JP2010276916A - Photosensitive letterpress printing plate precursor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a photosensitive letterpress printing plate precursor with a heat-sensitive mask layer which is thin in film thickness and has high light-shielding properties and high scratch resistance, and which ensures a smaller variation of optical density than a conventional mask layer. <P>SOLUTION: The water-developable photosensitive letterpress printing plate precursor is obtained by sequentially laminating at least (A) a support, (B) a photosensitive resin layer and (C) a heat-sensitive mask layer, wherein the heat-sensitive mask layer (C) comprises carbon black and a dispersing binder, and the dispersing binder comprises a butyral resin, a cationic polyamide and an anionic polymeric compound. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a photosensitive letterpress printing original plate used for producing a letterpress printing plate by computer platemaking technology, and in particular, a heat sensitive mask layer coating which provides a heat sensitive mask layer having a high light shielding property and scratch resistance while being a thin film. The present invention relates to a liquid manufacturing method.

  In recent years, in the field of letterpress printing, computer plate making technology (Computer to Plate, CTP technology) known as digital image forming technology has become very common. The CTP technique is a method for obtaining a relief uneven pattern by directly outputting information processed on a computer onto a printing plate. This technology eliminates the need for a negative film manufacturing process and reduces costs and the time required to create the negative.

  In CTP technology, a conventionally used negative film is replaced by a mask that is formed and integrated in the printing plate to cover areas that should not be polymerized. As a method for obtaining this integrated mask, an image mask is formed by providing an infrared-sensitive layer (thermal mask layer) opaque to actinic radiation on a photosensitive resin layer and evaporating the infrared-sensitive layer with an infrared laser. Is widely used (see Patent Document 1).

  The heat-sensitive mask layer is generally made of carbon black, which is a radiation opaque material, and a binder. The thermal mask layer is ablated by an infrared laser, and a thinner layer is preferable from the viewpoint of ablation efficiency. In addition, the thinner the film, the less the wrinkle effect on the relief. However, the heat-sensitive mask layer is generally required to have a transmission optical density (light-shielding property) of 2.0 or more in order to block the transmission of chemical radiation to the photopolymerization layer. An ideal heat-sensitive mask layer is a layer having a transmission optical density (light-shielding property) of a predetermined level or more while being a thin film.

The optical density (light-shielding property) of the heat-sensitive mask layer is generally defined by the following formula.
Optical density = log (100 / T) = εcl
Here, T is the transmittance (%), c is the concentration of the infrared absorbing material (mol·l ⁻¹ ), l is the thickness (cm), and ε is the molecular extinction coefficient (l · mol ^{−1 ·} cm ⁻¹ ). is there. As can be understood from the above formula, it is possible to increase the optical density by increasing the concentration of the infrared absorbing material (carbon black), but in this case, the film becomes too brittle and innumerable scratches occur in the processing process. To do. Since the light cannot be shielded from the damaged portion, an unnecessary image is formed on the relief. In addition, the optical density can be increased by increasing the thickness of the coating film, but in this case, high energy is required for ablation, and this causes wrinkles on the relief. Relief wrinkles are a particularly significant problem in water-developed plates in which the photosensitive resin layer is flexible.

  On the other hand, it is known that the light shielding property changes depending on the dispersion state of carbon black even if the carbon black concentration and the layer thickness are the same. In general, the better the dispersion state, the higher the optical density can be achieved. The dispersion state of carbon black is greatly influenced by the binder resin.

  Until now, as a binder resin of a heat sensitive mask layer, a nylon resin (see Patent Document 2), a polyvinyl alcohol resin (see Patent Document 3), a thermally decomposable polymer (see Patent Document 4), or a method using a plurality of polymers It has been known. When nylon resin is used, the thermal mask layer has good scratch resistance, but the dispersion state of carbon black is not good, and it is necessary to increase the layer thickness in order to achieve a predetermined optical density. On the other hand, when a polyvinyl alcohol resin is used, there is a drawback that the film has poor scratch resistance. Even when a thermally decomposable polymer is used, satisfactory ablation efficiency cannot be obtained. Accordingly, there is currently no thermal mask layer that has a high optical density (light-shielding property) and excellent scratch resistance despite being a thin film.

  As a result of intensive studies to achieve the above object, the present inventors have obtained a desired effect by using a butyral resin and a polar group-containing polyamide as a binder for improving the dispersibility of carbon black in the thermal mask layer. I found out that

  In Patent Document 5, as a method for producing a heat-sensitive mask layer, a dispersion binder is dissolved in a solvent, carbon black is dispersed therein to prepare a dispersion, and a PET film support subjected to a release treatment on both sides is coated with a bar coater. There has been proposed a method of coating using a coating. Since the heat-sensitive mask layer coating solution used here is extremely unstable in dispersibility immediately after adjustment, it was necessary to store it at room temperature for about one month to stabilize the dispersion before coating. In addition, the thermal mask layer obtained by applying the thermal mask layer coating liquid has high light-shielding properties and relatively small variation in optical density. Therefore, it was necessary to further reduce the variation in optical density.

Special table hei 7-506201 JP-A-8-305030 JP-A-9-171247 JP 2002-214792 A Japanese Patent Application No. 2008-15284

  The present invention was created in view of the current state of the prior art, and an object of the present invention is to provide a thermal mask layer that can cope with high resolution with less variation in optical density than conventional ones. In addition, it is possible to improve the productivity and to prepare a heat-sensitive mask layer coating solution that can be easily dispersed and stabilized in a short time.

  As a result of intensive investigations to achieve such an object, the present inventors have used a butyral resin, a cationic polyamide, and an anionic polymer compound as a binder for improving the dispersibility of carbon black in the thermal mask layer. The present inventors have found that a desired effect can be obtained and have completed the present invention.

The present invention is as follows.
(1) A water-developable photosensitive relief printing original plate in which at least (A) a support, (B) a photosensitive resin layer, and (C) a thermal mask layer are sequentially laminated, and (C) the thermal mask layer comprises 1. A photosensitive letterpress printing original plate comprising carbon black and a dispersion binder, wherein the dispersion binder contains a butyral resin, a cationic polyamide, and an anionic polymer compound.
(2) The photosensitive relief printing original plate of (1) whose ratio of cationic polyamide and anionic polymer compound is 99-75: 1-25.
(3) The photosensitive relief printing original plate of (1) or (2) whose weight ratio of butyral resin and polar group-containing polyamide is 20-80: 20-80.
(4) The photosensitive relief printing original plate of (1)-(3) whose weight ratio of carbon black and a dispersion | distribution binder is 25-50: 20-75.
(5) The photosensitive relief printing original plate of (1) to (4), wherein the cationic high polyamide is a polyamide having any one of primary to tertiary amine groups and quaternary ammonium salts.
(6) The photosensitive relief printing original plate of (1) to (5), wherein the anionic polymer compound is an aqueous resin having any of a carboxyl group, a sulfonic acid group, and a sulfate group.
(7) The photosensitive relief printing original plate of (1)-(6) which provided the thermal mask layer using the solvent containing water and at least 1 sort (s) of alcohol as a solvent for thermal mask layer coating liquids.
(8) The photosensitive relief printing original plate as described in (7) whose alcohol in a thermal mask layer coating liquid is methanol, ethanol, isopropanol, butanol, isobutanol, or heptanol.

  The photosensitive letterpress printing original plate of the present invention is intended to improve the dispersibility of carbon black by using a butyral resin as a carbon black dispersion binder of a heat-sensitive mask layer, and appropriately use a cationic polyamide and an anionic polymer compound. By using it at a proper ratio, the dispersibility is improved and the dispersion stabilization time is shortened. Therefore, according to the present invention, the heat-sensitive mask layer coating liquid can be easily adjusted in a short time, and as a result, production and cost can be improved. The heat-sensitive mask layer obtained by applying this heat-sensitive mask layer coating solution has a high light shielding property while being a thin film.

Hereinafter, the photosensitive relief printing original plate of the present invention will be described in detail.
The relief printing original plate of the present invention has a structure in which at least (A) a support, (B) a photosensitive resin layer, and (C) a thermal mask layer are sequentially laminated.

  The (A) support used in the original plate of the present invention is flexible, but is preferably a material excellent in dimensional stability. For example, a metal support such as steel, aluminum, copper, or nickel, a polyethylene terephthalate film And a thermoplastic resin support such as a polyethylene naphthalate film, a polybutylene terephthalate film, or a polycarbonate film. Among these, a polyethylene terephthalate film having excellent dimensional stability and sufficiently high viscoelasticity is particularly preferable. The thickness of the support is from 50 to 350 μm, preferably from 100 to 250 μm, from the viewpoint of mechanical properties, shape stability, or handleability during plate making. Moreover, in order to improve the adhesiveness of a support body and the photosensitive resin layer, you may provide an adhesive agent between them as needed.

  The photosensitive resin layer (B) used in the original plate of the present invention comprises a synthetic polymer compound, a photopolymerizable unsaturated compound, and essential components of a photopolymerization initiator, a plasticizer, a thermal polymerization inhibitor, a dye, and a pigment. , UV absorbers, fragrances, or optional additives such as antioxidants.

  As the synthetic polymer compound, conventionally known soluble synthetic polymer compounds can be used. For example, polyether amide (for example, JP-A No. 55-79437), polyether ester amide (for example, JP-A No. 58-113537). Etc.), tertiary nitrogen-containing polyamide (for example, JP-A-50-76055), ammonium salt type tertiary nitrogen atom-containing polyamide (for example, JP-A-53-36555), amide compound having one or more amide bonds And an addition polymer of an organic diisocyanate compound (for example, JP-A-58-140737), an addition polymer of a diamine having no amide bond and an organic diisocyanate compound (for example, JP-A-4-97154), and the like. . Of these, tertiary nitrogen atom-containing polyamides and ammonium salt type tertiary nitrogen atom-containing polyamides are preferred.

  Examples of the photopolymerizable unsaturated compound include ring-opening addition reaction products of polyglycidyl ether of polyhydric alcohol, methacrylic acid and acrylic acid. Examples of the polyhydric alcohol include dipentaerythritol, pentaerythritol, trimethylolpropane, glycerin, ethylene glycol, diethylene glycol, triethylene glycol, and an ethylene oxide adduct of phthalic acid. Among them, trimethylolpropane is preferable.

  Examples of the photopolymerization initiator include benzophenones, benzoins, acetophenones, benzyls, benzoin alkyl ethers, benzyl alkyl ketals, anthraquinones, thioxanthones, and the like. Specifically, benzophenone, chlorobenzophenone, benzoin, acetophenone, benzyl, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, benzoin isobutyl ether, benzyl dimethyl ketal, benzyl diethyl ketal, benzyl diisopropyl ketal, anthraquinone, 2-ethylanthraquinone Examples include 2-methylanthraquinone, 2-allyl anthraquinone, 2-chloroanthraquinone, thioxanthone, and 2-chlorothioxanthone.

  The thermal mask layer (C) used in the original plate of the present invention is composed of carbon black, which is a material having a function of absorbing infrared laser and converting it into heat, and a function of blocking ultraviolet light, and a dispersion binder thereof. . Further, as an optional component other than these, a pigment dispersant, a filler, a surfactant, a coating aid, or the like can be contained within a range that does not impair the effects of the present invention.

In the present invention, a cationic polyamide and an anionic polymer compound are used in combination in addition to a butyral resin as a carbon black dispersion binder. The butyral resin can improve the dispersibility of carbon black and contribute to high light-shielding properties. However, when the butyral resin alone is used, the coating film of the thermal mask layer becomes brittle, and the scratch resistance is poor. Therefore, cationic polyamide is used to overcome this scratch resistance. Cationic polyamide is excellent in the dispersibility of carbon black due to the effect of containing a cationic group, and even if a part of the butyral resin is replaced, the dispersibility is not lowered. However, when only the butyral resin and the cationic polyamide are used, it takes a long time to stabilize the dispersion of carbon black in adjusting the heat-sensitive mask layer. Therefore, in the present invention, an anionic polymer compound is used for shortening the dispersion stabilization time. The anionic polymer compound is adsorbed on the carbon black while avoiding the site where the cationic polyamide is adsorbed, and promotes its dispersion stabilization.
In addition, since both the butyral resin, the cationic polyamide, and the anionic polymer compound are dissolved in alcohol and water, when these are used together as a dispersion binder, the heat-sensitive mask layer is excellent in handling during film formation and developability in a solvent and water. Can be easily created. A heat-sensitive mask layer comprising a butyral resin, a cationic polyamide, and an anionic polymer compound can be suitably used as a heat-sensitive mask layer for a water-developable plate because it easily disperses in water.

  The butyral resin used as the dispersion binder is also called polyvinyl butyral, and is a kind of polyvinyl acetal produced by reacting polyvinyl alcohol and butyraldehyde with an acid catalyst.

  As the cationic polyamide used as the dispersion binder, a copolymerized polyamide having a cationic group is preferable. The polyamide to be used may be appropriately selected from conventionally known cationic polyamides, and examples thereof include primary to tertiary amine group-containing polyamides and quaternary ammonium base-containing polyamides.

  The anionic polymer compound used as the dispersion binder is a polymer compound having a molecular weight of 10,000 or more obtained by copolymerizing two or more types of monomers, and one or more types of monomers are carboxyl groups or sulfonic acid groups. A monomer having an anionic group such as a sulfate group can be used. For example, a carboxyl group-containing polyacrylic urethane, which is a block copolymer of acrylic acid and polyurethane, a sulfonic acid group-containing polyester obtained by condensation polymerization of a sulfonic acid group-containing dicarboxylic acid and a diol, an acrylic acid monomer and a sulfonic acid type Examples thereof include a block copolymer with a monomer. Of these, carboxyl group-containing polyacryl urethane and sulfonic acid group-containing polyester are preferred.

The ratio of the cationic polyamide to the anionic polymer compound in the dispersion binder is preferably 99 to 75: 1 to 25. When an anionic polymer compound is not used, a long time for stabilizing the dispersion of the heat-sensitive mask layer coating solution is required. When an excessive amount of an anionic polymer compound is used, the charge balance for maintaining the dispersion of carbon black is lost, and the dispersion of carbon black does not proceed. Therefore, not only a long dispersion stabilization time for the heat-sensitive mask layer coating solution is required, but also the saturated optical density (light shielding property) is inferior, and the variation becomes large.

  (C) The thermal mask layer preferably has an optical density of 2.0 or more with respect to actinic radiation, more preferably an optical density of 2.0 to 3.0, and particularly preferably 2.2 to 2. The optical density is 5.

  (C) The layer thickness of the thermal mask layer is preferably 0.5 to 2.5 μm, more preferably 1.0 to 2.0 μm. If it is more than the said minimum, a high coating technique is not required but an optical density more than fixed can be obtained. Moreover, if it is below the said upper limit, high energy is not required for evaporation of a thermal mask layer, and it is advantageous in cost.

  (C) It is preferable to protect the printing original plate by providing a peelable flexible cover film on the thermal mask layer. Suitable examples of the peelable flexible cover film include a polyethylene terephthalate film, a polyethylene naphthalate film, and a polybutylene terephthalate film.

The method for producing the relief printing original plate of the present invention is not particularly limited, but is generally produced as follows.
First, components such as a binder other than carbon black of the heat-sensitive mask layer are dissolved in a suitable solvent, and carbon black is dispersed therein to prepare a dispersion. Next, such a dispersion is applied on a support for a heat sensitive mask layer (for example, a PET film), and the solvent is evaporated to prepare one laminate. Further, separately from this, a photosensitive resin layer is formed on the support by coating, and the other laminate is prepared. The two laminated bodies thus obtained are laminated so that the photosensitive resin layer is adjacent to the thermal mask layer under pressure and / or heating. The heat-sensitive mask layer support functions as a protective film on the surface of the printing original plate after completion.
In the present invention, in order to produce the thermal mask layer (C), the composition for the thermal mask layer is dissolved in a solvent to prepare a coating liquid, but alcohol is used from the viewpoint of dispersion as a solvent for preparing each component. Is preferred. Specific alcohols are preferably methanol, ethanol, isopropanol, butanol, isobutanol, and heptanol.

  As a method for producing a printing plate from the printing original plate of the present invention, when a protective film is present, the protective film is first removed from the photosensitive printing plate. Thereafter, the thermal mask layer is irradiated imagewise with an IR laser to form a mask on the photosensitive resin layer. Examples of suitable IR lasers include ND / YAG laser (1064 nm) or diode laser (eg, 830 nm). Laser systems suitable for computer plate making technology are commercially available, and for example, CDI Spark (Esco Graphics) can be used. This laser system includes a rotating cylindrical drum that holds a printing original, an IR laser irradiation device, and a layout computer, and image information is directly transferred from the layout computer to the laser device.

  After the image information is written on the heat-sensitive mask layer, the photosensitive printing original plate is irradiated with actinic rays through the mask. This can be done with the plate attached to the laser cylinder, but removing the plate from the laser device and irradiating with a conventional flat irradiation unit is advantageous in that it can cope with non-standard plate sizes. It is general. As the actinic ray, ultraviolet rays having a wavelength of 150 to 500 nm, particularly 300 to 400 nm can be used. As the light source, a low-pressure mercury lamp, a high-pressure mercury lamp, an ultrahigh-pressure mercury lamp, a metal halide lamp, a xenon lamp, a zirconium lamp, a carbon arc lamp, an ultraviolet fluorescent lamp, or the like can be used. Thereafter, the irradiated plate is developed to obtain a printing plate. The development step can be performed with a conventional development unit.

  Hereinafter, the present invention will be specifically described by way of examples, but the present invention is not limited thereto.

Preparation of Dispersion Binder As a dispersion binder, butyral resin, tertiary amine group-containing polyamide, quaternary ammonium group-containing polyamide, carboxyl group-containing acrylic urethane, and sulfonic acid group-containing polyester were prepared. As the butyral resin, BM-5 manufactured by Sekisui Chemical Co., Ltd. was used. As the tertiary amine group-containing polyamide, one synthesized as follows was used. As the non-polar group-containing polyamide, Macromelt 6900 manufactured by Henkel Corporation was used. RWU-0018 manufactured by Shannan Synthetic Chemical Co., Ltd. was used as the carboxyl group-containing acrylic urethane, and Bironal MD-1335 manufactured by Toyobo Co., Ltd. was used as the sulfonic acid group-containing polyester.

Synthesis of tertiary amine group-containing polyamide, quaternary ammonium base-containing polyamide 50 parts by weight ε-caprolactam, N, N, -di (γ-aminopropyl) piperazine adipate 40 parts by weight, 10 parts by weight of 3-bisaminomethylcyclohexane adipate And 100 parts by weight of water were charged into an autoclave, purged with nitrogen, sealed and gradually heated. From the time when the internal pressure reached 10 kg / m ³ , water was distilled off until the pressure could not be maintained, returned to normal pressure in about 2 hours, and then reacted at normal pressure for 1 hour. The maximum polymerization reaction temperature was 255 ° C. As a result, a tertiary amine group-containing polyamide having a melting point of 137 ° C. and a specific viscosity of 1.96 was obtained.
10 parts by weight of this tertiary ammonium group-containing polyamide was dissolved in 100 parts by weight of methanol, hydrochloric acid was added, and the mixture was reacted at room temperature for about 2 hours to be quaternized. Thereby, a quaternary ammonium base-containing polyamide was obtained.

Preparation of thermal mask layer coating liquid Dispersion binder is dissolved in a solvent according to the composition (weight ratio) described in the thermal mask layer composition in Table 1, and carbon black is dispersed therein to prepare a dispersion liquid. A working liquid was used. The solvent used was a mixed solution of methanol and ethanol in a weight ratio of 70:30.

Preparation of heat-sensitive mask layer A PET film support (Toyobo Co., Ltd., E5000, thickness 100 μm) subjected to release treatment on both sides is coated with a heat-sensitive mask layer coating solution so that the layer thickness becomes 1.5 μm. Coating was performed using an appropriately selected bar coater, and drying was performed at 120 ° C. for 5 minutes to form a thermal mask layer.

Performance Evaluation The performance of each thermal mask layer obtained as described above was evaluated as follows.
・ Scratch resistance:
The thermal mask layer prepared on the PET film support is cut into a 20 cm × 20 cm square, and another PET film (Toyobo Co., Ltd., E5000, thickness 100 μm) is overlaid on the layer surface to maintain the state. After scratching once in the left-right direction without applying any force, the scratches formed on the surface of the thermal mask layer were inspected using a 10 × loupe.
○: No scratch.
X: There are 5 or more scratches of 50 μm or more.
・ Dispersion stabilization time:
The optical density increases as time passes immediately after adjustment. The thermal mask layer coating solution was prepared, and the optical density of the thermal mask layer prepared on the PET film support was measured every few days. A black and white transmission densitometer DM-520 (Dainippon Screen Mfg. Co., Ltd.) was used for the measurement. The time taken for the optical density to become saturated and constant was taken as the dispersion stabilization time.
-Light shielding (saturated optical density):
The optical density increases as time passes immediately after adjustment. The thermal mask layer coating solution was prepared, and the optical density of the thermal mask layer prepared on the PET film support was measured every few days. The density at which the increase in optical density stopped and became constant was defined as the saturated optical density, which was used as a measure of light shielding properties. A black and white transmission densitometer DM-520 (Dainippon Screen Mfg. Co., Ltd.) was used for the measurement.
・ Optical density variation:
A sample of A4 size was measured at 20 points, and the standard deviation was taken as the variation in optical density.

The results of these performance evaluations are shown in Table 1 below.

As is apparent from Table 1, in Examples 1 to 5 in which a butyral resin, a cationic group-containing polyamide, and an anionic group-containing polymer compound were used in combination as a carbon black dispersion binder for the thermal mask layer, the thermal mask layer was applied in a short time. The dispersion of the working liquid can be stabilized, and the variation in the optical density of the heat-sensitive mask layer to be applied is extremely small.
However, Comparative Example 1 which does not use an anionic group-containing polymer compound is excellent in light-shielding properties (saturated optical density), but requires a long time for dispersion stabilization. There is also a variation in optical density.
Comparative Example 2 in which an anionic polymer compound is used in excess, and Comparative Example 3 in which no cationic group-containing polyamide is used require time to stabilize the dispersion of the heat-sensitive mask layer coating solution. Is much inferior. In particular, Comparative Example 2 has poor carbon black dispersibility and large variations in optical density.
The comparative example 4 which does not use a butyral resin is inferior in light-shielding property (saturated optical density), and variation in optical density is also observed.
For this reason, when the heat-sensitive mask layers of Comparative Examples 2 to 4 having inferior light-shielding properties are used, the thickness of the heat-sensitive mask layer must be increased in order to provide a light-shielding property at a level that can serve as a negative. As a result, high ablation energy is required. Moreover, when using the heat-sensitive mask layers of Comparative Examples 1 to 3 that require time for dispersion stabilization, a dispersion stabilization period of one month or more must be provided after adjusting the heat-sensitive mask layer coating solution, which is disadvantageous in terms of production and cost. Inferior in terms.

  From the above results, if a butyral resin, a cationic group-containing polyamide and an anionic group-containing polymer compound are used in combination as a carbon black dispersion binder in the thermal mask layer, a thermal mask layer having high light-shielding properties and scratch resistance can be obtained with a thin film. The heat-sensitive mask layer coating liquid to be applied can be produced in a short time.

  The photosensitive letterpress printing original plate of the present invention is extremely useful as a CTP plate to be ablated with an infrared laser because it has a high light shielding property and scratch resistance even with a thin heat-sensitive mask layer.

Claims (8)

A water-developable photosensitive relief printing original plate in which at least (A) a support, (B) a photosensitive resin layer, and (C) a thermal mask layer are sequentially laminated, and (C) the thermal mask layer is carbon black A photosensitive relief printing original plate comprising a dispersion binder, wherein the dispersion binder contains a butyral resin, a cationic polyamide, and an anionic polymer compound. The photosensitive letterpress printing original plate according to claim 1, wherein the ratio of the cationic polyamide to the anionic polymer compound is 99 to 75: 1 to 25.   3. The photosensitive letterpress printing original plate according to claim 1, wherein a weight ratio of the butyral resin to the cationic polyamide is 20 to 80:20 to 80. 4.   The photosensitive letterpress printing original plate according to any one of claims 1 to 3, wherein the weight ratio of carbon black to the dispersion binder is 25 to 50:20 to 75.   The photosensitive relief printing original plate according to any one of claims 1 to 4, wherein the cationic high polyamide is a polyamide having any one of a primary to tertiary amine group and a quaternary ammonium salt.   6. The photosensitive letterpress printing original plate according to claim 1, wherein the anionic polymer compound is an aqueous resin having any of a carboxyl group, a sulfonic acid group, and a sulfate group. The photosensitive relief printing original plate in any one of Claims 1-6 which provided the thermal mask layer using the solvent containing water and at least 1 sort (s) of alcohol as a solvent for thermal mask layer coating liquids.   The photosensitive letterpress printing original plate according to claim 7, wherein the alcohol in the thermal mask layer coating solution is methanol, ethanol, isopropanol, butanol, isobutanol, or heptanol.