CN103285747B - Three-dimensional PTFE microporous membrane for filtration and preparation method thereof - Google Patents

Abstract

The invention relates to a PTFE membrane for filtering and a manufacturing method thereof, in particular to a three-dimensional PTFE microporous membrane for filtering and a manufacturing method thereof. A kind of three-dimensional PTFE microporous membrane for filtering, described PTFE microporous membrane is a multi-layer membrane; The air permeability of described PTFE microporous membrane is 4-8 centimeters per second, elongation at break is 150-180%, average pore diameter 0.2-2.5 microns. The three-dimensional PTFE microporous membrane for filtration prepared by the invention can not only take into account the air permeability and tensile breaking strength at the same time, but also form fine protrusions through active treatment on the surface of the three-dimensional membrane, greatly improving surface activity and adhesion.

Description

A kind of three-dimensional PTFE microporous membrane for filtration and preparation method thereof

technical field

The invention relates to a PTFE membrane for filtering and a manufacturing method thereof, in particular to a three-dimensional PTFE microporous membrane for filtering and a manufacturing method thereof.

Background technique

Polytetrafluoroethylene (PTFE) has excellent high and low temperature resistance, outstanding chemical corrosion resistance, has the title of "King of Plastics", and good dielectric properties and hydrophobicity. The PTFE membrane prepared by using polytetrafluoroethylene as a raw material can better protect the filter substrate to prolong its service life, improve the filtration accuracy and filtration efficiency of the filter material, and meet the requirements of industrial environmental protection and clean production. The Chinese patent that the patent publication number is 101920559A (201-12-22) discloses a preparation method of polytetrafluoroethylene film and products thereof, although the polytetrafluoroethylene film prepared by the method has certain dimensional stability, but Air permeability is not high. At present, PTFE membrane is used as a membrane material with excellent performance for filtering and separating fine particles, and the important physical parameters to measure its performance are air permeability and tensile breaking strength. The former determines the difficulty of the dust-laden flue gas passing through the filter medium, which shows the transmission of the medium to the gas; while the latter determines the service life of the membrane, because the higher the fracture strength, the longer the service life. However, air permeability and tensile breaking strength are a pair of contradictions. Tensile breaking strength is the tensile breaking strength per unit area. The formula is strength P=strength F/sectional area S. The thicker the thickness, the smaller the cross-sectional area S. The greater the strength P, but the thicker the membrane, the lower the air permeability and the worse the filtration performance. How to make a PTFE microporous membrane with good air permeability and high tensile breaking strength has always been a technical problem for filter people.

At the same time, in order to exert its superior performance as a filter material, PTFE membrane material must be attached to the surface of the filter substrate for use. As we all know, PTFE has a small limit surface tension, low surface energy, and high inertia. It is difficult to bond with other materials and the firmness after bonding is not strong. Therefore, how to improve the surface activity of PTFE membrane materials and firmly adhere to the filter substrate Together is also one of the contents of the present invention's research.

Contents of the invention

The first object of the present invention is to provide a kind of three-dimensional PTFE microporous membrane for filtering in order to solve the above-mentioned technical problems. Another object of the present invention is to provide a method for preparing a three-dimensional PTFE microporous membrane for filtration. The three-dimensional PTFE microporous membrane for filtration prepared by the invention can not only take into account the air permeability and tensile breaking strength at the same time, but also form fine protrusions through active treatment on the surface of the three-dimensional membrane, greatly improving surface activity and adhesion.

The first object of the present invention is achieved by the following technical solutions: a kind of three-dimensional PTFE microporous membrane for filtration, the PTFE microporous membrane is a multilayer film; the air permeability of the PTFE microporous membrane is 4-8 cm/s, the elongation at break is 150-180%, and the average pore size is 0.2-2.5 microns.

The traditional PTFE film production adopts six processes of mixing, beating, extrusion, calendering, longitudinal drawing and horizontal drawing. In the extrusion section, the cylindrical billet enters the preforming cavity at the inlet end of the pushing cylinder for compaction, gradually fills the material cavity in the middle of the pushing cylinder, and finally forms the die opening through the pushing cylinder outlet. At this stage, the cross-sectional area of the blank is reduced from large to large, which is called the compression ratio (R·R), which is obtained from the quotient of the cross-sectional area S1 of the preforming cavity at the inlet end of the pushing cylinder and the cross-sectional area S2 of the forming die at the outlet end. The size of the compression ratio directly affects the quality of the membrane product. The larger the compression ratio, the thicker the film, the higher the strength, and the smaller the air permeability. In the traditional process, the extrusion section adopts a circular die, and what is extruded is a cylindrical film rod, which has a high compression ratio and good breaking strength. However, due to the use of a circular die, the widening ability is poor. When rolling, The material will flow to the middle and both sides at the same time, and the flow speed in the middle is often greater than that on both sides, which will cause tearing of the calendering belt or produce skirts, affecting the uneven distribution of air holes in the finished film, resulting in defective products and low yield . In the current advanced process, the die of the extrusion section is changed from a round die to a flat die, but it is a one-layer flat die, which improves the widening ability, and the film produced in this way has uniform air permeability, good air permeability, and high yield, but the disadvantage is that The breaking strength of the membrane is not high, and the service life is affected. Therefore, the inventor has changed the existing one-layer flat die into a multi-layer flat die through long-term research, so that what is extruded is a microscopically multi-layered flat die column, which is passed through calendering and longitudinal stretching and The film produced after the lateral expansion process is a three-dimensional film laminated together on the microcosmic level, which greatly increases the breaking strength of the film; Good air permeability while maintaining breaking strength, the air permeability of the PTFE microporous membrane obtained in the present invention is 4-8 cm/s, the elongation at break is 150-180%, and the average pore diameter is 0.2-2.5 microns.

In addition, at the same time, PTFE membrane material as a filter material must be attached to the surface of the filter substrate to exert its superior performance. However, the PTFE membrane prepared by the traditional method has small limit surface tension, low surface energy, high inertia, and it is difficult to bond with other materials and the firmness after bonding is not great. In order to improve the ability of the PTFE membrane to bond with other materials, the invention performs plasma treatment on the three-dimensional PTFE membrane, opens the nodules of the membrane to increase the air flow, and at the same time forms fine protrusions on the surface of the membrane to improve the surface activity and enhance the connection with the substrate. of lamination fastness. Plasma technology has the advantages of simplicity, rapidity, dry process, and modification only involves the surface of the material without affecting the structure and performance of the body. It uses various active particles such as ions, electrons, free radicals, and excited atoms generated by plasma. The principle of treating the material surface with molecules is that when high-energy particles in the plasma bombard the material surface, the energy is transferred, and its energy generally exceeds the bond energy of C-C, C-F or other C-containing bonds, so it can chemically or chemically interact with the material surface. The physical interaction makes the C-C and C-F bonds open, and a large number of free radicals are generated on the surface of the material. When in contact with nitrogen, peroxy radicals or peroxyl groups are rapidly formed and can exist stably for a long time at room temperature. Since peroxyl radicals mainly exist on the surface of PTFE, observed under a microscopic microscope, there are many small protrusions on the surface, and the surface is rough, creating conditions for lamination with glass fiber fabrics. However, in plasma technology, if the process is not properly controlled, such as the excitation power or frequency is not high, or the protrusions on the film surface are uneven, or even the surface layer is broken, but too low can not form effective protrusions; in addition, the vacuum is too small to make the reaction The purity is not high, resulting in the poor quality of the final prepared membrane, and the cost will increase a lot after the vacuum is too high, but the inventor has made the microporous membrane with a surface with a Uniform fine protrusions, these uniform fine protrusions greatly improve the adhesion fastness of the surface of the PTFE membrane material attached to the filter substrate.

Preferably, the microporous membrane is a multilayer membrane having protrusions on the surface with a density of 30,000-50,000 per square centimeter and a particle size of 0.1-4 microns.

Another object of the present invention is achieved by the following technical solutions: a kind of manufacture method of filtering three-dimensional PTFE microporous membrane as claimed in claim 1, it comprises the following steps successively:

a. Mixing: mix polytetrafluoroethylene powder and additives and stir evenly to obtain a mixture;

b. Blanking: first put the above mixture into an oven and infiltrate it with a sizing agent at 40-50°C, and then make a columnar blank column through a preforming device;

c. Extrusion: Extrude the above-mentioned columnar billet column flat die to form an extruded strip sheet by using a multi-layer superimposed flat unit; the extrusion pressure is 3.5-4.5MPa, and the extrusion speed is 1.5-5m/min. The width of the belt-out sheet is 200-500mm, and the thickness is 3.0-5.0mm;

d. Calendering: the above-mentioned extruded strip sheet is calendered under the action of a pressure roller with a line pressure of 20-25 kg/cm and a line speed of 1.5-5m/min to form a broadband with a thickness of 400-700 microns.

e. Longitudinal stretching: longitudinally stretching the above broadband at a temperature of 150-250°C to obtain a longitudinal baseband;

f. Lateral expansion: First, expand the above-mentioned longitudinal base tape laterally at a temperature of 150-350°C to form a transverse web, and then solidify and mold the transverse web at a temperature of 340-370°C to obtain a PTFE membrane blank;

g. Surface modification: first place the above-mentioned PTFE membrane blank in an acetone solution to soak to remove surface pollutants, then clean it with deionized water, then dry it in a vacuum and enter the plasma generator for surface modification treatment. A finished film is obtained.

Preferably, the auxiliary agent in step a is a mixture of emulsifier, coupling agent, binder and water; the weight ratio of the auxiliary agent to the polytetrafluoroethylene powder is 1:0.25.

Preferably, the wetting agent in step b is paraffin or kerosene; the weight ratio of the wetting agent to the polytetrafluoroethylene powder is 1:1.25.

Preferably, the soaking time in step b is 11-14 hours.

Preferably, in step b, the temperature at which the preforming device makes the columnar blank column is 40°C.

Preferably, the curing molding time in step f is 40-60 seconds.

Preferably, ultrasonic immersion is used for immersion in acetone solution in step g, and ultrasonic cleaning is used for deionized water cleaning in step g. Ultrasonic immersion can be more efficient and cleaner.

As preferably, the plasma generator described in step g is filled with nitrogen with a purity greater than 99%, and its pressure is controlled to be 1.8-2.2Pa, the excitation power is 80-120W, the frequency is 13.30-14.60MHz, and the vacuum degree is 65- 75Pa.

The preparation method of the three-dimensional PTFE microporous membrane of the present invention is also obtained through long-term research by the inventor, and through the cooperation of various process steps and process parameters, the effect of the three-dimensional PTFE microporous membrane of the present invention is achieved.

The beneficial effects of the present invention are:

1. The present invention changes the existing one-layer flat die into a multi-layer flat die, so that the three-dimensional film prepared by the multi-layer flat die can maintain good air permeability while improving the breaking strength.

2. In order to improve the bonding ability of PTFE membranes with other materials, the present invention carries out plasma treatment to three-dimensional PTFE membranes, opens the nodules of the membranes and increases the air flow while forming small protrusions on the surface of the membranes, improves surface activity, and promotes compatibility with other materials. Lamination fastness of substrate.

3. The preparation method of the three-dimensional PTFE microporous membrane of the present invention is also obtained through long-term research by the inventor, and through the cooperation of various process steps and process parameters, the effect of the three-dimensional PTFE microporous membrane of the present invention is achieved.

detailed description

This specific embodiment is only an explanation of the present invention, and it is not a limitation of the present invention. Those skilled in the art can make modifications to this embodiment without creative contribution as required after reading this specification, but as long as they are within the rights of the present invention All claims are protected by patent law.

Example 1

A kind of manufacture method of three-dimensional PTFE microporous membrane for filtering, polytetrafluoroethylene powder and auxiliary agent are mixed and stirred evenly, obtain mixing agent, and described auxiliary agent is emulsifier glycerin, silane coupling agent, silica gel adhesive and A mixture of water, wherein the weight ratio of the auxiliary agent to the polytetrafluoroethylene powder is 1:0.25. Then put the above mixture into an oven and soak paraffin or kerosene with a sizing agent at 40°C for 11 hours, and then make a columnar green column at 40°C through a preforming device, wherein the sizing agent and the poly The weight ratio of tetrafluoroethylene powder is 1:1.25. Then, the above-mentioned columnar base column flat die is extruded by a multi-layer laminated flat unit to form an extruded strip sheet, the pressure during extrusion is 3.5MPa, the extrusion speed is 1.5m/min, and the width of the extruded strip sheet is 200mm. The thickness is 3.0mm. The above-mentioned extruded strip sheet is calendered under the action of a pressure roller with a line pressure of 20 kg/cm and a line speed of 1.5m/min to make a wide band with a thickness of 400? Stretching produces a longitudinal base tape. Then the above-mentioned longitudinal base tape is laterally expanded into a transverse web at a temperature of 150° C., and then the transverse web is cured and formed at 340° C. The curing and molding time is 60 seconds. After curing and molding, a PTFE membrane blank is obtained; first Put the above-mentioned PTFE membrane blank in an acetone solution to soak away the surface pollutants, then clean it with deionized water, and then dry it in a vacuum and enter it into a plasma generator for surface modification treatment to obtain a finished membrane, in which acetone Ultrasonic leaching is used for immersion in the solution, and ultrasonic cleaning is used for deionized water cleaning. Ultrasonic cleaning is not only efficient but also clean. In addition, when performing surface modification treatment in the plasma generator, the plasma generator is filled with nitrogen with a purity greater than 99%, and then the dry PTFE sample is placed in the plasma area, the background pressure is 1.8Pa, and the mass flow rate is used to The nitrogen flow rate is controlled by the meter, and the discharge is performed after the pressure and light are stable. After a certain period of treatment, the discharge is stopped, the power is turned off, and the sample is exposed to the atmosphere for oxidation. The excitation power is 80W, the frequency is 13.30MHz, and the vacuum degree is 65Pa.

Example 2

A kind of manufacture method of three-dimensional PTFE microporous membrane for filtering, polytetrafluoroethylene powder and auxiliary agent are mixed and stirred evenly, obtain mixing agent, and described auxiliary agent is emulsifying agent, coupling agent, binding agent and water, wherein , the weight ratio of the auxiliary agent to the polytetrafluoroethylene powder is 1:0.25. Then put the above mixture into an oven and infiltrate it with paraffin wax or kerosene as a wetting agent at 45°C for 12 hours, and then make a columnar base column at 40°C through a preforming device, wherein the wetting agent and the polytetrafluoroethylene The weight ratio of vinyl fluoride powder is 1:1.25. Extrude the above-mentioned cylindrical billet column flat die to form an extruded strip sheet by using a multi-layer laminated flat unit; the pressure during the extrusion is 4.0MPa, the extrusion speed is 3.0m/min, and the width of the extruded strip sheet is 250mm. The thickness is 4.0mm. The above-mentioned extruded strip sheet was calendered under the action of a pressure roller with a line pressure of 22 kg/cm and a line speed of 3 m/min to form a wide band with a thickness of 550 microns. The above-mentioned wide band was stretched longitudinally at a temperature of 200° C. to obtain a longitudinal base band. Then the above-mentioned longitudinal base tape is laterally expanded into a transverse web at a temperature of 220° C., and then the transverse web is cured and molded at 355° C. The curing and molding time is 50 seconds. After curing and molding, a PTFE membrane blank is obtained; first Put the above-mentioned PTFE membrane blank in an acetone solution to soak away the surface pollutants, then clean it with deionized water, then dry it in a vacuum and enter it into a plasma generator for surface modification treatment to obtain a finished membrane; among them, acetone Ultrasonic leaching is used for immersion in the solution, and ultrasonic cleaning is used for deionized water cleaning. Ultrasonic cleaning is not only efficient but also clean. When performing surface modification treatment in the plasma generator, the plasma generator is filled with nitrogen with a purity greater than 99%, and the dry PTFE sample is placed in the plasma area. The background pressure is 2.0Pa, and the nitrogen gas is controlled by a mass flow meter. Flow rate, discharge after the pressure and light are stable, stop the discharge after a certain period of time, turn off the power and expose the sample to the atmosphere for oxidation. The excitation power is 100W, the frequency is 13.77MHz, and the vacuum degree is 70Pa.

Example 3

A kind of manufacturing method of three-dimensional PTFE microporous membrane for filtration, polytetrafluoroethylene powder and auxiliary agent are mixed and stirred uniformly, obtain mixture, wherein, described auxiliary agent is emulsifier, coupling agent, binding agent and water , the weight ratio of the auxiliary agent to the polytetrafluoroethylene powder is 1:0.25. Then put the above mixture into the oven and soak it with paraffin wax or kerosene as a wetting agent at 50°C for 14 hours, and then make a columnar green column at 40°C through a preforming device; the wetting agent and the polytetrafluoroethylene The weight ratio of the powder is 1:1.25. The above-mentioned columnar billet column flat die is extruded by a multi-layer laminated flat unit to form an extruded strip sheet; the pressure during the extrusion is 4.5MPa, the extrusion speed is 5m/min, and the extruded strip sheet is 500mm wide and thick. 5.0mm. The above-mentioned extruded strip sheet was calendered under the action of a pressure roller with a line pressure of 25 kg/cm and a line speed of 5 m/min to form a wide band with a thickness of 700 microns. The above-mentioned wide band was stretched longitudinally at a temperature of 250° C. to obtain a longitudinal base band. Then the above-mentioned longitudinal base tape is laterally expanded into a transverse web at a temperature of 350°C, and then the transverse web is cured and molded at a temperature of 340°C to 370°C. The curing and molding time is 60 seconds, and the PTFE film is obtained after curing and molding Blank; first place the above PTFE membrane blank in acetone solution to soak to remove surface pollutants, then clean it with deionized water, then dry it in vacuum and enter it into a plasma generator for surface modification treatment to obtain a finished membrane. Among them, ultrasonic immersion is used for immersion in acetone solution, and ultrasonic cleaning is used for deionized water cleaning. Ultrasonic cleaning is not only efficient but also clean. In addition, when performing surface modification treatment in the plasma generator, the plasma generator is filled with nitrogen with a purity greater than 99%, and the dry PTFE sample is placed in the plasma area, with a background pressure of 2.2Pa. Control the flow of nitrogen gas, discharge after the pressure and light are stable, stop the discharge after a certain period of time, turn off the power and expose the sample to the atmosphere for oxidation. The excitation power is 120W, the frequency is 14.60MHz, and the vacuum degree is 75Pa.

Comparative example 1

The comparative example is designed according to the technology taught by the patent publication number 101920559A (201-12-22). A method for preparing a polytetrafluoroethylene film, which is characterized in that it includes the following steps: (1) Mixing: mix polytetrafluoroethylene resin powder and liquid lubricant in a weight ratio of 1: (0.2 to 0.28) Stand at a temperature of 40°C to 80°C for 10 to 16 hours to mix the resin powder and liquid lubricant to form a polytetrafluoroethylene material; (2) Compacting and calendering: the polytetrafluoroethylene material is Press the blank into a cylindrical blank at a temperature of ℃ to 50℃, extrude the blank into a rod at a temperature of 40℃ to 60℃ through a pusher, and then roll it into a polystyrene at a temperature of 40℃ to 60℃ through a calender. Fluorovinyl tape; (3) Longitudinal stretching: stretch the polytetrafluoroethylene tape longitudinally in an oven at 180°C to 300°C to obtain a degreased base tape; (4) Transverse stretching and heat setting: degrease the The base tape is stretched transversely at 180°C-210°C, and then sintered at 250°C-380°C for 20-80 seconds to obtain a heat-set film; (5) Cooling water spray: spray the heat-set film Cooling water to obtain a polytetrafluoro microporous film with good qualitative balance in transverse and longitudinal dimensions.

The PTFE membrane that above-mentioned embodiment and comparative example make is carried out elongation at break, membrane surface average pore diameter, air permeability detection, and elongation at break of the present invention is detected by GB7689 regulation, and air permeability of the present invention is by the regulation of GB/T5453-1997 Detection, the specific test results are shown in Table 1:

Table 1 Example and Comparative Example Experimental Test Results

As can be seen from the test data in Table 1, the air permeability and elongation at break of the PTFE membrane manufactured by the embodiment of the present invention are much higher than those of the comparative example; in addition, the average pore diameter of the membrane surface of the comparative example is almost non-existent, which cannot be measured. It shows that the PTFE membrane prepared in the embodiment of the present invention not only has good breaking strength but also has good air permeability. the

Claims (8)

1. filter the manufacture method with three-dimensional PTFE microporous barrier, it is characterized in that: described PTFE microporous barrier is multilayer film; The air penetrability of described PTFE microporous barrier is 4-8 cel, and elongation at break is 150-180%, and average pore size is 0.2-2.5 micron;

Described microporous barrier is that to have density be 30000-50000/square centimeter on surface, and particle diameter is the multilayer film of the projection of 0.1-4 micron;

Its preparation method comprises the following steps successively:

A, batch mixing: polytetrafluoroethylene (PTFE) pulvis mixed with auxiliary agent and stirs, obtaining intermixture;

B, striking adobe: first above-mentioned intermixture to be inserted in baking oven and to infiltrate with size at 40-50 DEG C, then making column base post by pre-shaping device;

C, to extrude: adopt the flat unit of multilayer build-up that above-mentioned column base post flat-die is extruded formation and extrude band sheet material; Described when extruding pressure be 3.5 ~ 4.5MPa, extruded velocity is 1.5 ~ 5.0m/min, extrudes that to be with sheet material wide be 200 ~ 500mm, and thick is 3.0 ~ 5.0mm;

D, calendering: be with the online pressure of sheet material to be 20 ~ 25 kilograms per centimeter above-mentioned extruding, linear velocity is press and smooth under the pressure roller effect of 1.5 ~ 5m/min to make the broadband that thickness is 400 ~ 700 microns;

E, longitudinal stretching: above-mentioned broadband longitudinal stretching at the temperature of 150 ~ 250 DEG C is obtained longitudinal base band;

F, horizontal expanding: first by above-mentioned longitudinal base band horizontal expanding transversely web at 150 ~ 350 DEG C of temperature, then by described horizontal web curing molding at 340 ~ 370 DEG C, obtained PTFE film base;

G, surface modification: first above-mentioned PTFE film base is placed in acetone soln and embathes surface contaminant, cleaner by washed with de-ionized water, then enter in plasma generator after drying in a vacuum and carry out surface modification treatment, obtain finished film.

2. a kind of manufacture method of filtering with three-dimensional PTFE microporous barrier as claimed in claim 1, is characterized in that: auxiliary agent described in step a is the mixture of emulsifying agent, coupling agent, adhesive and water; The weight ratio of described auxiliary agent and described polytetrafluoroethylene (PTFE) pulvis is 1:0.25.

3. a kind of manufacture method of filtering with three-dimensional PTFE microporous barrier as claimed in claim 2, is characterized in that: size described in step b is paraffin or kerosene; The weight ratio of described size and described polytetrafluoroethylene (PTFE) pulvis is 1:1.25.

4. a kind of manufacture method of filtering with three-dimensional PTFE microporous barrier as claimed in claim 3, is characterized in that: the time infiltrated described in step b is 11-14 hour.

5. a kind of manufacture method of filtering with three-dimensional PTFE microporous barrier as claimed in claim 4, is characterized in that: in step b, pre-shaping device makes the temperature of column base post is 40 DEG C.

6. a kind of manufacture method of filtering with three-dimensional PTFE microporous barrier as claimed in claim 5, is characterized in that: in step f, the time of curing molding is 40-60 second.

7. a kind of manufacture method of filtering with three-dimensional PTFE microporous barrier as claimed in claim 6, is characterized in that: embathe in acetone soln in step g and adopt ultrasonic embathing; In step g, washed with de-ionized water adopts ultrasonic cleaning.

8. a kind of manufacture method of filtering with three-dimensional PTFE microporous barrier as claimed in claim 7, it is characterized in that: in plasma generator described in step g, be filled with the nitrogen that purity is greater than 99%, and to control its pressure be 1.8-2.2Pa, exciting power is 80-120W, frequency 13.30-14.60MHz, vacuum is 65-75Pa.