JP7681256B2 - How to handle developer - Google Patents

Description

The present invention relates to a processing method for reusing used aqueous developer for flexographic printing plates.

In recent years, photopolymer plates for flexographic printing that can be developed with an aqueous developer have come to be widely used due to considerations of the working environment and 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 disposing of the developer waste liquid that is generated during this process. For example, the methods proposed in Patent Documents 1 to 4 are such methods.

Patent Document 1 discloses a method for reducing the amount of developer waste by transferring waste developer generated in a 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.

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 components from the developer liquid. However, this method has the problem that the cationic flocking agent remains in the processed liquid after sludge removal, and if the liquid is reused for development, sludge will flocculate in the developing device, making it impossible to reuse the processed liquid.

Cited Document 3 discloses a method for separating and removing the separated resin components using a centrifugal sedimentation type centrifuge process with an inside disk. However, the centrifugation process in this method does not completely remove the resin components, with only a small amount remaining, making it necessary to wash the plate using unused water or developer during plate-making finishing.

Cited Document 4 discloses a method of using a ceramic filter to separate a developer into a high-concentration developer and a low-concentration developer with different resin concentrations, and then returning the low-concentration developer to the circulation path for reuse. However, this method has the problem that the high-concentration developer has a high water content, resulting in a large amount of waste.

Japanese Patent Application Publication No. 11-212274 JP 2001-47060 A Japanese Patent Application Publication No. 07-328620 JP 2018-54969 A

The present invention was devised in consideration of the problems of the conventional technology, and its purpose is to provide a processing method for reusing an aqueous developer used in developing a photosensitive resin layer of a flexographic printing plate, which can efficiently separate and remove resin components from a large amount of developer.

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

That is, the present invention has the following configurations (1) to ( 3 ).
(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 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) 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 ) The method according to (1) or (2) , wherein the centrifuge centrifuges the filtrate at a centripetal acceleration of 200 to 4000 G.

In the processing method of the present invention, the used aqueous developer obtained after developing a flexographic printing plate having a photosensitive resin layer is separated into mother liquid and solid components by a centrifuge, and the separated mother liquid is filtered by a cross-flow filtration method to further remove the resin components, and the permeated water is circulated and reused as the developer, thereby reducing the amount of water used for development and the final amount of developer waste.

1 shows an image pattern for evaluation used in the imaging exposure process of the examples.

The following describes the flexographic printing original plate used in the processing method of the present invention, the developing method thereof, and the processing method for used developer.

The flexographic printing plate used in the processing method of the present invention is preferably a water-developable flexographic printing plate having a photosensitive resin layer obtained from a photosensitive resin composition on a support, and is preferably a water-developable flexographic printing plate 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 also contain a water-soluble or hydrophilic polymer component, but if a large amount is contained, the swelling tendency in aqueous ink increases, and the quality is likely to deteriorate.

The support used for the flexographic printing plate is preferably a material that is flexible but has excellent dimensional stability, such as a metal support such as steel, aluminum, copper, or nickel, or a thermoplastic resin film such as a polyethylene terephthalate film, a polyethylene naphthalate film, a polybutylene terephthalate film, or a polycarbonate film. Among these, a polyethylene terephthalate film is particularly preferred, as it has excellent dimensional stability and sufficiently high viscoelasticity.

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 conventionally known rubber components can be used. The water-dispersible synthetic rubber polymer is preferably solid at room temperature in order to impart rubber elasticity. Specific examples of water-dispersible 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, chlorinated polyethylene, and the like. Examples of polymers obtained by copolymerizing these polymers with other components such as acrylic acid and methacrylic acid can also 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 in terms of developability and physical properties. As the water-dispersible synthetic rubber polymer, water-dispersible latex is preferred. The water-dispersible latex may be a latex having a cross-linked structure in the molecule, which is expressed by the gelation degree. When using a latex having a cross-linked structure in the molecule, it is preferable that the latex is a hydrophobic polymer obtained from a water-dispersible latex having a weight average gelation degree of 20 to 80%. These may be used alone or in combination of two or more types. Note that water-dispersible latex is a latex in which fine particles of a rubber polymer are dispersed in water to form a stable suspension. A polymer is obtained by removing water from this water-dispersible latex.

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

The photosensitive resin composition may contain a water-soluble or hydrophilic polymer component in addition to 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 hydrophilic groups have been introduced into polyamides, partially saponified polyvinyl acetate and its derivatives, and anionic acrylic polymers.

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 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. In terms of compatibility with the synthetic rubber copolymer, it is preferable that the photopolymerizable unsaturated compound contains one having a common skeleton with the synthetic rubber copolymer. These photopolymerizable unsaturated compounds may be used alone or in combination of two or more kinds.

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 such acrylates 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.

Specific examples of ethylenically unsaturated compounds 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 unsaturated carboxylic acid, polyhydric (meth)acrylates obtained by addition reaction of unsaturated epoxy compounds such as glycidyl (meth)acrylate with carboxylic acid or amine, and polyhydric (meth)acrylamides such as methylene bis(meth)acrylamide.

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 that have the function of generating radicals by self-decomposition or hydrogen abstraction upon 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 types.

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 consist 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, organic solvents, etc. 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 bicarbonate. Examples of the organic solvent include methanol, ethanol, isopropyl alcohol, cellosolve, glycerin, ethylene glycol, polyethylene glycol, dimethylformamide, dimethylacetamide, and acetone. In addition, a defoaming agent may be added to the developer to suppress the generation of bubbles. There are no particular limitations on the defoaming agent as long as it is water-soluble, and examples of the defoaming agent that can be used include higher alcohols, fatty acid derivatives, silica, alumite, and silicone.

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 parts of the flexographic printing plate using an aqueous developer after exposure and form a relief image. The washing out of the uncured parts can be done, for example, by rubbing out the photosensitive resin composition in the uncured parts with the developer using a brush, or by rubbing out the photosensitive resin composition in the uncured parts using a combination of a spray 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 for storage. 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.

The processing method of the present invention is characterized by including a processing step A in which the used developer obtained after developing a flexographic printing plate with an aqueous developer using the developing device configured as described above is separated into a mother liquor and a solid component by a centrifuge, a processing step B in which the mother liquor obtained in 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 processing step B is returned to the developing section or the developer tank. Preferably, the permeate obtained in processing step B is returned to the rinsing section of the developing device and used for finish washing.

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 using 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 depending on the specific gravity relationship between the developing solution and the resin. The shape of the rotating part can be a cylindrical shape, a conical shape, or a truncated cone, but a cylindrical shape is preferable in terms of processing efficiency.

It is preferable that the centripetal acceleration of the centrifuge is 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 liquid that the centrifuge can process is determined by the volume inside the centrifuge, but when the developer is directly processed by connecting it to a developing machine, a centrifuge with an optimal processing amount for the amount of developer in the developing machine should be prepared. When the amount of washout liquid is 50 liters, the processing amount is preferably 2 liters or more per minute, and when the amount of washout liquid is 200 liters, the processing amount is preferably 8 liters or more per minute. In the present invention, it is possible to add a flocculant to the washout liquid before processing in order to enhance the centrifugation effect, but it is preferable not to use a flocculant in order to make it easier to reuse the washout liquid.

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

In processing step B, a membrane filter of the cross-flow filtration system is used to separate the mother liquor processed in processing step A into a permeate from which the resin components have been separated and a highly concentrated liquid in which the resin components have been concentrated. In the case of cross-flow filtration, in order to reduce the load on the filtration filter, it is preferable to send the highly concentrated liquid obtained in processing step B to a storage tank and then repeat processing step B, i.e., filtration and separation using a filtration filter. On the other hand, since the permeate obtained in processing step B contains a small amount of resin components, it can be circulated to the rinsing section before being returned 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 processing step A and, if necessary, multiple processing steps B are performed, it is also preferable to process the concentrated liquid obtained in processing step B again in processing step A in order to reduce the load on the filtration filter.

Examples of filter materials 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 module form, it is preferable to use hollow fiber or tubular types for organic membranes, and tubular or multi-lumen types for ceramic and metal membranes. Of these, ceramic membranes are particularly compatible with aqueous developers.

The mother liquor obtained in process A and the concentrated liquid obtained in process B are preferably passed through the filtration filter at a flow rate of 1 m/sec or more relative to the filtration membrane. If the flow rate is slower than this, the filtration membrane is likely to become clogged, resulting in a decrease in the filtration flow rate. A high flow rate is not particularly problematic, but it places restrictions on the selection of pumps and piping in terms of equipment design. The pressure of these liquids on the filtration membrane varies depending on the type of membrane, but is preferably 1 MPa or more. If it is lower than this, there is a risk that a sufficient permeate flow rate will not be obtained. On the other hand, a high pressure is not particularly problematic, but it may place restrictions on the selection of pumps and piping in terms of equipment design. It is common to use multiple filtration filters to increase the filtration area in order to increase the processing flow rate, but the more filters are used, the higher the cost.

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. More preferably, it is 0.1 to 1.8 μm, and even more preferably, it is 0.2 to 1.6 μm. If the pore size is less than this range, the filter is prone to clogging, and if it exceeds this range, the resin components cannot be sufficiently removed, which may result in contamination of the printing plate or brush.

The filtration filter is preferably equipped with a backwashable mechanism. If the filter becomes clogged during long-term operation, the clog can be easily removed by backwashing, making maintenance easier. Furthermore, regular backwashing allows for even longer operation. An example of a backwashable mechanism is one equipped with a pump that backflows low-concentration developer into the separation device to remove water-insoluble polymers that have accumulated on the ceramic filter. Backwashing may be automated or performed manually.

The effects of the treatment method of the present invention are shown in the following examples, but the present invention is not limited to these.

(1) Preparation of photosensitive resin composition 91 parts by mass of butadiene latex (manufactured by Nippon Zeon, LX111NF, solid content concentration 55%) as latex, 15 parts by mass of oligobutadiene acrylate (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%) manufactured by Kyoeisha Chemical Co., Ltd. as a hydrophilic polymer, 0.1 parts by mass of hydroquinone monomethyl ether as a polymerization inhibitor, 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 toluene and water were distilled off under reduced pressure to obtain a photosensitive resin composition.

(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.

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

(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 with 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.

(5) Preparation of flexographic printing original plate having photosensitive resin composition on support The above-mentioned 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. Lamination was performed 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.

<Picture Exposure Process>
Using an exposure device equipped with 30 60 W Philips 10R fluorescent lamps, the above-mentioned flexographic printing original plate having 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 original plate was set in an ESKO CDI4835, and an evaluation image pattern having 150 LPI, 10% dots and 100 μm fine lines as shown in Figure 1 was drawn on the infrared-sensitive layer.

<Developing process>
The flexographic printing plate prepared in the drawing exposure process was fixed on an adhesive plate and developed by inserting it into a 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 a developer circulated from a developing tank and dispersed in the developer. The developer used was 200 L of a 1 wt% aqueous solution of sodium oleate, and was set at 40°C. In the rinsing section, tap water was used as a running water structure or permeated water from which resin was removed using a filtration filter was used in circulation. In the drying section, hot air at 60°C was supplied. Twenty flexographic printing plates were passed through this developing machine continuously for 10 hours, and the following evaluations were performed.

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

<Measurement of Resin Removal Rate>
The weight of the printing plate before development in the development process was measured in advance, and 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 2 g was placed on aluminum foil, and vacuum dried at 80°C for 2 hours to remove water, and the weights before and after vacuum drying were measured. The developer resin concentration in the developer tank, the amount of resin in the developer tank, and the amount of resin removed were calculated in that 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) = concentration of developer resin 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

<Measurement of Water Content of Discharged Developer>
After the development process, the developer discharged was collected in a drum can and the total weight was measured to determine 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 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) x 100

<Printing plate soiling>
The surface of the last printing plate after 20 sheets were developed was visually observed to determine whether or not aggregates of the water-insoluble polymer were observed on the printing plate. If aggregates were observed, they were marked with "x", and if not, they were marked with "o".

Example 1
As a centrifuge used in the treatment process A, a centrifuge was prepared in which a nonwoven fabric was provided so as to cover the entire inner wall inside a cylindrical rotor [inner diameter R = 30 cm, height H of the cylindrical rotor = 20 cm, bottom sealed type], and the centripetal acceleration was 1000 G. As a device for filtering and separating using a cross-flow filtration method used in the treatment process B, seven elements of Noritake's MEMBRALOX, dimensions of hexagonal shape with a diagonal width of 27 mm x length of 500 mm, membrane material Al ₂ O ₃ , and membrane shape of 4φ x 19 holes were used together as a filter module of the cross-flow filtration method. A pressure of 3 MPa was applied to the module to pass the liquid at a flow rate of 100 L/min. A filter element with an average pore size of 1.4 μm was prepared. A processing system was constructed by connecting each device so that used developer from a developing device having a developing section, a rinsing section, and a developer tank could enter a centrifuge via a storage tank, mother liquor discharged from the centrifuge could enter a filtration separation device having a filtration filter via a storage tank, concentrated liquid discharged from the filtration separation device could return to the storage tank, and permeated water could return to the developing device.

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 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.

At this time, the processing speed was measured from the flow rate of the permeated water obtained in processing step B. The surface of the last printing plate after 20 sheets were developed was visually observed to evaluate the contamination of the printing plate. 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 used as the discharged developer, and the moisture content of the discharged developer was measured. The evaluation results are shown in Table 1.

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 high at 70%. As a result, the contamination of the printing plate due to resin adhesion 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 contamination 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, so that 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.

Example 2
In Example 2, the processing was carried out in the same manner as in Example 1, except that the centrifuge used in the processing step A of Example 1 was changed to a centrifuge with a centrifuge having a centrifuge acceleration of 2000 G. The evaluation results are shown in Table 1. The processing solution was able to further reduce the staining of the printing plate due to resin adhesion in the development section, since the centrifuge acceleration was set to 2000 G, and the resin component removal rate was improved. In addition, since the concentrated water was repeatedly processed in the processing step B after processing in the processing step B, the processing efficiency of the developer achieved a high processing capacity of 8.9 L/min. Furthermore, in Example 2, it was possible to supply the permeated water of the filtration filter to the rinsing section, and it was also possible to return it to the developer tank together with the rinsing of the printing plate as a circulation process. As a result, the water content of the discharged developer was able to be reduced to 74%.

Example 3
Example 3 was treated in the same manner as Example 1, except that the average pore size 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 was slightly decreased, a high resin removal rate of 71% was achieved. Due to the high resin component removal rate, it was possible to further reduce staining of the printing plate due to resin adhesion in the development section. Furthermore, it was possible to wash the printing plate by supplying the permeated water of the filtration filter to the rinsing section. In addition, it was possible to reduce the moisture content of the discharged developer to 78%.

Example 4
In Example 4, the processing step A was additionally performed after the same processing as in Example 1. As a result, the concentration in the storage tank was reduced and the developer could be reused without being discarded, so the water content of the discharged developer was measured using only the developer in the centrifuge as the discharged developer. The evaluation results are shown in Table 1. In Example 4, the concentrated water separated in the processing step B was fed again to the centrifuge in the processing step A to remove the resin components, so that the load on the filtration filter was reduced and the filter life was significantly improved. Furthermore, by removing the resin components in the developer, the staining of the printing plate due to the resin adhesion in the development section was 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 high at 85%.

<Comparative Example 1>
In Comparative Example 1, the developer was processed using only the centrifuge in Processing Step A, without using the filtration filter in Processing Step B. Other than that, the procedure was the same 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, which caused contamination of the printing plate.

<Comparative Example 2>
In Comparative Example 2, the developer was processed only with the filtration filter in processing step B without using the centrifuge in processing step A. Other than that, the same procedure was carried out as in Example 1. The evaluation results are shown in Table 1. In Comparative Example 2, the water content of the discharged developer could not be reduced because the solid components were not concentrated by the centrifuge. In addition, because the developer was processed only with the filtration filter, the filter was clogged, requiring frequent filter replacement, and the workability was poor.

The processing method of the present invention allows efficient separation and removal of resin components from the aqueous developer used to develop flexographic printing plates, and allows the used developer to be reused, significantly reducing the amount of water used for development and the amount of waste liquid.

Claims (3)

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. The processing method according to claim 1, characterized in that the developing device 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 the developer tank. 3. The method according to claim 1 , wherein the centrifuge centrifuges the filtrate at a centripetal acceleration of 200 to 4000 G.