Method and device for producing recycled developer from development waste liquid

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

Method and apparatus for producing recycled developer from waste developer

[0001] The present invention relates to a method and an apparatus for producing a recycled developer from a developer waste solution, and more particularly to a method and an apparatus that can efficiently filter and remove a photosensitive resin composition from a developer waste solution generated by developing a water-developable flexographic printing plate precursor having a photosensitive resin layer, regardless of whether a coagulation occurs.

[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. Platemaking of such flexographic printing plates is performed, for example, by selectively exposing the photosensitive resin layer to ultraviolet light and developing the exposed photosensitive resin layer with an aqueous developer. The photosensitive resin composition in the unexposed portions of the photosensitive resin layer is physically removed from the printing plate by brushing or other means 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, resulting in a decrease in development speed and the aggregation of the dispersed photosensitive resin composition, forming aggregates. These aggregates reattach 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, replace it with a new developer, and resume platemaking. However, repeatedly discarding used developer and replacing it with a new developer is undesirable in terms of environmental impact and production costs. Therefore, attempts have been made to remove the photosensitive resin composition from the used developer and reuse it as a regenerated developer.

[0003] For example, Patent Document 1 proposes an apparatus that recovers used developer using a developer regeneration means, removes suspended solids, and supplies the removed developer to a developer supply means, thereby enabling the developer to be recycled and reused. This apparatus can recover photosensitive resin compositions that have aggregated in the developer by removing suspended solids using a filter, but photosensitive resin compositions that are dispersed in the developer without aggregating cannot be recovered because they pass through the filter. If a finer mesh filter is used as a countermeasure, frequent filter replacement is required, which is inefficient. Furthermore, if a flocculant is used to aggregate and recover the photosensitive resin composition, problems arise 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 device including a dispersion filter that aggregates the photosensitive resin composition dispersed in the developer and an aggregate filter that removes the aggregated photosensitive resin composition from the developer that has passed through the dispersion filter, in which the developer from which the aggregated photosensitive resin composition has been removed is allowed to stand to separate into a high-concentration layer and a low-concentration layer. This device can aggregate and recover the photosensitive resin composition that is dispersed in the developer without aggregating, but because separation into a high-concentration layer and a low-concentration layer is required, the separation takes time, and there is a problem that it is not possible to efficiently concentrate the used developer and separate the photosensitive resin composition.

[0005] Japanese Patent Laid-Open No. 9-258458 Japanese Patent Laid-Open No. 2011-232407

[0006] The present invention has been made in order to solve the above-mentioned problems of the conventional art, and an object of the present invention is to provide a method and apparatus for producing a recycled developer, which can efficiently filter and remove a photosensitive resin composition from a developer waste solution generated by the development of a water-developable flexographic printing plate, regardless of whether the photosensitive resin composition aggregates, and which can maintain high filtration performance, and which can concentrate the developer waste solution to a high concentration for disposal.

[0007] To achieve this objective, the inventors investigated efficient methods for filtering and separating photosensitive resin compositions from waste developer solutions and methods for maintaining filtration performance. As a result, they adopted a polymeric porous flat membrane sheet, which had not previously been used to regenerate used developer solutions, as a filtering and separating means for the photosensitive resin composition. Microfiltration membranes are prone to clogging due to the synthetic rubber polymers in the photosensitive resin composition, making them difficult to use. However, flat membrane sheets have high membrane cleanability through aeration, allowing for efficient removal of photosensitive resin compositions adhering to the membrane surface or between membranes. However, when waste developer solutions are concentrated to a high concentration, the photosensitive resin composition can aggregate and adhere to the surface of the flat membrane sheet, resulting in clogging. Therefore, it was further discovered that by employing a cleaning means capable of aerating the filtration surface of the flat membrane sheet so that soft sponge pieces come into contact with it, it is possible to filter and remove not only agglomerates of the photosensitive resin composition from the waste developer, but also the photosensitive resin composition that is dispersed without agglomeration, and further, since the surface deposits that accumulate during filtration and separation by the flat membrane sheet can be easily removed and washed away with the sponge pieces, the waste developer can be concentrated to a high concentration and disposed of.

[0008] That is, the present invention was completed based on the above findings and has the following features (1) to (6): (1) A method for producing a recycled developer from a developer waste 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 method comprising: introducing the developer waste into a treatment tank; separating and removing the photosensitive resin composition contained in the developer waste using a polymeric porous flat membrane sheet provided in the treatment tank; and obtaining a recycled developer; and introducing sponge pieces into the treatment tank and aerating the polymeric porous flat membrane sheet so that the sponge pieces contact the polymeric porous flat membrane sheet, thereby removing and cleaning the polymeric porous flat membrane sheet. (2) The method described in (1), wherein the polymeric porous flat membrane sheet comprises a polymeric porous membrane that forms a mesh-like network structure and a sheet-like substrate supporting the polymeric porous flat membrane sheet. (3) The method described in (1) or (2), wherein the sponge pieces are made of a material that has a specific gravity greater than that of the liquid in the treatment tank when retaining water and has a maximum side dimension of 0.1 to 10 mm. (4) An apparatus for producing a recycled developer from a developer waste 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 comprising: a processing tank for receiving the developer waste and separating and removing the photosensitive resin composition contained in the developer waste; the processing tank comprising a polymer porous flat membrane sheet for separating and removing the photosensitive resin composition from the developer waste; and the processing tank comprising: 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 described in (4), wherein the polymer porous flat membrane sheet comprises a polymer porous membrane that forms a mesh-like network structure and a sheet-like substrate supporting the polymer porous flat membrane. (6) The apparatus described in (4) or (5), wherein the sponge pieces are made of a material that has a specific gravity greater than that of the liquid in the processing tank when retaining water and has a maximum side dimension of 0.1 to 10 mm.

[0009] According to the method and apparatus of the present invention, a polymeric porous flat membrane sheet with a high-performance fine pore size is used as a means for filtering and separating the photosensitive resin composition from the developer waste, so that not only aggregates of the photosensitive resin composition but also dispersed photosensitive resin composition that has not aggregated can be efficiently removed from the developer waste, allowing a recycled developer to be easily obtained. Furthermore, according to the method and apparatus of the present invention, sponge pieces are placed in a treatment tank in which a polymeric porous flat membrane sheet is immersed, and the sponge pieces are aerated so that they hit the surface of the flat membrane sheet, thereby removing and cleaning any dirt attached to the surface of the flat membrane sheet. Therefore, clogging of the flat membrane sheet is unlikely to occur, high filtration performance can be maintained, and the developer waste can be concentrated to a high concentration for disposal.

[0010] Fig. 1 is a schematic diagram of an example of a development processing system incorporating an apparatus for producing a recycled developer from a developer waste solution of the present invention. Fig. 2 is a schematic diagram of an example of an apparatus for producing a recycled developer from a developer waste solution of the present invention. Fig. 3 is a schematic explanatory diagram of an example of a method for removing deposits from the surface of a polymeric porous flat membrane sheet of the apparatus of the present invention.

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

[0012] Figure 1 is a schematic diagram illustrating an example of a development processing system incorporating the apparatus of the present invention. As shown in Figure 1, a water-developable flexographic printing plate blank (not shown) having a photosensitive resin layer enters the development processing system, travels in a transport direction 31, and is first developed by a developing brush 32 rubbing the plate against itself in the presence of a developer discharged from a developer discharge port 39. During development, portions of the photosensitive resin layer of the flexographic printing plate blank that were not exposed in the previous process are removed. The developer used in development is sent to and stored in a developer tank 33.

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

[0014] The flexographic printing plate precursor to be developed has a photosensitive resin layer made of a photosensitive resin composition containing a water-dispersible resin on a support, and an aqueous developer is used as a washout solution. The photosensitive resin composition that forms the photosensitive resin layer is water-developable and preferably contains a synthetic rubber polymer, a photopolymerizable unsaturated monomer compound, and a photopolymerization initiator as main components.

[0015] The support used for the flexographic printing plate precursor is preferably a material that is flexible but has excellent dimensional stability, and examples of such support include metal supports such as steel, aluminum, copper, and nickel, and thermoplastic resin films such as polyethylene terephthalate film, polyethylene naphthalate film, polybutylene terephthalate film, and polycarbonate film. Among these, polyethylene terephthalate film is particularly preferred because of its excellent dimensional stability and sufficiently high viscoelasticity.

[0016] The synthetic rubber polymer is used to impart appropriate rubber elasticity to the photosensitive resin layer, and conventionally known rubber components can be used. The synthetic rubber polymer is preferably 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. Examples of polymers obtained by copolymerizing these polymers with other components such as acrylic acid and methacrylic acid are also included. 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 synthetic rubber polymers are preferably water-dispersible latexes. Water-dispersible latexes can be latexes having a crosslinked structure within the molecule. As the latex having a crosslinked structure in the molecule, a hydrophobic polymer obtained from a water-dispersed latex having a weight average gelation degree of 20 to 80% is preferred. The water-dispersed latex is a stable suspension in which fine particles of a rubber polymer are dispersed in water, and the polymer can be 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 the composition does not adversely affect performance, such as polybutadiene, polychloroprene, polyacrylonitrile-butadiene, polyurethane, polyisoprene, polystyrene-isoprene copolymer, and polystyrene-butadiene copolymer.

[0018] The photosensitive resin composition may contain a water-soluble or water-dispersible polymer in addition to the water-dispersible synthetic rubber polymer. Examples of the water-soluble or water-dispersible polymer include water-soluble polyamides and water-dispersible polyamides in which a hydrophilic group has been introduced into a polyamide, partially saponified polyvinyl acetate and its derivatives, and anionic acrylic polymers.

[0019] The photopolymerizable unsaturated monomer compound is used for crosslinking and curing by ultraviolet light. The photopolymerizable unsaturated monomer compound may be a compound having only one ethylenically unsaturated bond, or may be a compound having two or more ethylenically unsaturated bonds. The photopolymerizable unsaturated monomer compound may contain an oligomer having a photopolymerizable group introduced therein or a polymer having a photopolymerizable group introduced therein. In terms of compatibility with the synthetic rubber copolymer, the photopolymerizable unsaturated monomer compound preferably contains one having a common skeleton with the synthetic rubber copolymer.

[0020] The photopolymerization initiator is used to polymerize polymerizable unsaturated groups by irradiation with light, and is preferably one that has the function of generating radicals by self-decomposition or hydrogen abstraction upon light absorption. Specific examples of the photopolymerization initiator that can be used include benzoin alkyl ethers, benzophenones, anthraquinones, benzils, acetophenones, and diacetyls. Not only one type of photopolymerization initiator but also two or more types of photopolymerization initiators may be used in combination.

[0021] The developer used in the present invention is an aqueous developer containing water as the main component, and is used to remove water-dispersible uncured portions of the photosensitive resin. The aqueous developer may be water alone, or may be an aqueous solution to which a water-soluble development accelerator has been added. Examples of the development accelerator include surfactants, acids, bases, and salts. From the viewpoint of development speed, it is preferable to add a water-soluble development accelerator. Commercially available soaps or detergents may also 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 paratoluenesulfonic acid. Examples of bases include lithium hydroxide, sodium hydroxide, potassium hydroxide, and calcium hydroxide. The development accelerator may be a combination of a surfactant, an acid, a base, and a salt, and the optimal formulation of the development accelerator may be determined depending on the components of the photosensitive resin composition.

[0023] The aqueous developer may contain a water-soluble organic solvent in addition to water. Examples of such organic solvents include methanol, ethanol, isopropyl alcohol, cellosolve, glycerin, ethylene glycol, and polyethylene glycol. A defoaming agent may also be added to suppress foaming. Any water-soluble defoaming agent may be used, and examples of defoaming agent components include higher alcohols, fatty acid derivatives, silica, alumite, and silicone.

[0024] Next, the configuration of the apparatus of the present invention will be described using Figures 2 and 3. A first feature of the apparatus of the present invention is the use of a polymeric porous flat membrane sheet to separate and remove the photosensitive resin composition contained in the developer waste solution. Conventionally, the filtration and removal of photosensitive resin compositions from developer waste solution in a treatment tank has been carried out exclusively by filters. While filters are effective in filtering and removing aggregated photosensitive resin compositions, it has been difficult to remove photosensitive resin compositions that are dispersed in the solution without being aggregated. In the present invention, by employing a polymeric porous flat membrane sheet with a pore size not previously 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 use of the polymer porous flat membrane sheet in the present invention is explained with reference to the schematic diagram of an example of the apparatus of the present invention in Figure 2. As shown in Figure 2, the apparatus 1 of the present invention has a treatment tank 10 that receives waste developer sent from a developer tank in a conveying direction 21, and membrane elements 12 consisting of a number of polymer porous flat membrane sheets 11 are immersed in the waste developer in the treatment tank 10. The photosensitive resin composition is separated and removed from the waste developer in the treatment tank 10 by the polymer porous flat membrane sheets 11, and the waste developer is collected through water collection pipes 13 connected to each flat membrane sheet 11. The collected, filtered waste developer is sent in a conveying direction 22 as a regenerated developer and supplied to a developing brush or a rinsing brush. Conventionally known porous flat membrane sheets can be used as appropriate, and details thereof will be described later.

[0026] A second feature of the device of the present invention is that it is equipped with a cleaning means 14 in which sponge pieces are placed in the treatment tank 10 and which can be aerated so that the sponge pieces in the developer waste solution come into contact with the polymer porous flat membrane sheet 11, thereby cleaning to remove deposits on the surface of the flat membrane sheet 11. If the flat membrane sheet 11 continues to remove the photosensitive resin composition from the developer waste solution, the photosensitive resin composition and the like that have not been filtered and that have adhered to the surface of the flat membrane sheet 11 will accumulate, making clogging more likely. The cleaning means 14 of the present invention allows the high-performance flat membrane sheet 11 to be continuously used without reducing its filtration efficiency by using soft sponge pieces in the liquid to remove deposits on the surface of the flat membrane sheet 11.

[0027] The method for removing deposits on the surface of a flat membrane sheet 11 using the cleaning means 14 of the present invention is explained with reference to the schematic diagram of Fig. 3. As shown in Fig. 3, in the treatment tank 10 of the device 1 of the present invention, the flat membrane sheet 11 is immersed together with sponge pieces in a developer waste solution containing a photosensitive resin composition, and by aeration in the cleaning means 14 so that the sponge pieces come into contact with the flat membrane sheet 11, deposits on the surface of the flat membrane sheet 11 can be removed and cleaned.

[0028] The cleaning means 14 has the role of generating bubbles in the waste developer in the processing tank 10, and using these bubbles to cause the sponge pieces in the processing tank 10 to flow and hit the flat membrane 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 provided below the flat membrane sheet, have a tube shape with perforations at the top, introduce air into the tube, and aerate the air from the perforations so that the air can be sent to the surface of the flat membrane sheet, or can be configured to have multiple nozzles or the like so that the air can be sent directly toward the surface of the flat membrane sheet.

[0029] The sponge pieces preferably have a specific gravity greater than that of the liquid in the treatment tank 10 when retaining water (for example, a specific gravity of 1.02 or greater when retaining water). If the specific gravity of the sponge pieces is lower than this, the sponge pieces may float on the liquid surface in 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 both organic and inorganic materials can be used. Usable materials include conventionally known sponge materials such as polyvinyl alcohol, polyolefins such as polyethylene and polypropylene, EVA resin, polyurethane foam, polyester, nylon, melamine foam, and processed sea sponges. Note that because the flat membrane sheet 11 of the device 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 membrane sheet, it is preferable for the sponge pieces to have high water absorption, water retention, and excellent abrasion resistance, and polyvinyl alcohol, polyolefins, 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 membrane sheet 11, but a maximum side dimension of 1 to 10 mm is preferred. The shape of the sponge pieces is not particularly limited as long as they have fluidity in the liquid, but they can be, for example, spherical, cubic, polyhedral, or shapes similar to these. The surface of the sponge pieces preferably has moderate irregularities, and voids can also be provided inside the sponge pieces. From the standpoint of cleaning performance and flowability, the amount of sponge pieces used is desirably 1% by mass or more and less than 40% by mass of the amount of developer waste liquid. If it is less than 1% by mass, the amount in contact with the flat membrane sheet 11 will be small, and the cleaning function will tend to be reduced. Furthermore, if it is 40% by mass or more, the fluidity in the developer waste liquid will be poor, and the cleaning function will tend to be impaired.

[0031] After filtration, the concentrated developer waste liquid obtained in the treatment tank 10 can be replenished with the developer waste liquid from the conveying direction 21, and the separation and removal of the photosensitive resin composition can be repeatedly carried out. According to the present invention, by repeatedly carrying out the separation and removal of the photosensitive resin composition, the concentrated developer waste liquid can be concentrated to a higher concentration and discarded, and therefore the amount of concentrated waste liquid can be reduced.

[0032] The polymer porous flat membrane sheet used in the present invention preferably comprises 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 to maintain the membrane shape, but also absorbs stress applied to the membrane. The polymer material that constitutes the membrane material can function as a separation membrane by appropriately intertwining with the membrane substrate and forming an appropriate porous structure.

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

[0034] The thickness of the nonwoven fabric is preferably 80 to 150 μm. Because the nonwoven fabric is used as a water-permeable membrane substrate, if it is too thick, it may hinder water permeation, and if it is too thin, it may not be strong enough to withstand long-term use.

[0035] To ensure the strength of the nonwoven fabric, it is preferable to bond the fibers together with a binder. The bonding method may be any of a method using core-sheath fibers in which a binder component is formed in the sheath portion, or a method in which a nonwoven fabric is produced and then impregnated with an adhesive component. However, a preferred method is to prepare a nonwoven fabric by combining the fibers with binder fibers and then fusing the fibers together with heat. A nonwoven fabric is produced by appropriately combining drawn yarns and undrawn yarns, and then applying heat and pressure. Since the undrawn yarns soften at a lower temperature than the drawn yarns, they function as a binder.

[0036] The nonwoven fabric can be produced by any method, such as melt-blowing, thermal bonding, or papermaking. However, the fiber diameter and basis weight are selected to ensure liquid permeability. The fiber diameter is preferably 5 to 12 μm, more preferably 7 to 10 μm. If the fiber diameter is too small, the strength will be low and the fabric will not withstand long-term use. If the fiber diameter is too thick, the fabric will not be well-balanced with the overall structure and will not have sufficient strength, which may also make the fabric unsuitable for long-term use. Furthermore, if the fiber diameter is too thick relative to the membrane thickness, the nonwoven fabric will have a coarse structure overall, resulting in insufficient retention of the polymer components constituting the membrane in the nonwoven fabric, leading to defects and other problems, or an insufficient amount of polymer filling, which may result in voids in the membrane. The basis weight per 1 μm of thickness is preferably 0.4 to 0.8 g / m ２ , more preferably 0.5 to 0.7 g / m ２ A smaller basis weight is preferable, but if it is too small, the strength will be low and the membrane will not be able to withstand long-term use, and if it is too large, there will be fewer voids and the membrane may have poor liquid permeability.

[0037] On the other hand, the membrane material is preferably made 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 a method in which a polymer material is mixed with a solvent to prepare a solution, which is then applied to a nonwoven fabric substrate and dried in air (dry method), a method in which the solution is introduced into a coagulation bath to coagulate (wet method), and a method in which the temperature is suddenly changed (thermally induced phase separation method). However, the dry method, in which a substrate coated with a polymer solution is dried in a gas phase, is preferred because it is easy to control the membrane formation and does not require complicated equipment.

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

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

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

[0041] The polymeric material that makes up the membrane is hydrophobic. This can make it difficult for liquids to pass through the membrane when it is first used, and fouling can easily occur due to hydrophobic interactions. One way to avoid this is to make the membrane hydrophilic.

[0042] Common hydrophilization methods include adding a hydrophilizing agent to a polymer solution, adding a hydrophilizing agent after membrane production, and surface-treating the membrane. Among these, preferred are adding a hydrophilizing agent after membrane production and surface-treating the membrane. Hydrophilizing agents are chemical substances that have both hydrophobic and hydrophilic moieties in a single molecule and have the ability to adhere to the membrane surface or internal network. Examples of such agents include sugars, cellulose derivatives, and surfactants. Specific examples include hydroxypropyl cellulose, sucrose fatty acid esters, and sodium lauryl sulfate. Another method for hydrophilizing a membrane after production involves immersing the membrane in a solution of the aforementioned hydrophilizing agent, followed by heating or drying to adhere the agent.

[0043] Next, an example of a method for producing a polymeric porous flat membrane sheet of the present invention will be described. First, a nonwoven fabric is impregnated with a solution containing a polymer that will form the membrane. The impregnation method may be any method, such as immersion or impregnation using a die.

[0044] After the nonwoven fabric is impregnated with the polymer solution, it is introduced into a drying zone for solvent evaporation. At this time, it is preferable to take care not to expose the membrane directly to wind. In the drying zone, it is important to control the temperature and humidity. The preferred temperature is 10 to 40°C, more preferably 15 to 30°C. The preferred relative humidity is 40 to 85%, more preferably 50 to 85%.

[0045] In addition, in order to develop a good membrane structure and pore size in the above-mentioned dry membrane formation, it is preferable to use a combination of a solvent and a non-solvent having appropriate vapor pressure. As the solvent, tetrahydrofuran or a mixed solvent containing tetrahydrofuran as the main component (50 wt % 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 2-propanol and 1-butanol can be used.

[0046] The porous membrane obtained as described above is preferably hydrophilized. In order to maintain anti-fouling performance for as long as possible, it is preferable to apply an appropriate amount of a hydrophilizing agent, such as non-thermally denatured hydroxypropyl cellulose, to the membrane. The hydroxypropyl cellulose solution is preferably prepared by uniformly dissolving hydroxypropyl cellulose in an aqueous solution containing equal amounts of 2-propanol and pure water at a weight ratio of 0.5 to 1.0%. The ratio of 2-propanol to pure water and the amount of hydroxypropyl cellulose dissolved may be varied depending on the characteristics of the porous membrane used. After immersing the porous membrane in this hydroxypropyl cellulose solution, excess solution is removed using a water washing bath, a scraping spatula, or a roller bar, followed by a heat treatment to fix the hydroxypropyl cellulose to the membrane. While this heat treatment can be performed using any method, such as hot water, warm air, or infrared radiation, heat treatment using hot water is preferred because it is low-cost, simple, and uniform. The heat treatment temperature is preferably 50 to 72°C, more preferably 60 to 70°C. The hydrophilized membrane is then dried and wound up. The drying conditions are preferably a temperature of 40°C to 70°C and a relative humidity of 1% to 20% to efficiently remove moisture and prevent thermal denaturation of hydroxypropyl cellulose. This series of treatments is carried out continuously.

[0047] The flat membrane sheet produced in this manner can have an average pore diameter of, for example, 0.2 to 0.5 μm, as measured using a perm 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 consideration the membrane strength and filtration efficiency over long-term use. This flow rate value also indirectly represents the degree of pore opening on the membrane surface and the density of the membrane structure. The larger this value, the greater the degree of pore opening on the membrane surface and the tendency for the membrane structure to be coarse. Conversely, the smaller the value, the smaller the degree of pore opening or the tendency for the membrane structure to be dense. These are closely related to membrane strength and filtration efficiency, and can therefore serve as indicators of whether a membrane can be used over a long period of time.

[0048] The porous polymer membrane constituting the flat membrane sheet of the present invention preferably has a structure that gradually becomes sparser from the surface that comes into contact with the liquid to be treated to the inner layer portion when the cross section of the membrane is observed under an electron microscope at 5,000 times magnification, and the polymer material constituting the membrane preferably forms a three-dimensional network of meshes that are moderately entangled with the nonwoven fabric of the membrane substrate. In this case, if the network density is too high, the water permeability performance will be impaired, and if it is too low, membrane components may detach from the substrate over long-term use, causing the membrane to no longer function as a membrane.

[0049] The device of the present invention having the polymeric porous flat membrane sheet and cleaning means as described above, and the method for recycling developer waste liquid using the same, use a high-performance flat membrane sheet that can filter and separate even particles with small particle diameters, so that not only the photosensitive resin composition that has aggregated in the developer waste liquid but also the photosensitive resin composition that is dispersed without aggregation can be efficiently recovered, and further, the cleaning means aerates so that sponge pieces come into contact with the deposits that have accumulated on the surface of the flat membrane sheet as it is filtered and separated, thereby removing the deposits on the surface of the flat membrane sheet and effectively preventing clogging, so that high filtration performance can be maintained for a long time.

[0050] The following examples demonstrate the effects of the method and apparatus of the present invention, but the present invention is not limited thereto. The evaluation of specific values ​​in the examples was carried out based on the following methods.

[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 conditions (25°C) Number of accumulations (25 times) - Measurement principle: Particle size measurement by dynamic light scattering method Particles constantly change their position, orientation, and shape due to Brownian motion (such as translation and rotation) in solution. When these particles are irradiated with laser light and the scattered light is detected, fluctuations in the scattering intensity dependent on the Brownian motion of the particles are observed. Using this principle, the speed of the Brownian motion of the particles (diffusion coefficient) can be obtained by observing the temporal fluctuations of the scattered light, and further, the particle size can be determined.

[0052] (B) Turbidity measurement - Equipment used: Rex portable turbidity meter WGZ-20B - Measurement conditions: Light source LED, measurement wavelength 860 nm, measurement intensity NTU 0.00-20 - Measurement principle: 90-degree scattered light method. When light from the LED light source is projected into the sample solution, scattered light is generated in proportion to the concentration of SS / turbidity substances. Meanwhile, a current signal proportional to the scattered light is generated from the light-receiving element positioned at 90 degrees to the light source. The turbidity value (mg / L) can be obtained from this current signal.

[0053] (Example of the present invention) The treatment performance of developer waste liquid (non-volatile component 5%) containing a photosensitive resin composition was evaluated using the recycled developer manufacturing apparatus 1 shown in Figures 2 and 3. The membrane element of the polymer porous flat membrane sheet was composed of a resin mesh (Nihon Filcon Co., Ltd. DOP-18K) on the front and back surfaces of a support plate, a nonwoven fabric (polyethylene terephthalate nonwoven fabric) (Hirose Paper Co., Ltd. 05TH-60), a separation membrane (membrane component is chlorinated polyvinyl chloride, thickness 130 μm, average pore size 0.3 μm, pure water FR 30 mL / cm ２ / min / bar were attached in this order.

[0054] In order to enhance the physical cleaning of the membrane surface, hexahedral PVA sponge pieces (2 mm x 2 mm x 2 mm) were added to the treatment tank 10 of the device 1 in an amount equivalent to 5% of the total volume. ２ Hit: 0.2m ３ Suction filtration operation was carried out using a tube pump at a filtration rate of 1000 / day. Intermittent operation was carried out by repeating 7-minute suction filtration operations followed by 3-minute stops. The aeration rate was adjusted to 16 L / min per membrane element. The suction filtration operation lasted a total of 40 hours, and the non-volatile components of the concentrated developer waste solution at the end of processing were 20%.

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

[0056] Comparative Example 1 The performance of treating a waste developer solution (5% non-volatile component) containing a photosensitive resin composition was evaluated using the recycled developer manufacturing apparatus 1 shown in Figures 2 and 3. The experiment was carried out in the same manner as in the present invention, except that no sponge pieces were put into the treatment tank and aeration was not performed.

[0057] Membrane element membrane area 1m ２ Hit: 0.2m ３ Suction filtration operation was carried out using a tube pump at a filtration rate of 1000 / day. Intermittent operation was carried out by repeating 7-minute suction filtration operations followed by 3-minute stops. The suction filtration operation lasted a total of 18 hours, after which clogging occurred and the operation was stopped. The non-volatile components of the concentrated developer waste solution at the end of processing were 11.8%.

[0058] The transmembrane pressure (TMP), which indicates the pressure difference between the permeate side and the feed side of the filtration membrane, was measured at the start and end of treatment to determine the state of membrane clogging. The particle size distribution and turbidity of the developer waste solution before treatment and the filtrate after treatment were measured to evaluate the filtration performance. The evaluation results for 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 maximum distribution): 800 nm for the developer waste solution before treatment, 80 nm for the filtrate after treatment. Turbidity of the liquid: Unmeasurable (opaque (white suspension) for the developer waste solution before treatment), 19.1 for the filtrate after treatment.

[0059] (Comparative Example 2) Using the recycled developer manufacturing apparatus 1 shown in Figures 2 and 3, the treatment performance of developer waste liquid (non-volatile components 5%) containing a photosensitive resin composition was evaluated. However, instead of a polymeric porous flat membrane sheet, a membrane element was used in which a resin mesh (Nihon Filcon Co., Ltd. DOP-18K) was attached to the front and back surfaces of a support plate, and a filter (Kureha Tech Co., Ltd. Bonden R301) was attached to the mesh. Note that no sponge pieces were put into the treatment tank.

[0060] Membrane element membrane area 1m ２ Hit: 0.2m ３ Suction filtration operation was carried out using a tube pump at a filtration rate of 1000 / day. Intermittent operation was carried out by repeating 7-minute suction filtration operations followed by 3-minute stops. The aeration rate was adjusted to 16 L / min per membrane element. The suction filtration operation lasted a total of 40 hours, and the non-volatile content of the concentrated developer waste solution at the end of processing was 6.3%.

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

[0062] According to the method and apparatus of the present invention, not only aggregates of the photosensitive resin composition but also dispersed, non-aggregated photosensitive resin composition can be efficiently removed from waste developer to easily obtain a recycled developer, and the clogging of the flat membrane sheet is unlikely to occur, allowing high filtration performance to be maintained. Therefore, the method and apparatus of the present invention are extremely useful in the industry.

[0063] REFERENCE SIGNS LIST 1 Regenerated developer manufacturing apparatus 10 Treatment tank 11 Polymer porous flat membrane sheet 12 Membrane element 13 Water collection pipe 14 Cleaning means 21 (Waste developer) transport direction 22 (Regenerated developer) transport direction 31 Transport direction 32 Developer brush 33 Developer tank 34 Developer pump 35 Transfer switching valve 36 Regenerated developer pump 37 Rinse brush 38 Regenerated developer outlet 39 Developer outlet

Claims

1. A method for producing a recycled developer from waste developer liquid generated by the development of a water-developable flexographic printing plate having a photosensitive resin layer made of a photosensitive resin composition containing a water-dispersible resin, the method comprising: introducing the waste developer liquid into a treatment tank; separating and removing the photosensitive resin composition contained in the waste developer liquid using a polymeric porous flat membrane sheet provided in the treatment tank; and removing and cleaning any deposits on the polymeric porous flat membrane sheet by introducing sponge pieces into the treatment tank and aerating the polymeric porous flat membrane sheet so that the sponge pieces come into contact with the polymeric porous flat membrane sheet.

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

3. The method according to claim 1 or 2, wherein the sponge pieces are made of a material that has a specific gravity greater than that of the liquid in the treatment tank when filled with water and has a maximum side dimension of 0.1 to 10 mm.

4. An apparatus for producing a recycled developer from a developer waste generated by the development of a water-developable flexographic printing plate having a photosensitive resin layer made of a photosensitive resin composition containing a water-dispersible resin, the apparatus comprising: a processing tank for receiving the developer waste and separating and removing the photosensitive resin composition contained in the developer waste; the processing tank comprising a polymeric porous flat membrane sheet for separating and removing the photosensitive resin composition from the developer waste; and the processing tank comprising: sponge pieces placed in the processing tank; and cleaning means configured to remove deposits from the polymeric porous flat membrane sheet by aerating the sponge pieces so that they come into contact with the polymeric porous flat membrane sheet.

5. The device according to claim 4, wherein the polymeric porous flat membrane sheet comprises a polymeric porous membrane that forms a mesh-like network structure and a sheet-like substrate that supports the membrane.

6. The device according to claim 4 or 5, wherein the sponge pieces are made of a material that has a specific gravity greater than that of the liquid in the treatment tank when filled with water and has a maximum side dimension of 0.1 to 10 mm.

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