How to process developer

Abstract

To provide a processing method for efficiently reusing a water type developer which is used for development of a photosensitive resin layer of a flexographic printing original plate.SOLUTION: There is provided a processing method for using a development device comprising: a developing part; and a developer tank, for reusing a used developer which is acquired after developing a flexographic printing original plate by a water type developer, the flexographic printing original plate comprising, on a support medium, a photosensitive resin layer, and the method comprises: a processing step A for separating the used developer into mother liquid and a solid component, by a centrifugal machine; a processing step B for filtering and separating the mother liquid acquired in the processing step A, into permeable water and concentrated liquid, by a cross flow filtration system; and a circulating step for circulating the permeable water acquired in the processing step B into a developing part or developer tank of the development device.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a method for treating a used aqueous developer for a flexographic printing plate precursor for reuse. [Background technology]

[0002] In recent years, photopolymer plates for flexographic printing that can be developed with an aqueous developer have come to be widely used in consideration of the working environment and the local environment. After exposure, it is necessary to remove the unexposed areas of these aqueous development type photopolymer plates with a developer, and there is a demand for an environmentally friendly method for treating the waste developer generated during this process. For example, the methods proposed in Patent Documents 1 to 4 are such methods.

[0003] Patent Document 1 discloses a method for reducing the amount of developer waste by transferring the developer waste generated in the washing tank to a concentration tank and reusing the filtrate generated by circulating between the concentration tank and a membrane filter in the washing tank. However, this method is unable to deal with a sudden increase in resin concentration because the filtrate flow rate is low in general-purpose equipment. In addition, the filtration method has the problem that the filter becomes clogged, requiring frequent cleaning and replacement of the filter element.

[0004] Patent Document 2 discloses a method of adding a cationic flocking agent and a polymeric water-absorbent resin to waste developer liquid to flocculate the sludge, and then filtering the flocculated sludge to remove the resin component from the developer liquid. However, this method has a problem in that the cationic flocking agent remains in the treated liquid after sludge removal, and if the treated liquid is reused for development, sludge flocculation occurs in the developing device, making it impossible to reuse the treated liquid.

[0005] Cited Document 3 discloses a method for separating and removing the resin components using a centrifugal separation process using a centrifugal settling type with an inside disk. However, the centrifugal separation process in this method does not completely remove the resin components, and a small amount remains, so it is necessary to wash the plate using unused water or developer during the finishing process of the platemaking.

[0006] Cited Document 4 discloses a method of separating a developer into a high-concentration developer and a low-concentration developer having different resin concentrations using a ceramic filter, and returning the low-concentration developer to the circulation path for reuse. However, this method has a problem in that the high-concentration developer has a high water content, resulting in a large amount of waste. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 11-212274 [Patent Document 2] JP 2001-47060 A [Patent Document 3] Japanese Patent Application Publication No. 07-328620 [Patent Document 4] JP 2018-54969 A Summary of the Invention [Problem to be solved by the invention]

[0008] The present invention has been made in view of the above problems of the conventional technology, and an object of the present invention is to provide a processing method for efficiently separating and removing resin components from a large amount of developer, for reusing an aqueous developer used in developing a photosensitive resin layer of a flexographic printing original plate. [Means for solving the problem]

[0009] As a result of intensive research into achieving this object, the present inventors have discovered that by separating an aqueous developer used after developing a flexographic printing plate having a photosensitive resin layer into a mother liquor and a solid component by centrifugation, and then further separating the separated mother liquor into a permeated water and a concentrated water by filtration using a cross-flow filtration method, and returning the permeated water to the developing section of a developing device or to a developer tank for reuse, it is possible to efficiently separate and remove the resin component from the used developer in a simple manner, and as a result, the developer can be reused, and the amount of water used and the amount of waste liquid can be greatly reduced, which led to the completion of the present invention.

[0010] That is, the present invention provides the following (1) to ( 3 ) configuration. (1) A processing method for reusing a used developer obtained after developing a flexographic printing original plate having a photosensitive resin layer on a support with an aqueous developer using a developing device having a developing section and a developing solution tank, comprising: a processing step A for separating the used developer into a mother liquid and a solid component by a centrifuge; a processing step B for filtering and separating the mother liquid obtained in the processing step A into a permeate and a concentrated solution by a cross-flow filtration method using a microfiltration filter having an average pore size of 0.2 to 1.6 μm; and a circulation step for returning the permeate obtained in the processing step B to the developing section of the developing device or the developing solution tank, and further repeating the processing step B for sending the concentrated solution obtained in the processing step B to a storage tank and filtering and separating it with the microfiltration filter. The concentrate thus obtained is then treated again in the treatment step A. A processing method comprising: (2) The processing method according to (1), characterized in that the developing apparatus further has a rinsing section, and the permeated water obtained in processing step B is returned to the rinsing section and used for finishing washing of the flexographic printing plate before being returned to the developing section or developer tank. ( 3 (1) The centrifuge is characterized in that the filtrate is centrifuged at a centripetal acceleration of 200 to 4000 G. Or (2) The processing method described in Effect of the Invention

[0011] In the processing method of the present invention, a used aqueous developer obtained after developing a flexographic printing original plate having a photosensitive resin layer is separated into a mother liquid and a solid component by a centrifuge, and the separated mother liquid is filtered by a cross-flow filtration system to further remove the resin component, and the permeated water is circulated and reused as a developer, so that the amount of water used for development can be reduced and the final amount of developer waste can be reduced. [Brief description of the drawings]

[0012] [Figure 1] 1 shows an image pattern for evaluation used in the imaging exposure process of the examples. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] The flexographic printing original plate used in the processing method of the present invention, the developing method thereof, and the processing method of the used developer will be described below.

[0014] The flexographic printing plate precursor used in the processing method of the present invention is preferably a water-developable flexographic printing plate precursor having a photosensitive resin layer obtained from a photosensitive resin composition on a support, and using an aqueous developer as a washout solution. The photosensitive resin composition preferably contains a synthetic rubber polymer, a photopolymerizable unsaturated compound, and a photopolymerization initiator as main components. The processing method of the present invention is effective when the photosensitive resin layer contains a water-dispersible synthetic rubber polymer, and may further contain a water-insoluble synthetic rubber polymer. The photosensitive resin composition may contain a water-soluble or hydrophilic polymer component, but if a large amount of the component is contained, the swellability in aqueous ink increases, and the quality tends to deteriorate.

[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 supports include metal supports such as steel, aluminum, copper, nickel, etc., and thermoplastic resin films such as polyethylene terephthalate film, polyethylene naphthalate film, polybutylene terephthalate film, polycarbonate film, etc. Among these, polyethylene terephthalate film, which has excellent dimensional stability and sufficiently high viscoelasticity, is particularly preferred.

[0016] The water-dispersible synthetic rubber polymer used in the photosensitive resin composition is used to impart appropriate rubber elasticity to the photosensitive resin layer, and a conventionally known rubber component can be used. The water-dispersible synthetic rubber polymer is preferably solid at room temperature in order to impart rubber elasticity. Specific examples of the water-dispersible synthetic rubber polymer include polybutadiene, polychloroprene, polyacrylonitrile-butadiene, polyacrylic, epichlorohydrin, polyurethane, polyisoprene, polystyrene-isoprene copolymer, polystyrene-butadiene copolymer, methyl methacrylate-butadiene copolymer, ethylene-propylene copolymer, butyl polymer, chlorinated polyethylene, and the like, and polymers obtained by copolymerizing these polymers with other components such as acrylic acid and methacrylic acid, and the like can be mentioned. Among the water-dispersible synthetic rubber polymers, water-dispersible synthetic rubber polymers having a butadiene skeleton and / or a styrene skeleton are preferred from the standpoint of developability and physical properties. As the water-dispersible synthetic rubber polymer, a water-dispersible latex is preferred. The water-dispersed latex may be a latex having a crosslinked structure in the molecule, which is expressed by the gelation degree. When using a latex having a crosslinked structure in the molecule, it is preferable that the latex is a hydrophobic polymer obtained from a water-dispersed latex having a weight average gelation degree of 20 to 80%. These may be used alone or in combination of two or more kinds. The water-dispersed latex is a latex in which rubber polymer particles are dispersed in water to form a stable suspension. A polymer is obtained by removing water from this water-dispersed latex.

[0017] The photosensitive resin composition may contain a water-insoluble synthetic rubber polymer to the extent that it does not adversely affect the performance. Examples of the water-insoluble synthetic rubber polymer include polybutadiene, polychloroprene, polyacrylonitrile-butadiene, polyurethane, polyisoprene, polystyrene-isoprene copolymer, and polystyrene-butadiene copolymer. By containing the water-insoluble synthetic rubber polymer, physical properties and water resistance are improved.

[0018] The photosensitive resin composition may contain a water-soluble or hydrophilic polymer component other than the water-dispersible synthetic rubber polymer. Examples of the water-soluble or hydrophilic polymer component 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 compound contained in the photosensitive resin composition is contained in order to cure and crosslink by ultraviolet light. The photopolymerizable unsaturated 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 compound may contain an oligomer having a photopolymerizable group introduced therein or a polymer having a photopolymerizable group introduced therein. The photopolymerizable unsaturated compound preferably contains one having a common skeleton with the synthetic rubber copolymer in terms of compatibility with the synthetic rubber copolymer. These photopolymerizable unsaturated compounds may be used alone or in combination of two or more kinds.

[0020] Specific examples of ethylenically unsaturated compounds having only one ethylenically unsaturated bond include (meth)acrylates having a hydroxyl group such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 3-chloro-2-hydroxypropyl (meth)acrylate, β-hydroxy-β'-(meth)acryloyloxyethyl phthalate, propyl (meth)acrylate, butyl (meth)acrylate, isoamyl (meth)acrylate, 2-ethyl (meth)acrylate, butyl ... Examples of the alkyl (meth)acrylate include alkyl (meth)acrylates such as ethylhexyl (meth)acrylate, lauryl (meth)acrylate, and stearyl (meth)acrylate; phenoxyalkyl (meth)acrylates such as phenoxyethyl acrylate and nonylphenoxyethyl (meth)acrylate; and alkoxyalkylene glycol (meth)acrylates such as ethoxydiethylene glycol (meth)acrylate, methoxytriethylene glycol (meth)acrylate, and methoxydipropylene glycol (meth)acrylate.

[0021] Specific examples of the ethylenically unsaturated compound having two or more ethylenically unsaturated bonds include alkyl diol di(meth)acrylates such as 1,9-nonanediol di(meth)acrylate, polyethylene glycol di(meth)acrylates such as diethylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylates such as dipropylene glycol di(meth)acrylate, polyhydric (meth)acrylates of polyhydric alcohols such as trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, and glycerol tri(meth)acrylate, polyhydric (meth)acrylates obtained by addition reaction of ethylene glycol diglycidyl ether with an unsaturated carboxylic acid, polyhydric (meth)acrylates obtained by addition reaction of an unsaturated epoxy compound such as glycidyl (meth)acrylate with a carboxylic acid or an amine, and polyhydric (meth)acrylamides such as methylene bis(meth)acrylamide.

[0022] The photopolymerization initiator contained in the photosensitive resin composition is not particularly limited as long as it can polymerize a polymerizable unsaturated group by irradiation with light, and conventionally known initiators can be used. In particular, initiators having a function of generating radicals by self-decomposition or hydrogen abstraction due to light absorption are preferable. Specific examples include benzoin alkyl ethers, benzophenones, anthraquinones, benzils, acetophenones, and diacetyls. The photopolymerization initiator may be used alone or in combination of two or more.

[0023] The developer used in the processing method of the present invention is preferably an aqueous developer containing 50% by mass or more of water. The aqueous developer may be composed of water only, but is preferably an aqueous solution to which a water-soluble development accelerator has been added in terms of the stability of the development speed and development quality. Examples of the development accelerator include surfactants, acids, bases, and organic solvents. Commercially available soaps and detergents may be used as the surfactant, and examples of the chemical structure include cationic surfactants, anionic surfactants, nonionic surfactants, and amphoteric surfactants. Examples of the acid 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 the base include lithium hydroxide, sodium hydroxide, potassium hydroxide, calcium hydroxide, sodium carbonate, and sodium hydrogen carbonate. Examples of the organic solvent include methanol, ethanol, isopropyl alcohol, cellosolve, glycerin, ethylene glycol, polyethylene glycol, dimethylformamide, dimethylacetamide, and acetone. In addition, an antifoaming agent may be added to the developer to suppress the generation of bubbles. The defoaming agent is not particularly limited as long as it is water-soluble, and for example, higher alcohols, fatty acid derivatives, silica, alumite, and silicone can be used.

[0024] The developing device used in the processing method of the present invention has a developing section and a developer tank, and may further have a rinsing section. The developing section is not particularly limited as long as it can wash out the photosensitive resin composition in the uncured part of the flexographic printing plate using an aqueous developer after exposure to form a relief image. The washing out of the uncured part can be, for example, a method of rubbing out the photosensitive resin composition in the uncured part with the developer using a brush, or a method of rubbing out the photosensitive resin composition in the uncured part by combining a spray jet and a brush. The developer tank is a tank for storing the developer, and the developer used in the development can be processed and regenerated and then circulated and stored. In addition, the rinsing section performs a rinsing process to wash out the developer containing resin components that adhere to the surface of the printing plate after the development process and the resin residue in the developing device called scum. In the rinsing process, new developer containing no resin components or new water is generally used.

[0025] The processing method of the present invention is characterized by comprising a processing step A in which a used developer obtained after developing a flexographic printing plate with an aqueous developer using the developing apparatus having the above-mentioned configuration is separated into a mother liquor and a solid component by a centrifuge, a processing step B in which the mother liquor obtained in the processing step A is filtered and separated into a permeate and a concentrated liquid by a cross-flow filtration method, and a circulation step in which the permeate obtained in the processing step B is returned to the developing section or the developer tank. Preferably, the permeate obtained in the processing step B is returned to the rinsing section of the developing apparatus and used for finish washing.

[0026] In the processing step A, the used developer obtained after development with an aqueous developer is separated into mother liquor and solid components by a centrifuge. The centrifuge used in the processing step A is a device that separates by applying centrifugal force to the liquid in the rotating part by rotating the rotating part at high speed, and a conventionally known centrifuge can be used. For example, a centrifugal sedimentation type centrifuge that separates resin components by specific gravity difference by centrifugal force, a centrifugal filtration type centrifuge in which holes are opened on the side of the rotating part and a filter cloth is stretched on the inner surface of the rotating part and filtration is performed by centrifugal force, and a centrifugal decanter type centrifuge in which a screw or impeller is present in the rotating part and the sedimentation component and the floating component are separated are possible. The centrifugal filtration type is not practically suitable because the filter cloth frequently becomes clogged, but it is preferable to select various methods of the centrifugal sedimentation type and centrifugal decanter type according to the specific gravity relationship between the developer and the resin. The shape of the rotating part can be a cylindrical shape, a conical shape, or a truncated cone, and a cylindrical shape is preferable in terms of processing efficiency.

[0027] The centrifuge preferably performs centrifugation at a centripetal acceleration in the range of 200 to 4000 G. More preferably, the centripetal acceleration is in the range of 500 to 2500 G. The amount of processing solution that the centrifuge can process is determined by the volume inside the centrifuge, but when the developer is directly processed by connecting to a developing machine, a centrifuge with an optimal processing amount for the amount of developer in the developing machine may be prepared. When the amount of the washout solution is 50 liters, the processing amount is preferably 2 liters or more per minute, and when the amount of the washout solution is 200 liters, the processing amount is preferably 8 liters or more per minute. In the present invention, although it is possible to add a flocculant to the washout solution before processing in order to enhance the centrifugal separation effect, it is preferable not to use a flocculant in order to facilitate reuse of the washout solution.

[0028] In the centrifugal sedimentation type centrifuge, a bag made of nonwoven fabric or resin sheet can be provided inside the centrifugal separator to easily remove the photosensitive resin aggregate. By providing a bag made of nonwoven fabric or resin sheet inside the separator, the photosensitive resin aggregate accumulated inside the separator can be removed outside the separator together with the bag made of nonwoven fabric or resin sheet. As a method for easily removing the aggregate, nonwoven fabric is preferred. The bag made of resin sheet preferably has fine holes and is fixed along the inner wall surface of the separator.

[0029] In the processing step B, the mother liquor processed in the processing step A is separated into permeate from which the resin components have been separated and a highly concentrated solution in which the resin components have been concentrated, using a membrane filter of the cross-flow filtration method. In the case of cross-flow filtration, in order to reduce the load on the filter, it is preferable to send the highly concentrated solution obtained in the processing step B to a storage tank and then repeat the processing step B, i.e., filtration and separation using a filter. On the other hand, since the permeate obtained in the processing step B contains a small amount of resin components, it can be circulated to the rinsing section before returning it to the developing section of the developing device or the developer tank, and used as washing water for finishing washing of the printing plate. In addition, after performing the processing step A and, if necessary, multiple processing steps B, it is also preferable to process the concentrated solution obtained in the processing step B again in the processing step A in order to reduce the load on the filter.

[0030] Examples of the material for the filtration filter include organic membranes such as polysulfone resin, polyimide resin, polyacrylonitrile resin, cellulose acetate, ethyl cellulose, and nitrocellulose, ceramic membranes mainly composed of alumina, silica, titanium oxide, and zirconia, and metal membranes made by sintering alloys. As for the form of the module, it is preferable to use a hollow fiber or tubular type for organic membranes, and a tubular type or multi-lumen type for ceramic membranes and metal membranes. Among these, ceramic membranes are particularly compatible with aqueous developers.

[0031] The flow rate of the mother liquor obtained in the process A and the concentrated liquid obtained in the process B through the filtration filter is preferably set so that the flow rate of these liquids relative to the filtration membrane is 1 m / sec or more. If it is slower than this, the filtration membrane is likely to be clogged and the filtration flow rate is likely to decrease. There is no particular problem with a high flow rate, but the selection of pumps and piping is restricted in terms of the design of the device. In addition, the pressure of these liquids applied to the filtration membrane is preferably 1 MPa or more, although it varies depending on the type of membrane. If it is lower than this, there is a risk that a sufficient permeate flow rate cannot be obtained. On the other hand, there is no particular problem even if the pressure is high, but there is a risk that the selection of pumps and piping is restricted in terms of the design of the device. It is common to use multiple filtration filters to increase the filtration area in order to increase the processing flow rate, but the cost increases with the number of filters used.

[0032] The pore size of the filter is preferably an average pore size within the range of 0.05 to 2.0 μm, as measured by observing the cross section of the filter under an optical microscope. Filters having pore sizes within this range are generally known as precision filters. The pore size is more preferably 0.1 to 1.8 μm, and even more preferably 0.2 to 1.6 μm. If the pore size is less than the above range, the filter is likely to become clogged, whereas if it exceeds the above range, the resin component cannot be sufficiently removed, which may result in contamination of the printing plate or brush.

[0033] The filtration filter is preferably provided with a backwashable mechanism. When the filter becomes clogged during long-term operation, the clog can be easily removed by backwashing, making maintenance easier. In addition, regular backwashing allows for even longer operation. An example of a backwashable mechanism is one that includes a pump that backflows a low-concentration developer into the separation device, and removes water-insoluble polymers that have accumulated on the ceramic filter. Backwashing may be automated or performed manually. EXAMPLES

[0034] The effects of the treatment method of the present invention will be illustrated by the following examples, but the present invention is not limited thereto.

[0035] (1) Preparation of photosensitive resin composition As the latex, 91 parts by mass of butadiene latex (manufactured by Nippon Zeon, LX111NF, solid content concentration 55%), 15 parts by mass of oligobutadiene acrylate (manufactured by Kyoeisha Chemical Co., Ltd., ABU-3: molecular weight 2700) as a photopolymerizable unsaturated compound, 10 parts by mass of lauryl methacrylate, 10 parts by mass of trimethylolpropane trimethacrylate, 1 part by mass of benzyl dimethyl ketal as a photopolymerization initiator, 20 parts by mass of PFT-3 (polymer having a molecular weight of about 20,000 having a urethane urea structure, solid content concentration 25%) as a hydrophilic polymer manufactured by Kyoeisha Chemical Co., Ltd., 0.1 parts by mass of hydroquinone monomethyl ether as a polymerization inhibitor, and 9 parts by mass of liquid butadiene as a plasticizer were mixed in a container with 5 parts by mass of toluene, and then kneaded at 105 ° C. using a pressure kneader, and then the toluene and water were distilled off under reduced pressure to obtain a photosensitive resin composition.

[0036] (2) Preparation of protective layer coating solution A low-saponification polyvinyl alcohol (PVA405, manufactured by Kuraray Co., Ltd.), a plasticizer (Sunflex SE270, manufactured by Sanyo Chemical Industries, Ltd., aliphatic polyhydric alcohol-based polyether polyol, solid content concentration 85%), and NBR latex (SX1503A, manufactured by Nippon Zeon Co., Ltd., solid content concentration 42%) were dissolved in a water / isopropyl alcohol mixture to a solid content weight ratio of 35 / 35 / 30, to prepare a protective layer coating solution.

[0037] (3) Preparation of infrared-sensitive layer coating solution A carbon black dispersion (AMBK-8, manufactured by Orient Chemical Industries Co., Ltd.) and a copolymer polyamide (PA223, manufactured by Toyobo Co., Ltd.) were dissolved in a mixture of methanol, ethanol, and isopropyl alcohol to give a solids weight ratio of 63 / 37 to prepare an infrared-sensitive layer coating solution.

[0038] (4) Preparation of laminated film The infrared-sensitive layer coating liquid was applied to a 100 μm PET film with a release treatment on both sides using an appropriate type of bar coater, and dried at 120° C. for 5 minutes to laminate an infrared-sensitive layer with a thickness of 1.5 μm on the PET film. The optical density at this time was 2.3 when measured using a black-and-white transmission densitometer DM-520 (Dainippon Screen Mfg. Co., Ltd.). Next, the protective layer coating liquid was applied to the infrared-sensitive layer using an appropriate type of bar coater, and dried at 120° C. for 5 minutes to obtain a laminated film in which an infrared-sensitive layer with a thickness of 1.5 μm and a protective layer with a thickness of 0.5 μm were laminated in this order on the PET film.

[0039] (5) Preparation of a flexographic printing original plate having a photosensitive resin composition on a support The photosensitive resin composition was placed on a 125 μm PET film coated with a copolymer polyester adhesive, and a laminated film was placed on top of it. The laminate was laminated at 100° C. using a heat press machine to obtain a flexographic printing original plate consisting of a PET support, an adhesive layer, a photosensitive resin layer, a protective layer, an infrared-sensitive layer, and a release-treated PET protective film (cover film). The total thickness of the plate was 1.14 mm.

[0040] <Picture exposure process> Using an exposure device equipped with 30 60W Philips 10R fluorescent lamps, the above-mentioned flexographic printing plate precursor with a size of 900 mm x 1200 mm was irradiated with ultraviolet light from the 125 μm PET support side to form a base, and then the cover film was peeled off and the flexographic printing plate precursor was set in an ESKO CDI4835 to draw an evaluation image pattern having 150LPI 10% dots and 100 μm fine lines as shown in Figure 1 on the infrared-sensitive layer.

[0041] <Developing process> The flexographic printing plate made in the drawing exposure process was fixed on an adhesive plate and developed by inserting it into the developing machine. The developing machine moved the plate in the long side direction at a speed of 45 mm / min, passing through the developing section, rinsing section, and drying section in that order. In the developing section, the unexposed parts were removed with the developer circulated from the developing tank and dispersed in the developer. The developer used was 200 L of a 1 wt% aqueous solution of sodium oleate, and the temperature was set at 40°C. In the rinsing section, tap water was used as a running water or the permeated water from which the resin had been removed using a filtration filter was used in circulation. In the drying section, hot air at 60°C was supplied. 20 sheets of flexographic printing plates were passed through this developing machine continuously for 10 hours, and the following evaluations were performed.

[0042] <Processing speed measurement> The flow rate of the permeated water flowing from the filtration filter to the developing device was received in a cup for 20 seconds, the volume (L) was measured, and this measurement was multiplied by three to obtain the processing speed (L / min).

[0043] <Measurement of resin removal rate> The weight of the printing plate before development in the development process was measured in advance, and then the weight of the printing plate after development was measured, and the "amount of resin dissolved in the developer (kg)" was calculated from the difference. After developing 20 sheets, the developer in the developer tank was sampled, about 2g was placed on aluminum foil, and vacuum dried at 80°C for 2 hours to remove the water, and the weight was measured before and after vacuum drying. The developer resin concentration in the developer tank, the amount of resin in the developer tank, and the amount of resin removed were then calculated in order using the following formula. Developer resin concentration in developer tank (%) = weight after vacuum drying (g) ÷ weight before vacuum drying (g) × 100-1 (sodium oleate concentration) Amount of resin in the developer tank (kg) = Developer resin concentration in the developer tank (%) x amount of developer tank liquid after developing 20 sheets (L) Resin removal rate (%) = (amount of resin dissolved in the developer (kg) - amount of resin in the developer tank (kg)) ÷ amount of resin dissolved in the developer (kg) x 100

[0044] <Measurement of water content in discharged developer> After the development process was completed, the developer discharged was collected in a drum and the total weight was measured, which was the amount of discharged developer. Approximately 2 g of this discharged developer was placed on aluminum foil and vacuum dried at 80°C for 2 hours to remove the water. The weights before and after vacuum drying were measured, and the moisture content was calculated using the following formula. Moisture percentage (%) = (Weight before vacuum drying (g) - Weight after vacuum drying (g)) ÷ Weight before vacuum drying (g) × 100

[0045] <Printing plate stains> The surface of the last printing plate after 20 developments was observed with the naked eye to judge whether or not aggregates of the water-insoluble polymer were observed on the printing plate. If they were observed, it was marked as "X", and if they were not, it was marked as "O".

[0046] <Example 1> The centrifuge used in process A was a cylindrical rotor [inner diameter R = 30 cm, height H = 20 cm, bottom sealed type] with a nonwoven fabric covering the entire inner wall, and a centripetal acceleration of 1000 G. The device for filtering and separating using the cross-flow filtration method used in process B was a Noritake MEMBRALOX, hexagonal with dimensions of 27 mm across x 500 mm long, with a membrane material of Al. 2 O 3 Seven elements with a membrane shape of 4φ×19 holes were used as a cross-flow filtration filter module. A pressure of 3 MPa was applied to the module to pass liquid at a flow rate of 100 L / min. Filter elements with an average pore size of 1.4 μm were prepared. Each device was connected to construct a processing system so that used developer from a developing device having a developing section, a rinsing section, and a developing solution tank enters a centrifuge via a storage tank, the mother liquor from the centrifuge enters a filtration separation device having a filtration filter via a storage tank, the concentrated liquid from the filtration separation device returns to the storage tank, and the permeated water returns to the developing device.

[0047] Using this processing system, the used developer generated when 20 sheets were developed in the developing process was processed in processing process A, and then processed in processing process B. The concentrated solution obtained in processing process B was repeatedly processed again in processing process B. Meanwhile, the permeated water obtained in processing process B was returned to the rinsing section and used as washing water for the finishing wash of the printing plates, and then returned to the developer tank to be used as regenerated developer.

[0048] At this time, the processing speed was measured from the flow rate of the permeated water obtained in processing step B. Printing plate staining was evaluated by visually observing the surface of the last printing plate after 20 sheets were developed. The developer in the developer tank was sampled and the resin removal rate was measured. The developer in the storage tank and inside the centrifuge was combined and regarded as the discharged developer, and the moisture content of the discharged developer was measured. The evaluation results are shown in Table 1.

[0049] In Example 1, the high-concentration concentrate concentrated by the filter in the processing step B is repeatedly subjected to the cross-flow filtration in the processing step B to rapidly remove the resin, so that the load on the filter can be reduced. That is, in Example 1, the processing solution amount, which is the processing capacity of the developer, was 7.8 L / min, and a high processing capacity was achieved. In addition, the resin removal rate was as high as 70%. As a result, the staining of the printing plate due to the adhesion of resin in the development section could be reduced. Furthermore, by supplying the permeated water of the filter to the rinsing section, the rinsing of the printing plate was also good, and the staining of the printing plate could be reduced. In addition, the obtained permeated water was circulated to the developer tank after being used in the rinsing section and could be used as the developer. Only solid components were accumulated in the centrifuge in the processing step A, and dehydration was progressing, and the moisture content of the discharged developer could be reduced to 77%. As a result, the amount of water used and the amount of waste liquid could be significantly reduced.

[0050] <Example 2> Example 2 was processed in the same manner as Example 1, except that the centrifuge used in processing step A of Example 1 was changed to a centrifuge with a centripetal acceleration of 2000G. The evaluation results are shown in Table 1. Since the removal rate of the resin component was improved by setting the centripetal acceleration of the centrifuge to 2000G, the soiling of the printing plate due to resin adhesion in the developing section could be further reduced. And, since the concentrated water was repeatedly processed in processing step B after being processed in processing step B, a high processing capacity of 8.9 L / min was achieved for the processing efficiency of the developer. Furthermore, in Example 2, it was also possible to supply the permeated water of the filtration filter to the rinsing section and return it to the developer tank together with the rinsing and cleaning of the printing plate as a circulation step. As a result, the discharged developer water content rate could be reduced to 74%.

[0051] <Example 3> Example 3 was processed in the same manner as Example 1, except that the average pore diameter of the membrane filtration filter in Example 1 was changed from 1.4 μm to 0.5 μm. The evaluation results are shown in Table 1. Although the processing speed decreased slightly, a high removal rate of 71% was achieved for the resin removal rate. Since the removal rate of the resin component was high, the soiling of the printing plate due to resin adhesion in the developing section could be further reduced. Furthermore, the printing plate could be cleaned by supplying the permeated water of the filtration filter to the rinsing section. Also, the discharged developer water content rate could be reduced to 78%.

[0052] <Example 4> Example 4 was processed in the same manner as Example 1, and then an additional processing step A was further performed. As a result, the concentration in the storage tank decreased and it became possible to reuse it without discarding it. Therefore, only the developer inside the centrifuge was used as the discharged developer, and the discharged developer water content rate was measured. The evaluation results are shown in Table 1. In Example 4, since the concentrated water separated by the processing in processing step B was reused in the centrifuge in processing step A to remove the resin component, the load on the filtration filter could be reduced and the filter life could be significantly improved. And, since the resin component in the developer was removed, the soiling of the printing plate due to resin adhesion in the developing section could be further reduced. The processing efficiency of the developer was a high processing capacity of 7.8 L / min, and the resin removal rate was also as high as 85%.

[0053] <Comparative Example 1> In Comparative Example 1, the developer was treated only with the centrifuge in Treatment Step A without using the filtration filter in Treatment Step B. Otherwise, it was carried out in the same manner as in Example 1. The evaluation results are shown in Table 1. In Comparative Example 1, the resin removal rate in the developer tank was slow, and the resin concentration temporarily increased immediately after plate making, resulting in printing plate contamination.

[0054] <Comparative Example 2> In Comparative Example 2, the developer was treated only with the filtration filter in Treatment Step B without using the centrifuge in Treatment Step A. Otherwise, it was carried out in the same manner as in Example 1. The evaluation results are shown in Table 1. In Comparative Example 2, since there was no concentration of solid components by the centrifuge, the discharged developer moisture rate could not be reduced. In addition, since the developer was treated only with the filtration filter, filter clogging occurred, the frequency of filter replacement was high, and the workability was poor.

[0055]

Table 1

Industrial Applicability

[0056] The treatment method of the present invention can efficiently separate and remove the resin component from the aqueous developer used for developing the flexographic printing original plate and reuse the used developer, so that the amount of water and the amount of waste liquid used for development can be significantly reduced.

Claims

1. The present invention relates to a processing method for reusing a used developer obtained after developing a flexographic printing original plate having a photosensitive resin layer on a support with an aqueous developer using a developing apparatus having a developing section and a developer tank, the processing method comprising: a processing step A in which the used developer is separated into a mother liquor and a solid component by a centrifuge; a processing step B in which the mother liquor obtained in the processing step A is filtered and separated into a permeate and a concentrate by a cross-flow filtration method using a precision filter having an average pore size of 0.2 to 1.6 μm; and a circulation step in which the permeate obtained in the processing step B is returned to the developing section of the developing apparatus or to the developer tank, the processing step further comprising: sending the concentrate obtained in the processing step B to a storage tank, and repeatedly carrying out the processing step B in which the concentrate obtained in the processing step B is filtered and separated by the precision filter, and then processing the concentrate thus obtained again in the processing step A.

2. 2. The processing method according to claim 1, wherein the developing apparatus further comprises a rinsing section, and the permeated water obtained in the processing step B is returned to the rinsing section for use in finishing washing of the flexographic printing plate, and then returned to the developing section or the developer tank.

3. 3. The method according to claim 1, wherein the centrifuge centrifuges the filtrate at a centripetal acceleration of 200 to 4000 G.

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