Photosensitive Flukiso printing plate original

Abstract

The present invention addresses the problem of economically providing a photosensitive flexographic printing plate original plate in which resistance to plate surface contamination can be sustained in the printing step, and with which printed matter can be reliably obtained even in long-run printing.　The present invention is a flexographic printing plate 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. When exposure and development have been performed so that at least 99 out of 100 3% dots at 175 lpi are reproduced, the contact angle with the tripropylene glycol diacrylate of the photosensitive resin layer after photocuring is 40–70° inclusive, and the percentage change in weight after 24 hours of immersion at 50°C in the tripropylene glycol diacrylate of the photosensitive resin layer after photocuring is –4.0 to 4.0% inclusive.

Description

[Technical Field]

[0001] The present invention relates to a photosensitive flexographic printing plate precursor and a flexographic printing plate. [Background technology]

[0002] Printing technology has developed remarkably in recent years, and flexographic printing in particular has a wide range of applications due to its ability to print on any type of media, including cardboard, paper containers, labels, flexible packaging, and electronics. Furthermore, in consideration of the environment, water-developable flexographic plates have also appeared, replacing the conventional process of developing with organic solvents.

[0003] Relief printing, typified by flexographic printing, involves applying ink to the apexes of raised reliefs and then pressing the plate against the substrate to transfer the ink. This printing method can result in ink spilling over the apexes of the reliefs, particularly the apexes of the dots, onto the dot slopes and into the recesses during printing. The spilled ink then spreads across the plate surface, wetting the dots and creating a printing defect known as "networking." This occurs because the viscosity of flexographic ink is lower than that of letterpress ink, making it particularly susceptible to networking. Furthermore, the time required to wipe off the ink that has spread onto the printing plate results in lost production and reduced productivity. Various methods have been proposed to address these issues.

[0004] Patent Document 1 proposes a method for suppressing ink entanglement by using a water-developable photosensitive flexographic printing plate precursor containing a fluorine-containing compound having an ionic functional group.

[0005] Patent Document 2 proposes a method for suppressing ink entanglement by controlling the surface energy of a relief formed by photocuring a photosensitive resin layer using a water-developable photosensitive flexographic printing plate precursor containing a silicone component. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] International Publication No. 2018 / 88336 [Patent Document 2] Japanese Patent Application Publication No. 2018-120131 Summary of the Invention [Problem to be solved by the invention]

[0007] In Patent Document 1, the ink penetration into the recesses can be controlled, which can provide a certain effect of suppressing ink entanglement, but there is a problem in that print density can decrease during long-run printing. When this occurs, it is necessary to stop the printing press and adjust the printing pressure as needed.

[0008] In Patent Document 2, the ink penetration into the recesses can be controlled, and therefore a certain degree of ink entanglement suppression effect can be obtained, but there is a problem in that the halftone dots become thicker during long-run printing.

[0009] The present invention has been made in view of the above circumstances, and aims to economically provide a photosensitive flexographic printing plate precursor that has sustainable plate surface stain resistance during the printing process and that can provide stable printed products even during long-run printing. [Means for solving the problem]

[0010] The inventors have found that the decrease in print density in the invention described in Patent Document 1 is due to the uncured components in the printing relief being extracted into the ink, causing the printing relief to become thinner (lower in height). They have also found that the thickening of dots in the technology described in Patent Document 2 is due to the expansion of convex portions because the printing relief contains, as a main component, a rubber component that easily swells in ink. Taking these findings into consideration, the inventors have conducted extensive research and arrived at the present invention.

[0011] That is, the present invention provides a photosensitive flexographic printing plate precursor comprising at least a substrate and a photosensitive resin layer, wherein the photosensitive resin layer contains 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 to light so as to reproduce 99 or more out of 100 175 lpi 3% halftone dots, the photocured photosensitive resin layer has a contact angle of 40° or more and 70° or less with tripropylene glycol diacrylate, and the photocured photosensitive resin layer has a mass change rate of -4.0% or more and 4.0% or less after immersion in tripropylene glycol acrylate at 50°C for 24 hours.

[0012] The present invention also relates to a flexographic printing plate having, on a substrate, a resin layer on which at least a printing relief is formed, wherein the contact angle of the raised portions of the printing relief with tripropylene glycol diacrylate is 40° or more and 70° or less, and the mass change rate of the raised portions of the printing relief after immersion in tripropylene glycol diacrylate at 50°C for 24 hours is -4.0% or more and 4.0% or less. [Effects of the Invention]

[0013] According to the present invention, in the printing process, plate surface contamination caused by ink wetting and spreading between halftone dots can be prevented, and even in long-run printing, high-quality printed matter with stable halftone dot density can be continuously provided without the need to stop the printing press. DETAILED DESCRIPTION OF THE INVENTION

[0014] The present invention will be described in detail below. In the present invention, the term "not less than" means that the value is equal to or greater than the indicated value. The term "not more than" means that the value is equal to or smaller than the indicated value.

[0015] The flexographic printing plate and the photosensitive flexographic printing plate precursor of the present invention each have a substrate, which supports a resin layer on which a printing relief is formed in the flexographic printing plate of the present invention or a photosensitive resin layer in the photosensitive flexographic printing plate precursor of the present invention.

[0016] The substrate is preferably one that has excellent dimensional stability against heat and physical stress, and plastic sheets such as polyester, and metal plates such as steel, stainless steel, and aluminum can be used.

[0017] The thickness of the substrate is preferably 100 μm or more and 350 μm or less from the viewpoint of handleability and flexibility. If it is 100 μm or more, the handleability as a support is improved, and if it is 350 μm or less, the flexibility as a photosensitive flexographic printing plate precursor and a flexographic printing plate is improved.

[0018] Furthermore, the substrate may be subjected to an easy-adhesion treatment in order to improve the adhesion between the substrate and the photosensitive resin layer. Examples of the easy-adhesion treatment method include mechanical treatment such as sandblasting, physical treatment such as corona discharge, and chemical treatment such as coating. From the viewpoint of adhesion, it is preferable to provide an easy-adhesion layer by coating.

[0019] The flexographic printing plate of the present invention has a resin layer on a substrate on which at least a printing relief is formed. Also, the photosensitive flexographic printing plate precursor of the present invention comprises at least a photosensitive resin layer on a substrate. By forming irregularities in the photosensitive resin layer by a predetermined method, the printing relief in the flexographic printing plate can be formed, i.e., the resin layer on which the printing relief is formed is obtained.

[0020] In the photosensitive flexographic printing plate precursor of the present invention, the photosensitive resin layer contains at least (a) a hydrophilic polymer, (b) a hydrophilic monomer, (c) a photopolymerization initiator, (d) a hydrophilic plasticizer, and (e) an ink repellent agent.

[0021] The hydrophilic polymer (a) in the photosensitive resin layer of the photosensitive flexographic printing plate precursor of the present invention functions as a binder resin for the water-developable photosensitive flexographic printing plate precursor.

[0022] (a) To suppress the swelling rate of the hydrophilic polymer in UV ink, it is preferable to use a hydrophilic polymer with an SP (solubility parameter) that is significantly different from the SP value of the UV ink components, and more preferable is a hydrophilic polymer with an SP value of 12 or more. By using a hydrophilic polymer with an SP value of 12 or more, the swelling rate of the UV ink can be controlled to 4.0% or less.

[0023] Furthermore, the (a) hydrophilic polymer preferably has at least one of a hydroxyl group, an amino group, an amide group, a carboxyl group, or a phosphate group as a functional group, as this provides excellent water-developability, and more preferably has at least a hydroxyl group. Examples of such (a) hydrophilic polymers include polyvinyl alcohol, polyamide, polyvinylpyrrolidone, polyether, and water-soluble polyester. Polyvinyl alcohol is particularly preferred due to its water solubility, ease of processing, and the sharpness of the resulting printing relief. While the solubility of polyvinyl alcohol can be varied depending on the degree of saponification, fully saponified polyvinyl alcohol is preferred due to the difficulty of processing it as an aqueous solution due to intramolecular hydrogen bonding and the rigidity of the resin itself. Regarding the degree of saponification, from the standpoint of water-developability, a degree of saponification of 50 mol% to 99 mol% is preferred, and more preferably 60 mol% to 90 mol%.

[0024] The degree of saponification can be measured by subjecting a 3% aqueous solution of partially saponified polyvinyl alcohol to complete saponification treatment with 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, thereby calculating the degree of saponification.

[0025] The content of the (a) hydrophilic polymer in the photosensitive resin layer is preferably 20% by mass or more and 80% by mass or less, based on 100% by mass of the photosensitive resin layer. By including 20% ​​by mass or more, more preferably 30% by mass or more of the (a) hydrophilic polymer, strength sufficient for printing can be obtained. Furthermore, by including 80% by mass or less, more preferably 60% by mass or less, appropriate hardness for a flexographic printing plate can be obtained after photocuring.

[0026] (b) Hydrophilic monomers are monomers with hydrophilic functional groups, and have carbon-carbon unsaturated groups that initiate a polymerization reaction when exposed to light. The hydrophilic functional groups are preferably at least one of hydroxyl, amino, amide, carboxyl, and phosphate groups, with hydroxyl groups being more preferred. They form part of the printing relief when cured by light, and the presence of hydrophilic functional groups makes water development easier and, because their polarity is different from that of UV ink components, suppresses swelling and changes in physical properties due to UV ink exposure.

[0027] Specific examples of (b) hydrophilic monomers 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.

[0028] The content of the (b) hydrophilic monomer in the photosensitive resin layer is preferably 1.0% by mass to 50% by mass, and more preferably 1.0% by mass to 30% by mass, relative to 100% by mass of the photosensitive resin layer. By incorporating the hydrophilic monomer in this amount, photosensitivity is imparted to the resin composition, and after photocuring, a hardness suitable for a flexographic printing plate can be obtained.

[0029] (c) The photopolymerization initiator may be any one that can initiate polymerization of a polymerizable carbon-carbon unsaturated group by light. Among them, those that have the function of generating radicals by self-decomposition or hydrogen abstraction upon light absorption are preferably used. Examples include benzoin alkyl ethers, benzophenones, anthraquinones, benzils, acetophenones, and diacetyls.

[0030] The content of the (c) photopolymerization initiator in the photosensitive resin layer is preferably 0.1% by mass or more and 20% by mass or less, and more preferably 0.5% by mass or more and 10% by mass or less, relative to 100% by mass of the photosensitive resin composition, so that the photocuring reaction proceeds sufficiently upon exposure and the unexposed areas are not excessively affected by scattered light from the exposed areas.

[0031] A (d) hydrophilic plasticizer is a compound that is not photocurable and has the function of softening the (a) hydrophilic polymer. (a) Hydrophilic polymers strengthen the printing relief through hydrogen bonding between their hydrophilic functional groups, making it difficult to achieve the flexibility required for flexographic printing plates. Therefore, a (d) hydrophilic plasticizer with a hydrophilic functional group that is compatible with the (a) hydrophilic polymer penetrates between the molecules of the (a) hydrophilic polymer, disrupting the intermolecular network and softening the printing relief. Furthermore, because the (d) hydrophilic plasticizer is not photocurable, it does not lose its flexibility-imparting function even after photocuring. To achieve such hydrophilicity, the hydrophilic functional group of the (d) hydrophilic plasticizer is preferably at least one of a hydroxyl group, an amino group, an amide group, a carboxyl group, and a phosphate group, with a hydroxyl group being more preferred.

[0032] Furthermore, since both (b) the hydrophilic monomer and (d) the hydrophilic plasticizer have at least one of a hydroxyl group, an amino group, an amide group, a carboxyl group, and a phosphate group, it is possible to effectively suppress changes in mass and physical properties due to swelling and elution of components contained in the UV ink, such as tripropylene glycol diacrylate, as will be described later.

[0033] Examples of such (d) hydrophilic plasticizers include polyethylene glycol and derivatives thereof, polypropylene glycol and derivatives thereof, glycerin derivatives, trimethylolethane derivatives, trimethylolpropane derivatives, and pentaerythritol derivatives.

[0034] (d) The weight-average molecular weight of the hydrophilic plasticizer is preferably 200 or more and 4,000 or less. By setting the weight-average molecular weight to 200 or more, more preferably 300 or more, changes in physical properties due to extraction with UV ink can be suppressed and loss of bulk in the printed relief can be prevented. By setting the weight-average molecular weight to 4,000 or less, more preferably 1,000 or less, a flexible printed relief can be obtained.

[0035] The content of the (d) hydrophilic plasticizer in the photosensitive resin layer is preferably 5% by mass or more and 60% by mass or less, based on 100% by mass of the photosensitive resin layer. By setting it to 5% by mass or more, more preferably 20% by mass or more, a flexible relief suitable for flexographic printing can be obtained. Furthermore, by setting it to 60% by mass or less, more preferably 45% by mass or less, a relief with strength suitable for flexographic printing can be obtained.

[0036] In addition, the total mass of (a) hydrophilic polymer, (b) hydrophilic monomer, and (d) hydrophilic plasticizer in the photosensitive resin layer is preferably 50% by mass or more and 100% by mass or less, based on the total mass of the polymer, monomer, and plasticizer in the photosensitive resin layer. By making it 50% by mass or more, more preferably 80% by mass or more, swelling of the relief due to UV ink can be suppressed, and thickened dots can be prevented during long-run printing.

[0037] (e) An ink repellent agent is a compound having a molecular structure with a relatively high polarity and a molecular structure with ink repellency. The relatively high polarity molecular structure is retained inside the photosensitive resin layer, and the ink repellent molecular structure is oriented toward the surface of the photosensitive layer, thereby achieving ink repellency. The ink repellent molecular structure in the (e) ink repellent agent is preferably at least one of a structure containing a fluorine atom and a structure containing a silicon atom. A fluoroalkyl structure is more preferred as the structure containing a fluorine atom, and a dimethylsiloxane structure is more preferred as the structure containing a silicon atom.

[0038] The content of the (e) ink repellent agent in the photosensitive resin layer is preferably 0.1% by mass or more and 5.0% by mass or less, relative to 100% by mass of the photosensitive resin layer. By setting the blending amount to 0.1% by mass or more, more preferably 0.3% by mass or more, and even more preferably 0.4% by mass or more, an antifouling effect can be obtained, and by setting the blending amount to 5.0% by mass or less, more preferably 3.0% by mass or less, good ink receptivity can be obtained when the printing relief is formed by exposure and development.

[0039] A polymerization inhibitor may be added to the photosensitive resin layer of the photosensitive flexographic printing plate precursor of the present invention in order to improve its thermal stability. Preferred polymerization inhibitors include phenols, hydroquinones, catechols, and hydroxyamine derivatives.

[0040] The content of the polymerization inhibitor in the photosensitive resin layer is preferably 0.001% by mass or more and 5% by mass or less relative to 100% by mass of the photosensitive resin layer.

[0041] Furthermore, other components such as dyes, pigments, surfactants, antifoaming agents, ultraviolet absorbers, and perfumes may be added to the photosensitive resin layer as needed.

[0042] The thickness of the photosensitive resin layer is preferably 0.3 mm or more and 5.0 mm or less from the viewpoint of obtaining sufficient relief depth and improving printability. By making the thickness of the photosensitive resin layer 0.3 mm or more, more preferably 0.5 mm or more, the unevenness required for flexographic printing can be effectively obtained. Furthermore, by making the thickness 5.0 mm or less, more preferably 3.0 mm or less, the actinic rays used for exposure can sufficiently reach the bottom of the photosensitive resin layer, thereby effectively forming a printing relief.

[0043] The photosensitive flexographic printing plate precursor of the present invention preferably has a cover film on the photosensitive resin layer from the viewpoint of surface protection and prevention of adhesion of foreign matter, etc. 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 provided for the purpose of preventing adhesion of the surface of the photosensitive resin layer.

[0044] The cover film is preferably made of a plastic sheet such as polyester or polyethylene.

[0045] The thickness of the cover film is preferably 10 μm or more and 150 μm or less from the viewpoint of handling and cost.

[0046] The surface of the cover film may be roughened, which improves adhesion to the original film.

[0047] The photosensitive flexographic printing plate precursor of the present invention may further have 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 printing, and is instantly sublimated or ablated in part or in whole by the heat generated. This creates a difference in optical density between the laser-irradiated and unirradiated areas, allowing the plate precursor to effectively function in the same way as a conventional original film.

[0048] A method for producing the photosensitive flexographic printing plate precursor of the present invention will be described below, although the photosensitive flexographic printing plate precursor of the present invention is not limited to those produced by the method described here.

[0049] (a) Hydrophilic polymer is dissolved in a water / alcohol mixed solvent by heating, and then (b) hydrophilic monomer, (c) photopolymerization initiator, (d) hydrophilic plasticizer, and (e) ink repellent agent, as well as other additives as necessary, are added and thoroughly mixed by stirring to obtain a photosensitive resin composition solution. However, components (b) to (e) or other additives may be added before dissolving the hydrophilic polymer (a).

[0050] The obtained photosensitive resin composition solution is cast onto a substrate, optionally provided with an adhesive layer, and dried to form a photosensitive resin layer made of the photosensitive resin composition. A cover film, optionally coated with an anti-stick layer, is then adhered to the photosensitive resin layer to obtain a photosensitive flexographic printing plate precursor. Alternatively, a photosensitive flexographic printing plate precursor can be obtained by preparing a photosensitive resin sheet from the photosensitive resin composition solution by dry film formation, and then laminating the photosensitive sheet between the substrate and the cover film.

[0051] The photosensitive flexographic plate precursor of the present invention is subjected to sufficient exposure, and then passes through development and drying steps to form a printing relief having projections and depressions in the shape of a printed image, and can be used as the flexographic printing plate of the present invention.

[0052] When the photosensitive flexographic printing plate precursor does not have a heat-sensitive mask layer (hereinafter referred to as an analog plate), if a cover film is present, it is peeled off, and a negative or positive original film is adhered to the photosensitive resin layer, and the photosensitive resin layer is photo-cured by irradiating it with ultraviolet light.

[0053] Furthermore, when the photosensitive flexographic printing plate precursor has a heat-sensitive mask layer (hereinafter referred to as a CTP plate), the cover film is peeled off, an image corresponding to the original film is drawn using a laser drawing machine, and then the photosensitive resin layer is photo-cured by irradiating it with ultraviolet light.

[0054] Ultraviolet light irradiation is usually carried out using a high-pressure mercury lamp, ultra-high-pressure mercury lamp, metal halide lamp, xenon lamp, carbon arc lamp, chemical lamp, etc., which are capable of irradiating wavelengths of 300 nm or more and 400 nm or less. When reproducibility of particularly fine thin lines or isolated points is required, it is also possible to expose the substrate for a short time (back exposure) before peeling off the cover film.

[0055] Next, the exposed photosensitive flexographic printing plate precursor is immersed in a developer, and the uncured portion is rubbed off with a brush using a brush-type developing device to form a printing relief on the substrate. A spray-type developing device can also be used instead of a brush-type developing device. The temperature of the developing solution is preferably 15°C or higher and 40°C or lower.

[0056] After forming the printing relief, the plate is dried at 50° C. to 70° C. for about 10 minutes, and if necessary, further treated with actinic light in the atmosphere or in a vacuum to obtain a photosensitive resin plate.

[0057] It is important that the contact angle of the raised printing relief portions of the flexographic printing plate of the present invention to tripropylene glycol diacrylate is 40° or more and 70° or less. Similarly, it is important that the photosensitive flexographic printing plate precursor of the present invention, when exposed and developed so as to reproduce 99 or more of 100 175 lpi 3% halftone dots, has a contact angle of 40° or more and 70° or less of tripropylene glycol diacrylate to the photosensitive resin layer after photocuring (i.e., the raised printing relief portions of the flexographic printing plate).

[0058] Here, "exposure so that 99 or more out of 100 175 lpi 3% halftone dots are reproduced" refers to a standard for sufficient exposure. Note that "175 lpi" refers to the number of lines forming halftone dots arranged per inch (2.54 cm). Hereinafter, these conditions will also be referred to as "standard exposure conditions." As mentioned above, the flexographic printing plate of the present invention can be suitably obtained by subjecting the photosensitive flexographic printing plate precursor of the present invention to sufficient exposure and then passing it through the development and drying processes. Therefore, by applying the standard exposure conditions to the photosensitive flexographic printing plate precursor of the present invention, the properties after exposure and development under the same conditions can be discussed in the same way as the properties of the flexographic printing plate of the present invention.

[0059] Tripropylene glycol diacrylate is a typical monomer component contained in UV inks. By setting the contact angle with tripropylene glycol diacrylate to 40° or more, preferably 43° or more, ink entanglement and net thickening due to ink seeping into recesses can be prevented. Furthermore, by setting the contact angle to 70° or less, preferably 67° or less, and more preferably 55° or less, good ink adhesion can be achieved.

[0060] It is also important that the flexographic printing plate of the present invention has a mass change rate of −4.0% or more and 4.0% or less after immersion in tripropylene glycol diacrylate at 50°C for 24 hours in the raised portions of the printing relief. Similarly, it is also important that the photosensitive flexographic printing plate precursor of the present invention, when exposed and developed under the above-mentioned standard exposure conditions, has a mass change rate of −4.0% or more and 4.0% or less after photocuring in the photosensitive resin layer (i.e., the raised portions of the printing relief of the flexographic printing plate) after immersion in tripropylene glycol diacrylate at 50°C for 24 hours. By ensuring that the mass change rate of the raised portions of the printing relief in tripropylene glycol diacrylate at 50°C for 24 hours is 4.0% or less, preferably 1.0% or less, it is possible to prevent thickening of the printing relief due to swelling of the printing relief even with ink, which is particularly noticeable during long-run printing. Furthermore, by setting the mass change to -4.0% or more, preferably -3.0% or more, it is possible to prevent the printing relief from losing volume, and to continuously obtain good printed matter with stable halftone dot density. The mass change due to ink immersion is preferably as close to 0.0% as possible.

[0061] The flexographic printing plate of the present invention has a tensile modulus E of 30 mm x 30 mm of a solid image portion of the printing relief, which is measured after storing for 24 hours in an environment of 30°C and 20% relative humidity. A Similarly, when the photosensitive flexographic printing plate precursor of the present invention is exposed and developed so that 99 or more of 100 175 lpi 3% halftone dots are reproduced, the tensile modulus E of a 30 mm x 30 mm solid image portion of the printing relief measured after storing the plate in an environment of 30°C and 20% relative humidity for 24 hours is preferably 1.0 MPa or more and 20.0 MPa or less. A is preferably 1.0 or more and 20.0 MPa or less.

[0062] E A By setting E to 0.5 MPa or more, more preferably 1.0 MPa or more, strength that can withstand the printing pressure during flexographic printing can be obtained. A By setting the pressure to 20.0 MPa or less, more preferably 10.0 MPa or less, good ink receptivity can be obtained even with a kiss-touch printing pressure.

[0063] The flexographic printing plate of the present invention has a tensile modulus E of 30 mm x 30 mm measured after immersing a 30 mm x 30 mm solid image portion of the printing relief in tripropylene glycol diacrylate at 50°C for 24 hours. B and the aforementioned E A Difference ΔE B (=E B -E A Similarly, when the photosensitive flexographic printing plate precursor of the present invention is exposed and developed so that 99 or more of 100 175 lpi 3% halftone dots are reproduced, the tensile modulus E B and the aforementioned E A Difference ΔE B (=E B -E A ) is preferably −1.0 MPa or more and 1.0 MPa or less.

[0064] ΔE B By setting the pressure to 1.0 MPa or less, more preferably 0.8 MPa or less, it is possible to prevent a decrease in ink adhesion and to stably obtain a constant print density even during long-run printing. B By setting the pressure to -1.0 MPa or more, more preferably -0.8 MPa or more, it is possible to suppress changes in the shape of the relief and prevent net thickening.

[0065] The flexographic printing plate of the present invention has a tensile modulus E of 30 mm x 30 mm of a solid image portion of the printing relief, measured after storage for 2 hours under an environment of 40°C and a relative humidity of 80%. C and the aforementioned E A Difference ΔE C (=E C -E A Similarly, when the photosensitive flexographic printing plate precursor of the present invention is exposed and developed under the above-mentioned standard exposure conditions to form a printing relief, the tensile modulus E of a 30 mm x 30 mm solid image portion of the printing relief measured after storing it in an environment of 40°C and a relative humidity of 80% for 2 hours is preferably -1.0 MPa or more and 1.0 MPa or less. C and the aforementioned E A Difference ΔE C (=E C -E A ) is preferably −1.0 MPa or more and 1.0 MPa or less.

[0066] ΔE C By setting ΔE to 1.0 MPa or less, and more preferably 0.8 MPa or less, the printing plate is less susceptible to the humidity of the printing environment, and even if the same type of flexographic printing plate is used in summer and winter, when the humidity differs greatly, a constant print density can be stably obtained without being affected by seasonal fluctuations. C By setting the pressure to -1.0 MPa or more, preferably -0.8 MPa or more, it is possible to suppress changes in the shape of the relief and prevent thickening of the net even during long printing in a high-temperature and high-humidity environment.

[0067] In addition, the flexographic printing plate of the present invention preferably has a picture image formed in the printing relief with a resolution of 175 lpi or more. A resolution of 175 lpi or more allows for clear printing of photographic images. Furthermore, the higher the resolution, the more susceptible the image is to ink smearing and dot thickening. At a resolution of 175 lpi or more, the ink smearing and dot thickening suppression effect, which is a feature of the present invention, is particularly pronounced in clear printed images.

[0068] The flexographic printing plate of the present invention can be suitably used in flexographic printing using UV inks. Examples of commercially available UV inks for flexographic printing include PHA (manufactured by T&K TOKA Corporation), "FLASH DRY" (registered trademark, manufactured by Toyo Ink Co., Ltd.), and "UVAFLEX" (registered trademark) Y77 (manufactured by Zeller+Gmelin). The composition of these UV inks for flexographic printing includes, for example, pigments, resins such as acrylic oligomers, acrylate monomers, and polymerization initiators. By using the flexographic printing plate of the present invention in printing, plate surface contamination caused by ink wetting and spreading between halftone dots is prevented, and high-quality printed products free of halftone dot tangles can be consistently obtained. Furthermore, even during long-run printing, high-quality printed products with stable halftone dot density and no halftone dot thickening can be consistently obtained.

[0069] The flexographic printing plate of the present invention can be suitably used for printing sticker labels using UV inks. In sticker label printing, reproduction of high-resolution images such as photographic images is sometimes required to improve the appeal of the product to which the sticker label is attached. The present invention is particularly effective in suppressing ink entanglement and dot thickening in high-resolution images of 175 lines or more, and therefore can be suitably used for such applications.

[0070] The photosensitive resin layer of the present invention is particularly suitable for use in flexographic printing, but can also be used for letterpress printing plates, dry-off printing, lithographic printing, intaglio printing, stencil printing, and as a photoresist. [Example]

[0071] The present invention will be described in detail below with reference to examples.

[0072] [Evaluation method, printing method for evaluation] The evaluations in the examples and comparative examples were carried out by the following methods.

[0073] (1) Ink contact angle The ease with which the ink spreads on the plate surface was evaluated as the contact angle of the ink. A 1 μL drop of tripropylene glycol diacrylate was placed on a solid area of ​​the plate surface at room temperature, and the contact angle was measured 50 seconds after the drop was placed using a contact angle meter "DMe-201" (Kyowa Interface Science Co., Ltd.). The average value of the nine points was taken as the contact angle of tripropylene glycol diacrylate.

[0074] (2) Mass change rate A 3cm x 3cm section cut from the solid area of ​​the plate surface, approximately 0.8mm deep from the surface, was used as the evaluation sample, and its mass (M0) before immersion was measured using a precision balance. The sample was immersed in tripropylene glycol diacrylate at a temperature of 50°C for 24 hours. The sample was then removed from the tripropylene glycol diacrylate, and the tripropylene glycol diacrylate was wiped off the sample surface with gauze. The mass (M1) after immersion was immediately measured using a precision balance. The rate of mass change due to ink immersion was calculated as (M1 - M0) / M0, and the average value for nine samples was calculated.

[0075] (3) Tensile modulus From a flexographic printing plate having a solid image area of ​​30 mm x 30 mm or more in size in the printing relief, the solid image area was cut out to a size of 30 mm x 30 mm, and then the substrate, adhesive layer, and part of the photosensitive resin layer were removed by sanding from the substrate side, to create an evaluation sample with a thickness of 500 to 600 μm.

[0076] The evaluation sample was stored and treated under the following conditions (A) to (C). Condition (A): Stored for 24 hours in an environment of 30°C and 20% relative humidity. Condition (B): After immersion in tripropylene glycol diacrylate at 50°C for 24 hours, the ink on the surface was wiped off with gauze. Condition (C): Stored in an environment of 40°C and 80% relative humidity for 2 hours.

[0077] Each of the evaluation samples stored and treated under the above conditions (A) to (C) was punched out into a dumbbell shape of the scaled test piece A28 described in JIS K7139 to prepare test pieces (A) to (C) for evaluating the tensile modulus of elasticity.

[0078] The tensile modulus was measured according to a method in accordance with JIS K7161-1:2014. Specifically, the stress-strain curve of the above test specimen was measured using a tensile testing machine (Tensilon universal testing machine RTM-100 manufactured by Orientec Co., Ltd.) with a chuck distance of 10 mm and a tensile speed of 100 mm / min, and the slope of the stress-strain curve between two points of strain 0.5% to 5.0% was taken as the tensile modulus. The tensile modulus of each of the test specimens (A) to (C) was calculated as the tensile modulus E A ,E B ,E C It was decided.

[0079] Regarding the tensile tester, an alternative may be used as long as it is compatible with measurements according to the above standards.

[0080] (4) Printing method for evaluation The printing plate was attached to the plate cylinder of a flexographic printing press (MPS) equipped with a 1000-line anilox roll using 0.38 μm thick cushion tape (TESA "tesa softprint" (registered trademark) 52017). Flexographic ink (T&K TOKA "UV Flexo Beni PHA-LO3") was used to print on art paper at a speed of 70 m / min. The printing pressure was gradually applied, and the plate was fixed at a pressure of 60 μm from the pressure at which the solid areas no longer faded.

[0081] (5)Print density To evaluate ink receptivity, print density was evaluated for solid image areas of 30mm x 30mm or larger on flexographic printing plates. The print density of the printed matter was measured using a spectrophotometer / densitometer (X-rite's "SpectroEye") at 100m and 10,000m after printing.

[0082] In addition, to simulate a printing environment under high humidity, a flexographic printing plate was also stored for two hours at 40°C and a relative humidity of 80%, and the print density of the printed matter was measured 100 m after the start of printing.

[0083] (6) Ink deposition area ratio Considering that ink wetting is caused by ink spreading onto the plate surface, evaluations using an actual printing press were conducted using the ink deposition area ratio on the plate surface as a substitute indicator of ink wetting. For 175 lpi 5% and 30% dot screens, the presence or absence of ink wetting was confirmed on the printed matter, and after printing 10,000 m, the surface of the flexographic printing plate was observed with a 50x magnifying glass, and the ratio of the area where ink was deposited to the total area of ​​the recesses between the dots on the plate was evaluated as the ink deposition area ratio. The lower the ink deposition area ratio, the less likely the plate is to welt.

[0084] (7) Rate of change in dot diameter Printed material was sampled 100 meters after printing and 10,000 meters after printing, and dot thickening was evaluated based on the rate of change in dot diameter. The 175 lpi 30% dot area of ​​the printed material was magnified under a microscope to measure the dot diameter, and the rate of change from the dot diameter of 105 μm in the CTP data was calculated. The smaller the difference between the rate of change in dot diameter after 100 meters and after 10,000 meters, the less dot thickening there was over the long run.

[0085] [(a) Hydrophilic polymer 1] Partially saponified polyvinyl alcohol ("JR-05" manufactured by Nippon Vinyl Acetate & Poval Co., Ltd.) with a saponification degree of 70-74 mol% was swollen in acetone, and 1.0 mol% of succinic anhydride was added. The mixture was stirred at 60°C for 6 hours to add carboxyl groups to the molecular chains. The polymer was washed with acetone to remove unreacted succinic anhydride and then dried. The acid value was measured and found to be 10.0 mg KOH / g. The carboxyl group-containing polymer obtained by this procedure was designated as Hydrophilic Polymer 1.

[0086] [(a) Hydrophilic polymer 2] Partially saponified polyvinyl alcohol ("JMR-20M" manufactured by Nippon Vinyl Acetate & Poval Co., Ltd.) with a saponification degree of 63 to 67 mol% was swollen in acetone, and 1.0 mol% of succinic anhydride was added. The mixture was stirred at 60°C for 6 hours to add carboxyl groups to the molecular chains. The polymer was washed with acetone to remove unreacted succinic anhydride and then dried. The acid value was measured and found to be 10.2 mg KOH / g. The carboxyl group-containing polymer obtained by this procedure was designated as Hydrophilic Polymer 2.

[0087] [(a) Hydrophilic polymer 3] A copolymer of (dimethylaminoethyl methacrylate) / (2-hydroxyethyl methacrylate) in a mass ratio of 2 / 1 (manufactured by Kyoeisha Chemical Co., Ltd.) having an amino group and a hydroxyl group in the side chain was used as (a) hydrophilic polymer 3.

[0088] [(a) Hydrophilic polymer 4] A pressure-resistant reactor equipped with a stirrer and a temperature-controlling jacket was initially charged with 125 parts by mass of water and 2 parts by mass of a reactive emulsifier, ammonium salt of (α-sulfo(1-nonylphenoxy)methyl-2-(2-propenyloxy)ethoxy-poly(oxy-1,2-ethanediyl) ("ADEKA REASOAP" manufactured by Asahi Denka Kogyo Co., Ltd.), and the internal temperature was raised to 80°C.

[0089] Next, an oily mixture of a monomer mixture consisting of 10 parts by mass of styrene, 60 parts by mass of butadiene, 23 parts by mass of butyl acrylate, 5 parts by mass of methacrylic acid, and 2 parts by mass of acrylic acid and 2 parts by mass of t-dodecyl mercaptan was added at a constant flow rate over 5 hours. Next, an aqueous solution consisting of 28 parts by mass of water, 1.2 parts by mass of sodium peroxodisulfate, 0.2 parts by mass of sodium hydroxide, and 2 parts by mass of the ammonium salt of (α-sulfo(1-nonylphenoxy)methyl-2-(2-propenyloxy)ethoxy-poly(oxy-1,2-ethanediyl)) was added at a constant flow rate over 6 hours.

[0090] The temperature of 80°C was then maintained for 1 hour to complete the polymerization reaction, followed by cooling. The pH of the produced copolymer latex was adjusted to 7 with sodium hydroxide, and unreacted monomers were removed by steam stripping. The mixture was then filtered through a 200-mesh wire screen, and the solids concentration of the filtrate was finally adjusted to 40% by mass to obtain an aqueous dispersion of hydrophilic polymer 4.

[0091] [Example 1] (Preparation of laminated film 1 for substrate) A mixture of 260 parts by weight of a toluene solution of 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. 25 parts by weight of an ethyl acetate solution of polyisocyanate resin ("Coronate" (registered trademark) 3015E manufactured by Tosoh Corporation) and 14 parts by weight of an industrial adhesive ("EC-1368" manufactured by Sumitomo 3M Limited) were added and mixed to obtain a coating liquid for the easy-adhesion layer 1.

[0092] 50 parts by mass of polyvinyl alcohol ("GOHSENOL" (registered trademark) KH-17, manufactured by Nippon Synthetic Chemical Industry Co., Ltd.) having a saponification degree of 78.5 to 81.5 mol% was mixed in a mixed solvent of 200 parts by mass of an alcohol mixture ("SOLMIX" (registered trademark) H-11, manufactured by Nippon Alcohol Co., Ltd.) and 200 parts by mass of water at 70°C for 2 hours, and then 1.5 parts by mass of glycidyl methacrylate ("BLEMMER" (registered trademark) G, manufactured by NOF Corporation) was added and mixed for 1 hour. Further, a 2 / 1 mass ratio (dimethylaminoethyl methacrylate) / (2-hydroxyethyl methacrylate) was added to the mixed solvent. 3 parts by mass of a copolymer (manufactured by Kyoeisha Chemical Co., Ltd.), 5 parts by mass of benzyl methyl ketal ("Irgacure" (registered trademark) 651 manufactured by Ciba-Geigy), 21 parts by mass of a diacrylic acid adduct of propylene glycol diglycidyl ether ("Epoxy Ester 70PA" manufactured by Kyoeisha Chemical Co., Ltd.), and 20 parts by mass of ethylene glycol diglycidyl ether dimethacrylate were added and mixed for 90 minutes. After cooling to 50°C, 0.1 parts by mass of "Megafac" (registered trademark) F-556 (manufactured by DIC Corporation) was added and mixed for 30 minutes to obtain a coating liquid for the easy-adhesion layer 2.

[0093] The coating liquid for easy adhesion layer 1 was applied to a 188 μm thick polyester (PET) film ("Lumirror" (registered trademark) T60 manufactured by Toray Industries, Inc.) 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. The coating liquid for easy adhesion layer 2 was applied thereon 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. In this way, a substrate laminate film 1 consisting of easy adhesion layer 2 / easy adhesion layer 1 / PET substrate was obtained.

[0094] (Preparation of laminated film 1 for heat-sensitive mask layer) As the film for the cover film, a polyester (PET) film ("Lumirror" S10 manufactured by Toray Industries, Inc.) having a thickness of 100 μm and whose surface was not roughened was used.

[0095] 11 parts by mass of polyvinyl alcohol ("GOHSENOL" (registered trademark) AL-05, manufactured by Nippon Synthetic Chemical Industry Co., Ltd.) with a saponification degree of 91 to 94 mol% was dissolved in a mixed solvent of 55 parts by mass of water, 15 parts by mass of methanol, and 20 parts by mass of n-propanol to obtain a coating liquid for the peel-aid layer.

[0096] 23 parts by mass of carbon black (MA-100 manufactured by Mitsubishi Chemical Corporation), 1 part by mass of an alcohol-insoluble acrylic resin (DIANAL® BR-95 manufactured by Mitsubishi Rayon Co., Ltd.), 6 parts by mass of acetyl tributyl citrate (ATBC manufactured by J-Plus Corporation) as a plasticizer, and 30 parts by mass of diethylene glycol monoethyl ether monoacetate were premixed. This mixture was then kneaded and dispersed using a three-roll mill to obtain a carbon black dispersion.

[0097] To the carbon black dispersion, 20 parts by weight of epoxy resin ("Araldite" 6071, manufactured by Asahi Chiba Co., Ltd.), 27 parts by weight of melamine resin ("Yu-Ban" (registered trademark) 62, manufactured by Mitsui Chemicals, Inc.), 0.7 parts by weight of phosphoric acid monomer ("Light Ester" P-1M, manufactured by Kyoeisha Chemical Co., Ltd.), and 140 parts by weight of methyl isobutyl ketone were added and stirred for 30 minutes. Further addition of methyl isobutyl ketone was then performed to obtain a coating solution for the heat-sensitive mask layer 1.

[0098] 10 parts by mass of polyvinyl alcohol ("GOHSENOL" (registered trademark) KL-05, manufactured by Nippon Synthetic Chemical Industry Co., Ltd.) with a saponification degree of 78 to 82 mol% was dissolved in 40 parts by mass of water, 20 parts by mass of methanol, and 30 parts by mass of n-propanol to obtain a coating liquid for the adhesive layer.

[0099] The coating liquid for the peeling aid layer was applied to the film for the cover film using a bar coater so that the film thickness after drying would be 0.25 μm, and dried at 100° C. for 25 seconds. The coating liquid for the heat-sensitive mask layer 1 was then applied to that using a bar coater so that the film thickness after drying would be 2.0 μm, and dried at 140° C. for 30 seconds. The coating liquid for the adhesive layer was then applied to that using a bar coater so that the film thickness after drying would be 1.0 μm, and dried at 180° C. for 30 seconds, resulting in a laminated film 1 for the heat-sensitive mask layer having a laminated structure of adhesive layer / heat-sensitive mask layer 1 / peeling aid layer / cover film.

[0100] The optical density of the heat-sensitive mask layer laminate film 1 was measured using light transmitted through an orthochromatic filter as incident light and the above-mentioned cover film as a blank for zero point correction, and was found to be 3.6.

[0101] (Preparation of photosensitive flexographic printing plate precursor 1) Into a three-neck flask equipped with a stirring spatula and a condenser, (a) 40 parts by mass of hydrophilic polymer 1, (d) 30 parts by mass of trimethylolpropane tri(polyethylene glycol) ether (weight average molecular weight: 400, manufactured by Nippon Nyukazai Co., Ltd., TMP-60) as a hydrophilic plasticizer, 40 parts by mass of an alcohol mixture (manufactured by Nippon Alcohol Co., Ltd., "Solmix" (registered trademark) H-11) 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 (a) and component (d).

[0102] After cooling this solution to 70°C, 5 parts by mass of glycidyl methacrylate was added and reacted for 1 hour to be added to (a) Hydrophilic Polymer 1. At this time, the glycidyl group of glycidyl methacrylate was subjected to an addition reaction with the carboxyl group of Hydrophilic Polymer 1, resulting in ring-opening of the glycidyl group and generation of a hydroxyl group.

[0103] Next, (b) 10 parts by mass of polyethylene glycol monomethacrylate (monofunctional hydroxyl group, NOF Corporation, "BLEMMER" (registered trademark) AE400) as a hydrophilic monomer, 10 parts by mass of a 1:2 adduct of tripropylene glycol and glycidyl acrylate (difunctional hydroxyl group, NOF Corporation, "EPOXY ESTER" (registered trademark) 200PA) as a photopolymerization initiator, (c) 1.3 parts by mass of benzyl dimethyl ketal as a photopolymerization initiator, (e) 0.6 parts by mass of a fluorine-containing quaternary ammonium salt compound (NEOS Corporation, "Ftergent 320") as an ink repellent agent, and 0.05 parts by mass of 2-(2'-hydroxy-3'-t-butyl-5'-methylphenyl)-5-chlorobenzotriazole as an ultraviolet absorber were added and stirred for 60 minutes to obtain a composition solution for photosensitive resin layer 1.

[0104] The composition solution for photosensitive resin layer 1 was cast onto substrate laminate film 1, adjusted so that the plate thickness after drying (substrate laminate film 1 + photosensitive resin layer) would be 1.14 mm, and dried at 60°C for 2.5 hours. A 50 / 50 mass ratio water / ethanol mixed solvent was applied to the obtained photosensitive resin layer, and heat-sensitive mask layer laminate film 1 was pressure-bonded to obtain photosensitive flexographic printing plate precursor 1 having a laminate structure of cover film / peeling auxiliary layer / heat-sensitive mask layer 1 / adhesive layer / photosensitive resin layer 1 / easy-adhesion layer 2 / easy-adhesion layer 1 / PET substrate.

[0105] (Flexographic printing plate 1 making) Photosensitive flexographic printing plate precursor 1 was cut into a 10 cm x 10 cm piece and was exposed to a high-intensity chemical lamp (Philips TL-K 40W / 10R) from the PET substrate side, with an integrated light intensity of 700 mJ / cm 2 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 emitting in the infrared region, with the PET substrate side in contact with the drum, and a test pattern (having 175 lines, 1% to 50% halftone dots, 30 μm wide thin lines, 120 μm diameter isolated points, 300 μm wide cut lines, and a 40 mm × 40 mm solid area) was printed at an output of 2.4 J / cm. 2The image was then drawn using a laser to form an image mask from the heat-sensitive mask layer. After that, in the same way as for the back exposure, the high-intensity chemical lamp TL-K 40W / 10R was used in the atmosphere, with an integrated light intensity of 12,000 mJ / cm. 2 The main exposure was performed from the image mask side so that the film was approximately 100% white. The film was then developed for 80 seconds in tap water adjusted to 25°C using a batch exposure developer (Inglese, srl "Inglese" W43), and dried in an oven at 60°C for 10 minutes. The film was then exposed to a high-intensity chemical lamp TL-K 40W / 10R with an integrated light intensity of 12,000 mJ / cm. 2 Post-exposure was carried out so that the flexographic printing plate 1 was obtained.

[0106] When the 175-line, 3% halftone dots on flexographic printing plate 1 were checked with a magnifying glass, it was confirmed that 100 out of 100 halftone dots were reproduced. The ink contact angle of flexographic printing plate 1 was a high value of 49°. The mass change rate was also small at -1.9%.

[0107] The tensile modulus is E A is 3.9 MPa, E B is 3.1 MPa, E C is 3.2 MPa, and ΔE B is -0.8MPa, ΔE C was -0.7MPa.

[0108] The print density was 1.72 after 100m of printing and 1.70 after 10,000m of printing, showing stable print density even over long runs.

[0109] The ink deposition area ratio was 0% (no ink deposition) for both the 175 lpi 5% halftone dot and the 175 lpi 30% halftone dot, and no ink entanglement was observed on the printed matter.

[0110] The rate of change in dot diameter of the printed matter was -4.1% after 100 m of printing and -4.0% after 10,000 m of printing, showing almost no change with the printing length.

[0111] Furthermore, when a flexographic printing plate stored in a high-humidity environment for two hours was used, the print density of the printed matter after 100 meters of printing was 1.73, demonstrating that the print density was stable even in a high-humidity environment.

[0112] [Example 2] A composition solution for photosensitive resin layer 2 was obtained in the same manner as the composition solution for photosensitive resin layer 1 in Example 1, except that 20 parts by mass of (a) hydrophilic polymer 1 and 20 parts by mass of hydrophilic polymer 2 were used instead of 40 parts by mass of (a) hydrophilic polymer 1 in the photosensitive resin composition.

[0113] A photosensitive flexographic printing plate precursor 2 having a laminate structure of cover film / peeling auxiliary layer / heat-sensitive mask layer 1 / adhesive layer / photosensitive resin layer 2 / easy-adhesion layer 2 / easy-adhesion layer 1 / PET substrate was produced in the same manner as in Example 1, except that a composition solution for photosensitive resin layer 2 was used instead of the composition solution for photosensitive resin layer 1.

[0114] (Flexographic printing plate 2 making) Flexographic printing plate 2 was obtained in the same manner as in Example 1, except that photosensitive flexographic printing plate precursor 2 was used.

[0115] When the 175-line, 3% halftone dots on flexographic printing plate 2 were checked with a magnifying glass, it was confirmed that 100 out of 100 halftone dots were reproduced. The ink contact angle of flexographic printing plate 2 was a high value of 49°. The mass change rate was also small at -1.7%.

[0116] The tensile modulus is E A is 3.2 MPa, E B is 2.7 MPa, E C is 2.9 MPa, and ΔE B is -0.5MPa, ΔE C was -0.3MPa.

[0117] The print density was 1.74 after 100m of printing and 1.73 after 10,000 prints, showing stable print density even over long runs.

[0118] The ink deposition area ratio was 0% (no ink deposition) for both the 175 lpi 5% halftone dot and the 175 lpi 30% halftone dot, and no ink entanglement was observed on the printed matter.

[0119] The rate of change in dot diameter of the printed matter was -2.2% at both the 100m and 10,000m printing stages, and there was no change with printing length.

[0120] Furthermore, when a flexographic printing plate stored in a high-humidity environment for two hours was used, the print density of the printed matter after 100 meters of printing was 1.73, demonstrating that the print density was stable even in a high-humidity environment.

[0121] [Example 3] A composition solution for photosensitive resin layer 3 was obtained in the same manner as the composition solution for photosensitive resin layer 1 in Example 1, except that 35 parts by mass of (a) hydrophilic polymer 1 and 5 parts by mass of (a) hydrophilic polymer 3 were used instead of 40 parts by mass of (a) hydrophilic polymer 1 in the photosensitive resin composition.

[0122] A photosensitive flexographic printing plate precursor 3 having a laminate structure of cover film / peeling auxiliary layer / heat-sensitive mask layer 1 / adhesive layer / photosensitive resin layer 3 / easy-adhesion layer 2 / easy-adhesion layer 1 / PET substrate was produced in the same manner as in Example 1, except that a composition solution for photosensitive resin layer 3 was used instead of the composition solution for photosensitive resin layer 1.

[0123] (Flexographic printing plate 3 production) Flexographic printing plate 3 was obtained in the same manner as in Example 1, except that photosensitive flexographic printing plate precursor 3 was used.

[0124] When the 175-line, 3% halftone dots on flexographic printing plate 3 were checked with a magnifying glass, it was confirmed that 100 out of 100 halftone dots were reproduced. The ink contact angle of flexographic printing plate 3 was a high value of 46°. The mass change rate was also small at +0.5%.

[0125] The tensile modulus is E A is 3.5 MPa, E B is 3.0 MPa, E Cis 3.1 MPa, and ΔE B is -0.5MPa, ΔE C was -0.4MPa.

[0126] The print density was 1.72 after 100m of printing and 1.71 after 10,000 prints, showing stable print density even over long runs.

[0127] The ink deposition area ratio was 0% (no ink deposition) for both the 175 lpi 5% halftone dot and the 175 lpi 30% halftone dot, and no ink entanglement was observed on the printed matter.

[0128] The rate of change in dot diameter of the printed matter was +0.5% after 100m of printing and +0.7% after 10,000m of printing, showing almost no change with print length.

[0129] Furthermore, when a flexographic printing plate stored in a high-humidity environment for two hours was used, the print density of the printed matter after 100 meters of printing was 1.71, demonstrating that the print density was stable even in a high-humidity environment.

[0130] [Comparative Example 1] A composition solution for photosensitive resin layer 4 was obtained in the same manner as the composition solution for photosensitive resin layer 1 in Example 1, except that trimethylolpropane (molecular weight: 134) was used instead of trimethylolpropane tri(polyethylene glycol) ether as the (d) hydrophilic plasticizer in the photosensitive resin composition.

[0131] A photosensitive flexographic printing plate precursor 4 having a laminate structure of cover film / peeling auxiliary layer / heat-sensitive mask layer 1 / adhesive layer / photosensitive resin layer 4 / easy-adhesion layer 2 / easy-adhesion layer 1 / PET substrate was produced in the same manner as in Example 1, except that a composition solution for photosensitive resin layer 4 was used instead of the composition solution for photosensitive resin layer 1.

[0132] (Flexographic printing plate 4 making) Flexographic printing plate 4 was obtained in the same manner as in Example 1, except that photosensitive flexographic printing plate precursor 4 was used.

[0133] When the 175-line, 3% halftone dots on flexographic printing plate 4 were checked with a magnifying glass, it was confirmed that 100 out of 100 halftone dots were reproduced. The ink contact angle of flexographic printing plate 4 was a high value of 49°. On the other hand, the mass change rate was -5.3%, indicating that a large amount was extracted from flexographic printing plate 4 into tripropylene glycol diacrylate.

[0134] The tensile modulus is E A is 3.4 MPa, E B is 4.5 MPa, E C is 2.6 MPa, and ΔE B +1.1MPa, ΔE C was -0.8MPa.

[0135] The print density was 1.70 after 100m of printing and 1.65 after 10,000 prints, so the print density decreased slightly over the long run, and some printing areas were faint.

[0136] The ink deposition area ratio was 0% (no ink deposition) for both the 175 lpi 5% halftone dot and the 175 lpi 30% halftone dot, and no ink buildup was observed on the printed matter.

[0137] The rate of change in dot diameter of the printed matter varied slightly with the print length, at -3.9% after 100m of printing and -4.4% after 10,000m of printing. Also, at 10,000m of printing, fading occurred in the solid areas and print density decreased.

[0138] When a flexographic printing plate stored in a high humidity environment for 2 hours was used, the print density of the printed matter after 100 meters of printing was 1.71, and the print density was stable in a high humidity environment.

[0139] Comparative Example 2 A composition solution for photosensitive resin layer 5 was obtained in the same manner as the composition solution for photosensitive resin layer 1 in Example 1, except that the 1:2 adduct of tripropylene glycol and glycidyl acrylate was changed to polyethylene glycol dimethacrylate ("Blenmer" AD400, manufactured by NOF Corporation) having no hydroxyl group as one component of the (b) hydrophilic monomer in the photosensitive resin composition.

[0140] A photosensitive flexographic printing plate precursor 5 having a laminate structure of cover film / peeling auxiliary layer / heat-sensitive mask layer / adhesive layer / photosensitive resin layer 5 / easy-adhesion layer 2 / easy-adhesion layer 1 / PET substrate was produced in the same manner as in Example 1, except that a composition solution for photosensitive resin layer 5 was used instead of the composition solution for photosensitive resin layer 1.

[0141] (Flexographic printing plate 5 making) Flexographic printing plate 5 was obtained in the same manner as in Example 1, except that photosensitive flexographic printing plate precursor 5 was used.

[0142] When 175 lpi 3% halftone dots were checked with a magnifying glass on flexographic printing plate 5, it was confirmed that 100 out of 100 halftone dots were reproduced. The ink contact angle of flexographic printing plate 5 was a high value of 48°. On the other hand, the mass change rate was -5.1%, indicating that a large amount was extracted from flexographic printing plate 5 into tripropylene glycol diacrylate.

[0143] The tensile modulus is E A is 4.0 MPa, E B is 5.5 MPa, E C is 3.6 MPa, and ΔE B +1.5MPa, ΔE C was -0.4MPa.

[0144] The print density was 1.70 after 100m of printing and 1.55 after 10,000 prints, so the print density decreased over the long run and some of the printed areas were faded.

[0145] The ink deposition area ratio was 0% (no ink deposition) for both the 175-line 5% dot and the 175-line 30% dot, and no ink intertwining was observed on the print. The rate of change in dot diameter on the print was -4.1% after 100 meters of printing and -4.4% after 10,000 meters of printing, so the change with print length was small, but at 10,000 meters of printing, fading had occurred in the solid areas and print density had decreased.

[0146] The rate of change in dot diameter of printed matter was -4.1% after 100 m of printing and -4.4% after 10,000 m of printing, showing little change due to printing length.

[0147] When a flexographic printing plate stored in a high humidity environment for 2 hours was used, the print density of the printed matter after 100 meters of printing was 1.71, and the print density was stable in a high humidity environment.

[0148] Comparative Example 3 (Preparation of laminated film 2 for substrate) A PET film having a thickness of 100 μm and coated with an elastomer-containing adhesive was used as the laminated film 2 for substrates.

[0149] (Preparation of laminated film 2 for heat-sensitive mask layer) As the film for the cover film, a polyester (PET) film ("Lumirror" S10 manufactured by Toray Industries, Inc.) having a thickness of 100 μm and whose surface was not roughened was used.

[0150] A coating liquid for the heat-sensitive mask layer 2 was obtained by mixing 10 parts by mass of a 20% by mass aqueous solution of ethylene-acrylic acid copolymer (SG-2000, manufactured by Lead City), which is an anionic polymer having a carboxylic acid group as an anionic polar functional group, 5 parts by mass of a 20% by mass aqueous solution of carbon black ("BONJET" CW-2, manufactured by Orient Chemical Industry Co., Ltd.), 0.05 parts by mass of a release agent (KF-351, manufactured by Shin-Etsu Chemical Co., Ltd.), 30 parts by mass of water, and 15 parts by mass of ethanol.

[0151] The coating liquid for the heat-sensitive mask layer 2 was applied onto the film for the cover film using a bar coater so that the film thickness after drying would be 3.0 μm, and then dried at 90°C for 2 minutes to obtain a laminated film 2 for the heat-sensitive mask layer having a laminated structure of heat-sensitive mask layer 2 / cover film.

[0152] (Preparation of photosensitive flexographic printing plate precursor 6) 100 parts by mass of the aqueous dispersion of hydrophilic polymer 4 was mixed with 5 parts by mass of 3-methacryloxypropyltrimethoxysilane (KBM305 manufactured by Shin-Etsu Chemical Co., Ltd.) and 10 parts by mass of liquid polybutadiene (LBR352 manufactured by Kuraray Co., Ltd.) as a plasticizer, and the mixture was dried under reduced pressure at 80°C to obtain a dried mixture of hydrophilic polymer 4 and liquid polybutadiene. 110 parts by mass of this mixture and 75 parts by mass of a hydrophobic polymer, styrene-butadiene-styrene copolymer (D-KX405 manufactured by Kraton), were mixed at 140°C using a pressure kneader, and then a mixture of 40 parts by mass of liquid polybutadiene (LBR-352 manufactured by Kuraray), 10 parts by mass of 1,9-nonanediol diacrylate and 10 parts by mass of 1,6-hexanediol dimethacrylate as non-hydrophilic monomers, (c) 5 parts by mass of 2,2-dimethoxyphenylacetophenone as a photopolymerization initiator, 2 parts by mass of a surfactant (NT-12 manufactured by Daiichi Kogyo Seiyaku), and 5 parts by mass of 2,6-di-t-butyl-p-cresol as a stabilizer was added little by little over 15 minutes, and after the addition was completed, the mixture was kneaded for a further 20 minutes to obtain a composition for photosensitive resin layer 6.

[0153] The composition for the photosensitive resin layer 6 was sandwiched between a 100 μm thick PET film for substrate coated with an elastomer-containing adhesive and a 100 μm thick PET film coated with a 5 μm thick polyvinyl alcohol (PVA) layer, and molded into a 1.14 mm thick plate using a press heated to 120° C. Next, the PET film on the PVA layer side was peeled off to obtain a laminate consisting of the photosensitive resin layer 6 / elastomer-containing adhesive layer / PET substrate.

[0154] The obtained laminate was laminated with a laminate film 2 for a heat-sensitive mask layer to produce a photosensitive flexographic printing plate precursor 6 consisting of a laminate structure of cover film / heat-sensitive mask layer 2 / photosensitive resin layer 6 / elastomer-containing adhesive layer / PET substrate.

[0155] (Plate making for flexographic printing plate 6) The PET substrate side of photosensitive flexographic printing plate precursor 6 was exposed using an ultraviolet exposure machine (JE-A2-SS manufactured by Nippon Denshi Seiki) so that the pattern height after curing would be approximately 0.6 mm. 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 emitting in the infrared region, with the PET substrate side in contact with the drum. A test pattern (175 lines, 1% to 50% halftone dots, 30 μm wide thin lines, 120 μm diameter isolated points, 300 μm wide cut lines, and a 40 mm x 40 mm solid area) was printed at an output of 2.4 J / cm. 2 The plate was then exposed to UV light from the heat-sensitive mask layer side in the atmosphere for 10 minutes using the UV exposure device. After exposure, a 1% Nissan soap solution (aqueous developer) was prepared, and the plate was washed (developed) at 40°C for 5 minutes using a washing machine (JOW-A3-P manufactured by Nippon Denshi Seiki Co., Ltd.) to remove the unexposed areas, yielding flexographic printing plate 6.

[0156] When the 175 lpi 3% halftone dots on flexographic printing plate 6 were examined with a magnifying glass, it was confirmed that 99 out of 100 halftone dots were reproduced. The ink contact angle of flexographic printing plate 6 was a high value of 47°. On the other hand, the mass change rate was +6.2%, indicating that the plate swelled considerably compared to Example 1.

[0157] The tensile modulus is E A is 3.0 MPa, E B is 1.1 MPa, E C is 2.8 MPa, and ΔE B is -1.9MPa, ΔE C was -0.2 MPa.

[0158] The print density increased over the long run, reaching 1.73 after 100 meters of printing and 1.90 after 10,000 prints. This is thought to be due to the flexographic printing plate swelling and softening due to the ink during the long run.

[0159] The ink deposition area rate was 0% (no ink deposition) for the 175 line 30% halftone dots, but 60% for the 175 line 5% halftone dots, meaning that a large amount of ink had accumulated on the plate surface, and ink entanglement was observed in the printed matter.

[0160] The rate of change in dot diameter of the printed matter was +3.0% after 100m of printing and +15.3% after 10,000m of printing, with the dot diameter becoming thicker during long-run printing. As the print density increased, the swelling of the flexographic printing plate during long-run printing had a significant effect.

[0161] When a flexographic printing plate stored in a high humidity environment for 2 hours was used, the print density of the printed matter after 100 meters of printing was 1.72, and the print density was stable in a high humidity environment.

[0162] Comparative Example 4 (Preparation of photosensitive flexographic printing plate precursor 7) A composition solution for photosensitive resin layer 7 was obtained in the same manner as the composition solution for photosensitive resin layer 1 in Example 1, except that the fluorine-containing quaternary ammonium salt compound, which is the ink repellent agent (e) in the photosensitive resin composition, was not added.

[0163] A photosensitive flexographic printing plate precursor 7 having a laminate structure of cover film / peeling auxiliary layer / heat-sensitive mask layer 1 / adhesive layer / photosensitive resin layer 7 / easy-adhesion layer 2 / easy-adhesion layer 1 / PET substrate was produced in the same manner as in Example 1, except that a composition solution for photosensitive resin layer 7 was used instead of the composition solution for photosensitive resin layer 1.

[0164] (Flexographic printing plate 7) Flexographic printing plate 7 was obtained in the same manner as in Example 1, except that photosensitive flexographic printing plate precursor 7 was used.

[0165] When the 175-line, 3% halftone dots on flexographic printing plate 7 were checked with a magnifying glass, it was confirmed that 100 out of 100 halftone dots were reproduced. The ink contact angle of flexographic printing plate 1 was a low value of 25°. The mass change rate was also small at -1.9%.

[0166] The tensile modulus is E A is 4.0 MPa, E B is 3.2 MPa, E C is 3.3 MPa, and ΔE B is -0.8MPa, ΔE C was -0.7MPa.

[0167] The print density was 1.72 after 100m of printing and 1.71 after 10,000m of printing, showing stable print density even over long runs.

[0168] The ink deposition area rate was 0% (no ink deposition) for the 175 line 30% halftone dots, but 60% for the 175 line 5% halftone dots, meaning that a large amount of ink had accumulated on the plate surface, and ink entanglement was observed in the printed matter.

[0169] The rate of change in dot diameter of the printed matter was -4.1% after 100 m of printing and -4.0% after 10,000 m of printing, showing almost no change with the printing length.

[0170] Furthermore, when a flexographic printing plate stored in a high-humidity environment for 2 hours was used, the print density of the printed matter after 100 meters of printing was 1.73, indicating that the print density was stable in a high-humidity environment.

[0171] [Example 4] (Preparation of photosensitive flexographic printing plate precursor 8) A composition solution for photosensitive resin layer 8 was obtained in the same manner as the composition solution for photosensitive resin layer 1 in Example 1, except that the amount of the fluorine-containing quaternary ammonium salt compound, which is the ink repellent agent (e) in the photosensitive resin composition, added was changed from 0.6 parts by mass to 0.3 parts by mass.

[0172] Photosensitive flexographic printing plate precursor 8 having a laminate structure of cover film / peeling auxiliary layer / heat-sensitive mask layer 1 / adhesive layer / photosensitive resin layer 8 / easy-adhesion layer 2 / easy-adhesion layer 1 / PET substrate was produced in the same manner as in Example 1, except that the composition solution for photosensitive resin layer 8 was used instead of the composition solution for photosensitive resin layer 1.

[0173] (Flexographic printing plate making for plate 8) Flexographic printing plate 8 was obtained in the same manner as in Example 1, except that photosensitive flexographic printing plate precursor 8 was used.

[0174] When the 175-line, 3% halftone dots on flexographic printing plate 8 were checked with a magnifying glass, it was confirmed that 100 out of 100 halftone dots were reproduced. The ink contact angle of flexographic printing plate 1 was a relatively high value of 42°. The mass change rate was also small at -1.9%.

[0175] The tensile modulus is E A is 3.9 MPa, E B is 3.1 MPa, E C is 3.2 MPa, and ΔE B is -0.8MPa, ΔE C was -0.7MPa.

[0176] The print density was 1.72 after 100m of printing and 1.70 after 10,000m of printing, showing stable print density even over long runs.

[0177] The ink deposition area rate was 0% (no ink deposition) for the 175-line 30% halftone dots, but 3% for the 175-line 5% halftone dots, indicating some ink deposition on the plate surface. However, no ink buildup was observed on the printed matter.

[0178] The rate of change in dot diameter of the printed matter was -4.1% after 100 m of printing and -4.0% after 10,000 m of printing, showing almost no change with the printing length.

[0179] Furthermore, when a flexographic printing plate stored in a high-humidity environment for two hours was used, the print density of the printed matter after 100 meters of printing was 1.73, and the print density was also stable in a high-humidity environment.

Claims

1. The photosensitive resin layer comprises 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, the hydrophilic plasticizer being at least one selected from a derivative of trimethylolethane having a polyethylene glycol chain in the molecule, a derivative of trimethylolpropane having a polyethylene glycol chain in the molecule, and a derivative of pentaerythritol having a polyethylene glycol chain in the molecule, and the weight average of the hydrophilic plasticizer is a photosensitive flexographic printing plate precursor having a molecular weight of 200 or more and 4,000 or less, (d) a content of a hydrophilic plasticizer of 20% by mass or more and 60% by mass or less, relative to 100% by mass of the photosensitive resin layer, and when exposed and developed so that 99 or more out of 100 175-line 3% halftone dots are reproduced, the photosensitive resin layer after photocuring has a contact angle of 40° or more and 70° or less with tripropylene glycol diacrylate, and the photosensitive resin layer after photocuring has a rate of mass change of -4.0% or more and 4.0% or less after immersion in tripropylene glycol acrylate at 50°C for 24 hours.

2. 2. The photosensitive flexographic printing plate precursor according to claim 1, wherein the hydrophilic plasticizer (d) is a derivative of trimethylolpropane having a polyethylene glycol chain in the molecule.

3. 2. The photosensitive flexographic printing plate precursor according to claim 1, wherein the hydrophilic plasticizer (d) is trimethylolpropane tri(polyethylene glycol) ether.

4. The photosensitive flexographic printing plate precursor according to any one of claims 1 to 3, wherein (e) the ink repellent agent contains at least one compound selected from the group consisting of a compound containing a fluorine atom and a compound containing a silicon atom.

5. 5. The photosensitive flexographic printing plate precursor according to claim 1, wherein the hydrophilic polymer (a) has at least one of a hydroxyl group, an amino group, an amide group, a carboxyl group, and a phosphate group.

6. The photosensitive flexographic printing plate precursor according to any one of claims 1 to 5, wherein the hydrophilic monomer (b) has at least one of a hydroxyl group, an amino group, an amide group, a carboxyl group, and a phosphate group.

7. The photosensitive flexographic printing plate precursor according to any one of claims 1 to 5, wherein the hydrophilic plasticizer (d) has at least one of a hydroxyl group, an amino group, an amide group, a carboxyl group, and a phosphate group.

8. The photosensitive flexographic printing plate precursor according to any one of claims 1 to 5, wherein both the hydrophilic monomer (b) and the hydrophilic plasticizer (d) have at least one of a hydroxyl group, an amino group, an amide group, a carboxyl group, and a phosphate group.

9. 9. The photosensitive flexographic printing plate precursor according to claim 1, wherein a total mass of the (a) hydrophilic polymer, (b) hydrophilic monomer, and (d) hydrophilic plasticizer in the photosensitive resin layer is 50% by mass or more and 100% by mass or less with respect to a total mass of the polymer, monomer, and plasticizer in the photosensitive resin layer.

10. When exposed and developed so that 99 or more of 100 175-line 3% halftone dots are reproduced, the tensile modulus E of a 30 mm x 30 mm solid image portion of the printing relief is measured after storing it for 24 hours in an environment of 30°C and 20% relative humidity. Ａ The tensile modulus E measured after immersing a 30 mm x 30 mm solid image portion of the printing relief in tripropylene glycol diacrylate at 50°C for 24 hours is 0.5 MPa or more and 20.0 MPa or less. Ｂ and the aforementioned E Ａ Difference ΔE Ｂ (=E Ｂ -E Ａ 10. The photosensitive flexographic printing plate precursor according to claim 1, wherein the compressive strength (MPa) is -1.0 MPa or more and 1.0 MPa or less.