Powder washing method

Abstract

To provide a powder cleaning method that enables powders to be satisfactorily filtered from slurry including the powders and solvents and enables the filtered powders to be satisfactorily cleaned.SOLUTION: A powder cleaning method with use of a filter is provided, the filter comprises a vessel which has an upper portion and a lower portion separated from each other by a porous layer, and has a liquid supply port at the upper portion and a liquid outlet at the lower portion. The method has: a step (1) (filtering step) in which slurry including a good solvent for powder and liquid and a poor solvent for powder is supplied to the upper portion of the filter from the liquid supply port, and the slurry is filtered while pressure of the upper portion of the filter is so maintained as to be higher than pressure of the lower portion, as a result, a cake layer is formed; and a step (2) (cleaning step) after the step (1), in which cleaning liquid including the poor solvent for powder is supplied to the upper portion of the filter from the liquid supply port to thereby clean the cake layer while the pressure of the upper portion of the filter is so maintained as to be the pressure or more of the upper portion upon completion of the filtering step. Both of the filtering step (1) and the cleaning step (2) are performed while maintaining the state that whole surface of an upper portion of the cake layer is always coated with the liquid.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a method for washing powders.

Background Art

[0002] In the production process of a polymer compound, after the polymer compound obtained by a polymerization reaction is crystallized, reprecipitated, etc., a step of filtering and washing a suspension (slurry) containing the obtained polymer compound powder and a solvent (mother liquor) is widely adopted. In the washing step, impurities contained in the polymer compound are removed by passing a solvent through the cake layer of the polymer compound obtained by filtering the slurry. In particular, since functional polymers (such as organic electroluminescence materials (organic EL materials)) are required to be of high purity, it is necessary to avoid poor washing and sufficiently remove impurities.

Summary of the Invention

Problems to be Solved by the Invention

[0003] An object of the present invention is to provide a method for washing powders, which can filter and wash powders well from a slurry containing powders and a solvent.

Means for Solving the Problems

[0004] The present inventor used a conventional method using a pressure filter to filter a suspension (slurry) containing a polymer compound powder and a solvent (mother liquor containing a good solvent and a poor solvent for the polymer compound), and then washed the obtained cake layer of the polymer compound with a poor solvent. It was found that problems such as cracks occurring in the cake layer formed after filtration or aggregates (lumps) of the polymer compound occurring in the cake layer after washing occurred, which affected the quality of the polymer compound.

[0005] The present inventors have conducted unique and detailed studies on these phenomena. Specifically, at the end of the filtration process of the slurry, when the mother liquor is extruded (dehydrated) from the cake layer under pressure conditions and the surface of the cake layer is exposed or gas is introduced into the cake layer, it has been found that cracks (fissures) occur in the cake layer. Also, after the filtration process, when the pressure in the space above the cake layer of the pressure filter is depressurized (for example, returned to normal pressure), and then a washing liquid is introduced and pressurized again for washing, since the pressure in the space above the cake layer of the filter becomes lower than the pressure at the lower part of the filter, it has also been found that cracks (fissures) occur in the cake layer due to the pressure difference.

[0006] In addition, the cake layer after filtration usually contains a mother liquor containing a good solvent and a poor solvent. When cracks (fissures) occur in the cake layer by the above operation, even if the cake layer is washed with a washing liquid containing a poor solvent thereafter, the washing liquid bypasses the cracks, and the mother liquor contained in the cake layer cannot be replaced by the washing liquid. In fact, it has been confirmed that the content rate of the good solvent in the filtrate after washing is lower than the theoretical value, while the content of the good solvent remains high in the wet cake layer obtained after washing. Therefore, it has been found that the polymer compound in the cake layer gradually dissolves in the remaining good solvent and blocks to form aggregates (lumps), and since the washing is insufficient for the aggregates, the good solvent and impurities remain.

[0007] When aggregates are generated in the cake layer after washing, the proportion of the good solvent and impurities remaining in the cake of the polymer compound increases, so problems such as deviation from product specifications may occur depending on the use of the polymer compound. Also, once aggregates of a certain size or more are generated, it becomes difficult for the aggregates to dissolve easily in the good solvent, so it takes time and labor to dissolve them again with the good solvent, which also hinders the efficiency improvement of the process.

[0008] Based on the above facts, the inventor intensively studied to solve the problems of the present invention. As a result, it was found that it is important that the entire surface of the cake layer is not exposed from the liquid surface during filtration and washing of the slurry. In addition, filtration is performed while maintaining the pressure (internal pressure) at the upper part of the filter higher than the pressure (internal pressure) at the lower part, and the washing liquid is introduced and the cake layer is washed while maintaining the pressure (internal pressure) at the upper part of the filter at or higher than the pressure (internal pressure) at the end of filtration, thereby suppressing the occurrence of cracks (fissures) and aggregates in the cake layer and enabling a good washing operation. Further studies led to the completion of the present invention.

[0009] That is, the present invention provides the following [1] to

[10] . [1] A method for washing a powder using a filter, comprising: The filter is composed of a container in which the upper and lower parts are separated by a porous layer, and has a liquid supply port at the upper part of the container and a liquid discharge port at the lower part. (1) A step of forming a cake layer by supplying a slurry containing a powder, a good solvent for the powder, and a poor solvent for the powder from the liquid supply port to the upper part of the filter and filtering while maintaining the pressure at the upper part of the filter higher than the pressure at the lower part (filtration step), and (2) Then, while maintaining the pressure at the upper part of the filter at or higher than the pressure at the upper part at the end of the filtration step, a washing liquid containing a poor solvent for the powder is supplied from the liquid supply port to the upper part of the filter to wash the cake layer (washing step). having A washing method in which both the filtration step (1) and the washing step (2) are carried out while maintaining a state in which the entire upper surface of the cake layer is covered with liquid. [2] The washing method according to [1], wherein the filtration step (1) is carried out by pressurizing the upper part of the filter. [3] The washing method according to [1] or [2], wherein the powder is a powder of a polymer compound. [4] The washing method according to [3], wherein the polymer compound is a material for an organic EL element (particularly, a light-emitting material or a charge-transporting material). [5] The washing method according to any one of [1] to [4], wherein the average particle diameter of the powder is 0.3 to 3000 μm. [6] The cleaning method according to any one of [1] to [5], wherein the good solvent is an aromatic hydrocarbon solvent and the poor solvent is at least one selected from the group consisting of water, an alcohol solvent, a ketone solvent, an aliphatic hydrocarbon solvent, a nitrile solvent, and an ester solvent. [7] The cleaning method according to any one of [1] to [6], wherein in the filtration step (1), the pressure at the upper part of the filter is 1 to 300 kPaG. [8] The cleaning method according to any one of [1] to [7], wherein in the cleaning step (2), the pressure at the upper part of the filter is 5 to 350 kPaG. [9] The cleaning method according to any one of [1] to [8], further including, after the cleaning step (2), a step of pressurizing the upper part of the filter to extrude the cleaning liquid of the cake layer and drying the cake to obtain a powder.

[10] A method for producing a powder cleaned using a filter, wherein the filter comprises a container separated by porous layers at the upper and lower parts, has a liquid supply port at the upper part of the container and a liquid discharge port at the lower part, (1) A step (filtration step) of supplying a slurry containing a powder, a good solvent for the powder, and a poor solvent for the powder from the liquid supply port to the upper part of the filter and filtering while maintaining the pressure at the upper part of the filter higher than the pressure at the lower part to form a cake layer, and (2) Then, a step (cleaning step) of supplying a cleaning liquid containing a poor solvent for the powder from the liquid supply port to the upper part of the filter while maintaining the pressure at the upper part of the filter at or higher than the pressure at the upper part at the end of the filtration step and cleaning the cake layer having, wherein both the filtration step (1) and the cleaning step (2) are carried out while maintaining a state where the entire upper surface of the cake layer is covered with liquid.

Advantages of the Invention

[0010] According to the method for washing powder of the present invention, the powder can be satisfactorily filtered and washed from a slurry containing the powder and a solvent (mother liquor). Specifically, when filtering and washing the slurry, the generation of cracks (fissures) in the powder cake layer can be suppressed, and further, the aggregates (lumps) formed due to poor washing caused by such cracks can be suppressed. Thereby, it is possible to obtain a washed powder having a low impurity content and excellent solubility in a good solvent.

Brief Description of the Drawings

[0011]

Figure 1

Embodiments for Carrying Out the Invention

[0012] Hereinafter, preferred embodiments of the present invention will be described in detail.

[0013] 1. Filter The filter used in the method for washing powder of the present invention is not particularly limited as long as it is composed of a container in which the upper part and the lower part are separated by a porous layer, and has a liquid supply port at the upper part of the container and a liquid discharge port at the lower part, and a widely known filter can be adopted.

[0014] The shape of the filter is not particularly limited, and examples thereof include a cylindrical shape, a conical shape, a cubic shape, an inverted conical shape, etc. Since the inside of the container may be pressurized or depressurized, the upper part of the filter is preferably hemispherical (for example, dome-shaped, bell-shaped) in consideration of pressure resistance. Further, the material of the filter may be determined according to the resistance to the liquid to be permeated and the required pressure resistance, and is not particularly limited. Since filtration is carried out using the pressure difference between the upper and lower parts of the filter, it is preferably made of a pressure-resistant material. Examples of the material of the filter include stainless steel, glass lining, glass, and at least a combination of two or more of them. Further, the material of the upper part of the container may be made transparent, or the container may be provided with a sight glass or the like so that the flow of the fluid inside the container and the powder slurry can be visually observed.

[0015] The size of the filter can be freely selected in consideration of the amount of slurry (or filter cake) to be processed, the size of the manufacturing equipment, ease of handling, working space, etc. For example, when a cylindrical shape is selected for the filter, the length (height) of the cylindrical portion is usually 1 cm to 500 cm, preferably 5 cm to 350 cm, more preferably 10 cm to 200 cm, and its inner diameter is usually 1 cm to 150 cm, preferably 10 cm to 100 cm, more preferably 15 cm to 80 cm.

[0016] The porous layer serves as a filter for separating powder and solvent from a slurry (suspension) containing powder and solvent. The porous layer is preferably installed horizontally inside the filter. The porous layer may also be referred to as a filter plate. The material of the porous layer can be selected in consideration of the resistance to the liquid to be permeated, and there is no particular limitation. For example, paper (such as cellulose); resin (such as polyamide, polyester, polyolefin, polytetrafluoroethylene (PTFE) (Teflon (registered trademark)), etc.); glass; ceramic; or metal (such as stainless steel, iron, aluminum, copper, nickel, etc.). The pore diameter of the porous layer is, for example, 0.1 μm to 300 μm, preferably 0.5 μm to 200 μm, more preferably 1 μm to 100 μm.

[0017] A filter medium may be provided on the upper surface of the porous layer to hold the powder cake layer formed by filtration and washing and to facilitate removal. The filter medium preferably covers the entire upper part of the porous layer. The material of the filter medium is not particularly limited as long as it is insoluble in the solvent and can hold the powder. For example, paper (such as cellulose); resin (such as polyamide, polyester, polyolefin, polytetrafluoroethylene (PTFE) (Teflon (registered trademark)), etc.). Usually, a cloth-like filter cloth is used.

[0018] Normally, at the upper part of the filter, there is a liquid supply port equipped with a charging valve for supplying slurry and cleaning liquid to the filter, a filter internal pressure gauge for measuring the internal pressure of the upper part of the container, and a pressurizing valve and an exhaust valve for adjusting the internal pressure. Also, at the lower part of the filter, there is a liquid discharge port equipped with a filtrate extraction valve, and it may have a decompression valve as needed. As an example of the filter, a schematic diagram of a pressure filter is shown in Fig. 1. At the upper part of the pressure filter 1, there are a charging valve V1, a filter internal pressure gauge 4, a pressurizing valve V4, and an exhaust valve V2. At the lower part of the filter, there is a filtrate extraction valve V3.

[0019] 2. Cleaning method of the present invention The cleaning method of the present invention has the following (1) filtration step and (2) cleaning step. (1) Filtration step The filtration step is a step of supplying slurry from the liquid supply port to the upper part of the filter and forming a cake layer by filtration while maintaining the pressure (internal pressure) at the upper part of the filter higher than the pressure (internal pressure) at the lower part.

[0020] The slurry contains powder, a good solvent for the powder, and a poor solvent for the powder. The powder is not particularly limited as long as it is a substance soluble in the good solvent and poorly soluble in the poor solvent, and is preferably an organic compound, more preferably a polymer compound.

[0021] Examples of the polymer compound include compounds obtained by polymerizing a predetermined monomer and having two or more repeating units (hereinafter also referred to as structural units) derived from the monomer. The polymer compound has a molecular weight distribution, and the weight average molecular weight (Mw) in terms of polystyrene is in the range of 1×10 3 ~1×10 8 , further 3×10 3 ~1×10 7 , particularly in the range of 1×10 4 ~1×10 6 .

[0022] As a method for polymerizing a polymer compound, for example, there are a method of polymerizing a monomer compound by a Suzuki coupling reaction, a method of polymerizing by a Buchwald coupling reaction, a method of polymerizing by a Stille coupling reaction, a method of polymerizing by a Kumada coupling reaction, a method of polymerizing by a Yamamoto coupling reaction, and the like. Among them, since impurities such as low molecular weight components and hydroxyl group-containing polymer compounds can be adsorbed and removed by the above-mentioned molding adsorbent, typically, a polymer compound produced by a method of polymerizing by a Suzuki coupling reaction is mentioned.

[0023] The polymer compound is preferably used as a material for, particularly, an organic EL element or the like, especially as a light-emitting material or a charge transporting material. Here, the charge transporting material may be either a hole transporting material or an electron transporting material.

[0024] Examples of the polymer compound used as a light-emitting material include polymer compounds containing an arylene group such as a phenylene group, a naphthalenediyl group, a fluorenediyl group, a phenanthrenediyl group, a dihydrophenanthrenediyl group, an anthracenediyl group, and a pyrenediyl group; an aromatic amine residue such as a group formed by removing two hydrogen atoms from an aromatic amine; and a divalent heterocyclic group such as a carbazolediyl group, a phenoxazinediyl group, and a phenothiazinediyl group.

[0025] Examples of the polymer compound used as a hole transporting material include polyvinylcarbazole and its derivatives; polyarylene having an aromatic amine structure in its side chain or main chain and its derivatives. Examples of the polymer compound used as an electron transporting material include polyphenylene, polyfluorene, and their derivatives. The polymer compound may be doped with a metal.

[0026] Examples of the polymer compound as a light-emitting material or a charge transporting material include a conjugated polymer compound and a non-conjugated polymer compound, and a conjugated polymer compound is preferred.

[0027] The conjugated polymer compound mentioned above means a polymer compound containing an aromatic ring in the main chain, and 80% or more of the bonds between the aromatic rings contained in the main chain are directly bonded, conjugated bonding groups such as vinylene groups, or atoms such as oxygen atoms, sulfur atoms, and nitrogen atoms having unpaired electrons. In the conjugated polymer compound, the above-mentioned bonding form is preferably a direct bond or a nitrogen atom having an unpaired electron, and more preferably a direct bond. The non-conjugated polymer compound mentioned above means a polymer compound containing an aromatic ring in the main chain, and less than 80% of the bonds between the aromatic rings contained in the main chain are directly bonded, conjugated bonding groups such as vinylene groups, or atoms such as oxygen atoms, sulfur atoms, and nitrogen atoms having unpaired electrons, or a polymer compound not containing an aromatic ring in the main chain but having an aromatic ring in the side chain.

[0028] Examples of the conjugated polymer compound include polymer compounds in which benzene, naphthalene, phenanthrene, fluorene, etc. are the aromatic rings of the main chain. The aromatic ring may be one kind or two or more kinds.

[0029] The aromatic ring may have a substituent, and examples of the substituent include an alkyl group, a cycloalkyl group, an alkoxy group, an amino group, an aryl group, and a crosslinking group may also be included. The crosslinking group is a group capable of generating a new bond by being subjected to heating, ultraviolet irradiation, near-ultraviolet irradiation, visible light irradiation, infrared irradiation, or a radical reaction, etc. Examples of the crosslinking group include a vinyl group, a styryl group, a benzocyclobutanoyl group, an acetyl group, a norbornyl group, an oxetanyl group, etc.

[0030] The shape and size of the powder are not particularly limited as long as they can be filtered through the porous layer. Examples of the shape of the powder include granular, powdery, and fibrous shapes. Examples of the size of the powder include those having an average particle diameter of 0.3 to 3000 μm, preferably 0.5 to 2000 μm, more preferably 1 to 1000 μm. Here, the average particle diameter means the cumulative 50% particle diameter based on volume, and is a numerical value measured using a laser diffraction / scattering particle size distribution analyzer. The numerical values described above are those measured after dispersing in a poor solvent such as water or methanol.

[0031] When the powder is a polymer compound, a good solvent for the polymer compound can be specifically defined as a solvent in which the solubility (20 °C) of the polymer compound is 1 g / 100 g or more.

[0032] A poor solvent for the polymer compound can be specifically defined as a solvent in which the solubility (20 °C) of the polymer compound is less than 1 g / 100 g.

[0033] The good solvent and the poor solvent can be determined according to the type of the polymer compound. For example, water; aromatic hydrocarbon solvents such as toluene, xylene, mesitylene, cyclohexylbenzene, and tetralin; ether solvents such as tetrahydrofuran (THF), 1,4-dioxane, dimethoxyethane, and anisole; amide solvents such as N,N-dimethylacetamide (DMA), N,N-dimethylformamide (DMF), and N-methyl-2-pyrrolidone; alcohol solvents such as methanol, ethanol, ethylene glycol, isopropyl alcohol, propylene glycol, ethylene glycol monomethyl ether, and ethylene glycol monobutyl ether; ketone solvents such as acetone, methyl ethyl ketone, cyclopentanone, cyclohexanone, methyl amyl ketone, and methyl isobutyl ketone; aliphatic hydrocarbon solvents such as pentane, hexane, and heptane; nitrile solvents such as acetonitrile; halogenated hydrocarbon solvents such as chloroform; ester solvents such as methyl acetate and ethyl acetate; dimethyl sulfoxide (DMSO); etc. The solvent may be used alone or in combination of two or more.

[0034] In particular, when the polymer compound is a material for an organic EL element or the like, examples of the good solvent include aromatic hydrocarbon solvents such as toluene, xylene, mesitylene, cyclohexylbenzene, and tetralin, and preferably toluene and xylene. Examples of the poor solvent include water; alcohol solvents such as methanol, ethanol, ethylene glycol, isopropyl alcohol, propylene glycol, ethylene glycol monomethyl ether, and ethylene glycol monobutyl ether; ketone solvents such as acetone, methyl ethyl ketone, cyclopentanone, cyclohexanone, methyl amyl ketone, and methyl isobutyl ketone; aliphatic hydrocarbon solvents such as pentane, hexane, and heptane; nitrile solvents such as acetonitrile; ester solvents such as methyl acetate and ethyl acetate, etc., and preferably methanol and acetone. The solvent may be used alone or in combination of two or more.

[0035] Since the ratio of the poor solvent to the good solvent in the total solvent varies depending on the solubility of the powder (especially the powder of the polymer compound), there is no particular limitation. Generally, the ratio of the poor solvent to the good solvent (poor solvent / good solvent; weight ratio) is usually 1 to 10, and more preferably 3 to 8.

[0036] The content of the powder in the slurry (especially the powder of the polymer compound) is usually 0.001 to 10% by weight, preferably 0.01 to 1% by weight, and more preferably 0.05 to 0.5% by weight because the fluidity during liquid feeding can be kept good.

[0037] Typical examples of the slurry include a slurry containing the powder of the polymer compound obtained after the polymerization reaction and the reaction solvent, and a slurry containing the powder of the polymer compound and the solvent after reprecipitation treatment using a poor solvent after dissolving the polymer compound in a good solvent.

[0038] The filtration process can be carried out by utilizing the pressure difference between the upper space and the lower space after supplying the slurry to the upper part of the container or while supplying the slurry. Specifically, methods such as pressurizing the upper space (pressure filtration), depressurizing the lower space (vacuum filtration), and combined use of them are adopted. Pressure filtration can be carried out, for example, by pressurizing the upper space using an inert gas such as nitrogen. Vacuum filtration can be carried out by providing additional equipment such as a vacuum source (pump) according to the capacity of the filter and depressurizing the lower space. Also, when the powder to be filtered and washed is an electronic material used in precision equipment, even a small amount of dust, dirt, etc. is not desired to be mixed in. Therefore, when the equipment is under negative pressure, there is a possibility of bringing in dust and dirt from the outside. Therefore, generally, pressure filtration is preferred.

[0039] When adopting typical pressure filtration, it is important to set the pressure at the upper part of the filter to exceed the pressure at the lower part of the filter (usually, atmospheric pressure) for filtration. The pressure at the upper part of the filter is usually 1 - 300 kPaG, preferably 10 - 180 kPaG. The filtration process is preferably carried out with the pressure as constant as possible.

[0040] The temperature of the filtration process can be appropriately selected considering factors such as the type of solvent and the solubility of the powder in the solvent. Usually, it is 0 - 50 °C, preferably 5 - 30 °C.

[0041] In the filtration process, if the liquid is blown off from the cake layer by pressurization from the upper part of the filter, cracks will occur in the cake layer. To avoid this, it is crucial to always maintain a state where the entire surface of the cake layer is covered with liquid. For this purpose, the surface of the cake layer can be smoothed (made the thickness uniform) and adjusted to be horizontal by applying vibration to the filter as necessary so that there is no unevenness in the height of the liquid level.

[0042] Taking an example using the filter shown in Fig. 1, filtration is carried out by closing the pressure valve V4 and the exhaust valve V2, opening the filtrate extraction valve V3, and supplying the slurry from the charging valve V1. In this case, the pressure at the upper part of the filter is maintained in a pressurized state, and filtration is carried out without exposing the upper surface of the cake layer.

[0043] (2) Washing step The washing step is a step of supplying a washing liquid containing a poor solvent for the powder from the liquid supply port to the upper part of the filter while maintaining the pressure (internal pressure) at the upper part of the filter above the pressure (internal pressure) at the upper part at the end of the filtration step after filtration to wash the cake layer.

[0044] In this washing step, by passing a washing liquid containing a poor solvent through the cake layer, the solvent containing the good solvent and the poor solvent contained in the cake layer is replaced with the poor solvent. Thereby, impurities that can be dissolved in the poor solvent contained in the cake layer can be removed, and the formation of aggregates in which the powder is dissolved and fixed by the good solvent in the cake layer can be suppressed. When shifting from the filtration step to the washing step, the supply of the washing liquid to the filter and the discharge of the filtrate may be either continuous or intermittent. Also, the supply of the washing liquid and the discharge of the filtrate in the washing step may be either continuous or intermittent.

[0045] The washing liquid preferably contains a poor solvent as a main component, and the content of the poor solvent in the washing liquid is usually 80% by weight or more, preferably 90% by weight or more, more preferably 95% by weight or more.

[0046] The poor solvent can be the same as that described in the filtration step of (1) above. For example, when the powder is a polymer compound (especially a material for an organic EL element, etc.), examples of the poor solvent include water; alcohol solvents such as methanol, ethanol, ethylene glycol, isopropyl alcohol, propylene glycol, ethylene glycol monomethyl ether, and ethylene glycol monobutyl ether; ketone solvents such as acetone, methyl ethyl ketone, cyclopentanone, cyclohexanone, methyl amyl ketone, and methyl isobutyl ketone; aliphatic hydrocarbon solvents such as pentane, hexane, and heptane; nitrile solvents such as acetonitrile; ester solvents such as methyl acetate and ethyl acetate, etc. Methanol and acetone are preferred.

[0047] The cleaning liquid may be a single-component solvent or a solvent composed of a combination of two or more solvents as long as it contains the poor solvent. For example, when the powder is a polymer compound, an alcohol solvent such as methanol is used as the poor solvent, and then, in consideration of handleability, the alcohol solvent can be washed with a solvent obtained by adding another solvent (for example, water) to the alcohol solvent. Also, the cleaning may be performed once or two or more times. Specifically, after washing with methanol as the cleaning liquid, it can be washed with a mixed solution of water and methanol (for example, a 5 to 30 wt% methanol aqueous solution, etc.).

[0048] The cleaning step can be carried out by utilizing the pressure difference between the upper space and the lower space after supplying the cleaning liquid to the upper part of the container or while supplying the cleaning liquid. Specifically, methods such as pressurizing the upper space (pressure filtration), depressurizing the lower space (vacuum filtration), and a method combining them are adopted. Pressure filtration and vacuum filtration can be carried out in the same manner as the filtration step. Among them, for the same reason as in the filtration step, pressure filtration is preferred.

[0049] During a series of processes from the filtration step to the washing step, it is important to always maintain the pressure at the top of the filter higher than the pressure at the bottom of the filter without depressurizing (returning to normal pressure) the pressure at the top of the filter midway to prevent cracks (fissures) in the cake layer. When adopting typical pressure filtration, it is more preferable to perform filtration while maintaining the pressure (internal pressure) at the top of the filter at or above the pressure (internal pressure) at the top at the end of the filtration step. The pressure at the top of the filter in the washing step is usually 5 to 350 kPaG, preferably 20 to 200 kPaG. The washing step is preferably carried out with the pressure as constant as possible.

[0050] Even in the washing step, following the filtration step, in order to prevent cracks (fissures) in the cake layer, it is always carried out while maintaining the entire upper surface of the cake layer covered with liquid.

[0051] Taking an example using the filter shown in Fig. 1, the transition from the filtration step to the washing step is carried out by closing the pressure valve V4 and the exhaust valve V2, closing the filtrate extraction valve V3, maintaining the pressure at the top of the filter in a pressurized state without depressurizing, and supplying the washing liquid from the charging valve V1. After supplying the washing liquid, or while supplying the washing liquid, the filtrate extraction valve V3 is opened to pass the washing liquid through the cake layer for washing. In this case, the pressure at the top of the filter is maintained in a pressurized state to perform washing without exposing the upper surface of the cake layer.

[0052] (3) After washing After the washing step, the top of the filter is pressurized or the bottom of the filter is depressurized to extrude (blow out) the washing liquid from the cake layer. Then, the cake (powder) is taken out from the filter and dried to obtain the desired powder. Taking an example using the filter shown in Fig. 1, the charging valve V1 and the exhaust valve V2 are closed, the filtrate extraction valve V3 is opened, the pressure valve V4 is opened to supply gas (for example, an inert gas such as nitrogen) to the top of the filter, and the washing liquid in the cake layer is extruded.

[0053] The cake (powder) produced through the above-described filtration step (1) and washing step (2) is suitable because the impurity content is reduced and the generation of aggregates is reduced.

[0054] In particular, when the obtained cake (powder) is a material (polymer compound) such as an organic EL element, a high-quality element with a low content of impurities and good solvent can be produced. Also, when producing a coating-type ink using the material, since no aggregates are contained and it can be easily dissolved in a good solvent, the productivity of the ink can be increased, and thus the performance of the organic EL element can be stabilized.

Example

[0055] Examples are shown below to explain the present invention in more detail, but the present invention is not limited thereto.

[0056] <Aggregate generation rate (weight%)> In the examples and comparative examples, the quality of the powder washing effect was evaluated using the aggregate generation rate in the wet cake of the powder obtained by filtering the slurry containing the powder and the solvent as an index. Specifically, aggregates with a length of 1 cm or more in the long axis direction were selected from the obtained wet cake, and the percentage of the weight (Y) of the aggregates with respect to the weight (X) of the entire wet cake was calculated.

[0057] Generation rate (weight%) = [Weight of aggregates (Y) / Weight of entire wet cake (X)] × 100

[0058] The closer the aggregate generation rate is to 0%, the better the washing, and the larger it is, the worse the washing. Here, the reason for evaluating "aggregates with a length of 1 cm or more in the long axis direction" as an undesirable component is that the content ratio of the good solvent and / or impurities in the aggregates increases, which may cause a decrease in performance when an organic EL element is produced using the powder. Another reason is that when dissolving aggregates in a good solvent, relatively large aggregates require time to dissolve because the contact area with the solvent relatively decreases, which may impair the productivity of the ink.

[0059] <Example 1> Powder (a conjugated polymer compound containing fluorene and triarylamine as constituent units, weight average molecular weight: 1×10 5 , average particle diameter: 20 μm, for example, refer to JP-A-2021-080401.) 0.75 kg, a slurry composed of 85 kg of toluene and 553 kg of methanol was fed into a filter (filter diameter 0.80 m, filtration area 0.50 m 2 , filter capacity 171 L) similar to the apparatus shown in Fig. 1 with the filtrate extraction valve V3 closed. After charging the slurry to about 80% of the filter capacity, the exhaust valve V2 was closed, and the filtrate extraction valve V3 was gradually opened to perform filtration. As filtration progressed and the supply of the entire amount of the slurry into the filter was completed, the charging valve V1 was closed. The pressure valve V4 was opened to pressurize the inside of the filter with nitrogen gas, and when the liquid level reached a position 5 cm from the upper surface of the cake layer, the filtrate extraction valve V3 and the pressure valve V4 were closed to stop filtration. At this time, the internal pressure of the filter was 23 kPaG.

[0060] Next, with valves V2, V3, and V4 closed, the charging valve V1 was opened to supply 150 kg of methanol for washing at a pressure of 25 kPaG, and the filtrate extraction valve V3 was gradually opened to perform washing filtration while preventing the surface of the cake layer from being exposed. After the washing with the specified amount of methanol was completed, the charging valve V1 was closed, the pressure valve V4 was opened, and the washing liquid remaining in the filter was drained with nitrogen gas for 10 minutes, and then the filtrate extraction valve V3 was closed.

[0061] Next, 150 kg of a 20 wt% aqueous methanol solution for washing was fed into the filter by opening the charging valve V1, and the filtrate extraction valve V3 was opened to perform washing filtration. After the washing with the specified amount of the 20 wt% aqueous methanol solution was completed, the charging valve V1 was closed, the pressure valve V4 was opened, and the washing liquid remaining in the filter was drained with nitrogen gas for 1 hour, and then the filtrate extraction valve V3 was closed. Aggregates with a length of 1 cm or more in the long axis direction were not observed in the obtained cake layer.

[0062] <Example 2> 0.75 kg of the powder (the same as in Example 1), 77 kg of toluene, and 508 kg of methanol were used to form a slurry, which was fed into the same filter as in Example 1 with the filtrate extraction valve V3 closed. After charging the slurry to about 80% of the filter capacity, the exhaust valve V2 was closed, and the filtrate extraction valve V3 was gradually opened to perform filtration. After filtration progressed and the supply of the entire amount of the slurry into the filter was completed, the charging valve V1 was closed. The pressure valve V4 was opened to pressurize the inside of the filter with nitrogen gas, and when the liquid level reached a position 3 cm from the upper surface of the cake layer, the filtrate extraction valve V3 and the pressure valve V4 were closed to stop filtration. At this time, the internal pressure of the filter was 50 kPaG.

[0063] Next, with valves V2, V3, and V4 closed, the charging valve V1 was opened to supply 141 kg of washing methanol at a pressure of 60 kPaG, and the filtrate extraction valve V3 was gradually opened to perform washing filtration while preventing the surface of the cake layer from being exposed. After washing with the specified amount of methanol was completed, the charging valve V1 was closed, the pressure valve V4 was opened, and the washing liquid remaining in the filter was drained with nitrogen gas for 10 minutes, after which the filtrate extraction valve V3 was closed.

[0064] Next, 140 kg of a 20 wt% methanol aqueous solution for washing was supplied into the filter by opening the charging valve V1, and washing filtration was performed by opening the filtrate extraction valve V3. After washing with the specified amount of 20 wt% methanol water was completed, the charging valve V1 was closed, the pressure valve V4 was opened, and the washing liquid remaining in the filter was drained with nitrogen gas for 1 hour, after which the filtrate extraction valve V3 was closed. Aggregates with a length of 1 cm or more in the long axis direction were not observed in the obtained cake layer.

[0065] <Example 3> 0.80 kg of the powder (the same as in Example 1), 90 kg of toluene, and 550 kg of methanol were used to form a slurry, which was fed into a filter similar to the apparatus shown in Fig. 1 (filter diameter 0.70 m, filtration area 0.38 m 2, with the filter capacity of 193 L, the supply was started with the filtrate extraction valve V3 closed. After charging the slurry to about 80% of the filter capacity, the exhaust valve V2 was closed, and the filtrate extraction valve V3 was gradually opened to conduct filtration. As the filtration progressed and the supply of the entire amount of the slurry into the filter was completed, the charging valve V1 was closed. The pressurizing valve V4 was opened to pressurize the inside of the filter with nitrogen gas. When the liquid level reached a position about 2 cm from the upper surface of the cake layer, the filtrate extraction valve V3 and the pressurizing valve V4 were closed to stop the filtration. At this time, the pressure inside the filter was 135 kPaG.

[0066] Next, with the valves V2, V3, and V4 closed, the charging valve V1 was opened to supply 144 kg of methanol for washing at a pressure of 140 kPaG. While preventing the surface of the cake layer from being exposed, the filtrate extraction valve V3 was gradually opened to conduct washing filtration. After the washing with the specified amount of methanol was completed, the charging valve V1 was closed, the pressurizing valve V4 was opened, and the washing liquid remaining in the filter was drained with nitrogen gas for 10 minutes, and then the filtrate extraction valve V3 was closed.

[0067] Next, 147 kg of a 20 wt% aqueous methanol solution for washing was supplied into the filter by opening the charging valve V1, and the filtrate extraction valve V3 was opened to conduct washing filtration. After the washing with the specified amount of the 20 wt% aqueous methanol solution was completed, the charging valve V1 was closed, the pressurizing valve V4 was opened, and the washing liquid remaining in the filter was drained with nitrogen gas for 1 hour, and then the filtrate extraction valve V3 was closed. Aggregates with a length of 1 cm or more in the long axis direction were not observed in the obtained cake layer.

[0068] <Comparative Example 1> 0.75 kg of powder (the same as in Example 1), 78 kg of toluene, and 514 kg of methanol were used to form a slurry, which was fed into the same filter as in Example 1 with the filtrate extraction valve V3 closed. The supply was started, and after charging the filter to about 80% of its capacity with the slurry, the exhaust valve V2 was closed, and the filtrate extraction valve V3 was gradually opened to perform filtration. As filtration progressed and the supply of the entire amount of slurry into the filter was completed, the charging valve V1 was closed. The pressure valve V4 was opened to pressurize the inside of the filter with nitrogen gas. Filtration was stopped by closing the filtrate extraction valve V3 and the pressure valve V4 when the liquid level reached a position 10 cm above the upper surface of the cake layer. At this time, the pressure inside the filter was 40 kPaG. Thereafter, the filtrate extraction valve V3 was opened to depressurize the inside of the pressure filter.

[0069] Next, with the exhaust valve V2 and the filtrate extraction valve V3 closed, the charging valve V1 was opened to supply 58 kg of methanol for washing at a pressure of 10 - 20 kPaG. While preventing the surface of the cake layer from being exposed, the filtrate extraction valve V3 was gradually opened to perform washing filtration. After that, the charging valve V1 was closed, the pressure valve V4 was opened, and the washing liquid remaining in the filter was drained with nitrogen gas for 10 minutes. Then, the filtrate extraction valve V3 was closed.

[0070] Next, 58 kg of a 20 wt% aqueous methanol solution for washing was supplied into the filter by opening the charging valve V1, and washing filtration was performed by opening the filtrate extraction valve V3. After the washing with the 20 wt% aqueous methanol solution was completed, the charging valve V1 was closed, the pressure valve V4 was opened, and the washing liquid remaining in the filter was drained with nitrogen gas for 1 hour. Then, the filtrate extraction valve V3 was closed. When the obtained cake layer was separated into aggregates with a size of 1 cm or more in the major axis direction and powder with a size of less than 1 cm, the weight of the aggregates of 1 cm or more was 17 g, and the total weight of the cake was 3.78 kg.

[0071] <Comparative Example 2> A slurry with the same composition as in Example 1 was fed into the same filter as in Example 1 with the filtrate extraction valve V3 closed. After charging the filter to about 80% of its capacity with the slurry, the exhaust valve V2 was closed, and the filtrate extraction valve V3 was gradually opened to perform filtration. After filtration progressed and the supply of the entire amount of the slurry into the filter was completed, the charging valve V1 was closed. The pressure valve V4 was opened to pressurize the inside of the filter with nitrogen gas, and filtration was performed until the filtrate stopped flowing. Since it was confirmed that the filter cake layer was cracked (i.e., cracks had occurred), the washing process in that state was not carried out.

[0072] The above results are shown in Table 1.

Table 1

[0073] From Table 1, in Examples 1 to 3, in the filtration process and washing process of the slurry, the surface of the cake layer was not exposed from the liquid level, and the pressure at the upper part of the filter during washing was greater than the same pressure at the end of filtration. Therefore, the cake layer could be washed well, and no aggregates were generated in the wet powder after the washing process. On the other hand, in Comparative Example 1, since the pressure at the upper part of the filter during washing was smaller than the same pressure at the end of filtration, cracks occurred in the cake layer and aggregates were generated. This is presumably because the washing methanol preferentially flowed into the cracked part, and in some parts of the cake layer, the good solvent (toluene) contained inside the cake layer was not replaced by the poor solvent (methanol) and remained in the cake layer. As a result, poor washing occurred in Comparative Example 1. Also, in Comparative Example 2, in the filtration process and washing process of the slurry, since the surface of the cake layer was exposed from the liquid level, cracks occurred in the cake layer, and the good solvent (toluene) of the cake layer could not be replaced by the poor solvent (methanol).

Industrial Applicability

[0074] According to the cleaning method of the present invention, the powder in the slurry can be cleaned well. When the cake (powder) is a material (polymer compound) such as an organic EL element, a high-quality element with a low content of impurities and good solvent can be produced. Also, when producing a coating-type ink using the material, since no aggregates are contained and it can be easily dissolved in a good solvent, the productivity of the ink can be increased, and thus the performance of the organic EL element can be stabilized.

Explanation of symbols

[0075] 1: Pressure filter 2: Filter medium (filter cloth) 3: Filter plate (porous layer) 4: Pressure gauge inside the filter V1: Charge valve V2: Exhaust valve V3: Filtrate extraction valve V4: Pressure valve

Claims

1. A method for washing a powder using a filter, comprising: The filter consists of a container with its upper and lower parts separated by a porous layer, having a liquid supply port at the upper part of the container and a liquid discharge port at the lower part, (1) A step of forming a cake layer by supplying a slurry containing a powder, a good solvent for the powder, and a poor solvent for the powder from the liquid supply port to the upper part of the filter and filtering while maintaining the pressure at the upper part of the filter higher than the pressure at the lower part (filtration step), and (2) Subsequently, a step of washing the cake layer by supplying a cleaning liquid containing a poor solvent for the powder from the liquid supply port to the upper part of the filter while maintaining the pressure at the upper part of the filter at or higher than the pressure at the upper part at the end of the filtration step (washing step) having, A washing method in which both the filtration step (1) and the washing step (2) are carried out while maintaining a state where the entire upper surface of the cake layer is covered with liquid.

2. The washing method according to claim 1, wherein the filtration step (1) is carried out by pressurizing the upper part of the filter.

3. The washing method according to claim 1 or 2, wherein the powder is a powder of a polymer compound.

4. The washing method according to claim 3, wherein the polymer compound is a material for an organic EL element.

5. The washing method according to any one of claims 1 to 4, wherein the average particle diameter of the powder is 0.3 to 3000 μm.

6. The washing method according to any one of claims 1 to 5, wherein the good solvent is an aromatic hydrocarbon solvent and the poor solvent is at least one selected from the group consisting of water, an alcohol solvent, a ketone solvent, an aliphatic hydrocarbon solvent, a nitrile solvent, and an ester solvent.

7. The washing method according to any one of claims 1 to 6, wherein in the filtration step (1), the pressure at the upper part of the filter is 1 to 300 kPaG.

8. The washing method according to any one of claims 1 to 7, wherein in the washing step (2), the pressure at the upper part of the filter is 5 to 350 kPaG.

9. The washing method according to any one of claims 1 to 8, further comprising, after the washing step (2), a step of pressurizing the upper part of the filter to extrude the washing liquid of the cake layer and drying the cake to obtain the powder.

10. A method for producing a powder washed using a filter, comprising: The filter consists of a container with its upper and lower parts separated by a porous layer, having a liquid supply port at the upper part of the container and a liquid discharge port at the lower part, (1) A step of forming a cake layer by filtering a slurry containing a powder, a good solvent for the powder, and a poor solvent for the powder from a liquid supply port to the upper part of a filter while maintaining the pressure at the upper part of the filter higher than the pressure at the lower part (filtration step), and (2) Then, a step of washing the cake layer by supplying a cleaning liquid containing a poor solvent for the powder from the liquid supply port to the upper part of the filter while maintaining the pressure at the upper part of the filter at or higher than the pressure at the upper part at the end of the filtration step (washing step) are provided, A manufacturing method in which both the filtration step (1) and the washing step (2) are carried out while maintaining a state in which the entire upper surface of the cake layer is covered with liquid.

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