JP3404796B2 - Filter media - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used as an air filter for clean rooms, a liquid prefilter used for cleaning electronic equipment, a liquid or gas prefilter used for the manufacture of pharmaceuticals, and the like. The present invention relates to a filter material for microfiltration. More specifically, the present invention relates to a non-woven fabric in which the intersections of ultrafine composite fibers are heat-sealed, and a composite monofilament net is heat-sealed so that the pore diameter does not change due to heating, and the filter material for microfiltration has good fold shape such as folds.

[0002]

2. Description of the Related Art In recent years, industries related to electronics, biochemicals, etc. have been developed, and there are many opportunities to use gas and liquid after cleaning them. Conventionally, ultrafine glass fiber nonwoven fabrics, synthetic fiber nonwoven fabrics, etc. have been used as filter media for such microfiltration. However, the glass fiber non-woven fabric is weak in alkali resistance, folds that are processed for the purpose of taking a large filtering surface area during filtration, and when processed into various three-dimensional shapes, there are problems such as so-called poor shapeability. is there. On the other hand, the synthetic fiber non-woven fabric has the advantages that it is lighter in weight because it has a smaller specific gravity than the glass fiber non-woven fabric, has a good shape compared to the glass fiber non-woven fabric, is inexpensive, and is easy to handle without scattering fine glass powder. The synthetic fiber non-woven fabric filter material has been rapidly used. As the synthetic fiber nonwoven fabric filter material, polyester spunbonded nonwoven fabric, polypropylene meltblown nonwoven fabric or the like is used, but the phenomenon that the pore size increases due to opening due to heating, friction, vibration, etc.,
That is, there is a problem that the pore size stability is poor.

As an improved non-woven fabric filter material,
A filter medium is known in which a non-woven fabric and a net-like sheet are fused together. Japanese Unexamined Patent Publication (Kokai) No. 1-194912 discloses a filter in which an electretized ultrafine fiber nonwoven fabric and a net-like material are heat-sealed, and Japanese Unexamined Patent Publication No. 4-346805 discloses a heat-fusible monofilament and metal. A filter medium is disclosed in which a net is fused with a thin wire. In each of the above-mentioned non-woven fabrics fused with a net-like sheet, regular fibers such as melt-blown polypropylene and melt-blown polyester are used as ultrafine fibers constituting the non-woven fabrics. The ultrafine fiber web in which the intersections of the fibers are not heat-sealed, or the web is partially heat-sealed at the intersections of the fibers by using an embossing roll or a calendar roll. Alternatively, the net is laminated on the web or the thermocompression bonded non-woven fabric, and the non-woven fabric and the net are fused by using a heating means such as a calendar roll or a drier.

By the way, when microscopically observing the heat fusion state of the non-woven fabric, such a non-woven fabric filter medium may sufficiently heat-bond the intersections of the fibers by heating without impairing the ventilation resistance of the filter medium. Have difficulty. For example, in the case of the embossing roll method, the parts other than the thermocompression bonding portion are not fused, and in the case of the calendar roll method, a large amount of the non-woven fabric is fused on the front and back sides, but the central part is fused. Even if there are few or many parts, the fusion state is not uniform. In the case where the fusion state of the fibers is not uniform, the non-woven fabric is pleated and further tubular, and the end faces on both sides thereof are heat-sealed with synthetic resin end face members, or the end face members. When bonding with a binder, heat when sterilizing the filter medium with heat, heat during high-temperature filtration, vibration of the housing during filtration, etc. There is a drawback that it becomes large, that is, the so-called pore size stability is poor. In particular, those with a high basis weight of about 25 g / m ² or more are likely to have insufficient heat fusion at the intersections of the fibers, resulting in poor pore size stability, and sometimes the maximum pore size change rate of 25% or more due to heating. It was a certain thing. In addition, the filter medium thermocompression-bonded at a high temperature and a high pressure by a calendar roll method or the like has some improvement in the pore size stability, but the whole fiber is melted and changed into a film shape, so that the ventilation resistance becomes extremely high. There is.

[0005]

DISCLOSURE OF THE INVENTION The present invention has a problem that the maximum hole diameter does not change due to heating, vibration, etc., which is a problem of the above-mentioned prior art, and yet it has high strength and is in the shape of valleys or other complicated shapes. The object is to provide a filter material for microfiltration that can be easily processed.

[0006]

Means for Solving the Problems As a result of intensive studies to solve the above-mentioned problems, the present inventors have found that the intended purpose can be achieved by the following constitution, Has been completed. That is, the structure of the present invention is as follows. (1) A filter medium having a maximum pore diameter of 120 μm or less obtained by heat-sealing a heat-fusible ultrafine composite fiber nonwoven fabric having a fiber diameter of 10 μm or less and a heat-fusible composite monofilament net.
I, low-melting of the ultrafine composite fiber and the composite monofilament
The melting point difference of the point components is 15 ° C or less, and the intersection point of the fibers
The filter material in which the low melting point resins of each other have an interpenetrating structure . (2) The melting point difference of the ultrafine composite fiber is 15 ° C or more,
The melting point difference of the composite monofilament is 15 ° C. or more.
Filter media. (3) A melt-blown non-woven fabric obtained by heat-sealing heat-fusible ultrafine composite fibers and a heat-fusible composite monofilament having a fiber diameter of about 30 to 4000 d / f and a weaving density of about 0.5 to 25 fibers / 25 mm. The above-mentioned filter medium obtained by laminating the used net and then heat-sealing. (4) The filter medium as described above, wherein the maximum pore diameter change rate after heating is 20% or less. (5) Air permeability of 0.1 to 100 cc / cm ² . se
c, a filter medium obtained by pleating the above filter medium having a tensile strength of 2 to 100 kg / 5 cm. (6) The filter medium according to any one of the above, wherein the nonwoven fabric is electretized.

In the present invention, the heat fusible ultrafine composite fiber nonwoven fabric having a fiber diameter of 10 μm or less is obtained by spinning at least two kinds of thermoplastic resins having a melting point difference of 15 ° C. or more by a composite spinning method. It refers to a product obtained by heating a web having an average fiber diameter of 10 μm or less at a heat fusion temperature or higher to fuse the intersections of the fibers. Thermoplastic resins that can be used in the composite spinning method include polypropylene, polyethylene, poly-4-methylpentene,
There are resins such as binary or ternary copolymers of propylene and other α-olefins, polyethylene terephthalate, polyamides and polycarbonates. In the composite spinning method, a composite melt blow method, a composite spun bond method, which uses a spinneret for composite spinning such as a parallel type, a sheath core type, a multi-divided type, and a sea-island type,
There are usual composite spinning methods and the like. Especially composite melt blow
The method is preferable because it gives ultrafine fibers. In the present invention, the fiber diameter is 10 μm because its use is a filter material for precision filtration.
The following fibers are used. The fiber diameter is preferably 0.1 to
The thickness is 10 μm, more preferably 0.2 to 7 μm. The resin is subjected to composite spinning in various combinations having a melting point difference of 15 ° C. or more. Examples of this combination include polypropylene / polyethylene, polypropylene / propylene-ethylene-butene-1 copolymer, polyethylene terephthalate / low melting point polyester, polyethylene terephthalate / polyamide and the like.

The heat-fusible ultrafine composite fibers are spun by a composite melt-blowing method or the like, and the obtained web is heated at a temperature higher than the temperature at which the low melting point resin of the composite fibers is melted, and the intersection of the fibers is heat-bonded. It is a non-woven fabric. Heating is above the softening point of the low melting point resin,
The temperature is lower than the melting point of the high melting point resin. For heating, dry heat circulation type dryer, through-air type dryer, calendar
It is performed by using a heating device such as a roll or an embossing roll. Among the above heating devices, a non-woven fabric having a high air permeability can be obtained by heat-sealing using a device such as a through-air type dryer which can heat-bond the non-woven fabric with almost no pressure. . Moreover, a non-woven fabric having a maximum maximum pore size can be obtained by thermo-compression bonding using a thermo-compression-type heating device such as a calendar roll. The non-woven fabric used in the filter medium of the present invention is a product in which ultrafine and heat-fusible composite fibers are used and the intersections of the fibers are heat-bonded. Therefore, by performing the heating temperature at a temperature not lower than the softening point of the low melting point resin of the composite fiber and not higher than the melting point of the high melting point resin, the high melting point resin retains the shape of the fiber without melting and the intersection point of the fibers is It is made into a non-woven fabric by fusing low melting point resin. Therefore, the pore size becomes stable without being opened by sterilization heating in a later step, high temperature filtration at the time of filtration, or vibration. Moreover, a kind of film formation due to complete melting of the fibers does not occur, and even if it occurs, it is extremely small. Therefore, it is possible to obtain a material having a high air permeability and a small pore size. On the other hand, a heat-bonded nonwoven fabric using regular ultrafine fibers obtained by a conventional melt blow method or the like has a large amount of unfused fibers, or because the bonding of the fused parts is extremely weak, The material after fusion of the nets described below to the non-woven fabric is opened by heat sterilization, heating such as high temperature filtration, heating during end face sealing, or vibration of the housing. Further, in the product heated at a high temperature with a calendar roll or the like, the fiber is completely melted, the shape of the fiber disappears and film formation occurs, or the product heated at a high temperature by a through air type heater is The fibers melt and aggregate into beads. Therefore, the air permeability is small and the hole diameter is large. In particular, this tendency is greater as the fiber diameter is smaller.

The nonwoven fabric used in the filter medium of the present invention has a basis weight of about 3 to 1000 g / m ² , more preferably 4 to 70.
0 g / m ² can be used. Further, the pore size of the non-woven fabric can be changed by changing the processing conditions such as the unit weight of the non-woven fabric, the heating temperature, the linear pressure of the calendar roll, the processing time and the like. The smaller the fineness of the nonwoven fabric, the larger the basis weight, and the larger the linear pressure of the calendar roll, the smaller the pore size of the nonwoven fabric obtained. When the nonwoven fabric used in the filter medium of the present invention has a rate of change in maximum pore size of 20% or less before and after heating at 80 ° C. for 20 minutes, it is a filter medium for microfiltration, which does not open and is stable for a long period of time. Is preferred as

In the present invention, the filter medium is the above-mentioned non-woven fabric to which the heat-fusible composite monofilament net is heat-sealed. The net is obtained by spinning at least two kinds of thermoplastic resins having a melting point difference of 15 ° C. or more by a composite spinning method, and woven or knitting the obtained heat-fusible composite monofilament to obtain a net-like sheet. Or a sheet-like material obtained by heating the net at a temperature higher than the heat fusion temperature and fusing the intersections of the fibers. The composite form of the monofilament, the resin that can be used in the filament, the combination of resins, and the like may be the same composite form and the combination of resins as those used for the nonwoven fabric. In particular, when the difference in melting point between the ultra-fine fiber low-melting point resin and the monofilament low-melting point resin is 15 ° C. or less, the low-melting point resin has an interpenetrating structure at the crossing points of the fibers due to the heat treatment described later. The net is strongly heat-sealed and is not easily peeled off at the interface, which is preferable. In particular, the low melting point resin of ultrafine fibers and the low melting point resin of monofilament are preferably the same type, for example, polyolefin / polyolein, polyester / polyester and the like. The net has a fineness of about 30 to 4000 d /
It is preferable that the product of f is woven with a weaving density of about 0.5 to 25 yarns / 25 mm. The above-mentioned non-woven fabric and net are laminated as non-woven fabric / net, net / non-woven fabric / net, etc., or the above-mentioned laminate is further laminated in two stages and heated by the above-mentioned known heating method to obtain non-woven fabric. And the net is a heat-sealed filter medium. Of course, a spunbonded non-woven fabric having a relatively large fineness, a heat-bonded non-woven fabric of staple, or the like may be laminated on the laminate.

The filter medium of the present invention preferably has the following conditions in terms of ventilation resistance and microfiltration. Nonwoven fabric having a maximum pore size of about 0.1 to 120 μm, preferably about 0.2 to 10
It is 0 μm, more preferably about 0.3 to 90 μm. When the maximum pore size is 0.1 μm or less, the ventilation resistance at the time of filtration becomes large, and a product having a maximum pore size of 120 μm or more is not suitable for microfiltration. Moreover, the air permeability is about 0.1 to 200 cc / cm.
² ． sec, preferably 0.2 to 150 cc / cm ² .
sec, more preferably 0.2 to 100 cc / cm ² .
It is a sec thing. Needless to say, the physical properties of the nonwoven fabric, such as the maximum pore size and the air permeability, are those of the filter material in which the nonwoven fabric and the net are heat-sealed, which will be described later.

The filter material of the present invention can be used by being attached to a housing or the like without folds or the like. Further, the filter medium can be used by attaching it to a housing by using a pleat folding machine, a molding machine or the like to form an arbitrary shape such as a sharp angled valley shape, a U shape, an uneven shape. Further, the filter medium after being shaped into the above various shapes can be further made into a cylindrical shape or a spiral shape. In the case of a cylindrical shape, the left and right ends are fused or bonded with a binder or the like. The housing may be of various shapes depending on the application to be filtered. For example, a cylindrical core member having a large number of openings on its side surface, a porous cylindrical outer frame member, and a cylindrical housing whose main constituent members are seal members at both end surfaces, and a rectangular frame-shaped housing. , And a rectangular housing mainly composed of a metal net or the like, or a box-shaped multi-layered housing in which a filter medium is mounted in multiple layers in a box shape, or any other shaped housing that can be mounted in a place to be filtered. Can be used.

The filter medium of the present invention may be an electretized one. Examples of the method of electretization include a method of electretizing between a spinneret and a collecting surface while collecting fibers at the time of spinning, a method of electretizing before spinning the web or the like after spinning. is there. Further, there is a method of making a non-woven fabric, a non-woven fabric in which a non-woven fabric and a net are heat-sealed, a pleated filter medium, a filter medium attached to a housing, etc. into an electret. The electretization is performed by direct current corona discharge having a voltage of about 1 to 30 kilovolts. Further, it is preferable that the non-woven fabric has a surface electrification density of about 10 to 45 cron / cm ² . In the filter material of the present invention, the heat-fusible ultrafine composite fibers of the non-woven fabric may have a density gradient. Further, the filter medium of the present invention may be a laminate of other non-woven fabrics or sheets having different fiber materials, fiber diameters and the like. When the other nonwoven fabric is laminated, the other nonwoven fabric is a regular fiber melt blown nonwoven fabric having a fiber diameter of 0.1 to 20 μm, a regular fiber having a fiber diameter of 11 to 100 μm, or a heat-fusible ultrafine composite fiber nonwoven fabric, or the like. A laminated sheet of a non-woven fabric and a composite monofilament can be exemplified.

[0014]

EXAMPLES The present invention will be described in more detail with reference to Examples and Comparative Examples. In each example, the physical properties of the filter medium, the filtration performance, and the like were evaluated by the methods described below.

Fiber diameter of non-woven fabric: 10 small pieces were cut from a web, a non-woven fabric or a filter material, and a photograph of the scanning electron microscope at a magnification of 100 to 5000 times was used to measure the diameter of a total of 100 fiber diameters. The average value (μm) is shown.

Tensile strength: 5 cm using a tensile strength tester
The breaking strength (kg / 5 cm) of the width is shown.

Air permeability: Using a Frazier type air permeability tester, air permeability was determined by the method specified in JIS-L1006A. Unit cc / cm ² . sec.

Maximum pore size: The maximum pore size (μm) was determined by a method specified in ASTM-F-316-86 using a bubble point tester.

Maximum pore diameter change rate after heating: Using the above bubble point tester and in the same manner as above, at 80 ° C., 10
The change rate (%) of the maximum pore size after the partial heat treatment was determined.

Filtration accuracy: A circulating filtration tester comprising a water tank containing 50 liters of water, a pump, and a filter (housing) was used. One filter material was attached to the housing of the filter, and 5 g of cake (Carborundum # 4000) was placed in the water tank while circulating water at a flow rate of 30 liters per minute.
Added. Filtered water collected 1 minute after addition of cake
0 cc is filtered with a membrane filter. The size of the particles collected on the membrane filter was measured by a particle size distribution analyzer, and the size of the largest particle (maximum outflow diameter, unit: μm) was taken as the filtration accuracy of the filter medium.

Pressure loss: In the above circulation type filtration accuracy test, only the water was circulated at a flow rate of 30 liters per minute without adding a cake. 1 minute after the start of circulation, pressure loss (kg / c
m ² ) is measured.

Example 1 As the first component, melt flow rate 120 (MFR, g / g)
Polypropylene having a melting point of 164 ° C for 10 minutes at 230 ° C) was used as a second component, and a melt flow rate of 120 (MFR,
g / 10 minutes, 190 ° C.), and a linear low-density polyethylene having a melting point of 121 ° C. were used to perform composite melt-blow spinning from a parallel type composite melt-blow spinneret having a hole diameter of 0.3 mm and a number of holes of 501. The spinning conditions are such that the composite ratio is 50% by weight to 50% by weight,
The spinning temperature was 280 ° C. for polypropylene and 260 ° C. for linear low-density polyethylene, and the fiber discharged from the spinning hole was extruded at a total discharge rate of 120 g / min.
Was introduced at a pressure of 1.2 kg / cm ² G and was blown onto a conveyor net equipped with a jet gas suction device. The heat-fusible ultrafine composite fiber web had a fiber diameter of 2.7 μm. This web was heated at a temperature of 140 ° C. for 10 seconds using a through-air type heater to obtain a nonwoven fabric having a basis weight of 99 g / m ² in which the intersections of the fibers were heat-sealed.

MFR18 (g / 10 minutes, 190 ° C), linear low density polyethylene having a melting point of 124 ° C is a sheath component, and MF
R8 (g / 10 minutes, 230 ° C), polypropylene having a melting point of 164 ° C is the core component, and a heat-meltable composite monofilament with a composite ratio of 50/50 (weight ratio) and a fineness of 250 d / f is used. A plain woven fabric was woven at a weave density of × 17/25 mm, and then the net was heated at a temperature of 135 ° C. using a tenter-type heater to obtain a net in which the intersections of the fibers were heat-sealed.

The above materials were laminated in three layers of net / nonwoven fabric / net, and a temperature of 140 was applied using a through air type heater.
After heating at 10 ° C for 10 seconds, it was immediately treated with a calendar roll at a temperature of 30 ° C to obtain a filter medium in which the non-woven fabric and the net were heat-sealed. This filter medium was heated and left at 80 ° C. for 20 minutes, and the change rate of the maximum pore size before and after the heating was determined.

A fold-folding machine was used to obtain a filter medium having a pleat height of 20 mm and a pleat shape of W. The pleated filter medium has an outer diameter 30 having a large number of holes on its side surface.
It was wound around a hollow metal core having a height of 250 mm and a height of 250 mm to obtain a filter medium having an inner diameter of about 30 mm and an outer diameter of 70 mm. The left and right ends of the filter medium were heat-sealed. Furthermore, metal end face seal members having openings with a diameter of 30 mm were adhered to the upper and lower ends with a binder to obtain a cylindrical filter medium. This filter material has an outer shape 7
The surface area was increased by about 9.1 times as compared with the 0 mm unfolded product. Table 1 shows the maximum pore size of the filter medium before heating, the maximum pore size change rate of the filter medium after heating, the air permeability, the tensile strength, etc., and the filtration performance of the filter medium folded and processed into a hollow cylindrical shape. The test results are shown. It can be seen from Table 1 that the filter medium of the present invention has a maximum rate of change in pore size after heating of 4% and is excellent in stability of pore size upon heating, and that the product after pleating has a filtration accuracy of 4 μm.

Example 2 By the same method as described in Example (1) above, a composite melt-blow spinning process was performed to obtain a non-woven fabric having heat-fusible ultrafine fibers heat-fused. However, in Example (1), the combination of the composite components is the same as in Example (1) polypropylene (first component) /
Melting point 137 ° C, MFR40 (g / 10 minutes, 230 ° C)
Of propylene. ethylene. Butene-1 random copolymer (second component), the spinning conditions were polypropylene at 290 ° C. and copolymer at 300 ° C., and the fibers discharged from the spinning holes were heated to a temperature of 390 ° C. with a pressure of 1.4.
It was sprayed under the condition of kg / cm ² . Further, the heating condition temperature by the through air type heater was 145 ° C. The heat-fusible ultrafine composite fiber web had a fiber diameter of 1.3 μm.
The non-woven fabric after the heat fusion treatment had a basis weight of 102 g / m ² .

Instead of the net described in the above Example (1), the composite component is the same as that used in the ultrafine fiber nonwoven fabric of the above Example (2): random copolymer (sheath) / the above Example (1).
The same polypropylene (core) as the one used as the core component of the net, the composite ratio of the sheath 40 / core 60 (weight ratio), and the fiber density of the fineness and the weft are the same as those in the above Example (1). used. However, the heating temperature by the tenter type heater is 14
The temperature was 5 ° C.

Laminated in three layers of net / nonwoven / net,
As in the above Example (1), a filter material in which a nonwoven fabric and a net were heat-sealed by heating with a through-air type heater at a temperature of 145 ° C. for 10 seconds and then immediately treated with a calendar roll at a temperature of 30 ° C. Got

This filter medium was pleated and then processed into a cylindrical filter medium in the same manner as in Example (1). Table 1 shows the physical properties, filtration performance and the like of the filter medium before the pleating process and the cylindrical filter medium. The surface area of this filter medium was increased by about 9.1 times as compared with the filter material having an outer diameter of 70 mm and not having a fold. From Table 1, it can be seen that the filter medium of the present invention has a maximum pore size change rate after heating of 0% and has good pore size stability against heating, and the filter material after pleating has a filtration accuracy of 1.0 μm.

Example 3 MFR43 (g / 10 minutes, 190 ° C.) high density polyethylene as a sheath component, polyethylene terephthalate having an intrinsic viscosity of 0.60 and a melting point of 253 ° C. as a core component, and a pore size of 0.3.
mm and the number of holes was 501, and the composite melt-blow was spun from a sheath-core type melt-blow spinneret. The spinning condition is a composite ratio of 40 (sheath).
/ 60 (core) (weight ratio), spinning temperature is 260 ° C for high density polyethylene, 280 ° C for polyethylene terephthalate
The fiber discharged from the spinning hole was extruded under the condition that the total discharge amount was 120 g / min.
It was introduced at a rate of kg / cm ² G and sprayed onto a conveyor net equipped with a jet gas suction device. The heat-fusible ultrafine composite fiber web had a fiber diameter of 3.8 μm. This web was heated for 10 seconds at a temperature of 145 ° C. using a through-air type heater, and a fiber basis weight 100 g / m ² where the intersections of the fibers were heat-sealed
A non-woven fabric was obtained.

In place of the net described in Example (1) above, the composite component is the same high density polyethylene (sheath) as that used in the microfiber nonwoven fabric of Example (3) / Example (1) above.
The same polypropylene (core) as the one used as the core component of the net, the composite ratio is 60 (sheath) / 40 (core) (weight ratio)
Then, a heat-fusible composite monofilament having a fineness of 500 d / f was woven into a plain woven cloth with a weaving density of 11 × 11 pieces / 25 mm in both directions, and heated at a temperature of 145 ° C. using a tenter-type heater. A net was used in which the intersections of the fibers were heat-sealed.

The net / nonwoven fabric / net three-layered product was heated at a temperature of 145 ° C. for 10 seconds using a through-air type heater in the same manner as in Example (1), and immediately thereafter, a calender roll at a temperature of 30 ° C. was used. To obtain a filter material in which the non-woven fabric and the net are heat-sealed.

This filter medium was pleated and then processed into a cylindrical filter medium in the same manner as in Example (1). Table 1 shows the physical properties and filtration performance of this filter medium. This filter medium is 70
The surface area was increased by about 9.1 times as compared with the non-folded product of mm. From Table 1, the filter medium of the present invention has a maximum rate of change in pore size after heating of 1.8% and has good pore size stability against heating, and the filter material after pleating has a filtration accuracy of 8.3 μm.
It turns out that it is a good one.

Comparative Example 1 MFR120 (g / 10 minutes, 230 ° C.), melting point 163 ° C.
The polypropylene of (1) was melt-blown from a spinneret for a regular fiber meltblown having a pore size of 0.3 mm and a number of pores of 501. The spinning conditions are as follows: the spinning temperature is 280 ° C., the discharge rate is 120 g / min, the fibers discharged from the spinning holes are air at a temperature of 360 ° C., and the pressure is 1.3 kg / c.
It was introduced at m ² G and sprayed onto a conveyor-net equipped with the same jet gas suction device as in Example (1). The ultrafine regular fiber web had a fiber diameter of 2.6 μm. This web was heated for 10 seconds at a temperature of 145 ° C. using the same through-air type heater as in Example (1) to give a basis weight of 101 g /
A m ² non-woven fabric was obtained.

The net used in Example (1) and the above non-woven fabric were laminated in three layers of net / non-woven fabric / net, and the mixture was heated at a temperature of 145 ° C. for 10 hours using a through air type heater.
It was treated for 2 seconds to obtain a filter medium in which the nonwoven fabric and the net were heat-sealed.
This filter medium was pleated and then processed into a cylindrical filter medium in the same manner as in Example (1). Table 1 shows the physical properties and filtration performance of this filter medium. The surface area of this filter medium was increased by about 9.1 times as compared with the filter material having an outer diameter of 70 mm and not having a fold. From Table 1, the filter medium of Comparative Example (1) has a finer fiber diameter smaller than that of Example (1), but the maximum pore diameter change rate after heating is 20.
% Or more, and it can be seen that the pore size stability deteriorates due to the opening due to heating. Moreover, the filtration accuracy of the fold-folded product is 13.5.
Since it is μm, it can be seen from the product of Example (1) that the pore size stability against heating and the filtration accuracy are both poor.

Comparative Example 2 Using the same non-woven fabric as in Comparative Example (1) and the same net as in Example (1), three layers of net / nonwoven fabric / net were laminated. Using a sul-air-type heater,
Treat at a temperature of 145 ° C for 10 seconds and immediately
It was treated with a calender roll at .degree. C. to obtain a filter material in which the non-woven fabric and the net were heat-sealed. This filter medium was pleated and then processed into a cylindrical filter medium in the same manner as in Example (1). The surface area of this filter medium was increased by about 9.1 times as compared with the filter material having an outer diameter of 70 mm and not having a fold. From Table 1, the filter medium of Comparative Example (2) has finer fiber diameters smaller than that of Example (1), but the maximum rate of change in pore size after heating is 20% or more, and the pore size is stable by heating. In addition, the product after the pleating process has a filtration accuracy of 11.6 μm, which means that the product is worse than the product of Example (1).

Comparative Example 3 In Comparative Example (1), the ultrafine fiber web was
A non-woven fabric having a basis weight of 103 g / m ² obtained by heating with an air-type heater for 10 seconds at a temperature of 145 ° C. and immediately after being treated with a calendar roll at a temperature of 140 ° C. and the same net as in Example (1) above. It was used and laminated in three layers of net / nonwoven fabric / net. The laminate was treated with a through-air type heater at a temperature of 145 ° C. for 10 seconds and immediately thereafter at a temperature of 140 ° C.
Was treated with a calendar roll to obtain a filter material in which the non-woven fabric and the net were heat-sealed. This filter medium was pleated and then processed into a cylindrical filter medium in the same manner as in Example (1). The surface area of this filter medium was increased by about 9.1 times as compared with the filter material having an outer diameter of 70 mm and not having a fold. From Table 1, the filter medium of Comparative Example (3) has finer fiber diameters smaller than those of Example (1), but the maximum rate of change in pore size after heating is 20% or more, and the pore size is stable by heating. In addition, the product after the pleating process had a filtration accuracy of 8.3 μm, which indicates that the product was worse than the product of Example (1).

COMPARATIVE EXAMPLE 4 In Comparative Example (1), the ultrafine fiber web was treated at a temperature of 145 ° C. with an embossing roll having a convex area of 12% and a flat roll to obtain a basis weight of 101 g / m ^2. Using the non-woven fabric of Example 1 and the same net as in Example (1), three layers of net / non-woven fabric / net were laminated. The laminate was treated with a calender roll at a temperature of 145 ° C. to obtain a filter medium in which the nonwoven fabric and the net were heat-sealed. This filter medium was pleated and then processed into a cylindrical filter medium in the same manner as in Example (1). The surface area of this filter medium was increased by about 9.1 times as compared with the filter material having an outer diameter of 70 mm and not having a fold. From Table 1, the filter medium of Comparative Example (3) has finer fiber diameters smaller than those of Example (1), but the maximum rate of change in pore size after heating is 20% or more, and the pore size is stable by heating. In addition, the product after the pleating process has a filtration accuracy of 10.1 μm, which means that the product is worse than the product of Example (1).

Example 4 The composite melt-blow ultrafine fiber web obtained in the above Example (2) was treated for 10 seconds at a temperature of 145 ° C. using a through air type heater, and immediately thereafter, a calender at a temperature of 140 ° C. -Fabrication 104 in which the intersection points of the fibers are heat-bonded by the roll treatment.
Using a non-woven fabric of g / m ² and the net of Example (2) above, they were laminated in three layers of net / non-woven fabric / net. The laminate was treated with a calender roll at a temperature of 138 ° C. to obtain a filter medium in which the nonwoven fabric and the net were heat-sealed. This filter medium was pleated and then processed into a cylindrical filter medium in the same manner as in Example (1). The surface area of this filter medium was increased by about 9.1 times as compared with the filter material having an outer diameter of 70 mm and not having a fold. From Table 1, it is found that the filter medium of Example (4) has a maximum pore size change rate after heating of 0% and good pore size stability, and the pleat-folded product has good filtration accuracy of 0.8 μm. I understand.

Example 5 Using the heat-bonded nonwoven fabric having a basis weight of 99 g / m ² obtained in Example (1) and the net obtained in Example (3),
It was laminated in three layers of net / nonwoven fabric / net. The laminate is heated at 140 ° C. for 10 hours using a through air type heater.
It was treated for 2 seconds to obtain a filter medium in which the net and the non-woven fabric were heat-sealed.
This filter medium was pleated and then processed into a cylindrical filter medium in the same manner as in Example (1). This filter medium is 70
The surface area was increased by about 9.1 times as compared with the non-folded product of mm. From Table 1, it can be seen that the filter medium of Example (5) has a maximum rate of change in pore diameter of 0% after heating, and the filter material after pleating has a good filtration accuracy of 5.6 μm.

Example 6 The composite melt-blown ultrafine fiber web obtained in the above Example (1) was treated with a calendar roll at a temperature of 130 ° C. to obtain a heat-bonded nonwoven fabric having a basis weight of 103 g / m ² . . The non-woven fabric and the net obtained in Example (1) were laminated in three layers of net / non-woven fabric / net. The laminate was treated with a calender roll at a temperature of 120 ° C. to obtain a filter medium in which the net and the non-woven fabric were heat-sealed. This filter medium was pleated and then processed into a cylindrical filter medium in the same manner as in Example (1). The surface area of this filter medium was increased by about 9.1 times as compared with the filter material having an outer diameter of 70 mm and not having a fold. From Table 1, it can be seen that the filter medium of Example (6) has a maximum pore size change rate after heating of 20% or less and has a good pore size stability, and the product after pleating has a good filtration accuracy of 6.8 μm. I know there is something.

Example 7 The filter medium obtained by the above Example (1), in which the nonwoven fabric and the net were heat-sealed, was placed directly on the ground electrode, and a DC voltage of 14 kv / cm was applied from the discharge electrode on the ground electrode. In a high electric field
It was treated for 0 seconds to obtain an electretized filter medium. The filter medium was cut into a size of 30 cm × 30 cm, placed on a table in an office where many people come and go, and floating dust was naturally adsorbed to the filter medium. Two months later, the condition of dirt on the filter medium was measured according to JIS.
The grade was 2.5 when judged by the gray scale for contamination specified by -L0805 (1st grade: large contamination, 5th grade: small contamination). On the other hand, when the filter material obtained in the above-mentioned Example (1) which was not electretized was observed at the same time for the stain condition, it was found to be 4.5.
It was in class.

[0043]

Since the filter medium of the present invention heat-bonds the ultrafine fiber nonwoven fabric and the respective composite fibers of the monofilament net, the rate of change in pore diameter is small even when heated. Therefore, even when used for heat sterilization, high-temperature filtration, or a portion vibrating near a motor, high-precision filtration can be stably performed, and stable use can be achieved for a long time. Further, this filter material was able to be processed into pleats, unevenness and the like. In addition to the above-mentioned effect, the pleated filter medium has the effect of having a long filtration life because it has a larger surface area. Further, as the non-woven fabric web, the one using the composite melt-blowing web does not have a finishing agent such as an antistatic agent attached to the fibers, so that it can be used as a filter material for microfiltration in the food field.

[0044]

[Table 1]

Claims (6)

(57) [Claims] 1. A filter having a maximum pore size of 120 μm or less obtained by heat-sealing a heat-fusible ultrafine composite fiber nonwoven fabric having a fiber diameter of 10 μm or less and a heat-fusible composite monofilament net.
Material, said ultrafine composite fiber and said composite monofilament
The melting point difference of the low melting point component of 15 ° C or less, and
The low melting point resins of each other have an interpenetrating structure at the intersection.
Filter material. 2. The melting point difference of the ultrafine composite fibers is 15 ° C. or more.
And the melting point difference of the composite monofilament is 15 ° C or more.
The filter medium according to claim 1. 3. A non-woven fabric obtained by heat-melting a melt-blown heat-fusible ultrafine composite fiber, and having a fiber diameter of about 30 to 4000 d /
The filter medium according to claim 1, wherein f, a net using a heat-fusible composite monofilament having a weaving density of about 0.5 to 25 fibers / 25 mm are laminated and then heat-sealed. 4. The filter medium according to claim 1, wherein the maximum pore diameter change rate after heating is 20% or less. 5. An air permeability of 0.1 to 100 cc / cm ² .
The filter medium obtained by pleating the filter medium according to claims 1 to 4 having a sec and a tensile strength of 2 to 100 kg / 5 cm. 6. The filter medium according to claim 1, wherein the non-woven fabric is electretized.