Dispensing roller and dispensing device

Abstract

The invention discloses a dispensing roller and a dispensing device, and belongs to the technical field of diaphragm preparation. A plurality of pits are formed in the surface of the dispensing roller, and recesses are formed in the bottoms of at least part of the pits. The pits are further formed in the bottoms of the pits, so that the overall material carrying amount of the dispensing roller can be increased, coating points which are good in appearance, high in binding power and high in surface density can be obtained after dispensing through the pits, a good coating can be prepared on the surface of the diaphragm, and the performance of the diaphragm is improved. The dispensing device comprises a gravure roller, a coating head, a compression roller and the dispensing roller, the coating head is matched with the gravure roller so as to be used for coating the gravure roller with slurry; the gravure roller is connected with the dispensing roller so as to transfer the slurry on the gravure roller into the pit of the dispensing roller; the dispensing roller is matched with the pressing roller so that the diaphragm can be pressed to the dispensing roller through the pressing roller, and the slurry in the pits of the dispensing roller can be coated on the surface of the diaphragm. The device is simple in structure and convenient to operate.

Description

Technical Field

[0001] The invention relates to the technical field of diaphragm preparation, and in particular to a dispensing roller and a dispensing device. Background Art

[0002] In recent years, non-full coverage coating is a hot topic in the field of lithium-ion battery separator coating. Currently, research on coating methods such as traditional spraying, dot matrix spraying and dot roller coating is quite popular.

[0003] Among them, traditional spraying has achieved large-scale mass production in the past few years. However, due to the poor controllability of the spray point morphology, the surface density in the TD (perpendicular to the winding-unwinding) direction is easily affected by the equipment, resulting in uneven surface density, which brings hidden dangers to subsequent battery processing.

[0004] Dot spraying uses computer numerical control to control the "shower-type coating head" to create regular circular spray points, which are arranged in a honeycomb pattern on the entire membrane surface. However, due to the complexity of the equipment and high requirements for the slurry, it is difficult to achieve in actual technology.

[0005] In contrast, common dot roller coating is achieved by engraving a mesh-like "small round cake" protruding from the surface of the roller (such as Figure 1 As shown in the figure, the flexographic roller and the gravure roller are laminated, and then the "small round cake" transfers the slurry on the gravure roller and then coats it on the membrane surface. However, the coating points obtained by this method often have difficulty in obtaining a good morphology and high adhesion, and the corresponding coating quality is poor, which may affect the stability and safety of the diaphragm.

[0006] In view of this, the present invention is proposed. Summary of the invention

[0007] The object of the present invention is to provide a coating roller and a coating device to solve or improve the above technical problems.

[0008] The present invention can be implemented like this:

[0009] In a first aspect, the present invention provides a coating roller, wherein a plurality of pits are provided on the surface of the coating roller, and at least a portion of the pits have recesses at their bottoms.

[0010] In an optional embodiment, all the pits have recesses at their bottoms.

[0011] In an optional embodiment, the number of recesses disposed at the bottom of each pit is multiple.

[0012] In an optional embodiment, the multiple recesses arranged at the bottom of each pit are evenly distributed; or, the multiple recesses arranged at the bottom of each pit are gradually sparsely arranged along the direction from the edge to the center of the pit.

[0013] In an optional embodiment, on the same horizontal projection plane, the total projection area of ​​the recesses provided in each pit accounts for 30% to 80% of the projection area of ​​the pit.

[0014] In an optional embodiment, among the multiple recesses arranged at the bottom of each pit, each recess has the same shape and size.

[0015] Wherein, the depth of a single cavity is 2 μm to 20 μm;

[0016] and / or, the width of a single recess is 5 μm to 30 μm;

[0017] and / or, the area of ​​a single cavity is 10 μm 2 ~600μm 2 ;

[0018] And / or, the distance between two adjacent recesses is 100 μm to 1500 μm.

[0019] In an optional embodiment, each pit has at least one of the following features:

[0020] Feature 1: The area of ​​each pit is 2000μm 2 ~250000μm 2 ;

[0021] Feature 2: The width of each pit is 50 μm to 1000 μm;

[0022] Feature 3: The depth of each pit is 20 μm to 400 μm.

[0023] In an optional embodiment, the plurality of pits are evenly distributed on the surface of the coating roller.

[0024] In an optional embodiment, the roller diameter of the dot coating roller is 60 mm to 250 mm.

[0025] In a second aspect, the present invention provides a dot coating device, the dot coating device comprising a gravure roller, a coating head, a pressure roller, and a dot coating roller as described in any one of the above embodiments;

[0026] The coating head cooperates with the gravure roller to apply the slurry to the gravure roller; the gravure roller is connected with the spot coating roller to transfer the slurry on the gravure roller to the pits of the spot coating roller; the spot coating roller cooperates with the pressure roller to press the diaphragm toward the spot coating roller through the pressure roller and coat the slurry in the pits of the spot coating roller on the surface of the diaphragm.

[0027] The beneficial effects of the present invention include:

[0028] By further setting a cavity in the pit, the overall material carrying amount of the spot coating roller can be increased, and the setting of the cavity is also conducive to making the action area of ​​the slurry more concentrated, avoiding the slurry from continuously diffusing to the surroundings due to fluidity, so as to obtain coating points with good morphology (such as flat, three-dimensional, clear edges, etc.), strong adhesion and high surface density after spot coating, which is conducive to preparing a good coating on the surface of the diaphragm and improving the performance of the diaphragm. The spot coating device including the gravure roller, the coating head, the pressure roller and the above-mentioned spot coating roller has a simple structure and is easy to operate. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0030] Figure 1 It is a schematic diagram of the surface structure of a spot coating roller in the prior art;

[0031] Figure 2 A schematic diagram of the surface structure of the coating roller provided by the present invention;

[0032] Figure 3 This is a CCD photograph of the coating obtained from the control group in the test example;

[0033] Figure 4 This is the CCD photo of the coating obtained in the experimental group of the test example;

[0034] Figure 5 This is the SEM image of a single coating point in the coating obtained from the control group in the test example;

[0035] Figure 6 This is the SEM image of a single coating point in the coating obtained from the experimental group in the test example;

[0036] Figure 7 Schematic diagram of the dot coating process in the test example. DETAILED DESCRIPTION

[0037] In order to make the purpose, 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 in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings here can be arranged and designed in various different configurations.

[0038] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. 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.

[0039] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, further definition and explanation thereof is not required in subsequent drawings.

[0040] In the description of the present invention, it should be noted that if the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inside", "outside", etc. appear, the orientation or position relationship indicated is based on the orientation or position relationship shown in the drawings, or the orientation or position relationship in which the product of the invention is usually placed when in use. It is only for the convenience of describing the present invention and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention. In addition, if the terms "first", "second", "third", etc. appear, they are only used to distinguish the description, and cannot be understood as indicating or implying relative importance.

[0041] In addition, the terms "horizontal" and "vertical" do not mean that the components must be absolutely horizontal or suspended, but can be slightly tilted. For example, "horizontal" only means that its direction is more horizontal than "vertical", which does not mean that the structure must be completely horizontal, but can be slightly tilted.

[0042] In the description of the present invention, it is also necessary to explain that, unless otherwise clearly specified and limited, the terms "set", "install", "connect", and "connect" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0043] In addition, if the specific conditions are not specified in the examples, the experiments were carried out according to conventional conditions or conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments is not specified, they are all conventional products that can be purchased commercially.

[0044] The coating roller and coating device provided by the present invention are described in detail below.

[0045] The present invention provides a dot coating roller, such as Figure 2As shown, the surface of the coating roller is provided with a plurality of pits, and at least the bottoms of some of the pits are provided with recesses.

[0046] In some embodiments, the plurality of pits may be evenly distributed on the surface of the coating roller; in other optional embodiments, the plurality of pits may be unevenly distributed on the surface of the coating roller. The distribution form of the pits on the surface of the coating roller may be set according to actual needs.

[0047] In some preferred embodiments, a plurality of pits are evenly distributed on the surface of the coating roller, which is more conducive to obtaining a coating with better uniformity and consistency.

[0048] In some embodiments, the area of ​​each pit can be 2000 μm 2 ~250000μm 2 , such as 2000μm 2 , 5000μm 2 、8000μm 2 , 10000μm 2 、12000μm 2 , 15000μm 2 、18000μm 2 , 20000μm 2 , 22000μm 2 or 25000μm 2 etc., can also be 2000μm 2 ~250000μm 2 Other values ​​within the range.

[0049] The above-mentioned “area” refers to the maximum cross-sectional area of ​​a single pit, which will affect the size of the coating spot.

[0050] In some embodiments, the pit width of each pit can be 50μm to 1000μm, such as 50μm, 100μm, 200μm, 300μm, 400μm, 500μm, 600μm, 700μm, 800μm, 900μm or 1000μm, or other values ​​within the range of 50μm to 1000μm.

[0051] The above-mentioned “pit width” refers to the maximum width of the side wall of a single pit, which affects the spacing between two adjacent coating dots.

[0052] In some embodiments, the depth of each pit can be 20μm to 400μm, such as 20μm, 50μm, 80μm, 100μm, 120μm, 150μm, 180μm, 200μm, 220μm, 250μm, 280μm, 300μm, 320μm, 350μm, 380μm or 400μm, etc., or it can be other values ​​within the range of 20μm to 400μm.

[0053] The above-mentioned “depth” refers to the maximum depth of a single pit, which will affect the coating amount, coating thickness and three-dimensional shape of the coating point in a single coating.

[0054] In some embodiments, taking the coating roller placed horizontally as an example, the cross-sectional shape of the pit can be circular, quadrilateral (including square, rectangle or rhombus), polygonal (side length>4) or irregular, etc.

[0055] In some embodiments, taking the horizontal placement of the coating roller as an example, along the longitudinal direction (which can also be understood as the depth direction of the pit), the shape and area of ​​the cross section corresponding to each longitudinal height of the pit are equal. In other embodiments, along the longitudinal direction, the shape of the cross section corresponding to each longitudinal height of the pit is different, but the area is the same. In other embodiments, along the longitudinal direction, the shape of the cross section corresponding to each longitudinal height of the pit is the same, but the area is different (for example, the area can be gradually increased or gradually reduced). In other embodiments, along the longitudinal direction, the shape and area of ​​the cross section corresponding to each longitudinal height of the pit are different. Exemplarily, the pit can be in the form of a bowl, a pyramid or a cube, etc.

[0056] In some common implementations, the bottom of the pit is rounded.

[0057] In some embodiments, the bottoms of some of the pits may be provided with recesses. In other embodiments, the bottoms of all the pits may be provided with recesses.

[0058] When only the bottoms of some of the pits are provided with recesses, the pits provided with recesses may be distributed continuously or at intervals.

[0059] In some embodiments, the number of recesses disposed at the bottom of each pit is only one, and the recess may be disposed in the central area of ​​the pit or at a position near the edge of the bottom of the pit.

[0060] In other embodiments, the number of recesses disposed at the bottom of each pit is multiple, such as 2, 3, 4, 8, 10 or 20, etc. The specific number can be set according to needs.

[0061] Similarly, the multiple recesses arranged at the bottom of a single pit may be distributed continuously or at intervals.

[0062] In some embodiments, the plurality of recesses disposed at the bottom of a single recess are evenly distributed. In some embodiments, the plurality of recesses disposed at the bottom of a single recess are unevenly distributed, for example, the plurality of recesses disposed at the bottom of a single recess are gradually sparsely arranged along the direction from the edge to the center of the recess.

[0063] In some embodiments, on the same horizontal projection plane, the total projection area of ​​the recesses provided in a single pit accounts for 30% to 80% of the projection area of ​​the pit, such as 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75% or 80%, etc., and may also be other values ​​within the range of 30% to 80%.

[0064] In an optional manner, the recesses arranged in a single pit may be small and dense or large and sparse, wherein "small" and "large" are relative concepts, and "dense" and "sparse" are also relative concepts, and the specific size is not excessively limited.

[0065] In the present invention, the shape of the concave cavity is not limited, and can be circular, square, polygonal, or teardrop-shaped, for example but not by way of limitation.

[0066] In some embodiments, among the multiple recesses disposed at the bottom of each pit, the shapes and sizes of each recess are equal. In addition, the shapes and / or sizes of the recesses are also different.

[0067] In some embodiments, the depth of a single recess may be 2 μm to 20 μm, such as 2 μm, 5 μm, 8 μm, 10 μm, 12 μm, 15 μm, 18 μm or 20 μm, or other values ​​within the range of 2 μm to 20 μm.

[0068] In some embodiments, the width of a single recess may be 5 μm to 30 μm, such as 5 μm, 8 μm, 10 μm, 12 μm, 15 μm, 18 μm, 20 μm, 22 μm, 25 μm, 28 μm or 30 μm, or other values ​​within the range of 5 μm to 30 μm.

[0069] In some embodiments, the area of ​​a single cavity may be 10 μm 2 ~600μm 2 , such as 10μm 2 , 20μm 2 , 50μm 2 , 100μm 2 、150μm 2 , 200μm 2 , 250μm 2 、300μm 2 、350μm 2 , 400μm 2 , 450μm 2 , 500μm 2 、550μm 2 or 600μm 2 etc., can also be 10μm2 ~600μm 2 Other values ​​within the range.

[0070] In some embodiments, the spacing between two adjacent recesses may be 100 μm to 1500 μm, such as 100 μm, 200 μm, 400 μm, 600 μm, 800 μm, 1000 μm, 1200 μm or 1500 μm, or other values ​​within the range of 100 μm to 1500 μm.

[0071] It should be noted that the dot coating roller provided by the present invention is in the form of a gravure roller. A common gravure roller is a roller used for printing and coating, which is made of a hollow metal tube and has a pattern of a certain depth and shape on the surface, usually various types of grooves or small holes. The working principle of a common gravure roller is to extrude materials such as ink, paint, glue, etc. from the grooves or small holes on the plate surface, and then evenly apply them to the surface of the object to be printed or coated through the surface of the plate roller. During the printing process, the gravure roller squeezes materials such as ink, paint, glue, etc. from the grooves by pressure, and forms a coating of a certain thickness on the surface of the object.

[0072] The present invention further arranges recesses in the pits on the surface of the coating roller, which can, on the one hand, increase the overall material carrying capacity of the coating roller; on the other hand, the arrangement of the recesses is not only conducive to making the action area of ​​the slurry more uniform, but also reduces the fluidity of the slurry, thereby avoiding the slurry from being concentrated in a certain area due to fluidity or gravity, so that the coating roller has better slurry transfer ability, which is conducive to obtaining coating points with good morphology (such as flat, three-dimensional, clear edges, etc.), strong adhesion, high surface density and uniform surface density after coating, which is conducive to preparing a coating with high surface density and good quality on the surface of the diaphragm, thereby improving the performance of the diaphragm.

[0073] In some embodiments, the roller diameter of the dispensing roller may be 60 mm to 250 mm, such as 60 mm, 80 mm, 100 mm, 120 mm, 150 mm, 180 mm, 200 mm, 220 mm or 250 mm, etc., and may be specifically set according to actual needs.

[0074] Furthermore, the present invention also provides a dot coating device, which includes a gravure roller, a coating head, a pressure roller and the above-mentioned dot coating roller.

[0075] The coating head cooperates with the gravure roller to apply the slurry to the gravure roller; the gravure roller is connected with the spot coating roller to transfer the slurry on the gravure roller to the pits of the spot coating roller; the spot coating roller cooperates with the pressure roller to press the diaphragm toward the spot coating roller through the pressure roller and coat the slurry in the pits of the spot coating roller on the surface of the diaphragm.

[0076] In addition, the dot coating device may also include auxiliary pressure rollers to transport the diaphragm to be coated with the slurry and maintain the diaphragm with appropriate tension. The specific number of auxiliary pressure rollers can be set according to actual conditions.

[0077] Exemplarily, the above-mentioned dot coating roller is used for coating to form a non-full coverage coating. Preferably, the dot coating roller can form a non-full coverage coating with uniform size, shape, and uniform dot distribution.

[0078] In some practical operations, the vehicle speed can be controlled to 50 m / min, and the ratio of the vehicle speed to the coating roller speed can be controlled to 0.9 to 1.1 (eg, 0.9, 1.0 or 1.1).

[0079] The "vehicle speed" can be understood as the conveying speed of the diaphragm. Different ratios of the vehicle speed to the coating roller speed can produce membrane surfaces with different morphologies.

[0080] As mentioned above, the spot coating device provided by the present invention, which includes a gravure roller, a coating head, a pressure roller and a spot coating roller, has a simple structure, is easy to operate, and has a high promotion value.

[0081] Test example

[0082] In order to verify the effect of the spot coating roller provided by the present invention on improving the coating surface density of the lithium ion battery separator, the following test was conducted.

[0083] The dot coating roller provided by the present invention was used as an experimental group, and the traditional dot coating roller was used as a control group.

[0084] Specifically, the diameter of the dot coating roller of the control group is 150 mm, and the roller surface is provided with a plurality of non-continuous and evenly distributed pits formed by square reticulations, the bottom of the pit is a circular plane, and the area of ​​a single pit is 6000 μm 2 The pit width is 200 μm and the pit depth is 140 μm. The shape and size of each pit are equal.

[0085] The difference between the experimental group and the control group is that the coating roller of the experimental group is provided with a cavity at the bottom of each pit. The number and shape (square) of the cavity provided in each pit are equal (wherein the number of the cavity is 200 as an example). On the same horizontal projection plane, the total projection area of ​​the cavity provided in a single pit accounts for 50% of the projection area of ​​the pit. The cavity width of a single cavity is about 5 μm, and the cavity depth is about 16 μm.

[0086] The same isolation film material (ND7T22, Shanghai Enjie New Material Technology Co., Ltd.) and slurry with the same solid content (WP-23, solid content of 15wt%) were used, and all other process parameters were kept consistent, with a vehicle speed of 50m / min, a ratio of vehicle speed to spot coating roller speed of 0.9-1.1, and a pressure of 20N. The same roller coating equipment was used for the experiment to ensure the uniformity of the experimental conditions.

[0087] Reference for coating process Figure 7 , including: the membrane to be coated is conveyed in the direction of pressing roller 1-pressing roller 2-pressing roller 3-pressing roller 4, and pressing rollers 1 to 4 jointly control the conveying speed, direction and tension of the membrane. The coating head cooperates with the gravure roller to apply the slurry on the gravure roller, the gravure roller is connected with the spot coating roller to transfer the slurry on the gravure roller to the pits of the spot coating roller, and the spot coating roller cooperates with the pressing roller 4 to press the membrane to the spot coating roller through the pressing roller 4 and make the slurry in the pits of the spot coating roller be coated on the surface of the membrane.

[0088] The coating was repeated multiple times (5 times) in both the experimental group and the control group.

[0089] ①. Compare the surface density of the isolation films after coating in the experimental group and the control group (compared by average data), and the results are shown in Table 1. The surface density is measured by weighing method, and the thickness (recorded as H), area (recorded as S), and mass (recorded as m) of the sample are measured respectively. The surface density of the sample (recorded as ρ) is calculated according to the surface density calculation formula specified in GB / T 6343-2009: ρ = m / (H×S).

[0090] Table 1 Surface density comparison results

[0091]

[0092] It can be seen from Table 1 that the surface density obtained in the experimental group is significantly higher than that in the control group, increasing by more than 30%.

[0093] ② Use CCD photo or similar image analysis tools to isolate the three-dimensionality of points on the film. The results are as follows: Figures 3 to 6 shown.

[0094] Depend on Figures 3 to 6 As shown: Compared with the control group, the paint dots obtained by the experimental group are more three-dimensional, highly round, have clear edges, a smooth surface, and a higher amount of paint.

[0095] ③. Measure the adhesion after coating under the condition of a vehicle speed of 1:1. Specifically, the diaphragm and the electrode sheet were hot-pressed at high temperature and then peeled off using a stretching machine. The results are shown in Table 2, where the experimental number n (n=1~4) refers to the nth time of 4 repetitions.

[0096] Table 2 Adhesion strength comparison results

[0097]

[0098] It can be seen from Table 2 that the bonding force obtained in the experimental group is significantly higher than that in the control group.

[0099] To sum up, the present invention further arranges recesses in the pits on the surface of the coating roller, which can, on the one hand, increase the overall material carrying capacity of the coating roller; on the other hand, the arrangement of the recesses is also beneficial to making the action area of ​​the slurry more uniform, avoiding the slurry from being concentrated in a certain area due to fluidity or gravity, thereby reducing the fluidity of the slurry, so that the coating roller has better slurry transfer ability, which is beneficial to obtaining coating points with good morphology (such as flat, three-dimensional coating points, clear edges, etc.), strong adhesion, high surface density and uniform surface density after coating, which is beneficial to preparing a coating with high surface density and good quality on the surface of the diaphragm, thereby improving the performance of the diaphragm.

[0100] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A dot coating roller, characterized in that: The surface of the coating roller is provided with a plurality of pits, and at least some of the bottoms of the pits are provided with recesses.

2. The coating roller according to claim 1, characterized in that: The bottoms of all the pits are provided with recesses.

3. The coating roller according to claim 1, characterized in that: The number of the recessed holes arranged at the bottom of each of the recessed holes is multiple.

4. The dot coating roller according to claim 3, characterized in that: The multiple recesses arranged at the bottom of each of the recesses are evenly distributed; or, the multiple recesses arranged at the bottom of each of the recesses are gradually sparsely arranged along the direction from the edge to the center of the recess.

5. The dot coating roller according to claim 3, characterized in that: On the same horizontal projection plane, the total projection area of ​​the recesses arranged in each of the pits accounts for 30% to 80% of the projection area of ​​the pits.

6. The dot coating roller according to claim 3, characterized in that: Among the multiple recesses arranged at the bottom of each pit, each recess has the same shape and size; Wherein, the depth of a single cavity is 2 μm to 20 μm; and / or, the width of a single recess is 5 μm to 30 μm; and / or, the area of ​​a single cavity is 10 μm 2 ~600μm 2 ; And / or, the distance between two adjacent recesses is 100 μm to 1500 μm.

7. The dot coating roller according to any one of claims 1 to 6, characterized in that: Each of the pits has at least one of the following features: Feature 1: The area of ​​each of the pits is 2000 μm 2 ~250000μm 2 ; Feature 2: The width of each of the pits is 50 μm to 1000 μm; Feature 3: The depth of each of the pits is 20 μm to 400 μm.

8. The dot coating roller according to claim 7, characterized in that: A plurality of the pits are evenly distributed on the surface of the coating roller.

9. The dot coating roller according to any one of claims 1 to 6, characterized in that: The roller diameter of the dot coating roller is 60 mm to 250 mm.

10. A dot coating device, characterized in that: The dot coating device comprises a gravure roller, a coating head, a pressure roller and a dot coating roller as claimed in any one of claims 1 to 9; The coating head cooperates with the gravure roller to apply the slurry on the gravure roller; the gravure roller is connected with the dot coating roller to transfer the slurry on the gravure roller to the pits of the dot coating roller; The dot coating roller cooperates with the pressing roller to press the membrane toward the dot coating roller through the pressing roller and to coat the slurry in the recesses of the dot coating roller on the surface of the membrane.

Images