A mesh grid explosion-proof film for rail transit power electronic capacitors and a preparation method thereof

Abstract

The present invention discloses a mesh grid explosion-proof membrane for rail transit power electronic capacitors, including a polypropylene base film and a metal coating, with margins and thickened margins on both sides of the mesh grid explosion-proof membrane, and the metal coating between the margins and the thickened margins is alternately distributed with continuous coating areas and mesh grid areas along the longitudinal direction; the mesh grid area is divided into a number of electrode units by insulating gaps, and each electrode unit is provided with a coating strip on at least one side, and a thickening portion is provided at the junction of the continuous coating area and the mesh grid area to form a groove area, and the insulating gap and the coating strip at the junction are both located at the bottom of the groove area; the present invention also discloses a method for preparing the mesh grid explosion-proof membrane. The present invention improves the reliability of the safety protection of the coating strip and the dielectric strength of the polypropylene base film on the basis of ensuring that the heating loss of the mesh grid explosion-proof membrane is at a low level, effectively prevents continuous breakdown and self-healing, and increases the service life of the capacitor.

Description

Technical Field

[0001] The invention belongs to the technical field of polymer films, and in particular relates to a mesh-shaped grid explosion-proof film for rail transit power electronic capacitors and a preparation method thereof. Background Art

[0002] Rail transit runs at high speeds and carries a large number of passengers, so safety is particularly important. As the core device for high-speed operation of vehicles, the power electronic capacitors used in traction converters are important for safety. At the same time, on-board applications also require power electronic capacitors to be small in size, light in weight, carry large currents, have long life expectancy, have strong resistance to vibration and shock, and be adaptable to various climate environments such as severe cold and heat.

[0003] The power capacitors in traction converters usually use self-healing metallized film capacitors. Self-healing metallized film capacitors use a single layer of polypropylene film as the medium, and a thin layer of metal is evaporated on the surface as the conductive electrode. When an excessively high voltage is applied, the electrical weak point of the polypropylene film is broken down, the impedance of the breakdown point is significantly reduced, and the current density flowing through increases sharply, causing the metallized coating to generate high heat. The metal conductor around the breakdown point evaporates rapidly, forming a blank area of ​​the metal coating, and the breakdown point automatically restores insulation.

[0004] In order to further improve the reliability of self-healing metallized film capacitors, the self-healing metallized film adopts a metallized safety film structure, that is, a split electrode design, which divides the entire metal electrode into many small blocks. The blocks are isolated by demetallized insulating tapes, and the different blocks are connected by fuses (fuses). When a short-circuit breakdown occurs, the fuse will melt because it cannot withstand the large current, thereby isolating the breakdown block from the non-breakdown block, limiting the short-circuit current at the breakdown point, and achieving good self-healing at the breakdown point. However, as the grid blocks become denser, the surface area of ​​the dielectric film occupied by the insulating tape also increases, which reduces the utilization efficiency of the film material.

[0005] The existing metallized safety film structure adopts the method of horizontal partitioning of the coating, so that the surface area of ​​the dielectric film occupied by the gap strips of the grid-type metallized safety film is reduced by multiples, which can improve the utilization rate of the dielectric film. However, when the coating is partitioned horizontally, the currents of each grid unit will be superimposed on each other, and some blocks will produce large additional heat loss after the currents of multiple other blocks and fuses are superimposed, increasing the risk of voltage breakdown. In order to reduce this heat loss, the patent with publication number CN 101866744 B discloses a longitudinal partitioned metallized grid-type safety film electrode structure, in which the coating between the margin and the thickened edge is alternately distributed in the longitudinal direction by continuous coating areas and grid pattern areas with approximately equal widths, and each electrode block has an independent coating narrow strip that acts as a micro fuse and is connected to the adjacent continuous coating area or coating thickened edge; in this method, there is no direct current connection path between the small block electrodes in the grid pattern area, and they will not be superimposed on each other, so the working current heat generation of the entire grid pattern area is kept at the minimum level near the margin. However, when the base film of the metallized safety film is punctured due to a weak point, an arc will be generated and a gradient-changing thermoelectric field will be formed, and the heat has an obvious lag compared to the current diffusion; when a high-voltage breakdown occurs, the current flowing through the coating is large, and the narrow strip of the coating is easily melted by the temperature rise and current at the breakdown point, thus playing a timely protective role; under low-voltage conditions, the current flowing through the narrow strip of the coating is small, while the temperature and current at the breakdown point increase instantaneously, and the coatings at the narrow strip of the coating and the breakdown point are both melted and evaporated by high temperature. It is possible that the narrow strip of the coating has not completely melted and the breakdown point has already healed itself.

[0006] It is normal for metallized film capacitors to self-heal appropriately, but excessive self-healing will cause the medium around the self-healing point to be negatively affected by heat and force; if the narrow strip of the coating that acts as a fuse cannot react in time, even effective self-healing will form a vicious cycle and reduce the service life of the metallized safety film. Therefore, on the basis of ensuring that the overall heat loss of the metallized safety film is at a low level, how to improve its self-protection function and extend its service life urgently requires further research and development in structure and material design. Summary of the invention

[0007] Based on the deficiencies of the prior art, the present invention provides a mesh-type grid explosion-proof membrane for rail transit power electronic capacitors. The protection function of the narrow strips of the coating is improved and the service life is extended by designing a longitudinal partitioned grid and reducing the thickness of the partition joints. The present invention also discloses a method for preparing the mesh-type grid explosion-proof membrane.

[0008] In order to achieve the above-mentioned purpose of the invention, the following method is provided, which is implemented by the following steps:

[0009] A mesh grid explosion-proof film for rail transit power electronic capacitors, comprising a polypropylene base film and a metal coating coated on the polypropylene base film, wherein one side of the mesh grid explosion-proof film extending in the longitudinal direction is a margin without metal coating, and the other side of the mesh grid explosion-proof film extending in the longitudinal direction is a thickened side of metal coating, and the metal coating between the margin and the thickened side is alternately distributed with continuous coating areas and mesh grid areas in the longitudinal direction; a plurality of insulating gaps are arranged in the mesh grid area, and the mesh grid area is divided into a plurality of columns of electrode units by the insulating gaps, and the number of electrode units in each column is 1 to 3, and the electrode units in two adjacent columns are not connected in series, and at least one side of each electrode unit is provided with a coating narrow strip; the electrode units in a column closest to the thickened side are connected to the thickened side through their respective coating narrow strips, and for the electrode units in other columns, when the number of electrode units in the column is 1 or 2, the electrode units in the column are connected to the continuous coating area through their respective coating narrow strips, and when the number of electrode units in the column is 3 When the electrode units on both sides of the column are connected to the continuous coating area through their own coating strips, the electrode unit in the middle is connected to the two adjacent electrode units in the column through the coating strips; the ratio of the width of the continuous coating area to the mesh grid area in the longitudinal direction is 1 to 3:3, and the upper and lower sides of the continuous coating area and the mesh grid area are both provided with reduced thickness parts, and the reduced thickness parts extend in the transverse direction, so that the junction of the continuous coating area and the mesh grid area forms a V-shaped or U-shaped groove area through the reduced thickness part, and the insulating gap and the coating strips located at the junction of the continuous coating area and the mesh grid area are both located at the bottom of the groove area.

[0010] The electrode units in the horizontal direction of the mesh grid explosion-proof membrane of the present invention are relatively independent and not connected in series. When the power electronic capacitor is working, the current of each electrode unit is almost not superimposed, and the current and heat generated by the mesh grid explosion-proof membrane are kept at a low level; at the same time, the continuous coating area and the mesh grid area are connected by a reduced thickness design, so that the coating narrow strip is located in the groove area, and the thickness of the coating narrow strip is lower than the thickness in the middle of the electrode unit. On the one hand, the relative resistance of the coating narrow strip is improved, and on the other hand, it helps the coating narrow strip to be evaporated in time when breakdown occurs, thereby improving the reliability of safety protection; the area of ​​the electrode unit obtained by separation by insulating gaps is reduced, and the capacity loss of each breakdown is greatly reduced, and the structural design of the insulating gap is conducive to the flow direction of the edge current in the electrode unit. The present invention avoids problems such as premature failure of the capacitor due to excessive current by designing a longitudinal partitioned grid for the metal coating and setting the thickness reduction at the junction of the partitions, thereby increasing the service life of the capacitor.

[0011] The method for preparing the mesh grid explosion-proof film for the rail transit power electronic capacitor comprises the following steps:

[0012] Step 1: melt and plasticize the raw material of the polypropylene base film and extrude it to obtain a sheet fluid; cast the sheet fluid through a chilled roller and a high-pressure air knife to obtain a membrane;

[0013] Step 2, the film obtained in step 1 is longitudinally stretched and transversely stretched by a longitudinal stretching machine and a transverse stretching machine respectively, rolled up after corona treatment, and subjected to aging treatment to obtain a polypropylene base film with a thickness of 1.5 to 10 μm;

[0014] Step 3, printing shielding oil on the corona surface of the polypropylene base film obtained in step 2, and then forming a metal coating by vacuum evaporation to obtain a metallized film;

[0015] Step four, slitting, winding, and then heat treating in a vacuum environment, and then cooling to room temperature; wherein the heat treatment adopts gradient heating and heat preservation, the final temperature of the gradient heating is 120-130°C, and the total heating and heat preservation time is 1-2h.

[0016] The raw materials of the polypropylene base film include, by mass percentage, 15-30% of polypropylene homopolymer B, 4-8% of polypropylene copolymer, 2-3% of maleic anhydride, 1-1.5% of nano inorganic powder, 0.3-0.5% of anti-thermal degradation agent, 0.02-0.06% of β nucleating agent, and the balance is polypropylene homopolymer A; wherein the isotacticity of the polypropylene homopolymer A and the polypropylene homopolymer B is ≥95%, the melt flow rate of the polypropylene homopolymer A is 4.0-8.5g / 10min, and the melt flow rate of the polypropylene homopolymer B is 1.0-4.0g / 10min; the polypropylene copolymer is a block copolymer prepared by adding polyethylene components during the homopolymerization of polypropylene, and the melt flow rate is 1.0-2.5g / 10min.

[0017] The invention improves the processing performance and temperature resistance of the mesh grid explosion-proof film by selecting a high-tactic polypropylene homopolymer and a polypropylene copolymer for compounding. When forming a sheet fluid, a three-phase mixed state is presented. The film component configuration formed after biaxial stretching is complicated. Compared with using a polypropylene homopolymer alone, the dielectric strength at high temperature is significantly improved. In addition, by mixing raw materials with different melt flow rates, the film thickness can be guaranteed to be uniform during the film preparation process, and melt fracture and tensile fracture are not easy to occur. By adding a polypropylene copolymer, a certain branch structure is provided, which plays a role of connection and buffering between molecular chains, and a large number of flexible long chain segment functional groups on its surface are more likely to form a spatial three-dimensional mesh structure in the system through molecular interaction, thereby improving the toughness of polypropylene and the compatibility of polypropylene with other particles. Nanoparticles have the characteristics of large specific surface area and few surface defects. By adding nano inorganic powder, the crystallization performance of the polymer can be affected by the nano effect. An appropriate amount of nanoparticles can also affect the mechanical properties of the composite material, while improving strength and toughness, improving the processability of the raw materials, and also playing the role of anti-adhesion and anti-aging. Maleic anhydride grafting can greatly improve the affinity and dispersibility of nano inorganic powder, which is helpful to improve the tensile and impact strength of polypropylene base film. By using a β nucleating agent to promote the formation of a large number of β crystals, the impact strength and heat deformation temperature of polypropylene are improved, so that the tensile toughness and ductility at high temperature are better, thereby reducing the thickness of the stretched film, and the surface roughness of the polypropylene base film can be adjusted at the same time. By using an anti-thermal degradation agent to suppress thermal degradation in the extruder, the amount of the anti-thermal degradation agent added is basically exhausted during the sheet fluid molding, and almost no residue is left in the polypropylene base film. The polypropylene base film prepared by the present invention has a small thickness and different roughness on both sides, which can ensure the evaporation and impregnation requirements of the polypropylene base film when used for power electronic capacitors, and has a higher dielectric strength.

[0018] The present invention designs the structure of the metal plating layer, selects the raw materials of the polypropylene base film, and optimizes the preparation method, so that the thickness of the polypropylene base film obtained is uniform, the surface roughness is appropriate, and the DC voltage breakdown strength at 100°C is greater than 560V / μm; and on the basis of ensuring that the overall heat loss is at a low level, the self-protection function and the electrical strength of the mesh grid explosion-proof film are improved, continuous breakdown and self-healing are effectively prevented, and the service life is extended. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a schematic diagram of the structure of the mesh grid explosion-proof membrane described in Example 1;

[0020] Figure 2 for Figure 1 Section along line AA;

[0021] Figure 3 for Figure 1 Section along line BB;

[0022] Figure 4 This is a schematic diagram of the stacked and rolled mesh explosion-proof membranes described in Example 1;

[0023] Figure 5 This is a schematic diagram of the structure of the mesh grid explosion-proof membrane described in Example 2;

[0024] Figure 6 This is a schematic diagram of the stacked and rolled mesh explosion-proof membranes described in Example 2. DETAILED DESCRIPTION

[0025] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0026] In the following embodiments, the raw materials of the polypropylene base film are all common commercial products. Among them, the polypropylene raw material: polypropylene homopolymer A adopts polypropylene resin with the brand name HC300BF (Northern Europe Chemicals), polypropylene homopolymer B adopts polypropylene resin with the brand name PPH-FA03 (Singapore TPC), and polypropylene copolymer adopts low melt index block copolymer with the brand name EPS30R (Qilu Petrochemical); the characteristics of the polypropylene raw material are tested as follows: the melt flow rate of polypropylene is tested according to GB / T3682-2000 using a melt flow rate tester, and it meets the requirements of ISO1133-97 and ASTM1238 standards; the isotacticity is measured by infrared method; after testing: the isotacticity of polypropylene homopolymer A is 98.5%, and the melt flow rate is 7.0g / 10min; the isotacticity of polypropylene homopolymer B is 98%, and the melt flow rate is 3.0g / 10min; the melt flow rate of polypropylene copolymer is 1.8g / 10min. The β-nucleating agent was purchased from Guangdong Weilinna New Materials Technology Co., Ltd., model WBG-II; nano-titanium dioxide used P25, with a particle size of 20 to 30 nm.

[0027] Example 1

[0028] like Figures 1 to 3As shown, a mesh grid explosion-proof membrane for rail transit power electronic capacitors includes a polypropylene base film 2 and a metal coating 1 coated on the polypropylene base film 2. The transverse direction of the mesh grid explosion-proof membrane is the left-right direction, and the longitudinal direction of the mesh grid explosion-proof membrane is the up-down direction; the right side of the mesh grid explosion-proof membrane extending in the longitudinal direction is a margin 5 without the metal coating 1, and the left side of the mesh grid explosion-proof membrane extending in the longitudinal direction is a thickened edge 101 of the metal coating 1, and the metal coating 1 between the margin 5 and the thickened edge 101 is alternately distributed with a continuous coating area 102 and a mesh grid area 103 along the longitudinal direction. The continuous coating area 102 and the mesh grid area 103 have the same width in the longitudinal direction. The upper and lower sides of the continuous coating area 102 and the mesh grid area 103 are provided with reduced thickness portions 6, and the reduced thickness portions 6 extend in the transverse direction so that the junction of the continuous coating area 102 and the mesh grid area 103 forms a V-shaped or U-shaped groove area through the reduced thickness portions 6.

[0029] A plurality of insulating gaps 3 are arranged in the mesh grid area 103, and the insulating gaps 3 include transverse gap bars, longitudinal gap bars and oblique gap bars 305. The transverse gap bars include a first transverse portion 304 located in the mesh grid area 103 and a second transverse portion 303 located at the edge of the mesh grid area 103, which are used to separate the mesh grid area 103 into rows; the first transverse portion 304 penetrates the mesh grid area 103 in the transverse direction and divides the mesh grid area 103 into two upper and lower rows; the second transverse portions 303 are arranged symmetrically with respect to the first transverse portion 304, and the second transverse portions 303 are spaced apart at the bottom of the groove area, and the number of the second transverse portions 303 in each row is the same as the number of columns of the electrode units. The longitudinal gap strip is located between the mesh grid area 103 and the thickened edge 101, and is used to separate the thickened edge 101 from the mesh grid area 103; the longitudinal gap strip includes a first longitudinal portion 301 and a second longitudinal portion 302 located on the upper and lower sides of the first longitudinal portion 301, the middle portion of the first longitudinal portion 301 is connected to the left end of the first transverse portion 304 (i.e., the end close to the thickened edge 101), the second longitudinal portion 302 has a gap with the upper and lower ends of the first longitudinal portion 301, and the ends of the upper and lower second longitudinal portions 302 away from the first longitudinal portion 301 are respectively connected to the left ends of the upper and lower second transverse portions 303 (i.e., the ends close to the thickened edge 101). The oblique interstitial bars 305 are arranged between two adjacent columns of electrode units to separate the mesh grid area 103 into columns; the oblique interstitial bars 305 are arranged symmetrically with respect to the first transverse portion 304, one end of the oblique interstitial bars 305 is connected to the first transverse portion 304, and the other end of the oblique interstitial bars 305 is connected to the right end of the second transverse portion 303 (i.e., the end close to the margin 5), and the oblique interstitial bars 305 are inclined to the left from the middle to the edge of the mesh grid area 103, and the angle between the oblique interstitial bars 305 and the first transverse portion 304 is 60-70°. The mesh grid area 103 is separated by the transverse interstitial bars, the longitudinal interstitial bars and the oblique interstitial bars 305, and the electrode units of the first and last columns are right-angled trapezoids, and the electrode units of the remaining columns are parallelograms.

[0030] A first coating strip 401 is arranged at the midpoint of the left side edge of the two leftmost electrode units, and the first coating strip 401 is located in the gap between the second longitudinal portion 302 and the first longitudinal portion 301, and the two electrode units are connected to the thickened edge 101 through the first coating strip 401, and the thickness of the first coating strip 401 is the same as the thickness of the middle part of the electrode unit; the upper side or lower side of the other electrode units are provided with a second coating strip 402, and the second coating strip 402 is located at the left end of the second transverse portion 303 (that is, the end close to the thickened edge 101), and the second coating strips 402 of these electrode units are located at the bottom of the groove area (that is, the thickness of the second coating strip 402 is less than the thickness of the middle part of the electrode unit), and these electrode units are connected to the continuous coating area 102 through the second coating strip 402.

[0031] Among them, the longitudinal widths of the mesh grid area 103 and the continuous coating area 102 are both 20 mm, the side length of the first transverse portion 304 between the two leftmost electrode units is 15 mm, the side length of the first transverse portion 304 between the two rightmost electrode units is 6 mm, the side lengths of the remaining electrode units along the transverse direction are 11.5 mm, the width of the insulating gap 3 is 0.4 mm, the width of the first coating strip 401 and the second coating strip 402 is 0.4 mm, the width of the margin 5 is 3.5 mm, and the width of the thickened edge 101 is 5 mm.

[0032] When the mesh grid explosion-proof film is made into capacitor electrodes, Figure 4 As shown, the upper and lower layers of mesh explosion-proof membrane are stacked and rolled, and the margins 5 and thickened edges 101 of the upper and lower layers are staggered and correspond to each other, and are staggered a certain distance in the horizontal direction, so that the thickened edges 101 on both sides of the laminate are located in a protruding position; at the same time, one side edge of the upper mesh grid area 103 is located at the horizontal center line of the lower continuous coating area 102, and the other side edge of the upper mesh grid area 103 is located at the horizontal center line of the lower mesh grid area 103.

[0033] Example 2

[0034] like Figure 5 As shown, a mesh grid explosion-proof membrane for rail transit power electronic capacitors includes a polypropylene base film 2 and a metal coating 1 coated on the polypropylene base film 2. The transverse direction of the mesh grid explosion-proof membrane is the left-right direction, and the longitudinal direction of the mesh grid explosion-proof membrane is the up-down direction; the right side of the mesh grid explosion-proof membrane extending in the longitudinal direction is a margin 5 without the metal coating 1, and the left side of the mesh grid explosion-proof membrane extending in the longitudinal direction is a thickened edge 101 of the metal coating 1, and the metal coating 1 between the margin 5 and the thickened edge 101 is alternately distributed with a continuous coating area 102 and a mesh grid area 103 along the longitudinal direction. The continuous coating area 102 and the mesh grid area 103 have the same width in the longitudinal direction. The upper and lower sides of the continuous coating area 102 and the mesh grid area 103 are provided with reduced thickness portions 6, and the reduced thickness portions 6 extend in the transverse direction so that the junction of the continuous coating area 102 and the mesh grid area 103 forms a V-shaped or U-shaped groove area through the reduced thickness portions 6.

[0035] A plurality of insulating gaps 3 are arranged in the mesh grid area 103 , and the insulating gaps 3 include transverse gap bars, longitudinal gap bars and oblique gap bars 305 . The transverse gap strips include a first transverse portion 304 located in the mesh grid area 103 and a second transverse portion 303 located at the edge of the mesh grid area 103, which is used to separate the mesh grid area 103 into rows; the longitudinal gap strips are located between the mesh grid area 103 and the thickened edge 101, which is used to separate the thickened edge 101 from the mesh grid area 103, and the longitudinal gap strips include a first longitudinal portion 301 and a second longitudinal portion 302 located on the upper and lower sides of the first longitudinal portion 301, the middle part of the first longitudinal portion 301 is connected to the left end of the first transverse portion 304 (i.e., the end close to the thickened edge 101), the second longitudinal portion 302 has a gap with the upper and lower ends of the first longitudinal portion 301, and the ends of the upper and lower second longitudinal portions 302 away from the first longitudinal portion 301 are respectively connected to the left ends of the upper and lower second transverse portions 303 (i.e., the ends close to the thickened edge 101). The oblique interstitial bars 305 are arranged between two adjacent columns of electrode units to separate the mesh grid area 103 into columns. The second transverse portion 303 and the oblique interstitial bars 305 are arranged symmetrically about the transverse center line of the mesh grid area 103. The second transverse portions 303 are spaced at the bottom of the groove area. The number of second transverse portions 303 in each row is the same as the number of columns of electrode units. The two oblique interstitial bars 305 symmetrically arranged above and below are connected at the transverse center line of the mesh grid area 103. The oblique interstitial bars 305 are inclined to the left from the middle to the edge of the mesh grid area 103, and the angle between the upper and lower oblique interstitial bars 305 is 130-140°. The end of the oblique interstitial bar 305 away from the transverse center line of the mesh grid area 103 is connected to the end of the second transverse portion 303 close to the margin 5. The mesh grid area 103 is separated by horizontal gap bars, vertical gap bars and oblique gap bars 305. The number of electrode units in the leftmost and rightmost columns is 2, and the electrode units in these two columns are in the shape of a right-angled trapezoid. The number of electrode units in the remaining columns is 2 and 3, which are arranged alternately, and the electrode units in these columns are in the shape of a parallelogram.

[0036] A first coating strip 401 is provided at the midpoint of the left side of the two leftmost electrode units, and the first coating strip 401 is located at the gap between the second longitudinal portion 302 and the first longitudinal portion 301. The two electrode units are connected to the thickened edge 101 through the first coating strip 401, and the thickness of the first coating strip 401 is the same as the thickness of the middle of the electrode unit. For the other two electrode unit columns, the first transverse portion 304 completely separates the two upper and lower adjacent electrode units, and the upper or lower sides of these electrode units are provided with a second coating strip 402, and the second coating strip 402 is located at the left end of the second transverse portion 303 (i.e., the end close to the thickened edge 101), and the second coating strip 402 of these electrode units is located at the bottom of the groove area (i.e., the thickness of the second coating strip 402 is less than the thickness of the middle of the electrode unit), and these electrode units are connected to the continuous coating area 102 through the second coating strip 402. For a column of three electrode units, the right end of the first transverse portion 304 (i.e., the end close to the retained edge 5) is connected to the oblique gap strip 305, and the left end of the first transverse portion 304 (i.e., the end close to the thickened edge 101) is provided with a third coating strip 403, so that the electrode unit located in the middle is connected to the two adjacent electrode units above and below through the third coating strip 403, and the upper side edge of the electrode unit located on the upper side and the lower side edge of the electrode power source located on the lower side are both provided with second coating strips 402, and these second coating strips 402 are also located at the left end of the second transverse portion 303 (i.e., one end close to the thickened edge 101), so that the electrode units on the upper and lower sides are connected to the continuous coating area 102 through the second coating strips 402.

[0037] Among them, the width of the mesh grid area 103 is 30 mm, the width of the continuous coating area 102 is 10 mm, the side length of the first transverse portion 304 between the two leftmost electrode units is 15 mm, the side length of the first transverse portion 304 between the two rightmost electrode units is 6 mm, the side length of the remaining electrode units along the transverse direction is 11.5 mm, the width of the insulating gap 3 is 0.4 mm, the width of the first coating narrow strip, the second coating narrow strip and the third coating narrow strip are all 0.4 mm, the width of the margin 5 is 3.5 mm, and the width of the thickened edge 101 is 5 mm.

[0038] When the mesh grid explosion-proof film is made into capacitor electrodes, Figure 6 As shown, two layers of mesh grid explosion-proof membrane are stacked and rolled, and the margins 5 and thickened edges 101 of the upper and lower layers are staggered and correspond to each other, and are staggered a certain distance in the horizontal direction, so that the thickened edges 101 on both sides of the stack are located in a protruding position; at the same time, the edges of both sides of the upper continuous coating area 102 are located in the lower mesh grid area 103, and overlap with the first transverse portion 304 (the first transverse portion 304 of the electrode unit column with 3 numbers).

[0039] Embodiments 3 to 5

[0040] The mesh grid explosion-proof membrane for rail transit power electronic capacitors has a structure according to Example 1, and its preparation method comprises the following steps:

[0041] Step 1: cryogenically treat the polypropylene raw material (polypropylene homopolymer A, polypropylene homopolymer B, polypropylene copolymer), and then grind and mix with other raw materials of the polypropylene base film at a temperature not higher than 0° C. for 6 minutes; melt and plasticize at 210° C. and extrude to obtain a sheet fluid; and cast the sheet fluid through a 95° C. chilled roller and a 95° C. high-pressure air knife to obtain a membrane;

[0042] Step 2, the film obtained in step 1 is sequentially stretched longitudinally and transversely by a longitudinal stretching machine and a transverse stretching machine, and then rolled up after corona treatment, and subjected to aging treatment to obtain a polypropylene base film with a thickness of 3 μm; wherein, during the longitudinal stretching, preheating is performed to raise the temperature of the film body to 120°C, and then one or both sides of the film are controlled to be heated to 150°C for longitudinal stretching, and the longitudinal stretching ratio is 5 times. After the longitudinal stretching, the shaping is performed by first controlling the tension heat setting and then free shrinkage heat setting. When the tension heat setting is controlled, the additional stretching degree is 1.03, and the shaping temperature is 155°C; during the transverse stretching, the stretching temperature is controlled to be 160°C, and the transverse stretching ratio is 8 times. After the transverse stretching, the shaping is performed by first fixing the length heat setting and then free shrinkage heat setting, and the shaping temperature is 170°C; during the corona treatment, the voltage is 12kV, the output power is 15kW, the frequency is 20 kHz, and the electrode gap is 2mm; the aging treatment is performed by placing it away from light in an environment with a humidity of ≤40% and a temperature of 25°C for 1 day;

[0043] Step 3: printing shielding oil (silicone oil) on the corona surface of the polypropylene base film obtained in step 2, and subjecting the polypropylene base film with the shielding pattern printed on the surface to an aluminum evaporation device (1200° C.) and a cold drum treatment (-10° C.) in a vacuum environment of 0.02 to 0.03 Pa, to form an aluminum metal layer (thickness 20 nm) on the surface of the polypropylene base film except the shielding pattern, and then subjecting the polypropylene base film to a zinc evaporation device (700° C.) and a cold drum treatment (-10° C.) to form a zinc metal layer (thickness 15 nm except for the thickened edge and the reduced thickness portion); wherein the zinc evaporation device is provided with a nozzle and a shielding plate, and the thickened edge and the reduced thickness portion of the metal coating are formed by controlling the thickness of the zinc metal layer, to obtain a metallized film;

[0044] Step four, slitting, winding, and then heat treating in a vacuum environment, and then cooling to room temperature to obtain; wherein, the heat treatment adopts gradient heating, specifically: heating to 60°C, keeping warm for 20 minutes, then heating to 90°C, keeping warm for 20 minutes, then heating to 125°C and keeping warm for 20 minutes, and the heating rate is 5°C / min.

[0045] Example 6

[0046] The mesh grid explosion-proof membrane for rail transit power electronic capacitors has the structure of Example 1, and its preparation method is the same as that of Examples 3 to 5. The raw materials of the polypropylene base membrane are the same as those of Example 5, except that the raw materials of the polypropylene base membrane are directly melted without deep cold treatment and low-temperature grinding.

[0047] The surface of the polypropylene base film prepared in the above embodiment is smooth and wrinkle-free, without visible cracks, bubbles, inclusions and other defects, and the end face is neat and wrinkle-free. After testing, the longitudinal tensile strength is greater than 150Mpa, the transverse tensile strength is greater than 240Mpa, and the elongation at break is ≥40%, all of which meet the national standard requirements for the physical and chemical properties of biaxially oriented polypropylene films for capacitors; the heat shrinkage rate is measured after heating at 120°C for 15 minutes, the longitudinal heat shrinkage rate is ≤1.2%, the transverse heat shrinkage rate is 0, and the maximum use temperature is ≥130°C.

[0048] Comparative Examples 1, 2, and 3

[0049] The mesh grid explosion-proof membrane for rail transit power electronic capacitors has the structure of Example 1, and its preparation method is the same as that of Examples 3 to 5, except that: the raw material of the polypropylene base membrane in Comparative Example 1 does not contain polypropylene copolymer, the raw material of the polypropylene base membrane in Comparative Example 2 contains 20% polypropylene copolymer, and the raw material of the polypropylene base membrane in Comparative Example 3 does not contain nano inorganic powder.

[0050] Comparative Example 4

[0051] The mesh grid explosion-proof membrane for rail transit power electronic capacitors has the structure of Example 1, and the raw materials of the polypropylene base membrane are the same as those of Example 3, except that no heat treatment is performed in step 4 of the preparation method.

[0052] The raw material ratios of the polypropylene-based films in Examples 3 to 6 and Comparative Examples 1 to 4 are shown in Table 1. The raw materials in Table 1 are expressed in percentage by mass, and the remainder is polypropylene homopolymer A.

[0053] Table 1 Raw material ratio of polypropylene base film in the examples and comparative examples (unit: %)

[0054]

[0055] The mesh grid explosion-proof membrane prepared in the embodiment and the comparative example was made into a capacitor (the initial value of capacitance C was about 150nF) according to the same process steps as the prior art, and subjected to double "85" test (85℃, 85%RH, applying AC voltage of 305V for 1000h) and DC test, and the capacity change rate (ΔC / C), loss tangent change value (ΔDF), and 100℃ DC breakdown strength were measured as shown in Table 2.

[0056] Table 2 Performance test results of mesh explosion-proof membrane

[0057]

[0058] From the results in Table 2, it can be seen that by comparing Example 3 with Example 6, it is found that after the polypropylene raw material is treated with cryogenic grinding, the dielectric strength of the prepared mesh grid explosion-proof membrane is significantly improved, indicating that cryogenic grinding is conducive to crystallization refinement and uniform organization, and is conducive to improving the dielectric properties of the polypropylene base film; by comparing Example 3 with Comparative Examples 1 and 2, it can be seen that the addition of polypropylene copolymer is more than using only linear polypropylene homopolymer, the obtained dielectric strength at high temperature is significantly improved, but too much polypropylene copolymer will reduce the temperature resistance of the film, thereby having a negative effect on the high temperature dielectric strength; by comparing Example 3 with Comparative Example 3, it can be inferred that an appropriate amount of nano-inorganic powder improves the crystallinity and surface roughening degree of the polypropylene base film by improving the processability of the raw materials, and has a certain effect on improving the performance of the further prepared mesh grid explosion-proof membrane; by comparing Example 3 with Comparative Example 4, it can be inferred that heat treatment helps the metal coating to be more closely combined with the polypropylene base film, reducing the possibility of air residue and external air intrusion, and the metallized film can be improved by heat treatment. The pressure resistance and stability of the mesh grid explosion-proof membrane. In conclusion, the mesh grid explosion-proof membrane prepared by controlling raw materials and processes in the present invention has good electrical strength, small capacity loss, high safety performance, and can extend the service life of the mesh grid explosion-proof membrane.

[0059] The above embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the patent of the present invention. It should be pointed out that, for those of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

[0060] It should be understood that the orientation or positional relationship indicated by the terms "center", "longitudinal", "lateral", "up", "down", "left", "right", "bottom" and the like in the above text is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation of the present invention. In addition, the terms "first", "second", and "third" are used for descriptive purposes only, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. In the description of the present invention, unless otherwise specified, "several" means more than two.

[0061] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A mesh grid explosion-proof film for rail transit power electronic capacitors, comprising a polypropylene base film and a metal coating coated on the polypropylene base film, wherein one side of the mesh grid explosion-proof film extending in the longitudinal direction is a margin without metal coating, and the other side of the mesh grid explosion-proof film extending in the longitudinal direction is a thickened side of the metal coating, and the metal coating between the margin and the thickened side is alternately distributed with continuous coating areas and mesh grid areas in the longitudinal direction; characterized in that: A plurality of insulating gaps are arranged in the mesh grid area, and the mesh grid area is divided into a plurality of columns of electrode units by the insulating gaps. The number of electrode units in each column is 1 to 3, and the electrode units in two adjacent columns are not connected in series. A narrow plating strip is arranged on at least one side of each electrode unit; the electrode units in a column closest to the thickened edge are connected to the thickened edge through their respective narrow plating strips, and for the electrode units in other columns, when the number of electrode units in the column is 1 or 2, the electrode units in the column are connected to the continuous plating area through their respective narrow plating strips, and when the number of electrode units in the column is 3, the electrode units in the column are located between the two thickened edges. The electrode units on the side are connected to the continuous coating area through their own coating strips, and the electrode unit in the middle is connected to the two adjacent electrode units in the column through the coating strips; the ratio of the width of the continuous coating area to the mesh grid area in the longitudinal direction is 1 to 3:3, and the upper and lower sides of the continuous coating area and the mesh grid area are both provided with reduced thickness parts, and the reduced thickness parts extend in the transverse direction, so that the junction of the continuous coating area and the mesh grid area forms a V-shaped or U-shaped groove area through the reduced thickness part, and the insulating gap and the coating strips located at the junction of the continuous coating area and the mesh grid area are both located at the bottom of the groove area.

2. The mesh grid explosion-proof membrane for rail transit power electronic capacitors according to claim 1 is characterized in that: The insulating gaps include transverse gap bars, longitudinal gap bars and oblique gap bars; the transverse gap bars include a first transverse portion located in the mesh grid area and a second transverse portion located at the edge of the mesh grid area, which are used to divide the mesh grid area into rows, and the second transverse portions are spaced apart at the transverse center line of the groove area, and the number of the second transverse portions in each row is the same as the number of columns of electrode units; the longitudinal gap bars are located between the mesh grid area and the thickened edge, and are used to separate the thickened edge from the mesh grid area; the oblique gap bars are arranged between two adjacent columns of electrode units, and are used to divide the mesh grid area into columns; the mesh grid area is separated by the transverse gap bars, the longitudinal gap bars and the oblique gap bars, and the electrode units in the first and last columns are right-angled trapezoids, and the electrode units in the remaining columns are parallelograms.

3. The mesh grid explosion-proof membrane for rail transit power electronic capacitors according to claim 2 is characterized in that: The first transverse portion penetrates the mesh grid area in the transverse direction and divides the mesh grid area into two upper and lower rows; the second transverse portion and the oblique gap strips are symmetrically arranged with respect to the first transverse portion; the middle portion of the longitudinal gap strip is connected to the end of the first transverse portion close to the thickened edge, and the upper and lower ends of the longitudinal gap strip are respectively connected to the ends of the upper and lower second transverse portions close to the thickened edge; one end of the oblique gap strip is connected to the first transverse portion, and the other end of the oblique gap strip is connected to the end of the second transverse portion close to the retained edge; the narrow strips of the coating of a column of electrode units closest to the thickened edge are located between the longitudinal gap strips, and the narrow strips of the coating of the electrode units in this column are located at the midpoint of the side of the electrode unit, and the narrow strips of the coating of the electrode units in other columns are all located at one end of the second transverse portion close to the thickened edge.

4. The mesh grid explosion-proof membrane for rail transit power electronic capacitors according to claim 2 is characterized in that: The second transverse portion and the oblique gap strips are arranged symmetrically about the transverse center line of the mesh grid area, and the two oblique gap strips symmetrically connected at the transverse center line of the mesh grid area, and the end of the oblique gap strip away from the transverse center line of the mesh grid area is connected to the end of the second transverse portion close to the margin; the number of electrode units in the first and last columns is 2, and the number of electrode units in the remaining columns is 2 and 3, which are arranged alternately; for the electrode unit column with 2, the first transverse portion completely separates the upper and lower adjacent two electrode units, and for the electrode unit column with 3, the first transverse portion completely separates the upper and lower adjacent two electrode units, and .... There are three rows of electrode units, the end of the first transverse part close to the retained edge is connected to the oblique gap strip, and a narrow coating strip is arranged at the end of the first transverse part close to the thickened edge, so that the electrode unit in the middle is connected to the two adjacent electrode units above and below through the narrow coating strip; the narrow coating strips of the electrode units in a row closest to the thickened edge are located between the longitudinal gap strips, and the narrow coating strips of the electrode units in this row are located at the midpoint of the side of the electrode units, and the narrow coating strips of the electrode units in other rows are located at one end of the second transverse part close to the thickened edge or one end of the first transverse part close to the thickened edge.

5. The mesh grid explosion-proof membrane for rail transit power electronic capacitors according to claim 1 is characterized in that: The longitudinal width of the mesh grid area is 10-30 mm, the transverse side length of the electrode unit is 5-15 mm, the width of the insulating gap is 0.3-0.5 mm, the width of the coating narrow strip is 0.3-0.5 mm, the margin width is 1-5 mm, and the thickened edge width is 2-6.5 mm.

6. The method for preparing a mesh-shaped explosion-proof membrane for rail transit power electronic capacitors according to any one of claims 1 to 5, characterized in that: The following steps are involved: Step 1: melt and plasticize the raw material of the polypropylene base film and extrude it to obtain a sheet fluid; cast the sheet fluid through a chilled roller and a high-pressure air knife to obtain a membrane; Step 2, the film obtained in step 1 is longitudinally stretched and transversely stretched by a longitudinal stretching machine and a transverse stretching machine respectively, rolled up after corona treatment, and subjected to aging treatment to obtain a polypropylene base film with a thickness of 1.5 to 10 μm; Step 3, printing shielding oil on the corona surface of the polypropylene base film obtained in step 2, and then forming a metal coating by vacuum evaporation to obtain a metallized film; Step four, slitting, winding, and then heat treating in a vacuum environment, and then cooling to room temperature; wherein the heat treatment adopts gradient heating and heat preservation, the final temperature of the gradient heating is 120-130°C, and the total heating and heat preservation time is 1-2h.

7. The method for preparing the mesh grid explosion-proof film for rail transit power electronic capacitors according to claim 6, characterized in that: The raw materials of the polypropylene base film include, by mass percentage, 15-30% of polypropylene homopolymer B, 4-8% of polypropylene copolymer, 2-3% of maleic anhydride, 1-1.5% of nano inorganic powder, 0.3-0.5% of anti-thermal degradation agent, 0.02-0.06% of β nucleating agent, and the balance is polypropylene homopolymer A; wherein, the isotacticity of the polypropylene homopolymer A and the polypropylene homopolymer B is ≥95%, the melt flow rate of the polypropylene homopolymer A is 4.0-8.5g / 10min, and the melt flow rate of the polypropylene homopolymer B is 1.0-4.0g / 10min; the polypropylene copolymer is a block copolymer prepared by adding polyethylene components during the homopolymerization of polypropylene, and the melt flow rate is 1.0-2.5g / 10min.

8. The method for preparing the mesh grid explosion-proof film for rail transit power electronic capacitors according to claim 7, characterized in that: The beta nucleating agent includes amide compounds and / or rare earth composite organic matter; the anti-thermal degradation agent is di-tert-butyl-p-cresol; and the nano inorganic powder is powdered nano silicon dioxide and / or nano titanium dioxide.

9. The method for preparing the mesh grid explosion-proof film for rail transit power electronic capacitors according to claim 6, characterized in that: In step 2, during the longitudinal stretching, preheating is performed to raise the temperature of the membrane body to 120-130°C, and then one or both sides of the membrane are controlled to heat up to 150-160°C for longitudinal stretching, and the longitudinal stretching ratio is 4-6 times. The shaping after longitudinal stretching adopts first controlled tension heat setting and then free shrinkage heat setting. The additional stretching degree during controlled tension heat setting is 1.01-1.05, and the shaping temperature is 150-160°C; during transverse stretching, the stretching temperature is controlled to be 160-180°C, the transverse stretching ratio is 7-10 times, and the shaping after transverse stretching adopts first fixed length heat setting and then free shrinkage heat setting, and the shaping temperature is 170-180°C; during the corona treatment, the voltage is 10-15kV, the output power is 10-20kW, the frequency is 10-25kHz, and the electrode gap is 1-3mm; the aging treatment is placed away from light for 1-2 days under an environment with a humidity of ≤40% and a temperature of 15-35°C.

10. The method for preparing the mesh grid explosion-proof film for rail transit power electronic capacitors according to claim 6, characterized in that: Before melting in step 1, the polypropylene raw material is subjected to deep freezing treatment, and then ground and mixed with other raw materials of the polypropylene base film at a temperature not higher than 0°C for 5 to 10 minutes; the extrusion temperature is 200 to 230°C, the temperature of the chilled roller is 95 to 100°C, and the gas temperature of the high-pressure air knife is 95 to 100°C; the shielding oil in step 3 is silicone oil, paraffin oil or fluorine oil; during the vacuum evaporation, the vacuum degree is ≤0.05Pa, and the metal used is aluminum and / or zinc; the gradient heating in step 4 is specifically: heating to 60 to 70°C, keeping warm for 15 to 25 minutes, then heating to 90 to 100°C, keeping warm for 20 to 30 minutes, and then heating to 120 to 130°C and keeping warm for 20 to 30 minutes, wherein the heating rate is 5 to 10°C / min.

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