Roll press machine

Abstract

To provide a roll press machine capable of manufacturing material sheets with a dense structure using minimal energy. [Solution] A roll press machine comprising a pair of pressure rolls that have a pressure roll shaft supported by a bearing and rotates, for continuously compressing a thin sheet; a temperature measuring unit capable of measuring the surface temperature of the pressure rolls; and a pressure roll surface temperature adjustment mechanism that adjusts the surface temperature of the pressure rolls by heating or cooling the pressure rolls from the surface based on the surface temperature of the rotating pressure rolls measured by the temperature measuring unit.

Description

Technical Field

[0001] The present invention relates to a roll press machine.

Background Art

[0002] As a manufacturing process for electrode materials for secondary batteries such as lithium batteries, a slurry obtained by kneading particulate active materials and a binder for fixing these active materials on a current collector sheet is applied to both sides of the current collector sheet, the applied sheet is dried, and then it is generally manufactured by pressing with a roll press.

[0003] In roll pressing, in order for the thickness of the electrode sheet after pressing to be uniform (compression processing accuracy of ±1.0 to 2.0 μm is required) and to increase the density of the active material, highly accurate compression processing is required.

[0004] In the continuous compression processing of electrode materials for secondary batteries using a roll press machine, even when operating for a long time, heat generated by mechanical friction of the pressure roll bearing part is conducted to the pressure roll, and a device in which the pressure roll is unlikely to undergo thermal deformation is desired. As such a roll press machine for preventing thermal deformation of the pressure roll, Patent Document 1 is known.

[0005] On the other hand, instead of cold (room temperature) roll pressing as described in Patent Document 1, a method of performing roll pressing at a warm temperature adjusted to a surface temperature of 70°C to 100°C and heat-treating the binder contained in the sheet while pressing the electrode composition is described in Patent Document 2.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Summary of the Invention

[0007] Patent Document 2 states that it uses "a roll press adjusted to a surface temperature of 70°C or higher but less than 100°C," but it does not describe the specific configuration for achieving a roll surface temperature of 70°C or higher but less than 100°C. There is a concern that a large amount of energy will be required to heat the entire roll to achieve a roll surface temperature of 70°C or higher but less than 100°C.

[0008] The objective of the present invention is to provide a roll press machine capable of producing material sheets having a dense structure with less energy. [Means for solving the problem]

[0009] The configuration of the present invention for solving the above problems is as follows. A roll press machine comprising: a pair of pressure rolls having a pressure roll shaft supported by a bearing and rotating, for continuously compressing a thin sheet; a temperature measuring unit capable of measuring the surface temperature of the pressure rolls; and a pressure roll surface temperature adjustment mechanism that adjusts the surface temperature of the pressure rolls by heating or cooling the pressure rolls from the surface based on the surface temperature of the rotating pressure rolls measured by the temperature measuring unit. [Effects of the Invention]

[0010] According to the present invention, a roll press machine capable of manufacturing material sheets having a dense structure with less energy can be provided.

[0011] Other issues, configurations, and effects not mentioned above will be clarified by the following description of the embodiments. [Brief explanation of the drawing]

[0012] [Figure 1] A schematic diagram of the overall configuration of a roll press machine. [Figure 2] Front view of a roll press machine. [Figure 3] Cross-sectional view of a sheet being continuously compressed by pressure rolls. [Figure 4] A schematic diagram of the overall configuration of a roll press machine according to an embodiment of the present invention. [Figure 5A] A diagram illustrating the method for measuring the surface temperature of a pressure roll. [Figure 5B] This diagram illustrates the concept of temperature change on the surface of a pressure roll as it completes one rotation. [Figure 6] A diagram illustrating the relationship between the wavelength of irradiated electromagnetic waves and the absorption rate of electromagnetic wave energy by the irradiated object. [Figure 7] A flowchart illustrating the temperature control of the pressure roll. [Modes for carrying out the invention]

[0013] Figure 1 is a schematic diagram of the overall configuration of a roll press machine to which the present invention can be applied. The roll press machine 1 is equipment for continuously compressing a sheet 11 having coated portions 11a on both sides of a base material 11b made of a conductive metal foil such as aluminum foil or copper foil, as shown in Figure 3, to increase the density of the active material and achieve a uniform thickness, for example, as an electrode material for lithium-ion secondary batteries. However, the roll press machine 1 is not limited to equipment for compressing a sheet 11 having coated portions 11a on both sides of a base material 11b made of a conductive metal foil such as aluminum foil or copper foil. For example, it can also be used as equipment for compressing thin film sheets, such as a polyester film laminated with adhesive-free aramid paper on both sides. In other words, the roll press machine 1 according to one embodiment of the present invention is suitably used for compressing any thin film sheet.

[0014] As shown in Fig. 1, the roll press machine 1 includes, from the upstream side, for example, an unwinder 4 that winds an unwinding coil of a sheet 11 having a width of about 1 m and a length of about 500 m, an upstream conveying mechanism 6 that conveys the sheet 11 fed out from the unwinder 4, a preheating roll 10 for preheating the sheet 11, a pair of pressing rolls (upper pressing roll 2A and lower pressing roll 2B) for compressing the sheet 11, a downstream conveying mechanism 7 that conveys the compressed sheet 11, and a winder 5 that winds the compressed sheet 11 to generate a winding coil.

[0015] The upstream conveying mechanism 6 includes a plurality of guide rolls 8 and a dancer roll 9. The rotation axis of the dancer roll 9 is configured to be displaceable vertically along an arc-shaped orbit centered on a support point. By the vertical displacement of the dancer roll 9 along the arc-shaped orbit, a predetermined tension (appropriate tension) is applied to the sheet 11, and in cooperation with the guide rolls 8, the sheet 11 is conveyed to the preheating roll 10.

[0016] Similarly, the downstream conveying mechanism 7 includes a plurality of guide rolls 8, a dancer roll 9, and a thickness gauge 3. By the vertical displacement of the dancer roll 9 along the arc-shaped orbit, a predetermined tension is applied to the sheet 11. The thickness gauge 3 installed between two guide rolls measures the thickness of the sheet 11 when passing through the thickness gauge 3 while a predetermined tension is applied by the dancer roll 9.

[0017] In Fig. 1, the number of guide rolls 8 is shown fewer for the convenience of explanation. However, for example, the number is not limited to that shown in this figure, and a configuration may be adopted in which 10 to 30 guide rolls 8 are provided in each of the upstream conveying mechanism 6 and the downstream conveying mechanism 7. Also, in Fig. 1, the dancer roll 9 and the preheating roll 10 are shown separately from the guide rolls 8, but in some cases, the dancer roll 9 and the preheating roll 10 may also be called guide rolls 8 including these.

[0018] Fig. 2 shows a front view of a pair of pressure rolls (front view of region A in Fig. 1). A pair of pressure rolls (upper pressure roll 2A and lower pressure roll 2B) arranged facing each other vertically are rotatable by rolling bearings 22 that support their respective pressure roll shafts 20 at both ends, bearing boxes 23 that hold the rolling bearings 22, and a housing 21 that holds the bearing boxes 23. Further, a pressure mechanism 24 composed of, for example, a hydraulic cylinder or the like is arranged between the bearing box 23 that holds the rolling bearings 22 supporting both ends of the pressure roll shaft 20 of the lower pressure roll and the lower part of the housing 21. The pressure mechanism 24 moves up and down to adjust the gap between the pair of pressure rolls and the load applied to the pressure rolls based on the thickness of the sheet 11 measured by the thickness gauge 3 described above.

[0019] Also, the pressure rolls 2A and 2B in this embodiment are, for example, solid rolls made of metal, with a roll diameter of 300 to 800 mmφ. As a typical example, a roll with a diameter of 500 mmφ is used.

[0020] In Figs. 1 and 2, the sheet 11 is continuously compression processed by a pair of pressure rolls while being conveyed at a conveyance speed of, for example, about 100 m / min. The thickness Tb of the base material 11b shown in Fig. 3 is, for example, about 15 μm, and the thickness including the coating part 11a coated with the active material on both sides of this base material 11b, that is, the thickness Ta of the sheet 11, is about 150 μm before the compression processing. The sheet 11 having a thickness of about 150 μm is compressed to about 100 μm by the compression processing by a pair of pressure rolls. Thereby, the density of the active material, that is, the coating parts 11a on both sides is improved. On the other hand, as described above, the compression processing accuracy is required to be ±1.0 to 2.0 μm.

[0021] Incidentally, the active material layer coated on both sides of the substrate 11b of the sheet 11 shown in Figure 3 consists of particles containing a composite oxide of lithium and a transition metal, such as LiCoO2, LiNiO2, LiAlMnO4, LiMnO2, and LiMn2O4, if it is a positive electrode active material, and a compound of particles containing a carbon-based material [such as graphite, non-graphitizable carbon, amorphous carbon, etc.] which is a well-known negative electrode active material for lithium-ion batteries, and a binder that dries and solidifies by volatilizing the solvent component, thereby firmly bonding and fixing the active material particles together.

[0022] Conventional electrode sheets were dried and solidified by heating them before roll pressing using a roll press machine to volatilize the solvent components. However, in reality, the solvent components did not completely volatilize even during the roll pressing stage, and in some cases, cracks could occur in the electrodes after roll pressing or after supplying electrolyte to the formed electrodes.

[0023] Therefore, the technology described in Patent Document 2 describes pressurizing the electrode composition using a roll press adjusted to a surface temperature of 70°C or higher and less than 100°C. However, during roll pressing, changes in the surface temperature of the pressurizing roll can cause fluctuations in the performance of the manufactured electrodes, so controlling the surface temperature of the roll press is important. In addition, heating a solid press roll made of stainless steel, for example, requires a large amount of energy.

[0024] In this invention, in order to accurately control the surface temperature of the pressure roll on the surface that contacts the sheet during roll pressing, and to reduce the energy required to heat the pressure roll, the configuration described in the following embodiment was adopted. Hereinafter, embodiments of the present invention will be described with reference to the drawings. [Examples]

[0025] Figure 4 shows a schematic diagram of the overall configuration of a roll press machine according to an embodiment of the present invention. The features of this embodiment are that, compared to the conventional roll press machine shown in Figure 1, a thermometer 50 (for measuring the surface temperature of the upper pressure roll 2A) and a thermometer 51 (for measuring the surface temperature of the lower pressure roll 2B) are added for non-contact measurement of the surface temperatures of the pressure rolls 2A and 2B, as well as a heater 60 for heating the upper pressure roll 2A and a heater 61 for heating the lower pressure roll 2B. As a thermometer for non-contact measurement of surface temperature, a well-known thermometer that measures temperature by detecting infrared radiation emitted from an object can be used.

[0026] Furthermore, since a temperature distribution may occur in the width direction of a 1m wide pressure roll (for example, the ends of the pressure roll may be cooler than the center due to heat dissipation), thermometers may be installed at the ends and center of the pressure roll, or the surface of the pressure roll may be monitored in two dimensions using thermography (images). Alternatively, thermocouples may be embedded inside the pressure roll. As for the heater, a device that heats by irradiating with laser light, a device that heats by irradiating with infrared light, or a device in which a heating element is embedded inside the pressure roll can be used.

[0027] The change in surface temperature of the pressure roll is explained using Figures 5A and 5B. Figure 5A is an excerpt of the upper pressure roll 2A from Figure 4. The upper pressure roll 2A is rotating counterclockwise. In Figure 5A, A, B, C, and D indicate the positions of the surface of the pressure roll 2A. Figure 5B shows the concept of the surface temperature change of the pressure roll at positions A, B, C, and D as the pressure roll 2A completes one rotation. At point A, where the pressure roll 2A contacts the sheet 11, thermal energy is required for the binder to undergo a thermal change. Although the sheet 11 is preheated by the preheating roll 10, the temperature of the sheet 11 is lower than the surface temperature of the pressure roll 2A. Therefore, heat is absorbed from the surface of the pressure roll 2A by the sheet 11, and the surface temperature of the pressure roll decreases until the pressure roll 2A separates from the sheet 11 (to position A').

[0028] When the pressure roll 2A leaves the sheet 11 (moves away from position A'), the heat on the surface of the pressure roll 2A dissipates into the atmosphere, so the temperature gradually decreases, although the rate of temperature decrease is smaller than when it was in contact with the sheet 11. At position D, the surface of the pressure roll 2A is heated by the heater (also called a "heater") 60, causing the surface temperature to rise sharply. After completing one rotation and reaching position A again, the pressure roll 2A comes into contact with the sheet 11 again, and the temperature drops sharply. While the sheet is being heated and pressurized by the pressure roll, this temperature change is repeated on the surface of the pressure roll.

[0029] The amount of heat naturally dissipated into the atmosphere between position A' and position D varies depending on the ambient temperature and humidity of the environment in which the pressure roll 2A is placed. Furthermore, the degree of temperature drop upon contact with the sheet 11 varies depending on the preheating temperature of the sheet 11 and the amount of binder in the sheet 11 (since heat for the binder to volatilize is absorbed from the surface of the pressure roll 2A, the rate of temperature drop of the pressure roll 2A will be greater if the sheet contains a large amount of binder). For this reason, the amount of heat supplied from the heater 60 to the pressure roll 2A is adjusted based on the measurement value from the thermometer 50 so that the surface temperature of the pressure roll 2A during sheet pressurization reaches the set temperature, i.e., the temperature most suitable for manufacturing the electrode sheet.

[0030] The heater 60 is preferably installed just before the pressure roll 2A contacts the sheet 11. This is because the temperature at which the pressure roll contacts the sheet 11 can be adjusted with greater precision. It is desirable that the heater 60 be placed within 1 / 4 of the outer circumference of the pressure roll (within 1 / 4 of a rotation) before the pressure roll contacts the sheet 11.

[0031] Furthermore, as shown in Figure 5B, the temperature of the roll surface decreases over time after the pressure roll comes into contact with the sheet 11. Therefore, in addition to the thermometer 50, another thermometer may be added, for example, at position B in Figure 5A. Based on the temperature measurements at the two positions, the slope of the temperature decrease can be calculated to predict the temperature TN of the roll surface when it comes into contact with the sheet. If the predicted TN is lower than the set temperature (target temperature) TS, the amount of heating by the heater 60 can be increased to adjust the surface temperature of the pressure roll at the contact surface with the sheet 11 so that it reaches temperature TS.

[0032] To control the temperature of the pressure roll over a wide range from low to high temperatures, it is desirable to use multiple heat sources in the heater 60. Figure 6 shows a graph with the wavelength of electromagnetic waves on the horizontal axis, the absorption rate of electromagnetic wave energy with iron as an example of the irradiated object on the left vertical axis, and the electromagnetic wave emissivity of halogen lamp heaters and infrared lamp heaters on the right vertical axis. Since iron pressure rolls have a high absorption rate in the visible to near-infrared range, it is desirable to use halogen lamp heaters as the heater. On the other hand, in order to improve heating efficiency, it is preferable to use metal heaters or SiC heaters that irradiate with electromagnetic waves in the infrared range in combination.

[0033] The thermometers 50 and 51 and the heaters 60 and 61 are connected to the control computer 54 by signal lines (not shown). The control computer 54 predicts TN based on the temperatures measured by the thermometers 50 and 51, and adjusts the degree of heating of the heaters 60 and 61 based on the difference between the predicted TN and the set temperature TS.

[0034] As shown in Figure 2, the pressure roll 2 is elongated horizontally, and its surface temperature may vary horizontally. Therefore, by installing multiple thermometers horizontally, more precise temperature control becomes possible. Furthermore, by installing multiple heaters according to the thermometer placement, more precise temperature control becomes possible.

[0035] Furthermore, a heater with width in the horizontal direction may be used. The surface temperature of the pressure roll 2 varies depending on the feed speed of the sheet 11, the thickness of the sheet 11 (Ta in Figure 3), the composition of the sheet 11 (material, etc.), etc. Therefore, it is preferable that the program of the control computer 54 has multiple control patterns according to these conditions and can be switched between. In addition, in order to maintain a uniform temperature of the roll, the temperature distribution is measured in real time using a thermograph or multiple temperature sensors arranged in the axial direction. This makes it possible to identify areas with uneven temperatures and concentrate heating on those areas.

[0036] Figure 7 shows a flowchart for temperature adjustment of the pressure roll. Operation is started (step S800). Before starting the roll pressing of the sheet, a process is performed to bring the temperature of the pressure roll surface to the target temperature while the pressure roll is rotating. First, the temperature of the pressure roll surface is measured (initial monitoring) (step S801). Next, the surface temperature of the pressure roll measured by the thermometer 50 is compared with the target temperature (also called the "set temperature" or "reference temperature") (step S802).

[0037] If the surface temperature of the pressure roll is lower than the target temperature (if YES in step S803), heat is radiated from the heater 60 to the surface of the pressure roll to heat it (step S804). If the surface temperature of the pressure roll is higher than the target temperature (if NO in step S803), air is blown onto the surface of the pressure roll using a blower (not shown) to cool it (step S805). The temperature of the surface of the pressure roll is measured using the thermometer 50 (step S806). The surface temperature of the pressure roll is checked to see if it is the target temperature (step S807). If the surface temperature of the pressure roll is not the target temperature (if YES in step S803, return to step S801 and repeat steps S801 to S807 until the surface temperature of the pressure roll reaches the target temperature).

[0038] In step S807, once the surface temperature of the pressure roll reaches the target temperature, heating or airflow to the surface of the pressure roll is stopped (step S808), the sheet 11 is fed out from the unwinder 4 in Figure 1 (step S809), and roll pressing of the sheet 11 on the pressure roll is started (step S810). Even after roll pressing of the sheet on the pressure roll has started, the surface temperature of the pressure roll is measured, and roll pressing of the sheet 11 is continued while correcting any deviation from the target temperature (repeat steps S801 to S807).

[0039] In steps S804 and S805, temperature can also be adjusted by adjusting the rotation speed of the pressure roll while simultaneously heating or cooling with a heater or blower. That is, by lowering the rotation speed of the pressure roll, the amount of energy that the pressure roll surface receives from the heater per unit time, or the amount of energy that the blower removes from the heated roll surface per unit time, can be increased, thereby improving the heating or cooling effect.

[0040] Furthermore, by controlling (adjusting) the temperature of the external environment in which the pressure roll is placed and preheating the sheet 11, it is possible to minimize temperature drops due to external factors. As for the thermometer, a non-contact infrared sensor, a thermocouple placed inside the roll, or even a thermograph can be used. For cooling, when a high temperature is detected, the cooling temperature sensor confirms that it has exceeded the standard value and concentrates cool air on the overheated area. The direction and spread of the cool air are adjusted using ducts or nozzles, and the cool air is automatically stopped when it returns to the appropriate range.

[0041] In the heating process, low temperatures are detected through temperature monitoring, and heating begins when the temperature sensor detects a temperature below a reference value. Heating is performed locally or globally, and once the temperature reaches the reference value, the heat supply is gradually reduced or stopped through feedback control. A reference temperature range is set at the start, and the roll surface temperature is measured in real time at 1-second intervals. If the temperature exceeds the reference range, cooling is activated; if it falls below the reference range, heating is activated. If the temperature deviation is large, the power is adjusted to high; if it is close to the reference value, the power is adjusted to low. Once the temperature stabilizes, the power is reduced or stopped to achieve efficient temperature control. [Explanation of Symbols]

[0042] 1: Roll press machine 2A: Upper pressure roll 2B: Lower pressure roll 3: Thickness gauge 4: Unwinding machine 5: Winder 6: Upstream conveying mechanism 7: Downstream conveying mechanism 8: Guide Roll 9: Dancer Roll 10: Preheating roll 11: Sheet 11a: Coating section 11b: Base material 20: Pressure Roll Shaft 21: Housing 22: Rolling bearings 23: Bearing box 24: Pressurization mechanism 50: Thermometer 51: Thermometer 54: Control computer 60: Heater 61: Heater

Claims

1. A pair of pressure rolls that have a pressure roll shaft supported by a bearing and rotate, for continuously compressing a thin sheet, A temperature measuring unit capable of measuring the surface temperature of the pressure roll, A roll press machine characterized by comprising a pressure roll surface temperature adjustment unit that adjusts the surface temperature of the pressure roll by heating or cooling the pressure roll from the surface, based on the surface temperature of the pressure roll while it is rotating, as measured by the temperature measurement unit.

2. In the roll press machine according to claim 1, The roll press machine is characterized in that the pressure roll surface temperature adjustment unit has a heater that heats the surface of the pressure roll without contact.

3. In the roll press machine according to claim 1, The roll press machine is characterized in that the pressure roll surface temperature adjustment unit has a blower that cools the surface of the pressure roll without contact.

4. In the roll press machine according to claim 1, At least two of the temperature measuring units are provided along the rotation direction of the pressure roll, A roll press machine characterized by comprising a temperature estimation unit that estimates the surface temperature of the pressure roll at the contact point between the pressure roll and the thin film sheet, based on the surface temperature of the pressure roll measured by at least two of the temperature measurement units.

5. In the roll press machine according to claim 1, The roll press machine is characterized in that the temperature measurement unit has multiple types of heating sources with different wavelength characteristics of the electromagnetic waves it emits.

6. In the roll press machine according to claim 1, The roll press machine is characterized in that the pressure roll surface temperature adjustment unit is provided between the contact portion between the pressure roll and the thin film sheet and a position within one-quarter of the outer circumference of the pressure roll before the pressure roll contacts the contact portion.

7. In the roll press machine according to claim 1, A roll press machine characterized in that the thin film-like sheet is an electrode material for secondary batteries.

Images