Blue bopp termination adhesive tape base film for lithium battery and preparation method and application thereof

Abstract

This invention belongs to the field of thin films and relates to a blue BOPP termination tape base film for lithium batteries, its preparation method, and its application. The blue BOPP termination tape base film for lithium batteries comprises, sequentially arranged, an upper surface layer, an upper secondary surface layer, a core layer, a lower secondary surface layer, and a lower surface layer; the upper surface layer comprises homopolymer or copolymer polypropylene, and the lower surface layer comprises homopolymer or copolymer polypropylene; the upper and lower secondary surface layers comprise homopolymer polypropylene and 5-10 wt% modified mica filler masterbatch; the core layer comprises homopolymer polypropylene and 5-10 wt% iron blue filler masterbatch. The blue BOPP termination tape base film for lithium batteries of this invention is prepared by a one-step co-extrusion biaxial stretching process, eliminating the need for an additional blue adhesive layer, and exhibits good electrolyte resistance, reducing the precipitation of iron blue from the core layer into the electrolyte, thus meeting the requirements of lithium-ion battery production and application processes.

Description

Technical Field

[0001] This invention relates to the field of thin films, and more particularly to a blue BOPP termination tape base film for lithium batteries, its preparation method, and its application. Background Technology

[0002] A lithium battery cell mainly consists of five parts: positive electrode, negative electrode, separator, electrolyte, and encapsulation shell. During the cell manufacturing process, CCD is required for visual recognition and positioning, so termination tape is used to attach components such as separator, tabs, electrode sheets, gaskets, copper foil, and aluminum foil.

[0003] However, currently, these types of termination tapes are generally prepared by coating a colored adhesive layer onto the surface of a transparent BOPET film substrate. However, PET resin generally has poor resistance to electrolytes, and the colorants in the colored adhesive layer are prone to leaching out in the electrolyte, causing electrolyte contamination and leading to a decrease in lithium battery life. Summary of the Invention

[0004] Therefore, the purpose of this invention is to provide a blue BOPP termination tape base film for lithium batteries, its preparation method, and its application. The film is prepared using polypropylene resin as a substrate through a one-step co-extrusion biaxial stretching process, eliminating the need for an additional blue adhesive layer. The prepared termination tape base film exhibits good electrolyte resistance, reducing the precipitation of iron blue from the core layer into the electrolyte, thus meeting the requirements of lithium-ion battery production and application processes.

[0005] First aspect:

[0006] A blue BOPP termination tape base film for lithium batteries includes an upper surface layer, an upper secondary surface layer, a core layer, a secondary secondary surface layer, and a lower surface layer. The upper surface layer comprises homopolymer or copolymer polypropylene, and the lower surface layer comprises homopolymer or copolymer polypropylene. Both the secondary and secondary secondary surface layers comprise homopolymer polypropylene and 5-10 wt% modified mica filler masterbatch, wherein the modified mica filler masterbatch comprises homopolymer polypropylene and modified mica, and the modified mica is obtained by modifying mica with a silane coupling agent. The core layer comprises homopolymer polypropylene and 5-10 wt% iron blue filler masterbatch, wherein the iron blue filler masterbatch comprises homopolymer polypropylene and modified iron blue, and the modified iron blue is obtained by modifying iron blue with a hydroxyl-terminated hyperbranched polyester.

[0007] The blue BOPP termination tape base film for lithium batteries of the present invention is sequentially composed of an upper surface layer, an upper secondary surface layer, a core layer, a secondary secondary surface layer, and a lower surface layer, and is prepared by a multi-layer co-extrusion biaxial stretching process. First, the present invention uses polypropylene resin (PP) as the substrate. PP is formed by the free radical polymerization of propylene, and its molecular chain contains only non-polar C-C and CH bonds, resulting in lower polarity compared to PET. Lithium battery electrolytes are of moderate polarity. According to the principle of "like dissolves like," PET's polarity is closer to that of the electrolyte than PP. Furthermore, ester bonds themselves have hygroscopic properties and potential interactions with organic solvents. Therefore, the PP substrate has better electrolyte resistance than PET, giving the termination tape base film superior electrolyte resistance. Second, the present invention incorporates iron blue in the form of masterbatch into the core layer. The core layer containing iron blue filler masterbatch does not directly contact the external lithium battery electrolyte, ensuring the color stability of the prepared termination tape base film and reducing iron blue precipitation into the electrolyte, eliminating the need for an additional blue adhesive layer coating process. Finally, this invention further enhances the protection of the lithium battery by incorporating modified mica filler masterbatch into the upper and lower layers to form a dense protective layer. The physical barrier effect of this layer further prevents electrolyte penetration into the core layer. Through this design, the blue BOPP termination tape base film for lithium batteries of this invention reduces the precipitation of iron blue into the electrolyte and reduces electrolyte penetration into the core layer, exhibiting good electrolyte resistance.

[0008] This invention incorporates 5-10 wt% iron blue filler masterbatch into the core layer. Iron blue, chemically known as ferric ferrocyanide, provides the blue color required for CCD recognition. Its thermal stability and acid / alkali resistance ensure structural and color stability during the preparation of the BOPP termination tape base film and its subsequent application in lithium batteries. To improve the dispersion performance of iron blue in the core layer, this invention modifies iron blue by coating it with hydroxyl-terminated hyperbranched polyester to obtain modified iron blue. Then, using polypropylene resin as a carrier, iron blue filler masterbatch is prepared and added to the core layer. Specifically, the preparation method of the iron blue filler masterbatch includes the following steps: first, iron blue is mixed with hydroxyl-terminated hyperbranched polyester to obtain modified iron blue; then, the modified iron blue is mixed with homopolymer polypropylene, followed by extrusion granulation to obtain the iron blue filler masterbatch.

[0009] This invention incorporates 5-10 wt% modified mica filler masterbatch into the upper and lower surface layers, effectively forming two physical barrier networks within the film. This helps prevent water and acidic / alkaline substances in the electrolyte from penetrating into the core layer of the terminating tape base film. To improve the compatibility of mica with the polypropylene substrate and its dispersibility within the polypropylene to ensure a uniform barrier effect, this invention uses a long-chain alkylsilane coupling agent to modify the mica surface. The abundant hydroxyl groups on the mica surface undergo a dehydration condensation reaction with the silane coupling agent to form Si-O-Si covalent bonds, resulting in an organic coating on the mica surface. However, directly feeding the modified mica into the extruder of a BOPP film production line still results in poor dispersion, and the high precision required for the modified mica feeding is incompatible with the 300-400 m / min production speed of BOPP films. To reduce the aforementioned problems and meet the needs of high-speed BOPP film production, this invention prepares modified mica-filled masterbatch by mixing modified mica with polypropylene. This allows the modified mica-filled masterbatch to be uniformly dispersed in the upper and lower layers, effectively forming a dense, uniform, and sufficiently strong physical barrier network. This prevents water, acids, and alkalis in the electrolyte from entering the core layer, thereby protecting the iron blue of the core layer and ensuring the color stability of the terminating tape base film. Specifically, the preparation method of the modified mica-filled masterbatch includes the following steps: first, mixing mica with a silane coupling agent to obtain modified mica; then, mixing the modified mica with homopolymer polypropylene; and finally, extruding and granulating to obtain the modified mica-filled masterbatch.

[0010] As a preferred embodiment, the mica is wet-processed mica with a particle size of 4-6 μm. Mica is a sheet-like material with a certain thickness and length, and its particle size has a crucial impact on film performance. Compared with dry-processed mica, wet-processed mica has a smaller and more uniform particle size distribution, resulting in a more suitable aspect ratio. It can form a more uniform and dense physical barrier network structure in a polypropylene matrix. If the mica particle size is too small, the aspect ratio will be too low. On the one hand, it will be impossible to form a dense network structure, reducing the effective barrier capability against water, acids, alkalis, and other substances in the electrolyte. On the other hand, the formed network structure will have insufficient mechanical strength and will be easily destroyed, ultimately leading to poor protection of the iron blue in the core layer. If the mica particle size is too large, although it can provide higher mechanical strength, it is easy to form defects in the film, affecting the film's appearance. Furthermore, during biaxial stretching of the film, excessively large particle size will cause stress concentration at the mica location, which can not only lead to film defects but may even cause film rupture in severe cases.

[0011] As a preferred embodiment, the silane coupling agent is a long-chain alkyl coupling agent, wherein the long-chain alkyl group has ≥18 carbon atoms; when preparing the modified mica, the mass ratio of mica to the silane coupling agent is 1:(0.02~0.04). Using a long-chain alkyl silane coupling agent has the following advantages: firstly, the longer the carbon chain of the long-chain alkyl group, the better the thermal stability of the long-chain alkyl silane coupling agent, resulting in a more stable structure during the preparation of modified mica filler masterbatch and subsequent processing; secondly, the longer the carbon chain, the closer it is to the chemical structure and polarity of polypropylene resin, resulting in better compatibility, which is beneficial for the dispersion of mica in polypropylene, and also reduces the precipitation of the silane coupling agent. The mass ratio of mica to silane coupling agent should be controlled at 1:(0.02~0.04). If the amount of silane coupling agent added is too small, it will not be able to fully coat the mica, and some mica will not be modified, affecting the dispersion of mica in the upper and lower sublayers, and ultimately affecting the film surface quality of the termination tape base film. If the amount of silane coupling agent added is too large, there will be more residue, which will bring potential risks to the subsequent production of termination tape base film and product quality.

[0012] As a preferred embodiment, the preparation method of the modified mica filler masterbatch includes the following steps: first, mixing the mica with the silane coupling agent at 55-65°C for 25-35 minutes to obtain the modified mica; then, mixing the modified mica with the homopolymer polypropylene, extruding through a twin-screw extruder at a processing temperature of 220-230°C and a rotation speed of 240-260 rpm / min, and then granulating to obtain the modified mica filler masterbatch; the modified mica filler masterbatch comprises 50-70 wt% of the homopolymer polypropylene and 30-50 wt% of the modified mica. When the modified mica content in the modified mica filler masterbatch is too high, the processing is difficult and it is hard to mix it evenly with polypropylene; when the modified mica content in the modified mica filler masterbatch is too low, a relatively large amount of modified mica filler masterbatch needs to be added to the final formulation of the terminating tape base film, which is not conducive to the production efficiency of the terminating tape base film.

[0013] As a preferred embodiment, the particle size of the iron blue is 0.2~0.5μm. If the particle size of the iron blue is too small, it will be expensive and difficult to disperse in the polypropylene system; if the particle size of the iron blue is too large, it will easily form stress concentration points and cavitation during the subsequent processing of the BOPP termination tape base film, resulting in the blue effect of the prepared BOPP termination tape base film deviating from the standard value and a decrease in mechanical properties.

[0014] As a preferred embodiment, the hydroxyl-terminated hyperbranched polyester has a hydroxyl value greater than 450 mg KOH / g and a branching degree greater than 0.4. When preparing the modified iron blue, the mass ratio of iron blue to the hydroxyl-terminated hyperbranched polyester is 1:(0.01~0.05). In this invention, hydroxyl-terminated hyperbranched polyester is used to coat and modify iron blue. The abundant hydroxyl groups in the hydroxyl-terminated hyperbranched polyester can form numerous hydrogen bonds and complexes with the surface of iron blue, thereby effectively coating the iron blue. The higher the hydroxyl value of the hydroxyl-terminated hyperbranched polyester, the better the coating effect on iron blue, and the coating can be completed in a shorter time. The higher the branching degree of the hydroxyl-terminated hyperbranched polyester, the more active hydroxyl groups are located at the branch ends. Even if the molecular chain of the hydroxyl-terminated hyperbranched polyester is too long, the activity of the hydroxyl groups at the branch ends will not decrease, and it still has better reactivity than linear polyesters. The mass ratio of the iron blue to the hydroxyl-terminated hyperbranched polyester is controlled at 1:(0.01~0.05). This ensures effective coating of the iron blue without affecting its compatibility with polypropylene, thus guaranteeing the dispersibility of the modified iron blue in the polypropylene resin. If the proportion of the hydroxyl-terminated hyperbranched polyester is too low, the iron blue cannot be completely coated; if the proportion is too high, there will be too much residual organic matter, which is detrimental to subsequent processing and film use.

[0015] As a preferred embodiment, the preparation method of the iron blue filler masterbatch further includes the following steps: first, mixing the iron blue with the hydroxyl-terminated hyperbranched polyester at 115~125℃ for 25~35min to obtain the modified iron blue; then, mixing the modified iron blue with the homopolymer polypropylene, extruding through a twin-screw extruder, setting the processing temperature to 220~230℃ and the rotation speed to 390~410rpm / min, and then granulating to obtain the iron blue filler masterbatch; the iron blue filler masterbatch comprises 60~80wt% of the homopolymer polypropylene and 20~40wt% of the modified iron blue.

[0016] As a preferred embodiment, at 230℃ and a load of 2.16 kg, the melt index of the homopolymer polypropylene is 2~4 g / 10 min, and the melt index of the copolymer polypropylene is 7~9 g / 10 min.

[0017] The second aspect: A method for preparing a blue BOPP termination tape base film for lithium batteries as described in the first aspect includes the following steps: The raw materials of the upper surface layer, the upper sub-surface layer, the core layer, the lower sub-surface layer, and the lower surface layer are respectively fed into the batching unit, metered, and then co-extruded through a die head in multiple layers. After casting using the flat film method, the film is chilled into a thick sheet. The thick sheet is then subjected to a simultaneous biaxial stretching process in both the longitudinal and transverse directions to form a biaxially stretched film, thus obtaining the blue BOPP termination tape base film for lithium batteries.

[0018] Third aspect: A lithium-ion battery, comprising the blue BOPP termination tape base film for lithium batteries as described in the first aspect. Detailed Implementation

[0019] The present invention will now be described more fully. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. Experimental methods in the following examples or comparative examples, where specific conditions are not specified, are generally performed under conventional conditions in the art or as recommended by the manufacturer; the raw materials, reagents, etc., used, unless otherwise specified, are all commercially available from the conventional market.

[0020] As one embodiment, this embodiment provides a blue BOPP termination tape base film for lithium batteries, comprising an upper surface layer, an upper secondary surface layer, a core layer, a lower secondary surface layer, and a bottom surface layer arranged sequentially; wherein, the upper surface layer comprises homopolymer or copolymer polypropylene, and the bottom surface layer comprises homopolymer or copolymer polypropylene; both the upper secondary surface layer and the lower secondary surface layer comprise homopolymer polypropylene and 5-10 wt% modified mica filler masterbatch, the modified mica filler masterbatch comprising homopolymer polypropylene and modified mica, the modified mica being obtained by modifying mica with a silane coupling agent; the core layer comprises homopolymer polypropylene and 5-10 wt% iron blue filler masterbatch, the iron blue filler masterbatch comprising homopolymer polypropylene and modified iron blue, the modified iron blue being obtained by modifying iron blue with a hydroxyl-terminated hyperbranched polyester.

[0021] Furthermore, the mica is wet-processed mica with a particle size of 4~6μm.

[0022] In this embodiment of the invention, the specific type of mica used is HY-TM6 from Shenzhen Haiyang Powder Technology Co., Ltd.

[0023] Furthermore, the silane coupling agent is a long-chain alkyl coupling agent, and the long-chain alkyl group has ≥18 carbon atoms; when preparing modified mica, the mass ratio of mica to silane coupling agent is 1:(0.02~0.04).

[0024] In this embodiment of the invention, the selected silane coupling agent is octadecyltriethylsilane coupling agent, specifically model JH-N3119 from Hubei Jianghan New Material Co., Ltd.

[0025] Furthermore, the preparation method of modified mica filler masterbatch includes the following steps: first, mica and silane coupling agent are mixed at 55~65℃ for 25~35min to obtain modified mica; then, the modified mica is mixed with homopolymer polypropylene and extruded through a twin-screw extruder, with the processing temperature set at 220~230℃ and the rotation speed at 240~260rpm / min, and then granulated to obtain modified mica filler masterbatch; the modified mica filler masterbatch includes 50~70wt% homopolymer polypropylene and 30~50wt% modified mica.

[0026] Furthermore, the particle size of the iron blue is 0.2~0.5μm.

[0027] In this embodiment of the invention, the specific model of the selected iron blue is ZT-09 from Shandong Zhongtian Qunqing New Material Co., Ltd.

[0028] Furthermore, the hydroxyl-terminated hyperbranched polyester has a hydroxyl value greater than 450 mg KOH / g and a branching degree greater than 0.4; when preparing modified iron blue, the mass ratio of iron blue to hydroxyl-terminated hyperbranched polyester is 1:(0.01~0.05).

[0029] In this embodiment of the invention, the specific model of the hydroxyl-terminated hyperbranched polyester selected is Hyper H204 from Wuhan Hyperbranched Resin Technology Co., Ltd., which has a hydroxyl content of 490 mg KOH / g and a branching degree of 0.5.

[0030] Furthermore, the preparation method of the iron blue filler masterbatch includes the following steps: first, iron blue and hydroxyl-terminated hyperbranched polyester are mixed at 115~125℃ for 25~35min to obtain modified iron blue; then, the modified iron blue is mixed with homopolymer polypropylene and extruded through a twin-screw extruder, with the processing temperature set at 220~230℃ and the rotation speed at 390~410rpm / min, and then granulated to obtain iron blue filler masterbatch; the iron blue filler masterbatch includes 60~80wt% homopolymer polypropylene and 20~40wt% modified iron blue.

[0031] Furthermore, at 230°C and a load of 2.16 kg, the melt index of the homopolymer polypropylene is 2~4 g / 10 min, and the melt index of the copolymer polypropylene is 7~9 g / 10 min.

[0032] This invention also provides a method for preparing a blue BOPP termination tape base film for lithium batteries, comprising the following steps: The raw materials of the upper surface layer, the upper secondary surface layer, the core layer, the lower secondary surface layer, and the lower surface layer are respectively fed into the batching unit, metered, and then co-extruded through a die head in multiple layers. After casting using the flat film method, the film is chilled into a thick sheet. The thick sheet is then subjected to a simultaneous biaxial stretching process in both the longitudinal and transverse directions to produce a biaxially stretched film, which yields the blue BOPP termination tape base film for lithium batteries.

[0033] Furthermore, the melt extrusion temperature of the upper and lower surface layers is 210~230℃, the melt extrusion temperature of the upper and lower surface layers is 180~200℃, and the melt extrusion temperature of the core layer is 210~230℃; the temperature of the quenching roller during quenching is 35~50℃; the temperature during biaxial stretching is 100~120℃, and the ratio of longitudinal stretching to transverse stretching is 4~5 times.

[0034] This invention also provides a lithium-ion battery, including the blue BOPP termination tape base film for lithium batteries described in this invention.

[0035] Example 1 This embodiment provides a blue BOPP termination tape base film for lithium batteries, comprising an upper surface layer, an upper secondary surface layer, a core layer, a lower secondary surface layer, and a bottom surface layer arranged sequentially. The composition and content of each layer are as follows: Top layer: 100wt% homopolymer polypropylene.

[0036] Top layer: 90wt% homopolymer polypropylene and 10wt% modified mica filler masterbatch.

[0037] Core layer: 90wt% homopolymer polypropylene and 10wt% iron blue filler masterbatch.

[0038] Next surface layer: has the same components and content as the previous surface layer in this embodiment.

[0039] Bottom layer: 100wt% homopolymer polypropylene.

[0040] At 230°C and a load of 2.16 kg, the melt index of the homopolymer polypropylene used in this example is 3 g / 10 min.

[0041] The preparation method of modified mica includes the following steps: mica HY-TM6 is dried at 110℃ for 2 hours, then added to a high-speed mixer with a rotation speed of 100 rpm / min. An ethanol solution of 50 wt% silane coupling agent JH-N3119 is added through a spray device. The effective addition mass of silane coupling agent JH-N3119 is 5% of mica HY-TM6. After mixing at 60℃ for 30 minutes, the powder is taken out and dried again at 110℃ to obtain modified mica.

[0042] The modified mica-filled masterbatch is composed of 60 wt% homopolymer polypropylene and 40 wt% modified mica. Its preparation method includes the following steps: the processing temperature of the twin-screw extruder is set to 230℃ and the rotation speed is 250 rpm / min. The homopolymer polypropylene and modified mica are added to the twin-screw extruder according to the ratio. The homopolymer polypropylene is the main feed and the modified mica is the side feed. After extrusion, the modified mica-filled masterbatch is prepared by granulation.

[0043] The preparation method of modified iron blue includes the following steps: iron blue ZT-09 is dried at 110℃ for 2 hours, and then added to a high-speed mixer. The speed is set to 100 rpm / min. An ethanol solution of 30 wt% terminal hydroxyl hyperbranched polyester Hyper H204 is added through a spray device. The effective added mass of terminal hydroxyl hyperbranched polyester Hyper H204 is 5% of iron blue ZT-09. After mixing at 120℃ for 30 minutes, the powder is taken out and dried at 150℃ to remove excess ethanol, thus obtaining modified iron blue.

[0044] The iron blue filler masterbatch is composed of 60 wt% homopolymer polypropylene and 40 wt% modified iron blue. Its preparation method includes the following steps: the processing temperature of the twin-screw extruder is set to 230℃ and the rotation speed is 400 rpm / min. The homopolymer polypropylene and modified iron blue are added to the twin-screw extruder according to the ratio. The homopolymer polypropylene is the main feed and the modified iron blue is the side feed. After extrusion, the masterbatch is granulated to obtain the iron blue filler masterbatch.

[0045] This embodiment also provides a method for preparing a blue BOPP termination tape base film for lithium batteries, comprising the following steps: The raw materials of the upper surface layer, the upper sub-surface layer, the core layer, the lower sub-surface layer, and the lower surface layer are respectively fed into the batching unit, metered, and then co-extruded through a die head in multiple layers. Then, according to the flat film method, the film is cast and cooled into a thick sheet. The thick sheet is then subjected to a simultaneous biaxial stretching process in both the longitudinal and transverse directions to produce a biaxially stretched film, which yields the blue BOPP termination tape base film for lithium batteries.

[0046] The melt extrusion temperature of the upper and lower surface layers is 220℃, the melt extrusion temperature of the upper and lower sub-surface layers is 200℃, and the melt extrusion temperature of the core layer is 220℃; the temperature of the quenching roller during quenching is 40℃; the temperature during biaxial stretching is 110℃, the longitudinal stretching ratio is 4, and the transverse stretching ratio is 5.

[0047] Example 2 This embodiment provides a blue BOPP termination tape base film for lithium batteries, comprising an upper surface layer, an upper secondary surface layer, a core layer, a lower secondary surface layer, and a bottom surface layer arranged sequentially. The composition and content of each layer are as follows: Top layer: 100wt% homopolymer polypropylene.

[0048] Top layer: 95wt% homopolymer polypropylene and 5wt% modified mica filler masterbatch.

[0049] Core layer: 90wt% homopolymer polypropylene and 10wt% iron blue filler masterbatch.

[0050] Next surface layer: has the same components and content as the previous surface layer in this embodiment.

[0051] Bottom layer: 100wt% homopolymer polypropylene.

[0052] The preparation methods of the modified mica-filled masterbatch and the iron blue-filled masterbatch in this embodiment are the same as those in Example 1.

[0053] The preparation method of the blue BOPP termination tape base film for lithium batteries in this embodiment is the same as that in Example 1.

[0054] Example 3 This embodiment provides a blue BOPP termination tape base film for lithium batteries, comprising an upper surface layer, an upper secondary surface layer, a core layer, a lower secondary surface layer, and a bottom surface layer arranged sequentially. The composition and content of each layer are as follows: Top layer: 100wt% homopolymer polypropylene.

[0055] Top layer: 90wt% homopolymer polypropylene and 10wt% modified mica filler masterbatch.

[0056] Core layer: 95wt% homopolymer polypropylene and 5wt% iron blue filler masterbatch.

[0057] Next surface layer: has the same components and content as the previous surface layer in this embodiment.

[0058] Bottom layer: 100wt% homopolymer polypropylene.

[0059] The preparation methods of the modified mica-filled masterbatch and the iron blue-filled masterbatch in this embodiment are the same as those in Example 1.

[0060] The preparation method of the blue BOPP termination tape base film for lithium batteries in this embodiment is the same as that in Example 1.

[0061] Example 4 This embodiment provides a blue BOPP termination tape base film for lithium batteries, comprising an upper surface layer, an upper secondary surface layer, a core layer, a lower secondary surface layer, and a bottom surface layer arranged sequentially. The composition and content of each layer are as follows: Top layer: 100wt% homopolymer polypropylene.

[0062] Top layer: 95wt% homopolymer polypropylene and 5wt% modified mica filler masterbatch.

[0063] Core layer: 95wt% homopolymer polypropylene and 5wt% iron blue filler masterbatch.

[0064] Next surface layer: has the same components and content as the previous surface layer in this embodiment.

[0065] Bottom layer: 100wt% homopolymer polypropylene.

[0066] The preparation methods of the modified mica-filled masterbatch and the iron blue-filled masterbatch in this embodiment are the same as those in Example 1.

[0067] The preparation method of the blue BOPP termination tape base film for lithium batteries in this embodiment is the same as that in Example 1.

[0068] Comparative Example 1 This comparative example provides a blue BOPP termination tape base film for lithium batteries, comprising an upper surface layer, an upper secondary surface layer, a core layer, a lower secondary surface layer, and a bottom surface layer arranged sequentially. The composition and content of each layer are as follows: Top layer: 100wt% homopolymer polypropylene.

[0069] Top layer: 98wt% homopolymer polypropylene and 2wt% modified mica filler masterbatch.

[0070] Core layer: 90wt% homopolymer polypropylene and 10wt% iron blue filler masterbatch.

[0071] Next surface layer: The components and contents are the same as those of the previous surface layer in this comparative example.

[0072] Bottom layer: 100wt% homopolymer polypropylene.

[0073] The preparation methods of the modified mica-filled masterbatch and the iron blue-filled masterbatch in this comparative example are the same as those in Example 1.

[0074] The preparation method of the blue BOPP termination tape base film for lithium batteries in this comparative example is the same as that in Example 1.

[0075] Comparative Example 2 This comparative example provides a blue BOPP termination tape base film for lithium batteries, comprising an upper surface layer, an upper secondary surface layer, a core layer, a lower secondary surface layer, and a bottom surface layer arranged sequentially. The composition and content of each layer are as follows: Top layer: 100wt% homopolymer polypropylene.

[0076] Top layer: 90wt% homopolymer polypropylene and 10wt% modified mica filler masterbatch.

[0077] Core layer: 98wt% homopolymer polypropylene and 2wt% iron blue filler masterbatch.

[0078] Next surface layer: The components and contents are the same as those of the previous surface layer in this comparative example.

[0079] Bottom layer: 100wt% homopolymer polypropylene.

[0080] The preparation methods of the modified mica-filled masterbatch and the iron blue-filled masterbatch in this comparative example are the same as those in Example 1.

[0081] The preparation method of the blue BOPP termination tape base film for lithium batteries in this comparative example is the same as that in Example 1.

[0082] Comparative Example 3 This comparative example provides a blue BOPP termination tape base film for lithium batteries, comprising an upper surface layer, an upper secondary surface layer, a core layer, a lower secondary surface layer, and a bottom surface layer arranged sequentially. The composition and content of each layer are as follows: Top layer: 100wt% homopolymer polypropylene.

[0083] Top layer: 85wt% homopolymer polypropylene and 15wt% modified mica filler masterbatch.

[0084] Core layer: 90wt% homopolymer polypropylene and 10wt% iron blue filler masterbatch.

[0085] Next surface layer: The components and contents are the same as those of the previous surface layer in this comparative example.

[0086] Bottom layer: 100wt% homopolymer polypropylene.

[0087] The preparation methods of the modified mica-filled masterbatch and the iron blue-filled masterbatch in this comparative example are the same as those in Example 1.

[0088] The preparation method of the blue BOPP termination tape base film for lithium batteries in this comparative example is the same as that in Example 1.

[0089] Comparative Example 4 This comparative example provides a blue BOPP termination tape base film for lithium batteries, comprising an upper surface layer, an upper secondary surface layer, a core layer, a lower secondary surface layer, and a bottom surface layer arranged sequentially. The composition and content of each layer are as follows: Top layer: 100wt% homopolymer polypropylene.

[0090] Top layer: 90wt% homopolymer polypropylene and 10wt% modified mica filler masterbatch.

[0091] Core layer: 87wt% homopolymer polypropylene and 13wt% iron blue filler masterbatch.

[0092] Next surface layer: The components and contents are the same as those of the previous surface layer in this comparative example.

[0093] Bottom layer: 100wt% homopolymer polypropylene.

[0094] The preparation methods of the modified mica-filled masterbatch and the iron blue-filled masterbatch in this comparative example are the same as those in Example 1.

[0095] The preparation method of the blue BOPP termination tape base film for lithium batteries in this comparative example is the same as that in Example 1.

[0096] Comparative Example 5 This comparative example provides a blue BOPP termination tape base film for lithium batteries, comprising an upper surface layer, an upper secondary surface layer, a core layer, a lower secondary surface layer, and a bottom surface layer arranged sequentially. The composition and content of each layer are as follows: Top layer: 100wt% homopolymer polypropylene.

[0097] Top layer: 90wt% homopolymer polypropylene and 10wt% modified mica filler masterbatch.

[0098] Core layer: 90wt% homopolymer polypropylene and 10wt% commercially available blue masterbatch for polypropylene (Anmicolor 401646).

[0099] Next surface layer: The components and contents are the same as those of the previous surface layer in this comparative example.

[0100] Bottom layer: 100wt% homopolymer polypropylene.

[0101] The preparation method of the modified mica-filled masterbatch in this comparative example is the same as that in Example 1.

[0102] The preparation method of the blue BOPP termination tape base film for lithium batteries in this comparative example is the same as that in Example 1.

[0103] Comparative Example 6 This comparative example provides a blue BOPP termination tape base film for lithium batteries, comprising an upper surface layer, an upper secondary surface layer, a core layer, a lower secondary surface layer, and a bottom surface layer arranged sequentially. The composition and content of each layer are as follows: Top layer: 100wt% homopolymer polypropylene.

[0104] Top layer: 90 wt% homopolymer polypropylene and 10 wt% unmodified mica filler masterbatch (compared to Example 1, i.e., the step of treating mica with silane coupling agent is omitted, and masterbatch is prepared directly with polypropylene in a twin-screw extruder process).

[0105] Core layer: 90wt% homopolymer polypropylene and 10wt% iron blue filler masterbatch.

[0106] Next surface layer: The components and contents are the same as those of the previous surface layer in this comparative example.

[0107] Bottom layer: 100wt% homopolymer polypropylene.

[0108] The preparation method of the iron blue filler masterbatch in this comparative example is the same as that in Example 1.

[0109] The preparation method of the blue BOPP termination tape base film for lithium batteries in this comparative example is the same as that in Example 1.

[0110] Performance Evaluation The following performance tests were performed on the termination tape base films prepared in the above embodiments and comparative examples: (1) Film surface quality: Randomly select a 50×50cm area of ​​the finished product of the termination tape base film, and observe the surface crystal points, bright spots, protrusions and other defective positions with the naked eye, and record the total number; if the number is <5, it is rated as excellent; if the number is <10, it is rated as good; if the number is <15, it is rated as medium; other situations are rated as poor.

[0111] (2) Film color: Ideally, the standard values ​​for blue tape film used in lithium batteries are L=65, a=-40, b=-30. The L, a, and b values ​​of the finished tape base film are tested using a spectrophotometer, and the color difference is calculated according to GB / T 7921-2008 with the aforementioned standard values. A color difference > 20 is recorded as unqualified, and a color difference ≤ 20 is recorded as qualified.

[0112] (3) Tensile strength of film: tested according to GB / T 1040.3-2006.

[0113] (4) Evaluation of resistance to iron blue precipitation and electrolyte performance: The fully expanded finished base film sample (tensile standard sample, dimensions 10mm width, 50mm gauge length, and 150mm total length) was immersed in a commercially available electrolyte (Bailingwei Reagent 936456) at 25℃ in a 500mL standard PP wide-mouth bottle (height 170mm) for 48 hours. The sample was then removed. The base film sample was laid flat on dust-free filter paper and drained at room temperature in the dark for 10 minutes to ensure no free droplets remained.

[0114] Iron blue leaching ability: Test the L, a, b values ​​of the base film of the termination tape according to the film color test method of method (2), and calculate the color difference with the L, a, b values ​​before soaking. If the color difference value change is >1.5, it is recorded as unqualified iron blue leaching ability, and if the color difference value change is ≤1.5, the iron blue leaching ability is recorded as qualified.

[0115] Electrolyte resistance performance: The film after soaking is subjected to transverse tensile strength test according to method (3). If the tensile strength decreases by more than 20 MPa, the electrolyte resistance performance is recorded as unqualified.

[0116] Table 1. Performance test results of the blue BOPP termination tape base film for lithium batteries prepared in the examples and comparative examples.

[0117] As can be seen from Table 1, the blue BOPP termination tape base film for lithium batteries prepared in the examples all meet the color requirements. It also has good resistance to iron blue precipitation and electrolyte resistance, and has excellent mechanical properties, which can meet the long-term use requirements of lithium-ion batteries.

[0118] Compared with the examples, Comparative Example 1 showed that the amount of modified mica filler masterbatch added was too small, which failed to form a dense physical barrier network, resulting in substandard electrolyte resistance and excessive reduction in mechanical strength after immersion.

[0119] Compared with the example, Comparative Example 2 had too little iron blue filler masterbatch added, and the color of the terminating tape base film differed greatly from the color standard value required for CCD recognition of blue tape film for lithium batteries, which was not conducive to meeting the CCD recognition requirements in the lithium-ion battery production process.

[0120] Compared with the examples, Comparative Example 3 had an excessive amount of modified mica filler masterbatch added, resulting in more defects such as crystal points, bright spots, and protrusions on the surface of the terminating tape base film, and poor film quality.

[0121] Compared with the example, Comparative Example 4 showed that the amount of iron blue filler masterbatch added was too much, which caused the color of the termination tape base film to deviate significantly from the color standard value required for CCD recognition. At the same time, it affected the dispersion of iron blue in the core layer, making it easier for it to precipitate into the electrolyte, resulting in the termination tape base film's iron blue precipitation resistance being unqualified.

[0122] Compared with the examples, Comparative Example 5 replaced the Tirion blue filler masterbatch with a commercially available blue masterbatch for polypropylene. The commercially available blue masterbatch for polypropylene is not a pure inorganic pigment and has not been modified by a compatibilizer (such as the hydroxyl-terminated hyperbranched polyester in the examples). It has poor compatibility with the polypropylene substrate and is more likely to precipitate into the electrolyte, ultimately resulting in the Tirion blue precipitation resistance of the termination tape base film being unqualified.

[0123] Compared with the examples, Comparative Example 6 did not undergo silane coupling agent treatment, resulting in poor compatibility with the polypropylene substrate and easy aggregation within it. Consequently, the final quality of the termination tape base film was poor, failing to form an effective and uniform barrier network. Consequently, it could not effectively prevent electrolyte penetration into the core layer, leading to decreased electrolyte resistance. Once the electrolyte entered the core layer, it would cause iron blue to precipitate more easily, making the iron blue precipitation resistance also unqualified.

[0124] The embodiments described above are merely examples of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention.

Claims

1. A blue BOPP termination tape base film for lithium batteries, characterized in that, The system comprises an upper surface layer, an upper sub-surface layer, a core layer, a lower sub-surface layer, and a lower surface layer. The upper surface layer comprises homopolymer or copolymer polypropylene, and the lower surface layer comprises homopolymer or copolymer polypropylene. Both the upper and lower sub-surface layers comprise homopolymer polypropylene and 5-10 wt% modified mica filler masterbatch, wherein the modified mica filler masterbatch comprises homopolymer polypropylene and modified mica, and the modified mica is obtained by modifying mica with a silane coupling agent. The core layer comprises homopolymer polypropylene and 5-10 wt% iron blue filler masterbatch, wherein the iron blue filler masterbatch comprises homopolymer polypropylene and modified iron blue, and the modified iron blue is obtained by modifying iron blue with a hydroxyl-terminated hyperbranched polyester.

2. The blue BOPP termination tape base film for lithium batteries according to claim 1, characterized in that, The mica is wet-processed mica, and the particle size of the mica is 4~6μm.

3. The blue BOPP termination tape base film for lithium batteries according to claim 2, characterized in that, The silane coupling agent is a long-chain alkyl coupling agent, wherein the long-chain alkyl group has ≥18 carbon atoms; when preparing the modified mica, the mass ratio of the mica to the silane coupling agent is 1:(0.02~0.04).

4. The blue BOPP termination tape base film for lithium batteries according to claim 3, characterized in that, The preparation method of the modified mica-filled masterbatch includes the following steps: first, mixing the mica with the silane coupling agent at 55~65℃ for 25~35min to obtain the modified mica; then, mixing the modified mica with the homopolymer polypropylene, extruding through a twin-screw extruder, setting the processing temperature to 220~230℃ and the rotation speed to 240~260rpm / min, and then granulating to obtain the modified mica-filled masterbatch; the modified mica-filled masterbatch includes 50~70wt% of the homopolymer polypropylene and 30~50wt% of the modified mica.

5. The blue BOPP termination tape base film for lithium batteries according to claim 1, characterized in that, The particle size of the iron blue is 0.2~0.5μm.

6. The blue BOPP termination tape base film for lithium batteries according to claim 5, characterized in that, The hydroxyl-terminated hyperbranched polyester has a hydroxyl value greater than 450 mg KOH / g and a branching degree greater than 0.4; when preparing the modified iron blue, the mass ratio of the iron blue to the hydroxyl-terminated hyperbranched polyester is 1:(0.01~0.05).

7. The blue BOPP termination tape base film for lithium batteries according to claim 6, characterized in that, The preparation method of the iron blue filler masterbatch further includes the following steps: first, mixing the iron blue with the hydroxyl-terminated hyperbranched polyester at 115~125℃ for 25~35min to obtain the modified iron blue; then, mixing the modified iron blue with the homopolymer polypropylene, extruding it through a twin-screw extruder, setting the processing temperature to 220~230℃ and the rotation speed to 390~410rpm / min, and then granulating it to obtain the iron blue filler masterbatch; the iron blue filler masterbatch includes 60~80wt% of the homopolymer polypropylene and 20~40wt% of the modified iron blue.

8. The blue BOPP termination tape base film for lithium batteries according to claim 1, characterized in that, At 230℃ and a load of 2.16 kg, the melt index of the homopolymer polypropylene is 2~4 g / 10 min, and the melt index of the copolymer polypropylene is 7~9 g / 10 min.

9. The method for preparing the blue BOPP termination tape base film for lithium batteries according to any one of claims 1 to 8, characterized in that, Includes the following steps: The raw materials of the upper surface layer, the upper sub-surface layer, the core layer, the lower sub-surface layer, and the lower surface layer are respectively fed into the batching unit, metered, and then co-extruded through a die head in multiple layers. After casting using the flat film method, the film is chilled into a thick sheet. The thick sheet is then subjected to a simultaneous biaxial stretching process in both the longitudinal and transverse directions to form a biaxially stretched film, thus obtaining the blue BOPP termination tape base film for lithium batteries.

10. A lithium-ion battery, characterized in that, Includes the blue BOPP termination tape base film for lithium batteries as described in any one of claims 1 to 8.

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