A method of coating an oil barrier and the resulting oil barrier

Abstract

This invention discloses a coating method for an oily diaphragm and the resulting oily diaphragm. The coating method includes the following steps: coating an oily slurry containing a solute and an organic solvent onto the diaphragm surface to obtain a coated film; then immersing the coated film in a coagulation bath within a coagulation tank for phase separation to form a strip-coated diaphragm. The distance L between the surface of the coagulation bath and the center of the first guide roller that contacts the coated film after entering the coagulation tank is 350-500 mm. Using this method, not only can the wrinkles on the diaphragm surface and the uniformity of the coating be relatively easily controlled, but also, in the coagulation tank, the slurry coated on the diaphragm surface comes into contact with a solution of a specific concentration, rapidly undergoing phase separation, changing from a liquid to a solid state, forming a stable coating adhering to the diaphragm surface. This increases the production speed to ≥70 m / min while ensuring a yield rate of ≥90%.

Description

Technical Field

[0001] This invention relates to the field of diaphragm preparation technology, and more specifically, to a coating method for an oily diaphragm and the resulting oily diaphragm. Background Technology

[0002] The process of coating diaphragms with polyvinylidene fluoride (PVDF) and aramid fibers can be divided into two types: water-based coating and oil-based coating. Water-based coating involves dispersing PVDF and adhesive in water, then spraying or roller-coating it onto the diaphragm surface. Oil-based coating involves dissolving PVDF in an organic solvent, coating it onto the diaphragm surface, and then extracting the organic solvent. Currently, in oil-based coating, the coated diaphragm is mainly immersed in the extraction solution. This extraction method has low efficiency, and the solvent extraction rate can only be improved by reducing the speed of the diaphragm conveyor belt. This method reduces the production efficiency of the diaphragm and is not conducive to increasing diaphragm yield. Summary of the Invention

[0003] The purpose of this invention is to overcome the above-mentioned deficiencies of the prior art and to provide a coating method for an oily diaphragm and the resulting oily diaphragm.

[0004] The present invention solves its technical problems by adopting the following technical solutions.

[0005] This invention provides a coating method for an oily diaphragm, comprising the following steps: coating an oily slurry containing a solute and an organic solvent onto the surface of the diaphragm to obtain a coated film; then immersing the coated film in a coagulation bath in a coagulation tank for phase separation to form a film, thereby obtaining a strip-coated diaphragm, wherein the distance L between the surface of the coagulation bath and the center of the first guide roller that contacts the coated film after it enters the coagulation tank is 350-500 mm.

[0006] The present invention provides an oily diaphragm prepared by the above preparation method.

[0007] The present invention has the following beneficial effects: This invention provides a coating method for oily diaphragms. By controlling the distance L between the liquid level in the coagulation tank and the center position of the first guide roller that the diaphragm contacts after entering the coagulation tank, not only can the wrinkles on the diaphragm surface and the uniformity of the coating be relatively easy to control, but also, in the coagulation tank, the slurry coated on the diaphragm surface comes into contact with a solution of a specific concentration, and phase separation occurs rapidly. The slurry changes from a liquid state to a solid state, forming a stable coating that adheres to the diaphragm surface, thereby increasing the production speed to ≥70m / min while ensuring a pass rate of ≥90%. Attached Figure Description

[0008] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0009] Figure 1 A schematic diagram of the production process for coating oily diaphragms; Figure 2 This is a schematic diagram of an intermittent coating gravure roller; Figure 3 This is a schematic diagram of the coating appearance. Detailed Implementation

[0010] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0011] The following is a detailed description of an oily diaphragm coating method and the resulting oily diaphragm provided by an embodiment of the present invention.

[0012] In a first aspect, the present invention provides a coating method for an oily diaphragm, comprising the following steps: coating an oily slurry containing a solute and an organic solvent onto the surface of the diaphragm to obtain a coated film, and then immersing the coated film in a coagulation bath in a coagulation tank for phase separation to form a film, thereby obtaining a strip-coated diaphragm, wherein the distance L between the surface of the coagulation bath and the center of the first guide roller that contacts the coated film after it enters the coagulation tank is 350-500 mm.

[0013] Currently, intermittent coating methods only provide partial coverage. After application, the coating will be placed in an aquatic environment, making it very difficult to ensure the regularity and integrity of the coating edges. (See also...) Figure 1Through extensive practical experience, the inventors discovered that the distance L1 between the tension roller in the unwinding mechanism and the first guide roller in the coagulation mechanism is a crucial factor affecting coating quality. When the distance L1 between the tension roller and the first guide roller in the coagulation tank is large, the diaphragm cannot be effectively flattened when the coating tension is low, leading to uneven coating. Conversely, excessive tension can easily cause wrinkles. The distance L between the liquid surface in the coagulation tank and the first guide roller (roller 1) below the liquid surface is also a significant factor affecting L1. When L is small, film wrinkles and coating uniformity are relatively easy to control, but production efficiency decreases (the coating begins phase separation upon contact with the liquid surface; when L is small, the phase separation time is short before contacting the first guide roller, and the coating phase separation is not yet sufficient, resulting in weak strength and susceptibility to damage). When L is large, L1 is also large, easily leading to wrinkles and uneven coating defects. If the coagulation tank concentration is too low, the phase separation speed is too fast, resulting in excessively large coating pores and reduced adhesion; if the coagulation tank concentration is too high, phase separation is too slow, affecting production efficiency. Therefore, traditional production methods have difficulty balancing production efficiency and product yield, specifically: production speed ≤ 40m / min, product yield ≤ 75%.

[0014] To overcome the aforementioned deficiencies in the existing technology, the present invention provides a coating method for an oily diaphragm. By controlling the distance L between the liquid level in the coagulation tank and the center position of the first guide roller that the coating membrane contacts after entering the coagulation tank, not only can the wrinkles on the diaphragm surface and the uniformity of the coating be relatively easy to control, but also, in the coagulation tank, the slurry coated on the surface of the coating membrane comes into contact with a solution of a specific concentration, and phase separation occurs rapidly. The slurry changes from a liquid state to a solid state, forming a stable coating that adheres to the diaphragm surface, thereby increasing the production speed to ≥70m / min while ensuring a pass rate of ≥90%.

[0015] In some optional embodiments, the process includes the following steps: after the diaphragm is unwound by an unwinding mechanism including a tension roller, it enters a coating mechanism including a material box and a gravure roller for coating the oily slurry in the material box onto the surface of the diaphragm; the coating mechanism coats the diaphragm with the oily slurry to obtain a coated film; the coated film is coagulated in a coagulation bath in the coagulation tank to obtain a strip-coated diaphragm; the strip-coated diaphragm is then washed by a washing mechanism, dried by a drying mechanism, and then stored by a winding mechanism.

[0016] In some alternative embodiments, the viscosity of the oily slurry is 280-420 mPa·s.

[0017] In some alternative embodiments, the solvent in the oily slurry includes one or more of NMP, DMAC, and acetone.

[0018] In some alternative embodiments, the solute in the oily slurry includes one or more of polyvinylidene fluoride and aramid fibers.

[0019] In some alternative embodiments, the coagulation bath comprises an organic solvent and an inorganic solvent, wherein the organic solvent comprises one or more of NMP, DMAC, and acetone, and the inorganic solvent comprises water, wherein the concentration of the organic solvent in the coagulation bath is 25-40%, and the temperature is 25±5℃.

[0020] In some alternative embodiments, the gravure roller is an intermittent coating gravure roller, wherein the coating is performed in a forward coating manner, the forward coating speed ratio of the gravure roller is 70%-85%, the coating method is single-sided coating or double-sided coating, and the stripes of the striped diaphragm obtained by coating are vertical stripes, horizontal stripes or diagonal stripes.

[0021] In some alternative embodiments, the tension between the tension roller and the first guide roller in the coagulation tank is 0.08-0.15 N / mm. Practice has shown that when the tension between the tension roller and the first guide roller in the coagulation tank is too low, the diaphragm cannot be effectively flattened, resulting in uneven coating. If the tension is too high, wrinkles are easily generated. Controlling the tension between the tension roller and the first guide roller in the coagulation tank to 0.08-0.15 N / mm can overcome these defects and obtain a high-quality strip-coated diaphragm.

[0022] In some alternative implementations, the production speed is 70-90 m / min.

[0023] Secondly, the present invention provides an oily diaphragm prepared by the above-described preparation method.

[0024] The present invention will be further described below with reference to embodiments.

[0025] This invention provides a method for coating an oily diaphragm, see [link to relevant documentation]. Figure 1 This includes the following steps: After being unwound by an unwinding mechanism including a tension roller, the diaphragm enters a coating mechanism including a material box and a gravure roller for coating the oily slurry in the material box onto the surface of the diaphragm. The coating mechanism coats the diaphragm with oily slurry to obtain a coated film. The coated film is then solidified in a coagulation bath in the coagulation tank to obtain a strip-coated diaphragm. The strip-coated diaphragm is then washed by a water washing mechanism, dried by a drying mechanism, and then stored by a winding mechanism.

[0026] Slurry viscosity testing method: A rotational rheometer was used, with a test temperature of 25±1℃, a rotation speed of 60rpm, a test time of 60s, and a rotor type of L1.

[0027] Forward coating: The rotation direction of the gravure roller is the same as the forward direction of the diaphragm being coated.

[0028] Coating speed ratio: The ratio of the linear speed of the gravure roller to the speed of the diaphragm being coated, which can be set via the control panel.

[0029] Coagulation tank concentration: solvent weight / (solvent weight + pure water weight), wherein the solvent composition is consistent with the solvent in the slurry, and can be one or more combinations of NMP, DMAC, and acetone.

[0030] The distance L between the liquid surface of the coagulation tank and the first guide roller (roller 1) below: the distance between the liquid surface of the coagulation tank and the center surface of the first guide roller after the diaphragm enters the coagulation tank. Measurement method: steel ruler measurement.

[0031] Coating tension: Set via control panel and detected by tension roller.

[0032] Traditional intermittent coating gravure roller, see Figure 2 The gravure roller is designed with engraving and non-engraving areas. The engraving area has grooves and is used to carry and transfer the paste, while the non-engraving area is a flat section that cannot carry or transfer the paste. The engraving and non-engraving areas are arranged alternately. The shape, depth and other parameters of the engraving area are set according to the coating thickness, and the width of the engraving and non-engraving areas is set according to the coating width.

[0033] Pass rate: Number of film rolls that meet the standards / Total production input * 100%.

[0034] Types of defects affecting yield: Methods for detecting coating edge regularity and coating integrity: Online defect instrumentation. See attached diagram for an illustration of coating appearance defects. Figure 3 Standard: Defect area ≤2mm², ≤10 defects / roll.

[0035] Method for detecting coating thickness uniformity: Online thickness gauge. Standard: Coating thickness difference < 0.2 μm.

[0036] Method for detecting wrinkles: Online defect instrument inspection. Standard: Wrinkles are not allowed.

[0037] The table below shows the preparation process and results of the oily slurry in the examples and comparative examples.

[0038]

[0039] Note: For examples not noted in the table above, the prepared oily diaphragms meet the requirements for coating edge regularity, coating integrity, coating thickness uniformity, and absence of wrinkles mentioned above.

[0040] As shown in the table above, the oil-based diaphragm coating method provided by this invention controls the distance L between the coagulation bath surface and the center of the first guide roller that contacts the coating film after entering the coagulation tank to be within the range of 350-500 mm. The viscosity of the coating slurry is 280-420 mPa·s (the solvent of the slurry is one or more of NMP, DMAC, and acetone; the solute is one or two of polyvinylidene fluoride and aramid). The gravure roller adopts a traditional intermittent coating gravure roller, wherein the coating adopts a forward coating method with a forward coating speed ratio of 70%-85%, and single-sided or double-sided coating can be used. The coating tension between the tension roller and the first guide roller is 0.08-0.15 N / mm. The solution concentration in the coagulation tank is 25-40%. The production speed is 70-90 m / min. The base film to be coated can be a wet base film, a dry base film, a ceramic coated film, etc. When the above conditions are met, the production efficiency can be improved, while ensuring a yield of ≥90%. If the preparation conditions do not meet the above requirements, defects such as irregular edges, incomplete coating, poor thickness uniformity, and wrinkles will occur in the strip-coated diaphragm.

[0041] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for coating an oily diaphragm, characterized in that, Includes the following steps: An oily slurry containing solute and organic solvent is coated onto the surface of a diaphragm to obtain a coated film. The coated film is then immersed in a coagulation bath in a coagulation tank for phase separation to form a strip-coated diaphragm. The distance L between the surface of the coagulation bath and the center of the first guide roller that contacts the coated film after it enters the coagulation tank is 350-500 mm.

2. The coating method according to claim 1, characterized in that, Includes the following steps: After being unwound by an unwinding mechanism including a tension roller, the diaphragm enters a coating mechanism including a material box and a gravure roller for coating the oily slurry in the material box onto the surface of the diaphragm. The coating mechanism coats the diaphragm with oily slurry to obtain a coated film. The coated film is then solidified in a coagulation bath in the coagulation tank to obtain a strip-coated diaphragm. The strip-coated diaphragm is then washed by a water washing mechanism, dried by a drying mechanism, and then stored by a winding mechanism.

3. The coating method according to claim 2, characterized in that, The viscosity of the oily slurry is 280-420 mPa·s.

4. The coating method according to claim 3, characterized in that, The solvent in the oily slurry includes one or more of NMP, DMAC, and acetone.

5. The coating method according to claim 3, characterized in that, The solute in the oily slurry includes one or more of polyvinylidene fluoride and aramid fiber.

6. The coating method according to claim 2, characterized in that, The coagulation bath includes an organic solvent and an inorganic solvent. The organic solvent includes one or more of NMP, DMAC, and acetone. The inorganic solvent includes water. The concentration of the organic solvent in the coagulation bath is 25-40%, and the temperature is 25±5℃.

7. The coating method according to claim 2, characterized in that, The gravure roller is an intermittent coating gravure roller, wherein the coating is carried out in a forward coating manner, the forward coating speed ratio of the gravure roller is 70%-85%, the coating method is single-sided coating or double-sided coating, and the stripes of the striped diaphragm obtained by coating are vertical stripes, horizontal stripes or diagonal stripes.

8. The coating method according to claim 2, characterized in that, The tension between the tension roller and the first guide roller in the solidification tank is 0.08-0.15 N / mm.

9. The coating method according to claim 2, characterized in that, The production speed is 70-90 m / min.

10. An oily diaphragm, characterized in that, It is prepared by the method for preparing an oily diaphragm as described in any one of claims 1-9.

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