CN115411458A - Five-layer co-extrusion diaphragm and preparation method thereof - Google Patents
Five-layer co-extrusion diaphragm and preparation method thereof Download PDFInfo
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- 238000001125 extrusion Methods 0.000 title claims abstract description 67
- 238000002360 preparation method Methods 0.000 title claims abstract description 14
- 239000010410 layer Substances 0.000 claims abstract description 205
- 239000012792 core layer Substances 0.000 claims abstract description 43
- 239000002344 surface layer Substances 0.000 claims abstract description 28
- 239000000155 melt Substances 0.000 claims description 38
- 239000000463 material Substances 0.000 claims description 34
- 239000002994 raw material Substances 0.000 claims description 29
- 238000000034 method Methods 0.000 claims description 28
- 238000005266 casting Methods 0.000 claims description 24
- 239000012528 membrane Substances 0.000 claims description 23
- 238000010438 heat treatment Methods 0.000 claims description 20
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- 238000001816 cooling Methods 0.000 claims description 14
- 238000002425 crystallisation Methods 0.000 claims description 14
- 230000008025 crystallization Effects 0.000 claims description 14
- 238000000137 annealing Methods 0.000 claims description 12
- 239000004743 Polypropylene Substances 0.000 claims description 10
- 229920001155 polypropylene Polymers 0.000 claims description 10
- 239000004698 Polyethylene Substances 0.000 claims description 8
- 229920000573 polyethylene Polymers 0.000 claims description 8
- 239000004677 Nylon Substances 0.000 claims description 7
- 229920001778 nylon Polymers 0.000 claims description 7
- 239000002131 composite material Substances 0.000 claims description 5
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- 239000011347 resin Substances 0.000 abstract description 8
- 229920005989 resin Polymers 0.000 abstract description 8
- 239000011229 interlayer Substances 0.000 abstract description 7
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 abstract description 3
- 229910001416 lithium ion Inorganic materials 0.000 abstract description 3
- 230000008569 process Effects 0.000 description 14
- 210000004379 membrane Anatomy 0.000 description 13
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- GELKBWJHTRAYNV-UHFFFAOYSA-K lithium iron phosphate Chemical compound [Li+].[Fe+2].[O-]P([O-])([O-])=O GELKBWJHTRAYNV-UHFFFAOYSA-K 0.000 description 2
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 description 1
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
- H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
- H01M50/409—Separators, membranes or diaphragms characterised by the material
- H01M50/449—Separators, membranes or diaphragms characterised by the material having a layered structure
- H01M50/457—Separators, membranes or diaphragms characterised by the material having a layered structure comprising three or more layers
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
- H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
- H01M50/403—Manufacturing processes of separators, membranes or diaphragms
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
Abstract
The invention relates to the technical field of lithium ion battery diaphragm manufacturing, in particular to a five-layer co-extrusion diaphragm and a preparation method thereof, wherein the five-layer co-extrusion diaphragm comprises a core layer, supporting layers and surface layers, the upper surface and the lower surface of the core layer are respectively provided with the supporting layers, one surfaces of the two supporting layers, which are far away from the core layer, are respectively provided with the surface layers, and the thickness ratio of the core layer to the supporting layers to the surface layers is (1-5). Five layers of coextrusion diaphragms are extruded and formed through five layers of coextrusion die heads, the five layers of coextrusion diaphragms are compared with three layers of coextrusion diaphragms, namely, transition layers are additionally arranged, even if the difference between the extrusion quantities of the middle layer and the outer layer is large during manufacturing, the difference between the extrusion quantities of adjacent layers is small after the transition layers are additionally arranged, and when the viscosity of the resin in the middle layer and the viscosity of the resin in the outer layer are greatly different, the interlayer surface turbulence can be greatly reduced through the existence of the transition layers, and the diaphragms with more uniform thickness are obtained. The thickness of the diaphragm is controlled more precisely and the probability of curling and wrinkling is reduced.
Description
Technical Field
The invention relates to the technical field of lithium ion battery diaphragm manufacturing, in particular to a five-layer co-extrusion diaphragm and a preparation method thereof.
Background
With the increase of the application share of the lithium iron phosphate battery in the power battery by virtue of the safety and cost advantages of the lithium iron phosphate battery, the demand of a matched dry-method diaphragm is obviously increased. In the future, the market scale of the power battery superposition energy storage is further expanded, the dry-method diaphragm shipment quantity with cost advantage is greatly increased year by year, and the market share is expected to be further improved. At present, the dry-method diaphragm is in the innovative era of thinning and multilayering. The smaller the thickness of the diaphragm is, the shorter the distance of lithium ions passing through the diaphragm is, the smaller the internal resistance of the manufactured battery is, the better the rate performance and the cycle performance are, the thinner diaphragm can provide a larger space for an electrode active substance, the specific capacity of the battery is higher, and the requirements of high energy density, high rate and the like of a power battery are met.
In the process of realizing the localization of lithium battery separators, the thicknesses of the power type dry separators are changed from 32 μm to 25 μm, 24 μm and 22 μm along with the technical progress. The thickness of the diaphragm of the mainstream dry method in 2018 is reduced to 20 micrometers, and the thickness of the diaphragm is increased towards large-scale application of 18 micrometers and 16 micrometers. In 2020-2021, the dry-process membrane thickness was shifted from 14 μm to 12 μm with the development of the state of the art in membrane manufacturing. No doubt, thinning and multilayering are the inevitable trend of dry-process separator development, and the thickness of the separator product will gradually evolve from 12 μm to the direction of 10 μm, 9 μm and even smaller.
After the conventional dry-process separator is thinned, the mechanical strength of the separator is reduced, the separator is easily broken down to cause short circuit of a battery, and the stability and safety of the separator product are challenged, so that the mechanical strength must be satisfied while the thickness of the separator is reduced. With the development of the multilayer co-extrusion diaphragm technology, the problem that the mechanical strength is reduced after the diaphragm becomes thinner is well solved. The multilayer co-extrusion barrier diaphragm is formed by adopting more than 2 extruders to mix resin raw materials with different functions, such as: the preparation method comprises the following steps of carrying out distributed melt extrusion on copolymers such as polyethylene, polypropylene and the like, converging the copolymers at a multilayer co-extrusion die head through respective runners, carrying out blow molding or sheet casting molding, cooling and compounding the copolymers together to obtain a co-extrusion base film with more than three layers, and carrying out a stretching pore-forming process on the base film to obtain a required multilayer diaphragm product. The advantages of different resins are integrated and designed to obtain a product with the advantages of multiple materials, and meanwhile, the multilayer coextrusion has high mechanical property. The multilayer co-extrusion barrier film technology is a multilayer co-extrusion one-step forming technology, traditional compounding is not needed, post-processing technologies such as coating and the like can be used, raw material cost and production procedures can be effectively reduced, production cost can be saved, thinning feasibility can be achieved in film thickness control, the multilayer co-extrusion composite film can fully utilize various plastic raw materials with different properties, compounding can be carried out as required, excellent properties can be obtained, the barrier property is good, the strength and puncture resistance are high, the adhesive property is strong, and good anti-slip property and the like are achieved. The domestic three-layer co-extrusion dry-method diaphragm is mature in technology, the current three-layer co-extrusion diaphragm also becomes the main production expansion flow of the domestic dry-method diaphragm, and the current 12-micron three-layer co-extrusion diaphragm is supplied to the market in batches.
With the further thinning of the thickness of the diaphragm, the mechanical strength of the three-layer co-extrusion diaphragm can not meet the requirement, and in the traditional three-layer co-extrusion process, when a formula with a large interlayer proportion difference is processed, the interlayer pressure difference is often too large due to the too large difference of the extrusion quantities of adjacent layers, so that the interlayer slippage is caused. Meanwhile, due to the fact that the extrusion amount difference is too large, interlayer proportion is not adjusted, the layered structure is asymmetric, and the product is prone to curling, so that wrinkles and the like are generated.
Disclosure of Invention
The invention aims to provide a five-layer co-extrusion diaphragm and a preparation method thereof, and aims to solve the problems in the background art.
In order to achieve the above purpose, the technical scheme adopted by the invention is to provide a five-layer co-extrusion membrane, which comprises a core layer, a support layer and surface layers, wherein the support layer is arranged on the upper surface and the lower surface of the core layer, the surface layers are arranged on the surfaces, away from the core layer, of the two support layers, the thickness ratio of the core layer, the support layer and the surface layers is 1-5.
Further, the thickness ratio of the core layer, the support layer and the skin layer is 5.
Further, the melt index of the core layer material is less than the melt index of the support layer material, which is less than the melt index of the skin layer material.
Further, the invention also provides a preparation method of the five-layer co-extruded membrane, which is used for preparing the five-layer co-extruded membrane and comprises the following steps:
preparing raw materials, namely selecting polyethylene, nylon and polypropylene as raw materials, wherein the raw materials of the core layer, the supporting layer and the surface layer are one of the polyethylene, the nylon and the polypropylene;
performing five-layer co-extrusion, namely melting and extruding the raw materials of the three layers by using three extruders in a heating state to form a melt, injecting the melt into a five-layer co-extrusion die head for extrusion, and extruding to form a high-temperature melt with a five-layer composite structure of a surface layer, a support layer, a core layer, a support layer and a surface layer;
casting a sheet, namely casting the high-temperature melt with the five-layer structure into a sheet to prepare a five-layer co-extrusion base film;
performing heat treatment crystallization, namely performing heat treatment crystallization on the five-layer co-extruded base film to perfect the crystallization of the five-layer co-extruded base film;
cooling and annealing, namely cooling and annealing the five-layer co-extruded base film crystallized by the heat treatment;
and (3) stretching, namely performing cold stretching on the five-layer co-extruded base film after cooling and annealing, and then performing hot stretching to obtain a five-layer co-extruded diaphragm product.
Further, the preparation method of the five-layer co-extrusion diaphragm also comprises a slitting treatment step, wherein the five-layer co-extrusion diaphragm after the stretching treatment is slit according to the size required by a user, so that a final diaphragm finished product is obtained.
Further, in the five-layer co-extrusion step, three single-screw extruders with length-diameter ratio L/D being more than or equal to 34 are used for respectively melting and extruding the raw materials of the three layers at 180-240 ℃ to form a melt, and then the melt is injected into a five-layer co-extrusion die head.
Further, in the step of casting the cast piece, casting is carried out at 100-120 ℃ and the casting speed is 50-120m/min.
Further, in the step of casting the sheet, the film after the sheet casting is further drawn, subjected to on-line thickness measurement and qualified surface flaw detection and then wound.
Further, in the heat treatment crystallization step, the heat treatment condition is 100-150 ℃ and the treatment time is 8-14 hours.
Further, in the drawing treatment step, the cold drawing temperature is 50 to 100 ℃, the speed ratio of cold drawing is 1.0 to 1.5, the hot drawing temperature is 100 to 150 ℃, and the speed ratio is 1.0 to 3.0.
The invention has the beneficial effects that:
1. five layers of coextrusion diaphragms are extruded and formed through five layers of coextrusion die heads, the five layers of coextrusion diaphragms are compared with three layers of coextrusion diaphragms, namely, transition layers are additionally arranged, even if the difference between the extrusion quantities of the middle layer and the outer layer is large during manufacturing, the difference between the extrusion quantities of adjacent layers is small after the transition layers are additionally arranged, and when the viscosity of the resin in the middle layer and the viscosity of the resin in the outer layer are greatly different, the interlayer surface turbulence can be greatly reduced through the existence of the transition layers, and the diaphragms with more uniform thickness are obtained. The thickness of the diaphragm is controlled more precisely and the probability of curling and wrinkling is reduced.
2. The core layer material has a melt index less than the support layer material, and the support layer material has a melt index less than the skin layer material. Due to the difference of the melt indexes of the core layer, the support layer and the surface layer, the materials in the three layers have different pore sizes and pore size distribution after being stretched, and a staggered pore structure is formed in the vertical direction, so that the puncture strength of the diaphragm can be enhanced. And the strength of the material is increased along with the reduction of the melt index, and the core layer can endow the separator with higher mechanical strength by adopting the material with the low melt index.
3. On the premise that the proportion of the functional materials is the same, the five-layer co-extrusion process is used, so that the performance of the diaphragm can be greatly improved, and the thinning potential of the film is greatly improved.
4. The three-layer co-extrusion process is difficult in processing materials with large processing temperature span and large flow viscosity difference, and can be easily realized in the five-layer co-extrusion process. The stacking advantage of the functional material is obviously better than the blending advantage, the raw material selection of the five-layer co-extrusion is larger, a single raw material can be selected as far as possible in the function setting of each layer, the performance reduction loss caused by blending is avoided, the use amount of the functional raw material is reduced, and the processing technology control is more convenient.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and other drawings can be obtained by those skilled in the art without creative efforts.
FIG. 1 is a schematic structural diagram of a five-layer co-extruded membrane provided in embodiment 1 of the present invention;
FIG. 2 is a process flow diagram of a method for preparing a five-layer co-extruded membrane according to embodiment 1 of the present invention;
description of reference numerals:
1. a core layer; 2. a support layer; 3. a skin layer.
Detailed Description
The technical solutions of the present invention will be described clearly and completely with reference to the accompanying drawings, and it should be understood that the described embodiments are some, but not all embodiments of the present invention. All other embodiments, which can be obtained by a person skilled in the art without making any creative effort based on the embodiments in the present invention, belong to the protection scope of the present invention.
In the description of the present invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc., indicate orientations or positional relationships based on the orientations or positional relationships shown in the drawings, and are only for convenience of description and simplicity of description, but do not indicate or imply that the device or element being referred to must have a particular orientation, be constructed and operated in a particular orientation, and thus, should not be construed as limiting the present invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance.
In the description of the present invention, it should be noted that, unless otherwise explicitly specified or limited, the terms "mounted," "connected," and "connected" are to be construed broadly and may be, for example, fixedly connected, detachably connected, or integrally connected; can be mechanically or electrically connected; they may be connected directly or indirectly through intervening media, or they may be interconnected between two elements. The specific meanings of the above terms in the present invention can be understood in specific cases to those skilled in the art.
In addition, the technical features involved in the different embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.
Example 1
Referring to fig. 1, a five-layer co-extrusion membrane provided as an embodiment of the present invention includes a core layer 1, a support layer 2 and a surface layer 3, the upper and lower surfaces of the core layer 1 are both provided with the support layers 2, one surfaces of the two support layers 2 far away from the core layer 1 are both provided with the surface layer 3, the thickness ratio of the core layer 1, the support layers 2 and the surface layers 3 is 1-5.
Specifically, the total thickness of the five-layer coextruded membrane structure is 10 μm, the thickness ratio of the core layer 1, the support layer 2 and the skin layer 3 is 5. Five layers of coextrusion diaphragms are extruded and formed through five layers of coextrusion die heads, the five layers of coextrusion diaphragms are compared with three layers of coextrusion diaphragms, namely, transition layers are additionally arranged, even if the difference between the extrusion quantities of the middle layer and the outer layer is large during manufacturing, the difference between the extrusion quantities of adjacent layers is small after the transition layers are additionally arranged, and when the viscosity of the resin in the middle layer and the viscosity of the resin in the outer layer are greatly different, the interlayer surface turbulence can be greatly reduced through the existence of the transition layers, and the diaphragms with more uniform thickness are obtained. The membrane thickness control is more precise and the probability of curling and wrinkling is reduced.
The functional film is produced by using the three-layer and five-layer co-extrusion processes, and the mechanical property of the film produced by using the five-layer co-extrusion process is obviously better than that of the film produced by using the three-layer co-extrusion process after the film is formed on the premise that the use ratio of the functional material is consistent. On the premise that the proportion of the functional materials is the same, the five-layer co-extrusion process is used, so that the performance of the diaphragm can be greatly improved, and the thinning potential of the film is greatly improved.
The three-layer co-extrusion process is difficult in the aspect of processing materials with large processing temperature span and large flow viscosity difference, and can be easily realized in the five-layer co-extrusion process. The stacking advantage of the functional materials is obviously better than the blending advantage, the raw material selection of the five-layer coextrusion is larger, single raw materials can be selected as far as possible in the function setting of each layer, the performance reduction loss caused by blending is avoided, the use amount of the functional raw materials is reduced, and the processing technology control is more convenient.
Further, the melt index of the material of the core layer 1 is smaller than that of the material of the support layer 2, and the melt index of the material of the support layer 2 is smaller than that of the material of the skin layer 3. Due to the difference of the melt indexes of the core layer 1, the support layer 2 and the surface layer 3, materials in the three layers have different pore sizes and pore size distribution after stretching, and a staggered pore structure is formed in the vertical direction, so that the puncture strength of the diaphragm can be enhanced. And the strength of the material increases as the melt index decreases, the use of a low melt index material for the core layer 1 can impart higher mechanical strength to the separator.
Example 2
As a method for preparing a five-layer co-extruded membrane provided by an embodiment of the present invention, the five-layer co-extruded membrane described in example 1 is prepared, the total thickness of the five-layer co-extruded membrane structure in example 1 is 10 μm, the thickness ratio of the core layer 1, the support layer 2 and the skin layer 3 is 5.
The preparation method comprises the following steps:
preparing raw materials, namely selecting polyethylene, nylon and polypropylene as raw materials, wherein the raw materials of the core layer 1, the support layer 2 and the surface layer 3 are one of polyethylene, nylon and polypropylene;
performing five-layer co-extrusion, namely melting and extruding the raw materials of the three layers by using three extruders in a heating state to form a melt, injecting the melt into a five-layer co-extrusion die head for extrusion, and extruding to form a high-temperature melt with a five-layer composite structure comprising a surface layer 3, a support layer 2, a core layer 1, a support layer 2 and a surface layer 3;
casting a sheet, namely casting the high-temperature melt with the five-layer structure into a sheet to prepare a five-layer co-extrusion base film;
performing heat treatment crystallization, namely performing heat treatment crystallization on the five-layer co-extruded base film to perfect the crystallization of the five-layer co-extruded base film;
cooling and annealing, namely cooling and annealing the five-layer co-extruded base film crystallized by the heat treatment;
and (3) stretching, namely performing cold stretching on the five-layer co-extruded base film after cooling and annealing, and then performing hot stretching to obtain a five-layer co-extruded diaphragm product.
Specifically, the raw material of the core layer 1 in this embodiment is polypropylene, and the melt index is 0.8g/10min; the raw material of the supporting layer 2 is polypropylene with a melt index of 1.2g/10min; the raw material of the surface layer 3 is selected from polypropylene, and the melt index is 2.0g/10min; due to the difference of the melt indexes of the core layer 1, the support layer 2 and the surface layer 3, materials in the three layers have different pore sizes and pore size distribution after stretching, and a staggered pore structure is formed in the vertical direction, so that the puncture strength of the diaphragm can be enhanced. And the strength of the material increases as the melt index decreases, the use of a material having a low melt index for the core layer 1 can impart higher mechanical strength to the separator.
As a variable embodiment, the core layer 1, the support layer 2 and the skin layer 3 may also be made of polyethylene or nylon, and the materials of the core layer 1, the support layer 2 and the skin layer 3 may be completely the same or not completely different, and are not limited specifically. But to ensure that the melt index of the material of the core layer 1 is less than the melt index of the material of the support layer 2 and the melt index of the material of the support layer 2 is less than the melt index of the material of the skin layer 3.
Further, in the five-layer co-extrusion step, three single-screw extruders with length-diameter ratio L/D more than or equal to 34 are used for respectively melting and extruding the three layers of raw materials at 180-240 ℃ to form a melt, and then the melt is injected into a five-layer co-extrusion die head. In the step of casting the casting sheet, casting is carried out at the temperature of 100-120 ℃, and the casting speed is 50-120m/min.
Specifically, in this embodiment, three single screw extruders with length/diameter ratios L/D equal to or greater than 34 are used to respectively melt and extrude the raw materials adopted for the core layer 1, the support layer 2, and the surface layer 3 at 220 ℃ to form a melt, and then the melt is injected into a five-layer co-extrusion die head to be extruded, so as to form a high-temperature melt having a five-layer composite structure of the surface layer 3, the support layer 2, the core layer 1, the support layer 2, and the surface layer 3; and then cooling the high-temperature melt with the five-layer structure through a casting sheet to form a casting film, wherein casting is carried out at 110 ℃, and the casting speed is controlled at 90m/min, so that the five-layer co-extrusion base film is prepared. And (4) further drawing, measuring the thickness on line and rolling after the surface flaw detection is qualified. Wherein the total thickness of the gaps of the five extrusion openings of the five-layer co-extrusion die head is more than 10 mu m, so that the extruded diaphragm basement membrane is more than 10 mu m, and then the thickness of the diaphragm basement membrane is 10 mu m in the subsequent stretching treatment step. The thickness of the five extrusion opening gaps is 1.
Further, in the heat treatment crystallization step, the heat treatment condition is 100-150 ℃ and the treatment time is 8-14 hours. In the embodiment, the heat treatment condition of the five-layer co-extruded base film is 135 ℃, and the treatment time is 12 hours.
Further, in the step of stretching treatment, the cold stretching temperature is 50-100 ℃, the speed ratio of cold stretching is 1.0-1.5, the hot stretching temperature is 100-150 ℃, and the speed ratio is 1.0-3.0.
Specifically, in this embodiment, the five-layer co-extruded base film is subjected to cooling annealing treatment after crystallization is completed. Performing cold stretching on the five-layer co-extruded base film after cooling and annealing, and then performing hot stretching, wherein the cold stretching temperature is 80 ℃, and the speed ratio is 1.1; the hot stretching temperature is 120 ℃, and the speed ratio is 1.9. Wherein, the speed ratio refers to the ratio of the linear speeds of the stretching roller and the unwinding roller in the stretching process, and the effective stretching of the base film can be realized only when the speed of the stretching roller is greater than that of the unwinding roller. Wherein, the cold stretching and the hot stretching have different functions, and the cold stretching is to draw out the micropore structure, so the speed ratio needs to be smaller. The hot stretching is to enlarge the microporous structure and increase the speed ratio, so that the two speed ratios of cold stretching and hot stretching are different.
Furthermore, the preparation method of the five-layer co-extruded diaphragm further comprises a slitting treatment step, wherein the slitting treatment is carried out on the five-layer co-extruded diaphragm obtained after the stretching treatment according to the size required by a user, so that a final diaphragm finished product meeting the design size requirement is obtained.
The five-layer co-extrusion diaphragm is prepared by the steps of raw material preparation, five-layer co-extrusion, tape casting, heat treatment crystallization, cooling annealing, stretching treatment and the like, and the prepared five-layer co-extrusion diaphragm has the advantages of smaller structural thickness than that of the conventional dry diaphragm, reduction of the thickness to 8-10 mu m, excellent mechanical property and good safety performance. And the thickness control precision is high, the thickness is uniform, the special five-layer structure is adopted, and the anti-wrinkle capability is strong.
The embodiments of the present invention are preferred embodiments of the present invention, and the scope of the present invention is not limited by these embodiments, so: all equivalent changes made according to the structure, shape and principle of the invention are covered by the protection scope of the invention.
Claims (10)
1. A five-layer co-extruded membrane is characterized by comprising a core layer (1), support layers (2) and surface layers (3), wherein the support layers (2) are respectively arranged on the upper surface and the lower surface of the core layer (1), the surface layers (3) are respectively arranged on the surfaces, far away from the core layer (1), of the two support layers (2), the thickness ratio of the core layer (1), the support layers (2) and the surface layers (3) is 1-5.
2. The five-layer co-extruded membrane of claim 1, wherein the thickness ratio of the core layer (1), the support layer (2) and the skin layer (3) is 5.
3. The five-layer coextruded membrane according to claim 1, wherein the melt index of the material of the core layer (1) is less than the melt index of the material of the support layer (2), and the melt index of the material of the support layer (2) is less than the melt index of the material of the skin layer (3).
4. A method for preparing a five-layer co-extruded membrane, characterized in that the five-layer co-extruded membrane of any one of the claims 1 to 3 is prepared, the method comprising the following steps:
preparing raw materials, namely selecting polyethylene, nylon and polypropylene as raw materials, wherein the raw materials of the core layer (1), the support layer (2) and the surface layer (3) are one of polyethylene, nylon and polypropylene;
five-layer co-extrusion, namely respectively melting and extruding the raw materials of the three layers by using three extruders in a heating state to form a melt, then injecting the melt into a five-layer co-extrusion die head for extrusion, and extruding to form a high-temperature melt with a five-layer composite structure of a surface layer (3), a support layer (2), a core layer (1), a support layer (2) and a surface layer (3);
casting a sheet, namely casting the high-temperature melt with the five-layer structure into a sheet to prepare a five-layer co-extruded base film;
performing heat treatment crystallization, namely performing heat treatment crystallization on the five-layer co-extruded base film to perfect the crystallization of the five-layer co-extruded base film;
cooling and annealing, namely cooling and annealing the five-layer co-extruded base film crystallized by the heat treatment;
and (3) stretching, namely performing cold stretching on the five-layer co-extruded base film after cooling and annealing, and then performing hot stretching to obtain a five-layer co-extruded diaphragm product.
5. The preparation method of the five-layer co-extruded membrane as claimed in claim 4, further comprising a slitting treatment step of slitting the five-layer co-extruded membrane after the stretching treatment according to the size required by a user to obtain a final membrane finished product.
6. The preparation method of the five-layer co-extrusion diaphragm as claimed in claim 4, wherein in the five-layer co-extrusion step, three single-screw extruders with length-diameter ratio L/D being more than or equal to 34 are used to respectively melt and extrude the raw materials of the three layers at 180-240 ℃ to form a melt, and then the melt is injected into a five-layer co-extrusion die head.
7. The method for preparing a five-layer co-extruded membrane structure according to claim 4, wherein in the step of casting the sheet, casting is performed at 100-120 ℃ and the casting speed is 50-120m/min.
8. The preparation method of the five-layer co-extruded diaphragm as claimed in claim 4, wherein in the step of casting the sheet, the cast film is further rolled after traction, on-line thickness measurement and qualified surface defect detection.
9. The method for preparing a five-layer co-extruded separator as claimed in claim 4, wherein in the heat treatment crystallization step, the heat treatment conditions are 100-150 ℃ and the treatment time is 8-14 hours.
10. The method for preparing a five-layer co-extruded membrane as in claim 4, wherein in the stretching step, the cold stretching temperature is 50-100 ℃, the speed ratio of cold stretching is 1.0-1.5, the hot stretching temperature is 100-150 ℃, and the speed ratio is 1.0-3.0.
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