JP2024051371A - Flexographic printing plate original plate and manufacturing method of flexographic printing plate - Google Patents

Abstract

To provide a flexographic printing plate original plate which can suppress in-curling of a flexographic printing plate even after printing.SOLUTION: A flexographic printing plate original plate has at least a support and a photosensitive resin layer, wherein the photosensitive resin layer contains at least a hydrophilic plasticizer (component A), an ethylenically unsaturated group-containing monomer (component B) having a chemical structure having the number of repetition of ethylene oxide of 2 or more, and a hydroxyl group, and a hydrophilic polymer (component C), a content in the photosensitive resin layer of the component A is 30 mass% or less, and tensile elastic modulus after photocuring of the photosensitive resin layer is 2.5 MPa or less.SELECTED DRAWING: None

Description

The present invention relates to a flexographic printing plate precursor and a method for producing a flexographic printing plate using the same.

Taking advantage of its flexibility, flexographic printing is widely used in applications such as paper containers, labels, soft packaging, and electronics. A commonly used method for forming a relief on a flexographic printing plate used in flexographic printing is to selectively photo-cure the image area by irradiating the photosensitive resin layer of the flexographic printing plate master with ultraviolet light through an image mask or master film, and then remove the uncured area with a developer.

In recent years, due to environmental considerations, development of flexographic printing plate precursors that can be developed with water has progressed. For example, as a technology for shortening the development process, increasing the flexibility of the relief precursor or the relief structure, and suppressing the curl phenomenon, a developable relief precursor (see, for example, Patent Document 1) has been proposed, which is a photosensitive composition of a developable relief precursor, the photosensitive composition including at least one ethylenically unsaturated monomer containing at least one ionic group, at least one photoinitiator or photoinitiator system, at least one water-soluble and/or water-dispersible binder, and optionally one or more additives. Also, as a photosensitive flexographic printing plate precursor that can obtain stable prints even during long-run printing, a photosensitive flexographic printing plate precursor has been proposed that includes at least a substrate and a photosensitive resin layer, the photosensitive resin layer containing at least (a) a hydrophilic polymer, (b) a hydrophilic monomer, (c) a photopolymerization initiator, (d) a hydrophilic plasticizer, and (e) an ink repellent agent, and when exposed and developed so that 99 or more out of 100 175-line 3% halftone dots are reproduced, the contact angle of the photosensitive resin layer after photocuring with tripropylene glycol diacrylate is 40° to 70°, and the mass change rate of the photosensitive resin layer after photocuring after immersion in tripropylene glycol acrylate at 50° C. for 24 hours is -4.0% to 4.0% (see, for example, Patent Document 2).

JP 2022-085860 A International Publication No. 2022/131234

The relief precursor described in Patent Document 1 suppresses resin shrinkage due to water evaporation, and thus suppresses warping. However, the inventors' investigations revealed that the plate surface temperature can reach 30°C to nearly 40°C during printing, and that there are still issues with warping of the relief due to shrinkage that occurs during printing. The photosensitive flexographic printing plate precursor described in Patent Document 2 also has the issue that the relief after printing is prone to warping inward (in-curl).

In flexographic printing, it is common to attach a flexographic printing plate to the plate cylinder using double-sided adhesive cushion tape, and then peel off the flexographic printing plate when printing is completed. Also, the same flexographic printing plate is often used multiple times depending on the printing order. If in-curl occurs on the flexographic printing plate after printing, it can cause misalignment when attaching it to the cylindrical curved surface of the plate cylinder, reducing workability, so there is a need to suppress in-curl after printing.

In view of the above problems, the present invention aims to provide a flexographic printing plate precursor that can suppress in-curl of the flexographic printing plate even after printing.

In order to solve the above problems, the present invention mainly has the following configuration.
(1) A flexographic printing plate precursor having at least a support and a photosensitive resin layer, the photosensitive resin layer containing at least a hydrophilic plasticizer (component A), an ethylenically unsaturated group-containing monomer (component B) having a hydroxyl group and a chemical structure in which the number of ethylene oxide repeats is two or more, and a hydrophilic polymer (component C), the content of component A in the photosensitive resin layer being 30 mass% or less, and the tensile modulus of elasticity of the photosensitive resin layer after photocuring being 2.5 MPa or less.
(2) The flexographic printing plate precursor according to (1), wherein the content of Component B in the photosensitive resin layer is from 20% by mass to 60% by mass.
(3) The flexographic printing plate precursor according to (1) or (2), wherein Component B contains a monofunctional monomer.
(4) The flexographic printing plate precursor according to any one of (1) to (3), wherein the photosensitive resin layer further contains a polyfunctional monomer (component D), and the content of Component D in the photosensitive resin layer is 10 mass % or less.
(5) The flexographic printing plate precursor according to any one of (1) to (4), comprising a partially saponified polyvinyl alcohol and/or a partially saponified polyvinyl alcohol derivative as the component C.
(6) The flexographic printing plate precursor according to (5), wherein the partially saponified polyvinyl alcohol and/or the partially saponified polyvinyl alcohol derivative has a degree of saponification of 55 mol % or more and 75 mol % or less.
(7) The flexographic printing plate precursor according to any one of (1) to (6), wherein the amount of warping after immersion in ethylene oxide-modified trimethylolpropane triacrylate following photocuring of the photosensitive resin layer is 3 mm or less.
(8) A method for producing a flexographic printing plate, comprising: an exposure step of irradiating a photosensitive resin layer of the flexographic printing plate precursor according to any one of (1) to (7) with ultraviolet light to partially photo-cure the photosensitive resin layer; and a development step of removing an uncured portion of the photosensitive resin layer.

The flexographic printing plate precursor of the present invention can suppress in-curl of the flexographic printing plate even after printing.

The present invention will be described in detail below.

The flexographic printing plate precursor of the present invention (hereinafter, sometimes referred to as "printing plate precursor") is a precursor of a flexographic printing plate (hereinafter, sometimes referred to as "printing plate") used in flexographic printing, and has at least a support and a photosensitive resin layer. The support has the function of holding the photosensitive resin layer. The photosensitive resin layer is a layer that is cured by irradiation with active energy rays such as ultraviolet rays. By having the photosensitive resin layer, it is possible to form a desired relief, for example, by irradiating ultraviolet rays in an imagewise manner. A cover film may be further provided on the photosensitive resin layer, which can protect the surface of the photosensitive resin layer and suppress adhesion of foreign matter, etc. Also, a heat-sensitive mask layer may be provided on the photosensitive resin layer.

The support is preferably made of a material that is flexible and has excellent dimensional stability. Specific examples include plastic sheets such as polyester, and metal plates such as steel, stainless steel, and aluminum. Two or more of these may be used.

From the standpoint of ease of handling and flexibility, the thickness of the support is preferably 100 μm or more and 350 μm or less.

The support is preferably subjected to an easy-adhesion treatment, which can improve adhesion with the photosensitive resin layer. Examples of easy-adhesion treatment methods include mechanical treatments such as sandblasting, physical treatments such as corona discharge, and chemical treatments such as coating. Among these, from the viewpoint of adhesion, it is preferable to provide an easy-adhesion layer by coating.

The printing plate precursor of the present invention is characterized in that the photosensitive resin layer contains at least a hydrophilic plasticizer (component A), an ethylenically unsaturated group-containing monomer (component B) having a chemical structure with 2 or more ethylene oxide repeats and a hydroxyl group, and a hydrophilic polymer (component C), the content of component A in the photosensitive resin layer is 30 mass% or less, and the tensile modulus of elasticity after photocuring of the photosensitive resin layer is 2.5 MPa or less. The present inventors have found that the in-curl after printing of a flexographic printing plate is due to the affinity of the photosensitive resin layer components with the ink components and their extraction into the ink, and the tensile modulus of elasticity of the photosensitive resin layer after photocuring.

In the photosensitive resin layer, component C strengthens the relief of the printing plate by hydrogen bonding between hydrophilic groups. As described below, component A does not have an ethylenically unsaturated group and therefore does not photocure, while the hydrophilic group provides excellent compatibility with component C, and the hydrophilic group allows component C to enter the interpolymer network formed by hydrogen bonding, thereby softening the relief of the printing plate. On the other hand, component A tends to be easily extracted into the ink during printing, but in the present invention, by making the content of component A in the photosensitive resin layer 30% by mass or less, the in-curl of the printing plate can be suppressed even after printing. Component B has the effect of photocuring the photosensitive resin layer by photopolymerization in the exposure step described below. In the present invention, the content of component A, which softens the relief of the printing plate, is kept to 30% by mass or less, while component B has a chemical structure with two or more ethylene oxide repeating units, thereby softening the relief of the printing plate. Furthermore, the ethylene oxide structure has a common partial structure with ethylene oxide group-containing acrylates such as ethylene oxide modified trimethylolpropane triacrylate, which are generally contained in flexographic inks such as UV inks and EB inks described below, and therefore has high affinity with flexographic inks. During printing, when the printing plate and flexographic ink come into contact with each other, the components in the flexographic ink are partially incorporated into the relief, so that even if some components are extracted from the relief of the printing plate into the flexographic ink, the total amount of free components can be kept at the same level as before printing, and in-curl of the printing plate can be suppressed even after printing. Furthermore, since component B has a hydroxyl group, it has excellent compatibility with component C, and bleed-out of component B in the printing plate precursor can be suppressed, and in-curl of the printing plate can be suppressed.

Furthermore, the tensile modulus of elasticity of the photosensitive resin layer after photocuring is an index representing the flexibility of the relief of the printing plate, and if it is 2.5 MPa or less, in-curl of the printing plate can be suppressed even after printing. As described above, the printing plate obtained from the printing plate precursor of the present invention can maintain the total amount of free components at the same level as before printing due to the balance between the incorporation of components in the flexographic ink into the relief during printing and the extraction of components of the relief into the flexographic ink. Therefore, by setting the tensile modulus of elasticity of the photosensitive resin layer after photocuring in this range, the tensile modulus of elasticity of the relief can be maintained low even after printing, and in-curl can be suppressed. Therefore, the printing plate has excellent workability even when the same flexographic printing plate is used multiple times.

Next, we will explain each component of the photosensitive resin layer.

Component A in the present invention refers to a compound that has a hydrophilic group, does not have an ethylenically unsaturated group, and has a weight average molecular weight of less than 10,000. Examples of hydrophilic groups include hydroxyl groups, amino groups, amide groups, carboxyl groups, and phosphate ester groups. Two or more of these may be used. Among these, hydroxyl groups are preferred. By having a hydrophilic group, it is possible to provide excellent affinity with component C, suppress extraction from the photosensitive resin layer in the printing plate precursor, and reduce the tensile modulus after photocuring. In addition, it is possible to suppress extraction from the relief of the printing plate during printing, and suppress in-curl.

Examples of component A include polyethylene glycol and its derivatives, polypropylene glycol and its derivatives, glycerin and its derivatives, trimethylolethane and its derivatives, trimethylolpropane and its derivatives, pentaerythritol and its derivatives, triethanolamine, polyoxydiethyleneamine, N-methyldiethanolamine, alkylbenzenesulfonamide, lactic acid, malic acid, diethyl phosphate, dipropyl phosphate, etc. Two or more of these may be contained.

The weight average molecular weight of component A is preferably 200 or more and 4,000 or less. By making the weight average molecular weight 200 or more, extraction by flexographic inks such as UV inks and EB inks described below can be suppressed, and in-curl of the printing plate can be further suppressed even after printing. The weight average molecular weight is more preferably 300 or more. On the other hand, by making the weight average molecular weight 4,000 or less, the relief of the printing plate can be made more flexible. The weight average molecular weight is more preferably 1,000 or less.

The content of component A in the photosensitive resin layer is 30% by mass or less. As mentioned above, component A tends to be easily extracted into the ink during printing, and if the content of component A is more than 30% by mass, the in-curl of the printing plate after printing increases. On the other hand, the content of component A is preferably 5% by mass or more, which can make the relief of the printing plate more flexible.

Component B has a chemical structure with two or more ethylene oxide repeat units, a hydroxyl group, and an ethylenically unsaturated group.

Examples of ethylenically unsaturated groups include vinyl groups, acryloyl groups, and methacryloyl groups. Two or more of these may be present.

As described above, component B has a chemical structure with an ethylene oxide repeat number of 2 or more, which makes the relief of the printing plate flexible and can suppress in-curl of the printing plate even after printing. The ethylene oxide repeat number is more preferably 4 or more. On the other hand, the ethylene oxide repeat number is preferably 30 or less, which can improve the strength of the relief of the printing plate. The ethylene oxide repeat number is more preferably 20 or less, which has better compatibility with component C, can suppress bleed-out of component B in the printing plate precursor, and can suppress in-curl of the printing plate.

Furthermore, because component B has a hydroxyl group, it has excellent compatibility with component C, which can suppress bleeding out of component B in the printing plate precursor and suppress in-curl of the printing plate.

As component B, a monofunctional monomer is preferred. Here, monofunctional means having only one ethylenically unsaturated group in the molecule. By using a monofunctional monomer, the relief of the printing plate can be made more flexible, and the tensile modulus after photocuring can be maintained lower. Therefore, in-curl of the printing plate can be further suppressed even after printing.

Component B may, for example, be polyethylene glycol mono(meth)acrylate, polyethylene glycol polypropylene glycol mono(meth)acrylate, polyethylene glycol polybutylene glycol mono(meth)acrylate, etc. Here, (meth)acrylate is a general term for acrylate and methacrylate. Two or more of these may be contained.

The content of component B in the photosensitive resin layer is preferably 20% by mass or more and 60% by mass or less. By making the content of component B 20% by mass or more, the relief of the printing plate can be made more flexible and the tensile modulus after photocuring can be maintained lower. Therefore, the in-curl of the printing plate can be further suppressed even after printing. On the other hand, by making the content of component B 60% by mass or less, the strength of the relief of the printing plate can be improved and the printing reproducibility of fine images can be improved.

Component C is a polymer having a hydrophilic group, and refers to a compound having a weight average molecular weight of 10,000 or more. By having Component C have a hydrophilic group, it is possible to improve the developability with a developer containing 50% by mass or more of water, that is, the so-called water developability, in the development step described below. Examples of hydrophilic groups include hydroxyl groups, amino groups, amide groups, carboxyl groups, phosphate groups, pyrrolidone skeletons, and alkylene oxide groups. Two or more of these may be contained. Among these, hydroxyl groups are preferred.

Component C may be, for example, partially saponified polyvinyl alcohol or its derivatives, polyamide, polyvinylpyrrolidone, polyether, carboxyl group-containing polyester, sulfonic acid group-containing polyester, etc. Two or more of these may be included. Among these, partially saponified polyvinyl alcohol or its derivatives are preferred from the viewpoints of water developability, ease of processing, and sharpness of the relief of the resulting printing plate. In addition, as a derivative of partially saponified polyvinyl alcohol or its derivatives, those having functional groups in the side chain and/or main chain may be mentioned. As an example of the functional group, for example, (meth)acryloyl group, etc., can be mentioned, which can improve the fine image reproducibility in the printing plate. In addition, as a method for introducing a functional group into partially saponified polyvinyl alcohol, for example, the method described in Japanese Patent No. 6295642 may be mentioned. From the viewpoint of water developability, the degree of saponification of partially saponified polyvinyl alcohol or its derivatives is preferably 55 mol% or more. On the other hand, due to the influence of hydrogen bonds due to hydroxyl groups, the tensile modulus of the photosensitive resin layer after photocuring tends to be higher as the degree of saponification is higher. From the viewpoint of making the relief of the printing plate more flexible and easily adjusting the tensile modulus of elasticity of the photosensitive resin layer after photocuring to a preferred range described later, the saponification degree of the partially saponified polyvinyl alcohol is preferably 75 mol% or less, more preferably 70 mol% or less. Here, the saponification degree in the present invention can be calculated by preparing a 3 mass% aqueous solution of partially saponified polyvinyl alcohol or its derivative, subjecting it to a complete saponification treatment using an excess of 0.5 mol/L aqueous sodium hydroxide solution, and then measuring the amount of sodium hydroxide required for complete saponification by titration with 0.5 mol/L hydrochloric acid. Note that, when the photosensitive resin layer contains two or more types of partially saponified polyvinyl alcohol or its derivatives, the saponification degree in the present invention means the saponification degree of the two or more types of partially saponified polyvinyl alcohol and its derivatives as a whole.

The content of component C in the photosensitive resin layer is preferably 20% by mass or more, and more preferably 30% by mass or more. On the other hand, the content of component C in the photosensitive resin layer is preferably 70% by mass or less, and more preferably 60% by mass or less.

The weight average molecular weight of component C is preferably 20,000 or more, which can improve the fine image reproducibility of the printing plate. On the other hand, the weight average molecular weight of component C is preferably 200,000 or less, which can shorten the development time of the printing plate precursor and improve productivity. Here, the weight average molecular weight in the present invention can be determined by GPC measurement. For example, the weight average molecular weight can be measured using a gel permeation chromatograph-multiangle light scattering photometer manufactured by Wyatt Technology under the conditions of a column temperature of 40°C and a flow rate of 0.7 mL/min.

In the present invention, it is preferable that the photosensitive resin layer further contains a polyfunctional monomer (component D). Here, a polyfunctional monomer means that the molecule has a total of two or more ethylenically unsaturated groups. In the present invention, among compounds having ethylenically unsaturated bonds, those having a chemical structure with two or more ethylene oxide repeats and a hydroxyl group are classified as component B, whether monofunctional or polyfunctional, and component D does not contain either or both of a chemical structure with two or more ethylene oxide repeats or a hydroxyl group, and has a total of two or more ethylenically unsaturated groups in the molecule. By containing component D, the crosslink density of the relief in the printing plate can be increased, and the print reproducibility of fine images can be improved.

Component D preferably has the hydrophilic group described above. By having a hydrophilic group, it has excellent affinity with component C, and can suppress bleeding out of component D in the printing plate precursor and suppress in-curl of the printing plate.

Examples of component D include 2-hydroxy-3-acryloyloxypropyl methacrylate, a reaction product of 2-acryloyloxyethyl succinic acid and glycidyl methacrylate, a reaction product of 2-acryloyloxyethyl-2-hydroxyethyl-phthalic acid and methacrylic acid, a reaction product of 2-hydroxyethyl acrylate and methacrylic acid, and a reaction product of ethylene glycol diglycidyl ether, acrylic acid and methacrylic acid. Two or more of these may be included.

The content of component D in the photosensitive resin layer is preferably 10% by mass or less, which can make the relief of the printing plate more flexible and suppress in-curl. On the other hand, the content of component D in the photosensitive resin layer is preferably 1% by mass or more, which can further improve the print reproducibility of fine images. The content of component D in the photosensitive resin layer is more preferably 2% by mass or more.

The photosensitive resin layer may contain photopolymerization initiators, polymerization inhibitors, colorants, UV absorbers, surface modifiers, defoamers, surfactants, fragrances, etc., as necessary.

The thickness of the photosensitive resin layer is preferably 0.3 mm or more, and more preferably 0.5 mm or more. On the other hand, the thickness of the photosensitive resin layer is preferably 5 mm or less, and more preferably 3 mm or less.

In the present invention, the tensile modulus of elasticity of the photosensitive resin layer after photocuring is an index representing the flexibility of the relief of the printing plate, and is 2.5 MPa or less. As described above, the printing plate obtained from the printing plate precursor of the present invention can maintain the total amount of free components at the same level as before printing due to the balance between the incorporation of components in the flexographic ink into the relief during printing and the extraction of components of the relief into the flexographic ink. Therefore, by setting the tensile modulus of elasticity of the photosensitive resin layer after photocuring in this range, the tensile modulus of the relief can be maintained low even after printing, and in-curl can be suppressed. The tensile modulus of elasticity of the photosensitive resin layer after photocuring is more preferably 2.0 MPa or less. On the other hand, the tensile modulus of elasticity of the photosensitive resin layer after photocuring is preferably 1.0 MPa or more, which can suppress deformation of the relief of the printing plate during printing and improve the printing reproducibility of fine images. The tensile modulus of elasticity of the photosensitive resin layer after photocuring is more preferably 1.5 MPa or more.

Here, the tensile modulus of elasticity of the photosensitive resin layer after photocuring in the present invention can be measured by vacuum-contacting a sensitivity measurement gray scale (21 STEP SENSITIVITY GUIDE manufactured by STOUFFER GRAPHIC ARTS EQUIPMENT CO.) with the photosensitive resin layer, exposing the photosensitive resin layer to light on one side under conditions where the gray scale sensitivity is 16±1 steps using a high-intensity chemical lamp (TL 80W/10R manufactured by Philips), and then punching out a dumbbell-shaped No. 2 sample as described in JIS K6251:2017 to prepare a tensile test sample, using a method in accordance with JIS K7161-1:2014. Specifically, a stress-strain curve is measured using a tensile tester (Orientec Co., Ltd. Tensilon Universal Tester RTM-100) at a temperature of 20°C, a relative humidity of 60%, a chuck distance of 10 mm, and a tensile speed of 100 mm/min. The slope of the stress-strain curve between two points of strain 0.5% to 5.0% is taken as the tensile modulus. The tensile modulus is measured for five samples for each tensile test, and the average value is calculated. Methods for extracting the photosensitive resin layer from the printing plate include, for example, peeling it off from the support, and cutting it out near the interface with the support.

One way to set the tensile modulus of the photosensitive resin layer after photocuring within the above range is, for example, to set the composition of the photosensitive resin layer within the above-mentioned preferred range.

The amount of warping after immersion in ethylene oxide modified trimethylolpropane triacrylate after photocuring of the photosensitive resin layer is preferably 3 mm or less, more preferably 0 mm or less. Ethylene oxide modified trimethylolpropane triacrylate is generally contained in flexographic inks such as UV inks and EB inks, and the amount of warping described above is an index that indicates the degree of in-curl after printing. When the amount of warping is 3 mm or less, even when the same flexographic printing plate is used multiple times, it is easy to wind it around the plate cylinder, and workability is excellent. On the other hand, from the viewpoint of suppressing thickening of the printed matter due to swelling, the amount of in-curl after printing is completed is preferably -10 mm or more, more preferably -3 mm or more.

Here, the amount of warping after immersion in ethylene oxide-modified trimethylolpropane triacrylate after photocuring of the photosensitive resin layer in the present invention can be measured by the following method. First, for the printing plate precursor, the photosensitive resin layer is photocured under the same conditions as for measuring the tensile modulus of elasticity after photocuring of the photosensitive resin layer, and then a circular sample with a diameter of 50 mm is cut out and immersed in ethylene oxide-modified trimethylolpropane triacrylate maintained at a temperature of 50°C for 24 hours, after which the ethylene oxide-modified trimethylolpropane triacrylate on the surface of the removed circular sample is wiped off with gauze. The circular sample is placed on a 5 mm thick glass plate with the support side facing down in an environment of 23°C and 50% humidity. When the photosensitive resin layer is aligned so that it faces inward, the height from the glass surface in contact with the circular sample to the bottom end of the support that is the highest and the height from the bottom end of the substrate that is the second highest are measured using a JIS Class 1 metal ruler in mm to the first decimal place, and the average of the two measurements is taken as the amount of warping. When the photosensitive resin layer is aligned so that it faces outward, the height from the glass surface in contact with the sample to the bottom end of the support that is the highest is similarly measured and taken as the amount of warping. In the latter case, the amount of warping is expressed with a negative sign. The amount of warping is measured for five circular samples each, and the average is calculated.

One way to control the amount of warping after immersion in ethylene oxide-modified trimethylolpropane triacrylate after photocuring of the photosensitive resin layer within the above range is, for example, to set the composition of the photosensitive resin layer within the above-mentioned preferred range.

When the printing plate precursor of the present invention has a cover film on the photosensitive resin layer, the photosensitive resin layer may be in direct contact with the cover film, or one or more layers may be present between the photosensitive resin layer and the cover film. Examples of layers between the photosensitive resin layer and the cover film include an anti-adhesion layer that prevents adhesion of the surface of the photosensitive resin layer.

As the cover film, for example, a plastic sheet such as polyester or polyethylene is preferably used. The thickness of the cover film is preferably 10 to 150 μm. The surface of the cover film may be roughened to improve the adhesion of the original film.

When the printing plate precursor of the present invention further has a heat-sensitive mask layer on the photosensitive resin layer, the heat-sensitive mask layer preferably substantially blocks ultraviolet light, absorbs infrared laser light during drawing, and is instantly sublimated or ablated in part or in whole by the heat. This creates a difference in optical density between the laser-irradiated and non-irradiated areas, allowing the plate precursor to function in the same way as a conventional original film. Furthermore, an adhesion adjustment layer may be provided between the heat-sensitive mask layer and the photosensitive resin layer, which can improve adhesion between the heat-sensitive mask layer and the photosensitive resin layer.

Next, an example of a method for producing the printing plate precursor of the present invention will be described.

First, components A to C, and if necessary a photopolymerization initiator and other additives, are dissolved in a solvent with heating and thoroughly mixed by stirring to obtain a photosensitive resin composition solution. Each component may be added to the solvent simultaneously and dissolved, or component C may be dissolved by heating and then the other components may be added. A water/alcohol mixed solvent is preferred as the solvent.

Next, a photosensitive resin layer is formed on the support on which an easy-adhesion layer is provided as necessary. Examples of methods for forming the photosensitive resin layer include a method of casting a photosensitive resin composition solution and drying it, and a method of laminating a separately formed photosensitive resin layer sheet to a support on which an easy-adhesion layer is provided as necessary. Thereafter, it is preferable to adhere a cover film on which an anti-tack layer or a heat-sensitive mask layer is formed as necessary to the photosensitive resin layer.

Next, a method for producing a flexographic printing plate using the printing plate precursor of the present invention will be described. The method for producing a flexographic printing plate of the present invention includes an exposure step in which the photosensitive resin layer of the printing plate precursor of the present invention described above is irradiated with ultraviolet light to partially photocure the photosensitive resin layer, and a development step in which the uncured parts of the photosensitive resin layer are removed.

First, the exposure process will be described. In the case where the printing plate precursor has a heat-sensitive mask layer, that is, a so-called CTP plate, a cover film, if any, is peeled off, and an image corresponding to the original film is drawn using a laser drawing machine, after which the photosensitive resin layer is photocured by irradiating it with ultraviolet light. In the case where the printing plate precursor does not have a heat-sensitive mask layer, the photosensitive resin layer is photocured by irradiating it with ultraviolet light through the original film.

The ultraviolet light preferably has a wavelength of 300 to 400 nm, and examples of lamps used for ultraviolet irradiation include high-pressure mercury lamps, ultra-high-pressure mercury lamps, metal halide lamps, xenon lamps, carbon arc lamps, and chemical lamps. When reproducibility of particularly fine thin lines and independent points is required, it is also possible to expose the support side for a short period of time (back exposure) before peeling off the cover film.

Next, the development process will be described. The exposed printing plate precursor is immersed in a developer, and the uncured portions of the photosensitive resin layer are removed with the developer using a brush-type or spray-type developer, thereby forming a relief image on the substrate. The developer preferably contains 50% by mass or more of water, and may contain additives such as surfactants as necessary. The developer temperature during development is preferably 15 to 40°C.

After development, it is preferable to dry the film at 50 to 70°C for about 10 minutes. If necessary, post-exposure may be performed in the atmosphere or in a vacuum by irradiating the film with actinic rays.

Next, a method for producing a printed matter using a flexographic printing plate will be described. It is preferable that the method includes a step of applying ink to the surface of the flexographic printing plate obtained by the above-mentioned method, and a step of transferring the ink to a substrate. Examples of flexographic printing machines include in-line type, center drum type, and stack type.

Preferable inks include ultraviolet-curable inks (UV inks) and electron beam-curable inks (EB inks). Flexographic UV inks and EB inks preferably contain, for example, pigments, resins such as acrylic oligomers, and acrylate monomers. More specifically, examples of flexographic UV inks include FLEXOCURE FORCE (manufactured by Flint) and SICURA FLEX (manufactured by Siegwerk).

By using the printing plate obtained using the printing plate precursor of the present invention for printing with these flexographic inks, it is possible to suppress in-curl of the flexographic printing plate even after printing. The amount of in-curl after printing is preferably 3 mm or less, and from the viewpoint of excellent workability in attaching to the plate cylinder at the time of next use, 0 mm or less is more preferable. On the other hand, from the viewpoint of suppressing thickening of the printed matter due to swelling, the amount of in-curl after printing is preferably -10 mm or more, and more preferably -3 mm or more. Here, a negative value of the amount of in-curl means warping toward the support (out-curl).

The present invention will be described in detail below with reference to examples. First, the materials used in the examples and comparative examples will be described.

[Synthesis Example 1: Synthesis of Hydrophilic Polymer 1]
Partially saponified polyvinyl alcohol (JMR-50M manufactured by Nippon Vinyl Acetate & Poval Co., Ltd.) having a degree of saponification of 63 to 67 mol % was swollen in acetone, to which 1.0 mol % of succinic anhydride was added, and the mixture was stirred at 60° C. for 6 hours to add carboxyl groups to the molecular chains. This polymer was washed with acetone to remove unreacted succinic anhydride and then dried to obtain hydrophilic polymer 1.

3 g of the obtained hydrophilic polymer 1 was collected and subjected to acetone reflux at 80°C for 3 hours using a Soxhlet extractor, then transferred to a petri dish and dried by heating at 105°C for 30 minutes. The oxidation was measured according to JIS K0020:1992 and found to be 11.1 mgKOH/g.

The weight average molecular weight of the obtained hydrophilic polymer 1 was measured using a gel permeation chromatograph-multiangle light scattering photometer manufactured by Wyatt Technology under the conditions of a column temperature of 40°C and a flow rate of 0.7 mL/min, and was found to be 37,000.

A 3% by weight aqueous solution of the obtained hydrophilic polymer 1 was prepared and subjected to a complete saponification treatment using an excess of 0.5 mol/L aqueous sodium hydroxide solution. The degree of saponification was calculated from the amount of sodium hydroxide required for complete saponification by titration with 0.5 mol/L hydrochloric acid, and was found to be 65 mol%.

[Synthesis Example 2: Synthesis of hydrophilic polymer 2]
Hydrophilic polymer 2 was obtained in the same manner as in Synthesis Example 1, except that a partially saponified polyvinyl alcohol having a saponification degree of 70 to 74 mol% (JR-05 manufactured by Nippon Vinyl Acetate & Poval Co., Ltd.) was used instead of the partially saponified polyvinyl alcohol having a saponification degree of 63 to 67 mol% (JMR-50M manufactured by Nippon Vinyl Acetate & Poval Co., Ltd.). The acid value, measured in the same manner as in Synthesis Example 1, was 10.0 mgKOH/g, the weight average molecular weight was 28,000, and the saponification degree was 72 mol%.

[Synthesis Example 3: Synthesis of hydrophilic polymer 3]
Hydrophilic polymer 3 was obtained in the same manner as in Synthesis Example 1, except that a partially saponified polyvinyl alcohol having a saponification degree of 78 to 82 mol% ("GOHSENOL" (registered trademark) KL-05, manufactured by Mitsubishi Chemical Corporation) was used instead of the partially saponified polyvinyl alcohol having a saponification degree of 63 to 67 mol% (JMR-50M, manufactured by Japan Vinyl Acetate & Poval Co., Ltd.). The acid value, measured in the same manner as in Synthesis Example 1, was 10.5 mgKOH/g, the weight average molecular weight was 26,000, and the saponification degree was 80 mol%.

[Production Example 1: Preparation of Support]
A mixture of 260 parts by weight of a toluene solution of a saturated polyester resin ("Vylon" (registered trademark) 31SS manufactured by Toyobo Co., Ltd.) and 2 parts by weight of benzoin ethyl ether (PS-8A manufactured by Wako Pure Chemical Industries, Ltd.) was heated at 70 ° C. for 2 hours, cooled to 30 ° C., and 7 parts by weight of ethylene glycol diglycidyl ether dimethacrylate was added and mixed for 2 hours. Furthermore, 25 parts by weight of an ethyl acetate solution of a polyvalent isocyanate resin ("Coronate" (registered trademark) 3015E manufactured by Tosoh Corporation) and 14 parts by weight of an industrial adhesive (EC-1368 manufactured by Sumitomo 3M Co., Ltd.) were added and mixed to obtain a coating liquid for an easy-adhesion layer 1.

50 parts by weight of polyvinyl alcohol with a saponification degree of 78.5 to 81.5 mol% ("GOHSENOL" (registered trademark) KH-17, manufactured by Nippon Synthetic Chemical Industry Co., Ltd.) was mixed for 2 hours at 70°C in a mixed solvent of 200 parts by weight of an alcohol mixture ("SOLMIX" (registered trademark) H-11, manufactured by Nippon Alcohol Co., Ltd.) and 200 parts by weight of water, and then 1.5 parts by weight of glycidyl methacrylate ("BLEMMER" (registered trademark) G, manufactured by NOF Corporation) was added and mixed for 1 hour, and then a dimethylaminoethyl methacrylate/2-hydroxyethyl methacrylate weight ratio of 2/1 was added. 3 parts by weight of copolymer (Kyoeisha Chemical Co., Ltd.), 5 parts by weight of benzyl methyl ketal (Ciba Geigy's "Irgacure" (registered trademark) 651), 21 parts by weight of diacrylic acid adduct of propylene glycol diglycidyl ether (Kyoeisha Chemical Co., Ltd., Epoxy Ester 70PA), and 20 parts by weight of ethylene glycol diglycidyl ether dimethacrylate were added and mixed for 90 minutes, cooled to 50°C, and then 0.1 parts by weight of "Megafac" (registered trademark) F-556 (DIC Corporation) was added and mixed for 30 minutes to obtain a coating liquid for easy adhesion layer 2.

On a 188 μm thick polyester (PET) film ("Lumirror" (registered trademark) T60 manufactured by Toray Industries, Inc.), the coating liquid for easy adhesion layer 1 was applied using a bar coater so that the film thickness after drying would be 30 μm, and the film was heated in an oven at 180°C for 3 minutes to remove the solvent, forming easy adhesion layer 1. On top of that, the coating liquid for easy adhesion layer 2 was applied using a bar coater so that the film thickness after drying would be 20 μm, and the film was heated in an oven at 130°C for 3 minutes to remove the solvent, forming easy adhesion layer 2. In this way, a support consisting of easy adhesion layer 2/easy adhesion layer 1/PET substrate was obtained.

[Production Example 2: Preparation of Laminated Film for Heat-Sensitive Mask Layer]
As the film for the cover film, a polyester (PET) film ("Lumirror" (registered trademark) S10 manufactured by Toray Industries, Inc.) having a thickness of 100 μm and having a surface that was not roughened was used.

11 parts by weight of polyvinyl alcohol with a saponification degree of 91 to 94 mol% ("GOHSENOL" (registered trademark) AL-05, manufactured by Nippon Synthetic Chemical Industry Co., Ltd.) was dissolved in a mixed solvent of 55 parts by weight of water, 15 parts by weight of methanol, and 20 parts by weight of n-propanol to obtain a coating liquid for the peeling auxiliary layer.

23 parts by weight of carbon black (MA-100, manufactured by Mitsubishi Chemical Corporation), 1 part by weight of alcohol-insoluble acrylic resin (Dianal (registered trademark) BR-95, manufactured by Mitsubishi Rayon Co., Ltd.), 6 parts by weight of acetyl tributyl citrate (ATBC, manufactured by J-Plus Corporation) as a plasticizer, and 30 parts by weight of diethylene glycol monoethyl ether monoacetate were mixed in advance and kneaded and dispersed using a three-roll mill to obtain a carbon black dispersion.

20 parts by mass of epoxy resin ("Araldite" (registered trademark) 6071, manufactured by Asahi Chiba Co., Ltd.), 27 parts by mass of melamine resin ("U-Ban" (registered trademark) 62, manufactured by Mitsui Chemicals, Inc.), 0.7 parts by mass of phosphoric acid monomer (Light Ester P-1M, manufactured by Kyoeisha Chemical Co., Ltd.), and 140 parts by mass of methyl isobutyl ketone were added to the obtained carbon black dispersion and stirred for 30 minutes. After that, further methyl isobutyl ketone was added so that the solid content concentration became 33% by mass, and a coating liquid for a heat-sensitive mask layer was obtained.

10 parts by weight of polyvinyl alcohol with a saponification degree of 78 to 82 mol% ("GOHSENOL" (registered trademark) KL-05, manufactured by Nippon Synthetic Chemical Industry Co., Ltd.) was dissolved in a mixed solvent of 40 parts by weight of water, 20 parts by weight of methanol, and 30 parts by weight of n-propanol to obtain a coating liquid for the adhesive layer.

The coating liquid for the peeling aid layer was applied to the film for the cover film using a bar coater so that the dry thickness was 0.25 μm, and then dried at 100°C for 25 seconds to form a peeling aid layer. The coating liquid for the heat-sensitive mask layer was applied to the film for the cover film using a bar coater so that the dry thickness was 2.0 μm, and then dried at 140°C for 30 seconds to form a heat-sensitive mask layer. The coating liquid for the adhesive layer was applied to the film for the cover film using a bar coater so that the dry thickness was 1.0 μm, and then dried at 180°C for 30 seconds to form an adhesive layer. In this way, a laminated film for the heat-sensitive mask layer having a laminated structure of adhesive layer/heat-sensitive mask layer/peeling aid layer/cover film was obtained.

The optical density of the laminated film for the heat-sensitive mask layer was measured using light transmitted through an orthochromatic filter as the incident light, and the film for the cover film was used as a blank for zero point correction, resulting in a value of 3.6.

Next, we will explain the evaluation methods used in the examples and comparative examples.

(1) Tensile Modulus As a layer corresponding to the photosensitive resin layer of the printing plate precursor obtained in each of the Examples and Comparative Examples, the composition solution for the photosensitive resin layer used in each of the Examples and Comparative Examples was cast onto a polyester (PET) film ("Lumirror" (registered trademark) S10, manufactured by Toray Industries, Inc.) having a thickness of 250 μm so as to give a dry film thickness of 0.7 mm, dried at 60° C. for 2.5 hours, and then peeled off from the PET film to give a photosensitive resin layer for evaluation of tensile modulus.

The photosensitive resin layer obtained for evaluating the tensile modulus was vacuum-attached to a sensitivity measurement gray scale (21 STEP SENSITIVITY GUIDE, manufactured by STOUFFER GRAPHIC ARTS EQUIPMENT CO.), and one side was exposed to light using a high-intensity chemical lamp (TL 80W/10R, manufactured by Philips) under conditions that resulted in a gray scale sensitivity of 16±1 steps. The layer was then punched out into a dumbbell-shaped No. 2 sample as described in JIS K6251:2017 to prepare a sample for tensile testing. The tensile test samples were stored for 24 hours in an environment with a temperature of 20°C and a relative humidity of 60%, and then a stress-strain curve was measured using a tensile tester (Orientec Co., Ltd. Tensilon Universal Tester RTM-100) at a temperature of 20°C and a relative humidity of 60%, with a chuck distance of 10 mm and a tensile speed of 100 mm/min. The slope of the stress-strain curve between two points with strains of 0.5% and 5.0% was taken as the tensile modulus. The tensile modulus was measured for each of five samples, and the average value was taken as the tensile modulus.

(2) Durometer A hardness before and after immersion in ink For the printing plates obtained in each Example and Comparative Example, a circular sample with a diameter of 50 mm was cut out from the solid pattern area and placed on a 5 mm thick glass plate with the support side facing down. In an environment of 23°C temperature and 50% humidity, the needle of a Durometer A hardness tester GS-709N (manufactured by Techlock Co., Ltd.) was gently pressed against the sample, and the hardness indicated by the needle was read. The hardness was measured at three randomly selected points, and the average value was taken as the Durometer A hardness before immersion in ink.

Next, the circular sample was immersed in Durometer A ethylene oxide modified trimethylolpropane triacrylate ("Miramar" (registered trademark) M3130, manufactured by Miwon Specialty Chemical Co., Ltd.) for 24 hours, and the ethylene oxide modified trimethylolpropane triacrylate on the surface of the removed circular sample was wiped off with gauze. The sample was placed on a 5 mm thick glass plate with the support side facing down, and the Durometer A hardness was measured in the same manner as above for three randomly selected points other than the measurement points before immersion in ink, and these were taken as the Durometer A hardness after immersion in ink.

(3) Fine image reproducibility of printing plate For the printing plates obtained in each of the Examples and Comparative Examples, dot areas with dot densities of 1 to 5% were observed under magnification using a 30x loupe. A state in which there were no more than four chips on the outermost periphery of the dot area and no chips were observed inside the outermost periphery was considered to be a state in which the image was reproduced successfully. The lowest dot density at which the image was reproduced was regarded as the result of the fine image reproduction evaluation.

(4) Printing reproducibility of fine images The printing plates obtained in each Example and Comparative Example were attached to the plate cylinder of a flexographic printing machine equipped with a 1,000-line anilox roll using a 0.38 μm thick tesa “softprint” (registered trademark) 52017 (manufactured by TESA) as a cushion tape. Using a UV flexographic red PHA-LO3 (manufactured by T&K TOKA Co., Ltd.), printing was performed on art paper at a speed of 70 m/min. The printing pressure was gradually applied, and the printing pressure was fixed at a pressure of 60 μm from the pressure at which the solid part was no longer blurred. After printing for 100 m, the printed matter was sampled, and the diameter of the halftone dots was measured at 5 randomly selected points from the halftone dots with a halftone dot density of 3% at 150 lpi using an optical microscope digital microscope VHX-2000 (manufactured by Keyence Co., Ltd.) under conditions of lens Z250 and 200 times magnification, and the average value was calculated. Print reproducibility was evaluated based on the following criteria: when the average diameter was 50 μm or less, it was given 5 points; when it was more than 50 μm but not more than 70 μm, it was given 3 points; and when it was more than 70 μm, it was given 1 point.

(5) Amount of warping after immersion in ink For the printing plates obtained in each Example and Comparative Example, a circular sample with a diameter of 50 mm was cut out from the solid pattern area and immersed in ethylene oxide modified trimethylolpropane triacrylate ("Miramar" (registered trademark) M3130, manufactured by Miwon Specialty Chemical Co., Ltd.) kept at a temperature of 50° C. for 24 hours, and then the ethylene oxide modified trimethylolpropane triacrylate on the surface of the removed circular sample was wiped off with gauze. The circular sample was placed on a 5 mm thick glass plate with the support side facing down in an environment of a temperature of 23° C. and a humidity of 50%. When the photosensitive resin layer is aligned so that the photosensitive resin layer side is on the inside, the height from the glass surface in contact with the circular sample to the bottom end of the support that is the highest and the height from the bottom end of the substrate that is the second highest were read to the first decimal place in mm using a JIS Class 1 metal ruler, and the average of the two measured values was taken as the amount of warping. When the photosensitive resin layer is aligned so that the photosensitive resin layer is aligned so that the photosensitive resin layer is on the outside, the height from the glass surface in contact with the sample to the bottom end of the support that is the highest was similarly read and taken as the amount of warping. In the latter case, the amount of warping was expressed with a negative sign. The amount of warping was measured for each of five circular samples, and the average value was calculated. The average value of 3.0 mm or less was considered to be acceptable.

[Example 1]
(Preparation of composition solution for photosensitive resin layer)
Into a three-neck flask equipped with a stirring spatula and a cooling tube, 40 parts by mass of the hydrophilic polymer 1 obtained in Synthesis Example 1 as Component C, 30 parts by mass of trimethylolpropane tri(polyethylene glycol) ether (weight average molecular weight: 400, TMP-60 manufactured by Nippon Nyukazai Co., Ltd.) as Component A, 40 parts by mass of an alcohol mixture ("Solmix" (registered trademark) H-11 manufactured by Nippon Alcohol Co., Ltd.) as a solvent, and 60 parts by mass of distilled water were placed, and the mixture was heated at 77° C. for 2 hours with stirring to dissolve Component C and Component A.

After cooling the solution to 70°C, 5 parts by mass of glycidyl methacrylate was added and stirred for 1 hour to add glycidyl methacrylate to hydrophilic polymer 1. The addition reaction causes the glycidyl group of glycidyl methacrylate to open, and hydrophilic polymer 1 has a hydroxyl group.

Next, polyethylene glycol monomethacrylate (number of ethylene oxide repeat units: 10, hydroxyl groups: present, number of ethylenically unsaturated groups: 1, NOF Corp.'s "Blenmer" (registered trademark) AE400) was added as component B, 1.6 parts by mass of benzyl dimethyl ketal was added as a photopolymerization initiator, 0.6 parts by mass of a fluorine-containing quaternary ammonium salt compound (NEOS Corp.'s "Ftergent" (registered trademark) 320) was added as an ink repellent, and 0.05 parts by mass of 2-(2'-hydroxy-3'-t-butyl-5'-methylphenyl)-5-chlorobenzotriazole was added as an ultraviolet absorber, and the mixture was stirred for 60 minutes to obtain a composition solution for photosensitive resin layer 1.

[Preparation of printing plate precursor 1]
The composition solution for photosensitive resin layer 1 was cast onto the support obtained in Production Example 1, with the plate thickness after drying (support + photosensitive resin layer) adjusted to 1.14 mm, and dried for 2.5 hours at 60° C. A mixed solvent of 50 parts by mass of water/50 parts by mass of ethanol was applied onto the obtained photosensitive resin layer, and the laminate film for the heat-sensitive mask layer obtained in Production Example 2 was pressure-bonded to obtain a printing plate precursor 1 having a laminate structure of cover film/peeling auxiliary layer/heat-sensitive mask layer/adhesive layer/photosensitive resin layer 1/easy adhesion layer 2/easy adhesion layer 1/PET substrate.

[Plate making of printing plate 1]
The printing plate precursor 1 was cut to 20 cm x 20 cm, and back exposure was performed from the support side using a high-intensity chemical lamp (TL 80W/10R manufactured by Philips) so that the accumulated light amount was about 800 mJ/ ^cm2 . Next, the cover film was peeled off, and the plate was attached to an external drum-type plate setter (CDI SPARK 2530 manufactured by Esco Graphics Co., Ltd.) equipped with a fiber laser having an infrared light emission region so that the support side was in contact with the drum, and a 15 cm x 15 cm solid pattern and an image with a 150 lpi dot density of 1 to 5% and an area of each dot density of 2 cm x 2 cm were drawn with a laser with an output of 2.4 J/ ^cm2 to form an image mask from the thermal mask layer. Thereafter, main exposure was performed from the image mask side in the atmosphere using a high-intensity chemical lamp TL 80W/10R in the same manner as the back exposure so that the accumulated light amount was about 12,000 mJ/ ^cm2 . Thereafter, using a batch-type exposure and development machine (Inglese W43 manufactured by Inglese, s.r.l.), the plate was developed for 80 seconds using tap water adjusted to 25° C. as a developer, and then dried in an oven at 60° C. for 10 minutes. Subsequently, using a high-intensity chemical lamp TL 80W/10R, post-exposure was performed so that the accumulated light amount was about 12,000 mJ/ ^cm2 , thereby obtaining printing plate 1.

[Example 2]
A printing plate precursor and a printing plate were obtained in the same manner as in Example 1, except that a 1:2 adduct of tripropylene glycol and glycidyl acrylate (number of ethylenically unsaturated groups: 2, Epoxy Ester 200PA, manufactured by Kyoeisha Chemical Co., Ltd.) was added as Component D instead of the composition solution for photosensitive resin layer 1, and a composition solution for photosensitive resin layer 2 was used in the amounts shown in Table 1.

[Example 3]
A printing plate precursor and a printing plate were obtained in the same manner as in Example 1, except that a composition solution for photosensitive resin layer 3, in which hydrophilic polymer 2 obtained in Synthesis Example 2 was used instead of hydrophilic polymer 1 as Component C, was used instead of the composition solution for photosensitive resin layer 1.

[Examples 4 and 5, Comparative Example 1]
Printing plate precursors and printing plates were obtained in the same manner as in Example 1, except that the composition solutions of photosensitivities 4 to 6 having the blending amounts as shown in Table 1 were used instead of the composition solution for photosensitive resin layer 1.

[Comparative Example 2]
A printing plate precursor and a printing plate were obtained in the same manner as in Example 3, except that a composition solution for photosensitive resin layer 7 using polyethylene glycol diacrylate (number of ethylene oxide repeating units: 9, hydroxyl groups: none, number of ethylenically unsaturated groups: 2, Light Ester 9EG manufactured by Kyoeisha Chemical Co., Ltd.) was used in place of component B in place of the composition solution for photosensitive resin layer 3.

[Comparative Example 3]
A printing plate precursor and a printing plate were obtained in the same manner as in Example 1, except that a composition solution for photosensitive resin layer 8 in which hydrophilic polymer 2 obtained in Synthesis Example 3 was used instead of hydrophilic polymer 1 was used instead of the composition solution for photosensitive resin layer 1.

[Comparative Example 4]
A printing plate precursor and a printing plate were obtained in the same manner as in Example 3, except that a composition solution for photosensitive resin layer 9 in which bis(2-ethylhexyl) adipate (DOA, manufactured by J-Plus Co., Ltd.) was used instead of Component A was used instead of the composition solution for photosensitive resin layer 3.

The main configurations and evaluation results of each example and comparative example are shown in Table 1.

Claims (8)

A flexographic printing plate precursor having at least a support and a photosensitive resin layer, the photosensitive resin layer containing at least a hydrophilic plasticizer (component A), an ethylenically unsaturated group-containing monomer (component B) having a chemical structure with 2 or more ethylene oxide repeats and a hydroxyl group, and a hydrophilic polymer (component C), the content of component A in the photosensitive resin layer being 30 mass% or less, and the tensile modulus of elasticity of the photosensitive resin layer after photocuring being 2.5 MPa or less. The flexographic printing plate precursor according to claim 1, wherein the content of component B in the photosensitive resin layer is 20% by mass or more and 60% by mass or less. The flexographic printing plate precursor according to claim 1 or 2, which contains a monofunctional monomer as component B. The flexographic printing plate precursor according to claim 3, wherein the photosensitive resin layer further contains a polyfunctional monomer (component D), and the content of component D in the photosensitive resin layer is 10% by mass or less. The flexographic printing plate precursor according to claim 1 or 2, which contains partially saponified polyvinyl alcohol and/or a partially saponified polyvinyl alcohol derivative as component C. The flexographic printing plate precursor according to claim 5, wherein the degree of saponification of the partially saponified polyvinyl alcohol and/or the partially saponified polyvinyl alcohol derivative is 55 mol% or more and 75 mol% or less. The flexographic printing plate precursor according to claim 1 or 2, in which the amount of warping after immersion in ethylene oxide-modified trimethylolpropane triacrylate following photocuring of the photosensitive resin layer is 3 mm or less. A method for producing a flexographic printing plate, comprising an exposure step of irradiating the photosensitive resin layer of the flexographic printing plate precursor according to claim 1 or 2 with ultraviolet light to partially photo-cure the photosensitive resin layer, and a development step of removing uncured portions of the photosensitive resin layer.