A modified polypropylene film, and a method for preparing and using the same

Abstract

The application provides a modified polypropylene film and a preparation method and application thereof. The preparation raw material of the modified polypropylene film comprises modified polypropylene; the modifier of the modified polypropylene comprises terpene alcohol; and the preparation method comprises the following steps: (1) melting, filtering and extruding the preparation raw material of the modified polypropylene film to obtain a molten material; (2) casting the molten material obtained in the step (1) on a casting roller, and after cooling and forming, performing bidirectional stretching to obtain the modified polypropylene film. In the application, the modified polypropylene is prepared by selecting a specific modifier, and the modified polypropylene is used as the preparation raw material to prepare the modified polypropylene film with excellent performance, so that the modified polypropylene film is suitable for being used as a composite current collector base film.

Description

Technical Field

[0001] This invention belongs to the field of polymer membrane technology, specifically relating to a modified polypropylene membrane, its preparation method, and its application. Background Technology

[0002] Currently, composite current collectors based on polymer films are receiving widespread attention and application in the new energy industry. The preparation process typically involves depositing a metal (aluminum, copper, etc.) layer onto a polymer film (such as polypropylene, polyethylene, polyester, etc.) using physical vapor deposition (PVD). The resulting surface-metallized film with a certain conductivity is the composite current collector. Compared to traditional current collectors, polymer film-based composite current collectors offer advantages such as low cost, light weight, and good internal insulation. These characteristics enable composite current collectors to reduce battery costs and improve battery energy density and safety when used in batteries.

[0003] Among numerous composite current collectors based on polymer membranes, those based on polypropylene membranes are relatively common. However, the following problems exist in the preparation of composite current collectors using traditional polypropylene membranes as the base membrane: ① Due to the weak polarity of the polypropylene membrane itself, its surface tension is low. The affinity between the low surface tension polypropylene membrane and the high surface tension metal layer is poor, resulting in low adhesion at the interface and weak bonding, i.e., poor surface adhesion performance of the polypropylene membrane. ② The dielectric constant of the polypropylene membrane is 2.1, which is relatively low. This makes the polypropylene membrane susceptible to breakdown by locally high electrostatic voltages during the preparation of composite current collectors using physical vapor deposition, resulting in pore defects.

[0004] Therefore, in order to address the aforementioned problems of traditional polypropylene membranes and to prepare high-performance composite current collectors, it is necessary to develop a modified polypropylene membrane. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a modified polypropylene membrane, its preparation method, and its applications. In this invention, modified polypropylene is prepared by selecting a specific modifier, and this modified polypropylene is used as a raw material to prepare a high-performance modified polypropylene membrane, making it suitable as a composite current collector base membrane.

[0006] To achieve this objective, the present invention adopts the following technical solution:

[0007] In a first aspect, the present invention provides a modified polypropylene film, wherein the raw material for preparing the modified polypropylene film includes modified polypropylene;

[0008] The modifier for the modified polypropylene includes terpene alcohols.

[0009] In this invention, modified polypropylene is prepared by selecting a specific modifier, and this modified polypropylene is used as a raw material to prepare a modified polypropylene film with excellent performance, making it suitable as a composite current collector base film.

[0010] In this invention, on the one hand, the hydroxyl groups in terpene alcohol molecules are used to increase the surface tension of the prepared modified polypropylene film. Furthermore, terpene alcohol molecules have a conjugated structure, which can form an electronic conjugated system with metal atoms. The increase in surface tension and the formation of the conjugated structure jointly promote the interaction force between metal atoms and the modified polypropylene film, thereby improving the adhesion between the base film and the metal layer in the prepared composite current collector. On the other hand, the dielectric constant of terpene alcohol-modified polypropylene is higher than that of polypropylene. Introducing terpene alcohol-modified polypropylene into the raw materials for preparing modified polypropylene film can increase the dielectric constant of the modified polypropylene film, thereby solving the problem of pores caused by the puncture of polypropylene film during physical vapor deposition.

[0011] In this invention, the dielectric constant of the modified polypropylene film is improved by introducing polar functional groups and conjugated structures into the modified polypropylene film.

[0012] The following are preferred technical solutions of the present invention, but are not intended to limit the technical solutions provided by the present invention. The purpose and beneficial effects of the present invention can be better achieved and realized through the following preferred technical solutions.

[0013] As a preferred embodiment of the present invention, the grafting rate of terpene alcohol in the modified polypropylene is ≥0.05% (for example, it can be 0.05%, 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10%), preferably 0.05%-10%.

[0014] In this invention, the grafting rate is the ratio of the mass of the terpene alcohol monomer grafted onto the polypropylene to the mass of the grafted polypropylene.

[0015] In this invention, by controlling the grafting rate of terpene alcohols in modified polypropylene within a specific range, the performance of the modified polypropylene film is improved, resulting in higher dielectric constant and higher mechanical properties. If the grafting rate of terpene alcohols in the modified polypropylene is too low, the improvement in the performance of the prepared polypropylene film is limited; if the grafting rate of terpene alcohols in the modified polypropylene is too high, the excessively high grafting rate of the modified polypropylene will affect the orientation and crystallization of polypropylene polymers during stretching, thereby leading to a decrease in the tensile strength of the prepared modified polypropylene film.

[0016] Preferably, the terpene alcohol includes any one or a combination of at least two of 4-terpene alcohol, α-terpineol, carvacrol, lavenderol, nerol, and geraniol.

[0017] In this invention, the preparation method of the modified polypropylene includes the following steps:

[0018] The reactor was fully purged and dried with nitrogen. Then, a well-mixed mixture of terpene alcohol, polypropylene, organic solvent, and catalyst was added to the reactor. The mixture was then heated to 60-100℃ under a nitrogen atmosphere and reacted for 2-24 hours. The mixture was then cooled to room temperature and discharged from the reactor with nitrogen. After filtration, washing, and drying, modified polypropylene was obtained.

[0019] Preferably, the organic solvent is selected from C6-C20 alkane solvents (e.g., C6, C7, C8, C9, C10, C11, C12, C13, C14, C15, C16, C17, C18, C19 or C20, etc.), and further selected from n-hexane.

[0020] Preferably, the catalyst is selected from any one of Ziegler-Natta catalyst, DQC catalyst or HR catalyst.

[0021] It should be noted that there are no special restrictions on the manufacturers of catalysts in this invention. For example, HR catalysts are purchased from Sinopec Catalyst Co., Ltd.

[0022] The added terpene alcohol has a mass of 0.50-150g, polypropylene has a mass of 890.0-999.5g, organic solvent has a volume of 800-2000mL, and catalyst has a mass of 10-50g.

[0023] In this invention, the mass of the added terpene alcohol can be 0.50g, 1.00g, 2.00g, 5.00g, 10.0g, 20.0g, 40.0g, 60.0g, 80.0g, 100g, 120g, 135g or 150g, etc.

[0024] The mass of the polypropylene can be 890.0g, 900.0g, 910.0g, 920.0g, 930.0g, 940.0g, 950.0g, 960.0g, 970.0g, 980.0g, 990.0g, or 999.5g, etc.

[0025] The volume of the organic solvent can be 800mL, 900mL, 1000mL, 1100mL, 1200mL, 1300mL, 1400mL, 1500mL, 1600mL, 1700mL, 1800mL, 1900mL, or 2000mL, etc.

[0026] The mass of the catalyst can be 10g, 15g, 20g, 25g, 30g, 35g, 40g, 45g, or 50g, etc.

[0027] The reaction temperature for preparing modified polypropylene can be 60℃, 65℃, 70℃, 75℃, 80℃, 85℃, 90℃, 95℃ or 100℃, and the reaction time can be 2h, 4h, 6h, 8h, 10h, 12h, 14h, 16h, 18h, 20h, 22h or 24h, etc.

[0028] As a preferred embodiment of the present invention, the melt index of the polypropylene in the modified polypropylene is 3.0-4.0 g / 10 min, for example, it can be 3.0 g / 10 min, 3.1 g / 10 min, 3.2 g / 10 min, 3.3 g / 10 min, 3.4 g / 10 min, 3.5 g / 10 min, 3.6 g / 10 min, 3.7 g / 10 min, 3.8 g / 10 min, 3.9 g / 10 min, or 4.0 g / 10 min, etc.

[0029] In this invention, by selecting polypropylene with a specific melt index range, film formation is facilitated during the stretching step of preparing the modified polypropylene film, and the resulting modified polypropylene film exhibits good performance. If the melt index of the polypropylene is too low and the molecular weight is too high, the film-forming properties of the modified polypropylene film during the stretching process will be poor; if the melt index of the polypropylene is too high and the molecular weight is too low, its film-forming properties will be poor, and the mechanical properties of the prepared modified polypropylene film will be poor.

[0030] In this invention, the test conditions for melt flow index are 230℃ / 2.16kg.

[0031] Preferably, the molecular weight distribution of the polypropylene in the modified polypropylene is 4.5-5.5, for example, it can be 4.5, 4.6, 4.7, 4.8, 4.9, 5.0, 5.1, 5.2, 5.3, 5.4 or 5.5, etc.

[0032] In this invention, by controlling the molecular weight distribution of polypropylene within a specific range, the modified polypropylene film prepared exhibits better mechanical properties and a higher yield. If the molecular weight distribution index of polypropylene is too high, the content of low molecular weight polypropylene will be higher, resulting in poorer mechanical properties and poorer film-forming properties of the prepared film; if the molecular weight distribution index of polypropylene is too low, the film-forming properties of the modified polypropylene will deteriorate during the film-stretching process, leading to a decrease in product yield.

[0033] Preferably, the isotacticity of the polypropylene in the modified polypropylene is ≥95%, for example, it can be 95%, 95.5%, 96%, 96.5%, 97%, 97.5% or 98%, etc.

[0034] In this invention, by controlling the isotacticity of polypropylene to ≥95%, the mechanical properties of the modified polypropylene film can be further improved. The higher the isotacticity of polypropylene, the higher the regularity of polypropylene molecules. The improvement of polypropylene regularity can enhance the orientation and crystallinity of the prepared film, thereby improving the mechanical properties of the modified polypropylene film.

[0035] As a preferred technical solution of the present invention, based on the mass percentage of the raw materials for preparing the modified polypropylene film being 100%, the mass percentage of the modified polypropylene is ≥0.5%, for example, it can be 0.5%, 1%, 2%, 5%, 7%, 10%, 13%, 15%, 18%, 20% or 24%, etc.

[0036] In this invention, by controlling the mass percentage of modified polypropylene in the raw materials for preparing the modified polypropylene film to be ≥0.5%, the performance of the modified polypropylene film can be significantly improved. If the mass percentage of modified polypropylene is too low, the improvement on the performance of the modified polypropylene film is limited.

[0037] Preferably, the raw materials for preparing the modified polypropylene film also include polypropylene.

[0038] As a preferred embodiment of the present invention, the thickness of the modified polypropylene film is ≥1μm (for example, it can be 1μm, 2μm, 5μm, 7μm, 10μm, 12μm, 15μm, 18μm, 20μm, 24μm, 27μm or 30μm, etc.), preferably 2 to 20μm.

[0039] The thinner the modified polypropylene film, the more it can promote the improvement of the energy density of the composite current collector. However, the production difficulty must be taken into account at the same time. Since the thinner the modified polypropylene film, the greater the production difficulty and the lower the yield rate, in this invention, the thickness of the modified polypropylene film is controlled to be ≥1μm. This can not only prepare a modified polypropylene film with excellent performance, but also take into account the production process of the modified polypropylene film, so that it has a high yield rate.

[0040] In a second aspect, the present invention provides a method for preparing a modified polypropylene film as described in the first aspect, the method comprising the following steps:

[0041] (1) The raw materials for the preparation of modified polypropylene film are melted, filtered, and extruded to obtain molten material;

[0042] (2) The molten material obtained in step (1) is extended onto the casting roller, cooled and shaped, and then biaxially stretched to obtain the modified polypropylene film.

[0043] In this invention, modified polypropylene is selected as the raw material for preparing modified polypropylene film, and a melt extrusion-biaxial stretching process is used to prepare a modified polypropylene film with high dielectric constant and good mechanical properties, making it suitable as a composite current collector base film.

[0044] As a preferred embodiment of the present invention, the melting temperature is 200-260℃, for example, it can be 200℃, 205℃, 210℃, 215℃, 220℃, 225℃, 230℃, 235℃, 240℃, 245℃, 250℃, 255℃ or 260℃, etc.

[0045] Preferably, the filtration method includes filtration through a filter with a screen size of 10 μm.

[0046] Preferably, the cooling and molding method is water cooling treatment.

[0047] Preferably, the cooling and molding temperature is 15-60℃, for example, it can be 15℃, 20℃, 25℃, 30℃, 35℃, 40℃, 45℃, 50℃, 55℃ or 60℃, etc.

[0048] It should be noted that the melting and extrusion in this invention are carried out in a twin-screw extruder.

[0049] As a preferred embodiment of the present invention, the bidirectional stretching includes synchronous stretching and asynchronous stretching.

[0050] Preferably, the synchronous stretching process includes preheating, stretching, and heat setting.

[0051] Preferably, the preheating area includes a first preheating area and a second preheating area.

[0052] Preferably, the temperature of the first preheating zone is 130-145℃, for example, it can be 130℃, 132℃, 135℃, 137℃, 140℃, 142℃ or 145℃, etc.

[0053] Preferably, the temperature of the second preheating zone is 145-155℃, for example, it can be 145℃, 146℃, 147℃, 148℃, 149℃, 150℃, 151℃, 152℃, 153℃, 154℃ or 155℃, etc.

[0054] Preferably, the stretching temperature includes a first stretching temperature and a second stretching temperature.

[0055] Preferably, the first stretching temperature is 155-160°C, for example, it can be 155°C, 156°C, 157°C, 158°C, 159°C or 160°C.

[0056] Preferably, the second stretching temperature is 160-165°C, for example, it can be 160°C, 161°C, 162°C, 163°C, 164°C or 165°C.

[0057] Preferably, the longitudinal stretching ratio is 6-8, for example, it can be 6, 6.3, 6.5, 6.8, 7, 7.2, 7.5, 7.7 or 8, etc.

[0058] Preferably, the transverse stretching zone of the stretching is 5-7, for example, it can be 5, 5.2, 5.5, 5.8, 6, 6.3, 6.5, 6.8 or 7, etc.

[0059] Preferably, the heat setting temperature is 165-169℃, for example, it can be 165℃, 166℃, 167℃, 168℃ or 169℃, etc.

[0060] Preferably, the asynchronous stretching process includes longitudinal stretching, transverse stretching, and heat treatment.

[0061] Preferably, the preheating temperature for the longitudinal stretching is 115-140℃, for example, it can be 115℃, 118℃, 120℃, 124℃, 127℃, 130℃, 132℃, 135℃, 138℃ or 140℃, etc.

[0062] Preferably, the longitudinal stretching temperature is 140-150℃, for example, it can be 140℃, 141℃, 142℃, 143℃, 144℃, 145℃, 146℃, 147℃, 148℃, 149℃ or 150℃, etc.

[0063] Preferably, the longitudinal stretching ratio is 6-8, for example, it can be 6, 6.3, 6.5, 6.8, 7, 7.2, 7.5, 7.7 or 8, etc.

[0064] Preferably, the longitudinal stretching process further includes a post-processing step.

[0065] Preferably, the post-processing method includes cooling to room temperature.

[0066] Preferably, the preheating temperature for the transverse stretching is 120-140℃, for example, it can be 120℃, 122℃, 124℃, 126℃, 128℃, 130℃, 132℃, 134℃, 136℃, 138℃ or 140℃, etc.

[0067] Preferably, the stretching temperature for the transverse stretching is 140-160℃, for example, it can be 140℃, 142℃, 144℃, 146℃, 148℃, 150℃, 152℃, 154℃, 156℃, 158℃ or 160℃, etc.

[0068] Preferably, the heat setting temperature for the transverse stretching is 165-169°C, for example, it can be 165°C, 166°C, 167°C, 168°C or 169°C.

[0069] Preferably, the stretching ratio of the transverse stretching is 5-7, for example, it can be 5, 5.2, 5.5, 5.8, 6, 6.3, 6.5, 6.8 or 7, etc.

[0070] Preferably, the heat treatment temperature is 110-140℃, for example, it can be 110℃, 112℃, 115℃, 118℃, 120℃, 124℃, 127℃, 130℃, 132℃, 135℃, 138℃ or 140℃, etc.

[0071] Preferably, the biaxial stretching process further includes a post-processing step.

[0072] Preferably, the post-processing method includes: after being cooled by air in the platform area, the film enters the winding system via the traction system for film winding.

[0073] Preferably, the winding tension is 20-30 N / m, for example, it can be 20 N / m, 21 N / m, 22 N / m, 23 N / m, 24 N / m, 25 N / m, 26 N / m, 27 N / m, 28 N / m, 29 N / m or 30 N / m, etc.

[0074] In this invention, the method for preparing the modified polypropylene film includes the following steps:

[0075] (1) The raw material for the preparation of modified polypropylene film is placed in a twin-screw extruder, melted at 200-260℃, filtered through a 10μm filter, and then extruded through a die to obtain the molten material;

[0076] (2) The molten material obtained in step (1) is extended onto the casting roller, cooled and formed by water at 15-60℃, then stretched biaxially, cooled by air in the platform area, and then entered the winding system through the traction system. The film is wound up under the condition of winding tension of 20-30N / m to obtain the modified polypropylene film.

[0077] The bidirectional stretching can be synchronous or asynchronous.

[0078] The bidirectional stretching is synchronous stretching, and the synchronous stretching includes the following process:

[0079] ① Preheating: Divided into two stages, with the temperature increasing sequentially, namely 130-145℃ and 145-155℃;

[0080] ②Stretching: Divided into two sections, with temperatures increasing sequentially, namely 155-160℃ and 160-165℃; stretching ratio: longitudinal stretching ratio is 6-8, and transverse stretching ratio is 5-7;

[0081] ③ Heat setting: temperature is 165-169℃;

[0082] Alternatively, the bidirectional stretching can be asynchronous stretching, which includes the following process:

[0083] ① Longitudinal stretching: Preheating temperature: 115-140℃; stretching temperature: 140-150℃; longitudinal stretching ratio: 6-8, then cool to room temperature;

[0084] ② Transverse stretching: Preheating temperature: 120-140℃; stretching temperature: 140-160℃; heat setting temperature: 165-169℃; transverse stretching ratio: 5-7;

[0085] ③ Heat treatment: The heat treatment temperature is 110-140℃. The purpose is to eliminate internal stress in the membrane and improve the thermal stability of the membrane.

[0086] Thirdly, the present invention also provides a composite current collector, the composite current collector comprising a metal layer and a polymer film layer;

[0087] The polymer film layer is a modified polypropylene film as described in the first aspect.

[0088] The modified polypropylene membrane provided in the first aspect of the present invention serves as a carrier and support layer for composite current collectors.

[0089] Preferably, the material of the metal layer is selected from metals or metal alloys, and the metal is selected from any one or a combination of at least two of copper, aluminum, silver, gold, and nickel.

[0090] Preferably, the composite current collector comprises a first protective layer, a first metal layer, a polymer film layer, a second metal layer, and a second protective layer, which are sequentially stacked.

[0091] The polymer film layer is a modified polypropylene film as described in the first aspect.

[0092] As a preferred embodiment of the present invention, the materials of the first metal layer and the first metal layer are each independently selected from metals or metal alloys.

[0093] Preferably, the metal is selected from any one or a combination of at least two of copper, aluminum, silver, gold, and nickel.

[0094] Preferably, the thickness of the first metal layer and the first metal layer are each independently selected from 500-2000 nm (e.g., 500 nm, 700 nm, 1000 nm, 1200 nm, 1500 nm, 1800 nm or 2000 nm, etc.), and more preferably 700-1500 nm.

[0095] In this invention, the first metal layer and the first metal layer are each prepared independently by any one or a combination of at least two of physical vapor deposition (such as resistance heating vacuum evaporation, electron beam heating vacuum evaporation, laser heating vacuum evaporation, magnetron sputtering, etc.), electroplating, or chemical plating.

[0096] Preferably, the materials of the first protective layer and the second protective layer are each independently selected from any one or a combination of at least two of the following: alumina, nickel oxide, chromium oxide, cobalt oxide, copper oxide, copper chromium oxide, formic acid-copper complex, nickel-chromium alloy, graphite, carbon nanotubes, carbon nanofibers, and graphene.

[0097] Preferably, the thickness of the first protective layer and the second protective layer are each independently selected from 10-150nm (e.g., 10nm, 20nm, 30nm, 40nm, 50nm, 60nm, 70nm, 80nm, 90nm, 100nm, 110nm, 120nm, 130nm, 140nm or 150nm, etc.), and more preferably 20-100nm.

[0098] Preferably, the sum of the thicknesses of the first protective layer and the second protective layer is ≤ one-tenth of the sum of the thicknesses of the first metal layer and the second metal layer.

[0099] In this invention, the preparation methods of the first protective layer and the second protective layer each independently include any one or a combination of at least two of the following: physical vapor deposition, chemical vapor deposition, in-situ forming, and coating. The physical vapor deposition method preferably includes vacuum evaporation and magnetron sputtering; the chemical vapor deposition method preferably includes atmospheric pressure chemical vapor deposition and plasma-enhanced chemical vapor deposition; the in-situ forming method preferably includes a method for forming a metal oxide passivation layer in situ on the surface of the metal layer; and the coating method preferably includes die coating, blade coating, and extrusion coating.

[0100] Fourthly, the present invention provides a battery comprising a composite current collector as described in the third aspect.

[0101] Compared with the prior art, the present invention has the following beneficial effects:

[0102] (1) The present invention obtained modified polypropylene by selecting a specific modifier, and used the modified polypropylene as the raw material to prepare the modified polypropylene film with strong surface adhesion, high dielectric constant and good mechanical properties. Its surface tension is 38-59 mN / m, dielectric constant is 2.6-4.0 mN / m and tensile strength is 185-225 MPa.

[0103] (2) Using the modified polypropylene film provided by the present invention as the base film to prepare a composite current collector can solve the problems of weak adhesion between the base film and the metal layer and many pore defects in the prepared composite current collector, thereby preparing a composite current collector with stable structure and low defects. The adhesion between the polymer film (modified polypropylene film) and the metal layer in the composite current collector is relatively large, ranging from 0.9 to 2.7 N / cm, and there are no pores on the prepared composite current collector. In addition, the sheet resistance of the composite current collector is relatively small, ranging from 17 to 18 mΩ, which promotes the application of composite current collectors in batteries. Attached Figure Description

[0104] Figure 1 This is a schematic diagram of the composite current collector provided in Example 1;

[0105] Wherein, 1-first protective layer, 2-first metal layer, 3-polymer film layer, 4-second metal layer, 5-second protective layer. Detailed Implementation

[0106] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be considered as specific limitations thereof.

[0107] The sources of some components in the following examples and comparative examples are as follows:

[0108] Polypropylene: melt index of 3.0 g / 10 min (230℃ / 2.16 kg), molecular weight distribution index of 4.5, isotacticity of 96%, purchased from TPC Singapore, model FS3028;

[0109] Polypropylene: melt index of 3.0 g / 10 min (230℃ / 2.16 kg), molecular weight distribution index of 4.5, isotacticity of 93%, purchased from TPC Singapore, model FS3025;

[0110] Catalyst: HR catalyst, purchased from Sinopec Catalyst Co., Ltd.

[0111] The polypropylene used in the following preparation examples is polypropylene of type FS3028.

[0112] Preparation Examples 1-9 and Comparative Example 1

[0113] Preparation Examples 1-5 provide a 4-terpenol modified polypropylene, Preparation Examples 6-9 and Preparation Comparative Example 1 provide an α-terpineol modified polypropylene, a lavenderol modified polypropylene, a geraniol modified polypropylene, and a propenol modified polypropylene, respectively.

[0114] The preparation method of the above-mentioned modified polypropylene is as follows:

[0115] The reactor was fully purged and dried with nitrogen. Then, a well-mixed modifier, polypropylene, n-hexane (1500 mL), and HR catalyst were added to the reactor. The modification reaction was carried out under a nitrogen atmosphere and then cooled. The mixture was discharged from the reactor with nitrogen. After filtration, washing, and drying, modified polypropylene was obtained.

[0116] The amounts of modifier, polypropylene, and HR catalyst are detailed in Table 1 below, as are the reaction temperature and time.

[0117] Table 1

[0118]

[0119] Example 1

[0120] This embodiment provides a modified polypropylene film and its preparation method. The raw materials for preparing the modified polypropylene film include the following components by mass percentage: 0.5% 4-terpene alcohol modified polypropylene and 99.5% polypropylene provided in Preparation Example 1;

[0121] Among them, the melt index of polypropylene is 3.0 g / 10 min (230℃ / 2.16 kg), the molecular weight distribution index is 4.5, and the isotacticity is 96%.

[0122] The grafting rate of 4-terpene alcohol in 4-terpene alcohol-modified polypropylene is 0.05%.

[0123] The preparation method of the above-mentioned modified polypropylene film is as follows:

[0124] (1) The raw material for the preparation of modified polypropylene film is placed in a twin-screw extruder, melted at 240°C, filtered through a 10μm filter, and then extruded through a die to obtain the molten material. The temperature of the die is 250°C.

[0125] (2) The molten material obtained in step (1) is extended onto the casting roller, cooled and formed by water at 20°C, then stretched biaxially, cooled by air in the platform area, and then entered the winding system through the traction system. Under the condition of winding tension of 30 N / m, the film is wound up to obtain a modified polypropylene film with a thickness of 4.5 μm.

[0126] The bidirectional stretching is asynchronous stretching, and the asynchronous stretching includes the following process:

[0127] ① Longitudinal stretching: Preheating temperature: 138℃; stretching temperature: 145℃; longitudinal stretching ratio: 7; after longitudinal stretching, cool to room temperature.

[0128] ② Transverse stretching: Preheating temperature: 130℃; stretching temperature: 152℃; heat setting temperature: 165℃; transverse stretching ratio: 6;

[0129] ③ Heat treatment: Heat treatment temperature 130℃.

[0130] Example 2

[0131] This embodiment provides a modified polypropylene film and its preparation method. The only difference from Example 1 is that, by mass percentage, the raw materials for preparing the modified polypropylene film include the following components: 50% 4-terpene alcohol modified polypropylene and 50% polypropylene provided in Preparation Example 1, with other conditions being the same as in Example 1.

[0132] Example 3

[0133] This embodiment provides a modified polypropylene film and its preparation method. The only difference from Example 1 is that the raw material for preparing the modified polypropylene film is the 4-terpene alcohol modified polypropylene provided in Example 1, and the other conditions are the same as in Example 1.

[0134] Example 4

[0135] This embodiment provides a modified polypropylene film and its preparation method. The only difference from Example 1 is that, by mass percentage, the raw materials for preparing the modified polypropylene film include the following components: 0.4% 4-terpene alcohol modified polypropylene and 99.6% polypropylene provided in Example 1, with other conditions being the same as in Example 1.

[0136] Example 5

[0137] This embodiment provides a modified polypropylene film and its preparation method. The only difference from Example 1 is that the 4-terpene alcohol modified polypropylene provided in Preparation Example 1 is replaced with the 4-terpene alcohol modified polypropylene with a grafting rate of 1.0% provided in Preparation Example 2. Other conditions are the same as in Example 1.

[0138] Example 6

[0139] This embodiment provides a modified polypropylene film and its preparation method. The only difference from Example 1 is that the 4-terpene alcohol modified polypropylene provided in Preparation Example 1 is replaced with the 4-terpene alcohol modified polypropylene with a grafting rate of 5.0% provided in Preparation Example 3. Other conditions are the same as in Example 1.

[0140] Example 7

[0141] This embodiment provides a modified polypropylene film and its preparation method. The only difference from Example 1 is that the 4-terpene alcohol modified polypropylene provided in Preparation Example 1 is replaced with the 4-terpene alcohol modified polypropylene with a grafting rate of 10.0% provided in Preparation Example 4. Other conditions are the same as in Example 1.

[0142] Example 8

[0143] This embodiment provides a modified polypropylene film and its preparation method. The only difference from Example 1 is that the 4-terpene alcohol modified polypropylene provided in Preparation Example 1 is replaced with the 4-terpene alcohol modified polypropylene with a grafting rate of 11.0% provided in Preparation Example 5. Other conditions are the same as in Example 1.

[0144] Example 9

[0145] This embodiment provides a modified polypropylene film and its preparation method. The only difference from Example 1 is that the 4-terpene alcohol modified polypropylene provided in Preparation Example 1 is replaced with the 4-terpene alcohol modified polypropylene with a grafting rate of 0.04% provided in Preparation Example 6. Other conditions are the same as in Example 1.

[0146] Example 10

[0147] This embodiment provides a modified polypropylene film and its preparation method. The only difference from Example 1 is that the raw material for preparing the modified polypropylene film is only the 4-terpene alcohol modified polypropylene with a grafting rate of 10.0% provided in Preparation Example 4. Other conditions are the same as in Example 1.

[0148] Example 11

[0149] This embodiment provides a modified polypropylene film and its preparation method. The only difference from Example 10 is that the 4-terpene alcohol modified polypropylene with a grafting rate of 10.0% provided in Preparation Example 4 is replaced with the α-terpineol modified polypropylene with a grafting rate of 10.0% provided in Preparation Example 7. Other conditions are the same as in Example 10.

[0150] Example 12

[0151] This embodiment provides a modified polypropylene film and its preparation method. The only difference from Example 10 is that the 4-terpene alcohol modified polypropylene with a grafting rate of 10.0% provided in Preparation Example 4 is replaced with the lavender alcohol modified polypropylene with a grafting rate of 10.0% provided in Preparation Example 8. Other conditions are the same as in Example 10.

[0152] Example 13

[0153] This embodiment provides a modified polypropylene film and its preparation method. The only difference from Example 10 is that the 4-terpene alcohol modified polypropylene with a grafting rate of 10.0% provided in Preparation Example 4 is replaced with the geraniol modified polypropylene with a grafting rate of 10.0% provided in Preparation Example 9. Other conditions are the same as in Example 10.

[0154] Example 14

[0155] This embodiment provides a modified polypropylene film and its preparation method. The only difference from Example 1 is that the polypropylene (FS3028) with a melt index of 3.0 g / 10 min (230℃ / 2.16 kg), a molecular weight distribution index of 4.5, and an isotacticity of 96% is replaced with polypropylene (FS3025) with a melt index of 3.0 g / 10 min (230℃ / 2.16 kg), a molecular weight distribution index of 4.5, and an isotacticity of 93%. All other conditions are the same as in Example 1.

[0156] Comparative Example 1

[0157] This comparative example provides a polypropylene film and its preparation method. The only difference from Example 1 is that the raw material for preparing the polypropylene film is only polypropylene (FS3028), and the other conditions are the same as in Example 1.

[0158] Comparative Example 2

[0159] This embodiment provides a modified polypropylene film and its preparation method. The only difference from Example 10 is that the 4-terpene alcohol modified polypropylene with a grafting rate of 10.0% provided in Preparation Example 4 is replaced with the allyl alcohol modified polypropylene with a grafting rate of 10.0% provided in Comparative Example 1. Other conditions are the same as in Example 10.

[0160] Application Example 1

[0161] This application example provides a composite current collector and its preparation method. A schematic diagram of the composite current collector is shown below. Figure 1 As shown, it includes a first protective layer 1, a first metal layer 2, a polymer film layer 3, a second metal layer 4, and a second protective layer 5, which are stacked sequentially.

[0162] The polymer film layer 3 is the modified polypropylene film provided in Example 1.

[0163] The preparation method of the composite current collector is as follows:

[0164] The modified polypropylene film provided in Example 1 was placed in a magnetron sputtering chamber. Using 99.99% pure copper metal as the target and argon gas as the gas source, a 100nm thick copper metal layer was deposited on both sides of the modified polypropylene film using magnetron sputtering to obtain a composite film. This composite film was then used as a substrate for electroplating to thicken the conductive copper layer, obtaining a first protective layer 1 and a second protective layer 5. The electroplating process consisted of three steps: ① Electroplating to thicken the metal layer: The electroplating solution consisted of 120g / L copper sulfate, 100g / L sulfuric acid, 50mg / L chloride ions, 1.2mg / L sodium 3-mercapto-1-propanesulfonate, and 0.5mg / L... 1. Electroplating treatment: 2-Mercaptopyridine, 180 mg / L polyethylene glycol 10000, electroplating solution temperature 25℃, average cathode current density 2A / dm2, electroplating treatment for 5 min; 2. Preparation of first protective layer 1 and second protective layer 5: After electroplating, the plated film is cleaned in a water bath, and then a surface protective layer is prepared in a protective layer preparation tank containing 5 g / L potassium dichromate aqueous solution at 25℃ for 25 s, and finally cleaned again in a water bath; 3. Drying: The cleaned film is dried in an oven at 65℃ to obtain a composite current collector with a total thickness of 1.2 μm (wherein, the thickness of the metal layer is 1170 nm and the thickness of the protective layer is 30 nm).

[0165] Application Example 2-14

[0166] Application Examples 2-14 provide a composite current collector and its preparation method, respectively. The difference from Application Example 1 is that the modified polypropylene membrane provided in Example 1 is replaced with the modified polypropylene membrane provided in Examples 2-14 in turn, while other conditions are the same as in Application Example 1.

[0167] Comparative Application Examples 1-2

[0168] Comparative Application Examples 1-2 provide a composite current collector and its preparation method, respectively. The difference from Application Example 1 is that the modified polypropylene membrane provided in Example 1 is replaced with the polypropylene membrane provided in Comparative Example 1 and the modified polypropylene membrane provided in Comparative Example 2 in turn. Other conditions are the same as in Application Example 1.

[0169] The purpose of this invention in preparing modified polypropylene films is to improve the surface adhesion and dielectric constant of the polymer films, thereby enhancing the performance of composite current collectors prepared using these modified polypropylene films as substrates. The surface adhesion of the polypropylene film mainly depends on its surface tension, ultimately manifested in the adhesion between the base film and the metal layer in the composite current collector. Changes in the dielectric constant of the polypropylene film directly affect the number of pores in the prepared composite current collector. Therefore, this invention tested the surface tension and dielectric constant of the prepared modified polypropylene film, the adhesion between the base film and the metal layer in the prepared composite current collector, and the number of pore defects. Furthermore, the tensile strength of the prepared modified polypropylene film and the sheet resistance of the prepared composite current collector were also tested. The specific methods are as follows:

[0170] ① Surface tension: The surface tension of the modified polypropylene film prepared above was tested according to standard GB / T 14216-2008;

[0171] ② Dielectric constant: The dielectric constant of the modified polypropylene film prepared above was tested according to standard SJ / T1147-1993;

[0172] ③ Tensile strength: The tensile strength of the modified polypropylene film prepared above was tested according to standard GB / T 1040.3-2006.

[0173] ④ Adhesion between the polypropylene film and the metal layer in the composite current collector: A layer of Permacel P-94 double-sided adhesive is bonded to a 1mm thick aluminum foil, the composite current collector is bonded on top of the double-sided adhesive, and a layer of ethylene-acrylic acid copolymer film (DuPont Nurcel 0903, 50μm thick) is covered on top of the composite current collector, and then subjected to a 1.3×10⁵ N / m 2 The sample was hot-pressed at 120℃ for 10 seconds, cooled to room temperature, and cut into strips of 150mm×15mm. Finally, the ethylene-acrylic acid copolymer film of the sample strip was fixed to the upper clamp of the tensile testing machine, and the rest was fixed to the lower clamp. After fixing, the two were peeled at an angle of 180° and a speed of 100mm / min to test the peel force, that is, the adhesion force between the polypropylene film and the metal layer.

[0174] ⑤ Number of pore defects per unit area of ​​composite current collector: The prepared composite current collector sample is placed in a surface quality detection system (micro-vision charge-coupled device CCD) to scan its surface. Then, the light signal is converted into an electrical signal and transmitted to a computer to count the number of pore defects per unit area of ​​composite current collector with a pore diameter of less than 100μm (generally, the finished product should not have pores larger than 100μm).

[0175] ⑥ Sheet resistance: Place the prepared composite current collector sample on the sample stage and use a four-probe sheet resistance meter to test the sheet resistance of the sample.

[0176] The performance test results of the modified polypropylene membranes or polypropylene membranes provided in the above embodiments and comparative examples are shown in Table 2 below:

[0177] Table 2

[0178] serial number Surface tension (mN / m) Dielectric constant Tensile strength (MPa) Example 1 38 2.6 195 Example 2 46 3.1 209 Example 3 52 3.5 220 Example 4 34 2.3 183 Example 5 42 2.8 225 Example 6 45 3.0 211 Example 7 50 3.2 185 Example 8 51 3.2 176 Example 9 35 2.3 185 Example 10 57 3.9 197 Example 11 59 4.0 199 Example 12 56 3.9 194 Example 13 55 3.8 191 Example 14 37 2.4 170 Comparative Example 1 32 2.1 180 Comparative Example 2 35 2.2 187

[0179] As shown in the table above, this invention utilizes polypropylene with specific melt flow index, specific molecular weight distribution index, and specific regularity, along with a specific modifier, and controls the grafting rate of the modifier within a specific range to prepare a high-performance modified polypropylene. Using this modified polypropylene as the raw material for preparing modified polypropylene films, and controlling the content of modified polypropylene in the films within a specific range, the resulting modified polypropylene films exhibit high surface tension, high dielectric constant, and high tensile strength. The surface tension is 38–59 mN / m, the dielectric constant is 2.6–4.0 mN / m, and the tensile strength is 185–225 MPa.

[0180] Compared with Example 1, if the content of modified polypropylene in the raw materials for preparing the modified polypropylene film is too low (Example 4), the performance improvement of the prepared modified polypropylene film compared with the polypropylene film (Comparative Example 1) is limited, and its surface tension, dielectric constant and tensile strength are all low.

[0181] Compared with Example 1, if the grafting rate of the modifier in the modified polypropylene is low (Example 9), the surface tension, dielectric constant and tensile strength of the prepared modified polypropylene film are also poor; if the grafting rate of the modifier in the modified polypropylene is high (Example 8), the mechanical properties of the prepared modified polypropylene film are poor.

[0182] Compared with Example 1, the polypropylene film prepared with polypropylene (Comparative Example 1) has lower surface tension, dielectric constant and tensile strength; if polypropylene modified with other modifiers is used to prepare polypropylene film (Comparative Example 2), the surface tension, dielectric constant and tensile strength of the prepared modified polypropylene film are also poor.

[0183] In summary, this invention utilizes polypropylene with specific melt flow index, specific molecular weight distribution index, and specific regularity, along with a specific modifier, and controls the grafting rate of the modifier within a specific range to prepare a high-performance modified polypropylene. Using this modified polypropylene as the raw material for preparing a modified polypropylene film, and controlling the content of modified polypropylene in the film within a specific range, the resulting modified polypropylene film exhibits high surface tension, high dielectric constant, and high tensile strength.

[0184] The performance test results of the composite current collectors provided in the above application examples and comparative application examples are shown in Table 3 below:

[0185] Table 3

[0186]

[0187] As can be seen from the table above, in this invention, by designing the raw materials for preparing modified polypropylene membranes, a modified polypropylene membrane with excellent performance was prepared. The adhesion between the polymer membrane (modified polypropylene membrane) and the metal layer is relatively large, ranging from 0.9 to 2.7 N / cm. Furthermore, the prepared composite current collector has no pores and has a low sheet resistance of 17 to 18 mΩ.

[0188] Compared with Application Example 1, if the content of modified polypropylene in the raw materials for preparing the modified polypropylene film is too low (Application Example 4), the performance improvement of the prepared composite current collector is limited compared with the composite current collector (compared to Application Example 1), with lower adhesion, more pores, and higher sheet resistance.

[0189] Compared with Application Example 1, if the grafting rate of the modifier in the modified polypropylene is low (Application Example 9), the prepared composite current collector has lower adhesion, more pores, and higher sheet resistance.

[0190] Compared with Application Example 1, the composite current collector prepared with polypropylene film (Comparative Example 1) has lower adhesion, more pores, and higher sheet resistance; if polypropylene modified with other modifiers is used to prepare polypropylene film, the performance of the resulting composite current collector (Comparative Example 2) is also poor.

[0191] In summary, this invention, through the design of the raw materials for preparing modified polypropylene membranes, yields a high-performance modified polypropylene membrane, and further produces a composite current collector with strong adhesion between the modified polypropylene membrane and the metal layer, no pores, and low sheet resistance.

[0192] The applicant declares that the detailed process flow of this invention is illustrated by the above embodiments, but this invention is not limited to the above detailed process flow, that is, it does not mean that this invention must rely on the above detailed process flow to be implemented. Those skilled in the art should understand that any improvements to this invention, equivalent substitutions of raw materials for the product of this invention, addition of auxiliary components, and selection of specific methods, etc., all fall within the protection scope and disclosure scope of this invention.

Claims

1. A modified polypropylene film, characterized in that, The raw materials for preparing the modified polypropylene film include modified polypropylene; The modifier for the modified polypropylene includes terpene alcohols; The grafting rate of terpene alcohol in the modified polypropylene is 0.05%-10%; The modified polypropylene has a melt flow index of 3.0-4.0 g / 10min. The modified polypropylene has a molecular weight distribution of 4.5-5.

5. The isotacticity of the polypropylene in the modified polypropylene is ≥95%; Based on the mass percentage of the raw materials used to prepare the modified polypropylene film being 100%, the mass percentage of the modified polypropylene is ≥0.5%.

2. The modified polypropylene film according to claim 1, characterized in that, The terpene alcohols include any one or a combination of at least two of the following: 4-terpene alcohol, α-terpineol, carvacrol, lavenderol, nerol, and geraniol.

3. A method for preparing a modified polypropylene film as described in claim 1 or 2, characterized in that, The preparation method includes the following steps: (1) The raw materials for the preparation of modified polypropylene membrane are melted, filtered, and extruded to obtain molten material; (2) The molten material obtained in step (1) is extended onto the casting roller, cooled and shaped, and then biaxially stretched to obtain the modified polypropylene film.

4. A composite current collector, characterized in that, The composite current collector includes a metal layer and a polymer layer; The polymer layer is a modified polypropylene film as described in any one of claims 1-2, or a modified polypropylene film prepared by the method described in claim 3.

5. A battery, characterized in that, The battery includes the composite current collector as described in claim 4.

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