JP2001246211A - Method for manufacturing electret filter medium, electret filter medium and electret filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing an electret filter medium excellent in pleating processability, capable of highly keeping the collection efficiency of a filter and capable of avoiding pressure loss or structural pressure loss to the utmost, the electret filter medium and an electret filter. SOLUTION: The electret filter medium is manufactured by laminating a sheetlike article constituted of fibers and a porous artricle constituted of synthetic fibers so that the almost entire contact surfaces of them are bonded to form a laminate and electrifging-and-magnetizing the laminate to obain the electret filter medium. The electret filter medium and the electret filter are also disclosed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an electret filter medium, an electret filter medium and an electret filter, and more particularly, to a method for producing an electret filter medium for purifying air by adsorbing and removing fine particles in the air. The present invention relates to an electret filter medium produced by this method and an electret filter using the same.

[0002]

2. Description of the Related Art An electret filter is a filter capable of adsorbing and removing fine particles in the air by electrostatic force of a charge semipermanently fixed to a constituent filter fiber, and has a simple structure and a good effect of removing fine particles. Therefore, it is adopted for various uses. For example, air filters for purifying the air inside vehicles such as automobiles and railway vehicles, exhaust filters and main filters for vacuum cleaners, filters for air purifiers, filters for air conditioners, filters for intake and exhaust of OA equipment, air conditioning for buildings It is used for filters for clean rooms and filters for clean rooms. In such a field of use, the filter medium is fold-folded and used in order to keep the pressure loss of the filter low.

On the other hand, as an electretized fiber, a melt blown nonwoven fabric, a spunbonded nonwoven fabric, or a nonwoven fabric formed by slitting an electretized film into a fibrous shape and then forming a nonwoven fabric is used. Due to low rigidity, mechanical strength is insufficient,
There was a problem that it was difficult to fold the folds.

In order to solve this problem, there has been proposed an electret filter in which an electret nonwoven fabric and a network of synthetic fibers are heat-sealed over the entire surface, and a method for producing the same (see, for example, JP-A-1-194912). . In this production method, an electretized nonwoven fabric and a net of synthetic fibers are partially fused and integrated using an embossing roll, and the entire surface is thermally fused.

[0005]

However, in the manufacturing method according to the prior art, the heat applied to the electretized nonwoven fabric is excessively applied, so that the charge applied to the fibers is lost.
As a result, there is a problem that the electret effect is reduced and the collection efficiency of the filter is reduced. Moreover, since the embossing rolls are used for joining, the embossed pressed portion is completely crushed, which not only causes an increase in the pressure loss of the filter medium due to a decrease in the filtration area, but also causes a significant unevenness on the surface of the filter medium. In addition, due to the weak bonding of the part that is not embossed, the peeling of this part at the time of actual use causes the surface to become more uneven, resulting in a structural pressure loss when using folds. Is raised.

Further, an electret filter in which an electret-formed nonwoven fabric and a porous sheet are partially heat-sealed and a method for producing the same have been proposed (for example, Japanese Patent Application Laid-Open No. 3-293008). Since the fusion is partial, an increase in the structural pressure loss as described above is inevitable.

Therefore, an object of the present invention has been made in view of the above-mentioned problems of the prior art, and is not only excellent in crease folding workability, but also can maintain a high filter collection efficiency, and has a pressure loss of a filter medium. The object of the present invention is to provide a method for producing an electret filter medium, which can minimize pressure loss and structural pressure as much as possible, an electret filter medium produced by this method, and an electret filter using the same.

[0008]

The above object is achieved by the invention described in each claim. That is, the characteristic configuration of the method for manufacturing the electret filter medium according to the present invention is such that the sheet-like material made of the fiber and the contact surface of the porous material made of the synthetic fiber are bonded almost over the entire surface. Later, this is to be electretized.

[0009] According to this configuration, since the heating step is not performed after the electretization, the electret effect is not reduced due to the loss of the electric charge once the electret is formed. Collection efficiency does not decrease. In addition, since the sheet-like material and the porous material are joined over almost the entire surface, the surface of the filter medium is smooth, and when subjected to crease folding, the shape of the crease in the ventilation state is not easily deformed. It is possible to reliably suppress the increase in structural pressure loss as occurs in the filter medium of the technology. In addition, it is preferable that the joining at the contact surface between the sheet-like material and the porous material is performed on the entire surface, but it is sufficient that the joining is performed over substantially the entire surface.

Therefore, according to the present invention, the electret filter not only has excellent crease folding workability, but also can maintain a high filter collection efficiency, and can avoid pressure loss and structural pressure loss of the filter medium as much as possible. A method for producing a filter medium can be provided.

The porous material is composed of a core-sheath composite fiber made of two or more kinds of fiber components, wherein a high melting point component is disposed in a core and a low melting point component is disposed in a sheath.
It is preferable that the melting point of the low melting point component constituting the sheath is lower than the melting point of the sheet material.

According to this configuration, the mechanical strength is high, and the joining can be surely performed by a thermal treatment such as thermal fusion.
Moreover, heat shrinkage and the like hardly occur in the sheet-like material, so that it is excellent in appearance and convenient. As such a porous material, for example, a core-sheath conjugate fiber composed of a combination of polypropylene-polyethylene, a core-sheath conjugate fiber composed of a combination of polyethylene terephthalate-low-melting point copolymer polyester, which can be heat-fused at a relatively low temperature, and the like And the like.

[0013] The laminate of the sheet and the porous material by bonding is heated and pressed to a temperature lower than the melting point of the fibers constituting the sheet and higher than the melting point of the low melting point component fibers in the porous material. It is preferable to carry out.

According to this configuration, only the low-melting point component of the porous material can be heated and fused, and the two can be firmly joined.
The so-called dead space, which is not filtered by the sheet-like material, can be reduced as much as possible, and the increase in pressure loss can be effectively suppressed, and the surface unevenness can be reduced, even if folds are applied. In addition, the problem that the structural pressure loss increases during use as in the prior art can be more reliably prevented.

In this case, the bonding between the sheet-like material and the porous material is performed between rolls heated to a temperature lower than the melting point of the fibers constituting the sheet-like material and higher than the melting point of the low-melting component fibers in the porous material. It is preferable to perform the insertion and heat fusion. Roll clearance, rotation speed,
This is because, by appropriately selecting the diameter, the temperature control method, and the like, the sheet-like material and the porous material can be easily and reliably joined, which is convenient.

It is preferable that the fibers constituting the sheet are a spunbonded nonwoven fabric or a meltblown nonwoven fabric.

These nonwoven fabrics have high rigidity in strength,
However, raw material cost is low because of high productivity,
This is because the manufacturing cost of the filter medium can be reduced.

Further, a characteristic configuration of the electret filter medium according to the present invention is that the filter medium is manufactured according to any one of claims 1 to 4.

According to this structure, not only the rigidity is high and the folding processability is excellent, but also the collection efficiency of the filter can be maintained high, and the pressure loss and the structural pressure loss of the filter medium are minimized. A possible electret filter media can be provided.

Still further, a feature of the electret filter according to the present invention is that the electret filter medium of claim 5 is fold-folded and fixed to an outer frame.

According to this configuration, it is possible to provide an electret filter which can maintain the collection efficiency of the filter at a high level and can avoid the pressure loss and the structural pressure loss of the filter medium as much as possible.

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described in detail below. The method for manufacturing the electret filter medium of the present embodiment includes a sheet-like material made of fibers,
After laminating so that the contact surface with the porous material made of synthetic fiber is joined almost over the entire surface, this is made into an electret. The electret filter medium thus manufactured is folded in a fold, and an outer frame of a predetermined size is attached and fixed thereto, thereby manufacturing an electret filter.

The fibers constituting the sheet-like material include polypropylene, polyethylene, poly-3-methyl-1-butene, poly-4-methyl-1-pentene, polyvinylidene fluoride, polytetrafluoroethylene, polycarbonate, polystyrene, and polyvinylidene chloride. , Polyethylene terephthalate, polyamide, polyacrylonitrile,
Examples include insulating organic fibers such as polysulfone and polyphenylene oxide, and insulating inorganic fibers such as borosilicate glass and quartz glass. In particular, polypropylene, poly-3-methyl-1-butene, poly-4-methyl-1-pentene, polyvinylidene fluoride, polycarbonate and the like are preferable because they can increase the amount of accumulated charge when electretized.

The fibers constituting the sheet-like material may be either short fibers or long fibers, and various forms such as woven fabric, knitted fabric and non-woven fabric can be used as the aggregate form, and are spun-bonded non-woven fabric or melt-blown non-woven fabric. Is more preferable. Furthermore, the cross section of the fiber is also circular, triangular,
Various shapes such as rectangles and irregular shapes can be used. Fibers having a fiber diameter of 100 μm or less can be used.
Those having a thickness of 1 to 100 μm, particularly 0.5 to 70 μm, are preferred. This is because it is easy to manufacture and suitable for use as an air purifying filter. As the basis weight of the sheet made of a fiber, can be used and 1-200 g / m ^2, preferably having 5 to 100 g / m ^2, 10 to 50
g / m ² are more preferred. This is because low pressure loss can be achieved, which is advantageous in terms of cost.

The fiber material constituting the porous material can be arbitrarily selected from polypropylene, polyethylene, EVA (ethylene-vinyl acetate copolymer), polyester and the like. It is preferable to include a component that is 40 ° C. or lower. This is because the appearance of the sheet material is not changed by heat shrinkage or the like, and the sheet material and the porous material can be reliably joined at a lower temperature.

The form of the porous material may be any of various porous forms such as a net shape and a spongy shape, and the production method thereof is not particularly limited. Particularly, a mesh-like sheet composed of a core-sheath composite fiber composed of a combination of polypropylene and polyethylene, a core-sheath composite fiber composed of a combination of polyethylene terephthalate and a low-melting copolymer polyester, which can be heat-fused at a relatively low temperature. Are preferred. These are convenient because they have high mechanical strength and can be surely joined by a thermal treatment such as thermal fusion.

The thickness of the porous material is preferably about 0.05 to 2 mm, more preferably 0.1 to 1 mm. Although the opening shape and the opening ratio of the porous material are not particularly limited, the shape is preferably a circle, a square, a hexagon, a rhombus, and the like, and the opening ratio is preferably 80 to 99%. If the opening ratio is too small, the pressure loss (ventilation resistance) increases, which is not preferable.

Next, as a method of laminating a sheet-like material and a porous material, for example, a sheet-like material and a porous material composed of fibers containing a component having a lower melting point than the fibers constituting the sheet-like material are laminated. As a method of performing the above, these are simultaneously inserted between two rolls having a smooth surface and heated to a temperature not lower than the melting point of the low melting point component in the porous material and not higher than the melting point of the sheet-like material. By narrowing the gap between the rolls, a certain amount of rolling force is applied to the sheet-like material and the porous material,
A method such as passing between both rolls can be used. In this case, the temperatures of the two rolls may be set to the same predetermined temperature or may be set to different temperatures. As a method for setting the temperature of the roll (particularly, the roll surface temperature) to a predetermined temperature, a method of circulating a heating fluid inside the roll can be used. Further, the clearance between the two rolls, the roll rotation speed, the roll diameter, and the like can be appropriately selected according to the application and purpose.

Examples of the fiber aggregate form in the sheet-like material, for example, a method of electretization into a nonwoven fabric, include corona charging, electric field charging, hot electric field charging, and electron beam irradiation, but are not limited thereto. Instead, another charging method may be used as long as the charge is stably held at a high charge amount. In the case of corona charging or electric field charging, the electric field strength is preferably 10 kV / cm or more,
An electric field strength of 15 kV / cm or more is more preferable. In the case of electron beam irradiation, it is preferable to irradiate at about 0.1 to 1 Mrad.

[0030]

(Example 1) A sheet having a fiber diameter of 20
A core-sheath composite using a polypropylene spunbond nonwoven fabric (melting point 180 ° C.) having a thickness of 25 μm, a thickness of 0.2 μm and a basis weight of 25 g / m ² , and a porous material made of polypropylene at the core and polyethylene at the sheath (melting point 90 ° C.). Fabric weight 50 g / m ² , opening ratio 95%, thickness 0.4
mm mesh sheet was used. In a state where both are stacked, 10
It was inserted between two rolls having a smooth surface heated to 0 ° C., passed through both rolls under light pressure, and both were laminated, and then electretized by a corona charging method. The contact surfaces of the sheet-like material and the mesh-like sheet were thermally fused over the entire surface.

Comparative Example 1 In the same manner as in Example 1, a sheet-like material and a mesh-like sheet (however, a mesh-like porous sheet made of a polypropylene-polyethylene composite yarn containing no low-melting-point component) were prepared. After only the material was electretized under the same conditions as in Example 1, a sheet-like material and a net-like sheet were laminated under the same conditions as in Example 1. The contact surface between the sheet-like material and the net-like sheet was thermally fused over the entire surface.

(Example 2) A polypropylene melt meltblown nonwoven fabric (melting point: 180 ° C) having a fiber diameter of 2.3 µm, a thickness of 0.3 µm, and a basis weight of 30 g / m ² was used as a sheet-like material. ,
A net-like sheet having a basis weight of 50 g / m ² , an opening ratio of 95%, and a thickness of 0.4 mm, made of a core-sheath type conjugate fiber made of polyethylene (melting point 90 ° C.) was used. In a state where both are overlapped, it is inserted between two rolls having a smooth surface heated to 100 ° C. After passing between the two rolls with light pressure applied, the two are laminated, and then the corona charging method is used. Electretized. Sheet-like objects and net-like sheets
The contact surfaces were heat-sealed over the entire surface.

(Comparative Example 2) In the same manner as in Example 2, a sheet-like material and a mesh-like sheet (however, a mesh-like porous sheet made of a polypropylene-polyethylene composite yarn containing no low melting point component) were prepared. After only the material was electretized under the same conditions as in Example 2, a sheet-like material and a net-like sheet were laminated under the same conditions as in Example 2. The contact surface between the sheet-like material and the net-like sheet was thermally fused over the entire surface.

For Examples 1 and 2 and Comparative Examples 1 and 2, the collection efficiency of 0.3 μm particles at a wind speed of 10 cm / s was measured. Table 1 shows the results.

[0035]

[Table 1] From Table 1, the particle collection efficiency of Examples 1 and 2 in which the sheet-like material and the net-like sheet were laminated and then electretized was compared with those of Comparative Examples 1 and 2 in which the sheet-like material was electretized and then the net-like sheet was laminated. It turns out that it is excellent compared with the particle collection efficiency. However, the filter media of Example 1 and Comparative Example 1 are used for room air conditioners, automotive air conditioners, and for cleaning the intake and exhaust of copying machines.
In particular, since it is used for applications requiring low pressure loss, the collection efficiency is lower than those of Example 2 and Comparative Example 2, but the filter medium of Example 1 is superior to the filter medium of Comparative Example 1. It is clear that.

This is because, in the case of Comparative Examples 1 and 2, since the heat treatment was performed after the electret formation, the charge disappeared, whereas in the case of Examples 1 and 2, such a case was observed. Probably because it did not occur. When these are folded in a fold and fixed to a predetermined outer frame and ventilated, the fold shape is little changed and the pressure loss is kept low.

[Other Embodiments] (1) As a method of laminating a sheet-like material and a porous material, they are inserted between two rolls set at a predetermined temperature. Alternatively, together with this method, both rolls may be arranged in a housing controlled at a predetermined temperature, and the sheet-like material and the porous material may be inserted into this.

Alternatively, the sheet material and the porous material may be joined and laminated by using a hot press method in which the material is heated to a predetermined temperature and then pressed by a press.

(2) In the above embodiment, an example was shown in which a core-sheath composite fiber composed of composite fibers having different melting points was used as the porous material. A composite fiber having an island structure (comprising a low melting point component) may be used.

[0040]

As described above, according to the present invention, according to the present invention, not only the foldability is excellent but also the collection efficiency of the filter can be maintained high, and the pressure loss and the structural pressure loss of the filter medium can be reduced. A method of manufacturing an electret filter medium that can be avoided as much as possible, an electret filter medium manufactured by this method, and an electret filter using the same can be provided.

Claims (6)

[Claims] 1. Production of an electret filter medium in which a sheet-like material made of fibers and a porous material made of synthetic fibers are laminated so that the contact surfaces thereof are joined over substantially the entire surface, and this is electretized. Method. 2. The method according to claim 1, wherein the porous material is composed of a composite fiber formed in a core-sheath shape from two or more types of fiber components, wherein a high-melting component is disposed in a core and a low-melting component is disposed in a sheath. 2. The method for producing an electret filter medium according to claim 1, wherein the melting point of the low melting point component constituting the sheath is lower than the melting point of the sheet-like material. 3. The lamination of the sheet-like material and the porous material by bonding is heated to a temperature lower than the melting point of the fibers constituting the sheet-like material and higher than the melting point of the low-melting component fibers in the porous material. The method for producing an electret filter medium according to claim 2, which is performed by pressing. 4. The method for producing an electret filter medium according to claim 1, wherein the fibers constituting the sheet material are spunbonded nonwoven fabrics or meltblown nonwoven fabrics. 5. An electret filter medium produced according to claim 1. 6. An electret filter wherein the electret filter medium of claim 5 is crease-folded and fixed to an outer frame.