CN112275145B - Preparation method of polytetrafluoroethylene film for mask - Google Patents
Preparation method of polytetrafluoroethylene film for mask Download PDFInfo
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- CN112275145B CN112275145B CN202010974110.3A CN202010974110A CN112275145B CN 112275145 B CN112275145 B CN 112275145B CN 202010974110 A CN202010974110 A CN 202010974110A CN 112275145 B CN112275145 B CN 112275145B
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- -1 polytetrafluoroethylene Polymers 0.000 title claims abstract description 72
- 229920001343 polytetrafluoroethylene Polymers 0.000 title claims abstract description 71
- 239000004810 polytetrafluoroethylene Substances 0.000 title claims abstract description 71
- 238000002360 preparation method Methods 0.000 title claims abstract description 9
- 239000002994 raw material Substances 0.000 claims abstract description 129
- 239000000463 material Substances 0.000 claims abstract description 57
- 239000002131 composite material Substances 0.000 claims abstract description 38
- 238000000034 method Methods 0.000 claims abstract description 22
- 238000002156 mixing Methods 0.000 claims abstract description 22
- 238000007731 hot pressing Methods 0.000 claims abstract description 20
- 238000013329 compounding Methods 0.000 claims abstract description 18
- 150000001335 aliphatic alkanes Chemical class 0.000 claims abstract description 16
- 239000011347 resin Substances 0.000 claims abstract description 16
- 229920005989 resin Polymers 0.000 claims abstract description 16
- 239000006185 dispersion Substances 0.000 claims abstract description 15
- 239000000843 powder Substances 0.000 claims abstract description 13
- 238000012216 screening Methods 0.000 claims abstract description 10
- 238000009998 heat setting Methods 0.000 claims abstract description 8
- 239000004745 nonwoven fabric Substances 0.000 claims abstract description 7
- 238000003825 pressing Methods 0.000 claims abstract description 7
- 230000006835 compression Effects 0.000 claims description 22
- 238000007906 compression Methods 0.000 claims description 22
- 238000001125 extrusion Methods 0.000 claims description 20
- 239000005662 Paraffin oil Substances 0.000 claims description 12
- 238000012545 processing Methods 0.000 claims description 12
- 238000012546 transfer Methods 0.000 claims description 12
- 238000004804 winding Methods 0.000 claims description 10
- 238000001035 drying Methods 0.000 claims description 6
- 239000003350 kerosene Substances 0.000 claims description 2
- 239000012528 membrane Substances 0.000 abstract description 8
- 238000004519 manufacturing process Methods 0.000 abstract description 7
- 238000001914 filtration Methods 0.000 description 19
- 239000004744 fabric Substances 0.000 description 9
- 239000011248 coating agent Substances 0.000 description 8
- 238000000576 coating method Methods 0.000 description 8
- 239000010410 layer Substances 0.000 description 8
- 239000004743 Polypropylene Substances 0.000 description 7
- 229920001155 polypropylene Polymers 0.000 description 7
- 239000000758 substrate Substances 0.000 description 7
- 230000000694 effects Effects 0.000 description 5
- 230000035699 permeability Effects 0.000 description 5
- 230000001580 bacterial effect Effects 0.000 description 4
- 239000000835 fiber Substances 0.000 description 4
- 239000012982 microporous membrane Substances 0.000 description 4
- 238000005096 rolling process Methods 0.000 description 4
- 239000000126 substance Substances 0.000 description 4
- 239000002216 antistatic agent Substances 0.000 description 3
- 239000000446 fuel Substances 0.000 description 3
- 239000013618 particulate matter Substances 0.000 description 3
- 239000007888 film coating Substances 0.000 description 2
- 238000009501 film coating Methods 0.000 description 2
- 239000002245 particle Substances 0.000 description 2
- 239000011148 porous material Substances 0.000 description 2
- 230000029058 respiratory gaseous exchange Effects 0.000 description 2
- 230000005070 ripening Effects 0.000 description 2
- 229920002545 silicone oil Polymers 0.000 description 2
- GNFTZDOKVXKIBK-UHFFFAOYSA-N 3-(2-methoxyethoxy)benzohydrazide Chemical compound COCCOC1=CC=CC(C(=O)NN)=C1 GNFTZDOKVXKIBK-UHFFFAOYSA-N 0.000 description 1
- 241000894006 Bacteria Species 0.000 description 1
- 239000000853 adhesive Substances 0.000 description 1
- 230000001070 adhesive effect Effects 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 150000001875 compounds Chemical class 0.000 description 1
- 230000001276 controlling effect Effects 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 230000005611 electricity Effects 0.000 description 1
- 238000010438 heat treatment Methods 0.000 description 1
- 239000000203 mixture Substances 0.000 description 1
- 238000004886 process control Methods 0.000 description 1
- 230000001105 regulatory effect Effects 0.000 description 1
- 238000011160 research Methods 0.000 description 1
- 230000000241 respiratory effect Effects 0.000 description 1
- 238000007873 sieving Methods 0.000 description 1
- 239000002356 single layer Substances 0.000 description 1
- 230000003068 static effect Effects 0.000 description 1
- 230000001360 synchronised effect Effects 0.000 description 1
- 238000009423 ventilation Methods 0.000 description 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Chemical compound O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 1
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D71/00—Semi-permeable membranes for separation processes or apparatus characterised by the material; Manufacturing processes specially adapted therefor
- B01D71/06—Organic material
- B01D71/30—Polyalkenyl halides
- B01D71/32—Polyalkenyl halides containing fluorine atoms
- B01D71/36—Polytetrafluoroethene
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D46/00—Filters or filtering processes specially modified for separating dispersed particles from gases or vapours
- B01D46/54—Particle separators, e.g. dust precipitators, using ultra-fine filter sheets or diaphragms
- B01D46/543—Particle separators, e.g. dust precipitators, using ultra-fine filter sheets or diaphragms using membranes
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D67/00—Processes specially adapted for manufacturing semi-permeable membranes for separation processes or apparatus
- B01D67/0002—Organic membrane manufacture
Landscapes
- Chemical & Material Sciences (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Engineering & Computer Science (AREA)
- Manufacturing & Machinery (AREA)
- Shaping By String And By Release Of Stress In Plastics And The Like (AREA)
Abstract
The invention relates to a preparation method of a polytetrafluoroethylene film for a mask. Belongs to the technical field of polytetrafluoroethylene stretched films. The method comprises the following steps: mixing polytetrafluoroethylene dispersion resin micro powder with short-chain alkane oil, curing, and screening to obtain a first raw material and screen residues; preparing a second raw material by using the excess sieve material; respectively manufacturing a first blank and a second blank; respectively manufacturing a first rod-shaped object and a second rod-shaped object; respectively manufacturing a first raw material belt and a second raw material belt; preparing a composite raw material belt; preparing a pre-stretched film; transversely stretching to obtain a transversely stretched film; performing longitudinal stretching and heat setting simultaneously to obtain a biaxially oriented film; and (3) pressing the biaxial tension film and the non-woven fabric to form the polytetrafluoroethylene film for the mask. According to the invention, the raw material belts with different properties are prepared from the first raw material and the second raw material, then the raw material belts are subjected to hot-pressing compounding, and the membrane is prepared by a biaxial stretching process.
Description
Technical Field
The invention relates to a method for using a film for a mask, in particular to a preparation method for a polytetrafluoroethylene film for a mask. Belongs to the technical field of polytetrafluoroethylene stretched films.
Background
In the prior art, most of the films for masks are melt-blown fabrics made of polypropylene materials. Although polypropylene materials are cheap and easy to obtain, the cost of melt-blown equipment is high, so that the price of melt-blown cloth is always kept at a certain level. Especially, in recent half a year, the melt-blown fabric is influenced by epidemic situations, the melt-blown fabric price is high and far exceeds the value of the melt-blown fabric. In this case, a polytetrafluoroethylene film having more excellent performance is preferable as the mask film.
Compared with melt-blown cloth, the polytetrafluoroethylene film has the following advantages:
1. the fiber diameter of the polypropylene melt-blown cloth is 1-5 mu m, and the fiber diameter of the polytetrafluoroethylene membrane is 100-200 nm, so that the filtration precision is higher; effectively block bacteria and PM2.5 particles;
2. the polytetrafluoroethylene film is lighter and thinner, the thickness of the polytetrafluoroethylene film is 1/3-1/6 of melt-blown fabric, and the breathing resistance of the polytetrafluoroethylene film is only half of that of the melt-blown fabric;
3. the polytetrafluoroethylene film has better moisture permeability, and the water vapor generated by breathing can be better discharged.
The utility model discloses a utility model with application number CN201420594254.6 discloses a sub-high-efficient polytetrafluoroethylene microporous membrane combined material, including the substrate layer, bond line and polytetrafluoroethylene micropore rete, polytetrafluoroethylene microporous membrane and substrate complex be individual layer or multilayer film and individual layer or multilayer substrate complex. The low-resistance and high-efficiency composite material is prepared by sandwich compounding of a plurality of layers of PTFE and base materials, the respiratory resistance is within 150Pa, and the efficiency is more than 99.97%. Although the mechanical property of the PTFE microporous membrane is improved, the PTFE microporous membrane is not tightly bonded with the substrate layer due to the non-adhesiveness of the polytetrafluoroethylene resin, so that the phenomenon of leakage between interfaces is generated, and the filtering effect is finally influenced.
Disclosure of Invention
The invention aims to solve the technical problems and provides a polytetrafluoroethylene film-coating material for a mask, which has high filtering precision, high filtering efficiency and good film-coating fastness.
The technical scheme for solving the problems is as follows:
a preparation method of a polytetrafluoroethylene film for a mask comprises the following steps:
a. taking the polytetrafluoroethylene dispersion resin micro powder and the short-chain alkane oil according to the mass ratio of 1 (0.2-0.3), and mixing the taken raw materials in a three-dimensional mixer at high speed;
b. after uniformly mixing, curing for 12-24 h at 40-60 ℃ in a closed environment;
c. screening the aged raw materials to obtain screened materials and screened residual materials, wherein the screened materials are used as first raw materials for later use;
d. collecting the oversize materials, drying the oversize materials to obtain secondary processing materials, then taking the secondary processing materials and short-chain alkane oil according to the mass ratio of 1 (0.2-0.3), and mixing the taken raw materials in a three-dimensional mixer at a high speed; after uniformly mixing, curing for 1-5 h at 40-60 ℃ in a closed environment to obtain a second raw material for later use;
e. respectively placing the first raw material and the second raw material in a briquetting machine for prepressing to prepare a first blank and a second blank;
f. extruding the first blank and the second blank through a first pushing press and a second pushing press respectively to obtain a first rod-shaped object and a second rod-shaped object;
g. respectively enabling the first rod-shaped object and the second rod-shaped object to pass through a calender to prepare a first raw material belt and a second raw material belt;
h. after the first raw material belt and the second raw material belt are stacked, hot-pressing and compounding are carried out through a hot-pressing roller, and the composite raw material belt is prepared;
i. performing prestretching on the composite raw material belt at normal temperature to obtain a prestretched film; the pre-stretching comprises transverse pre-stretching and longitudinal pre-stretching, the longitudinal pre-stretching is performed prior to the transverse pre-stretching, the stretching ratio of the transverse pre-stretching is 3-5 times of the bandwidth of the composite raw material belt, the longitudinal pre-stretching is calculated by the growth rate of the composite raw material belt, and the growth rate is controlled to be 5-10% of that of the composite raw material belt;
j. transversely stretching the pre-stretched film in a first temperature section with the temperature of an oven being 200-280 ℃ to obtain a transversely stretched film; the stretching ratio of the transverse stretching is 3-6 times of the width of the pre-stretched film; removing short-chain alkane oil while stretching transversely;
k. longitudinally stretching the transversely stretched film in a second temperature range of the oven at the temperature of 280-320 ℃, and performing heat setting while longitudinally stretching to obtain a biaxially stretched film; the longitudinal stretching is calculated by the growth rate of the transverse stretching film, and the growth rate is controlled to be 10-30% of that of the transverse stretching film; continuously removing the short paraffin oil while stretching longitudinally;
and l, pressing the biaxial tension film and the non-woven fabric to form the polytetrafluoroethylene film for the mask.
In the prior art, the PTFE membrane material is used through a composite base material to make up the defect of poor mechanical property, but the PTFE membrane has non-adhesiveness and chemical stability, so that the surface adhesion effect of the PTFE membrane and other materials is poor.
In order to overcome the technical problem, the inventor adopts a first raw material and a second raw material, respectively prepares the first raw material belt and the second raw material belt, and then compounds the first raw material belt and the second raw material belt in a hot-pressing manner to form a composite raw material belt; the film obtained by stretching the composite raw material tape has better substrate adhesion compared with the conventional single-layer stretched film.
The first material is a screened material obtained by uniformly mixing polytetrafluoroethylene dispersion resin micro powder and short paraffin oil and curing; and drying the screen residue to obtain powder again, and then uniformly mixing the powder with the short paraffin oil again and curing to form a second raw material.
The second feedstock is different in molecular weight from the first feedstock. Because the polytetrafluoroethylene dispersion resin fine powder is not a uniform molecular weight substance, but a substance having a molecular weight within a certain range, such substances have similar physicochemical properties, and it is difficult to further separate them, which is not necessary in terms of production. The polytetrafluoroethylene dispersion resin micropowder of the same product produced by different manufacturers always has difference in specific quality, which is mainly caused by difference of process control. Therefore, the value ranges of the molecular weights of the polytetrafluoroethylene dispersion resin micro powder produced by some manufacturers are concentrated, the similarity between the components is high, and the quality is better. In the specific production practice, the polytetrafluoroethylene dispersion resin micro powder produced by foreign manufacturers is found to have more screened materials and less screened residues after the treatment of the steps a, b and c. And after the polytetrafluoroethylene dispersion resin micro powder produced by some domestic manufacturers is treated in the steps a, b and c, more screening materials are sieved, but more screening residues are also sieved. The inventor finds in further research that the biaxially oriented film produced after the screen residue is removed has higher filtration efficiency (up to 99.9995%), and has smaller fiber diameter and smaller pore diameter when observed under an electron microscope; the diameter of the fiber is between 100 and 150nm, and the aperture is between 0.2 and 0.5 μm. Obviously, the membrane has obvious improvement on air permeability, moisture permeability and filtration efficiency. But the production cost is not low because the screening residues are removed in the production process. In addition, such films have poor adhesion to woven or non-woven substrates and are difficult to laminate together by direct hot pressing; the use of adhesive for compounding significantly reduces the air permeability, moisture permeability and filtration efficiency of the membrane, which is naturally irreparable.
In order to solve the problem of compounding with the base material, the invention prepares the second raw material by processing the excess material of the screen. And then, preparing the second raw material into a second raw material belt, and performing hot-pressing compounding on the second raw material belt and the first raw material belt to form the composite raw material belt. In contrast, the molecular weight of the raw material of the first raw material tape is lower, and the molecular weight of the raw material of the second raw material tape is higher. Based on the composite raw material tape, the properties of the two surfaces of the polytetrafluoroethylene film prepared by stretching are slightly different. Wherein the side formed by the second material has a better affinity for the substrate.
More preferably, an antistatic agent is further added into the first raw material and the second raw material, wherein the antistatic agent is silicone oil, and the addition amount of the antistatic agent is 1-5 wt% of the mass of the first raw material and the mass of the second raw material respectively.
In the technical scheme of the invention, the addition of the silicone oil can obviously reduce the static electricity on the polytetrafluoroethylene film. Thereby improving the combination property of the polytetrafluoroethylene film and the base material.
In the above technical solution of the present invention, the base material to be combined with the film is generally selected from nonwoven fabrics made of polypropylene.
In the prior art, the problem of bow easily occurs when the raw material belt is stretched. "bowing" is a phenomenon of non-uniform transverse stretching occurring in the transverse drawing and heat treatment stages of tentering processing, and refers to a phenomenon that a line marked in a preheating zone (perpendicular to the machine direction) becomes bowed toward the entrance or exit side of a film after transverse stretching, occurring in the transverse drawing and heat setting (curing) after stretching. Bowing will cause differences in molecular orientation at the middle and edge of the film, which in turn leads to lateral differences in film properties. The inventors of the present invention have studied the effect of temperature on the stretching effect and have found that stretching becomes easier as the temperature is increased. Different temperature sections can thus be set in the stretching device to compensate as much as possible for the inhomogeneity of the stretching effect due to the flexibility of the material, but this is very demanding for the device. And when the composite raw material belt is adopted for stretching, the problems can be effectively alleviated. The inventor solves the technical problem by compounding the first raw material belt and the second raw material belt and then stretching the first raw material belt and the second raw material belt: the first compounding and the second stretching can make the fibril between two layers entangled and the node fused, so as to increase the stacking density of the interface layer and reach the aim of regulating and controlling the film microstructure in large range during stretching. Because the larger the bulk density of the interface layer is, the faster the stress transfer is during stretching, the smaller the pore diameter of the film is, and the thickness tends to be uniform. However, this does not mean that the parameters for stretching can be set as desired, and it has been found experimentally that the "bowing" phenomenon can be improved by performing the stretching after the pre-stretching. And since the transverse direction pre-stretching and the transverse direction stretching of the present invention are actually performed together based on the transverse direction stretching assembly of the stretching apparatus, the longitudinal direction stretching cannot be performed during this interval. Therefore, the invention is provided with longitudinal pre-stretching, transverse stretching and longitudinal stretching. Longitudinal pretension occurs between the unwind roll and the transverse tension module by virtue of the speed differential between the unwind roll and the transverse tension module. Longitudinal stretching occurs between the wind-up roll and the transverse stretching assembly by means of the speed difference between the wind-up roll and the transverse stretching assembly. The heat setting treatment is also performed simultaneously with the longitudinal stretching. Therefore, the fibril can be uniformly stretched, and the problems that the stretching in a large range occurs on local parts (two sides) and the stretching degree is not enough in the local part (middle) are avoided.
Preferably, in the step c, the sieve used in the sieving treatment is a 100-200 mesh sieve.
Preferably, in the above aspect, the short-paraffin oil is aviation kerosene.
Preferably, in the above aspect, the first presser control parameter is: the extrusion speed is 10-12 mm/min, the extrusion diameter is 18-20 mm, the length-diameter ratio L/D of the neck ring mold is 20-30, the cone angle is 40-50 degrees, and the compression ratio is 150-160; the second pusher control parameters are: the extrusion speed is 8-10 mm/min, the extrusion diameter is 18-20 mm, the length-diameter ratio L/D of the neck ring mold is 40-50, the cone angle is 20-30 degrees, and the compression ratio is 100-120.
Preferably, in the step g, the roll pressing temperature during rolling is 150 to 180 ℃.
Preferably, in the step h, the temperature of the compression roller is 150-180 ℃, the speed of the compression roller is 1-2 m/min, and the pressure of the compression roller is 0.5-1.0 MPa during hot-pressing compounding.
As a preferable mode of the above technical solution, the transverse pre-stretching and the transverse stretching are performed together based on a transverse stretching unit of a stretching device;
the transverse stretching assembly is divided into a transverse pre-stretching area and a transverse stretching area in the interval; the transverse pre-stretching area is a workshop temperature area, and the transverse stretching area is a first temperature area of the oven;
the transverse stretching assembly comprises a first chain clamp row positioned on one side of the stretching device and a second chain clamp row positioned on the other side of the stretching device, and the first chain clamp row and the second chain clamp row are formed by a plurality of chain clamps; the first chain clamp row and the second chain clamp row respectively run circularly and are synchronous;
the stretching rate of the transverse pre-stretching is controlled to be 3-5 times/20-30 s; the transverse stretching speed is 3-6 times/5-10 s, and the transverse pre-stretching and the transverse stretching are carried out in the following specific mode:
the first chain clamp row and the second chain clamp row evenly fix two sides of a workpiece, and the first chain clamp row and the second chain clamp row rotate synchronously along with the advancing direction of the workpiece, so that the distance between the first chain clamp row and the second chain clamp row is gradually expanded at a constant speed.
Preferably, the first chain clamp row and the second chain clamp row respectively comprise a workpiece feeding end, an intermediate working section, a workpiece releasing end and an intermediate conveying section, and the workpiece feeding end, the intermediate working section, the workpiece releasing end and the intermediate conveying section are sequentially connected end to form a dynamic closed cycle;
the first chain clamp row and the second chain clamp row are respectively switched from an open state to a closed state so as to engage and fix two sides of the workpiece;
the middle working section keeps the running speed of the first chain clamp row and the second chain clamp row consistent with the advancing speed of the workpiece;
the first chain clamp row and the second chain clamp row are respectively converted into an opening state from a closing state so as to release two sides of the workpiece;
in the intermediate transfer section, the first and second rows of chain grippers are transferred back to the workpiece feed end.
Preferably, the first and second chain gripper rows are each converted from an open state to a closed state when transitioning from the workpiece release end to the intermediate transfer section;
in the intermediate transfer section, the first chain gripper row and the second chain gripper row are transferred in a closed state;
when the middle conveying section is transited to the workpiece feeding end, the first chain clamp row and the second chain clamp row are respectively converted into an opening state from a closing state, and enter the workpiece feeding end in the opening state;
at the workpiece feeding end, the first chain clamp row and the second chain clamp row are respectively changed into a closed state from an open state, so that two sides of the workpiece are occluded and fixed, and the workpiece enters the middle working section in the closed state;
in the middle working section, keeping the running speed of the first chain clamp row and the second chain clamp row consistent with the advancing speed of the workpiece;
when the middle working section is transited to the workpiece release end, the first chain clamp row and the second chain clamp row are respectively converted into an open state from a closed state, so that two sides of the workpiece are released; so as to reciprocate.
Preferably, the longitudinal pre-stretching is realized based on a speed difference between an unwinding speed of the composite raw material tape and a traveling speed of the transverse stretching assembly.
Preferably, a winding step is further included between step K and step l, and the longitudinal stretching is realized based on a speed difference between a traveling speed and a winding speed of the transverse stretching assembly.
The invention has the following beneficial effects:
(1) the polytetrafluoroethylene membrane is prepared by adopting the first raw material and the second raw material to prepare raw material belts with different properties, then performing hot-pressing compounding on the raw material belts and the raw material belts, and performing biaxial stretching process.
(2) The polytetrafluoroethylene coating prepared by the invention has the filtering resistance of not more than 45Pa under the air flow of 32L/min, which is determined by a YG461G type full-automatic ventilation instrument.
(3) The polytetrafluoroethylene coating prepared by the invention has the particle filtering efficiency PFE of over 99.58 percent and the bacterial filtering efficiency BFE of 100 percent, which are determined by a GK-1000 type filter material comprehensive performance tester.
Detailed Description
The present invention will be described in further detail with reference to specific examples.
Example 1
A preparation method of a polytetrafluoroethylene film for a mask comprises the following steps:
a. taking the polytetrafluoroethylene dispersion resin micro powder and the short-chain alkane oil according to the mass ratio of 1:0.2, and mixing the taken raw materials in a three-dimensional mixer at high speed;
b. after being mixed evenly, the mixture is aged for 24 hours at 40 ℃ in a closed environment;
c. screening the cooked raw materials by using a 200-mesh sieve to obtain screened materials and screened residual materials, wherein the screened materials are used as first raw materials for later use;
d. collecting the oversize materials, drying the oversize materials to obtain secondary processing materials, taking the secondary processing materials and short-chain alkane oil according to the mass ratio of 1:0.2, and mixing the taken raw materials in a three-dimensional mixer at a high speed; after uniformly mixing, curing for 5 hours at 40 ℃ in a closed environment to obtain a second raw material for later use;
e. respectively placing the first raw material and the second raw material in a briquetting machine for prepressing to respectively prepare a first blank and a second blank;
f. extruding the first blank and the second blank through a first pushing press and a second pushing press respectively to obtain a first rod-shaped object and a second rod-shaped object;
g. respectively enabling the first rod-shaped object and the second rod-shaped object to pass through a calender to prepare a first raw material belt and a second raw material belt;
h. after the first raw material belt and the second raw material belt are stacked, hot-pressing and compounding are carried out through a hot-pressing roller, and the composite raw material belt is prepared;
i. performing prestretching on the composite raw material belt at normal temperature to obtain a prestretched film; the pre-stretching comprises transverse pre-stretching and longitudinal pre-stretching, the longitudinal pre-stretching is performed prior to the transverse pre-stretching, the stretching ratio of the transverse pre-stretching is 3 times of the bandwidth of the composite raw material belt, the longitudinal pre-stretching is calculated by the growth rate of the composite raw material belt, and the growth rate is controlled to be 5% of the composite raw material belt;
j. transversely stretching the pre-stretched film in a first temperature zone of an oven at the temperature of 250-280 ℃ to obtain a transversely stretched film; the stretching ratio of transverse stretching is 3 times of the width of the pre-stretched film; removing short-chain alkane oil while stretching transversely;
k. longitudinally stretching the transversely stretched film in a second temperature range of 280-300 ℃ of the oven, and performing heat setting while longitudinally stretching to obtain a biaxially stretched film; the longitudinal stretching is calculated by the growth rate of the transverse stretching film, and the growth rate is controlled to be 10 percent of that of the transverse stretching film; continuously removing the short paraffin oil while stretching longitudinally; preparing a biaxially oriented film;
l, rolling the biaxial stretching film;
and m, pressing and pasting the rolled biaxial tension film and the polypropylene non-woven fabric to form the polytetrafluoroethylene film for the mask.
In this example, the short paraffin oil is jet fuel. The polytetrafluoroethylene dispersion resin is under the trademark of JBP-108.
The first pusher control parameters are: the extrusion speed is 10mm/min, the extrusion diameter is 18mm, the length-diameter ratio L/D of the neck ring die is 20, the cone angle is 40 degrees, and the compression ratio is 150. The second pusher control parameters are: the extrusion speed is 8mm/min, the extrusion diameter is 18mm, the length-diameter ratio L/D of the neck ring die is 40, the cone angle is 20 degrees, and the compression ratio is 100. In the step h, the compression roller temperature is 150 ℃, the compression roller speed is 2m/min, and the compression roller pressure is 0.5Mpa during hot-pressing compounding.
The transverse pre-stretching and the transverse stretching are performed together based on a transverse stretching component of a stretching device;
the transverse stretching assembly is divided into a transverse pre-stretching area and a transverse stretching area in the interval; the transverse pre-stretching area is a workshop temperature area, and the transverse stretching area is a first temperature area of the oven;
the transverse stretching assembly comprises a first chain clamp row positioned on one side of the stretching device and a second chain clamp row positioned on the other side of the stretching device, and the first chain clamp row and the second chain clamp row are formed by a plurality of chain clamps; the first chain clamp row and the second chain clamp row respectively run circularly;
the stretching rate of the transverse pre-stretching is controlled to be 3-5 times/20-30 s; the transverse stretching speed is 3-6 times/5-10 s, and the transverse pre-stretching and the transverse stretching are specifically carried out by the following steps:
the first chain clamp row and the second chain clamp row evenly fix two sides of a workpiece, and the first chain clamp row and the second chain clamp row rotate synchronously along with the advancing direction of the workpiece, so that the distance between the first chain clamp row and the second chain clamp row is gradually expanded at a constant speed.
The first chain clamp row and the second chain clamp row respectively comprise a workpiece feeding end, a middle working section, a workpiece releasing end and a middle conveying section, and the workpiece feeding end, the middle working section, the workpiece releasing end and the middle conveying section are sequentially connected end to form dynamic closed circulation;
the first chain gripper row and the second chain gripper row are respectively converted from an open state to a closed state when the workpiece is transited from the workpiece releasing end to the middle conveying section;
the first chain clamp row and the second chain clamp row are respectively switched from an open state to a closed state so as to engage and fix two sides of the workpiece;
the middle working section keeps the running speed of the first chain clamp row and the second chain clamp row consistent with the advancing speed of the workpiece;
the first chain clamp row and the second chain clamp row are respectively converted into an opening state from a closing state so as to release two sides of the workpiece;
in the intermediate transfer section, the first and second rows of chain grippers are transferred back to the workpiece feed end.
More specifically:
in the intermediate transfer section, the first chain gripper row and the second chain gripper row are transferred in a closed state;
when the middle conveying section is transited to the workpiece feeding end, the first chain clamp row and the second chain clamp row are respectively converted into an opening state from a closing state, and enter the workpiece feeding end in the opening state;
at the workpiece feeding end, the first chain clamp row and the second chain clamp row are respectively changed into a closed state from an open state, so that two sides of the workpiece are occluded and fixed, and the workpiece enters the middle working section in the closed state;
in the middle working section, keeping the running speed of the first chain clamp row and the second chain clamp row consistent with the advancing speed of the workpiece;
when the middle working section is transited to the workpiece release end, the first chain clamp row and the second chain clamp row are respectively converted into an open state from a closed state, so that two sides of the workpiece are released; so as to reciprocate.
The longitudinal pre-stretching is realized based on the speed difference between the unwinding speed of the composite raw material belt and the advancing speed of the transverse stretching assembly.
And a winding step is further included between the step K and the step l, and the longitudinal stretching is realized based on the speed difference between the advancing speed and the winding speed of the transverse stretching assembly.
The polytetrafluoroethylene coating film obtained in this example had a filtration resistance of 44.8Pa at an air flow rate of 31.8L/min, as measured by a model YG461G full-automatic air permeameter.
The polytetrafluoroethylene coating prepared in the embodiment has a particulate matter filtering efficiency PFE of over 99.56% and a bacterial filtering efficiency BFE of 100% determined by a GK-1000 type filter material comprehensive performance tester.
Example 2
A preparation method of a polytetrafluoroethylene film for a mask comprises the following steps:
a. taking the polytetrafluoroethylene dispersion resin micro powder and short-chain alkane oil according to the mass ratio of 1:0.25, and mixing the taken raw materials in a three-dimensional mixer at high speed;
b. after mixing uniformly, ripening for 18h at 45 ℃ in a closed environment;
c. screening the cooked raw materials by using a 150-mesh sieve to obtain sieved materials and sieved residues, wherein the sieved materials are used as first raw materials for later use;
d. collecting the oversize materials, drying the oversize materials to obtain secondary processing materials, taking the secondary processing materials and short-chain alkane oil according to the mass ratio of 1:0.25, and mixing the taken raw materials in a three-dimensional mixer at a high speed; after uniformly mixing, curing for 2.5h at the temperature of 45 ℃ in a closed environment to obtain a second raw material for later use;
e. respectively placing the first raw material and the second raw material in a briquetting machine for prepressing to respectively prepare a first blank and a second blank;
f. extruding the first blank and the second blank through a first pushing press and a second pushing press respectively to obtain a first rod-shaped object and a second rod-shaped object;
g. respectively enabling the first rod-shaped object and the second rod-shaped object to pass through a calender to prepare a first raw material belt and a second raw material belt;
h. after the first raw material belt and the second raw material belt are stacked, hot-pressing and compounding are carried out through a hot-pressing roller, and the composite raw material belt is prepared;
i. performing prestretching on the composite raw material belt at normal temperature to obtain a prestretched film; the pre-stretching comprises transverse pre-stretching and longitudinal pre-stretching, the longitudinal pre-stretching is performed prior to the transverse pre-stretching, the stretching ratio of the transverse pre-stretching is 4 times of the bandwidth of the composite raw material belt, the longitudinal pre-stretching is calculated by the growth rate of the composite raw material belt, and the growth rate is controlled to be 8% of the composite raw material belt;
j. transversely stretching the pre-stretched film in a first temperature zone of an oven at the temperature of 240-250 ℃ to obtain a transversely stretched film; the stretching ratio of transverse stretching is 4 times of the width of the pre-stretched film; removing short-chain alkane oil while stretching transversely;
k. longitudinally stretching the transversely stretched film in a second temperature range of 280-300 ℃ of the oven, and performing heat setting while longitudinally stretching to obtain a biaxially stretched film; the longitudinal stretching is calculated by the growth rate of the transverse stretching film, and the growth rate is controlled to be 20 percent of that of the transverse stretching film; continuously removing the short paraffin oil while stretching longitudinally; preparing a biaxially oriented film;
l, rolling the biaxial stretching film;
and m, pressing and pasting the rolled biaxial tension film and the polypropylene non-woven fabric to form the polytetrafluoroethylene film for the mask.
In this example, the short paraffin oil is jet fuel. The polytetrafluoroethylene dispersion resin is under the trademark of JBP-108.
The first pusher control parameters are: the extrusion speed is 11mm/min, the extrusion diameter is 19mm, the length-diameter ratio L/D of the neck ring die is 25, the cone angle is 45 degrees, and the compression ratio is 155. The second pusher control parameters are: the extrusion speed is 9mm/min, the extrusion diameter is 19mm, the length-diameter ratio L/D of the neck ring die is 45, the cone angle is 25 degrees, and the compression ratio is 110. In the step h, the press roll temperature is 165 ℃, the press roll speed is 1.5m/min, and the press roll pressure is 0.8MPa during hot-pressing compounding.
The transverse pre-stretching and the transverse stretching are performed together based on a transverse stretching component of a stretching device;
the transverse stretching assembly is divided into a transverse pre-stretching area and a transverse stretching area in the interval; the transverse pre-stretching area is a workshop temperature area, and the transverse stretching area is a first temperature area of the oven;
the transverse stretching assembly comprises a first chain clamp row positioned on one side of the stretching device and a second chain clamp row positioned on the other side of the stretching device, and the first chain clamp row and the second chain clamp row are formed by a plurality of chain clamps; the first chain clamp row and the second chain clamp row respectively run circularly;
the stretching rate of the transverse pre-stretching is controlled to be 4 times/25 s; the rate of the transverse stretching is 4 times/8 s, and the transverse pre-stretching and the transverse stretching are specifically carried out by:
the first chain clamp row and the second chain clamp row evenly fix two sides of a workpiece, and the first chain clamp row and the second chain clamp row rotate synchronously along with the advancing direction of the workpiece, so that the distance between the first chain clamp row and the second chain clamp row is gradually expanded at a constant speed.
The first chain clamp row and the second chain clamp row respectively comprise a workpiece feeding end, a middle working section, a workpiece releasing end and a middle conveying section, and the workpiece feeding end, the middle working section, the workpiece releasing end and the middle conveying section are sequentially connected end to form dynamic closed circulation;
the first chain gripper row and the second chain gripper row are respectively converted from an open state to a closed state when the workpiece is transited from the workpiece releasing end to the middle conveying section;
the first chain clamp row and the second chain clamp row are respectively switched from an open state to a closed state so as to engage and fix two sides of the workpiece;
the middle working section keeps the running speed of the first chain clamp row and the second chain clamp row consistent with the advancing speed of the workpiece;
the first chain clamp row and the second chain clamp row are respectively converted into an opening state from a closing state so as to release two sides of the workpiece;
in the intermediate transfer section, the first and second rows of chain grippers are transferred back to the workpiece feed end.
More specifically:
in the intermediate transfer section, the first chain gripper row and the second chain gripper row are transferred in a closed state;
when the middle conveying section is transited to the workpiece feeding end, the first chain clamp row and the second chain clamp row are respectively converted into an opening state from a closing state, and enter the workpiece feeding end in the opening state;
at the workpiece feeding end, the first chain clamp row and the second chain clamp row are respectively changed into a closed state from an open state, so that two sides of the workpiece are occluded and fixed, and the workpiece enters the middle working section in the closed state;
in the middle working section, keeping the running speed of the first chain clamp row and the second chain clamp row consistent with the advancing speed of the workpiece;
when the middle working section is transited to the workpiece release end, the first chain clamp row and the second chain clamp row are respectively converted into an open state from a closed state, so that two sides of the workpiece are released; so as to reciprocate.
The longitudinal pre-stretching is realized based on the speed difference between the unwinding speed of the composite raw material belt and the advancing speed of the transverse stretching assembly.
And a winding step is further included between the step K and the step l, and the longitudinal stretching is realized based on the speed difference between the advancing speed and the winding speed of the transverse stretching assembly.
The polytetrafluoroethylene coating film obtained in this example had a filtration resistance of 42.7Pa at an air flow rate of 31.9L/min, as measured by a model YG461G full-automatic air permeameter.
The polytetrafluoroethylene coating prepared in the embodiment has a particulate matter filtering efficiency PFE of over 99.58% and a bacterial filtering efficiency BFE of 100% determined by a GK-1000 type filter material comprehensive performance tester.
Example 3
A preparation method of a polytetrafluoroethylene film for a mask comprises the following steps:
a. taking the polytetrafluoroethylene dispersion resin micro powder and short-chain alkane oil according to the mass ratio of 1:0.3, and mixing the taken raw materials in a three-dimensional mixer at high speed;
b. after mixing uniformly, ripening for 12h at 60 ℃ in a closed environment;
c. screening the cooked raw materials by using a 100-mesh sieve to obtain screened materials and screened residual materials, wherein the screened materials are used as first raw materials for later use;
d. collecting the oversize materials, drying the oversize materials to obtain secondary processing materials, taking the secondary processing materials and short-chain alkane oil according to the mass ratio of 1:0.3, and mixing the taken raw materials in a three-dimensional mixer at a high speed; after uniformly mixing, curing for 2h at 60 ℃ in a closed environment to obtain a second raw material for later use;
e. respectively placing the first raw material and the second raw material in a briquetting machine for prepressing to respectively prepare a first blank and a second blank;
f. extruding the first blank and the second blank through a first pushing press and a second pushing press respectively to obtain a first rod-shaped object and a second rod-shaped object;
g. respectively enabling the first rod-shaped object and the second rod-shaped object to pass through a calender to prepare a first raw material belt and a second raw material belt;
h. after the first raw material belt and the second raw material belt are stacked, hot-pressing and compounding are carried out through a hot-pressing roller, and the composite raw material belt is prepared;
i. performing prestretching on the composite raw material belt at normal temperature to obtain a prestretched film; the pre-stretching comprises transverse pre-stretching and longitudinal pre-stretching, the longitudinal pre-stretching is performed prior to the transverse pre-stretching, the stretching ratio of the transverse pre-stretching is 5 times of the bandwidth of the composite raw material belt, the longitudinal pre-stretching is calculated by the growth rate of the composite raw material belt, and the growth rate is controlled to be 10% of the composite raw material belt;
j. transversely stretching the pre-stretched film in a first temperature section with the temperature of an oven being 260-280 ℃ to obtain a transversely stretched film; the stretching ratio of transverse stretching is 6 times of the width of the pre-stretched film; removing short-chain alkane oil while stretching transversely;
k. longitudinally stretching the transversely stretched film in a second temperature range of 280-300 ℃ of the oven, and performing heat setting while longitudinally stretching to obtain a biaxially stretched film; the longitudinal stretching is calculated by the growth rate of the transverse stretching film, and the growth rate is controlled to be 30 percent of that of the transverse stretching film; continuously removing the short paraffin oil while stretching longitudinally; preparing a biaxially oriented film;
l, rolling the biaxial stretching film;
and m, pressing and pasting the rolled biaxial tension film and the polypropylene non-woven fabric to form the polytetrafluoroethylene film for the mask.
In this example, the short paraffin oil is jet fuel. The polytetrafluoroethylene dispersion resin is under the trademark of JBP-108.
The first pusher control parameters are: the extrusion speed is 12mm/min, the extrusion diameter is 20mm, the length-diameter ratio L/D of the neck ring die is 30, the cone angle is 50 degrees, and the compression ratio is 160. The second pusher control parameters are: the extrusion speed is 10mm/min, the extrusion diameter is 20mm, the length-diameter ratio L/D of the neck ring die is 50, the cone angle is 30 degrees, and the compression ratio is 120. In the step h, the compression roller temperature is 180 ℃, the compression roller speed is 1m/min, and the compression roller pressure is 1.0Mpa during hot-pressing compounding.
The transverse pre-stretching and the transverse stretching are performed together based on a transverse stretching component of a stretching device;
the transverse stretching assembly is divided into a transverse pre-stretching area and a transverse stretching area in the interval; the transverse pre-stretching area is a workshop temperature area, and the transverse stretching area is a first temperature area of the oven;
the transverse stretching assembly comprises a first chain clamp row positioned on one side of the stretching device and a second chain clamp row positioned on the other side of the stretching device, and the first chain clamp row and the second chain clamp row are formed by a plurality of chain clamps; the first chain clamp row and the second chain clamp row respectively run circularly;
the stretching rate of the transverse pre-stretching is controlled to be 5 times/30 s; the rate of the transverse stretching is 6 times/10 s, and the transverse pre-stretching and the transverse stretching are specifically carried out by:
the first chain clamp row and the second chain clamp row evenly fix two sides of a workpiece, and the first chain clamp row and the second chain clamp row rotate synchronously along with the advancing direction of the workpiece, so that the distance between the first chain clamp row and the second chain clamp row is gradually expanded at a constant speed.
The first chain clamp row and the second chain clamp row respectively comprise a workpiece feeding end, a middle working section, a workpiece releasing end and a middle conveying section, and the workpiece feeding end, the middle working section, the workpiece releasing end and the middle conveying section are sequentially connected end to form dynamic closed circulation;
the first chain gripper row and the second chain gripper row are respectively converted from an open state to a closed state when the workpiece is transited from the workpiece releasing end to the middle conveying section;
the first chain clamp row and the second chain clamp row are respectively switched from an open state to a closed state so as to engage and fix two sides of the workpiece;
the middle working section keeps the running speed of the first chain clamp row and the second chain clamp row consistent with the advancing speed of the workpiece;
the first chain clamp row and the second chain clamp row are respectively converted into an opening state from a closing state so as to release two sides of the workpiece;
in the intermediate transfer section, the first and second rows of chain grippers are transferred back to the workpiece feed end.
More specifically:
in the intermediate transfer section, the first chain gripper row and the second chain gripper row are transferred in a closed state;
when the middle conveying section is transited to the workpiece feeding end, the first chain clamp row and the second chain clamp row are respectively converted into an opening state from a closing state, and enter the workpiece feeding end in the opening state;
at the workpiece feeding end, the first chain clamp row and the second chain clamp row are respectively changed into a closed state from an open state, so that two sides of the workpiece are occluded and fixed, and the workpiece enters the middle working section in the closed state;
in the middle working section, keeping the running speed of the first chain clamp row and the second chain clamp row consistent with the advancing speed of the workpiece;
when the middle working section is transited to the workpiece release end, the first chain clamp row and the second chain clamp row are respectively converted into an open state from a closed state, so that two sides of the workpiece are released; so as to reciprocate.
The longitudinal pre-stretching is realized based on the speed difference between the unwinding speed of the composite raw material belt and the advancing speed of the transverse stretching assembly.
And a winding step is further included between the step K and the step l, and the longitudinal stretching is realized based on the speed difference between the advancing speed and the winding speed of the transverse stretching assembly.
The polytetrafluoroethylene coating film obtained in this example had a filtration resistance of 38.7Pa at an air flow rate of 32.0L/min, as measured by a model YG461G full-automatic air permeameter.
The polytetrafluoroethylene coating prepared by the embodiment has the particulate matter filtering efficiency PFE of more than 99.62% and the bacterial filtering efficiency BFE of 100% determined by a GK-1000 type filter material comprehensive performance tester.
Claims (10)
1. A preparation method of a polytetrafluoroethylene film for a mask comprises the following steps:
a. taking the polytetrafluoroethylene dispersion resin micro powder and the short-chain alkane oil according to the mass ratio of 1 (0.2-0.3), and mixing the taken raw materials in a three-dimensional mixer at high speed;
b. after uniformly mixing, curing for 12-24 h at 40-60 ℃ in a closed environment;
c. screening the aged raw materials to obtain screened materials and screened residual materials, wherein the screened materials are used as first raw materials for later use;
d. collecting the oversize materials, drying the oversize materials to obtain secondary processing materials, then taking the secondary processing materials and short-chain alkane oil according to the mass ratio of 1 (0.2-0.3), and mixing the taken raw materials in a three-dimensional mixer at a high speed; after uniformly mixing, curing for 1-5 h at 40-60 ℃ in a closed environment to obtain a second raw material for later use;
e. respectively placing the first raw material and the second raw material in a briquetting machine for prepressing to respectively prepare a first blank and a second blank;
f. extruding the first blank and the second blank through a first pushing press and a second pushing press respectively to obtain a first rod-shaped object and a second rod-shaped object;
g. respectively enabling the first rod-shaped object and the second rod-shaped object to pass through a calender to prepare a first raw material belt and a second raw material belt;
h. after the first raw material belt and the second raw material belt are stacked, hot-pressing and compounding are carried out through a hot-pressing roller, and the composite raw material belt is prepared;
i. performing prestretching on the composite raw material belt at normal temperature to obtain a prestretched film; the pre-stretching comprises transverse pre-stretching and longitudinal pre-stretching, the longitudinal pre-stretching is performed prior to the transverse pre-stretching, the stretching ratio of the transverse pre-stretching is 3-5 times of the bandwidth of the composite raw material belt, the longitudinal pre-stretching is calculated by the growth rate of the composite raw material belt, and the growth rate is controlled to be 5-10% of that of the composite raw material belt;
j. transversely stretching the pre-stretched film in a first temperature section with the temperature of an oven being 200-280 ℃ to obtain a transversely stretched film; the stretching ratio of the transverse stretching is 3-6 times of the width of the pre-stretched film; removing short-chain alkane oil while stretching transversely;
k. longitudinally stretching the transversely stretched film in a second temperature range of the oven at the temperature of 280-320 ℃, and performing heat setting while longitudinally stretching to obtain a biaxially stretched film; the longitudinal stretching is calculated by the growth rate of the transverse stretching film, and the growth rate is controlled to be 10-30% of that of the transverse stretching film; continuously removing the short paraffin oil while stretching longitudinally;
and l, pressing the biaxial tension film and the non-woven fabric to form the polytetrafluoroethylene film for the mask.
2. The method for preparing a polytetrafluoroethylene film for a mask according to claim 1, wherein the method comprises the steps of: in the step c, during screening treatment, the used screen is a 100-200-mesh screen.
3. The method for preparing a polytetrafluoroethylene film for a mask according to claim 1, wherein the method comprises the steps of: the short paraffin oil is aviation kerosene.
4. The method for preparing a polytetrafluoroethylene film for a mask according to claim 1, wherein the method comprises the steps of: the first pusher control parameters are: the extrusion speed is 10-12 mm/min, the extrusion diameter is 18-20 mm, the length-diameter ratio L/D of the neck ring mold is 20-30, the cone angle is 40-50 degrees, and the compression ratio is 150-160; the second pusher control parameters are: the extrusion speed is 8-10 mm/min, the extrusion diameter is 18-20 mm, the length-diameter ratio L/D of the neck ring mold is 40-50, the cone angle is 20-30 degrees, and the compression ratio is 100-120.
5. The method for preparing a polytetrafluoroethylene film for a mask according to claim 1, wherein the method comprises the steps of: in the step h, when hot-pressing compounding is carried out, the temperature of a compression roller is 150-180 ℃, the speed of the compression roller is 1-2 m/min, and the pressure of the compression roller is 0.5-1.0 Mpa.
6. The method for preparing a polytetrafluoroethylene film for a mask according to claim 1, wherein the method comprises the steps of: the transverse pre-stretching and the transverse stretching are performed together based on a transverse stretching component of a stretching device;
the transverse stretching assembly is divided into a transverse pre-stretching area and a transverse stretching area in the interval; the transverse pre-stretching area is a workshop temperature area, and the transverse stretching area is a first temperature area of the oven;
the transverse stretching assembly comprises a first chain clamp row positioned on one side of the stretching device and a second chain clamp row positioned on the other side of the stretching device, and the first chain clamp row and the second chain clamp row are formed by a plurality of chain clamps; the first chain clamp row and the second chain clamp row respectively run circularly;
the stretching rate of the transverse pre-stretching is controlled to be 3-5 times/20-30 s; the transverse stretching speed is 3-6 times/5-10 s, and the transverse pre-stretching and the transverse stretching are specifically carried out by the following steps:
the first chain clamp row and the second chain clamp row evenly fix two sides of a workpiece, and the first chain clamp row and the second chain clamp row rotate synchronously along with the advancing direction of the workpiece, so that the distance between the first chain clamp row and the second chain clamp row is gradually expanded at a constant speed.
7. The method for preparing a polytetrafluoroethylene film for a mask according to claim 6, wherein the method comprises the steps of: the first chain clamp row and the second chain clamp row respectively comprise a workpiece feeding end, a middle working section, a workpiece releasing end and a middle conveying section, and the workpiece feeding end, the middle working section, the workpiece releasing end and the middle conveying section are sequentially connected end to form dynamic closed circulation;
the first chain clamp row and the second chain clamp row are respectively switched from an open state to a closed state so as to engage and fix two sides of the workpiece;
the middle working section keeps the running speed of the first chain clamp row and the second chain clamp row consistent with the advancing speed of the workpiece;
the first chain clamp row and the second chain clamp row are respectively converted into an opening state from a closing state so as to release two sides of the workpiece;
in the intermediate transfer section, the first and second rows of chain grippers are transferred back to the workpiece feed end.
8. The method for preparing a polytetrafluoroethylene film for a mask according to claim 7, wherein the method comprises the steps of:
the first chain gripper row and the second chain gripper row are respectively converted from an open state to a closed state when the workpiece is transited from the workpiece releasing end to the middle conveying section;
in the intermediate transfer section, the first chain gripper row and the second chain gripper row are transferred in a closed state;
when the middle conveying section is transited to the workpiece feeding end, the first chain clamp row and the second chain clamp row are respectively converted into an opening state from a closing state, and enter the workpiece feeding end in the opening state;
at the workpiece feeding end, the first chain clamp row and the second chain clamp row are respectively changed into a closed state from an open state, so that two sides of the workpiece are occluded and fixed, and the workpiece enters the middle working section in the closed state;
in the middle working section, keeping the running speed of the first chain clamp row and the second chain clamp row consistent with the advancing speed of the workpiece;
when the middle working section is transited to the workpiece release end, the first chain clamp row and the second chain clamp row are respectively converted into an open state from a closed state, so that two sides of the workpiece are released; so as to reciprocate.
9. The method for preparing a polytetrafluoroethylene film for a mask according to claim 6, wherein the method comprises the steps of: the longitudinal pre-stretching is realized based on the speed difference between the unwinding speed of the composite raw material belt and the advancing speed of the transverse stretching assembly.
10. The method for preparing a polytetrafluoroethylene film for a mask according to claim 6, wherein the method comprises the steps of: and a winding step is further included between the step K and the step l, and the longitudinal stretching is realized based on the speed difference between the advancing speed and the winding speed of the transverse stretching assembly.
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