JPH0747098B2 - Filter material - Google Patents

Description

TECHNICAL FIELD The present invention relates to a filter medium, and more particularly to a filter medium which is used for air conditioning of various facilities, a pre-filter for clean rooms, etc., and has a low pressure loss and a high durability that can withstand long-term use. The present invention relates to a filter material for an air filter.

[Prior Art] In recent years, attempts have been made to apply a non-woven fabric of permanently charged (electretized) ultrafine fibers as a filter material for a high-performance air filter. This is intended to hold dust and the like by the attraction of static electricity due to charging. Although the non-woven fabric has the advantage of high particle removal efficiency, it has the drawback of having a low bending rigidity when compared with the conventionally used glass fiber filter paper. That is, when the nonwoven fabric alone is bent and used as a filter medium for an air filter, the filter medium is largely deformed due to pressure loss, so that the filter mediums are overlapped with each other to cause an increase in pressure loss at an early stage or insufficient strength. Because of the poor dimensional stability, it was inconvenient to use it as a filter material of high precision. Attempts have also been made to increase the areal weight in order to improve the strength and rigidity of the nonwoven fabric, but the initial pressure loss as a filter medium became too large, and it could not be substituted for the glass fiber filter paper.

[Problems to be Solved by the Invention] In order to solve the above problems, an auxiliary member (backing material) having high air permeability and rigidity is pasted with a liquid or powder adhesive on the downstream side of a non-woven fabric of electretized ultrafine fibers. Attempts have also been made to increase the rigidity of the ultrafine fibers by combining them. Although this method is effective in improving the rigidity of the nonwoven fabric, a large amount of adhesive is required to obtain high adhesive strength, the adhesive causes clogging of the nonwoven fabric, and as a result, pressure loss increases and service life is extended. The tendency of shortening was recognized. On the other hand, if the amount of adhesive used is as small as possible, the pressure loss can be reduced and the service life can be extended, but there is a problem that delamination occurs between the nonwoven fabric and the backing material during the assembly process of the dust collector. It was

In order to solve the above problems, the present invention has been made as a result of extensive studies, and it is an object of the present invention to provide a high-performance air filter medium having a low pressure loss and long-term use without delamination. To do.

[Means for Solving the Problems] The constitution of the present invention which has been able to solve the above-mentioned problems is a filter medium in which an upstream side and a downstream side are constituted by a non-woven fabric layer, and the non-woven fabric layer on the upstream side has the entire surface. Or part of it is composed of a heat-sealing material with a core-sheath structure or a side-by-side structure and has a fineness of 0.
5 to 6 denier fibers are used, which is composed of a non-woven fabric layer having a density gradient such that the fiber packing density increases in the depth direction,
The downstream non-woven fabric layer is composed of a non-woven fabric layer composed of electretized fine fibers having an average fineness of 0.01 to 0.1 denier, and the boundary portion between the upstream non-woven fabric layer and the downstream non-woven fabric layer is the upstream side. The essential point is that the heat-fusible material constituting the above is integrated by heat fusion.

[Operation] First, in the present invention, it is important that the non-woven fabric arranged on the upstream side of the gas flow uses fibers whose surface is wholly or partially made of a heat-fusible material.

The core-sheath structure fibers mentioned here are those in which at least the sheath portion (that is, the surface layer portion) is heat-fusible.

Nonwoven fabrics containing heat-sealing fibers with a core-sheath structure, or webs that are precursors to the webs, are superposed with non-woven fabrics of ultrafine fibers, and when thermocompression bonded, the sheaths of the heat-sealing fibers are dot-shaped over the entire overlapping surface. Alternatively, bonding is performed linearly at extremely fine intervals to obtain strong interlayer fusion. That is, the upstream non-woven fabric layer and the downstream non-woven fabric layer are fused and integrated. The interlayer fusion has an effect that, compared with the case where the conventional liquid or powder adhesive is used for adhesion, the adhesive of the ultrafine fibers does not cause clogging and the expected pressure loss does not increase. .

Examples of the heat-sealing fiber include a side-by-side type composite fiber in addition to the core-sheath structure conjugate fiber, and the side-by-side structure conjugate fiber also has a heat-melting component in the form of droplets, similar to the core-sheath structure fiber. It is a composite fiber with a structure that does not cause solidification or outflow.

As is clear from the above, the content of the heat-sealing fiber in the present invention needs to be at least about 30% or more, more preferably 50% or more, and may be 100% in some cases. Further, the heat-fusible fiber-containing nonwoven fabric may be flame-retardant, and the method of imparting flame-retardancy is not limited at all, but for example, a method of internally kneading a flame-retardant agent or spraying from the outside, dipping, coating, etc. Can be mentioned.

In the present invention, the fineness of the heat-sealing fiber-containing nonwoven fabric (nonwoven fabric on the upstream side) is 0.5 to 6 denier. That is, when the fineness exceeds the above range, the dust to be filtered is not collected by the nonwoven fabric and is accumulated on the downstream electretized ultrafine fiber nonwoven fabric, causing clogging at an early stage of the filter medium. The result is that the service life cannot be extended.

Next, in the present invention, it is important to impart a fiber packing density gradient in the thickness direction of the heat-sealing fiber-containing nonwoven fabric. This is to extend the service life of the filter medium according to the present invention. The molding method is (1) a method of thermocompression bonding with a temperature gradient in the thickness direction, (2) a method of forming a gradient in the mixing ratio of the heat-sealing fibers in the thickness direction by using a nonwoven fabric having two or more layers, (3)
Examples thereof include a method of forming a gradient according to the fineness of the fiber used, or (4) a method of forming a density gradient by infiltrating and fixing the resin powder in one direction.

In the present invention, the heat-sealing fiber-containing nonwoven fabric may be formed by laminating two or more nonwoven fabrics having different fiber configurations. For example, in order to collect polydisperse dust, arrange a thick fiber layer or a layer having a small range packing density on the upstream side and a thin fiber layer or a layer having a large fiber packing density on the downstream side, and heat. It is also within the technical scope of the present invention to impart rigidity with a fiber layer having a high mixing ratio of fusion bonding fibers and to hold dust in a layer having a low mixing ratio of heat bonding fibers.

Further, the non-woven fabric of electretized ultrafine fibers (non-woven fabric on the downstream side) in the present invention needs to be composed of fibers having an average fineness of 0.01 to 0.1 denier. This is because it is necessary to increase the particle removal efficiency as much as possible in order to use it as a filter material for a high performance air filter, and the particle removal efficiency becomes insufficient if the fineness is larger than the above range.

The ultrafine fiber nonwoven fabric may be electretized either before or after heat fusion with the heat fusion bonding fiber-containing nonwoven fabric. Examples of the ultrafine fiber nonwoven fabric in the present invention include polyolefin type and polyester type, and polypropylene is most preferable. The above-mentioned electretization means a state in which positive and negative electrification remains even after removing the external electric field.

[Examples] Example 1 A web of 1.5 denier polyester fibers in which the mixing ratio of 0.03 denier polypropylene ultrafine fiber non-woven fabric (weight per unit area 40 g / m ² ) and 3 denier core-sheath heat-sealing fibers is 70% (80g / m ² ) and the mold temperature of the non-woven fabric surface of the ultrafine fibers is 140 ℃, and the mold temperature of the opposite surface is 135 ℃.
Thermocompression bonding was performed for a minute. Then, the thermo-compression-bonded filter medium was subjected to a charging treatment by corona discharge for 50 seconds at a DC applied voltage of +22 KV and a distance between electrodes of 15 mm to electretize the ultrafine fiber nonwoven fabric to prepare a filter medium according to the present invention (Example 1). did.

When a unit type air filter having a length of 610 mm, a width of 610 mm and a width of 150 mm was manufactured using the prepared filter medium, an air filter having an excellent folding property was obtained.

Next, the present inventors conducted a dust test using the above unit type air filter. The results are shown in Table 1. In Table 1, for comparison, the dust test results of a commercially available unit type air filter made of glass fiber filter paper are also shown as Comparative Example 1. In Table 1, the removal efficiency is the colorimetric efficiency when using JIS 11 class dust, and the dust retention amount is JIS
The time when the pressure loss reached 30 mmAq when 15 kinds of dust was used was judged as the life, and the retention amount at that time was shown.

As is clear from Table 1, Example 1 has lower pressure loss and higher removal efficiency than Comparative Example 1, and can be used for a long period of time due to the increased dust holding amount.

Example 2 1-denier core-sheath structure flame-retardant heat-sealing fiber: a web containing 100% (60 g / m ² and the flame-retardant heat-sealing fiber mixed at a mixing ratio of 50).
% Of 3 denier flame-retardant polyester fiber web (80 g / m ² ) was superposed and thermocompression bonded at 130 ° C. for 45 seconds to prepare a two-layer type heat-sealing fiber-containing nonwoven fabric. Next, a 0.03 denier polypropylene ultrafine fiber non-woven fabric (weight per unit area: 20 g / m ² ) was superposed on the above two-layer non-woven fabric and thermocompression-bonded at 140 ° C., followed by charging treatment by corona discharge to carry out the filtering material of the present invention (implementation). Example 2) was created.

As a comparative example, the flame-retardant two-layer web of Example 2 was used.
Create a flame-retardant non-woven fabric by thermocompression bonding at 0 ° C for 45 seconds, and uniformly disperse the chlorinated polyethylene powder between the flame-retardant non-woven fabric and 0.03 denier polypropylene ultrafine fiber non-woven fabric, and at 120 ° C. And thermocompression bonded to prepare a filter medium. The amount of powder of chlorinated polyethylene used was 20 g / m ² and 38 g / m ² , respectively, and they were referred to as Comparative Example 2 and Comparative Example 3, respectively. As another comparative example, a filter medium (Comparative Example 4) was prepared by coating an emulsion adhesive of a copolyester resin instead of chlorinated polyethylene at a solid content of 27 g / m ² .

A dust test on a flat plate was performed for each of the above filter media. The results are shown in Table 2. The wind speed in the test was 10 cm / sec, the filtration area was 0.25 m ² , and the presence or absence of delamination in Table 2 was determined by folding each filter medium.

As is clear from Table 2, the value of Comparative Example 2 is close to that of Example 2 as far as the initial pressure loss and the amount of dust retained, but delamination occurs due to the low adhesive strength of both nonwoven fabrics. On the other hand, in Comparative Examples 3 and 4, although practical adhesive strength can be obtained, Example 2 was used in the initial pressure loss and the dust holding amount.
Is understood to be inferior to.

Example 3 As a non-woven fabric of ultrafine fibers to be electret, 0.03
Denier polypropylene extra fine fiber nonwoven fabric (weight of 10
Using 0 g / m ² ), a non-woven fabric containing heat-sealing fibers having the following constitution was fused to the non-woven fabric. The non-woven fabric containing heat-sealing fibers has a web of 6% denier and 100% of heat-sealing fibers having a core-sheath structure (weight of 50 g / m ² ). % Polyester fiber web of 1 denier (weight per unit area of 35 g / m ² ), 1.5 denier polyester fiber web of core-sheath structure with fusion ratio of 40% (denier weight of 50 g / m ² ). , And a 3 denier core-sheath structure heat fusion fiber having a mixing ratio of 40% and a 3 denier polyester fiber web (weight per unit area: 50 g / m ² ) are laminated in the above-mentioned order. After this, a plate-shaped mold was used on the non-woven fabric side of the ultrafine fibers, and a 6-denier polyester fiber web side on the opposite side was linear with a diameter of 1 mm and had an opening of 5 mm.
Was applied and thermocompression bonded with a gauge pressure of 3 mmHg. The thus obtained laminate was subjected to a charging treatment by corona discharge to prepare a filter medium (Example 3) according to the present invention.

A unit type air filter was manufactured using the prepared filter medium and a dust test was conducted. The results are shown in Table 3. For comparison, Table 3 shows the results of Comparative Example 1 at the same time. As a life test of the air filter, JIS 15 type dust (mixed dust) and JIS 11 type dust having a smaller particle size than the dust were tested and shown in Table 3 at the same time.
In comparison with Comparative Example 1, each of them exhibited a long life performance with respect to any dust.

[Advantages of the Invention] As described above, according to the present invention, by adopting the above-described structure, it is possible to realize a filter medium that suppresses an increase in initial pressure loss, is usable for a long period of time, and has high rigidity. Further, when a unit type air filter is assembled using the filter material according to the present invention, the upstream side and the downstream side non-woven fabric are heat-sealed by the heat-fusible material on the upstream side. Since it is strong, the filter medium has good foldability despite its high rigidity and is easy to assemble, and the unit type air filter has remarkable effects in terms of maintainability and running cost reduction. To do.

Claims (1)

[Claims] 1. A filter medium comprising a non-woven fabric layer on the upstream side and the downstream side, wherein the non-woven fabric layer on the upstream side is entirely or partially formed of a heat-sealing material having a core-sheath structure or a side-by-side structure. It is composed of a nonwoven fabric layer having a density of 0.5 to 6 denier and having a density gradient such that the fiber packing density increases in the depth direction. The downstream nonwoven fabric layer has an average fineness of 0.01 to 0.1 denier. Of the non-woven fabric layer made of electretized ultrafine fibers, the boundary between the upstream non-woven fabric layer and the downstream non-woven fabric layer is integrated by heat fusion of the heat fusible material constituting the upstream side. A filter medium characterized by being made into a material.