A method for producing zero-bubble melt for lithium battery separator production

Abstract

This invention discloses a zero-bubble melt production method for lithium battery separator production, comprising the following steps: (1) setting up a settling tank and two supply tanks, and before normal production, filling both the settling tank and the two supply tanks with white oil that has been settling; (2) during normal production, the first supply tank supplies white oil to the extrusion system. When the liquid level in the first supply tank drops to the set low liquid level, the oil supply stops, and the second supply tank is switched to supply white oil. The settling tank replenishes white oil to the first supply tank; (3) when the second supply tank supplies white oil, when the white oil injected into the first supply tank reaches the high liquid level, it is settling and heated. When the liquid level in the second supply tank drops to the set low liquid level, the first supply tank is switched to supply white oil, and the settling tank replenishes white oil to the second supply tank. When the white oil reaches the high liquid level, it is settling and heated; (4) the two supply tanks supply oil in a cycle according to the above steps.

Description

Technical Field

[0001] This invention relates to a zero-bubble melt production method for lithium battery separators, belonging to the field of lithium-ion battery production technology. Background Technology

[0002] Currently, most lithium-ion battery separator production lines use twin-screw extruder systems for melt extrusion. These systems consist of two identical screws, and stable melt extrusion is ensured through precise process parameter settings. However, because the melt contains air bubbles, if these bubbles cannot be effectively eliminated, the resulting separator will have thin spots (white spots) on its surface, affecting product quality. While the process parameters for twin-screw extrusion systems are relatively mature, the generation of air bubbles in the extrusion system still cannot be completely avoided.

[0003] White oil is an important raw material for melt preparation. Existing white oil supply systems consist of two tanks: a settling tank and a supply tank. During production, white oil is injected into the settling tank via an external pipeline. Pre-treatment of the tank by heating and settling eliminates air bubbles within the white oil. The settled white oil is then transferred to the supply tank and stopped once it reaches a preset high level (80-110cm). The supply tank then delivers white oil to the extruder through an inlet at its bottom. The supply tank also has a heating function to prevent the white oil entering the extruder from entering at too low a temperature (30-40°C), which could lead to air bubble formation. When the liquid level in the supply tank reaches a preset low level (50-30cm), the settling tank injects the settled white oil from the top of the supply tank until the set level (80-110cm) is reached. Figure 1 As shown, the existing bottom-supply design inevitably leads to the formation of air bubbles when replenishing oil at low liquid levels inside the tank, which is detrimental to the extruder system. Simultaneously, the supply tank needs to continuously supply white oil, and the white oil injected first into the supply tank has a very high probability of generating air bubbles due to its short settling time. This will result in periodic air bubble formation in the melt within the extruder. Since the settling tank needs to replenish oil to the supply tank when the supply tank is at a low liquid level, the heating temperature of the settling tank must be consistent with that of the supply tank. Typically, the white oil temperature in the supply tank needs to be set at a high temperature to avoid the impact of sudden cooling on the melt upon entering the extruder. However, setting the settling tank to a high temperature (50-90°C) is not conducive to eliminating air bubbles, which is also a problem that urgently needs to be solved. Summary of the Invention

[0004] The purpose of this invention is to provide a zero-bubble melt production method for lithium battery separator production, in order to solve the technical problem that bubbles are easily generated in the melt during the production of lithium battery separators in the prior art.

[0005] The present invention adopts the following technical solution: a zero-bubble melt production method for lithium battery separator production, which includes the following steps: (1) setting up a settling tank and two supply tanks as white oil tanks for the white oil injection system. Before normal production, the settling tank and the two supply tanks are filled with white oil that has been settling. (2) During normal production, the first supply tank supplies white oil to the extrusion system. When the liquid level of the first supply tank drops to the set low liquid level, the oil supply stops, and the second supply tank is switched to supply white oil. The settling tank replenishes white oil to the first supply tank. (3) When the second supply tank supplies white oil, when the white oil injected into the first supply tank reaches the high liquid level, it is settling and heated. When the liquid level of the second supply tank drops to the set low liquid level, the first supply tank is switched to supply white oil. The settling tank replenishes white oil to the second supply tank. When the white oil reaches the high liquid level, it is settling and heated. (4) The two supply tanks circulate oil supply according to the above steps.

[0006] When the supply tank supplies oil to the extrusion system, the temperature of the white oil in the supply tank is higher than the temperature of the white oil in the settling tank.

[0007] The supply tank is set with a low liquid level of 300-500mm and a high liquid level of 1100-1300mm. The difference between the high and low liquid levels is 600-1000mm.

[0008] When the liquid level in the settling tank is lower than the set low level, add oil to the settling tank. When the liquid level in the settling tank reaches the high level after adding oil, stop adding oil.

[0009] The set low liquid level of the settling tank is 600-800mm, the set high liquid level of the settling tank is 1000-1200mm, and the difference between the set high liquid level and the set low liquid level of the settling tank is 200-600mm.

[0010] Both the settling tank and the supply tank use the same tank body, with a maximum white oil capacity of 1900-2100L, more preferably 2000L. The settling tank is replenished with oil every 350-400L of white oil consumed, more preferably 375L; the supply tank is replenished with oil every 700-800L of white oil consumed, more preferably 750L.

[0011] The oil replenishment flow rates of both the settling tank and the supply tank are equal to twice the maximum flow rate of white oil used by the extruder.

[0012] Each settling tank and supply tank is equipped with a vertical agitator. When the settling tank and supply tank reach the set high liquid level after being replenished with oil, and are not in the oil supply state, the vertical agitator is activated to agitate the white oil in the tank.

[0013] When starting the vertical mixer, the mixing frequency of the vertical mixer motor is set to 0-5Hz, and the mixing time is set to 0-3min.

[0014] A pneumatic diaphragm pump is used to pump white oil from the settling tank into the oil inlet at the top of the supply tank. When the pneumatic diaphragm pump fails, the connecting valve between the bottom of the settling tank and the supply tank is opened, and the white oil in the settling tank flows by gravity into the supply tank through the connecting valve.

[0015] The beneficial effects of this invention are as follows: By modifying the white oil injection system, and through secondary settling of the white oil and an auxiliary stirring system, this invention greatly eliminates air bubbles during white oil supply, thereby preventing the formation of white spots. During normal production, when the liquid level in the first supply tank drops to a low level, oil supply stops, and the supply is switched to the second supply tank. Since it takes time for the white oil in the second supply tank to drop to a low level, the white oil injected into the second supply tank is again sufficiently settling and heated. When the supply of white oil is switched back to the first supply tank, the settling tank replenishes the second supply tank, and this cycle continues. Therefore, the white oil in the supply tanks can be sufficiently settling and heated, thus avoiding the problem of periodically appearing white spots due to a large number of air bubbles not being eliminated during replenishment. Because the white oil injected into the settling tank contains many air bubbles, the temperature setting of the settling tank in existing white oil injection systems is relatively high, which is not conducive to the elimination of air bubbles and increases the risk of white spots. The two supply tanks allow the settling tank to be set at a lower temperature, improving the effect of air bubble elimination. Since the white oil in the settling tank does not need to be used immediately after being added to the supply tank, there is sufficient time for it to heat up to the set temperature of the supply tank.

[0016] This invention improves the white oil injection process and optimizes the white oil pretreatment method, greatly reducing the generation of raw material bubbles, thereby avoiding the generation of bubbles in the melt in the extrusion system, thus preventing the formation of white spots and improving product quality.

[0017] As a preferred embodiment, the present invention sets a smaller difference between high and low liquid levels to increase the frequency of oil replenishment, thereby solving the problem of white oil temperature fluctuation.

[0018] As a preferred embodiment, each tank of the present invention is equipped with a vertical agitator. By agitating at a constant speed and time, the small air bubbles generated in the initial stage of white oil injection can be effectively eliminated, thus solving the problem of increased air bubbles caused by increased oil replenishment frequency. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of a prior art white oil supply system; Figure 2 This is a schematic diagram of the white oil supply system used in this invention.

[0020] In the diagram: 1-Station tank, 2-Supply tank, 3-Diaphragm pump, 4-Connecting valve, 5-Mold temperature controller, 6-Vertical mixer. Detailed Implementation

[0021] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0022] A method for producing zero-bubble melt for lithium battery separator production according to an embodiment of the present invention includes the following steps: (1) Set up a settling tank 1 and two supply tanks 2 as white oil tanks for the white oil injection system. Before normal production, fill both the settling tank 1 and the two supply tanks 2 with white oil that has been settling. (2) During normal production, the first supply tank supplies white oil to the extrusion system. When the liquid level of the first supply tank drops to the set low level, stop supplying oil and switch to the second supply tank to supply white oil. The settling tank 1 replenishes white oil to the first supply tank. (3) When the second supply tank supplies white oil, when the white oil injected into the first supply tank reaches the high level, settling and heating are performed. When the liquid level of the second supply tank drops to the set low level, switch to the first supply tank to supply white oil. The settling tank replenishes white oil to the second supply tank. When the white oil reaches the high level, settling and heating are performed. (4) The two supply tanks 2 supply oil in a cycle according to the above steps.

[0023] In this embodiment, when the supply tank supplies oil to the extrusion system, the temperature of the white oil in supply tank 2 is higher than that in the settling tank 1. The white oil in the tanks is heated by a mold temperature controller, and the temperature of the white oil in the tanks is usually kept consistent with the temperature of the mold temperature controller. The temperature of the white oil in the settling tank is 50-60°C, and the temperature of the white oil in the supply tank is 65-80°C. Taking a white oil temperature of 70°C in the supply tank as an example, after replenishing the oil, the temperature in the supply tank usually drops by 2-3°C. Therefore, heating the white oil in the supply tank with a mold temperature controller after replenishing the oil allows the white oil to quickly reach the required temperature. The low liquid level set for supply tank 2 is 300-500mm, and the high liquid level set for supply tank 2 is 1100-1300mm. The difference between the high and low liquid levels set for supply tank 2 is 600-1000mm (preferably 800mm). When the liquid level in the settling tank 1 falls below the set low level, oil is added to the settling tank 1. Once the high level is reached after oil addition, oil addition stops. The set low level for the settling tank 1 is 600-800 mm, and the set high level is 1000-1200 mm. The difference between the set high and low levels is 200-600 mm (preferably 400 mm). Both the settling tank 1 and the supply tank 2 use the same tank body with a jacket. The temperature of the white oil inside the tank is controlled by heating the jacket layer using a mold temperature controller 5. The maximum white oil capacity of the tank is 2000 L. Oil is added to the settling tank every 375 L of white oil consumed; oil is added to the supply tank 2 every 750 L of white oil consumed. The oil addition flow rate for both the settling tank 1 and the supply tank 2 is twice the maximum white oil flow rate used by the extruder.

[0024] In this embodiment, each settling tank 1 and supply tank 2 is equipped with a vertical stirrer 6. When the set high liquid level is reached after the settling tank and supply tank 2 are replenished with oil, and the tank is not in an oil supply state, the vertical stirrer 6 is started to stir the white oil in the tank. When the vertical stirrer 6 is started, the stirring frequency of the vertical stirrer 6 motor is set to 0-5Hz, and the stirring time is set to 0-3min.

[0025] When replenishing oil in supply tank 2, a pneumatic diaphragm pump 3 is used to pump white oil from the settling tank 1 into the oil filling port at the top of supply tank 2; when the pneumatic diaphragm pump 3 fails, the connecting valve 4 between the bottom of the settling tank 1 and the supply tank 2 is opened, and the white oil in the settling tank 1 flows by gravity to the supply tank 2 through the connecting valve 4.

[0026] This invention, through modifications to the white oil injection system, utilizes a secondary settling process and an auxiliary stirring system to significantly eliminate air bubbles during white oil supply, thereby preventing the formation of white spots. During normal production, when the liquid level in the first supply tank drops to a low level, oil supply stops, and the system switches to a second supply tank. Since it takes time for the white oil level in the second supply tank to drop to a low level, the white oil injected into the second supply tank undergoes sufficient settling and heating again. When the system switches back to the first supply tank, the settling tank replenishes the second supply tank, and this cycle continues. Therefore, the white oil in the supply tanks receives sufficient settling and heating, thus preventing the periodic appearance of white spots caused by unresolved air bubbles generated during replenishment.

[0027] Because the white oil injected into the settling tank contains many air bubbles, the existing white oil injection system uses a high temperature setting in the settling tank, which is not conducive to bubble elimination and increases the risk of white spots. The dual supply tank setup allows the settling tank to be set at a lower temperature, improving the bubble elimination effect. Since the white oil in the settling tank does not need to be used immediately after being added to the supply tank, there is sufficient time for it to heat up to the set temperature of the supply tank.

[0028] Due to the significant difference between the high and low liquid levels within the tank, the oil replenishment frequency is reduced. Because the white oil temperature in the settling tank is low, injecting a large amount of white oil into the supply tank will cause a substantial drop in the overall temperature of the white oil in the supply tank. If the white oil in one supply tank is not heated to the set temperature, while the other supply tank reaches a low liquid level and switches over, the low-temperature white oil in the supply tank will be sent to the extruder, which is detrimental to the elimination of air bubbles inside the extruder. This invention sets a smaller difference between the high and low liquid levels, increasing the oil replenishment frequency, thereby solving the problem of white oil temperature fluctuations.

[0029] This invention features vertical agitators installed inside each tank to help eliminate air bubbles generated after oil replenishment, thus preventing an increase in air bubbles due to increased oil replenishment frequency and improving the settling effect. The vertical agitator consists of three U-shaped stainless steel supports, and through constant-speed and timed stirring, it effectively eliminates small air bubbles generated in the initial stage of white oil injection.

[0030] The operating mode of each tank in this embodiment is as follows: Under normal circumstances, the external engineer pumps white oil into the settling tank. When the supply tank needs replenishment, a pneumatic diaphragm pump pumps white oil into the supply tank. After the white oil level reaches 1100mm, the vertical agitator starts and agitates according to the set frequency and time. If the pneumatic diaphragm pump is damaged, the connecting valve at the bottom of the tank can be opened, allowing the white oil in the settling tank to flow into the supply tank by gravity, or the external engineer can automatically pump white oil into the supply tank. The settling tank can automatically replenish the supply tank. When the supply tank needs replenishment, the bottom discharge valve automatically switches, and the replenishment valve at the oil inlet at the top of the supply tank automatically opens.

[0031] The density of the white oil is 0.85 g / ml. The diaphragm pump flow rate is 200 L / min ÷ 0.85 g / ml × 60 min = 14117 kg / h. The extruder oil supply is the sum of the two white oil injections. The extruder injects white oil in two stages. The first injection mixes with the raw material, while the second injection lubricates the raw material. The weight ratio of the first to second injections is approximately 65:15, meaning the total white oil content is 75-80% of the raw material. The extruder solids content is 80%, and the maximum equipment usage is 910 kg / h. =728Kg / h; The settling tank and supply tank use the same tank body with a heating structure. The maximum capacity of white oil in each tank is 2000L, the tank height is 1600mm, and the white oil replenishment level range is 100-500mm, usually 600mm. Therefore, the normal operating oil level in the tank is 600mm, and the normal oil volume is 600mm*(2000L÷1600mm)=750L; Tank replenishment flow rate = 2×Extruder maximum white oil flow rate 2000L; Settling tank replenishment level setting For the 800-1100mm section, replenish oil for every (2000L ÷ 1600mm) * 300mm = 375L consumed; replenish oil in the supply tank for every 750L consumed, calculated based on the extruder's maximum extrusion rate: 728Kg / h ÷ 0.85 ÷ 60min = 14L / min; the time for each supply of white oil to the settling tank is 750L ÷ 14L / min = 53min; the oil replenishment time in the settling tank is 750L ÷ 200L / min = 3.8min; the settling time reaches approximately 50 minutes.

[0032] This invention, when applied to actual diaphragm production, shows the following improvement effect on diaphragm spot formation: The spot ratio is the percentage of diaphragm rolls with spots appearing during normal production, calculated as the number of diaphragm rolls with spots appearing each month ÷ the total number of diaphragm rolls produced each month × 100%. As shown in the table and from actual production, this invention effectively reduces the spot ratio, increases product extrusion volume, and ensures the melt remains compact, thereby improving product quality and significantly increasing the yield of A-grade products.

[0033] Table 1 Improvement effect of circular spots

[0034] The circular spots on the diaphragm are detected using a high-precision defect detector, which is installed before the winding machine. A high-brightness, stable, and uniform backlight is placed below the diaphragm, and a high-resolution (50 nm) linear or area array CCD camera (Kunshan Gaopin Precision Instruments Co., Ltd., GP-300C) and matching lens are mounted above the diaphragm to ensure that the field of view covers the width of the diaphragm. As the diaphragm passes through, the circular spots are classified according to the set brightness threshold, the grayscale value (grayscale value within the range of 50-255 is judged as a circular spot), and the area (<4mm). 2The system automatically identifies abnormally bright areas in an image, marks and records the location, size, and quantity of bright spots and defects, and issues an alarm or triggers the sorting device.

Claims

1. A method for producing zero-bubble melt for lithium battery separator production, characterized in that: It includes the following steps: (1) Set up a settling tank and two supply tanks as white oil tanks for the white oil injection system. Before normal production, fill the settling tank and the two supply tanks with white oil that has been settling. (2) During normal production, the first supply tank supplies white oil to the extrusion system. When the liquid level in the first supply tank drops to the set low level, stop supplying oil and switch to the second supply tank to supply white oil. The settling tank replenishes white oil to the first supply tank. (3) When the second supply tank supplies white oil, when the white oil injected into the first supply tank reaches the high level, settling and heating are performed. When the liquid level in the second supply tank drops to the set low level, switch to the first supply tank to supply white oil. The settling tank replenishes white oil to the second supply tank. When the white oil reaches the high level, settling and heating are performed. (4) The two supply tanks supply oil in a cycle according to the above steps.

2. The zero-bubble melt production method for lithium battery separator production according to claim 1, characterized in that: When the supply tank supplies oil to the extrusion system, the temperature of the white oil in the supply tank is higher than the temperature of the white oil in the settling tank.

3. The zero-bubble melt production system for lithium battery separator production according to claim 1, characterized in that: The supply tank is set with a low liquid level of 300-500mm and a high liquid level of 1100-1300mm. The difference between the high and low liquid levels is 600-1000mm.

4. The zero-bubble melt production method for lithium battery separator production according to claim 1, characterized in that: When the liquid level in the settling tank is lower than the set low level, add oil to the settling tank. When the liquid level in the settling tank reaches the high level after adding oil, stop adding oil.

5. The zero-bubble melt production method for lithium battery separator production according to claim 4, characterized in that: The set low liquid level of the settling tank is 600-800mm, the set high liquid level of the settling tank is 1000-1200mm, and the difference between the set high liquid level and the set low liquid level of the settling tank is 200-600mm.

6. The zero-bubble melt production system for lithium battery separator production according to claim 4, characterized in that: Both the settling tank and the supply tank use the same tank body, with a maximum white oil capacity of 1900-2100L. The settling tank is replenished every 350-400L of white oil consumed, and the supply tank is replenished every 700-800L of white oil consumed.

7. The zero-bubble melt production method for lithium battery separator production according to claim 4, characterized in that: The oil replenishment flow rates of both the settling tank and the supply tank are equal to twice the maximum flow rate of white oil used by the extruder.

8. The zero-bubble melt production method for lithium battery separator production according to claim 1, characterized in that: Each settling tank and supply tank is equipped with a vertical agitator. When the settling tank and supply tank reach the set high liquid level after being replenished with oil, and are not in the oil supply state, the vertical agitator is activated to agitate the white oil in the tank.

9. The zero-bubble melt production method for lithium battery separator production according to claim 7, characterized in that: When starting the vertical mixer, the mixing frequency of the vertical mixer motor is set to 0-5Hz, and the mixing time is set to 0-3min.

10. The zero-bubble melt production method for lithium battery separator production according to claim 1, characterized in that: A pneumatic diaphragm pump is used to pump white oil from the settling tank into the oil inlet at the top of the supply tank. When the pneumatic diaphragm pump fails, the connecting valve between the bottom of the settling tank and the supply tank is opened, and the white oil in the settling tank flows by gravity into the supply tank through the connecting valve.

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