High-puncture-strength aluminum-plastic film for lithium battery and preparation process of high-puncture-strength aluminum-plastic film

Abstract

The high-puncture-strength aluminum plastic film for the lithium battery comprises a nylon surface layer, a nylon bonding layer, a nylon inner layer, an aluminum foil bonding layer, a passivated aluminum foil layer, a heat sealing bonding layer and a heat sealing layer which are sequentially arranged in a stacked mode, and the nylon bonding layer comprises bonding resin and reinforcing fibers. The reinforcing fibers are arranged in the bonding layer between the two nylon layers, so that the puncture strength of the aluminum plastic film is improved. The invention further discloses a preparation process of the high-puncture-strength aluminum-plastic film for the lithium battery.

Description

Technical Field

[0001] This invention relates to the field of aluminum-plastic film technology, specifically to an aluminum-plastic film for lithium batteries with high puncture strength and its preparation process. Background Technology

[0002] As a key material for lithium battery packaging, aluminum-plastic film's main structure, from the outside in, consists of a nylon layer, an aluminum foil layer, and a heat-sealing layer. Puncture resistance is an important property of aluminum-plastic film, meaning its ability to resist puncture by external forces.

[0003] Chinese invention patent CN106025108A discloses an aluminum-plastic film for puncture-resistant lithium battery packaging. This aluminum-plastic film comprises an outer film layer, an puncture-resistant layer, an inner film layer, an aluminum foil layer, and a heat-sealing layer, stacked sequentially. These layers are bonded together with adhesive. The outer film layer is a polytetrafluoroethylene (PTFE) film, the inner film layer is a polyester film, and the puncture-resistant layer is composed of interwoven warp and weft yarns, with the warp yarns being aramid yarns and the weft yarns being nylon yarns. However, while this structure improves the puncture resistance of the aluminum-plastic film to some extent, the puncture-resistant layer, being composed of interwoven aramid and nylon yarns, has significantly lower ductility and deep-drawing performance than homogeneous films.

[0004] Therefore, there is an urgent need to develop a new type of aluminum-plastic film for lithium batteries with high puncture strength. Summary of the Invention

[0005] One of the objectives of this invention is to overcome the deficiencies in the prior art and provide an aluminum-plastic film for lithium batteries with high puncture strength, which also has good deep-drawing performance.

[0006] To solve the above-mentioned technical problems, the present invention provides an aluminum-plastic film for lithium batteries with high puncture strength, comprising a nylon surface layer, a nylon adhesive layer, a nylon inner layer, an aluminum foil adhesive layer, a passivated aluminum foil layer, a heat-sealing adhesive layer, and a heat-sealing layer stacked in sequence, wherein the nylon adhesive layer comprises adhesive resin and reinforcing fibers.

[0007] A preferred technical solution is that the nylon adhesive layer comprises a first adhesive layer, a second adhesive layer, and a third adhesive layer stacked sequentially, wherein the components of the second adhesive layer include reinforcing fibers.

[0008] A preferred technical solution is that the thickness ratio of the first adhesive layer, the second adhesive layer and the third adhesive layer is 1:(1~1.2):1.

[0009] Furthermore, the thickness ratio of the first adhesive layer, the second adhesive layer, and the third adhesive layer can be selected as a point value of 1:1:1, 1:1.1:1, or 1:1.2:1, or the above two point values ​​as an interval value of the maximum and minimum values.

[0010] A preferred technical solution is that the components of the second adhesive layer include a solvent-based two-component adhesive and reinforcing fibers; The solvent-based two-component adhesive includes a main agent and a curing agent, wherein the solid content of the main agent is 29% to 31%, and the reinforcing fiber includes modified sepiolite fiber. The mass ratio of the main agent to the reinforcing fiber is 100:(0.5~2). The modified sepiolite fiber is obtained by acid activation, polyvinyl alcohol debinding, and modification of sepiolite microparticles; Furthermore, the second adhesive layer also includes trimethylolpropane.

[0011] Furthermore, the mass ratio of the main agent to the reinforcing fiber can be selected as a point value of 100:0.5, 100:1, 100:1.5, or 100:2, or a range of the above two point values ​​as the maximum and minimum values.

[0012] A preferred technical solution is that the first adhesive layer comprises a first adhesive, and the third adhesive layer comprises a third adhesive. Both the first adhesive and the third adhesive are solvent-based two-component adhesives. The solid content of the main component of both the first adhesive and the third adhesive is 29% to 31%. The components of the first adhesive, the second adhesive, and the third adhesive also include ethyl acetate. The mass ratio of the main agent to ethyl acetate in the first adhesive is 100:(0.1~0.15). In the second adhesive, the mass ratio of the main component to ethyl acetate is 100:(0.06~0.09). The mass ratio of the main agent to ethyl acetate in the third adhesive is 100:(0.01~0.05).

[0013] Furthermore, the mass ratio of the main agent to ethyl acetate in the first adhesive can be selected as a point value of 100:0.1, 100:0.13, or 100:0.15, or a range of the above two point values ​​as the maximum and minimum values; the mass ratio of the main agent to ethyl acetate in the second adhesive can be selected as a point value of 100:0.06, 100:0.07, 100:0.08, or 100:0.09, or a range of the above two point values ​​as the maximum and minimum values; the mass ratio of the main agent to ethyl acetate in the third adhesive can be selected as a point value of 100:0.01, 100:0.02, 100:0.03, 100:0.04, or 100:0.05, or a range of the above two point values ​​as the maximum and minimum values.

[0014] The second objective of this invention is to provide a process for preparing an aluminum-plastic film for lithium batteries with high puncture strength, comprising the following steps: S01: Three layers of adhesive are applied to the surface of the PA film using a multi-layer slit coating method. The three layers of adhesive are, from top to bottom, the first adhesive, the second adhesive, and the third adhesive. S02: Dry the three-layer adhesive on the surface of the PA film, and bond another PA film to the PA film with the three-layer adhesive to obtain a protective film; the protective film has a nylon surface layer, a nylon adhesive layer and a nylon inner layer stacked in sequence; S1: Apply aluminum foil adhesive to side A of the passivated aluminum foil and bond the protective film and side A of the passivated aluminum foil together; apply heat-sealing adhesive to side B of the passivated aluminum foil and bond the heat-sealing film and side B of the passivated aluminum foil together to obtain a high puncture strength aluminum-plastic film for lithium batteries.

[0015] A preferred technical solution is that the sepiolite fiber in the second adhesive is modified sepiolite fiber, and the modification of the modified sepiolite fiber includes the following steps: Modified sepiolite fiber is obtained by mixing and grinding 100 parts by weight of sepiolite fiber, 1-5 parts by weight of silane coupling agent and 1-2 parts by weight of trimethylolpropane.

[0016] Furthermore, the number of parts of the silane coupling agent can be selected as 1, 2, 3, 4, 5 points or the above two points as the range of maximum and minimum values, and the number of parts of trimethylolpropane can be selected as 1, 1.5, 2 points or the above two points as the range of maximum and minimum values.

[0017] The preferred technical solution is that the preparation process of the second adhesive includes: The main component, curing agent, and modified sepiolite fiber of the second adhesive are mixed to obtain the second adhesive.

[0018] A preferred technical solution is that the modified sepiolite fiber further includes an acid activation step before modification, wherein the average particle size of the sepiolite microparticle raw material used in the acid activation step is 200 mesh to 800 mesh.

[0019] Furthermore, the average particle size of the sepiolite microparticle raw material can be selected as 200 mesh, 325 mesh, or 800 mesh.

[0020] A preferred technical solution is that the acid activation step and the modification step further include the following steps: 0.7-1.2 parts of acid-activated sepiolite fiber were mixed with 100 parts of polyvinyl alcohol aqueous solution and stirred for 1.7-2.3 h, followed by sonication for 0.4-0.6 h, then stirring for 0.4-0.6 h, followed by solid-liquid separation to obtain a solid product, and finally dried at a constant temperature of 80-93℃ to obtain unbound sepiolite. The concentration of polyvinyl alcohol in the aqueous solution is 4~6 g / L, and the stirring speed is 2550~2750 r / min.

[0021] Furthermore, the concentration of the polyvinyl alcohol can be selected as a point value of 4 g / L, 5 g / L, or 6 g / L, or a range of the above two point values ​​as the maximum and minimum values.

[0022] The advantages and beneficial effects of this invention are as follows: The aluminum-plastic film for high puncture strength lithium batteries of this invention has a reasonable formulation and excellent puncture strength. Furthermore, the nylon adhesive layer is configured as a three-layer stack, with reinforcing fibers placed in the middle layer of the nylon adhesive layer, thereby improving the puncture strength of the aluminum-plastic film. The multi-layer slit coating method enables the application of three layers of adhesive to the PA film surface in one step, resulting in high coating efficiency and more uniform adhesive coating thickness. Detailed Implementation

[0023] The specific embodiments of the present invention will be further described below with reference to examples. These examples are only used to more clearly illustrate the technical solutions of the present invention and should not be construed as limiting the scope of protection of the present invention.

[0024] raw material: Sepiolite microparticles: 200 mesh, 325 mesh, 800 mesh, Hebei Jinghang Mineral Products Co., Ltd.; Adhesive: VN930 / CA-N6, Shanghai Weikai Optoelectronic New Materials Co., Ltd.; This adhesive is a solvent-based two-component adhesive, consisting of the main component VN930 and the curing agent CA-N6. The solid content of the main component VN930 is 29%~31%. The solid content of the curing agent CA-N6 is 73%~77%.

[0025] Aluminum foil: 8021 O state, Henan Mingtai; Outer adhesive: VN830 / CA-N6 (aluminum-plastic film outer adhesive), Shanghai Weikai Optoelectronic New Materials Co., Ltd.; Inner layer adhesive: VP118 / CA-P2 (inner layer adhesive for aluminum-plastic film), Shanghai Weikai Optoelectronic New Materials Co., Ltd.; PA film: PHA lithium battery film (thicknesses of 15μm and 30μm respectively, functional biaxially oriented nylon film), Xiamen Changsu Industrial Co., Ltd.; Ternary copolymer polypropylene: PP FL7632, Singapore polyolefin; POE elastomer: XM-7070S, Mitsui Chemicals, Japan.

[0026] 1. Examples and Comparative Examples Example 1

[0027] Acid activation of sepiolite: 325-mesh sepiolite particles and 6 wt% hydrochloric acid were mixed at a mass ratio of 1:18 to obtain a mixture. The mixture was stirred at room temperature, and 6 wt% hydrochloric acid was intermittently introduced into the mixture until the pH value of the mixture was 3. The mixture was treated with a disperser for 1 hour (rotation speed of 2700 r / min), and then filtered using a circulating water multi-purpose vacuum pump and a Buchner funnel to obtain a filter cake. The filter cake was crushed and mixed with deionized water, then stirred, washed, and filtered again. This process was repeated until the pH of the sepiolite dispersion was 7. Finally, the solid product was dried to obtain acid-activated sepiolite.

[0028] Polyvinyl alcohol dissociation of sepiolite: One part of acid-activated sepiolite was pulverized and mixed with 100 parts of an aqueous solution of polyvinyl alcohol (type 17-88) to obtain a dispersion (polyvinyl alcohol concentration of 5 g / L). The dispersion was treated with a disperser for 2 hours (speed of 2700 r / min), then sonicated for 0.5 hours, and then treated with a disperser for another 0.5 hours (speed of 2700 r / min). Finally, the mixture was filtered and the filter cake was placed in a constant temperature drying oven at 90℃ and dried to constant weight. Finally, the mixture was subjected to air jet milling to obtain unbound sepiolite.

[0029] Modification of sepiolite: The modified sepiolite was obtained by mixing sepiolite, coupling agent (KH550) and trimethylolpropane in a mass ratio of 100:3:1.5 and then ball milling the mixture in a planetary ball mill for 2 hours.

[0030] The heat-sealing film of Example 1 was prepared using a casting machine (casting temperature 251℃) with a thickness of 30 μm. The masterbatch used in the heat-sealing film of Example 1 was obtained by granulation of ternary copolymer polypropylene of grade PP FL7632 and POE elastomer of grade XM-7070S in a mass ratio of 7:3.

[0031] The first adhesive is prepared by mixing the main agent VN930, the curing agent CA-N6, and ethyl acetate in a mass ratio of 100:14:0.14.

[0032] The second adhesive is prepared by mixing 100 parts of main agent VN930, 14 parts of curing agent CA-N6, 0.07 parts of ethyl acetate, and 1 part of modified sepiolite by weight. The third adhesive is prepared by mixing the main agent VN930, the curing agent CA-N6, and ethyl acetate in a mass ratio of 100:14:0.03.

[0033] The production process of the protective film in Example 1 includes the following steps: S01: Three layers of adhesive are applied to the surface of a 15μm PA film using a three-slit coating method. The three layers of adhesive are, from top to bottom, the first adhesive, the second adhesive, and the third adhesive. The thickness ratio of the three layers of adhesive is 1:1.1:1. S02: After drying the three layers of adhesive on the surface of the PA film, another 15μm PA film is bonded to the PA film with the three layers of adhesive to obtain a protective film; the protective film has a nylon surface layer, a nylon adhesive layer and a nylon inner layer stacked in sequence. In SO2, the drying temperature is 90℃ and the compounding temperature is 110℃; The production process of the high puncture strength lithium battery aluminum-plastic film in Example 1 includes the following steps: S1: A passivating solution containing chromate is applied to both surfaces of a 45μm aluminum foil using a coating machine to obtain a passivated aluminum foil; S2: Apply a 3μm outer layer of adhesive to side A of the passivated aluminum foil and bond the protective film and side A of the passivated aluminum foil together. S3: A 3μm inner layer adhesive is coated on the B side of the passivated aluminum foil, and the heat-sealing film and the B side adhesive of the passivated aluminum foil are bonded together to obtain a high puncture strength aluminum-plastic film for lithium batteries.

[0034] Example 2

[0035] The production process of the high puncture strength lithium battery aluminum-plastic film in Example 2 is based on Example 1, except that in S01: a single-layer slit coating of an adhesive is applied to the surface of a 15μm PA film. The adhesive is prepared by mixing a first adhesive, a second adhesive and a third adhesive in a mass ratio of 1:1.1:1.

[0036] Example 3

[0037] The production process of the high puncture strength lithium battery aluminum-plastic film in Example 3 is based on Example 1, with the following differences: The second adhesive, by weight, is prepared by mixing 100 parts of main agent VN930, 14 parts of curing agent CA-N6, 0.07 parts of ethyl acetate, 1 part of modified sepiolite, and 0.015 parts of trimethylolpropane.

[0038] The modification process of the modified sepiolite in Example 3 includes: mixing the unbound sepiolite and the coupling agent (KH550) at a mass ratio of 100:3 and then ball milling them in a planetary ball mill for 2 hours to obtain the modified sepiolite.

[0039] Example 4

[0040] The production process of the high puncture strength lithium battery aluminum-plastic film in Example 4 is based on Example 3, except that: by mass parts, the second adhesive is prepared by mixing 100 parts of main agent VN930, 14 parts of curing agent CA-N6, 0.07 parts of ethyl acetate, and 1 part of modified sepiolite.

[0041] Example 5

[0042] The production process of the high puncture strength lithium battery aluminum-plastic film in Example 5 is based on Example 1, except that the concentration of polyvinyl alcohol used in the polyvinyl alcohol unbundling process of sepiolite in Example 5 is 3 g / L.

[0043] Example 6

[0044] The production process of the high puncture strength lithium battery aluminum-plastic film in Example 6 is based on Example 1, except that the concentration of polyvinyl alcohol used in the polyvinyl alcohol unbundling process of sepiolite in Example 6 is 7 g / L.

[0045] Example 7

[0046] The production process of the high puncture strength lithium battery aluminum-plastic film in Example 7 is based on Example 1, except that the polyvinyl alcohol unbundling process of sepiolite in Example 7 is as follows: 1 part of acid-activated sepiolite is pulverized and mixed with 100 parts of an aqueous solution of polyvinyl alcohol (type 17-88) to obtain a dispersion (the concentration of polyvinyl alcohol is 5 g / L). The dispersion is treated with a disperser for 2 hours (speed is 2700 r / min), then the dispersion is sonicated for 0.5 hours, and then the dispersion is treated with a disperser for another 0.5 hours (speed is 2700 r / min). Finally, the mixture is filtered, washed, and the filter cake is placed in a constant temperature drying oven at 90°C and dried to constant weight. Finally, the unbundled sepiolite is obtained by air jet milling.

[0047] Example 8

[0048] The production process of the high puncture strength lithium battery aluminum-plastic film in Example 8 is based on Example 1, except that the raw material of acid-activated sepiolite used in Example 8 is 200-mesh sepiolite microparticles.

[0049] Example 9

[0050] The production process of the high puncture strength lithium battery aluminum-plastic film in Example 9 is based on Example 1, except that the raw material of acid-activated sepiolite used in Example 9 is 800-mesh sepiolite microparticles.

[0051] Comparative Example 1 The production process of the high puncture strength lithium battery aluminum-plastic film of Comparative Example 1 is based on Example 1, except that the protective film used in S2 is a 30μm single-layer PA film.

[0052] Comparative Example 2 The production process of the high puncture strength lithium battery aluminum-plastic film of Comparative Example 2 is based on Example 1, except that S01: three layers of adhesive are applied to the surface of the 15μm PA film by a three-layer slit coating. The three layers of adhesive are all first adhesives from top to bottom, and the thickness ratio of the three layers of adhesive is 1:1.1:1.

[0053] 2. Detection methods for the examples and comparative samples 2.1. Heat sealing strength The heat-sealing strength of aluminum-plastic film was determined according to the testing standard QB / T2358-1998; 2.2. Puncture strength Perform the puncture according to the requirements of "6.6.13 Puncture Strength" in GB / T 10004-2008.

[0054] 2.3. Drawing performance The die core used for deep drawing is made of polytetrafluoroethylene, and the die size is 32 mm × 80 mm with a corner radius R = 0.6 mm. The deep-drawing performance test process is as follows: S1: Adjust the forming depth of the stamping forming tester according to the test requirements (default is 0.6mm), and adjust the compressed air pressure so that the pressure of the booster cylinder on the mold is greater than or equal to 6 tons; S2: Take a sample film with a flat, clean, and wrinkle-free surface, and cut a film with a width of not less than 100 mm and a length of not less than 200 mm for testing; S3: Place the heat-sealed surface (film) towards the mold core into the stamping forming tester. Ensure the film is flat and wrinkle-free, with sufficient allowance for side pressure.

[0055] S4: Press the button to perform stamping. After stamping, carefully remove the sample for later use.

[0056] To determine the maximum drawing depth of the sample film (the customer should use aluminum-plastic film below this depth), several groups of sample films from the same batch were taken (100 sample films per group). The breakage rate of the sample film at each drawing depth x was tested, where x was 5mm, 5.1mm, 5.2mm, 5.3mm, 5.4mm, 5.5mm, 5.6mm, 5.7mm, 5.8mm, 5.9mm, 6mm, and 6.1mm. The minimum drawing depth corresponding to a breakage rate greater than 0 is the maximum drawing depth of the sample film.

[0057] 3. Performance test results of the examples and comparative samples

[0058] The heat-sealing strength of the aluminum-plastic films in both the examples and comparative examples was 70~80 N / 15 mm, which meets the standard of ≥50 N / 15 mm for aluminum-plastic films. Electron microscopy revealed that the reinforcing fiber dispersion uniformity in Example 1 was better, while that in Example 8 was worse.

[0059] Based on Comparative Examples 1 and 2, the reason for the increased puncture strength in Example 1 may be that the reinforcing fibers form a fiber network within the adhesive layer, which disperses the local puncture force on the aluminum-plastic film to the surrounding area.

[0060] The decrease in puncture strength in Examples 5, 6, and 7, based on Example 1, may be due to the loss of polyvinyl alcohol on the surface of the sepiolite fibers in Example 7 after washing. In Example 1, the appropriate amount of polyvinyl alcohol present on the surface of the unwashed sepiolite fibers crosslinked with the adhesive components (increasing the cohesive strength of the adhesive layer).

[0061] Examples 1 and 2 show that the preferred nylon adhesive layer structure is beneficial to improving the puncture strength of the aluminum-plastic film.

[0062] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A high-puncture-strength aluminum-plastic film for lithium batteries, comprising a nylon outer layer, a nylon adhesive layer, a nylon inner layer, an aluminum foil adhesive layer, a passivated aluminum foil layer, a heat-sealing adhesive layer, and a heat-sealing layer stacked sequentially, characterized in that, The nylon adhesive layer comprises adhesive resin and reinforcing fibers.

2. The high puncture strength aluminum-plastic film for lithium batteries according to claim 1, characterized in that, The nylon adhesive layer comprises a first adhesive layer, a second adhesive layer, and a third adhesive layer stacked sequentially, wherein the second adhesive layer comprises reinforcing fibers.

3. The high puncture strength lithium battery aluminum-plastic film according to claim 2, characterized in that, The thickness ratio of the first adhesive layer, the second adhesive layer and the third adhesive layer is 1:(1~1.2):

1.

4. The high puncture strength lithium battery aluminum-plastic film according to claim 3, characterized in that, The second adhesive layer comprises a solvent-based two-component adhesive and reinforcing fibers; The solvent-based two-component adhesive includes a main agent and a curing agent, wherein the solid content of the main agent is 29% to 31%, and the reinforcing fiber includes modified sepiolite fiber. The mass ratio of the main agent to the reinforcing fiber is 100:(0.5~2). The modified sepiolite fiber is obtained by acid activation, polyvinyl alcohol debinding, and modification of sepiolite microparticles; Furthermore, the second adhesive layer also includes trimethylolpropane.

5. The high puncture strength lithium battery aluminum-plastic film according to claim 4, characterized in that, The first adhesive layer comprises a first adhesive, and the third adhesive layer comprises a third adhesive. Both the first adhesive and the third adhesive are solvent-based two-component adhesives. The solid content of the main component of both the first adhesive and the third adhesive is 29% to 31%. The components of the first adhesive, the second adhesive, and the third adhesive also include ethyl acetate. The mass ratio of the main agent to ethyl acetate in the first adhesive is 100:(0.1~0.15). In the second adhesive, the mass ratio of the main agent to ethyl acetate is 100:(0.06~0.09). The mass ratio of the main agent to ethyl acetate in the third adhesive is 100:(0.01~0.05).

6. A process for preparing a high-puncture-strength aluminum-plastic film for lithium batteries, based on the high-puncture-strength aluminum-plastic film for lithium batteries according to any one of claims 1 to 5, characterized in that, Includes the following steps: S01: Three layers of adhesive are applied to the surface of the PA film using a multi-layer slit coating method. The three layers of adhesive are, from top to bottom, the first adhesive, the second adhesive, and the third adhesive. S02: Dry the three-layer adhesive on the surface of the PA film, and bond another PA film to the PA film with the three-layer adhesive to obtain a protective film; the protective film has a nylon surface layer, a nylon adhesive layer and a nylon inner layer stacked in sequence; S1: Apply aluminum foil adhesive to side A of the passivated aluminum foil and bond the protective film and side A of the passivated aluminum foil together; apply heat-sealing adhesive to side B of the passivated aluminum foil and bond the heat-sealing film and side B of the passivated aluminum foil together to obtain a high puncture strength aluminum-plastic film for lithium batteries.

7. The preparation process of the high puncture strength lithium battery aluminum-plastic film according to claim 6, characterized in that, The sepiolite fiber in the second adhesive is modified sepiolite fiber, and the modification of the modified sepiolite fiber includes the following steps: Modified sepiolite fiber is obtained by mixing and grinding 100 parts by weight of sepiolite fiber, 1-5 parts by weight of silane coupling agent and 1-2 parts by weight of trimethylolpropane.

8. The preparation process of the high puncture strength lithium battery aluminum-plastic film according to claim 7, characterized in that, The preparation process of the second adhesive includes: The main component, curing agent, and modified sepiolite fiber of the second adhesive are mixed to obtain the second adhesive.

9. The preparation process of the high puncture strength lithium battery aluminum-plastic film according to claim 7, characterized in that, The modified sepiolite fiber includes an acid activation step before modification, and the average particle size of the sepiolite microparticle raw material used in the acid activation step is 200 mesh to 800 mesh.

10. The preparation process of the high puncture strength lithium battery aluminum-plastic film according to claim 9, characterized in that, The acid activation step and the modification step also include the following steps: 0.7-1.2 parts of acid-activated sepiolite fiber were mixed with 100 parts of polyvinyl alcohol aqueous solution and stirred for 1.7-2.3 h, followed by sonication for 0.4-0.6 h, then stirring for 0.4-0.6 h, followed by solid-liquid separation to obtain a solid product, and finally dried at a constant temperature of 80-93℃ to obtain unbound sepiolite. The concentration of polyvinyl alcohol in the aqueous solution is 4~6 g / L, and the stirring speed is 2550~2750 r / min.

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