A PET film resistant to battery electrolyte and preparation method thereof

Abstract

The present invention relates to the field of PET film preparation, and in particular to a PET film resistant to battery electrolyte and a preparation method thereof, wherein the PET film comprises the following raw materials in parts by weight: 60-80 parts of modified polyethylene terephthalate slices, 15-40 parts of polyamide slices, 5-20 parts of toughening agents, 0.5-1 parts of coupling agents, 1-5 parts of reinforcing materials, and 0.1-1 parts of thermal stabilizers. The PET film of the present invention not only has excellent chemical resistance and can well resist the corrosion of electrolyte, but also has good toughness and pitting performance, and can avoid the rupture of the packaging film.

Description

Technical Field

[0001] The invention relates to the field of PET film preparation, and in particular to a battery electrolyte-resistant PET film and a preparation method thereof. Background Art

[0002] Lithium-ion polymer batteries are widely used in 3C and electric vehicle power batteries. However, in the production process of lithium batteries, there is a problem that the electrolyte is easy to contaminate the aluminum-plastic packaging film of the lithium battery during the injection and secondary sealing processes. The outermost layer of the aluminum-plastic packaging film used for lithium-ion polymer batteries is often made of polyamide material. However, polyamide materials have poor electrolyte resistance and will be corroded and swelled by the electrolyte. When electrolyte contamination occurs, the outer layer of the aluminum-plastic packaging film of the lithium-ion polymer battery will be damaged, resulting in substandard quality.

[0003] There are two main solutions to this problem on the market: the first is to compound a polyester layer on the polyamide outer layer to prevent corrosion by the electrolyte; however, due to the poor toughness of polyester materials, its compounding on the polyamide outer layer will reduce the overall toughness of the aluminum-plastic packaging film, especially in the cold punching process, which can easily cause the aluminum layer in the packaging film to rupture; the other is to apply a coating to prevent electrolyte contamination, but the high hardness of the coating cannot guarantee the overall toughness of the film at the same time, and the packaging film will still rupture during the cold punching process. Summary of the invention

[0004] In order to solve the above-mentioned technical problems, the present invention provides a PET film resistant to battery electrolyte and a preparation method thereof. The PET film not only has excellent chemical resistance and can effectively resist the corrosion of the electrolyte, but also has good toughness and pitting performance, thus avoiding the rupture of the packaging film.

[0005] In order to achieve the above-mentioned purpose, the present invention provides a PET film resistant to battery electrolyte, which comprises the following raw materials in parts by weight: 60-80 parts of modified polyethylene terephthalate slices, 15-40 parts of polyamide slices, 5-20 parts of toughening agent, 0.5-1 part of coupling agent, 1-5 parts of reinforcing material, and 0.1-1 part of thermal stabilizer.

[0006] In some embodiments, the intrinsic viscosity of the modified polyethylene terephthalate chips is 0.65-0.7 dl / g.

[0007] In some embodiments, the modified polyethylene terephthalate slices are obtained by the following steps: terephthalic acid, ethylene glycol, cyclohexanediol and 40-60wt% of a catalyst are added into a reactor and stirred, heated for esterification reaction, and after completion, compound A is obtained, and then the remaining catalyst and auxiliary agent are added and continued to be stirred, and after reducing pressure, a co-condensation reaction is carried out in a vacuum environment, and stirring is stopped after removing the diol to obtain polymer B, and after cooling and pelletizing, the modified polyethylene terephthalate slices are obtained.

[0008] In some embodiments, the molar ratio of terephthalic acid, ethylene glycol and cyclohexanediol is 1:(0.7-0.85):(0.35-0.5).

[0009] Preferably, the cyclohexanediol is 1,4-cyclohexanedimethanol, which is a cis-trans isomer with 30% cis and 70% trans.

[0010] In some embodiments, the conditions of the esterification reaction are: pressure 0.2-0.3 MPa, temperature 225-250° C., and reaction time 60-80 min.

[0011] In some embodiments, the conditions of the co-condensation reaction are: pressure <0.1 kPa, temperature 265-280° C., and reaction time 60-100 min.

[0012] In some embodiments, the catalyst is added in an amount of 0.07-0.1% of the molar amount of terephthalic acid.

[0013] In some embodiments, the catalyst includes at least one of tetrabutyl titanate, cobalt acetate, zinc acetate, and germanium oxide.

[0014] Preferably, the catalyst is a mixture of tetrabutyl titanate, cobalt acetate, zinc acetate and germanium oxide, and the molar ratio of each substance is (0.1-0.3):(0.5-0.7):1:(0.6-0.8).

[0015] Further preferably, the catalyst is a mixture of tetrabutyl titanate, cobalt acetate, zinc acetate and germanium oxide, and the molar ratio of each substance is 0.25:0.6:1:0.7.

[0016] In some embodiments, the auxiliary agent is tributyl phosphate.

[0017] In some embodiments, the additive is added in an amount of 0.02-0.04% of the molar amount of terephthalic acid.

[0018] Preferably, the additive is added in an amount of 0.03% of the molar amount of terephthalic acid.

[0019] In some embodiments, the stirring speed before decompression is 25-35 rpm, and the stirring speed in the vacuum environment after decompression is 50-60 rpm, preferably 55 rpm.

[0020] In some embodiments, the intrinsic viscosity of the polyamide chips is 2-3 dL / g.

[0021] Preferably, the polyamide chips are nylon 66, and the intrinsic viscosity is 2.7 dL / g.

[0022] In the injection process and the secondary sealing process of producing lithium batteries, the electrolyte is easy to contaminate the aluminum-plastic packaging film of the lithium battery. In order to prevent the aluminum-plastic packaging film from being damaged, the applicant found that the PET film prepared by using a specific ratio of modified polyethylene terephthalate chips and polyamide chips with a certain intrinsic viscosity in combination with the conditions of each step can not only resist electrolyte corrosion, but also have excellent toughness, and can well avoid the problem of packaging film rupture. The applicant believes that the possible reason is that these two specific substances can produce good compatibility during the co-extrusion process, combined with the high rigidity and modulus, chemical resistance of modified polyethylene terephthalate and the high toughness of PA66, the two complement each other and give the prepared PET film excellent comprehensive performance, so that it can be used for the outer layer of the aluminum-plastic packaging film of lithium-ion polymer batteries without being easily damaged. At the same time, it can effectively prevent the penetration of air, especially oxygen, maintain the stability of the internal environment of the battery, which is conducive to improving battery safety.

[0023] In some embodiments, the reinforcing material is at least one of modified calcium carbonate whiskers, white carbon black, glass microspheres, glass fibers, and montmorillonite.

[0024] Preferably, the reinforcing material is modified calcium carbonate whisker and white carbon black, and the weight ratio of the two is 1:(0.5-1).

[0025] In some embodiments, the modified calcium carbonate whiskers are obtained by the following steps:

[0026] (1) Add an equal volume of 0.2 mol / L CaCl 2 Solution and NaCO 3 The solution is simultaneously added dropwise into a reactor containing distilled water at 80-90° C., stirred at a speed of 120-200 r / min for 4 hours, and after the reaction is completed, the mixture is aged at a constant temperature of 80-90° C. for 1 hour, then filtered and pulped and washed twice, and dried to obtain calcium carbonate whiskers;

[0027] (2) The obtained calcium carbonate whiskers are made into a slurry, and an anhydrous ethanol solution containing 3 wt% sodium stearate is added for ultrasonic dispersion for 1 hour, and then stirred in a water bath at 80° C. and a speed of 1200 r / min for 0.5 hour, filtered and dried to obtain the modified calcium carbonate whiskers.

[0028] In some embodiments, the amount of distilled water added in step (1) is NaCO 3 Half the volume of the solution.

[0029] In some embodiments, the slurry in step (2) is a mixture of calcium carbonate whiskers and water, and the mass fraction of calcium carbonate whiskers in the slurry is 8-9%.

[0030] In some embodiments, the white carbon black is fumed white carbon black with a specific surface area of ​​160-180 m 2 / g, and the average particle size is 10-15nm.

[0031] Preferably, the white carbon black is fumed white carbon black with a specific surface area of ​​170 m 2 / g, and the average particle size is 12nm.

[0032] The fumed silica of the present invention is selected from Evonik Degussa, and its model is R974.

[0033] The applicant found in the study that adding certain reinforcing materials to the system, especially when the reinforcing materials are specific calcium carbonate whiskers and fumed silica, is conducive to improving the punching performance of the prepared PET film. The possible reason is that on the one hand, the calcium carbonate whiskers have a large specific surface area and many chemical and physical defects on the surface, which makes it more likely to be physically entangled and chemically combined with the modified polyethylene terephthalate and the polymer chain in the polyamide structure in the system. When the PET film is subjected to external force, some microcracks will be generated on the surface of the calcium carbonate whiskers, thereby transmitting and absorbing more impact. Impact energy, accelerates the dissipation of energy, and can prevent and passivate the further expansion of cracks. At the same time, the calcium carbonate whiskers have non-polar groups after modification, which form a good combination with the polymer in the system, giving the PET film high toughness and stress transfer, thereby improving the impact strength; on the other hand, since the silanol group on the surface of the fumed silica is fully exposed, the contact area with the polymer is increased to form a hydrogen bond network, which can improve the tensile strength and elongation at break to a certain extent. In addition, the addition of fumed silica is beneficial to increase the crystallization rate of polyester and polyamide and reduce the thermal shrinkage of PET film.

[0034] In some embodiments, the toughening agent is calcium stearate soap and / or butyl epoxy furoate.

[0035] Preferably, the toughening agent is calcium stearate soap and butyl epoxy furoate in a weight ratio of 1:(0.2-0.6).

[0036] In some embodiments, the coupling agent is a silane coupling agent, specifically, the silane coupling agent is at least one of KH550, KH560, and KH570.

[0037] In some embodiments, the thermal stabilizer is trimethyl phosphate.

[0038] Another aspect of the present invention provides a method for preparing a PET film resistant to battery electrolyte, comprising the following steps:

[0039] S1, mixing the raw materials according to the proportion, adding them into a granulator for granulation treatment, and obtaining substance A;

[0040] S2, pre-crystallizing and drying the substance A to obtain substance B;

[0041] S3, using a twin-screw extruder to melt and plasticize the substance B to obtain a mixture;

[0042] S4, subjecting the mixture obtained in S3 to a sheet casting process to obtain a pretreated sheet;

[0043] S5, sequentially stretching the pretreated sheet longitudinally and transversely, heat-setting, cooling, and winding to obtain the PET film;

[0044] The longitudinal stretching temperature is 110-120°C, the longitudinal stretching ratio is 3.0-4.0, the transverse stretching temperature is 120-135°C, and the transverse stretching ratio is 2.5-4.0.

[0045] In some embodiments, the granulation temperature in step S1 is 85-95°C, the pre-crystallization temperature in step S2 is 160-170°C, and the melting temperature of the twin-screw extruder in step S3 is 260-285°C.

[0046] Compared with the prior art, the present invention has the following beneficial effects:

[0047] (1) The PET film prepared by the present invention by using a specific ratio of modified polyethylene terephthalate chips and polyamide chips with a certain intrinsic viscosity in combination with the conditions of each step can not only resist electrolyte corrosion, but also have excellent toughness and pitting performance, and can well avoid the problem of packaging film rupture;

[0048] (2) The present invention uses specific calcium carbonate whiskers and fumed silica as reinforcing materials, which is beneficial to improving the mechanical properties of the prepared PET film. On the one hand, the calcium carbonate whiskers are physically entangled and chemically bonded with the modified polyethylene terephthalate in the system and the polymer chain in the polyamide structure, which can transmit and absorb more impact energy. At the same time, the non-polar groups of the modified calcium carbonate whiskers form a good bond with the polymer in the system, giving the PET film high toughness and stress transfer, thereby improving the impact strength. On the other hand, since the silanol groups on the surface of the fumed silica are relatively fully exposed, the contact area between the fumed silica and the polymer is increased, forming a hydrogen bond network, which can improve the tensile strength and elongation at break to a certain extent. In addition, the addition of fumed silica is beneficial to increasing the crystallization rate of polyester and polyamide, and reducing the thermal shrinkage of the PET film. DETAILED DESCRIPTION

[0049] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0050] Example 1

[0051] A PET film resistant to battery electrolyte comprises the following raw materials in parts by weight: 70 parts of modified polyethylene terephthalate slices, 27 parts of polyamide slices, 10 parts of a toughening agent, 0.8 parts of a coupling agent, 3 parts of a reinforcing material, and 0.5 parts of trimethyl phosphate.

[0052] The modified polyethylene terephthalate slices are obtained by the following steps: terephthalic acid, ethylene glycol, cyclohexanediol and 50 wt% of a catalyst are added into a reactor and stirred, and the mixture is heated to 235° C. at 0.2 MPa for 70 minutes to carry out an esterification reaction, and compound A is obtained after completion, and the remaining catalyst and auxiliary agent are added and stirred continuously at a stirring speed of 30 rpm, and after reducing pressure, a co-condensation reaction is carried out in a vacuum environment at a stirring speed of 55 rpm, and stirring is stopped after the diol is removed to obtain a polymer B, and the modified polyethylene terephthalate slices are obtained after cooling and pelletizing.

[0053] The molar ratio of terephthalic acid, ethylene glycol and cyclohexanediol is 1:0.8:0.4.

[0054] Cyclohexanediol is 1,4-cyclohexanedimethanol, which is a cis-trans isomer with 30% cis and 70% trans.

[0055] The conditions of the co-condensation reaction are: pressure <0.1 kPa, temperature 275°C, and reaction time 80 min.

[0056] The amount of catalyst added was 0.09% of the molar amount of terephthalic acid.

[0057] The catalyst is a mixture of tetrabutyl titanate, cobalt acetate, zinc acetate and germanium oxide, and the molar ratio of each substance is 0.25:0.6:1:0.7.

[0058] The auxiliary agent is tributyl phosphate, and the amount of the auxiliary agent added is 0.03% of the molar amount of terephthalic acid.

[0059] The polyamide chips were nylon 66 with an intrinsic viscosity of 2.7 dL / g, purchased from Sinopec Shanghai Petrochemical Co., Ltd.

[0060] The reinforcing materials are modified calcium carbonate whiskers and white carbon black, and the weight ratio of the two is 1:0.75.

[0061] The intrinsic viscosity of the modified polyethylene terephthalate chips obtained in this example is 0.678 dL / g.

[0062] Modified calcium carbonate whiskers are obtained by the following steps:

[0063] (1) Add an equal volume of 0.2 mol / L CaCl 2 Solution and NaCO 3 The solution was simultaneously added dropwise into a reactor containing distilled water at 85°C, stirred at a speed of 160 r / min for 4 hours, and aged at 85°C for 1 hour after the reaction was completed, then filtered and pulped and washed twice, and dried to obtain calcium carbonate whiskers;

[0064] (2) The obtained calcium carbonate whiskers are made into a slurry, and an anhydrous ethanol solution containing 3 wt% sodium stearate is added for ultrasonic dispersion for 1 hour, and then stirred in a water bath at 80° C. and a speed of 1200 r / min for 0.5 hour, filtered and dried to obtain the modified calcium carbonate whiskers.

[0065] The amount of distilled water added in step (1) is NaCO 3 Half the volume of the solution.

[0066] The slurry in step (2) is a mixture of calcium carbonate whiskers and water, and the mass fraction of calcium carbonate whiskers in the slurry is 8.5%.

[0067] The white carbon black is fumed white carbon black, selected from Evonik Degussa, model R974, with a specific surface area of ​​170m 2 / g, and the average particle size is 12nm.

[0068] The toughening agent is calcium stearate soap and butyl epoxy furoate, with a weight ratio of 1:0.4; the coupling agent is KH550.

[0069] The method for preparing the battery electrolyte-resistant PET film comprises the following steps:

[0070] S1. Mix the raw materials according to the proportion, add them into a granulator and perform granulation at 90° C. to obtain substance A;

[0071] S2, pre-crystallizing and drying the substance A at 165° C. to obtain substance B;

[0072] S3, using a twin-screw extruder to melt and plasticize the substance B at 275° C. to obtain a mixture;

[0073] S4, subjecting the mixture obtained in S3 to a sheet casting process at 25° C. to obtain a pretreated sheet;

[0074] S5, sequentially stretching the pretreated sheet longitudinally and transversely, heat-setting, cooling, and winding to obtain the PET film;

[0075] The longitudinal stretching temperature was 115° C., the longitudinal stretching ratio was 3.5, the transverse stretching temperature was 130° C., and the transverse stretching ratio was 3.0.

[0076] Example 2

[0077] A PET film resistant to battery electrolyte comprises the following raw materials in parts by weight: 60 parts of modified polyethylene terephthalate slices, 15 parts of polyamide slices, 5 parts of toughening agents, 0.5 parts of coupling agents, 1 part of reinforcing materials, and 0.1 parts of trimethyl phosphate.

[0078] The modified polyethylene terephthalate slices are obtained by the following steps: terephthalic acid, ethylene glycol, cyclohexanediol and 60wt% of a catalyst are added into a reactor and stirred, and the mixture is heated to 225°C at 0.3MPa for esterification reaction for 60min to obtain compound A, and the remaining catalyst and auxiliary agent are added and stirred continuously at a stirring speed of 30rpm. After decompression, the mixture is stirred at a rotation speed of 55rpm in a vacuum environment for co-condensation reaction, and the stirring is stopped after the diol is removed to obtain polymer B. The modified polyethylene terephthalate slices are obtained after cooling and pelletizing.

[0079] The molar ratio of terephthalic acid, ethylene glycol and cyclohexanediol is 1:0.7:0.5.

[0080] Cyclohexanediol is 1,4-cyclohexanedimethanol, which is a cis-trans isomer with 30% cis and 70% trans.

[0081] The conditions of the co-condensation reaction are: pressure <0.1 kPa, temperature 265°C, and reaction time 60 min.

[0082] The amount of catalyst added was 0.07% of the molar amount of terephthalic acid.

[0083] The catalyst is a mixture of tetrabutyl titanate, cobalt acetate, zinc acetate and germanium oxide, and the molar ratio of each substance is 0.25:0.6:1:0.7.

[0084] The auxiliary agent is tributyl phosphate, and the amount of the auxiliary agent added is 0.02% of the molar amount of terephthalic acid.

[0085] The intrinsic viscosity of the modified polyethylene terephthalate chips obtained in this example is 0.668 dL / g.

[0086] The polyamide chips were nylon 66 with an intrinsic viscosity of 2.7 dL / g, purchased from Sinopec Shanghai Petrochemical Co., Ltd.

[0087] The reinforcing materials are modified calcium carbonate whiskers and white carbon black, and the weight ratio of the two is 1:0.5.

[0088] Modified calcium carbonate whiskers are obtained by the following steps:

[0089] (1) Add an equal volume of 0.2 mol / L CaCl 2 Solution and NaCO 3 The solution was simultaneously added dropwise into a reactor containing distilled water at 85°C, stirred at a speed of 160 r / min for 4 hours, and aged at 85°C for 1 hour after the reaction was completed, then filtered and pulped and washed twice, and dried to obtain calcium carbonate whiskers;

[0090] (2) The obtained calcium carbonate whiskers are made into a slurry, and an anhydrous ethanol solution containing 3 wt% sodium stearate is added for ultrasonic dispersion for 1 hour, and then stirred in a water bath at 80° C. and a speed of 1200 r / min for 0.5 hour, filtered and dried to obtain the modified calcium carbonate whiskers.

[0091] The amount of distilled water added in step (1) is NaCO 3 Half the volume of the solution.

[0092] The slurry in step (2) is a mixture of calcium carbonate whiskers and water, and the mass fraction of calcium carbonate whiskers in the slurry is 8.5%.

[0093] The white carbon black is fumed white carbon black, selected from Evonik Degussa, model R974, with a specific surface area of ​​170m 2 / g, and the average particle size is 12nm.

[0094] The toughening agent is calcium stearate soap and butyl epoxy furoate, with a weight ratio of 1:0.4; the coupling agent is KH550.

[0095] The method for preparing the battery electrolyte-resistant PET film comprises the following steps:

[0096] S1. Mix the raw materials according to the proportion, add them into a granulator and perform granulation at 85° C. to obtain substance A;

[0097] S2, pre-crystallizing and drying the substance A at 160° C. to obtain substance B;

[0098] S3, using a twin-screw extruder to melt and plasticize the substance B at 260° C. to obtain a mixture;

[0099] S4, subjecting the mixture obtained in S3 to a sheet casting process at 25° C. to obtain a pretreated sheet;

[0100] S5, sequentially stretching the pretreated sheet longitudinally and transversely, heat-setting, cooling, and winding to obtain the PET film;

[0101] The longitudinal stretching temperature was 110° C., the longitudinal stretching ratio was 3.0, and the transverse stretching temperature was 120° C., the transverse stretching ratio was 2.5.

[0102] Example 3

[0103] A PET film resistant to battery electrolyte comprises the following raw materials in parts by weight: 80 parts of modified polyethylene terephthalate slices, 40 parts of polyamide slices, 20 parts of toughening agents, 1 part of coupling agents, 5 parts of reinforcing materials and 1 part of trimethyl phosphate.

[0104] The modified polyethylene terephthalate slice is obtained by the following steps: terephthalic acid, ethylene glycol, cyclohexanediol and 40wt% of a catalyst are added into a reactor and stirred, and the mixture is heated to 250°C at 0.2MPa for esterification reaction for 80min to obtain compound A, and the remaining catalyst and auxiliary agent are added and stirred continuously at a stirring speed of 30rpm. After decompression, the mixture is stirred at a rotation speed of 55rpm in a vacuum environment for co-condensation reaction, and the stirring is stopped after the diol is removed to obtain polymer B. The modified polyethylene terephthalate slice is obtained after cooling and pelletizing.

[0105] The molar ratio of terephthalic acid, ethylene glycol and cyclohexanediol is 1:0.85:0.35.

[0106] Cyclohexanediol is 1,4-cyclohexanedimethanol, which is a cis-trans isomer with 30% cis and 70% trans.

[0107] The conditions of the co-condensation reaction are: pressure <0.1 kPa, temperature 265°C, and reaction time 60 min.

[0108] The amount of catalyst added was 0.1% of the molar amount of terephthalic acid.

[0109] The catalyst is a mixture of tetrabutyl titanate, cobalt acetate, zinc acetate and germanium oxide, and the molar ratio of each substance is 0.25:0.6:1:0.7.

[0110] The auxiliary agent is tributyl phosphate, and the amount of the auxiliary agent added is 0.04% of the molar amount of terephthalic acid.

[0111] The intrinsic viscosity of the modified polyethylene terephthalate chips obtained in this example is 0.691 dL / g.

[0112] The polyamide chips were nylon 66 with an intrinsic viscosity of 2.7 dL / g, purchased from Sinopec Shanghai Petrochemical Co., Ltd.

[0113] The reinforcing materials are modified calcium carbonate whiskers and white carbon black, and the weight ratio of the two is 1:1.

[0114] Modified calcium carbonate whiskers are obtained by the following steps:

[0115] (1) Add an equal volume of 0.2 mol / L CaCl 2 Solution and NaCO 3 The solution was simultaneously added dropwise into a reactor containing distilled water at 85°C, stirred at a speed of 160 r / min for 4 hours, and aged at 85°C for 1 hour after the reaction was completed, then filtered and pulped and washed twice, and dried to obtain calcium carbonate whiskers;

[0116] (2) The obtained calcium carbonate whiskers are made into a slurry, and an anhydrous ethanol solution containing 3 wt% sodium stearate is added for ultrasonic dispersion for 1 hour, and then stirred in a water bath at 80° C. and a speed of 1200 r / min for 0.5 hour, filtered and dried to obtain the modified calcium carbonate whiskers.

[0117] The amount of distilled water added in step (1) is NaCO 3 Half the volume of the solution.

[0118] The slurry in step (2) is a mixture of calcium carbonate whiskers and water, and the mass fraction of calcium carbonate whiskers in the slurry is 8.5%.

[0119] The white carbon black is fumed white carbon black, selected from Evonik Degussa, model R974, with a specific surface area of ​​170m 2 / g, and the average particle size is 12nm.

[0120] The toughening agent is calcium stearate soap and butyl epoxy furoate, with a weight ratio of 1:0.4; the coupling agent is KH550.

[0121] The method for preparing the battery electrolyte-resistant PET film comprises the following steps:

[0122] S1. Mix the raw materials according to the proportion, add them into a granulator and perform granulation at 95° C. to obtain substance A;

[0123] S2, pre-crystallizing and drying the substance A at 170° C. to obtain substance B;

[0124] S3, using a twin-screw extruder to melt and plasticize the substance B at 285° C. to obtain a mixture;

[0125] S4, subjecting the mixture obtained in S3 to a sheet casting process at 25° C. to obtain a pretreated sheet;

[0126] S5, sequentially stretching the pretreated sheet longitudinally and transversely, heat-setting, cooling, and winding to obtain the PET film;

[0127] The longitudinal stretching temperature was 120° C., the longitudinal stretching ratio was 4.0, and the transverse stretching temperature was 135° C., the transverse stretching ratio was 4.0.

[0128] Example 4

[0129] This embodiment provides a PET film resistant to battery electrolyte and a preparation method thereof. The specific implementation method is the same as that of Example 1, except that the raw materials include 50 parts of modified polyethylene terephthalate slices and 50 parts of polyamide slices.

[0130] Example 5

[0131] This embodiment provides a PET film resistant to battery electrolyte and a preparation method thereof. The specific implementation method is the same as that of Example 1, except that the modified polyethylene terephthalate slices in the raw material are replaced by commercially available unmodified polyethylene terephthalate slices;

[0132] The intrinsic viscosity of the polyethylene terephthalate chips is 0.675 dL / g.

[0133] Example 6

[0134] This embodiment provides a PET film resistant to battery electrolyte and a preparation method thereof. The specific implementation method is the same as that of Example 1, except that the reinforcing material in the raw material does not include modified calcium carbonate whiskers.

[0135] Example 7

[0136] This embodiment provides a PET film resistant to battery electrolyte and a preparation method thereof. The specific implementation method is the same as that of Example 1, except that the reinforcing material in the raw material does not include fumed silica.

[0137] Performance Testing

[0138] 1. Electrolyte resistance

[0139] 3 ml of electrolyte was dripped on the surface of the PET film prepared in Examples 1-7 respectively. After 48 hours at 25°C and a relative humidity of 50%, the dripped electrolyte was wiped off with a dust-free cloth moistened with alcohol, and the corrosion on the surface of the film was observed with the naked eye. If the surface of the film does not turn white, it means that the electrolyte resistance is excellent, which is recorded as √; if the surface of the film turns white, it means that the electrolyte resistance is poor, which is recorded as ×. The test results are shown in Table 1.

[0140] The electrolyte is a mixed solution of dimethyl carbonate, ethylene carbonate and ethyl methyl carbonate in a volume ratio of 1:1:1, and 1 mol of lithium hexafluorophosphate is added and mixed evenly.

[0141] 2. Punching performance

[0142] The PET films prepared in Examples 1-7 were respectively subjected to 6 mm depth punching. If cracks were observed on the films, it indicated that the punching performance was poor, which was recorded as ▲; if no cracks were observed on the films, it indicated that the punching performance was good, which was recorded as ◆. The test results are shown in Table 1.

[0143] Table 1

[0144] serial number Electrolyte resistance Punching performance Example 1 √ ◆ Example 2 √ ◆ Example 3 √ ◆ Example 4 √ ▲ Example 5 × ▲ Example 6 √ ▲ Example 7 √ ▲

[0145] It can be seen from the test data in Table 1 that the PET films prepared in Examples 1-3 of the present invention can have excellent electrolyte resistance and cratering performance at the same time. Example 4 adjusts the ratio of modified polyethylene terephthalate slices and polyamide slices in the raw materials, which has no obvious effect on the electrolyte resistance, but causes the cratering performance of the PET film to deteriorate; Example 5 uses modified polyethylene terephthalate slices instead of modified polyethylene terephthalate slices, resulting in significant deterioration of the electrolyte resistance and cratering performance of the PET film; Examples 6 and 7 change the type of reinforcing material, which has no obvious effect on the electrolyte resistance of the PET film, but significantly deteriorates the cratering performance.

[0146] Finally, it should be noted that the above specific implementation methods are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to examples, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the spirit and scope of the technical solution of the present invention, which should be included in the scope of the claims of the present invention.

Claims

1. A PET film resistant to battery electrolyte, It is characterized in that The raw materials include, by weight: 60-80 parts of modified polyethylene terephthalate slices, 15-40 parts of polyamide slices, 5-20 parts of toughening agent, 0.5-1 parts of coupling agent, 1-5 parts of reinforcing material, and 0.1-1 parts of heat stabilizer; The modified polyethylene terephthalate slices are obtained by the following steps: adding terephthalic acid, ethylene glycol, cyclohexanediol and 40-60wt% of a catalyst into a reactor and stirring, heating to carry out an esterification reaction, obtaining compound A after completion, adding the remaining catalyst and auxiliary agent and continuing to stir, carrying out a co-condensation reaction in a vacuum environment after reducing pressure, stopping stirring after removing the diol, obtaining polymer B, and obtaining the modified polyethylene terephthalate slices after cooling and pelletizing; The intrinsic viscosity of the polyamide chips is 2-3 dL / g; The reinforcing material is modified calcium carbonate whisker and white carbon black, and the weight ratio of the two is 1: (0.5-1); The modified calcium carbonate whisker is obtained by the following steps: (1) Add an equal volume of 0.2 mol / L CaCl 2 Solution and NaCO 3 The solution is simultaneously added dropwise into a reactor containing distilled water at 80-90° C., stirred at a speed of 120-200 r / min for 4 hours, and after the reaction is completed, the mixture is aged at a constant temperature of 80-90° C. for 1 hour, then filtered and pulped and washed twice, and dried to obtain calcium carbonate whiskers; (2) preparing the obtained calcium carbonate whiskers into a slurry, adding an anhydrous ethanol solution containing 3 wt% sodium stearate to ultrasonically disperse for 1 hour, then stirring in a water bath at 80° C. and a speed of 1200 r / min for 0.5 hour, filtering and drying to obtain the modified calcium carbonate whiskers; The white carbon black is gas phase white carbon black with a specific surface area of ​​160-180m 2 / g, and the average particle size is 10-15nm.

2. A battery electrolyte-resistant PET film according to claim 1, It is characterized in that The molar ratio of terephthalic acid, ethylene glycol and cyclohexanediol is 1:(0.7-0.85):(0.35-0.5).

3. The battery electrolyte-resistant PET film according to claim 1, It is characterized in that The conditions of the esterification reaction are: pressure 0.2-0.3 MPa, temperature 225-250° C., and reaction time 60-80 min.

4. The battery electrolyte-resistant PET film according to claim 1, It is characterized in that The conditions of the co-condensation reaction are: pressure <0.1 kPa, temperature 265-280° C., and reaction time 60-100 min.

5. The battery electrolyte-resistant PET film according to claim 1, It is characterized in that The toughening agent is calcium stearate soap and / or butyl epoxy furoate.

6. A method for preparing a battery electrolyte-resistant PET film according to any one of claims 1 to 5, It is characterized in that The following steps are involved: S1, mixing the raw materials according to the proportion, adding them into a granulator for granulation treatment, and obtaining substance A; S2, pre-crystallizing and drying the substance A to obtain substance B; S3, using a twin-screw extruder to melt and plasticize the substance B to obtain a mixture; S4, subjecting the mixture obtained in S3 to a sheet casting process to obtain a pretreated sheet; S5, sequentially stretching the pretreated sheet longitudinally and transversely, heat-setting, cooling, and winding to obtain the PET film; The longitudinal stretching temperature is 110-120°C, the longitudinal stretching ratio is 3.0-4.0, the transverse stretching temperature is 120-135°C, and the transverse stretching ratio is 2.5-4.

0.

7. The method for preparing the battery electrolyte-resistant PET film according to claim 6, It is characterized in that The granulation temperature in the step S1 is 85-95°C, the pre-crystallization temperature in the step S2 is 160-170°C, and the melting temperature of the twin-screw extruder in the step S3 is 260-285°C.