JP3465761B2 - Electret filter - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a filter used for trapping fine particles mixed in a gas or a liquid, and has a low pressure loss without fluffing or delamination, although it is particularly bulky. And an electret filter having high collection efficiency.

[0002]

2. Description of the Related Art Japanese Patent Publication No. 56-47299 and Japanese Patent Publication No. 57-105217 disclose an electret filter composed of electret split fibers. The former discloses an electret filter in which only charged split fibers are collected, and the filter produced in that example has a composition of 0.0
It is estimated to have a relatively low bulk density of the order of 5 g / cc. Since the electret filter composed of such split fibers has a weak fiber entanglement force, the split fibers are often fluffed, which is not preferable as a filter in a field requiring precise filtration. The latter discloses an electret filter which is simply a mixture of electret split fibers and thinner non-electret fibers. This technique attempts to improve the mechanical trapping effect and prevent the trapping efficiency of the filter from being lowered by mixing thin electret fibers with electret fibers. However, even in the latter filter, there is a problem that the electret split fibers are often fluffed.

[0003]

DISCLOSURE OF THE INVENTION The present invention relates to a conventional bulky electret filter comprising electret split fibers, which eliminates the fluffing and delamination of split fibers generated on the front and back surfaces, and has a high collection efficiency with low pressure loss. It is intended to provide an electret filter having

[0004]

In the electret filter of the present invention, at least one heat-sealing fiber layer and an electret split fiber layer are laminated with the surface being a heat-sealing fiber layer, and mechanically in the thickness direction of the layer. The present invention relates to an electret filter having a fusion-bonded portion in which fibers are entangled to each other across layers by entanglement.

In the present invention, these multi-layered fiber layers are entangled by needle punching or air punching so that the packing density of the fibers does not increase in the thickness direction of the layer, and then fused by heating. Be integrated. Entangling of fibers is performed in the thickness direction over different fiber layers, electret split fibers are mixed in the heat fusion fiber layer, or heat fusion fibers are mixed in the electret split fiber layer,
The layers are integrated by a strong fusion bond, and despite the bulky filter, an electret filter without fluffing and delamination can be obtained.

In the present invention, the heat fusion fiber layer and the electret split fiber layer are laminated alternately in at least one layer, and an embodiment thereof before needle punching is illustrated in FIG. This embodiment comprises 7 layers, 1 is a heat fusion fiber layer, and 2 is an electret split fiber layer. The basis weight of the heat-sealing fiber layer is 5 to 30 g / m
² , more preferably 10 to 20 g / m ² , and the basis weight of the electret split fiber layer is 10 to 100 g / m ^2.
m ^2, more preferably from 20 to 50 g / m ^2, the electret filter is obtained by suppressing the generation of fluff and delamination of the electret split fibers In this range.

In the present invention, the heat-sealing fiber layer is a fiber layer in which a main fiber is melted by heat and is fused with an adjacent fiber, and the content of the heat-sealing fiber in the layer of the fibers is 50% or more. It is preferably 70% or more, more preferably 80% or more, and may be 100%. The fineness of the heat-fusible fiber used in the present invention is 1 to 100 denier, more preferably 3 to 50 denier, and most preferably 5 to 30 denier. As the cross section of the heat-sealing fiber, various shapes such as a round cross section and a short cross section are used. The heat-sealing fiber may be a resin having a single component or a resin having a plurality of components. Examples of the heat-bonding fibers composed of multiple components include cross-sectional shapes having a side-by-side structure and a sheath core structure. For example, for fibers having a sheath core structure, a resin whose melting temperature is lower in the sheath portion than in the core portion is used. Examples of such a combination include a combination of polyethylene or ethylene vinyl acetate copolymer for the sheath, a combination of polypropylene for the core, a copolymer polyester of which the sheath has a low melting temperature, and a combination of polyethylene terephthalate for the core. In this way, by combining resins having different melting temperatures and forming fibers having a low melting temperature on the surface of the fiber, only the surface portion can be melted at a predetermined temperature, and the shape of the internal fiber can be maintained as it is.

The content of electret split fibers in the electret split fiber layer in the present invention is 5
0% or more, preferably 70% or more, more preferably 80%
% Or more, and may be 100%. The higher the content, the more preferable because the filter exhibits high filtration performance. The electret split fiber in the present invention preferably maintains the surface charge density at a holding rate of 70% or more with respect to the value of the initial surface charge density at an ambient temperature of 120 ° C. This is because it is important to have sufficient collection efficiency even after the sheath component of the heat-sealed fiber is melted by heat and the bond between the fibers is achieved.

The resin of the electret split fiber in the present invention is a polyolefin-based polymer such as polypropylene, polyethylene or syndiotactic polystyrene, an α-polyolefin-based polymer such as poly-4-methyl-1-pentene, a fluorine-based polymer such as Teflon, and the like.
Examples include polycarbonate and polyester. A cast film is produced from these resins by melt extrusion, and then this film is stretched 5 to 10 times in the longitudinal or transverse direction to form a stretched film. After that, electret film is obtained by charging and electret film is obtained by splitting with an opening cutter to obtain fibers. The stretched film can be electretized by a charging method such as corona discharge, electric field discharge, electron beam irradiation, and triboelectric charging, or a combination of these charging methods.

In the present invention, it is preferable to use an additive in order to impart heat resistance to the electret split fiber. As such an additive, bis (4-t
-Butylphenyl) sodium, sodium 2,2'-
Resin modifiers such as ethylidene bis (4,6-di-t-butylphenyl) phosphate, tris (3,5-di-
t-Butyl-4-hydroxybenzyl) isocyanurate, 1,1,3-tris (2-methyl-4-hydroxy-5-t-butylphenyl) butane, 1,1bis (2 ′)
-Methyl-4'-hydroxy-5'-t-butylphenyl) butane, 2,2-thio-diethylenebis [3-
(3,5-di-t-butyl-4-hydroxyphenyl)
Propionate], 3,9-bis [2- {3-t-butyl-4-hydroxy-5-methylphenyl) propionyloxy} -1,1-dimethylethyl] -2,8,10
-Tetraoxaspiro [5,5] undecane, bis (2,4-di-t-butylphenyl) pentaerythritol diphosphite, bis (2,6-di-t-butyl-
4-methylphenyl) pentaerythritol diphosphite, ethylidenebis (4,6-di-t-butylphenyl) octylphosphite, tris- (2,4-di-)
an antioxidant such as t-butylphenyl) phosphite,
Heavy metal deactivators such as 3- (N-salicyloyl) amino-1,2,4-triazole, decanedicarboxylic acid disalicyloyl hydrazide, 2- (2'-hydroxy-
5'-methylphenyl) benzotriazole, 2-
(2'-Hydroxy-3'-t-butyl-5'-methylphenyl) -5-chlorobenzotriazole, 2,2 '
-Methylenebis [4- (1,1,3,3-tetramethylbutyl) -6- (2N-benzotriazol-2-yl) phenol], bis (5-benzoyl-4-hydroxy-2-methoxyphenyl) methane , Tetrakis (2,2,6,6-tetramethyl-4-piperidyl)-
1,2,3,4-butane tetracarboxylate, 1,
2,2,6,6-pentamethyl-4-piperidyl / β,
β, β ′, β′-tetramethyl-3,9- [2,4,8,
10-Tetraoxaspiro (5,5) undecane] diethyl (mixed) -1,2,3,4-butanetetracarboxylate Light stabilizers such as magnesium stearate, aluminum stearate, aluminum laurate Examples thereof include fatty acid metal salts. The addition amount of these varies depending on the type of additive,
A range of 0.05 to 5% by weight is effective.

As a split method for producing split fibers from an electret film, there is a method of splitting the film with a needle type cutter, a screw type cutter, a blade type cutter or the like. The average split width of the electret split fibers used in the present invention is 10 μm to 500 μm.
m, more preferably 20 μm to 300 μm, and most preferably 40 μm to 200 μm. The thickness of the electret film is preferably 3 μm to 30 μm. The surface charge density of the electret split fibers preferably has, but is not limited to, the maximum surface charge density given by the Loose equation.

In the present invention, after the heat fusion fiber layer and the electret split fiber layer are multilayered, the fibers are entangled in the layer thickness direction by needle punching. FIG. 2 is a cross-sectional view after needle punching, in which 1 is a heat fusion fiber layer, 2 is a split fiber layer, and 3 is an arrangement state of fusion parts of entangled fibers generated by needle punching for connecting layers. ing. As a result, the heat fusion fibers are arranged in the electret split fiber layer, and / or the electret split fibers are arranged in the heat fusion fiber layer in a direction substantially perpendicular to the thickness direction of the layer. The needle punching has a punch density of 10 to 500 punches / inch ² , more preferably 30 to ²⁰⁰ punches / inch ² , and most preferably 50 to 50 punches / inch ² .
It is 100 punches / inch ² . If the punch density exceeds this range, mixing of the heat fusion fiber and the electret split fiber is promoted, resulting in loss of bulkiness and fuzzing.

Next, when the multilayer is heat-treated in a heating oven, the heat-sealing fibers are fused and integrated with the electret split fibers or the heat-sealing fibers to obtain a bulky and fluff-free filter. The heat treatment temperature is determined by the melting point of the heat-sealing fiber used, and is preferably 130 ° C. for polyethylene and 120 ° C. for ethylene vinyl acetate copolymer or copolyester. When heat-treated at these temperatures for a short time, the electret split fiber has a very small decrease in the electret property, so that the decrease in the collection efficiency is not a problem. In the present invention, at least one layer of the heat fusion fiber layer and at least one layer of the electret split fiber layer are alternately laminated, but any one of the heat fusion fiber layer may be a reinforcing material. The reinforcing material here is a plastic net,
It is a non-woven fabric and is used to improve filter rigidity, filter handling, and to make the filter easier to pleats. This reinforcement can be on the surface of the filter or in the middle layer of the filter. In the present invention, the heat fusible fiber layer and the electret split fiber layer may be mixed with antibacterial fiber, deodorant fiber, aromatic fiber, flame-retardant fiber, fusible fiber or electret fiber within a range not losing the function of those fiber layers. I don't care. Hereinafter, the present invention will be described in more detail with reference to Examples.

[0014]

【Example】

Examples 1-3 Polypropylene with a thickness of 8.5 μm and an average split width of 65 μm
Made of pyrene (containing 0.3% aluminum laurate)
Ctlet film split fiber made of 20g
/ M²The electret split fiber layer and sheath
Polyethylene terephthalate core with polymerized polyester
10 g / m of basis weight of heat-sealing fiber²Thermal fusion fiber layer
(Fineness 4 denier) and the heat fusion fiber layers come on the front and back
So that 5 layers are stacked and then the punch density is 5
0, 100, 200 punches / inch ²Needle pad
Punched, then hot air orb at 120 ° C for 30 seconds
Filter 1 (Example 1) and fill
2 (Example 2) and filter 3 (Example 3)
Made The obtained filter has a wind velocity of 10
While flowing air at cm / sec, upstream and downstream of the filter
At the side, the atmospheric dust concentration of particles with a diameter of 0.3 μm
(RION) to measure the particle collection efficiency. Pressure
The force loss was read with a Manostar gauge. Filter
For fluff, fold a 10 cm square filter in two
And the fluff of the monofilament exceeding 2 mm at the apex of the fold
If there is a fluff, the filaments exceed 2 mm
When there was no fluff, it was determined that there was no fluff.

Comparative Examples 1 to 3 As a comparative example, the same electret split fiber layer as in Example 1 was needle punched at a needle punch density of 50,500 punches / inch ² , and the same conditions as in Example 1 were compared. Filters 1 and 2 were prepared. As Comparative Example 3, the punch density was 5 with the same fiber layer structure as in Example 1.
Needle punching was performed at 00 punches / inch ² to obtain a filter in the same manner. The results of these tests are shown in Table 1. Although Examples 1, 2, and 3 are similar to Comparative Examples 1 and 2 in filtering performance, a significant difference occurs in terms of fluffing. In Comparative Example 3, the density of the needle punch was too high, so that there was fuzz and a decrease in filtration performance was also recognized. Delamination was not a problem in any of Examples and Comparative Examples.

Example 4 An electret split fiber having the same specifications as in Example 1 was used. Electret split fiber layer having a basis weight of 40 g / m ^2, ethylene vinyl acetate copolymer and heat fusion fiber layer having a basis weight of 15 g / m ² of heat fusion fibers made of polypropylene (fibers 6 deniers) and this heat as a reinforcing material Net made of the same resin as the fiber (mesh size 4 mm, basis weight 50 g / m
² ) and the electret split fiber layer are overlapped as a middle layer, needle punching is performed with a punch number of 100 punches / inch ² , and an air slew type oven at 120 ° C. is used for 20 times.
Heat treatment was performed for a second to produce the filter of Example 4. The test results are shown in Table 2. Since the filter of Example 4 uses a net as a reinforcing material, it has excellent split workability and good wind pressure resistance, and fluffing did not occur even when the filter surface (heat fusion fiber layer side) was cleaned by air blow.

Example 5 An electret split fiber having the same specifications as in Example 1 was used.
Weight used 30g / m ²Electret split fiber
Fiber layer, basis weight 1 using the heat-sealing fiber having the same specifications as in Example 1
5 g / m²Heat-bonded fiber layer of, and basis weight as reinforcement material 1
2 g / m²Electrets with spunbond nonwoven fabric
Overlay the prit fiber layer as the middle layer and punch 50
Degree punch / inch²Needle punching with, then 12
Oven heat treated at 0 ° C. for 1 minute, filter of Example 5
Was produced. This filter is made of spunbond non-woven fabric.
Extremely excellent dimensional stability due to vertical and horizontal tension
I was there.

Comparative Example 4 As a comparative example, a comparative example 4 was prepared in the same manner as in example 1 except that the fiber layer having the same fiber layer structure as in example 1 was not needle punched. Although this filter had no fuzz, delamination easily occurred at the interface between the heat-sealing fiber layer and the electret split fiber layer.

[0019]

As described above, according to the present invention, the electret split fiber layers are alternately laminated with the heat-sealing fiber layers as the surface, and the fiber entanglement is performed across the layers in the thickness direction of these layers. By providing an electret filter that forms a fused portion, it is possible to provide an electret filter having high collection efficiency with low pressure loss without surface fluffing and delamination despite having bulkiness. it can.

[0020]

[Table 1]

[0021]

[Table 2]

[Brief description of drawings]

FIG. 1 is a schematic view showing a laminated state of an electret split fiber layer and a heat fusion fiber layer used in the present invention. In FIG. 1, 1: heat fusion fiber layer 2: electret split fiber layer

FIG. 2 is a sectional view of an electret filter according to the present invention. Reference numeral 1 is an electret split fiber layer, 2 is a heat fusion fiber layer, and 3 is a fusion portion of entangled fibers that connect these layers. In FIG. 2, 1: heat-fusion fiber layer 2: electret split fiber layer 3: entangled portion is shown.

Claims (4)

(57) [Claims] 1. At least one heat-sealing fiber layer and an electret split fiber layer are laminated with the surface being a heat-sealing fiber layer, and the fibers are entangled beyond the layers by mechanical entanglement in the thickness direction of these layers. An electret filter, characterized in that it has a fused fusion portion partially or entirely. 2. The electret filter according to claim 1, wherein any one of the heat-sealing fiber layers is a reinforcing material. 3. The electret filter according to claim 2, wherein the reinforcing material is a plastic net. 4. The electret filter according to claim 2, wherein the reinforcing material is a non-woven fabric.