A method for the manufacture of an electrically charged fibrous filter from a highly molecular non-polar fiber material wherein a web film of the fiber material is continuously fed and stretched. At least one side of the stretched web film is homopolarly charged by a plurality of corona charging elements. The charged web film material is then fibrillated, collected and processed into a filter.
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10. A method for the manufacture of an electrically charged fibrous filter from a highly molecular non-polar material, comprising the steps of:
continuously feeding a film of said material; heating said film stretching said film along the longitudinal axis thereof as defined by the path of movement of said film; homopolarly electrically charging at least one side of said film; fibrillating the charged film into fiber material; and collecting the fiber material to form a filter.
30. A method for the manufacture of an electrically charged fibrous filter from a highly molecular non-polar material, comprising the steps of:
continuously feeding a film of said material; stretching said film in two stages along the longitudinal axis thereof as defined by the path of movement of said film, and including the step of applying heat to both said two stages; homopolarly charging said film in said second stage; fibrillating the charged film into fiber material substantially along said longitudinal axis; and collecting the fiber material to form a filter.
19. A method for the manufacture of an electrically charged fibrous filter from a highly molecular non-polar material, comprising the steps of:
continuously feeding a film of said material; heating said film; stretching said film; homopolarly electrically charging at least one side of said film; fibrillating the charged film into fiber material; and collecting the fiber material on a roller and simultaneously taking one or more layers lying on top of the other together from said roller to form a filter.
20. A method for the manufacture of an electrically charged fibrous filter from a highly molecular non-polar material, comprising the steps of:
continuously feeding a film of said material; heating said film; stretching said film; homopolarly electrically charging at least one surface of said film using a corona device spaced from the surface of said film whereby the electric charge is sprayed onto the surface of said film; fibrillating the charged material into fiber material; and collecting the fiber material to form a filter.
1. A method for the manufacture of an electrically charged fibrous filter from a high molecular non-polar material, comprising the steps of:
continuously feeding a film of high molecular isotactic polypropylene material at a rate of 12.2 meters per minute; stretching said film in two stages, said first stage of stretching stretches said film at a ratio of 1:6 at a temperature of approximately 110°C, said second stage of stretching stretches said film at a ratio of 1:1.5 at a temperature of substantially 130°C; homopolarly charging at least one side of the stretched film with a plurality of corona charging elements, said plurality of corona discharge elements being connected to minus 10 KV, said step of charging including the use of a metal plate connected to an opposite polarity voltage source and a grid whereby said charging corona elements are between said metal plate and said film, said metal plate being connected to a voltage of plus 3 KV, said grid being connected to a voltage of minus 2.3 KV, said corona charging elements being spaced substantially 5 mm from the means for supporting said film during said second stage of stretching; fibrillating the charged film into fiber material; and collecting the fiber material ; and processing the collected fiber material into a filter to form a filter. .Badd.
2. A method for the manufacture of an electrically charged fibrous filter from a high molecular non-polar material, comprising the steps of:
continuously feeding a film of high molecular isotactic polypropylene material at a rate of 12.2 meters per minute; stretching said film in two stages, said first stage of stretching stretches said film at a ratio of 1:6 at a temperature of approximately 110°C, said second stage of stretching stretches said film at a ratio of 1:1.5 at a temperature of substantially 130°C; homopolarly charging at least one side of the stretched film with a plurality of corona charging elements, said plurality of corona discharge elements being connected to minus 3.2 KV, said step of charging including the use of a metal plate connected to an opposite polarity voltage source whereby said charging corona elements are between said metal plate and said film and said metal plate being connected to a voltage of plus 3 KV, said corona charging elements being spaced substantially 5 mm from the means for supporting said film during said second stage of stretching; fibrillating the charged film into fiber material; and collecting the fiber material ; and processing the collected fiber material into a filter to form a filter. .Badd.
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16. A method for the manufacture of an electrically charged fibrous filter from a highly molecular non-polar material, comprising the steps of:
continuously feeding a film of said material; heating said film stretching said film; homopolarly electrically charging at least one side of said film; fibrillating the charged film into fiber material substantially in the longitudinal direction thereof as defined by the path of feeding of the film; and collecting the fiber material to form a filter.
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44. A method for the manufacture of an electrically charged fibrous filter from a highly molecular non-polar material, comprising the steps of:
continuously feeding a film of said material; stretching said film along the longitudinal axis thereof as defined by the path of movement of said film and including the step of applying heat to said film; homopolarly charging the stretched film on both surfaces thereof by spraying one surface with a charge of one polarity and spraying the other surface of said film with an equal charge of the opposite polarity; fibrillating the charged film into fiber material substantially along said longitudinal axis; and collecting the fiber material to form a filter.
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devices. 49. .Badd.An electret fibrous web having unique filtration properties prepared by a method comprising the steps of: continuously feeding a film of highly molecular non-polar material; heating said film; stretching said film along the longitudinal axis thereof as defined by the path of movement of said film; homopolarly electrically charging at least one side of said film; fibrillating the charged film into fiber material; and collecting the fiber material. .Baddend. 50. .Badd.An electret fibrous web having unique filtration properties prepared by a method comprising the steps of: continuously feeding a film of a highly molecular non-polar material; heating said film; stretching said film; homopolarly electrically charging at least one side of said film; fibrillating the charged film into fiber material substantially in the longitudinal direction thereof as defined by the path of feeding of the film; and collecting the fiber material. .Baddend. 51. .Badd.An electret fibrous web having unique filtration properties prepared by a method comprising the steps of: continuously feeding a film of a highly molecular non-polar material; heating said film; stretching said film; homopolarly electrically charging at least one side of said film; fibrillating the charged film into fiber material; and collecting the fiber material. .Baddend. 52. .Badd.An electret fibrous web having unique filtration properties prepared by a method comprising the steps of: continuously feeding a film of a highly molecular non-polar material; heating said film; stretching said film; homopolarly electrically charging at least one surface of said film using a corona device spaced from the surface of said film whereby the electric charge is sprayed onto the surface of said film; fibrillating the charged material into fiber material; and collecting the fiber material. .Baddend. 53. .Badd.An electret fibrous web having unique filtration properties prepared by a method comprising the steps of: continuously feeding a film of a highly molecular non-polar material; stretching said film along the longitudinal axis thereof as defined by the path of movement of said film and including the step of applying heat to said film; homopolarly charging the stretched film on both surfaces thereof by spraying one surface with a charge of one polarity and spraying the other surface of said film with an equal charge of the opposite polarity; fibrillating the charged film into fiber material substantially along said longitudinal axis; and collecting the fiber material to form a filter. .Baddend. 54. .Badd.An electret fibrous web comprising fibers which are fibrillated from a film and which contain electric charges embedded therein so as to enhance filtration properties of the web. .Baddend. 55. .Badd.A fibrous web of claim 54 in which said fibrillated-film fibers carry opposite charges on opposite sides of the fiber. .Baddend. |
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.Badd.This is a continuation reissue of application Ser. No. 315,139 filed Oct. 26, 1981, now abandoned, which is a division reissue of Ser. No. 929,680 filed July 31, 1978, now Re. 30,782. .Baddend.
The invention relates to a method for the manufacture of an electrically charged fibrous filter, whose fibre material consists of a high molecular non-polar substance.
Such a method is known in the art and from this method it appears that charging of fibre material in an electric field to obtain a charged fibrous filter is difficult because of electric breakdown through the pores of the material. Covering the electrodes, between which the forming field strength is applied, with a semi-conducting material, admittedly offers the possibility of bringing the fibre material to a higher charged state, but at the same time has the drawback that this state is reached only after a longer period of time.
It is the object of the invention to provide for a rapid manufacture of highly charged fibre filters.
According to the invention the method is characterized in that it comprises continuously feeding a film of the high molecular non-polar substance, stretching the film, homopolarly charging the stretched film with the aid of corona elements, fibrillating the stretched charged film, collecting the fibre material and processing the collected fibre material into a filter of the desired shape.
Because the risk of breakdown of charging a solid film material is much less than that of an open fibre material, a charging system known per se, operating much faster and much more effectively, comprising corona elements can be used.
In the preferential embodiment of the invention the film is locally bilaterally charged by means of corona elements that carry on either side of the film equal but opposite potentials. Thereby the film is charged to almost twice as high a voltage as by means of unilateral charging, at one and the same corona voltage.
Charging with the aid of corona elements in turn entails that the film can be fed continuously and be stretched into a well splittable material. This material can be fibrillated in several ways. For this purpose, a needle roller with metal needles running against the film is used with, surprisingly no substantial loss of charge.
Preferably, the fibre material is collected in layers onto a take-up roller and there processed into filter cloth of the thickness and shape desired by taking one or more layers, which are laying one on top of the other, together and at the same time from the roller.
The invention will now further be elucidated with reference to the following drawings, wherein.
FIG. 1 schematically shows an embodiment of a device in which, for the manufacture of a well splittable charged film, use has been made for the method according to the invention.
FIG. 2 shows an improved second stage for stretching a film with which the film can be provided with an injected charge on both surfaces.
FIG. 3 shows a preferential construction of a process stage have been are charged unipolarly, it is preferable to apply unipolarly unipolar charges of opposite polarity to the fibre. Even for bipolarly charged aerosols the filter mat can be composed of alternatively positively and negatively charged fibre layers. The unipolar charging can also be implemented by the two-stage charging of FIG. 2. Preferably, then the potential of plate 17 is chosen the same as that of spraying wires 25 and at spraying wires 30 a voltage is applied that is sufficiently negative of greater magnitude with respect to plate 17.
FIG. 3 shows a preferential embodiment of a charging step with corona elements 18, 19 on each side of the film carrying equal but opposite potentials. This charging step 18, 19 can follow a stretching step that is already known in the art. If, however, charging step 18, 19 coincides with the stretching step, then charging preferably is implemented in a furnace that is not shown.
FIG. 4 shows one of the applied charging devices 18 and 19 on an enlarged scale. Between spraying wires 25/30 and curved plates 12/17 over which film 1 is guided, there is a metal grid 27 so as to better distribute the charge that is injected by the thin corona wires. The charge the film acquires is determined by the potential of the grid. In case of a slow throughput rate the film is roughly charged up to the potential of the grid. An additional advantage of the device used is that the risk of dielectric breakdown of the film and also of a spark discharge to the bare parts of plates 12/17 is very small, because the grid screens the corona wires from the film. Due to this grid, it is also possible to feed the small corona wires with an alternating current instead of with a direct current, if so desired.
Metal plate 26 over spraying wires 25/30 is interconnected with grounded plates 12/17. Because plate 26 increases the corona formation considerably, the spraying intensity with an upper plate is substantially higher than in an arrangement without it.
In a simplified construction of the charging device, which gives a somewhat less uniform charging, the grid is left out. In that case plate 26, preferably, must be connected via terminal 32 to a positive voltage with respect to plate 12/17. For in case of a positive voltge on plates 26 there need not be applied a large negative corona voltage on the small corona wires. In fact the corona voltage can be halved, if the potential is chosen equal (but opposite) to that of the cornoa wires. This, too, reduces the risk of dielectric breakdown in the film considerably, particularly when the film is very thin.
A film of isotactic polypropylene with a thickness of 45μ and a width of 5 cm was stretched to a ratio of 1:6 over block 8 the temperature of which was 110°C In a second stage stretching and charging was implemented over plate 12 of a temperature of 130°C, at a stretching ratio of 1:1.5. The transport velocity was 12.2 m/min. In spraying device 18 placed over plate 12 corona wires 25 had been connected to -3.2 KV and top plate 26 to +3 KV. The distance from corona wires 25 to plate 12 amounted to 5 mm. The film was fibrillated with a needle roller of 60 rows, the needles of which stood 500μ apart. The charged fibrillate was spread to approx. 45 cm and wound up on roller 24 into a filter with a thickness of 3 mm.
The collection efficiency of this filter and an equivalent uncharged filter was tested with a heterodisperse NaCl aerosol at a linear air velocity of 10 cm/sec and an aerosol concentration of 15 mg-NaCl/m3. For comparison also a commercial filter made from glass fibres from 1 to 10μ was tested.
| ______________________________________ |
| filter initial pressure |
| weight penetration |
| loss |
| gram/m2 |
| % mm H2 O |
| ______________________________________ |
| charged filter |
| 163 0.5 1.5 |
| non-charged filter |
| 163 53 2.8 |
| filter with glass fibers |
| 167 21 5.0 |
| ______________________________________ |
The method of Example I was repeated, but the charging was now done with the spraying device of FIG. 3, with the voltage on the corona wires amounting to -10 KV and that on the grid to -2.3 KV. The processing into a filter was equal to that of the above mentioned example.
| ______________________________________ |
| filter initial pressure |
| weight penetration |
| loss |
| gram/m2 |
| % mm H2 O |
| ______________________________________ |
| charged filter |
| 163 0.3 1.1 |
| non-charged filter |
| 163 53 2.8 |
| ______________________________________ |
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