Pigment suspension purification apparatus

Abstract

The present invention provides a pigment suspension purification apparatus capable of efficiently removing fine pigment particles, which are impurities. [Solution] The pigment suspension purification apparatus 1 comprises a stock tank 3 containing a pigment suspension 2 containing fine pigment particles, a filtration means 5 that passes the pigment suspension 2 through an ultrafiltration membrane 4 in a cross-flow manner to remove at least a portion of the fine pigment particles, a circulation means 10 that circulates the pigment suspension 2 between the stock tank 3 and the filtration means 5, and a pH adjusting agent supply means 6 that supplies a pH adjusting agent to the stock tank 3. Furthermore, it is equipped with a monitoring unit 11 that monitors the pH of the pigment suspension 2 in the stock tank 3, and based on the monitoring results from the monitoring unit 11, it controls whether or not to supply a pH adjusting agent to the stock tank 3 by the pH adjusting agent supply means 6 and the supply flow rate.

Description

Technical Field

[0001] The present invention relates to an apparatus for purifying a pigment suspension.

Background Art

[0002] In recent years, the inkjet recording method has been used for printing business documents using plain paper or the like as a recording medium, and for printing photographic images using glossy paper or the like as a recording medium, and its usage frequency has been increasing significantly. As a colorant used when recording an image by the inkjet recording method, pigments have become the mainstream from the viewpoint of image fastness and the like.

[0003] Many impurities such as inorganic metals may be mixed into the pigment suspension used as a raw material for ink during the manufacturing or processing process. And in order to ensure the storage stability of the ink and the ejection stability of the ink when ejecting from the recording head by the inkjet method, it is necessary to remove impurities from the pigment suspension.

[0004] Among the impurities, fine pigments having a primary particle diameter of 10 nm or less are factors that reduce the ejection stability of the ink in the thermal inkjet method due to their high aggregability and adhesiveness. Therefore, in order to suppress the decrease in the ejection stability of the ink, it is necessary to reduce the amount of fine pigments in the pigment suspension used as a raw material for the ink as much as possible.

[0005] As a method for removing impurities from a liquid composition, so-called dead-end filtration in which the entire amount of the liquid composition is filtered at once with an ultrafiltration membrane is common. However, the 10% particle diameter (D10) in the volume-based particle size distribution of the pigment contained in the pigment suspension used as a raw material for ink is about 20 to 50 nm. Therefore, when trying to separate the pigment in the pigment suspension and the fine pigment having a primary particle diameter of 10 nm or less by dead-end filtration using an ultrafiltration membrane, the ultrafiltration membrane will be clogged immediately. On the other hand, if an ultrafiltration membrane with a large membrane pore diameter is used to prevent clogging, the necessary pigment will easily pass through the membrane and the yield will decrease.

[0006] To resolve these problems, a method has been proposed in which a liquid containing two types of nanoparticles, such as pigments, with different particle size distributions is separated and purified by cross-flow filtration (Patent Document 1). In addition, a method has been proposed in which the pH of the dispersion is controlled and cross-flow filtration is performed to control the aggregation of particles such as pigments (Patent Document 2). [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2010-46621 [Patent Document 2] Japanese Patent Publication No. 2001-11081 [Overview of the Initiative] [Problems that the invention aims to solve]

[0008] However, the method proposed in Patent Document 1 made it difficult to purify the pigment suspension to a level where the decrease in the ejection stability of the ink ejected by the thermal inkjet method was sufficiently suppressed. This is thought to be because the fine pigment particles aggregate to form secondary particles, making filtration difficult. Furthermore, even with the method proposed in Patent Document 2, it was difficult to purify the pigment suspension to a level where the decrease in the ejection stability of the ink ejected by the thermal inkjet method was sufficiently suppressed.

[0009] Therefore, the object of the present invention is to provide a pigment suspension purification apparatus capable of efficiently removing fine pigment particles, which are impurities. [Means for solving the problem]

[0010] In other words, the present invention provides a pigment suspension purification apparatus comprising: a stock tank for containing a pigment suspension containing fine pigment particles; a filtration means for passing the pigment suspension through an ultrafiltration membrane in a cross-flow manner to remove at least a portion of the fine pigment particles; a circulation means for circulating the pigment suspension between the stock tank and the filtration means; and a pH adjusting agent supply means for supplying a pH adjusting agent to the stock tank, wherein the apparatus further comprises a monitoring unit for monitoring the pH of the pigment suspension in the stock tank, and controls whether or not to supply the pH adjusting agent to the stock tank by the pH adjusting agent supply means and the supply flow rate based on the monitoring results from the monitoring unit. [Effects of the Invention]

[0011] According to the present invention, it is possible to provide a pigment suspension purification apparatus that can efficiently remove fine pigment particles, which are impurities. [Brief explanation of the drawing]

[0012] [Figure 1A] This is a schematic diagram showing one embodiment of the pigment suspension purification apparatus of the present invention. [Figure 1B] This is a schematic diagram showing an example of a pH adjusting agent supply method. [Figure 1C] This is a schematic diagram showing another example of a pH adjusting agent supply method. [Figure 2] This is a schematic diagram showing the purification apparatus for the pigment suspension used in Example 1. [Figure 3] This is a schematic diagram showing the purification apparatus for the pigment suspension used in Example 2. [Figure 4] This is a schematic diagram showing the purification apparatus for the pigment suspension used in Comparative Example 1. [Figure 5] This is a schematic diagram showing the purification apparatus for the pigment suspension used in Comparative Example 2. [Modes for carrying out the invention]

[0013] <Purification apparatus for pigment suspensions> Hereinafter, the present invention will be described in more detail by giving preferred embodiments. Physical property values are values at normal temperature (25°C) and normal pressure (1 atm) unless otherwise specified. The purification apparatus for a pigment suspension of the present invention (hereinafter also simply referred to as "purification apparatus") is an apparatus including a stock solution tank, a filtration means, a circulation means, and a pH adjuster supply means. The stock solution tank is a part for storing a pigment suspension containing fine pigments. The filtration means is a means for passing the pigment suspension through an ultrafiltration membrane in a cross-flow manner to remove at least a part of the fine pigments. The circulation means is a means for circulating the pigment suspension between the stock solution tank and the filtration means. The pH adjuster supply means is a means for supplying a pH adjuster to the stock solution tank. And the purification apparatus of the present invention further includes a monitoring unit for monitoring the pH of the pigment suspension in the stock solution tank, and controls the presence or absence and supply flow rate of the pH adjuster supplied to the stock solution tank by the pH adjuster supply means in response to the monitoring result from the monitoring unit.

[0014] Since the purification apparatus of the present invention includes a monitoring unit for monitoring the pH of the pigment suspension in the stock solution tank, it filters with a cross-flow filtration means while immediately controlling the pH of the pigment suspension that fluctuates due to the influence of desalting or water addition. That is, since the purification apparatus of the present invention has a pH control mechanism with higher responsiveness than before, it can efficiently remove fine pigments that are impurities in the pigment suspension.

[0015] A pigment suspension containing pigments prepared by a fine particle size method such as a solvent milling method contains many fine pigments with a primary particle size of 10 nm or less generated in the fine particle size process. The purification apparatus of the present invention is suitable as an apparatus for producing such a pigment suspension containing fine pigments. In addition, a pigment suspension obtained by suspending the pigment immediately after fine particle size in water contains many impurities such as water-soluble inorganic salts and organic solvents in addition to the fine pigments. Therefore, by using the purification apparatus of the present invention, a further improvement in the productivity of the pigment suspension is expected.

[0016] (Purification Apparatus for Pigment Suspension) FIG. 1A is a schematic diagram showing an embodiment of a purification apparatus for a pigment suspension according to the present invention. The purification apparatus 1 of the embodiment shown in FIG. 1A includes a stock solution tank 3 for containing the pigment suspension 2, a filtration means 5 for passing the pigment suspension through an ultrafiltration membrane 4 in a crossflow manner, and a pH adjuster supply means 6 for supplying a pH adjuster to the stock solution tank 3. The filtration means 5 is a means capable of removing at least a part of the fine pigments having a primary particle diameter of 10 nm or less, which are impurities in the pigment suspension 2. The purification apparatus 1 further includes a flow path 8 for supplying the pigment suspension from the stock solution tank 3 to the filtration means 5, and a flow path 9 for returning the pigment suspension that has not passed through the ultrafiltration membrane 4 to the stock solution tank 3. Then, the purification apparatus 1 further includes a circulation means 10 for circulating the pigment suspension between the stock solution tank 3 and the filtration means 5 through the flow path 8 and the flow path 9, and a water supply means 7 for supplying water to the stock solution tank 3. Further, the purification apparatus 1 further includes a monitoring unit 11 for monitoring the pH of the pigment suspension 2 in the stock solution tank 3 and transmitting the monitoring result of the pH to the pH adjuster supply means 6. The presence or absence and the supply flow rate of the pH adjuster supplied to the stock solution tank 3 by the pH adjuster supply means 6 are controlled based on the monitoring result of the pH by the monitoring unit 11.

[0017] The pigment suspension 2 is a liquid in which pigments such as organic pigments are dispersed and suspended in an aqueous medium containing water. As the pH adjuster, a general acidic aqueous solution or basic aqueous solution can be used. Among them, it is preferable to use an aqueous solution of a strong acid or an aqueous solution of a strong base as the pH adjuster.

[0018] Specific examples of the filtration means 5 include those using housings or membrane modules. Specific examples of the ultrafiltration membrane 4 include ceramic filters, hollow fiber membrane filters, and filter cloth. Among these, it is preferable to use a ceramic filter as the ultrafiltration membrane 4 from the viewpoint of acid resistance and alkali resistance. From the viewpoint of removal performance of fine pigment particles, it is preferable that the pore size of the ultrafiltration membrane 4 is 0.1 μm or larger. The ultrafiltration membranes 4 can be installed in parallel or in series. The stock solution tank 3 is preferably equipped with a stirring means capable of stirring and homogenizing the pigment dispersion 2 contained within. It is also preferable to add water or a pH adjusting agent to the pigment suspension before filtration with the filtration means to change the pigment concentration and the pH of the pigment suspension, thereby dissolving secondary aggregates of the pigment.

[0019] A specific example of the monitoring unit 11 is a general pH detector having a glass electrode. The presence or absence of pH adjusting agent supply to the stock solution tank 3 by the pH adjusting agent supply means 6 and the supply flow rate are controlled based on the pH monitoring results of the pigment dispersion 2 in the stock solution tank 3 by the monitoring unit 11. The presence or absence of pH adjusting agent supply and the supply flow rate can be controlled based on the real-time monitoring results of the pigment dispersion 2 in the stock solution tank 3, as long as the configuration allows for control. The presence or absence of pH adjusting agent supply and the supply flow rate may also be controlled by the PLC, which receives the pH monitoring results and activates the pH adjusting agent supply means 6. Alternatively, a control means such as a PC may be used instead of a PLC.

[0020] Specific methods for controlling the supply and flow rate of pH adjusting agents based on pH monitoring results include, for example, controlling the flow rate of pH adjusting agents using a pump from a pH adjusting agent storage tank. Alternatively, a pH adjusting agent storage tank can be installed upstream of the stock tank 3, and the flow rate of the pH adjusting agent can be controlled by an opening adjustment valve placed between the stock tank 3 and the pH adjusting agent storage tank. Common pumps such as tube pumps, diaphragm pumps, centrifugal pumps, and magnetic centrifugal pumps can be used.

[0021] In purification apparatuses that remove impurities by cross-flow filtration, diafiltration is generally performed to efficiently remove impurities while preventing membrane clogging. The purification apparatus of the present invention preferably has a configuration that allows for diafiltration. Specifically, the purification apparatus 1 preferably has a detection means for detecting the amount of liquid in the pigment suspension 2 in the raw material tank 3, and a control means for controlling the amount of water added to the raw material tank 3 based on the detected value of the detection means. Specific examples of the detection means for detecting the amount of liquid in the pigment suspension in the raw material tank 3 include level sensors and tank load cells. Specific examples of the control means for controlling the amount of water added to the raw material tank 3 include a control means that adds water using a water supply means 7 when the amount of pigment suspension 2 in the raw material tank 3 falls below a predetermined value, and stops adding water using the water supply means 7 when it rises above the predetermined value.

[0022] The purification apparatus of the present invention preferably has a heating means for raising the temperature of the pigment suspension as a means for more efficiently removing fine pigment particles and other impurities. Examples of heating means include a hot water supply means for supplying hot water to the stock tank 3; a heating means such as a jacket for heating the stock tank 2; and heat exchangers provided in the flow paths, flow paths 8 and 9 for supplying water from the water supply means 7 to the stock tank 3.

[0023] From the viewpoint of productivity, the purification apparatus of the present invention preferably has a pigment suspension input means for introducing a pigment suspension into a stock solution tank and a pigment suspension discharge means for discharging the pigment suspension from the stock solution tank. Specific examples of the pigment suspension input means include general pumps such as tube pumps, diaphragm pumps, centrifugal pumps, and magnetic centrifugal pumps, or a configuration in which a container placed at the top of the stock solution tank is opened and closed with a valve. Specific examples of the pigment suspension discharge means include general pumps such as tube pumps, diaphragm pumps, centrifugal pumps, and magnetic centrifugal pumps, or a configuration in which a container placed at the bottom of the stock solution tank is opened and closed with a valve.

[0024] From the viewpoint of more precisely controlling the pH of the pigment suspension, it is preferable that the configuration of the pH adjusting agent supply means be highly responsive to changes in the pH of the pigment suspension. Figure 1B is a schematic diagram showing an example of a pH adjusting agent supply means. The pH adjusting agent supply means 6 shown in Figure 1B comprises a pH adjusting agent storage tank 12 for storing the pH adjusting agent, a pump 14 for pressurizing the pH adjusting agent to the stock solution tank 3, and an inverter 15 for controlling the flow rate of the pH adjusting agent supplied to the stock solution tank 3. Thus, it is preferable that the pH adjusting agent supply means 6 includes an inverter 15 for controlling the flow rate of the pH adjusting agent supplied to the stock solution tank 3 by the pH adjusting agent supply means 6. With this configuration, it is possible to be highly responsive to changes in the pH of the pigment suspension and to control the pH of the pigment suspension more precisely.

[0025] Figure 1C is a schematic diagram showing another example of a pH adjusting agent supply means. The pH adjusting agent supply means 6 shown in Figure 1C comprises a pH adjusting agent storage tank 12 for storing the pH adjusting agent, a pump 14 for pumping the pH adjusting agent to the stock solution tank 3, and an intermediate tank 16 for storing the pH adjusting agent, which is located between the pH adjusting agent storage tank 6 and the pump 14. The pH adjusting agent supply means 6 further comprises a control means for controlling the amount of pH adjusting agent stored in the intermediate tank 16 to be constant. With this configuration, the pH adjusting agent can be appropriately supplied from the intermediate tank to the stock solution tank, resulting in high responsiveness to pH changes in the pigment suspension and enabling more precise control of the pH of the pigment suspension.

[0026] The control means for controlling the amount of pH adjusting agent stored in the intermediate tank 16 to a constant level preferably includes, for example, a detection means 17 for detecting the amount of pH adjusting agent in the intermediate tank 16, and a control means 19 for controlling the amount of pH adjusting agent to be replenished based on the value detected by the detection means 17. Specific examples of the detection means 17 include level sensors and tank load cells. Specific examples of the control means for controlling the amount of pH adjusting agent to be replenished include a control means that replenishes the pH adjusting agent in the intermediate tank 16 when the amount falls below a predetermined level, and stops replenishing the pH adjusting agent when the amount exceeds the predetermined level. [Examples]

[0027] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited in any way by the following examples unless it exceeds the gist of the invention. Unless otherwise specified, amounts of components indicated in "parts" and "%" are based on mass.

[0028] (Example 1) A purification apparatus 20 with the configuration shown in Figure 2 was prepared. The purification apparatus 20 shown in Figure 2 comprises a stock tank 21, a pH adjuster storage tank 22, a cross-flow type hollow fiber membrane module 23, a supply pipe 24, and a centrifugal pump 25. The purification apparatus 20 further comprises a circulation pipe 26, a water supply pipe 27, an opening control valve 28, a pH adjuster supply pipe 29, a tube pump 30, a pH detector 31, a control unit 32, and a stirrer 33.

[0029] The stock solution tank 21 is a cone-bottomed tank and is configured to allow the supply of pigment suspension from a supply port at the bottom to the supply pipe 24. The circulation pipe 26, water supply pipe 27, and pH adjuster supply pipe 29 are configured to allow the pigment suspension, water, and pH adjuster to be introduced from the top surface of the stock solution tank 21, respectively. The agitator 33 is installed so as to be inserted from the top surface of the stock solution tank 21. The pH detector 31 is installed so as to be inserted from the lower side surface of the stock solution tank 21. The pH adjuster supply pipe 29 is made of tubing.

[0030] The pH adjuster storage tank 22 is a rectangular parallelepiped tank and is configured to supply the pH adjuster from a supply port at the bottom to the pH adjuster supply pipe 29. A centrifugal pump 25 is used as a circulation means to circulate the pigment suspension between the stock tank 21 and the hollow fiber membrane module 23. A tube pump 30 is used as a pH adjuster supply means to supply the pH adjuster to the stock tank 21. Both the centrifugal pump 25 and the tube pump 30 can have their flow rates controlled by adjusting the frequency with an inverter. The pH detector 31 and the tube pump 30 are electrically connected via a control unit 32. The output of the tube pump 30 can be controlled by the inverter according to instructions from the control unit 32. The water supply means includes the stock tank 21 and the pure water supply equipment 100 of the utility equipment, which are connected via a water supply pipe 27 with an opening adjustment valve 28 in the middle.

[0031] [specification] The specifications of the purification apparatus 20 shown in Figure 2 are as follows. ·Stock tank: 35L • pH adjuster storage tank: 5L ·Hollow fiber membrane module: D02-S05U-05-N, pore size 0.05μm, membrane area 0.34m 2 Made by Spectrum Laboratories • pH adjuster: 47% sulfuric acid aqueous solution (1+2) • pH detector: 2-wire pH meter / ORP meter FLXA21, FU20 (both manufactured by Yokogawa Electric) • Control unit: MELSEC iQ-F (manufactured by Mitsubishi Electric)

[0032] [Preparation of Pigment Suspension] The types and quantities of materials shown in Table 1 were mixed and kneaded using a kneader (Trimix, manufactured by Inoue Seisakusho) to obtain a compound. CI Pigment Blue 15:3 (PB15:3) was used as the copper phthalocyanine blue. To the obtained compound, ion-exchanged water in an amount equal to 100 g per 20 g of sodium chloride was added and stirred to dissolve the sodium chloride and diethylene glycol, obtaining a pigment suspension.

[0033] TIFF2026046854000002.tif22170

[0034] [process] After adding 20 kg of pigment suspension to the stock tank 21 of the purification apparatus 20 shown in Figure 2, water was added to bring the total volume of the pigment suspension to 30 kg. Furthermore, a pH adjusting agent was added to the amount required to make the pH of the pigment suspension, as detected by the pH detector 31, 1.50. The centrifugal pump 25 was driven and adjusted so that the membrane inlet pressure of the hollow fiber membrane module 23 was 0.15 MPa. As a result, the membrane outlet pressure of the hollow fiber membrane module 23 was 0.1 MPa, the flow rate of the permeate that passed through the hollow fiber membrane module 23 was 0.28 L / min, and the flow rate of the pigment suspension returning to the stock tank 21 from the circulation pipe 26 was 7.8 L / min. Then, the control unit 32 was set so that the pH detected by the pH detector 31 was 1.50, and cross-flow filtration was started. The mass of the discharged permeate was measured, and for every 1 kg of permeate discharged, the opening adjustment valve 28 was opened and 1 kg of water was added to the stock tank 21. The pigment suspension in the stock tank 21 was sampled every 15 minutes and filtered for 60 minutes.

[0035] [evaluation] The pH and percentage of fine pigment particles in the pigment suspension in the stock tank 21 were measured every 15 minutes. The results are shown in Table 2. For pH, the maximum and minimum values ​​over 15 minutes are shown in Table 2, except for the initial value (0 min). The percentage of fine pigment particles is the proportion of fine pigment particles with a primary particle size of 10 nm or less contained in the pigment suspension. The primary particle size of the fine pigments is the average value of the primary particle sizes of 1,000 fine pigments measured using a scanning electron microscope (SEM).

[0036] TIFF2026046854000003.tif29170

[0037] As shown in Table 2, the proportion of fine pigment particles in the pigment suspension decreased from 10% to 4% after 1 hour of treatment, indicating that the fine pigment particles were successfully removed.

[0038] (Example 2) A purification apparatus 90 with the configuration shown in Figure 3 was prepared. The purification apparatus 90 shown in Figure 3 comprises a stock tank 101, a pH adjuster storage tank 102, a membrane housing 103, a pH detector 34, a control unit 35, a load cell 36, a stirrer 37, an intermediate tank 38, a supply pipe 39, and a magnetic centrifugal pump 40. The purification apparatus 90 further comprises a circulation pipe 41, a water supply pipe 42, an opening adjustment valve 43, a pH adjuster supply pipe 44, an electric diaphragm pump 45, a level sensor 46, an electromagnetic diaphragm pump 47, and a pH adjuster supply pipe 48.

[0039] The stock solution tank 101 is a cone-bottomed tank and is configured to allow the supply of pigment suspension from a supply port at the bottom to the supply pipe 39. The circulation pipe 41, water supply pipe 42, and pH adjuster supply pipe 44 are configured to allow the pigment suspension, water, and pH adjuster to be introduced into the stock solution tank 101 from the top surface. The agitator 37 is installed so as to be inserted from the top surface of the stock solution tank 21. The stock solution tank 101 is equipped with a load cell 36, and the opening of the opening adjustment valve 43 is adjusted based on the volume of the stock solution tank 101 detected by the load cell 36, thereby controlling the volume of the stock solution tank 101. The pH detector 34 is installed so as to be inserted from the lower side surface of the stock solution tank 101.

[0040] The pH adjuster storage tank 102 is a rectangular parallelepiped tank and is configured to supply the pH adjuster from a supply port at the bottom to the pH adjuster supply pipe 48. The intermediate tank 38 is a rectangular parallelepiped tank and is configured to supply the pH adjuster from a supply port at the bottom to the pH adjuster supply pipe 44. The pH adjuster supply pipe 48 is configured to allow the pH adjuster to be introduced from the top surface of the intermediate tank 38. The level sensor 46 is provided so as to be inserted from the top surface of the intermediate tank 38.

[0041] A magnetic centrifugal pump 40 was used as a circulation means for circulating the pigment suspension between the stock tank 101 and the membrane housing 103. An electric diaphragm pump 45 and an electromagnetic diaphragm pump 47 were used as pH adjusting agent supply means for supplying a pH adjusting agent to the stock tank 101. Both the magnetic centrifugal pump 40 and the electric diaphragm pump 45 can have their flow rates controlled by adjusting the frequency with an inverter. The electromagnetic diaphragm pump 47 is controlled based on the detection value of the level sensor 46 and operates to maintain a constant volume in the intermediate tank 38. The electric diaphragm pump 45 operates to maintain a constant pH detected by the pH detector 34. For responsiveness, the pH detector 34 and the electric diaphragm pump 45 are electrically connected via a control unit 35. The output of the electric diaphragm pump 45 can be controlled by an inverter in response to instructions from the control unit 35. A ceramic membrane is inserted into the membrane housing 103, and it is configured to enable cross-flow filtration. The water supply means includes a pure water supply facility 82 of the utility equipment, which is connected to the stock tank 101 via a water supply pipe 42 equipped with an opening adjustment valve 43 along the way.

[0042] [specification] The specifications of the purification apparatus 90 shown in Figure 3 are as follows. ·Stock tank: 35L • pH adjuster storage tank: 5L ·Intermediate tank: 1L ·Ceramic membrane: EC0760 / 1178 / 100nmZ, pore size 0.10um, membrane area 0.16m 2 , made by PALL • pH adjuster: 47% sulfuric acid aqueous solution (1+2) pH detector: Sensor unit SE554, converter unit Liquiline CM442, manufactured by Knick. • Control unit: MELSEC iQ-R (manufactured by Mitsubishi Electric) • Load cell: Shinryo Co., Ltd.

[0043] [Preparation of Pigment Suspension] A pigment suspension was prepared in the same manner as in Example 1 described above.

[0044] [process] After adding 20 kg of pigment suspension to the stock tank 101 of the purification apparatus 90 shown in Figure 3, water was added to bring the total volume of the pigment suspension to 30 kg. Furthermore, a pH adjusting agent was added to the amount required to make the pH of the pigment suspension, as detected by the pH detector 34, 1.50. The magnetic centrifugal pump 40 was driven and adjusted so that the inlet pressure of the membrane housing 103 was 0.15 MPa. As a result, the outlet pressure of the membrane housing 103 was 0.1 MPa, the flow rate of the permeate that passed through the ceramic membrane was 0.5 L / min, and the flow rate of the pigment suspension returning to the stock tank 101 from the circulation pipe 41 was 7.8 L / min. The amount of pigment suspension in the stock tank 101 was 25 kg. Then, the control unit 35 was set so that the pH detected by the pH detector 34 was 1.50, and cross-flow filtration was started. Based on the amount of pigment suspension in the stock tank 101 detected by the load cell 36, the opening of the opening adjustment valve 43 was controlled so that the amount of pigment suspension in the stock tank 101 was within ±0.5 kg. The pigment suspension in the stock tank 21 was sampled every 15 minutes and filtered for 60 minutes.

[0045] [evaluation] The pH and percentage of fine pigment particles in the pigment suspension in the stock tank 101 were measured every 15 minutes. The results are shown in Table 3. For pH, the maximum and minimum values ​​over 15 minutes are shown in Table 3, except for the initial value (0 min).

[0046] TIFF2026046854000004.tif28170

[0047] As shown in Table 3, the proportion of fine pigment particles in the pigment suspension decreased from 10% to 3% after 1 hour of treatment, indicating that the fine pigment particles were successfully removed.

[0048] (Comparative Example 1) A purification apparatus 110 with the configuration shown in Figure 4 was prepared. The purification apparatus 110 shown in Figure 4 comprises a stock tank 51, a pH adjuster storage tank 52, a dead-end type hollow fiber membrane module 53, a supply pipe 54, and a centrifugal pump 55. The purification apparatus 110 further comprises a water supply pipe 57, an opening control valve 58, a pH adjuster supply pipe 59, and a tube pump 60.

[0049] The stock solution tank 51 is a cone-bottomed tank and is configured to allow the pigment suspension to be supplied from the supply port at the bottom to the supply pipe 54. The water supply pipe 57 and the pH adjuster supply pipe 59 are configured to allow the pigment suspension and pH adjuster to be introduced from the top surface of the stock solution tank 51, respectively. The pH adjuster supply pipe 59 is made of tubing.

[0050] The pH adjuster storage tank 22 is a rectangular parallelepiped tank and is configured to supply the pH adjuster from a supply port at the bottom to the pH adjuster supply pipe 59. A centrifugal pump 55 is used to transfer the pigment suspension from the stock tank 21 to the hollow fiber membrane module 53. A tube pump 60 is used as the pH adjuster supply means for supplying the pH adjuster to the stock tank 51. Both the centrifugal pump 55 and the tube pump 60 can have their flow rates controlled by adjusting the frequency with an inverter. The water supply means includes a pure water supply facility 92 of the utility equipment, which is connected to the stock tank 51 via a water supply pipe 57 equipped with an opening control valve 58.

[0051] [specification] The specifications of the purification apparatus 110 shown in Figure 4 are as follows. ·Stock tank: 35L • pH adjuster storage tank: 5L ·Hollow fiber membrane module: D02-S05U-05-N, pore size 0.05μm, membrane area 0.34m 2 Made by Spectrum Laboratories • pH adjuster: 47% sulfuric acid aqueous solution (1+2)

[0052] <Preparation of Pigment Suspension> [Preparation of Pigment Suspension] A pigment suspension was prepared in the same manner as in Example 1 described above.

[0053] [process] After adding 20 kg of pigment suspension to the stock tank 51 of the purification apparatus 110 shown in Figure 4, water was added to bring the total volume of the pigment suspension to 30 kg. A pH adjusting agent was added in an amount that brought the pH of the pigment suspension to 1.50, as measured using a calibrated pH meter (product name "D-220P", manufactured by HORIBA, pH electrode 9680S-10D). The opening control valve 56 was closed, and the centrifugal pump 55 was driven to adjust the membrane inlet pressure of the hollow fiber membrane module 53 to 0.15 MPa, and dead-end filtration was started. As a result, the hollow fiber membrane module began to clog immediately after the start of filtration, and after 1 minute, almost no permeate could be obtained.

[0054] (Comparative Example 2) A purification apparatus 70 with the configuration shown in Figure 5 was prepared. The purification apparatus 70 shown in Figure 5 comprises a stock tank 71, a pH adjuster storage tank 72, a cross-flow type hollow fiber membrane module 73, a supply pipe 74, and a centrifugal pump 75. The purification apparatus 70 further comprises a circulation pipe 76, a water supply pipe 77, an opening control valve 78, a pH adjuster supply pipe 79, and a tube pump 80.

[0055] The stock solution tank 71 is a conical-bottomed tank and is configured to allow the pigment suspension to be supplied from the supply port at the bottom to the supply pipe 74. The circulation pipe 76, water supply pipe 77, and pH adjuster supply pipe 79 are configured to allow the pigment suspension, water, and pH adjuster to be introduced from the top surface of the stock solution tank 71, respectively. The pH adjuster supply pipe 79 is made of tubing.

[0056] The pH adjuster storage tank 72 is a rectangular parallelepiped tank and is configured to supply the pH adjuster from a supply port at the bottom to the pH adjuster supply pipe 79. A centrifugal pump 75 is used as a circulation means for circulating the pigment suspension between the stock tank 71 and the hollow fiber membrane module 73. A tube pump 80 is used as a pH adjuster supply means for supplying the pH adjuster to the stock tank 71. Both the centrifugal pump 75 and the tube pump 80 can have their flow rates controlled by adjusting the frequency with an inverter. The water supply means includes a pure water supply facility 95 of the utility equipment, which is connected to the stock tank 71 via a water supply pipe 77 equipped with an opening control valve 78.

[0057] [specification] The specifications of the purification apparatus 70 shown in Figure 5 are as follows: ·Stock tank: 35L • pH adjuster storage tank: 5L ·Hollow fiber membrane module: D02-S05U-05-N, pore size 0.05μm, membrane area 0.34m 2 Made by Spectrum Laboratories • pH adjuster: 47% sulfuric acid aqueous solution (1+2)

[0058] [Preparation of Pigment Suspension] A pigment suspension was prepared in the same manner as in Example 1 described above.

[0059] [process] After adding 20 kg of pigment suspension to the stock tank 101 of the purification apparatus 70 shown in Figure 5, water was added to bring the total volume of the pigment suspension to 30 kg. A pH adjusting agent was added in an amount that made the pH of the pigment suspension, as measured using a calibrated pH meter (product name "D-220P", manufactured by HORIBA, pH electrode 9680S-10D), 1.50. The centrifugal pump 75 was driven and adjusted so that the membrane inlet pressure of the hollow fiber membrane module 73 was 0.15 MPa. As a result, the membrane outlet pressure of the hollow fiber membrane module 73 was 0.1 MPa, the flow rate of the permeate that passed through the hollow fiber membrane module 73 was 0.28 L / min, and the flow rate of the pigment suspension returning from the circulation pipe 76 to the stock tank 71 was 7.8 L / min. Then, the tube pump and the opening control valve 78 were adjusted so that the ratio of the flow rate of the pH adjusting agent to the flow rate of the water was 1:280, and cross-flow filtration was started. The mass of the discharged permeate was measured, and for every 1 kg of permeate discharged, the opening adjustment valve 78 was opened and 1 kg of a mixed solution of water and pH adjuster was added to the stock solution tank 71. The pigment suspension in the stock solution tank 71 was sampled every 15 minutes and filtered for 60 minutes.

[0060] [evaluation] The pH and percentage of fine pigment particles in the pigment suspension in the stock tank 71 were measured every 15 minutes. The results are shown in Table 4. For pH, the maximum and minimum values ​​over 15 minutes are shown in Table 4, except for the initial value (0 min).

[0061] TIFF2026046854000005.tif29170

[0062] As shown in Table 4, the proportion of fine pigment in the pigment suspension decreased from 10% to 8% after 1 hour of treatment, indicating that the removal efficiency is lower compared to the examples.

[0063] This embodiment includes the following configuration. (Configuration 1) A stock tank containing a pigment suspension containing fine pigment particles, A filtration means for passing the pigment suspension through an ultrafiltration membrane in a cross-flow manner to remove at least a portion of the fine pigment particles, A circulation means for circulating the pigment suspension between the stock solution tank and the filtration means, A pigment suspension purification apparatus comprising a pH adjusting agent supply means for supplying a pH adjusting agent to the stock solution tank, Furthermore, it is equipped with a monitoring unit that monitors the pH of the pigment suspension in the stock solution tank, A pigment suspension purification apparatus characterized by controlling the presence or absence of supply of the pH adjusting agent to the stock solution tank by the pH adjusting agent supply means and the supply flow rate based on the monitoring results from the monitoring unit. (Configuration 2) The pigment suspension purification apparatus according to Configuration 1, wherein the pH adjusting agent supply means is equipped with an inverter that controls the flow rate of the pH adjusting agent supplied to the stock solution tank by the pH adjusting agent supply means. (Configuration 3) The pH adjusting agent supply means further comprises A pH adjusting agent storage tank for storing the aforementioned pH adjusting agent, A pump for pumping the pH adjusting agent into the stock solution tank, An intermediate tank for storing the pH adjusting agent is placed between the pH adjusting agent storage tank and the pump, The pigment suspension purification apparatus according to configuration 2, further comprising a control means for controlling the amount of the pH adjusting agent stored in the intermediate tank to a constant level. [Explanation of Symbols]

[0064] 1: Purification equipment 2: Pigment suspension 3: Raw solution tank 4: Ultrafiltration membrane 5: Filtration methods 6: pH adjusting agent supply means 7:Water supply means 8: Flow channel 9: Flow channel 10: Circulation means 11: Monitoring Department

Claims

1. A stock tank containing a pigment suspension containing fine pigment particles, A filtration means for passing the pigment suspension through an ultrafiltration membrane in a cross-flow manner to remove at least a portion of the fine pigment particles, A circulation means for circulating the pigment suspension between the stock solution tank and the filtration means, A pigment suspension purification apparatus comprising a pH adjusting agent supply means for supplying a pH adjusting agent to the stock solution tank, Furthermore, it is equipped with a monitoring unit that monitors the pH of the pigment suspension in the stock solution tank, A pigment suspension purification apparatus characterized by controlling the presence or absence of supply of the pH adjusting agent to the stock solution tank by the pH adjusting agent supply means and the supply flow rate based on the monitoring results from the monitoring unit.

2. The pigment suspension purification apparatus according to claim 1, wherein the pH adjusting agent supply means comprises an inverter that controls the flow rate of the pH adjusting agent supplied to the stock solution tank by the pH adjusting agent supply means.

3. The pH adjusting agent supply means further, A pH adjusting agent storage tank for storing the aforementioned pH adjusting agent, A pump for pumping the pH adjusting agent into the stock solution tank, An intermediate tank for storing the pH adjusting agent is placed between the pH adjusting agent storage tank and the pump, The apparatus for purifying a pigment suspension according to claim 2, further comprising a control means for controlling the amount of the pH adjusting agent stored in the intermediate tank to a constant level.

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