Method and device for reducing coating defects of disc type ceramic membrane

Abstract

The invention provides a method and device for reducing coating defects of a disc-type ceramic membrane, and the method comprises the following steps: positively mounting a clamp on a spraying station, enabling the ceramic membrane to dynamically rotate, and cleaning and activating the front surface of the ceramic membrane by adopting a low-temperature plasma technology; carrying out negative pressure suction on the ceramic membrane while the ceramic membrane is dynamically rotated, and spraying a membrane preparation liquid on the front surface of the ceramic membrane by adopting ultrasonic atomization; and dynamically rotating the ceramic membrane, and performing negative pressure suction on the ceramic membrane, so that the circular arc part of the ceramic membrane is dynamically dip-coated in the membrane preparation liquid. According to the method, dynamic rotation of the ceramic membrane, negative pressure and ultrasonic spraying are cooperated, ultrasonic atomized liquid drops are sucked into a micropore structure or surface gaps when making contact with the surface of the ceramic membrane, pinholes or defects of the membrane layer are avoided, and the uniform, dense and defect-free membrane layer is formed; and non-contact with the ceramic membrane can be realized, and the coating defect caused by improper contact before the membrane layer is dried is effectively prevented.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of disk-shaped ceramic membranes, and particularly relates to a method and device for reducing coating defects of disk-shaped ceramic membranes. BACKGROUND

[0002] Disk-shaped ceramic membranes are disc-shaped filter media made of ceramic materials, which have high mechanical strength, high temperature resistance, corrosion resistance, good chemical stability and other advantages, and are widely used in water treatment, food and beverage, biological medicine, chemical separation and other fields.

[0003] In the application process of disk-shaped ceramic membranes, the ceramic membrane sheet rotates at high speed and performs high-speed shearing on the material, which accelerates the damage of the membrane layer, especially the circular arc part with the maximum linear velocity, which is more easily damaged. Therefore, the membrane layer has high quality requirements. However, in the coating process of the traditional ceramic membrane sheet, especially when there are processing defects in the circular arc part of the ceramic membrane sheet or the ceramic membrane sheet is improperly contacted, coating unevenness, cracks, large pores and other membrane layer defects exist, which greatly affect the filtration efficiency, greatly limit the industrial application of disk-shaped ceramic membranes, and especially limit the application in the filtration and separation field of high-end products such as semiconductors, biological medicines and new energy. Therefore, it is urgent to design a method and device for reducing coating defects of disk-shaped ceramic membranes. SUMMARY

[0004] The present application aims to disclose a method and device for reducing coating defects of disk-shaped ceramic membranes, which has the following advantages: 1. The ceramic membrane sheet is dynamically rotated and cleaned and activated on the surface by low-temperature plasma technology, which efficiently removes surface pollutants and improves the wettability and coating adhesion of the ceramic membrane sheet surface; 2. The ceramic membrane sheet is dynamically rotated, sprayed by negative pressure and ultrasonic waves, and the ultrasonic atomized droplets are “sucked” into the microporous structure or surface gap when contacting the ceramic membrane sheet surface, which improves the adhesion of the membrane forming liquid and avoids impact damage to the formed membrane area, avoids the generation of pinholes or defects in the membrane layer, ensures the uniformity of the membrane microstructure, forms a uniform, dense and defect-free membrane layer, and improves the filtration efficiency; 3. The ceramic membrane sheet is immersed and coated by dynamic rotation and negative pressure on the circular arc part of the ceramic membrane sheet, which can cover the surface of the circular arc part of the ceramic membrane sheet with a uniform and dense membrane layer, optimizes the circular arc angle film forming process, reduces the processing requirements of the circular arc angle, improves the processing yield of the ceramic membrane sheet, reduces the processing cost of the ceramic membrane sheet, and improves the filtration precision; 4. The ceramic membrane sheet is fixed by a clamp, and no contact with the ceramic membrane sheet can be realized in the whole process, which effectively prevents coating defects caused by improper contact before the membrane layer is dried.

[0005] To achieve the above-mentioned purpose, the present application provides a method for reducing coating defects of disk-shaped ceramic membranes, which comprises the following steps:

[0006] Step one: preparation of film forming solution;

[0007] Step two: install the ceramic membrane on the fixture and clean and dry it;

[0008] Step three: install the fixture in the forward direction on the spraying station, make the ceramic membrane rotate dynamically, and use low-temperature plasma technology to clean and activate the positive surface of the ceramic membrane;

[0009] Step four: while the ceramic membrane is rotating dynamically, perform negative pressure suction on the ceramic membrane, and use ultrasonic atomization to spray the film forming solution on the positive surface of the ceramic membrane, and then perform drying treatment after the spraying is completed;

[0010] Step five: install the fixture in the reverse direction on the spraying station, and repeat steps three and four;

[0011] Step six: install the fixture on the dip coating station again, make the ceramic membrane rotate dynamically, and perform negative pressure suction on the ceramic membrane, so that the circular arc part of the ceramic membrane is dynamically dip coated in the film forming solution;

[0012] Step seven: perform drying on the ceramic membrane together with the fixture, and then take out the ceramic membrane for calcination.

[0013] In some embodiments, in step one, the film forming solution comprises the following components in the following weight proportions: dispersant 0.001-0.5 parts, binder 0.1-1 part, defoaming agent 0.0001-0.01 part, sintering aid 0.01-0.2 part, and metal compound 1 part; the above components are ultrasonically dispersed in a constant temperature water bath at 10-40°C for 5-60 min to obtain the film forming solution, and the solid content of the film forming solution is 0.1-40 wt%.

[0014] In some embodiments, the dispersant is one or more of sodium polyacrylate, polyacrylamide, and polyacrylic acid; the binder is one or more of PVA, PVB, PEG, and HPC; the defoaming agent is one or more of alcohol, organosilicon, polyether, and ester; the sintering aid is one or more of yttrium nitrate, cerium nitrate, lanthanum nitrate, aluminum oxide, titanium oxide, zirconium oxide, and silicon oxide; and the metal compound is one or more of aluminum oxide, titanium oxide, zirconium oxide, silicon oxide, cerium oxide, yttrium oxide, and lanthanum oxide.

[0015] In some embodiments, in step two, the ceramic membrane is washed or soaked with an organic solvent for 5-120 min, then washed, soaked, and ultrasonically cleaned with pure water for 2-3 times, each time for 5-120 min, and finally dried at 50-200°C for 10-240 min.

[0016] In some embodiments, in step three, the ceramic membrane and the clamp are preheated to 50-200 DEG C in an oven, and then taken out and installed in a spraying station, the dynamic rotating speed of the ceramic membrane is 2-100 RPM, the low-temperature plasma technology is used to clean and activate the surface of the ceramic membrane for 5-120 s by ionizing air to generate a mixture of electrons, ions, atoms and atomic groups, and remove surface contaminants.

[0017] In some embodiments, in step four, the spraying environment temperature is controlled to be 20-60 DEG C and the relative humidity is controlled to be 20-80%; the ceramic membrane is negatively pumped by a negative pressure generating device, and the pressure is controlled to be-100-0 kPa; the dynamic rotating speed of the ceramic membrane is controlled to be 2-100 RPM; the membrane forming liquid is magnetically stirred in a constant temperature water bath at 10-40 DEG C, a peristaltic pump is used for liquid feeding, the liquid feeding flow is controlled to be 0-65 ml / min, and the surface of the ceramic membrane is sprayed by an ultrasonic atomization spraying device for 1-60 min; after the spraying is completed, the ceramic membrane and the clamp are taken out together and placed in a constant temperature and humidity box, the ceramic membrane is in a suspended state, and dried for 30-300 min, the temperature of the constant temperature and humidity box is controlled to be 20-80 DEG C and the relative humidity is controlled to be 20-80%.

[0018] In some embodiments, in step six, the dipping environment temperature is controlled to be 20-60 DEG C and the relative humidity is controlled to be 20-80%; the ceramic membrane is negatively pumped by a negative pressure generating device, and the pressure is controlled to be-100-0 kPa; the dynamic rotating speed of the ceramic membrane is controlled to be 2-50 RPM; the dynamic dipping time of the arc part of the ceramic membrane in the membrane forming liquid is controlled to be 0-240 s.

[0019] In some embodiments, in step seven, after the dipping is completed, the ceramic membrane and the clamp are dried together, the ceramic membrane is in a suspended state during the drying process, dried in a constant temperature and humidity box for 30-300 min, the temperature of the constant temperature and humidity box is controlled to be 20-80 DEG C and the relative humidity is controlled to be 20-80%, and then calcined at 400-1300 DEG C for 10-240 min.

[0020] To achieve the above object, the application also provides a device for reducing defects of disc-shaped ceramic membrane coating, characterized by comprising a ceramic membrane surface spraying mechanism and a ceramic membrane arc part dipping mechanism.

[0021] The ceramic membrane surface spraying mechanism comprises a spraying chamber, a fixed plate installed in the spraying chamber, a first motor installed on the fixed plate, a hollow rotating shaft driven by the first motor, a clamp connected with the hollow rotating shaft, a ceramic membrane installed on the clamp, a track above the ceramic membrane, and a moving seat sliding on the track.

[0022] Further comprising a vacuum pump, and a rotary joint connected with the vacuum pump; the rotary joint is connected with the hollow rotating shaft;

[0023] Further comprising a magnetic stirrer, a peristaltic pump connected with the magnetic stirrer, a first ultrasonic nozzle and a second ultrasonic nozzle connected with the peristaltic pump; the first ultrasonic nozzle is arranged towards the ceramic membrane arc part, and the second ultrasonic nozzle is arranged on the moving seat and towards the ceramic membrane surface;

[0024] Further comprising a low-temperature plasma processing machine, and a plasma torch of the low-temperature plasma processing machine is arranged on the moving seat and towards the ceramic membrane surface;

[0025] The ceramic membrane arc part immersion coating mechanism comprises a second motor, a clamp driven by the second motor, a ceramic membrane installed on the clamp, a rotary joint connected with the clamp, a vacuum pump connected with the rotary joint, a lifting platform, and a membrane preparation liquid tank placed on the lifting platform; the ceramic membrane arc part is dynamically immersed in the membrane preparation liquid.

[0026] In some embodiments, the clamp comprises two hollow tubes and flanges connected with the hollow tubes; the ceramic membrane is clamped by the two flanges, the two flanges are connected by bolts and nuts, a sealing ring is arranged between the ceramic membrane and the flanges, and the hollow tubes are provided with internal threads.

[0027] In some embodiments, in the ceramic membrane surface spraying mechanism, one hollow tube of the clamp is screwed with the hollow rotating shaft, and the other hollow tube of the clamp is sealed by bolts; a sealing ring is arranged between the bolts and the hollow tubes.

[0028] In some embodiments, the fixing plate is provided with a fixing seat, the fixing seat is provided with a groove, and the hollow rotating shaft and the hollow tube are connected by extending into the groove.

[0029] In some embodiments, the track is a screw rod, the moving seat is a nut seat, and a third motor is further arranged to drive the screw rod to rotate.

[0030] Compared with the prior art, the present application has the following advantages:

[0031] I. The ceramic membrane is dynamically rotated and cleaned and activated by low-temperature plasma technology, so that the surface pollutants are efficiently removed, and the wetting performance and coating adhesion of the ceramic membrane surface are improved.

[0032] Second, the dynamic rotation of the ceramic diaphragm, negative pressure and ultrasonic spraying are used in coordination. When the ultrasonic atomized droplets contact the surface of the ceramic diaphragm, they are "sucked" into the microporous structure or surface gaps, which improves the adhesion of the membrane-making liquid and does not cause impact damage to the film-forming area, avoiding pinholes or defects in the membrane layer, ensuring the uniformity of the membrane layer's microstructure, forming a uniform, dense, defect-free membrane layer, and improving filtration efficiency.

[0033] 3. The use of dynamic rotation of the ceramic diaphragm and negative pressure to dip-coat the arc portion of the ceramic diaphragm can make the surface of the arc portion of the ceramic diaphragm covered with a uniform and dense film layer, optimize the arc angle film forming process, reduce the arc angle processing requirements, improve the processing yield of the ceramic diaphragm, reduce the processing cost of the ceramic diaphragm, and improve the filtration accuracy;

[0034] 4. The ceramic diaphragm is fixed by a clamp. During the whole process, the ceramic diaphragm can be kept contactless, which effectively prevents coating defects caused by improper contact before the film layer dries. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 A comparison chart of the bubble point pressure of the ceramic diaphragm coating of the present invention (a) and the bubble point pressure of the conventional ceramic diaphragm coating (b);

[0036] Figure 2 A comparison diagram of the bubble point pore size distribution of the ceramic diaphragm coating of the present invention (c) and the bubble point pore size distribution of the traditional ceramic diaphragm coating (d);

[0037] Figure 3 The SEM image (e) of the ceramic diaphragm coating surface of the present invention and the SEM image (f) of the traditional ceramic diaphragm coating surface;

[0038] Figure 4 The SEM image (g) of the cross section of the ceramic diaphragm coating of the present invention and the SEM image (h) of the cross section of the conventional ceramic diaphragm coating;

[0039] Figure 5 Comparison of surface roughness of the ceramic diaphragm coating, ceramic diaphragm (support) and traditional ceramic diaphragm coating shown in the present invention;

[0040] Figure 6 A comparison of the pore size distribution of the ceramic diaphragm coating after plasma activation treatment (I) and without plasma activation treatment (J) shown in the present invention;

[0041] Figure 7 A comparison diagram of the pore size distribution of the ceramic diaphragm coating at different ambient humidity levels shown in the present invention;

[0042] Figure 8 Schematic diagram of the structure of the clamp shown in the present invention;

[0043] Figure 9 It is a structural schematic diagram of the ceramic diaphragm surface spraying mechanism shown in the present invention;

[0044] Figure 10 Schematic diagram of the structure of the arc portion dipping mechanism of the ceramic diaphragm shown in the present invention. DETAILED DESCRIPTION

[0045] The present invention is described in detail below with reference to the various embodiments shown in the accompanying drawings, but it should be noted that these embodiments are not limitations of the present invention, and any equivalent transformations or substitutions in functions, methods, or structures made by ordinary technicians in this field based on these embodiments are all within the scope of protection of the present invention.

[0046] Example 1:

[0047] This embodiment discloses a method for reducing coating defects of a disc-type ceramic membrane, comprising the following steps:

[0048] Step 1: prepare membrane solution;

[0049] Specifically, the film-forming solution comprises the following components by weight: 0.5 parts dispersant, 1 part binder, 0.01 parts defoamer, 0.2 parts sintering aid, and 1 part metal compound. These components are ultrasonically dispersed in a 40°C water bath for 30 minutes to obtain the film-forming solution. The dispersant is sodium polyacrylate, the binder is PVA, the defoamer is an alcohol, the sintering aid is yttrium nitrate, and the metal compound is aluminum oxide.

[0050] Dispersants ensure uniform dispersion of metal compound particles in the liquid phase, preventing agglomeration and forming a stable suspension. Uniform dispersion of components improves the consistency of the film's chemical and physical properties. Ultrasonic dispersion further breaks up particle agglomerations through cavitation, improving dispersion uniformity and achieving particularly effective results for nanoscale metal compounds. Uniform dispersion of components improves the consistency of the film's chemical and physical properties. A low-temperature water bath prevents solvent volatilization or component degradation caused by high temperatures, maintaining system stability. Binders provide mechanical strength, enhance the film's flexibility and adhesion, and prevent cracking during drying or sintering. Defoamers eliminate bubbles introduced by stirring and ultrasound, reducing film defects such as pinholes and cracks and improving surface smoothness. Defoamers and binders synergistically reduce microscopic defects and enhance film reliability. Sintering aids lower the sintering temperature of the metal compound, promote interparticle diffusion, form a densified structure, and improve the film's mechanical or electrical properties. Sintering aids optimize grain boundary structure, potentially improving the film's hardness, thermal stability, or electrical conductivity.

[0051] Step 2: Install the ceramic diaphragm on the fixture and clean and dry it;

[0052] Specifically, the ceramic membrane 80 is washed or soaked with an organic solvent for 80 minutes, then washed, soaked and ultrasonically cleaned with pure water for 3 times, each for 60 minutes, and finally dried at 100℃ for 120 minutes.

[0053] Through organic solvent treatment, organic pollutants can be removed, and grease, residual adhesive or organic additives such as dispersants and defoamers in the membrane-forming solution on the surface of the membrane can be dissolved and removed; the open porosity can be improved; the membrane has a porous structure, and organic solvents such as ethanol and acetone can dredge the pores blocked by organic matter and restore the porosity; the surface can be adjusted, and solvent cleaning can change the wettability of the membrane surface, laying a foundation for subsequent water washing or functionalization treatment.

[0054] Through multiple washing with pure water, solvent residues can be completely removed, avoiding secondary pollution or surface defects caused by organic solvents during drying; ion impurities can be removed, and water washing can dissolve and flush away inorganic salt impurities such as sintering aid residues and metal ions, improving the chemical purity of the membrane. In addition, ultrasonic synergy, ultrasonic cavitation effect peeling off particulate pollutants, enhancing the cleanliness of the pores, the cleaning effect is more significant for complex structures such as asymmetric pores and tortuous pores.

[0055] Through high-temperature drying, water is completely removed, avoiding bubbles or cracks caused by residual water during subsequent applications such as coating deposition; structural stabilization, appropriate temperature drying can reduce the shrinkage stress of the membrane caused by rapid drying, maintaining the stability of the geometric shape; pretreatment effect, 100℃ drying can be used as a preheating stage to reduce the risk of thermal shock.

[0056] This cleaning and drying process can significantly improve the performance of the ceramic membrane through step-by-step processing, with high surface cleanliness; good pore function recovery, improving the flux of porous ceramic membranes such as permeability and filtration efficiency; interface performance optimization, clean surface enhancing the adhesion and uniformity of subsequent modifications such as coating and activation; reliability improvement, reducing the performance degradation caused by impurities such as membrane pollution.

[0057] Step three: install the fixture in the forward direction on the spraying station, make the ceramic membrane dynamically rotate, and use low-temperature plasma technology to clean and activate the front surface of the ceramic membrane;

[0058] Specifically, the ceramic membrane and the fixture are preheated to 200℃ in an oven, then taken out and installed on the spraying station, the ceramic membrane is dynamically rotated at a speed of 60RPM, and low-temperature plasma technology is used to clean and activate the surface of the ceramic membrane for 100s using air as the gas source, ionizing to produce a mixture of electrons, ions, atoms and atomic groups, to remove surface pollutants, improve the wettability of the membrane surface and the adhesion of the coating.

[0059] Preheating can remove adsorbed moisture and volatile contaminants, and high-temperature baking can evaporate the moisture and organic solvent residues adsorbed on the surface of the membrane and clamp, avoiding interference with the reaction activity during subsequent plasma treatment; it can also reduce thermal stress, preheating can reduce the temperature gradient between the membrane and subsequent plasma treatment (which may be accompanied by local temperature rise), preventing cracking or deformation caused by sudden heating; it can also initially improve the surface energy: high temperature can partially remove weakly bound contaminants such as grease, providing a cleaner initial surface for plasma activation.

[0060] Dynamic rotation of the ceramic membrane can achieve the following effects: 1. Uniform treatment: rotation ensures that the plasma acts on the entire surface of the membrane, avoiding uneven treatment such as edge effects or shadow zones caused by static spraying; 2. Enhance contaminant stripping: centrifugal force assists in removing particle contaminants desorbed during plasma cleaning, improving cleaning efficiency; 3. Optimize coating pre-coverage: the activated surface in the rotating state is more conducive to uniform adhesion of the coating.

[0061] Using low-temperature plasma cleaning and activation, 1. It can deeply clean the ceramic membrane: during the production process, the ceramic membrane may have oil stains on the surface due to skin contact and equipment contact, which can directly cause the slurry to not adsorb at the oil stain site during the later coating of the membrane-forming solution, i.e., the coating is missing. Some oil stains, such as oil on the equipment, need to be soaked in alcohol to remove them, but the alcohol soaking process will leave residues on the surface of the ceramic membrane, affecting the adsorption of the membrane-forming solution. High-energy ions and electrons in the plasma collide with the surface of the ceramic membrane, physically stripping nanoscale contaminants such as organic matter and dust; active oxygen atoms (O) and free radicals (·OH) generated by air plasma oxidize and decompose organic contaminants such as oil and residual adhesives, generating volatile products such as CO2 and H2O, which are then pumped away; 2. It can activate the surface of the ceramic membrane: the plasma introduces polar groups such as —OH and —COOH to the surface of the ceramic membrane, significantly increasing the surface energy and making the membrane hydrophilic, improving its wettability with water-based solutions or coatings; plasma etching can form a nanoscale concave-convex structure, increasing the specific surface area and further improving the adhesion, i.e., the mechanical anchoring effect; 3. It can provide chemical bonding sites for the ceramic membrane: the activated surface generates dangling bonds or active sites, forming stronger chemical bonds (such as Si—O—C and Ti—O—N) with the subsequent coating, rather than just physical adsorption, increasing the adhesion of the coating.

[0062] This process achieves efficient and uniform surface modification while ensuring the integrity of the ceramic membrane substrate through the synergistic effect of heat, force, and plasma.

[0063] Step four: while the ceramic membrane is dynamically rotating, it is subjected to negative pressure suction, and ultrasonic atomization is used to spray the membrane-forming solution onto the positive surface of the ceramic membrane. After spraying is complete, drying is performed.

[0064] Specifically, the spraying environment temperature is controlled at 50°C and the relative humidity is controlled at 70%; the ceramic diaphragm is subjected to negative pressure suction by using a negative pressure generating device, and the pressure is controlled at -100 kPa; the dynamic rotating speed of the ceramic diaphragm is controlled at 60 RPM; the membrane liquid is subjected to magnetic stirring under the condition of a constant temperature water bath at 40°C, the liquid inlet flow is controlled at 55 ml / min by using a peristaltic pump, and the ceramic diaphragm surface is sprayed for 30 min by using an ultrasonic atomization spraying device; after the spraying is completed, the ceramic diaphragm and the clamp are taken out together and placed in a constant temperature and humidity box, the ceramic diaphragm is in a suspended state, and is dried for 200 min, the temperature of the constant temperature and humidity box is controlled at 50°C and the relative humidity is controlled at 70%. The ceramic diaphragm is suspended and dried without contact, which can effectively prevent coating defects caused by improper contact before drying of the membrane layer.

[0065] The negative pressure suction is adopted, thereby generating negative pressure inside the ceramic diaphragm, so that the atomized droplets sprayed are "sucked" into the micropore structure or surface gap when reaching the ceramic diaphragm surface, the permeability and anchoring effect of the droplets are significantly enhanced, the rebound and splashing of the surface droplets are reduced, the initial adhesion is improved, and more uniform and continuous bottom spreading is promoted, which is crucial for forming a defect-free, low-porosity dense separation layer.

[0066] The dynamic rotation of the ceramic diaphragm ensures that the atomized droplets can be uniformly deposited on the ceramic diaphragm surface from all angles, which effectively avoids the "shadow effect" (part of the area cannot be sprayed) and "coffee ring effect" (solution migrates and accumulates to the edge) caused by static spraying, and a membrane layer with extremely high thickness distribution consistency is obtained.

[0067] The droplets generated by ultrasonic atomization are smaller in size, usually micron or even sub-micron, narrower in distribution, lower in flight speed, and smaller in momentum, and small droplets are more easily "sucked" into the ceramic diaphragm pores by negative pressure, which is beneficial to form a thinner and homogeneous separation layer. At the same time, the low momentum reduces the impact damage of the droplets to the formed membrane area, avoids the generation of pinholes or defects, and ensures the uniformity of the membrane layer microstructure.

[0068] Step five: reversely mount the clamp on the spraying station, and repeat steps three and four, so that the ceramic diaphragm can be cleaned and coated with the membrane liquid on both sides. The ceramic diaphragm clamp is designed to switch the front and back sides, and the ceramic diaphragm is not in contact during production, which can effectively prevent coating defects caused by improper contact before drying of the membrane layer.

[0069] Step six: mount the clamp on the dip coating station again, so that the ceramic diaphragm is dynamically rotated and subjected to negative pressure suction, and the circular arc part of the ceramic diaphragm is dynamically dip coated in the membrane liquid;

[0070] Specifically, the dip coating environment temperature is controlled at 50℃, and the relative humidity is controlled at 70%; the ceramic membrane is subjected to negative pressure suction by using a negative pressure generating device, and the pressure is controlled at-100kPa; the dynamic rotation speed of the ceramic membrane is controlled at 40RPM; and the dynamic dip coating time of the ceramic membrane arc part in the membrane forming liquid is controlled at 200s.

[0071] The negative pressure suction is adopted, so that the negative pressure is generated inside the ceramic membrane, and when the ceramic membrane arc part collides with the membrane forming liquid, the membrane forming liquid is "sucked" into the microporous structure or the surface gap, which significantly enhances the permeability and anchoring effect of the liquid droplets, reduces the rebound and splashing of the surface liquid droplets, improves the initial adhesion, promotes more uniform and continuous bottom spreading, and is crucial for forming a defect-free, low porosity dense separation layer.

[0072] The dynamic rotation of the ceramic membrane ensures the dynamic dip coating of the ceramic membrane arc part in the membrane forming liquid, so that the arc part can be uniformly dip coated with the membrane forming liquid, which effectively avoids the "shadow effect" (part of the area cannot be sprayed) and "coffee ring effect" (solution migrates and accumulates to the edge) caused by static spraying, and a membrane layer with extremely high thickness distribution consistency is obtained.

[0073] The ceramic membrane arc part surface can be covered with a uniform and dense membrane layer, the arc angle film forming process is optimized, the processing requirements of the arc angle are reduced, the processing yield of the ceramic membrane is improved, the processing cost of the ceramic membrane is reduced, and the disc type ceramic membrane filtration precision is improved.

[0074] Step seven: drying the ceramic membrane together with the clamp, and then taking out the ceramic membrane for calcination.

[0075] Specifically, after the dip coating is completed, the ceramic membrane is dried together with the clamp, and the ceramic membrane is in a suspended state during the drying process. The drying is performed in a constant temperature and humidity box for 200min, the temperature of the constant temperature and humidity box is controlled at 60℃, and the relative humidity is controlled at 70%, and then the ceramic membrane is calcined at 800℃ for 180min.

[0076] The ceramic membrane is dried in a suspended state without contact, which can effectively prevent coating defects caused by improper contact before drying.

[0077] The bubble point is an index for detecting the size of the membrane layer pore channel. The test gas pressure increases from small to large, and the pressure value of the first bubble is the bubble point pressure of the membrane. The smaller the bubble point pressure, the larger the pore size. Figure 1 and Figure 2It can be known that the ceramic membrane coating bubble point pressure is large, the bubble point aperture is small, the traditional ceramic membrane coating bubble point pressure is small, the bubble point aperture is large, the ceramic membrane surface of the present application is more easy to keep the uniformity of microstructure, and the film layer with small surface roughness and no defects is more easy to form. The ceramic membrane coating bubble point pressure is large, the bubble point aperture is small, because the ceramic membrane dynamic rotation, negative pressure and ultrasonic wave are cooperated to spray, the ultrasonic wave atomized droplet is absorbed into the micro-porous structure or the surface gap when contacting the ceramic membrane surface, the adhesion of the film forming liquid is strong, the ceramic membrane surface is filled flat, there is no defect, the tight and uniform film can be formed, and the strong pressure can be resisted.

[0078] Combining Figure 3 , Figure 4 and Figure 5 , it can be known that the ceramic membrane coating surface obtained by the present application is uniform, the roughness is small, and there is no defect, while the traditional ceramic membrane coating surface is uneven, pitted, has cracks and large holes, and the roughness is large.

[0079] From Figure 6 , it can be seen that under the same conditions, the ceramic membrane coating aperture of the plasma activation treatment (I) is smaller, and the filtering effect is better, while the ceramic membrane coating aperture of the non-plasma activation treatment (J) is larger.

[0080] From Figure 7 , it can be known that under the same conditions, when the environmental humidity H=70%, the ceramic membrane coating aperture is smaller, and the filtering effect is better.

[0081] Example two:

[0082] The present embodiment discloses a device for reducing the defects of the disc type ceramic membrane coating to realize the method of example one, which comprises a ceramic membrane surface spraying mechanism and a ceramic membrane arc part dipping coating mechanism.

[0083] As Figure 8 shown, the clamp 1 comprises two hollow pipes 11 and flanges 12 connected on the hollow pipes 11. The ceramic membrane 2 is clamped by the two flanges 12, and the two flanges 12 are connected by bolts and nuts, so that the ceramic membrane 2 and the clamp 1 form an integrated structure and can rotate synchronously.

[0084] A sealing ring 13 is arranged between the ceramic membrane 2 and the flange 12, so as to ensure the sealing property and prevent the air leakage phenomenon when the ceramic membrane 2 is subjected to negative pressure suction. The hollow pipe 11 is provided with an internal thread, so as to facilitate the connection.

[0085] Through the clamp 1, the non-contact operation can be realized during the coating process of the ceramic membrane 2, and the above-mentioned operations can be realized by contacting the clamp 1 during the disassembly and drying process, so that the coating defects caused by improper contact before the film layer is dried can be effectively prevented.

[0086] As Figure 9 shown, the ceramic membrane surface spraying mechanism comprises a spraying chamber 8, a fixed plate 41 installed in the spraying chamber 8, a first motor 42 installed on the fixed plate 41, a hollow rotating shaft 45 driven by the first motor 42, and a clamp 1 connected to the hollow rotating shaft 45, and a ceramic membrane 2 installed on the clamp 1.

[0087] It also comprises a vacuum pump 4 and a rotary joint 44 connected to the vacuum pump 4. One end of the hollow rotating shaft 45 is connected to the clamp 1, and the other end of the hollow rotating shaft 45 is connected to the rotary joint 44.

[0088] The vacuum pump 4 generates negative pressure, which is transmitted to the ceramic membrane 2 through the hollow rotating shaft 45 and the clamp 1, thereby generating negative pressure inside the ceramic membrane 2. When the sprayed atomized droplets reach the surface of the ceramic membrane 2, they are "sucked" into the microporous structure or surface gap, significantly enhancing the permeability and anchoring effect of the droplets, reducing the rebound and splashing of the surface droplets, improving the initial adhesion, promoting more uniform and continuous bottom spreading, and being crucial for forming a defect-free, low-porosity dense separation layer.

[0089] The rotating shaft of the first motor 42 and the hollow rotating shaft 45 are connected by a belt 43. The first motor 42 drives the hollow rotating shaft 45 to rotate, and the hollow rotating shaft 45 drives the ceramic membrane 2 to rotate dynamically. The rotating speed of the first motor 42 can be adjusted according to actual conditions, thereby controlling the rotating speed of the ceramic membrane 2.

[0090] One of the hollow tubes 11 of the clamp 1 is screwed with the hollow rotating shaft 45, which is convenient to disassemble and assemble. On the one hand, it realizes the connection of the clamp 1 and the hollow rotating shaft 45, and the ceramic membrane 2 can rotate with the hollow rotating shaft 45. On the other hand, through the communication of the hollow rotating shaft 45 and the hollow tube 11, negative pressure adsorption can be generated on the ceramic membrane 2. The other hollow tube 11 of the clamp 1 is screwed and sealed by a bolt 14. A sealing ring 15 is arranged between the bolt 14 and the hollow tube 11 to ensure the sealing and prevent air leakage when the ceramic membrane 2 is subjected to negative pressure suction. The fixed plate 41 is provided with a fixed seat 46, the fixed seat 46 is provided with a groove 460, and the hollow rotating shaft 45 and the hollow tube 11 are connected by extending into the groove 460.

[0091] It also comprises a track 7 above the ceramic membrane 2 and a moving seat 71 sliding on the track 7. Specifically, the track 7 is a lead screw, the moving seat 71 is a nut seat, and a third motor is further provided to drive the lead screw to rotate. The moving seat 71 can move back and forth on the track 7.

[0092] Low temperature plasma processing machine 6 is also included to ionize air to generate a mixture of electrons, ions, atoms and radicals to clean and activate the surface of ceramic membrane 2, remove contaminants on the surface of ceramic membrane 2, and improve the wettability and coating adhesion of the surface of ceramic membrane 2.

[0093] Plasma spray gun 61 of low temperature plasma processing machine 6 is mounted on moving seat 71 and arranged to face the surface of ceramic membrane 2, so that the surface of ceramic membrane 2 can be cleaned and activated. Plasma spray gun 61 is of rotary or straight spray type. Moving seat 71 moves back and forth in a small range on track 7, so that plasma spray gun 61 can move back and forth in the radius range of ceramic membrane 2, so that the surface of ceramic membrane 2 can be fully cleaned and activated. The movement of plasma spray gun 61 is uniform acceleration, the initial speed is 0-20 mm / s, and the acceleration is -5-5 mm / s 2 .

[0094] Low temperature plasma processing machine 6 is used to clean and activate the surface of ceramic membrane 2 while ceramic membrane 2 is dynamically rotating. Dynamic rotation of ceramic membrane 2 can ensure that plasma acts on the entire surface of ceramic membrane 2, avoiding uneven treatment such as edge effect or shadow area caused by static spraying; can enhance the stripping of contaminants, centrifugal force can assist in removing particle contaminants desorbed in plasma cleaning, and improve the cleaning efficiency.

[0095] Magnetic stirrer 5, peristaltic pump 51 connected to magnetic stirrer 5, first ultrasonic nozzle 52 and second ultrasonic nozzle 54 connected to peristaltic pump 51 are also included. The membrane-forming liquid is placed in magnetic stirrer 5 and delivered to first ultrasonic nozzle 52 and second ultrasonic nozzle 54 for atomization by peristaltic pump 51. Ultrasonic atomization produces smaller droplets, typically micron or even sub-micron, narrower distribution, lower flight speed, smaller momentum, and smaller droplets are more easily "sucked" into the ceramic membrane hole by negative pressure, which is beneficial to the formation of a thinner and more uniform separation layer. At the same time, low momentum reduces the impact damage of droplets on the formed membrane area, avoiding the generation of pinholes or defects, and ensuring the uniformity of the microstructure of the membrane layer.

[0096] First ultrasonic nozzle 52 is connected to fixed plate 41 by support 53, and first ultrasonic nozzle 52 is arranged to face the arc part of ceramic membrane 2, so as to spray the membrane-forming liquid on the arc part of ceramic membrane 2 to form a uniform and dense membrane on the surface of the arc part.

[0097] The second ultrasonic nozzle 54 is installed on the moving seat 71 and arranged facing the surface of the ceramic membrane 2, so as to spray the membrane-forming liquid on the front and back surfaces of the ceramic membrane 2, and form a uniform and dense membrane on the front and back surfaces of the ceramic membrane 2. The second ultrasonic nozzle 54 reciprocates back and forth in a small range on the track 7 with the moving seat 71, so that the second ultrasonic nozzle 54 can reciprocate in the radius range of the ceramic membrane 2, so that the membrane-forming liquid sprayed by the second ultrasonic nozzle 54 can uniformly cover the ceramic membrane 2. The movement of the second ultrasonic nozzle 54 is uniform acceleration, the initial speed is 0-20 mm / s, and the acceleration is-5-5 mm / s 2 .

[0098] The ceramic membrane 2 is dynamically rotated, and the ceramic membrane 2 is subjected to negative pressure suction, and the surface of the ceramic membrane 2 is sprayed with the membrane-forming liquid by ultrasonic atomization, so as to form a uniform, dense and defect-free membrane layer. The dynamic rotation of the ceramic membrane 2 ensures that the atomized droplets can be uniformly deposited on the surface of the ceramic membrane 2 from all angles, which effectively avoids the "shadow effect" (part of the area cannot be sprayed) and "coffee ring effect" (solution migrates and accumulates to the edge) caused by static spraying, and a membrane layer with high thickness distribution consistency is obtained.

[0099] The working process in the ceramic membrane surface spraying mechanism is as follows: the forward mounting clamp 1, the first motor 42 drives the ceramic membrane 2 to dynamically rotate, the plasma torch 61 sprays plasma to clean and activate the surface of the ceramic membrane 2, after the cleaning and activation is completed, the low-temperature plasma treatment machine 6 stops working, the vacuum pump 4 starts working to generate negative pressure in the ceramic membrane 2, and the first ultrasonic nozzle 52 and the second ultrasonic nozzle 54 spray the ceramic membrane 2 by atomization, after the spraying is completed, the reverse mounting clamp 1 is installed again, and the above operation is repeated to complete the spraying of the front and back surfaces of the ceramic membrane 2.

[0100] Finally, the clamp 1 is detached from the hollow rotating shaft 45, the bolt 14 is detached, and then the clamp 1 is installed in the ceramic membrane arc portion dip coating mechanism.

[0101] As shown in Figure 10 , the ceramic membrane arc portion dip coating mechanism comprises a bracket 33, a second motor 34 installed on the bracket 33, a clamp 1 driven by the second motor 34, and a ceramic membrane 2 installed on the clamp 1.

[0102] It also comprises a lifting platform 31 and a membrane-forming liquid tank 32 placed on the lifting platform 31. The membrane-forming liquid tank 32 is filled with membrane-forming liquid, and the arc portion of the ceramic membrane 2 is dip coated in the membrane-forming liquid. The lifting platform 31 can adjust the height of the membrane-forming liquid tank 32, thereby facilitating the dip coating operation.

[0103] One hollow tube 11 of the clamp 1 is connected with the rotating shaft of the second motor 34, specifically, the rotating shaft of the second motor 34 is provided with external threads, and the hollow tube 11 is screwed with the rotating shaft of the second motor 34, which is convenient for disassembly and assembly. The second motor 34 can drive the clamp 1, so that the ceramic diaphragm 2 can rotate dynamically. The dynamic rotation of the ceramic diaphragm 2 ensures that liquid droplets can be uniformly deposited on the surface of the arc part of the ceramic diaphragm 2, effectively avoiding the "shadow effect" (part of the area cannot be sprayed) caused by static spraying, and obtaining a film layer with extremely high thickness distribution consistency.

[0104] Further comprising a vacuum pump 35 and a rotary joint 36 connected with the vacuum pump 35, and the other hollow tube 11 of the clamp 1 is screwed with the rotary joint 36, so as not to affect the rotation of the clamp 1. The vacuum pump 35 generates negative pressure, which is sucked through the hollow tube 11 to the ceramic diaphragm 2, so as to generate negative pressure inside the ceramic diaphragm 2, so that when the liquid droplets of the film-forming liquid contact the surface of the arc part of the ceramic diaphragm 2, they are "sucked" into the microporous structure or surface gap, which significantly enhances the permeability and anchoring effect of the liquid droplets, reduces the rebound and splashing of the surface liquid droplets, improves the initial adhesion, promotes more uniform and continuous bottom spreading, and is crucial for forming a defect-free, low-porosity dense separation layer.

[0105] The above series of detailed descriptions are only specific descriptions of the feasible embodiments of the present application, and are not intended to limit the protection scope of the present application. Any equivalent embodiments or changes made without departing from the spirit of the present application shall be included in the protection scope of the present application.

[0106] In addition, it should be understood that although the present specification is described in terms of embodiments, not every embodiment contains only one independent technical solution, and the description manner of the specification is only for the sake of clarity, and the person skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by the person skilled in the art.

Claims

1. A method for reducing coating defects of a disc-type ceramic membrane, characterized in that: The steps include: Step 1: prepare membrane solution; Step 2: Install the ceramic diaphragm on the fixture and clean and dry it; Step 3: Install the fixture in the spraying station in the forward direction to rotate the ceramic diaphragm dynamically, and use low-temperature plasma technology to clean and activate the front surface of the ceramic diaphragm; Step 4: While the ceramic diaphragm is dynamically rotating, negative pressure suction is applied to the ceramic diaphragm, and the membrane-forming liquid is sprayed on the positive surface of the ceramic diaphragm using ultrasonic atomization. After the spraying is completed, the membrane is dried; Step 5: Install the fixture on the spray station in reverse and repeat steps 3 and 4; Step 6: Install the fixture on the dipping station, rotate the ceramic diaphragm dynamically, and apply negative pressure suction to the ceramic diaphragm so that the arc portion of the ceramic diaphragm is dynamically dipped in the film-making liquid; Step 7: Dry the ceramic diaphragm together with the fixture, and then take out the ceramic diaphragm and bake it.

2. A method for reducing coating defects of disc-type ceramic membranes according to claim 1, characterized in that: In step 1, the film-forming liquid includes the following components in parts by weight: 0.001 to 0.5 parts of a dispersant, 0.1 to 1 parts of a binder, 0.0001 to 0.01 parts of a defoaming agent, 0.01 to 0.2 parts of a sintering aid, and 1 part of a metal compound; the above components are ultrasonically dispersed in a constant temperature water bath at 10 to 40° C. for 5 to 60 minutes to obtain a film-forming liquid, wherein the solid content of the film-forming liquid is 0.1 to 40 wt%.

3. The method for reducing coating defects of a disc-type ceramic membrane according to claim 2, characterized in that: The dispersant is one or more of sodium polyacrylate, polyacrylamide, and polyacrylic acid; the binder is one or more of PVA, PVB, PEG, and HPC; the defoamer is one or more of alcohols, silicones, polyethers, and esters; the sintering aid is one or more of yttrium nitrate, cerium nitrate, lanthanum nitrate, aluminum oxide, titanium oxide, zirconium oxide, and silicon oxide; and the metal compound is one or more of aluminum oxide, titanium oxide, zirconium oxide, silicon oxide, cerium oxide, yttrium oxide, and lanthanum oxide.

4. The method for reducing coating defects of a disc-type ceramic membrane according to claim 1, characterized in that: In step 2, the ceramic diaphragm is rinsed or soaked with an organic solvent for 5 to 120 minutes, then rinsed, soaked and ultrasonically cleaned with pure water 2 to 3 times, each time for 5 to 120 minutes, and finally dried at 50 to 200° C. for 10 to 240 minutes.

5. The method for reducing coating defects of disc-type ceramic membrane according to claim 1, characterized in that: In step three, the ceramic diaphragm and fixture are preheated to 50-200°C in an oven, then taken out and installed on the spraying station. The dynamic rotation speed of the ceramic diaphragm is 2-100RPM. Low-temperature plasma technology is used, with air as the gas source, to ionize and generate a mixture of electrons, ions, atoms and atomic clusters to clean and activate the surface of the ceramic diaphragm for 5-120s to remove surface pollutants.

6. The method for reducing coating defects of a disc-type ceramic membrane according to claim 2, characterized in that: In step 4, the spraying environment temperature is controlled at 20-60°C and the relative humidity is controlled at 20-80%; a negative pressure generating device is used to perform negative pressure suction on the ceramic diaphragm, and the pressure is controlled at -100-0kPa; the dynamic rotation speed of the ceramic diaphragm is controlled at 2-100RPM; the membrane-making liquid is magnetically stirred under constant temperature water bath conditions of 10-40°C, and a peristaltic pump is used for liquid inlet, and the liquid inlet flow rate is controlled at 0-65ml / min. An ultrasonic atomization spraying device is used to spray the surface of the ceramic diaphragm for 1-60 minutes; after the spraying is completed, the ceramic diaphragm and the fixture are taken out together and placed in a constant temperature and humidity chamber. The ceramic diaphragm is in a suspended state and dried for 30-300 minutes. The temperature of the constant temperature and humidity chamber is controlled at 20-80°C and the relative humidity is controlled at 20-80%.

7. The method for reducing coating defects of disc-type ceramic membranes according to claim 1, characterized in that: In step six, the dipping environment temperature is controlled at 20-60°C and the relative humidity is controlled at 20-80%. A negative pressure generating device is used to perform negative pressure suction on the ceramic diaphragm, and the pressure is controlled at -100-0 kPa. The dynamic rotation speed of the ceramic diaphragm is controlled at 2-50 RPM. The dynamic dipping time of the arc portion of the ceramic diaphragm in the film-making solution is controlled at 0-240 seconds.

8. The method for reducing coating defects of a disc-type ceramic membrane according to claim 1, characterized in that: In step seven, after the dip coating is completed, the ceramic diaphragm and the fixture are dried together. During the drying process, the ceramic diaphragm is in a suspended state and is dried in a constant temperature and humidity chamber for 30 to 300 minutes. The temperature of the constant temperature and humidity chamber is controlled at 20 to 80°C and the relative humidity is controlled at 20 to 80%. Then, it is calcined at 400 to 1300°C for 10 to 240 minutes.

9. A device for reducing coating defects of disc-type ceramic membranes, characterized in that: It includes a ceramic diaphragm surface spraying mechanism and a ceramic diaphragm arc portion dipping mechanism; The ceramic diaphragm surface spraying mechanism includes a spraying chamber, a fixed plate installed in the spraying chamber, a first motor installed on the fixed plate, a hollow rotating shaft driven by the first motor, a fixture connected to the hollow rotating shaft, a ceramic diaphragm installed on the fixture, a track located above the ceramic diaphragm, and a movable seat sliding on the track; It also includes a vacuum pump and a rotary joint connected to the vacuum pump; the rotary joint is connected to the hollow shaft; The invention also includes a magnetic stirrer, a peristaltic pump connected to the magnetic stirrer, and a first ultrasonic nozzle and a second ultrasonic nozzle connected to the peristaltic pump; the first ultrasonic nozzle is arranged facing the arc portion of the ceramic diaphragm, and the second ultrasonic nozzle is installed on a movable base and arranged facing the surface of the ceramic diaphragm; It also includes a low-temperature plasma treatment machine, wherein the plasma spray gun of the low-temperature plasma treatment machine is installed on a movable seat and arranged facing the surface of the ceramic diaphragm; The ceramic diaphragm arc portion dipping mechanism includes a second motor, a fixture driven by the second motor, a ceramic diaphragm mounted on the fixture, a rotary joint connected to the fixture, a vacuum pump connected to the rotary joint, a lifting platform, and a film-making liquid tank placed on the lifting platform; the ceramic diaphragm arc portion is dynamically dipped in the film-making liquid.

10. The device for reducing coating defects of disc-type ceramic membranes according to claim 9, characterized in that: The fixture includes two hollow tubes and flanges connected to the hollow tubes; the ceramic diaphragm is clamped by the two flanges, and the two flanges are connected by bolts and nuts. A sealing ring is provided between the ceramic diaphragm and the flanges, and the hollow tube is provided with an internal thread.

11. The device for reducing coating defects of disc-type ceramic membranes according to claim 10, characterized in that: In the ceramic diaphragm surface spraying mechanism, one hollow tube of the fixture is threadedly connected to the hollow shaft, and the other hollow tube of the fixture is threadedly sealed by bolts, with a sealing ring provided between the bolts and the hollow tube.

12. The device for reducing coating defects of disc-type ceramic membranes according to claim 11, characterized in that: The fixing plate is provided with a fixing seat, the fixing seat is provided with a groove, and the hollow rotating shaft and the hollow tube both extend into the groove for connection.

13. The device for reducing coating defects of disc-type ceramic membranes according to claim 9, characterized in that: The track is a screw rod, the movable seat is a nut seat, and a third motor is also included to drive the screw rod to rotate.

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