JP2006150275A - Method for filter material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a filter material in which a PTFE porous film and a permeable supporting material are unified by excellent adhering force without damaging permeability. <P>SOLUTION: Two layers of permeable heat-fusible members with different softning points are prepared, a polytetrafuruoroeyhylene (PTFE) porous film 11, a heat-fusible member with a higher softning point 121, a heat-fusible member with a lower softning point 122 and the permeable support material 13 are stacked in this order, and the laminate is pressurized under a heating condition, thereby the filter material 1 unified by melting by heat the two layers of the fusible-members being manufactured. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a filter medium used for collecting dust and collecting a target substance, and a filter unit using the filter medium.

  Conventionally, various dust collectors have been used for dust removal and collection of valuable powders and chemical compounds, and in recent years they are excellent in miniaturization and handling. Type filter media are widely used.

  The filter medium is generally configured to include a filter and a breathable support, and as the breathable support, a relatively hard and firm spunbond formed member mainly composed of polyester or polypropylene, Cylindrical or flat plates that are pleated to increase the area within the volume are used. A method of forming such a filter into a cartridge type has already been disclosed (see, for example, Patent Document 1 and Patent Document 2).

  On the other hand, in recent years, PTFE porous membranes have been widely used as the filter because of its excellent collection properties, heat resistance, chemical resistance, low energy detergency, etc. It is used in a form laminated with a breathable support such as canvas. Lamination of the PTFE porous membrane and the air-permeable support material is performed by, for example, a method using an adhesive, a method of thermally melting the air-permeable support material and fusing the PTFE porous membrane, and the like. . However, since the air-permeable support material generally has irregularities in the surface shape thereof, the PTFE porous membrane may be damaged by the irregularities during lamination, which may cause cracks. In the conventional laminating technique, for example, the PTFE porous membrane is adhered only to the surface convex portion of the air-permeable support material, and the PTFE porous membrane is not adhered to the surface concave portion. For this reason, when the filter medium is used or when the filter medium is finally pleated, the PTFE porous membrane is destroyed, and as a result, sufficient collection efficiency cannot be obtained, and the dust detachability also deteriorates. There is a risk of increased pressure loss.

Therefore, in order to solve this problem, a PTFE porous material is formed by disposing a breathable heat-sealing member such as a hot-melt non-woven fabric between the PTFE porous membrane and the breathable support material, and thermally melting the member. A method of integrating a membrane and a breathable support material has been studied (for example, Patent Document 3). According to such a method, damage due to surface irregularities of the breathable support material can be avoided.
JP 2001-293310 A JP 2001-293316 A Japanese Patent Laid-Open No. 09-206568

  However, recently, there is a demand for a material having superior adhesion between the porous PTFE membrane and the air-permeable support material as compared with the filter medium disclosed in Patent Document 3.

  The present invention has been made in view of such circumstances, and manufacture of a filter medium that can integrate a PTFE porous membrane and a breathable support material with an excellent adhesive force without impairing the breathability. It aims to provide a method.

In order to achieve the above object, a method for producing a filter medium according to the present invention includes laminating a polytetrafluoroethylene (PTFE) porous membrane, a breathable heat-fusible member, and a breathable support material in this order. A filter medium that integrates the PTFE porous membrane and the breathable support material by heat-treating the surface of either the porous membrane or the breathable support material and thermally melting the breathable heat-fusible member A manufacturing method of
The breathable heat fusion member is a two-layer breathable heat fusion member having different softening points,
A method for producing a filter medium, wherein a heat-sealing member is arranged so that a layer having a high softening point is located on the heat treatment side of the laminate. Hereinafter, of the two breathable heat-sealing members, a layer having a high softening point is referred to as a “high softening point layer”, and a layer having a low softening point is referred to as a “low softening point layer”.

  Conventionally, when the PTFE porous membrane and the air-permeable support material are heat-sealed with the hot-melt nonwoven fabric, heat treatment is generally performed from the PTFE porous membrane side of the laminate. Therefore, the present inventors examined a laminating method by this heat fusion. As a result, according to the conventional method, for example, when the thickness of the nonwoven fabric is increased for the purpose of avoiding the influence of the uneven shape of the breathable support, the heat from the PTFE porous membrane is directed to the breathable support side of the nonwoven fabric. Since it was not sufficiently transmitted, it was found that the nonwoven fabric may be bonded (fused) to the breathable support in a state where the nonwoven fabric is not sufficiently melted. In particular, if the air-permeable support is a concavo-convex surface formed by embossing or the like, the fusion-bonded portion is limited to the convex portion, so that the adhesion area is reduced. For this reason, the adhesiveness as a whole is significantly reduced. On the other hand, when the thickness of the non-woven fabric is reduced, heat is rapidly and sufficiently transferred, so that the non-woven fabric is sufficiently melted and the adhesion is excellent, but the melt of the non-woven fabric is a void in the breathable support. As a result, the weight per unit area and the air permeability are reduced.

  Therefore, the present inventors, based on these findings, use a two-layer breathable heat-sealing member having different softening points, and provide a high softening point layer on the PTFE side subjected to heat treatment and a low softening point side on the breathable support material side. It has been found that the conventional problem as described above can be solved by disposing a softening point layer and performing heat treatment from the PTFE porous membrane side. If two layers of the breathable heat-sealing member are arranged in this manner, the high softening point layer can be sufficiently melted by performing heat treatment from the PTFE porous membrane side at a temperature at which the high softening point layer melts. Since the low softening point layer has a lower softening point than the high softening point layer, for example, even if heat is not sufficiently transferred to the low softening point layer through the high softening point layer, the low softening point layer is sufficiently melted. It can be done. For this reason, the PTFE porous membrane and the high softening point layer, the high softening point layer and the low softening point layer, the low softening point layer and the breathable support material are sufficiently thermally fused, respectively, The material does not enter the pores of the air-permeable support material, and the weight per unit area does not decrease or the air permeability does not decrease. In addition, even when the surface of the air-permeable support material has an uneven shape and is bonded to the air-permeable heat-sealing member only by the convex portions, the low softening point layer is sufficiently melted, However, the adhesive strength of the bonded portion is sufficiently stronger than before. In the case where the heat treatment is on the breathable support material side, the same effect can be obtained if the breathable heat fusion member is arranged so that the high softening point layer is located on the breathable support material side. Can do. As described above, according to the production method of the present invention, it is possible to provide a filter medium having excellent air permeability and excellent adhesiveness.

  Below, the manufacturing method of the filter material of this invention is demonstrated concretely. Hereinafter, unless otherwise specified, a breathable heat-sealing member is disposed so that a high softening point layer is located on the PTFE porous membrane side and a low softening point layer is located on the breathable support material side, and this laminate is referred to as the PTFE. It is set as the description about the form which heat-processes from the porous membrane side. In the case where the heat treatment is performed from the breathable support material side, the breathable heat fusion member is arranged so that the high softening point layer is located on the breathable support material side and the low softening point layer is located on the PTFE porous membrane side. What is necessary is just to arrange | position and other conditions are not restrict | limited in particular.

  “Softening point” generally refers to the temperature at which a heated substance begins to soften and begin to deform. In the present invention, differential thermal analysis (DSC) is performed on each layer of the breathable heat-sealing member, and the peak value is obtained. Is the softening point of each layer. The DSC can be measured using, for example, trade name DSC-6200 (manufactured by SEIKO Instrument Inc.). This softening point determination method is used only for specifying the softening point, and does not limit the manufacturing method, use, application, etc. of the filter medium of the present invention.

  In the present invention, the difference in softening point between the high softening point layer and the low softening point layer is not particularly limited, but is preferably 5 ° C. or higher. If the difference between the softening points is 5 ° C. or more, for example, even if the heat necessary for melting the high softening point layer in practice is not transferred to the low softening point layer, the low softening point layer is sufficiently Can be melted. For this reason, even when laminating continuously, for example, the importance of setting time for transferring heat can be greatly reduced, and a desired production rate can be secured.

  The upper limit of the difference between the softening points is not particularly limited, but is preferably 60 ° C. or less. If it is 60 ° C. or lower, for example, even if it is treated at a high temperature to melt the high softening point layer, damage to the other fusion member due to heat is extremely suppressed, and melting of the low softening point layer is prevented. It can be sufficiently avoided that the air-permeable support is clogged due to the excessive progress. The difference is more preferably 5 to 30 ° C.

  The softening point of the high softening point layer is, for example, 140 to 235 ° C. On the other hand, the softening point of the low softening point layer is, for example, 105 to 200 ° C.

  The material of each layer of the breathable heat fusion member is not particularly limited as long as it can be melted and fused by heat, and examples thereof include various resins such as polyester, nylon, polyolefin, and urethane. . In addition, the form of each layer is not particularly limited as long as it exhibits air permeability. For example, the nonwoven fabric, woven fabric, knitted fabric, net, etc. formed from resin fibers as described above are used. Examples thereof include a porous film, and a nonwoven fabric is particularly preferable. Note that the two-layer breathable heat-sealing member may be arranged with an independent high softening point layer and a low softening point layer in order during the production of the filter medium, or a high softening point layer and a low softening point layer. You may use the laminated body integrated previously.

  For the combination of the high softening point layer and the low softening point layer, for example, two types of fusion members having a softening point difference of 5 ° C. or more may be selected from commercially available products. As the commercially available fusion member, for example, various non-woven fabrics are preferable. The product name Elves, the product name Niace, the product name Marix, etc., manufactured by Unitika Co., Ltd., the product name Superlace, the product name Haibon, manufactured by Toyobo Co., Ltd. Product name Shan Fine, product name Balcompo, product name Borans, product name Spash made by Asahi Kasei Co., Ltd. product name Eltus, product name Espancione made by Kanebo Co., Ltd., product name Okiron made by Daiki Shoji Co., Ltd. The brand name is Milife. Moreover, as a laminated body in which two layers of nonwoven fabrics having different softening points are integrated in advance, for example, a commercial product such as trade name Milife TLY0505E (manufactured by Nisseki Plast Co., Ltd.) can be used.

  Further, since the high-softening point layer is mainly intended for fusion with the PTFE porous membrane and the low-softening point layer is fusion with the air-permeable support material, in addition to the difference in softening point, PTFE is further added. It can also be determined appropriately according to the type of the material and the type of the breathable support material.

In addition to the softening point, each layer is preferably selected based on characteristics such as basis weight, strength, and air permeability. The fragile air permeability of each layer is preferably 50 cm ³ / cm ² / sec or more, preferably 100 cm ³ / cm ² / sec or more, more preferably, since the air permeability of the obtained filter medium can be sufficiently secured. Is in the range of 200 to 400 cm ³ / cm ² / sec, and the upper limit is not particularly limited, but is, for example, 500 cm ³ / cm ² / sec or less. Moreover, when the air-permeable heat fusion member is a laminate in which a high softening point layer and a low softening point layer are integrated in advance, the same range is preferable.

  The thickness of each layer is, for example, 10 to 300 μm, preferably 10 to 200 μm, and more preferably 10 to 100 μm. Moreover, the total thickness of the high softening point layer and the low softening point layer is, for example, 20 to 600 μm, preferably 20 to 400 μm, and more preferably 20 to 200 μm.

The fragile air permeability of the PTFE porous membrane can sufficiently ensure the air permeability of the obtained filter medium, and for example, it can sufficiently suppress an increase in pressure loss when used in a dust collector, so that it is at least 4 cm ³ / cm ² / sec. The upper limit is not particularly limited, but is preferably 30 cm ³ / cm ² / sec or less, and more preferably 8 to 20 cm ³ / cm ² / sec.

  The thickness of the PTFE porous membrane can be determined as appropriate depending on, for example, the size of the filter medium to be produced. For example, the thickness is in the range of 2 to 100 μm, and the pore diameter is in the range of 0.5 to 50 μm, for example. .

  The PTFE porous membrane can be manufactured, for example, as follows. That is, first, a liquid lubricant is added to the unfired PTFE fine powder and mixed uniformly. The PTFE fine powder is not particularly limited, and a commercially available product can be used. The liquid lubricant is not particularly limited as long as it can wet the PTFE powder and can be removed later. Hydrocarbon oils such as naphtha, white oil, liquid paraffin, toluene, xylene, alcohols, ketones And solvents of esters and the like can be used. These may be used alone or in combination of two or more.

  The addition ratio of the liquid lubricant to the PTFE fine powder can be appropriately determined according to the type of the PTFE fine powder, the type of the liquid lubricant, and the conditions of sheet molding described later. For example, for 100 parts by weight of the PTFE fine powder The liquid lubricant is in the range of 5 to 50 parts by weight.

  Next, the mixture is formed into a sheet in an unfired state. Examples of the forming method include a rolling method in which the mixture is extruded into a rod shape and then rolled with a pair of rolls, and an extrusion method in which the mixture is extruded into a plate shape to form a sheet. Moreover, you may combine both methods. Although the thickness of this sheet-like molded object can be suitably determined according to the conditions of the extending | stretching performed later, etc., it is the range of 0.1-0.5 mm, for example.

  The liquid lubricant contained in the obtained sheet-like molded body is preferably removed by, for example, a heating method or an extraction method before the subsequent stretching step. The solvent used in the extraction method is not particularly limited, and examples thereof include normal decane, dodecane, naphtha, kerosene, and sumoyl.

  Then, it extends | stretches with respect to the said sheet-like molded object. The sheet-like molded body is made porous by uniaxial stretching or biaxial stretching at a temperature not higher than the melting point (327 ° C.) of PTFE. For example, in the longitudinal direction of the sheet-like molded body, the sheet is stretched at a temperature of 150 to 327 ° C. so that the length thereof is in the range of 2 to 30 times the length before stretching, and then the sheet is formed. In the width direction of the shaped molded body, it is stretched at a temperature of 30 to 320 ° C. so that its length is in a range of 2 to 30 times the length before stretching. After the stretching, the stretched state is maintained and heated to a temperature equal to or higher than the melting point (327 ° C.) of PTFE and fired to improve mechanical strength and increase dimensional stability. Thus, a PTFE porous membrane can be produced. In addition, in this invention, the manufacturing method of a PTFE porous membrane is not limited to the above-mentioned method, You may create with another method and may use a commercial item.

  The air-permeable support material is not particularly limited, for example, in terms of the surface shape (for example, the shape and number of irregularities), but is preferably one that can be pleated. Further, as a constituent material of the breathable support material, for example, a woven fabric, a fusion member, a metal or plastic mesh, a metal or plastic net, a plastic foam, or the like can be used. Among the constituent materials, a fiber member is preferable, and a fusion member is particularly preferable from the viewpoint of cost. Examples of the fibers include semi-synthetic fibers such as cellulose and viscose, and synthetic fibers such as polyester, polyolefin, polyamide, acrylic, polysulfone, polyamideimide, polyimide, polyphenylene sulfide, and polyvinylidene fluoride. The breathable support material may be a commercially available product. For example, the product name Acter series manufactured by Toray Industries, Inc., the product name VC-1 series manufactured by Japan Vilene Co., Ltd., the product name Borance manufactured by Toyobo Co., Ltd. Name best shots.

  Next, an example of the production method of the present invention will be described with reference to FIG. FIG. 1 is a cross-sectional view showing an example of a laminated form of components used in the manufacturing method of the present invention.

  First, as shown in FIG. 1, the PTFE porous membranes 11 and 2, the breathable heat-sealing members 121 and 122 and the breathable support 13 are laminated in this order. As described above, the breathable heat-sealing member includes a high softening point layer and a low softening point layer having different softening points, the high softening point layer 121 is the PTFE porous membrane side, and the low softening point layer 122 is the breathable support. It arrange | positions so that it may be located in the material side. When heat treatment is performed from the breathable support side instead of the PTFE porous membrane side, on the contrary, a low softening point layer is located on the PTFE porous membrane side and a high softening point layer is located on the breathable support material side. Thus, a breathable heat fusion member may be disposed.

  And the filter medium of this invention can be formed by heat-processing with respect to the laminated body 1 shown in FIG. 1 from the PTFE porous membrane 11 side. Specifically, the high softening point layer 121 and the low softening point layer 122 are thermally melted by the heat treatment, and the PTFE porous film 11 and the high softening point layer 121, the high softening point layer 121 and the low softening point layer 122, low The softening point layer and the air-permeable support material 13 are integrated as a whole by heat-sealing each. And since the said air-permeable heat sealing | fusion member fuse | melts by the fusion | melting of the material, air permeability is ensured, for example in the part without a fiber, and a void | hole part. The filter medium may be further pleated.

  The conditions for the heat treatment can be set according to the softening points of the high softening point layer and the low softening point layer to be used. The heating temperature is preferably, for example, a temperature 5 ° C. or more away from the softening point of the high softening point layer, more preferably 5-30 ° C., particularly preferably 5-15 ° C. is there. The heating time can be appropriately determined according to the thickness of the breathable heat-sealing member, the thickness of each layer constituting the member, and the heating temperature, and is, for example, 20 seconds or less, particularly preferably 5 seconds or less.

  It is preferable that the thermal fusion of the laminate is performed while applying an appropriate pressure to the laminate. The pressure is, for example, 0.1 to 0.7 MPa, and preferably 0.3 to 0.5 MPa. Under these conditions, it is preferable to nip with a roll or the like.

  The filter medium of the present invention obtained by such a manufacturing method is excellent in ventilation as described above, and also excellent in adhesiveness of constituent members. For this reason, for example, there is no problem such as generation of cracks caused by peeling of the constituent members at the time of use or pleating, which is extremely useful. The use is not particularly limited. For example, for the purpose of dust removal, application to vacuum cleaners, dust collectors in plants, valuable powders such as wheat flour in the food field, or chemical compounds, cement and metal powders. Etc. can be applied to an apparatus for the purpose of collecting the like. The filter medium of the present invention can be used by being attached to a general dust collecting part, a collecting part or the like in these apparatuses. Further, the filter medium of the present invention is preferably used with a cartridge type filter medium, or attached to a frame and used as an air filter unit.

  The pressure loss of the filter medium of the present invention is, for example, 100 to 500 Pa, and preferably 150 to 300 Pa. Moreover, the collection efficiency is 97-100%, for example, Preferably it is 98-100%. In addition, the said collection efficiency was measured using the dioctyl phthalate aerosol which is 13 types of test dust according to JISZ8901, and the collection efficiency of the particle | grains of 0.3-0.5 micrometer was calculated | required.

  Next, examples of the present invention will be described together with comparative examples.

A PTFE porous membrane, a breathable heat-sealing member (high softening point layer, low softening point layer) and a breathable support were arranged in this order. The breathable heat-sealing member was disposed so that the high softening point layer was located on the PTFE porous membrane side. And the target filter material was produced (300 micrometers in thickness) by carrying out pressure lamination (pressurization conditions 0.5MPa) of this laminated body using the heating roll heated at 190 degreeC. The heat treatment was performed from the PTFE porous membrane side. The PTFE porous membrane is made of Nitto Denko Corporation with a thickness of 10 μm and an average pore size of 1.5 μm, and the high softening point layer is a trade name Moyster M16 (Daki non-woven fabric, PET non-woven fabric, thickness 0.08 mm, basis weight 16g / m ² in volume, breathability 400cm ³ / cm ² / sec, DSC peak temperature 185 ° C), low softening point layer is trade name Shanfine PM010JF (manufactured by Toyobo Co., Ltd., PP non-woven fabric by melt blow method, thickness 0.09mm , Weight per unit area 10g / m ² , Breathability 45cm ³ / cm ² / sec, DSC peak temperature 162 ° C), As a breathable support, trade name AXTER G2260-1S (manufactured by Toray Industries, embossed, thickness 0.6mm, basis weight Amount 260 g / m ² and breathability 12 cm ³ / cm ² / sec) were used respectively. The difference between the softening points of the high softening point layer and the low softening point layer is 23 ° C.

As a breathable heat-sealing member, an integrated product (trade name: Milife) that combines a PET nonwoven fabric (high softening point layer) with a DSC peak temperature of 220 ° C and a PET nonwoven fabric (low softening point layer) with a DSC peak temperature of 195 ° C. TLY0505E, manufactured by Nisseki Plast Co., Ltd., with a thickness of 0.05 mm, weight per unit area of 10 g / m ² , breathability of 400 cm ³ / cm ² / sec), PTFE porous membrane, breathable heat fusion member, and breathability A target filter medium filter was prepared (thickness: 250 μm) in the same manner as in Example 1 except that the supports were laminated in this order and these were pressure-laminated at 230 ° C. The breathable heat-sealing member was disposed so that the PET nonwoven fabric (high softening point layer) having a DSC peak temperature of 220 ° C. was positioned on the PTFE porous membrane side. The difference between the softening points of the high softening point layer and the low softening point layer is 25 ° C.

Except for using the product name Borans 4141P (made by Toyobo Co., Ltd., thickness 1.0 mm, weight per unit area 140 g / m ² , breathability 220 cm ³ / cm ² / sec) as an air-permeable support, the above examples The target filter medium was prepared in the same manner as in No. 2 (thickness 220 μm). The difference between the softening points of the high softening point layer and the low softening point layer is 25 ° C.

(Comparative Example 1)
In place of the two-layer breathable heat-sealing member, one-layer product name Ecule 3151A (Toyobo Co., Ltd., PET-based nonwoven fabric, thickness 0.13 mm, basis weight 15 g / m ² , breathability 400 cm ³ / cm ² / sec, A filter medium was prepared (thickness: 240 μm) in the same manner as in Example 1 except that only DSC peak temperature (252 ° C.) was used and pressure lamination was performed at 210 ° C.

(Comparative Example 2)
A filter medium was prepared in the same manner as in Example 1 except that the breathable heat-sealing member in Example 1 was disposed so that the high softening point layer was located on the breathable support side.

  The filter media of Examples 1 to 3, Comparative Example 1 and Comparative Example 2 were confirmed for air permeability and adhesiveness by the following methods.

(Visual test for adhesion)
As shown in FIG. 2, an adhesion test (visual observation) was performed on each filter medium. FIG. 2 is a cross-sectional view showing an outline of the adhesion test, and the same portions as those in FIG. As a test tool, as shown in FIG. 2, a funnel-shaped lower base material 211 composed of a stainless steel tube portion, a taper portion, and a cylindrical portion, and an upper base material 212 having a circular opening at the top are formed. Used tools. A filter medium cut into a circle (diameter: 4.7 cm) was disposed on a convex portion provided on the inner side surface of the lower substrate 211 through a commercially available O-ring made of silicon or chloroprene. At this time, the filter medium 1 was arranged so that the air-permeable support 13 was on the lower side. And the upper base material 212 was further arrange | positioned through the O-ring made from a silicon | silicone or chloroprene at the PTFE porous membrane side of the said filter medium.

  Then, from the tube portion of the lower base material 211 of the test tool toward the direction of the arrow, pressurization was performed with air for 10 seconds (pressure 0.7 MPa) and left for 5 seconds. This operation was repeated once. And about the filter medium after a pressurization process, the presence or absence of a crack, peeling of the air-permeable support body 13 and the low softening point layer 122, or the presence or absence of peeling of the high softening point layer 121 and the low softening point layer 122 was confirmed. .

  The air permeability of the filter medium was measured according to the fragile method described in JIS K1096.

(Adhesion test)
As shown in FIG. 3, each filter medium was subjected to a 180 ° C. folding peel test. FIG. 3 is a cross-sectional view showing an outline of the peeling test, in which the same parts as those in FIG. First, the filter medium 1 (length 100 mm, width 20 mm) was placed and fixed on a horizontal table so that the PTFE porous membrane 11 was on top. Then, as shown in the cross-sectional view of FIG. 3, an adhesive tape 3 (trade name No. 500: manufactured by Nitto Denko Corporation) having a length of 20 cm, a width of 2 cm, and a thickness of 170 μm is applied from the center side in the longitudinal direction of the filter medium 1. After pasting toward one end (the length of the pasted portion is 6 cm), the adhesive tape 3 is folded back 180 ° at the end of the filter medium 1 and is not adhered to the filter medium 1 The end of the adhesive tape 3 was pulled at a pulling speed of 300 mm / min in the direction of the arrow in FIG. The average force required to pull the tape 20 mm was then measured. In addition, by pulling an adhesive tape, Examples 1-4 are between the high softening point layer 121 and the low softening point layer 122, and the comparative example 1 and the comparative example 2 are the nonwoven fabric 122 and the air-permeable support body 13. In each case, peeling occurred.

(Table 1)
Adhesive breathability
Visual (N / 20mm) (cm ³ / cm ² / sec)
Example 1 No peeling 9.1 2.4
Example 2 No peeling 6.3 3.3
Example 3 No peeling 10.3 4.5
Example 4 No peeling 3.2 3.1
Comparative Example 1 Peeling 0.6 3.1
Comparative Example 2 Peeling 1.2 0.3

  As shown in Table 1, according to the filter media of Examples 1 to 4, compared with Comparative Examples 1 and 2 that do not use a low softening point layer, high softening is also obtained by a test using the measuring tool of FIG. No peeling or cracking was observed between the point layer and the low softening point layer, and the adhesive strength between the two was extremely high. Moreover, Examples 1-4 were excellent also in air permeability. On the other hand, in Comparative Examples 1 and 2, peeling occurred and the adhesive strength was inferior.

  According to the production method of the present invention, it is possible to produce a filter medium that is excellent in air permeability and also excellent in adhesion between the porous PTFE membrane and the air permeable support material. For this reason, even when the filter medium is used or when it is processed into a pleated shape, there is no problem such as cracking of the PTFE porous membrane or peeling, and excellent collection efficiency can be maintained.

It is sectional drawing which shows an example of the lamination | stacking state of each member in the manufacturing method of this invention. It is sectional drawing which shows the outline of the test tool used for the Example of this invention. It is sectional drawing which shows the form of the peeling test in the Example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Laminated body 11 PTFE porous membrane 121 High softening point layer 122 Low softening point layer 13 Breathable support material

Claims (9)

A polytetrafluoroethylene (PTFE) porous membrane, a breathable heat-sealing member, and a breathable support material are laminated in this order, and heat treatment is performed from the surface of either the PTFE porous membrane or the breathable support material. A method for producing a filter medium that integrates the PTFE porous membrane and the breathable support material by thermally melting the breathable heat fusion member,
The breathable heat fusion member is a two-layer breathable heat fusion member having different softening points,
A method for producing a filter medium, wherein a heat-sealing member is arranged so that a layer having a high softening point is positioned on the heat treatment side of the laminate. The manufacturing method according to claim 1, wherein the heat-sealing member is arranged so that the layer having a high softening point is located on the PTFE porous membrane side, and heat treatment is performed from the PTFE porous membrane side. The method according to claim 1 or 2, wherein a difference in softening point between the two-layer breathable heat-sealing members is 5 ° C or more. The method according to claim 3, wherein the difference in softening point between the two-layer breathable heat-sealing members is 5 to 60 ° C. The manufacturing method according to any one of claims 1 to 4, wherein the fragile air permeability of the two-layer breathable heat-sealing member is 50 cm ³ / cm ² / sec or more. The manufacturing method according to any one of claims 1 to 5, wherein the PTFE porous membrane has a fragile air permeability of 4 cm ³ / cm ² / sec or more. The manufacturing method according to any one of claims 1 to 6, wherein the breathable heat fusion member is a nonwoven fabric. The manufacturing method as described in any one of Claims 1-7 which heat-processes on pressurization conditions. The manufacturing method according to any one of claims 1 to 8, further comprising pleating after the PTFE porous membrane and the breathable support material are integrated.

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