Method for manufacturing a regenerating developer, and method for manufacturing a flexographic printing plate using the same.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Patents
- Current Assignee / Owner
- TOYOBO MC CORP
- Filing Date
- 2022-03-07
- Publication Date
- 2026-07-31
Smart Images
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Abstract
Description
Technical Field
[0001] The present invention relates to a method for producing a regenerated developer from a developer waste liquid generated by developing a water-developable flexographic printing original plate, and a method for producing a flexographic printing plate using the regenerated developer as a developer.
Background Art
[0002] A flexographic printing original plate generally has a structure in which a photosensitive resin layer formed from a photosensitive resin composition is provided on a support. Plate making of such a flexographic printing original plate is performed, for example, by selectively exposing the photosensitive resin layer with ultraviolet rays and developing the exposed photosensitive resin layer with an aqueous developer. By development, the photosensitive resin composition in the unexposed portion of the photosensitive resin layer is removed from the printing plate and dispersed or dissolved in the developer. When the development of the photosensitive resin layer is repeated using the same developer, the concentration of the photosensitive resin composition dispersed in the developer increases, the development rate decreases, or the dispersed photosensitive resin composition aggregates to form resin aggregates. These resin aggregates redeposit on the surface of the printing plate, deteriorating the quality of the plate surface. Therefore, it becomes necessary to discard the developer in which the concentration of the photosensitive resin composition has increased and replace it with a new developer to resume plate making. However, repeatedly discarding the used developer and replacing it with a new developer is not preferable from the viewpoints of environmental load and manufacturing cost. Therefore, attempts have been made to remove and reuse the photosensitive resin composition from the used developer.
[0003] Patent Document 1 discloses a method of aggregating the resin component dispersed in the developer with a flocculant and separating the aggregated resin solid content. However, the flocculant is expensive, and the use of the flocculant is not preferable from the cost viewpoint. Furthermore, the developer to which the flocculant is added has a fundamental problem that it cannot be reused as a developer because the development rate is significantly reduced.
[0004] Furthermore, Patent Document 2 discloses a method for reusing a developer by agglomerating a photosensitive resin composition using a special dedicated dispersion filter, and then filtering the aggregates with another aggregate filter. However, this method requires the use of a special dedicated dispersion filter and an aggregate filter, which necessitates the cumbersome task of maintaining both filters.
[0005] Furthermore, Patent Document 3 discloses a method for producing a regenerated developer by removing undissolved resin components from the developer waste solution by treating it with a ceramic filter. However, even with this method, it is necessary to frequently backwash the filter to prevent clogging, resulting in a heavy maintenance burden. [Prior art documents] [Patent Documents]
[0006] [Patent Document 1] Japanese Patent Application Publication No. 06-194824 [Patent Document 2] Japanese Patent Publication No. 2011-232407 [Patent Document 3] International Publication No. 2018 / 061958 [Overview of the project] [Problems that the invention aims to solve]
[0007] The present invention was devised to solve the problems of the prior art described above, and its purpose is to provide a method for easily producing a regenerated developer by agglomerating and separating the photosensitive resin composition dispersed in the developing waste liquid of a water-developable flexographic printing plate without requiring special pretreatment or frequent maintenance of the equipment, and a method for producing a flexographic printing plate using the regenerated developer as the developer. [Means for solving the problem]
[0008] As a result of diligent research to achieve the above objective, the inventors of the present invention have discovered that by allowing the developing waste liquid to stand in a tank for a long period of time, the photosensitive resin composition dispersed in the developing waste liquid floats and aggregates due to the difference in specific gravity, forming a solid-liquid mixed phase containing resin aggregates below the liquid surface of the developing waste liquid, and then discharging this solid-liquid mixed phase from an outlet installed on the upper side of the tank, and using the liquid remaining in the tank as the regenerated developing liquid, a regenerated developing liquid with a low solid content concentration can be obtained with a high recovery rate in a simple manner, thus completing the present invention.
[0009] In other words, the present invention has the following configurations (1) to (12). (1) A method for producing a recycled developer from developing waste liquid generated by developing a water-developable flexographic printing plate having a photosensitive resin layer made of a photosensitive resin composition containing a water-dispersible resin, The method described above is A step of allowing the developing waste liquid to stand in a tank, causing the photosensitive resin composition dispersed in the developing waste liquid to float and aggregate, thereby forming a solid-liquid mixed phase containing resin aggregates below the liquid surface of the developing waste liquid, and A process in which the solid-liquid mixed phase containing resin aggregates is discharged from an outlet installed on the side of the tank, and the liquid remaining in the tank is obtained as a regenerating developer. Includes, The liquid level of the developing waste liquid in the tank at the start of the discharge is higher than the height of the lowest point of the opening of the discharge port. A method characterized by the following. (2) The method according to (1), characterized in that the liquid level of the developing waste liquid in the tank at the start of discharge is 3% or more of the depth of the tank than the height of the lowest position of the opening of the discharge port. (3) The method according to (1), characterized in that, when the liquid level of the developing waste liquid in the tank at the start of discharge is 53% or more of the depth of the tank, the height is 3% or more of the depth of the tank than the height of the lowest position of the opening of the discharge port. (4) The method according to any one of (1) to (3), characterized in that the liquid level of the developing waste liquid in the tank at the start of discharge is higher than the lowest position of the opening of the discharge port by a height of 30% or less of the depth of the tank. (5) The method according to any one of (1) to (4), characterized in that, if the level of the developing waste liquid in the tank after the standing period is less than or equal to the height of the lowest position of the outlet opening, water or developing liquid is transferred to the tank before discharge to raise the level of the developing waste liquid in the tank above the height of the lowest position of the outlet opening. (6) The method according to any one of (1) to (5), further comprising the step of transferring the developing waste liquid from the developing tank to the tank before the developing waste liquid is allowed to stand in the tank. (7) The method according to any one of (1) to (6), characterized in that the lowest position of the opening of the discharge port is at a height of 50% or more of the depth of the tank. (8) The method according to any one of (1) to (7), characterized in that the lowest position of the opening of the discharge port is at a height of 55 to 90% of the depth of the tank. (9) The method according to any one of (1) to (8), characterized in that the tank has the shape of a substantially rectangular parallelepiped, a substantially cubic, or a substantially cylindrical shape. (10) The method according to (9), characterized in that, when the tank has a substantially rectangular parallelepiped or substantially cubic shape, the maximum width of the opening of the discharge port is 50% or more of the maximum width of the tank. (11) The method according to any one of (1) to (10), characterized in that the solid content concentration of the regenerating developer is 3.5% by mass or less. A method for producing a water-developable flexographic printing plate, characterized in that a regenerated developer obtained by the method described in any one of (1) to (11) is used as a developer. [Effects of the Invention]
[0010] According to the method of the present invention, a regenerated developer with a low solid content concentration can be produced with a high recovery rate by a simple method without requiring special pretreatment for aggregating the photosensitive resin composition or frequent maintenance of the apparatus.
Brief Description of the Drawings
[0011] [Figure 1] An example of a developing apparatus for a water-developable flexographic printing original plate used in the method of the present invention is shown. [Figure 2] An example of the shape of a discharge port installed on the side surface of a tank used in the method of the present invention is shown. [Figure 3] Another example of the shape of a discharge port installed on the side surface of a tank used in the method of the present invention is shown. [Figure 4] An example of a state where the lid of the discharge port installed on the side surface of a tank used in the method of the present invention is closed is shown. [Figure 5] An example of a state where the lid of the discharge port installed on the side surface of a tank used in the method of the present invention is open is shown.
Embodiments for Carrying Out the Invention
[0012] A method for producing a regenerated developer from the developing waste liquid of a water-developable flexographic printing original plate of the present invention, and a method for producing a water-developable flexographic printing plate using the regenerated developer as a developer will be described in detail below.
[0013] First, an example of a developing apparatus for a water-developable flexographic printing original plate used in the method of the present invention is shown in FIG. 1. In FIG. 1, 1 is a developing tank, where a developer 2 used for developing the flexographic printing original plate is stored. 3 is a pipe, and the developer with an increased concentration of the photosensitive resin composition due to repeated development is transferred as developing waste liquid from the developing tank 1 to a settling tank 4 through this pipe 3. FIG. 1 shows the state after the developing waste liquid has been settled in the settling tank 4. Resin aggregates 5 float and gather at the upper part, forming a solid-liquid mixed phase containing resin aggregates below the liquid level of the developing waste liquid. 6 is a discharge port installed on the side of the settling tank 4, and the solid-liquid mixed phase containing resin aggregates 5 is discharged from this discharge port 6 to a resin aggregate recovery tank 7. 8 is a pump, and the regenerated developer from which resin aggregates 5 have been removed and the solid content concentration has decreased is returned to the developing tank 1 by this pump 8 through a pipe 9.
[0014] Note that in FIG. 1, a settling tank is provided as a tank, and the mode of transferring the developing waste liquid from the developing tank to the settling tank has been described. Thus, by providing the settling tank separately from the developing tank, the next development can be carried out while the settling is in progress, and there is also an advantage that resin components separated by settling do not accumulate on brushes or the like immersed in the liquid of the developing tank, for example. However, the present invention is not limited to such a mode. For example, the developing tank may have the same configuration as the settling tank, and the same process as that performed in the settling tank may be performed in the developing tank. In the present invention, the settling tank or such a developing tank can be used as a tank for settling the developing waste liquid when producing the regenerated developer from the developer.
[0015] In the method for producing the regenerated developer of the present invention, the developing waste liquid used as a raw material is generated by developing a water-developable flexographic printing original plate. Therefore, first, the configuration and development of the water-developable flexographic printing original plate and the generation of the developing waste liquid therefrom will be described.
[0016] A water-developable flexographic printing plate has a basic structure in which a photosensitive resin layer, made of a photosensitive resin composition containing a water-dispersible resin, is provided on a support. In addition to the water-dispersible resin, the photosensitive resin composition contains a photopolymerizable monomer and a photopolymerization initiator.
[0017] Examples of water-dispersible resins include styrene-based, olefin-based, polyester-based, polyurethane-based, 1,2-polybutadiene-based, vinyl chloride-based, and polyamide-based resins. Particularly preferred water-dispersible resins are latex with a total weight-average gelation degree of 30% or more. The latex may consist of a single type of latex or a mixture of multiple types of latex. For example, polybutadiene latex, polystyrene-butadiene copolymer latex, polyacrylonitrile-butadiene copolymer latex, and methyl methacrylate-butadiene copolymer latex can be used. Among these, polybutadiene latex and acrylonitrile-butadiene copolymer are preferred. The latex preferably has a total weight-average gelation degree of 30% or more, and more preferably 50% or more. Using latex with a gelation degree in this range makes flotation and aggregation more likely.
[0018] Water-dispersible resins are the main components of the photosensitive resin layer. Therefore, the photosensitive resin composition dispersed in used developer contains a large amount of water-dispersible resin derived from the components of the photosensitive resin layer in the unexposed portion of the flexographic printing plate. These water-dispersible resins have a lower specific gravity than water. Therefore, as described later, they can float to the surface and be easily separated from the remaining aqueous developer by standing still.
[0019] The photopolymerizable monomer can be any monomer that can crosslink the above-mentioned water-dispersible resin and has good compatibility with the water-dispersible resin; it is not particularly limited. Specifically, it can be acrylic acid esters, acrylamides, methacrylic acid esters, methacrylamides, allyl compounds, vinyl ethers, vinyl esters, styrenes, and crotonic acid esters, and is selected from compounds having an addition-polymerizable unsaturated bond. The above compounds may be used individually or in combination of two or more. Furthermore, the amount blended is preferably 3 parts by mass or more and 80 parts by mass, and more preferably 5 parts by mass or more and 20 parts by mass, per 100 parts by mass of the above-mentioned water-dispersible resin.
[0020] The photosensitive resin layer may contain a plasticizer to impart flexibility. Any known compound can be selected as the plasticizer, but those that are liquid and have a specific gravity of less than 1.0 are particularly preferred from the viewpoint of resin levitation. Specifically, these include butadiene, styrene-butadiene copolymers, and polyacrylonitrile-butadiene copolymers.
[0021] As the photopolymerization initiator, any known compound commonly used in photosensitive resin compositions can be arbitrarily selected, but benzoin-based, phenone-based, and anthraquinone-based compounds are particularly preferred. Specifically, examples of benzoin-based photopolymerization initiators include benzoin, benzoin methyl ether, benzoin ethyl ether, benzoin-n-propyl ether, α-methylbenzoin, α-ethylbenzoin, α-phenylbenzoin, and α-allylbenzoin; examples of phenone-based photopolymerization initiators include benzophenone, ω-bromoacetophenone, and acetophenone; and examples of anthraquinone-based photopolymerization initiators include anthraquinone, chloroanthraquinone, methylanthraquinone, and ethylanthraquinone. These photopolymerization initiators may be used individually or in combination of two or more. The amount of photopolymerization initiator blended is preferably 0.1 parts by mass to 5 parts by mass, and more preferably 0.5 parts by mass to 2.0 parts by mass, per 100 parts by mass of the water-dispersible resin.
[0022] The photosensitive resin layer can be improved by adding dyes, pigments, polymerization inhibitors, antioxidants, and photodegradation inhibitors as needed. Furthermore, to improve abrasion resistance, resins compatible with water-dispersible resins, such as polyamide resins, epoxy resins, and polyurethane resins, can be blended in.
[0023] The developer used for developing water-developable flexographic printing plates is an aqueous developer mainly composed of water, and more preferably contains water, an alkaline compound such as sodium hydroxide or sodium carbonate, and a surfactant. The alkaline compound is added to bring the pH of the developer to the alkaline range (preferably 8.0 to 11.0). The surfactant is added to promote the dispersion of the photosensitive resin in water and to maintain the dispersion state. The concentration of the surfactant in the developer is 0.5 to 10% by mass. The developer may also contain organic solvents, etc., as long as they do not reduce the solubility of the alkaline compound or surfactant. The developer is preferably used at a temperature of 25°C to 50°C, and particularly preferably at 35°C to 45°C.
[0024] Suitable surfactants include sodium alkylnaphthalene sulfonate and sodium alkylbenzene sulfonate. Other usable surfactants include anionic surfactants containing carboxylates, sulfates, sulfonates, and phosphates; nonionic surfactants containing polyethylene glycol chains, polyhydric alcohol derivatives, and sorbitan derivatives; cationic surfactants containing primary to tertiary amine salts and quaternary ammonium salts; and amphoteric surfactants containing amino acid-type and betaine-type hydrophilic groups.
[0025] The method for developing a flexographic printing plate is not particularly limited as long as it is a method that can wash away the photosensitive resin composition in the un-photocured areas of the printing plate using an aqueous developer and form a relief image. For example, methods include rubbing with a brush using the developer, and methods that combine spraying and brushing to rub away the photosensitive composition in the un-photocured areas. For such a brush, the diameter of the brush filaments, the diameter of the bristle holes, and the pitch spacing of the bristle holes can be appropriately selected. Specifically, a bristle hole pitch spacing of 6 to 10 mm, a bristle bristle hole diameter of 5 to 8 mm, and a filament diameter of 160 to 200 μm are preferred. Generally, the developer is repeatedly used in the above-mentioned development method until the concentration of the photosensitive resin composition exceeds a certain level and the development speed decreases, after which it is referred to as developing waste liquid. The present invention is a method for producing a recycled developer from the developing waste liquid thus generated. This method will be described in detail below.
[0026] In the method of the present invention, the developing waste liquid is left to stand in tank 4. A high concentration of photosensitive resin composition is dispersed in the developing waste liquid. Since this photosensitive resin composition mainly consists of water-dispersible resin, its specific gravity is less than 1.0, which is lighter than water, the main component of the aqueous developer used for developing water-developable flexographic printing plates. Therefore, when left to stand, the photosensitive resin composition dispersed in the developing waste liquid floats to the surface due to the difference in specific gravity and moves spatially closer to each other. The photosensitive resin composition that had already partially aggregated in the developing waste liquid then aggregates further to form resin aggregates 5. As a result, in tank 4, as shown in Figure 1, a separated state is achieved in which the resin aggregates 5 are located just below the liquid surface of the developing waste liquid, and the other components constituting the developing waste liquid (aqueous developer mainly composed of water) are located below them. It should be noted that the resin aggregates 5 located just below the liquid surface of the developing waste liquid do not actually exist as resin aggregates 5 alone, but rather as a solid-liquid mixed phase in which the resin aggregates 5 and the aqueous developing solution are mixed. Tank 4 has an outlet 6 on its side for discharging the resin aggregates 5. In this invention, by discharging the solid-liquid mixed phase containing the resin aggregates 5 formed below the liquid surface of the developing waste liquid from the outlet 6 of Tank 4, the resin aggregates 5 can be efficiently removed, and a regenerated developing solution with a low solid content concentration can be obtained with a high recovery rate.
[0027] When allowing developing waste liquid to stand in a tank, it is important to leave it still for a certain period of time without stirring or other disturbances. The standing time is preferably 5 hours or more, and more preferably 8 hours or more. There is no particular upper limit to the standing time, but 24 hours is sufficient. By allowing sufficient standing time in this way, most of the photosensitive resin composition dispersed in the developing waste liquid will float and aggregate, and a solid-liquid mixed phase containing resin aggregates can be reliably formed below the liquid surface of the developing waste liquid.
[0028] The tank shape is preferably a roughly rectangular prism, a roughly cubic shape, or a roughly cylindrical shape, with a roughly rectangular prism or a roughly cylindrical shape being preferred because they have a larger surface area ratio. A roughly rectangular prism is particularly preferred because it allows for effective use of space within the device and facilitates discharge from the outlet.
[0029] The discharge port located on the side of the tank is preferably approximately circular, approximately square, approximately rectangular, or slit-shaped, and among these, a rectangle with its longitudinal direction in the width direction of the tank is particularly preferred in terms of ease of separation, as shown in Figure 2. Also, as shown in Figure 3, there may be multiple slit shapes in the height direction. The height of the discharge port is preferably 1 cm to 10 cm, and more preferably 4 cm to 8 cm. If it is smaller, resin aggregates are more likely to clog the discharge port, and if it is larger, the drainage capacity will increase and the recovery rate may decrease. Furthermore, if the tank has the shape of an approximately rectangular parallelepiped or approximately cube, the maximum width of the discharge port opening is preferably 50% or more of the maximum width of the tank, and more preferably 85% or more. Note that if the tank has the shape of an approximately rectangular parallelepiped or approximately cube, the maximum width of the tank refers to the larger of the depth and the width. Furthermore, if the tank has the shape of an approximately cylindrical shape, the circumferential length of the discharge port is preferably 1 / 8 or more of the circumference of the cross-sectional shape of the tank in the horizontal plane. By setting the maximum width and circumferential length of the discharge port opening as described above, discharge can be made smoother.
[0030] It is preferable that the discharge port located on the side of the tank is provided with an openable and closable lid, as shown in Figures 4 and 5. When the liquid level of the developing waste liquid is above the discharge port, the resin aggregates 5 floating just below the liquid level of the developing waste liquid can be easily separated and discharged by opening the lid from a closed position. The structure of the lid may be shaped to match the discharge port, or it may be a plate-like structure that slides. The lid can be opened and closed manually or electrically.
[0031] The tank's outlet is located on the side of the tank. By placing it on the side, resin aggregates floating just below the liquid surface of the developing waste liquid can be easily separated. Preferably, the lowest point of the outlet opening is at a height of 50% or more of the tank's depth, and more preferably at a height of 55-90% of the tank's depth. If it is located at a height of less than 50%, the difference in height between the outlet and the liquid surface of the developing waste liquid becomes too large, increasing the drainage volume, causing the resin aggregates floating just below the liquid surface of the developing waste liquid to break down and increasing the solid content concentration in the regenerated developing solution.
[0032] In the method of the present invention, two discharge methods are employed depending on the relationship between the liquid level of the developing waste liquid after standing and the position of the discharge port. First, if the liquid level of the developing waste liquid in the tank after standing is higher than the lowest position of the discharge port opening, the discharge port can be opened to separate and discharge the resin aggregates floating just below the liquid level of the developing waste liquid from the discharge port. Preferably, the liquid level of the developing waste liquid in the tank at the start of discharge is 3% or more, more preferably 5% or more, and even more preferably 7% or more, than the lowest position of the discharge port opening. If this height difference is less than the lower limit, there is a risk that the resin aggregates floating just below the liquid level of the developing waste liquid will not be sufficiently discharged and will remain in the tank. Furthermore, the upper limit of this height difference is preferably 30% or less, more preferably 20% or less, and even more preferably 15% or less. If this height difference exceeds the above upper limit, the wastewater volume will increase, potentially causing the resin aggregates floating just below the liquid surface of the developing waste liquid to break down and increasing the solid content concentration in the regenerated developing solution.
[0033] If the lowest point of the outlet opening is at a height of 50% or more of the tank depth, and the liquid level of the developing waste liquid in the tank at the start of discharge is at least 3% of the tank depth higher than the lowest point of the outlet opening, then the tank depth is such that, for example, the liquid level of the developing waste liquid in the tank at the start of discharge is at least 53% of the tank depth. In such a case, for example, the explanation above regarding the preferred range of liquid level of the developing waste liquid in the tank at the start of discharge still holds true.
[0034] On the other hand, if the liquid level of the developer waste in the tank after standing is below the height of the lowest point of the outlet opening, it cannot be discharged as is. In this case, standing allows the photosensitive resin composition dispersed in the developer waste to float and aggregate, forming a solid-liquid mixed phase containing resin aggregates below the liquid level of the developer waste. Then, water or developer is transferred to the tank to raise the liquid level above the outlet. By opening the outlet in this state, the resin aggregates floating just below the liquid level of the developer waste can be separated and discharged from the outlet. When transferring water, it is desirable to add surfactants or pH adjusters, as this may dilute the regenerated developer and reduce the development speed. In this case as well, the same conditions apply to the liquid level of the developer waste in the tank at the start of discharge as when the liquid level of the developer waste in the tank after standing is higher than the lowest point of the outlet opening.
[0035] In either case, when opening the outlet from the tank to discharge the resin aggregates floating just below the surface of the developing waste liquid, water may be injected towards the outlet from a nozzle installed on the wall opposite the outlet to wash away the resin aggregates. Alternatively, the resin aggregates floating just below the surface of the developing waste liquid may be sucked out from the outlet. Possible methods of suction include using a pump from the piping connected to the outlet or using a wet / dry vacuum cleaner. Discharge becomes faster and more efficient by either washing it away or using suction.
[0036] The developing waste liquid used as a raw material for manufacturing the regenerated developing solution preferably has a solid content concentration of 5.0% by mass or more, and more preferably 6.0% by mass or more, in terms of the ease with which resin aggregates are formed. This solid content is mainly a photosensitive resin composition dispersed in the developing waste liquid.
[0037] When a separate tank is provided for storing developing waste liquid, the solid-liquid mixed phase containing resin aggregates can be separated and discharged from the tank. The liquid remaining in the tank can then be reused as regenerated developer, either directly or indirectly, by returning it to the developing tank. Indirectly, for example, a separate tank for regenerated developer can be provided to temporarily store the regenerated developer, which can then be returned to the developing device as needed. Directly, the regenerated developer can be returned to the developing or rinsing section of the developing machine.
[0038] The regenerated developer produced by the method of the present invention has a low solid content concentration of 3.5% by mass or less, preferably 3.0% by mass or less, because resin condensates are efficiently removed, and sufficient developability can be maintained. This solid content is mainly a photosensitive resin composition dispersed in the regenerated developer. Therefore, the regenerated developer obtained by the method of the present invention can be used without any problems as a substitute for ordinary developers in the manufacture of water-developable flexographic printing plates. In addition, since the resin solid content in the regenerated developer can be reduced to a very low level in the method of the present invention, it is not particularly necessary to separate resin condensates with a filter. However, if it is desired to obtain a regenerated developer with a lower resin solid content more stably in continuous operation, it may be combined with filtration using a simple filter such as a nonwoven fabric. [Examples]
[0039] The effects of the method for producing the regenerating developer of the present invention are shown in the following examples, but the present invention is not limited to these examples. Examples 1 to 8 are provided to illustrate particularly preferred methods of the present invention. Furthermore, the measurements and performance evaluations in the examples and comparative examples were carried out according to the following procedure.
[0040] <Solid content concentration in developing waste liquid> Ten grams of developer waste liquid, from which resin aggregates had been removed, was placed in a petri dish and subjected to vacuum drying. The non-volatile content after drying was expressed as mass %, and this value was defined as the solid content concentration in the developer waste liquid.
[0041] <Solid content concentration in regenerating developer> Ten grams of the regenerated developer solution, from which resin aggregates had been removed, was placed in a petri dish and subjected to vacuum drying. The non-volatile content after drying was expressed as mass%, and this value was defined as the solid content concentration in the regenerated developer solution.
[0042] <Recovery rate of regenerated developer> After the solid-liquid mixture containing resin aggregates was discharged from the outlet, the liquid remaining in the standing tank was collected, its volume was measured, and the percentage relative to the volume of the developing waste liquid initially transferred to the standing tank was calculated. This value was defined as the recovery rate of the regenerated developing solution. In Example 2, after the solid-liquid mixed phase containing resin aggregates was discharged from the outlet, the liquid remaining in the standing tank was recovered, its volume was measured, and the percentage relative to the volume of the developing waste liquid immediately before the discharge of the solid-liquid mixed phase was calculated. This value was defined as the recovery rate of the regenerated developing solution. In Comparative Example 1, after the resin aggregates were discharged by overflow, the liquid remaining in the standing tank was recovered, its volume was measured, and the percentage relative to the volume of the developing waste liquid initially transferred to the standing tank was calculated. This value was defined as the recovery rate of the regenerated developing liquid. For Comparative Example 2, the volume of liquid extracted from the outlet installed at the bottom of the standing tank was measured, and the percentage of this volume relative to the volume of the developing waste liquid initially transferred to the standing tank was calculated. This value was defined as the recovery rate of the regenerated developing solution. For Comparative Example 3, after the resin aggregates were scooped up and collected with a ladle, the liquid remaining in the standing tank was collected, its volume was measured, and the percentage relative to the volume of the developing waste liquid initially transferred to the standing tank was calculated. This value was defined as the recovery rate of the regenerated developing solution.
[0043] <Development speed> Development was performed using the regenerated developer prepared in each example and comparative example, and the distance that the printing plate could be washed in the depth direction in one minute was measured and evaluated according to the following criteria. ○: 0.05 mm / min or more △: 0.03 mm / min or more, less than 0.05 mm / min ×: Less than 0.03 mm / min
[0044] <Image Reproducibility> Development was performed using the regenerated developer prepared in each example and comparative example, and the diameter of the smallest independent point reproduced on the developed printing plate was measured and evaluated according to the following criteria. ○: Successfully reproduces a diameter of 200 μm. △: Successfully reproduces a diameter of 300 μm. ×: Failed to reproduce a diameter of 400 μm.
[0045] <Presence or absence of resin adhesion to the surface of the printing plate> Development was carried out using the regenerated developer prepared in each example and comparative example, and the presence or absence of resin aggregates adhering to the surface of the resulting printing plate was visually determined and evaluated according to the following criteria. ○: No adhesion to the printing surface ×: Adhesion present on the printing surface.
[0046] Example 1 The latex consists of 73 parts by mass of butadiene latex (manufactured by Nippon Zeon, LX111NF, solid content concentration 55%) and acrylonitrile-butadiene latex (manufactured by Nippon Zeon, SX1503A 24 parts by mass of (solids content 42%), 15 parts by mass of oligobutadiene acrylate (ABU-3, manufactured by Kyoeisha Chemical Co., Ltd., number average molecular weight 2700) as a photopolymerizable compound, 10 parts by mass of lauryl methacrylate, 10 parts by mass of trimethylolpropane trimethacrylate, 1 part by mass of benzyldimethyl ketal as a photopolymerization initiator, 20 parts by mass of PFT-3 (a polymer with a urethane urea structure and a number average molecular weight of approximately 20,000, solids content 25%) manufactured by Kyoeisha Chemical Co., Ltd., as a hydrophilic polymer, 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. The mixture was then kneaded at 105°C using a pressurized kneader, and the toluene and water were subsequently removed by vacuum distillation to prepare a photosensitive resin composition. Next, an A2 size water-developable flexographic printing plate having a photosensitive resin layer made from this photosensitive resin composition was prepared and exposed (image area ratio 50%). Using a flexographic printing plate after exposure, development was repeatedly performed under the following conditions to obtain a developed waste liquid with a solid content of 7.5% by mass. This flexographic printing plate had a photosensitive resin layer made of a photosensitive resin composition containing polybutadiene latex and polyacrylonitrile-butadiene copolymer latex (weight-average gelation degree 80%) as a water-dispersible resin. <Developing equipment> The developing apparatus used had the structure shown in Figure 1. <Developer> For the developing solution, 0.46 kg of laundry soap (manufactured by the Japan Consumers' Co-operative Union; ingredients: sodium fatty acid, potassium fatty acid) was dissolved in 45 liters of tap water, and this solution was heated to a developing solution temperature of 40°C before use. <Developing Brush> For the developing brush, a support plate made of 10 mm thick PVC resin plywood was used, with nylon brushes with a diameter of 150 μm embedded in it under the following conditions. Hair bundle implantation hole diameter: 20mm Hair bundle implantation density: 120 hairs / hole
[0047] Next, the obtained developed waste liquid was transferred from the developing tank 1 to the standing tank 4 and left to stand in the standing tank 4 for 5 hours. This allowed the photosensitive resin composition dispersed in the developed waste liquid to float and aggregate, forming a solid-liquid mixed phase containing resin aggregates 5 below the liquid surface of the developed waste liquid. The volume of the developed waste liquid transferred to the standing tank 4 was 45 liters, and the liquid level of the developed waste liquid in the standing tank 4 immediately after the transfer was 75% of the depth of the standing tank 4.
[0048] The stationary tank 4 is a roughly rectangular parallelepiped with dimensions of 43 cm wide x 76 cm deep x 19 cm high, and a rectangular outlet 6 with dimensions of 5 cm high x 70 cm long is installed on one side, as shown in Figure 2. The outlet 6 is positioned such that the lowest point of its rectangular opening is at 70% of the depth of the stationary tank 4. The outlet 6 has a lid, the top of which is fixed to the wall by a fixed shaft, and the lid can be opened and closed around the fixed shaft, as shown in Figures 4 and 5.
[0049] After standing, the solid-liquid mixed phase containing resin aggregates 5 was discharged from outlet 6 by opening the lid of outlet 6 and collected in resin aggregate recovery tank 7. Subsequently, the liquid remaining in the standing tank 4 was recovered as regenerated developer. The amount of regenerated developer recovered was 35 liters, with a recovery rate of 78%. This regenerated developer contained a small amount of resin aggregates, but the solid content concentration excluding the resin aggregates had decreased to 3.0% by mass. Using this regenerated developer, the development speed, image reproducibility, and the presence or absence of resin adhesion to the printing plate surface were evaluated. The evaluation results are shown in Table 1.
[0050] Example 2 Except for changing the position of the outlet 6 on one side of the standing tank 4 so that the lowest point of the rectangular opening of the outlet is at a height of 85% of the depth of the standing tank 4, the developing waste liquid was allowed to stand in the same manner as in Example 1. In this case, immediately after transferring the developing waste liquid to the standing tank 4, the liquid level of the developing waste liquid in the standing tank 4 was below the height of the lowest point of the outlet opening, making it impossible to discharge the solid-liquid mixed phase from the outlet. Therefore, before discharging the solid-liquid mixed phase from the outlet, 6 liters of water were transferred to the standing tank 4 from the side opposite to the side where the outlet is located to raise the liquid level of the developing waste liquid in the standing tank 4 to above the height of the lowest point of the outlet opening. After that, the solid-liquid mixed phase was discharged in the same manner as in Example 1, and the regenerated developing solution was recovered. The amount of regenerated developing solution recovered was 44 liters, and the recovery rate was 98%. This regenerated developer contained a small amount of resin aggregates, but the solid content concentration excluding the resin aggregates had decreased to 2.7% by mass. Using this regenerated developer, the development speed, image reproducibility, and the presence or absence of resin adhesion to the printing plate surface were evaluated. The evaluation results are shown in Table 1.
[0051] Example 3 Except for changing the shape of the discharge port 6 installed on one side of the standing tank 4 from a rectangular shape with dimensions of 5 cm high x 70 cm long to a slit shape consisting of three rectangles, each with dimensions of 1.5 cm high x 70 cm long, as shown in Figure 3, and setting the height of the lowest point of each of the three rectangles to be at 72%, 65%, and 58% of the depth of the standing tank 4, the developing waste liquid was allowed to stand in the same manner as in Example 1, the solid-liquid mixed phase was discharged, and the regenerated developer was recovered. The recovered regenerated developer amounted to 33 liters, with a recovery rate of 73%. This regenerated developer contained a small amount of resin aggregates, but the solid content concentration excluding the resin aggregates had decreased to 3.0% by mass. Using this regenerated developer, the development speed, image reproducibility, and the presence or absence of resin adhesion to the printing plate surface were evaluated. The evaluation results are shown in Table 1.
[0052] Example 4 Except for changing the position of the outlet 6 on one side of the standing tank 4 so that the lowest point of the rectangular opening of the outlet is at a height of 60% of the depth of the standing tank 4, the developing waste liquid was allowed to stand in the same manner as in Example 1, the solid-liquid mixed phase was discharged, and the regenerated developer was recovered. The recovered amount of regenerated developer was 29 liters, and the recovery rate was 64%. This regenerated developer contained a small amount of resin aggregates, but the solid content concentration excluding the resin aggregates had decreased to 3.0% by mass. Using this regenerated developer, the development speed, image reproducibility, and the presence or absence of resin adhesion to the printing plate surface were evaluated. The evaluation results are shown in Table 1.
[0053] Example 5 Except for reducing the number of development cycles and lowering the solid content concentration of the waste developer transferred to the standing tank 4 from 7.5% by mass to 4.0% by mass, the waste developer was allowed to stand, the solid-liquid mixed phase was discharged, and the regenerated developer was recovered in the same manner as in Example 1. The recovered amount of regenerated developer was 35 liters, and the recovery rate was 77%. This regenerated developer contained a small amount of resin aggregates, but the solid content concentration excluding the resin aggregates had decreased to 3.0% by mass. Using this regenerated developer, the development speed, image reproducibility, and the presence or absence of resin adhesion to the printing plate surface were evaluated. The evaluation results are shown in Table 1.
[0054] Example 6 The stationary tank 4 was changed to a roughly cubic shape with dimensions of 39 cm wide x 39 cm deep x 39 cm high. A rectangular outlet 6 with dimensions of 5 cm high x 36 cm long, as shown in Figure 2, was installed on one side of the tank. The outlet 6 was positioned so that the lowest point of the rectangular opening of the outlet was at 65% of the depth of the stationary tank 4. Except for these changes, the developing waste liquid was allowed to stand, the solid-liquid mixed phase was discharged, and the regenerated developer was recovered in the same manner as in Example 1. The recovered regenerated developer amounted to 38 liters, with a recovery rate of 84%. This regenerated developer contained a small amount of resin aggregates, but the solid content concentration excluding the resin aggregates had decreased to 3.0% by mass. Using this regenerated developer, the development speed, image reproducibility, and the presence or absence of resin adhesion to the printing plate surface were evaluated. The evaluation results are shown in Table 1. The volume of the approximately cubic-shaped stationary tank 4 used in Example 6 is approximately the same as the volume of the approximately rectangular stationary tank 4 used in Example 1.
[0055] Example 7 The standing tank 4 was changed to a roughly cylindrical shape with dimensions of 66 cm in diameter and 19 cm in height. A rectangular outlet 6 with dimensions of 5 cm in height and 70 cm in circumference, as shown in Figure 2, was installed on one side of the tank. The outlet 6 was positioned so that the lowest point of the rectangular opening of the outlet was at 70% of the depth of the standing tank 4. Except for these changes, the developing waste liquid was allowed to stand, the solid-liquid mixed phase was discharged, and the regenerated developer was recovered in the same manner as in Example 1. The recovered regenerated developer amounted to 35 liters, with a recovery rate of 78%. This regenerated developer contained a small amount of resin aggregates, but the solid content concentration excluding the resin aggregates had decreased to 3.0% by mass. Using this regenerated developer, the development speed, image reproducibility, and the presence or absence of resin adhesion to the printing plate surface were evaluated. The evaluation results are shown in Table 1. The volume of the roughly cylindrical stationary tank 4 used in Example 7 is approximately the same as the volume of the roughly rectangular stationary tank 4 used in Example 1.
[0056] Example 8 As latex, styrene-butadiene latex (manufactured by Nippon Zeon, Nipol C4850 solids content concentration) A photosensitive resin composition was prepared in the same manner as in Example 1, except that 71 parts by mass of 70% butadiene, 15 parts by mass of oligobutadiene acrylate (ABU-3, manufactured by Kyoeisha Chemical Co., Ltd.: number average molecular weight 2700) as a photopolymerizable compound, 10 parts by mass of lauryl methacrylate, 10 parts by mass of trimethylolpropane trimethacrylate, 1 part by mass of benzyldimethyl ketal as a photopolymerization initiator, 20 parts by mass of PFT-3 (a polymer with a urethane urea structure and a number average molecular weight of approximately 20,000, 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, and 9 parts by mass of liquid butadiene as a plasticizer were mixed with 5 parts by mass of toluene in a container, kneaded at 105°C using a pressurized kneader, and then toluene and water were removed by vacuum distillation to prepare a photosensitive resin composition. The plates were then exposed and developed to obtain developing waste liquid. The flexographic printing plate had a photosensitive resin layer made of a photosensitive resin composition containing styrene-butadiene copolymer latex (weight-average gelation degree 60%) as a water-dispersible resin. The developing waste liquid was allowed to stand in the same manner as in Example 1, the solid-liquid mixed phase was discharged, and the regenerated developer was recovered. The recovered regenerated developer amounted to 35 liters, with a recovery rate of 78%. This regenerated developer contained a small amount of resin aggregates, but the solid content concentration excluding the resin aggregates had decreased to 3.2% by mass. Using this regenerated developer, the development speed, image reproducibility, and the presence or absence of resin adhesion to the printing plate surface were evaluated. The evaluation results are shown in Table 1.
[0057] Comparative Example 1 Except for changing the standing tank 4 to one without an outlet, the developing waste liquid was allowed to stand in the same manner as in Example 1. Then, water was poured into the standing tank 4 until it overflowed from the top, thereby removing the solid-liquid mixed phase containing the resin aggregates 5 from the top of the standing tank 4 and collecting it in the resin aggregate recovery tank 7. After that, the liquid remaining in the standing tank 4 was recovered as regenerated developer. The amount of regenerated developer recovered was 40.5 liters, and the recovery rate was 90%. The solid content concentration in this regenerated developer, excluding the resin aggregates, was 4.5% by mass, which was significantly higher than in Examples 1 to 8. The development speed, image reproducibility, and presence or absence of resin adhesion to the printing plate surface were evaluated using this regenerated developer, but all were inferior to Examples 1 to 8 due to the high solid content concentration. The evaluation results are shown in Table 1.
[0058] Comparative Example 2 Except for changing the shape of the outlet installed in the standing tank 4 to a circular shape with a diameter of 5 cm and changing the installation position of the outlet to the center of the bottom of the standing tank 4, the developing waste liquid was allowed to stand in the same manner as in Example 1. After that, the liquid was gently drained from the outlet by opening the outlet on the bottom of the standing tank 4 to obtain the regenerated developing solution. The outlet was closed to end the draining of the liquid before the solid-liquid mixed phase containing resin aggregates was extracted, so that the solid-liquid mixed phase remained in the standing tank 4. The recovered regenerated developing solution was 31.5 liters, and the recovery rate was 70%. The solid content concentration in this regenerated developing solution, excluding resin aggregates, was 4.0% by mass, which was significantly higher than in Examples 1 to 8. The developing speed, image reproducibility, and presence or absence of resin adhesion to the printing plate surface were evaluated using this regenerated developing solution, but the image reproducibility was inferior to that in Examples 1 to 8 due to the high solid content concentration. The evaluation results are shown in Table 1.
[0059] Comparative Example 3 In Example 1, instead of using the standing tank 4, the developing waste liquid was left to stand in the developing tank 1 for 5 hours, after which the solid-liquid mixed phase containing resin aggregates was scooped up and recovered with a ladle. In this method, the resin aggregates and the developing solution (developing solution separated from the resin aggregates) were scooped up together, resulting in 30 liters of recovered regenerated developing solution, with a recovery rate of 67%. The solid content concentration in this regenerated developing solution, excluding the resin aggregates, was 4.5% by mass, which was significantly higher than in Examples 1-8. Using this regenerated developing solution, the development speed, image reproducibility, and the presence or absence of resin adhesion to the printing plate surface were evaluated. However, due to the high solid content concentration, resin adhesion to the printing plate surface was observed, and the results were inferior to Examples 1-8. The evaluation results are shown in Table 1. Furthermore, in the method of Comparative Example 3, when the regenerated developing solution was removed from the bottom of the developing tank, resin aggregates adhered to the inside of the developing tank, requiring cleaning of the developing tank. Therefore, the method of Comparative Example 3 had poor workability, and it was not possible to easily produce regenerated developing solution from developing waste liquid.
[0060] Comparative Example 4 In Comparative Example 4, the developing waste liquid was allowed to stand, the solid-liquid mixed phase was discharged, and the regenerated developing solution was recovered in the same manner as in Example 1, except that the position of the outlet 6 on one side of the standing tank 4 was changed so that the lowest point of the rectangular opening of the outlet was at a height of 40% of the depth of the standing tank 4. In Comparative Example 4, the difference in height between the liquid level of the developing waste liquid and the position of the outlet was large, resulting in a large drainage volume. As a result, only 17 liters of regenerated developing solution were recovered, and the recovery rate was low at 30%. In addition, because of the large difference in height between the liquid level of the developing waste liquid and the position of the outlet, the resin aggregates broke down during discharge, and some of it remained in the standing tank 4 without being completely discharged. As a result, the solid content concentration in this regenerated developing solution, excluding the resin aggregates, was 4.0% by mass, which was significantly higher than in Examples 1 to 8. Using this regenerated developer, we evaluated the development speed, image reproducibility, and the presence or absence of resin adhesion to the printing plate surface. However, due to the high solid content concentration, slight resin adhesion to the printing plate surface was observed, which was inferior to Examples 1-8. The evaluation results are shown in Table 1.
[0061] [Table 1] [Industrial applicability]
[0062] According to the method of the present invention, a regenerated developer with a low solid content concentration can be produced in a simple manner with a high recovery rate, without requiring special pretreatment or equipment maintenance for agglomerating the photosensitive resin composition. Therefore, the present invention is extremely useful. [Explanation of symbols]
[0063] 1 developer tank 2. Developer 3 Piping 4. Static tank 5 Resin aggregate 6 Outlet 7. Resin aggregate recovery tank 8 pumps 9 Piping
Claims
1. A method for producing a regenerated developer without using a coagulant from developing waste liquid generated by developing a water-developable flexographic printing plate having a photosensitive resin layer made of a photosensitive resin composition containing a water-dispersible resin, The method described above is A step of allowing the developing waste liquid to stand in a tank, causing the photosensitive resin composition dispersed in the developing waste liquid to float and aggregate, thereby forming a solid-liquid mixed phase containing resin aggregates below the liquid surface of the developing waste liquid, and A process in which the solid-liquid mixed phase containing resin aggregates is discharged from an outlet installed on the side of the tank, and the liquid remaining in the tank is obtained as a regenerating developer. Includes, The liquid level of the developing waste liquid in the tank at the start of the discharge is higher than the lowest point of the opening of the discharge port, and The opening of the discharge port is a rectangular slit having a longitudinal direction in the width direction of the tank, and the width of the slit in the height direction of the tank is 4 cm to 8 cm. A method characterized by the following.
2. The method according to claim 1, characterized in that the liquid level of the developing waste liquid in the tank at the start of the discharge is 3% or more of the depth of the tank than the height of the lowest position of the opening of the discharge port.
3. The method according to claim 1, characterized in that, when the liquid level of the developing waste liquid in the tank at the start of the discharge is set to 53% or more of the depth of the tank, the height is 3% or more higher than the height of the lowest point of the opening of the discharge port.
4. The method according to any one of claims 1 to 3, characterized in that the liquid level of the developing waste liquid in the tank at the start of the discharge is higher by a height of 30% or less of the depth of the tank than the height of the lowest position of the opening of the discharge port.
5. The method according to any one of claims 1 to 4, further comprising the step of transferring water or developer to the tank before discharge, if the level of the developing waste liquid in the tank after the aforementioned standing is less than or equal to the height of the lowest position of the outlet opening, to raise the level of the developing waste liquid in the tank to a level higher than the height of the lowest position of the outlet opening.
6. The method according to any one of claims 1 to 5, further comprising the step of transferring the developing waste liquid from the developing tank to the tank before the developing waste liquid is allowed to stand in the tank.
7. The method according to any one of claims 1 to 6, characterized in that the lowest position of the opening of the discharge port is at a height of 50% or more of the depth of the tank.
8. The method according to any one of claims 1 to 7, characterized in that the lowest position of the opening of the discharge port is at a height of 55 to 90% of the depth of the tank.
9. The method according to any one of claims 1 to 8, characterized in that the tank has the shape of a substantially rectangular parallelepiped, a substantially cubic, or a substantially cylindrical shape.
10. The method according to claim 9, characterized in that, when the tank has a substantially rectangular parallelepiped or substantially cubic shape, the maximum width of the opening of the discharge port is 50% or more of the maximum width of the tank.
11. The method according to any one of claims 1 to 10, characterized in that the solid content concentration of the regenerating developer is 3.5% by mass or less.
12. A method for producing a water-developable flexographic printing plate, characterized in that a regenerated developer obtained by the method described in any one of claims 1 to 11 is used as a developer.