Preparation method of film-coated filter material

Abstract

The application discloses a preparation method of a film-coated filter material, which comprises the following steps: (1) uniformly mixing polytetrafluoroethylene resin and an extrusion aid to prepare a blank, and aging the blank to prepare a blank body; (2) extruding the blank body through two calender rollers to form a sheet, the roller surfaces of the two calender rollers have different roughnesses, so that the two surfaces of the sheet have different roughnesses; (3) longitudinally and transversely synchronously stretching the sheet to form a stretched film, and then shaping the stretched film; when shaping, the stretched film passes through a convex point roller to prepare a film with a point-shaped line on the surface, and the roughnesses of the two surfaces of the film are different; and (4) point-shapedly combining the film with a base material to prepare the film-coated filter material. Since the contact area of the film and the base material in the application can also reduce damage to the film during film coating, the service life of the film is improved, and the service life of the filter material is improved.

Description

TECHNICAL FIELD

[0001] The application relates to a preparation method of a film-coated filter material. BACKGROUND

[0002] Bag type dust removal is a technology for realizing particle matter capture by adopting a flexible medium as a core filter material, and the bag type dust removal has a high capture efficiency and a filtration efficiency of more than 99.9%, and is not affected by the nature of smoke dust, is a preferred technology for processing smoke dust, and has been widely applied to the cement industry.

[0003] At present, most of the bag type dust collectors adopt traditional filter materials such as needle felt materials, and belong to deep filtration, that is, separation is realized by relying on a micro dust particle layer intercepted on the filter material, and problems such as large filtration resistance and high backwashing frequency exist, which directly leads to short service life of the bag type dust collector, short ash removal period and complicated operation, and meanwhile, the bag type dust collector has a high price, and these factors limit the application of the bag type dust collector in industrial production. SUMMARY

[0004] In order to solve the above problems, the application provides a preparation method of a film-coated filter material.

[0005] (1) uniformly mixing polytetrafluoroethylene resin and a extrusion aid according to a set proportion to prepare a blank, aging the blank at low temperature, and then preparing a cylindrical blank body from the blank after aging;

[0006] (2) extruding the blank body through two calender rollers to form a sheet, the roller surfaces of the two calender rollers have different roughnesses, so that the two surfaces of the sheet have different roughnesses;

[0007] (3) longitudinally and transversely synchronously stretching the sheet to form a stretched film, and then shaping the stretched film; when shaping, the stretched film passes through a gap between a convex point roller and a smooth roller to prepare a thin film with a point-shaped line on the film surface, the roughnesses of the two surfaces of the thin film are different; the sheet is first deoiled before stretching, and the deoiling can be performed according to existing mature technologies;

[0008] (4) point-shapedly bonding the thin film and a base material to prepare a film-coated filter material. Preferably, the extrusion aid is aviation kerosene or isomeric alkane solvent oil.

[0009] The base material is selected from glass fiber cloth or needle felt.

[0010] In the application, the two surfaces of the sheet refer to the two surfaces in the thickness direction of the sheet, and the two surfaces of the thin film refer to the two surfaces in the thickness direction of the thin film.

[0011] In the present application, first, the blank is extruded by calender rollers to form a sheet with different roughness on both sides, so that a large number of micro recesses are formed on both sides of the sheet. During the stretching process, due to these recesses, strip-shaped grooves will be formed with the stretching of the sheet. When shaping, the convex points on the convex point roller can continue to form point-shaped lines on the film. When the film is bonded to the base material, due to the support of these grooves and point-shaped lines, the bonding area between the film and the base material can be reduced, thereby reducing the air permeation area of the film due to bonding, improving the air permeation area, and thus improving the air permeability. Since the contact area between the film and the base material is reduced, the damage to the film during coating is also reduced, the service life of the film is improved, and thus the service life of the filter material is improved. The coated filter material in the present application uses the film as the dust-facing surface when in use.

[0012] At present, the coated filter material is made by hot lamination or sizing. When hot lamination is performed, the pressure is mainly concentrated on the contact points between the base material and the film. The larger the contact area, the greater the damage to the film. Reducing the contact points not only improves the air permeability of the film, but also reduces the damage rate. When sizing is used, although it has little effect on the strength of the film, it has a greater effect on the air permeability of the film. When sizing is performed, all the pores at the contact between the film and the base material are blocked, which seriously affects the air permeability of the film.

[0013] The coated filter material prepared by the present application has an air permeability of 4.2-5.1 cm / s and a dust cleaning period of 590-630 s. The coated filter material produced by hot lamination has an air permeability of 2-3.0 cm / s and a dust cleaning period of 350-450 s. Due to the extension of the dust cleaning period, the service life of the coated filter material is improved.

[0014] Further, to ensure that the polytetrafluoroethylene resin can form a colloidal group, facilitating subsequent extrusion, the mass ratio of polytetrafluoroethylene resin to extrusion aid is 80:20-75:25.

[0015] Further, to ensure that the extrusion aid can completely penetrate into the polytetrafluoroethylene resin, so that the polytetrafluoroethylene resin particles can fuse together, the aging temperature of the blank is 45℃, and the aging time is 24h.

[0016] Specifically, the two calender rollers are a first calender roller and a second calender roller, wherein the roughness of the roller surface of the first calender roller is Ra 0.6-0.8 μm, and the roughness of the roller surface of the second calender roller is Ra 1.2-1.6 μm. Within the above roughness range, different depths of grooves can be formed on both sides of the film during the subsequent synchronous stretching process, and no cracks are generated. If the roughness is too large, cracks are easily generated on the film during the stretching process, affecting the quality of the film, and even making the film scrap. If the roughness is too small, grooves of sufficient depth cannot be formed during the stretching process, and sometimes grooves cannot be formed, so that a rough film surface cannot be formed.

[0017] Further, to ensure that a film with uniform thickness is formed after the stretching process, the variation range of the roughness of the roller surface of the second calender roller is ≤0.2 μm. If the variation of the roughness is too large, some areas with excessively large roughness form weak points, and during the stretching process, through holes are easily formed in these weak points, while areas with smaller roughness cannot be stretched sufficiently, so that the stretching magnitudes of different areas of the film are inconsistent, and the thickness uniformity of the film is poor.

[0018] Further, to ensure the smooth progress of the subsequent stretching, in step (2), the thickness of the sheet is 180-280 μm. When passing through the calender rollers, the polytetrafluoroethylene molecular chains in the blank are oriented to some extent, which is beneficial to the subsequent stretching.

[0019] Further, in step (3), when the longitudinal and transverse synchronous stretching is performed, the longitudinal stretching and the transverse stretching have the same ratio, the stretching ratio of the longitudinal stretching and the transverse stretching is 7-12 times, the stretching temperature is 230-250 °C, and the stretching speed is 16-20 m / min. Under the above stretching conditions, not only the stretching of the film can be smoothly completed, so that the air permeability of the film reaches the requirement, but also a large number of small recesses on the surface of the sheet can form a large number of strip-shaped grooves under the action of stretching, and the integrity of the film is maintained. The above stretching ratio is to make the film after stretching reach the set thickness. The stretching temperature and the stretching speed are to effectively improve the production efficiency on the premise of ensuring the quality. If the stretching temperature is too high, the flowability of the sheet increases, and the above recesses are easily formed into holes. If the stretching temperature is too low, the attraction between the polytetrafluoroethylene molecules is too large, and brittle fracture is easily generated during the stretching process. If the stretching speed is too large, the sliding speed of the polytetrafluoroethylene molecules cannot be synchronized with the stretching speed, causing a large number of fibers in the film to be broken, and the strength of the hard film.

[0020] Further, in step (3), when the shaping is performed, the shaping temperature is 354-355℃, the stretching film passes through the convex roller at a speed of 10-20m / min, and the extrusion force of the convex roller and the smooth roller on the stretching film is 0.1-5MPa. At the temperature and the speed of the stretching film passing through the convex roller, the re-arrangement of the polytetrafluoroethylene molecules in the film can be ensured, so that the mesh structure generated by the fibers in the film is kept stable, and the point pattern generated by the convex roller is kept stable, and the over-activity of the polytetrafluoroethylene molecules can be avoided, so that the groove generated by the concave part on the film disappears.

[0021] To avoid excessive extrusion on the stretching film, the stretching film passes through the gap between the convex roller and the smooth roller in the tangential direction. Under the extrusion force of the convex roller and the smooth roller on the stretching film, the over-extrusion on the stretching film can be avoided under the condition of forming the point pattern, so that the local over-thinning of the film is avoided, and the service life of the film is affected.

[0022] Specifically, the convex points on the roller surface of the convex roller have a mesh of 640-650, the diameter of the root of the convex point is 0.65-0.67μm, and the height of the convex point is 0.155-0.166μm. This design is mainly to make the dust better to generate the bridging phenomenon, reduce the contact area of the dust and the film, and facilitate the separation of the dust. The particle size of small particle dust is generally between 0.1-1μm, and when the diameter of the convex point is too large, the points on the baseband will be too dense, which will affect the bulging effect during the later stretching.

[0023] Further, in step (4), when the point-shaped lamination is performed, the side of the film with higher roughness faces the base material. This design can effectively reduce the bonding area between the film and the base material, maximize the air permeation area of the film, and reduce the air permeation loss. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 is a state diagram of the stretching film passing through the gap between the convex roller and the smooth roller. DETAILED DESCRIPTION

[0025] Firstly, the positional relationship between the convex roller and the smooth roller will be described. Please refer to Figure 1 , the convex roller and the smooth roller are rotatably installed on the rack, the convex roller and the smooth roller are arranged in the vertical direction, the center axes of the convex roller and the smooth roller extend in the horizontal direction and are located in the same vertical plane, the convex roller is located directly above the smooth roller, the convex roller and the smooth roller are steel rollers with heating jackets, in the working state, the stretching film passes through the gap between the convex roller and the smooth roller in the horizontal direction, and the point pattern is formed on the film under the extrusion of the convex roller and the smooth roller.

[0026] The convex point roller and the light roller are arranged in a vertical direction, and the stretched film passes through the gap between the convex point roller and the light roller in a horizontal direction, so that the stretched film passes through the gap between the convex point roller and the light roller in a tangential direction during work. When the stretched film passes through the gap between the convex point roller and the light roller, the convex point roller and the light roller simultaneously press on the stretched film to form a point pattern.

[0027] Example 1

[0028] The raw material used is DuPont 605XTX polytetrafluoroethylene dispersion resin, and aviation kerosene is mixed at a ratio of 80:20. After aging at 45°C for 24h, a cylindrical blank is prepared, and an extrusion rod is extruded. The blank is extruded by two calender rollers to form a sheet. The two calender rollers are an upper roller and a lower roller located below the upper roller. The roughness Ra of the surface of the upper roller is 0.6-0.8um, and the roughness Ra of the surface of the lower roller is 1.4-1.6um.

[0029] The rod is pressed into a sheet with a thickness of 180um by the two calender rollers. After deoiling the sheet at 100°C, bidirectional stretching is performed at a stretching ratio of 8 times, a temperature of 240°C, and a stretching line speed of 16m / min to form a stretched film. The stretched film is shaped at 350°C. During shaping, the stretched film passes through the gap between the convex point roller and the light roller in a horizontal direction at a speed of 12m / min, and the extrusion pressure of the convex point roller and the light roller on the stretched film is 0.2MPa. This causes the film surface to form regular protrusions, resulting in a thin film with a point pattern on the film surface, and the roughness of the two surfaces of the thin film is different. The convex points on the surface of the convex point roller have a count of 650, a root diameter of 0.65um, and a height of 0.155um.

[0030] After hot pressing the thin film and the glass fiber cloth, a glass fiber film-coated filter material is prepared. The glass fiber film-coated filter material has an air permeability of 4.8cm / s, and the dust filtration efficiency system is tested according to the standard ISO 11057-2011. The dust cleaning cycle reaches 600s. The specification of the glass fiber cloth is 750 type.

[0031] Example 2

[0032] The raw material used is Daikin F104 polytetrafluoroethylene dispersion resin, and aviation kerosene is mixed at a ratio of 77:23. After aging at 45°C for 24h, a cylindrical blank is prepared, and an extrusion rod is extruded. The blank is extruded by two calender rollers to form a sheet. The two calender rollers are an upper roller and a lower roller located below the upper roller. The roughness Ra of the surface of the upper roller is 0.6-0.8um, and the roughness Ra of the surface of the lower roller is 1.3-1.5um.

[0033] The material rod is pressed into a sheet with a thickness of 210 μm by two calender rollers. After the sheet is deoiled at 120°C, it is biaxially stretched at a draw ratio of 9 times, a temperature of 250°C, and a stretching line speed of 18 m / min to form a stretched film. The stretched film is shaped at 345°C, during which the stretched film passes through the gap between a convex roller and a smooth roller in the horizontal direction at a speed of 10 m / min, and the extrusion pressure of the convex roller and the smooth roller on the stretched film is 0.3 MPa, so that the film surface forms regular protrusions to make a film with a point-like texture, and the roughness of the two surfaces of the film is different. The number of convex points on the roller surface of the convex roller is 640, the diameter of the root of the convex point is 0.67 μm, and the height of the convex point is 0.165 μm.

[0034] After the film is hot-pressed and overlapped with the glass fiber cloth, a glass fiber film-coated filter material is prepared. The air permeability of the glass fiber film-coated filter material is 5.1 cm / s, and the dust filtration efficiency system is tested according to the standard ISO 11057-2011, and the dust cleaning period reaches 630 s. The specification of the glass fiber cloth is 750 type.

[0035] Example 3

[0036] The raw material used is Dongyue DF204 polytetrafluoroethylene dispersion resin, and aviation kerosene is mixed at a ratio of 76:24. After aging at 45°C for 24 h, a cylindrical blank is prepared, and the blank is extruded into a rod. The blank is extruded into a sheet by two calender rollers, i.e. an upper roller and a lower roller located below the upper roller. The roughness Ra of the roller surface of the upper roller is 0.6-0.8 μm, and the roughness Ra of the lower roller is 1.3-1.5 μm.

[0037] The material rod is pressed into a sheet with a thickness of 210 μm by two calender rollers. After the sheet is deoiled at 100°C, it is biaxially stretched at a draw ratio of 7 times, a temperature of 240°C, and a stretching line speed of 16 m / min to form a stretched film. The stretched film is shaped at 355°C, during which the stretched film passes through the gap between a convex roller and a smooth roller in the horizontal direction at a speed of 15 m / min, and the extrusion pressure of the convex roller and the smooth roller on the stretched film is 2 MPa, so that the film surface forms regular protrusions to make a film with a point-like texture, and the roughness of the two surfaces of the film is different. The number of convex points on the roller surface of the convex roller is 640, the diameter of the root of the convex point is 0.67 μm, and the height of the convex point is 0.165 μm.

[0038] After the film is hot-pressed and overlapped with the needle-punched felt, a needle-punched felt film-coated filter material is prepared. The air permeability of the needle-punched felt film-coated filter material is 4.2 cm / s, and the dust filtration efficiency system is tested according to the standard ISO 11057-2011, and the dust cleaning period reaches 590 s. The specification of the needle-punched felt is aramid needle-punched felt, with a grammage of 500 g / m 2 , and a thickness of 2.1 mm.

[0039] Example 4

[0040] The raw material used was giant JF-4D polytetrafluoroethylene dispersion resin, and aviation kerosene was mixed at a ratio of 75:25, and after aging at 45°C for 24h, a cylindrical blank was prepared, an extrusion rod was extruded, and the blank was extruded by two calender rollers to form a sheet, and the two calender rollers were an upper roller and a lower roller located below the upper roller, wherein the roughness Ra of the surface of the upper roller was 0.6-0.8um, and the roughness Ra of the surface of the lower roller was 1.2-1.4um.

[0041] The rod was pressed into a sheet with a thickness of 280um by two calender rollers, and after deoiling the sheet at 100°C, bidirectional stretching was performed at a stretching ratio of 12 times, a temperature of 230°C, and a stretching line speed of 20m / min to form a stretched film. The stretched film was shaped at 355°C, and during shaping, the stretched film passed through the gap between the convex roller and the smooth roller at a speed of 18m / min in the horizontal direction, and the extrusion force of the convex roller and the smooth roller on the stretched film was 5MPa, so that the film surface formed regular protrusions to make a thin film with a point-like pattern on the film surface, and the roughness of the two surfaces of the thin film was different. The number of convex points on the surface of the convex roller was 650, the diameter of the root of the convex point was 0.65um, and the height of the convex point was 0.166um.

[0042] After hot pressing the thin film and the needle felt, a needle felt film filter material was prepared, and the air permeability of the needle felt film filter material was 4.3cm / s, and the dust filtration efficiency system was tested according to standard ISO 11057-2011, and the dust cleaning cycle reached 610s. The type of needle felt was polyester needle felt, and the grammage was 500g / m 2 .

[0043] Comparative Example 1

[0044] The raw material used was DuPont 605XTX polytetrafluoroethylene dispersion resin, and aviation kerosene was mixed at a ratio of 80:20, and after aging at 45°C for 24h, a cylindrical blank was prepared, an extrusion rod was extruded, and the blank was extruded by two calender rollers to form a sheet, and the two calender rollers were an upper roller and a lower roller located below the upper roller, wherein the upper roller and the lower roller were both mirror surface rollers.

[0045] The rod was pressed into a sheet with a thickness of 180um by two calender rollers, and after deoiling the sheet at 100°C, bidirectional stretching was performed at a stretching ratio of 8 times, a temperature of 240°C, and a stretching line speed of 16m / min to form a stretched film. The stretched film was shaped at 350°C.

[0046] The film is hot-pressed and overlapped with the glass fiber cloth to form a glass fiber film-coated filter material. The glass fiber film-coated filter material has a gas permeability of 2.6 cm / s, and the dust filtration efficiency system is tested according to the standard ISO 11057-2011. The dust cleaning cycle reaches 410 s. The glass fiber cloth is the same as that in Example 1, and is a 750 type glass fiber cloth.

[0047] The comparative example is based on Example 1. The upper roller and the lower roller are replaced by mirror surface rollers, and the convex point roller and the corresponding mirror roller are removed.

[0048] Comparative Example 2

[0049] The raw material used is Dongyue DF204 polytetrafluoroethylene dispersion resin, and aviation kerosene is mixed at a ratio of 76:24. After aging at 45°C for 24h, a cylindrical blank is prepared, and an extruded rod is formed. The blank is extruded by two calender rollers to form a sheet. The two calender rollers are an upper roller and a lower roller located below the upper roller. Both the upper roller and the lower roller are mirror surface rollers.

[0050] The rod is pressed into a sheet with a thickness of 210μm by two calender rollers. After deoiling the sheet at 100°C, bidirectional stretching is performed at a stretching ratio of 7 times, a temperature of 240°C, and a stretching line speed of 16m / min to form a stretched film. The stretched film is shaped at 355°C.

[0051] The film is hot-pressed and overlapped with the needle-punched felt to form a needle-punched felt film-coated filter material. The needle-punched felt film-coated filter material has a gas permeability of 2.2 cm / s, and the dust filtration efficiency system is tested according to the standard ISO 11057-2011. The dust cleaning cycle reaches 380 s. The needle-punched felt is the same as that in Example 3, and is an aramid needle-punched felt.

[0052] The comparative example is based on Example 3. The upper roller and the lower roller are replaced by mirror surface rollers, and the convex point roller and the corresponding mirror roller are removed.

Claims

1. A method for preparing a membrane filter material, characterized in that, Includes the following steps: (1) After mixing polytetrafluoroethylene resin and extrusion aid in a set ratio, a blank is prepared. The blank is aged at low temperature, and then the aged blank is made into a cylindrical blank. (2) The billet is extruded by two calendering rolls to form a sheet with a thickness of 180-280μm. The two calendering rolls have different surface roughness, so that the two surfaces of the sheet have different surface roughness. The two calendering rolls are the first calendering roll and the second calendering roll, wherein the surface roughness of the first calendering roll is Ra0.6-0.8μm, the surface roughness of the second calendering roll is Ra1.2-1.6μm, and the variation range of the surface roughness of the second calendering roll is ≤0.2μm. (3) The sheet is stretched in both longitudinal and transverse directions simultaneously to form a stretched film. The ratio of longitudinal stretching to transverse stretching is the same, and the stretching ratio of longitudinal stretching to transverse stretching is 7-12 times. The stretching temperature is 230-250℃ and the stretching speed is 16-20m / min. Then the stretched film is shaped. During the shaping process, the stretched film passes through the gap between the convex roller and the smooth roller to form a film with dotted texture on the film surface. The roughness of the two surfaces of the film is different. The shaping temperature is 354-355℃. The speed of the stretched film passing through the convex roller is 10-20m / min. The extrusion pressure of the convex roller and the smooth roller on the stretched film is 0.1-5MPa. The mesh number of the convex dots on the roller surface of the convex roller is 640-650. The diameter of the root of the convex dot is 0.65-0.67μm and the height of the convex dot is 0.155-0.166μm. Both the convex roller and the smooth roller are steel rollers with heating jackets. (4) The film and the substrate are dot-bonded together, with the side of the film with higher roughness facing the substrate, and hot-pressed to form a membrane filter material; the substrate is made of glass fiber cloth or needle-punched felt.

2. The preparation method according to claim 1, characterized in that, The mass ratio of polytetrafluoroethylene resin to extrusion aid is 80:20-75:

25.

3. The preparation method according to claim 1, characterized in that, The aging temperature of the billet is 45℃ and the aging time is 24h.

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