Modified linear polyurethane resin and preparation method thereof, and preparation method of swelling adhesive tape

Abstract

The invention provides modified linear polyurethane resin and a preparation method thereof, and a preparation method of a swelling adhesive tape, the preparation method of the modified linear polyurethane resin comprises the following steps: mixing and heating isocyanate, terminal dihydric alcohol and dibutyltin dilaurate to obtain thermoplastic polyurethane resin; the preparation method comprises the following steps: adding alkaloid with double amino functional groups into N-methyl pyrrolidone, dissolving, mixing with thermoplastic polyurethane resin, heating to generate a chain-extended linear polyurethane solution, heating, and drying to obtain the modified linear polyurethane resin. The hard segment structure of the modified linear polyurethane resin is loosely arranged, so that the hot melting fluidity of the modified linear polyurethane resin is improved, the soft segment structure is an amino-terminated aliphatic chain, chain segment movement at low temperature is promoted, the glass transition temperature is reduced, and the hard segment structure and the soft segment structure improve the processing plasticity, so that the modified linear polyurethane resin is suitable for tape casting extrusion; more permeation channels are provided through loose hard segment arrangement and weak hydrogen bond interaction, and the expansion rate of the modified linear polyurethane resin is increased.

Description

Technical Field

[0001] The present disclosure relates to the technical field of polyurethane materials, and in particular to a modified linear polyurethane resin and a preparation method thereof, as well as a preparation method of a swelling tape. Background Art

[0002] As people continue to pursue high-energy-density power batteries, battery size has gradually increased, and the voids within the batteries have correspondingly increased. These voids can cause internal component movement, battery short circuits, and expansion, among other failures. Swelling tape, a material used to fill voids in lithium-ion batteries, primarily interacts with the electrolyte, expanding three-dimensionally. This allows it to tightly fill the voids, securely securing the battery cell to the steel casing and improving the battery's seismic safety.

[0003] Current swelling tapes generally shrink longitudinally when exposed to electrolyte, causing the expanded tape to concentrate in the middle of the battery cell, leaving both ends of the cell exposed and unable to provide protection. The expanded tape undergoes vitrification at low temperatures (below 5°C) and degrades at high temperatures (above 120°C), posing a significant safety threat to lithium-ion batteries. Casting technology offers better film uniformity and quality. Current swelling tapes are generally coated with polyurethane resins, but polyurethane resins have a high melt viscosity, and the melt is not completely plasticized and easily degraded during melting, making film formation difficult and unsuitable for cast-type processing.

[0004] Comparative document CN202411328616.1 discloses a high-temperature resistant swelling tape for lithium batteries and its preparation method, comprising a substrate film and an adhesive composite; the substrate film is a three-layer composite film consisting of an outer layer, an intermediate layer, and an inner layer; the outer layer is composed of 75-95wt% polyethylene terephthalate-ethylene glycol-1,4-cyclohexane dimethanol copolymer and 5-25wt% compatibilizer; the intermediate layer is polycarbonate polyurethane; and the inner layer is composed of 70-90wt% ethylene-acrylate copolymer and 10-30wt% compatibilizer. However, this solution uses a polycarbonate polyurethane intermediate layer, which cannot solve the problem of vitrification of the expanded tape at low temperatures, and cannot form a film of uniform thickness in the casting process.

[0005] Another example is a high-temperature resistant swellable tape disclosed in the comparative document CN202211518383.2, which includes a base layer and a pressure-sensitive adhesive layer. The material used to form the base layer is a thermoplastic polyurethane with a Shore hardness of not less than 70D; the thermoplastic polyurethane includes at least one of polyether thermoplastic polyurethane and polyester thermoplastic polyurethane. The high-temperature resistant swellable tape provided in the present invention can swell at room temperature or a relatively high temperature (not exceeding 85°C), and the shape remains unchanged after swelling, and there will be no defects in the shape after cooling. The thermoplastic polyurethane in this scheme includes polyether thermoplastic polyurethane and polyester thermoplastic polyurethane, which also cannot solve the problem of vitrification of the expanded tape at low temperature, and cannot be applied to the film-forming process of the casting method to obtain a swollen tape with better film uniformity. Summary of the Invention

[0006] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a hot-melt modified linear polyurethane resin with good fluidity, good processing plasticity, low glass transition temperature and suitable for cast extrusion, a modified linear polyurethane resin and a preparation method, as well as a preparation method for a swelling tape.

[0007] The purpose of this disclosure is achieved through the following technical solutions:

[0008] A modified linear polyurethane resin, wherein the modified linear polyurethane resin comprises one of the following structural formulas:

[0009]

[0010] A method for preparing a modified linear polyurethane resin, characterized in that it is used to prepare the modified linear polyurethane resin described in the above embodiment, comprising the following steps:

[0011] Isocyanate, terminal diol and dibutyltin dilaurate are mixed and heated to obtain thermoplastic polyurethane resin after polyaddition reaction;

[0012] The alkaloid with diamino functional groups is added to N-methylpyrrolidone and dissolved, and then mixed with thermoplastic polyurethane resin and heated to generate a chain-extended linear polyurethane solution after chain extension reaction;

[0013] The chain-extended linear polyurethane solution is heated and dried to obtain a modified linear polyurethane resin.

[0014] In one embodiment, the isocyanate includes at least one of diphenylmethane-4,4'-diisocyanate and polymeric polyphenylmethane polyisocyanate.

[0015] In one embodiment, the terminal diol comprises at least one of ethylene glycol and polyethylene glycol.

[0016] In one embodiment, the diamino functional group alkaloid comprises at least one of lysine, asparagine, glutamine and arginine.

[0017] In one embodiment, the molar ratio of the NCO groups of the isocyanate to the OH groups of the terminal diol in the thermoplastic polyurethane resin is 1.5:1 to 2.5:1.

[0018] In one embodiment, the alkaloid with a diamino functional group is dissolved in N-methylpyrrolidone and then mixed with a thermoplastic polyurethane resin and heated. The mass ratio of the thermoplastic polyurethane resin to the alkaloid with a diamino functional group is 3.5:1 to 6:1.

[0019] In one embodiment, the glass transition temperature of the modified linear polyurethane resin is less than -60°C.

[0020] A method for preparing a swelling tape, characterized by comprising the following steps:

[0021] Providing a modified linear polyurethane resin obtained by the preparation method of the modified linear polyurethane resin described in any of the above embodiments;

[0022] crushing the modified linear polyurethane resin to obtain crushed modified linear polyurethane resin;

[0023] placing the crushed modified linear polyurethane resin into a casting machine and heating it, and casting and extruding the molten modified linear polyurethane resin to form a swelling tape precursor film;

[0024] The swelling tape precursor film is coated with pressure-sensitive adhesive on both sides and attached to a release film to obtain a swelling tape.

[0025] In one embodiment, the swelling ratio of the swollen precursor film is 100%-350%.

[0026] Compared with the prior art, the present disclosure has at least the following advantages:

[0027] The modified linear polyurethane resin has a linear structure. The hard segment structure of the modified linear polyurethane resin is loosely arranged, which weakens the intermolecular forces and improves the fluidity of the hot-melt modified linear polyurethane resin. The linear molecular chain has less intermolecular entanglement, making the molecular chain segments relatively easy to move, thereby lowering the glass transition temperature of the modified linear polyurethane resin. The soft segment structure of the modified linear polyurethane resin is an amino-terminated fatty chain. The amino group at the end of the fatty chain forms a weak hydrogen bond with the hard segment, further weakening the hard segment's bond to the soft segment, promoting segment movement at low temperatures, and further lowering the glass transition temperature of the modified linear polyurethane resin. The alternating hard and soft segment structures of the modified linear polyurethane resin improve processing plasticity, making the modified linear polyurethane resin suitable for cast extrusion. The loose hard segment arrangement and weak hydrogen bonding provide more penetration channels for solvent molecules, accelerating solvent diffusion. The linear polyurethane molecular chains are less entangled, and the resistance to chain segment movement is low, thereby improving the expansion rate of the modified linear polyurethane resin. The amino-terminated fatty chain increases the molecular chain length, thereby improving the thermal degradation resistance and electrolyte corrosion resistance of the modified linear polyurethane resin.

[0028] The modified linear polyurethane resin has a lower viscosity after heating, improved thermal stability and better processing plasticity, so that the modified linear polyurethane resin is extruded into a swollen precursor film with better uniformity in a casting machine. The swollen precursor film has a wide temperature range of use, high expansion, resistance to solvent corrosion and good tensile strength. The swollen precursor film extruded by casting has good uniformity, and the swollen tape obtained by adhering the swollen precursor film to a release film has a higher surface flatness and better transparency. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the technical solutions of the embodiments of the present disclosure, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present disclosure and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without creative work.

[0030] Figure 1 1 is a flow chart of the steps of a method for preparing a modified linear polyurethane resin according to an embodiment;

[0031] Figure 2 A flowchart of a method for preparing a swelling tape according to an embodiment of the present invention;

[0032] Figure 3 is the DSC graph of modified linear polyurethane resin;

[0033] Figure 4 The test diagrams of the swollen precursor film of Example 1 before and after immersion;

[0034] Figure 5 This is a diagram showing the expansion of the swollen precursor film after the electrolyte is dropped into it in Example 1. DETAILED DESCRIPTION

[0035] To facilitate understanding of the present disclosure, a more comprehensive description of the present disclosure will be provided below with reference to the accompanying drawings. The accompanying drawings illustrate preferred embodiments of the present disclosure. However, the present disclosure can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and comprehensive understanding of the disclosure.

[0036] It should be noted that when an element is referred to as being "fixed to" another element, it may be directly attached to the other element or there may be an intermediate element. When an element is referred to as being "connected to" another element, it may be directly connected to the other element or there may be an intermediate element. The terms "vertical," "horizontal," "left," "right," and similar expressions used herein are for illustrative purposes only and do not represent the only implementation methods.

[0037] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this disclosure pertains. The terms used herein in the specification of this disclosure are intended only to describe specific embodiments and are not intended to limit this disclosure. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0038] In order to better understand the technical solutions and beneficial effects of the present disclosure, the present disclosure is further described in detail below with reference to specific embodiments:

[0039] A modified linear polyurethane resin according to an embodiment of the present invention comprises one of the following structural formulas:

[0040]

[0041] The modified linear polyurethane resin has a linear structure. The hard segment structure of the modified linear polyurethane resin is loosely arranged, which weakens the intermolecular forces and improves the fluidity of the hot-melt modified linear polyurethane resin. The linear molecular chain has less intermolecular entanglement, making the molecular chain segments relatively easy to move, thereby lowering the glass transition temperature of the modified linear polyurethane resin. The soft segment structure of the modified linear polyurethane resin is an amino-terminated fatty chain. The amino group at the end of the fatty chain forms a weak hydrogen bond with the hard segment, further weakening the hard segment's bond to the soft segment, promoting segment movement at low temperatures, and further lowering the glass transition temperature of the modified linear polyurethane resin. The alternating hard and soft segment structures of the modified linear polyurethane resin improve processing plasticity, making the modified linear polyurethane resin suitable for cast extrusion. The loose hard segment arrangement and weak hydrogen bonding provide more penetration channels for solvent molecules, accelerating solvent diffusion. The linear polyurethane molecular chains are less entangled, and the resistance to chain segment movement is low, thereby improving the expansion rate of the modified linear polyurethane resin. The amino-terminated fatty chain increases the molecular chain length, thereby improving the thermal degradation resistance and electrolyte corrosion resistance of the modified linear polyurethane resin.

[0042] like Figure 1 As shown, the present application also provides a method for preparing a modified linear polyurethane resin, which is used to prepare the modified linear polyurethane resin described in any of the above embodiments, comprising the following steps:

[0043] S101: mixing isocyanate, terminal diol, and dibutyltin dilaurate, heating them, and performing a polyaddition reaction to obtain a thermoplastic polyurethane resin;

[0044] S103: adding an alkaloid having a diamino functional group to N-methylpyrrolidone, dissolving the alkaloid, and then mixing the alkaloid with a thermoplastic polyurethane resin and heating the mixture to generate a chain-extended linear polyurethane solution after a chain extension reaction;

[0045] S105 heats and dries the chain-extended linear polyurethane solution to obtain a modified linear polyurethane resin.

[0046] In this embodiment, isocyanate and terminal diols undergo gradual addition polymerization under the catalysis of dibutyltin dilaurate to form a thermoplastic polyurethane resin with an alternating structure of soft segments and hard segments; an alkaloid with a diamino functional group reacts with the isocyanate end groups of the thermoplastic polyurethane resin to produce an extended linear polyurethane; and the extended linear polyurethane solution is heated and dried to rapidly volatilize the water, ammonia, and N-methylpyrrolidone produced during the reaction, thereby obtaining a modified linear polyurethane resin with higher purity.

[0047] It is understood that the alkaloid with a diamino functional group is an amino-terminated fatty chain extender. The chain extension forms a modified linear polyurethane resin with a soft amino-terminated fatty chain. The amino-terminated fatty chain increases the flexibility of the molecular chain, lowers the glass transition temperature of the modified linear polyurethane resin, and improves its low-temperature flexibility. The amino-terminated fatty chain extender can react with the isocyanate groups in the polyurethane prepolymer to form longer molecular chains, thereby increasing the molecular weight of the polyurethane. Longer molecular chains are more resistant to chain breakage during thermal degradation. Due to the increased thermal stability and improved processing plasticity, the processing window of the modified linear polyurethane resin is widened. This enables the material to be processed by cast extrusion over a wider temperature and pressure range.

[0048] The above-mentioned preparation method of the modified linear polyurethane resin is characterized in that the molecular chains of the modified linear polyurethane resin are arranged linearly, so that the modified linear polyurethane resin has good fluidity and a low glass transition temperature; the alkaloid with a diamino functional group is an amino-terminated fatty chain extender, and the modified linear polyurethane resin has a soft amino-terminated fatty chain, which improves the flexibility and processing plasticity of the modified linear polyurethane resin; the amino-terminated fatty chain extender improves the thermal stability of the modified linear polyurethane resin by increasing the molecular weight; the improved thermal stability and processing plasticity of the modified linear polyurethane resin enable the modified linear polyurethane resin to be processed by cast extrusion within a wider temperature and pressure range; the amino-terminated fatty chain extender makes the molecular chain more compact by increasing the molecular weight, reduces the path of electrolyte penetration, and improves the corrosion resistance of the modified linear polyurethane resin.

[0049] Furthermore, the modified linear polyurethane resin has a viscosity of 5.0 Pa·s to 8.0 Pa·s at 200°C. In this embodiment, the modified linear polyurethane resin has a low viscosity when molten, allowing the melt of the modified linear polyurethane resin to easily pass through the die of the casting machine, reducing extrusion pressure, thereby allowing the modified linear polyurethane resin to be smoothly cast and extruded on the casting machine.

[0050] Furthermore, the isocyanate, the terminal diol, and dibutyltin dilaurate are mixed and heated. The heating temperature for the polyaddition reaction is 60°C-95°C and the heating time is 4-6 hours. In this embodiment, dibutyltin dilaurate maintains good catalytic activity at a temperature of 60°C-95°C, and the heating time is 4-6 hours, allowing the isocyanate and terminal diol to react completely.

[0051] Furthermore, the bis-amino-functional alkaloid is dissolved in N-methylpyrrolidone and then mixed with the thermoplastic polyurethane resin and heated. The chain extension reaction is heated at a temperature of 60°C to 100°C for a time of 4 to 8 hours. In this embodiment, the process of mixing and heating the bis-amino-functional alkaloid solution with the thermoplastic polyurethane resin is not affected by a catalyst. Temperature has a greater influence on the chain extension reaction. When the temperature is higher, the heating time is shortened, while when the temperature is lower, a longer heating time is required to ensure complete reaction between the bis-amino-functional alkaloid and the thermoplastic polyurethane resin.

[0052] Furthermore, the chain-extended linear polyurethane solution is dried at a temperature of 70° C. to 100° C. In this embodiment, the chain-extended linear polyurethane solution is heated to rapidly volatilize the water, ammonia, and N-methylpyrrolidone generated during the reaction, thereby obtaining a modified linear polyurethane resin with higher purity.

[0053] In one embodiment, the isocyanate comprises at least one of diphenylmethane-4,4'-diisocyanate and polymeric polyphenylmethane polyisocyanate. In the present embodiment, the isocyanate groups (-NCO) in diphenylmethane-4,4'-diisocyanate and polymeric polyphenylmethane polyisocyanate are highly reactive and react rapidly with terminal diols to form a polyurethane structure, and the reaction conditions are mild. The molecular weight of the polymeric polyphenylmethane polyisocyanate is lower than 5000, and the low-molecular-weight polymeric polyphenylmethane polyisocyanate has higher activity in the reaction, thereby making the low-molecular-weight polymeric polyphenylmethane polyisocyanate react rapidly with the terminal diols to form a polyurethane material.

[0054] In one embodiment, the terminal diol comprises at least one of ethylene glycol and polyethylene glycol. In this embodiment, ethylene glycol and polyethylene glycol are introduced into the modified linear polyurethane resin as soft segments to improve the flexibility of the modified linear polyurethane resin.

[0055] Furthermore, in one embodiment, the molecular weight of the polyethylene glycol is 1000-3000. In this embodiment, when the molecular weight of the polyethylene glycol is less than 1000, a continuous soft phase cannot be formed, and the improvement in flexibility is limited. When the molecular weight of the polyethylene glycol is greater than 3000, the viscosity of the modified linear polyurethane resin increases significantly. When the molecular weight of the polyethylene glycol is 1000-3000, the polyethylene glycol forms a soft segment chain extension structure, which significantly improves the flexibility of the modified linear polyurethane resin and improves the stability of the modified linear polyurethane resin.

[0056] In one embodiment, the alkaloid with a diamino group comprises at least one of lysine, asparagine, glutamine, and arginine. In this embodiment, lysine, asparagine, glutamine, and arginine all have diamino groups at their terminal ends. In the modified linear polyurethane resin prepared from the alkaloid with a diamino group, the diamino groups form amino-terminated fatty chains and weak hydrogen bonds, weakening the bond between the hard segments and the soft segments, promoting segment motion at low temperatures, and thereby lowering the glass transition temperature of the modified linear polyurethane resin.

[0057] In one embodiment, the molar ratio of the isocyanate NCO groups to the terminal diol OH groups of the thermoplastic polyurethane resin is 1.5:1 to 2.5:1. In this embodiment, the isocyanate NCO groups are hard segment groups, and the terminal diol OH groups are soft segment groups. By controlling the molar ratio of the isocyanate NCO groups to the terminal diol OH groups to be 1.5:1 to 2.5:1, the hard and soft segments interact in the polyurethane through hydrogen bonding and other means, giving the thermoplastic polyurethane resin both strength and elasticity, thereby controlling the strength and elasticity of the modified linear polyurethane resin prepared from the thermoplastic polyurethane resin.

[0058] In one embodiment, the alkaloid with diamino functional groups is dissolved in N-methylpyrrolidone and then mixed with a thermoplastic polyurethane resin and heated. The mass ratio of the thermoplastic polyurethane resin to the alkaloid with diamino functional groups is 3.5:1 to 6:1. In this embodiment, a chain extension reaction is carried out between a diamino-functional alkaloid and a thermoplastic polyurethane resin. By controlling the mass ratio of the thermoplastic polyurethane resin to the diamino-functional alkaloid, the tensile strength and flexibility of the modified linear polyurethane resin are enhanced. The amount and mass ratio of the diamino-functional alkaloid added also affect the viscosity, fluidity, and heat resistance of the modified linear polyurethane resin, such as the glass transition temperature. When the proportion of the alkaloid chain extender glutamine is too high, the excessive weak hydrogen bonds and excessively long soft fatty chain length weaken the binding of the hard segment to the glutamine segment, thereby increasing the plasticity and viscosity of the molecular chain and reducing the mechanical strength and solvent corrosion resistance. When the composition of the polyurethane hard segment is relatively high, the tensile strength increases, but due to the compact segment structure and strong intermolecular binding, fewer weak hydrogen chains are formed between the polyurethane and the chain extender, resulting in a significant decrease in the tensile shear strength and mechanical strength, and poor plasticity.

[0059] In one embodiment, the modified linear polyurethane resin has a glass transition temperature of less than -60°C. In this embodiment, the linear structure and amino-terminated fatty chains of the modified linear polyurethane resin result in a low glass transition temperature. The modified linear polyurethane resin maintains good flexibility and elasticity even at extremely low temperatures, making it stable over a wide temperature range.

[0060] like Figure 2As shown, the present application also provides a method for preparing a swelling tape, comprising the following steps: providing a modified linear polyurethane resin obtained by the preparation method of the modified linear polyurethane resin described in any of the above examples;

[0061] S201 crushes the modified linear polyurethane resin to obtain crushed modified linear polyurethane resin;

[0062] S203: placing the crushed modified linear polyurethane resin into a casting machine for heating, and casting and extruding the molten modified linear polyurethane resin to form a swelling tape precursor film;

[0063] S205: Coat both sides of the swelling tape precursor film with a pressure-sensitive adhesive and attach the film to a release film to obtain a swelling tape.

[0064] In this embodiment, the modified linear polyurethane resin is crushed to improve the melting efficiency and uniformity of the modified linear polyurethane resin; the viscosity of the modified linear polyurethane resin after heating is low, and by adjusting the soft and hard chains and molecular weight of the modified linear polyurethane resin, the modified linear polyurethane resin has good heat resistance and a low glass transition temperature, so that the formed swelling precursor film has the characteristics of wide temperature range use; the loose hard segment arrangement and weak hydrogen bonding of the modified linear polyurethane resin provide more penetration channels for solvent molecules, accelerate solvent diffusion, and there are fewer entanglements between the linear polyurethane molecular chains and low resistance to chain segment movement, thereby increasing the expansion rate of the modified linear polyurethane resin and making the swelling precursor film have high expansion; the modified linear polyurethane resin of the swelling precursor film increases the length of the molecular chain through the amino-terminated fatty chain, thereby improving the heat degradation resistance and solvent corrosion resistance of the modified linear polyurethane resin, and the hard segment and soft segment of the modified linear polyurethane resin of the swelling precursor film interact through hydrogen bonds, etc., so that the swelling precursor film has good tensile strength.

[0065] The above-mentioned method for preparing the swelling tape has a lower viscosity after heating of the modified linear polyurethane resin, improved thermal stability and better processing plasticity, so that the modified linear polyurethane resin is extruded in a cast film machine to form a swelling precursor film with good uniformity. The swelling precursor film has a wide temperature range of use, high expansion, resistance to solvent corrosion and good tensile strength. The swelling tape obtained by adhering the swelling precursor film to a release film has a higher surface flatness and better transparency.

[0066] Furthermore, the casting machine is equipped with a screw heating zone assembly and a casting die control assembly. The screw heating zone assembly is used to heat the modified linear polyurethane resin at a heating temperature of 100°C to 200°C. The casting die assembly is used to control the thickness of the swollen precursor film formed by extrusion. The thickness of the swollen precursor film is 10 μm to 80 μm. The casting machine has a take-off speed of 0.1 m / min to 3 m / min, and a screw speed of 1 rpm to 95 rpm. In this embodiment, the modified linear polyurethane resin is melted into a melt by controlling the addition temperature to 100°C to 200°C. The take-off speed and screw speed of the casting machine control the uniformity of the flow of the modified linear polyurethane resin melt. The casting die assembly then controls the extrusion to form a uniform swollen precursor film, resulting in a uniform swollen precursor film with good thickness consistency.

[0067] Furthermore, the modified linear polyurethane resin has a crushed diameter of 2 mm to 5 mm. In this embodiment, the crushed modified linear polyurethane resin has a diameter of 2 mm to 5 mm. The modified linear polyurethane resin particles have a large specific surface area, resulting in a short melting time. The modified linear polyurethane resin particles completely melt within a temperature range of 100°C to 200°C, ensuring uniformity of the modified linear polyurethane resin melt.

[0068] Furthermore, the screw heating zone assembly is sequentially provided with a feed section, a temperature rise metering section and a die section. When the screw heating zone assembly of the casting machine is heated, the modified linear polyurethane resin is subjected to gradient temperature control. The temperature of the feed section is 100°C, the temperature of the temperature rise metering section is 200°C, and the temperature of the die section is 100°C. In this embodiment, when the solid modified linear polyurethane particles are transported to the feed end, the temperature of the feed section is 100°C, so that the solid modified linear polyurethane particles are preheated and softened. The lower temperature prevents the modified linear polyurethane from melting prematurely during feeding and causing blockage. The heating metering section is used to homogenize and pressurize the melt of the modified linear polyurethane so that the modified linear polyurethane is completely melted. The temperature of the heating metering section is relatively high, which reduces the melt viscosity of the modified linear polyurethane and reduces the wall sticking effect of the modified linear polyurethane, thereby improving the plasticity of the modified linear polyurethane melt; the temperature of the die section is reduced to 100°C, which reduces the temperature of the modified linear polyurethane melt, reduces the outlet expansion, and utilizes rapid cooling molding to make the obtained swollen precursor film uniform in thickness.

[0069] In one embodiment, the swelling precursor film has an expansion rate of 100%-350%. In this embodiment, the swelling precursor film's expansion rate is measured by immersion in an electrolyte solution composed of propylene carbonate (PC) and ethylene carbonate (EC) as solvents and lithium hexafluorophosphate (LiPF6) as a solute. When the swelling tape is filled in the battery gap and the lithium battery is injected with the electrolyte, the swelling precursor film of the swelling tape expands after being immersed in the electrolyte, allowing the swelling tape to secure the battery cell to the steel casing, thereby improving the shock resistance and safety of the lithium-ion battery.

[0070] Compared with the prior art, the present disclosure has at least the following advantages:

[0071] The modified linear polyurethane resin has a linear structure. The hard segment structure of the modified linear polyurethane resin is loosely arranged, which weakens the intermolecular forces and improves the fluidity of the hot-melt modified linear polyurethane resin. The linear molecular chain has less intermolecular entanglement, making the molecular chain segments relatively easy to move, thereby lowering the glass transition temperature of the modified linear polyurethane resin. The soft segment structure of the modified linear polyurethane resin is an amino-terminated fatty chain. The amino group at the end of the fatty chain forms a weak hydrogen bond with the hard segment, further weakening the hard segment's bond to the soft segment, promoting segment movement at low temperatures, and further lowering the glass transition temperature of the modified linear polyurethane resin. The alternating hard and soft segment structures of the modified linear polyurethane resin improve processing plasticity, making the modified linear polyurethane resin suitable for cast extrusion. The loose hard segment arrangement and weak hydrogen bonding provide more penetration channels for solvent molecules, accelerating solvent diffusion. The linear polyurethane molecular chains are less entangled, and the resistance to chain segment movement is low, thereby improving the expansion rate of the modified linear polyurethane resin. The amino-terminated fatty chain increases the molecular chain length, thereby improving the thermal degradation resistance and electrolyte corrosion resistance of the modified linear polyurethane resin.

[0072] The modified linear polyurethane resin has a lower viscosity after heating, improved thermal stability and better processing plasticity, so that the modified linear polyurethane resin has better uniformity when formed into a swollen precursor film by blown film extrusion on a cast film machine. The swollen precursor film has a wide temperature range of use, high expansion, resistance to solvent corrosion and good tensile strength. The swollen precursor film extruded by cast film has better uniformity, and the swollen tape obtained by adhering the swollen precursor film to a release film has higher surface flatness and better transparency.

[0073] The following examples illustrate some specific embodiments, where percentages are expressed by weight. It should be noted that the following examples do not exhaust all possible situations, and that the materials used in the following examples, unless otherwise specified, can be obtained from commercial sources.

[0074] Example 1

[0075] Under N2 protection, polyether polyol N210 and polydiphenylmethane-4,4'-diisocyanate PMDI were added to a three-necked flask with a stirring function, and 0.05 g of dibutyltin dilaurate (DBTDL) was slowly added dropwise, mixed and heated, wherein the molar ratio of PMDI to N210 was 2.0. The reaction temperature was controlled to 70°C and the reaction was kept at this temperature for 5 hours to obtain a linear thermoplastic polyurethane resin;

[0076] Glutamine was dissolved in N-methylpyrrolidone (NMP) and then mixed with thermoplastic polyurethane resin and heated, wherein the mass ratio of linear TPU to glutamine was 4.0. The temperature was maintained at 70°C for 5 hours, and the chain extension reaction was performed to generate a chain-extended linear polyurethane solution.

[0077] The chain-extended linear polyurethane solution was heated at 95° C. for drying to obtain a modified linear polyurethane resin.

[0078] The modified linear polyurethane resin was crushed into particles with a diameter of 2-5 mm and then heated by the screw of a casting machine. A gradient temperature control was employed in the screw heating zone: 100°C in the feed section, 200°C in the metering section, and 100°C in the die section. The pulling speed was controlled at 2 m / min and the screw speed at 30 rpm. The film was extruded through the casting die assembly of the casting machine to form a 50 μm thick swollen precursor film. Both sides of the swollen precursor film were then adhered to a release film to obtain the swollen adhesive tape.

[0079] Example 2

[0080] Under N2 protection, polyether polyol N210 and polydiphenylmethane-4,4'-diisocyanate PMDI were added to a three-necked flask with a stirring function, and 0.05 g of dibutyltin dilaurate (DBTDL) was slowly added dropwise, mixed and heated, wherein the molar ratio of PMDI to N210 was 2.0. The reaction temperature was controlled to 70°C and the reaction was kept at this temperature for 5 hours to obtain a linear thermoplastic polyurethane resin;

[0081] Glutamine was dissolved in N-methylpyrrolidone (NMP) and then mixed with thermoplastic polyurethane resin and heated, wherein the mass ratio of linear TPU to glutamine was 5.0. The temperature was maintained at 70°C for 5 hours, and the chain extension reaction was performed to generate a chain-extended linear polyurethane solution.

[0082] The chain-extended linear polyurethane solution was heated at 95° C. for drying to obtain a modified linear polyurethane resin.

[0083] The modified linear polyurethane resin was crushed into particles with a diameter of 2-5 mm and then heated by the screw of a casting machine. A gradient temperature control was employed in the screw heating zone: 100°C in the feed section, 200°C in the metering section, and 100°C in the die section. The pulling speed was controlled at 2 m / min and the screw speed at 30 rpm. The film was extruded through the casting die assembly of the casting machine to form a 50 μm thick swollen precursor film. The swollen precursor film was then adhered to a release film to obtain the swollen adhesive tape.

[0084] Example 3

[0085] Under N2 protection, polyether polyol N210 and polydiphenylmethane-4,4'-diisocyanate PMDI were added to a three-necked flask with a stirring function, and 0.05 g of dibutyltin dilaurate (DBTDL) was slowly added dropwise, mixed and heated, wherein the molar ratio of PMDI to N210 was 2.0. The reaction temperature was controlled to 70°C and the reaction was kept at this temperature for 5 hours to obtain a linear thermoplastic polyurethane resin;

[0086] Glutamine was dissolved in N-methylpyrrolidone (NMP) and then mixed with thermoplastic polyurethane resin and heated, wherein the mass ratio of linear TPU to glutamine was 6. The temperature was maintained at 70°C for 5 hours, and the chain extension reaction was performed to generate a chain-extended linear polyurethane solution.

[0087] The chain-extended linear polyurethane solution was heated at 95° C. for drying to obtain a modified linear polyurethane resin.

[0088] The modified linear polyurethane resin was crushed into particles with a diameter of 2-5 mm and then heated by the screw of a casting machine. A gradient temperature control was employed in the screw heating zone: 100°C in the feed section, 200°C in the metering section, and 100°C in the die section. The pulling speed was controlled at 2 m / min and the screw speed at 30 rpm. The film was extruded through the casting die assembly of the casting machine to form a 50 μm thick swollen precursor film. The swollen precursor film was then adhered to a release film to obtain the swollen adhesive tape.

[0089] Example 4

[0090] Under N2 protection, polyether polyol N210 and polydiphenylmethane-4,4'-diisocyanate PMDI were added to a three-necked flask with a stirring function, and 0.05 g of dibutyltin dilaurate (DBTDL) was slowly added dropwise, mixed and heated, wherein the molar ratio of PMDI to N210 was 2.0. The reaction temperature was controlled to 70°C and the reaction was kept at this temperature for 5 hours to obtain a linear thermoplastic polyurethane resin;

[0091] Glutamine was dissolved in N-methylpyrrolidone (NMP) and then mixed with thermoplastic polyurethane resin and heated, wherein the mass ratio of linear TPU to arginine was 4.0. The temperature was maintained at 70°C for 5 hours, and the chain extension reaction was performed to generate a chain-extended linear polyurethane solution.

[0092] The chain-extended linear polyurethane solution was heated at 95° C. for drying to obtain a modified linear polyurethane resin.

[0093] The modified linear polyurethane resin was crushed into particles with a diameter of 2-5 mm and then heated by the screw of a casting machine. A gradient temperature control was employed in the screw heating zone: 100°C in the feed section, 200°C in the metering section, and 100°C in the die section. The pulling speed was controlled at 2 m / min and the screw speed at 30 rpm. The film was extruded through the casting die assembly of the casting machine to form a 50 μm thick swollen precursor film. The swollen precursor film was then adhered to a release film to obtain the swollen adhesive tape.

[0094] Example 5

[0095] Under N2 protection, polyether polyol N210 and polydiphenylmethane-4,4'-diisocyanate PMDI were added to a three-necked flask with a stirring function, and 0.05 g of dibutyltin dilaurate (DBTDL) was slowly added dropwise, mixed and heated, wherein the molar ratio of PMDI to N210 was 2.0. The reaction temperature was controlled to 70°C and the reaction was kept at this temperature for 5 hours to obtain a linear thermoplastic polyurethane resin;

[0096] Glutamine was dissolved in N-methylpyrrolidone (NMP) and then mixed with thermoplastic polyurethane resin and heated, wherein the mass ratio of linear TPU to lysine was 4.0. The temperature was maintained at 70°C for 5 hours, and the chain extension reaction was performed to generate a chain-extended linear polyurethane solution.

[0097] The chain-extended linear polyurethane solution was heated at 95° C. for drying to obtain a modified linear polyurethane resin.

[0098] The modified linear polyurethane resin was crushed into particles with a diameter of 2-5 mm and then heated by the screw of a casting machine. A gradient temperature control was employed in the screw heating zone: 100°C in the feed section, 200°C in the metering section, and 100°C in the die section. The pulling speed was controlled at 2 m / min and the screw speed at 30 rpm. The film was extruded through the casting die assembly of the casting machine to form a 50 μm thick swollen precursor film. The swollen precursor film was then adhered to a release film to obtain the swollen adhesive tape.

[0099] Example 6

[0100] Under N2 protection, polyether polyol N210 and polydiphenylmethane-4,4'-diisocyanate PMDI were added to a three-necked flask with a stirring function, and 0.05 g of dibutyltin dilaurate (DBTDL) was slowly added dropwise, mixed and heated, wherein the molar ratio of PMDI to N210 was 2.0. The reaction temperature was controlled to 70°C and the reaction was kept at this temperature for 5 hours to obtain a linear thermoplastic polyurethane resin;

[0101] Glutamine was dissolved in N-methylpyrrolidone (NMP) and then mixed with thermoplastic polyurethane resin and heated. The mass ratio of linear TPU to asparagine was 4.0. The temperature was maintained at 70°C for 5 hours. After the chain extension reaction, a chain-extended linear polyurethane solution was generated.

[0102] The chain-extended linear polyurethane solution was heated at 95° C. for drying to obtain a modified linear polyurethane resin.

[0103] The modified linear polyurethane resin was crushed into particles with a diameter of 2-5 mm and then heated by the screw of a casting machine. A gradient temperature control was employed in the screw heating zone: 100°C in the feed section, 200°C in the metering section, and 100°C in the die section. The pulling speed was controlled at 2 m / min and the screw speed at 30 rpm. The film was extruded through the casting die assembly of the casting machine to form a 50 μm thick swollen precursor film. The swollen precursor film was then adhered to a release film to obtain the swollen adhesive tape.

[0104] Comparative Example 1

[0105] Under N2 protection, polyether polyol N210 and polydiphenylmethane-4,4'-diisocyanate PMDI were added to a three-necked flask with a stirring function, and 0.05 g of dibutyltin dilaurate (DBTDL) was slowly added dropwise, mixed and heated, wherein the mass ratio of PMDI to N210 was 2.0. The reaction temperature was controlled to 70°C and the reaction was kept at this temperature for 5 hours to obtain a linear thermoplastic polyurethane resin;

[0106] The linear thermoplastic polyurethane resin has a high viscosity and is not completely plasticized, so it cannot be extruded through a casting machine for blown film.

[0107] Comparative Example 2

[0108] Under N2 protection, polyether polyol N210 and polydiphenylmethane-4,4'-diisocyanate PMDI were added to a three-necked flask with a stirring function, and 0.05 g of dibutyltin dilaurate (DBTDL) was slowly added dropwise, mixed and heated, wherein the molar ratio of PMDI to N210 was 2.0. The reaction temperature was controlled to 70°C and the reaction was kept at this temperature for 5 hours to obtain a linear thermoplastic polyurethane resin;

[0109] Glutamine was dissolved in N-methylpyrrolidone (NMP) and then mixed with thermoplastic polyurethane resin and heated, wherein the mass ratio of linear TPU to glutamine was 3. The temperature was maintained at 70°C for 5 hours, and the chain extension reaction was performed to generate a chain-extended linear polyurethane solution.

[0110] The chain-extended linear polyurethane solution was heated at 95° C. for drying to obtain a modified linear polyurethane resin.

[0111] After crushing the modified linear polyurethane resin into particles with a diameter of 2-5 mm, the resin was heated by the screw of a casting machine. A gradient temperature control was used in the screw heating zone: 100°C in the feed section, 200°C in the metering section, and 100°C in the die section. The pull-out speed was controlled at 2 m / min and the screw speed at 30 rpm. The resin was extruded through the casting die assembly of the casting machine to form a 50 μm thick swellable precursor film. The swellable precursor film was then coated on both sides with a pressure-sensitive adhesive and attached to a release film to produce a swellable tape.

[0112] Comparative Example 3

[0113] Under N2 protection, polyether polyol N210 and polydiphenylmethane-4,4'-diisocyanate PMDI were added to a three-necked flask with a stirring function, and 0.05 g of dibutyltin dilaurate (DBTDL) was slowly added dropwise, mixed and heated, wherein the molar ratio of PMDI to N210 was 2.0. The reaction temperature was controlled to 70°C and the reaction was kept at this temperature for 5 hours to obtain a linear thermoplastic polyurethane resin;

[0114] Glutamine was dissolved in N-methylpyrrolidone (NMP) and then mixed with thermoplastic polyurethane resin and heated, wherein the mass ratio of linear TPU to glutamine was 7. The temperature was maintained at 70°C for 5 hours, and the chain extension reaction was performed to generate a chain-extended linear polyurethane solution.

[0115] The chain-extended linear polyurethane solution was heated at 95° C. for drying to obtain a modified linear polyurethane resin.

[0116] After crushing the modified linear polyurethane resin into particles with a diameter of 2-5 mm, the resin was heated by the screw of a casting machine. A gradient temperature control was used in the screw heating zone: 100°C in the feed section, 200°C in the metering section, and 100°C in the die section. The pull-out speed was controlled at 2 m / min and the screw speed at 30 rpm. The resin was extruded through the casting die assembly of the casting machine to form a 50 μm thick swellable precursor film. The swellable precursor film was then coated on both sides with a pressure-sensitive adhesive and attached to a release film to produce a swellable tape.

[0117] Table 1 Chain extender dosage table for examples and comparative examples

[0118]

[0119] As can be seen from Table 1, when the polyurethane:alkaloid chain extender mass ratio of Examples 1-6 is in the range of 4-6, its viscosity at 200°C is 5.0-7.0, the fluid has good fluidity in the melting zone, and has good processing properties. When no chain extender is added to Comparative Example 1, its viscosity is too high, and the polyurethane plasticity in the screw extrusion zone is too low, and it cannot flow. When the glutamine ratio of Comparative Example 2 is too high, the plasticity of the modified polyurethane in the screw extrusion zone is too high, the fluid viscosity is too low, and a uniform film cannot be formed. When the glutamine ratio of Comparative Example 3 is too low, the viscosity of the modified polyurethane in the screw extrusion zone is too high, affecting the processing fluidity.

[0120] Table 2 Test results of swollen precursor films of Examples and Comparative Examples

[0121]

[0122] It should be noted that when testing the expansion rate of immersion in electrolyte in Examples 1-6 and Comparative Examples 2 and 3, the swollen precursor film was immersed in the electrolyte for 1 minute and then immersed for 24 hours to measure the expansion rate of the electrolyte (24h).

[0123] As shown in Table 2, the tensile strength of the swollen precursor films prepared in the polyurethane:chain extender mass ratio range of 4-6 in Examples 1-6 is above 0.5 MPa, the tensile shear strength does not decrease much before and after immersion, and the tape peel strength is 0.8 kN m -1 As shown above, the expansion rate of the swollen precursor film is higher than 230-300%. After soaking in the electrolyte for 24 hours, there is little change, which shows that the swollen precursor films of Examples 1-6 have good high mechanical modulus and expansion rate.

[0124] It can be seen from Comparative Examples 2 and 4-6 that when the proportion of the alkaloid chain extender glutamine is too high, its mechanical strength drops to below 0.5 MPa, and the tensile shear strength, peel strength, and expansion rate also decrease accordingly. This is because the excessive weak hydrogen bonds and excessively long soft fatty chain lengths greatly weaken the constraints of the hard segments on the glutamine chain segments, increasing the plasticity and viscosity of the molecular chain, but reducing the mechanical strength and solvent corrosion resistance (after 24 hours).

[0125] When the molar ratio of the chain extender in Comparative Example 3 is too low, the composition of the polyurethane hard segment is relatively too high. Although the tensile strength increases, due to the tight segment structure and strong intermolecular binding effect, the polyurethane forms fewer weak hydrogen chains with the chain extender, resulting in a significant decrease in tensile shear strength and mechanical strength, and poor plasticity, which affects the peel strength and expansion rate.

[0126] from Figure 3It can be seen that the glass transition temperature of Example 1 is below -60°C, and the melt state of Example 1 remains stable at 100°C-250°C, indicating that Example 1 has a lower glass transition temperature and better thermal stability at 100°C-250°C.

[0127] from Figure 4 and Figure 5 It can be seen that the swelling precursor film of Example 1 swells under the action of the electrolyte after being pasted and fixed. After being pasted and fixed, the surface begins to wrinkle and have an undulating morphology due to the limited horizontal swelling. This swelling change fills and wraps the gap between the battery cell and the shell in a three-dimensional manner, and plays a good protective role for the battery cell.

[0128] The above-described embodiments merely represent several implementation methods of the present disclosure. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the disclosed patent. It should be noted that a person of ordinary skill in the art may make various modifications and improvements without departing from the scope of the present disclosure, all of which fall within the scope of protection of the present disclosure. Therefore, the scope of protection of the disclosed patent shall be determined by the appended claims.

Claims

1. A modified linear polyurethane resin, characterized in that: The modified linear polyurethane resin includes one of the following structural formulas:

2. A method for preparing a modified linear polyurethane resin, characterized in that: The method for preparing the modified linear polyurethane resin according to claim 1 comprises the following steps: Isocyanate, terminal diol and dibutyltin dilaurate are mixed and heated to obtain thermoplastic polyurethane resin after polyaddition reaction; The alkaloid with diamino functional groups is added to N-methylpyrrolidone and dissolved, and then mixed with thermoplastic polyurethane resin and heated to generate a chain-extended linear polyurethane solution after chain extension reaction; The chain-extended linear polyurethane solution is heated and dried to obtain a modified linear polyurethane resin.

3. The method for preparing the modified linear polyurethane resin according to claim 2, wherein: The isocyanate includes at least one of diphenylmethane-4,4'-diisocyanate and polymeric polyphenylmethane polyisocyanate.

4. The method for preparing the modified linear polyurethane resin according to claim 2, wherein: The terminal diol includes at least one of ethylene glycol and polyethylene glycol.

5. The method for preparing the modified linear polyurethane resin according to claim 2, wherein: The alkaloid with a diamino functional group includes at least one of lysine, asparagine, glutamine and arginine.

6. The method for preparing the modified linear polyurethane resin according to claim 2, wherein: The molar ratio of the NCO group of the isocyanate to the OH group of the terminal diol in the thermoplastic polyurethane resin is 1.5:1 to 2.5:

1.

7. The method for preparing a modified linear polyurethane resin according to claim 2, wherein: The alkaloid with diamino functional groups is added into N-methylpyrrolidone and dissolved, and then mixed with thermoplastic polyurethane resin and heated. The mass ratio of the thermoplastic polyurethane resin to the alkaloid with diamino functional groups is 3.5:1 to 6:

1.

8. The method for preparing a modified linear polyurethane resin according to claim 2, wherein: The glass transition temperature of the modified linear polyurethane resin is less than -60°C.

9. A method for preparing a swelling tape, characterized in that: The steps include: Provided is a modified linear polyurethane resin obtained by the method for preparing the modified linear polyurethane resin according to any one of claims 2 to 8; crushing the modified linear polyurethane resin to obtain crushed modified linear polyurethane resin; placing the crushed modified linear polyurethane resin into a casting machine and heating it, and casting and extruding the molten modified linear polyurethane resin to form a swelling tape precursor film; The swelling tape precursor film is coated with pressure-sensitive adhesive on both sides and attached to a release film to obtain a swelling tape.

10. The method for preparing a swelling tape according to claim 9, characterized in that: The swelling ratio of the swollen precursor film is 100%-350%.

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