WO2022158412A1

WO2022158412A1 - Substrate for filter, and filtration material for filter

Info

Publication number: WO2022158412A1
Application number: PCT/JP2022/001331
Authority: WO
Inventors: 隆之中村; 元道福田; 常括竹内; 祐介志水
Original assignee: 三菱製紙株式会社
Priority date: 2021-01-21
Filing date: 2022-01-17
Publication date: 2022-07-28

Abstract

The present invention addresses the problem of obtaining: a substrate for a filter in which pressure loss does not readily increase when affixed through thermal fusion, and in which high peel strength is obtained between a porous film and the substrate for a filter; and a filtration material for a filter in which the substrate for a filter is used.　The present invention is a substrate for a filter to be used as a filtration material for a filter in which a porous film is affixed by thermal fusion, wherein the substrate for a filter is a wet non-woven fabric including non-binder fibers (NB) and thermally fusible binder fibers (B). The present invention is also a filtration material for a filter in which the aforementioned substrate for a filter is used.

Description

Filter base material and filter medium

The present invention relates to a filter substrate and a filter medium.

BACKGROUND ART Conventionally, porous membranes have been used as filter media for air filters and filter media for liquid filters. Porous membrane materials include polytetrafluoroethylene (PTFE).
Moreover, polyolefins, such as polyethylene (PE) and polypropylene (PP), are mentioned. In particular, these porous membranes can achieve high collection efficiency and low pressure loss, so they are used as filter media for air filters in clean room filters and cyclone vacuum cleaner filters that require high collection efficiency. .
In addition, due to its high chemical resistance, filters for water purification, industrial wastewater, industrial water, etc., may be subjected to harsh conditions such as cleaning work with strong alkalis such as sodium hydroxide. It is also widely used as a filter medium for liquid filters.
However, as described in Non-Patent Document 1, the porous membrane has low mechanical strength and also has a problem in dimensional stability, so it is difficult to use the porous membrane alone. Therefore, there is a need for a filter material that is a composite of a filter substrate and a porous membrane. Nonwoven fabrics are often used as filter substrates from the viewpoint of flexibility and porosity.

Hereinafter, "filter base material" may be abbreviated as "base material", and "filter medium" may be abbreviated as "filter medium".

Combining the base material and the porous membrane is performed by bonding by heat fusion, bonding with an adhesive, or the like. Bonding with an adhesive is not preferable because the adhesive clogs the pores of the porous membrane, which may lead to an increase in pressure loss and a decrease in collection efficiency. Therefore, it is preferable to form a composite by bonding by thermal fusion. Lamination by thermal fusion bonding involves lamination by heat-pressure treatment, and the heat-pressure treatment increases the density of the base material, which may increase the pressure loss. In addition, due to insufficient peel strength due to heat and pressure treatment, the porous membrane may peel off from the substrate during use of the filter. Therefore, the filter base material is required to have a high peel strength, which is difficult to achieve a high density when bonded by thermal fusion bonding.

Also, although PTFE has high chemical resistance, it may be difficult to use it as a liquid filter under severe conditions unless the filter base material also has high chemical resistance. For example, if the base material for a filter shrinks or deteriorates during cleaning work with strong alkali, when it is used again as a filter, damage to the base material or liquid leakage may occur, resulting in use as a filter for liquids. can be difficult to do.

The base material to be combined with the porous membrane is, for example, made of polyolefin-based resin or polyester-based resin, has a weight per unit area of 40 g/m ² to 120 g/m ² , a thickness of 0.3 mm to 0.9 mm, and is burstable. A nonwoven fabric having a strength of 199 kPa to 600 kPa, a puncture strength of 8 N to 24 N, and a porosity of 65% to 90% is disclosed (see Patent Document 1). However, with the base material disclosed in Patent Document 1, there is a concern that the base material becomes denser and the pressure loss increases when the base material is attached by thermal fusion bonding, and the peel strength between the porous membrane and the base material is not sufficient. Therefore, there was a concern that problems such as peeling of the porous membrane from the substrate would occur. In addition, in the filtration membrane element disclosed in Patent Document 1, although applications utilizing the high chemical resistance of the PTFE porous membrane have been proposed, the chemical resistance of the nonwoven fabric on which the PTFE porous membrane is laminated has not been considered. There was a concern that the non-woven fabric would deteriorate, break or shrink during cleaning work after use as a filtration membrane element.

Patent Document 2 discloses a spunbond nonwoven fabric made of core-sheath composite fibers of polyester/polyethylene as a base material (see Patent Document 2). However, even in the base material of Patent Document 2, the base material has a high density during bonding by thermal fusion bonding, and there is a concern that the pressure loss will increase, and the peel strength between the base material and the porous membrane is not sufficient. There was a concern that problems such as the porous membrane peeling off from the substrate would occur. In addition, the filter medium of Patent Document 2 is assumed to be used only for air filters, and is not assumed to be used as a filter for liquids. There was a concern that problems such as deterioration of the nonwoven fabric would occur when it was used.

Under these circumstances, there is a demand for a filter base material that does not easily increase the pressure loss during bonding by thermal fusion bonding and that provides high peel strength between the porous membrane and the base material. ing. In addition, there is a demand for a filter base material that is excellent in chemical resistance and does not easily deteriorate even when placed under severe conditions such as strong alkali.

JP 2014-240047 A JP-A-10-211409

An object of the present invention is to obtain a filter base material in which the pressure loss does not easily increase and a high peel strength can be obtained between the porous membrane and the filter base material when they are attached by thermal fusion bonding. is. Another object of the present invention is to obtain a filter base material that is excellent in chemical resistance and is resistant to deterioration even when used under severe conditions such as strong alkali.

Another object of the present invention is to provide a filter material for filters that is resistant to pressure loss, has peel strength, has excellent chemical resistance, and is resistant to deterioration even when used under severe conditions such as strong alkali.

The above issues can be resolved by the following means.

[Filter substrate <1>]
1. In a filter base material for use as a filter material for a filter by laminating a porous membrane by thermal fusion,
(1) the filter substrate is a wet-laid nonwoven fabric containing non-binder fibers (NB) and heat-fusible binder fibers (B);
(2) The blending ratio of the heat-fusible binder fiber (B) is 20 to 90% by mass, and the blending ratio of the non-binder fiber (NB) is 10, based on the total fiber components contained in the wet-laid nonwoven fabric. 80% by mass of the filter base material.
2. 2. The filter substrate according to claim 1, wherein said non-binder fibers (NB) are at least one selected from the group consisting of synthetic fibers and wood pulp.
3. 3. The filter substrate according to the preceding item 1 or 2, wherein the heat-fusible binder fiber (B) is a sheath-core fiber.
4. 4. The filter substrate according to any one of 1 to 3 above, which has a basis weight of 30 to 120 g/m ² .
[Filter substrate <2>]
5. In a filter base material for use as a filter material for a filter by laminating a porous membrane by thermal fusion,
(1) the filter base material is a wet-laid nonwoven fabric comprising a layer (X) and a layer (Y), at least one of which is the layer (X) as the outermost layer;
(2) The layer (X) contains synthetic fibers as non-binder fibers (NB) and heat-fusible binder fibers (B), and the blending ratio of the heat-fusible binder fibers (B) is 50% by mass. A layer with a basis weight of 5 g/m ² or more and 60 g/m ² or less,
(3) Layer (Y) contains synthetic fibers as non-binder fibers (NB) and heat-fusible binder fibers (B), and the blending ratio of heat-fusible binder fibers (B) is 50% by mass. less than 100 g/m 2 and a basis weight of 25 g/m ² or more and 120 g/m ² or less.
6. 6. The filter substrate according to 5 above, wherein the synthetic fiber as the non-binder fiber (NB) is a polyester fiber.
7. 7. The filter substrate according to 5 or 6 above, wherein the heat-fusible binder fiber (B) is a sheath-core fiber.
[Filter substrate <3>]
8. In a filter base material for use as a filter material for a filter by laminating a porous membrane by thermal fusion,
(1) the filter substrate is a wet-laid nonwoven fabric containing non-binder fibers (NB) and heat-fusible binder fibers (B);
(2) containing a drawn polyester fiber as the non-binder fiber (NB),
(3) The heat-fusible binder fiber (B) contains a core-sheath type polyester fiber (CSP) whose sheath is a crystalline copolyester,
(4) A filter base material, wherein the compounding ratio of the core-sheath type polyester fiber (CSP) is 5% by mass or more with respect to the total fibers contained in the filter base material.
9. The crystalline copolyester of the sheath of the core-sheath type polyester fiber (CSP) is
(i) a copolymer polyester whose dicarboxylic acid component is terephthalic acid and whose diol component is ethylene glycol and tetramethylene glycol;
(ii) a copolymer polyester in which the dicarboxylic acid component is terephthalic acid and the diol component is ethylene glycol, tetramethylene glycol and ε-caprolactone; and (iii) the dicarboxylic acid component is terephthalic acid and isophthalic acid and the diol component is ethylene. 9. The filter substrate according to 8 above, which is at least one selected from the group consisting of copolymerized polyesters of glycol and tetramethylene glycol.
10. 10. The filter base material according to item 8 or 9, which has a basis weight of 30 to 180 g/m ² .
[Filter material for filter]
11. A filter material for a filter comprising the filter substrate and the porous membrane according to any one of the preceding items 1 to 10.
12. 12. The filter medium for filters according to 11 above, wherein the material of the porous membrane is polytetrafluoroethylene.

According to the present invention, it is possible to obtain a filter substrate that achieves both high collection efficiency and low pressure loss, and provides high peel strength between the porous membrane and the filter substrate.
Moreover, according to the present invention, it is possible to obtain a filter base material which is excellent in chemical resistance and hardly deteriorates even when used under severe conditions such as strong alkali.

The filter material for filters of the present invention is resistant to pressure loss, has peel strength, has excellent chemical resistance, and is resistant to deterioration even when used under severe conditions such as strong alkali.

The filter base material of the present invention is a filter base material for use as a filter material for a filter by laminating a porous membrane by heat-sealing, and the filter base material is a non-binder fiber (NB) and heat-sealed. It is a wet-laid nonwoven fabric containing adhesive binder fibers (B).

<Wet nonwoven fabric>
A wet-laid nonwoven fabric is a nonwoven fabric produced by a wet-laid papermaking method that provides a uniform texture. In the wet papermaking method, each fiber is dispersed in water to prepare a slurry. The slurry is made into paper using a paper machine to obtain a wet-laid nonwoven fabric.

Chemicals added during papermaking include wet strength agents to prevent paper breakage in wet paper conditions, and internal or external sizing agents to stabilize peeling from the Yankee dryer.

In the wet papermaking method, for example, a fourdrinier method, a cylinder method, an inclined wire method, or the like can be used. The filter substrate of the present invention can also be produced using a combination paper machine in which two or more of the same or different papermaking systems selected from these papermaking systems are installed online.
In order to produce a filter base material excellent in uniformity, it is preferable to use a papermaking method such as a Fourdrinier method or an inclined wire method, which can gently dewater the slurry on the wire.
In the case where the filter base material of the present invention has a multi-layered structure of two or more layers, the "paper-making method" in which wet paper sheets made by each paper-making method are laminated, after forming one layer, It can be produced by a "casting method" or the like in which a slurry in which fibers are dispersed is cast and laminated on the layer. In the casting method, when the slurry in which the fibers are dispersed is cast, the layer previously formed may be in a wet paper state or in a dry state. Also, two or more layers can be heat-sealed to form a multi-layered nonwoven fabric.

In the present invention, the mechanical strength of the filter substrate is improved by incorporating the step of raising the temperature of the nonwoven fabric to the melting point or softening temperature of the heat-fusible binder fiber (B) or higher in the manufacturing process.

<Heat fusion>
A filter material for a filter is obtained by laminating the base material for a filter of the present invention and a porous membrane by heat-sealing. Bonding can be performed by heat and pressure treatment. The heat-pressing treatment can be performed by stacking sheets using a hot press or by stacking wound sheets using a hot calender. In order to obtain sufficient peel strength between the wet-laid nonwoven fabric and the porous membrane, the temperature during the heat-pressing treatment is preferably 100° C. or higher, and is higher than the melting point of the heat-fusible binder fiber (B). is more preferable, and 160° C. or higher is even more preferable.

<Porous membrane>
In the present invention, porous membranes such as polyolefins such as polyethylene (PE) and polypropylene (PP); polyethylene terephthalate; polyurethane; polyimide; If a porous membrane with a low heat resistance temperature is used, the porous membrane may soften during heat and pressure treatment, clogging the pores and failing to obtain sufficient Frazier air permeability for use as a filter. Therefore, it is preferable to use PTFE, which has excellent heat resistance. PTFE also has excellent chemical resistance.

[Filter substrate <1>]
The filter substrate <1> of the present invention is a filter substrate for use as a filter material by laminating porous membranes by thermal fusion,
(1) the filter substrate is a wet-laid nonwoven fabric containing non-binder fibers (NB) and heat-fusible binder fibers (B);
(2) The blending ratio of the heat-fusible binder fiber (B) is 20 to 90% by mass, and the blending ratio of the non-binder fiber (NB) is 10, based on the total fiber components contained in the wet-laid nonwoven fabric. It is characterized by being ~80% by mass.

<Non-binder fiber (NB)>
The non-binder fiber (NB) means that the cross-sectional shape of the fiber does not change even at the melting point or softening temperature of the heat-fusible binder fiber (B), or even if the cross-sectional shape changes, the fiber shape is maintained. It is a fiber that has character and serves as the main fiber. In general, the melting point or softening point of the synthetic fiber as the non-binder fiber (NB) is higher than the melting point or softening point of the heat-fusible binder fiber (B).
Also, the non-binder fibers (NB) in the present invention preferably contain organic fibers. Inorganic fibers such as glass fibers and carbon fibers are included in non-binder fibers (NB) in a broad sense. If the binder fibers (NB) are only inorganic fibers, the substrate may be damaged during the heat and pressure treatment. Therefore, the non-binder fibers (NB) preferably contain organic fibers, and more preferably do not contain inorganic fibers.

The cross-sectional shape of the non-binder fibers (NB) is preferably circular. However, fibers having irregular cross-sections such as T-shaped, Y-shaped, and triangular can also be contained within a range that does not impair other characteristics.

The blending ratio of the non-binder fibers (NB) is 10 to 80% by mass, more preferably 20 to 75% by mass, and 30 to 70% by mass with respect to the total fiber components contained in the wet-laid nonwoven fabric. is more preferred. If the blending ratio of the non-binder fibers (NB) is less than 10% by mass, the thickness of the base material is too low during lamination by thermal fusion bonding, resulting in a base material with too high a density, resulting in high pressure loss of the filter medium. too large to be suitable as a filter. On the other hand, when the blending ratio of the non-binder fibers (NB) is more than 80% by mass, the amount of the heat-fusible binder fibers (B) is small, so the fibers easily fall off from the base material, and when used as a filter, the fibers fall off. A problem arises in that the fibers flow downstream and adversely affect it.

The non-binder fibers (NB) preferably contain wood pulp. As wood pulp, bleached hardwood kraft pulp (abbreviation: LBKP, English notation: Hardwood Bleached Kraft Pulp), softwood bleached kraft pulp (abbreviation: NBKP, English notation: Softwood Bleached Kraft Pulp), hardwood bleached sulfite pulp (abbreviation: LBSP) , English name: Hardwood Bleached Sulfite Pulp), Softwood Bleached Sulfite Pulp (abbreviation: NBSP, English name: Softwood Bleached Sulfite Pulp), Hardwood Unbleached Kraft Pulp (abbreviation: LUKP, English name: Hardwood Unbleached Sulfite Pulp) Bleached kraft pulp (abbreviation: NUKP, English notation: Softwood Unbleached Kraft Pulp) and the like. If the fibers of the wood pulp are fine, the pressure loss tends to increase, so although there is no particular limitation, it is preferable that the fiber diameter of the wood pulp is large.

When the non-binder fibers (NB) contain wood pulp, the blending ratio of the wood pulp is not particularly limited, but it is preferably less than 50% by mass, preferably 40% by mass, based on the total fiber components contained in the wet-laid nonwoven fabric. It is more preferably less than 30% by mass, and even more preferably less than 30% by mass. If the blending ratio of the wood pulp is 50% by mass or more, the wood pulp clogs the pores of the base material, which may increase the pressure loss. Peel strength may be reduced.

Also, as non-binder fibers (NB), cotton pulp, straw pulp, bamboo pulp, esparto pulp, bagasse pulp, and hemp pulp can be used.

Non-binder fibers (NB) preferably comprise synthetic fibers. Synthetic fibers as non-binder fibers (NB) include, for example, polyester fibers such as polyethylene terephthalate (PET) fibers and polybutylene terephthalate fibers; polyolefin fibers such as polypropylene fibers and polyethylene fibers; polystyrene or modified polymers and copolymers of these polymers. Polyacrylonitrile fiber; Polyvinyl alcohol fiber; Polyamide fiber; Urethane fiber; Polyphenylene sulfide fiber; fiber obtained by spinning the material; and the like.
As described above, the synthetic fiber as the non-binder fiber (NB) does not change its cross-sectional shape even at the melting point or softening temperature of the heat-fusible binder fiber (B), or changes its cross-sectional shape. It also has the feature of maintaining the fiber shape. Therefore, by blending synthetic fibers, it is possible to obtain the effect that the thickness is less likely to decrease during bonding by thermal fusion bonding, and that the base material is less likely to have a high density.

The fineness of synthetic fibers as non-binder fibers (NB) is preferably 0.1 to 6.0 decitex, more preferably 0.6 to 3.3 decitex. If the fineness of the synthetic fiber is less than 0.1 decitex, the papermaking property tends to be poor, the texture tends to be poor, and the cost is increased. On the other hand, when the fineness of the synthetic fiber exceeds 6.0 decitex, the texture tends to be poor. The synthetic fiber preferably has a fiber length of 2 to 20 mm, more preferably 3 to 10 mm. When the fiber length of the synthetic fiber is less than 2 mm, the fiber tends to come off from the wire in the wet papermaking method, and the yield may decrease. On the other hand, if the fiber length of the synthetic fiber exceeds 20 mm, the screen may be clogged with fibers in the wet papermaking method, making papermaking difficult. In addition, the texture may become uneven due to the entanglement of the fibers.

<Heat-fusible binder fiber (B)>
The fineness of the heat-fusible binder fiber (B) is preferably 0.1 to 6.0 decitex, more preferably 0.2 to 3.3 decitex. When the fineness of the heat-fusible binder fiber (B) is less than 0.1 decitex, the resulting nonwoven fabric has a small thickness and a high density, which may increase the pressure loss. On the other hand, if the heat-fusible binder fiber (B) has a fineness of more than 6.0 decitex, the texture of the nonwoven fabric may be poor and may not be suitable as a filter base material.
The fiber length of the heat-fusible binder fiber (B) is preferably 2-20 mm, more preferably 3-10 mm. When the fiber length of the heat-fusible binder fiber (B) is less than 2 mm, the fiber tends to come off from the wire in the wet papermaking method, and the yield may decrease. On the other hand, if the fiber length of the heat-fusible binder fibers (B) exceeds 20 mm, the fibers may clog the screen in the wet papermaking method, making papermaking difficult. In addition, the texture may become uneven due to the entanglement of the fibers.

Examples of heat-fusible binder fibers (B) include single fibers and composite fibers such as core-sheath fibers (core-shell type) and parallel fibers (side-by-side type).
Examples of monofilaments include fibers of polyethylene, unstretched polyester, unstretched polyphenylene sulfide, and the like.
Composite fibers can improve the mechanical strength without forming a film on the surface of the nonwoven fabric.
Core-sheath fibers include, for example, a combination of polypropylene (core) and polyethylene (sheath), a combination of polypropylene (core) and ethylene vinyl alcohol (sheath), a combination of high-melting polyester (core) and low-melting polyester (sheath), polyester (core) and a combination of polyethylene (sheath). In addition, full-melting type single fibers made only of low-melting resin such as polyethylene tend to form a film in the drying process, and pressure loss may increase, but it can be used as long as it does not impair the characteristics. be able to. In this study, since there is a core portion, the heat-fusible binder fiber (B) is preferably a core-sheath fiber that does not easily decrease in thickness during lamination by heat-sealing.

The blending ratio of the heat-fusible binder fiber (B) is 20 to 90% by mass, more preferably 25 to 80% by mass, more preferably 30 to 70% by mass, based on the total fiber components contained in the wet-laid nonwoven fabric. % is more preferred. If the blending ratio of the heat-fusible binder fibers (B) is less than 10% by mass, there is a problem that a large amount of fibers fall off due to insufficient components for stopping the non-binder fibers (NB). On the other hand, when the blending ratio of the heat-fusible binder fiber (B) is more than 90% by mass, the non-woven fabric has a small thickness and a high density. Unsuitable as a filter due to increased pressure loss.

The melting point of the heat-fusible binder fiber (B) is preferably less than 180°C, preferably less than 170°C, and more preferably less than 160°C. When the melting point of the heat-fusible binder fiber (B) is higher than 180° C., it is necessary to apply a high temperature during lamination by heat-sealing, thereby crushing the synthetic fiber as the non-binder fiber (NB). As it becomes easier, the pressure loss may increase.

<Wet heat adhesive binder fiber (b)>
In addition to the heat-fusible binder fibers (B), wet heat adhesive binder fibers (b) can also be used. Hot water-soluble fibers such as polyvinyl alcohol (PVA)-based fibers can be used as the wet heat adhesive binder fibers (b). The wet heat adhesive binder fiber (b) hardly dissolves in water at room temperature and maintains its fiber form, but when heated on the dryer surface of the wet papermaking method, it begins to dissolve easily, and at that moment the touch roll By pressurizing with a pressurizing facility such as the following, followed by dehydration and drying, it is re-solidified and a binder effect is obtained.

The effect of this wet heat adhesive binder fiber (b) on the adhesive strength can be considered from the softening point in water. The softening point in water roughly indicates the temperature at which the wet paper is heated by a drier in the wet papermaking process, and the wet heat adhesive binder fibers (b) begin to melt and exhibit the adhesive function. As the wet heat adhesive binder (B) having a lower softening point in water is used, the wet heat adhesive binder fiber (b), which is a precondition for adhesion, becomes easier to dissolve and the adhesion effect increases. However, if the softening point in water is too low, there arises a problem that adhesion to the drier is likely to occur.
In order for the wet heat adhesive binder fiber (b) to dissolve, the temperature of the wet paper must be higher than its softening point in water. When the temperature of the wet paper is lower than the softening point of the wet heat adhesive binder fiber (b) in water, the wet heat adhesive binder fiber (b) does not dissolve, and therefore the binder effect is completely lost.
In the case of the Yankee dryer, the steam temperature of the dryer is about 130 to 160°C, and the temperature of the wet paper in contact with it is considered to be 60 to 90°C. The binder fiber (b) preferably has a softening point in water of 65 to 85°C. However, since the wet heat adhesive binder fiber (b) forms a film to close the pores of the base material and does not contribute to adhesion to the porous film even if the heat and pressure treatment is performed in the absence of moisture. Although the blending ratio is not particularly limited, when the wet heat adhesive binder fiber (b) is used, it is preferably less than 20% by mass based on the total fiber components contained in the wet nonwoven fabric. Moreover, there is no problem even if the wet heat adhesive binder fiber (b) is not contained.

Although the fineness of the wet heat adhesive binder fiber (b) is not particularly limited, it is preferably 0.3 to 5.0 dtex, more preferably 1.0 to 3.0 dtex. If the fineness is less than 0.3 decitex, it may fall off from the papermaking wire. On the other hand, if it exceeds 5.0 decitex, it may be difficult to obtain sufficient strength due to the small specific surface area. The fiber length is preferably 3 to 6 mm in consideration of texture and dispersibility.

<Basis weight>
The filter substrate <1> is not particularly limited, but preferably has a basis weight in the range of 30 to 120 g/m ² . If the grammage is less than 30 g/m ² , the strength of the base material is weak and may break during use as a filter. If it is greater than 120 g/m ² , the pressure loss will be high and may not be suitable for use as a filter.

<Density>
Although the density of the filter substrate <1> is not particularly limited, it is preferably 0.1 to 0.5 g/cm ³ . The density can be appropriately adjusted by adjusting the papermaking conditions during wet papermaking, the type of fiber, the blending ratio of fiber, basis weight and thickness. If the density is less than 0.1 g/cm ³ , the fibers may come off during lamination by heat-sealing, causing trouble. If the density exceeds 0.5 g/cm ³ , the pressure loss increases, and it may not be suitable as a base material for filters.

<Production of filter substrate <1>>
The filter substrate <1> can be produced by a wet papermaking method. Filter substrate <1> is a nonwoven fabric produced by a wet papermaking method. That is, the filter substrate <1> is prepared by dispersing the non-binder fiber (NB) and the heat-fusible binder fiber (B) in water at a predetermined ratio to prepare a slurry. It can be produced by making paper using

In the wet papermaking method, for example, a fourdrinier method, a cylinder method, an inclined wire method, or the like can be used. Filter substrate <1> can also be produced using a combination paper machine in which two or more of the same or different papermaking methods selected from these papermaking methods are installed online.
In order to produce a filter base material excellent in uniformity, it is preferable to use a papermaking method such as a Fourdrinier method or an inclined wire method, which can gently dewater the slurry on the wire.
In the case where the filter substrate <1> has a multi-layered structure of two or more layers, the "paper-making method" in which the wet paper made by each paper-making method is laminated, after forming one layer, It can be produced by a "casting method" or the like in which a slurry in which fibers are dispersed is cast and laminated on the layer. In the casting method, when the slurry in which the fibers are dispersed is cast, the layer previously formed may be in a wet paper state or in a dry state. Also, two or more layers can be heat-sealed to form a multi-layered nonwoven fabric.

[Filter material for filter <1>]
The present invention includes a filter medium <1> including the aforementioned filter substrate <1> and a porous membrane.
That is, the filter material <1> is a filter material including a filter substrate and a porous membrane,
(1) The filter substrate is a wet-laid nonwoven fabric containing non-binder fibers (NB) and heat-fusible binder fibers (B),
(2) The blending ratio of the heat-fusible binder fiber (B) is 20 to 90% by mass, and the blending ratio of the non-binder fiber (NB) is 10, based on the total fiber components contained in the wet-laid nonwoven fabric. It is characterized by being ~80% by mass.
The filter base material and the porous membrane are preferably bonded together by thermal fusion.
Polyolefins such as polyethylene (PE) and polypropylene (PP); polyethylene terephthalate; polyurethane; polyimide; and polytetrafluoroethylene (PTFE). If a porous membrane with a low heat resistance temperature is used, the porous membrane may soften during heat and pressure treatment, clogging the pores and failing to obtain sufficient Frazier air permeability for use as a filter. Therefore, it is preferable to use PTFE, which has excellent heat resistance. PTFE also has excellent chemical resistance.
The thickness of the porous membrane is preferably 1-50 μm, more preferably 2-30 μm.

<Fragile Air Permeability>
In order to obtain a low pressure loss, it is preferable to increase the Frazier air permeability of the filter medium. The Frazier air permeability is the air permeability specified by the A method (Frazier type method) described in JIS L1096:2010. The filter medium <1> for filter preferably has a Frazier air permeability of 10 cm ³ /cm ² ·s or more, more preferably 20 cm ³ /cm ² ·s or more. If the Frazier air permeability is lower than 10 cm ³ /cm ² ·s, the pressure loss increases and may not be suitable as a filter medium.

<Production of filter material <1> for filter>
The filter substrate <1> of the present invention and the porous membrane can be heat-sealed to produce a filter medium for a filter.
Bonding can be performed by heat and pressure treatment. The heat-pressing treatment can be performed by stacking sheets using a hot press or by stacking wound sheets using a hot calender. In order to obtain sufficient peel strength between the wet-laid nonwoven fabric and the porous membrane, the temperature during the heat-pressing treatment is preferably 100° C. or higher, and is higher than the melting point of the heat-fusible binder fiber (B). is more preferable, and 160° C. or higher is even more preferable.
The pressure in the heat pressure treatment is preferably 1 to 100 kgf/cm, more preferably 2 to 90 kgf/cm, still more preferably 3 to 80 kgf/cm.

[Filter substrate <2>]
The filter substrate <2> of the present invention is a filter substrate for use as a filter material by laminating porous membranes by thermal fusion,
(1) the filter base material is a wet-laid nonwoven fabric comprising a layer (X) and a layer (Y), at least one of which is the layer (X) as the outermost layer;
(2) The layer (X) contains synthetic fibers as non-binder fibers (NB) and heat-fusible binder fibers (B), and the blending ratio of the heat-fusible binder fibers (B) is 50% by mass. A layer with a basis weight of 5 g/m ² or more and 60 g/m ² or less,
(3) Layer (Y) contains synthetic fibers as non-binder fibers (NB) and heat-fusible binder fibers (B), and the blending ratio of heat-fusible binder fibers (B) is 50% by mass. It is characterized by being a layer having a basis weight of 25 g/m ² or more and 120 g/m ² or less.

When the filter substrate <2> has two layers, it has the following structure.
Layer (X)/Layer (Y)
When the filter substrate <2> has three layers, the following structure can be exemplified.
Layer (X)/Layer (Y)/Layer (Y)
Layer (X)/Layer (Y)/Layer (X)
Layer (X) should be exposed on at least one surface. When the layer structure is layer (Y)/layer (X)/layer (Y), the layer (X) does not come into contact with the porous film, so sufficient peel strength cannot be obtained.
The filter base material <2> is used as a filter medium for a filter by laminating porous membranes by thermal fusion. Layer (X) is a layer in contact with the porous membrane.

<Non-binder fiber (NB)>
In the filter substrate <2>, the synthetic fibers described in the filter substrate <1> can be used as the non-binder fibers (NB).

In the filter substrate <2>, the blending ratio of the synthetic fibers is preferably 10 to 80% by mass, more preferably 20 to 75% by mass, based on the total fiber components contained in the wet-laid nonwoven fabric. , 30 to 70% by mass. If the blending ratio of the synthetic fibers is less than 10% by mass, the thickness of the base material will be too low during the lamination by thermal fusion bonding, resulting in a base material with too high a density. May not be suitable as a filter. On the other hand, when the blending ratio of the synthetic fibers is more than 80% by mass, the amount of the heat-fusible binder fibers (B) is small, so the fibers tend to fall off from the base material, and when used as a filter, the dropped fibers flow downstream. Problems may arise that the water may flow out and cause adverse effects.

In the present invention, wood pulp can also be used in addition to synthetic fibers as the non-binder fibers (NB). In the filter substrate <2>, the wood pulp described in the filter substrate <1> can be used as the wood pulp.

When the wet-laid nonwoven fabric contains wood pulp, the blending ratio of the wood pulp is not particularly limited, but it is preferably less than 50% by mass, and less than 40% by mass, based on the total fiber components contained in the wet-laid nonwoven fabric. More preferably, it is less than 30% by mass, and there is no problem even if it does not contain wood pulp. If the blending ratio of the wood pulp is 50% by mass or more, the wood pulp clogs the pores of the nonwoven fabric, which may cause a problem of increased pressure loss. As a result, the problem of reduced peel strength may occur.

<Heat-fusible binder fiber (B)>
In the filter base material <2>, the heat-fusible binder fiber (B) can be the heat-fusible binder fiber (B) described in the filter base material <1>.

The blending ratio of the heat-fusible binder fiber (B) is preferably 20 to 90% by mass, more preferably 25 to 80% by mass, more preferably 30% by mass, based on the total fiber components contained in the wet-laid nonwoven fabric. More preferably, it is up to 70% by mass. If the blending ratio of the heat-fusible binder fiber (B) is less than 10% by mass, there may be a problem in that a large amount of fibers fall off due to insufficient components for binding the synthetic fibers. On the other hand, when the blending ratio of the heat-fusible binder fiber (B) is more than 90% by mass, the nonwoven fabric has a small thickness and a high density. The problem is that it is not suitable as a filter.

The blending ratio of the heat-fusible binder fiber (B) in the layer (X) is 50% by mass or more, more preferably 60% by mass or more, based on the total fiber components contained in the layer (X). , more preferably 70% by mass or more. Moreover, the compounding ratio of the heat-fusible binder fiber (B) in the layer (X) may be 100% by mass.

The blending ratio of the heat-fusible binder fiber (B) in the layer (Y) is less than 50% by mass, more preferably less than 40% by mass, based on the total fiber components contained in the layer (Y). , and more preferably less than 30% by mass. Moreover, the compounding ratio of the heat-fusible binder fiber (B) in the layer (Y) may be 0% by mass. When the layer (Y) is a plurality of layers, the layer (Y) may be one or more layers among the plurality of layers, but the layer (Y) may be the outermost layer on the side not in contact with the porous membrane. preferable.

In the present invention, in addition to the heat-fusible binder fiber (B), the wet heat adhesive binder fiber (b) can also be used as the binder fiber. In the filter substrate <2>, the wet heat adhesive binder fiber (b) may be the wet heat adhesive binder fiber (b) described in the filter substrate <1>.

Other fibers used in the present invention include cotton pulp, straw pulp, bamboo pulp, esparto pulp, bagasse pulp, and hemp pulp.

<Basis Weight>
The filter substrate <2> is not particularly limited, but preferably has a total basis weight of 30 g/m ² to 180 g/m ² , more preferably 40 g/m ² to 160 g/m ² . If the grammage is less than 30 g/m ² , the strength of the base material is weak and may break during use as a filter. If it is greater than 180 g/m ² , the pressure loss will be high and may not be suitable for use as a filter.

The basis weight of layer (X) is 5 g/m ² to 60 g/m ² , more preferably 10 g/m ² to 50 g/m ² . If the layer (X) has a basis weight of less than 5 g/m ² , the effect of increasing the adhesive strength with the porous membrane cannot be sufficiently obtained. If the basis weight of the layer (X) is more than 60 g/m ² , the pressure loss will be high and it will not be suitable for use as a filter.

The basis weight of layer (Y) is 25 g/m ² to 120 g/m ² , more preferably 30 g/m ² to 110 g/m ² . If the basis weight of the layer (Y) is less than 25 g/m ² , the layer (Y) is not suitable for use as a filter because of its weak strength and breakage when used as a filter. If the basis weight of the layer (Y) is greater than 120 g/m ² , the pressure loss will be high and it will not be suitable for use as a filter.

<Density>
The density of the filter substrate <2> is not particularly limited, but is preferably 0.1 to 0.5 g/cm ³ . The density can be appropriately adjusted by adjusting the papermaking conditions during wet papermaking, the type of fiber, the blending ratio of fiber, basis weight and thickness. If the density is less than 0.1 g/cm ³ , fibers may fall off during the heat-pressing treatment, causing trouble. If the density exceeds 0.5 g/cm ³ , the pressure loss increases, and it may not be suitable as a base material for filters.

<Production of filter substrate <2>>
Filter substrate <2> can be produced by a wet papermaking method. Filter substrate <2> is a nonwoven fabric produced by a wet papermaking method. That is, each layer of the filter substrate <2> is prepared by dispersing the non-binder fiber (NB) and the heat-fusible binder fiber (B) in water at a predetermined ratio to prepare a slurry, and the resulting slurry is used for papermaking. It can be manufactured by making paper using a machine.

In the wet papermaking method, for example, a fourdrinier method, a cylinder method, an inclined wire method, or the like can be used. Filter substrate <2> can also be produced using a combination paper machine in which two or more of the same or different papermaking methods selected from these papermaking methods are installed online.
In order to produce a filter base material excellent in uniformity, it is preferable to use a papermaking method such as a Fourdrinier method or an inclined wire method, which can gently dewater the slurry on the wire.
In addition, the filter substrate <2> was prepared by laminating wet paper made by each papermaking method, and after forming one layer, a slurry in which fibers were dispersed was applied to the layer. It can be manufactured by a "casting method" or the like in which the film is cast and laminated. In the casting method, when the slurry in which the fibers are dispersed is cast, the layer previously formed may be in a wet paper state or in a dry state. Also, two or more layers can be heat-sealed to form a multi-layered nonwoven fabric.

[Filter material for filter <2>]
The present invention includes a filter material <2> for a filter, which includes the aforementioned base material for a filter <2> and a porous membrane.
That is, the filter material <2> is a filter material including a filter substrate and a porous membrane,
(1) the filter base material is a wet-laid nonwoven fabric comprising a layer (X) and a layer (Y), at least one of which is the layer (X) as the outermost layer;
(2) The layer (X) contains synthetic fibers as non-binder fibers (NB) and heat-fusible binder fibers (B), and the blending ratio of the heat-fusible binder fibers (B) is 50% by mass. A layer with a basis weight of 5 g/m ² or more and 60 g/m ² or less,
(3) Layer (Y) contains synthetic fibers as non-binder fibers (NB) and heat-fusible binder fibers (B), and the blending ratio of heat-fusible binder fibers (B) is 50% by mass. It is characterized by being a layer with a basis weight of 25 g/m ² or more and 120 g/m ² or less.
The filter substrate and the porous membrane are preferably bonded together by thermal fusion.
Polyolefins such as polyethylene (PE) and polypropylene (PP); polyethylene terephthalate; polyurethane; polyimide; and polytetrafluoroethylene (PTFE). If a porous membrane with a low heat resistance temperature is used, the porous membrane may soften during heat and pressure treatment, clogging the pores and failing to obtain sufficient Frazier air permeability for use as a filter. Therefore, it is preferable to use PTFE, which has excellent heat resistance. PTFE also has excellent chemical resistance.
The thickness of the porous membrane is preferably 1-50 μm, more preferably 2-30 μm.

<Fragile Air Permeability>
In order to obtain a low pressure loss, it is preferable to increase the Frazier air permeability of the filter medium. The Frazier air permeability is the air permeability specified by the A method (Frazier type method) described in JIS L1096:2010. The filter medium <2> for filter preferably has a Frazier air permeability of 10 cm ³ /cm ² ·s or more, more preferably 20 cm ³ /cm ² ·s or more. If the Frazier air permeability is lower than 10 cm ³ /cm ² ·s, the pressure loss increases and may not be suitable as a filter medium.

<Production of filter material <2> for filter>
The filter substrate <2> of the present invention and the porous membrane are laminated by thermal fusion to produce the filter medium <2> for the filter.
Bonding can be performed by heat and pressure treatment. The heat-pressing treatment can be performed by stacking sheets using a hot press or by stacking wound sheets using a hot calender. In order to obtain sufficient peel strength between the wet-laid nonwoven fabric and the porous membrane, the temperature during the heat-pressing treatment is preferably 100° C. or higher, and is higher than the melting point of the heat-fusible binder fiber (B). is more preferable, and 160° C. or higher is even more preferable.
The pressure in the heat pressure treatment is preferably 1 to 100 kgf/cm, more preferably 2 to 90 kgf/cm, still more preferably 3 to 80 kgf/cm.

[Filter substrate <3>]
Filter base material <3> is a filter base material for use as a filter material by bonding porous membranes by thermal fusion,
(1) the filter substrate is a wet-laid nonwoven fabric containing non-binder fibers (NB) and heat-fusible binder fibers (B);
(2) containing a drawn polyester fiber as the non-binder fiber (NB),
(3) The heat-fusible binder fiber (B) contains a core-sheath type polyester fiber (CSP) whose sheath is a crystalline copolyester,
(4) The compounding ratio of the core-sheath type polyester fiber (CSP) is 5% by mass or more with respect to the total fibers contained in the filter base material.
Since the filter substrate <3> of the present invention contains the heat-fusible binder fiber (B), the step of raising the temperature above the melting point or softening temperature of the heat-fusible binder fiber (B) is omitted. By incorporating it into the manufacturing process of the filter substrate <3>, the heat-fusible binder fiber (B) is melted or softened and bound, and the mechanical strength of the filter substrate <3> can be improved. .

<Non-binder fiber (NB)>
Filter substrate <3> contains drawn polyester fibers as non-binder fibers (NB).
The non-binder fibers (NB) are difficult to melt or soften in the drying process and the heat calendering process when manufacturing the filter substrate <3>, and can be used as the filter substrate <3> while maintaining the shape of the fiber. It is the main fiber that forms the skeleton of
By including stretched polyester fibers as non-binder fibers (NB), it is difficult to reduce the thickness during lamination by heat and pressure treatment, and it is difficult to increase the density of the filter substrate <3>, resulting in a low pressure loss. effect is obtained. In general, the melting point or softening point of the non-binder fibers (NB) is higher than the melting point or softening point of the heat-fusible binder fibers (B).

As the polyester of the stretched polyester fiber, a polyester whose main repeating unit is alkylene terephthalate can be mentioned, but polyethylene terephthalate with high heat resistance is preferable.

If necessary, synthetic fibers other than stretched polyester fibers can also be used as non-binder fibers (NB). As the synthetic fiber, the synthetic fiber described in the filter substrate <1> can be used.

Wood pulp can also be used as the non-binder fiber (NB). In the filter substrate <3>, the wood pulp described in the filter substrate <1> can be used as the wood pulp.

The blending ratio of the non-binder fibers (NB) is preferably 10 to 90% by mass, more preferably 20 to 75% by mass, based on the total fibers contained in the filter substrate <3>. More preferably, it is 30 to 70% by mass. If the blending ratio of the non-binder fibers (NB) is less than 10% by mass, the thickness of the base material is too low during lamination by thermal fusion bonding, resulting in a base material with too high a density, resulting in a high pressure loss of the filter medium. too large to be suitable as a filter. On the other hand, when the blending ratio of the non-binder fibers (NB) is more than 90% by mass, since the amount of the heat-fusible binder fibers (B) is small, the fibers easily fall off from the base material, and when used as a filter, the fibers fall off. A problem arises in that the fibers flow downstream and adversely affect it.

When the filter substrate <3> contains a non-binder fiber (NB) other than the drawn polyester fiber, the blending ratio is not particularly limited, but it is 50% by mass based on the total fibers contained in the filter substrate. It is preferably less than 40% by mass, more preferably less than 30% by mass. Non-binder fibers (NB) other than drawn polyester fibers are not essential components, so the blending ratio may be 0% by mass. If the blending ratio of non-binder fibers (NB) other than drawn polyester fibers is 50% by mass or more, the fibers may easily fall off from the filter base material, and when used as a filter, the dropped fibers may flow downstream. Problems may arise that the water may flow out and cause adverse effects.

When the filter substrate <3> contains wood pulp as the non-binder fiber (NB), the blending ratio of the wood pulp is not particularly limited. %, more preferably less than 40% by mass, even more preferably less than 30% by mass, and there is no problem even if it does not contain wood pulp. If the blending ratio of the wood pulp is 50% by mass or more, the wood pulp clogs the pores of the filter base material, which may cause a problem of increased pressure loss. In some cases, the problem of reduced peel strength may occur because the adhesion of the adhesive is inhibited.

<Heat-fusible binder fiber (B)>
The filter substrate <3> contains, as the heat-sealable binder fiber (B), a sheath-core polyester fiber (CSP) whose sheath is made of crystalline copolyester.
As the crystalline copolyester for the sheath, the dicarboxylic acid component is terephthalic acid, and the diol component is ethylene glycol and tetramethylene glycol. can be preferably used.

Since the filter substrate <3> contains the core-sheath type polyester fiber (CSP), the filter substrate <3> is manufactured and then laminated with the porous membrane by heat pressure treatment such as hot calendering. Even after performing, the core of the sheath-core type polyester fiber (CSP) does not melt and maintains the fiber shape, so that the tensile strength of the filter can be increased.

In the present invention, "crystallinity" means that when the temperature of the fiber is raised to the temperature of the molten state and then lowered, the temperature is lowered while the fibers are entangled while undergoing molecular motion in the molten state. It has the property of partially aligning and crystallizing at the crystallization temperature while the molecular motion slows down at .

As a method for confirming the presence or absence of crystallinity, a differential scanning calorimeter (manufactured by PerkinElmer, device name: DSC8500) was used to heat the core-sheath polyester fiber (CSP) from 0 ° C. at a heating rate of 10 ° C./min. After raising the temperature to exceed the melting point of the sheath, it is continuously cooled to 0 ° C. at a cooling rate of 10 ° C./min, and the presence or absence of an exothermic peak due to crystallization is confirmed. sex. Also, the peak temperature of the exothermic peak is defined as the crystallization temperature.

The melting point was measured using a differential scanning calorimeter (manufactured by PerkinElmer, device name: DSC8500), and the temperature was raised from 0°C to 300°C at a heating rate of 10°C/min. is observed and the peak temperature is taken as the melting point.

The core of the core-sheath polyester fiber (CSP) is polyester whose main repeating unit is alkylene terephthalate, preferably polyethylene terephthalate, which has high heat resistance.

The cross-sectional shape of the core-sheath type polyester fiber (CSP) is not particularly limited, but a circular shape is preferable. In addition, the core/sheath volume ratio is preferably 30/70 to 70/30, more preferably 40/60 to 60/40.

The melting point of the crystalline copolyester of the sheath is preferably 130°C or higher, more preferably 140°C or higher, and still more preferably 150°C or higher. When the melting point of the crystalline polyester is high, higher adhesive strength can be obtained, and since it has high chemical resistance, it is difficult to deteriorate and shrink even when used under harsh conditions. .

The blending ratio of the core-sheath type polyester fiber (CSP) is 5% by mass or more, more preferably 10% by mass or more, relative to the total fibers contained in the filter substrate <3>. Further, it is preferably 70% by mass or less, more preferably 65% by mass or less, even more preferably 60% by mass or less, particularly preferably 55% by mass or less, and 50% by mass or less. It can be. If the blending ratio of the core-sheath type polyester fiber (CSP) is less than 5% by mass, the effect of increasing the chemical resistance of the filter substrate <3> cannot be sufficiently obtained. On the other hand, if it exceeds 70% by mass, the surface of the filter substrate <3> tends to form a film, and after bonding the porous membrane and the filter substrate together by heat calendering or the like, the pressure loss increases and the filter can be used as a filter. can be difficult to do.

<Other heat-fusible binder fibers (B)>
A heat-fusible binder fiber (B) other than the core-sheath type polyester fiber (CSP) can be blended into the filter substrate <3> as needed.

As the heat-fusible binder fiber (B) other than the core-sheath type polyester fiber (CSP), the heat-fusible binder fiber (B) described in the filter substrate <1> can be used.

In the present invention, in addition to core-sheath type polyester fibers (CSP), wet heat adhesive binder fibers (b) can also be used as binder fibers. In the filter base material <3>, the wet heat adhesive binder fiber (b) described in the filter base material <1> can be used as the wet heat adhesive binder fiber (b).

The blending ratio of the binder fiber, including the core-sheath type polyester fiber (CSP), is preferably 10 to 90% by mass, preferably 25 to 80% by mass, based on the total fibers contained in the filter substrate <3>. and more preferably 30 to 70% by mass. If the blending ratio of the binder fiber (B) is less than 10% by mass, there may be a problem that the amount of the component that stops the non-binder fiber (NB) is insufficient, resulting in a large amount of falling-off fiber. On the other hand, when the blending ratio of the binder fiber (B) is more than 90% by mass, the filter base material has a small thickness and a high density. , the problem that it is not suitable as a filter may occur.

<Basis Weight>
The basis weight of the filter substrate <3> is not particularly limited, but is preferably 30 g/m ² to 180 g/m ² , more preferably 40 g/m ² to 160 g/m ² . If the grammage is less than 30 g/m ² , the strength of the base material is weak and may break during use as a filter. If it is greater than 180 g/m ² , the pressure loss will be high and may not be suitable for use as a filter.

<Density>
Although the density of the filter substrate <3> is not particularly limited, it is preferably 0.1 to 0.5 g/cm ³ . The density can be appropriately adjusted by adjusting the papermaking conditions during wet papermaking, the type of fiber, the blending ratio of fiber, basis weight and thickness. If the density is less than 0.1 g/cm ³ , fibers may fall off during the heat-pressing treatment, causing trouble. If the density exceeds 0.5 g/cm ³ , the pressure loss increases, and it may not be suitable as a base material for filters.

[Filter material for filter <3>]
The present invention includes a filter medium <3> including the aforementioned filter substrate <3> and a porous membrane.
That is, the filter material <3> is a filter material including a filter substrate and a porous membrane,
(1) the filter substrate is a wet-laid nonwoven fabric containing non-binder fibers (NB) and heat-fusible binder fibers (B);
(2) containing a drawn polyester fiber as the non-binder fiber (NB),
(3) The heat-fusible binder fiber (B) contains a core-sheath type polyester fiber (CSP) whose sheath is a crystalline copolyester,
(4) The compounding ratio of the core-sheath type polyester fiber (CSP) is 5% by mass or more with respect to the total fibers contained in the filter base material.
It is preferable that the filter material <3> for a filter is formed by bonding a porous membrane and a base material for a filter together by heat-sealing.
Polyolefins such as polyethylene (PE) and polypropylene (PP); polyethylene terephthalate; polyurethane; polyimide; and polytetrafluoroethylene (PTFE). If a porous membrane with a low heat resistance temperature is used, the porous membrane may soften during heat and pressure treatment, clogging the pores and failing to obtain sufficient Frazier air permeability for use as a filter. Therefore, it is preferable to use PTFE, which has excellent heat resistance. PTFE also has excellent chemical resistance.
The thickness of the porous membrane is preferably 1-50 μm, more preferably 2-30 μm.

<Fragile Air Permeability>
In order to obtain a low pressure loss, it is preferable to increase the Frazier air permeability of the filter medium <3> for filter. The Frazier air permeability is the air permeability specified by the A method (Frazier type method) described in JIS L1096:2010. The filter medium <3> for filter preferably has a Frazier air permeability of 10 cm ³ /cm ² ·s or more, more preferably 20 cm ³ /cm ² ·s or more. If the Frazier air permeability is lower than 10 cm ³ /cm ² ·s, the pressure loss increases and may not be suitable as a filter medium.

<Production of Filter Material <3> for Filter>
The filter substrate <3> of the present invention and the porous membrane can be heat-sealed to produce a filter medium for a filter.
Bonding can be performed by heat and pressure treatment. The heat-pressing treatment can be performed by stacking sheets using a hot press or by stacking wound sheets using a hot calender. In order to obtain sufficient peel strength between the wet-laid nonwoven fabric and the porous membrane, the temperature during the heat-pressing treatment is preferably 100° C. or higher, and is higher than the melting point of the heat-fusible binder fiber (B). is more preferable, and 160° C. or higher is even more preferable.
The pressure in the heat pressure treatment is preferably 1 to 100 kgf/cm, more preferably 2 to 90 kgf/cm, still more preferably 3 to 80 kgf/cm.

[Examples 1-1 to 1-10, Comparative Examples 1-1 to 1-6]
Base material for filter <1>, filter medium for filter <1>
The parts and ratios described in the examples below are based on mass.
<Heat-fusible binder fiber (B)>
・Core-sheath binder (PET-low melting point PET core-sheath fiber, fineness 2.2 decitex, fiber length 5 mm, sheath melting point 120°C)

<Wood pulp: non-binder fiber (NB)>
・NBKP Chinook (freeness 680ml CSF)

<Synthetic fiber: non-binder fiber (NB)>
・PET fiber (stretched PET fiber, fineness 1.7 decitex, fiber length 5 mm)

<Inorganic fiber: non-binder fiber (NB)>
・Glass fiber (fiber diameter 9 μm, fiber length 6 mm)

<Porous membrane>
・PP porous membrane (polypropylene resin membrane, film thickness 20 μm)
・Porous PTFE membrane (polytetrafluoroethylene resin membrane, thickness 15 μm)
<Preparation of base material for filter and filter medium for filter>
Each fiber was dispersed with a pulper so as to have the fiber composition shown in Table 1, paper was made with a cylinder paper machine, and then dried with a cylinder dryer to prepare a filter base material composed of a wet-laid nonwoven fabric.
The filter base material and the PP porous membrane are heat-pressed with a hot roll at a linear pressure of 20 kgf / cm and a temperature of 160 ° C., and laminated by thermal fusion bonding. Filter media for filters of 1-5 and Comparative Examples 1-1 to 1-3 were produced.
In addition, a PTFE porous membrane was laminated on the filter base material by heat-pressing with a hot roll at a linear pressure of 20 kgf / cm and a temperature of 160 ° C., and laminated by thermal fusion bonding. 1-10 and filter media for filters of Comparative Examples 1-4 to 1-6 were prepared.

<Evaluation method>
The filter substrates and filter media produced in Examples 1-1 to 1-10 and Comparative Examples 1-1 to 1-6 were measured and evaluated by the following methods.

1) Basis weight The basis weight and thickness of the filter substrate were measured according to JIS P 8124:2011 and 8118:2014.

2) Collection efficiency (unit: %)
JIS Class 8 powder and JIS Class 11 powder were mixed at a ratio of 1:1 and diluted with water to a concentration of 0.05% by mass. After wetting with , 100 ml of the test liquid was filtered under the conditions of a filtration area of 14 cm ² and a differential pressure ΔP = 320 mmHg with the porous membrane surface of the filter material for the filter set on the upstream side. The number of particles up to 1.0 μm was measured with a liquid particle counter manufactured by Rion (trade name: KL-01), and the collection efficiency was calculated.

3) Frazier air permeability The air permeability required to obtain a low pressure loss when the filter material for the filter is used as a filter is measured by the A method (Frazier type method) described in JIS L1096:2010. did.

4) Life test Repeatedly evaluate the repair efficiency of the filter material using the test liquid of 2) above, and repeat the evaluation until the Frazier air permeability measured by the method of 3) falls below 10 cm ³ /cm ² s. and evaluated the life.

5) Peel strength Peel strength was measured by cutting a filter material of 25 mm in the width direction and 150 mm in the flow direction, using a Tensilon universal testing machine, sandwiching a wet-laid nonwoven fabric and a porous membrane between jigs and pulling them. was judged visually.

◯: The porous membrane was not peeled off from the substrate at all.
Δ: The porous film was seen to be peeled off from the substrate by applying a strong force. ×: By applying a force smaller than Δ, the porous film was easily peeled off from the substrate.
- : Unable to evaluate

6) Strength during heat and pressure treatment Evaluation was performed by confirming the state of the filter base material during heat and pressure treatment.

◯: No breakage such as breakage of the filter base material was observed during the heat-pressure treatment. ×: Breakage such as breakage was found in the filter base material during the heat-pressure treatment.

Table 2 shows the above evaluation results. In Table 2, "-" indicates that evaluation was not possible.

The filter substrates of Examples 1-1 to 1-10 are filter substrates to be used as filter media by bonding porous membranes by heat sealing, and the filter media are non-binder fibers. (NB) and a heat-fusible binder fiber (B), wherein the blending ratio of the heat-fusible binder fiber (B) is 20 to 90% by mass with respect to all fiber components contained in the wet-laid nonwoven fabric. and the blending ratio of non-binder fibers (NB) is 10 to 80% by mass.
The filter media obtained by laminating the porous membrane and the filter substrates of Examples 1-1 to 1-10 by thermal fusion bonding exhibited high peel strength. On the other hand, the porous membrane and the filter substrate of Comparative Example 1-1 or Comparative Example 1-4 were not damaged during the heat and pressure treatment, but were bonded together by heat sealing. I couldn't do it.

In addition, the filter media of Examples 1-1 to 1-10 are stronger than the filter media obtained by bonding the porous membrane and the filter substrate of Comparative Example 1-2 or Comparative Example 1-5 by thermal fusion bonding. , high Frazier air permeability and life are obtained. In addition, in Comparative Examples 1-3 and 1-6, since only glass fibers were used as the non-binder fibers (NB), the base material was damaged during the heat and pressure treatment.

The PP porous membrane used in Examples 1-1 to 1-5 has a lower heat resistance temperature than the PTFE porous membrane used in Examples 1-6 to 1-10, so softening occurs during heat pressure treatment. and some of the holes were blocked. In Examples 1-6 to 1-10, filter media for filters with more favorable Frazier air permeability could be obtained compared to Examples 1-1 to 1-5.

[Examples 2-1 to 2-15, Comparative Examples 2-1 to 2-5]
Base material for filter <2>, filter medium for filter <2>
The parts and ratios described in the examples below are based on mass.

<Synthetic fiber: non-binder fiber (NB)>
・PET fiber (stretched PET fiber, fineness 1.7 decitex, fiber length 5 mm)
<Heat-fusible binder fiber (B)>
・PET-low melting point PET core-sheath fiber (CSP) (core-sheath binder, fineness 2.2 decitex, fiber length 5 mm, sheath melting point 120°C)
・Full-melting PET binder fiber (B) (full-melting binder, fineness 1.2 decitex, fiber length 5 mm, melting point 230°C)

<Wood pulp: non-binder fiber (NB)>
・NBKP Chinook (freeness 680ml CSF)

<Preparation of base material for filter (wet nonwoven fabric)>
Each fiber was put into water so that the fiber composition shown in Table 3 was obtained, and mixed and dispersed for 10 minutes with a vertical pulper to prepare a slurry. (X), the outermost layer on the side in contact with the porous membrane), and each fiber is put into water so that the fiber blend is as shown in Table 3, and mixed and dispersed for 10 minutes with a vertical pulper to prepare a slurry. After that, a layer (layer (Y), a layer not in contact with the porous membrane) obtained by wet papermaking by a cylinder method is laminated, dried with a Yankee dryer at a surface temperature of 130 ° C., and a papermaking speed of 20 m / min. Thus, a wet-laid nonwoven fabric having a two-layer structure was obtained.

[Comparative Examples 2-6 and 2-7]
Each fiber was put into water so as to have the fiber composition shown in Table 3, and mixed and dispersed for 10 minutes with a vertical pulper to prepare a slurry. A layered wet-laid nonwoven fabric was obtained.

<Preparation of filter material for filter>
The filter substrates of Examples 2-1 to 2-15 and the filter substrates of Comparative Examples 2-1 to 2-7 were subjected to heat and pressure treatment with hot rolls at 120° C. to bond the PTFE porous membranes together. to obtain a filter medium.

<Evaluation method>
The filter substrates and filter media produced in Examples 2-1 to 2-15 and Comparative Examples 2-1 to 2-7 were evaluated by the following methods.
1) Pressure Loss Pressure loss was measured in accordance with JIS B9908-2:2019 and evaluated as follows. It should be noted that pressure loss increases when the base material has a high density during bonding by thermal fusion.

◯: The pressure loss was less than 200% with respect to the porous membrane alone.
Δ: The pressure loss was 200% to 300% with respect to the porous membrane alone.
x: The pressure loss was more than 300% with respect to the porous membrane alone.

2) Peeling strength The peeling of the base material is determined by rubbing the end of the filter material for the filter with the porous membrane bonded together 20 times in the vertical direction with a stainless steel rod weighing 5 kg standing upright. It was confirmed.

◯: The porous membrane was not peeled off from the filter substrate at all.
x: The porous membrane was peeled off from the filter substrate.

3) Base material strength JIS Class 8 powder and JIS Class 11 powder were mixed at a ratio of 1:1, diluted with water to a concentration of 0.05% by mass, and used as a test liquid. After wetting the filter material with water, 100 ml of the test liquid was filtered under the conditions of a filtration area of 14 cm ² and a differential pressure ΔP of 320 mmHg with the porous membrane surface of the filter material facing upstream. Checked the condition of the filter media.

◯: Damage such as tearing was not observed.
x: Damage such as tearing was confirmed.

Table 3 shows the above evaluation results.

It is a wet-laid nonwoven fabric consisting of two or more layers, at least one layer is a layer containing synthetic fibers as non-binder fibers (NB) and heat-fusible binder fibers (B), and the outermost layer on the side in contact with the porous membrane ( The blending ratio of the heat-fusible binder fiber (B) in X) is 50% by mass or more, and the blending ratio of the heat-fusible binder fiber (B) in the layer (Y) on the side not in contact with the porous membrane is 50%. % by mass, the basis weight of the outermost layer (X) on the side in contact with the porous membrane is 5 g/m ² or more and 60 g/m ² or less, and the basis weight of the layer (Y) on the side not in contact with the porous membrane is The filter substrates of Examples 2-1 to 2-15, which are 25 g/m ² or more and 120 g/m ² or less, have low pressure loss, high peel strength, and high substrate strength. I know there is.

In Comparative Example 2-1, in which the blending ratio of the heat-fusible binder fibers (B) in the outermost layer (X) on the side in contact with the porous membrane is less than 50% by mass, the heat-fusible binder that adheres to the porous membrane It is presumed that sufficient peel strength was not obtained as a result of the small amount of fiber (B).

In Comparative Example 2-2, in which the basis weight of the outermost layer (X) on the side in contact with the porous membrane was less than 5 g/m ² , the amount of heat-fusible binder fibers (B) adhering to the porous membrane was small. It is presumed that sufficient base material strength was not obtained.

In Comparative Example 2-3, in which the basis weight of the outermost layer (X) on the side in contact with the porous membrane is ^more than 60 g/m It is presumed that the basis weight of the outermost layer (X) on the side was large and the pressure loss increased as a result of the high density.

In Comparative Example 2-4, in which the blending ratio of the heat-fusible binder fiber (B) in the layer (Y) on the side not in contact with the porous membrane is 50% by mass or more, the blending ratio of the heat-fusible binder fiber (B) It is presumed that the pressure loss increased as a result of the high density of the layer (Y) on the side not in contact with the porous membrane, which has a large ratio.

In Comparative Example 2-5, in which the basis weight of the layer (Y) on the side not in contact with the porous membrane was less than 25 g/m ² , the basis weight of the filter base material was low, and the strength of the base material was weakened. It is presumed that it was damaged during use as a filter.

In Comparative Example 2-6, which is a wet-laid nonwoven fabric having a single-layer structure in which the blending ratio of the heat-fusible binder fiber (B) is 50% by mass or more, the blending ratio of the heat-fusible binder fiber (B) is high. Therefore, it is presumed that the pressure loss increased.

In Comparative Example 2-7, which is a wet-laid nonwoven fabric having a single-layer structure in which the blending ratio of the heat-fusible binder fiber (B) is less than 50% by mass, the blending ratio of the heat-fusible binder fiber (B) is low. Therefore, it is presumed that the peel strength was lowered.

[Examples 3-1 to 3-12, Comparative Examples 3-1 to 3-5]
Base material for filter <3>, filter medium for filter <3>
The parts and ratios described in the examples below are based on mass.

<Non-binder fiber (NB)>
・Stretched PET fiber 1
A drawn PET fiber 1 was a drawn polyester fiber made of polyethylene terephthalate and having a fineness of 1.7 decitex and a fiber length of 5 mm.

・Stretched PET fiber 2
A drawn PET fiber 2 was a drawn polyester fiber made of polyethylene terephthalate and having a fineness of 0.6 decitex and a fiber length of 5 mm.

- Wood pulp NBKP Chinook (freeness 680 ml CSF) was used as wood pulp.

<Binder fiber (B)>
・Sheath and core PET fiber 1
The core part is polyethylene terephthalate (melting point: 260°C), the sheath part has a dicarboxylic acid component of terephthalic acid, a diol component of ethylene glycol and tetramethylene glycol, a melting point of 180°C, and a crystallization temperature of 126°C. A core-sheath type polyester fiber (Casven (registered trademark) 8080 manufactured by Unitika Ltd.) having a fineness of 1.2 decitex and a fiber length of 5 mm, which is a crystalline copolyester having a temperature of 100° C., was used as a core-sheath PET fiber 1 .

・Sheath and core PET fiber 2
The core part is polyethylene terephthalate (melting point: 260°C), the sheath part has dicarboxylic acid components of terephthalic acid and isophthalic acid, diol components of ethylene glycol and diethylene glycol, and a softening temperature of 75°C. A core-sheath type polyester fiber (manufactured by Teijin Ltd. TJ04CN (product number)) having a fineness of 2.2 decitex and a fiber length of 5 mm, which is a copolyester, was used as a core-sheath PET fiber 2 .

・Unstretched PET fiber 1
Unstretched polyester fiber (melting point: 260° C.) (TA07N (product number) manufactured by Teijin Limited) made of polyethylene terephthalate containing isophthalic acid as a dicarboxylic acid component and having a fineness of 1.2 decitex and a fiber length of 5 mm was used as unstretched PET fiber 1. did.

・Wet heat PVA fiber 1
Wet heat adhesive binder fiber (b) (VPB041 manufactured by Kuraray Co., Ltd.) made of polyvinyl alcohol resin and having a fineness of 0.44 decitex and a fiber length of 3 mm was used as wet heat PVA fiber 1 .

<Production of base material for filter>
Each fiber was put into water so as to have the fiber composition shown in Table 4, and mixed and dispersed for 10 minutes with a vertical pulper to prepare a slurry. The paper was laminated by a paper-making method, dried with a Yankee dryer at a surface temperature of 130° C., and made at a paper-making speed of 20 m/min to obtain a wet-laid nonwoven filter substrate. The fiber blend and target basis weight for the slanted wire and the circular mesh are the same.

<Preparation of filter material for filter>
The filter substrates of Examples 3-1 to 3-12 and Comparative Examples 3-1 to 3-5 and the PTFE porous membranes were laminated, subjected to heat pressure treatment with hot rolls at 120 ° C., and pasted by heat fusion. A combination was performed to obtain a filter medium for a filter.

<Evaluation method>
The filter substrates and filter media produced in Examples 3-1 to 3-12 and Comparative Examples 3-1 to 3-5 were evaluated by the following methods.

1) Chemical resistance From the base material for the filter, cut out 20 samples of 250 mm in the winding flow direction and 50 mm in the width direction, and according to JIS P 8113: 2006, a desktop material testing machine (device name: STA-1150, (manufactured by Orientec Co., Ltd.), the tensile strength was measured, and the average value (initial value) for 10 sheets was obtained. The remaining 10 samples were immersed in a 10% by weight sodium hydroxide solution at a temperature of 80° C. for 1 week. After washing with water and drying, the tensile strength was measured to obtain an average value (after immersion) for 10 sheets. The average value (after immersion)/average value (initial value)×100 was defined as the percentage of residual tensile strength (%), which was used as an index of alkali resistance.

Good: The residual rate of tensile strength was 80% or more.
x: The residual rate of tensile strength was less than 80%.

2) Pressure loss The pressure loss of the filter material for filters was measured in accordance with JIS B 9908-2:2019, and the following evaluations were made. It should be noted that pressure loss increases when the filter base material has a high density during bonding by thermal fusion bonding.

○: The pressure loss was less than 200% with respect to the porous membrane alone.
Δ: The pressure loss was 200% to 300% with respect to the porous membrane alone.
x: The pressure loss was more than 300% with respect to the porous membrane alone.

Table 4 shows the above evaluation results.

The filter substrates of Examples 3-1 to 3-12 exhibited high chemical resistance, and the filter media of Examples 3-1 to 3-12 exhibited low pressure loss.

On the other hand, in Comparative Example 3-1, in which the blending ratio of core-sheath type polyester fibers (CSP) whose sheath is crystalline copolyester is less than 5%, sufficient chemical resistance was not obtained.

In addition, in Comparative Examples 3-2 to 3-4, in which the sheath did not contain a core-sheath type polyester fiber (CSP), which is a crystalline copolyester, sufficient chemical resistance was not obtained.

In Comparative Example 3-5, which does not contain stretched polyester fibers as non-binder fibers (NB), the pressure loss was high.

The filter base material of the present invention can be suitably used as a filter material by laminating a porous membrane. The filter material for filters of the present invention can be used for various purposes as a filter material.

Claims

In a filter base material for use as a filter material for a filter by laminating a porous membrane by thermal fusion,
(1) the filter substrate is a wet-laid nonwoven fabric containing non-binder fibers (NB) and heat-fusible binder fibers (B);
(2) The blending ratio of the heat-fusible binder fiber (B) is 20 to 90% by mass, and the blending ratio of the non-binder fiber (NB) is 10, based on the total fiber components contained in the wet-laid nonwoven fabric. 80% by mass of the filter base material.
The filter substrate according to claim 1, wherein the non-binder fibers (NB) are at least one selected from the group consisting of synthetic fibers and wood pulp.
The filter substrate according to claim 1 or 2, wherein the heat-fusible binder fibers (B) are core-sheath fibers.
The filter base material according to any one of claims 1 to 3, which has a basis weight of 30 to 120 g/m 2 .
In a filter base material for use as a filter material for a filter by laminating a porous membrane by thermal fusion,
(1) the filter base material is a wet-laid nonwoven fabric comprising a layer (X) and a layer (Y), at least one of which is the layer (X) as the outermost layer;
(2) The layer (X) contains synthetic fibers as non-binder fibers (NB) and heat-fusible binder fibers (B), and the blending ratio of the heat-fusible binder fibers (B) is 50% by mass. A layer with a basis weight of 5 g/m 2 or more and 60 g/m 2 or less,
(3) Layer (Y) contains synthetic fibers as non-binder fibers (NB) and heat-fusible binder fibers (B), and the blending ratio of heat-fusible binder fibers (B) is 50% by mass. less than 100 g/m 2 and a basis weight of 25 g/m 2 or more and 120 g/m 2 or less.
The filter substrate according to claim 5, wherein the synthetic fibers as the non-binder fibers (NB) are polyester fibers.
The filter substrate according to claim 5 or 6, wherein the heat-fusible binder fibers (B) are core-sheath fibers.
In a filter base material for use as a filter material for a filter by laminating a porous membrane by thermal fusion,
(1) the filter substrate is a wet-laid nonwoven fabric containing non-binder fibers (NB) and heat-fusible binder fibers (B);
(2) containing a drawn polyester fiber as the non-binder fiber (NB),
(3) The heat-fusible binder fiber (B) contains a core-sheath type polyester fiber (CSP) whose sheath is a crystalline copolyester,
(4) A filter base material, wherein the compounding ratio of the core-sheath type polyester fiber (CSP) is 5% by mass or more with respect to the total fibers contained in the filter base material.
The crystalline copolyester of the sheath of the core-sheath type polyester fiber (CSP) is
(i) a copolymer polyester whose dicarboxylic acid component is terephthalic acid and whose diol component is ethylene glycol and tetramethylene glycol;
(ii) a copolymer polyester in which the dicarboxylic acid component is terephthalic acid and the diol component is ethylene glycol, tetramethylene glycol and ε-caprolactone; and (iii) the dicarboxylic acid component is terephthalic acid and isophthalic acid and the diol component is ethylene. 9. The filter substrate according to claim 8, which is at least one selected from the group consisting of copolymerized polyesters of glycol and tetramethylene glycol.
10. The filter substrate according to claim 8, which has a basis weight of 30 to 180 g/m 2 .
A filter material for a filter comprising the filter substrate and the porous membrane according to any one of claims 1 to 10.
12. The filter material for a filter according to claim 11, wherein the material of the porous membrane is polytetrafluoroethylene.