Apparatus and method for measuring step difference in slit die

Abstract

The present application relates to an apparatus and method for measuring the step difference between a lip and a shim of a slit die.

Description

Technical Field

[0001] This application claims priority and benefit based on Korean Patent Application No. 10-2021-0147971, filed with the Korean Intellectual Property Office on November 1, 2021.

[0002] This application relates to an apparatus and method for measuring the step difference between the lip and the gasket of a slit die. Background Technology

[0003] Recently, rising energy prices due to the depletion of fossil fuels and increasing concerns about environmental pollution have led to a growing demand for environmentally friendly alternative energy sources. Consequently, research into various power generation technologies, such as nuclear, solar, wind, and tidal power, is ongoing. Furthermore, there is significant interest in power storage devices for more efficient use of such generated energy.

[0004] In particular, with technological advancements and increasing demand for mobile devices, the need for batteries as an energy source is rapidly growing. To meet these demands, numerous studies are being conducted on batteries.

[0005] Typically, regarding battery shape, there is a high demand for angled or pouch-shaped secondary batteries that can have a smaller thickness and are suitable for products such as mobile phones. Regarding materials, there is a high demand for lithium-ion batteries or lithium-ion polymer batteries that offer advantages such as high energy density, high discharge voltage, and high output stability.

[0006] Typically, a secondary battery is constructed as an electrode assembly comprising stacked positive and negative electrodes and a separator between the positive and negative electrodes. The positive and negative electrodes are each manufactured by applying a slurry containing active material onto a current collector.

[0007] The current collector needs to be coated with a slurry of uniform thickness to ensure uniform characteristics of the secondary battery. For this purpose, slurry coating equipment such as a die coater is used. Slurry coating equipment includes a slot die that applies slurry in a thin layer over a large area.

[0008] The slit-die coating method offers advantages in terms of maintenance and productivity compared to other coating methods. Therefore, the slit-die coating method is currently widely used in the manufacturing process of flat panel display panels and in the application of slurry to the current collectors of secondary battery electrodes.

[0009] Like a pen that dispenses ink through its nib, a slit die dispenses slurry through its tip for dispensing ink, thus applying slurry to the collector while the slit die itself moves or the collector moves.

[0010] At the two opposite ends of the slit die, with reference to the width direction of the collector, there is a step offset (shim offset or gap) between the lip and the gasket. During the coating process using the slit die, the ink is dispersed in the gap caused by this step offset due to surface tension.

[0011] In this case, when the step difference between the lip and the gasket is below a predetermined level, the distribution occurs uniformly, resulting in minimal deviation in the width of the applied slurry. However, when the step difference between the lip and the gasket is as follows... Figure 1 As shown, when the deviation from the predetermined level occurs, the deviation in the width of the applied slurry increases.

[0012] Therefore, management is needed to prevent the step difference between the lip and the pad from deviating from a predetermined level. For this purpose, a method for measuring the step difference between the lip and the pad needs to be designed. Summary of the Invention

[0013] Technical issues

[0014] This application provides an apparatus and method for measuring the step difference between the lip and the gasket of a slit die.

[0015] Technical solution

[0016] One embodiment of this application provides an apparatus for measuring the step difference of a slit die, the apparatus comprising: a laser sensor configured to measure the step difference between a lip and a gasket of the slit die, the slit die comprising: two or more bodies having lips at one end thereto, and a gasket disposed between the two or more bodies and configured to discharge ink, the laser sensor being configured to face the lip and the gasket of the slit die; and a clamp configured to contact at least a portion of the body where the ink discharge portion of the slit die is located.

[0017] Another embodiment of this application provides a method for measuring the step difference of a slit die, the slit die comprising: two or more bodies having lips at one end thereon, and a gasket disposed between the two or more bodies and configured to discharge ink, the method comprising: contacting a clamp of a device for measuring the step difference with at least a portion of the upper end of the body where the ink discharge portion of the slit die is located, the device having a laser sensor; and measuring the step difference between the lip of the slit die and the gasket by means of the laser sensor.

[0018] Beneficial effects

[0019] According to one embodiment of this application, an apparatus for measuring the step difference of a slit die can measure the step difference between the lip and the gasket.

[0020] According to another embodiment of this application, an apparatus for measuring the step difference of a slit die can determine the step difference between the measured lip and the gasket, which makes it possible to manage the step difference at an appropriate level.

[0021] The apparatus for measuring the step difference of a slit die head according to another embodiment of this application is highly portable. Therefore, the apparatus can measure the step difference between the lip and the gasket after ink coating, which allows for on-the-fly inspection of step difference variations based on process changes.

[0022] According to another embodiment of this application, an apparatus for measuring the step difference of a slit die head can check the step difference based on changes in the ink coating process, and adjust the step difference between the lip and the gasket when the change in step difference is severe. Attached Figure Description

[0023] Figure 1 This diagram illustrates the problem of uneven coating interface that occurs when there is a large step difference between the lip of the slit die and the gasket.

[0024] Figure 2 This is an exploded perspective view of a device for measuring step difference according to one embodiment.

[0025] Figure 3 This is a combined perspective view of a device for measuring step difference according to one embodiment.

[0026] Figure 4 This is a combined cross-sectional view of a device for measuring step difference according to another embodiment.

[0027] Figure 5 This is a perspective view illustrating the state of contact between the device for measuring step difference and the slit die head according to another embodiment.

[0028] Figure 6 (a) is a top plan view of an apparatus for measuring step difference according to yet another embodiment. Figure 6 (b) is a front view of an apparatus for measuring step difference according to yet another embodiment. Figure 6 (c) is a side view of an apparatus for measuring step difference according to yet another embodiment.

[0029] Figure 7 This is a cross-sectional view of the ink discharge tip of a single die head.

[0030] Figure 8 (a) is a side view illustrating the state of contact between the device for measuring the step difference of a slit die head according to an embodiment of this application and a single die head. Figure 8 (b) is a side view illustrating the state of contact between the device for measuring the step difference of a slit die head according to another embodiment of this application and a single die head.

[0031] Figure 9 This is a cross-sectional view of the ink discharge tip of the dual-die head.

[0032] Figure 10 (a) is a side view illustrating the state of contact between the device for measuring the step difference of a slit die head according to an embodiment of this application and the dual die heads. Figure 10 (b) is a side view illustrating the state of contact between the device for measuring the step difference of a slit die head according to another embodiment of this application and the dual die heads.

[0033] Figure 11 (a) is a cross-sectional view of an experimental slit mold manufactured according to one embodiment. Figure 11 (b) is an image of the slit mold formed by laser sensing through a device used to measure the step difference.

[0034] <Explanation of reference marks>

[0035] 100: Equipment used to measure step difference

[0036] 110: Main body

[0037] 120: Laser sensor

[0038] 123: Detector

[0039] 130: Fixture

[0040] 131: Through hole

[0041] 133: Contact Department

[0042] 140: Handle

[0043] 200: Single mold head

[0044] 211: First subject 213: First lip

[0045] 221: Second Body 223: Second Lip

[0046] 230: Gasket

[0047] 300: Dual-mode head

[0048] 311: First subject 313: First lip

[0049] 321: Second Body 323: Second Lip

[0050] 331: Third subject 333: Third lip

[0051] 340: First gasket; 350: Second gasket Detailed Implementation

[0052] The present disclosure will now be described in detail with reference to the accompanying drawings. However, the drawings are intended to illustrate the present disclosure by way of example, and the scope of the disclosure is not limited by these drawings.

[0053] Figure 2 This is an exploded perspective view of a device for measuring step difference according to one embodiment. Figure 3 This is a combined perspective view of a device for measuring step difference according to one embodiment.

[0054] Figure 4 This is a combined cross-sectional view of a device for measuring step difference according to another embodiment. Figure 6 (a) is a top plan view of an apparatus for measuring step difference according to yet another embodiment. Figure 6 (b) is a front view of an apparatus for measuring step difference according to yet another embodiment. Figure 6 (c) is a side view of an apparatus for measuring step difference according to yet another embodiment.

[0055] The device 100 for measuring the step difference of a slit die includes a laser sensor 120 and a clamp 130. In this case, the laser sensor 120 and the clamp 130 are spaced apart from each other. A body portion 110 may be further provided to accommodate the laser sensor 120 and the clamp 130. The laser sensor 120 and the clamp 130 are fixedly coupled to the body portion 110 by assembly, but the method of coupling is not particularly limited. The body portion 110 is not particularly limited, as long as it can secure the laser sensor 120 and the clamp 130. The body portion 110 may include two or more plates, and the cross-section of the body portion 110 may have… Shaped like a "ロ" or "ロ".

[0056] Figure 5 This is a perspective view illustrating the state of contact between the device for measuring step difference and the slit die head according to another embodiment.

[0057] The laser sensor 120 is configured to face the lip and the end of the gasket on the ink discharge tip side of the slit die, which is the object of measurement. Specifically, the slit die includes: two or more bodies 211, 221 having lips 213, 223 at one end, and a gasket 230 disposed between the two or more bodies to discharge ink, with the laser sensor 120 configured to face the end of the lips and the gasket.

[0058] The laser sensor 120 can emit a laser beam toward the lip and the end of the slit die head, detect the laser beam reflected by the surface of the lip and the slit die head, and obtain the shape of the end.

[0059] The laser sensor 120 may include: a laser emitter (not shown) configured to emit a laser beam toward the lip and the end of the slit die; and a detector 123 configured to detect the laser beam reflected by the surfaces of the lip and the slit die.

[0060] The laser emitter (not shown) of the laser sensor 120 is configured such that a laser beam emitted from a light source reaches the object being measured. In this case, the laser beam is light with high straightness, and the object being measured is located on the extension line of the emission direction of the laser beam.

[0061] There are no particular restrictions on the laser beam emitted from the laser sensor 120, as long as the laser beam is well reflected by the surface to which it is to be emitted, and does not affect the material or shape of the ink discharge tip of the slit die. For example, the laser beam can be a visible light laser beam in the range of 380 nm to 800 nm. Specifically, the laser beam can be a blue laser beam, and more specifically, it can be a 405 nm laser beam.

[0062] The detector 123 of the laser sensor 120 can be a plate-shaped sensor capable of detecting a laser beam reflected by the surfaces of the lip and gasket of the slit die. In order for the reflected laser beam to reach the detector, the angle at which the plate-shaped sensor of the detector 123 is set can be adjusted and determined taking into account the emission angle of the laser beam and the shape of the lip and gasket.

[0063] The laser sensor 120 may include an output section (not shown) that obtains the shape of the lip and gasket on the ink discharge tip side of the slit die based on information detected by the detector 123. The shape obtained by the output section is a vertical cross-section along the length direction of the end on the ink discharge tip side. For example, obtaining a shape similar to... Figure 7 and Figure 9 The shape shown is similar to the one described above. Based on this shape, the height difference between specified points, i.e., the step difference, can be obtained by measuring the coordinates of the step difference measurement points.

[0064] The clamp 130 is configured to contact at least a portion of the body containing the ink discharge section of the slit die. The clamp 130 contacts and supports at least a portion of the body to maintain the measurement position and the distance between the laser sensor 120 and the object being measured, such that the laser sensor 120 can measure the step difference between the lip and the gasket.

[0065] The distance between the lips and the laser sensor can be between 17mm and 23mm, or between 17.8mm and 22.2mm, i.e., 20±2.2mm. Sensing is performed while maintaining a predetermined interval between the measuring sensor and the object; sensing cannot be performed if the predetermined interval deviates from the predetermined distance.

[0066] There are no particular limitations on the contact area between the fixture 130 and the main body, as long as the device 100 used to measure the step difference can be stably positioned. Stability increases with increasing contact area. Therefore, the contact area can be designed to be maximized, taking into account the overall dimensions of the device used to measure the step difference.

[0067] like Figure 8 (a) and Figure 10 As shown in (a), the clamp 130 may have a bevel cutting angle along the inclined surface of the body. The shape is formed by the cross-section of the mold. When the step difference measurement object is a single mold head, the clamp 130 can contact the upper surface of the first body 211 or the second body 221 of the single mold head. When the step difference measurement object is a dual mold head, the clamp 130 can contact the upper surface of the first body 311 or the third body 331 of the dual mold head.

[0068] like Figure 8 (b) and Figure 10 As shown in (b), the clamp 130 may have a bevel cutting along the inclined surface of the body. The shape is formed by the cross-section of the mold. When the step difference measurement object is a single mold head, the clamp 130 can contact the upper surfaces of the first body 211 and the second body 221 of the single mold head. When the step difference measurement object is a dual mold head, the clamp 130 can contact the upper surfaces of the first body 311 and the third body 331 of the dual mold head.

[0069] Reference Figure 7 and Figure 9 ,from Figure 7 and Figure 9 As shown by the arrow indicating the part in contact with the clamp, the surface of the main body where the ink is dispensed is an inclined surface that is tilted at a predetermined angle relative to the side of the lip. Therefore, in order to increase the contact area with the clamp, the contact portion 133 of the clamp may also have an inclination angle that is the same as or similar to the inclination angle of the inclined surface.

[0070] Because the clamp 130 is the part that contacts the body and lip of the slit die, the clamp 130 is made of a material that will not scratch the body and lip of the slit die that contact the clamp 130. For example, the material of the clamp may contain acetal, but is not limited to this.

[0071] The fixture 130 of the device 100 for measuring step difference is positioned closer to the slit die than the laser sensor 120, such that the fixture 130 contacts the body of the slit die. Therefore, the fixture 130 has at least one through-hole 131, allowing a laser beam emitted from the laser sensor 120 to reach the ink discharge tip of the slit die, and a reflected laser beam to reach the detector.

[0072] The through-hole 131 can be a single hole that allows the laser beam to reach the ink discharge tip of the slit die and allows the reflected laser beam to reach the detector.

[0073] The through-hole 131 may include a first hole for the laser beam to reach the ink discharge tip of the slit die head, and a second hole for the reflected laser beam to reach the detector.

[0074] The device for measuring the step difference of a slit die according to this embodiment of the present application further includes a determination unit (not shown).

[0075] The determination unit compares the step difference between the lip and the gasket, measured by the laser sensor, with a reference value. If the step difference between the lip and the gasket, as measured by the laser sensor, exceeds the reference value, the determination unit decides to reassemble the slit die. The reference value is an important factor used to determine the coating amount, coating pattern, etc. It verifies whether the designed step difference is maintained. If the step difference increases to a value equal to or greater than the allowable value, the slit die is reassembled to keep the step difference within the reference value.

[0076] The reference value can be 300 μm. When the step difference between the lip and the gasket is equal to or less than 300 μm, the ink dispersion caused by the step difference is constant, and the deviation of the width of the applied paste remains at a predetermined level.

[0077] Figure 7 This is a cross-sectional view of the ink discharge tip of a single die head.

[0078] The slit mold head can be a single mold head 200. The slit mold head 200 includes: a first body 211 having a first lip 213, a second body 221 having a second lip 223, and a gasket 230 disposed between the first body 211 and the second body 221.

[0079] The laser sensor 120 measures the step difference between the end of the first lip 213 and the end of the gasket 230. The determination unit compares the step difference between the end of the first lip 213 and the end of the gasket 230 measured by the laser sensor with a reference value. In this case, the reference value can be the step difference that is targeted when assembling the single mold head 200. For example, the reference value can be 300 μm.

[0080] In addition, the laser sensor 120 can further measure the step difference between the end of the first lip 213 and the end of the second lip 223.

[0081] Figure 8 (a) is a side view illustrating the state of contact between the device for measuring the step difference of a slit die head according to an embodiment of this application and a single die head. Figure 8 (b) is a side view illustrating the contact state between a device for measuring the step difference of a slit die head according to another embodiment of this application and a single die head. Figure 8 (a) and Figure 8 As shown in (b), the shape of the contact between the fixture 130 and the single mold head can vary depending on the shape of the fixture 130.

[0082] Figure 9 This is a cross-sectional view of the ink discharge tip of the dual-die head.

[0083] The slit head can be a dual head 300. The slit head 300 includes: a first body 311 having a first lip 313, a second body 321 having a second lip 323, a third body 331 having a third lip 333, a first gasket 340 disposed between the first body 311 and the second body 321, and a second gasket 350 disposed between the second body 321 and the third body 331.

[0084] The laser sensor 120 can measure the step difference between the end of the first lip 313 and the end of the first gasket 340, and the step difference between the end of the second lip 323 and the end of the second gasket 350. The determination unit can compare at least one of the step differences measured by the laser sensor between the end of the first lip 313 and the end of the first gasket 340, and the step difference between the end of the second lip 323 and the end of the second gasket 350, with a reference value. In this case, the reference value can be a step difference that is targeted when assembling the dual-mold head 300. For example, the reference value associated with the step difference between the end of the first lip 313 and the end of the first gasket 340 can be 300 μm.

[0085] In addition, the laser sensor 120 can further measure the step difference between the end of the first lip 313 and the end of the second lip 323, as well as the step difference between the end of the second lip 323 and the end of the third lip 333.

[0086] Figure 10 (a) is a side view illustrating the state of contact between the device for measuring the step difference of a slit die head according to an embodiment of this application and the dual die heads. Figure 10 (b) is a side view illustrating the contact state between the apparatus for measuring the step difference of a slit die head according to another embodiment of this application and the dual die heads. Figure 10 (a) and Figure 10 As shown in (b), the shape in which the clamp 130 contacts the dual mold head can vary depending on the shape of the clamp 130.

[0087] The device 100 for measuring the step difference of a slit die according to an embodiment of this application may further include a handle 140.

[0088] The device 100 for measuring step difference is a portable device that can be easily carried, moved, and stored by the user. High portability is advantageous for the device used to measure step difference in slit head measurements because once the slit head is mounted on the coating equipment by stacking the body and shims, it is difficult to disassemble and reassemble.

[0089] The handle can be designed to make it easy for the measurer to carry the equipment, and when measuring step difference, the measurer holds the handle with his hand while the fixture is in contact with the slit die.

[0090] The device 100 for measuring step difference may further include a controller (not shown) configured to control the laser sensor 120. As needed, the components in the device 100 for measuring step difference—that is, the components required for power supply, control execution, and data output—are connected to each other via wires. Furthermore, the device 100 for measuring step difference can be easily disassembled, connected, and installed to provide portability. After disassembly, the components of the device 100 can be stored in a carrying case.

[0091] Another embodiment of this application provides a method for measuring the step difference of a slit die, the slit die comprising: two or more bodies having a lip at one end thereon, and a pad disposed between the two or more bodies and configured to discharge ink, the method comprising: contacting a clamp of a device for measuring the step difference with at least a portion of the upper end of the body where the ink discharge portion of the slit die is located, the device having a laser sensor; and measuring the step difference between the lip of the slit die and the pad by means of the laser sensor.

[0092] In this case, to avoid redundant description, the description of the device used to measure the step difference can be used instead of the description of the method for measuring the step difference of the slit die.

[0093] The method for measuring the step difference of the slit die head may further include comparing the step difference between the lip and the gasket, measured by a laser sensor, with a reference value.

[0094] The method for measuring the step difference of the slit die head may further include reassembling the slit die head when the step difference between the lip and the gasket, as measured by the laser sensor, exceeds a reference value. In this case, the reference value may be 300 μm.

[0095] Invention patterns

[0096] The present application will now be described in more detail with reference to embodiments. However, the following embodiments are intended to illustrate the present application, and the scope of the present application is not limited to the following embodiments.

[0097] [Example]

[0098] Manufacturing with Figure 11 The experimental slit mold of the specifications shown in (a) was used, and the step difference offset was measured using a device for measuring step difference. Ten step differences were measured under the conditions set in Table 1, and the error of the measurement data was to be evaluated. In this context, "measuring instrument readjustment measurement reproducibility" refers to the reproducibility of the data when the measuring instrument is separated from the slit mold after measurement and the measurement position is adjusted. "Sensor continuous measurement repeatability" refers to the repeatability of the measurement data when continuous measurements are taken without separating the measuring instrument from the slit mold after measurement.

[0099] The master (certification) specimen is a Mitutoyo master (certification) specimen with an arbitrarily preset step difference level. The accuracy of the data values ​​measured using the device for measuring step difference according to this application is verified. Master (certification) specimens with step differences of 50 μm, 100 μm, and 300 μm are used respectively. In this case, the step difference is selected such that it must be adjusted to the level of the step difference between the die lip and the gasket.

[0100] [Table 1]

[0101]

[0102] In this case, the device used to measure the step difference uses a laser with the following conditions.

[0103] - Reference distance (Z-axis): 20±2.2mm (repeatability 0.3μm)

[0104] - Measurement range (X-axis): 7.5 mm (repeatability 0.3 μm)

[0105] - Data interval: 2.5μm

[0106] - Light source: Blue LED (blue semiconductor laser)

[0107] - Wavelength: 405nm visible light

[0108] - Output: 10mV

[0109] The results of the step difference of the experimental mandrel measured each time the measuring instrument, i.e., the measuring position of the device used to measure the step difference, was readjusted according to the plan in Table 1 are shown in Table 2 below.

[0110] [Table 2]

[0111]

[0112]

[0113] based on Figure 11 In (a), the bottom shim offset is a step difference of ①-②, the bottom die head offset is a step difference of ①-③, the top shim offset is a step difference of ③-④, and the top die head offset is a step difference of ③-⑤. In this case, ① to ⑤ refer to the steps respectively with... Figure 11 The red dots shown in (a) indicate the locations of the step difference measurement points.

[0114] Figure 11 (b) shows an image of a slit mold formed by laser sensing using a device for measuring step difference. The step difference measurement point is specified on the image, and then the offset value is obtained.

[0115] The results of measuring the thickness of the certification specimen, which were obtained each time the measuring instrument was readjusted according to the plan in Table 1, i.e., the measuring position of the device used to measure the step difference and the measuring position of the certification specimen, are shown in Table 3 below.

[0116] [Table 3]

[0117]

[0118] The results of fixing the measuring instrument according to the plan in Table 1 and continuously sensing the step difference of the experimental mandrel are shown in Table 4 below.

[0119] [Table 4]

[0120]

[0121] The results of the step difference of the experimental mold head measured according to the plan in Table 1 are shown in Table 5 below, and the results of the target thickness and measured thickness of the certification sample are shown in Table 6 below.

[0122] [Table 5]

[0123]

[0124] [Table 6]

[0125]

[0126]

[0127] As can be determined from Tables 2 to 6, the device for measuring step difference according to this application can measure the step difference (offset) between the lip and the gasket of the slit die head, and the measured values ​​have high reproducibility and reliability.

Claims

1. An apparatus for measuring the step difference of a slit die, the apparatus comprising: Main body; A laser sensor configured to measure the step difference between the lip and the gasket of a slit die, the slit die comprising: two or more bodies having a lip at one end thereto, and a gasket disposed between the two or more bodies and configured to discharge ink, the laser sensor being configured to face the lip and the gasket of the slit die. as well as A clamp configured to contact at least a portion of the body containing the ink discharge section of the slit die head, to maintain the distance between the laser sensor and the lip and the distance between the laser sensor and the gasket, such that the laser sensor can measure the step difference between the lip and the gasket. The laser sensor and the clamp are fixedly attached to the main body.

2. The device according to claim 1, further comprising: The determination unit is configured to compare the step difference between the lip and the gasket, as measured by the laser sensor, with a reference value.

3. The device according to claim 2, wherein when the step difference between the lip and the gasket measured by the laser sensor exceeds the reference value, the determination unit determines to reassemble the slit mold head.

4. The device according to claim 2, wherein the reference value is 300 μm.

5. The device according to claim 1, wherein the slit die head comprises: A first body having a first lip; A second body having a second lip; as well as A gasket is disposed between the first body and the second body, and The laser sensor measures the step difference between the end of the first lip and the end of the gasket.

6. The device of claim 5, wherein the laser sensor further measures the step difference between the end of the first lip and the end of the second lip.

7. The device according to claim 1, wherein the slit die head comprises: A first body having a first lip; A second body having a second lip; A third body with a third lip; A first gasket is disposed between the first body and the second body; as well as A second gasket is disposed between the second body and the third body, and The laser sensor measures the step difference between the end of the first lip and the end of the first pad, and the step difference between the end of the second lip and the end of the second pad.

8. The device of claim 7, wherein the laser sensor further measures the step difference between the end of the first lip and the end of the second lip, and the step difference between the end of the second lip and the end of the third lip.

9. The device according to claim 1, wherein the distance between the lip and the laser sensor is more than 17 mm and less than 23 mm.

10. The device according to claim 1, wherein the device is a portable device.

11. A method of measuring a step difference of a slit die, the slit die comprising: The method comprises two or more bodies having lips at one end, and a gasket disposed between the two or more bodies and configured to discharge ink. A device is provided for measuring the step difference of a slit die head, the device comprising a main body, and a laser sensor and a fixture fixedly coupled to the main body; The clamp is brought into contact with at least a portion of the upper end of the body where the ink discharge portion of the slit die is located, to maintain the distance between the laser sensor and the lip and the distance between the laser sensor and the gasket, such that the laser sensor can measure the step difference between the lip and the gasket; and The laser sensor measures the step difference between the lip of the slit die and the gasket.

12. The method of claim 11, further comprising: The step difference between the lip and the pad, measured by the laser sensor, is compared with a reference value.

13. The method of claim 12, further comprising: When the step difference between the lip and the gasket, as measured by the laser sensor, exceeds the reference value, it is determined that the slit die head should be reassembled.

14. The method of claim 12, wherein the reference value is 300 μm.

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