenecarboxylate, 1-hydroxy Benzyl-2-naphthalenecarboxylate, phenyl 3-hydroxy-2-naphthalenecarboxylate, methylene dibenzoate, 1,4-bis (2-vinyloxyethoxy) benzene, 2-benzyloxynaphthalene, benzyl 4-benzyloxybenzoate, Examples thereof include dimethyl phthalate, dibenzyl terephthalate, dibenzoylmethane, and 4-methylphenoxy-p-biphenyl. These sensitizers can be used alone or in combination of two or more.

  Examples of the storage stabilizer include 1,1,3-tris (2-methyl-4hydroxy-5-tert-butylphenyl) butane and 1,1,3-tris (2-methyl-4-hydroxy-). 5-cyclohexylphenyl) butane, 4,4′-butylidenebis (2-tert-butyl-5-methylphenol), 4,4′-thiobis (2-tert-butyl-5-methylphenol), 2,2′- Hindered phenol compounds such as thiobis (6-tert-butyl-4-methylphenol) and 2,2′-methylenebis (6-tert-butyl-4-methylphenol), 4-benzyloxy-4 ′-(2- Methyl glycidyloxy) diphenyl sulfone, sodium-2,2′-methylenebis (4,6-ditert-butylphenyl) phosphate, and the like. Others can be used in combination of two or more.

  In addition to sensitizers and storage stabilizers, additives such as pigments, waxes, and antifoaming agents, and additives for arbitrarily coloring the thermosensitive coloring layer 4 are added as necessary. You can also.

  In the present invention, the heat-sensitive coloring layer 4 has a function of (i) coloring in a pixel shape when heating is performed in a pixel shape from the base material side, and (ii) a heated portion, That is, the pixel-colored portion has a function of peeling from the substrate. Various methods can be exemplified as a method for performing the function (ii), and there is no particular limitation. In the present invention, (1) the thermosensitive coloring layer 4 is made to contain a substance that enhances peelability during heating. Configuration, (2) a configuration in which a release layer is formed between the substrate 2 and the thermosensitive coloring layer 4, or (3) a pixel shape together with the thermosensitive coloring layer 4 between the substrate 2 and the thermosensitive coloring layer 4. The function (ii) can be achieved by the structure for forming the release layer transferred to the film. Details of the (2) release layer and (3) release layer will be described later.

(Thermal release agent or lubricant)
As (1) substances that enhance the releasability between the substrate 2 and the thermosensitive coloring layer, there are a substance that melts by heating and exhibits this performance, and a substance that works as a solid powder. Examples of the former include waxes such as polyethylene wax and paraffin wax, amides, esters and salts of higher fatty acids, and phosphate esters such as higher alcohols and lecithin. On the other hand, examples of the latter include Teflon (registered trademark), fluororesin such as polyvinyl fluoride, guanamine resin, boron nitride, silica, wood powder, talc and the like. Those that work as a solid powder can impart a protective function such as scratch resistance to the thermosensitive coloring layer 4 itself after transfer.

  The method for forming the thermosensitive coloring layer 4 is not particularly limited. For example, water is used as a dispersion medium, and a leuco dye, a developer, and, if necessary, an adhesive resin, a release agent, a lubricant, and a sensitizer. It can be formed by applying a coating solution prepared by mixing and stirring a preservability improving agent and the like onto the substrate 2 and drying.

  The thickness of the thermosensitive coloring layer 4 is not particularly limited, but is preferably about 3.0 to 10.0 μm.

(Release layer)
In the present invention, instead of (1) the thermosensitive coloring layer 4 containing a release agent or lubricant, as shown in FIG. 1, (2) a release layer is provided between the substrate 2 and the thermosensitive coloring layer. It can also be set as the provided structure.

  The release layer 3 is a layer that melts at the time of thermal transfer to improve the peelability of the thermosensitive coloring layer 4 from the substrate 2 and remains on the substrate 2 after transfer. Examples of the release layer 3 include an acrylic resin, a urethane resin, a resin obtained by modifying each of these resins with silicone, a polyvinyl acetal resin, a polyvinyl alcohol resin, or a mixture thereof, but is not limited thereto. Absent. The thickness of the release layer is about 0.1 to 5.0 μm.

(Peeling layer)
In the present invention, instead of (1) the configuration in which the thermosensitive coloring layer 4 contains a release agent or a lubricant, and (2) the configuration in which a release layer is formed between the base material and the thermosensitive coloring layer, in the present invention, FIG. As shown in FIG. 2, (3) a configuration in which a release layer 6 is provided between the substrate 2 and the thermosensitive coloring layer 4 can also be adopted.

As the wax, various waxes that melt upon heating and exhibit releasability are preferable. Suitable waxes include, for example, microcrystalline wax, carnauba wax, paraffin wax, Fischer-Tropsch wax, various low molecular weight polyethylene, wood wax, beeswax, whale wax, ibota wax, wool wax, shellac wax, candelilla wax, Various waxes such as petrolactam, partially modified wax, fatty acid ester, fatty acid amide and the like can be mentioned. Particularly preferred waxes are microcrystalline wax and carnauba wax which have a relatively high melting point and are hardly soluble in a solvent. The release layer is preferably a thin layer, for example, about 0.1 to ² g / m ² in a dry state so as not to reduce the sensitivity of the thermal transfer sheet.

(Heat seal layer)
In addition, a heat seal layer for improving the adhesion between the heat-sensitive color forming layer 4 and the first medium 21 peeled in a pixel shape at the time of transfer is directly on the heat-sensitive color developing layer 4 or indirectly through another layer. It is good also as providing (not shown). Note that, as described above, in the case of imparting adhesiveness to the thermosensitive coloring layer 4, the layer is unnecessary, and therefore the heat seal layer is an arbitrary layer. The heat seal layer is preferably formed from a material having transparency and adhesiveness. For example, acrylic resin, vinyl resin, polyester resin, urethane resin, polyamide resin, epoxy resin, rubber resin A conventionally known adhesive mainly composed of a resin, an ionomer resin or the like can be widely used. Although there is no limitation in particular about the film thickness of a heat seal layer, it is preferable that it is the range of 0.1-50 micrometers, and 1-10 micrometers is more preferable.

(Back layer)
Further, when a material lacking durability against high heat is used as the base material 2, the surface of the base material 2 on the side in contact with the heating means, for example, the thermal head, that is, the surface on which the thermosensitive coloring layer 4 of the base material is provided. It is preferable to provide a back layer (not shown) for improving the slipperiness of the thermal head and preventing sticking on the opposite surface. The back layer includes a heat-resistant resin and a heat release agent or a substance that functions as a lubricant as basic constituent components. By providing such a back layer, for example, thermal printing can be performed without causing sticking even in a thermal transfer sheet using a heat-sensitive plastic film as a base material 2, and the plastic film is difficult to cut and processed. Benefits such as ease of use. Furthermore, blocking when the thermal transfer sheet 1 of the present invention is wound into a roll can be prevented.

  The back layer can be formed by suitably using a binder resin to which a slip agent, a surfactant, inorganic particles, organic particles, a pigment and the like are added. Binder resins used in the back layer are, for example, cellulose resins such as ethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, methyl cellulose, cellulose acetate, cellulose acetate butyrate, and nitrified cotton, polyvinyl alcohol, polyvinyl acetate, polyvinyl butyral, and polyvinyl acetal. , Polyvinyl pyrrolidone, acrylic resin, polyacrylamide, vinyl resins such as acrylonitrile-styrene copolymer, polyester resin, polyurethane resin, silicone-modified or fluorine-modified urethane resin, and the like.

Among these, it is preferable to use a crosslinked resin using several reactive groups, for example, those having a hydroxyl group, and using a polyisocyanate or the like as a crosslinking agent. The means for forming the back layer is as described above, by dissolving or dispersing a material obtained by adding a slip agent, a surfactant, inorganic particles, organic particles, pigments, etc. to a binder resin in an appropriate solvent, The coating solution is coated by a conventional coating means such as a gravure coater, roll coater, wire bar, etc., and dried. The coating amount of the back layer is usually about 0.01 to 10 g / m ^{2 in} a dry state.

<First heating step>
In the first heating step, the first medium 21 is superposed on the thermal coloring layer 4 side of the thermal transfer sheet 1, and pixel-like heating is performed by the first heating means 11 from the other side of the base material of the thermal transfer sheet 1. In this step, the thermosensitive coloring layer 4 peeled off from the substrate in a pixel shape is transferred onto the first medium 21. Hereinafter, the first heating step will be specifically described with reference to FIG.

  In the first heating step, first, as shown in FIG. 3A, the first medium 21 is superposed on the thermal coloring layer 4 side of the thermal transfer sheet 1, and from the other side of the base material of the thermal transfer sheet 1. Heating is performed in a pixel shape by the first heating means 11.

(First medium)
The first medium 21 superimposed on the thermal transfer sheet is not particularly limited, and examples of the first medium include plain paper, high-quality paper, tracing paper, plastic film, and thermal transfer image receiving paper. Further, the first medium 21 may have a single layer structure or a laminated structure as shown in the figure. In addition, an intermediate transfer medium or the like that can transfer the pixel-like thermosensitive coloring layer 4 transferred thereon onto the second medium can be used as the first medium 21.

  Examples of the intermediate transfer medium that can be used as the first medium 21 include, but are not limited to, a configuration in which a release layer is provided on a base sheet. The release layer can be formed in the same manner as the release layer, which is an arbitrary configuration of the above-described thermal transfer sheet. When such a release layer is provided, when the pixel-like thermosensitive coloring layer 4 transferred onto the intermediate transfer medium is retransferred onto the second medium in the second heating step described later, The peeling layer is also transferred together with the pixel-like thermosensitive coloring layer 4, and after the transfer, it functions as a protective layer for the pixel-like thermosensitive coloring layer 4.

  Examples of the first heating unit 11 include a thermal plate constituting a conventionally known thermal transfer printer, a hot plate, a hot stamper, a hot roll, a line heater, and an iron.

  Although there is no limitation in particular about heating temperature, about 100-200 degreeC is preferable.

  By performing pixel-like heating from the other surface of the base material 2 of the thermal transfer sheet 1 by the first heating means 11, as shown in FIG. 3 (b), the thermosensitive coloring layer 4 is colored in pixels. At the same time, it is peeled off from the substrate 2. Further, the pixel-like thermosensitive coloring layer 4 peeled from the substrate 2 is transferred onto the first medium 21. In FIG. 3B, the heat-sensitive color developing layer 4 that is colored like a pixel is indicated by diagonal lines.

  FIG. 3 (c) shows a view of the thermal transfer sheet 1 after the first heating step as viewed from the thermal color developing layer 4 side. As shown in FIG. 3 (c), the thermal transfer sheet discharged after the first heating step has no colored portion, and only the non-colored thermal coloring layer 4 remains on the substrate 2. The configuration will be as follows. The remaining heat-sensitive color developing layer 4, that is, the heat-sensitive color developing layer 4 before heating, is colorless or white-opaque. Therefore, even when the heat transfer sheet 1 after transfer is viewed from the heat-sensitive color developing layer 4 side, discrimination of pixel information It becomes difficult. Therefore, according to the image forming method of the present invention including the step, it is possible to prevent the secret information from being recognized from the thermal transfer sheet discharged after the thermal transfer.

  As described above, in the first heating step, pixel-like heating is performed by the first heating unit 11 from the other surface of the base material of the thermal transfer sheet 1. In other words, the heating for causing the thermosensitive coloring layer 4 to develop a pixel shape is performed through the substrate 2. Therefore, when the base material 2 is thick or when the thermal conductivity of the base material 2 is low, the coloring sensitivity of the thermosensitive coloring layer is low, which may be insufficient from the viewpoint of coloring sensitivity.

  Further, when the thermosensitive coloring layer 4 transferred in a pixel shape on the first medium in the first heating step is located on the outermost surface of the printed matter, the coloring sensitivity is lowered due to the influence of moisture or the like. Can also occur.

  Therefore, in the present invention, by performing the second heating step, the color development sensitivity of the thermosensitive color developing layer 4 is increased, and the second medium is provided on the thermosensitive color developing layer 4, so that the heat sensitive color is affected by moisture and the like. The color development sensitivity of the color development layer 4 is prevented from decreasing. Hereinafter, the second heating step will be described.

<Second heating step>
The second heating step is a step of forming the second medium on the pixel-like thermosensitive coloring layer transferred onto the first medium by the second heating means. In the present invention, the following implementation is performed. The method of the form can be preferably used.

(I) First Embodiment The first embodiment in which the second medium is formed on the thermosensitive coloring layer 4 provided on the first medium is the first medium 21 used in the first heating step. Is an embodiment in the case of the intermediate transfer medium 21 </ b> A composed of the base material 25 and the release layer 26. Specifically, as shown in FIG. 4A, the second medium 22 and the heat-sensitive color developing layer 4 transferred onto the intermediate transfer medium 21A by the first heating step are overlapped to obtain an intermediate transfer medium. In this embodiment, a surface different from the surface onto which the 21A thermosensitive coloring layer 4 has been transferred is heated by a second heating means. In this embodiment, the surface to which the thermosensitive coloring layer 4 of the intermediate transfer medium 21A has been transferred by the second heating means 12 so that the printed matter finally produced has the form shown in FIG. 4B. It is good also as heating a different surface. In this case, the print 100 to be finally produced is formed on the second medium 22, the pixel-like thermosensitive coloring layer 4 formed on at least a part of the second medium 22, and the thermosensitive coloring layer 4. The peeling layer 26 to be formed has a configuration in which they are laminated in this order. Further, a surface different from the surface onto which the heat-sensitive color forming layer 4 of the intermediate transfer medium 21A has been transferred by the second heating means 12 so that the printed matter finally produced has the form shown in FIG. 4C. It is good also as heating. In this case, the print 100 to be finally produced includes the second medium 22, the pixel-like thermosensitive coloring layer 4 formed on at least a part of the second medium 22, the second medium 22, and the thermosensitive coloring. The release layer 26 formed so as to cover the layer 4 is laminated in this order.

  According to the first embodiment, when the thermal coloring layer 4 is re-transferred onto the second medium 22, heat from the second heating unit is applied to the thermal coloring layer 4 from the back side of the intermediate transfer medium 21A. Therefore, the color development sensitivity of the thermosensitive color development layer 4 can be increased.

  In the printed product finally produced in the embodiment, the release layer 26 is provided on one surface of the thermosensitive coloring layer 4, and the second medium 22 is provided on the other surface. Therefore, the coloring sensitivity of the thermosensitive coloring layer 4 whose coloring sensitivity has been increased in the second heating step is not lowered.

(I) Second Embodiment As shown in FIG. 5A, a second embodiment in which the second medium 22 is formed on the thermosensitive coloring layer 4 provided on the first medium 21 is as follows. The protective layer transfer sheet 50 in which the transparent protective layer 53 as the second medium is provided on the base sheet 51, and the thermosensitive coloring layer 4 transferred to the first medium 21 by the first heating step. This is an embodiment in which heating is performed by the second heating means 12 from the base material sheet 51 side of the overlapping and protective layer transfer sheet. According to this embodiment, the transparent protective layer 53 is transferred onto the thermosensitive coloring layer 4 transferred onto the first medium 21 as shown in FIG. 5B by the second heating step. In FIG. 5B, the transparent protective layer 53 is formed so as to cover the second medium 22 and the thermosensitive coloring layer 4, but the transparent protective layer 53 is transferred only on the thermosensitive coloring layer 4. Thus, the base sheet 51 side of the protective layer transfer sheet may be heated by the second heating means 12.

  According to the second embodiment, when the transparent protective layer 53 as the second medium is transferred onto the thermosensitive coloring layer 4, heat from the second heating means is applied to the thermosensitive coloring layer 4. The color development sensitivity of the color development layer 4 can be increased. The printed matter formed by this method is a first medium 21, a pixel-like thermosensitive coloring layer 4 provided on the first medium 21, and a second medium covering the pixel-like thermosensitive coloring layer 4. The transparent protective layer 53 is configured to be laminated in this order. Therefore, since the thermosensitive coloring layer 4 with increased coloring sensitivity is protected by the first medium 21 and the transparent protective layer 53, the coloring sensitivity of the thermosensitive coloring layer 4 is prevented from being lowered due to the influence of moisture or the like. can do.

"Transparent protective layer"
The protective layer transfer sheet 50 is not particularly limited, and a conventionally known one that has a transparent protective layer and has a function capable of transferring the transparent protective layer 53 by the second heating means 12 is appropriately selected. Can be used. For example, as shown in FIG. 4, a base sheet 51, a release layer 52, and a transparent protective layer 53 are laminated in this order, and the transparent protective layer 53 is covered by heating from the back side of the base sheet 51. A protective layer transfer sheet that can be transferred to a transfer member can be used, but the present invention is not limited to this configuration. For example, the release layer described above may be used instead of the release layer 52.

  The transparent protective layer 53 is made of a material having transparency so that the heat-sensitive color forming layer 4 colored in a pixel shape covered with the transparent protective layer 53 can be seen. Examples of such materials include polyethylene, polypropylene, polyvinyl fluoride, polyvinylidene fluoride, polyvinyl chloride, polyvinylidene chloride, ethylene-vinyl alcohol, polyvinyl alcohol, polymethyl methacrylate, polymethyl acrylate, polyether sulfone, and polyester. Examples include ether ketone, polyamide, tetrafluoroethylene-perfluoroalkyl vinyl ether, polyethylene terephthalate, and polyimide.

  In order to improve the adhesion between the transparent protective layer 53 and the thermosensitive coloring layer 4, it is preferable to use a protective layer transfer sheet 50 having a configuration in which an adhesive layer is laminated on the transparent protective layer 53. In addition, when the transparent protective layer itself has adhesiveness with the thermosensitive coloring layer 4, an adhesive layer is unnecessary.

  Further, in the above, the transparent protective layer 53 is transferred using the protective layer transfer sheet 50. However, the thermal transfer sheet 1 described above is provided with the heat-sensitive color developing layer 4 and the transparent protective layer 53 in the surface order. It is possible to transfer the heat-sensitive color developing layer 4 and the transparent protective layer 53 together by using this single thermal transfer sheet.

  Examples of the second medium 22 that can be used in the second embodiment include plain paper, high-quality paper, tracing paper, plastic film, thermal transfer image-receiving paper, and the like, which are conventionally known as transfer objects. The medium 22 is not particularly limited.

  Examples of the second heating means 12 include a thermal plate constituting a conventionally known thermal transfer printer, a hot plate, a hot stamper, a hot roll, a line heater, and an iron. The second heating unit 12 may be the same heating unit as the first heating unit 11 or a different heating unit.

  Although there is no limitation in particular about heating temperature, about 100-200 degreeC is preferable.

  According to the image forming method of the present invention described above, since the colored portion does not remain on the thermal transfer sheet discharged after image formation, confidential information is prevented from being recognized from the thermal transfer sheet discharged after thermal transfer. be able to. Furthermore, since the heat-sensitive color layer 4 transferred onto the first medium 21 is heated again, the color sensitivity of the heat-sensitive color layer 4 can be increased.

  Although the image forming method of the present invention has been described above, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention.

Next, an Example is given and this invention is demonstrated further more concretely.
Example 1
A 4.5 μm thick biaxially stretched polyethylene terephthalate film (manufactured by Toray Industries, Inc., Lumirror) is used as a base sheet, and a coating solution for the back layer having the following composition is applied to one side of the base sheet as a wire bar. By the coating method, it apply | coated so that the application quantity at the time of drying might be 1.0 g / m < ² >, and it dried (100 degreeC for 60 second), and formed the back layer. Next, on the surface opposite to the surface on which the back surface layer of the base material sheet is formed, a coating solution for a release layer having the following composition is applied to a dry coating amount of 1.0 g / m ² by a wire bar coating method. It is applied and dried (80 ° C. for 60 seconds) to form a release layer, and a thermal coloring layer coating solution having the following composition is further formed on the release layer by a wire bar coating method. The thermal transfer sheet of Example 1 was prepared by applying and drying so that the coating amount was 3.0 g / m ² (50 ° C. for 120 seconds) to form a thermosensitive coloring layer.

(Back layer coating liquid)
・ Acrylic nitrile-styrene copolymer 11 parts ・ Linear saturated polyester resin 0.3 part ・ Zinc stearyl phosphate 6 parts ・ Melamine resin powder 3 parts ・ Toluene / ethanol = 50/50 (mass ratio) 80 parts

(Release layer coating solution)
40 parts of silicone-modified acrylic resin having an epoxy group (Cell Top 226, manufactured by Daicel Chemical Industries, Ltd., solid content 50%)
・ Aluminum catalyst 10 parts (Cell Top CAT-A, manufactured by Daicel Chemical Industries, solid content 10%)
-Polyester resin 1.05 parts (Byron 220, glass transition point 67 ° C, number average molecular weight 3000, manufactured by Toyobo Co., Ltd.)
・ Methyl ethyl ketone 24 parts ・ Toluene 24 parts

(Coating solution for thermosensitive coloring layer)
The following A liquid and B liquid were pulverized and adjusted in a sand mill until each particle size became 1 μm, and A liquid and B liquid were blended.
(Liquid A)
・ 3-Dibutylamino-6-methyl-7-bromofluorane 3 parts ・ Polyvinyl alcohol 10% solution 15 parts ・ Water 30 parts (Liquid B)
・ Bisphenol-A 3.5 parts ・ P-benzylbiphenyl 0.5 part ・ Polyvinyl alcohol 10% solution 15 parts ・ Vinyl chloride-vinyl acetate copolymer emulsion 10% solution 10 parts Water 50 parts

(Preparation of protective layer transfer sheet)
Instead of the heat-sensitive color forming layer formed on the release layer in the thermal transfer sheet of Example 1, the coating amount for the transparent protective layer having the following composition is applied on the release layer by the wire bar coating method, and the coating amount at the time of drying is Except that a transparent protective layer was formed by applying and drying to 100 g / m ² (100 ° C. for 60 seconds), the back layer, the base sheet, the release layer were separated in the same manner as in the thermal transfer sheet of Example 1. A protective layer transfer sheet in which a mold layer and a transparent protective layer were laminated in this order was produced.

(Coating liquid composition for transparent protective layer)
・ Acrylic resin 3 parts ・ Vinyl chloride-vinyl acetate copolymer 10 parts ・ Acrylic acid ester copolymer 10 parts ・ Silica 1.5 parts ・ Polyethylene wax 0.1 part ・ Toluene / methyl ethyl ketone = 50/50 (mass ratio) 80 copies

  Using a thermal transfer sheet of Example 1 and using a printer for evaluation capable of printing under the following printing condition 1, in a 22.5 ° C. and 40% RH environment, on a transfer material comprising a card substrate having the following composition: In addition, the character pattern “DNP” (12 points) is printed under the following printing condition 1, and further, the protective layer transfer sheet prepared above is used to protect the entire printed matter under the following printing condition 1. A layer was provided to produce the print of Example 1.

(Printing condition 1)
Thermal head: KGT-217-12MPL20 (manufactured by Kyocera Corporation)
-Heating element average resistance: 3195 (Ω)
・ Print density in the main scanning direction: 300 dpi
-Sub-scanning direction printing density: 300 dpi
-Applied power: 0.13 (w / dot)
・ One line cycle: 5 (msec)
-Printing start temperature: 40 (° C)

(Material composition of card substrate)
-100 parts of polyvinyl chloride compound (degree of polymerization 800) (contains about 10% of additives such as stabilizers)
・ White pigment (titanium oxide) 10 parts ・ Plasticizer (DOP) 0.5 parts

(Example 2)
A transparent polyethylene terephthalate having a thickness of 12 μm was used as a base sheet, and a coating solution for a release layer having the following composition was applied to one surface of the base sheet by a wire bar coating method, and the coating amount when dried was 0.8 g / It is applied and dried so as to be m ² (80 ° C. for 60 seconds) to form a release layer, and on the release layer, a coating solution for a receiving layer having the following composition is formed by a wire bar coating method. The intermediate transfer medium was produced by applying and drying so that the application amount was 1.5 g / m ² (100 ° C. for 60 seconds) to form a receiving layer.

(Coating solution for release layer)
・ Acrylic resin 88 parts ・ Polyester resin 1 part ・ Polyethylene wax 11 parts ・ Toluene / methyl ethyl ketone = 50/50 (mass ratio) 100 parts

(Coating fluid for receiving layer)
・ Vinyl chloride-vinyl acetate copolymer 40 parts ・ Acrylic silicone 2.0 parts ・ Toluene / methyl ethyl ketone = 50/50 (mass ratio) 100 parts

  Using the thermal transfer sheet of Example 1, the “DNP” character pattern (12 points) was printed on the intermediate transfer medium prepared above under the above-mentioned printing condition 1, and the printed intermediate transfer medium was The printed matter of Example 2 was prepared by retransferring onto a white PVC card under the retransfer conditions described above.

(Retransfer conditions)
Laminator: Lami Packer LPD3212 (manufactured by Fuji Plastics)
Temperature: 150 ° C
Speed: 0.8 (set value)

(Comparative Example 1)
Using the thermal transfer sheet of Example 1, the alphabet of “DNP” (12-point gothic) was printed on a white PVC card under the printing conditions of Example 1 to produce a print of Comparative Example 1. .

(Comparative Example 2)
Instead of the heat-sensitive color developing layer coating solution of Example 1, a colored layer coating solution having the following composition was applied by a wire bar coating method, dried and colored to 1.0 g / m ^2. A layer is formed to produce a thermal transfer sheet. Using the thermal transfer sheet, the alphabet of “DNP” (12-point gothic) is printed on a white PVC card under the printing condition 1 above. Two prints were made.

(Coloring layer coating solution)
17.4 parts of colorant (carbon black dispersant, solid content 46%, blended with carbon black 40%, dispersant 6%, toluene / ethyl acetate = 1/1)
-Vinyl chloride-vinyl acetate copolymer 33.3 parts (Brand name Solvein CL, solid content 30%, glass transition point 75 ° C., weight average molecular weight 20000, manufactured by Nissin Chemical Industry Co., Ltd.)
Amine-modified acrylic resin 2.47 parts (solid content 45%, glass transition point 90 ° C., weight average molecular weight 45000, manufactured by DIC)
・ Toluene / methyl ethyl ketone = 50/50 (mass ratio) 46.83 parts

(Visibility evaluation)
In each Example and Comparative Example, the thermal transfer sheet after printing was visually confirmed, and a visibility evaluation test was performed based on the following evaluation criteria. The evaluation results are shown in Table 1.
"Evaluation criteria"
○: Character information cannot be read from the thermal transfer sheet after printing.
X: Character information can be read from the thermal transfer sheet after printing.

(Print evaluation)
The surface of the printed material of each Example and Comparative Example was visually confirmed, and printing evaluation was performed based on the following evaluation criteria. The evaluation results are also shown in Table 1.
"Evaluation criteria"
○: The density is high and the letters are clear.
(Triangle | delta): Although a density | concentration is thin, it can read.
X: Color development sensitivity is low and cannot be read.

  As is clear from Table 1, in Examples 1 and 2, the character information could not be read from the thermal transfer sheet discharged when the printed material was formed, and a good secret information leakage preventing effect was exhibited. Further, in Example 1, when the transparent protective layer is transferred onto the printed material, in Example 2, when the printed material is retransferred onto the transfer target, the printed portion is heated again. As a result, it was possible to form a printed matter with high color development sensitivity in which the color development sensitivity of the printing portion was increased. On the other hand, Comparative Example 1 in which the print portion was not heated again resulted in inferior color development sensitivity to the Examples. Further, in Comparative Example 2 in which the printed matter was formed without using the thermosensitive coloring layer, the character information could be read from the thermal transfer sheet discharged at the time of forming the printed matter, and the secret information leakage preventing effect could be exhibited. Absent.

DESCRIPTION OF SYMBOLS 1 Thermal transfer sheet 2 Base material 3 Release layer 4 Thermosensitive coloring layer 6, 26 Peeling layer 11 First heating means 12 Second heating means 21 First medium 21A Intermediate transfer medium 22 Second medium 25, 51 Base sheet 50 Protective layer transfer sheet 52 Release layer 53 Transparent protective layer 100 Printed matter

Claims (3)

An image forming method comprising:
A base material is provided on one surface of the base material, contains a leuco dye and a developer, and is peeled into a pixel shape when heated by a heating means from the other surface of the base material. A preparation step of preparing a thermal transfer sheet provided with a thermosensitive coloring layer;
A first medium is overlaid on the heat-sensitive color developing layer side of the thermal transfer sheet, and pixel-like heating is performed from the other surface of the base material of the thermal transfer sheet by first heating means, and the pixel form is peeled off from the base material. A first heating step of transferring the heat-sensitive color forming layer onto the first medium;
A second heating step of forming a second medium on the pixel-like thermosensitive coloring layer transferred onto the first medium by a second heating means;
An image forming method comprising: The first medium is an intermediate transfer medium;
In the second heating step, a surface different from the surface on which the thermosensitive coloring layer of the intermediate transfer medium is transferred is heated by a second heating means, and transferred onto the intermediate transfer medium onto the second medium. 2. The image forming method according to claim 1, wherein the image forming method is a step of retransferring the pixel-like thermosensitive coloring layer. The second medium is a transparent protective layer,
In the second heating step, the pixel-like heat-sensitive color-developing layer transferred onto the first medium and the transparent protective layer are superposed, and the surface side of the transparent protective layer that does not overlap the heat-sensitive color-developing layer is second heated. The image forming method according to claim 1, wherein the image forming method is a step of forming a transparent protective layer on the heat-sensitive color developing layer which is heated by means and transferred onto the first medium.

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