High-tension slurry suitable for matrix dispensing, diaphragm and preparation process

Abstract

The invention relates to the technical field of battery diaphragms, and provides a high-tension slurry suitable for matrix dispensing, a diaphragm and a preparation process. The high-tension slurry suitable for matrix dispensing is prepared from the following components in parts by weight: 0.5 to 1 part of dispersing agent, 15 to 20 parts of PVDF (Polyvinylidene Fluoride) powder, 45 to 55 parts of water, 15 to 18 parts of thickening agent, 13 to 23 parts of binder and 2.5 to 4 parts of surfactant, the thickening agent comprises hydroxymethyl cellulose, polyvinyl alcohol and a cardanol ether compound in a mass ratio of 5: 10: (1-5). According to the technical scheme, the problems of coating connection points, too high ventilation value and low coating coverage rate caused by small tension and high flowability of matrix type spot coating slurry in related technologies are solved.

Description

Technical Field

[0001] The invention relates to the technical field of battery separators, and in particular to a high-tension slurry suitable for matrix dot coating, a separator and a preparation process. Background Art

[0002] With the rapid update of electronic products and the rapid expansion of new energy electric vehicles in the market, lithium batteries, as an important energy storage device with high energy density and long life, are increasingly attracting the attention of producers and users. One of the core components of lithium batteries is the diaphragm, which can effectively isolate the positive and negative electrodes, prevent short circuits and electrolyte impregnation, thereby ensuring the safety and performance stability of lithium batteries. Compared with PP or PE base films, coating films have better high temperature stability, chemical stability, and higher mechanical strength and toughness. Therefore, the lithium battery diaphragm coating process is crucial to the performance and service life of lithium batteries.

[0003] As for the membrane coating process, the commonly used processes are roller coating, spray coating, scraper coating and spin coating. Among them, roller coating and spray coating are widely used because of their relatively simple processes, stable coating effects and easy operation. The roller coating process is to transfer the slurry to the membrane through an anilox roller. The coating feature is full-screen coating, that is, the slurry accounts for 100% of the coating area. The spray coating process sprays the slurry onto the membrane surface through a spray head. The coating feature is irregular dot coating, and the slurry accounts for less than 100% of the coating area.

[0004] At present, a new coating method - matrix dot coating, has a contact partial coating method with a coating roller in addition to roller coating. It uses tension difference to transfer the coating liquid from the anilox roller to the diaphragm. Its coating characteristics are that the coating points are relatively regular circles, and the size of the points and the distance between the two points can be changed by adjusting the equipment and process. However, due to the process characteristics of matrix dot coating, the requirements for slurry are also relatively high. For example, the high fluidity of the slurry will easily cause the slurry to flow from the head of the roller convex point to the bottom before being transferred to the diaphragm. After a long time, the slurry will accumulate to a certain height at the bottom, which will cause the coating points to be connected, affecting the appearance and characteristics; when coating on the surface of the base film, if the slurry tension is too small, it is easy to cause the slurry to flow into the pores of the base film, causing abnormal permeability, and the coating points will diffuse irregularly around, causing irregular shape of the points. Too high permeability value affects the electrochemical performance and safety performance of the battery. Therefore, it is necessary to obtain a high-tension slurry suitable for matrix dot coating, so that it can better match the dot coating process and solve the problems of coating dots, excessively high air permeability and low coating coverage caused by low slurry tension and high fluidity. Summary of the invention

[0005] The present invention proposes a high-tension slurry, a diaphragm and a preparation process suitable for matrix dot coating, which solves the problems of continuous coating points, excessively high air permeability and low coating coverage caused by low slurry tension and high fluidity in the matrix dot coating slurry in the related art.

[0006] The technical solution of the present invention is as follows: The present invention provides a high tension slurry suitable for matrix dot coating, comprising the following components in parts by weight: 0.5-1 part of a dispersant, 15-20 parts of PVDF powder, 45-55 parts of water, 15-18 parts of a thickener, 13-23 parts of a binder, and 2.5-4 parts of a surfactant; The components of the thickener include hydroxymethyl cellulose, polyvinyl alcohol and cardanol ether-based compounds in a mass ratio of 5:10:1-5.

[0007] As a further technical solution, the cardanol ether-based compound includes one or more of cardanol ether sulfosuccinic acid half ester disodium salt, cardanol polyoxyethylene ether sodium sulfate, and cardanol polyoxyethylene ether ammonium sulfate; Preferably, the cardanol ether-based compound comprises cardanol ether sulfosuccinic acid half ester disodium salt and cardanol polyoxyethylene ether ammonium sulfate in a mass ratio of 1:3 to 3:1.

[0008] In the present invention, when the cardanol ether-based compound is cardanol ether sulfosuccinic acid half ester disodium salt and cardanol polyoxyethylene ether ammonium sulfate in a mass ratio of 1:3 to 3:1, the air permeability value of the battery separator is further reduced.

[0009] As a further technical solution, the degree of polymerization of the polyvinyl alcohol is ≥1200.

[0010] In the present invention, when the degree of polymerization of polyvinyl alcohol in the components of the high-tension slurry is ≥1200, after the obtained high-tension slurry is coated on the surface of the battery separator, the air permeability of the battery separator is further reduced, which is more conducive to the passage of electrons.

[0011] As a further technical solution, the degree of polymerization of the polyvinyl alcohol is 1650~2500.

[0012] In the present invention, when the degree of polymerization of polyvinyl alcohol in the components of the high-tension slurry is 1650-2500, the obtained high-tension slurry is coated on the surface of the battery separator, which further reduces the air permeability value of the battery separator.

[0013] As a further technical solution, the surfactant includes one or more of sodium dodecyl sulfate, sucrose fatty acid esters, sodium dodecylbenzene sulfonate, hexadecyl triethanolamine, glycols, and inorganic salts.

[0014] As a further technical solution, the binder includes one or more of methyl methacrylate copolymer, acrylate copolymer, and styrene-butyl methacrylate copolymer; The dispersant includes ammonium polyacrylate.

[0015] The present invention also proposes a process for preparing a high tension slurry suitable for matrix dot coating, comprising the following steps: Water, a dispersant and a surfactant are mixed for the first time, PVDF powder is added for the second mixing, and a thickener and a binder are added for the third mixing to obtain a slurry.

[0016] As a further technical solution, the temperature of the first mixing is 50-65°C, the time is 10-150 min, the rotation speed is 1800-2200 r / min, and the revolution speed is 30-50 r / min; The second mixing time is 60-70 min, the rotation speed is 1500-2000 r / min, and the revolution speed is 30-50 r / min; The third mixing time is 25-30 min, the rotation speed is 1200-1500 r / min, and the revolution speed is 30-40 r / min.

[0017] The present invention also provides a diaphragm, comprising a base film and a coating coated on one side or both sides of the base film, wherein the coating is made of the high-tension slurry or the slurry obtained by the preparation process.

[0018] As a further technical solution, the coating speed is 50-150 m / min; the coating method includes matrix dot coating.

[0019] In the present invention, when the high-tension slurry is coated on the surface of the base film, it can be completely maintained on the surface of the base film, reducing the waste of slurry caused by flowing into the pores of the diaphragm, saving slurry and reducing costs.

[0020] The working principle and beneficial effects of the present invention are: In the present invention, the thickener in the components of the high-tension slurry includes hydroxymethyl cellulose, polyvinyl alcohol, and cardanol ether-based compounds in a mass ratio of 5:10:1-5, which synergistically adjust the surface tension of the slurry and cooperate with the remaining components of the high-tension slurry. The high-tension slurry finally obtained achieves that it is not easy to connect dots after spot coating, especially high coverage coating, which can increase the upper limit of spot coating coverage and increase the upper limit of coating coverage of a single plate roller; it also reduces the problem of abnormal permeability caused by the slurry flowing into the pores of the diaphragm and the decrease in coating pass rate caused by abnormal permeability, and significantly reduces the permeability value of the battery diaphragm; the high-tension slurry of the present invention has coating controllability, can better control the shape of the coating points, and can meet the battery winding process with high requirements on the point shape. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0022] Figure 1 This is a morphology diagram of the coating points on the surface of the battery separator prepared in Example 1 of the present invention; Figure 2 This is a morphology diagram of the coating points on the surface of the battery separator prepared in Comparative Example 1 of the present invention; Figure 3 This is a microscopic morphology of the coating points on the surface of the battery separator prepared in Example 1 of the present invention; Figure 4 This is a microscopic morphology of the coating points on the surface of the battery separator prepared in Comparative Example 1 of the present invention; Figure 5 This is a coverage diagram of the slurry obtained in Comparative Example 1 of the present invention after coating; Figure 6 This is a coverage diagram of the slurry obtained in Example 1 of the present invention after coating. DETAILED DESCRIPTION

[0023] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0024] In the following examples and comparative examples, the model of PVDF powder is FR902; The model of polyvinyl alcohol (degree of polymerization 500) is BF05; The model number of polyvinyl alcohol (degree of polymerization 1200~1400) is 1399; The model of polyvinyl alcohol (degree of polymerization 2750~2850) is BP28; The model of polyvinyl alcohol (degree of polymerization 1650~1750) is 100-27S; The model of polyvinyl alcohol (degree of polymerization 2300~2500) is PVA2488; The model of ammonium sulfate of cardanol polyoxyethylene ether is CPE-458Y, the model of sodium sulfate of cardanol polyoxyethylene ether is CPE-430Y, and the model of disodium salt of cardanol ether sulfosuccinate half ester is CPE-330Y, all of which were purchased from Guangzhou Shuangbang Trading Co., Ltd. The model of styrene-methyl methacrylate copolymer is TX-100S; The base film is a polyethylene film with a porosity of 36%.

[0025] Example 1 A high tension slurry suitable for matrix dot coating comprises the following components in parts by weight: 1 part of polyacrylate ammonium salt dispersant SN5027, 18 parts of PVDF powder, 50 parts of water, 16 parts of thickener, 18 parts of styrene-methyl methacrylate copolymer, and 3.5 parts of sodium dodecyl sulfate; The thickener comprises hydroxymethyl cellulose, polyvinyl alcohol (polymerization degree 500), and cardanol polyoxyethylene ether ammonium sulfate in a mass ratio of 5:10:3; The preparation process of a high tension slurry suitable for matrix dot coating comprises the following steps: Water, polyacrylic acid ammonium salt dispersant SN5027 and sodium dodecyl sulfate were mixed at 60° C., a rotation speed of 2000 r / min and a revolution speed of 40 r / min for 75 min, PVDF powder was added, mixed at a rotation speed of 1700 r / min and a revolution speed of 40 r / min and sand-milled for 65 min, a thickener and styrene-methyl methacrylate copolymer were added, mixed at a rotation speed of 1300 r / min and a revolution speed of 35 r / min for 28 min, and a slurry was obtained; A method for preparing a battery separator comprises the following steps: The slurry was dot-coated in a matrix manner on the upper surface of a base film with a thickness of 9 μm at a coating speed of 100 m / min, and dried at 55° C. for 2 min to obtain a battery separator.

[0026] Example 2 A high tension slurry suitable for matrix dot coating comprises the following components in parts by weight: 1 part of polyacrylate ammonium salt dispersant SN5027, 20 parts of PVDF powder, 55 parts of water, 18 parts of thickener, 23 parts of styrene-methyl methacrylate copolymer, 2 parts of sodium dodecyl sulfate, and 2 parts of sodium dodecylbenzene sulfonate; The thickener comprises hydroxymethyl cellulose, polyvinyl alcohol (polymerization degree 500), and cardanol polyoxyethylene ether ammonium sulfate in a mass ratio of 5:10:5; The preparation process of a high tension slurry suitable for matrix dot coating comprises the following steps: Water, polyacrylic acid ammonium salt dispersant SN5027, sodium dodecylbenzene sulfonate and sodium dodecyl sulfate were mixed at 65°C, a rotation speed of 1800 r / min and a revolution speed of 50 r / min for 10 min, PVDF powder was added, mixed at a rotation speed of 2000 r / min and a revolution speed of 30 r / min and sand-milled for 60 min, a thickener and styrene-methyl methacrylate copolymer were added, mixed at a rotation speed of 1500 r / min and a revolution speed of 30 r / min for 25 min, and a slurry was obtained; A method for preparing a battery separator comprises the following steps: The slurry was dot-coated in a matrix manner on the upper surface of a base film with a thickness of 9 μm at a coating speed of 150 m / min, and dried at 45° C. for 3 min to obtain a battery separator.

[0027] Example 3 A high tension slurry suitable for matrix dot coating comprises the following components in parts by weight: 0.5 parts of polyacrylate ammonium salt dispersant SN5027, 15 parts of PVDF powder, 45 parts of water, 15 parts of thickener, 13 parts of styrene-methyl methacrylate copolymer, and 2.5 parts of sodium dodecyl sulfate; The thickener comprises hydroxymethyl cellulose, polyvinyl alcohol (polymerization degree 500), and sodium cardanol polyoxyethylene ether sulfate in a mass ratio of 5:10:1; The preparation process of a high tension slurry suitable for matrix dot coating comprises the following steps: Water, polyacrylic acid ammonium salt dispersant SN5027 and sodium dodecyl sulfate were mixed at 50° C., a rotation speed of 2200 r / min and a revolution speed of 30 r / min for 150 min, PVDF powder was added, mixed at a rotation speed of 1500 r / min and a revolution speed of 50 r / min and sand-milled for 70 min, a thickener and styrene-methyl methacrylate copolymer were added, mixed at a rotation speed of 1200 r / min and a revolution speed of 40 r / min for 30 min, and a slurry was obtained; A method for preparing a battery separator comprises the following steps: The slurry was dot-coated in a matrix manner on the upper surface of a base film with a thickness of 9 μm at a coating speed of 50 m / min, and dried at 60° C. for 1 min to obtain a battery separator.

[0028] Example 4 The difference between this embodiment and embodiment 1 is that polyvinyl alcohol (degree of polymerization 500) is replaced by polyvinyl alcohol (degree of polymerization 1200-1400).

[0029] Example 5 The difference between this embodiment and embodiment 1 is that polyvinyl alcohol (degree of polymerization 500) is replaced by polyvinyl alcohol (degree of polymerization 2750-2850).

[0030] Example 6 The only difference between this embodiment and embodiment 1 is that polyvinyl alcohol (degree of polymerization 500) is replaced by polyvinyl alcohol (degree of polymerization 1650-1750).

[0031] Example 7 The difference between this embodiment and embodiment 1 is that polyvinyl alcohol (degree of polymerization 500) is replaced by polyvinyl alcohol (degree of polymerization 2300-2500).

[0032] Example 8 The only difference between this embodiment and embodiment 7 is that the ammonium sulfate of cardanol polyoxyethylene ether is replaced by an equal amount of disodium salt of cardanol ether sulfosuccinate half ester.

[0033] Example 9 The difference between this embodiment and embodiment 7 is that the ammonium sulfate of cardanol polyoxyethylene ether is replaced by a mixture of an equal amount of disodium salt of cardanol ether sulfosuccinate half ester and ammonium sulfate of cardanol polyoxyethylene ether; The mass ratio of cardanol ether sulfosuccinic acid half ester disodium salt and cardanol polyoxyethylene ether ammonium sulfate is 1:3.

[0034] Example 10 The difference between this embodiment and embodiment 7 is that the ammonium sulfate of cardanol polyoxyethylene ether is replaced by a mixture of an equal amount of disodium salt of cardanol ether sulfosuccinate half ester and ammonium sulfate of cardanol polyoxyethylene ether; The mass ratio of cardanol ether sulfosuccinic acid half ester disodium salt and cardanol polyoxyethylene ether ammonium sulfate is 3:1.

[0035] Embodiment 11 The difference between this embodiment and embodiment 7 is that the ammonium sulfate of cardanol polyoxyethylene ether is replaced by a mixture of an equal amount of disodium salt of cardanol ether sulfosuccinate half ester and sodium cardanol polyoxyethylene ether sulfate; The mass ratio of cardanol ether sulfosuccinic acid half ester disodium salt and cardanol polyoxyethylene ether sodium sulfate is 3:1.

[0036] Comparative Example 1 The difference between this comparative example and Example 1 is that the cardanol polyoxyethylene ether ammonium sulfate is replaced by an equal amount of sodium dodecyl sulfate.

[0037] Comparative Example 2 The only difference between this comparative example and Example 1 is that the thickener comprises hydroxymethyl cellulose and polyvinyl alcohol (degree of polymerization 500) in a mass ratio of 5:10.

[0038] Comparative Example 3 The only difference between this comparative example and Example 1 is that the thickener comprises hydroxymethyl cellulose and cardanol polyoxyethylene ether ammonium sulfate in a mass ratio of 5:3.

[0039] Comparative Example 4 The only difference between this comparative example and Example 1 is that the thickener comprises polyvinyl alcohol (polymerization degree 500) and cardanol polyoxyethylene ether ammonium sulfate in a mass ratio of 10:3.

[0040] The battery separators prepared in Example 1 and Comparative Example 1 were placed under a microscope to observe the morphology of the coating points. The results are as follows: Figure 1~2 As shown; Figure 1This is a morphology of the coating points on the surface of the battery separator prepared in Example 1. Figure 2 This is a morphology of the coating points on the surface of the battery separator prepared in Comparative Example 1. It can be seen that Figure 1 The morphology of the battery separator coating point in the Figure 2 The coating points of the battery diaphragm in the figure are severely deformed, indicating that the coating points of the high-tension slurry prepared by the formula of the present invention coated on the surface of the diaphragm have better shape control and can meet the battery winding process with higher requirements on point shape.

[0041] The battery separators prepared in Example 1 and Comparative Example 1 were placed under an electron microscope, and the finer microscopic morphology of the coating points on the battery separators was photographed at a magnification of 5k. The results are as follows: Figure 3~4 As shown; Figure 3 This is a microscopic morphology of the coating points on the surface of the battery separator prepared in Example 1. Figure 4 This is a microscopic morphology of the coating points on the surface of the battery separator prepared in Comparative Example 1. It can be seen that Figure 3 The particles at the coating point on the base film are well agglomerated, and the slurry basically does not block the gaps. Figure 4 The particles at the coating points on the base membrane are relatively scattered, and the slurry penetrates into the pores of the base membrane, blocking the pores of the base membrane.

[0042] The viscosity of the slurries prepared in Example 1 and Comparative Example 1 was tested using a viscometer. The viscosity of the slurry in Example 1 was 430 mPa·s, and the viscosity of the slurry in Comparative Example 1 was 440 mPa·s.

[0043] The surface tension of the slurries prepared in Examples 1 to 11 and Comparative Examples 1 to 4 was tested using a surface tension meter. The air permeability of the battery separators prepared in Examples 1 to 11 and Comparative Examples 1 to 4 was tested according to the method in GB / T 36363-2018: samples were taken horizontally on the battery separator, one sample was taken every 100 m, and then an air permeability test was performed. Ten points were measured for each sample, and the results were averaged, as shown in Table 1.

[0044] Table 1 Test results

[0045] Compared with Comparative Examples 1 to 4, the surface tension of the slurries prepared in Examples 1 to 11 is higher. After being coated on the surface of the battery separator, the air permeability of the battery separator is lower, indicating that the thickener components in the high-tension slurry are hydroxymethyl cellulose, polyvinyl alcohol, and cardanol ether-based compounds in a mass ratio of 5:10:1 to 5, combined with the remaining components of the high-tension slurry. After the obtained high-tension slurry is coated on the surface of the battery separator, the air permeability of the battery separator is significantly reduced.

[0046] Compared with Example 1, the surface tension of the slurry prepared in Examples 4 to 5 is higher. After being coated on the surface of the battery separator, the air permeability of the battery separator is lower, indicating that when the degree of polymerization of polyvinyl alcohol in the components of the high-tension slurry is ≥1200, the obtained high-tension slurry is coated on the surface of the battery separator, which further reduces the air permeability of the battery separator.

[0047] Compared with Examples 4 to 5, the surface tension of the slurry prepared in Examples 6 to 7 is higher. After being coated on the surface of the battery separator, the air permeability of the battery separator is lower, indicating that when the degree of polymerization of polyvinyl alcohol in the components of the high-tension slurry is 1650 to 2500, the obtained high-tension slurry is coated on the surface of the battery separator, which further reduces the air permeability of the battery separator.

[0048] Compared with Examples 7 to 8 and 11, the surface tension of the slurry prepared in Examples 9 to 10 is higher. After being coated on the surface of the battery separator, the air permeability of the battery separator is lower, indicating that when the cardanol ether-based compound is cardanol ether sulfosuccinic acid half ester disodium salt and cardanol polyoxyethylene ether ammonium sulfate in a mass ratio of 1:3 to 3:1, the air permeability of the battery separator is further reduced.

[0049] Comparison of the upper limits of the coating coverage of the two slurries in Example 1 and Comparative Example 1: When the slurry is coated, the coverage is increased until individual dots are connected, and the coverage is obtained. The results are as follows: Figures 5 and 6 shown.

[0050] Figure 5 The coverage diagram after slurry coating obtained in Comparative Example 1 is shown in FIG. Figure 6 The figure is a coverage diagram of the slurry obtained in Example 1 after coating, wherein the coverage of the slurry obtained in Example 1 after coating is 66.30%, and the coverage of the slurry obtained in Comparative Example 1 after coating is 57.00%. Compared with Comparative Example 1, the coverage of the slurry in Example 1 after coating is higher, indicating that the slurry prepared by the formula of the present invention can effectively increase the upper limit of the coating coverage of the plate roller and broaden the coating capacity of the plate roller.

[0051] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A high tension slurry suitable for matrix dot coating, characterized in that: The invention comprises the following components in parts by weight: 0.5-1 part of dispersant, 15-20 parts of PVDF powder, 45-55 parts of water, 15-18 parts of thickener, 13-23 parts of binder, and 2.5-4 parts of surfactant; The components of the thickener include hydroxymethyl cellulose, polyvinyl alcohol and cardanol ether-based compounds in a mass ratio of 5:10:1-5.

2. A high tension slurry suitable for matrix dot coating according to claim 1, characterized in that: The cardanol ether-based compound includes one or more of cardanol ether sulfosuccinic acid half ester disodium salt, cardanol polyoxyethylene ether sodium sulfate, and cardanol polyoxyethylene ether ammonium sulfate; Preferably, the cardanol ether-based compound comprises cardanol ether sulfosuccinic acid half ester disodium salt and cardanol polyoxyethylene ether ammonium sulfate in a mass ratio of 1:3 to 3:

1.

3. A high tension slurry suitable for matrix dot coating according to claim 1, characterized in that: The degree of polymerization of the polyvinyl alcohol is ≥1200.

4. A high tension slurry suitable for matrix dot coating according to claim 3, characterized in that: The degree of polymerization of the polyvinyl alcohol is 1650-2500.

5. The high tension slurry suitable for matrix dot coating according to claim 1, characterized in that: The surfactant includes one or more of sodium dodecyl sulfate, sucrose fatty acid ester, sodium dodecylbenzene sulfonate, hexadecyl triethanolamine, glycol, and inorganic salt.

6. A high tension slurry suitable for matrix dot coating according to claim 1, characterized in that: The binder includes one or more of methyl methacrylate copolymer, acrylate copolymer, and styrene-butyl methacrylate copolymer; The dispersant includes ammonium polyacrylate.

7. A process for preparing a high tension slurry suitable for matrix dot coating according to any one of claims 1 to 6, characterized in that: The following steps are involved: Water, a dispersant and a surfactant are mixed for the first time, PVDF powder is added for the second mixing, and a thickener and a binder are added for the third mixing to obtain a slurry.

8. A process for preparing a high tension slurry suitable for matrix dot coating according to claim 7, characterized in that: The temperature of the first mixing is 50-65°C, the time is 10-150 min, the rotation speed is 1800-2200 r / min, and the revolution speed is 30-50 r / min; The second mixing time is 60-70 min, the rotation speed is 1500-2000 r / min, and the revolution speed is 30-50 r / min; The third mixing time is 25-30 min, the rotation speed is 1200-1500 r / min, and the revolution speed is 30-40 r / min.

9. A diaphragm, characterized in that: It comprises a base film and a coating coated on one side or both sides of the base film, wherein the coating is made of the high-tension slurry described in any one of claims 1 to 6 or the slurry prepared by the preparation process described in any one of claims 7 to 8.

10. A diaphragm according to claim 9, characterized in that: The coating speed is 50-150 m / min; the coating method includes matrix dot coating.

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