JP2002002121A - Thermal transfer sheet and method of forming image - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thermal transfer sheet of which the image forming layer forming a black image has no light absorption at a laser wavelength in a near infrared region or the like, of which the lowering of the adhesiveness due to heat generation is reduced even when a high-output laser is used and which can form the black image being uniform and having high density. SOLUTION: The image forming layer of the thermal transfer sheet having at least a photothermal conversion layer and the image forming layer on a substrate and an image receiving layer of an image receiving sheet are laid on each other. A laser is cast from the substrate side of the thermal transfer sheet and the image forming layer of the part irradiated thereby is transferred onto the image receiving layer, so that an image be formed thereon. In the thermal transfer sheet used in this method of forming the image, the image forming layer is that for the black image which contains pigment constituents forming the black image, and the optical density of the image forming layer in the laser wavelength is 0.5 or less. In a preferable mode of this layer, at least one kind of the pigment constituents is a mixed pigment of yellow, magenta and cyan or an azo pigment.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal transfer material for forming an image by thermal transfer using laser light, and an image forming method for forming a high-resolution image by laser thermal transfer. Further, the present invention relates to a color proof (DDCP: direct digital color proof) in the printing field, or a thermal transfer sheet for producing a mask image and an image forming method.

[0002]

2. Description of the Related Art In the field of graphic arts, a printing plate is printed using a set of color separation films produced from a color original using a lithographic film. In order to check for errors in the color separation process and the necessity of color correction, a color proof is made from the color separation film. A color proof is desired to have high resolution which enables high reproducibility of a halftone image and high performance such as high process stability. In addition, in order to obtain a color proof similar to an actual printed matter, as a material used for a color proof, a material used for an actual printed matter, for example, a printing paper as a base material and a pigment as a coloring material are used. Is preferred. Also,
As a method for producing a color proof, there is a high demand for a dry method using no developer.

As a dry-type color proofing method, a recording system for directly producing a color proof from a digital signal has been developed with the recent spread of an electronic system in a pre-printing process (prepress field). The purpose of such an electronic system is to produce a color proof of high image quality, and generally reproduces a halftone image of 150 lines / inch or more. In order to record a proof of high image quality from a digital signal, a laser beam that can be modulated by the digital signal and can narrow down the recording light is used as a recording head. For this reason, it is necessary to develop a recording material that exhibits high recording sensitivity to laser light and high resolution that enables high-definition halftone dots to be reproduced.

As a recording material used in a transfer image forming method using a laser beam, a photothermal conversion layer that absorbs a laser beam and generates heat, a wax and a binder in which a pigment is thermally fusible, and the like are provided on a support. (See Japanese Patent Laid-Open No. 5-58)
No. 045). In the image forming method using these recording materials, the heat generated in the laser light irradiation area of the light-to-heat conversion layer melts the image forming layer corresponding to the area, and is transferred onto the image receiving sheet stacked on the transfer sheet. Then, a transfer image is formed on the image receiving sheet.

Japanese Patent Application Laid-Open No. 6-219052 discloses that a light-to-heat conversion layer containing a light-to-heat conversion substance, a very thin (0.03-0.3 μm) heat-peeling layer, and a coloring material are provided on a support. There is disclosed a thermal transfer sheet provided with image forming layers in this order. In this thermal transfer sheet, by being irradiated with laser light, the bonding force between the image forming layer and the light-to-heat conversion layer that are bonded by the interposition of the thermal release layer is reduced, and the thermal transfer sheet is laminated on the thermal transfer sheet. On the image receiving sheet,
A high-definition image is formed. The image forming method using the thermal transfer sheet utilizes so-called "ablation". Specifically, in a region irradiated with a laser beam, the heat release layer partially decomposes and evaporates. This utilizes a phenomenon in which the bonding force between the image forming layer and the light-to-heat conversion layer is weakened, and the image forming layer in that region is transferred to the image receiving sheet laminated thereon.

In these image forming methods, printing paper having an image receiving layer (adhesive layer) attached thereto can be used as an image receiving sheet material, and multicolor images can be easily formed by transferring images of different colors onto the image receiving sheet one after another. In particular, an image forming method utilizing ablation has an advantage that a high-definition image can be easily obtained, and has a color proof (DDCP: direct digital color proof) or It is useful for producing a high-definition mask image.

On the other hand, the factors that determine the recording speed in laser recording largely depend on the recording sensitivity of the recording material itself and the laser power. Particularly, by increasing the laser power, a high-resolution image can be easily recorded at a higher speed. can do. Further, even if a high-power laser beam is not used, the recording speed of an image can be increased by using a plurality of laser beams. The above reason is that the use of a plurality of laser beams reduces the irradiation area of each laser beam. Since a high-power laser beam is expensive, a multi-mode laser is often used to increase the recording speed.

However, when a transfer sheet for forming a black (black) image is used for image formation, black carbon is generally used as a black colorant in the image forming layer of the sheet, and the black carbon is in the vicinity of 830 nm. Has an absorption in the near-infrared region and has a light-to-heat conversion effect, so that the laser beam is absorbed in the image forming layer by laser irradiation at the time of image formation to generate heat. Due to local heat generation, the temperature reaches a high temperature, and a gas is generated at the interface between the image forming layer and the image receiving layer to form voids. As a result, transferability is impaired.

That is, if there is a gap between the closely adhered image forming layer and the image receiving layer, heat transfer to the image receiving layer is hindered, and the temperature cannot be raised to a temperature sufficient to plasticize the image receiving layer. The adhesiveness in the part is reduced. In addition, the heat energy not transferred to the image receiving layer stays in the thermal transfer layer or the light-to-heat conversion layer and the portion is excessively heated. As a result, the generation of gas is promoted, and the interface gap is further expanded. Further, the image forming layer in the excessively heated area is fused with the adjacent light-to-heat conversion layer, and the releasability is reduced. Due to the expansion of the voids, the adhesion between the image forming layer and the image receiving layer is further reduced, and the releasability is also reduced, so that the transfer failure is more remarkably accelerated.

As described above, particularly when a multi-mode laser or a high-power laser is used, absorption of laser energy in an image forming layer capable of forming a black image and generation of a gap between transfer / image receiving sheets due to heat generation. A material that does not generate and does not impair the adhesion is required. However, it has no or little light absorption in the near infrared region, has an image forming layer capable of forming a black image, has excellent adhesion between a transfer / image receiving sheet, has no density unevenness, and has a black density ( At present, a thermal transfer sheet for forming a black image capable of stably forming a high-quality image having a high OD) has not yet been provided.

[0011]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned conventional problems and achieve the following objects. That is, in the present invention, the image forming layer for forming a black image has no light absorption at a laser wavelength, and even when a high-power laser or a multi-mode laser is used, a decrease in adhesion due to heat generation is suppressed, and the uniformity is obtained. It is an object of the present invention to provide a thermal transfer sheet capable of stably forming a black image having a high density (OD). Further, the present invention provides an image forming method capable of stably forming a high-quality full-color image composed of yellow, magenta, cyan, and black with uniform and high density (OD) using a high-power laser or a multi-mode laser. The purpose is to provide.

[0012]

Means for solving the above problems are as follows. <1> The image forming layer of a thermal transfer sheet having at least a light-to-heat conversion layer and an image forming layer on a support is superimposed on the image receiving layer of an image receiving sheet having an image receiving layer, and a laser is provided from the support side of the thermal transfer sheet. A thermal transfer sheet used in an image forming method of forming an image by irradiating the image forming layer of the irradiated portion onto the image receiving layer, wherein the image forming layer contains a pigment component for forming a black image. An image forming layer for an image, wherein the optical density (OD) at a laser wavelength of the image forming layer is 0.5 or less.

<2> The thermal transfer sheet according to <1>, wherein the light-to-heat conversion layer has an optical density (OD) at a laser wavelength of 0.7 to 1.5. <3> The above <1> or <2>, wherein at least one of the pigment components for forming a black image contained in the image forming layer is a mixed pigment of a yellow pigment, a magenta pigment, and a cyan pigment.
<2> The thermal transfer sheet described in (1).

<4> The thermal transfer sheet according to <1> or <2>, wherein at least one of the pigment components for forming a black image contained in the image forming layer is an azo pigment. <5> The thermal transfer sheet according to any one of <1> to <4>, wherein the laser is a multi-beam two-dimensional array laser.

<6> A thermal transfer sheet having at least a light-to-heat conversion layer and an image forming layer on a support, and an image receiving sheet having an image receiving layer are used, and the thermal transfer sheet has at least four of black, yellow, magenta, and cyan. The image forming layer of the thermal transfer sheet of each color and the image receiving layer of the image receiving sheet are overlapped so as to be sequentially in contact with each other, and laser irradiation is performed from the support side of the thermal transfer sheet of each color to form the image forming layer of the irradiated portion. Are sequentially transferred onto the image receiving layer to form a full-color image.
5> The image forming method according to any one of [1] to [11], wherein the thermal transfer sheet is used.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The thermal transfer sheet of the present invention has an image forming layer having an optical density (OD) at a laser wavelength of 0.5 or less. Further, in the image forming method of the present invention, an image forming layer having an optical density (OD) of 0.5 or less at a laser wavelength is used as a thermal transfer sheet for forming a black image used in an image forming method for forming a full-color image. Black). Hereinafter, the thermal transfer sheet of the present invention and an image forming method using the same will be described in detail.

<Thermal Transfer Sheet> The thermal transfer sheet of the present invention comprises at least a light-to-heat conversion layer and an image forming layer on a support. If necessary, a heat-sensitive release layer, a cushion layer, an intermediate layer and the like may be used. The image forming layer of the thermal transfer sheet and the image receiving layer of the image receiving sheet are overlapped so as to be in contact with each other, and a laser beam is irradiated from the support side of the thermal transfer sheet so that the image forming layer of the irradiated portion is subjected to the image receiving layer. It is used in an image forming method of transferring an image onto a layer and forming an image.

[Image Forming Layer] The image forming layer provided on the thermal transfer sheet of the present invention contains a pigment component which expresses a black component as a coloring material, and has an optical density (OD) at a laser wavelength irradiated at the time of image formation. Black not more than 0.5 (black)
This is a colored layer for image formation. The image forming layer, in addition to the pigment component, is configured to contain at least an amorphous organic high-molecular polymer, if necessary, waxes, plasticizers, rosin, surfactants, other matting materials such as It may contain components.

The optical density (OD) of the image forming layer at a laser wavelength for irradiating an image is 0.5 or less, and more preferably 0.4 or less. When the optical density OD exceeds 0.5, when laser irradiation is performed image-wise, the heat generated by the absorption of laser energy of the image forming layer is large, causing poor adhesion between the thermal transfer sheet and the image receiving sheet, and causing image formation. The layer is fused with the light-to-heat conversion layer to lower the transferability, the transferability becomes nonuniform, and it becomes difficult to form a high-density transfer image without density unevenness.

The optical density of the image forming layer at the laser wavelength (O
D) can be determined from the absorbance of the image forming layer measured at the wavelength (laser wavelength) of the laser light used for image formation. For example, UV-visible light spectrophotometer UV-240
(Manufactured by Shimadzu Corporation).

-Pigment- The image forming layer of the thermal transfer sheet of the present invention is transferred to the image forming layer so that a desired image density (black) is obtained, and the optical density of the layer at the laser wavelength is obtained. (OD) is 0.5 or less. As the pigment, any pigment composition can be used as long as it can basically generate a black image as long as heat generation in the image forming layer when a high-power laser is used is suppressed and transferability is not impaired. Pigments having no or little absorption at a laser wavelength used for image formation (for example, a near infrared region around 750 to 1200 nm), or mixed pigments containing the pigment are preferable. .

The image forming layer may be composed of a pigment having no absorption at the laser wavelength or containing only a pigment having little absorption, a pigment having an absorption at the laser wavelength,
Pigments with no or low absorption (hereinafter referred to as
It may be referred to as "low absorption pigment". ) May be included. Examples of the low absorption pigment include a mixed pigment composed of a yellow pigment, a magenta pigment and a cyan pigment, an azo pigment and the like.

As the azo pigment, a black azo pigment may be used alone, or a plurality of azo pigments may be mixed to prepare a black azo pigment. Examples of the black azo pigment include 2-hydroxy-α-coupling components described in JP-A-10-203001.
Azo pigments using benzocarbazole-carboxylic acid allylamide and derivatives thereof, and JP-A-11-236514
And the like. As the azo pigment used when preparing a black color by mixing a plurality of azo pigments, various general-purpose azo pigments can be used, but heat resistance is used from the viewpoint of preventing decomposition due to heat generation during laser beam irradiation. Those having high properties are more preferable. However, the present invention is not limited to these.

The pigment components of the mixed pigments comprising the yellow pigment, magenta pigment and cyan pigment are generally roughly classified into organic pigments and inorganic pigments. The former is particularly excellent in the transparency of the coating film, and the latter is generally opaque. And the like, and may be appropriately selected according to the application. In particular, organic pigments that match yellow, magenta, and cyan commonly used in printing inks or have similar color tones can be preferably used. In addition, metal powder, fluorescent pigment, and the like can be used. Specific examples of suitable pigments include azo pigments, phthalocyanine pigments, anthraquinone pigments, dioxazine pigments, quinacridone pigments, isoindolinone pigments, and nitro pigments. Hereinafter, specific examples of the yellow pigment, the magenta pigment, and the cyan pigment are listed, but the present invention is not limited thereto.

1) Yellow pigments Hansa Yellow G, Hansa Yellow 5G, Hansa Yellow 10G, Hansa Yellow A, Pigment Yellow L,
Permanent Yellow NCG, Permanent Yellow F
GL, permanent yellow HR. 2) Magenta pigment Permanent Red 4R, Permanent Red F2R,
Permanent Red FRL, Lake Red C, Lake Red D, Pigment Scarlet 3B, Bordeaux 5B,
Alizarin Lake, Rhodamine Lake B. 3) Cyan pigments Phthalocyanine blue, Victoria blue lake, Fast sky blue.

Further, the azo pigment or the yellow pigment,
Low absorption pigments such as a mixed pigment of a magenta pigment and a cyan pigment are consistent with black generally used in printing inks, as long as the optical density (OD) of the image forming layer at the laser wavelength can be 0.5 or less, Alternatively, a black organic pigment having a similar color tone can be used in combination, and examples of the pigment include carbon black. Generally, since carbon black has absorption in the near-infrared region, it easily absorbs laser light and tends to locally generate heat at a high temperature. You may use together for the purpose of adjustment etc.

The content of the pigment in the image forming layer is 2
It is preferably from 0 to 70% by weight, more preferably from 25 to 50% by weight. As the content of the low absorption pigment in the content,
The optical density (OD) of the image forming layer at the laser wavelength is 0.5
It can be appropriately selected within the range which can be set as follows, but is preferably about 20 to 100% by weight, more preferably 30 to 70% by weight. If the content is less than 20% by weight, the content of the laser-absorptive pigment in the pigment is too large, and transfer failure due to heat generation may not be suppressed. However, only low-absorbing pigments may not be able to obtain a black color that matches or is close to the black color commonly used in printing inks. It is preferable to use a pigment having a property.

The pigment has an average particle size of from 0.03 to
1 μm is preferable, and 0.05 to 0.5 is more preferable.
If the particle size is less than 0.03 μm, the dispersion cost may increase, or the dispersion may gel, etc.
If it exceeds μm, coarse particles in the pigment may hinder the adhesion between the thermal transfer layer and the image receiving layer.

-Amorphous organic high-molecular polymer- The image forming layer preferably contains an amorphous organic high-molecular polymer as a binder component.
An amorphous organic high-molecular polymer at a temperature of from 150C to 150C is preferred. As the amorphous organic high-molecular polymer, for example, butyral resin, polyamide resin, polyethyleneimine resin, sulfonamide resin, polyester polyol resin, petroleum resin, styrene, vinyltoluene, α-methylstyrene, 2-methylstyrene, Styrene and its derivatives such as chlorostyrene, vinylbenzoic acid, sodium vinylbenzenesulfonate and aminostyrene, and homo- and copolymers of substituted methacrylates and methacrylates such as methyl methacrylate, ethyl methacrylate, butyl methacrylate and hydroxyethyl methacrylate And methacrylic acid,
Acrylic esters such as methyl acrylate, ethyl acrylate, butyl acrylate, α-ethylhexyl acrylate and acrylic acid, butadiene, dienes such as isoprene, acrylonitrile, vinyl ethers,
Maleic acid and maleic esters, maleic anhydride, cinnamic acid, vinyl chloride, vinyl acetate, and other vinyl monomers alone or copolymers with other monomers, and the like. These resins can be used as a mixture of two or more kinds.

The content of the amorphous organic high molecular polymer in the image forming layer is preferably 70 to 30% by weight, more preferably 70 to 40% by weight.

-Other components- Waxes Examples of the waxes include mineral waxes, natural waxes, and synthetic waxes. Examples of the mineral wax include petroleum wax such as paraffin wax, microcrystalline wax, ester wax, and oxidized wax, montan wax, ozokerite, and ceresin. Among them, paraffin wax is preferred. The paraffin wax is separated from petroleum, and various types are commercially available depending on the melting point. Examples of the natural wax include vegetable waxes such as carnauba wax, wood wax, ouriculi wax, and spal wax, and animal waxes such as beeswax, insect wax, shellac wax, and whale wax.

The above-mentioned synthetic waxes are generally used as a lubricant, and usually comprise higher fatty acid compounds. Examples of such synthetic waxes include the following. 1) Fatty acid-based wax Linear saturated fatty acid represented by the following general formula: CH ₃ (CH ₂ ) _n COOH wherein n represents an integer of 6 to 28. Specific examples include stearic acid, behenic acid, palmitic acid, 12-hydroxystearic acid, azelaic acid, and the like.

2) Fatty Acid Ester Wax Specific examples of fatty acid esters include ethyl stearate, lauryl stearate, ethyl behenate, hexyl behenate, and behenyl myristate. 3) Fatty acid amide wax Specific examples of the amide of the fatty acid include stearic acid amide and lauric acid amide. 4) Aliphatic alcohol-based wax Linear saturated aliphatic alcohol represented by the following general formula: CH ₃ (CH ₂ ) _n OH [wherein, n represents an integer of 6 to 28. Specific examples include stearyl alcohol and the like.

Among the synthetic waxes of the above 1) to 4),
Particularly, higher fatty acid amides such as stearic acid amide and lauric acid amide are preferable. In addition, the said wax-type compound can be used individually or in suitable combination as needed.

Plasticizer The plasticizer is preferably an ester compound. Dibutyl phthalate, di-n-octyl phthalate, di (2-ethylhexyl) phthalate, dinonyl phthalate, dilauryl phthalate, butyllauryl phthalate, Phthalates such as butylbenzyl phthalate, and di (2-adipate)
Known plasticizers such as aliphatic dibasic acid esters such as ethylhexyl) and di (2-ethylhexyl) sebacate, and phosphoric acid triesters such as tricresyl phosphate and tri (2-ethylhexyl) phosphate. Above all, esters of vinyl monomers, particularly esters of acrylic acid or methacrylic acid, are preferred because they have a large effect of improving transfer sensitivity, improving transfer unevenness, and controlling breaking elongation by addition.

Examples of the ester compound used as the plasticizer include polyethylene glycol dimethacrylate, 1,2,4-butanetriol trimethacrylate, trimethylolethane triacrylate, pentaerythritol acrylate, pentaerythritol tetraacrylate, and dipentaerythritol-poly. Acrylate and the like.

The plasticizer may be a polymer. Among them, polyester is preferable because of its large addition effect and its difficulty in diffusing under storage conditions. Examples of the polyester include sebacic acid-based polyester and adipic acid-based polyester. The additives contained in the image forming layer are not limited to these. Also, the plasticizer may be used alone,
Two or more kinds may be used in combination.

If the content of the additive in the image forming layer is too large, the resolution of the transferred image is reduced, the film strength of the image forming layer itself is reduced, and the adhesion between the photothermal conversion layer and the image forming layer is reduced. In some cases, transfer of the unexposed portion to the image receiving sheet may occur due to a decrease in the image quality. From the above viewpoint, the content of the wax is preferably from 0.1 to 30% by weight, more preferably from 1 to 20% by weight of the total solids in the image forming layer. The content of the plasticizer is set to 0.1% of the total solid content in the image forming layer.
It is preferably from 1 to 20% by weight, more preferably from 0.1 to 10% by weight.

Others In addition to the above components, a surfactant, a thickener and the like can be added to the image forming layer, if necessary.

The above components are dissolved in a solvent to form a coating liquid solution (coating solution for image forming layer), which is coated on a support by a known coating method and dried to form an image forming layer. be able to. Solvents that can be used for preparing the coating solution for the image forming layer include, for example, alcohols such as ethyl alcohol and propyl alcohol; acetone,
Ketones such as methyl ethyl ketone; esters such as ethyl acetate; aromatic hydrocarbons such as toluene and xylene; ethers such as tetrahydrofuran and dioxane; DM
It can be appropriately selected from amides such as F, N-methylpyrrolidone; cellosolves such as methylcellosolve. The solvents may be used alone or in combination of two or more.

As the layer thickness (dry layer thickness) of the image forming layer,
It is preferably from 0.1 to 1.5 μm, more preferably from 0.3 to 1.0 μm, most preferably from 0.5 to 0.7 μm. When the layer thickness exceeds 1.5 μm, transfer unevenness occurs, and the image density of the transferred image may be reduced or the resolution of the transferred image may be reduced. When the thickness is less than 0.1 μm, the strength of the film itself may be reduced. May decrease.

Further, it is preferred that the elongation at break of the image forming layer at 60 ° C. is 100% or more, since transfer unevenness hardly occurs. When the elongation at break at 23 ° C. is 10% or less, the resolution of the transferred image is improved. Is preferred. By including the plasticizer, waxes, and the like in the image forming layer, the elongation at break at each temperature can be adjusted to the above range.

In order to prevent damage, a thermal transfer image-receiving material or a protective cover film such as a polyethylene terephthalate sheet or a polyethylene sheet can be usually laminated on the surface of the image forming layer.

[Light-to-Heat Conversion Layer] The light-to-heat conversion layer contains a light-to-heat conversion material, a binder resin, and if necessary, a mat material, and further contains other components as necessary.
The light-to-heat conversion substance is a substance having a function of converting irradiated light energy to heat energy. Generally, it is a dye capable of absorbing laser light (including a pigment; the same applies hereinafter).

When recording an image with an infrared laser, it is preferable to use an infrared absorbing dye as the photothermal conversion material. As the infrared absorbing dye, for example, black pigments such as carbon black, phthalocyanine, macrocyclic compound pigments having absorption in the visible to near infrared region such as naphthalocyanine, used as a laser absorbing material for high-density laser recording such as optical disks Organic dyes (eg, cyanine dyes such as indolenine dyes, anthraquinone dyes, azulene dyes, and phthalocyanine dyes), and organic metal compound dyes such as dithiol nickel complexes.

Among them, cyanine dyes exhibit a high extinction coefficient with respect to light in the infrared region. Therefore, when used as a light-to-heat conversion material, the light-to-heat conversion layer can be made thinner.
As a result, the recording sensitivity of the thermal transfer sheet can be further improved, which is preferable. As the light-to-heat conversion material, an inorganic material such as a particulate metal material such as blackened silver can be used in addition to the pigment.

The content of the light-to-heat conversion material is preferably from 5 to 50% by weight, more preferably from 10 to 30% by weight, based on the total solid weight of the light-to-heat conversion layer.

As the binder resin contained in the light-to-heat conversion layer, a resin having at least a strength capable of forming a layer on a support and having a high thermal conductivity is preferable. Further, when recording an image, if the resin is heat resistant and does not decompose even by the heat generated from the light-to-heat conversion material, the surface of the light-to-heat conversion layer after light irradiation can be smoothed even if irradiated with high-energy laser. It is preferable because the property can be maintained. In particular,
A resin having a thermal decomposition temperature (temperature at which the weight is reduced by 5% in an air stream at a temperature rising rate of 10 ° C./min by the TGA method) is preferably 400 ° C. or more, and more preferably a resin having the thermal decomposition temperature of 500 ° C. or more. .

Further, the binder resin is 200 to 400.
C. preferably has a glass transition temperature of from 250 to
More preferably, it has a glass transition temperature of 350 ° C. If the glass transition temperature is less than 200 ° C., fog may occur in a transferred image, and if it exceeds 400 ° C., the solubility of the resin may be reduced and the production efficiency may be reduced. It is preferable that the binder resin has higher heat resistance (for example, thermal deformation temperature or thermal decomposition temperature) than a material used for another layer provided on the light-to-heat conversion layer.

Specifically, acrylic resins such as polymethyl methacrylate, polycarbonate, polystyrene,
Vinyl chloride / vinyl acetate copolymer, vinyl resin such as polyvinyl alcohol, polyvinyl butyral, polyester, polyvinyl chloride, polyamide, polyimide, polyetherimide, polysulfone, polyethersulfone, aramid, polyurethane, epoxy resin, urea / melamine Resins. Among these, a polyimide resin is preferable.

In particular, the polyimide resins represented by the following general formulas (I) to (VII) are soluble in an organic solvent and are preferred in terms of improving the productivity of a thermal transfer sheet. It is also preferable in that the viscosity stability, long-term storage property, and moisture resistance of the coating liquid for forming a light-to-heat conversion layer are improved.

[0052]

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In the above general formulas (I) and (II), Ar
¹ represents an aromatic group represented by the following structural formulas (1) to (3), and n represents an integer of 10 to 100.

[0054]

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[0055]

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In the general formulas (III) and (IV), Ar
² represents an aromatic group represented by the following structural formulas (4) to (7), and n represents an integer of 10 to 100.

[0057]

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[0058]

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In the above general formulas (V) to (VII), n and m
Each independently represents an integer of 10 to 100. Expression (V
In I), the ratio of n: m is 6: 4 to 9: 1.

Incidentally, as a guide for judging whether or not the resin is soluble in an organic solvent, it is based on that at 25 ° C., at least 10 parts by weight of the resin is dissolved with respect to 100 parts by weight of N-methylpyrrolidone. When it is dissolved in 10 parts by weight or more, it is preferably used as a resin for the light-to-heat conversion layer. More preferably, the resin dissolves in 100 parts by weight or more based on 100 parts by weight of N-methylpyrrolidone.

When the content of the binder resin in the light-to-heat conversion layer is too small, the cohesive force of the light-to-heat conversion layer is reduced, and the light-to-heat conversion layer is easily transferred together when the formed image is transferred to the image receiving sheet. This causes color mixing of the image. On the other hand, if the amount of the polyimide resin is too large, the thickness of the light-to-heat conversion layer becomes large in order to achieve a constant light absorptivity, which tends to cause a decrease in sensitivity. From the above, the solid content weight ratio (light-to-heat conversion material: resin) of the light-to-heat conversion material and the binder resin in the light-to-heat conversion layer is preferably 1:20 to 2: 1, and 1:10 to 2: 1.
Is more preferred.

The matting material contained in the light-to-heat conversion layer includes inorganic fine particles and organic fine particles. Examples of the inorganic fine particles include metal salts such as silica, titanium oxide, aluminum oxide, zinc oxide, magnesium oxide, barium sulfate, magnesium sulfate, aluminum hydroxide, magnesium hydroxide, and boron nitride; kaolin, clay, talc, and zinc. Hua, lead white, siegrite, quartz, diatomaceous earth, perlite, bentonite, mica, synthetic mica and the like. As the organic fine particles, for example, fluororesin particles, guanamine resin particles, acrylic resin particles,
Resin particles such as styrene-acryl copolymer resin particles, silicone resin particles, melamine resin particles, and epoxy resin particles can be used.

The particle size of the mat material is usually 0.3
To 30 μm, and preferably 0.5 to 20 μm. In addition, the amount of addition is 0.1 to 100 mg /
m ² is preferred.

If necessary, other components such as a surfactant, a thickener, and an antistatic agent may be added to the light-to-heat conversion layer.

The light-to-heat conversion layer is prepared by dissolving a light-to-heat conversion substance and a binder resin, preparing a coating solution containing a matting material and other components as necessary, coating the solution on a support, and drying the solution. It can be provided by doing. Coating and drying can be performed by using ordinary coating and drying methods. The temperature during drying is usually 300 ° C. or less,
200 ° C. or lower is preferred. When polyethylene terephthalate is used as the support, drying is preferably performed at a temperature of 80 to 150 ° C.

As an organic solvent for dissolving the binder resin, for example, n-hexane, cyclohexane,
Diglyme, xylene, toluene, ethyl acetate, tetrahydrofuran, methyl ethyl ketone, acetone, cyclohexanone, 1,4-dioxane, 1,3-dioxolane, dimethyl acetate, N-methyl-2-pyrrolidone, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, γ-butyrolactone, ethanol, methanol and the like.

Further, it is preferable to make the light-to-heat conversion layer thinner from the viewpoint that the sensitivity of the heat transfer sheet can be increased. The layer thickness of the light-to-heat conversion layer is preferably from 0.03 to 1.0 μm, more preferably from 0.05 to 0.5 μm. Also,
The light-to-heat conversion layer preferably has an optical density (OD) of 0.7 to 1.5 with respect to light having a laser wavelength from the viewpoint of improving the transfer sensitivity of the image forming layer. 7-1.
More preferably, it has an optical density of 3. The optical density (OD) is a transmission density and can be measured by, for example, a UV-visible light spectrophotometer UV-240 (manufactured by Shimadzu Corporation). The optical density at the laser wavelength is
If it is less than 0.7, it becomes insufficient to convert the irradiated light into heat, and the transfer density may decrease.
If it exceeds 5, the function of the light-to-heat conversion layer may be affected during recording and fog may occur.

[Support] The material of the support of the thermal transfer sheet is not particularly limited, and various support materials can be selected according to the purpose. Preferred examples of the support material include synthetic resin materials such as polyethylene terephthalate, polyethylene-2,6-naphthalate, polycarbonate, polyethylene, polyvinyl chloride, polyvinylidene chloride, polystyrene, and styrene-acrylonitrile copolymer. . Among them, biaxially stretched polyethylene terephthalate is preferable in consideration of mechanical strength and dimensional stability against heat. When the thermal transfer sheet of the present invention is used for producing a color proof using laser recording, the support of the thermal transfer sheet is preferably formed of a transparent synthetic resin material that transmits laser light.

The support is preferably subjected to a surface activation treatment and / or the provision of one or more undercoat layers in order to improve the adhesion to the light-to-heat conversion layer provided thereon. . Further, on the surface of the thermal transfer sheet opposite to the side on which the light-to-heat conversion layer is provided, various functional layers such as an anti-reflection layer can be provided or surface treatment can be performed, if necessary.

Examples of the surface activation treatment include a glow discharge treatment and a corona discharge treatment. The material of the undercoat layer preferably has high adhesiveness to both surfaces of the support and the light-to-heat conversion layer, has low thermal conductivity, and has excellent heat resistance. Examples of the material for such an undercoat layer include styrene, styrene-butadiene copolymer, and gelatin. The thickness of the entire undercoat layer is usually 0.01 to 2 μm.
Further, on the surface of the heat transfer sheet on which the light-to-heat conversion layer is not provided, various functional layers such as an antireflection layer and an antistatic layer can be provided, or a surface treatment can be performed, if necessary. .

[Other Layers] On the light-to-heat conversion layer of the heat transfer sheet, a gas is generated by the action of heat generated in the light-to-heat conversion layer, or adhered water or the like is released, thereby forming an image with the light-to-heat conversion layer. A heat-sensitive release layer containing a heat-sensitive material that weakens the bonding strength between the layers can be provided. As such a heat-sensitive material, a compound (polymer or low-molecular compound) which itself decomposes or degrades by heat to generate a gas,
A compound (a polymer or a low-molecular compound) that absorbs or adsorbs a considerable amount of easily vaporizable gas such as moisture can be used. These may be used in combination.

Examples of the polymer which decomposes or degrades by heat to generate a gas include self-oxidizing polymers such as nitrocellulose; chlorinated polyolefins, chlorinated rubber, polyvinyl chloride, polyvinyl chloride, polyvinylidene chloride and the like. Halogen-containing polymer; Acrylic polymer such as polyisobutyl methacrylate to which volatile compounds such as water are adsorbed; Cellulose esters such as ethyl cellulose to which volatile compounds such as water are adsorbed; Volatile compounds such as water are adsorbed Natural polymer compounds such as gelatin and the like.

Examples of the low molecular weight compound which decomposes or degrades by heat to generate a gas include a compound which generates a gas upon exothermic decomposition such as a diazo compound or azide. It is preferable that decomposition or alteration of the heat-sensitive material due to heat occurs at 280 ° C. or lower, and particularly at 23 ° C.
It preferably occurs at 0 ° C. or lower.

When a low-molecular compound is used as the heat-sensitive material of the heat-sensitive release layer, it is desirable to combine it with a binder. As the binder, a polymer (thermosensitive low molecular weight compound) which itself decomposes or degrades by heat to generate a gas can be used, but a normal polymer binder having no such properties is used. You can also. When a heat-sensitive low-molecular compound and a binder are used in combination, the weight ratio of the former to the latter is 0.0
2: 1 to 3: 1 are preferable, and 0.05: 1 to 2: 1 are more preferable.

The heat-sensitive release layer desirably covers almost the entire surface of the light-to-heat conversion layer, and the thickness thereof is generally 0.03 to 1 μm, and 0.05 to 1 μm.
0.5 μm is preferred.

In the case of a thermal transfer sheet having a structure in which a light-to-heat conversion layer, a heat-sensitive release layer, and an image forming layer are laminated in this order on a support, the heat-sensitive release layer is decomposed and deteriorated by heat transmitted from the light-to-heat conversion layer. Generates gas. Then, due to the decomposition or generation of gas, the heat-sensitive peeling layer partially disappears, or cohesive failure occurs in the heat-sensitive peeling layer, and the bonding force between the light-heat conversion layer and the image forming layer decreases. For this reason, depending on the behavior of the heat-sensitive release layer, a part of the heat-sensitive release layer may adhere to the image forming layer and appear on the surface of a finally formed image, which may cause color mixing of the image. Therefore, even when such transfer of the heat-sensitive release layer occurs, the heat-sensitive release layer is hardly colored, that is, high in visible light, so that no visual color mixture appears in the formed image. It is desirable to show permeability. Specifically, the light absorption of the heat-sensitive peeling layer is 50% or less, preferably 1 to visible light.
0% or less.

In the thermal transfer sheet of the present invention, instead of providing an independent heat-sensitive release layer, the above-mentioned heat-sensitive material is added to the coating solution for forming the light-to-heat conversion layer (coating solution for the light-to-heat conversion layer) to form a photothermographic material. It is also possible to form a conversion layer so as to serve as both a light-to-heat conversion layer and a heat-sensitive release layer.

As described above, by using a pigment having no or little absorption in a laser wavelength region used for image recording as a pigment contained in an image forming layer for forming a black image, a multi-mode laser or a high Even when an output laser is used, a decrease in adhesion due to heat generation is suppressed,
A uniform, high density (OD) black image can be stably formed. It is also useful for forming a high-quality full-color image composed of yellow, magenta, cyan, and black with uniform and high density (OD) using a multi-mode laser or a high-power laser.

[Image Receiving Sheet] The thermal transfer sheet of the present invention comprises:
It is used in combination with the following image receiving sheet. The image receiving sheet usually has a support and one or more image receiving layers provided thereon, and, if necessary, a cushion layer, a release layer, and an intermediate layer between the support and the image receiving layer. Any one of the layers
It is constituted by providing a layer or two or more layers. In addition, from the viewpoint of transportability, it is also a preferable embodiment to provide a back layer on the surface of the support on which the image receiving layer is not provided.

Examples of the support constituting the image receiving sheet include ordinary sheet-like base materials such as a plastic sheet, a metal sheet, a glass sheet, and paper. Examples of the plastic sheet include a polyethylene terephthalate sheet, a polycarbonate sheet, a polyethylene sheet, a polyvinyl chloride sheet, a polyvinylidene chloride sheet, a polystyrene sheet, a styrene-acrylonitrile sheet, and a polyester sheet. Examples of the paper include printing paper, coated paper, and the like.

It is preferable that the support has minute voids (voids) because curling can be prevented and image quality can be improved. As such a support, for example, a thermoplastic resin, a mixed melt obtained by mixing a filler made of an inorganic pigment or a polymer incompatible with the thermoplastic resin and the like, a single layer or a multilayer by a melt extruder. Film and
Further, it can be produced by stretching uniaxially or biaxially. In this case, the porosity is determined by the selection of the resin and the filler, the mixing ratio, the stretching conditions, and the like.

The thermoplastic resin is preferably a polyolefin resin such as polypropylene, or a polyethylene terephthalate resin because of its excellent crystallinity and stretchability and easy formation of voids. It is preferable to use the above-mentioned polyolefin resin and polyethylene terephthalate resin as main components, and appropriately use a small amount of another thermoplastic resin in combination. The inorganic pigment used as the filler has an average particle size of 1
-20 μm is preferred, and calcium carbonate, clay, diatomaceous earth, titanium oxide, aluminum hydroxide, silica and the like can be used. When polypropylene is used as the thermoplastic resin as the incompatible resin used as the filler, it is preferable to use polyethylene terephthalate as the filler. The content of the filler such as an inorganic pigment in the support is 2 to 30 by volume.
% Is common.

The thickness of the support of the image receiving sheet is usually from 10 to 400 μm, preferably from 25 to 200 μm. Further, the surface of the support is subjected to a surface treatment such as a corona discharge treatment or a glow discharge treatment in order to enhance the adhesion with the image receiving layer (or the cushion layer described later) and the adhesion with the image forming layer of the thermal transfer sheet. May be applied.

The image forming layer from the thermal transfer sheet is transferred to the image receiving sheet. In order to fix the layer, it is preferable that one or more image receiving layers are provided on the support. As the image receiving layer, a layer containing an organic polymer binder as a main component is preferable. As the organic polymer binder, a thermoplastic resin is preferable, and for example, a homopolymer of an acrylic monomer such as acrylic acid, methacrylic acid, an acrylate ester, a methacrylate ester and a copolymer thereof; methyl cellulose, ethyl cellulose, cellulose acetate Cellulosic polymers such as polystyrene, polyvinylpyrrolidone, polyvinylbutyral, polyvinyl alcohol, polyvinyl chloride, etc .; homopolymers and copolymers of vinyl monomers; condensation polymers such as polyesters and polyamides; butadiene-styrene copolymers And rubber-based polymers such as polymers.

The binder for the image receiving layer is used in order to obtain a proper adhesive strength between the image receiving layer and the image forming layer.
Is preferably a polymer having a temperature lower than 90 ° C. For this purpose, it is also possible to add a plasticizer to the image receiving layer.
Further, the binder polymer preferably has a Tg of 30 ° C. or higher in order to prevent blocking between sheets. As the binder polymer of the image receiving layer, a polymer which is the same as or similar to the binder polymer of the image forming layer may be used in terms of improving adhesion to the image forming layer during laser recording and improving sensitivity and image strength. Particularly preferred.

After the image is once formed on the image receiving layer by transfer, the image can be further transferred to a printing paper or the like. In this case, it is also preferable to form at least one of the image receiving layers from a photocurable material. Examples of the composition of such a photocurable material include: a) a photopolymerizable monomer composed of at least one kind of a polyfunctional vinyl or vinylidene compound capable of forming a photopolymer by addition polymerization; b) an organic polymer; c)
Examples of the combination include a photopolymerization initiator and, if necessary, a combination of additives such as a thermal polymerization inhibitor.

The a) polyfunctional vinyl monomer includes:
Unsaturated esters of polyols, especially esters of acrylic acid or methacrylic acid (eg, ethylene glycol diacrylate, pentaerythritol tetraacrylate) are used. Examples of the organic polymer b) include the organic polymer binder for forming an image receiving layer. As the photopolymerization initiator c), a general photoradical polymerization initiator such as benzophenone and Michler's ketone is used in a ratio of 0.1 to 20% by weight in the layer.

The thickness of the image receiving layer is 0.3 to 7 μm.
m is preferable, and 0.7 to 4 μm is more preferable. When the layer thickness is less than 0.3 μm, the film strength may be insufficient and the film may be easily broken when retransferred to the printing paper, and when the layer thickness exceeds 7 μm, the gloss of the image after the paper retransfer increases, and the printed matter may increase. The approximation to may decrease.

A cushion layer may be provided between the support and the image receiving layer. When the cushion layer is provided, the image forming layer at the time of laser thermal transfer, to improve the adhesion of the image receiving layer,
Image quality can be improved. Further, at the time of recording, even if foreign matter is mixed between the thermal transfer sheet and the image receiving sheet, the gap between the image receiving layer and the image forming layer is reduced due to the deformation of the cushion layer, and as a result, the size of image defects such as white spots is reduced. You can also. Furthermore, after transferring and forming the image,
When transferring this to a separately prepared printing paper or the like, the image receiving surface is deformed according to the paper uneven surface, so that the transferability of the image receiving layer can be improved, and by lowering the gloss of the transferred object, The similarity with the printed matter can also be improved.

The cushion layer is easily deformed when a stress is applied to the image receiving layer. To achieve the above effect, a material having a low elastic modulus, a material having rubber elasticity, or a material which is easily softened by heating. It is preferred to be made of a thermoplastic resin. The elastic modulus of the cushion layer is 1 at room temperature.
0 to 500 kgf / cm ² or less, preferably 30 to 15 kgf / cm ²
0 kgf / cm ² is particularly preferred. In addition, in order to allow a foreign substance such as rubber to penetrate, the penetration (25 ° C., 100 g, 5 seconds) specified by JIS K2530 is preferably 10 or more. The glass transition temperature of the cushion layer is 80 ° C. or lower, preferably 25 ° C. or lower. It is also possible to suitably add a plasticizer to the polymer binder in order to adjust these physical properties, for example, Tg.

Specific materials for the cushion layer include rubbers such as urethane rubber, butadiene rubber, nitrile rubber, acrylic rubber, and natural rubber, as well as polyethylene,
Polypropylene, polyester, styrene-butadiene copolymer, ethylene-vinyl acetate copolymer, ethylene-
Acrylic copolymer, vinyl chloride-vinyl acetate copolymer,
Examples include vinylidene chloride resin, vinyl chloride resin containing a plasticizer, polyamide resin, and phenol resin. The thickness of the cushion layer varies depending on the resin used and other conditions, but is usually 3 to 100 μm, preferably 10 to 52 μm.

The image receiving layer and the cushion layer need to be adhered to each other up to the stage of laser recording, but are preferably provided so as to be releasable in order to transfer an image to printing paper. In order to facilitate peeling, it is preferable to provide a peeling layer having a thickness of about 0.1 to 2 μm between the cushion layer and the image receiving layer. This release layer preferably has a function as a barrier for a coating solvent at the time of coating the image receiving layer.

The image receiving sheet used in combination with the thermal transfer sheet of the present invention may have a structure in which the image receiving layer also serves as a cushion layer. In this case, the image receiving sheet may be constituted by, for example, a support / cushion. And a support / undercoat layer / cushionable image receiving layer. Also in these embodiments, the cushioning image receiving layer is provided so as to be releasable so that the image retransferred to the printing paper can be re-transferred to the printing paper in that the image retransferred to the printing paper can be an image having excellent gloss. Is preferred. still,
The thickness of the cushioning image-receiving layer is preferably from 5 to 100 μm, more preferably from 10 to 40 μm.

When the cushion layer is provided, an intermediate layer may be provided for the purpose of preventing the fine particles contained in the image receiving layer and the back layer described below from sinking. The intermediate layer is difficult to deform when subjected to stress for the purpose, and it is necessary to use a material that can be applied to the cushion layer, and a polymer having a relatively high glass transition point such as PMMA, polystyrene, and cellulose triacetate is used. Can be contained.

The image receiving sheet is preferably provided with a back layer on the surface of the support on which the image receiving layer is not provided, from the viewpoint of improving the transportability of the image receiving sheet. The back layer may improve the transportability in a recording apparatus by adding an additive such as a surfactant, an antistatic agent such as tin oxide fine particles, and a matting agent such as silicon oxide and PMMA particles. Is preferred. The additives can be added not only to the back layer but also to the image receiving layer and other layers as needed. Although the type of the additive cannot be unconditionally specified depending on the purpose, for example, the matting agent can add about 0.5 to 80% of particles having an average particle size of 0.5 to 10 μm in a layer. The antistatic agent is appropriately selected from various surfactants and conductive agents so that the surface resistance of the layer is 10 ¹² Ω or less, preferably 10 ⁹ Ω or less under the conditions of 23 ° C. and 50% RH. Can be added.

<Image Forming Method> The thermal transfer sheet of the present invention is used in combination with the image receiving sheet, the image forming layer of the thermal transfer sheet and the image receiving layer of the image receiving sheet are overlapped, and the thermal transfer sheet is supported on the support side. Irradiate more laser,
An image is formed by transferring the image forming layer of the irradiated portion onto the image receiving layer.

As described above, the thermal transfer sheet and the image receiving sheet are used for image formation as a laminate in which the image forming layer of the thermal transfer sheet and the image receiving layer of the image receiving sheet are in contact with each other. It can be formed by various methods. As a method of forming the laminate, for example, the image forming layer of the thermal transfer sheet and the image receiving layer of the image receiving sheet are stacked,
A method of passing through a pressurizing and heating roller may be used. in this case,
The heating temperature is preferably 160 ° C. or lower, or 130 ° C. Further, as a method of forming the laminate,
A vacuum adhesion method may be used, or an image receiving sheet may be mechanically attached to a metal drum while being pulled, and a thermal transfer sheet may be further adhered to the metal drum while being mechanically pulled and adhered thereto. .

In the vacuum contact method, an image receiving sheet is first wound on a drum provided with a suction hole for evacuation, and then a heat transfer sheet having a size slightly larger than the image receiving sheet is uniformly air-squeezed by a squeeze roller. This is a method in which the sheet is pressed against the image receiving sheet while being extruded. Among the above-mentioned methods, the vacuum contact method is particularly preferable in that the temperature control of a heat roller or the like is not required, and the lamination can be performed quickly and uniformly.

Hereinafter, a specific procedure of the image forming method will be described. The image forming method is useful for forming a multicolor image, and can also be used for producing a black mask or forming a monochromatic image. First, the case of a monochrome image (including a black mask) will be described. An image forming laminate in which an image receiving sheet is laminated such that the image receiving layer is in contact with the surface of the image forming layer of the thermal transfer sheet is prepared. When the laser light is radiated imagewise in time sequence from the support side of the thermal transfer sheet of the laminate, the laser light irradiated area of the photothermal conversion layer of the thermal transfer sheet generates heat, and the adhesion between the photothermal conversion layer and the image forming layer is increased. Decrease.
Thereafter, when the image receiving sheet and the thermal transfer sheet are peeled off, the laser light irradiation area of the image forming layer is transferred onto the image receiving layer of the image receiving sheet.

The close contact between the thermal transfer material and the thermal transfer image receiving material may be performed immediately before the laser beam irradiation operation. In this laser beam irradiation operation, the thermal transfer image-receiving material side of the laminate is usually evacuated to the surface of a recording drum (a rotary drum having a vacuum forming mechanism therein and a large number of minute openings on the drum surface). The thermal transfer material to be laminated is entirely covered with the thermal transfer image receiving material, and the contact interface is reduced in pressure by evacuation to adhere. In this state, laser light irradiation is performed from the outside of the laminate, that is, from above the thermal transfer material side.
The laser beam is irradiated so as to reciprocate in the width direction of the drum, and the recording drum is rotated at a constant angular velocity during the irradiation operation.

In the image forming method of the present invention, the above-described thermal transfer sheet of the present invention comprising at least four types of thermal transfer sheets of black, yellow, magenta, and cyan and the image receiving sheet are used, and the thermal transfer sheets of the respective colors are used. The image forming layer and the image receiving layer of the image receiving sheet are overlapped so as to be sequentially in contact with each other, and laser irradiation is performed from the support side of the thermal transfer sheet of each color to sequentially transfer the image forming layer of the irradiated portion onto the image receiving layer, thereby providing a full color image. Form an image.

The specific modes for forming a multicolor image by the image forming method of the present invention may be, for example, the following modes (first and second modes). That is, in the first embodiment of the method for forming a multicolor image, an image receiving material is fixed on a rotating drum of a recording apparatus by a vacuum depressurization method, and a heat transfer material is similarly formed on the image receiving material by a vacuum depressurization method. And the image recording layer (hue 1) of the thermal transfer material.
Next, the laser light modulated based on the digital signal of the color separation image of the original image is irradiated from the support side of the thermal transfer material while rotating the drum, and then the thermal transfer material is fixed from the thermal transfer image receiving material while the thermal transfer image receiving material is fixed. Peel off. The steps of laminating the thermal transfer material of hue 2, hue 3 and, if necessary, hue 4 on the thermal transfer image receiving material on which the image of hue 1 is recorded by the same method as described above, laser recording, and peeling are sequentially repeated. Thereby, a thermal transfer image receiving material on which a multicolor image is formed can be obtained. In order to obtain a color proof image on the printing paper, the heat transfer image receiving material on which the multicolor image is formed from the above process is laminated so that the image surface thereof is in contact with the printing paper, and then heated and pressed through a laminator, etc. It can be obtained by peeling off this and transferring the image together with the image receiving layer onto the printing paper.

In the second embodiment of the method for forming a multicolor image, three types (three colors) of a laminate obtained by laminating thermal transfer materials each having an image forming layer containing a colorant having a different hue are used.
Alternatively, four kinds (four colors) are prepared, and for each of them, laser irradiation is performed based on a digital signal of each color image corresponding to each laminate obtained through a color separation filter, and then the thermal transfer material and the thermal transfer image receiving material are irradiated. Peel off. After the color separation images of each color are independently formed on each thermal transfer image receiving material, the respective color separation images are sequentially laminated on an actual support such as printing paper separately prepared or a support similar thereto. Can be formed.

The laser beam used for light irradiation has a wavelength of 7
A laser beam of 50 to 1200 nm is preferable. For example, a gas laser beam such as an argon ion laser beam, a helium neon laser beam, a helium cadmium laser beam, a solid laser beam such as a YAG laser beam, a semiconductor laser beam, a dye laser beam, and an excimer laser beam Or the light obtained by converting these laser lights to a half wavelength through a second harmonic element,
Can be selected as appropriate. In the image forming method of the present invention, a semiconductor laser is preferable in consideration of output power, ease of modulation, and the like, and among them, a multi-beam two-dimensional array laser is more preferable in terms of recording speed.

In the image forming method using the thermal transfer sheet according to the present invention, the laser beam is irradiated under the condition that the beam diameter on the light-to-heat conversion layer is in the range of 5 to 50 μm (particularly 6 to 30 μm). And the scanning speed is 1 m
/ Sec or more (especially 3 m / sec or more).

[0106]

EXAMPLES The present invention will be described below with reference to examples, but the present invention is not limited to these examples. still,
“Parts” and “%” in the examples all represent “parts by weight” and “% by weight”.

Example 1 <Preparation of Thermal Transfer Material> -Preparation of Coating Solution for Light-to-Heat Conversion Layer- The following components were mixed while stirring with a stirrer to prepare a coating solution for a light-to-heat conversion layer. (Composition of coating solution for light-to-heat conversion layer) Infrared absorbing dye 7.6 parts (NK-2014, manufactured by Nippon Kogyo Dye Co., Ltd.) Polyimide resin 29.3 parts (Licacoat SN-20 ( Thermal decomposition temperature 510 ° C), Nippon Rika Co., Ltd.) ・ N, N-dimethylformamide ・ ・ ・ 1500 parts ・ Surfactant ・ ・ ・ 0.5 parts (MegaFac F-177, Dainippon Ink & Chemicals, Inc.)・ Mat agent (silica gel particles) 1.7 parts (Sea Hostar KEP150, manufactured by Nippon Shokubai Co., Ltd.)

100 μm thick polyethylene terephthalate film (PET film; center line average surface roughness R)
a = 0.04 μm), after applying the coating solution for a light-to-heat conversion layer obtained above using a spin coater (wheeler), dried in an oven at 120 ° C. for 2 minutes, and supported. A light-to-heat conversion layer was formed on the body. The formed photothermal conversion layer has absorption at a wavelength of about 830 nm, and the absorbance (optical density: OD) of the layer is measured using a UV-visible spectrophotometer (UV-2).
400, manufactured by Shimadzu Corporation)
OD = 0.9. The thickness of the light-to-heat conversion layer was 0.3 μm (average value) when the cross section of the light-to-heat conversion layer was observed using a scanning electron microscope.

-Preparation of Coating Solution for Black Image Forming Layer- First, pigment dispersion mother liquors of a black pigment dispersion mother liquor A, a yellow pigment dispersion mother liquor, a magenta pigment dispersion mother liquor and a cyan pigment dispersion mother liquor were prepared by the following procedure. That is, the compounds having the following compositions were placed in a kneader mill, and a shearing force was applied while adding a small amount of n-propyl alcohol as a solvent to perform a pre-dispersion treatment. The same solvent was further added to the dispersion to prepare a dispersion finally having the following composition.
Next, glass beads were added thereto, and the mixture was subjected to sand mill dispersion for 2 hours, and then the glass beads were removed to prepare a pigment dispersion mother liquor of each color.

[Composition of Black Pigment-Dispersed Mother Liquid A] Polyvinyl butyral 12.6 parts (ESREC B BL-SH, manufactured by Sekisui Chemical Co., Ltd.) Pigment (carbon black) 15.0 parts (MA-100, manufactured by Mitsubishi Kasei Corporation) Dispersing aid: 0.8 parts (Solsperse S-20000, manufactured by ICI Corporation) n-propyl alcohol: 79.4 parts

[Composition of Yellow Pigment-Dispersed Mother Liquid] Polyvinyl butyral 7.1 parts (ESREC B BL-SH, manufactured by Sekisui Chemical Co., Ltd.) Pigment (P.Y.139, yellow pigment) -12.9 parts-Dispersing aid ... 0.6 parts (Solsperse S-20000, manufactured by ICI Co., Ltd.)-n-propyl alcohol ... 79.4 parts

[Composition of magenta pigment dispersed mother liquor] Polyvinyl butyral ... 12.6 parts (Denka butyral # 2000-L (Vicat softening point 57 ° C), manufactured by Denki Kagaku Kogyo KK) Pigment (magenta pigment)・ ・ ・ 15.0 parts (Simraf Perilian Carmine 6B-229, manufactured by Dainippon Ink & Chemicals, Inc.) ・ Dispersing aid ・ ・ ・ 0.6 part (Solsperse S-20000, manufactured by ICI Corporation) ・ n -Propyl alcohol: 79.4 parts

[Composition of cyan pigment-dispersed mother liquor]-Polyvinyl butyral ... 12.6 parts (ESREC B BL-SH, manufactured by Sekisui Chemical Co., Ltd.)-Pigment (cyan pigment) ... 15.0 parts ( Pigment Blue 15, # 700-10 FG CY-Blue)-Dispersing aid ... 0.8 parts (PW-36, manufactured by Kusumoto Kasei Co., Ltd.)-n-propyl alcohol ... 110 parts

Next, using each of the pigment dispersion mother liquors obtained above, the components having the following compositions were mixed with stirring with a stirrer to prepare a coating liquid (1) for a black image forming layer. [Composition of the coating solution (1) for the black image forming layer] 92.9 parts of the black pigment dispersion mother liquor A 31.0 parts of the yellow pigment dispersion mother liquor 31.0 parts of the magenta pigment dispersion mother liquor 31.0 parts-The above-mentioned mother liquid for dispersing cyan pigment ... 31.0 parts-Polyvinyl butyral ... 11.9 parts (Esrec B BL-SH, manufactured by Sekisui Chemical Co., Ltd.)-Wax compound stearic acid amide ( Neutron 2, manufactured by Nippon Seika Co., Ltd. 0.9 parts Behenamide (Diamid BM, manufactured by Nippon Kasei Co., Ltd.) 0.9 parts Lauric amide (Diamid Y, Nippon Kasei Co., Ltd.) 0.9 parts Palmitic amide (Diamid KP, manufactured by Nippon Kasei Co., Ltd.) 0.9 parts Erucamide (Diamid L-200, manufactured by Nippon Kasei Co., Ltd.) 0.9 parts Olein Acid amide ( Iamid O-200, Nippon Kasei Co., Ltd.) 0.9 parts Rosin (KE-311, Arakawa Chemical Co., Ltd.) 11.4 parts Surfactant 2.1 parts ( Megafac F-176P (solid content: 20%), manufactured by Dainippon Ink and Chemicals, Inc. ・ n-propyl alcohol: 1050 parts ・ Methyl ethyl ketone: 295 parts

The particles in the obtained coating solution (1) for a black image forming layer were measured with a laser scattering type particle size distribution analyzer to find that the average particle size was 0.25 μm and 1 μm or more. The percentage of particles was 0.5%.

The coating solution (1) for a black image forming layer was applied on the light-to-heat conversion layer of the support for 1 minute using a wheeler, and then dried in an oven at 100 ° C. for 2 minutes.
A black image forming layer was formed on the light-to-heat conversion layer. Thus, the heat transfer sheet (1) of the present invention in which the light-to-heat conversion layer and the black image forming layer are provided on the support in this order.
I got The thickness of the black image forming layer was found to be 0.65 μm (average value) by observing the cross section with a scanning electron microscope.

Optical density (OD; transmission density including light-to-heat conversion layer) of the black image forming layer of this thermal transfer sheet (1)
Was measured with a Macbeth densitometer TD-904 (W filter) to find that OD = 0.88. Further, a sample in which only the black image forming layer was directly formed on the support without forming the light-to-heat conversion layer on the support was prepared, and the optical density (OD) of the black image forming layer at a wavelength of 830 nm was prepared.
Was measured with a UV-visible light spectrophotometer UV-240 (manufactured by Shimadzu Corporation) to find that OD was 0.33.

<Preparation of Image Receiving Sheet> A coating solution for a cushioning intermediate layer and a coating solution for an image receiving layer having the following compositions were prepared. [Composition of Cushioning Intermediate Layer Coating Solution]-Vinyl chloride-vinyl acetate copolymer ... 20 parts (MPR-TSL, manufactured by Nissin Chemical Co., Ltd.)-Plasticizer (adipic acid-based polyester) ... 10 parts (Paraplex G40, manufactured by CP, HALL, COMPANY)-Surfactant: 0.5 part (MegaFac F-177, manufactured by Dainippon Ink and Chemicals, Inc.)-Antistatic agent: 0 0.3 parts (SAT-5 Super (IC), manufactured by Nippon Pure Chemical Co., Ltd.)-Methyl ethyl ketone (solvent)-60 parts-Toluene-10 parts-N, N-dimethylformamide-3.0 Department

[Composition of Coating Solution for Image-Receiving Layer] Polyvinyl butyral ... 8.0 parts (ESREC B BL-SH, manufactured by Sekisui Chemical Co., Ltd.) Antistatic agent ... 0.7 parts (Sun Stat 2012A, manufactured by Sanyo Chemical Industries, Ltd. ・ Surfactant: 0.1 part (trade name: Megafac F-177, manufactured by Dainippon Ink and Chemicals, Inc.) ・ n-propyl alcohol: 20 parts ・ Methanol ・ ・ ・ 20 parts ・ 1-Methoxy-2-propanol ・ ・ ・ 50 parts

<Image formation> A white PET support (trade name: Lumirror E) having a core of foamed polyester 135 μm thick and containing fine particles of calcium carbonate on both surfaces thereof
-68L, manufactured by Toray Industries, Inc.), and the cushioning intermediate layer coating liquid obtained above was dried on the support using a narrow width coating machine to a layer thickness of about 20 μm. The coating liquid for image-receiving layer (1) is then applied on the cushioning intermediate layer so that the layer thickness after drying is about 2 μm.
After further coating and drying so as to obtain m, the resultant was wound into a roll. Thereafter, the wound roll was allowed to stand at room temperature for one week, and this was used as an image receiving sheet.

A 1 mm diameter vacuum suction hole (3 cm ×
The image receiving sheet (2) obtained above was placed on a rotating drum having a diameter of 25 cm, in which an area of 8 cm was provided with one area density.
(5 cm × 35 cm) was wound and vacuum-adsorbed. Next, a 30 cm × 40 cm thermal transfer sheet (1) is laminated so as to protrude evenly from the image receiving sheet and to cover, and is squeezed by a squeeze roller while being closely attached so that air is sucked into a suction hole to form a laminate. did. The degree of pressure reduction in a state where the suction hole was closed was -150 mmHg with respect to 1 atm. Rotate the drum,
On the surface of the laminated body on the drum, a semiconductor laser beam (multi-beam two-dimensional array type semiconductor laser) having a wavelength of 830 nm was applied from the support side of the thermal transfer sheet (1) to the surface of the photothermal conversion layer.
The laser beam (image line) was recorded while condensed so as to form a spot of μm, and moved in a direction (sub-scanning direction) perpendicular to the rotation direction (main scanning direction) of the rotating drum. The laser beam irradiated here is a laser beam composed of a parallelogram multi-beam two-dimensional array of five rows in the main scanning direction and three rows in the sub-scanning direction. Laser irradiation conditions were as follows.

[Laser irradiation conditions] Laser power 110 mW Main scanning speed 6 m / sec Sub-scanning pitch 6.35 μm Ambient temperature and humidity 23 ° C., 50% RH

As described above, the laminated body on which the laser image recording was performed was removed from the drum, and the thermal transfer sheet (1) of the present invention was peeled off from the image receiving sheet. Was confirmed to have been transcribed.

<Evaluation> (Evaluation of image quality of image portion) The solid portion and the line drawing portion of the transferred image formed on the image receiving layer as described above were observed with an optical microscope, and each was evaluated according to the following criteria. (1) Solid part [Criterion] ◎: Good without micro transfer unevenness (clearness, gap). ：: Although some transfer defects and gaps were observed, there was no practical problem. Δ: Transfer unevenness was observed. X: Transfer drop was conspicuous and a uniform density was not obtained. (2) Line drawing part [Reference] A: High resolution was obtained without unevenness in the thin line part. Δ: Although slight unevenness was observed in the fine line portion, there was no practical problem. X: Inferior in transferability, and sufficient resolution was not obtained.

(Reflection Density and Transfer Rate of Image Area) An image receiving sheet on which a solid image (corresponding to 100%) was recorded by laser recording was overlapped so that the solid image was in contact with art paper, and a laminator (heat roller temperature 130 ° C.) , 4kg / cm
² and pressurized with compressed air at a speed of 0.3 m / min). After returning to room temperature, the art paper and the image receiving sheet were peeled off, and the image receiving layer was transferred onto the art paper. The optical reflection density at this time was measured with a reflection Macbeth densitometer (RD-918 / W filter, manufactured by Macbeth), and the reflection density r was measured.
Next, the unrecorded thermal transfer material (1) is overlaid so that the image forming layer thereof is in contact with the image receiving layer of the unused image receiving sheet, and a laminator (heat roller temperature: 130 ° C., 4 kg / cm ²⁾
Pressurized with compressed air at a speed of 0.3 m / min)
After peeling without laser recording to transfer only the image forming layer onto the image receiving layer, the transferred image (image forming layer) on the image receiving layer was overlaid on art paper in the same manner as described above, and passed through the laminator. After returning to room temperature, the art paper and the image receiving sheet were peeled off, the image receiving layer was transferred onto the art paper, and the optical reflection density R was measured in the same manner as described above. Using the obtained r and R, a transfer rate [%; (r / R) × 100] at the time of laser thermal transfer was determined. The results obtained are shown in Table 1 below.

Example 2 A black pigment-dispersed mother liquor B was prepared from the following compounds by the same preparation procedure as that for the black pigment-dispersed mother liquor A of Example 1, and the components having the following compositions were stirred with a stirrer. Then, the mixture was mixed to prepare a coating solution (2) for a black image forming layer. The heat transfer sheet (2) of the present invention was prepared in the same manner as in Example 1 except that the coating liquid (2) for the black image forming layer was used in place of the coating liquid (1) for the black image forming layer used in Example 1. ) Was prepared.

[Composition of Black Pigment-Dispersed Mother Liquid B] Polyvinyl butyral 12.6 parts (ESLEK B BL-SH, manufactured by Sekisui Chemical Co., Ltd.) Pigment 7.5 parts (carbon black; MA-100, manufactured by Mitsubishi Kasei Co., Ltd.-Pigment: 7.5 parts (azo black pigment; Chromofine Black A-1103, manufactured by Dainichi Seika Co., Ltd.)-Dispersing aid ... 0.8 Part (Solsperse S-20000, manufactured by ICI Co., Ltd.) n-propyl alcohol 79.4 parts

[Composition of Coating Solution (1) for Black Image Forming Layer] • Black pigment dispersion mother liquor B: 185.8 parts • Polyvinyl butyral: 11.9 parts (Eslek B BL-SH, Sekisui Chemical・ Wax compound stearic acid amide (Neutron 2, manufactured by Nippon Seika Co., Ltd.) 0.9 parts Behenic acid amide (Diamid BM, manufactured by Nippon Kasei Co., Ltd.) 0.9 Part Lauric amide (Diamid Y, Nippon Kasei Co., Ltd.) 0.9 parts Palmitic acid amide (Diamid KP, Nippon Kasei Co., Ltd.) 0.9 parts Erucamide (Diamid L-200) , Nippon Kasei Co., Ltd.) 0.9 parts Oleic acid amide (Diamid O-200, Nippon Kasei Co., Ltd.) 0.9 parts Rosin (KE-311, Arakawa Chemical Co., Ltd.)・ ・ 11.4 parts ・ Surfactivities Agent ... 2.1 parts (Megafac F-176P (20% solids), produced by Dainippon Ink & Chemicals Co., Ltd.), n-propyl alcohol ... 1050 parts Methyl ethyl ketone ... 295 parts

Optical density (OD; transmission density including light-to-heat conversion layer) of the black image forming layer of this thermal transfer sheet (2)
Was measured with a Macbeth densitometer TD-904 (W filter) to find that OD = 0.88. A light-to-heat conversion layer was not provided on the support, and only the black image forming layer was directly coated on the support to form a sample. The optical density (OD) of the black image forming layer at a wavelength of 830 nm was measured by UV.
-Visible light spectrophotometer UV-240 (Shimadzu Corporation)
OD = 0.35. Further, by the same method as in the first embodiment, the reflection density of the image portion,
Image quality and transfer rate were measured and evaluated. The results are shown in Table 1 below.

Comparative Example 1 0.9 parts of the yellow pigment-dispersed mother liquor, 0.9 parts of the magenta pigment-dispersed mother liquor, and 0 parts of the cyan pigment-dispersed mother liquor used in the preparation of the coating solution (1) for the black image forming layer in Example 1. .9 parts of the black pigment-dispersed mother liquor A (0.
A black image forming layer coating liquid (3) was prepared in the same manner as in the preparation of the black image forming layer coating liquid (1) in Example 1 except that the composition was changed to 9 parts × 3). And Example 1
Instead of the black image forming layer coating liquid (1) used in the above,
Except for using the black image forming layer coating solution (3),
A thermal transfer sheet (3) of a comparative example was produced in the same manner as in Example 1.

Optical density (OD; transmission density including light-to-heat conversion layer) of the black image forming layer of this thermal transfer sheet (3)
Was measured with a Macbeth densitometer TD-904 (W filter) to find that OD was 0.89. Further, a sample in which only the black image forming layer was directly formed on the support without forming the light-to-heat conversion layer on the support was prepared, and the optical density (OD) of the black image forming layer at a wavelength of 830 nm was prepared.
Was measured with a UV-visible light spectrophotometer UV-240 (manufactured by Shimadzu Corporation) to find that OD was 0.60. Further, the measurement and evaluation of the reflection density, image quality and transfer rate of the image area were performed in the same manner as in Example 1. The results are shown in Table 1 below.

[0132]

[Table 1]

From the results shown in Table 1 above, the image forming layer (black)
When the thermal transfer sheets (1) and (2) having an optical density (OD) at the laser wavelength of 0.5 or less are used, a high-density image can be formed without impairing transferability. did it. In addition, a uniform and high-resolution image could be formed without transfer unevenness (drops and gaps). on the other hand,
Optical density (OD) of the image forming layer (black) at the laser wavelength
In the thermal transfer sheet (3) having a value of more than 0.5, the transferability was poor, the image density was insufficient, and the density uniformity was poor. Also, the resolution of the line drawing section was poor.

Example 3 In the same manner as in Example 1, three supports provided with a light-to-heat conversion layer were prepared. With each composition shown below, a coating solution for a yellow image forming layer, a coating solution for a magenta image forming layer, and a coating solution for a cyan image forming layer were prepared by the same preparation procedure as the coating solution (1) for the black image forming layer. Forming a yellow image forming layer, a magenta image forming layer, and a cyan image forming layer on the light-to-heat conversion layer of each support, and forming a heat transfer sheet Y, a heat transfer sheet M, and a heat transfer sheet C.
Was prepared.

The optical density of the yellow image forming layer of the thermal transfer sheet Y was measured with a Macbeth densitometer (TD-904; Blue filter) to be 1.70. The optical density of the magenta image forming layer of the thermal transfer sheet M was measured with a Macbeth densitometer (TD-904; Green filter) and found to be 0.65. The optical density of the cyan image forming layer of the thermal transfer sheet C was measured using a Macbeth densitometer (TD-904; R
ed filter) was 0.63.

[Composition of coating solution for yellow image forming layer]-The above-mentioned yellow pigment-dispersed mother liquor ... 126 parts-Polyvinyl butyral ... 4.6 parts (Eslec B BL-SH, manufactured by Sekisui Chemical Co., Ltd.) Wax compound Stearamide (Neutron 2, manufactured by Nippon Seika Co., Ltd.): 0.7 parts Behenamide (Diamid BM, manufactured by Nippon Kasei Co., Ltd.): 0.7 parts Lauric amide (diamond) Mid Y, manufactured by Nippon Kasei Co., Ltd. 0.7 parts Palmitic amide (Diamid KP, manufactured by Nippon Kasei Co., Ltd.) 0.7 parts Erucamide (Diamid L-200, Nippon Kasei Co., Ltd.) 0.7 parts Oleic acid amide (Diamid O-200, manufactured by Nippon Kasei Co., Ltd.) 0.7 parts Nonionic surfactant 0.4 parts (Chemistat 1100, Sanyo Chemical Co., Ltd.) )) ・Rosin (KE-311, manufactured by Arakawa Chemical Co., Ltd.) 2.4 parts Surfactant 0.8 parts (MegaFac F-176P (solid content 20%), Dainippon Ink and Chemicals, Inc.・ N-propyl alcohol ・ ・ ・ 793 parts ・ Methyl ethyl ketone ・ ・ ・ 198 parts

[Composition of Magenta Image Forming Layer Coating Solution] • Magenta pigment dispersion mother liquor: 163 parts • Polyvinyl butyral: 4.0 parts (Denka butyral # 2000-L (Vicat softening point: 57 ° C.)) Denki Kagaku Kogyo Co., Ltd.) Wax compound Stearamide (Neutron 2, manufactured by Nippon Seika Co., Ltd.) 1.0 parts Behenamide (Diamid BM, manufactured by Nippon Kasei Co., Ltd.) 1 1.0 parts Lauric amide (Diamid Y, manufactured by Nippon Kasei Co., Ltd.) 1.0 parts Palmitic amide (Diamid KP, manufactured by Nippon Kasei Co., Ltd.) 1.0 parts Erucamide (Diamid L) -200, Nippon Kasei Co., Ltd.) 1.0 part Oleic amide (Diamid O-200, Nippon Kasei Co., Ltd.) 1.0 part Nonionic surfactant 0.7 part (Chemista Rosin (KE-311, manufactured by Arakawa Chemical Co., Ltd.) ... 4.6 parts-Monomer (PET-4A, manufactured by Shin-Nakamura Chemical Co., Ltd.) ... 5 parts · Surfactant ··· 1.3 parts (Megafac F-176P (solid content: 20%), manufactured by Dainippon Ink & Chemicals, Inc.) · n-Propyl alcohol ··· 848 parts · Methyl ethyl ketone ···・ 246 copies

[Composition of Cyan Image Forming Layer Coating Solution] Cyan pigment dispersed mother liquor: 118 parts Polyvinyl butyral: 5.2 parts (ESREC B BL-SH, manufactured by Sekisui Chemical Co., Ltd.) Wax compound Stearamide (Neutron 2, manufactured by Nippon Seika Co., Ltd.) 1.0 part Behenamide (Diamid BM, manufactured by Nippon Kasei Co., Ltd.) 1.0 part Lauric amide (Diamond) Mid Y, manufactured by Nippon Kasei Co., Ltd. 1.0 parts Palmitic amide (Diamid KP, manufactured by Nippon Kasei Co., Ltd.) 1.0 parts Erucamide (Diamid L-200, Nippon Kasei Co., Ltd.) 1.0 part Oleic acid amide (Diamid O-200, Nippon Kasei Co., Ltd.) 1.0 part Rosin (KE-311, Arakawa Chemical Co., Ltd.) 2.8 parts Monomer (PET-4A, 1.7 parts ・ Surfactant 1.7 parts (MegaFac F-176P (solid content 20%), manufactured by Dainippon Ink and Chemicals, Inc.) ・ n -Propyl alcohol: 890 parts ・ Methyl ethyl ketone: 247 parts

Using the thermal transfer sheets Y, M, and C obtained above and the thermal transfer sheet (1) for forming a black (K) image prepared in Example 1, the thermal transfer sheet of each of the four colors was used in Example 1. In the same manner as in the above, transfer images of a single color (Y, M, C, K) were formed on different image receiving sheets. Four image receiving sheets on which a single-color image has been transferred are superimposed and adhered in order so that the image-receiving layer surface comes into contact with the recording paper, and four colors are transferred onto the same recording paper to form a multicolor image. .

Reflection density (OD) of a multicolor image on recording paper
Was measured using a reflection Macbeth densitometer (RD-918, manufactured by Macbeth Co.), and Y (Blue filter) =
1.71, M (Green filter) = 1.47, C
(Red filter) = 1.49, K (W filter) =
1.80, which was a practically sufficient concentration.

[0141]

According to the present invention, the image forming layer for forming a black image has no light absorption at the laser wavelength, and the adhesion is reduced by heat even when a multi-mode laser or a high-power laser is used. And a thermal transfer sheet capable of stably forming a uniform and high-density (OD) black image can be provided. Another object of the present invention is to provide an image forming method capable of stably forming a high-quality full-color image composed of yellow, magenta, cyan, and black with uniform and high density (OD) using a multi-mode laser or a high-power laser. Can be.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI theme coat ゛ (Reference) B41M 5/26 B41M 5/26 Q A F term (Reference) 2C065 AB02 AC01 AF02 CA03 CA08 2C068 AA06 BB18 BC03 BC13 2H111 AA26 AA35 BA03 BA07 BA14 BA38 BA47 BA48 BA49 BA50 BA74 CA03

Claims (6)

[Claims] 1. An image forming layer of a thermal transfer sheet having at least a light-to-heat conversion layer and an image forming layer on a support, and the image receiving layer of an image receiving sheet having an image receiving layer are superimposed on the support side of the thermal transfer sheet. In a thermal transfer sheet used for an image forming method of forming an image by irradiating a laser and transferring an image forming layer of the irradiated portion onto the image receiving layer, the image forming layer contains a pigment component for forming a black image. A thermal transfer sheet, wherein the image forming layer has an optical density (OD) at a laser wavelength of 0.5 or less. 2. The thermal transfer sheet according to claim 1, wherein the optical density (OD) at the laser wavelength of the light-to-heat conversion layer is 0.7 to 1.5. 3. The thermal transfer sheet according to claim 1, wherein at least one of the pigment components for forming a black image contained in the image forming layer is a mixed pigment of a yellow pigment, a magenta pigment and a cyan pigment. 4. The thermal transfer sheet according to claim 1, wherein at least one of the pigment components for forming a black image contained in the image forming layer is an azo pigment. 5. The thermal transfer sheet according to claim 1, wherein the laser is a multi-beam two-dimensional array type laser. 6. A thermal transfer sheet having at least a light-to-heat conversion layer and an image forming layer on a support, and an image receiving sheet having an image receiving layer, wherein the thermal transfer sheet is at least four types of black, yellow, magenta, and cyan. The image forming layer of the thermal transfer sheet of each color and the image receiving layer of the image receiving sheet are superimposed so as to sequentially contact each other,
2. An image forming method for forming a full-color image by irradiating a laser beam from a support side of a thermal transfer sheet of each color and sequentially transferring an image forming layer of the irradiated portion onto the image receiving layer, wherein the black thermal transfer sheet is 6. An image forming method, which is the thermal transfer sheet according to any one of items 1 to 5.