Method and apparatus for producing recycled developer from waste developer solution

Abstract

Provided is a method that makes it possible to filter and remove a photosensitive resin composition from a development waste liquid produced by development of a water-washable flexographic printing plate regardless of whether the photosensitive resin composition is clumped and that also makes it possible to maintain high filtration performance and to highly concentrate the development waste liquid for disposal. According to the present invention, a method for producing a recycled developer from a development waste liquid produced by development of a water-washable flexographic printing plate that has a photosensitive resin layer that comprises a photosensitive resin composition that includes a water-dispersible resin is characterized by: guiding the development waste liquid into a processing tank, separating and removing the photosensitive resin composition included in the development waste liquid by means of a polymer porous flat membrane sheet that is provided inside the processing tank, and obtaining a recycled developer; and introducing sponge fragments into the processing tank and aerating such that the sponge fragments strike the flat membrane sheet to remove deposits from and clean the flat membrane sheet.

Description

[Technical Field]

[0001] The present invention relates to a method and apparatus for producing a regenerated developer from developing waste liquid, and more particularly to a method and apparatus for efficiently filtering and removing a photosensitive resin composition from developing waste liquid generated by developing a water-developable flexographic printing plate having a photosensitive resin layer, regardless of whether or not it is agglomerated. [Background technology]

[0002] Flexographic printing plates generally have a structure in which a photosensitive resin layer formed from a photosensitive resin composition is provided on a support. The plate-making process for such flexographic printing plates is carried out, for example, by selectively exposing the photosensitive resin layer with ultraviolet light and then developing the exposed photosensitive resin layer with an aqueous developer. The photosensitive resin composition in the unexposed areas of the photosensitive resin layer is physically removed from the printing plate by brushing during development and dispersed or dissolved in the developer. Repeated development of the photosensitive resin layer using the same developer increases the concentration of the photosensitive resin composition dispersed in the developer, leading to a decrease in development speed or the aggregation of the dispersed photosensitive resin composition, forming aggregates. These aggregates re-adhere to the surface of the printing plate, degrading the quality of the plate surface. Therefore, it is necessary to discard the developer with a high concentration of the photosensitive resin composition and replace it with a new developer to resume plate making. However, repeatedly discarding used developer and replacing it with a new one is undesirable in terms of environmental impact and manufacturing costs. Therefore, attempts are being made to remove the photosensitive resin composition from used developer and reuse it as a regenerated developer.

[0003] For example, Patent Document 1 proposes a device that uses a developer regeneration means to recover used developer, remove suspended matter, and supply the removed developer to a developer supply means, thereby enabling the developer to be recycled and reused. This device can recover the photosensitive resin composition that has aggregated in the developer by removing suspended matter with a filter, but the photosensitive resin composition that is dispersed in the developer without agglomerating passes through the filter and cannot be recovered. To address this, if the mesh of the filter used is made finer, the filter needs to be replaced frequently, which is inefficient. Furthermore, if a flocculant is used to agglomerate and recover the photosensitive resin composition, there are problems in terms of the cost and efficiency of the flocculant.

[0004] To overcome the problems of Patent Document 1, Patent Document 2 proposes a developing apparatus comprising a dispersion filter for agglomerating a photosensitive resin composition dispersed in a developing solution, and an agglomeration filter for removing the agglomerated photosensitive resin composition from the developing solution that has passed through the dispersion filter, wherein the developing solution from which the agglomerated photosensitive resin composition has been removed is allowed to stand and separated into a high-concentration layer and a low-concentration layer. This apparatus can agglomerate and recover the photosensitive resin composition dispersed in the developing solution without agglomeration, but because it is necessary to separate it into a high-concentration layer and a low-concentration layer, the separation takes time, and there is a problem that it is not possible to efficiently concentrate the used developing solution and separate the photosensitive resin composition. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 9-258458 [Patent Document 2] Japanese Patent Publication No. 2011-232407 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] The present invention was devised to solve the problems of the prior art described above, and its purpose is to provide a method and apparatus for producing a regenerated developer that can efficiently filter and remove the photosensitive resin composition from the developing waste liquid generated by developing a water-developable flexographic printing plate, regardless of whether or not the photosensitive resin composition has aggregated, while maintaining high filtration performance, and can concentrate the developing waste liquid to a high concentration before disposal. [Means for solving the problem]

[0007] To achieve this objective, the inventors investigated an efficient method for filtering and separating the photosensitive resin composition from developing wastewater, and a method for maintaining filtration performance. As a result, they adopted a polymer porous flat membrane sheet, which had not been conventionally used for the regeneration of used developing solution, as a means for filtering and separating the photosensitive resin composition. Microfiltration membranes were difficult to use because they tend to clog due to the synthetic rubber polymer in the photosensitive resin composition. However, the flat membrane sheet has high membrane cleaning properties by aeration, and the photosensitive resin composition adhering to the membrane surface and between the membranes can be efficiently removed. However, when the developing wastewater was concentrated to a high concentration, the photosensitive resin composition sometimes aggregated and adhered to the surface of the flat membrane sheet, causing clogging. Therefore, by employing a washing method that allows aeration so that soft sponge pieces come into contact with the filtration surface of the flat film sheet, it is possible to filter out not only aggregates of the photosensitive resin composition from the developing waste liquid, but also photosensitive resin composition that was dispersed without agglomeration. Furthermore, since the deposits on the surface that accumulate due to the filtration separation by the flat film sheet can be easily removed and washed with the sponge pieces, it was found that the developing waste liquid can be concentrated to a high concentration before disposal.

[0008] In other words, the present invention was completed based on the above findings and has the following configurations (1) to (6). (1) A method for producing a recycled developer from developing waste liquid generated by developing a water-developable flexographic printing plate having a photosensitive resin layer made of a photosensitive resin composition containing a water-dispersible resin, The developing waste liquid is introduced into a processing tank, the photosensitive resin composition contained in the developing waste liquid is separated and removed using a polymer porous flat membrane sheet provided in the processing tank, and a regenerated developing solution is obtained. A method characterized by introducing sponge pieces into the processing tank and aerating the polymer porous flat membrane sheet so that the sponge pieces come into contact with the polymer porous flat membrane sheet, thereby removing and cleaning any deposits on the polymer porous flat membrane sheet. (2) The method according to (1), characterized in that the polymer porous flat membrane sheet comprises a polymer porous membrane that forms a mesh-like network structure and a sheet-like substrate that supports it. (3) The sponge piece 、0 The method according to (1) or (2), characterized in that it consists of a material having a maximum side dimension of 0.1 to 10 mm. (4) An apparatus for producing a recycled developer from developing waste liquid generated by developing a water-developable flexographic printing plate having a photosensitive resin layer made of a photosensitive resin composition containing a water-dispersible resin, The apparatus has a processing tank for receiving the developing waste liquid and separating and removing the photosensitive resin composition contained in the developing waste liquid, The processing tank is equipped with a polymer porous flat membrane sheet for separating and removing the photosensitive resin composition from the developing waste liquid, and The apparatus is characterized in that the processing tank comprises sponge pieces introduced into the processing tank and a cleaning means configured to remove deposits from the polymer porous flat membrane sheet by aerating the sponge pieces so that they come into contact with the polymer porous flat membrane sheet. (5) The apparatus according to (4), characterized in that the polymer porous flat membrane sheet comprises a polymer porous membrane that forms a mesh-like network structure and a sheet-like substrate that supports it. (6) The sponge piece 、0 The apparatus according to (4) or (5), characterized in that it is made of a material having a maximum side dimension of 0.1 to 10 mm. [Effects of the Invention]

[0009] According to the method and apparatus of the present invention, a high-performance polymer porous flat membrane sheet with a high pore size is used as a means of filtering and separating the photosensitive resin composition from the developing waste liquid. Therefore, not only aggregates of the photosensitive resin composition but also the photosensitive resin composition that is dispersed without agglomeration can be efficiently removed from the developing waste liquid, and a regenerated developing solution can be easily obtained. Furthermore, according to the method and apparatus of the present invention, sponge pieces are introduced into a processing tank in which the polymer porous flat membrane sheet is immersed, and the sponge pieces are aerated so as to come into contact with the surface of the flat membrane sheet to remove and wash away any dirt adhering to the surface of the flat membrane sheet. As a result, clogging of the flat membrane sheet is less likely to occur, high filtration performance can be maintained, and the developing waste liquid can be concentrated to a high concentration before disposal. [Brief explanation of the drawing]

[0010] [Figure 1] Figure 1 is a schematic diagram of an example of a developing process system that incorporates the apparatus for producing recycled developing solution from developing waste liquid according to the present invention. [Figure 2] Figure 2 is a schematic diagram of an example of an apparatus for producing recycled developer from developing waste liquid according to the present invention. [Figure 3] Figure 3 is a schematic diagram illustrating an example of a method for removing deposits from the surface of a polymer porous flat membrane sheet using the apparatus of the present invention. [Modes for carrying out the invention]

[0011] The apparatus and method of the present invention are for producing a recycled developer from developing waste liquid generated by developing a water-developable flexographic printing plate having a photosensitive resin layer made of a photosensitive resin composition. The apparatus of the present invention is used by being incorporated into a general developing process system, for example, as shown in Figure 1.

[0012] Figure 1 schematically shows an example of a developing processing system in which the device of the present invention is incorporated. As shown in Figure 1, a water-developable flexographic printing original plate (not shown) having a photosensitive resin layer, when entering the developing processing system, advances according to the conveying direction 31 and is first developed by relatively rubbing with a developing brush 32 in the presence of the developing solution discharged from the developing solution discharge port 39. In development, among the photosensitive resin layer of the flexographic printing original plate, the unexposed portion of the previous process is removed. The developing solution used in development is sent to the developing solution tank 33 and stored therein.

[0013] Next, the flexographic printing original plate is rubbed on the surface by a roll-shaped rinse brush 37 while being sprayed with the developing solution or water discharged from the regenerated developing solution discharge port 38, and the debris remaining on the plate is removed. The developing solution or the like used here is also sent to the developing solution tank 33 and stored in the same manner. The liquid stored in the developing solution tank 33 is sent to the developing solution discharge port 39 as it is for reuse as a developing solution through the transfer switching valve 35 by the developing solution pump 34, or is removed of the photosensitive resin composition by the regenerated developing solution manufacturing apparatus 1 of the present invention and regenerated, and then sent to the regenerated developing solution discharge port 38. Figure 1 shows a general example of a developing processing system, and the regenerated developing solution manufacturing apparatus 1 of the present invention can be similarly incorporated into developing processing systems of other configurations.

[0014] The flexographic printing original plate to be developed has a photosensitive resin layer made of a photosensitive resin composition containing a water-dispersible resin on a support, and uses an aqueous developing solution as a washout solution. The photosensitive resin composition forming the photosensitive resin layer is water-developable and preferably contains a synthetic rubber-based polymer, a photopolymerizable unsaturated monomer compound, and a photoinitiator as main components.

[0015] For use as a support for flexographic printing plates, a flexible material with excellent dimensional stability is preferred. For example, metal supports such as steel, aluminum, copper, and nickel, or thermoplastic resin films such as polyethylene terephthalate film, polyethylene naphthalate film, polybutylene terephthalate film, or polycarbonate film can be used. Among these, polyethylene terephthalate film, which has excellent dimensional stability and sufficiently high viscoelasticity, is particularly preferred.

[0016] Synthetic rubber polymers are used to impart appropriate rubber elasticity to photosensitive resin layers, and conventionally known rubber components can be used. It is preferable that the synthetic rubber polymer be solid at room temperature to impart rubber elasticity. Examples of synthetic rubber polymers include polybutadiene, polychloroprene, polyacrylonitrile-butadiene, polyacrylic, epichlorohydrin, polyurethane, polyisoprene, polystyrene-isoprene copolymer, polystyrene-butadiene copolymer, methyl methacrylate-butadiene copolymer, ethylene-propylene copolymer, butyl polymer, and chlorinated polyethylene. Polymers obtained by copolymerizing these polymers with other components such as acrylic acid or methacrylic acid can also be used. Among synthetic rubber polymers, water-dispersible synthetic rubber polymers having a butadiene skeleton and / or a styrene skeleton are preferred in terms of developability and physical properties. Water-dispersible latex is preferred as the water-dispersible synthetic rubber polymer. Water-dispersible latex can be latex having a cross-linked structure within the molecule. As a latex having a cross-linked structure within the molecule, a hydrophobic polymer obtained from a water-dispersed latex with a weight-average gelation degree of 20-80% is preferred. Water-dispersed latex is a stable suspension in which fine particles of rubber polymer are dispersed in water, and the polymer is obtained by removing water from this water-dispersed latex.

[0017] The photosensitive resin composition may contain water-insoluble synthetic rubber polymers to the extent that they do not adversely affect its performance. Examples of such water-insoluble polymers include polybutadiene, polychloroprene, polyacrylonitrile-butadiene, polyurethane, polyisoprene, polystyrene-isoprene copolymer, and polystyrene-butadiene copolymer.

[0018] The photosensitive resin composition may contain water-soluble or water-dispersible polymers in addition to water-dispersible synthetic rubber polymers. Examples of water-soluble or water-dispersible polymers include water-soluble polyamides and water-dispersible polyamides obtained by introducing hydrophilic groups into polyamides, partially saponified polyvinyl acetate and its derivatives, and anionic acrylic polymers.

[0019] Photopolymerizable unsaturated monomer compounds are used for crosslinking and curing by ultraviolet light. Photopolymerizable unsaturated monomer compounds may have only one ethylenically unsaturated bond, or they may have two or more ethylenically unsaturated bonds. Photopolymerizable unsaturated monomer compounds may also contain oligomers or polymers into which photopolymerizable groups have been introduced. From the standpoint of compatibility with synthetic rubber copolymers, it is preferable that the photopolymerizable unsaturated monomer compound contains one that shares a common skeleton with the synthetic rubber copolymer.

[0020] Photopolymerization initiators are used to polymerize polymerizable unsaturated groups by light irradiation, and those that have the function of generating radicals by self-decomposition or hydrogen abstraction upon light absorption are particularly preferred. Specifically, for example, benzoin alkyl ethers, benzophenones, anthraquinones, benzyls, acetophenones, and diacetyls can be used. Not only one type of photopolymerization initiator, but two or more types may be used in combination.

[0021] The developer used in this invention is an aqueous developer mainly composed of water, and is used to remove water-dispersible uncured portions of the photosensitive resin. The aqueous developer may be water alone, or it may be an aqueous solution to which a water-soluble development accelerator has been added. Examples of development accelerators include surfactants, acids, bases, and salts. From the viewpoint of development speed, it is preferable to add a water-soluble development accelerator. Commercially available soap or detergent may be used as the development accelerator.

[0022] Examples of surfactants include cationic surfactants, anionic surfactants, and nonionic surfactants. Examples of acids include inorganic acids such as sulfuric acid, nitric acid, and phosphoric acid, and organic acids such as formic acid, acetic acid, oxalic acid, succinic acid, citric acid, maleic acid, and p-toluenesulfonic acid. Examples of bases include lithium hydroxide, sodium hydroxide, potassium hydroxide, and calcium hydroxide. The developing accelerator may be a combination of surfactants, acids, bases, and salts, and the optimal blend of developing accelerators should be determined according to the components of the photosensitive resin composition.

[0023] Aqueous developers may contain water-soluble organic solvents in addition to water. Examples of such organic solvents include methanol, ethanol, isopropyl alcohol, cellosolve, glycerin, ethylene glycol, and polyethylene glycol. Furthermore, defoaming agents may be added to suppress foam formation. Any water-soluble defoaming agent can be used, and examples of defoaming agent components include higher alcohols, fatty acid derivatives, silica, anodized aluminum, and silicone.

[0024] Next, the configuration of the apparatus of the present invention will be explained using Figures 2 and 3. The first feature of the apparatus of the present invention is the use of a polymer porous flat membrane sheet to separate and remove the photosensitive resin composition contained in the developing waste liquid. Conventionally, the filtration and removal of the photosensitive resin composition from the developing waste liquid in the processing tank was carried out solely by filters. While filters are effective in filtering and removing aggregated photosensitive resin composition, it was difficult to remove the photosensitive resin composition that was dispersed in the liquid without being aggregated. In the present invention, by employing a polymer porous flat membrane sheet with a pore size that has not been conventionally used in this field, it is possible to filter and remove all of the photosensitive resin composition, regardless of whether it is aggregated or not.

[0025] The usage of the polymer porous flat membrane sheet in the present invention will be explained with reference to a schematic diagram of an example of the apparatus of the present invention shown in Figure 2. As shown in Figure 2, the apparatus 1 of the present invention has a processing tank 10 that receives the developing waste liquid sent from the developing solution tank in the transport direction 21, and a number of membrane elements 12 made of polymer porous flat membrane sheets 11 are immersed in the developing waste liquid in the processing tank 10. The photosensitive resin composition is separated and removed from the developing waste liquid in the processing tank 10 by the polymer porous flat membrane sheets 11 and collected through a water collection pipe 13 connected to each flat membrane sheet 11. The collected filtered developing waste liquid is sent as a regenerated developing solution in the transport direction 22 and supplied to a developing brush or a rinsing brush. Conventional known polymer porous flat membrane sheets can be used as appropriate, and their details will be described later.

[0026] A second feature of the apparatus of the present invention is that a cleaning means 14 is provided that allows for cleaning by introducing sponge pieces into the processing tank 10 and aerating the polymer porous flat film sheet 11 so that the sponge pieces in the developing waste liquid come into contact with the flat film sheet 11, thereby removing deposits from the surface of the flat film sheet 11. If the photosensitive resin composition is continuously removed from the developing waste liquid using the flat film sheet 11, the photosensitive resin composition and other substances that have not been filtered and adhere to the surface of the flat film sheet 11 will accumulate, making it prone to clogging. The cleaning means 14 of the present invention allows for the continuous use of the high-performance flat film sheet 11 without reducing its filtration efficiency by applying soft sponge pieces in the liquid to the deposits on the surface of the flat film sheet 11 and removing them.

[0027] A method for removing deposits from the surface of a flat film sheet 11 using the cleaning means 14 of the present invention will be illustrated with a schematic diagram in Figure 3. As shown in Figure 3, in the processing tank 10 of the apparatus 1 of the present invention, the flat film sheet 11 is immersed together with a sponge piece in developing waste liquid containing a photosensitive resin composition. The cleaning means 14 allows for the removal of deposits from the surface of the flat film sheet 11 by aerating the air so that the sponge piece comes into contact with the flat film sheet 11.

[0028] The cleaning means 14 generates bubbles in the developing waste liquid in the processing tank 10, and these bubbles cause the sponge pieces in the processing tank 10 to flow and come into contact with the flat film sheet 11. The cleaning means 14 is not particularly limited as long as it can achieve the above role, but for example, it can be configured to be installed below the flat film sheet and have a perforated tube shape at the top in which air is introduced into the tube and aerated from the perforated part to send air to the surface of the flat film sheet, or it can be configured to have multiple nozzles or the like to send air directly toward the surface of the flat film sheet.

[0029] The sponge pieces preferably have a specific gravity greater than the liquid in the treatment tank 10 when hydrated (for example, a specific gravity of 1.02 or higher when hydrated). If the specific gravity of the sponge pieces is lower than this, the sponge pieces may float on the liquid surface of the treatment tank 10, potentially impairing the cleaning function. The material of the sponge pieces is not particularly limited as long as the surface is flexible, and either organic or inorganic materials can be used. Examples of usable materials include conventionally known sponge materials such as polyvinyl alcohol, polyethylene, polyolefins such as polypropylene, EVA resin, polyurethane foam, polyester, nylon, melamine foam, and processed sea sponges. In addition, since the flat film sheet 11 of the apparatus of the present invention is used to remove the photosensitive resin composition, the sponge pieces do not need to be microbial immobilization carriers. However, from the viewpoint of easily removing the synthetic rubber polymer in the photosensitive resin composition from the surface of the flat film sheet, it is preferable that they have high water absorption and retention and excellent abrasion resistance, and polyvinyl alcohol, polyolefin, EVA resin, polyurethane foam, etc., are preferred.

[0030] The size of the sponge pieces is not particularly limited as long as they can easily remove deposits from the surface of the flat film sheet 11, but it is preferable that the maximum side dimension is 1 to 10 mm. The shape of the sponge pieces is not particularly limited as long as they have fluidity in the liquid, but they can be spherical, cubic, polyhedron, or similar shapes. It is preferable that the surface of the sponge pieces has a moderate amount of irregularities, and voids can be provided inside the sponge pieces. From the viewpoint of cleaning performance and fluidity performance, the amount of sponge pieces used is preferably 1% by mass or more and less than 40% by mass of the amount of developing waste liquid. If it is less than 1% by mass, the amount in contact with the flat film sheet 11 is small and the cleaning function tends to decrease. Also, if it is 40% by mass or more, the fluidity in the developing waste liquid becomes poor and the cleaning function tends to be impaired.

[0031] After filtration, the concentrated developing waste liquid obtained in the processing tank 10 can be repeatedly separated and removed by adding developing waste liquid from the transport direction 21. According to the present invention, by repeatedly separating and removing the photosensitive resin composition, the concentrated developing waste liquid can be concentrated to a higher concentration before disposal, thereby reducing the amount of concentrated waste liquid.

[0032] In the present invention, the polymer porous flat membrane sheet used preferably consists of a polymer porous membrane (membrane material) that forms a mesh-like network structure and a sheet-like substrate (membrane substrate) that supports it. The membrane substrate not only supports the membrane material and maintains the shape of the membrane, but also plays a role in absorbing stress on the membrane. The polymer material constituting the membrane material can function as a separation membrane by appropriately intertwining with the membrane substrate and adopting a suitable porous structure.

[0033] The membrane substrate is preferably composed of a nonwoven fabric made of a polymer material that is insoluble in organic solvents and water, and is not limited as long as it has the ability to hold the membrane components and to withstand the stress applied to the membrane. The nonwoven fabric is preferably made of hydrocarbon-based, olefin-based, or condensation-based polymers, such as polyethylene, polyolefin, polyvinyl alcohol, polyethylene terephthalate, nylon, polyimide, polytetrafluoroethylene, and polyvinyl chloride.

[0034] The thickness of the nonwoven fabric is preferably 80 to 150 μm. Since the nonwoven fabric is used as a water-permeable membrane substrate, if it is too thick, it may hinder water permeability, and if it is too thin, it may not have sufficient strength and may not withstand long-term use.

[0035] To ensure the strength of the nonwoven fabric, it is preferable to fix the fibers together with a binder. Methods of fixation include using core-sheath structured fibers in which the binder component is formed in the sheath portion, or impregnating the nonwoven fabric with an adhesive component after its creation. However, it is preferable to create the nonwoven fabric by combining the binder fibers and then fuse the fibers together with heat. After creating the nonwoven fabric by appropriately combining drawn and undrawn yarns, heat and pressure are applied. At this time, the undrawn yarns soften at a lower temperature than the drawn yarns, thus acting as a binder.

[0036] Nonwoven fabrics can be manufactured using any of the following methods: melt-blown, thermal bonding, or papermaking. However, the fiber diameter and basis weight should be selected to ensure liquid permeability. The fiber diameter is preferably 5-12 μm, more preferably 7-10 μm. If the fiber diameter is too small, the strength will be low and it will not withstand long-term use. If the fiber diameter is too large, the overall proportion will be insufficient and it will not have enough strength, which may also prevent it from withstanding long-term use. Furthermore, if the fiber diameter is too large relative to the film thickness, the nonwoven fabric will have a rough overall structure. As a result, the polymer components constituting the film may not be sufficiently retained within the nonwoven fabric, leading to defects and other problems, or the amount of polymer filling may be insufficient, potentially creating voids in the film. The basis weight per 1 μm of thickness is preferably 0.4-0.8 g / m². 2 , more preferably 0.5~0.7 g / m 2 Therefore, a smaller basis weight is preferable, but if it is too small, the strength will be reduced, making it unsuitable for long-term use as a membrane. Conversely, if it is too large, the voids will be reduced, potentially resulting in poor liquid permeability.

[0037] On the other hand, the membrane material is preferably composed of a hydrophobic polymer material such as polyvinyl chloride and / or chlorinated polyvinyl chloride, and a mesh-like network structure with submicron-sized pores is formed by a phase separation method. Known phase separation methods include mixing the polymer material with a solvent to create a solution, applying it to a nonwoven fabric substrate and drying it in air (dry method), introducing it into a solidification bath and allowing it to solidify (wet method), and rapidly changing the temperature (thermal-induced phase separation method). However, the dry method, in which the substrate coated with the polymer solution is dried in the gas phase, is preferred because it allows for easy control of the film formation and does not require complex equipment.

[0038] The solvent used to dissolve the polymer material must dissolve the polymer constituting the film but not the nonwoven fabric, and generally, solvents that volatilize at 150°C or below or are water-soluble can be used. Specifically, tetrahydrofuran (THF), toluene, dimethylformamide (DMF), N-methyl-2-pyrrolidone (NMP), and dimethylacetamide (DMAC) are suitable, and may be used individually or in combination. When performing dry film formation, it is preferable to use THF or a mixed solvent with THF as the main component (50% by weight or more) because the solvent is volatilized in the gas phase to form the film.

[0039] As a non-solvent, water or alcohol is preferred. Among alcohols, ethanol (EtOH), propanol (1- or 2-propanol, IPA), and butanol (1- or 2-butanol, BuOH) are particularly preferred. These may be used individually or in combination.

[0040] The polymer concentration in the solution is preferably 5-20% by weight, and more preferably 6-18% by weight. If the polymer concentration is too low, the network structure of the membrane will not develop sufficiently, and the membrane itself may not withstand long-term use. If the concentration is too high, the solution may not penetrate into the interior of the nonwoven fabric, and the membrane may not function properly. The solvent-to-non-solvent ratio (solvent / non-solvent) is preferably 1-3, and more preferably 1.5-2.8. If the proportion of non-solvent is too high, the solubility of the polymer will be impaired, making it impossible to create a uniform solution and potentially preventing sufficient impregnation. If it is too low, it may not be able to promote phase separation.

[0041] The polymer material that makes up the membrane is hydrophobic. Therefore, it can be difficult to pass liquid through the membrane when it is first used, and hydrophobic interactions can easily lead to fouling problems. One way to avoid this is to make the membrane hydrophilic.

[0042] Common methods for hydrophilization include adding a hydrophilizing agent to a polymer solution, adding a hydrophilizing agent after the film has been fabricated, and surface treatment of the film. Of these, the preferred methods are adding a hydrophilizing agent after the film has been fabricated and surface treatment of the film. Hydrophilizing agents are chemical substances that possess both hydrophobic and hydrophilic parts within a single molecule and have the function of adhering to the film surface or internal network. Examples include sugars, cellulose derivatives, and surfactants. Specifically, examples include hydroxypropyl cellulose, sucrose fatty acid esters, and sodium lauryl sulfate. Another method for hydrophilization after film fabrication is to immerse the film in a solution containing the aforementioned hydrophilizing agent, and then fix it by applying heat or drying.

[0043] Next, an example of a method for producing the polymer porous flat membrane sheet of the present invention will be described. First, a solution containing a polymer that forms a membrane is impregnated into a nonwoven fabric. Any impregnation method can be used, such as immersion or impregnation using a die.

[0044] After impregnating the nonwoven fabric with a polymer solution, it is guided to a drying zone for solvent evaporation. At this time, care should be taken to prevent direct airflow on the film. In the drying zone, temperature and humidity control is important. The preferred temperature is 10-40°C, more preferably 15-30°C. The preferred relative humidity is 40-85%, more preferably 50-85%.

[0045] Furthermore, in the dry film formation process described above, it is preferable to use a combination of a solvent with an appropriate vapor pressure and a non-solvent in order to achieve a good film structure and pore size. As the solvent, tetrahydrofuran or a mixed solvent mainly composed of tetrahydrofuran (50% by weight or more) can be selected. As the non-solvent, 2-propanol, butanol, or a mixed solvent thereof can be selected, and preferably, a mixed solvent of two types, 2-propanol and 1-butanol, can be used.

[0046] The porous membrane obtained as described above is preferably hydrophilized. In order to maintain fouling resistance for as long as possible, it is preferable to apply an appropriate amount of a hydrophilizing agent, such as unheat-denatured hydroxypropyl cellulose, to the membrane. The hydroxypropyl cellulose solution is preferably prepared by uniformly dissolving hydroxypropyl cellulose in an aqueous solution of 2-propanol and pure water in an aqueous solution of equal weight ratios, in a range of 0.5% to 1.0% by weight. Depending on the characteristics of the porous membrane used, the ratio of 2-propanol to pure water and the amount of dissolved hydroxypropyl cellulose may be changed. After immersing the porous membrane in this hydroxypropyl cellulose solution, the excess solution is removed in a water washing tank, with a scraping spatula, or with a roller bar, and then heat treatment is performed to fix the hydroxypropyl cellulose to the membrane. The method of this heat treatment is not specified, such as using hot water, hot air, or infrared irradiation, but heat treatment using hot water is preferred because it is low-cost, simple, and provides uniform treatment. The heat treatment temperature at this time is preferably 50°C to 72°C, and more preferably 60°C to 70°C. Subsequently, the hydrophilized film is dried and rolled up. The drying conditions are preferably in the range of 40°C to 70°C and 1% to 20% relative humidity to efficiently remove moisture and suppress thermal denaturation of hydroxypropyl cellulose. These processes are carried out continuously.

[0047] The flat membrane sheets fabricated in this manner can have an average pore size of, for example, 0.2 to 0.5 μm when measured with a palm porometer (PPM) manufactured by Porous Materials. Furthermore, in this PPM measurement, the flow rate of the flat membrane sheet in a dry state can be 30 to 60 L / min at a pressure of 150 kPa. This range takes into account membrane strength and filtration efficiency during long-term use. This flow rate value indirectly represents the degree of porosity on the membrane surface and the density of the membrane structure. A larger value indicates a greater degree of porosity on the membrane surface and a coarser membrane structure. Conversely, a smaller value indicates a smaller degree of porosity or a denser membrane structure. Since these are closely related to membrane strength and filtration efficiency, they can serve as indicators of whether a membrane is suitable for long-term use.

[0048] In the present invention, the polymer porous membrane constituting the flat membrane sheet preferably has a structure that gradually becomes sparser from the surface in contact with the treated liquid to the inner layer when observed under a 5,000x electron microscope of its cross-section, and the polymer material constituting the membrane preferably forms a three-dimensional mesh on a network and is appropriately intertwined with the nonwoven fabric of the membrane substrate. However, if the density of the network is too high, it will hinder water permeability, and if it is too low, the membrane components may detach from the substrate after long-term use, and the membrane may no longer be able to perform its function.

[0049] The apparatus of the present invention, which has the polymer porous flat membrane sheet and washing means described above, and the method for regenerating developing waste liquid using the same, use a high-performance flat membrane sheet that can filter and separate even small particle sizes, so that not only photosensitive resin composition that is aggregated in the developing waste liquid but also photosensitive resin composition that is dispersed without agglomeration can be efficiently recovered. Moreover, the washing means removes deposits from the surface of the flat membrane sheet by aerating so that sponge pieces come into contact with the deposits that have accumulated on the surface as the flat membrane sheet is filtered and separated, thereby effectively preventing clogging and allowing high filtration performance to be maintained for a long time. [Examples]

[0050] The effects of the method and apparatus of the present invention are demonstrated in the following examples, but the present invention is not limited to these examples. The evaluation of specific values ​​in the examples was carried out according to the following method.

[0051] (A) Particle size distribution measurement • Equipment used: NanoSAQLA multi-sample nanoparticle size measurement system manufactured by Otsuka Electronics Co., Ltd. Measurement conditions: Cell type (glass cell), Temperature condition (25°C), Number of cumulative measurements (25 times) • Measurement principle: Particle size measurement using dynamic light scattering method In a solution, particles constantly change their position, orientation, and shape due to Brownian motion, such as translation and rotation. When these particles are irradiated with laser light and the scattered light is detected, fluctuations in the scattering intensity, which depend on the particle's Brownian motion, can be observed. Using this principle, by observing the temporal fluctuations of the scattered light, the velocity of the particle's Brownian motion (diffusion coefficient) can be obtained, and furthermore, the particle size can be determined.

[0052] (B) Turbidity measurement • Equipment used: REX WGZ-20B portable turbidimeter ·Measurement conditions: Light source LED Measurement wavelength 860 nm Measurement intensity NTU0.00~20 ·Measurement principle: 90 degree scattered light method When light from an LED light source is projected into a sample solution, scattered light is generated in proportion to the concentration of SS / turbidity substances. Meanwhile, a photodetector positioned at a 90-degree angle to the light source generates a current signal proportional to the scattered light. From this current signal, the turbidity value (mg / L) can be obtained.

[0053] (Example of the present invention) The processing performance of a regenerated developer manufacturing apparatus 1, shown in Figures 2 and 3, for developing waste liquid (5% non-volatile components) containing a photosensitive resin composition was evaluated. The membrane elements of the polymer porous flat membrane sheet consisted of a resin mesh on the front and back surfaces of the support plate (Nippon Philcon Co., Ltd. DOP-18K), a nonwoven fabric made of polyethylene terephthalate (Hirose Paper Co., Ltd. 05TH-60), and a separation membrane with chlorinated polyvinyl chloride as its membrane component, a thickness of 130 μm, an average pore size of 0.3 μm, and a pure water FR of 30 mL / cm³. 2 I used the / min / bar files pasted in this order.

[0054] To enhance the physical cleaning of the membrane surface, hexahedral PVA sponge pieces (2mm x 2mm x 2mm) were added to the processing tank 10 of apparatus 1 in an amount equivalent to 5% of the total volume. Film element film area 1 m 2 Hit, 0.2m 3 Suction filtration was performed using a tube pump at a filtration rate of [number] days. Intermittent operation was performed, consisting of 7 minutes of suction filtration followed by 3 minutes of stopping. The aeration rate was adjusted to 16 L / min per membrane element. The total suction filtration operation time was 40 hours, and the non-volatile components of the concentrated developing waste liquid at the end of the process were 20%.

[0055] The transmembrane pressure (TMP), which indicates the pressure difference between the permeate and supply sides of the filtration membrane, was measured at the start and end of processing to determine the state of membrane clogging. The particle size distribution and turbidity of the developing waste liquid before processing and the filtrate after processing were measured to evaluate the filtration performance. The evaluation results for each performance aspect are as follows. TMP: 8kPa (0.2m) at the start of processing 3 (estimated value from [day]), 29kPa at the end of processing. Particle size of the liquid (size of maximum distribution): Developer waste liquid before processing: 800 nm, filtrate after processing: 80 nm Turbidity of the liquid: Unmeasurable (opaque (white suspension)) for developing waste liquid before processing, 19.1 for filtrate after processing.

[0056] (Comparative Example 1) Using the reproduction developer manufacturing apparatus 1 shown in FIGS. 2 and 3, the treatment performance of a development waste liquid (non-volatile component 5%) containing a photosensitive resin composition was evaluated. The evaluation was carried out in the same manner as in the examples of the present invention, except that sponge pieces were not put into the treatment tank and aeration was not performed.

[0057] The membrane area of the membrane element was 1 m 2 per 0.2 m 3 Suction filtration operation was carried out using a tube pump at a filtration rate of / day. After carrying out the suction filtration operation for 7 minutes, intermittent operation was performed with a 3-minute stop repeated. The total suction filtration operation was 18 hours, and the operation was stopped because clogging occurred. The non-volatile component of the concentrated development waste liquid at the end of the treatment was 11.8%.

[0058] The transmembrane pressure value (TMP: Trans Membrane Pressure) indicating the pressure difference between the permeate side and the supply side of the filter membrane was measured at the start and end of the treatment to judge the state of membrane clogging. The particle size distribution and turbidity of the development waste liquid before treatment and the filtrate after treatment were measured to evaluate the filtration performance. The evaluation results of each performance are as follows. TMP: 8 kPa at the start of treatment, 35 kPa at the end of treatment Particle size of the liquid (size of the maximum distribution): 800 nm for the development waste liquid before treatment, 80 nm for the filtrate after treatment Turbidity of the liquid: Unmeasurable for the development waste liquid before treatment (opaque (white suspension)), 19.1 for the filtrate after treatment

[0059] (Comparative Example 2) Using the reproduction developer manufacturing apparatus 1 shown in FIGS. 2 and 3, the treatment performance of a development waste liquid (non-volatile component 5%) containing a photosensitive resin composition was evaluated. However, as the membrane element instead of the polymer porous flat membrane sheet, a resin mesh: Nippon Filcon Co., Ltd. DOP-18K was attached to the front and back surfaces of a support plate, and then a filter (Kureha Techno Co., Ltd. Bonden R301) was attached and used. Note that sponge pieces were not put into the treatment tank.

[0060] The membrane area of the membrane element was 1 m 2 per 0.2 m 3Suction filtration was performed using a tube pump at a filtration rate of [number] days. Intermittent operation was performed, consisting of 7 minutes of suction filtration followed by 3 minutes of stopping. The aeration rate was adjusted to 16 L / min per membrane element. The total suction filtration operation was 40 hours, and the non-volatile components of the concentrated developing waste liquid at the end of the process were 6.3%.

[0061] The transmembrane pressure (TMP), which indicates the pressure difference between the permeate and supply sides of the filtration membrane, was measured at the start and end of processing to determine the state of membrane clogging. The particle size distribution and turbidity of the developing waste liquid before processing and the filtrate after processing were measured to evaluate the filtration performance. The evaluation results for each performance aspect are as follows. TMP: 0.4 kPa at the start of processing (estimated value), 2.0 kPa at the end of processing Particle size of the liquid (size of maximum distribution): Developer waste liquid before processing: 800 nm, filtrate after processing: 750 nm Turbidity of the liquid: Unmeasurable for developing waste liquid before processing (opaque (white suspension)), unmeasurable for filtrate after processing (outside the detection range of this measurement method). [Industrial applicability]

[0062] According to the method and apparatus of the present invention, not only aggregates of the photosensitive resin composition but also photosensitive resin compositions dispersed without aggregation can be efficiently removed from developing waste liquid, making it easy to obtain a regenerated developing solution. Furthermore, clogging of the flat film sheet is less likely to occur, and high filtration performance can be maintained. Therefore, the method and apparatus of the present invention are extremely useful in the industry. [Explanation of symbols]

[0063] 1 Recycled developer manufacturing equipment 10 Processing Tanks 11. Polymer porous flat membrane sheet 12 film elements 13 Water collection pipe 14. Cleaning means 21 (Developing waste liquid) Conveying direction 22 (Regenerative developer) transport direction 31 Conveying direction 32 Developing Brushes 33 Developer tank 34. Developer pump 35 Transfer switching valve 36 Regeneration Developer Pump 37 Rinse Brush 38 Recycled developer discharge port 39 Developer solution outlet

Claims

1. A method for producing a recycled developer from developing waste liquid generated by developing a water-developable flexographic printing plate having a photosensitive resin layer made of a photosensitive resin composition containing a water-dispersible resin, The developing waste liquid is introduced into a processing tank, the photosensitive resin composition contained in the developing waste liquid is separated and removed using a polymer porous flat membrane sheet provided in the processing tank, and a regenerated developing solution is obtained. A method characterized by introducing sponge pieces into the processing tank and aerating the polymer porous flat membrane sheet so that the sponge pieces come into contact with the polymer porous flat membrane sheet, thereby removing and cleaning any deposits on the polymer porous flat membrane sheet.

2. The method according to claim 1, characterized in that the polymer porous flat membrane sheet comprises a polymer porous membrane that forms a mesh-like network structure and a sheet-like substrate that supports it.

3. The method according to 1 or 2, characterized in that the sponge piece is made of a material having a maximum side dimension of 0.1 to 10 mm.

4. An apparatus for producing a regenerated developer from developing waste liquid generated by developing a water-developable flexographic printing plate having a photosensitive resin layer made of a photosensitive resin composition containing a water-dispersible resin, The apparatus has a processing tank for receiving the developing waste liquid and separating and removing the photosensitive resin composition contained in the developing waste liquid, The processing tank is equipped with a polymer porous flat membrane sheet for separating and removing the photosensitive resin composition from the developing waste liquid, and The apparatus is characterized in that the processing tank comprises sponge pieces introduced into the processing tank and a cleaning means configured to remove deposits from the polymer porous flat membrane sheet by aerating the sponge pieces so that they come into contact with the polymer porous flat membrane sheet.

5. The apparatus according to claim 4, characterized in that the polymer porous flat membrane sheet comprises a polymer porous membrane that forms a mesh-like network structure and a sheet-like substrate that supports it.

6. The apparatus according to claim 4 or 5, characterized in that the sponge piece is made of a material having a maximum side dimension of 0.1 to 10 mm.

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