Method for solvent recovery from waste wash liquid of printing machine

Abstract: Object: The present invention provides a solvent recovery method and apparatus from printing machine waste wash liquid, generated mainly in automatic washing of printing machine, so as to enable a printing machine washing of high productivity, excellent safety and health effect and low cost. Solving means: This solvent recovery apparatus from printing machine waste wash liquid comprises a gravity separation tank 1 for receiving waste wash liquid used for washing of printing machine and separating it by a specific gravity difference; a vaporizer 2 for receiving, and heating and vaporizing, the separated liquid from said tank 1 in the order from the lower layer liquid H to the upper layer liquid L; a condenser 3 for receiving, and cooling and condensing by water W, the vapor from said vaporizer 2; and a distillate gravity separation tank 4 for receiving liquid from said condenser 3 and holding it statically to make separation of the liquid into organic solvent S and water W.

Description: BACKGROUND OF THE INVENTION: Field of the Invention: The present invention relates to a method and an apparatus for solvent recovery from waste wash liquid of printing machine, in which solvent is separated and regenerated to be recovered from waste wash liquid generated at the time when ink sticked on a printing machine, especially on a sheet-fed printing press, is dissolved and washed by the solvent. Description of the Prior Art: As shown in Fig. 6, a sheet-fed printing press 6 consists usually of an ink pot 6a, an ink fountain roller 6b, a ductor 6c, an inking roller group 6d, a damping device 6g, a plate cylinder 6e, a blanket cylinder 6f, etc. When a printing is made on a sheet of paper P by use of said sheet-fed printing press, ink I stored in the ink pot 6a is transferred from the ink fountain roller 6b to the inking roller group 6d and further from the inking roller group 6d to the plate cylinder 6e, on the other hand, a damping water W is applied to the plate cylinder 6e by the damping device 6g so that a printing image is formed there, and this printing image is transferred to the sheet of paper P via the blanket cylinder 6f. In said sheet-fed printing press, at the time of change of contents to be printed (plate change), change of kind of ink as so far been used (color change) may be required, and at the time of completion of printing work, the machine, without being left as it is, must be prepared for the next start (start of printing work). In such case, in order to avoid generation of printing failure and increase of loss of paper, it is indispensable to remove ink, paper dusts, etc. sticked on each portion of printing machine and make it clean. Such removal and cleaning of ink, paper dusts, etc. sticked on each portion of printing machine in the prior art is done by a washing device 7 as shown next; that is, ink I of the ink pot 6a is first taken out, the residual ink I is scraped by an ink spatula, then the ink remained in the ink pot 6a and the ink fountain roller 6b is wiped off by use of pieces of cloth soaked with wash liquid (consisting of a hydrocarbon race organic solvent of boiling point of 150 to 250°C). As for the inking roller group 6d, it is disengaged from the plate cylinder 6e, and while the inking roller group 6d only is rotated, wash liquid is jetted or dropped from a wash nozzle 7a disposed thereabove. By so doing, the residual ink sticked on the inking roller group 6d is softened and moved together with the wash liquid to be transferred to a doctor roller 6h. This mixture of waste wash liquid and ink transferred onto the surface of the doctor roller 6h is scraped by a doctor blade 7b to be collected in a wash liquid pan 7c and wasted. As sticking of ink, paper dust, starch powder, etc. on the blanket cylinder 6f causes deterioration of ink transfer to the paper P, removal thereof must be done very carefully. Hence, the blanket cylinder 6f is inched or moved slowly and wash liquid is poured or wiping by pieces of cloth soaked with wash liquid is done. Particularly, paper dusts, being hardly removed, are wiped off by pieces of cloth soaked with water. Recently, a system has been disclosed wherein washing is automatically done by use of a brush or a roller while water and wash liquid are supplied alternately. In said customary washing work of printing machines which is mainly dependent on manual work, there are problems such that, much time of work being required, productivity is low; workers' long term inhalation of vapor of wash liquid consisting mainly of organic solvent may harm health; sticking of ink to body or clothes looks dirty; there is a danger of being caught in rotating rollers, though slowly; etc., hence, in order to solve these problems, there is coming out a tendency to automate wash work by use of a large amount of wash liquid for washing of ink. Accompanying with automating the wash work, however, there arise problems that cost of wash liquid increases and, as the generated waste wash liquid, being colored by ink, will cause, if wasted as it is, an environmental pollution like water contamination etc., it is required to be burnt or consigned for disposal to waste disposal enterprises, which increases cost so much. As mentioned above, in the wash work of printing machines, particularly in case of manual work, there are problems of low productivity, health obstruction, dirt, lack of safety like accident of being caught in rollers, etc. On the other hand, if an automatic washing using a large amount of wash liquid is performed for solving the above problems in the manual work, cost increase of wash liquid as well as that of pollution control are brought about. A prior art arrangement for recovering and recycling a solvent from painting waste is described in EP-A-0 069 663. A gravity separation tank in this arrangement serves to separate heavy solid material from the solvent, which solvent then is further treated in a vaporizer in the next step. A second tank is provided as a buffer tank for the condensed liquid for transportation to another place. SUMMARY OF THE INVENTION It is an object of the present invention to provide a method for recovering solvent from waste wash liquid of a printing machine generated mainly in an automatic washing of such printing machine and an apparatus for carrying out this method which provide high productivity, excellent safety and health effect and low cost and particularly avoid the occurence of bumping. According to the present invention this object is solved by a method as defined in claim 1 and by the use of an apparatus for carrying out this method as defined in claim 2. In order to attain said object, the present invention provides a solvent recovery method from waste wash liquid of printing machine, comprising the following steps: Solvent recovery method according to the present invention comprises firstly a step of waste wash liquid gravity separation wherein waste wash liquid generated at the time when ink, paper dusts, starch powder, etc., sticked on an ink pot, an inking roller group, a plate cylinder, a blanket cylinder, an impression cylinder, etc., composing a printing machine, such as a sheet-fed printing press etc., are washed to be removed by organic solvent and water, is received and held statically, thereby gravity separation is made into two layers of a heavy liquid of large specific gravity consisting mainly of water and a light liquid of small specific gravity consisting mainly of organic solvent. Next, there is a step of distillation for obtaining distillate wherein the heavy liquid of lower layer separated by said waste wash liquid gravity separation step is taken out to be heated and boiled of water, and subsequently to vaporization of water being substantially completed, the light liquid of upper layer is taken out to be heated and boiled of organic solvent, and the obtained vapor is cooled indirectly to be condensed. The heating is preferably made indirectly. And there is a step of distillate gravity separation wherein the distillate obtained by said distillation step is held statically, thereby a gravity separation is made into two layers of water and organic solvent. According to the solvent recovery method of the present invention, organic solvent can be regenerated and recovered for reuse from waste wash liquid of printing machine and cost burden for organic solvent can be reduced, thereby automating wash work of printing machine using a large amount of organic solvent becomes possible, productivity of washing is enhanced accompanying therewith and workers are released from dirty and dangerous work. Incidentally, a bumping caused at the time when a mixture of heavy liquid and light liquid of which boiling points are greatly different from each other is vaporized can be prevented by the heavy liquid and the light liquid being separated in advance, and by so doing, compact sizing of vaporizer and prevention of accompanying of ink mist can be realized. Further, in order to attain said object, the present invention provides a solvent recovery apparatus from waste wash liquid of printing machine, comprising following construction: Solvent recovery apparatus according to the present invention comprises a waste wash liquid gravity separation tank wherein waste wash liquid of printing machine is received and held statically, thereby a gravity separation is made into two layers of a heavy liquid of large specific gravity consisting mainly of water and a light liquid of small specific gravity consisting mainly of organic solvent. And there is a vaporizer which receives firstly the heavy liquid of lower layer from the waste wash liquid gravity separation tank to heat, preferably to heat indirectly, and boil water, and subsequently to vaporization of water being substantially completed, receives the light liquid of upper layer to heat and boil organic solvent. Solvent recovery apparatus according to the present invention further comprises a condenser for condensing vapor from the vaporizer by making preferably an indirect cooling and a gravity separation tank for receiving and holding statically liquid from the condenser, thereby making gravity separation into two layers of water and organic solvent. In the present invention, vaporizer used for the solvent recovery apparatus from waste wash liquid of printing machine is preferably of a construction comprising an agitator and an external heater. Incidentally, temperature of the vaporizer heating surface in contact with the liquid is made to 230°C or less, thereby scaling of ink on the vaporizer heating surface can be prevented completely. Further, if the vaporizer is of a construction comprising therein a mist catching mechanism, it will be preferable as ink mist accompanying with vapor can be removed easily and compact sizing of vaporizer can be realized. And the mist catching mechanism provided in the vaporizer may be of a construction in which a plurality of shelves, having openings through which vapor is passable upwardly, are provided with spaces in the vertical direction so that the openings of adjacent shelves may not overlap with each other in the vertical direction, thereby flow of generated vapor can be bent suddenly. Further, said mist catching mechanism may be of a construction in which a weir is provided around the edge of each opening of shelf so that liquid on the shelf may not fall and a cap is provided above the opening with its lower peripheral edge being dipped in the liquid so as to cover said weir, thereby vapor, going up through the opening, can pass over the weir and go through the liquid on the shelf. According to said solvent recovery apparatus, an apparatus which is able to make an efficient solvent recovery by use of above-mentioned solvent recovery method from waste wash liquid of printing machine according to the present invention is provided. BRIEF DESCRIPTION OF THE DRAWINGS: In the accompanying drawings: Fig. 1 is a constructional view showing arrangement of a solvent recovery apparatus from waste wash liquid of printing machine of a first preferred embodiment according to the present invention. Fig. 2 is a constructional view showing arrangement of a solvent recovery apparatus from waste wash liquid of printing machine of a second preferred embodiment according to the present invention. Fig. 3 is a constructional view showing one example of arrangement of a vaporizer in the solvent recovery apparatus of Fig. 2. Fig. 4 is a constructional view showing another example of arrangement of a vaporizer in the solvent recovery apparatus of Fig. 2. Fig. 5 is a constructional view for explaining wash operation of printing machine. Fig. 6 is a constructional view for explaining wash operation of printing machine in the prior art. DESCRIPTION OF THE PREFERRED EMBODIMENTS: Herebelow, description is made concretely on preferred embodiments of the solvent recovery method and apparatus from waste wash liquid of printing machine according to the present invention with reference to Figs. 1 to 4, and before that, a wash method of printing machine is first described with reference to Fig. 5. Before washing of printing machine is carried out, a blanket cylinder 6f is wound with cloth or molton for wiping the surface thereof and a wash drum 8a is provided so as to make rotating contact with the blanket cylinder only while washing, further wash nozzles 8b, 8c, 8d and 8e for pouring (or jetting) organic solvent (and/or water) are provided respectively above an ink pot 6a, an inking roller group 6d, a doctor blade 7b and the wash drum as well as waste liquid receivers 8f, 8g and 8h are provided respectively below the ink pot 6a, the doctor blade 7b and the wash drum 8a. At the time of washing of printing machine, ink I in the ink pot 6a is taken out, and while rollers are moved slowly, the wash nozzles 8b, 8c and 8d are opened respectively for the ink pot 6a, the ink roller group 6d and the doctor blade 7b, in turn from the upstream side, thus organic solvent is poured repeatedly (solvent S recovered from the solvent recovery apparatus is used actively) and residual ink is washed. At his time, it is desirable to disengage the inking roller group 6d and a plate cylinder 6e. Upon completion of washing of upper rollers, the wash drum 8a makes contact with the blanket cylinder 6f, and while the blanket cylinder 6f is rotating, organic solvent S is poured from the wash nozzle 8e to the wash drum 8a and the surface of the blanket cylinder 6f is wiped by cloth or molton wetted by the organic solvent, thereby ink, paper dusts, starch powder, etc., sticked on the plate cylinder 6e and the blanket cylinder 6f are removed. In place of organic solvent, organic solvent in which water is dispersed, as the case may be, can be used. The waste wash liquid received in the waste liquid receivers 8f, 8g and 8h is transferred to a waste wash liquid gravity separation tank or stored in a waste liquid reservoir. Preferred embodiments of solvent recovery method and apparatus according to the present invention for recovering solvent from waste wash liquid generated by washing of printing machine, as mentioned above, are described. (First preferred embodiment) First preferred embodiment is described with reference to Fig. 1. In Fig. 1, numeral 1 designates a waste wash liquid gravity separation tank, which receives from above, and holds statically, the waste wash liquid containing organic solvent and water used for washing of printing machine as well as ink, paper dusts, starch powder, etc., as mentioned above, thereby makes gravity separation into two layers of a heavy liquid of large specific gravity consisting mainly of water and a light liquid of small specific gravity consisting mainly of organic solvent. Construction is so made that the separated liquid in the gravity separation tank 1 is taken out from a discharge port 1a provided at the lower portion and is sent to a vaporizer 2 of the next step by a liquid transfer pump 1b. Incidentally, a piping 1c is provided so that the liquid sent from the liquid transfer pump 1b can also be returned to the waste wash liquid gravity separation tank 1. Next, as to the vaporizer 2, numeral 2a designates an electric heater which is wound around the outer surface of the vaporizer 2 and is covered on its outer surface by a thermal insulation layer K of high heat insulation ability. Numeral 2b designates an agitator fitted to the center portion of an upper cover of the vaporizer 2, numeral 2c designates a liquid supply port, numeral 2d designates a waste ink discharge port provided at the bottom portion of the vaporizer 2, through which residue R consisting mainly of waste ink is discharged, numeral 2e designates a vapor discharge port and numeral 2f designates a motor for driving said agitator 2b. Numeral 3 designates a condenser for cooling and condensing vapor from the vaporizer 2, which consists of a cooling pipe 3a for vapor and a cooling water jacket 3b for cooling water. Numeral 4 designates a distillate gravity separation tank for receiving, and holding statically, distillate from the condenser 3, thereby making separation into two layers of water W of large specific gravity and organic solvent S of small specific gravity. The distillate gravity separation tank 4 comprises a water discharge port 4a provided at the lower portion thereof and a solvent discharge port 4b provided at the upper portion thereof. Numeral 4c designates a solvent discharge pump and a piping is provided so that the solvent can also be returned to the distillate gravity separation tank 4. Numeral 5 designates a waste ink tank for receiving the residue (waste ink) R stored on the bottom of the vaporizer 2 and numeral 5a designates a waste ink receiving port for receiving the waste ink. Operation of the apparatus of Fig. 1 having construction as mentioned above is described. The heavy liquid H of lower layer of the waste wash liquid gravity separation tank 1 is introduced into the vaporizer 2, which is maintained at a temperature of 230°C or less, to be heated indirectly and boiled of water, and subsequently to evaporation of water being substantially completed, the light liquid L of upper layer is supplied into the vaporizer 2 to be heated indirectly and boiled of organic solvent. The heavy liquid H and the light liquid L are so separately treated and a bumping is thereby prevented. Vapor generated at the vaporizer 2 is cooled to be condensed at the condenser 3 and introduced into the distillate gravity separation tank 4 to be held statically there. Thus, solvent S can be effectively recovered from the waste wash liquid of printing machine. (Second preferred embodiment) Next, second preferred embodiment according to the present invention is described with reference to Figs. 2 to 4. Incidentally, same or similar part in Figs. 2 to 4 as that shown in Fig. 1 is denoted with same numeral and repeated description is omitted. Within a vaporizer 2 of the apparatus shown in Fig. 2, there is provided a mist catcher 9 above the liquid level, a concrete construction of this mist catcher 9 is shown in Figs. 3 and 4. In the mist catcher 9 shown in Fig. 3, a plurality of shelves, having openings through which vapor is passable upwardly, are provided with spaces in the vertical direction so that the openings of adjacent shelves may not overlap with each other in the vertical direction, thereby flow of generated vapor can be bent suddenly. Thus, mist in the vapor generated at the vaporizer 2 can be caught easily and compact sizing of the vaporizer 2 can be realized. Next, in the mist catcher 9 shown in Fig. 4, construction is so made that a plurality of openings 9b, through which vapor is passable, are provided at shelves 9a for storing liquid, a weir 9c is provided around the edge of each opening 9b so that liquid on the shelf 9a does not fall and a cap 9d is provided above the opening 9b with its lower peripheral edge being dipped in the liquid so as to cover the weir 9c, thereby vapor, going up through the opening 9b, can pass over the weir 9c and go through the liquid on the shelf 9a. Other parts of the apparatus shown in Fig. 2 are same as those shown in Fig. 1 substantially. According to the solvent recovery apparatus of Fig. 2, as the mist accompanying with the vapor generated at the vaporizer 2 can be removed easily by the mist catcher 9, clear organic solvent S and water W, which are reusable for washing of printing machine, can be recovered and the amount of residue consisting mainly of ink (waste ink), which must otherwise be disposed as waste, can be reduced to a minimum. According to the present invention, as described above, the waste wash liquid is separated by a specific gravity difference, the separated waste liquid is heated and vaporized individually, the respective vapor is cooled to be condensed and held statically, and water and solvent, being separated by a specific gravity difference, are recovered. By practicing the present invention, accordingly, as organic solvent can be regenerated and recovered to be reused and cost burden of the organic solvent can be reduced, it has become possible that wash work of printing machine using large amount of organic solvent is automated, productivity of washing is enhanced accompanying therewith and workers are released from dirty and dangerous work. Incidentally, a bumping caused at the time when a mixture of heavy liquid and light liquid of which boiling points are greatly different each other is vaporized can be prevented by the heavy liquid H and the light liquid L being separated in advance, and by so doing, compact sizing of vaporizer and prevention of accompanying of ink mist can be realized. Especially, according to the solvent recovery apparatus of the present invention in which a mist catcher is provided within vaporizer, the mist accompanying with is provided within vaporizer, the mist accompanying with the vapor generated at the vaporizer can be removed easily, clear organic solvent S and water W, which are reusable for washing of printing machine, can be recovered and the amount of residue consisting mainly of ink (waste ink), which must otherwise be disposed as waste, can be reduced to a minimum. It is understood that the invention is not confined to the particular construction and arrangement of parts herein illustrated and described but embraces such modified forms thereof as come within the scope of the following claims.

Claims: A method for recovering solvent from a waste wash liquid which has been used to wash off ink from a printing machine and which contains a heavy liquid (H) comprising mainly water and a light liquid (L) comprising mainly organic solvent, comprising the steps of: separating said waste wash liquid by the specific gravity difference into a liquid component having a larger density and a liquid component having a smaller density; sequentially heating and vaporizing said liquid components separated in said separating step, wherein the liquid component having the larger density is heated and vaporized and then the liquid component having the smaller density is heated and vaporized, thereby avoiding the occurence of bumping; cooling and condensing the vapor; and holding the condensed liquid from the vapor statically to separate the light and heavy components by their specific gravity difference. Use of an apparatus for recovering solvent from a waste wash liquid which has been used to wash off ink from a printing machine in accordance with the method of claim 1, comprising: a first gravity separation tank (1) for receiving said waste wash liquid which contains the heavy liquid (H) comprising mainly water and the light liquid (L) comprising mainly organic solvent and separating the waste wash liquid by the specific gravity difference into liquid components, said first gravity separation tank (1) having a discharge port (1a) at a lower portion thereof for discharging a liquid component having a larger density; a vaporizer (2) adapted to sequentially receive liquid components separated in said gravity separation tank (1) from said discharge port (1a) of said first gravity separation tank (1) and to heat and vaporize said liquid components, wherein the liquid component having the larger density is treated before the liquid component having the smaller density, said vaporizer (2) comprises a means (2b) for agitating the waste liquid in said vaporizer (2); a condenser (3) for receiving and cooling and condensing vapor from said vaporizer (2); and a second gravity separation tank (4) for receiving condensed liquid from said condenser (3) and holding it statically to separate components of the liquid by their specific gravity difference, said second separation tank (4) having discharge ports (4a,4b) at different vertical portions for said separated liquid components of different density. Use according to claim 2, characterized in that a mist catching means (9) is provided within said vaporizer (2). Use according to claim 3, characterized in that said mist catching means (9) comprises a plurality of shelves (9a) arranged above each other with spaces in the vertical direction, said shelves (9) having openings (9b) through which vapor is passable upwardly and the openings (9b) of adjacent shelves (9a) are arranged such that they may not overlap with each other in the vertical direction, thereby changing the flow direction of generated vapor on its way upward through the shelves (9). Use according to claim 3, characterized in that said mist catching means (9) comprises a shelf (9a) having an opening (9b) through which vapor is passable upwardly, a weir (9c) provided around the edge of the opening (9b) of said shelf (9a) for storing liquid so that liquid on the shelf (9a) may not drop down from the shelf (9a), and a cap (9d) provided above the opening (9b) so as to cover the weir (9c) and with its lower peripheral edge arranged such that it is dipped into the liquid when the same is stored on the shelf (9a), thereby vapor going up through the opening (9b), can pass over the weir (9c) and through the liquid.

Inventors: MAKINO KATSUAKI, MATSUURA ISAO, OKAZAKI KATSUTOSHI, SOEDA HIROMITSU, MAKINO, KATSUAKI, MATSUURA, ISAO, OKAZAKI, KATSUTOSHI, SOEDA, HIROMITSU, Makino, Katsuaki, Mitsubishi Jukogyo K.K., Matsuura, Isao, Mitsubishi Jukogyo K.K., Okazaki, Katsutoshi, Mitsubishi Jukogyo K.K., Soeda, Hiromitsu, Mitsubishi Jukogyo K.K.
Applicants: MITSUBISHI HEAVY IND LTD, MITSUBISHI JUKOGYO KABUSHIKI KAISHA
Application year: 1996
Main classification: B01D5
IPC codes: B41F35, B01D1, B01D3