Polypropylene film on-line coating thickness uniformity control system

Abstract

The application discloses a polypropylene film online coating thickness uniformity control system applied to the technical field of thickness control, and through the arrangement of a gap plate assembly in the gap of a coating die, when the coating thickness fluctuates, the gap plate assembly is directly adjusted in position instead of adjusting the die itself, so that the adjustment of the gap size is realized, and the system is more suitable for the adjustment in the coating process compared with the prior art; in addition, through the arrangement of an observation strip and a micro camera, the perpendicularity of the gap plate assembly during transverse movement can be monitored, so that the adjustment accuracy of the gap size is ensured, the high uniformity of the coating thickness is ensured, and when the perpendicularity problem of the gap plate assembly occurs during transverse movement, the system does not need to be immediately stopped, and the perpendicularity can be compensated and corrected on line, so that the upper and lower size areas of the adjusted gap are consistent, and the adjustment of the coating thickness uniformity is effectively strengthened.

Description

Technical Field

[0001] This invention relates to the field of thickness control technology, and in particular to a control system for the uniformity of thickness in online coating of polypropylene films. Background Technology

[0002] Coating technology is one of the core processes in the manufacturing of functional films. Among them, slot die coating is widely used in the preparation of polypropylene film coatings due to its advantages such as high coating precision and wide applicability. The uniformity of coating thickness directly determines the quality grade of the film product and is a key indicator for measuring the level of coating process.

[0003] In the prior art, the adjustment of coating thickness is generally divided into two types. One is to directly change the coating thickness by adjusting the distance between the slit die and the film, such as the extrusion die with automatic gap adjustment function disclosed in Chinese Patent CN216631377U; the other is to adjust the size of the gap inside the slit die and control the extrusion amount of the die lip to adjust the coating thickness, such as the battery extrusion coating die and coating equipment disclosed in Chinese Patent CN221869086U.

[0004] However, both methods have the same problem: the components involved in the adjustment are too large, and the difference in size between the two is too great for the dimensions that need to be adjusted, which easily leads to over-adjustment. Therefore, they are suitable for product change, that is, adjustment before coating is applied. For adjusting coating thickness fluctuations during the coating process, the accuracy is poor. Summary of the Invention

[0005] The core of this invention lies in setting a gap plate assembly within the gap of the coating die. When the coating thickness fluctuates, there is no need to adjust the large die itself. Instead, the gap size can be adjusted by directly adjusting the position of the gap plate assembly. Compared with the prior art, this is more suitable for adjustment during the coating process, thus solving the problem of poor accuracy in adjusting the coating thickness during the coating process in the prior art.

[0006] To solve the above problems, the present invention adopts the following technical solution.

[0007] The online coating thickness uniformity control system for polypropylene film includes a control center, a thickness gauge connected to the control center, a gap plate assembly for adjusting the gap inside the coating die, and a sensor assembly for monitoring the movement and floating of the gap plate assembly. The thickness gauge is installed above the film and close to the coating die. The thickness gauge is used to measure the coating thickness. A self-adjusting space is carved inside the coating die. The gap plate assembly is installed in the self-adjusting space. The control system also includes an intelligent inflation / deflation assembly. The opening of the intelligent inflation / deflation assembly is fixedly inserted through the outside of the coating die and communicates with the self-adjusting space. The intelligent inflation / deflation assembly is connected to the control center. The self-adjusting space includes a receiving groove carved into the inner wall of the coating die gap, a pneumatic cavity carved into the inside of the coating die, and a guide groove carved into the inside of the coating die and connecting the receiving groove and the pneumatic cavity. The gap plate assembly includes a gap plate body located in the receiving groove, multiple piston pins fixedly connected to the end of the gap plate body away from the gap, and multiple mounting seats respectively installed at the center of the end of the piston pins. The mounting seats are interference-fitted with the guide groove.

[0008] Furthermore, the lower end of the gap plate is a right-angled trapezoidal structure, and the vertical surface of the right-angled trapezoid is located below the edge of the die lip of the coating die head and contacts the edge of the die lip. The inner diameter of the guide groove is not less than 10 times the inner gap size of the coating die head.

[0009] Furthermore, the sensor assembly includes at least two lasers mounted on the outer end of the mounting base and a laser rangefinder mounted on the inner wall of the pneumatic cavity, the laser emitted by the laser rangefinder falling onto the piston rod.

[0010] Optionally, at least two observation strips are fixedly embedded in the inner wall of the guide groove, and multiple observation strips correspond to multiple lasers. At least two miniature cameras are also provided on the mounting base, and multiple miniature cameras are arranged side by side with multiple lasers, with the shooting end of the miniature camera facing the same direction as the emitting end of the laser.

[0011] Furthermore, the observation strip includes a back plate and a pigment layer. The surface of the back plate facing the transparent protective plate is coated with a pigment layer, which consists of multiple linearly arranged color blocks with the edges of adjacent color blocks in contact. The length of the color blocks in the axial direction of the guide groove is 1 mm, and the colors of the multiple color blocks and the laser color of the laser are different or similar to each other.

[0012] Optionally, micro-motion compensation units are provided at both the upper and lower ends of the gap plate. The micro-motion compensation unit includes an electromagnetic strip fixedly embedded in the coating die head, a magnetic sheet fixedly connected to the gap plate, a sensing column set between the gap plate and the inner wall of the receiving groove, and a pressure sensor installed on the inner wall of the receiving groove. The detection end of the pressure sensor abuts against the sensing column.

[0013] Furthermore, the electromagnetic strip and the magnetic sheet correspond to each other, and the pressure sensor and the electromagnetic strip are misaligned. When the sensing column is compressed to its limit, the force that restores its elasticity is less than the frictional force between the piston column and the inner wall of the guide groove.

[0014] A control system for the uniformity of polypropylene film coating thickness is provided, and its control method includes the following steps: S1. First, the required coating is applied to the surface of the polypropylene film through a slit die. As the polypropylene film moves, the thickness gauge monitors the coating and the total thickness of the polypropylene film in real time. S2. When the total thickness is detected to deviate from the target value within the allowable fluctuation range, the gap plate assembly is moved by the intelligent inflation and deflation assembly to adjust the size of the gap inside the slit die head, so that the coating thickness changes adaptively. S21. When the total thickness is greater than the upper limit of the allowable fluctuation range, the control center controls the intelligent inflation and deflation component to inflate the self-adjusting space, thereby pushing the gap plate to move toward one side of the gap, making the gap size smaller. When the data obtained by the thickness gauge falls back to the allowable fluctuation range, the gap adjustment is completed. S22. When the total thickness is less than the lower limit of the allowable fluctuation range, the control center controls the intelligent inflation and deflation component to draw air out from the self-adjustment space, thereby adsorbing the gap plate to move away from the gap side, making the gap size larger. When the data obtained by the thickness gauge rises to within the allowable fluctuation range, the gap adjustment is completed. S3. Repeat steps S1-S2 continuously to continuously correct the total thickness so that it is within the allowable fluctuation range, making the coating thickness tend to be consistent.

[0015] Furthermore, in steps S21 and S22, inflation and deflation are discontinuous processes. After each inflation and deflation, there is a 3-5 second pause. When the thickness gauge obtains the adjusted total thickness data, it is determined whether to continue inflation or deflation based on the total thickness at this time.

[0016] Compared with the prior art, the advantages of this invention are: (1) This solution sets a gap plate assembly in the gap of the coating die head. When the coating thickness fluctuates, there is no need to adjust the die head itself which is too large. Instead, the gap size can be adjusted by directly adjusting the position of the gap plate assembly. Compared with the prior art, it is more suitable for adjustment in the coating process, so as to solve the problem of poor accuracy of coating thickness adjustment in the prior art.

[0017] (2) By setting up observation bars and miniature cameras, the verticality of the gap plate assembly during horizontal movement can be monitored and can be verified with the data of the laser rangefinder to ensure the accuracy of gap size adjustment and the high uniformity of coating thickness.

[0018] (3) With the micro-motion compensation unit set, when the gap plate assembly is adjusting the gap size by translation, if there is a difference in the verticality of the upper and lower ends, it is not necessary to stop the machine immediately. It can compensate and correct the verticality online, so that the upper and lower size areas of the gap after adjustment are consistent, effectively enhancing the adjustment of the coating thickness uniformity. Attached Figure Description

[0019] Figure 1 This is a block diagram of the main modules of the present invention; Figure 2 This is a schematic diagram of the system operation of the present invention; Figure 3 This is a cross-sectional schematic diagram of the coating die head of the present invention; Figure 4 for Figure 3 A schematic diagram at point A in the middle; Figure 5 This is a side view of the gap plate assembly of the present invention; Figure 6 This is a schematic diagram of the end face of the gap plate assembly of the present invention away from the gap; Figure 7 This is a schematic cross-sectional view of the observation bar of the present invention; Figure 8 This is a cross-sectional schematic diagram of the coating die head when a micro-motion compensation unit is added according to the present invention; Figure 9 for Figure 8 A schematic diagram at point B in the middle; Figure 10 This is a schematic diagram illustrating the process of fine-tuning the verticality of the gap plate assembly during movement according to the present invention.

[0020] Explanation of the labels in the diagram: 1 Self-adjusting space, 101 Receiving groove, 102 Pneumatic cavity, 103 Guide groove, 2 Gap plate assembly, 21 Gap plate body, 22 Piston column, 23 Mounting base, 201 Miniature camera, 202 Laser, 203 Laser rangefinder, 3 Observation strip, 31 Back plate, 32 Pigment layer, 33 Transparent protective plate, 41 Electromagnetic strip, 42 Magnetic sheet, 43 Sensing column, 44 Pressure sensor. Detailed Implementation

[0021] The technical solutions will now be clearly and completely described with reference to the accompanying drawings in the embodiments of the present invention.

[0022] First implementation method: like Figure 1The online coating thickness uniformity control system for polypropylene film includes a control center, a thickness gauge connected to the control center, a gap plate assembly 2 for adjusting the gap inside the coating die, and a sensor assembly for monitoring the movement and floating of the gap plate assembly 2. The thickness gauge is installed above the film and close to the coating die. The thickness gauge is used to measure the coating thickness. A self-adjusting space 1 is carved inside the coating die. The gap plate assembly 2 is installed in the self-adjusting space 1. The control system also includes an intelligent inflation / deflation assembly. The opening of the intelligent inflation / deflation assembly is fixedly inserted through the outside of the coating die and communicates with the self-adjusting space 1. The intelligent inflation / deflation assembly is connected to the control center. When needed, the intelligent inflation / deflation assembly can be controlled by the control center to inflate or deflate the self-adjusting space 1, thereby driving the gap plate assembly 2 to move laterally, causing the size of the gap between the gap plate assembly 2 and another inner wall to change, thereby adjusting the size of the effective material supply gap.

[0023] like Figures 2-3 In the figure, a represents the coating die, b represents the polypropylene film, and c represents the coating layer. The self-adjusting space 1 includes a receiving groove 101 carved into the inner wall of the gap of the coating die, a pneumatic cavity 102 carved into the inside of the coating die, and a guide groove 103 carved into the inside of the coating die and connecting the receiving groove 101 and the pneumatic cavity 102. Figures 5-6 The gap plate assembly includes a gap plate body 21 located in the receiving groove 101, a plurality of piston pins 22 fixedly connected to the end of the gap plate body 21 away from the gap, and a plurality of mounting seats 23 respectively installed at the center of the end of the piston pins 22. The mounting seats 23 are interference-fitted with the guide groove 103 to effectively ensure the stability of the gap plate body 21 and facilitate the maintenance of the stability of the gap inside the coating die.

[0024] The lower end of the gap plate 21 is a right-angled trapezoidal structure, and the vertical surface of the right-angled trapezoid is located below the edge of the die lip of the coating die head and in contact with the edge of the die lip. This ensures that the lower surface of the die lip is not easily exposed when the gap plate 21 moves towards or away from the gap under the drive of air pressure. This effectively prevents some coating material from seeping into the receiving groove 101, thus ensuring stable material output during coating and preventing fluctuations in coating thickness. The inner diameter of the guide groove 103 is not less than 10 times the size of the gap inside the coating die head. This means that a large amount of gas needs to be filled or extracted to make the gap plate 21 move laterally as expected. Compared to filling or extracting very little gas to drive the gap plate 21 to move laterally, this effectively ensures the stability of the gap plate 21, making the gap size relatively stable after adjustment. On the other hand, it effectively avoids over-adjustment, making the gap plate 21 less prone to excessive lateral movement.

[0025] like Figures 2-4The sensor assembly includes at least two lasers 202 mounted on the outer end of the mounting base 23 and a laser rangefinder 203 mounted on the inner wall of the pneumatic cavity 102. In this embodiment, there are two lasers 202, but in specific implementations, there may be other numbers, such as three or six. The laser emitted by the laser rangefinder 203 falls on the piston column 22. During the movement of the gap plate 21 driven by the inflation and deflation of the gas, the laser rangefinder 203 can record the distance of the gap plate assembly 2 moving along the axial direction of the piston column 22. The two lasers 202 can record the distance between the gap plate assembly 2 and the inner wall of the guide groove 103 respectively. After long-term operation, excessive wear occurs between the piston column 22 and the guide groove 103, which will cause the gap plate assembly 2 to become loose in the self-adjusting space 1. During lateral movement, the gap plate 21 will tilt to a certain extent. If the data obtained by the two lasers 202 are consistent, the verticality of the gap plate 21 is high (that is, during lateral movement, the upper and lower ends of the gap plate 21 do not tilt significantly). Conversely, it indicates that the upper and lower ends of the gap plate 21 are offset. The greater the difference between the two data, the greater the tilt amplitude between the upper and lower ends. Based on this, the staff can repair it in time to ensure stable coating and maintain the uniformity of the coating thickness during coating.

[0026] A control system for the uniformity of polypropylene film coating thickness is provided, and its control method includes the following steps: S1. First, the required coating is applied to the surface of the polypropylene film through a slit die. As the polypropylene film moves, the thickness gauge monitors the coating and the total thickness of the polypropylene film in real time. S2. When the total thickness is detected to deviate from the target value within the allowable fluctuation range, the gap plate assembly is moved by the intelligent inflation and deflation assembly to adjust the size of the gap inside the slit die head, so that the coating thickness changes adaptively. S21. When the total thickness is greater than the upper limit of the allowable fluctuation range, the control center controls the intelligent inflation and deflation component to inflate the self-adjusting space 1, thereby pushing the gap plate 21 to move toward the gap side, making the gap size smaller. When the data obtained by the thickness gauge falls back to the allowable fluctuation range, the gap adjustment is completed. S22. When the total thickness is less than the lower limit of the allowable fluctuation range, the control center controls the intelligent inflation and deflation component to draw air out from the self-adjustment space 1, thereby adsorbing the gap plate 21 to move away from the gap side, making the gap size larger. When the data obtained by the thickness gauge rises to within the allowable fluctuation range, the gap adjustment is completed. S3. Repeat steps S1-S2 continuously to continuously correct the total thickness so that it is within the allowable fluctuation range, making the coating thickness tend to be consistent.

[0027] In steps S21 and S22, inflation and deflation are discontinuous processes. After each inflation and deflation, there is a 3-5 second pause. When the thickness gauge obtains the adjusted total thickness data, it is determined whether to continue inflation or deflation based on the total thickness at this time. Through discontinuous operation, the operation accuracy of the transverse movement of the gap plate 21 is effectively improved, and over-adjustment is effectively avoided.

[0028] Alternatively, two threshold values ​​can be set for the allowable fluctuation range: a lower threshold and an upper threshold. The lower threshold is greater than the lower limit of the allowable fluctuation range, while the upper threshold is less than the upper limit. When the total thickness data reaches the lower or upper threshold, the intelligent inflation / deflation component can be triggered to inflate or deflate, thus adjusting the total thickness before it exceeds the allowable fluctuation range. This ensures that the total thickness remains within the allowable fluctuation range, thereby further improving the uniformity of the coating thickness and enhancing product quality.

[0029] In summary, this solution, by setting a gap plate assembly within the gap of the coating die, eliminates the need to adjust the bulky die itself when coating thickness fluctuates. Instead, the gap size can be adjusted directly by adjusting the position of the gap plate assembly. Compared to existing technologies, this solution is more suitable for adjustments during the coating process, thus solving the problem of poor precision in adjusting coating thickness during the coating process in existing technologies.

[0030] Second implementation method: This embodiment adds an observation bar 3 and a corresponding miniature camera 201 to the first embodiment, while the rest remains the same as the first embodiment.

[0031] like Figure 3 At least two observation strips 3 are fixedly embedded in the inner wall of the guide groove 103, and multiple observation strips 3 correspond to multiple lasers 202, such as... Figure 4 The mounting base 23 is also equipped with at least two miniature cameras 201. The multiple miniature cameras 201 are arranged side by side with multiple lasers 202, and the shooting end of the miniature camera 201 is aligned with the emitting end of the laser 202.

[0032] like Figure 7The observation strip 3 includes a back plate 31 and a pigment layer 32. The surface of the back plate 31 facing the transparent protective plate 33 is coated with the pigment layer 32. The pigment layer 32 consists of multiple linearly arranged color blocks, with the edges of adjacent color blocks in contact. The length of the color blocks in the axial direction of the guide groove 103 is 1 mm. The colors of the multiple color blocks and the laser color of the laser 202 are different or similar to each other, so that when the laser point of the laser 202 falls on the observation strip 3, it can produce a clear color contrast with the corresponding color block. This allows the miniature camera 201 to clearly show the difference between the two when acquiring image information at that location. The setup of two sets of observation strips 3 and miniature camera 201 allows the miniature camera 201 to acquire two sets of image information. The control center can compare the two sets of image information. If the positions of the two laser landing points tend to be consistent, and the data of the two lasers 202 tend to be consistent, it further indicates that the perpendicularity of the gap plate 21 is good. Apart from the case where both sets of data tend to be consistent, the other cases indicate that there is a certain problem with the perpendicularity of the gap plate 21. As a result, the staff can intervene earlier to ensure the accuracy of the gap size adjustment and ensure the high uniformity of the coating thickness.

[0033] Compared to the first embodiment, this embodiment, through the setting of the observation strip 3 and the miniature camera 201, can further monitor the verticality of the gap plate assembly 2 when it moves laterally, and can cross-reference the data with the laser rangefinder 203 to ensure the accuracy of the gap size adjustment and the high uniformity of the coating thickness.

[0034] The third implementation method: This embodiment adds a micro-motion compensation unit based on the second embodiment, while the rest remains the same as the second embodiment.

[0035] like Figures 8-9 Both the upper and lower ends of the gap plate 21 are equipped with micro-motion compensation units. Each micro-motion compensation unit includes an electromagnetic strip 41 fixedly embedded in the coating die head, a magnetic sheet 42 fixedly connected to the gap plate 21, a sensing column 43 disposed between the gap plate 21 and the inner wall of the receiving groove 101, and a pressure sensor 44 installed on the inner wall of the receiving groove 101. The detection end of the pressure sensor 44 abuts against the sensing column 43. Figure 10After determining that the perpendicularity of the gap plate 21 is abnormal, there is a tilt between the upper and lower sections of the gap plate 21. At this time, the data obtained by the two pressure sensors 44 will have a certain deviation. At this time, both electromagnetic strips 41 can be energized, and the electromagnetic strip 41 on the same side as the pressure sensor 44 with the larger data is energized with a reverse current, so that the electromagnetic strip 41 generates a magnetic repulsion force on the magnetic sheet 42. At the same time, the electromagnetic strip 41 on the other side is energized with a forward current, so as to generate a magnetic attraction force on the magnetic sheet 42 on that side. The two ends work together to drive the gap plate 21 to shift until the data of the two pressure sensors 44 tend to be consistent, which means that its perpendicularity has been corrected. The vertical dimension of the gap is stable after adjustment. Compared with the previous two implementation methods, after the perpendicularity is abnormal, there is no need to stop the machine immediately, and the perpendicularity can be corrected online, which effectively reduces the impact on the coating process. After the same roll of polypropylene film is coated, the machine is stopped for correction, thereby reducing the impact on coating efficiency without affecting the uniformity of coating thickness.

[0036] The electromagnetic strip 41 and the magnetic sheet 42 correspond to each other, and the pressure sensor 44 and the electromagnetic strip 41 are misaligned, so that the electromagnetic strip 41 is not likely to interfere with the pressure sensor 44 after being energized. When the sensing column 43 is compressed to the limit, the force that restores its elasticity is less than the friction between the piston column 22 and the inner wall of the guide groove 103, so that the setting of the sensing column 43 is not likely to affect the gap size.

[0037] It is worth noting that, generally speaking, the inclination of the spacer plate 21 will be relatively small. Figure 10 To clearly demonstrate the tilt, the tilt amplitude has been enlarged and does not represent the actual tilt amplitude during implementation.

[0038] In summary, with the micro-motion compensation unit in place, when the gap plate assembly 2 is adjusting the gap size by translation, if there is a difference in the verticality of the upper and lower ends, it is not necessary to stop the machine immediately. The verticality can be compensated and corrected online, so that the upper and lower size areas of the gap are consistent after adjustment, which effectively enhances the adjustment of the coating thickness uniformity.

[0039] The above description is merely a preferred embodiment of the present invention; it encompasses all the protection scope of the present invention. Any equivalent substitutions or modifications made by those skilled in the art within the technical scope disclosed in the present invention, based on the technical solutions and improved concepts of the present invention, should be covered within the protection scope of the present invention.

Claims

1. A polypropylene film online coating thickness uniformity control system, comprising a control center, a thickness gauge connected to the control center, a gap plate assembly (2) for adjusting the gap inside the coating die, and a sensor assembly for monitoring the movement and floating of the gap plate assembly (2), characterized in that: The thickness gauge is installed above the film and near the coating die head. The thickness gauge is used to measure the coating thickness. The coating die head has a self-adjusting space (1) inside. The gap plate assembly (2) is installed in the self-adjusting space (1). The control system also includes an intelligent inflation / deflation assembly. The opening of the intelligent inflation / deflation assembly is fixedly inserted through the outside of the coating die head and communicates with the self-adjusting space (1). The intelligent inflation / deflation assembly is connected to the control center signal. The self-adjusting space (1) includes a receiving groove (101) carved into the inner wall of the coating die gap, a pneumatic cavity (102) carved into the coating die, and a guide groove (103) carved into the coating die and connecting the receiving groove (101) and the pneumatic cavity (102). The gap plate assembly includes a gap plate body (21) located in the receiving groove (101), a plurality of piston pins (22) fixedly connected to the end of the gap plate body (21) away from the gap, and a plurality of mounting seats (23) respectively installed at the center of the end of the piston pins (22). The mounting seats (23) are interference-fitted with the guide groove (103).

2. The online coating thickness uniformity control system for polypropylene film according to claim 1, characterized in that: The lower end of the gap plate (21) is a right-angled trapezoidal structure, and the vertical surface of the right-angled trapezoid is located below the edge of the die lip of the coating die head and in contact with the edge of the die lip. The inner diameter of the guide groove (103) is not less than 10 times the inner gap size of the coating die head.

3. The online coating thickness uniformity control system for polypropylene film according to claim 1, characterized in that: The sensor assembly includes at least two lasers (202) mounted on the outer end of the mounting base (23) and a laser rangefinder (203) mounted on the inner wall of the pneumatic cavity (102), the laser emitted by the laser rangefinder (203) falling on the piston column (22).

4. The online coating thickness uniformity control system for polypropylene film according to claim 3, characterized in that: At least two observation strips (3) are fixedly embedded in the inner wall of the guide groove (103). The observation strips (3) correspond to the lasers (202). At least two miniature cameras (201) are also provided on the mounting base (23). The miniature cameras (201) are arranged side by side with the lasers (202), and the shooting end of the miniature camera (201) is aligned with the emitting end of the laser (202).

5. The online coating thickness uniformity control system for polypropylene film according to claim 4, characterized in that: The observation strip (3) includes a back plate (31) and a pigment layer (32). The back plate (31) is coated with a pigment layer (32) on the surface facing the transparent protective plate (33). The pigment layer (32) consists of multiple linearly arranged color blocks, with the edges of two adjacent color blocks in contact. The length of the color blocks in the axial direction of the guide groove (103) is 1 mm, and the colors of the multiple color blocks and the laser color of the laser (202) are different or similar to each other.

6. The online coating thickness uniformity control system for polypropylene film according to claim 5, characterized in that: Both ends of the gap plate (21) are provided with micro-motion compensation units. The micro-motion compensation unit includes an electromagnetic strip (41) fixedly embedded in the coating die head, a magnetic sheet (42) fixedly connected to the gap plate (21), a sensing column (43) set between the gap plate (21) and the inner wall of the receiving groove (101), and a pressure sensor (44) installed on the inner wall of the receiving groove (101). The detection end of the pressure sensor (44) abuts against the sensing column (43).

7. The online coating thickness uniformity control system for polypropylene film according to claim 6, characterized in that: The electromagnetic strip (41) and the magnetic sheet (42) correspond to each other, and the pressure sensor (44) and the electromagnetic strip (41) are misaligned. When the sensing column (43) is compressed to the limit, the force that restores its elasticity is less than the frictional force between the piston column (22) and the inner wall of the guide groove (103).

8. The online coating thickness uniformity control system for polypropylene film according to claim 1, characterized in that: Its control method includes the following steps: S1. First, the required coating is applied to the surface of the polypropylene film through the slit die head. As the polypropylene film moves, the thickness gauge monitors the coating and the total thickness of the polypropylene film in real time. S2. When the total thickness is detected to deviate from the target value within the allowable fluctuation range, the gap plate assembly is moved by the intelligent inflation and deflation assembly to adjust the size of the gap inside the slit die head, so that the coating thickness changes adaptively. S21. When the total thickness is greater than the upper limit of the allowable fluctuation range, the control center controls the intelligent inflation and deflation component to inflate the self-adjusting space (1), thereby pushing the gap plate (21) to move toward the gap side, making the gap size smaller. When the data obtained by the thickness gauge falls back to the allowable fluctuation range, the gap adjustment is completed. S22. When the total thickness is less than the lower limit of the allowable fluctuation range, the control center controls the intelligent inflation and deflation component to draw air out from the self-adjustment space (1), thereby adsorbing the gap plate (21) to move away from the gap side, making the gap size larger. When the data obtained by the thickness gauge rises to the allowable fluctuation range, the gap adjustment is completed. S3. Repeat steps S1-S2 continuously to continuously correct the total thickness so that it is within the allowable fluctuation range, making the coating thickness tend to be consistent.

9. The online coating thickness uniformity control system for polypropylene film according to claim 8, characterized in that: In steps S21 and S22, inflation and deflation are discontinuous processes. After each inflation and deflation, there is a 3-5 second pause. When the thickness gauge obtains the adjusted total thickness data, it is determined whether to continue inflation or deflation based on the total thickness at this time.

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