Real time film temperature monitoring and associated equipment for polymer film production

Abstract

The present disclosure relates to the real time monitoring of film temperature during the production of biaxially oriented films composed of polyolefins or other polymers having a strong IR absorption band in the 3.0-3.5 um wavelength range. The real time monitoring of film temperature can be achieved via one or more IR cameras in placed in connection with a machine direction orientation (MDO) unit and / or a transverse direction orientation (TDO) unit. Real time IR monitoring of film temperature helps to improve the manufacturability, performance, and yield of biaxially oriented films.

Description

Real Time Film Temperature Monitoring and Associated Equipment for Polymer Film ProductionRelated Applications

[0001] This application claims priority to U.S. Provisional Application No 63 / 682,599, filed on August 13, 2024, and titled REAL TIME FILM TEMPERATURE MONITORING AND ASSOCIATED EQUIPMENT FOR POLYMER FILM PRODUCTION, which is incorporated herein by reference in its entirety.Technical Field

[0002] The present invention relates to the real time monitoring of film temperature during the production of biaxially oriented cast or blown films composed of polyolefins or other polymers having a strong infrared (IR) absorption band in the 3.0-3.5 urn wavelength range. This approach improves upon current technology in which thermocouples are distributed and monitored throughout a transverse direction orientation (TDO) unit to monitor local air temperature. Real time IR monitoring of film temperature helps to improve the manufacturability, performance, and yield of biaxially oriented films such as Li battery separatorsBackground

[0003] Separators are an integral part of the performance, safety, and cost of lithium-ion batteries. During normal operation, the principal functions of the separator are to prevent electronic conduction (i.e., shorts or direct contact) between the anode and cathode while permitting ionic conduction via the electrolyte. Under abuse conditions, such as external short circuit or overcharge, the separator is required to shutdown at temperatures well below where thermal runaway can occur Shutdown results from the collapse of pores in the separator due to melting and viscous flow of the polymer, thus slowing down or stopping ion flow between the electrodes. Nearly all Li-ion battery separators contain polyethylene as part of a single- or multi-layer construction so that shutdown begins at ~130°C, the melting point of polyethylene.

[0004] Separators for the lithium-ion market are presently manufactured via “dry” or “wet” processes. In the dry process, polypropylene (PP) or polyethylene (PE) is extruded into a thin sheet and subjected to rapid drawdown The sheet is then annealed at 10-25 °C below the polymer melting point such that crystallite size and orientation are controlled. Next, the sheet is rapidly stretched in the machine direction (MD) to achieve slit-like pores or voids In some cases, the sheet is further stretched in the transverse direction (TD) to provide for biaxial orientation. Trilayer PP / PE / PP separators produced by the dry process are commonly used in lithium-ion rechargeable batteries.

[0005] Wet process separators composed of high molecular weight polyethylene are produced by extrusion of an oil / polymer mixture at elevated temperature, followed by phase separation, biaxial stretching, and extraction of the process oil (i.e., plasticizer). The resultant separators have elliptical or spherical pores with good mechanical properties in both the machine and transverse directions. PE-based separators manufactured this way using cast film or blown film technologies have found wide use in Li-ion batteries14898-5692-3229 1

[0006] In the cast film approach for battery separators or packaging film, the general trend is to increase productivity by going wider and faster. Such films at their maximum biaxial stretch ratio could be > 7 meters wide while held taught with mechanical clips in transverse direction orientation (TDO) equipment made by Bruckner Machinebau, Marchante, Dornier, or Japanese Steel Works.

[0007] Heretofore, no consideration has been given to real time monitoring of the film temperature at specific positions in the machine and / or transverse direction orientation equipment (MDO and / or TDO equipment). In this disclosure, infrared thermal imaging cameras (IR cameras) are integrated into the MDO and / or TDO equipment at specific positions to monitor film temperature and identify thermal gradients in either the transverse or machine directionSummary

[0008] An object of the present invention is to achieve real time monitoring of film temperature during machine direction, transverse direction, or biaxial orientation of a polymer film having a strong IR absorption band in the 3.0-3.5 urn wavelength range. In the case of biaxial orientation, it can be accomplished either sequentially or simultaneously. As used herein, “real time monitoring” is intended to mean that a property (e.g., temperature) is being monitored as the film is being processed or subjected to processing equipment The terms “film” and “sheet” can be used interchangeably

[0009] In a first embodiment of the disclosure, IR cameras (e.g , Fluke) are positioned in a transverse direction orientation (TDO) unit such that the temperature of the polymer film is monitored after the preheat zone, but prior to transverse stretching, and then in a second position after the maximum film width and transverse stretch has been achieved

[0010] In a second embodiment of the disclosure, IR cameras (e.g., Fluke) are positioned in a machine direction orientation (MDO) unit after the preheat rolls, but prior to machine direction stretching, and then in a second position after the maximum elongation and machine direction stretch has been achieved.

[0011] In a third embodiment of the disclosure, IR cameras (e.g., Fluke) are positioned to secure a radial image of film temperature for a polymer “bubble” created by extruding a polymer at elevated temperature through an annular die using a blown film process and equipment.

[0012] Additional objects and advantages of this disclosure will be apparent from the following detailed description of embodiments thereof which proceeds with reference to the accompanying drawingsBrief Description of the Drawings

[0013] Figure 1. Schematic of cast film “wet process” for the manufacture of battery separator films for Li batteries.

[0014] Figure 2. Schematic of blown film “wet process” for the manufacture of battery separator films for Li batteries.

[0015] Figure 3. IR image of blown film “bubble” composed of 45 wt % polyethylene and 55 wt.% naphthenic process oilDetailed Description

[0016] Wet process separators composed of high molecular weight polyethylene are produced by extrusion of an oil / polymer mixture at elevated temperature, followed by phase separation, biaxialstretching (stretching in both the machine and transverse directions), and extraction of the process oil (i.e., plasticizer) The resultant separators have elliptical or spherical pores with good mechanical properties in both the machine and transverse directions. PE-based separators manufactured this way using cast film or blown film technologies have found wide use in Li-ion batteries.

[0017] Figures 1 and 2 show schematics for the cast film and blown film processes, respectively, for the manufacture of Li battery separator films.

[0018] As shown in Figure 1, a common cast film process can include various combinations of the following: a polymer extruder (such as a twin screw extruder), a die, a roll stack unit (e.g., casting roll unit, chill roll, etc ), a machine direction orientation (MDO) unit, a transverse direction orientation (TDO) unit, a solvent extractor unit, a drier unit (e.g., air drier), a heat setting unit, a pull roll unit, and a winder unit. As can be appreciated more or less components can be included and thus the schematic in Figure 1 is intended only to be exemplary.

[0019] In a typical machine direction orientation (MDO) process, a polymer film is delivered to a machine direction orientation (MDO) unit. Prior to being stretched, the film can be heated or preheated in a preheat zone to a desired temperature. The film can thereafter be stretched and oriented in the machine direction in a machine stretching zone, which can involve passing the film through a series of rollers running at different speeds to achieve a desired stretch ratio. In the present disclosure, one or more IR cameras can be integrated with, or positioned in or adjacent to, the machine direction orientation (MDO) unit to monitor the temperature of the polymer prior to and / or after it is stretched in the machine direction stretching zone to identify any thermal gradients. For instance, in some embodiments, one or more IR cameras are positioned in a first position which is after the preheat zone and just prior to the machine direction stretching zone to monitor the real time temperature as the film enters the machine direction stretching zone, and one or more IR cameras are positioned in a second position that is just after the machine direction stretching zone to monitor the real time temperature as the film exits the machine direction stretching zone.

[0020] In a typical transverse direction orientation (TDO) process, the polymer film is delivered to a transverse direction orientation (TDO) unit. Prior to being stretched, the film can be heated or preheated in a preheat zone to a desired temperature. The film can thereafter be stretched and oriented in the transverse direction in a transverse stretching zone, which can involve use of a tenter frame or various chains and clips to stretch the film in the transverse direction and achieve a desired stretch ratio In the present disclosure, one or more IR cameras can be integrated with, or positioned in or adjacent to, the transverse direction orientation (TDO) unit to monitor the temperature of the polymer prior to and / or after it is stretched in the transverse direction stretching zone to identify any thermal gradients. For instance, in some embodiments, one or more IR cameras are positioned in a first position which is after the preheat zone and just prior to the transverse direction stretching zone to monitor the real time temperature as the film enters the transverse direction stretching zone, and one or more IR cameras are positioned in a second position that is just after the transverse direction stretching zone to monitor the real time temperature as the film exits the transverse direction stretching zone. The sheet is considered as being biaxially oriented after it has been stretched in both the machine direction and the transverse direction.

[0021] As can be appreciated, in some embodiments, the temperature of the polymer film is monitored in real time in connection with both the machine and transverse orientation processes. In other embodiments, the temperature of the polymer film is only monitored in real time in connection with one of the machine or transverse orientation processes.

[0022] As shown in Figure 2, a common blown film process can include various combinations of the following: a polymer extruder (such as a twin screw extruder), an annular die and blown film unit comprising an air ring that forms a bubble-like film structure, a solvent extractor unit, a drier unit (e.g., air drier), a machine direction orientation (MDO) unit, a transverse direction orientation (TDO) unit, a pull roll unit, and a winder unit As can be appreciated more or less components can be included and thus the schematic in Figure 2 is intended only to be exemplary.

[0023] In a typical blown film process, the extruded polymer is fed through an annular die and a blown film unit comprising an air ring is used to inflate and / or blow the extruded polymer into a bubble-like film structure in a film blowing zone. As the film is inflated (i.e , blown), the film can stretch in both the longitudinal (e g., machine direction), and circumferential (e.g., transverse direction), to achieve a biaxially oriented bubble or film. If desired, one or more IR cameras can also be integrated with, or positioned in or adjacent to, the blown film equipment unit to monitor the temperature of the polymer prior to, during, and / or after it is inflated or biaxially stretched to identify any thermal gradients. For example, one or more IR cameras can be positioned proximal the start of the blown film unit, and / or proximal the end of the blown film unit. In some embodiments, the one or more IR cameras can be positioned to provide a 360 degree temperature of the polymer bubble.

[0024] If desired, one or more IR cameras can also be positioned in or adjacent an additional machine direction orientation (MDO) unit to monitor the temperature of the polymer prior to and / or after it is additionally stretched in the machine direction to identify any thermal gradients (as previously discussed with Figure 1 ), and / or one or more IR cameras can also be positioned in or adjacent an additional transverse direction orientation (TDO) unit to monitor the temperature of the polymer prior to and / or after it is additionally stretched in the transverse direction to identify any thermal gradients (as previously discussed with Figure 1). It will thus be appreciated that additional real time monitoring of the polymer temperature can be employed as desired throughout the film manufacturing process.

[0025] In some embodiments, the polymer used in the film making process comprises polyethylene For instance, the polyethylene used in the manufacture of battery separators can range in molecular weight between 500,000 g / mol to 10 million g / mol. Representative polymers include 150 U and VH035 from KPIC (Korea), GUR 4120 and 4012 from Celanese (USA), and UH650 from Asahi-Kasei (Japan). However, it will be appreciated that the present disclosure is not limited to polymers used for battery separators. Rather, the processes disclosed herein are also applicable to any polymer films having an IR absorption band in the 3.0-3.5 urn range, including, but not limited to, polyethylenes, polypropylenes, polyethylene terephthalates, and combinations thereof Indeed, the real time monitoring of film temperature can be advantageous for the manufacture of other polymer films and are not limited to films for battery separators.

[0026] The plasticizer employed in the present invention is a nonevaporative solvent for the polymer, and is preferably a liquid at room temperature. The plasticizer has little or no solvating effect on the polymer at room temperature; it performs its solvating action at temperatures at or above the softening temperature of the polymer. For polyethylene homopolymers, the solvating temperature would be above about 180° C, and preferably in the range of between about 200° 0 and about 225° C. It is preferred to use a processing oil, such as a paraffinic oil, naphthenic oil, aromatic oil, or a mixture of two or more such oils.

[0027] Examples of suitable processing oils include: Risella 430X by Shell Oil Company; and Hydrocal™ 800 by Calumet Specialty Products; and Nytex 820 by Nynas Inc.

[0028] The polymer I oil mixture can be extruded through a sheet die or annular die, and then biaxially-oriented to form a thin, oil-filled film. Figure 3 shows an exemplary IR image and corresponding temperature profile for a blown film “bubble” composed of 45 wt % polyethylene and 55 wt.% naphthenic process oil. The emissivity of the FLIR camera for the IR image of FIG. 3 was set at 0.96.

[0029] Any solvent that is compatible with the oil can be used for the extraction step, provided it has a boiling point that makes it practical to separate the solvent from the plasticizer by distillation. Such solvents include 1,1 ,2 trichloroethylene, perchloroethylene, l,2-dichloroethane, 1,1,1-trichloroethane, 1 ,1 ,2-trichloroethane, methylene chloride, hexane, heptane, decane, and toluene. In some cases, it is desirable to select the processing oil such that any residual oil in the polymer sheet after extraction is electrochemically inactive.

[0030] After the solvent is removed via hot air drying or other means, the resultant porous polymer sheet is further stretched and annealed prior to winding into rolls of battery separator film.

Claims

What is claimed is:

1. An apparatus for real time temperature monitoring of a polymer film during a film forming process, comprising: a transverse direction orientation unit having one or more integrated IR cameras, the one or more integrated IR cameras being configured to measure real time film temperature of a polymer film having an absorption band in the 3.0-3.5 urn range.

2. The apparatus of claim 1, wherein the transverse direction orientation unit comprises a preheat zone and a transverse stretching zone, wherein a first IR camera is positioned after the preheat zone but prior to the transverse stretching zone, and a second IR camera is positioned after the transverse stretching zone where a maximum film width has been achieved.

3. The apparatus of claim 1 or 2, wherein the polymer film comprises one or more of polyethylene, polypropylene, polyethylene terephthalate, or combinations thereof.

4. The apparatus of claim 3, wherein the polymer film further comprises a plasticizer or process oil.

5. The apparatus of any one of claims 1-4, further comprising: a machine direction orientation unit having one or more integrated IR cameras, the one or more integrated IR cameras being configured to measure real time film temperature of the polymer film6. An apparatus for real time temperature monitoring of a polymer film during a film forming process, comprising: a machine direction orientation unit having one or more integrated IR cameras, the one or more integrated IR cameras being configured to measure real time film temperature of a polymer film having an absorption band in the 3 0-3 5 urn range7. The apparatus of claim 6, wherein the machine direction orientation unit comprises a preheat zone and a machine stretching zone, wherein a first IR camera is positioned after the preheat zone but prior to the machine stretching zone, and a second IR camera is positioned after the machine stretching zone where a maximum film elongation has been achieved.

8. The apparatus of claim 6 or 7, wherein the polymer film comprises one or more of polyethylene, polypropylene, polyethylene terephthalate, or combinations thereof.9 The apparatus of claim 8, wherein the polymer film further comprises a plasticizer or process oil.

10. The apparatus of any one of claims 6-9, further comprising: a transverse direction orientation unit having one or more integrated IR cameras, the one or more integrated IR cameras being configured to measure real time film temperature of the polymer film11. An apparatus for real time temperature monitoring of a polymer film during a blown film forming process, comprising: a blown film unit comprising an air ring, the blown film unit having one or more integrated IR cameras being configured to measure real time film temperature of a polymer film having an absorption band in the 3.0-3.5 urn range.

12. The apparatus of claim 11 , wherein the IR cameras are positioned to give a 360 degree temperature profile of the polymer film as it is in the form of a polymer bubble passing through the blown film unit.

13. The apparatus of claim 11 or 12, wherein the polymer film comprises polyethylene, polypropylene, polyethylene terephthalate, or combinations thereof.

14. The apparatus of claim 13, wherein the polymer film further comprises a plasticizer or process oil.

15. A method for real time temperature monitoring of a polymer film during a film forming process, comprising: extruding a polymer film; biaxially orienting the polymer film, wherein biaxially orienting the polymer film comprises machine direction orientation and transverse direction orientation; monitoring the temperature of the polymer film having an absorption band in the 3.0-3 5 urn range with one or more IR cameras.

16. The method of claim 15, wherein the film forming process comprises a blown film process, and wherein the polymer film is biaxially oriented in a blown film unit17. The method of claim 16, wherein the one or more IR cameras are integrated with the blown film unit18. The method of claim 16, wherein the one or more IR cameras are integrated with at least one of a transverse direction orientation unit or a machine direction orientation unit.

19. The method of claim 18, wherein the one or more IR cameras are integrated with the transverse direction orientation unit, wherein the transverse direction orientation unit comprises a preheat zone and a transverse stretching zone, wherein a first IR camera is positioned after the preheat zone but prior to the transverse stretching zone, and a second IR camera is positioned after the transverse stretching zone where a maximum film width has been achieved.

20. The method of claim 18, wherein the one or more IR cameras are integrated with the machine direction orientation unit, wherein the machine direction orientation unit comprises a preheat zone and a machine stretching zone, wherein a first IR camera is positioned after the preheat zone but prior to the machine stretching zone, and a second IR camera is positioned after the machine stretching zone where a maximum film elongation has been achieved21. The method of claim 18, wherein the one or more IR cameras are integrated with a transverse direction orientation unit and a machine direction orientation unit.

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