BOPP (Biaxially-oriented Polypropylene) composite film, preparation method thereof and capacitor

Abstract

The invention provides a BOPP composite film and a preparation method thereof and a capacitor, the BOPP composite film comprises a biaxially oriented polypropylene film and a polyvinyl alcohol film which are laminated, and the polyvinyl alcohol film comprises a polyvinyl alcohol matrix and peeled montmorillonite filled in the polyvinyl alcohol matrix. The BOPP composite film can effectively improve the energy storage density of a capacitor, and solves the problem that the energy storage density cannot be greatly improved due to the fact that a polypropylene film is limited by a dielectric constant.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of power capacitors, and relates to a BOPP composite film, a preparation method thereof and a capacitor. BACKGROUND

[0002] Since the 1970s, the emergence of polypropylene film has changed the capacitor dielectric material, and in the 1990s, polypropylene film has replaced insulating paper to become the main dielectric material of capacitors. The biaxially oriented polypropylene (BOPP) widely used at present has stable dielectric properties and good voltage resistance, wherein the relative dielectric constant is about 2.2, the dielectric loss tangent is about 2*10 -4 (0-30℃), and the breakdown strength exceeds 600kV / mm. Due to continuous optimization of the biaxial stretching equipment and process parameters, the thickness of BOPP can be as low as 3-5μm.

[0003] Although the BOPP film has many advantages, due to its low dielectric constant, the energy storage density is only 1.8J / cm -3 under a field strength of 200kV / mm, which cannot meet the demand for lightweight and miniaturization of capacitors in current power systems and pulse power systems. The energy in a thin film capacitor can be described as Therefore, the maximum energy storage density (U m ) of a thin film capacitor is determined by the dielectric constant (ε r ) and the breakdown strength (E b ) of the internal dielectric polymer. Based on the above formula, the synergistic improvement of the breakdown field strength and the dielectric constant of the polymer film is a feasible method to improve the energy storage density.

[0004] Chinese patent ZL201811229579.3 provides a high energy storage density polymer-based nanocomposite and a preparation method thereof. The method is to first premix the polymer base with two-dimensional hybrid fillers to obtain a masterbatch, then premix the masterbatch with the polymer base containing at least 5vol% of two-dimensional hybrid fillers in the material, and melt blend extrusion granulation at a screw speed of 400-1000 rpm, wherein the size of one or two two-dimensional hybrid fillers differs by at least 4 times. The energy storage density of the obtained composite material can be increased by at least 23.4% relative to pure polypropylene base, at least 77.1% relative to pure high-density polyethylene base, and at least 69.4% relative to pure polyvinylidene fluoride base. However, the method has high requirements for the dispersion of two-dimensional hybrid fillers, otherwise it will affect the breakdown strength and film forming property due to poor dispersion, in addition, the use of two-dimensional ceramic fillers is costly, and the process of preparing masterbatch by internal mixing will also cause the molecular weight of the polymer to decrease and the mechanical properties to deteriorate.

[0005] Chinese patent ZL202010010849.2 provides a capacitor film and a manufacturing method thereof. The capacitor film comprises a polypropylene film and a polyurethane-based coating layer. The capacitor film has simple composition and cheap raw materials. The conductivity of silver is high, and the addition amount of silver is small under the same conductivity effect, which is more conducive to the dispersion of the coating. The breakdown strength of the composite material is maintained at 500 MV / m. The method has limited improvement on the dielectric constant of polypropylene, which is only improved to 2.5. SUMMARY

[0006] The purpose of the present application is to provide a BOPP composite film, a preparation method thereof and a capacitor, which can effectively improve the energy storage density of the capacitor and solve the problem that the energy storage density of the polypropylene film cannot be greatly improved due to the limitation of the dielectric constant.

[0007] The present application is achieved by the following technical solutions:

[0008] A BOPP composite film comprises a biaxially oriented polypropylene film and a polyvinyl alcohol film arranged in layers. The polyvinyl alcohol film comprises a polyvinyl alcohol matrix and exfoliated montmorillonite filled in the polyvinyl alcohol matrix.

[0009] Preferably, the thickness ratio of the biaxially oriented polypropylene film and the polyvinyl alcohol film is 12 μm:(145-320) nm.

[0010] Preferably, the BOPP composite film comprises, by mass percentage:

[0011] The polyvinyl alcohol matrix is 10wt%-20wt%;

[0012] The exfoliated montmorillonite is 10wt%-20wt%;

[0013] Biaxially oriented polypropylene film 60wt%-80wt%.

[0014] The application provides a preparation method of the BOPP composite film.

[0015] S1, mixing polyvinyl alcohol particles, exfoliated montmorillonite powder, a crosslinking agent and a crosslinking reaction catalyst in water to obtain a coating liquid;

[0016] S2, coating the coating liquid on a biaxially oriented polypropylene film and drying to obtain the BOPP composite film.

[0017] Preferably, S1 specifically comprises:

[0018] dissolving the polyvinyl alcohol particles in water to obtain a PVA solution;

[0019] dispersing the exfoliated montmorillonite powder in water to obtain an MMT water dispersion liquid;

[0020] adding the PVA solution into the MMT water dispersion liquid to obtain a mixed liquid;

[0021] adding the crosslinking agent and the crosslinking reaction catalyst into the mixed liquid to obtain the coating liquid.

[0022] Preferably, in S1, the crosslinking agent is glutaraldehyde, and the crosslinking reaction catalyst is hydrochloric acid.

[0023] Further, the molar ratio of glutaraldehyde to the total moles of hydroxyl groups on the polyvinyl alcohol chain is 1:(15-25).

[0024] Further, the molar ratio of hydrochloric acid to glutaraldehyde is 1:(4-6).

[0025] Preferably, in S2, the drying temperature is 50-70 DEG C.

[0026] The application provides a capacitor comprising a dielectric, which is the BOPP composite film as described above.

[0027] Compared with the prior art, the application has the following beneficial effects:

[0028] The application adds exfoliated montmorillonite in the BOPP composite film, the exfoliated montmorillonite (MMT) is a single-layer nanosheet, due to its special layered structure, it has excellent anti-fracture and impact resistance, the well-arranged MMT nanosheet layer can realize charge injection blocking, significantly improve the dielectric and breakdown performance of the BOPP film, thereby realizing the improvement of the energy storage density.

[0029] The preparation method of the BOPP composite film of the application is realized by coating and drying, which is simple and easy to operate.

[0030] Further, the application prepares the dispersion liquid of polyvinyl alcohol and exfoliated montmorillonite respectively, and then mixes the two dispersion liquids, so that the polyvinyl alcohol can be fully dissolved and the exfoliated montmorillonite can be fully dispersed.

[0031] Further, the application repeats the coating process for multiple times, so that a uniform coating layer can be prepared on the surface of the biaxially oriented polypropylene film, and the film performance is stable.

[0032] The capacitor based on the BOPP composite film of the application has high dielectric and breakdown performance, and has high energy storage density. BRIEF DESCRIPTION OF DRAWINGS

[0033] In order to more clearly illustrate the technical solutions in the embodiments of the application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or the prior art description. Obviously, the drawings in the following description are some embodiments of the application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0034] Figure 1 It is a flow chart of the preparation method of the BOPP composite film of the application;

[0035] Figure 2 It is a Weibull distribution probability graph of the breakdown voltage of the BOPP composite film and the pure BOPP film of the application;

[0036] Figure 3 It is a relative dielectric constant spectrum of the BOPP composite film and the pure BOPP film of the application;

[0037] Figure 4 It is a schematic diagram of the energy storage density of the BOPP composite film and the pure BOPP film of the application. DETAILED DESCRIPTION

[0038] The present application is herein described, by way of example only, with the comprehension that the advantages and utility thereof are not limited thereto. It should be realized that various alterations, modifications, and improvements can be made hereto, and further applications can also be made thereof, without departing from the spirit and scope of the present application.

[0039] It should be noted that the process equipment or apparatus not specifically mentioned in the following examples are all conventional equipment or apparatus in the art.

[0040] It should be noted that the terms "comprising", "having", "including", and "containing", or any variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, system, product, or apparatus that comprises, has, includes or contains a list of steps or elements, but not those not expressly listed or inherent to such process, method, system, product, or apparatus, is nonetheless within the scope of such steps or elements. Furthermore, unless specifically stated otherwise, the order or sequence of any process steps can be varied or re-sequenced without departing from the spirit and scope of the present application. It is therefore contemplated to be within the scope of the present application that these steps be performed in other than the recited order, or be modified or combined in other respects, insofar as the technical content of the present application is not affected thereby.

[0041] The BOPP composite film comprises a biaxially oriented polypropylene film and a polyvinyl alcohol film stacked together, wherein the polyvinyl alcohol film comprises a polyvinyl alcohol matrix and exfoliated montmorillonite filled in the polyvinyl alcohol matrix.

[0042] The biaxially oriented polypropylene film is prepared by co-extruding polypropylene particles into a sheet and then stretching the sheet in two directions. This stretching process causes the molecular structure of the film to be oriented, thereby imparting excellent physical properties, stable dielectric properties, and good voltage resistance.

[0043] The exfoliated montmorillonite is a single-layer nanosheet of montmorillonite. Due to its special layered structure, it has excellent fracture resistance and impact resistance. The well-aligned exfoliated montmorillonite nanosheet can achieve charge injection blocking. Therefore, by combining the exfoliated montmorillonite with the biaxially oriented polypropylene film, the dielectric constant and breakdown field strength of the biaxially oriented polypropylene film can be improved.

[0044] The introduction of polyvinyl alcohol can form a PVA / MMT cross-linked structure nanocoating, thereby achieving good combination of the biaxially oriented polypropylene film and the exfoliated montmorillonite, and improving the dielectric constant and breakdown field strength of the biaxially oriented polypropylene film.

[0045] The thickness of the biaxially oriented polypropylene film is 12 μm, and the thickness of the polyvinyl alcohol film is 145-320 nm. That is, the thickness ratio of the biaxially oriented polypropylene film and the polyvinyl alcohol film is 12 μm:(145-320) nm.

[0046] The BOPP composite film comprises, by mass percentage:

[0047] The polyvinyl alcohol base is 10wt%-20wt%;

[0048] The exfoliated montmorillonite is 10wt%-20wt%;

[0049] The biaxially oriented polypropylene film is 60wt%-80wt%.

[0050] The preparation method of the BOPP composite film comprises:

[0051] S1, mixing polyvinyl alcohol particles, exfoliated montmorillonite powder, crosslinking agent and crosslinking reaction catalyst in water to obtain a coating liquid;

[0052] S2, coating the coating liquid on the biaxially oriented polypropylene film and drying to obtain the BOPP composite film.

[0053] In order to better dissolve the polyvinyl alcohol particles and disperse the exfoliated montmorillonite powder in the coating liquid, S1 specifically comprises:

[0054] Dissolving the polyvinyl alcohol particles in water to obtain a PVA solution;

[0055] Dispersing the exfoliated montmorillonite powder in water to obtain an MMT water dispersion liquid;

[0056] Adding the PVA solution to the MMT water dispersion liquid to obtain a mixed liquid;

[0057] Adding the crosslinking agent and the crosslinking reaction catalyst to the mixed liquid to obtain the coating liquid.

[0058] Before preparing the coating liquid, the raw materials are dried to remove water, specifically: vacuum drying the polyvinyl alcohol particles, the exfoliated montmorillonite powder and the biaxially oriented polypropylene film to remove water.

[0059] The preparation method of the PVA solution specifically comprises: dissolving the polyvinyl alcohol particles in deionized water (DI), heating and stirring until the particles are completely dissolved to prepare the PVA solution.

[0060] The preparation method of the MMT water dispersion liquid specifically comprises: adding the exfoliated montmorillonite powder to deionized water, heating and stirring, and then performing ultrasonic treatment to ensure uniform exfoliation.

[0061] The preparation method of the mixed solution is specifically as follows: the PVA solution is slowly added to the MMT water dispersion liquid, heated and stirred, and ultrasonic treatment is performed to ensure uniform dispersion.

[0062] The crosslinking agent is preferably glutaraldehyde (GA), and the crosslinking reaction catalyst is preferably hydrochloric acid (HCl), so as to ensure that the molar ratio of GA to the total number of moles of hydroxyl groups on the polyvinyl alcohol chain is 1:(15-25), and the molar ratio of HCl to GA is 1:(4-6).

[0063] The S2 specifically includes:

[0064] The biaxially stretched polypropylene film is immersed in the coating liquid on the surface, then vertically hung, and dried at 50-70℃ for 24h to make the crosslinking reaction fully occur.

[0065] In order to prepare a uniform biaxially stretched polypropylene film coating on the surface of the biaxially stretched polypropylene film, the above coating process needs to be repeated twice or four times on the same biaxially stretched polypropylene film, and the film is rotated by 180° each time, respectively producing a coating layer with a thickness of 155±10nm and 305±15nm.

[0066] The raw material information used in the embodiment of the present application is shown in Table 1.

[0067] Table 1 Raw material specifications and manufacturers

[0068]

[0069] Example 1

[0070] Preparation of raw materials:

[0071] Polyvinyl alcohol 10wt%;

[0072] Exfoliated montmorillonite 10wt%;

[0073] Biaxially stretched polypropylene film 80wt%.

[0074] (1) The polyvinyl alcohol particles, exfoliated montmorillonite powder and biaxially stretched polypropylene film are placed in a vacuum drying oven and dried at 60℃ for 24h to remove water.

[0075] (2) The polyvinyl alcohol particles are dissolved in deionized water, heated and stirred at 95℃ for 4h until the particles are completely dissolved, to prepare a PVA solution.

[0076] (3) The exfoliated montmorillonite powder is added to deionized water, heated and stirred at 95℃ for 30 minutes, and then ultrasonic treatment (Branson 8510R-MT, 250W, 44kHz) is performed for 30 minutes to ensure uniform exfoliation, to obtain an MMT water dispersion liquid.

[0077] (4) Slowly add the PVA solution into the MMT aqueous dispersion liquid to make the solution concentration reach 1.5wt% (0.75wt% MMT + 0.75wt% PVA + 98.5wt% deionized water), to obtain a mixed liquid;

[0078] (5) Heat and stir the above mixed liquid for 30 minutes, and perform ultrasonic treatment for 30 minutes to ensure uniform dispersion.

[0079] (6) Add the crosslinking agent glutaraldehyde and the crosslinking reaction catalyst hydrochloric acid into the above mixed liquid, to ensure that the molar ratio of glutaraldehyde to the total moles of hydroxyl groups on the PVA chain is 1:20, and the molar ratio of HCl to glutaraldehyde is 1:5, to obtain a coating liquid.

[0080] (7) Dip coat the biaxially stretched polypropylene film with the above coating liquid, and then vertically hang it in an oven for drying at 60°C for 24h to allow the crosslinking reaction to fully occur.

[0081] (8) Rotate the film by 180°, and repeat the coating process of step (7) once to obtain a polyvinyl alcohol film coating with a thickness of 155±10nm.

[0082] Example 2

[0083] Preparation raw materials:

[0084] Polyvinyl alcohol 20wt%;

[0085] Exfoliated montmorillonite 20wt%;

[0086] Biaxially stretched polypropylene film 60wt%.

[0087] (1) Dry the polyvinyl alcohol particles, exfoliated montmorillonite powder, and biaxially stretched polypropylene film in a vacuum drying oven at 60°C for 24h to remove water.

[0088] (2) Dissolve the polyvinyl alcohol particles in deionized water, and heat and stir at 95°C for 4h until the particles are completely dissolved to prepare a PVA solution.

[0089] (3) Add the exfoliated montmorillonite powder into deionized water, heat and stir at 95°C for 30 minutes, and then perform ultrasonic treatment (Branson 8510R-MT, 250W, 44kHz) for 30 minutes to ensure uniform exfoliation, to obtain an MMT aqueous dispersion liquid.

[0090] (4) Slowly add the PVA solution into the MMT aqueous dispersion liquid to make the solution concentration reach 1.5wt% (0.75wt% MMT + 0.75wt% PVA + 98.5wt% deionized water), to obtain a mixed liquid;

[0091] (5) The above mixture was heated and stirred for 30 minutes, and ultrasonic treatment was performed for 30 minutes to ensure uniform dispersion.

[0092] (6) The crosslinking agent glutaraldehyde and the crosslinking reaction catalyst hydrochloric acid were added to the above mixture, and the molar ratio of glutaraldehyde to the total moles of hydroxyl groups on the PVA chain was 1:20, and the molar ratio of HCl to glutaraldehyde was 1:5, to obtain a coating solution.

[0093] (7) The biaxially stretched polypropylene film was dip-coated with the above coating solution, and then vertically hung in an oven, dried at 60°C for 24h, so that the crosslinking reaction occurred fully.

[0094] (8) The film was rotated by 180°, and the coating process of step (7) was repeated three times to obtain a polyvinyl alcohol film coating with a thickness of 305±15nm.

[0095] Example 3

[0096] Preparation of raw materials:

[0097] Polyvinyl alcohol 15wt%;

[0098] Exfoliated montmorillonite clay 15wt%;

[0099] Biaxially stretched polypropylene film 70wt%.

[0100] (1) The polyvinyl alcohol particles, exfoliated montmorillonite clay powder, and biaxially stretched polypropylene film were placed in a vacuum drying oven and dried at 60°C for 24h to remove water.

[0101] (2) The polyvinyl alcohol particles were dissolved in deionized water, heated and stirred at 95°C for 4h until the particles were completely dissolved to obtain a PVA solution.

[0102] (3) The exfoliated montmorillonite clay powder was added to deionized water, heated and stirred at 95°C for 30 minutes, and then ultrasonic treatment (Branson 8510R-MT, 250W, 44kHz) was performed for 30 minutes to ensure uniform exfoliation to obtain an MMT aqueous dispersion.

[0103] (4) The PVA solution was slowly added to the MMT aqueous dispersion to obtain a mixture with a solution concentration of 1.5wt% (0.75wt% MMT + 0.75wt% PVA + 98.5wt% deionized water).

[0104] (5) The above mixture was heated and stirred for 30 minutes, and ultrasonic treatment was performed for 30 minutes to ensure uniform dispersion.

[0105] (6) Crosslinking agent glutaraldehyde and crosslinking reaction catalyst hydrochloric acid were added into the above mixture, ensuring the molar ratio of glutaraldehyde to the total moles of hydroxyl groups on PVA chain was 1:20, and the molar ratio of HCl to glutaraldehyde was 1:5, to obtain a coating solution.

[0106] (7) The biaxially stretched polypropylene film was dip-coated with the coating solution, and then vertically hung in an oven for drying at 60°C for 24 h, so that the crosslinking reaction was fully carried out.

[0107] (8) The film was rotated by 180°, and the coating process of step (7) was repeated once, to obtain a polyvinyl alcohol film coating with a thickness of 155±10 nm.

[0108] Example 4

[0109] Raw materials for preparation:

[0110] Polyvinyl alcohol 15 wt%;

[0111] Exfoliated montmorillonite clay 15 wt%;

[0112] Biaxially stretched polypropylene film 70 wt%.

[0113] (1) The polyvinyl alcohol particles, exfoliated montmorillonite clay powder, and biaxially stretched polypropylene film were placed in a vacuum drying oven and dried at 60°C for 24 h to remove water.

[0114] (2) The polyvinyl alcohol particles were dissolved in deionized water, heated and stirred at 95°C for 4 h until the particles were completely dissolved, to obtain a PVA solution.

[0115] (3) The exfoliated montmorillonite clay powder was added to deionized water, heated and stirred at 95°C for 30 min, and then ultrasonically treated (Branson 8510R-MT, 250W, 44kHz) for 30 min to ensure uniform exfoliation, to obtain an MMT aqueous dispersion.

[0116] (4) The PVA solution was slowly added to the MMT aqueous dispersion, so that the solution concentration reached 1.5 wt% (0.75 wt% MMT + 0.75 wt% PVA + 98.5 wt% deionized water), to obtain a mixture;

[0117] (5) The above mixture was heated and stirred for 30 min, and ultrasonically treated for 30 min to ensure uniform dispersion.

[0118] (6) Crosslinking agent glutaraldehyde and crosslinking reaction catalyst hydrochloric acid were added into the above mixture, ensuring the molar ratio of glutaraldehyde to the total moles of hydroxyl groups on PVA chain was 1:15, and the molar ratio of HCl to glutaraldehyde was 1:4, to obtain a coating solution.

[0119] (7) The biaxially stretched polypropylene film is immersed in the coating solution described above, and then vertically hung in an oven for drying at 60°C for 24 h to allow the cross-linking reaction to fully occur.

[0120] (8) The film is rotated 180°, and the coating process of step (7) is repeated once to obtain a polyvinyl alcohol film coating with a thickness of 155 ± 10 nm.

[0121] Example 5

[0122] Preparation raw materials:

[0123] Polyvinyl alcohol 15 wt%;

[0124] Exfoliated montmorillonite clay 15 wt%;

[0125] Biaxially stretched polypropylene film 70 wt%.

[0126] (1) The polyvinyl alcohol particles, exfoliated montmorillonite clay powder, and biaxially stretched polypropylene film are placed in a vacuum drying oven and dried at 60°C for 24 h to remove water.

[0127] (2) The polyvinyl alcohol particles are dissolved in deionized water, heated and stirred at 95°C for 4 h until the particles are completely dissolved to prepare a PVA solution.

[0128] (3) The exfoliated montmorillonite clay powder is added to deionized water, heated and stirred at 95°C for 30 minutes, and then ultrasonically treated (Branson 8510R-MT, 250W, 44kHz) for 30 minutes to ensure uniform exfoliation to obtain an MMT aqueous dispersion liquid.

[0129] (4) The PVA solution is slowly added to the MMT aqueous dispersion liquid to achieve a solution concentration of 1.5 wt% (0.75 wt% MMT + 0.75 wt% PVA + 98.5 wt% deionized water) to obtain a mixed solution;

[0130] (5) The mixed solution is heated and stirred for 30 minutes, and ultrasonically treated for 30 minutes to ensure uniform dispersion.

[0131] (6) The cross-linking agent glutaraldehyde and the cross-linking reaction catalyst hydrochloric acid are added to the mixed solution to ensure a molar ratio of 1:15 between the total moles of glutaraldehyde and the hydroxyl groups on the PVA chain, and a molar ratio of 1:4 between HCl and glutaraldehyde to obtain a coating solution.

[0132] (7) The biaxially stretched polypropylene film is immersed in the coating solution described above, and then vertically hung in an oven for drying at 50°C for 24 h to allow the cross-linking reaction to fully occur.

[0133] (8) The film is rotated 180°, and the coating process of step (7) is repeated once to obtain a polyvinyl alcohol film coating with a thickness of 155 ± 10 nm.

[0134] Example 6

[0135] Raw materials for preparation:

[0136] 15 wt% polyvinyl alcohol;

[0137] 15 wt% of exfoliated montmorillonite;

[0138] 70 wt% of biaxially oriented polypropylene film.

[0139] (1) Place polyvinyl alcohol particles, peeled montmorillonite powder and biaxially oriented polypropylene film in a vacuum drying oven and dry at 60°C for 24 hours to remove moisture.

[0140] (2) Dissolve polyvinyl alcohol particles in deionized water, heat and stir at 95°C for 4 hours until the particles are completely dissolved to prepare a PVA solution.

[0141] (3) Add the exfoliated montmorillonite powder to deionized water, heat and stir at 95°C for 30 minutes, and then perform ultrasonic treatment (Branson 8510R-MT, 250W, 44kHz) for 30 minutes to ensure uniform exfoliation and obtain MMT aqueous dispersion liquid.

[0142] (4) Slowly add the PVA solution to the MMT aqueous dispersion to make the solution concentration reach 1.5wt% (0.75wt% MMT + 0.75wt% PVA + 98.5wt% deionized water) to obtain a mixed solution;

[0143] (5) Heat and stir the above mixture for 30 minutes, and then perform ultrasonic treatment for 30 minutes to ensure uniform dispersion.

[0144] (6) Add the crosslinking agent glutaraldehyde and the crosslinking reaction catalyst hydrochloric acid to the above mixture to ensure that the molar ratio of glutaraldehyde to the total number of hydroxyl groups on the PVA chain is 1:25 and the molar ratio of HCl to glutaraldehyde is 1:6 to obtain the coating solution.

[0145] (7) Dip the biaxially oriented polypropylene film into the above coating solution, then hang it vertically in an oven and dry it at 70°C for 24 hours to allow the crosslinking reaction to occur fully.

[0146] (8) Rotate the film 180° and repeat the coating process of step (7) once to obtain a polyvinyl alcohol film coating with a thickness of 155±10nm.

[0147] Example 7

[0148] Raw materials for preparation:

[0149] 10 wt% polyvinyl alcohol;

[0150] 15 wt% of exfoliated montmorillonite;

[0151] Biaxially oriented polypropylene film, 75 wt%.

[0152] (1) Place polyvinyl alcohol particles, peeled montmorillonite powder and biaxially oriented polypropylene film in a vacuum drying oven and dry at 65°C for 18 hours to remove moisture.

[0153] (2) Dissolve polyvinyl alcohol particles in deionized water, heat and stir at 90°C for 5 hours until the particles are completely dissolved to prepare a PVA solution.

[0154] (3) Add the exfoliated montmorillonite powder to deionized water, heat and stir at 85°C for 30 minutes, and then perform ultrasonic treatment (Branson 8510R-MT, 250W, 44kHz) for 30 minutes to ensure uniform exfoliation and obtain MMT aqueous dispersion liquid.

[0155] (4) Slowly add the PVA solution to the MMT aqueous dispersion to make the solution concentration reach 1.5wt% (0.90wt% MMT + 0.60wt% PVA + 98.5wt% deionized water) to obtain a mixture;

[0156] (5) Heat and stir the above mixture for 30 minutes, and then perform ultrasonic treatment for 30 minutes to ensure uniform dispersion.

[0157] (6) Add the crosslinking agent glutaraldehyde and the crosslinking reaction catalyst hydrochloric acid to the above mixture to ensure that the molar ratio of glutaraldehyde to the total number of hydroxyl groups on the PVA chain is 1:20 and the molar ratio of HCl to glutaraldehyde is 1:6 to obtain the coating solution.

[0158] (7) Dip the biaxially oriented polypropylene film into the above coating solution, then hang it vertically in an oven and dry it at 60°C for 24 hours to allow the crosslinking reaction to occur fully.

[0159] (8) Rotate the film 180° and repeat the coating process of step (7) once to obtain a polyvinyl alcohol film coating with a thickness of 155±10nm.

[0160] Example 8

[0161] Raw materials for preparation:

[0162] 20wt% polyvinyl alcohol;

[0163] 10 wt% of exfoliated montmorillonite;

[0164] 70 wt% of biaxially oriented polypropylene film.

[0165] (1) Place polyvinyl alcohol particles, peeled montmorillonite powder and biaxially oriented polypropylene film in a vacuum drying oven and dry at 60°C for 24 hours to remove moisture.

[0166] (2) Dissolve polyvinyl alcohol particles in deionized water, heat and stir at 90°C for 4 hours until the particles are completely dissolved to prepare a PVA solution.

[0167] (3) Add the exfoliated montmorillonite powder to deionized water, heat and stir at 90°C for 40 minutes, and then perform ultrasonic treatment (Branson 8510R-MT, 250W, 44kHz) for 30 minutes to ensure uniform exfoliation and obtain MMT aqueous dispersion liquid.

[0168] (4) Slowly add the PVA solution to the MMT aqueous dispersion to make the solution concentration reach 1.5wt% (0.50wt% MMT + 1.00wt% PVA + 98.5wt% deionized water) to obtain a mixture;

[0169] (5) Heat and stir the above mixture for 30 minutes, and then perform ultrasonic treatment for 30 minutes to ensure uniform dispersion.

[0170] (6) Add the crosslinking agent glutaraldehyde and the crosslinking reaction catalyst hydrochloric acid to the above mixture to ensure that the molar ratio of glutaraldehyde to the total number of hydroxyl groups on the PVA chain is 1:25 and the molar ratio of HCl to glutaraldehyde is 1:4 to obtain the coating solution.

[0171] (7) Dip the biaxially oriented polypropylene film into the above coating solution, then hang it vertically in an oven and dry it at 70°C for 24 hours to allow the crosslinking reaction to occur fully.

[0172] (8) Rotate the film 180° and repeat the coating process of step (7) once to obtain a polyvinyl alcohol film coating with a thickness of 155±10nm.

[0173] Example 9

[0174] Raw materials for preparation:

[0175] 20wt% polyvinyl alcohol;

[0176] 15 wt% of exfoliated montmorillonite;

[0177] Biaxially oriented polypropylene film, 65 wt%.

[0178] (1) Place polyvinyl alcohol particles, peeled montmorillonite powder and biaxially oriented polypropylene film in a vacuum drying oven and dry at 50°C for 20 hours to remove moisture.

[0179] (2) Dissolve polyvinyl alcohol particles in deionized water, heat and stir at 95°C for 5 hours until the particles are completely dissolved to prepare a PVA solution.

[0180] (3) Add the exfoliated montmorillonite powder to deionized water, heat and stir at 95°C for 20 minutes, and then perform ultrasonic treatment (Branson 8510R-MT, 250W, 44kHz) for 30 minutes to ensure uniform exfoliation and obtain MMT aqueous dispersion liquid.

[0181] (4) Slowly add the PVA solution to the MMT aqueous dispersion to make the solution concentration reach 1.5wt% (0.64wt% MMT + 0.86wt% PVA + 98.5wt% deionized water) to obtain a mixture;

[0182] (5) Heat and stir the above mixture for 30 minutes, and then perform ultrasonic treatment for 30 minutes to ensure uniform dispersion.

[0183] (6) Add the crosslinking agent glutaraldehyde and the crosslinking reaction catalyst hydrochloric acid to the above mixture to ensure that the molar ratio of glutaraldehyde to the total number of hydroxyl groups on the PVA chain is 1:25 and the molar ratio of HCl to glutaraldehyde is 1:6 to obtain the coating solution.

[0184] (7) Dip the biaxially oriented polypropylene film into the above coating solution, then hang it vertically in an oven and dry it at 60°C for 24 hours to allow the crosslinking reaction to occur fully.

[0185] (8) Rotate the film 180° and repeat the coating process of step (7) once to obtain a polyvinyl alcohol film coating with a thickness of 155±10nm.

[0186] Example 10

[0187] Raw materials for preparation:

[0188] 13 wt% polyvinyl alcohol;

[0189] 13 wt% of exfoliated montmorillonite;

[0190] Biaxially oriented polypropylene film, 74 wt%.

[0191] (1) Place polyvinyl alcohol particles, peeled montmorillonite powder and biaxially oriented polypropylene film in a vacuum drying oven and dry at 70°C for 12 hours to remove moisture.

[0192] (2) Dissolve polyvinyl alcohol particles in deionized water, heat and stir at 85°C for 6 hours until the particles are completely dissolved to prepare a PVA solution.

[0193] (3) Add the exfoliated montmorillonite powder to deionized water, heat and stir at 90°C for 40 minutes, and then perform ultrasonic treatment (Branson 8510R-MT, 250W, 44kHz) for 30 minutes to ensure uniform exfoliation and obtain MMT aqueous dispersion liquid.

[0194] (4) Slowly add the PVA solution to the MMT aqueous dispersion to make the solution concentration reach 1.5wt% (0.75wt% MMT + 0.75wt% PVA + 98.5wt% deionized water) to obtain a mixed solution;

[0195] (5) Heat and stir the above mixture for 30 minutes, and then perform ultrasonic treatment for 30 minutes to ensure uniform dispersion.

[0196] (6) Add the crosslinking agent glutaraldehyde and the crosslinking reaction catalyst hydrochloric acid to the above mixture to ensure that the molar ratio of glutaraldehyde to the total number of hydroxyl groups on the PVA chain is 1:15 and the molar ratio of HCl to glutaraldehyde is 1:5 to obtain the coating solution.

[0197] (7) Dip the biaxially oriented polypropylene film into the above coating solution, then hang it vertically in an oven and dry it at 60°C for 24 hours to allow the crosslinking reaction to occur fully.

[0198] (8) Rotate the film 180° and repeat the coating process of step (7) once to obtain a polyvinyl alcohol film coating with a thickness of 155±10nm.

[0199] Comparative Example 1: No addition of exfoliated montmorillonite

[0200] Raw materials for preparation:

[0201] 30wt% polyvinyl alcohol

[0202] 70wt% biaxially oriented polypropylene film

[0203] like Figure 1 As shown, the BOPP composite film preparation method of this embodiment includes:

[0204] (1) Place polyvinyl alcohol particles and biaxially oriented polypropylene film in a vacuum drying oven and dry at 60°C for 24 hours to remove moisture.

[0205] (2) Dissolve polyvinyl alcohol particles in deionized water, heat and stir at 95°C for 4 hours until the particles are completely dissolved to prepare a PVA solution.

[0206] (3) Add the crosslinking agent glutaraldehyde and the crosslinking reaction catalyst hydrochloric acid to the above PVA solution, ensuring that the molar ratio of glutaraldehyde to the total number of hydroxyl groups on the PVA chain is 1:20 and the molar ratio of HCl to glutaraldehyde is 1:5, to obtain the coating solution.

[0207] (4) Dip the biaxially oriented polypropylene film into the above coating solution, then hang it vertically in an oven and dry it at 60°C for 24 hours to allow the crosslinking reaction to occur fully.

[0208] (5) Rotate the film 180° and repeat the coating process of step (7) once to obtain a polyvinyl alcohol film coating with a thickness of 155±10nm.

[0209] DC breakdown test, broadband dielectric spectrum test, and comprehensive ferroelectric performance test were performed on the BOPP composite film (PP / PVA-MMT) prepared in Example 1 of the present invention, the BOPP film (BOPP) before coating in Example 1, and the BOPP composite film (PP / PVA) without stripped montmorillonite in Comparative Example 1.

[0210] The DC breakdown field strength of the BOPP composite film with added exfoliated montmorillonite, the BOPP composite film without added exfoliated montmorillonite, and the pure BOPP film without coating treatment prepared according to the formulation and process of Example 1 of this invention was tested using an HJY-100kV computer-controlled breakdown tester. A 25mm "ball-to-ball" brass electrode was used, and the breakdown field strength was calculated according to the formula E=U / d. A Weibull distribution map was plotted.

[0211] like Figure 2 The figure shows the Weibull distribution probability diagrams of the breakdown voltages of the BOPP composite film with added exfoliated montmorillonite, the BOPP composite film without added exfoliated montmorillonite, and the uncoated pure BOPP film of the present invention. It can be observed from the figure that the breakdown field strength of the BOPP composite film with added exfoliated montmorillonite is 797.94 kV / mm, the breakdown field strength of the BOPP composite film without added exfoliated montmorillonite is 727.89 kV / mm, and the breakdown field strength of the pure BOPP film is 671.78 kV / mm. Compared with the pure BOPP film, the breakdown field strength of PP / PVA-MMT is significantly improved, and the breakdown field strength of PP / PVA-MMT is superior to that of PP / PVA, indicating that adding MMT plays an important role in improving the breakdown field strength.

[0212] The frequency response of the dielectric properties of thin films was tested using the Concept 80 broadband dielectric spectroscopy testing system, with a test bandwidth of 10 GHz. -1 Hz-10 4 The test frequency was Hz, the test temperature was room temperature, and the AC voltage was 1V. The sample underwent double-sided gold plating before testing.

[0213] like Figure 3The figure shows the relative permittivity spectra of the BOPP composite film with added exfoliated montmorillonite, the BOPP composite film without added exfoliated montmorillonite, and the uncoated pure BOPP film of the present invention. It can be observed from the figure that the relative permittivity of the BOPP composite film with added exfoliated montmorillonite at a 50Hz power frequency is 2.92, the relative permittivity of the BOPP without added exfoliated montmorillonite at a 50Hz power frequency is 2.70, and the relative permittivity of the pure BOPP film at a 50Hz power frequency is 2.39. Compared with the pure BOPP film, the dielectric constant of the PP / PVA-MMT composite film is improved, and the relative permittivity of PP / PVA-MMT is greater than that of PP / PVA, indicating that adding MMT plays an important role in improving the dielectric constant.

[0214] The hysteresis loop of the sample was tested using a ferroelectric performance comprehensive tester (Precision Premier II) to obtain the relationship between the polarization intensity of the sample and the applied electric field strength. The energy storage density of the thin film under different electric field strengths was calculated. Before the test, the sample surface was sputtered with gold. The applied voltage was a bipolar standard triangular wave, and the test temperature was room temperature.

[0215] like Figure 4 The diagram shows the energy storage density of the BOPP composite film with added exfoliated montmorillonite, the BOPP composite film without added exfoliated montmorillonite, and the uncoated pure BOPP film of the present invention. It can be observed from the diagram that the maximum energy storage density of the BOPP composite film with added exfoliated montmorillonite is 5.93 J / cm³. 3 The maximum energy storage density of BOPP without the addition of exfoliated montmorillonite is 5.56 J / cm³. 3 The maximum energy storage density of pure BOPP film is 3.66 J / cm³. 3 Compared with pure BOPP film, the maximum energy storage density of PP / PVA-MMT composite film is improved, and the energy storage density of PP / PVA-MMT is greater than that of PP / PVA, indicating that adding MMT plays an important role in improving energy storage density.

Claims

1. A BOPP composite film, characterized by, The BOPP composite film comprises a biaxially stretched polypropylene film and a polyvinyl alcohol film which are arranged in a laminated manner, and the polyvinyl alcohol film comprises a polyvinyl alcohol base and exfoliated montmorillonite filled in the polyvinyl alcohol base.

2. The BOPP composite film according to claim 1, characterized in that, The thickness ratio of the biaxially stretched polypropylene film and the polyvinyl alcohol film is 12 μm:(145-320) nm.

3. The BOPP composite film according to claim 1, characterized in that, The BOPP composite film comprises, by mass percentage: 10-20% of the polyvinyl alcohol base; 10-20% of the exfoliated montmorillonite; 60-80% of the biaxially stretched polypropylene film.

4. The process for the production of BOPP composite film according to any one of claims 1 to 3, characterized in that, The BOPP composite film comprises: S1, mixing polyvinyl alcohol particles, exfoliated montmorillonite powder, a crosslinking agent and a crosslinking reaction catalyst in water to obtain a coating liquid; S2, coating the coating liquid on the biaxially stretched polypropylene film and drying to obtain the BOPP composite film.

5. The method for preparing the BOPP composite film according to claim 4, characterized in that, S1 specifically comprises: dissolving the polyvinyl alcohol particles in water to obtain a PVA solution; dispersing the exfoliated montmorillonite powder in water to obtain an MMT aqueous dispersion; adding the PVA solution into the MMT aqueous dispersion to obtain a mixed liquid; adding the crosslinking agent and the crosslinking reaction catalyst into the mixed liquid to obtain the coating liquid.

6. The method for preparing the BOPP composite film according to claim 4, characterized in that, In S1, the crosslinking agent is glutaraldehyde, and the crosslinking reaction catalyst is hydrochloric acid.

7. The method for preparing BOPP composite film according to claim 6, characterized in that, The molar ratio of glutaraldehyde to the total moles of hydroxyl groups on the polyvinyl alcohol chain is 1:(15-25).

8. The method for preparing the BOPP composite film according to claim 6, characterized in that, The molar ratio of hydrochloric acid to glutaraldehyde is 1:(4-6).

9. The method for preparing the BOPP composite film according to claim 4, characterized in that, In S2, the drying temperature is 50-70°C.

10. A capacitor characterized by The medium is the BOPP composite film according to any one of claims 1-3.

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