Polyester film for blue adhesive tape and preparation method of polyester film

Abstract

The invention discloses a polyester film for a blue adhesive tape, which is used for binding and packaging a battery of a new energy electric vehicle. The polyester film is prepared from 70-85 parts by weight of high-viscosity polyethylene glycol terephthalate, 5-12 parts by weight of thermoplastic polyurethane, 2-4 parts by weight of siloxane resin powder, 1-3 parts by weight of melamine cyanurate, 2-5 parts by weight of organic modified montmorillonite, 1-3 parts by weight of a coupling agent and 1-3 parts by weight of a coupling agent. 1-3 parts by weight of aromatic polyimide micro powder and 0.3-0.5 part by weight of ethylene glycol monostearate. The invention also discloses a preparation method of the polyester film. The polyester film for the blue adhesive tape is excellent in dielectric strength, flexibility, puncture resistance and flame retardance, the characteristics directly correspond to strict requirements of automobile lithium battery shell packaging, and comprehensive guarantee is provided for safety, reliability and environmental adaptability.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of polymer film, in particular to a polyester film for packaging, and especially to a polyester film for blue tape and a preparation method thereof. BACKGROUND

[0002] The battery of a new energy electric vehicle is usually bound and packaged with a blue tape. This blue tape plays an important role in the insulation and physical protection of power batteries. However, with the progress of new energy vehicle technology and the improvement of market demand, the blue tape also faces some challenges and improvement needs. This blue tape is also called blue tape or PET blue film, which is a single-sided tape with pressure-sensitive adhesive (PSA) on the back of a PET substrate, and is named for its deep blue appearance. It is mainly used for insulation protection and fixation of power batteries, and is widely used in the packaging of lithium batteries in electric vehicles, mobile phones, laptops and other fields.

[0003] In the packaging and assembly process of new energy electric vehicle batteries, the blue tape needs to cope with the risk of thermal runaway, such as internal or external short circuit of the battery, which may cause the risk of fire or explosion. It also needs to cope with the risk of electric shock, such as the exposed conductive part of the battery without proper covering or protection, which may cause electric shock to the operator. The existing blue tape usually has problems of insufficient adhesion, insufficient tensile performance and tensile strength, poor insulation performance, and insufficient tear resistance.

[0004] CN 118931398 A discloses a blue tape for new energy vehicle batteries and a preparation method thereof. The blue tape includes a three-layer structure, the outer layer is a PET release film, the middle layer is a UV enhancement layer, and the inner layer is a blue PVC substrate film. The blue tape of the prior art uses PVC as the substrate, which has deficiencies in temperature change resistance, aging resistance, durability, insulation, strength and other aspects compared to traditional PET substrates. SUMMARY

[0005] The technical problem to be solved by the present application is to provide a polyester film for blue tape and a preparation method thereof to reduce or avoid the problems mentioned above.

[0006] To solve the above technical problems, the present application provides a polyester film for blue tape for the binding and packaging of batteries of new energy electric vehicles, wherein the polyester film is composed of 70-85 parts by weight of high-viscosity polyethylene terephthalate, 5-12 parts by weight of thermoplastic polyurethane, 2-4 parts by weight of silicone resin powder, 1-3 parts by weight of melamine cyanurate, 2-5 parts by weight of organically modified montmorillonite, 1-3 parts by weight of aromatic polyimide micro powder, and 0.3-0.5 parts by weight of ethylene glycol monostearate.

[0007] Preferably, the high viscosity polyethylene terephthalate has an intrinsic viscosity ≥ 0.8.

[0008] Preferably, the aromatic polyimide micro powder has a particle size of 1-5 μm.

[0009] The present application also provides a preparation method of the polyester film, comprising the following steps: firstly, pretreating each raw material; after the pretreatment of the raw materials, feeding all the raw materials into a double screw extruder according to the ratio for high shear melting blending; after the melting blending of the raw materials, extruding through the double screw extruder; after the extrusion, bidirectional stretching; after the bidirectional stretching, cooling the film through a cooling system; and finally, winding the cooled film through an automatic winding machine.

[0010] Preferably, the pretreatment of each raw material further comprises: preheating the high viscosity polyethylene terephthalate to 80-100 ℃; preheating the thermoplastic polyurethane to 50-70 ℃; and sieving the silicone resin powder through a mesh less than 100.

[0011] Preferably, the pretreatment of each raw material further comprises: mixing the organic modified montmorillonite with isopropyl alcohol according to a weight ratio of 1:0.5-1:2, and then treating through ultrasonic dispersion with a frequency of 20-40 kHz for 30-60 minutes.

[0012] Preferably, the high shear mixing parameters of the double screw extruder are set as: screw rotation speed of 250-500 rpm, shear rate of 100-500 s-1, and residence time of the material in the mixing zone of 60-90 seconds.

[0013] Preferably, the extrusion temperature of the double screw extruder is set to 250-280 ℃.

[0014] Preferably, the bidirectional stretching is performed by first performing longitudinal stretching with a stretching ratio of 2-4 times, and then performing transverse stretching with a stretching ratio of 3.5 times, and the temperature is controlled to be between 150-180 ℃ during the stretching.

[0015] Preferably, the cooling temperature of the film by the cooling system is 30-50 ℃, and the winding speed of the automatic winding machine is 5-15 m / min.

[0016] The polyester film for blue adhesive tape designed by the present application has excellent dielectric strength, flexibility, puncture resistance and flame retardance, which directly meets the strict requirements of the automobile lithium battery shell packaging and provides comprehensive guarantee for safety, reliability and environmental adaptability. BRIEF DESCRIPTION OF DRAWINGS

[0017] The following drawings are merely intended to illustrate and explain the present application, and do not limit the scope of the present application.

[0018] Figure 1 A structural diagram of a blue tape is shown according to one specific embodiment of the present application. DETAILED DESCRIPTION

[0019] In order to have a clearer understanding of the technical features, objects and effects of the present application, the specific embodiments of the present application will be described with reference to the accompanying drawings. In the drawings, the same components are denoted by the same reference numerals.

[0020] As Figure 1 shown, the present application proposes a blue tape which can be used for the bundling and packaging of the batteries of new energy electric vehicles, the blue tape is composed of a surface layer PET transparent film 1, an intermediate blue adhesive layer 2, a bottom layer PET transparent film 3, and a back blue adhesive layer 4. In order to protect the back blue adhesive layer 4, a layer of PET release film 5 can also be attached to the outside of the back blue adhesive layer 4.

[0021] Unlike the conventional blue tape which adopts a single layer of PET film, the present application adopts the intermediate blue adhesive layer 2 to bond and composite the surface layer PET transparent film 1 and the bottom layer PET transparent film 3 into a sandwich film, which replaces the conventional single layer of PET film to obtain excellent shear resistance, wear resistance and puncture resistance, and compared with the single layer of PET film, the sandwich film has better tensile strength, softness and conformability.

[0022] Further, the present application designs and proposes a polyester film for blue tape, that is, a specially designed PET transparent film which can bond two layers of polyester film into a sandwich film with blue adhesive, so that the sandwich film has the above-mentioned excellent performance.

[0023] Specifically, the polyester film for blue tape of the present application is composed of 70-85 parts by weight of high viscosity polyethylene terephthalate (PET), 5-12 parts by weight of thermoplastic polyurethane (TPU), 2-4 parts by weight of silicone resin powder, 1-3 parts by weight of melamine cyanurate (MCA), 2-5 parts by weight of organically modified montmorillonite, 1-3 parts by weight of aromatic polyimide (PI) micro powder, and 0.3-0.5 parts by weight of ethylene glycol monostearate (EGMS).

[0024] Further, the high viscosity polyethylene terephthalate (PET) is used as a base material to provide excellent mechanical properties, heat resistance and dimensional stability, and preferably a PET with a specific viscosity ≥0.8 is used.

[0025] The thermoplastic polyurethane (TPU) is used to improve the flexibility and conformability of the film and reduce the overall brittleness; at the same time, through the blending with the PET base, the softness and conformability of the film are significantly improved. It can be selected to use, for example, Desmopan series TPU of Bayer, Germany.

[0026] Silicone resin powder is used as a synergistic flame retardant to improve the flame retardant performance, form a dense silica layer on the surface to prevent the spread of fire; at the same time, it is used to enhance the wear resistance and smoothness of the material surface. Dow Corning 904H (Dow Corning 904H) can be selected.

[0027] Melamine cyanurate (MCA) is used to provide efficient nitrogen-based flame retardant function, release inert gas at high temperature to inhibit combustion. Conventional MCA on the market can be used.

[0028] Organically modified montmorillonite provides a layered reinforcing effect, which is used to enhance the puncture resistance and mechanical strength of the film, and at the same time, improve the barrier performance and adhesion. At the same time, due to its nanosheet structure, it enhances the barrier property and wear resistance, and can improve the adhesion of the blue adhesive. Cloisite 30B of Clariant (Switzerland) can be selected.

[0029] Aromatic polyimide (PI) micro powder is used to improve the electrical insulation performance (dielectric strength and volume resistance) of the material, enhance the puncture resistance and heat deformation resistance, and is particularly suitable for the high-strength protection requirements of automobile lithium batteries. The PI powder forms a micro-dispersed phase in the film, which can also enhance the overall mechanical properties. PI micro powder with a particle size of 1-5 μm can be selected, such as Kapton polyimide powder series of DuPont (Kapton Polyimide Powder).

[0030] Ethylene glycol monostearate (EGMS) is used to provide excellent dispersion effect while maintaining the overall mechanical properties and thermal stability of the material. Conventional EGMS on the market can be used.

[0031] In a specific embodiment, the polyester film of the blue adhesive tape of the present application can be prepared by the following method.

[0032] For example, before starting to prepare the polyester film, the raw materials are first pretreated to ensure the uniformity and compatibility of the components.

[0033] For example, high-viscosity PET (intrinsic viscosity ≥ 0.8) needs to be preheated to 80-100°C to reduce its viscosity and improve its flowability. Thermoplastic polyurethane (TPU) needs to be preheated to 50-70°C to prevent caking and ensure good mixing with the polyester matrix. Silicone resin powder (such as Dow Corning 904H) needs to be sieved through a mesh smaller than 100 to ensure the uniformity of the powder and avoid agglomeration. Melamine cyanurate (MCA), aromatic polyimide (PI) micro powder, and ethylene glycol monostearate (EGMS) can be directly added without pretreatment.

[0034] In order to avoid agglomeration, the organic modified montmorillonite needs to be subjected to ultrasonic dispersion treatment. For example, the organic modified montmorillonite (such as Cloisite 30B) can be mixed with isopropyl alcohol at a weight ratio of 1:0.5-1:2, and then subjected to ultrasonic dispersion treatment at a frequency of 20-40 kHz for 30-60 minutes to ensure uniform dispersion. Isopropyl alcohol has high volatility (boiling point 82.5°C) and will quickly volatilize before the melt extrusion of the polyester material or during the cooling process, and will not remain in the film.

[0035] After the raw materials are pretreated, all the raw materials are put into a twin-screw extruder according to the ratio for high-shear melt blending, wherein the high-shear mixing parameters of the twin-screw extruder are set as follows: screw rotation speed 250-500 rpm, shear rate 100-500 s-1, and residence time of the material in the mixing zone 60-90 seconds. The order of adding the components is as follows: first, the PET matrix is added, then the TPU and other additives are added, to ensure good mixing effect.

[0036] During the twin-screw extrusion process, high shear can form a micro-uniform dispersion system of PET, TPU and montmorillonite, high shear can strip the layered structure of montmorillonite, increase the interface interaction, and at the same time improve the dispersibility and uniformity of the material; meanwhile, high shear can enhance the micro-network structure, so that the mechanical strength and flexibility of the film are simultaneously improved.

[0037] After the raw materials are melt blended, the extrusion temperature of the twin-screw extruder is set to 250-280°C, and after extrusion, biaxial stretching is performed: first, longitudinal stretching is performed at a stretching ratio of 2-4 times, and then transverse stretching is performed at a stretching ratio of 3.5 times, and during the stretching process, the temperature is controlled between 150-180°C, to ensure that the film can be effectively stretched and maintain excellent physical properties.

[0038] After biaxial stretching, the film is cooled by a cooling system at a cooling temperature of 30-50°C to ensure rapid solidification of the film. Finally, the cooled film is wound by an automatic winding machine, and the winding speed is usually 5-15 m / min.

[0039] The functional properties of the polyester film for blue adhesive tape of the present application are described in detail below through specific examples.

[0040] Example 1

[0041] High-viscosity polyethylene terephthalate: 70 parts by weight; thermoplastic polyurethane: 5 parts by weight; silicone resin powder: 2 parts by weight; melamine cyanurate: 1 part by weight; organic modified montmorillonite: 2 parts by weight; aromatic polyimide micro powder: 1 part by weight; fatty acid ester dispersant: 0.3 parts by weight.

[0042] The polyester film thus prepared had a thickness of 50 μm. The film was measured for various performance parameters as follows: dielectric strength: 130 kV / mm; volume resistance: ≥1014Ω-cm; tensile strength: 162 MPa; elongation at break: 115%; puncture resistance: 85 N / mm; flame retardancy (UL-94): V-0; adhesion (to an adhesive): ≥30 N / 25 mm.

[0043] Example 2

[0044] High viscosity polyethylene terephthalate: 85 parts by weight; thermoplastic polyurethane: 12 parts by weight; silicone resin powder: 4 parts by weight; melamine cyanurate: 3 parts by weight; organically modified montmorillonite: 5 parts by weight; aromatic polyimide micro powder: 3 parts by weight; fatty acid ester dispersant: 0.5 parts by weight.

[0045] The polyester film thus prepared had a thickness of 60 μm. The film was measured for various performance parameters as follows: dielectric strength: 135 kV / mm; volume resistance: ≥1014Ω-cm; tensile strength: 170 MPa; elongation at break: 120%; puncture resistance: 90 N / mm; flame retardancy (UL-94): V-0; adhesion (to an adhesive): ≥32 N / 25 mm.

[0046] Example 3

[0047] High viscosity polyethylene terephthalate: 77.5 parts by weight; thermoplastic polyurethane: 8.5 parts by weight; silicone resin powder: 3 parts by weight; melamine cyanurate: 2 parts by weight; organically modified montmorillonite: 3.5 parts by weight; aromatic polyimide micro powder: 2 parts by weight; fatty acid ester dispersant: 0.4 parts by weight.

[0048] The polyester film thus prepared had a thickness of 75 μm. The film was measured for various performance parameters as follows: dielectric strength: 125 kV / mm; volume resistance: ≥1014Ω-cm; tensile strength: 165 MPa; elongation at break: 118%; puncture resistance: 87 N / mm; flame retardancy (UL-94): V-0; adhesion (to an adhesive): ≥31 N / 25 mm.

[0049] Example 4

[0050] High viscosity polyethylene terephthalate: 80 parts by weight; thermoplastic polyurethane: 7 parts by weight; silicone resin powder: 3.5 parts by weight; melamine cyanurate: 2.5 parts by weight; organically modified montmorillonite: 4 parts by weight; aromatic polyimide micro powder: 2.5 parts by weight; fatty acid ester dispersant: 0.4 parts by weight.

[0051] The polyester film thus obtained had a thickness of 85 μm. The film was measured for various performance parameters as follows: dielectric strength: 140 kV / mm; volume resistance: ≥1014Ω-cm; tensile strength: 167 MPa; elongation at break: 122%; puncture resistance: 92 N / mm; flame retardancy (UL-94): V-0; adhesion (to adhesive): ≥33 N / 25 mm.

[0052] Example 5

[0053] High viscosity polyethylene terephthalate: 75 parts by weight; thermoplastic polyurethane: 10 parts by weight; silicone resin powder: 3 parts by weight; melamine cyanurate: 2 parts by weight; organically modified montmorillonite: 4.5 parts by weight; aromatic polyimide micro powder: 2 parts by weight; fatty acid ester dispersant: 0.3 parts by weight.

[0054] The polyester film thus obtained had a thickness of 65 μm. The film was measured for various performance parameters as follows: dielectric strength: 132 kV / mm; volume resistance: ≥1014Ω-cm; tensile strength: 162 MPa; elongation at break: 116%; puncture resistance: 88 N / mm; flame retardancy (UL-94): V-0; adhesion (to adhesive): ≥32 N / 25 mm.

[0055] Example 6

[0056] High viscosity polyethylene terephthalate: 78 parts by weight; thermoplastic polyurethane: 9 parts by weight; silicone resin powder: 3 parts by weight; melamine cyanurate: 2 parts by weight; organically modified montmorillonite: 4 parts by weight; aromatic polyimide micro powder: 2 parts by weight; fatty acid ester dispersant: 0.4 parts by weight.

[0057] The polyester film thus obtained had a thickness of 70 μm. The film was measured for various performance parameters as follows: dielectric strength: 128 kV / mm; volume resistance: ≥1014Ω-cm; tensile strength: 160 MPa; elongation at break: 114%; puncture resistance: 85 N / mm; flame retardancy (UL-94): V-0; adhesion (to adhesive): ≥30 N / 25 mm.

[0058] The performance parameters of the polyester films of Examples 1 to 6 were summarized as follows: dielectric strength ≥ 120 kV / mm; volume resistance ≥ 1014Ω-cm; tensile strength ≥ 160 MPa; elongation at break ≥ 110%; puncture resistance ≥ 80 N / mm; flame retardancy rating UL94 V-0; adhesion (to adhesive) ≥ 30 N / 25 mm.

[0059] Comparative Example 1

[0060] The aromatic polyimide was replaced with a general polyimide, and the film thickness was 50 μm.

[0061] High viscosity polyethylene terephthalate: 70 parts by weight; thermoplastic polyurethane: 5 parts by weight; silicone resin powder: 2 parts by weight; melamine cyanurate: 1 part by weight; organically modified montmorillonite: 2 parts by weight; ordinary polyimide (instead of aromatic polyimide micro powder): 3 parts by weight; fatty acid ester dispersant: 0.3 parts by weight.

[0062] Performance parameters: dielectric strength: 115 kV / mm; volume resistance: > 1013 Ω-cm; tensile strength: 150 MPa; elongation at break: 100%; puncture resistance: 60 N / mm; flame retardancy (UL-94): V-1; adhesion (to adhesive): > 25 N / 25 mm.

[0063] Analysis: the use of ordinary polyimide instead of aromatic polyimide will greatly reduce the heat resistance, rigidity and dielectric properties of the film, resulting in a significant decrease in dielectric strength and puncture resistance.

[0064] Comparative Example 2

[0065] The content of thermoplastic polyurethane was reduced, and the film thickness was 55 μm.

[0066] High viscosity polyethylene terephthalate: 80 parts by weight; thermoplastic polyurethane: 3 parts by weight; silicone resin powder: 2 parts by weight; melamine cyanurate: 2 parts by weight; organically modified montmorillonite: 4 parts by weight; aromatic polyimide micro powder: 2 parts by weight; fatty acid ester dispersant: 0.4 parts by weight.

[0067] Performance parameters: dielectric strength: 125 kV / mm; volume resistance: > 1013 Ω-cm; tensile strength: 158 MPa; elongation at break: 105%; puncture resistance: 70 N / mm; flame retardancy (UL-94): V-2; adhesion (to adhesive): > 28 N / 25 mm.

[0068] Analysis: reducing the content of thermoplastic polyurethane will result in a decrease in the softness and conformability of the film, which in turn affects the tensile strength and puncture resistance.

[0069] Comparative Example 3

[0070] Silicone resin powder was not used, and the film thickness was 60 μm.

[0071] High viscosity polyethylene terephthalate: 75 parts by weight; thermoplastic polyurethane: 8 parts by weight; melamine cyanurate: 2 parts by weight; organically modified montmorillonite: 3 parts by weight; aromatic polyimide micro powder: 2 parts by weight; fatty acid ester dispersant: 0.4 parts by weight.

[0072] Performance parameters: dielectric strength: 120 kV / mm; volume resistance: > 1013 Ω-cm; tensile strength: 160 MPa; elongation at break: 110%; puncture resistance: 65 N / mm; flame retardancy (UL-94): V-1; adhesion (to adhesive): > 26 N / 25 mm.

[0073] Analysis: The use of no silicone resin will reduce the wear resistance and flame retardancy of the film, resulting in a decrease in the flame retardant properties and puncture resistance of the film.

[0074] Comparative Example 4

[0075] Omit melamine cyanurate, film thickness 65 μm.

[0076] High viscosity polyethylene terephthalate: 80 parts by weight; thermoplastic polyurethane: 7 parts by weight; silicone resin powder: 3 parts by weight; organically modified montmorillonite: 4 parts by weight; aromatic polyimide micro powder: 2.5 parts by weight; fatty acid ester dispersant: 0.4 parts by weight.

[0077] Performance parameters: dielectric strength: 125 kV / mm; volume resistance: > 1013 Ω-cm; tensile strength: 165 MPa; elongation at break: 100%; puncture resistance: 60 N / mm; flame retardancy (UL-94): V-2; adhesion (to adhesive): > 25 N / 25 mm.

[0078] Analysis: The removal of melamine cyanurate results in a significant decrease in the flame retardant properties of the film, and the puncture resistance becomes poor.

[0079] Comparative Example 5

[0080] No organically modified montmorillonite is used, and the film thickness is 70 μm.

[0081] High viscosity polyethylene terephthalate: 80 parts by weight; thermoplastic polyurethane: 9 parts by weight; silicone resin powder: 3 parts by weight; melamine cyanurate: 2 parts by weight; aromatic polyimide micro powder: 3 parts by weight; fatty acid ester dispersant: 0.5 parts by weight.

[0082] Performance parameters: dielectric strength: 118 kV / mm; volume resistance: > 1012 Ω-cm; tensile strength: 155 MPa; elongation at break: 90%; puncture resistance: 55 N / mm; flame retardancy (UL-94): V-2; adhesion (to adhesive): > 22 N / 25 mm.

[0083] Analysis: The use of no organically modified montmorillonite results in a decrease in the puncture resistance, tensile strength, adhesion, and other comprehensive properties of the film.

[0084] Comparative Example 6

[0085] Without fatty acid ester, film thickness 75 μm.

[0086] High viscosity polyethylene terephthalate: 75 parts by weight; thermoplastic polyurethane: 8 parts by weight; silicone resin powder: 2 parts by weight; melamine cyanurate: 1.5 parts by weight; organically modified montmorillonite: 3 parts by weight; aromatic polyimide micro powder: 2 parts by weight; ethylene glycol monostearate: 0.4 parts by weight.

[0087] Performance parameters: dielectric strength: 118 kV / mm; volume resistance: > 1010 Ω-cm; tensile strength: 155 MPa; elongation at break: 95%; puncture resistance: 60 N / mm; flame retardancy (UL-94): V-l; adhesion (to adhesive): > 22 N / 25 mm.

[0088] Analysis: Without high shear conditions, the dispersion of the material is relatively poor, especially in the dispersion of montmorillonite and silicone resin powder. This leads to a decline in certain properties of the film, such as tensile strength, puncture resistance, and flame retardancy, especially in flexibility and adhesion. Of course, although high shear conditions are not used, through appropriate temperature control, good melt mixing can still be achieved, ensuring that the main properties of the polymer matrix are relatively stable.

[0089] Comparative Example 7

[0090] Without high shear conditions, film thickness 80 μm.

[0091] High viscosity polyethylene terephthalate: 75 parts by weight; thermoplastic polyurethane: 8 parts by weight; silicone resin powder: 2 parts by weight; melamine cyanurate: 1.5 parts by weight; organically modified montmorillonite: 3 parts by weight; aromatic polyimide micro powder: 2 parts by weight; ethylene glycol monostearate: 0.4 parts by weight.

[0092] Process characteristics: hot melt mixing using a twin-screw extruder, setting normal mixing parameters, not using high shear conditions. The temperature range is controlled at 200-230°C to ensure that the polymer is fully melted, but to avoid excessive shear force.

[0093] Performance parameters: dielectric strength: 118 kV / mm; volume resistance: > 1010 Ω-cm; tensile strength: 155 MPa; elongation at break: 95%; puncture resistance: 60 N / mm; flame retardancy (UL-94): V-l; adhesion (to adhesive): > 22 N / 25 mm. 13

[0094] Analysis: Without high shear conditions, the dispersion of the material is relatively poor, especially in the dispersion of montmorillonite and silicone resin powder. This leads to a decline in certain properties of the film, such as tensile strength, puncture resistance, and flame retardancy, especially in flexibility and adhesion. Of course, although high shear conditions are not used, through appropriate temperature control, good melt mixing can still be achieved, ensuring that the main properties of the polymer matrix are relatively stable.

[0095] Comparative Example 8 ​

[0096] The intrinsic viscosity of the polyethylene terephthalate is reduced to a conventional value, and the film thickness is 85 μm.

[0097] Polyethylene terephthalate (IV = 0.6): 75 parts by weight; thermoplastic polyurethane: 8 parts by weight; silicone resin powder: 2 parts by weight; melamine cyanurate: 1 part by weight; organically modified montmorillonite: 3 parts by weight; aromatic polyimide micro powder: 2 parts by weight; ethylene glycol monostearate: 0.4 parts by weight.

[0098] Performance parameters: dielectric strength: 110 kV / mm; volume resistance: ≥ 10 12 Ω·cm; tensile strength: 140 MPa; elongation at break: 90%; puncture resistance: 50 N / mm; flame retardancy (UL-94): V-2; adhesion (to adhesive): ≥ 20 N / 25 mm.

[0099] Analysis: The low-viscosity polyethylene terephthalate has a shorter molecular chain, resulting in a decrease in the tensile strength and rigidity of the film. The film exhibits poor puncture resistance and adhesion. The polyester molecular chain with a low intrinsic viscosity is not as long as that of a high-viscosity polyester, and thus the flowability in the molten state is increased, which can result in a decrease in the elongation at break of the film and a negative impact on the mechanical strength and puncture resistance of the film. Key properties such as dielectric strength, tensile strength, and puncture resistance are decreased because the polyester matrix with a shorter molecular chain is not as strong and tough as a high-viscosity polyester, and thus cannot provide sufficient mechanical strength and insulation. The flame retardancy is reduced because the low-viscosity polyester molecular chain structure has poor load-bearing capacity for melamine cyanurate, resulting in poor flame retardancy (UL94 V-2).

[0100] The polyester films prepared in Examples 1-6 are used to prepare adhesive tapes 1-6, respectively. The basic parameters of the adhesive tapes 1-6 are as follows: surface PET transparent film 1: the polyester film of Examples 1-6, with thicknesses of 50, 60, 75, 85, 65, and 70 μm, respectively. Middle blue adhesive layer 2: a conventional acrylic pressure-sensitive adhesive with the addition of blue pigment, with a thickness of 20 μm. Bottom PET transparent film 3: the same polyester film as surface layer 1, with thicknesses of 50, 60, 75, 85, 65, and 70 μm, respectively. Back blue adhesive layer 4: also an acrylic pressure-sensitive adhesive, with a thickness of 15 μm. Release film 5: a conventional PET release film, with a thickness of 50 μm, coated with a silicone release layer.

[0101] The performance parameters of the six adhesive tapes are shown in the following table.

[0102]

[0103] The performance improvement ratio of the inventive tapes 1-6 over the conventional PET tapes is compared with the following parameters of the conventional PET tapes. The performance parameters of the conventional PET tapes are: dielectric strength 100 kV / mm; tensile strength 120 MPa; elongation at break 80%; puncture resistance 50 N / mm; adhesion 20 N / 25 mm; and flame retardant rating (UL-94) V-2.

[0104]

[0105] It can be found from the comparison that the inventive blue tapes have significant improvement in key performance. For example, the dielectric strength is significantly improved by 10%-30% due to the high dielectric properties and uniformity of the polyester film. The tensile strength is improved by 25%-37.5% due to the high viscosity polyester and the reinforcement of the fillers. The elongation at break is improved by 25%-50%, which reflects the flexibility after reinforcement. The puncture resistance is improved by 30%-60% due to the reinforcement of the fillers (such as montmorillonite and polyimide micro powder). The adhesion is improved by 50%-75%, which indicates that the adhesion of the polyester film to the adhesive layer is significantly enhanced. In addition, all the examples reach the UL-94 V-0 level, while the ordinary PET tapes only reach the V-2 level.

[0106] In summary, the polyester film of the present application can provide excellent mechanical strength and processing performance to the film by using high-viscosity polyethylene terephthalate. The thermoplastic polyurethane introduces an elastomer component, which makes the film have better flexibility and compliance. The silicone resin powder gives the film higher wear resistance and weather resistance while maintaining a smooth surface. Melamine cyanurate as an environmentally friendly flame retardant has better flame retardant performance than conventional flame retardant additives in cooperation with organically modified montmorillonite. The addition of aromatic polyimide micro powder significantly improves the heat resistance and dielectric properties of the film, while the ordinary polyimide micro powder in the comparative example shows a significant decrease in performance. The organically modified montmorillonite significantly enhances the puncture resistance, dielectric properties and flame retardancy through nano-dispersion, and the performance is significantly improved compared with ordinary mineral fillers.

[0107] In addition, the present application optimizes the process and proposes uniform dispersion under high shear conditions, which makes the compatibility of the fillers and the matrix material stronger, and the dielectric properties, mechanical strength and flame retardancy of the final film are significantly better than those of the comparative examples (the high shear process is not used in comparative examples 1 and 7, and the performance is significantly deteriorated). The use of fatty acid ester dispersant improves the dispersion effect of nano-fillers, and the film has better uniformity, smooth surface and no defects. This design is omitted in the comparative examples, resulting in a decrease in performance.

[0108] The present application shows the following differentiated performance advantages through the synergistic design of material formula and process. The prepared polyester film has higher dielectric strength: ≥120 kV / mm (embodiment), compared with ordinary PET tape only 100 kV / mm, or about 85-110 kV / mm of the comparative example. It has better mechanical strength and flexibility: tensile strength ≥160 MPa, elongation at break ≥110%, which is significantly higher than that of ordinary PET tape (tensile strength 120 MPa, elongation at break 80%). It has better puncture resistance: ≥80 N / mm, and the puncture resistance of the comparative example is generally lower than 60 N / mm, and the puncture resistance of ordinary PET tape is about 50 N / mm. The flame retardant performance is significantly improved: reaching UL94 V-0 level, while the ordinary PET tape is only V-2 level, and the comparative examples 1, 3 and 5 are only V-1 or lower. It has excellent adhesion: the adhesive force of the tape is ≥30 N / 25mm, which is significantly better than that of ordinary PET tape (20 N / 25mm), and also higher than that of the comparative examples (15-25 N / 25mm).

[0109] The blue tape prepared by the polyester film of the present application can meet the strict requirements of high-voltage environment for the electrical system of automobile lithium battery, and reduce the risk of short circuit. The UL94 V-0 level of flame retardant performance significantly improves the fire safety of lithium battery packaging materials. The physical protection ability to the battery shell is enhanced, especially in complex environment. Excellent flexibility can enhance the adhesion of the tape on irregular surfaces, reduce the phenomenon of lifting and cracking in the adhesion process. Through the optimization of fillers and process, the service life of the film is significantly prolonged, which is suitable for the environmental requirements of long-term use. The adhesion between the adhesive layer and the base film is improved, which ensures the stability of the tape in harsh environments such as high temperature and high humidity.

[0110] Through the synergistic effect between materials (such as the complex effect of aromatic polyimide and organically modified montmorillonite), the performance of the polyester film bag of the present application is not simply superimposed, but is the result of the interaction of materials. This innovative combination solves the balance problem between high dielectric, high mechanical strength and flexibility, and has a significant technical breakthrough for similar products.

[0111] In summary, the present application shows significant performance advantages compared with comparative examples 1-8 and conventional PET tape, especially in dielectric strength, flexibility, puncture resistance and flame retardancy. These characteristics directly correspond to the strict requirements of automobile lithium battery shell packaging, and provide comprehensive protection for safety, reliability and environmental adaptability.

[0112] Those skilled in the art should understand that, although the present application is described in the manner of multiple embodiments, not every embodiment contains only one independent technical solution. The description is only for the sake of clarity, and those skilled in the art should understand the specification as a whole and understand the technical solutions involved in each embodiment as being combined into different embodiments to understand the protection scope of the present application.

[0113] The above merely illustrates the specific embodiments of the present application, and is not intended to limit the scope of the present application. Any equivalent changes, modifications and combinations made by those skilled in the art without departing from the concept and principle of the present application shall fall within the scope of the present application.

Claims

1. A polyester film for a blue tape for bundling and packing a battery of a new energy electric vehicle, characterized by, The polyester film is composed of 70-85 parts by weight of high viscosity polyethylene terephthalate, 5-12 parts by weight of thermoplastic polyurethane, 2-4 parts by weight of silicone resin powder, 1-3 parts by weight of melamine cyanurate, 2-5 parts by weight of organically modified montmorillonite, 1-3 parts by weight of aromatic polyimide micro powder and 0.3-0.5 parts by weight of ethylene glycol monostearate.

2. The polyester film according to claim 1, wherein The high viscosity polyethylene terephthalate has an intrinsic viscosity of ≥0.

8.

3. The polyester film according to claim 1, wherein The particle size of the aromatic polyimide micro powder is 1-5 μm.

4. A method of producing a polyester film as claimed in any one of claims 1 to 3, characterized in that, The method comprises the following steps: firstly, pretreating each raw material; after the pretreatment of the raw materials, feeding all the raw materials into a double screw extruder according to the ratio for high shear melting blending; after the melting blending of the raw materials, extruding through the double screw extruder; after the extrusion, bidirectional stretching; after the bidirectional stretching, cooling the film through a cooling system; and finally, winding the cooled film through an automatic winding machine.

5. The method of claim 4, wherein, The pretreatment of each raw material further comprises: preheating the high viscosity polyethylene terephthalate to 80-100℃; preheating the thermoplastic polyurethane to 50-70℃; and sieving the silicone resin powder through a less than 100 mesh sieve.

6. The method of claim 4, wherein, The pretreatment of each raw material further comprises: mixing the organically modified montmorillonite with isopropyl alcohol according to a weight ratio of 1:0.5-1:2, and then treating through ultrasonic dispersion with a frequency of 20-40 kHz for 30-60 minutes.

7. The method of claim 4, wherein, The high shear mixing parameters of the double screw extruder are set as: screw rotation speed of 250-500 rpm, shear rate of 100-500 s-1, and residence time of the material in the mixing zone of 60-90 seconds.

8. The method of claim 4, wherein, The extrusion temperature of the extrusion of the double screw extruder is set to 250-280℃.

9. The method of claim 4, wherein, During the bidirectional stretching, longitudinal stretching is firstly performed with a stretching ratio of 2-4 times, and then transverse stretching is performed with a stretching ratio of 3.5 times, and in the stretching process, the temperature is controlled between 150-180℃.

10. The method of claim 4, wherein, The cooling temperature of the cooling system for the film is 30-50℃; and the winding speed of the automatic winding machine is 5-15 m / min.

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