CN113555644B

CN113555644B - Method for improving membrane surface crease of lithium battery membrane coating membrane

Info

Publication number: CN113555644B
Application number: CN202110808410.9A
Authority: CN
Inventors: 汤晓; 高飞飞; 王连广; 孙婧; 白磷; 秦文娟; 甘珊珊
Original assignee: Sinoma Lithium Film Co Ltd
Current assignee: Sinoma Lithium Film Co Ltd
Priority date: 2021-07-16
Filing date: 2021-07-16
Publication date: 2023-05-12
Anticipated expiration: 2041-07-16
Also published as: CN113555644A

Abstract

The invention discloses a method for improving membrane surface crease of a lithium battery membrane coating membrane, which comprises the following steps: (1) preheating coating linkage: preheating the base film before coating the base film, wherein the preheating roller is close to the gravure roller during coating; (2) constant force pressurized coating: when the base film is coated, a scraper of a coating device is enabled to always contact the roller surface of the gravure roller by utilizing a constant force pressurizing mechanism, so that the stability of a coating is kept; (3) sectional drying: the method comprises the steps of drying a coating film in a drying oven in a sectional manner, wherein the coating film is tightly adhered to a roller during drying, the drying pressure of a front section is negative pressure, the drying pressure of a rear section is positive pressure, and the drying temperature of the front section is lower than that of the rear section; (4) tension release: the surface of the winding core is uniformly fixed with ribs along the circumferential direction, the ribs extend along the circumferential direction of the winding core, the surfaces of the ribs are arc-shaped surfaces, buffer rings respectively fixed at the end parts of the winding core are arranged at the two ends of the ribs, and the thickness of the buffer rings is larger than that of the ribs.

Description

Method for improving membrane surface crease of lithium battery membrane coating membrane

Technical Field

The invention relates to a method for improving membrane surface crease of a lithium battery membrane coating membrane, and belongs to the technical field of lithium battery membrane production.

Background

The lithium battery diaphragm coating process is longer, and under the trend that the coating film is thinner at present, the appearance of the film surface is difficult to control, and the film can not be kept in a good state after being rolled only by the hot roller at the unreeling position and tension control. At present, when the lithium battery diaphragm coating film is coated, the problems of uneven base leakage, uneven thickness and the like are caused by film surface crease printing, wrinkling, streak or uneven coating, and the problems are mainly expressed as follows: (1) Macroscopically, the abrasion and uneven coating of the scraper at the gravure roll lead to streaks and folds; (2) Zhang Liwen uneven tension is formed due to membrane surface collapse and medium wave; (3) The oven has low efficiency, is easy to be dried, and needs higher temperature to cause the film surface to be wrinkled; (4) The film is in a transverse swinging posture after being wound on the winding core due to uneven winding, so that edge collapse is easy to occur, and the film surface is easy to be subjected to crease printing and the like due to bursting ribs and tension lines after being wound; (5) microscopically, coating irregularities cause leakage of a base, black spots, and the like.

These problems affect product consistency and product cost, and greatly limit the a-rate of the coating to the slitting process.

Disclosure of Invention

The invention aims to provide a method for improving membrane surface crease printing of a lithium battery membrane coating membrane, which improves the process from coating to slitting, thereby improving the membrane surface state and improving the product quality and the A-grade rate.

The invention adopts the following technical scheme: a method for improving membrane surface pleating of a lithium battery membrane coating film, comprising the following steps: (1) preheating coating linkage: preheating the base film before coating the base film, wherein the preheating roller is close to the gravure roller during coating; (2) constant force pressurized coating: when the base film is coated, a scraper of a coating device is enabled to always contact the roller surface of the gravure roller by utilizing a constant force pressurizing mechanism, so that the stability of a coating is kept; (3) sectional drying: the method comprises the steps of drying a coating film in a drying oven in a sectional manner, wherein the coating film is tightly adhered to a roller during drying, the drying pressure of a front section is negative pressure, the drying pressure of a rear section is positive pressure, the drying temperature of the front section is lower than that of the rear section, and the sectional drying ensures that the coating film is heated and eased, so that wrinkling and folding are avoided; (4) tension release: the use surface has the core of a roll of rib to the coating film after the stoving and rolls, the surface of core is fixed with the rib along circumference evenly, the rib extends along the circumference of core, the surface of rib is the arcwall face, the both ends of rib are equipped with the buffer ring of fixing respectively at the core tip of rolling, the thickness of buffer ring is greater than the thickness of rib, when the rolling, the membrane face is in the effect of support and keeps the level all the time, makes diaphragm coating tension obtain releasing simultaneously.

In the step (1), the preheating temperature of the base film is 65-80 ℃, the distance between the preheating roller and the gravure roller is less than or equal to 800mm, and the wrap angle of the base film passing through the preheating roller is more than or equal to 120 degrees during coating.

In the step (2), the force of the scraper on the roller surface of the gravure roller is a constant value, and the precision is +/-50 gf.

In the step (2), the constant force pressurizing mechanism comprises a pressurizing seat, a spring is arranged between the pressurizing seat and the scraper, one end of the spring is fixed on the pressurizing seat, the other end of the spring is fixed on the scraper, and a pressure test point is arranged at the position, close to the scraper, of the spring.

The sectional drying is divided into three sections, wherein the first section drying temperature is 65-80 ℃, the drying pressure is-40 to-10 Pa, the second section drying temperature is 65-90 ℃, the drying pressure is-100 to-60 Pa, the third section drying temperature is 20-60 ℃, and the drying pressure is 20-60 Pa.

In the second section, the distance between the passing rollers was 500.+ -.100 mm.

The sectional drying is carried out in the same oven, and the ratio of the lengths of the first section, the second section and the third section is 1: (1.5-2.5): 1, the total length of the oven is more than or equal to 18m.

The number of ribs on the winding core is eight or ten, the ribs are foam strips, and the buffer ring is a foam ring.

The radian of the upper surface of each rib is 109-115 degrees, the width is more than or equal to 45mm, the thickness is 5-15 mm, and the Shore hardness of rib materials is more than or equal to 50.

The thickness of the buffer ring is 0.5-1.5 mm thicker than that of the ribs.

The beneficial effects of the invention are as follows: the invention utilizes the preheating roller to heat the base film, the preheating roller is close to the gravure roller during coating, and the base film is heated by the hot roller to achieve the preheating effect, so that the fluidity of the slurry on the film surface is improved, and the drying efficiency is also improved; the contact pressure of the scraper and the miniature gravure roller is in a controllable stable state by utilizing a constant force pressurizing mechanism, so that crease marks caused by inconsistent stress release after rolling due to uneven film surface coating are avoided; the drying step adopts sectional drying, so that the drying efficiency is improved, and meanwhile, the heating is eased, and the generation of wrinkling and pleating is avoided; the winding step adopts an irregular winding core, ribs provide support for the film surface, tension lines are reduced, internal stress is released, and a buffer ring provides high-speed cutting-off force points, so that the effect of improving film surface crease printing in all directions is achieved. The invention provides a complete film surface crease printing improvement measure, which improves the film surface state and the product quality and A product rate.

Drawings

FIG. 1 is a flow chart of a method of improving membrane face pleating of a lithium battery separator coated membrane in accordance with one embodiment of the invention;

FIG. 2 is a schematic illustration of a constant force pressurizing mechanism;

FIG. 3 is a schematic view of a ribbed winding core;

FIG. 4 is a cross-sectional view of the ribbed winding core of FIG. 3;

FIG. 5 is a side view of the ribbed winding core of FIG. 3;

FIG. 6 is a schematic view of a wrap-up;

fig. 7 is a schematic diagram of a buffer ring.

In the figure: the device comprises a preheating roller, a 2-gravure roller, a 3-scraper, a 4-constant force pressurizing mechanism, a 41-pressurizing seat, a 42-spring, a 5-oven, a 51-first section, a 52-second section, a 52-third section, a 6-passing roller, a 7-negative pressure pump, an 8-circulating air filter, a 9-gas dehumidifier, a 101-winding core, 102-ribs, 103-buffer rings, a 10-compressing roller and 11-cutters.

Detailed Description

The invention will now be described in detail with reference to the drawings and specific examples.

As shown in fig. 1, a method for improving film surface pleating of a lithium battery separator coating film according to an embodiment of the present invention includes the steps of:

(1) Preheating and coating linkage: the base film is preheated before being coated, the preheating temperature of the base film is 65-80 ℃, the preheating roller 1 is close to the gravure roller 2 during coating, the distance between the preheating roller 1 and the gravure roller 2 is less than or equal to 800mm, and the wrap angle of the base film passing through the preheating roller 1 is more than or equal to 120 degrees.

Before the base film is coated, the film is heated to 65-80 ℃, the heating temperature can be adjusted in a small way according to the thickness of the base film, the PE base film enters a high-elasticity state at about 70 ℃, the base film is easy to deform due to external force at the temperature, and the tension at the coating position enables the maximum position in the whole process to be more easy to keep the flatness of the film, so that the occurrence probability of crease is reduced. Thus depending on the coating tension, the film is ironed while improving the flow of the slurry at the film face, increasing the consistency of the applied coating while reducing the coating defects due to the appearance of the base film.

When in coating, the preheating roller 1 is close to the gravure roller 2, and the volatilization of the coating solvent is quickened by utilizing heat conduction, so that the drying can be quickened, the temperature of an oven is reduced, the distance between the preheating roller and the gravure roller is less than or equal to 800mm, the time for reaching the gravure roller is about 0.5s according to 100m/min, and the heat dissipation is avoided. The film is heated.

(2) Constant force pressurized coating: when the base film is coated, the scraper 3 of the coating device is always contacted with the roller surface of the gravure roller 2 by utilizing a constant force pressurizing mechanism, so that the stability of the coated coating is maintained. The constant force pressurizing mechanism adopted in this embodiment is shown in fig. 2, and the constant force pressurizing mechanism comprises a pressurizing seat 41, a spring 42 is installed between the pressurizing seat 41 and the scraper 3, one end of the spring 42 is fixed on the pressurizing seat 41, the other end is fixed on the scraper 3, a pressure test point is arranged at the position, close to the scraper 3, of the spring 42, the force of the scraper on the roller surface of the gravure roller is a constant value, and the precision is +/-50 gf.

As the scraper is used as a wearing part, firstly the scraper is extremely easy to wear, secondly uneven coating is easy to cause, film surface defects are caused, and the scraper is always in light contact with the roller surface of the gravure roller through the constant force control mechanism, so that the stability of the coating is maintained. The specific principle is as follows: the scraper of the miniature gravure roll is soft and is in light contact with the gravure roll, the gravure roll is made of wear-resistant and hard materials, friction is easy to generate, and particularly, the problem that the gravure roll is inconsistent in material taking due to the fact that the surface of the gravure roll is not smooth due to wear after a period of use is solved, so that the scraper is always in certain contact pressure with the gravure roll by utilizing a constant force control mechanism, and the crease printing caused by inconsistent stress release after rolling due to uneven film surface coating is avoided.

(3) And (5) sectional drying: the coating film is dried in sections in the oven, the coating film is tightly adhered to the roller during drying, the drying pressure of the front section is negative pressure, the drying pressure of the rear section is positive pressure, the drying temperature of the front section is lower than that of the rear section, and the coating film is heated and eased by section drying, so that wrinkling and folding are avoided. In the embodiment, the sectional drying is divided into three sections, wherein the drying temperature of the first section 51 is 65-80 ℃, the drying pressure is-40 to-10 Pa, the drying temperature of the second section 52 is 65-90 ℃, the drying pressure is-100 to-60 Pa, and the drying temperature of the third section 53 is 20-60 ℃ and the drying pressure is 20-60 Pa. In the second section, the distance between the passing rollers 6 is 500.+ -.100 mm. The sectional drying is carried out in the same oven 5, and the ratio of the lengths of the first section, the second section and the third section is 1: (1.5-2.5): 1, the total length of the oven 5 is more than or equal to 18m, and the actual length is finely adjusted according to the integral design of the production line.

The temperature and pressure of each section in the oven can be adjusted in a small scale according to the thickness of the base film and the raw material of the base film, the first section is taken as the most important part, the coating is not dried, the coating can be heated at the position in a contact manner, a higher Wen Duguo roller is used, meanwhile, low-air-quantity hot air is used, the selection is specifically carried out according to the solid content of slurry and the width of the base film, and the coating is stable while preheating; the second section uses low negative pressure hot drying air, and is specifically selected according to the solid content of slurry and the width of a base film, wherein the distance between passing rollers is as small as possible, and is recommended to be 500+/-100 mm, so that the force born by the film surface is reduced, the volatilization effect is improved, and more than 80% of water is volatilized; and in the third section, the air quantity in the drying balance is used, the air inlet and outlet wind pressure is the same, the movement direction of the air nozzle and the film is kept at about 15 degrees, the final drying is carried out through the circulation of drying air and air exchange, the lower-temperature hot air is used, the specific temperature is selected according to the solid content of slurry and the width of the base film, the rest moisture is volatilized, the film is adhered to a roller tightly, the vibration of the film surface is reduced, and meanwhile, the film surface defect caused by the sudden temperature drop is avoided due to the excessive recovery of normal temperature. The first section 51 is a heating and micro negative pressure area, the second section 52 is a negative pressure drying area, the third section 53 is a moderating drying area, the first section 51 and the second section 52 use the negative pressure pump 7 to pump negative pressure, the third section 53 is connected with the circulating air filter 8 to balance wind pressure, and the negative pressure pump 7 and the circulating air filter 8 are connected with the gas dehumidifier 9.

The first section and the second section are dried by adopting negative pressure, and the lower the pressure is, the lower the boiling point of water is, the more easily volatilized, so that the drying speed of the coating film is higher; the whole drying process is mild and efficient, and local defects such as crease and print problems caused by unstable coating due to severe changes of environment (temperature, humidity and the like) are prevented.

(4) Tension release: the core 101 with ribs 102 on the surface is used for rolling the dried coating film, ribs 102 are uniformly fixed on the surface of the core 101 along the circumferential direction, the ribs 102 extend along the circumferential direction of the core 101, the surfaces of the ribs 102 are arc-shaped surfaces, buffer rings 103 respectively fixed at the end parts of the core 102 are arranged at two ends of the ribs 102, the thickness of the buffer rings 103 is greater than that of the ribs 102, and when the film is rolled, the film surface is always under the supporting effect and is kept flat, and meanwhile, the coating tension of the diaphragm is released. The number of ribs on the winding core is eight, the ribs are foam strips, and the buffer ring is a foam ring. The Shore hardness of the rib material is more than or equal to 50, the radian of the upper surface of the rib is 109-115 degrees, the width is more than or equal to 45mm, and the thickness is 5-15 mm.

According to the embodiment, eight foam strips are uniformly adhered to the outer surface of the winding core, eight ribs are adhered to the surface of the winding core, no support exists between every two adjacent ribs, the film is equivalent to being on two passing rollers on the winding core, one effect of the ribs is to adapt to the wrap angle of the diaphragm wound on the winding core, the diaphragm is ensured to be excessively gentle, and stress concentration is avoided. The principle of tension release is specifically as follows: the internal stress is difficult to release due to the fact that the film is uneven in thickness, surface density and the like, and a circle of collapse is easy to form inside the film due to the fact that a common round winding core is used, ribs 102 are arranged outside the winding core, the winding core 101 is provided with the fluctuation pipe diameter change, winding moment change can be caused during winding, the tension of a diaphragm is released during winding, and a tension action point is changed into a line from the whole surface, so that the film surface is always supported between two rollers. The schematic diagram of the winding is shown in fig. 6, and the film surface is cut off by a cutter 11 after the winding.

The thickness and hardness of the ribs influence the stress release effect of the diaphragm, so that excessive stretching or pleating is easily generated on the thick film surface, and the stress release is not obvious obviously. The thickness, hardness and other parameters of the ribs are selected according to the size of the winding core and the material of the membrane, so that the membrane surface is always under the supporting effect to be kept flat, and the coating tension of the membrane is released.

The two ends of the winding core 101 are coiled by using buffer rings 103 made of foam materials in an auxiliary mode, the thickness of the buffer rings is 0.5-1.5 mm thicker than that of the ribs, so that high-speed (more than or equal to 100 m/min) automatic winding replacement is achieved, and the capacity is not affected. Because the diaphragm is wound at a high speed and a pressing roller is needed, the last diaphragm can be tightly attached to the winding core, so that the diaphragm is adhered to the core and cut off at the same time to finish the winding replacement; as shown in FIG. 7, the surface of the winding core 101 is provided with ribs 102, so that the winding core 101 is not in a regular round shape any more, and if the winding core 101 is too fast (more than or equal to 50 m/min), the pinch roller 10 can vibrate violently when approaching the winding core, so that the winding replacement fails; therefore, the buffer rings 103 are arranged at two ends of the winding core to provide an acting point for the compression roller 10, vibration caused by irregular shapes is eliminated by the contact of the compression roller 10 with the buffer rings 103, the contact point between the compression roller 10 and the middle part of the winding core 101 is only the highest point of the ribs 102, and high-speed roll replacement can be realized by sticking double faced adhesive tape to the highest point of the ribs 102, and even if the winding core runs at high speed, the winding can be automatically cut off and replaced.

The invention can be realized by modifying the original production line; the hot roller coating linkage can improve the film surface by utilizing the temperature and tension to the greatest extent, meanwhile, the elastic scraper can prolong the stable time of the coating roller, a new drying mode is adopted, the shaking of an undried section is reduced, the drying process is stable and efficient, the probability of generating defects of the film surface is reduced, the drying efficiency is improved, and finally, the irregular winding core is matched, the coating internal stress is released, so that the film surface is always kept flat, and the effect of improving the film surface crease printing in all directions is realized.

The above embodiment is a preferred embodiment of the present invention, and in other embodiments of the present invention, the number of ribs is not limited, and ten ribs may be provided on each winding core; the rib is not limited in material, and the size of the rib can be flexibly selected according to actual needs.

In other embodiments of the present invention, the constant force control mechanism may take other forms, and is substantially equivalent to the tension control mechanism, and is widely used in the art, and the embodiments and figures are not limited thereto.

Claims

1. A method for improving membrane surface pleating of a lithium battery membrane coating membrane, which is characterized by comprising the following steps: (1) preheating coating linkage: preheating the base film before coating the base film, wherein the preheating roller is close to the gravure roller during coating; (2) constant force pressurized coating: when the base film is coated, a scraper of the coating device is enabled to always contact the roller surface of the gravure roller by utilizing a constant force pressurizing mechanism, so that the stability of a coated coating is maintained, the constant force pressurizing mechanism comprises a pressurizing seat, a spring is arranged between the pressurizing seat and the scraper, one end of the spring is fixed on the pressurizing seat, the other end of the spring is fixed on the scraper, and a pressure test point is arranged at the position, close to the scraper, of the spring; (3) sectional drying: the method comprises the steps of drying a coating film in a drying oven in a sectional manner, wherein the coating film is tightly adhered to a roller during drying, the drying pressure of a front section is negative pressure, the drying pressure of a rear section is positive pressure, the drying temperature of the front section is lower than that of the rear section, and the sectional drying ensures that the coating film is heated and eased, so that wrinkling and folding are avoided; (4) tension release: the use surface has the core of a roll of rib to the coating film after the stoving and rolls, and the surface of core is evenly fixed with the rib along circumference, and the rib extends along the circumference of core, and the surface of rib is the arcwall face, and the both ends of rib are equipped with the buffer ring of fixing respectively at core tip, and the thickness of buffer ring is greater than the thickness of rib, buffer ring thickness is 0.5~1.5mm than the rib, the rib is bubble silver, the buffer ring is bubble cotton ring, and the core both ends set up the buffer ring and provide the impetus for the pinch roller, and pinch roller and core middle part contact point are the rib peak, and when the rolling, the membrane face is in the effect of supporting all the time and keeps the level, makes diaphragm coating tension obtain releasing simultaneously.

2. The method for improving membrane surface pleating of a lithium battery membrane coating film according to claim 1, wherein the method comprises the following steps: in the step (1), the preheating temperature of the base film is 65-80 ℃, the distance between the preheating roller and the gravure roller is less than or equal to 800mm, and the wrap angle of the base film passing through the preheating roller is more than or equal to 120 degrees during coating.

3. The method for improving membrane surface pleating of a lithium battery membrane coating film according to claim 1, wherein the method comprises the following steps: in the step (2), the force of the scraper on the roller surface of the gravure roller is a constant value, and the precision is +/-50 gf.

4. The method for improving membrane surface pleating of a lithium battery membrane coating film according to claim 1, wherein the method comprises the following steps: the sectional drying is divided into three sections, wherein the first section drying temperature is 65-80 ℃, the drying pressure is-40 to-10 Pa, the second section drying temperature is 65-90 ℃, the drying pressure is-100 to-60 Pa, the third section drying temperature is 20-60 ℃, and the drying pressure is 20-60 Pa.

5. The method for improving membrane surface pleating of a lithium battery membrane coating film according to claim 4, wherein the method comprises the following steps: in the second section, the distance between the passing rollers was 500.+ -.100 mm.

6. The method for improving membrane surface pleating of a lithium battery membrane coating film according to claim 4, wherein the method comprises the following steps: the sectional drying is carried out in the same oven, and the ratio of the lengths of the first section, the second section and the third section is 1: (1.5-2.5): 1, the total length of the oven is more than or equal to 18m.

7. The method for improving membrane surface pleating of a lithium battery membrane coating film according to claim 1, wherein the method comprises the following steps: the number of the ribs on the winding core is eight or ten.

8. The method for improving membrane surface pleating of a lithium battery membrane coating film according to claim 1, wherein the method comprises the following steps: the radian of the upper surface of each rib is 109-115 degrees, the width is more than or equal to 45mm, the thickness is 5-15 mm, and the Shore hardness of rib materials is more than or equal to 50.