Method for manufacturing regenerated developing solution and photosensitive resin composition suitable for same

Abstract

The present invention relates to a method for producing a high-performance regenerated developing solution from a developing waste liquid of a water-developable flexographic printing original plate, said regenerated developing solution relating to the problems of developing speed and adhesion of aggregates on the surface of a printing plate. A method for producing a regenerated developing solution from a developing waste solution generated by developing a water-developing flexographic printing original plate having a photosensitive resin layer comprising a photosensitive resin composition is characterized in that: the developing waste solution is directly left to stand in a water tank without adding a coagulant to the developing waste solution; in a method for obtaining a liquid remaining in a water tank as a regenerated developing solution by floating and aggregating a photosensitive resin composition contained in a developing waste liquid and discharging the floating aggregate from the water tank, the true density of the photosensitive resin composition before photocuring is 0.91-0.97 g / cm3, and the photosensitive resin composition contains a water-soluble compound in a proportion of 1.5-15% by mass.

Description

Technical Field

[0001] The present invention relates to a method for producing a high-performance regenerated developer from a developer waste liquid generated by developing a water-developable flexographic printing original plate, and a photosensitive resin composition for a water-developable flexographic printing original plate suitable for the method. Background Art

[0002] The flexible printing original plate generally has a structure in which a photosensitive resin layer formed of a photosensitive resin composition is provided on a support. The platemaking of the flexible printing original plate involved can be carried out, for example, by selectively exposing the photosensitive resin layer using ultraviolet rays and developing the exposed photosensitive resin layer using an aqueous developer. The photosensitive resin composition in the photosensitive resin layer of the unexposed part is physically removed from the printing plate by brushing during development, and dispersed or dissolved in the developer. When the photosensitive resin layer is repeatedly developed using the same developer, the concentration of the photosensitive resin composition dispersed in the developer increases, the development speed decreases, and the dispersed photosensitive resin composition condenses to form a coagulant. The coagulant is then attached to the surface of the printing plate, which will reduce the quality of the plate. Therefore, it is necessary to discard the developer with an increased concentration of the photosensitive resin composition, replace it with a new developer, and then start platemaking. However, from the perspective of environmental burden and manufacturing cost, it is not preferred to repeatedly discard the used developer and replace it with a new developer. Therefore, an attempt is made to remove the photosensitive resin composition from the used developer and reuse it.

[0003] Patent Document 1 discloses a method of aggregating a resin component dispersed in a used developer using a coagulant and then separating the agglomerated resin solid component. However, the coagulant is expensive, and from the viewpoint of cost, it is not preferred to use the coagulant. Furthermore, since the developing speed of the developer to which the coagulant is added is greatly reduced, there is a fundamental problem that the developer cannot be reused as the developer.

[0004] In addition, Patent Document 2 discloses a method of providing a special dispersion filter to coagulate a photosensitive resin composition, and further filtering the coagulation using another coagulation filter to regenerate a developer for use. However, in this method, a special dispersion filter and a coagulation filter must be used, which requires complicated operations such as maintaining two filters.

[0005] Furthermore, Patent Document 3 discloses a method for producing a regenerated developer by treating developer waste liquid with a ceramic filter to remove undissolved resin components in the developer waste liquid. In this method, only one filter is required. However, in this method, in order to prevent the filter from being clogged, the filter needs to be backwashed frequently, which places a heavy burden on maintenance.

[0006] In order to eliminate the above-mentioned problems of the prior art, the applicant proposed in Patent Document 4 a method of leaving the developer waste liquid in a water tank for a long time, floating and condensing the photosensitive resin composition dispersed in the developer waste liquid by the specific gravity difference with water as the main component of the developer waste liquid, discharging the floating condensate from the water tank, and making the liquid remaining in the water tank into a regenerated developer. In this method, a regenerated developer with a low solid content concentration is obtained with a high recovery rate using a simple method. However, in recent years, with the increase in the resolution of printed products, there is a further demand for a method for producing a high-performance regenerated developer regarding the development speed and the re-adhesion of condensates on the surface of the printing plate. Prior art literature Patent Literature

[0007] Patent Document 1: Japanese Patent Application Laid-Open No. 06-194824 Patent Document 2: Japanese Patent Application Publication No. 2011-232407 Patent Document 3: International Publication No. 2018 / 061958 Patent Document 4: PCT / JP2022 / 9590 Summary of the invention Problem that the invention aims to solve

[0008] The present invention is created in view of the current status of the above-mentioned prior art, and its purpose is to provide a method for producing a high-performance regenerated developer solution involving the development speed and the re-adhesion of coagulants on the surface of the printing plate from the developer waste liquid generated by the development of the water-developable flexible printing original plate, and a photosensitive resin composition for a water-developable flexible printing original plate suitable for this method. Technical means of solving problems

[0009] In order to achieve the purpose involved, the inventors conducted in-depth research on the photosensitive resin composition used for the printing original plate as the development object, and found that: as a photosensitive resin composition, by using a specific range of true density and containing a water-soluble compound in a specific range of proportions in the photosensitive resin composition, a higher solid component recovery rate can be achieved when a regenerated developer is manufactured using a static method. As a result, a regenerated developer with a high development speed and less problem of re-adhesion of agglomerates on the surface of the printing plate can be produced.

[0010] The present invention has been accomplished based on the above findings and has the following structures (1) to (6). [1] A method for producing a regenerated developer from a developer waste liquid, characterized in that the developer waste liquid is generated by developing a water-developable flexographic printing plate having a photosensitive resin layer composed of a photosensitive resin composition containing at least a hydrophobic polymer, a hydrophilic polymer, a photopolymerizable unsaturated compound, a photopolymerization initiator and a plasticizer; The method comprises: a step of directly placing the waste developer liquid in a water tank without adding a coagulant to the waste developer liquid to float and coagulate the photosensitive resin composition contained in the waste developer liquid; and a step of discharging the floating coagulant from the water tank to obtain the liquid remaining in the water tank as a regenerated developer liquid; In the method, the true density of the photosensitive resin composition before photocuring is 0.91 to 0.97 g / cm 3 And the photosensitive resin composition contains a water-soluble compound in a ratio of 1.5 to 15 mass %. [2] The method according to [1], characterized in that the true density of the photosensitive resin composition after photocuring is 0.93 to 0.99 g / cm 3 . [3] The method according to [1] is characterized in that the water-soluble compound is a water-soluble photopolymerizable unsaturated compound selected from the group consisting of compounds having polyalkylene glycol in the compound structure, compounds containing carboxyl groups in the molecule, compounds containing hydroxyl groups in the molecule, compounds containing amino groups in the molecule, and mixtures thereof. [4] A method for producing a water-developable flexographic printing plate, characterized in that the regenerated developer obtained by the method according to any one of [1] to [3] is used as a developer. [5] A photosensitive resin composition for a water-developable flexographic printing plate, characterized in that it contains at least a hydrophobic polymer, a hydrophilic polymer, a photopolymerizable unsaturated compound, a photopolymerization initiator, and a plasticizer; the true density of the photosensitive resin composition before photocuring is 0.91 to 0.97 g / cm 3 And the photosensitive resin composition contains a water-soluble compound in a ratio of 1.5 to 15 mass %. [6] A water-developable flexographic printing original plate, characterized in that it comprises a support and a photosensitive resin layer; the photosensitive resin layer is composed of the photosensitive resin composition for a water-developable flexographic printing original plate described in [5]. Effects of the Invention

[0011] According to the method of the present invention, since a photosensitive resin composition having a true density in a specific range is used and a water-soluble compound is contained in the photosensitive resin composition in a specific range of proportions, it is possible to manufacture a high-performance regenerated developer having a high development speed and almost no problem of re-adhesion of agglomerates on the surface of the printing plate from the developer waste liquid generated by the development of a water-developable flexible printing original plate. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] [ Figure 1 ] shows an example of a developing device for a water-developable flexographic printing plate that can be used in the method of the present invention. [ Figure 2] shows an example of the shape of a discharge port provided on the side of a water tank that can be used in the method of the present invention. [ Figure 3 ] shows another example of the shape of a discharge port provided on the side of a water tank that can be used in the method of the present invention. [ Figure 4 ] shows an example of a state in which a lid of a drain outlet provided on the side of a water tank that can be used in the method of the present invention is closed. [ Figure 5 ] shows an example of a state in which a lid of a drain port provided on the side of a water tank that can be used in the method of the present invention is opened. Explanation of symbols 1 Development tank 2 Developer 3 piping 4 Static Tank 5 Condensate 6. Exhaust port 7 Coagulant recovery tank 8 Pumps 9 piping DETAILED DESCRIPTION

[0013] The method for producing a regenerated developer from the waste development liquid of a water-developable flexographic printing original plate of the present invention and the photosensitive resin composition used in the method are described in detail below.

[0014] First, a developing device for a water-developable flexographic printing original plate used in the method of the present invention is used. Figure 1 As shown. Figure 1 In the figure, 1 is a developing tank, in which a developer 2 for developing a flexographic printing plate is stored. 3 is a pipe, and the developer whose concentration of the photosensitive resin composition increases due to repeated development is transferred from the developing tank 1 to the stationary tank 4 via the pipe 3 as a development waste liquid. Figure 1 In the figure, the state of the developer waste liquid after being left to stand in the static tank 4 is shown, and the condensate 5 floats up and gathers in the upper layer, and a solid-liquid mixed phase containing the condensate is formed below the liquid surface of the developer waste liquid. 6 is a discharge port provided on the side of the static tank 4, for example, the solid-liquid mixed phase containing the condensate 5 is discharged from the discharge port 6 to the condensate recovery tank 7. 8 is a pump, and the regenerated developer liquid with a reduced solid component concentration after the condensate 5 is removed is returned to the developer tank 1 through the pump 8 via the pipe 9.

[0015] In addition, Figure 1In the invention, a method of setting a still tank as a water tank and transferring the developer waste liquid from the developer tank to the still tank is described. In this way, by separately setting the still tank and the developer tank, there is an advantage that the next development can be performed during the still period, and further, the solid components separated by stillness will not accumulate on the brush immersed in the developer tank liquid. However, the present invention is not limited to this method. For example, the developer tank and the still tank can be set to the same structure, and the same process as that performed in the still tank can be performed in the developer tank. In the present invention, the still tank or such a developer tank can be used as a water tank for stilling the developer waste liquid when manufacturing the regenerated developer from the developer.

[0016] In the method for producing a regenerated developer of the present invention, the developer waste liquid used as a raw material is generated by developing a water-developable flexographic printing original. The water-developable flexographic printing original has a basic structure in which a photosensitive resin layer composed of a photosensitive resin composition containing at least a hydrophobic polymer, a hydrophilic polymer, a photopolymerizable unsaturated compound, a photopolymerization initiator and a plasticizer is provided on a support. In the present invention, the support is not particularly limited, and a conventionally known support can be used.

[0017] The present invention is characterized in that the photosensitive resin composition constituting the photosensitive resin layer of the printing original plate has a true density of 0.91 to 0.97 g / cm before photocuring. 3 The photosensitive resin composition contains a water-soluble compound in a ratio of 1.5 to 15% by mass. The developer used for developing the water-developable flexographic printing plate is an aqueous developer containing water as a main component. The true density (specific gravity) of water at room temperature is 1.0 g / cm 3 Therefore, the true density of the photosensitive resin composition before photocuring is 0.91 to 0.97 g / cm 3 It means that the unexposed, unphotocured photosensitive resin composition is lighter than water, which is the main component of the aqueous developer used for developing the printing plate. At this time, the developer waste liquid generated by the development of the printing plate contains water-insoluble solid component particles of the photosensitive resin composition in the unphotocured photosensitive resin layer of the unexposed part removed from the printing plate. Therefore, when the developer waste liquid is left to stand, the water-insoluble solid component particles of the unexposed, unphotocured photosensitive resin composition contained in the developer waste liquid float and condense due to the difference in specific gravity with water. By removing the floating condensate, the developer waste liquid can be regenerated into a developer.

[0018] The upper limit of the true density of the photosensitive resin composition before photocuring needs to be 0.97 g / cm 3 , preferably 0.96 g / cm 3 , more preferably 0.95 g / cm 3When the true density before photocuring exceeds the above upper limit, the difference in specific gravity with water, which is the main component of the developer waste liquid, becomes smaller, the photosensitive resin composition is difficult to float and condense, and the standing time of the developer waste liquid becomes longer, which may cause the photosensitive resin composition to lose its practicality. In addition, the photosensitive resin composition that cannot be recovered remains in the regenerated developer and becomes a cause of adhesion to the surface of the printing plate. On the other hand, the lower limit of the true density of the photosensitive resin composition before photocuring needs to be 0.91 g / cm 3 , preferably 0.92 g / cm 3 , more preferably 0.93 g / cm 3 When the true density before photocuring is lower than the above lower limit, the photosensitive resin composition floats up too quickly, and the photosensitive resin composition will float up and condense as early as during the development of the printing original plate. There is a concern that the condensate from the photosensitive resin composition removed by development will adhere to the surface of the printing plate again.

[0019] In addition, the "true density" used in the present invention is the density that uses only the volume occupied by the substance itself as the volume for density calculation. Since pores and internal voids are not included in the volume, it is a density suitable for photosensitive resin compositions. As a specific method for measuring true density, the photosensitive resin composition can be measured by placing it in a GAY-LUSSAC type pycnometer, using a liquid to completely degas the voids in the sample, and calculating the relationship between its weight and volume to obtain the true density. The true density of the photosensitive resin composition can be controlled by adjusting the density of each component (hydrophobic polymer, hydrophilic polymer, photopolymerizable unsaturated compound, photopolymerization initiator and plasticizer, etc.) constituting the photosensitive resin composition and the mixing ratio of each component. Specifically, by comparing the average value of the density calculated based on the density of each component constituting the photosensitive resin composition and the percentage of each component with the actual measured value of the true density measured in the embodiment according to the method described later, fine-tuning can be performed to achieve the desired true density.

[0020] In the present invention, the true density before light curing is specified to be within a specific range (0.91 to 0.97 g / cm 3 ), which is a numerical range set in consideration of the true density after photocuring. The inventors found that when the printing plate is exposed and the photosensitive resin composition constituting the exposed part of the photosensitive resin layer in the printing plate is photocured, the volume of the resin composition will shrink slightly, so the true density will decrease slightly (0.02 g / cm 3 In the present invention, the upper limit of the true density before photocuring is set to "0.97 g / cm 3 " is because, if this value is used, the true density after light curing is "0.99g / cm 3", the specific gravity is still smaller than that of water which is the main component of the developer, so the water-insoluble solid component particles in the developer waste liquid of the resin composition derived from the photocuring part can also float and aggregate by standing and be removed.

[0021] As the water-insoluble solid component in the developer waste liquid, people have always only paid attention to the part of the un-photocured photosensitive resin composition in the photosensitive resin layer of the unexposed part of the printing original plate that is scraped off by a brush or the like during development. In contrast, in the present invention, attention is paid not only to the un-photocured photosensitive resin composition in the photosensitive resin layer of the unexposed part of the printing original plate, but also to the components in the developer waste liquid that are scraped off by a brush or the like during development in the photocured photosensitive resin composition in the photosensitive resin layer of the exposed part of the printing original plate. Specifically, even if dots are formed on the printing original plate by photocuring through exposure, dots with weak three-dimensional shapes due to insufficient photocuring will be scraped off the plate by brushing or the like during development and flow into the developer. In particular, in recent years, with the improvement of the resolution of printed products, the demand for manufacturing printing plates with small dots has become increasingly high. However, it is very difficult to form small dots with high precision on the printing original plate. As a result, dots with weak three-dimensional shapes due to insufficient photocuring will be scraped off the plate during development due to operations such as brushing the plate and flow into the developer, and exist in the developer waste liquid as water-insoluble solid components. Since these water-insoluble solid components come from the photosensitive resin composition "after" photocuring, their true density is greater than the water-insoluble solid components of the photosensitive resin composition "before" photocuring that have been concerned in the past. Therefore, in order to ensure that the water-insoluble solid components of the photosensitive resin composition "after" photocuring are condensed and removed by static floating, it is preferred to consider the true density "after" photocuring. The upper limit of the true density "before" photocuring specified in the present invention (0.97g / cm 3 ) is a value set in consideration of this point. In addition, the true density of the photosensitive resin composition "after" photocuring in the present invention is measured by using an evaluation sheet made from the photosensitive resin composition, covered on both sides with polyester films and having a photosensitive resin layer thickness of 500 μm, and exposing the sheet to an ultraviolet exposure amount (accumulated light amount) of 1000 mJ. It should be noted that the ultraviolet exposure amount can be measured using an ultraviolet cumulative light meter.

[0022] Next, the photosensitive resin composition containing a water-soluble compound in a ratio of 1.5 to 15% by mass as a photosensitive resin layer constituting the printing original plate, which is another feature of the present invention, is described. The "true density before photocuring is 0.91 to 0.97 g / cm 3The feature of " is to deal with the problem of "water-insoluble" compounds in the constituent components of the photosensitive resin composition (the re-adhesion of the coagulation produced by the coagulation of the "water-insoluble" compounds (solid components) on the surface of the printing plate). On the other hand, another feature is to deal with the problem of "water-soluble" compounds in the constituent components of the photosensitive resin composition. Most of the constituent components of the photosensitive resin composition (hydrophobic polymer, hydrophilic polymer, photopolymerizable unsaturated compound, photopolymerization initiator and plasticizer, etc.) are "water-insoluble" compounds, but there are also cases where "water-soluble" compounds are used. For example, in order to shorten the development time, there are cases where "water-soluble" compounds are used as photopolymerizable unsaturated compounds. The inventors have found that in a printing original plate prepared using a photosensitive resin composition mixed with a large amount of the "water-soluble" photopolymerizable unsaturated compound, a large amount of unphotocured, i.e., unphotopolymerized and "water-soluble" photopolymerizable unsaturated compounds remain on the photosensitive resin layer of the unexposed part, and these will be dissolved into the developer by the development of the aqueous developer, reducing the development time of the development waste liquid. speed. Therefore, in terms of balancing the shortening of the development time and the increase in the development speed of the developer waste liquid, it is preferred that the "water-soluble" photopolymerizable unsaturated compound is not mixed in a large amount in the photosensitive resin composition. In the present invention, the content ratio of the water-soluble compound in the photosensitive resin composition is limited to a specific range of 1.5 to 15% by mass based on such a recognition. In addition, the "water-soluble" compound in the photosensitive resin composition is not limited to the above-mentioned photopolymerizable unsaturated compound. For example, there are also hydrophilic polymers in which some of the hydrophilic polymers contain "water-soluble" components, and these hydrophilic polymers will also cause the same problems as the "water-soluble" photopolymerizable unsaturated compounds. In addition, among the commercially available "water-soluble" photopolymerizable unsaturated compounds, there are also cases where a small amount of unreacted products and partially reacted products are contained. These unreacted products and partially reacted products will also cause the same problems as the "water-soluble" photopolymerizable unsaturated compounds. Therefore, in the present invention, these hydrophilic polymers, unreacted products, and partially reacted products are also included in the water-soluble compounds, and their content ratio is limited to a specific range.

[0023] In the present invention, the upper limit of the content ratio of the water-soluble compound in the photosensitive resin composition needs to be 15% by mass, preferably 12% by mass, more preferably 10% by mass, further preferably 7% by mass, and particularly preferably 5% by mass. When the content ratio of the water-soluble compound in the photosensitive resin composition exceeds the above upper limit, the water-soluble compound in the photosensitive resin composition of the unexposed part will be dissolved into the developer in large quantities by the development of the aqueous developer, and there is a concern about reducing the development speed of the developer waste liquid. On the other hand, the lower limit of the content ratio of the water-soluble compound in the photosensitive resin composition needs to be 1.5% by mass, preferably 1.8% by mass, more preferably 2.0% by mass, and particularly preferably 2.2% by mass. When the content ratio of the water-soluble compound in the photosensitive resin composition is lower than the above lower limit, there is a concern about the poor effect of shortening the development time of the printing original. The content ratio of the water-soluble compound in the photosensitive resin composition can be controlled by adjusting the water-soluble compound content rate of each component (hydrophobic polymer, hydrophilic polymer, photopolymerizable unsaturated compound, photopolymerization initiator and plasticizer, etc.) constituting the photosensitive resin composition and the mixing ratio of each component. Specifically, by comparing the average value of the water-soluble compound content calculated based on the water-soluble compound content of each component constituting the photosensitive resin composition and the percentage of each component, and the measured value of the water-soluble compound content in the photosensitive resin composition measured according to the method described later in the embodiment, a fine adjustment can be made to achieve the desired value of the water-soluble compound content ratio in the photosensitive resin composition. When the water-soluble compound is a photopolymerizable unsaturated compound, in order to shorten the development time, any water-soluble photopolymerizable unsaturated compound that has been used can be used. As the water-soluble photopolymerizable unsaturated compound, there can be cited a water-soluble photopolymerizable unsaturated compound selected from the group consisting of a compound having a polyalkylene glycol in the compound structure, a compound containing a carboxyl group in the molecule, a compound containing a hydroxyl group in the molecule, a compound containing an amino group in the molecule, and a mixture thereof. Specifically, as the photopolymerizable unsaturated compound having a polyalkylene glycol in the compound structure, polyethylene glycol di(meth)acrylates such as diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, and tetraethylene glycol di(meth)acrylate can be cited. As the photopolymerizable unsaturated compound having a hydroxyl group in the molecule, polyol (meth)acrylates such as (meth)acrylate-2-hydroxyethyl (meth)acrylate, (meth)acrylate-2-hydroxypropyl, and glycerol mono(meth)acrylate can be cited. As the photopolymerizable unsaturated compound containing an amino group in the molecule, N,N-dimethylaminoethyl methacrylate, dimethylaminoethyl acrylate, diethylaminoethyl methacrylate, diethylaminoethyl acrylate, dimethylaminomethyl methacrylate, etc. can be cited. In addition, in the present invention, "compound" includes not only high molecular weight polymers such as resins, but also low molecular weight oligomers and monomers.The "compound" of the present invention is not limited to the form and may include liquid, semi-solid and solid. Specifically, hydrophobic polymers, hydrophilic polymers, photopolymerizable unsaturated compounds and plasticizers are "compounds" in the present invention, and organic compounds mixed in addition to these components are also included in the "compound". In the present invention, a water-soluble compound refers to a compound that dissolves in water, and the case where it transparently dissolves when mixed in water at 25°C under stirring is called water-soluble. The amount of water-soluble compounds in the photosensitive resin composition is the total amount of all water-soluble compounds contained in the photosensitive resin composition, and its content can be obtained by measuring the mass of the compound dissolved in the water-soluble test mixed in water at 25°C under stirring, and calculating the ratio of the mass of the water-soluble compound to the mass of the photosensitive resin composition used for the water-soluble test. On the other hand, a "water-insoluble" compound refers to a compound that is insoluble in water or becomes a translucent or turbid state ("water-dispersible"). Specifically, when the compound is mixed in water at 25°C under stirring at 10% by mass, it is not dissolved or becomes a translucent or turbid state ("dispersed in water") is called "water-insoluble". When the compound was transparently dissolved, filtration was performed using a cylindrical funnel-shaped glass filter (pore size 16 μ to 40 μ, manufactured by Shibata Scientific Co., Ltd.) to confirm that there was no undissolved compound.

[0024] Based on the necessary conditions that the photosensitive resin composition used in the method of the present invention should meet, the various components of the photosensitive resin composition that can be used in the method of the present invention (hydrophobic polymer, hydrophilic polymer, photopolymerizable unsaturated compound, photopolymerization initiator and plasticizer, etc.) are described in detail below.

[0025] (Hydrophobic polymer) In the present invention, "hydrophobic polymer" is a polymer obtained by polymerizing conjugated dienes. Hydrophobic polymers are the main constituents of the photosensitive resin composition together with hydrophilic polymers. As hydrophobic polymers, specifically, there can be mentioned: polymers obtained by polymerizing conjugated diene hydrocarbons or copolymers obtained by copolymerizing conjugated diene hydrocarbons with monoolefin unsaturated compounds. For example, there can be mentioned: butadiene polymers, isoprene polymers, chloroprene polymers, styrene-butadiene copolymers, styrene-butadiene-styrene copolymers, styrene-isoprene copolymers, styrene-isoprene-styrene copolymers, styrene-chloroprene copolymers, acrylonitrile-butadiene copolymers, acrylonitrile-isoprene copolymers, methyl methacrylate-butadiene copolymers, methyl methacrylate-isoprene copolymers, acrylonitrile-butadiene-styrene copolymers, acrylonitrile-isoprene-styrene copolymers, and the like. Among these, butadiene polymers are preferably used from the viewpoints of the characteristics of the flexographic printing plate, i.e., the resilience, strength and elongation properties of the plate, the hardness of the resin plate, the morphological stability when not exposed, or the ease of obtaining. These hydrophobic polymers can be used alone or in combination of two or more. In the present invention, the hydrophobic polymer can be a microparticle, and a polymer obtained by water-dispersed latex can be used. Since a variety of synthetic latexes are commercially available, it is sufficient to appropriately obtain the desired water-dispersed latex therefrom. When using water-dispersed latex, it can be added directly as a water-dispersed latex, or it can be added as a solid resin after drying and removing the water. The proportion of the hydrophobic polymer in the photosensitive resin composition forming the photosensitive resin layer is preferably in the range of 10 to 45% by mass.

[0026] (Hydrophilic polymer) In the present invention, "hydrophilic polymer" refers to a polymer containing units (monomer units) derived from unsaturated monomers and conjugated diene monomers containing at least one hydrophilic functional group such as carboxylic acid, sulfonic acid, phosphoric acid or polyalkylene glycol in the molecule. From the perspective of ease of separation and recovery, the solubility of the hydrophilic polymer in water is preferably water-dispersible. In addition, from the perspective of manufacturing, the hydrophilic polymer is preferably a polymer obtained by removing water from a water-dispersible latex. For example, there can be cited a polymer obtained by removing water from a water-dispersible latex in which polymer particles obtained by emulsion polymerization using units derived from hydrophilic unsaturated monomers, conjugated diene monomers, and other monomers that can be copolymerized with them as needed are dispersed in water. From the viewpoint of developability, the hydrophilic functional group in the hydrophilic polymer is preferably a carboxyl group. In addition, the carboxyl group can also be a metal salt of sodium, potassium, etc. From the viewpoint of ink resistance of the printing plate, the hydrophilic polymer may be internally crosslinked polymer particles, and from the viewpoint of the ease of floating and agglomeration, the gelation degree of the hydrophilic polymer as an index of internal crosslinking is preferably 10 to 90%. The proportion of the hydrophilic polymer in the photosensitive resin composition forming the photosensitive resin layer is preferably in the range of 10 to 45% by mass.

[0027] In addition, the value of the gelation degree of the hydrophilic polymer referred to here is determined based on the insolubility in toluene. The specific gelation degree is determined as follows. When it is a water-dispersed latex, the latex solution is spread on a PET film with a thickness of 100 μm, dried at 100°C for 1 hour, and 1 g of the hydrophilic polymer is taken out. After the obtained hydrophilic polymer is immersed in a toluene solution at 25°C for 48 hours, the insoluble components are separated using a filter, and dried at 110°C for 2 hours, and the weight after drying is measured. The gelation degree is measured by calculating the mass % of the dried insoluble components divided by the weight before immersion in the toluene solution.

[0028] The hydrophilic polymer is preferably granular, and its average particle size is preferably 400nm or less, and particularly preferably 150nm or less. When the average particle size is too large, the water-based developability of the obtained printing plate may decrease. As the hydrophilic polymer, a polymer obtained from a known water-dispersible latex can be used. As a specific latex, there can be cited: butadiene latex containing carboxyl groups recorded in Japanese Unexamined Patent Publication No. 1-300246, Japanese Unexamined Patent Publication No. 61-128243, Japanese Unexamined Patent Publication No. 6-194837, etc., diene polymer containing amino groups recorded in Japanese Unexamined Patent Publication No. 7-134411, etc., styrene butadiene latex synthesized using a reactive emulsifier recorded in Japanese Patent No. 3836433, etc. Among these, from the viewpoint of water developability and the physical properties of the printing plate, butadiene latex containing carboxyl groups and styrene butadiene latex containing carboxyl groups are preferred.

[0029] (Photopolymerizable unsaturated compound) In the present invention, in particular, as a photopolymerizable unsaturated compound, the use of a specific amount of a "water-soluble" compound as described above is necessary in order to balance the shortening of the development time and the increase in the development speed of the developer waste liquid. However, in the present invention, as a photopolymerizable unsaturated compound, it is not necessary to use only a "water-soluble" compound, and it is preferred to use a "water-insoluble" compound in addition to the "water-soluble" compound. As the photopolymerizable unsaturated compound, the existing well-known ones used for printing original plates can be used without particular limitation, and photopolymerizable oligomers and photopolymerizable monomers can be cited. These photopolymerizable unsaturated compounds can be used alone or in combination of two or more. The proportion of the photopolymerizable unsaturated compound in the photosensitive resin composition forming the photosensitive resin layer is preferably in the range of 1 to 50% by mass.

[0030] Photopolymerizable oligomer is a polymer that is combined with ethylenic unsaturated groups at the end and / or side chain of a conjugated diene polymer, and its number average molecular weight is more than 1000 and less than 10000. The conjugated diene polymer that constitutes the conjugated diene ethylenic polymer is composed of a homopolymer of a conjugated diene unsaturated compound or a copolymer of a conjugated diene unsaturated compound and a monoethylenic unsaturated compound. As related copolymers, can be enumerated: butadiene polymer, isoprene polymer, acrylonitrile-butadiene copolymer, acrylonitrile-isoprene copolymer, methyl methacrylate-isoprene copolymer, acrylonitrile-isoprene copolymer, methyl methacrylate-isoprene copolymer, methyl acrylate-butadiene copolymer, acrylonitrile-butadiene-styrene copolymer etc. Among these, from the viewpoint of rubber elasticity and photocurability, preferably butadiene polymer, isoprene polymer, acrylonitrile-butadiene copolymer, particularly preferably butadiene polymer, isoprene polymer.

[0031] The photopolymerizable monomer refers to a photopolymerizable compound having an ethylenically unsaturated group and a molecular weight of 500 or less, preferably a compound having at least two ethylenically unsaturated groups at the end and / or on the side chain. Examples of the photopolymerizable monomer include a multifunctional photopolymerizable monomer having two or more photopolymerizable unsaturated groups and a monofunctional photopolymerizable monomer having one photopolymerizable unsaturated group. Specific examples of the photopolymerizable monomer include hexamethylene di(meth)acrylate, ethylene glycol (meth)acrylate, diethylene glycol di(meth)acrylate, 1,4-butanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, glycerol di(meth)acrylate, triethylene glycol di(meth)acrylate, PEG#400 di(meth)acrylate, 1,3-butanediol dimethacrylate, neopentyl glycol di(meth)acrylate, PEG#200 di(meth)acrylate, 1,3-butanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, 1,10-decanediol di(meth)acrylate, ethylene oxide adduct di(meth)acrylate of bisphenol A, trimethylolpropane tri(meth)acrylate, ethylene oxide-modified trimethylolpropane tri(meth)acrylate, LIGHT ESTERP-2M (trade name, manufactured by Kyoeisha Chemical Co., Ltd.), oligopropylene glycol di(meth)acrylate, polytetramethylene glycol di(meth)acrylate, tricyclodecane dimethanol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, glycerol tri(meth)acrylate, tri(meth)acrylate of 3 mol ethylene oxide adduct of pentaerythritol, compounds having three ethylenically unsaturated groups such as pentaerythritol tri(meth)acrylate, compounds having three ethylenically unsaturated groups such as pentaerythritol tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, etc. Among these, compounds having three ethylenically unsaturated groups are particularly preferred.

[0032] In the present invention, in order to improve the mechanical strength of the printing plate and enhance the printing resistance, the photopolymerizable compound may contain a monofunctional photopolymerizable monomer having one photopolymerizable unsaturated group. As the relevant monofunctional photopolymerizable monomer, a commercially available monomer can be used. Specifically, alkyl (meth)acrylates such as methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, isopentyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, lauryl (meth)acrylate, octadecyl (meth)acrylate, cycloalkyl (meth)acrylates such as cyclohexyl (meth)acrylate, halogenated alkyl (meth)acrylates such as chloroethyl (meth)acrylate and chloropropyl (meth)acrylate, methoxyethyl (meth)acrylate, ethoxyethyl (meth)acrylate, alkoxyalkyl (meth)acrylates such as butoxyethyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, and propylene glycol (meth)acrylate. (meth)acrylates having a hydroxyl group such as 2-hydroxybutyl (meth)acrylate, 3-chloro-2-hydroxypropyl (meth)acrylate, β-hydroxy-β'-(meth)acryloyloxyethyl phthalate, (meth)acrylates having an amino group such as dimethylaminoethyl methacrylate, (meth)acrylate cycloalkyl esters such as cyclohexyl (meth)acrylate, (meth)acrylate alkoxyalkyl esters such as methoxyethyl (meth)acrylate, ethoxyethyl (meth)acrylate / butoxyethyl (meth)acrylate, (meth)acrylate phenoxyalkyl esters such as phenoxyethyl (meth)acrylate and nonylphenoxyethyl (meth)acrylate, (meth)acrylate phenoxyalkyl esters such as isobornyl (meth)acrylate, and heterocyclic monofunctional photopolymerizable monomers such as cyclotrimethylolpropane formal (meth)acrylate. Among these, particularly preferred monofunctional photopolymerizable monomers are methacrylate alkyl esters, and particularly preferred are linear methacrylate alkyl esters having 8 to 18 carbon atoms. The content of these alkyl methacrylates in the photosensitive resin composition obtained from the water-dispersed latex is preferably 1 to 30 parts by mass, particularly preferably 3 to 20 parts by mass.

[0033] (Photopolymerization Initiator) In order to photopolymerize the photopolymerizable unsaturated compound, a photopolymerization initiator is mixed into the photosensitive resin composition. As a photopolymerization initiator, any photopolymerization initiator can be used as long as it can polymerize the polymerizable carbon-carbon unsaturated group by light. Among them, it is preferred to use a photopolymerization initiator that has the function of self-decomposing by absorbing light and generating free radicals by hydrogen abstraction. For example, benzoin alkyl ethers, benzophenones, anthraquinones, dibenzoyls, acetophenones, diacetyl, etc. These polymerization initiators can be mixed with two or more, and it is particularly preferred to contain a compound composed of two types of benzyl alkyl ketal and benzophenone systems with different photosensitivity. The proportion of the photopolymerization initiator in the photosensitive resin composition forming the photosensitive resin layer is preferably in the range of 0.5 to 3.0 mass%.

[0034] (Plasticizer) In order to impart flexibility to the photosensitive resin composition, a plasticizer is mixed with the photosensitive resin composition. As the plasticizer, the existing known plasticizer used for printing original plates can be used, preferably a plasticizer that is liquid at room temperature and is water-insoluble or water-dispersible. As the plasticizer, it is preferred that the polymer has a repeating unit derived from a conjugated diene compound, or it can be a polymer having a hydrophilic group in at least one repeating unit. As the hydrophilic group, carboxyl, sulfonic acid, hydroxyl, amino, preferably carboxyl. As specific examples of conjugated diene compounds, butadiene, isoprene, styrene, and copolymers of these can be mentioned. Specifically, liquid polybutadiene, liquid polyisoprene, liquid styrene-butadiene copolymer, polybutadiene having a carboxyl group at a side chain or a terminal, styrene-butadiene copolymer having a carboxyl group at a side chain or a terminal, polybutadiene having a carboxyl group at a side chain or a terminal, and isoprene having a carboxyl group at a side chain or a terminal.

[0035] The carboxyl groups in the polymers of polybutadiene having a carboxyl group at the side chain or the terminal, styrene-butadiene copolymer having a carboxyl group at the side chain or the terminal, polybutadiene having a carboxyl group at the side chain or the terminal, and polyisoprene having a carboxyl group at the side chain or the terminal may also be metal salted. In particular, in the method of the present invention, metal salting is preferably performed because development is performed using an aqueous developer. As the metal salt, an alkali metal salt such as lithium, sodium, and potassium is preferred.

[0036] As the plasticizer, in addition to the polymer having a repeating unit derived from the above-mentioned conjugated diene compound, hydrocarbon oils such as paraffin oil, ester compounds such as adipic acid esters, sebacates, and phthalates, polyesters such as adipic acid polyesters, and phosphoric acid compounds such as phosphoric acid esters can also be used in combination. The proportion of the plasticizer in the photosensitive resin composition forming the photosensitive resin layer is preferably in the range of 3 to 20% by mass.

[0037] In addition to the above-mentioned hydrophobic polymer, hydrophilic polymer, photopolymerizable unsaturated compound, plasticizer, and photopolymerization initiator, the photosensitive resin composition of the present invention may contain additives such as hydrophilic compounds, ultraviolet absorbers, surface tension regulators, thermal polymerization inhibitors, dyes, pigments, fragrances, or antioxidants as needed.

[0038] In the photosensitive resin composition used in the method of the present invention, from the viewpoint of kneading using an extruder, the total content of the hydrophobic polymer and the hydrophilic polymer is preferably 40 to 95% by mass, the content of the photopolymerizable unsaturated compound is 5 to 35% by mass, and the content of the photopolymerization initiator is 0.1 to 10% by mass. In addition, from the viewpoint of water developability, the content ratio of the hydrophilic polymer when the total content of the hydrophobic polymer and the hydrophilic polymer is 100% by mass is preferably 40 to 90% by mass.

[0039] Next, the developer used as the source of the developer waste liquid in the method of the present invention is described. The developer used for the development of the water-developable flexographic printing plate is an aqueous developer containing water as the main component, and specifically preferably a developer containing alkaline compounds such as sodium hydroxide and sodium carbonate and surfactants in the water. In order to adjust the pH of the developer to the alkaline range (preferably 8.0 to 11.0), the alkaline compound is mixed. In order to promote the dispersion of the photosensitive resin composition in water and maintain the dispersed state, the surfactant is mixed. The concentration of the surfactant in the developer is 0.5 to 10% by mass. In addition, the developer may also contain an organic solvent, etc., within a range that does not reduce the solubility of the alkaline compound and the surfactant. The temperature of the developer is 25°C to 50°C, and it is particularly preferred to use it within 35°C to 45°C.

[0040] As surfactants, sodium alkylnaphthalene sulfonate, sodium alkylbenzene sulfonate, etc. are most suitable. In addition, anionic surfactants containing carboxylates, sulfates, sulfonates, phosphates, etc.; nonionic surfactants containing polyethylene glycol chains, polyol derivatives, dehydrated sorbitan derivatives, etc.; cationic surfactants containing primary, secondary, tertiary amine salts, quaternary ammonium salts, etc.; amphoteric surfactants containing amino acid type and betaine type hydrophilic groups can also be used.

[0041] The developing method of the water-developable flexographic printing plate is not particularly limited as long as it is a method that can use an aqueous developer to wash out the photosensitive resin composition of the uncured part of the printing plate to form a relief image. For example, there can be mentioned: a method of scrubbing with a developer using a brush, and a method of combining spray spraying and brush scrubbing of the photosensitive composition of the uncured part. As a brush, the brush filament diameter, the diameter of the implantation hole, and the spacing of the implantation holes can be appropriately selected. Specifically, it is preferred that the spacing of the implantation holes is 6 to 10 mm, the implantation hole diameter of the hair bundle is 5 to 8 mm, and the filament diameter is 160 to 200 μmm. Usually, in the above-mentioned developing method, the developer is repeatedly used until the concentration of the photosensitive resin composition exceeds a specific level, resulting in a decrease in the developing speed, which is called a waste developer. The waste developer is then allowed to stand and separate the photosensitive resin composition. In the present invention, the developer before the standing separation is referred to as a waste developer. The present invention is a method for producing a regenerated developer from the waste developer generated in this way. The following is a detailed description of this method.

[0042] In the method of the present invention, no coagulant is added to the waste developing liquid. Figure 1 The developer waste liquid is allowed to stand in a water tank 4 as shown. A high concentration of a photosensitive resin composition is contained in the developer waste liquid. As described above, the true density (specific gravity) of the photosensitive resin composition is controlled to be less than 1.0, and is lighter than water, which is the main component of the aqueous developer for developing water-developable flexographic printing plates. Therefore, when allowed to stand, the photosensitive resin composition contained in the developer waste liquid floats due to the specific gravity difference and approaches each other in space. Then, the photosensitive resin composition that has partially condensed in the developer waste liquid further condenses to form a condensate 5. As a result, in the water tank 4, as shown Figure 1 As shown, a separation state can be achieved in which the condensate 5 exists just below the liquid surface of the waste developer liquid and other components (aqueous developer with water as the main component) constituting the waste developer liquid exists below it. In addition, the condensate 5 existing just below the liquid surface of the waste developer liquid is not actually a single condensate 5, but exists in the form of a solid-liquid mixed phase in which the condensate 5 and the aqueous developer liquid are mixed. In order to easily remove the condensate, the water tank 4 can be provided with a discharge port 6 for discharging the condensate 5 on its side. In the present invention, by discharging the solid-liquid mixed phase containing the condensate 5 formed below the liquid surface of the waste developer liquid, for example, from the discharge port 6 of the water tank 4, the condensate 5 can be efficiently removed, and a regenerated developer with a low solid component concentration can be obtained with a high recovery rate. In addition, in the present invention, the method for removing the condensate is not limited to discharging from the discharge port on the side of the water tank. For example, although the removal efficiency is poor, a method of discharging from the discharge port on the bottom surface of the water tank by providing a discharge port, a method of pouring water into the water tank from the upper part of the water tank to make it overflow, and a method of scooping up the condensate with a spoon for recovery can also be adopted.

[0043] When the developer waste liquid is left standing in the tank, it is important to leave it in a static state for a certain period of time without stirring. The static time is preferably 5 hours or more, and more preferably 8 hours or more. The upper limit of the static time is not particularly limited, but 24 hours is sufficient. By achieving a sufficient static time in this way, the photosensitive resin composition contained in the developer waste liquid is almost all floated and condensed due to the difference in specific gravity, and a solid-liquid mixed phase containing condensates can be clearly formed under the liquid surface of the developer waste liquid.

[0044] The shape of the water tank is preferably a roughly rectangular parallelepiped, a roughly cube or a roughly cylindrical shape, and preferably a roughly rectangular parallelepiped or a roughly cylindrical shape with a larger surface area ratio. In particular, a roughly rectangular parallelepiped shape can effectively utilize the space in the device and is easy to discharge from the discharge port, so it is preferred.

[0045] The outlet disposed on the side of the water tank is preferably in a shape of approximately circular, approximately square, approximately rectangular, or slit. Among them, in terms of easy separation, it is particularly preferred to be as follows: Figure 2 As shown in FIG. 1 , a rectangular shape having a length direction along the width direction of the water tank is provided. Figure 3 As shown, the slit shape can exist in multiple forms in the height direction. The height of the discharge port is preferably 1 cm to 10 cm, and more preferably 4 cm to 8 cm. When it is smaller than that, the condensate is easy to clog the discharge port, and when it is larger than that, there is a possibility that the drainage capacity increases and the recovery rate decreases. In addition, when the water tank has a roughly rectangular or roughly cubic shape, the maximum width of the opening of the discharge port is preferably more than 50% of the maximum width of the water tank, and more preferably more than 85%. In addition, when the water tank has a roughly rectangular or roughly cubic shape, the maximum width of the water tank refers to the larger of the depth and width. In addition, when the water tank is roughly cylindrical, the length of the discharge port in the circumferential direction is preferably more than 1 / 8 of the circumference of the cross-sectional shape on the horizontal plane of the water tank. By setting the maximum width of the opening of the discharge port and the length in the circumferential direction as described above, discharge can be carried out smoothly.

[0046] The outlet disposed on the side of the water tank is preferably Figure 4 , 5 As shown, a lid that can be opened and closed is provided. When the liquid level of the waste developer liquid is above the discharge port, the condensate 5 floating just below the liquid level of the waste developer liquid can be easily separated and discharged by opening the lid from the closed state. The lid can be constructed in a shape that conforms to the discharge port or can be a plate-shaped sliding lid. The lid can be opened and closed manually or electrically.

[0047] The position of the outlet of the water tank is the side of the water tank. By setting it to the side, the condensed matter floating just below the liquid surface of the developer waste liquid can be easily separated. The lowest position of the opening of the outlet is preferably located at a height position of more than 50% of the depth of the water tank, and more preferably at a height position of 55 to 90% of the depth of the water tank. When it is arranged at a height position lower than 50%, the height difference with the liquid surface of the developer waste liquid is too large, the drainage capacity increases, the condensed matter floating just below the liquid surface of the developer waste liquid is dispersed, and the solid content concentration in the regenerated developer increases.

[0048] In the method of the present invention, the following two discharge methods can be adopted according to the relationship between the liquid level position of the developer waste liquid after standing and the position of the discharge port. First, when the liquid level of the developer waste liquid in the tank after standing is higher than the height of the lowest position of the opening of the discharge port, the condensate floating just below the liquid level of the developer waste liquid can be separated and discharged from the discharge port by opening the discharge port. The liquid level of the developer waste liquid in the tank at the start of discharge is preferably higher than the height of the lowest position of the opening of the discharge port by 3% or more of the depth of the water tank, more preferably higher by 5% or more, and further preferably higher by 7% or more. When the height difference is lower than the above lower limit, there is a concern that the condensate floating just below the liquid level of the developer waste liquid is not fully discharged and remains in the tank. In addition, the upper limit of the height difference is preferably 30% or less, more preferably 20% or less, and further preferably 15% or less. When the height difference exceeds the above upper limit, the drainage capacity increases, the condensate floating just below the liquid level of the developer waste liquid is dispersed, and there is a concern that the solid content concentration in the regenerated developer solution increases.

[0049] When the lowest position of the opening of the discharge port is at a height position of 50% or more of the depth of the water tank and the liquid level of the waste developer in the tank at the start of discharge is higher than the lowest position of the opening of the discharge port by 3% or more of the depth of the water tank, the depth of the water tank is, for example, such that the liquid level of the waste developer in the tank at the start of discharge is 53% or more of the depth of the water tank. Even in such a case, for example, the description of the preferred range of the liquid level of the waste developer in the tank at the start of discharge is also valid.

[0050] On the other hand, when the liquid level of the developer waste liquid in the tank after standing is below the height of the lowest position of the opening of the discharge port, since it cannot be discharged directly, the photosensitive resin composition contained in the developer waste liquid is floated and condensed by standing, and a solid-liquid mixed phase containing condensates is formed under the liquid level of the developer waste liquid, and then water or developer is transferred to the water tank to raise the liquid level to above the discharge port. By opening the discharge port in this state, the condensates floating just below the liquid level of the developer waste liquid can be separated and discharged from the discharge port. When transferring water, there is a concern that the regenerated developer will be diluted and the development speed will decrease, so it is desirable to add surfactants, pH adjusters, etc. In addition, in this case, for the liquid level of the developer waste liquid in the tank at the beginning of discharge, the same conditions apply as when the liquid level of the developer waste liquid in the tank after standing is higher than the height of the lowest position of the opening of the discharge port.

[0051] In any case, when the condensate floating just below the liquid surface of the waste developer liquid is discharged from the water tank at the open outlet, flowing water may be injected into the outlet from a nozzle provided on the wall surface opposite to the outlet to flush away the condensate. In addition, the condensate floating just below the liquid surface of the waste developer liquid may be filtered out from the outlet. As a filtration method, a method of using a pump to filter out through a pipe connected to the outlet, a method of using a dry and wet vacuum cleaner, etc. may be considered. By flushing and filtering out, the discharge becomes faster and more efficient.

[0052] From the perspective of facilitating the formation of aggregates, the developer waste liquid used as a raw material for producing the regenerated developer preferably has a solid content concentration of 5.0 mass % or more, and more preferably 6.0 mass % or more. In addition, the solid content is mainly compounds derived from the water-insoluble photosensitive resin composition components contained in the developer waste liquid.

[0053] When a stationary tank and a developing tank are provided separately as a tank for storing waste developer liquid, after the solid-liquid mixed phase containing condensates is separated and discharged from the stationary tank, the liquid remaining in the stationary tank can be directly and / or indirectly returned to the developing tank as a regenerated developer for reuse. When performing indirect return, for example, a tank for regenerated developer liquid can be provided to temporarily store the regenerated developer liquid and then return it to the developing device as needed. When performing direct return, it can be returned to the developing section or the rinsing section of the developing machine.

[0054] According to the method of the present invention, as a photosensitive resin composition, since a water-soluble compound is contained in a specific range of true density in the photosensitive resin composition at a specific range of proportions, a high-performance regenerated developer with a high development speed and almost no problem of reattachment of condensates on the surface of the printing plate can be manufactured. In particular, the regenerated developer manufactured according to the method of the present invention can maintain sufficient developability because the condensate is efficiently removed and the solid content concentration is 3.5% by mass or less, preferably less than 3.0% by mass or less. In addition, the solid content is a compound mainly derived from the water-insoluble photosensitive resin composition component contained in the regenerated developer. Therefore, the regenerated developer obtained according to the method of the present invention can be used without problems to replace the usual developer in the manufacture of water-developable flexographic printing plates. In addition, in the method of the present invention, since the solid content in the regenerated developer can be sufficiently reduced, it is not particularly necessary to use a filter to separate the condensate, but when it is desired to obtain a regenerated developer with less solid content more stably in continuous operation, it can also be combined with a simple filter such as a non-woven fabric. Example

[0055] The effects of the method for manufacturing the regenerated developer of the present invention are shown according to the following examples, but the present invention is not limited to these. In addition, in the examples and comparative examples, unless otherwise specified, parts and percentages are expressed on a mass basis. In addition, the measurements and performance evaluations in the examples and comparative examples are carried out in the following order.

[0056] <True density of the photosensitive resin composition before and after photocuring> A sample of the photosensitive resin composition before photocuring is placed in a GAY-LUSSAC pycnometer, and the voids of the sample are completely degassed and replaced with a liquid, and the true density of the photosensitive resin composition before photocuring is calculated by calculating the relationship between its weight and volume. On the other hand, an evaluation sheet with a photosensitive resin layer thickness of 500 μm and covered with polyester film on both sides is manufactured from the photosensitive resin composition, and the evaluation sheet is exposed to an ultraviolet exposure amount (accumulated light amount) of 1000 mJ as a sample, and the sample is placed in a GAY-LUSSAC pycnometer, and the voids of the sample are completely degassed and replaced with a liquid, and the true density of the photosensitive resin composition after photocuring is calculated by calculating the relationship between its weight and volume.

[0057] <Content of water-soluble compound in photosensitive resin composition> The water solubility test of the photosensitive resin composition was carried out by mixing it in water at 25°C under stirring, and the content of the water-soluble compound in the photosensitive resin composition was calculated according to the following formula. In the formula, the mass of the water-soluble compound remaining after drying is the mass of the solid content remaining after the solution of the dissolution test is dried. The content of water-soluble compound (%) = [(the mass of the water-soluble compound remaining after drying) / (the mass of the photosensitive resin composition subjected to the water solubility test)] × 100

[0058] <Concentration of Solid Components in the Waste Development Liquid> 10 g of the waste developer liquid from which the aggregates were removed was placed in a dish and dried under reduced pressure. The nonvolatile content after drying was expressed in mass %, and this value was taken as the solid content concentration in the waste developer liquid.

[0059] <Solid Content Concentration in Regenerated Developer> 10 g of the regenerated developer waste liquid from which the aggregates were removed was placed in a dish and dried under reduced pressure. The nonvolatile components after drying were expressed in mass %, and this value was taken as the solid component concentration in the regenerated developer waste liquid.

[0060] <Solid Component Removal Rate> The solid component removal rate was calculated from the solid component concentration in the developer waste liquid and the solid component concentration in the regenerated developer liquid according to the following formula. Solid content removal rate (%) = [(solid content concentration in developer waste liquid) - (solid content concentration in regenerated developer liquid)] / (solid content concentration in developer waste liquid) × 100

[0061] <Development Speed> For the printing original plate manufactured in each embodiment and comparative example, a new developer (not used for the development of the original plate once) and a regenerated developer manufactured in each embodiment and comparative example were used for development, and the distance that the printing plate was cleaned in the depth direction within 10 minutes was measured. The purpose of using a new developer for development is to study the effect of shortening the development time brought about by including a water-soluble compound in the photosensitive resin composition. It can be considered that the higher the development speed when using a new developer for development, the shorter the development time. On the other hand, the purpose of using a regenerated developer for development is to study the degree of decrease in the development speed of the development waste liquid caused by the water-soluble compounds dissolved into the developer by using a new developer for development. It can be considered that the higher the development speed when using a regenerated developer for development, the less water-soluble compounds are dissolved in the developer, and the lower the degree of decrease in the development speed of the development waste liquid. In addition, if the development speed is 0.5 mm / 10 minutes or more, it can be judged as good.

[0062] <Image Reproducibility> Development was carried out using the regenerated developer prepared in each of Examples and Comparative Examples, and the diameter of the minimum independent dot reproduced using the developed printing plate was measured. Evaluation was performed based on the following criteria. ○: Able to reproduce diameter 200μm △: Able to reproduce diameter 300μm ×: Unable to reproduce diameter 400 μm

[0063] <Whether there is condensation on the printing plate surface> Development was carried out using the regenerated developer prepared in each of Examples and Comparative Examples, and the presence or absence of adhesion of aggregates on the surface of the obtained printing plate was visually determined and evaluated based on the following criteria. 0: No page attached ×: There is a layout attached

[0064] The details of the components used in the photosensitive resin compositions of Examples and Comparative Examples are as follows. 〔Hydrophobic polymer〕 A1: Butadiene latex (Nipol LX111A2, manufactured by Japan Zeon Co., Ltd., non-volatile content 54.0%) A2: Acrylonitrile butadiene rubber latex (Nipol 1562, manufactured by Japan Zeon Co., Ltd.: latex with a combined AN content of 33.5% by mass and a concentration of 41% by weight) A3: Styrene-butadiene latex (NALSTAR-SR-101, manufactured by NIPPON A&L INC.: gelation degree 95%, average particle size 0.13 μm, non-volatile content 46%) A4: Styrene butadiene block copolymer (Clayton DX410, manufactured by Clayton: styrene content 18%, butadiene content 82%)

[0065] 〔Hydrophilic polymer〕 B1: Carboxyl-modified nitrile latex (CYATEX NA-106, manufactured by NIPPON A&L INC.: gelation degree 45%, average particle size 0.14 μm, solid content concentration 50%) B2: Carboxyl-modified styrene-butadiene latex (NALSTAR-SR-101, manufactured by NIPPON A&L INC.: gelation degree 95%, average particle size 0.24 μm, solid content 52%) B3: Carboxyl-modified styrene-butadiene latex (NALSTAR-SR-112, manufactured by NIPPON A&L INC.: gelation degree 70%, average particle size 0.13 μm, solid content 50%) B4: Carboxyl-modified styrene-butadiene latex (NALSTAR-SR-140, manufactured by NIPPON A&L INC.: gelation degree 60%, average particle size 0.15 μm, solid content concentration 48%) B5: Emulsion polymer of carboxyl-modified styrene-butadiene polymer produced by the following production method B6: Urea-urethane hydrophilic polymer solution prepared by the following preparation method [Method for producing hydrophilic polymer B5] A monomer mixture consisting of 57 parts by mass of butadiene, 15 parts by mass of styrene, 20 parts by mass of ethyl acrylate, 3 parts by mass of methacrylic acid and 5 parts by mass of acrylic acid was used, except for the composition ratio, polymerization was carried out according to the manufacturing example of Japanese Patent Gazette No. 3836433. After the polymerization reaction was completed, cooling was carried out. Next, after the pH of the generated copolymer latex was adjusted to 7 using sodium hydroxide, unreacted monomers were removed by steam stripping and filtered using a metal mesh of 200 meshes. The final solid content concentration was adjusted to 40% by mass to obtain an emulsion polymerization solution of hydrophilic polymer B5. [Method for producing hydrophilic polymer B6] 60.0 parts by mass of hexamethylene diisocyanate, 31.0 parts by mass of dimethylol propionic acid, 15.0 parts by mass of polytetramethylene glycol with a molecular weight of 850 and 3.0 parts by mass of di-n-butyltin dilaurate were dissolved in 150 parts by mass of tetrahydrofuran, and the solution was poured into a 1-liter flask with a stirrer, heated to 65°C while continuously stirring, and the reaction was continued for 2 hours. A solution of 92.0 parts by mass of acrylonitrile-butadiene oligomer (HycarATBN 1300×16, manufactured by Ube Industries, Ltd.) having an amino group at the end dissolved in another container in 135 parts by mass of tetrahydrofuran was added to the above-mentioned 1-liter flask while continuously stirring at room temperature. Tetrahydrofuran was distilled off from the polymer solution under reduced pressure, and the polymer with a number average molecular weight of 8500 was obtained by drying under reduced pressure. Next, an aqueous solution of 0.6 parts by mass of lithium hydroxide and 1.4 parts by mass of magnesium acetate dissolved in 42 parts by mass of ion exchange water was added to a solution of 25 parts by mass of the polymer dissolved in 33 parts by mass of tetrahydrofuran while continuously stirring at room temperature to obtain a ureaurethane-based hydrophilic polymer B6 having a solid content concentration of 25% by mass.

[0066] [Photopolymerizable unsaturated compound] C1: polybutadiene terminal diacrylate (BAC-45, manufactured by Osaka Organic Industry Co., Ltd.) C2: 3-methyl-1,5-pentanediol diacrylate, manufactured by Tokyo Chemical Industry) C3: 1,10-decanediol diacrylate (Model A-DOD-N, manufactured by Shin-Nakamura Chemical Industry Co., Ltd.) C4: Tricyclodecane dimethanol diacrylate C5: Polyethylene glycol #200 diacrylate (A-200, manufactured by Shin-Nakamura Chemical) C6: Glyceryl dimethacrylate (manufactured by Tokyo Chemical Industry) C7: Stearyl acrylate (manufactured by Osaka Organic Industry) C8: Dimethylaminoethyl methacrylate (manufactured by Mitsubishi Gas Chemical Industries, Ltd.) C9: Glycerol monoacrylate (BLEMMER GLM, manufactured by NOF Corporation)

[0067] 〔Plasticizer〕 D1: Liquid butadiene (LBR-361, manufactured by KURARAY) D2: Liquid styrene butadiene (L-SBR-841, manufactured by KURARAY)

[0068] [Photopolymerization initiator] Benzil dimethyl ketal (manufactured by Tokyo Chemical Industry)

[0069] [Other additives] Heat stabilizer: 4-methoxyphenol (manufactured by Tokyo Chemical Industry) Ultraviolet light absorber: Tinuvin 326 (manufactured by Tokyo Chemical Industry)

[0070] (Example 1) Preparation of photosensitive resin composition A dope was prepared by mixing 27.5 parts by weight of A1 butadiene latex as a hydrophobic polymer, 24 parts by weight of B1 carboxyl-modified nitrile latex as a hydrophilic polymer, 17.5 parts by weight of C1 polybutadiene terminal diacrylate as a photopolymerizable unsaturated compound, 12 parts by weight of C3 1,10-decanediol diacrylate as a photopolymerizable monomer, 12 parts by weight of C6 glycerol dimethacrylate as a photopolymerizable monomer, 5 parts by weight of D1 liquid butadiene as a plasticizer, 1.5 parts by weight of a photopolymerization initiator, 0.2 parts by weight of a heat stabilizer, and 0.01 parts by weight of an ultraviolet absorber in a container. The obtained dope was put into a heating kneading device, and the solvent was removed under reduced pressure to prepare a photosensitive resin composition.

[0071] Production of flexographic printing plates The obtained photosensitive resin composition is sandwiched by a support film coated with a polyester adhesive layer on a polyethylene terephthalate film having a thickness of 125 μm and a film coated with a release layer (polyvinyl alcohol) on a polyethylene terephthalate cover film. At this time, the adhesive layer and the release layer are in contact with the photosensitive resin composition. Next, a hot press is used to laminate at 100°C to obtain an A2-sized flexographic printing plate consisting of a polyethylene terephthalate film support, an adhesive layer, a photosensitive resin layer, a release layer and a cover film. The total thickness of the plate is 1.7 mm.

[0072] Next, the obtained flexographic printing original plate was exposed (image area ratio 50%). Using the exposed flexographic printing original plate, development was repeated under the following conditions to prepare a development waste liquid having a solid content concentration of 5.0 mass %. <Developing Device> As a developing device, use Figure 1 A developing device of the structure shown. <Developer> As a developer, sodium oleate was weighed to 1% of the total developer, dissolved in tap water, and heated to a developer temperature of 40° C. before use. <Developer Brush> As a developing brush, a developing brush prepared by embedding nylon bristles having a diameter of 150 μm in a supporting plate made of PVC resin plywood having a thickness of 10 mm under the following conditions was used. Hair bundle embedding hole diameter: 20mm Hair bundle embedding density: 120 hairs / hole

[0073] Next, the resulting waste developing liquid is Figure 1 The developer tank 1 is transferred to the static tank 4 and is allowed to stand in the static tank 4 for 5 hours, so that the photosensitive resin composition contained in the developer waste liquid floats and condenses, and a solid-liquid mixed phase containing condensates 5 is formed below the liquid surface of the developer waste liquid. In addition, the volume of the developer waste liquid transferred to the static tank 4 is 45 liters, and the liquid level of the developer waste liquid in the static tank 4 immediately after the developer waste liquid is transferred to the static tank 4 is 75% of the depth of the static tank 4.

[0074] The static tank 4 is a roughly rectangular parallelepiped shape with dimensions of 43 cm in width×76 cm in depth×19 cm in height, and a side surface of one side thereof is provided with a Figure 2 The discharge port 6 is a rectangular discharge port 6 with a size of 5 cm in height and 70 cm in length as shown. The discharge port 6 is set in such a way that the height of the lowest position of the rectangular opening of the discharge port is located at a height position of 70% of the depth of the static tank 4. The discharge port 6 has a cover, and the upper part of the cover is fixed to the wall surface by a fixing shaft, such as Figure 4 and Figure 5 As shown, the cover can be opened and closed with the fixed axis as the center.

[0075] After standing, the lid of the discharge port 6 was opened, and the solid-liquid mixed phase containing the coagulation 5 was discharged from the discharge port 6 and recovered in the coagulation recovery tank 7. After that, the liquid remaining in the standing tank 4 was recovered as a regenerated developer. The recovered regenerated developer was 35 liters. Using this regenerated developer, the development speed, image reproducibility and the presence or absence of coagulation on the printing plate surface were evaluated. The evaluation results are shown in Table 1.

[0076] Examples 2 to 16, Comparative Examples 1 to 4 A flexographic printing plate was prepared in the same manner as in Example 1 except that the mixing ratio of each component in the photosensitive resin composition constituting the photosensitive resin layer was changed to that shown in Tables 1 and 2, and the evaluation was performed in the same manner as in Example 1. The evaluation results are shown in Tables 1 and 2.

[0077] [Table 1]

[0078] [Table 2] (Note 1) The carboxyl-modified nitrile latex of B1 contains 3% by mass of a water-soluble resin. The carboxyl-modified styrene-butadiene rubber latex of B2 contains 5% by mass of a water-soluble resin. The carboxyl-modified styrene-butadiene rubber latex of B3 contained 4% by mass of a water-soluble resin. The carboxyl-modified styrene-butadiene rubber latex of B4 contains 4% by mass of a water-soluble resin. The carboxyl-modified styrene-butadiene polymer of B5 contains 6% by mass of a water-soluble resin. The hydrophilic polymer PFT of B6 contains 20 mass % of a water-soluble resin. C6 glycerol dimethacrylate contains 7% by mass of a water-soluble resin.

[0079] As can be seen from Tables 1 and 2, Examples 1 to 16 that meet the necessary conditions of the present invention are excellent in any evaluation of solid component removal rate, development speed, image reproducibility, and the presence or absence of coagulation on the surface of the printing plate. On the other hand, in Comparative Example 1 in which the true density of the photosensitive resin composition before photocuring is too low, the photosensitive resin composition floats and coagulates too early during the development process of the printing original plate, resulting in the coagulation of the photosensitive resin composition removed by development being attached to the surface of the printing plate again. In Comparative Example 2 in which the true density of the photosensitive resin composition before photocuring is too high, the specific gravity difference with water as the main component of the developer waste liquid is small, and the photosensitive resin composition is difficult to float and coagulate. The coagulation cannot be fully removed during the 5-hour standing of the developer waste liquid, and it has no practical application. In addition, the photosensitive resin composition that cannot be recovered remains in the regenerated developer and adheres to the surface of the printing plate. In Comparative Example 3 in which the content ratio of the water-soluble compound in the photosensitive resin composition is too low, the development speed in the new developer is low, and the effect of shortening the development time of the printing original plate is poor. In addition, the development speed of the regenerated developer is also low. In Comparative Example 4 where the content of the water-soluble compound in the photosensitive resin composition was too high, the water-soluble compound in the photosensitive resin composition in the unexposed portion was largely dissolved into the developer by development in the aqueous developer, and the development speed of the regenerated developer was significantly reduced. Industrial Applicability

[0080] According to the method of the present invention, a photosensitive resin composition having a true density in a specific range is used, and a water-soluble compound is contained in the photosensitive resin composition at a specific ratio, so that a high-performance regenerated developer having a high development speed and hardly causing the problem of re-adhesion of aggregates on the surface of the printing plate can be produced from the developer waste liquid generated by the development of a water-developable flexographic printing original plate. Therefore, the present invention is extremely useful.

Claims

1. A method for producing a regenerated developer from a developer waste liquid, characterized in that: The developer waste liquid is generated by developing a water-developable flexographic printing original plate having a photosensitive resin layer composed of a photosensitive resin composition containing at least a hydrophobic polymer, a hydrophilic polymer, a photopolymerizable unsaturated compound, a photopolymerization initiator and a plasticizer; The method comprises: a step of directly placing the waste developer liquid in a water tank without adding a coagulant to the waste developer liquid to float and coagulate the photosensitive resin composition contained in the waste developer liquid; and a step of discharging the floating coagulant from the water tank to obtain the liquid remaining in the water tank as a regenerated developer liquid; In the method, the true density of the photosensitive resin composition before photocuring is 0.91 to 0.97 g / cm 3 And the photosensitive resin composition contains a water-soluble compound in a ratio of 1.5 to 15 mass %.

2. The method according to claim 1, characterized in that The true density of the photosensitive resin composition after photocuring is 0.93 to 0.99 g / cm 3 .

3. The method according to claim 1, characterized in that The water-soluble compound is a water-soluble photopolymerizable unsaturated compound selected from the group consisting of a compound having a polyalkylene glycol in a compound structure, a compound containing a carboxyl group in a molecule, a compound containing a hydroxyl group in a molecule, a compound containing an amino group in a molecule, and a mixture thereof.

4. A method for producing a water-developable flexographic printing plate, characterized in that: The regenerated developer obtained by the method according to any one of claims 1 to 3 is used as the developer.

5. A photosensitive resin composition for a water-developable flexographic printing original plate, characterized in that: The photosensitive resin composition contains at least a hydrophobic polymer, a hydrophilic polymer, a photopolymerizable unsaturated compound, a photopolymerization initiator and a plasticizer; the true density of the photosensitive resin composition before photocuring is 0.91 to 0.97 g / cm 3 And the photosensitive resin composition contains a water-soluble compound in a ratio of 1.5 to 15 mass %.

6. A water-developable flexographic printing plate, characterized in that: The invention comprises a support and a photosensitive resin layer; the photosensitive resin layer is composed of the photosensitive resin composition for a water-developable flexographic printing original plate as claimed in claim 5.

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