CN114044935B - Preparation of porous polyolefin film material - Google Patents
Preparation of porous polyolefin film material Download PDFInfo
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- CN114044935B CN114044935B CN202111518129.8A CN202111518129A CN114044935B CN 114044935 B CN114044935 B CN 114044935B CN 202111518129 A CN202111518129 A CN 202111518129A CN 114044935 B CN114044935 B CN 114044935B
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- 229920000098 polyolefin Polymers 0.000 title claims abstract description 92
- 239000000463 material Substances 0.000 title claims abstract description 27
- 238000002360 preparation method Methods 0.000 title claims abstract description 19
- VTYYLEPIZMXCLO-UHFFFAOYSA-L Calcium carbonate Chemical compound [Ca+2].[O-]C([O-])=O VTYYLEPIZMXCLO-UHFFFAOYSA-L 0.000 claims abstract description 102
- 239000002245 particle Substances 0.000 claims abstract description 54
- 229910000019 calcium carbonate Inorganic materials 0.000 claims abstract description 44
- 238000000034 method Methods 0.000 claims abstract description 40
- 239000003795 chemical substances by application Substances 0.000 claims abstract description 28
- 239000002131 composite material Substances 0.000 claims abstract description 16
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims abstract description 11
- 238000002844 melting Methods 0.000 claims abstract description 10
- 230000008018 melting Effects 0.000 claims abstract description 10
- 238000002156 mixing Methods 0.000 claims abstract description 8
- 230000004048 modification Effects 0.000 claims abstract description 6
- 238000012986 modification Methods 0.000 claims abstract description 6
- 229910052731 fluorine Inorganic materials 0.000 claims description 28
- 239000011737 fluorine Substances 0.000 claims description 28
- YCKRFDGAMUMZLT-UHFFFAOYSA-N Fluorine atom Chemical compound [F] YCKRFDGAMUMZLT-UHFFFAOYSA-N 0.000 claims description 27
- 239000007822 coupling agent Substances 0.000 claims description 16
- -1 polyethylene Polymers 0.000 claims description 11
- 239000004698 Polyethylene Substances 0.000 claims description 8
- 238000000465 moulding Methods 0.000 claims description 8
- 229920000573 polyethylene Polymers 0.000 claims description 8
- 238000004519 manufacturing process Methods 0.000 claims description 7
- 230000005496 eutectics Effects 0.000 claims description 4
- 239000003960 organic solvent Substances 0.000 claims description 4
- 239000004743 Polypropylene Substances 0.000 claims description 3
- 229920001155 polypropylene Polymers 0.000 claims description 3
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- 239000004800 polyvinyl chloride Substances 0.000 claims description 3
- 238000002791 soaking Methods 0.000 claims description 2
- 238000001291 vacuum drying Methods 0.000 claims description 2
- 239000004088 foaming agent Substances 0.000 claims 1
- 239000011148 porous material Substances 0.000 abstract description 34
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- 230000008569 process Effects 0.000 abstract description 22
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- 238000009826 distribution Methods 0.000 description 5
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- 239000012982 microporous membrane Substances 0.000 description 4
- 238000005191 phase separation Methods 0.000 description 4
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- 239000000843 powder Substances 0.000 description 4
- YMWUJEATGCHHMB-UHFFFAOYSA-N Dichloromethane Chemical group ClCCl YMWUJEATGCHHMB-UHFFFAOYSA-N 0.000 description 3
- 125000002887 hydroxy group Chemical group [H]O* 0.000 description 3
- 239000000203 mixture Substances 0.000 description 3
- 238000011056 performance test Methods 0.000 description 3
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- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 description 2
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- XPBBUZJBQWWFFJ-UHFFFAOYSA-N fluorosilane Chemical compound [SiH3]F XPBBUZJBQWWFFJ-UHFFFAOYSA-N 0.000 description 2
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- 239000001257 hydrogen Substances 0.000 description 2
- 238000011031 large-scale manufacturing process Methods 0.000 description 2
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- 238000005470 impregnation Methods 0.000 description 1
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- 231100000331 toxic Toxicity 0.000 description 1
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J9/00—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof
- C08J9/26—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof by elimination of a solid phase from a macromolecular composition or article, e.g. leaching out
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
- B29C48/00—Extrusion moulding, i.e. expressing the moulding material through a die or nozzle which imparts the desired form; Apparatus therefor
- B29C48/001—Combinations of extrusion moulding with other shaping operations
- B29C48/0018—Combinations of extrusion moulding with other shaping operations combined with shaping by orienting, stretching or shrinking, e.g. film blowing
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
- B29C48/00—Extrusion moulding, i.e. expressing the moulding material through a die or nozzle which imparts the desired form; Apparatus therefor
- B29C48/03—Extrusion moulding, i.e. expressing the moulding material through a die or nozzle which imparts the desired form; Apparatus therefor characterised by the shape of the extruded material at extrusion
- B29C48/07—Flat, e.g. panels
- B29C48/08—Flat, e.g. panels flexible, e.g. films
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J2201/00—Foams characterised by the foaming process
- C08J2201/04—Foams characterised by the foaming process characterised by the elimination of a liquid or solid component, e.g. precipitation, leaching out, evaporation
- C08J2201/044—Elimination of an inorganic solid phase
- C08J2201/0444—Salts
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
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- C08J2323/00—Characterised by the use of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Derivatives of such polymers
- C08J2323/02—Characterised by the use of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Derivatives of such polymers not modified by chemical after treatment
- C08J2323/04—Homopolymers or copolymers of ethene
- C08J2323/06—Polyethene
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- 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
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- Health & Medical Sciences (AREA)
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- Medicinal Chemistry (AREA)
- Polymers & Plastics (AREA)
- Organic Chemistry (AREA)
- Manufacture Of Porous Articles, And Recovery And Treatment Of Waste Products (AREA)
Abstract
The invention provides a preparation method of a porous polyolefin membrane material, which comprises the following steps: carrying out surface grafting modification treatment on the inorganic pore-forming agent; mixing, melting and extruding the modified pore-forming agent and polyolefin in a double-screw extruder according to a certain mass ratio to prepare a composite material, and forming to obtain a composite polyolefin film material; the composite polyolefin film is placed in a water bath for dipping, ultrasonic treatment and stretching to remove the inorganic pore-forming agent, thus obtaining the porous polyolefin film material. According to the invention, the surface of the calcium carbonate particles is modified by a simple operation means, so that the calcium carbonate particles are more uniformly dispersed when the calcium carbonate particles are fused with a polyolefin matrix, the pore and pore diameter of the obtained porous polyolefin film are uniformly distributed, and the obtained porous film has high mechanical strength; the stretching film-making process can adopt a wet biaxial stretching process, which is favorable for removing pore-forming agents, and the porous polyolefin film with better mechanical strength is obtained; inorganic pore-forming agent calcium carbonate particles and water bath stretching are selected, so that the raw material source is wide, the price is low, the cost is low, and the environment is protected.
Description
Technical Field
The invention relates to the technical field of porous membrane materials, in particular to a preparation method of a porous polyolefin membrane material.
Background
The porous polyolefin film is a film-like material containing micropores, and is widely applied to battery diaphragms, ultrafiltration films, microfiltration films, medical protective materials and the like by virtue of excellent mechanical properties, insulating properties and chemical stability. The current methods for preparing porous polyolefin films can be largely classified into wet stretching processes and dry stretching processes according to the principle of pore formation. The dry stretching is also called a melt extrusion stretching method, and can be classified into a unidirectional stretching process and a bidirectional stretching process, which means that polyolefin resin is melted, extruded and blown to form a crystalline polymer film, and after crystallization treatment and annealing, a highly oriented multilayer structure is obtained, and the multilayer structure is further stretched at a high temperature, and the crystalline interface is peeled off to form a porous structure. The method has simple process and is environment-friendly, but the thickness, pore diameter and porosity of the product are not uniformly distributed, and the production requirement cannot be met. Wet stretching is also called a phase separation method, which is to mix some high-boiling-point small molecular substances with polyolefin resin, melt the mixture at high temperature (generally higher than the melting point of polymer) to form a homogeneous solution, extrude and press the solution to obtain a film, cool the film at a certain speed or quench the film to induce phase separation, biaxially stretch the film, extract small molecules with solvent to form a microporous structure, and prepare the microporous film material which is mutually communicated. The method has quick development in recent years, can better control the thickness, the aperture and the porosity of the film, and the prepared microporous film material has better mechanical strength, but the method has higher production cost. In the wet stretching process to prepare porous polymer film materials, calcium carbonate may be added as the primary filler to improve porosity and mechanical properties of the film. However, calcium carbonate particles are very prone to agglomeration and the surface is hydrophilic and not oleophilic, resulting in poor compatibility with the polymer and non-uniform pore size distribution of the membrane.
Patent application number CN201110152035.3 discloses a polylactic acid breathable film and a preparation process thereof, wherein polylactic acid, calcium carbonate and other auxiliary agents are mixed, melted, granulated, made into a film and stretched in proportion to obtain the polylactic acid breathable film; the polylactic acid breathable film is easy to degrade and is relatively environment-friendly. Patent application number CN87100579 discloses a method for preparing polyolefin porous membrane, which comprises mixing polyolefin resin with inorganic filler, shaping, stretching to prepare the polyolefin porous membrane with air permeability having concave-convex pattern on the surface. The pore size of the polyolefin membrane obtained by the method is limited by the size of calcium carbonate, and the pore size of the prepared polyolefin porous membrane is uneven and bigger.
The patent with the application number of CN201810246847.6 discloses the preparation of a polyolefin microporous membrane, which is prepared by mixing and extruding a polyolefin mixture and an inorganic pore-forming agent by an extruder, and then biaxially stretching, extracting and thermosetting the mixture to form the microporous membrane; stacking and further stretching the multiple microporous films to form a laminated porous film; the laminated porous film was peeled off to obtain a single-layer polyolefin microporous film. The film prepared by the method has good performance, but a plurality of microporous films are stacked and stretched, so that the pore-forming agent is not easy to remove, and the pore-forming agent is accumulated, so that the stretching process is uneven; in addition, the process also needs to peel off the multilayer film, the product is easy to damage in the peeling process, the workload is large, and the yield is low.
Patent application number CN202011478164.7 discloses a preparation method of a polyolefin microporous membrane, which comprises the steps of mixing, extruding and forming polyolefin resin and organic pore-forming agent, removing the pore-forming agent through a boiling type pore-forming agent removing unit, and stretching for multiple times to obtain the polyolefin microporous membrane. The method is complicated in removing the pore-forming agent, and the extracting agent is dichloromethane, so that the method is toxic and pollutes the environment.
In view of the above, there is a need for an improved preparation of porous polyolefin membrane materials that addresses the above-described problems.
Disclosure of Invention
The invention aims to provide a preparation method of a porous polyolefin membrane material, which solves the problems of poor dispersibility of an inorganic pore-forming agent and polyolefin in melting, uneven pore size distribution and large pore size of the porous polyolefin membrane caused by the inorganic pore-forming agent.
In order to achieve the above object, the present invention provides a preparation method of a porous polyolefin film material, comprising the steps of:
s1, grafting modification: dissolving a fluorine-containing coupling agent in an organic solvent to obtain a solution with the mass fraction of 0.5-7.0%, adding an inorganic pore-forming agent into the obtained solution, vibrating for a preset time in ultrasonic waves, centrifuging, and vacuum drying to constant weight to obtain a surface grafted modified inorganic pore-forming agent;
s2, eutectic molding: mixing, melting and extruding the modified inorganic pore-forming agent obtained in the step S1 and polyolefin according to the mass ratio of (2 percent: 98 percent) to (50 percent: 50 percent) in a double-screw extruder, and molding to obtain a composite polyolefin film;
s3, stretching and film making: and (2) placing the composite polyolefin film obtained in the step (S2) into a water bath for ultrasonic impregnation, and stretching to remove the inorganic pore-forming agent to obtain the porous polyolefin film.
As a further improvement of the present invention, the inorganic porogen in step S1 is calcium carbonate particles.
As a further improvement of the present invention, the fluorine-containing coupling agent in step S1 is a fluorine-containing silane coupling agent.
As a further improvement of the present invention, the stretching in step S3 is unidirectional stretching or bidirectional stretching.
As a further improvement of the present invention, the particle size of the calcium carbonate particles is in the range of 0.1 to 5.0um.
As a further improvement of the present invention, the preset time is 35min to 10h of vibration in ultrasonic wave in step S1.
As a further improvement of the invention, the ultrasonic temperature of the water bath in the step S3 is 60-80 ℃ and the soaking time is 1-30 min.
As a further improvement of the invention, the transverse stretching ratio of the biaxial stretching is 1:5-1:50, and the longitudinal stretching ratio is 1:5-1:50.
As a further improvement of the present invention, the polyolefin in step S2 includes, but is not limited to, polyethylene, polypropylene or polyvinyl chloride.
As a further improvement of the invention, the temperature of the mixed melting in the step S2 is 120-200 ℃.
The beneficial effects of the invention are as follows:
(1) According to the preparation of the porous polyolefin membrane material, the fluorine-containing silane coupling agent is grafted on the surface of the calcium carbonate particles, and meanwhile, the characteristics of the silane coupling agent and the hydrophobicity of fluorine are utilized, so that the calcium carbonate particles and the polyolefin matrix are more uniformly dispersed when being melted, the pore and pore size distribution of the obtained porous polyolefin membrane is uniform, and the mechanical property of the porous polyolefin membrane can be improved. In addition, the modification method of the calcium carbonate particles is simple, the fluorine-containing coupling agent is directly added, and the surface grafting is carried out on the calcium carbonate particles after the activation of the calcium carbonate particles by adding the surfactant is not needed.
(2) The preparation of the porous polyolefin film material provided by the invention can adopt a wet biaxial stretching process, is favorable for removing the pore-forming agent, and can obtain the porous polyolefin film with better mechanical strength.
(3) The preparation of the porous polyolefin membrane material provided by the invention adopts inorganic pore-forming agent modified calcium carbonate particles and water bath stretching, and has the advantages of wide raw material sources, low cost and environment friendliness.
(4) The preparation method of the porous polyolefin membrane material provided by the invention has the advantages of few raw materials, simple process flow and short production period, and is suitable for large-scale production.
(5) The preparation of the porous polyolefin film material provided by the invention solves the problems that the existing industrialized porous polyolefin film adopts inorganic powder to cause non-uniformity of holes and the inorganic powder is easy to fall off, adopts a modified coupling agent to strengthen acting force between the coupling agent and the inorganic powder, and the inorganic powder falls off partially in the two-way stretching and ultrasonic processes, so that the prepared porous polyolefin film can be used in the field of medical and health.
Drawings
FIG. 1 is a scanning electron microscope image of a porous polyolefin film prepared in example 2 of the present invention.
FIG. 2 is a scanning electron microscope image of a porous polyolefin film prepared in example 3 of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be described in detail with reference to the accompanying drawings and specific embodiments.
It should be noted that, in order to avoid obscuring the present invention due to unnecessary details, only structures and/or processing steps closely related to aspects of the present invention are shown in the drawings, and other details not greatly related to the present invention are omitted.
In addition, it should be further noted that the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus.
The invention provides a preparation method of a porous polyolefin film material, which comprises the following steps:
s1, grafting modification
And dissolving the fluorine-containing compound coupling agent in an organic solvent, preferably, the fluorine-containing compound coupling agent is fluorine-containing silane coupling agent, and uniformly stirring to obtain a solution with the mass fraction of 0.5-7.0%. Calcium carbonate particles with the granularity of 0.1-5.0 um are added into the obtained solution, and the solution is placed in ultrasonic waves for vibration for preset time, preferably 35 min-10 h.
The silane coupling agent can interact with hydroxyl groups in inorganic matters and long molecular chains in organic polymers to couple inorganic materials and organic materials. In the process, alkoxy at one end of the silane coupling agent molecule is hydrolyzed to generate silicon hydroxyl, and the silicon hydroxyl and hydroxyl on the surface of the calcium carbonate particles form hydrogen bond. Meanwhile, fluorine is contained in the silane coupling agent, hydroxyl on the surface of the calcium carbonate particles can also form a hydrogen bond with fluorine in the silane coupling agent, and the fluorine-containing silane coupling agent is uniformly coated on the surface of the calcium carbonate particles.
The surface of the calcium carbonate particles is modified by using the fluorine-containing silane coupling agent, so that the surface performance of the calcium carbonate particles is transited from inorganic to organic, the compatibility of the calcium carbonate particles with polyolefin is increased, the calcium carbonate particles are more uniformly dispersed when the calcium carbonate particles are miscible with the polyolefin, in addition, the addition of the coupling agent can prevent the calcium carbonate particles from being aggregated in a large amount, the problem of uneven dispersion is avoided, the pore and pore size distribution of the prepared porous polyolefin film is uniform, and the film performance is excellent.
And (3) putting the solution into a centrifuge for centrifugation, and drying the calcium carbonate particles to constant weight in vacuum after solid-liquid separation to obtain the modified inorganic pore-forming agent calcium carbonate particles grafted on the surface.
Wherein the fluorine-containing silane coupling agent is CF 3 (CH 2 ) 2 Si(OC 2 H 5 ) 3 、CF 3 CF 2 (CH 2 ) 2 Si(OC 2 H 5 ) 3 、CF 3 (CF 2 ) 4 (CH 2 ) 2 Si(OC 2 H 5 ) 3 。
S2, eutectic molding
Mixing and melting the modified calcium carbonate particles obtained in the step S1 and polyolefin (the polyolefin can be polyethylene, polypropylene or polyvinyl chloride) according to the mass ratio of (2 percent: 98 percent) to (50 percent: 50 percent) in a double-screw extruder, preferably, the melting temperature is 120-200 ℃, extruding, molding to obtain a composite polyolefin film, and cooling or quenching the composite polyolefin film at a certain speed to induce phase separation. The modified calcium carbonate particles are uniformly distributed in the composite polyolefin film by utilizing the good compatibility of the fluorine-containing silane coupling agent and the polyolefin.
In some embodiments, casting is selected for forming, the forming temperature is controlled to be 210-270 ℃, and the casting speed is 1-20 m/min. In other embodiments, blow molding is used, the molding temperature is controlled between 120 and 190 ℃, and the blow molding speed is 1 to 20m/min.
S3, stretching and film making
And (2) immersing the composite polyolefin film obtained in the step (S2) in a water bath at 60-80 ℃ for 1-30 min, and stretching to remove modified calcium carbonate particles (part of the calcium carbonate particles still exist in the porous polyolefin film at the moment) to obtain the porous polyolefin film. Stretching is carried out in a unidirectional stretching mode or a bidirectional stretching mode. The method is more conducive to the dropping of the coupling agent modified calcium carbonate particles from the composite polyolefin film during the biaxial stretching, the transverse stretching ratio is controlled to be 1:5-1:20 during the biaxial stretching, and the longitudinal stretching ratio is controlled to be 1:5-1:50; the two-way tensile strength is larger, the prepared porous polyolefin membrane is thinner, the pores and the pore diameters are uniformly distributed, and the size range of the pore diameters is 0.1-10 um.
The invention is described in detail below by means of several examples:
example 1
A method for preparing a porous polyolefin film material, comprising the steps of:
s1, grafting modification
CF is to be 3 (CH 2 ) 2 Si(OC 2 H 5 ) 3 Dissolving in ethanol as an organic solvent to obtain a solution with a mass fraction of 3.5%. Calcium carbonate particles with the particle size of 3um are added into the obtained solution, and the solution is placed in ultrasonic waves for vibrating for 5 hours. And (3) putting the solution into a centrifuge for centrifugation, and drying the calcium carbonate particles to constant weight in vacuum after solid-liquid separation to obtain modified calcium carbonate particles with the surface properties transiting from inorganic to organic.
S2, eutectic molding
And (2) mixing and melting the modified calcium carbonate particles obtained in the step (S1) and polyethylene in a mass ratio of 25% to 75% in a double-screw extruder, extruding at a melting temperature of 160 ℃, and carrying out tape casting molding at a temperature of 240 ℃ and a speed of 10m/min to obtain the composite polyethylene film. Quenching the obtained composite polyethylene film to induce phase separation, wherein the modified calcium carbonate particles are uniformly distributed in the composite polyethylene film.
S3, stretching and film making
And (2) placing the composite polyethylene film obtained in the step (S2) in a water bath at 70 ℃ for ultrasonic dipping for 20min, transversely stretching at a stretching ratio of 1:10, longitudinally stretching at a stretching ratio of 1:25, and removing modified calcium carbonate particles by adopting bidirectional stretching to obtain the porous polyolefin film. The pore size D50, the porosity and the longitudinal tensile strength of the porous polyolefin film were measured, respectively.
Pore diameter D50 was obtained from surface morphology analysis of a scanning electron microscope picture of the porous membrane, and statistical data.
The porosity test method (weighing method) is as follows: determining the pore volume V of the porous membrane based on the change in mass of the membrane before and after wetting with pure water 1 Framework volume V of the film 2 Can be obtained by the density and dry film quality of the film raw material; the porosity of the film is V 1 /(V 1 +V 2 )。
The tensile strength test method comprises the following steps: cutting a film sample into a sample strip with the thickness of 300mm multiplied by 50mm, stretching by an Instron universal strong stretching instrument, controlling the stretching rate to be 50mm/min, and obtaining the breaking strength of the sample strip as the maximum stretching strength.
Examples 2 to 3
A method for producing a porous polyolefin film is different from example 1 in that in step S1, the coupling agents are CF, respectively 3 CF 2 (CH 2 ) 2 Si(OC 2 H 5 ) 3 、CF 3 (CF 2 ) 4 (CH 2 ) 2 Si(OC 2 H 5 ) 3 The other points are substantially the same as in embodiment 1, and will not be described here again.
TABLE 1 preparation conditions and Performance test results for examples 1-3
As can be seen from Table 1, the pore size D50 of the porous polyolefin films obtained in examples 1-2 was substantially the same, and the pore size D50 of example 3 was significantly larger than that of examples 1 and 2, indicating that the pore size was related not only to the particle size of the calcium carbonate used and the draw ratio in the water bath, but also to the kind of coupling agent.
The pore size D50 of example 3 is significantly greater than examples 1 and 2, and the porosity, pore uniformity (poor pore uniformity as can be seen from fig. 2) and longitudinal tensile strength are significantly worse than examples 1 and 2; this is mainly because the fluorine content in the fluorine-containing silane coupling agent used in example 3 is too high, resulting in too strong hydrophobicity of the modified calcium carbonate particles and significantly improved compatibility with the polyolefin film, so that a larger stretching ratio is required to drop the calcium carbonate particles in the stretching and pore-forming process, resulting in larger pore diameter; too much calcium carbonate particles remain distributed in the porous polyolefin film after stretching, so the porosity is reduced and the pores are not uniform, resulting in poor longitudinal tensile strength.
The uniformity of pores and the longitudinal tensile strength of example 1 are inferior to those of example 2, mainly because the fluorosilane coupling agent used in example 2 has a larger steric hindrance than that of example 1, so that the fluorosilane coupling agent in example 2 is dispersed more uniformly on the surface of the calcium carbonate particles, and during the stretching and pore-forming process, part of the modified calcium carbonate particles remain in the porous polyolefin film (ensuring that the exfoliated calcium carbonate and the calcium carbonate remaining in the porous polyolefin film are within a better range), on one hand, the uniformity of pore-forming is facilitated, and on the other hand, the remaining modified calcium carbonate particles contribute to the improvement of the mechanical strength of the porous polyolefin film, and thus the obtained porous polyolefin film has uniform pores (as can be seen from fig. 2), and has superior mechanical strength. In addition, it is also demonstrated that the longitudinal tensile strength is closely related to the pore uniformity.
Comparative example 1
A porous polyolefin film material was produced, which was different from example 2 in thatIn step S1, the silane coupling agent used is free of fluorine and is CH 3 (CH 2 ) 3 Si(OC 2 H 5 ) 3 . The other components are substantially the same as those of embodiment 2, and will not be described in detail here. The results of the performance test of the obtained porous polyolefin film are shown in expression 3.
Table 2 results of the performance test of comparative example 1
From the data of comparative examples 1 and 2, it is understood that if the silane coupling agent contains fluorine, the effect on pore diameter, porosity and pore uniformity is not great, but the tensile strength of the porous polyolefin film is significantly lower with the calcium carbonate modified with the silane coupling agent containing no fluorine, which indicates that the fluorine-containing silane coupling agent can improve the mechanical strength of the porous polyolefin film. This is mainly because the addition of fluorine increases the compatibility of the modified calcium carbonate particles with the polyolefin, allowing the prepared porous polyolefin film to retain a certain amount of calcium carbonate, thereby increasing the mechanical strength of the porous polyolefin film.
From the data of comparative example 1 and example 1, it is understood that increasing the number of carbon atoms in the silane coupling agent with little or no fluorine can improve the mechanical properties of the resulting porous polyolefin film.
In summary, according to the preparation of the porous polyolefin membrane material provided by the invention, the fluorine-containing silane coupling agent is grafted on the surfaces of the calcium carbonate particles, and the characteristics of the silane coupling agent and the hydrophobicity of fluorine are utilized, so that the calcium carbonate particles and the polyolefin matrix are dispersed more uniformly when being melted, the pore and pore size distribution of the obtained porous polyolefin membrane is uniform, and the mechanical property of the porous polyolefin membrane can be improved; in addition, the modification method of the calcium carbonate particles is simple, the fluorine-containing coupling agent is directly added, and the surface grafting is carried out on the calcium carbonate particles after the activation of the calcium carbonate particles by adding the surfactant is not needed. The stretching film-making process can adopt a wet biaxial stretching process, which is favorable for removing pore-forming agents, and the porous polyolefin film with better mechanical strength is obtained; inorganic pore-forming agent modified calcium carbonate particles and water bath stretching are selected, so that the raw material source is wide, the price is low, the cost is low, and the environment is protected; the method has the advantages of less raw materials, simple process flow and short production period, and is suitable for large-scale production.
The above embodiments are only for illustrating the technical solution of the present invention and not for limiting the same, and although the present invention has been described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that modifications and equivalents may be made thereto without departing from the spirit and scope of the technical solution of the present invention.
Claims (3)
1. A preparation method of a porous polyolefin film material is characterized in that: the method comprises the following steps:
s1, grafting modification: dissolving a fluorine-containing coupling agent in an organic solvent to obtain a solution with the mass fraction of 0.5-7.0%, adding an inorganic pore-forming agent into the obtained solution, vibrating in ultrasonic waves for a preset time of 35 min-10 h, centrifuging, and vacuum drying to constant weight to obtain a surface grafted modified inorganic pore-forming agent; the inorganic pore-forming agent is calcium carbonate particles with the particle size range of 3 mu m; the fluorine-containing coupling agent is CF 3 CF 2 (CH 2 ) 2 Si(OC 2 H 5 ) 3 ；
S2, eutectic molding: mixing and melt-extruding the modified inorganic pore-foaming agent obtained in the step S1 and polyolefin according to the mass ratio of 25% to 75% in a double-screw extruder, and forming to obtain a composite polyolefin film;
s3, stretching and film making: soaking the composite polyolefin film obtained in the step S2 in water bath at 60-80 ℃ for 1-30 min, and stretching to remove the inorganic pore-forming agent to obtain a porous polyolefin film; the stretching adopts biaxial stretching, the transverse stretching ratio of the biaxial stretching is 1:10, and the longitudinal stretching ratio is 1:25.
2. The method for producing a porous polyolefin film material according to claim 1, wherein: the polyolefin in step S2 comprises one of polyethylene, polypropylene or polyvinyl chloride.
3. The method for producing a porous polyolefin film material according to claim 1, wherein: the temperature of the mixed melting in the step S2 is 120-200 ℃.
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