JP3380304B2 - Transfer sheet for overcoat and overcoat method - Google Patents

Description

Detailed Description of the Invention

[0001]

The present invention relates to a recording sheet,
TECHNICAL FIELD The present invention relates to a transfer sheet for an overcoat and an overcoat method for providing a recording sheet having an overcoat layer, which has high image quality, good color reproducibility, excellent gloss or matteness, and excellent water resistance and chemical resistance. It is a thing.

[0002]

2. Description of the Related Art As recording means for image or character information, various recording methods such as printing, silver salt photography, electrophotography, ink jet, fusion thermal transfer, sublimation type thermal transfer are known. In all recording methods, protection of the recording surface (water resistance, chemical resistance, scratch resistance, weather resistance, etc.) is one of the most important requirements along with image reproducibility.

Another important requirement is glossing of the recording surface. This is also a method of alleviating the non-uniformity of the recording surface.For example, a multicolored part of printing, a multicolored part of ink jet recording, a multicolored part of sublimation type or melting type thermal transfer recording, etc., is clearly a monochromatic part Compared with the non-recorded portion, it is different in terms of gloss, surface roughness, texture and the like. Such non-uniformity of the recording surface remarkably changes the glossy feeling of the recording surface when the recording surface is directly viewed or is viewed obliquely, which is not preferable.

As a means for protecting or homogenizing the recording surface, it has been conventionally practiced to provide a laminate layer on the recording surface. However, for example, although melt-lamination of polyethylene can achieve protection of the recording surface, glossing of the recording, and homogenization of the recording, there is a limit to the thickness that can be stably laminated, and in particular, a thin film is formed in consideration of adhesive strength (for example, A thickness of 10 μm or less) was difficult.
Therefore, there is a problem that curling is likely to occur after lamination depending on the thickness and rigidity of the recording material. Further, in the melt laminating, since the thinness is limited as described above, glare is generated on the surface depending on the viewing direction, which is not preferable for some applications. Further, when a non-woven fabric or the like is used as a support for the recording surface, if a laminate layer is provided thereon, not only curl but also the texture of the non-woven fabric is lost, which is a material problem.

When the thickness of the laminate is reduced in order to suppress the deterioration of image quality and glare, problems such as pinholes and weak adhesion between the laminate layer and the image receiving layer and peeling of the laminate cannot be avoided. .
In addition to the method of melt-laminating polyethylene or polypropylene, there is a method of laminating polyethylene film or polypropylene film by laminating. Even with these methods, uneven gloss unevenness on the recording sheet and weak solvent resistance can be eliminated, but the thickness of the laminating layer is too thick, which lowers the image quality that is most important, and causes unpleasant glare. However, there are drawbacks such as occurrence of curling and curling, and discoloration and bleeding due to a reaction between an adhesive component and an ink component on a recording surface during bonding.
Further, in the varnishing performed in the printing industry, it is not environmentally preferable from the viewpoint of using a solvent, and the use of varnishing by a method such as emulsion or UV / EB curing is limited in terms of the equipment. there were.

[0006]

Therefore, the problems to be solved by the present invention are that the recording sheet does not deteriorate the image quality, has high glossiness, water resistance, chemical resistance,
An object of the present invention is to provide a transfer sheet for overcoat, which easily provides a recording sheet having an overcoat layer having weather resistance and curl resistance.

[0007]

[Means for Solving the Problems] As a result of earnest research on means for solving the above problems, the following method has been found. That is, it is an invention of an overcoat transfer sheet characterized in that a transfer layer comprising a thermoplastic resin having a melting point lower than the softening point of the heat resistant sheet and a binder is provided on the surface of the heat resistant sheet. The surface of the heat-resistant sheet that is in contact with the transfer layer may be glossy or matte. An ultraviolet absorber may be contained in the transfer layer of the transfer sheet for overcoat. The thermoplastic resin used for the overcoat transfer sheet is preferably fine particles having an average particle diameter of 0.1 to 10 μm from the viewpoint of curl control. Further, the coating amount of the thermoplastic resin in the transfer layer is preferably 1 to 10 g / m ² in terms of solid content. The surface of the transfer overcoat layer may be glossed or matted.

In the overcoating method of the present invention, the transfer layer surface of the transfer sheet for overcoating is superposed on the recording surface of the recording sheet on which the recording image is recorded on the recording material, and the resultant is thermocompression bonded to form the transfer layer. It is possible to form an overcoat layer having a transparent and uniform surface by transferring it onto the recording surface.

Such a transfer sheet for overcoat can be produced by coating a heat resistant sheet with an overcoat layer composition containing a thermoplastic resin (mainly a polyolefin resin) and a binder as main components.

The present invention will be described in detail below. The resin forming the transfer layer used in the present invention is preferably a thermoplastic resin, and particularly preferably polyethylene or polypropylene. The thermoplastic resin is preferably 1
It is preferable that the slurry is a plastic pigment produced by emulsion polymerization from one or more vinyl monomers, or a dried product thereof, or a powder obtained by crushing solid plastic by various means into fine powder or fine particles. .

The size of these thermoplastic resin fine particles is usually preferably 0.1 to 50 μm in diameter for forming a film. Other thermoplastic resins having an ester bond include ethylene / vinyl acetate copolymers, polyester resins, polyacrylic ester resins,
Polycarbonate resin, polyvinyl acetate resin, styrene acrylate resin, etc. are available. Polyurethane resin having urethane bond, polyamide resin (nylon), urea having amide bond. As a resin having a bond, a urea resin or the like can be used, and as a copolymer containing at least one of the constitutional units of the above resin as a main component, for example, vinyl chloride-vinyl acetate copolymer, styrene-butadiene copolymer, etc. It is also possible to use them, and further to use the above resins alone or in combination of two or more kinds.
Any of the above thermoplastic resins can be preferably used for the purpose of the present invention, but from the viewpoint of the melting point of each thermoplastic resin and the heat resistance of the heat resistant sheet, polyethylene, polypropylene and the like are most suitable.

The melting point of the thermoplastic resin forming the transfer layer is preferably 165 ° C. or lower from the viewpoint of preventing thermal blurring of a recorded image. The thickness of the transfer overcoat layer depends on the material and surface roughness of the recording surface, but is preferably 1 to 30 μm. Here, if the thickness of the transfer overcoat layer is smaller than this range, it becomes difficult to uniformly cover the image receiving layer, and problems such as chemical resistance and water resistance are likely to occur. Properties, chemical resistance, etc. are not significantly improved as compared with the case of the transfer overcoat layer having a thickness within the range, and unpleasant glare may occur depending on the angle at which the image is viewed, and the image quality may be degraded.

In order to form the transfer overcoat layer,
In the transfer layer, in addition to the thermoplastic resin, a binder component such as starches, hydroxyethylcellulose, methylcellulose, ethylcellulose, carboxymethylcellulose, and other cellulose derivatives, casein, gelatin, and other proteins, oxidized starch, ester compounds, starch, and other saccharose are used. Aqueous natural polymer compounds, polyvinyl alcohol, modified polyvinyl alcohol, polyvinylpyrrolidone, polyacrylic acid, sodium polyacrylate,
Acrylic amide / acrylic acid ester copolymer, acrylic acid amide / acrylic acid ester / methacrylic acid terpolymer, alkali salt of styrene / maleic anhydride copolymer, latex, polyacrylamide, styrene / maleic anhydride copolymer Water-soluble synthetic polymer compounds such as polymers and latexes, water-soluble adhesive resins such as alkali salts of ethylene / maleic anhydride copolymers, polyvinyl acetate, polyurethane, polyacrylic acid esters, styrene / butadiene copolymers It is possible to use synthetic resin adhesives such as latex of acrylonitrile / butadiene copolymer, methyl acrylate / butadiene copolymer, acrylonitrile / butadiene / acrylic acid copolymer, ethylene / vinyl acetate copolymer, etc. , Its components and composition should be in consideration of the adhesion to the image receiving layer. It is Mel possible.

Further, if necessary, a thickener, a flow modifier, an antifoaming agent, a foam suppressor, an ultraviolet absorber, an antioxidant, a light stabilizer, a plasticizer, an optical brightener together with the overcoat layer composition. Can be used together or mixedly used. or,
For the purpose of lowering the melting point of the thermoplastic resin forming the transfer layer and promoting film formation, it is preferable to mix a plasticizer. Further, a substance that lowers the elastic modulus and the glass transition temperature of the thermoplastic resin that forms the transfer layer, or a substance that reduces the melt viscosity is added in advance or externally added to facilitate the formation of a film. It is preferable from the point. As such substances, there are mainly organic acid esters, phosphoric acid esters, sulfonic acid esters and amides, aliphatic esters, epoxy plasticizers, chlorine-containing plasticizers, and phthalic acid esters are particularly effective.

In order to obtain the transfer overcoat layer, it is possible to efficiently obtain it by using a transfer sheet for overcoat in which a transfer layer is applied to a heat resistant sheet as shown in the present invention. The heat-resistant sheet is preferably a sheet having a certain degree of heat resistance, at least a temperature higher than the melting point of the thermoplastic resin, specifically, polyethylene glycol terephthalate film, polyimide film, polyamide film, aluminum foil, etc. The metal foil, aluminum vapor deposition film, aluminum foil laminating film, etc. are preferable. These sheets may be further heat-treated with ceramic fine particles, heat-resistant resin, or the like. The thickness of the heat resistant sheet is preferably as thin as possible in order to improve heat conduction, and is about 3 to 50 μm. Here, if it is thinner than this thickness, it is difficult to handle, and wrinkles and bubbles are likely to be formed at the stage of forming the transfer overcoat layer. If the thickness is larger than this thickness, not only the thermal conductivity deteriorates, but also the adhesion to the recording image surface during transfer deteriorates, and the surface of the transfer overcoat layer tends to become uneven. The transfer layer can be provided by coating the whole or a part of the heat resistant sheet. Further, it is no problem to provide a mark for position detection on a certain portion of the heat resistant sheet.

In the transfer sheet for overcoat, the surface shape of the heat-resistant sheet which is in contact with the transfer layer is required to be a smooth surface when it is desired to obtain a glossy surface in the end, but it is finally matted. If it is desired to obtain a surface, a matte surface can be used, or there may be some uneven pattern. These surface shapes are transferred onto the recorded image in the step of forming the transfer overcoat layer. At this time, the unevenness of the heat resistant sheet is naturally transferred in reverse.

The transfer overcoat layer in the present invention is formed by superposing the transfer layer provided on the heat-resistant sheet on a recording sheet having a recorded image on the recording image surface, by using an independent heating device or an image recording printer. This can be achieved by heating and pressurizing by a heating device provided in, to thermally transfer the transfer layer onto the recording image surface. The heat-resistant sheet after use is wound up separately.

In the present invention, the uniformity of the surface plays a major role in improving the quality of the recorded image. For example, in sublimation-type thermal transfer recording and melt thermal transfer recording, a thermoplastic resin (recorded image surface or precoat layer) that cannot be avoided as long as image recording is performed by a thermal head.
The wrinkles and gloss unevenness of the recorded image surface due to the heat softening can be made uniform by transferring the transfer layer, so that the image quality can be improved. If the transfer surface shape of the transfer overcoat layer is smooth, it gives a glossy feeling, and if it is matte, it gives a matte feeling. What is important is that the difference in glossiness between the recorded portion (heated portion) and the non-recorded portion (non-heated portion) is made uniform by the transfer overcoat.

As a method for forming the overcoat layer, a resin for forming the transfer layer is applied on the surface of the recording sheet in advance, and after recording, the resin is overlaid with the heat resistant sheet and heat-melted to form the transfer overcoat layer. However, when the image is viewed microscopically, the resin particles of the overcoat layer composition may be concentrated at the place where the image may be diffused. Not suitable.

The thermoplastic resin forming the transfer layer may be dissolved in an organic solvent and applied on the heat-resistant sheet, or emulsified in an aqueous solution and applied as an emulsion on the heat-resistant sheet. A transfer layer can be obtained by drying by means of heating, hot air, far infrared rays, microwaves or the like. Also, a solventless thermosetting resin as a binder or a dispersion medium, a UV curable resin, an electron beam curable resin, or the like is used together with a thermoplastic resin on a heat resistant sheet, and then thermosetting or UV irradiation. The transfer layer can also be formed by curing or electron beam irradiation curing.

If necessary, in the transfer layer, in addition to the thermoplastic resin and the binder, a dye, a pigment, a wetting agent, a defoaming agent, a dispersant,
An antistatic agent, an ultraviolet absorber, an antioxidant, a release agent, a fluorescent dye, a fluorescent brightening agent, etc. are added to form a transfer layer,
It can also be used as a transfer overcoat layer. In particular, regarding the pigment, the purpose of improving blocking can be achieved by incorporating inorganic particles represented by silica, calcium carbonate, kaolin clay, barium sulfate, titanium oxide and the like into the thermoplastic resin layer.

A release layer may be provided between the heat resistant sheet and the transfer layer. Specific examples of the release agent for the release layer include solid waxes such as polyethylene wax and amide wax, surfactants such as phosphate ester, silicone oil, Teflon powder, silicone powder, and other fluorine-based and silicone-based compounds. Etc. These release agents may be dispersed in the transfer layer together with the thermoplastic resin, or may be provided as a release layer on the heat resistant sheet.

In order to provide the release layer on the heat resistant sheet, a curable silicone compound is most suitable as the release agent. Examples of the curable silicone compound include a heat reaction curable type, an ultraviolet curable type, an electron beam curable type, a catalyst curable type, etc., which may be appropriately selected and used depending on its affinity with a heat resistant sheet or a transfer layer component and releasability. You can

As the support used for the recording sheet for recording the image of the present invention, in addition to plain paper base paper, non-woven fabric, knitted fabric, woven fabric, art paper, coated paper, coated paper such as cast paper and synthetic paper are used. As the recording method, any recording method such as printing, hot pressing, vapor deposition transfer, electrophotography, silver salt photography, melt thermal transfer, sublimation thermal transfer, and inkjet recording can be used.

Examples of the method for coating the heat-resistant sheet with the thermoplastic resin for forming the transfer layer, the binder and the like include blade coating, air doctor coating, squeeze coating, air knife coating, reverse roll coating, gravure roll and the like. Transfer roll coat,
Methods such as bar coating and curtain coating are used.

[0026]

In the present invention, the melting point of the overcoat layer composition containing a thermoplastic resin and a binder as the main components is lower than the softening point of the heat resistant sheet, and the transfer layer comprising the composition is formed on the surface of the heat resistant sheet. A transfer sheet for overcoat comprising: a transfer sheet, wherein a transfer layer surface of the transfer sheet is superposed on a recording surface of a recording sheet having a recording image recorded on a recording material, By heat-pressing and transferring the transfer layer onto the recording surface of the recording sheet, an overcoat layer which is transparent and has a uniform shape and gloss on the surface of the overcoat layer can be formed. It is possible to obtain a recording sheet having excellent properties, physical properties, weather resistance, scratch resistance, and curl resistance.

[0027]

The present invention will be described in detail below with reference to examples, but the contents of the present invention are not limited to the examples.

Example 1 A polyethylene glycol terephthalate film having a smooth surface and a thickness of 12 μm (E150 made by Diamond Foil, softening point 230 ° C. according to ASTM D876-65) having a thickness of 12 μm was used as a heat resistant sheet, and a thermoplastic transfer layer was used.
Chemipearl (Mitsui Petrochemical, polyethylene aqueous dispersion, melting point 100 ° C) 20 parts (solid content weight), polyvinyl alcohol adhesive 7 parts (solid content weight), water 4
A transfer liquid for overcoat was produced by applying 0 part of the coating liquid so as to be 5 g / m ² (solid content weight) and drying. As a recording sheet, printing paper gravure-printed on art paper was used, the transfer layer surface of the overcoat transfer sheet was superposed on the printing surface of the printing paper, and passed through a heating and pressing device to obtain a recording sheet having a glossy surface.

Example 2 An overcoat transfer sheet was produced in the same manner as in Example 1 except that the coating amount of the transfer layer was 10 g / m ² (weight of solid content). Using this overcoat transfer sheet, a transfer overcoat layer was provided on the same recording sheet as in Example 1. The transfer overcoat layer was sufficiently adhered to the recorded image surface.

Example 3 A transfer sheet for overcoat was produced in the same manner as in Example 1 except that the coating amount of the transfer layer was 30 g / m ² (weight of solid content). Using this overcoat transfer sheet, a transfer overcoat layer was provided on the same recording sheet as in Example 1. The transfer overcoat layer was sufficiently adhered to the recorded image surface.

Example 4 An overcoat transfer sheet was produced in the same manner as in Example 1 except that the coating amount of the transfer layer was 2 g / m ² (solid content weight). Using this overcoat transfer sheet, a transfer overcoat layer was provided on the same recording sheet as in Example 1. The transfer overcoat layer was sufficiently adhered to the recorded image surface.

Example 5 An overcoat transfer sheet was prepared in the same manner as in Example 1 except that the coating amount of the transfer layer was 35 g / m ² (solid content weight). Using this overcoat transfer sheet, a transfer overcoat layer was provided on the same recording sheet as in Example 1. The transfer overcoat layer was sufficiently adhered to the recorded image surface.

Example 6 An overcoat transfer sheet was produced in the same manner as in Example 1 except that the coating amount of the transfer layer was 1.5 g / m ² (weight of solid content). Using this overcoat transfer sheet, a transfer overcoat layer was provided on the same recording sheet as in Example 1.

Example 7 A polyethylene glycol terephthalate film (Unitika Sand Mat D) having a matte surface of 12 μm thickness was used as a heat resistant sheet, and an ultraviolet curable silicone resin (X62- manufactured by Shin-Etsu Chemical Co., Ltd.) was used as a release layer.
7200) was applied by a gravure coater so as to be 1 g / m ² and cured by irradiation with ultraviolet rays. As a thermoplastic transfer layer, Chemipal (Mitsui Petrochemical, polyethylene aqueous dispersion) 20 parts (solid content weight), polyvinyl alcohol-based adhesive 7 parts (solid content weight), water 40 parts coating liquid 10 g / m ^A transfer sheet for overcoat was prepared by coating and drying so as to be ² (solid content weight). The same printing paper as in Example 1 is used as the recording sheet,
The printing surface and the transfer layer surface of the transfer sheet for overcoat were overlapped and passed through a heating and pressing device to obtain a recording sheet having a matte (matte) surface. The overcoat layer was sufficiently adhered to the recorded image surface.

Example 8 As a heat resistant sheet, a polymethylpentene film having a smooth surface with a thickness of 30 μm, Opulan M186
(Mitsui Petrochemical Co., Ltd., thermal softening point 175 ° C. according to ASTM D1525), and 20 parts (solid weight) of FLOWCEN G801 (manufactured by Iron Manufacturing Chemical, polyethylene fine particles, melting point 105 ° C.) as a thermoplastic transfer layer A coating liquid consisting of 7 parts of adhesive (weight of solid content), 1 part of surfactant, and 60 parts of water was applied at 5 g / m ² (weight of solid content) and dried to prepare a transfer sheet for overcoat. did. The same printing paper as in Example 1 was used as a recording sheet, and the printing surface and the transfer layer surface of the overcoat transfer sheet were superposed and passed through a heating and pressing device to obtain a recording sheet having a glossy surface. The overcoat layer was sufficiently adhered to the recorded image surface.

Example 9 A transfer sheet was prepared in the same manner as in Example 8. Using a printed non-woven fabric printed on a non-woven fabric as a recording sheet, the transfer layer surfaces of the overcoat transfer sheet were superposed and passed through a heating and pressing device to obtain a recording sheet having an overcoat layer.

Comparative Example 1 The gravure-printed printing paper used as the recording sheet in Example 1 was directly used as a sample of the recording sheet in Comparative Example 1.

Comparative Example 2 On the gravure printing paper used as the recording sheet in Example 1, low density polyethylene (MFR; 10 g / 10) was used.
Min, density; 0.918 g / cc) was melt-extruded and laminated to a thickness of 15 μm to obtain a recording sheet having an overcoat layer.

Comparative Example 3 On the gravure-printed printing paper used as the recording sheet in Example 1, low density polyethylene (MFR; 10 g / 10) was used.
Min, density: 0.918 g / cc) was melt-extruded and laminated to a thickness of 5 μm to obtain a recording sheet. The laminate layer had many pinholes and adhesion was poor, and only the polyethylene layer could be peeled off.

Comparative Example 4 A biaxially oriented polypropylene film (having a thickness of 12 μm) was formed on the gravure printing paper used as the recording sheet in Example 1.
m) was laminated with a synthetic rubber adhesive and laminated to obtain a recording sheet having an overcoat layer.

Comparative Example 5 As a heat resistant sheet, a biaxially oriented polystyrene film having a smooth surface with a thickness of 25 μm, an OPS film TH
(Asahi Kasei Kogyo Co., Ltd., thermal softening point 103 ° C. according to ASTM D1525) was used, and as a thermoplastic transfer layer, FLOWCEN G801 (manufactured by Iron Chemical Co., Ltd., polyethylene fine particles, melting point 10).
(5 ° C) 20 parts (weight of solid content), 7 parts of polyvinyl alcohol adhesive (weight of solid content), 1 part of surfactant, 60 parts of water so that the coating liquid becomes 5 g / m ² (weight of solid content). Was applied and dried to prepare an overcoat transfer sheet. As the recording sheet, the same printing paper as in Example 1 was used as the recording sheet, and the printing surface and the transfer layer surface of the overcoat transfer sheet were overlapped and passed through a heating and pressing device.
A recording sheet having an overcoat layer was obtained, but the transferability was not good.

Comparative Example 6 Using a printed non-woven fabric printed on a non-woven fabric as a recording sheet, low density polyethylene (MFR; 10 g / 10 min, density; 0.918 g / cc) was melt extruded to a thickness of 1
Lamination was performed at 5 μm to obtain a recording sheet having an overcoat layer.

Test: The recording sheet having the overcoat layer thus obtained was evaluated for the following points.

[Gloss Uniformity] The gloss values of the recorded portion and the non-recorded portion were measured with a 60 ° gloss meter. The gloss uniformity is judged to be excellent when the difference between the two gloss values is 2% or less in the relative evaluation, and is rated as poor when it is more than 2% and 5% or less, and is poor when the difference is more than 5%. did.

[Image Quality] When the recording on the recording sheet is evaluated at the distance and angle of clear vision under a fluorescent lamp, unpleasant glare occurs to make the recording difficult to see. When it did not occur, it was judged as excellent.

[Chemical resistance] A cotton containing acetone was placed on the recording portion of the recording sheet, and the case where the recording was affected by light rubbing was judged as poor, and the case where there was no change was judged as excellent.

[0047]

[Table 1]

Evaluation: In the examples, since the recording sheet has the overcoat layer melt-transferred through the overcoat transfer sheet, there is no uneven glossiness,
Both high-gloss and matte surfaces can be obtained. or,
Since the overcoat layer is thin, the recorded image does not cause unpleasant glare, and the image quality is good. The transfer overcoat layer evenly covers the recorded image surface, so that the chemical resistance is also good. In Comparative Example 1, Comparative Example 1 having no overcoat layer has low gloss non-uniformity and low chemical resistance. In Comparative Examples 2 and 4 in which the overcoat layer is provided by melt lamination or film bonding, recording is not performed. It has a fatal defect that the image is glaring. In Comparative Example 3 in which the overcoat layer was very thinly melt-laminated, glare could be suppressed, but the adhesiveness of the overcoat layer was poor, and the chemical resistance was also poor due to the effect of pinholes.

[0049]

According to the present invention, since the recording sheet has the overcoat layer melt-transferred through the transfer sheet for overcoat, there is no unevenness in gloss of the recording sheet, and the glossy surface is matted. The surface can be obtained, and the image quality is good without causing an unpleasant glare in the image. Further, the function of the overcoat layer makes it possible to obtain a recording sheet having excellent water resistance, chemical resistance, and weather resistance.

[Brief description of drawings]

FIG. 1 is a schematic view of a cross-sectional view of a transfer sheet for overcoat of the present invention.

FIG. 2 is a schematic view of a cross-sectional view of a recording sheet having an overcoat layer formed by using the overcoat transfer sheet of the present invention.

[Explanation of symbols]

1 Heat resistant sheet 2 Transfer layer 3 Overcoat transfer sheet 4 Transfer overcoat layer 5 recorded parts 6 recording layers 7 Support 8 recording sheets 9 Recording sheet having overcoat layer

─────────────────────────────────────────────────── --Continued from the front page (56) References JP-A-5-64973 (JP, A) JP-A-62-93885 (JP, A) JP-A-62-87388 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) B41M 7/00

Claims (4)

(57) [Claims] 1. An overcoat layer composition mainly comprising a thermoplastic resin and a binder has a melting point lower than the softening point of a heat resistant sheet, and the composition is formed on the surface of the heat resistant sheet on a recorded image. An overcoat transfer sheet provided with a transparent transfer layer that allows a recorded image to be clearly seen when it is superposed on. 2. The transfer sheet for overcoat according to claim 1, wherein the surface of the heat resistant sheet on the side in contact with the transfer layer is glossed or matte. 3. The transfer sheet for overcoat according to claim 1, wherein the coating amount of the thermoplastic resin in the transfer layer is ² to 30 g / m ² as a solid content. 4. The melting point of an overcoat layer composition containing a thermoplastic resin and a binder as a main component is lower than the softening point of a heat resistant sheet, and a transfer layer comprising the composition is provided on the surface of the heat resistant sheet. The transfer layer surface of the transfer sheet for overcoat formed as described above is superposed on the recording surface of the recording sheet on which a recording image is recorded on the recording material, and is heat-pressed to transfer the transfer layer onto the recording surface of the recording sheet. After that, the heat resistant sheet is peeled off, and an overcoat layer is formed on the recording surface so that the recording surface can be clearly seen.