JP2023082521A - Filter medium for liquid filter - Google Patents

Abstract

To provide a filter medium for a liquid filter which efficiently removes particles in a liquid, and is excellent in pleat processability, water pressure resistance and oil pressure resistance.SOLUTION: A filter medium for a liquid filter is formed by stacking a melt-blown non-woven fabric and a wet non-woven fabric composed of fibers having a fiber diameter of 5 μm or more, wherein a raw material resin of the melt-blown non-woven fabric is polypropylene or polybutylene terephthalate.SELECTED DRAWING: None

Description

The present invention relates to a filter medium for liquid filters. Hereinafter, "filter medium for liquid filter" may be abbreviated as "filter medium".

Filter media for liquid filters are mainly pleated to increase the surface area of the filter media and then formed into a predetermined shape to produce a liquid filter, which is combined with other parts and set in a filter for use. .

Methods for producing filter media include the meltblowing method, spunbond method, wet papermaking method, electrospinning method, biaxial stretching method, and the like, and are used in applications that take advantage of their respective characteristics. As a filter medium for a liquid filter, a filter medium produced by a melt blown method is preferably used. However, the filter medium produced by the melt-blown method has a very low density, and the surface of the filter medium is fuzzy, and the fibers tend to come off due to rubbing or the like. In addition, since it is flexible and has low rigidity, it has low pleating workability. Problems such as fluffing and detachment of fibers can be solved by applying pressure to the melt blown filter media with heated rolls. I had a problem with the drop.

Therefore, a filter medium produced by the melt blown method, which is flexible and has low rigidity, is used by being laminated with a rigid base material produced by the spunbond method (see, for example, Patent Document 1). However, since the base material produced by the spunbond method has a poor texture, when high water pressure or oil pressure is applied to the filter medium, the melt-blown filter medium digs into the voids of the spunbond base material, resulting in a decrease in filtration performance. .

In addition, the melt-blown filter material is the main filtration nonwoven fabric, and the nonwoven fabric produced by the wet papermaking method containing ultrafine fibers with a fiber diameter of 4 μm or less and adhesive fibers with a fiber diameter of 8 μm or more and less than 20 μm is used as the auxiliary filtration nonwoven fabric. It is disclosed that a cylindrical filter in which a filter nonwoven fabric and a pre-auxiliary filter nonwoven fabric are laminated adjacently and arranged around a porous cylinder can be manufactured with a long filtration life and good workability ( For example, see Patent Document 2). However, in order to provide an auxiliary filtration function, the auxiliary filtration nonwoven fabric contains ultrafine fibers with a low rigidity and a fiber diameter of 4 μm or less. There was a problem that shape maintenance was difficult.

JP 2010-19151 A Japanese Patent Application Laid-Open No. 2001-321620

An object of the present invention is to provide a filter medium for a liquid filter that efficiently removes particles in the liquid and is excellent in pleat workability, water pressure resistance, and oil pressure resistance.

The above problems can be solved by a filter medium for a liquid filter, which is obtained by laminating a melt-blown nonwoven fabric and a wet-laid nonwoven fabric made of fibers having a fiber diameter of 5 μm or more.

According to the present invention, it is possible to obtain a filter medium for a liquid filter which is excellent in pleat processability, does not damage the melt-blown nonwoven fabric even when high water pressure and high oil pressure are applied to the filter medium, and efficiently removes particles in the liquid.

As a method for increasing the collection efficiency of the filter medium for a liquid filter, it is effective to use a melt-blown nonwoven fabric made of melt-blown fibers with a small fiber diameter. Also, in order to increase the filtration life, it is important to maintain the low density characteristic of the meltblown nonwoven fabric. To this end, it is necessary to solve the problems of fluffing and fiber separation of low-density melt-blown nonwoven fabrics, provide pleat workability, and design filter media that can withstand high water pressure or high oil pressure.

The filter medium for a liquid filter of the present invention solves these problems and provides various properties, and is a filter medium for a liquid filter formed by laminating a melt-blown nonwoven fabric and a wet-laid nonwoven fabric made of fibers having a fiber diameter of 5 μm or more. .

Raw material resins for meltblown nonwoven fabrics include, for example, polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyamide (PA), polyacrylonitrile (PAN), polyvinylidene fluoride (PVdF). , polyvinyl alcohol (PVA), polyurethane (PU), polylactic acid (PLA), and the like. Among these, polypropylene and polybutylene terephthalate are preferably used, and polybutylene terephthalate is more preferable because it improves the pleating workability. Polybutylene terephthalate is also suitable for applications requiring heat resistance.

The average fiber diameter of the fibers of the meltblown nonwoven fabric is 0.1 to 4 μm, preferably 0.5 to 3 μm. If the average fiber diameter is less than 0.1 μm, the liquid permeation resistance may increase and the life of the liquid filter may be shortened, and if it exceeds 4 μm, filtration performance may be insufficient.

The average fiber diameter of the meltblown nonwoven fabric is determined by photographing 5 arbitrary locations of the nonwoven fabric with an electron microscope, measuring the diameter of 20 fibers per photograph for the 5 obtained photographs, and measuring 100 fibers in total. It was determined by averaging the diameters.

The basis weight of the meltblown nonwoven fabric is preferably 5-100 g/m ² , more preferably 10-70 g/m ² . If the basis weight of the meltblown nonwoven fabric is less than 5 g/m ² , filtration performance may be insufficient, and if it exceeds 100 g/m ² , liquid permeation resistance may increase, shortening the life of the liquid filter.

A crystal nucleating agent, a matting agent, a pigment, an antifungal agent, an antibacterial agent, a flame retardant, a hydrophilic agent, a light stabilizer, etc. may be added to the raw material resin of the meltblown nonwoven fabric within a range that does not impair the effects of the present invention. good.

Meltblown nonwoven fabrics are obtained by a known meltblown nonwoven fabric manufacturing method using raw material resins such as polypropylene and polybutylene terephthalate. Specifically, the raw material resin is melted and discharged from a spinning nozzle, and exposed to high-temperature and high-pressure gas to finely fiberize the raw material resin. A meltblown nonwoven fabric can be produced by collecting and depositing on a collector.

In order to produce a melt blown nonwoven fabric having an average fiber diameter of 0.1 to 4 μm, for example, the spinning nozzle hole diameter is preferably 0.15 to 0.4 mm, and the spinning temperature is 200 to 340° C. or less. The temperature of the high-temperature and high-pressure gas is preferably above the spinning temperature and below (spinning temperature + 60 ° C.), and the speed of the high-temperature and high-pressure gas (discharge air volume) per 1 m width is 2 to 30 m ³ /min / m, the distance from the surface of the nozzle spinneret to the wire mesh conveyor (DCD) is preferably 3 to 55 cm, and the width of the collector such as a wire mesh conveyor or perforated drum is 5 to 200 mesh. preferable.

Wet-laid nonwoven fabrics are produced by using a paper machine and dewatering a papermaking slurry in which fibers having a fiber length of 3 to 20 mm are uniformly dispersed in a large amount of water on a papermaking mesh. Therefore, since the fibers are uniformly dispersed, the texture of the wet-laid nonwoven fabric is better than dry-laid nonwoven fabrics such as meltblown nonwoven fabrics and spunbond nonwoven fabrics. In a filter material for a liquid filter formed by laminating a melt-blown nonwoven fabric and a wet-laid nonwoven fabric, when high water pressure or oil pressure is applied to the filter medium, the melt-blown nonwoven fabric pressed against the wet-laid nonwoven fabric is supported by the wet-laid nonwoven fabric with a uniform texture. The melt-blown nonwoven fabric is suppressed from biting into the voids of the wet-laid nonwoven fabric, and the deterioration of filtration performance due to biting can be suppressed. In addition, when the wet-laid nonwoven fabric is made of fibers having a fiber diameter of 5 μm or more, the rigidity of the liquid filter medium is increased, and excellent pleating processability can be obtained.

As a method of increasing the stiffness, there is a method of increasing the basis weight of the wet-laid nonwoven fabric. However, increasing the basis weight causes a decrease in liquid permeability and increases the thickness, which causes a problem that the area of the filter medium that can be incorporated into the filter unit is reduced. Therefore, the wet-laid nonwoven fabric of the present invention is required to have a low basis weight and high rigidity. In order to increase the rigidity of a wet-laid nonwoven fabric with a low basis weight, the selection and combination of fibers constituting the wet-laid nonwoven fabric are important.

When the fibers constituting the wet-laid nonwoven fabric are thick, the stiffness of the wet-laid nonwoven fabric can be increased. In the present invention, the fiber diameter of the fibers constituting the wet-laid nonwoven fabric is 5 μm or more, preferably 7 μm or more, and still more preferably 10 μm or more. If the fiber diameter is less than 5 μm, the liquid permeability may be lowered, or the rigidity of the wet-laid nonwoven fabric may be insufficient, resulting in a decrease in the pleating workability.

The fiber diameter of the fibers constituting the wet-laid nonwoven fabric is measured by an electron microscope before manufacturing the wet-laid nonwoven fabric (for each fiber having substantially the same material, fineness, fiber length, etc., that is, for each purchased unit). Photographs were taken twice, and the fiber diameters of 30 fibers in focus in the three photographs were measured and averaged.

The term "wet-laid nonwoven fabric made of fibers having a fiber diameter of 5 µm or more" means that the fiber diameter of all fibers constituting the wet-laid nonwoven fabric is 5 µm or more. Fibers constituting the wet-laid nonwoven fabric include main fibers and binder fibers.

The main fiber in the present invention is a fiber that has properties that are difficult to melt or soften due to heat treatment (for example, drying treatment, heat calendering treatment, etc.) during wet-laid nonwoven fabric production, and that maintains its fiber shape even after heat treatment. .

Synthetic fibers as main fibers include polyester, polyolefin, polyamide, polyacrylic, vinylon, vinylidene, polyvinyl chloride, polyester, benzoate, polychlal, and phenol fibers. Natural fibers include hemp pulp, cotton linter, and lint with little film; regenerated fibers include lyocell, rayon, and cupra; semi-synthetic fibers include acetate, triacetate, and promix; inorganic fibers include alumina fiber and alumina. - Fibers such as silica fiber, rock wool, glass fiber, micro glass fiber, zirconia fiber, potassium titanate fiber, alumina whisker, and aluminum borate whisker. In addition to the above fibers, wood pulp such as softwood pulp and hardwood pulp, woody pulp such as straw pulp, bamboo pulp and kenaf pulp, and herbaceous plants can also be used as plant fibers. In particular, polyester fibers and vinylon fibers are preferable for increasing rigidity. A higher degree of drawing of the main fibers is preferable because the degree of rigidity can be increased.

The fiber diameter of the main fibers is 5 μm or more, more preferably 5 to 30 μm, still more preferably 7 to 25 μm. If the fiber diameter of the main fibers is less than 5 μm, the wet-laid nonwoven fabric will have low rigidity, fail to obtain pleat workability, and have high liquid permeation resistance. On the other hand, if the fiber diameter of the main fibers exceeds 30 μm, the voids in the wet-laid nonwoven fabric become excessively large, and when high water pressure or the like is applied to the filter medium, the melt-blown nonwoven fabric may bite into the voids of the wet-laid nonwoven fabric, resulting in a decrease in filtration performance. .

The fiber length of the main fibers of the present invention is preferably 3-20 mm, more preferably 3-15 mm. If the fiber length of the main fibers is less than 3 mm, the main fibers may drop out of the papermaking net, and if the fiber length of the main fibers exceeds 20 mm, the texture may deteriorate.

The content of the main fibers is preferably 20 to 80% by mass, more preferably 30 to 70% by mass, more preferably 40 to 60% by mass, based on the total fibers constituting the wet-laid nonwoven fabric. More preferred. If the content of the main fibers is less than 20% by mass, the voids in the wet-laid nonwoven fabric may be insufficient, resulting in increased liquid permeation resistance. If the content of the main fibers exceeds 80% by mass, the content of the binder fibers becomes relatively low, which may result in insufficient stiffness.

In order to increase the tensile strength and stiffness of the wet-laid nonwoven fabric, the wet-laid nonwoven fabric preferably contains binder fibers. By bonding the intersections of the binder fibers or the intersections of the binder fibers and the main fibers, the tensile strength and stiffness of the wet-laid nonwoven fabric can be increased. In the present invention, binder fibers are fibers that have the property of being melted or softened by heat treatment (for example, drying treatment, heat calendering treatment, etc.) during wet-laid nonwoven fabric production.

Examples of binder fibers include composite fibers such as core-shell fibers, side-by-side fibers, and radially split fibers; and single fibers. Composite fibers are less likely to form a film, so the strength can be improved while maintaining the spaces of the wet-laid nonwoven fabric. Examples of combinations of core-sheath fibers include a combination of polypropylene (core) and polyethylene (sheath), a combination of polypropylene (core) and ethylene vinyl alcohol (sheath), a combination of polypropylene (core) and vinyl acetate alcohol (sheath), and polypropylene. A combination of (core) and polyethylene (sheath), a combination of high melting point polyester (core) and low melting point polyester (sheath), and the like. Examples of monofilaments include polyethylene fibers, propylene fibers, undrawn polyester fibers, and the like. From the viewpoint of increasing the tensile strength and rigidity of the nonwoven fabric, it is particularly preferable to use a polyester-based core-sheath fiber that is a combination of a high melting point polyester (core) and a low melting point polyester (sheath). In addition, full-melting type single fibers composed only of low melting point resin such as polyethylene fibers and hot water soluble binder fibers such as hot water soluble polyvinyl alcohol fibers are easy to form a film in the heating process, but their properties can be used as long as it does not interfere with

The fiber length of the binder fibers is preferably 3-12 mm, more preferably 3-10 mm. When the fiber length of the binder fiber is less than 3 mm, it tends to fall off from the papermaking net during the papermaking process, and the bonding points with other fibers may decrease, resulting in a decrease in stiffness. In addition, when the fiber length of the binder fiber exceeds 12 mm, the water dispersibility is impaired and the texture becomes uneven. It may bite into bad parts and reduce filtration performance.

The fiber diameter of the binder fibers is 5 μm or more, more preferably 5 to 20 μm, still more preferably 7 to 18 μm. If the fiber diameter of the binder fiber is less than 5 μm, the liquid permeation resistance increases. On the other hand, when the fiber diameter of the binder fiber exceeds 20 μm, the number of adhesion points with other fibers is reduced, and the stiffness may be lowered.

The binder fiber content is preferably 20 to 80% by mass, more preferably 30 to 70% by mass, and 40 to 60% by mass, based on the total fibers contained in the wet-laid nonwoven fabric. More preferred. If the binder fiber content is less than 20% by mass, the adhesion between the fibers tends to be insufficient, and the stiffness may be insufficient. If the binder fiber content exceeds 80% by mass, the liquid permeation resistance increases, which may cause practical problems.

In addition, the cross-sectional shape of the fibers blended in the wet-laid nonwoven fabric may include fibers having irregular cross-sections such as T-shaped, Y-shaped, triangular, etc., in addition to circular (perfect circle, ellipse, etc.).

Although the basis weight of the wet-laid nonwoven fabric of the present invention is not particularly limited, it is preferably 5 to 100 g/m ² , more preferably 10 to 70 g/m ² . If it is less than 5 g/m ² , sufficient rigidity may not be obtained. On the other hand, if it exceeds 100 g/m ² , the liquid permeation resistance increases and the life of the liquid filter may be shortened.

The wet-laid nonwoven fabric of the present invention is a nonwoven fabric produced by a wet method (papermaking method). In the wet process, a paper machine in which a paper making net such as a fourdrinier, a circular net, or an inclined wire is installed independently, or two or more machines of the same type or different types selected from these paper making nets are installed online. A wet-laid nonwoven fabric can be produced using a combination paper machine or the like. The wet paper (web) produced by the papermaking net is dried with a dryer. After drying, depending on the case, a thermoplastic resin may be added and dried with a drier. As the dryer, an air dryer, a Yankee dryer, a cylinder dryer, a suction drum dryer, an infrared dryer, or the like can be used.

Moreover, the stiffness of the wet-laid nonwoven fabric can be improved by incorporating a thermoplastic resin into the wet-laid nonwoven fabric. Examples of thermoplastic resins include acrylic, vinyl acetate, epoxy, synthetic rubber, urethane, polyester, vinylidene chloride, polyvinyl alcohol, starch, and phenolic resins. These thermoplastic resins may be used alone or in combination of two or more. The thermoplastic resin is not an essential component, and if the fiber alone provides sufficient stiffness, the thermoplastic resin is unnecessary.

When the wet-laid nonwoven fabric contains a thermoplastic resin, the content is preferably 0.01 to 10% by mass relative to the wet-laid nonwoven fabric. If the content of the thermoplastic resin exceeds 10% by mass, the wet-laid nonwoven fabric may have an excessively large liquid permeation resistance. Moreover, when the content of the thermoplastic resin is less than 0.01% by mass, the stiffness may not change as compared with the wet-laid nonwoven fabric containing no thermoplastic resin.

The method for incorporating the thermoplastic resin into the wet-laid nonwoven fabric is not particularly limited, but methods such as a size press method, a tab size press method, a spray method, an internal addition method, and a gravure coating method can be used.

Methods for laminating melt-blown nonwoven fabrics and wet-laid nonwoven fabrics include, for example, an ultrasonic heat-sealing method, a heat-sealing method using a heat embossing roll, a bonding method using a reactive adhesive, and a heat lamination method using a hot-melt resin. can be used.

EXAMPLES The present invention will be specifically described below with reference to Examples, but the present invention is not limited to these Examples. All parts and percentages in the examples are by mass unless otherwise specified.

<Melt blown nonwoven fabric 1>
Using a melt-blown nonwoven fabric manufacturing apparatus, a melt-blowing nozzle die arranged with a spinning nozzle hole diameter of 0.2 mm and a pitch of 0.8 mm is heated to a temperature of 240 ° C., and a polypropylene resin (melt flow rate (MFR): 1200 g / 10 minutes, measured Resin temperature: 230 ° C.) is supplied to the die, polypropylene fibers are discharged from the nozzle, and are discharged together with heated air (260 ° C., 8 m ³ /min/m) blown from both sides of the nozzle, DCD (spinneret surface to the wire mesh conveyor): The melt blown nonwoven fabric 1 having a basis weight of 20 g/m ² and an average fiber diameter of 2.2 µm was obtained by spraying on a wire mesh conveyor moving at a distance of 150 mm.

<Melt blown nonwoven fabric 2>
Using a melt-blown nonwoven fabric manufacturing apparatus, a melt-blowing nozzle die arranged with a spinning nozzle hole diameter of 0.25 mm and a pitch of 0.8 mm is heated to a temperature of 280 ° C., and polybutylene terephthalate resin (melt flow rate (MFR): 270 g / 10 minutes , measured resin temperature: 275 ° C.) is supplied to the die, polybutylene terephthalate fibers are discharged from the nozzle, and are discharged together with heated air (300 ° C., 8 m ³ /min/m) blown from both sides of the nozzle, DCD ( The distance from the surface of the spinneret to the wire mesh conveyor) was blown to a wire mesh conveyor moving at a distance of 110 mm to obtain a melt blown nonwoven fabric 2 having a basis weight of 20 g/m ² and an average fiber diameter of 2.3 µm.

<Main fiber 1>
A drawn polyester fiber having a fiber diameter of 5.2 μm and a fiber length of 5 mm was used as the main fiber 1 .

<Main fiber 2>
A drawn polyester fiber having a fiber diameter of 7.4 μm and a fiber length of 5 mm was used as the main fiber 2 .

<Main fiber 3>
A vinylon fiber having a fiber diameter of 14.3 μm and a fiber length of 5 mm was used as the main fiber 3 .

<Main fiber 4>
A drawn polyester fiber having a fiber diameter of 24.7 μm and a fiber length of 10 mm was used as the main fiber 4 .

<Main fiber 5>
As the sea-island type fiber, a fiber (fineness: 1.65 dtex, fiber length: 3 mm) manufactured by a composite spinning method in which 25 island components made of polypropylene exist in a sea component made of poly-L-lactic acid was prepared. . Next, this sea-island fiber is immersed in a 10 mass% sodium hydroxide aqueous solution at a temperature of 80° C. for 30 minutes to extract and remove poly-L-lactic acid, which is the sea component of the sea-island fiber, to obtain a polypropylene fiber (fiber diameter : 1.8 μm, fiber length 3 mm) was used as the main fiber 5.

<Main fiber 6>
An acrylic fiber having a fiber diameter of 4.0 μm and a fiber length of 3 mm was used as the main fiber 6 .

<Binder fiber 1>
Binder fiber 1 was a core-sheath fiber having a fiber diameter of 14.3 μm and a fiber length of 5 mm, the core component of which was polyester (melting point of 253° C.), and the sheath of which was polyethylene terephthalate-isophthalate copolymer (softening point of 75° C.).

<Binder fiber 2>
Binder fiber 2 is a core-sheath fiber having a fiber diameter of 11.8 μm and a fiber length of 10 mm, the core component of which is polypropylene (melting point: 158° C.), and the sheath component (adhesive component) is high-density polyethylene (melting point: 131° C.). .

(Production of wet-laid nonwoven fabric)
After pouring water into a 2 ^m3 dispersion tank, main fibers and binder fibers were added at the ratio shown in Table 1, dispersed for 5 minutes at a dispersion concentration of 0.2% by mass, and agitated with an agitator to make uniform paper. A fiber slurry (0.2% concentration) was prepared. Dilute and disperse the slurry with a large amount of water using a cylinder paper machine, form a web on a cylinder wire so that the dry weight is 20 g / m ² , and touch roll with a cylinder dryer with a surface temperature of 130 ° C. Wet-laid nonwoven fabrics 1 to 9 were obtained by drying while applying a pressure of 400 N/cm ² .

After pouring water into a 2 ^m3 dispersion tank, main fibers and binder fibers were added in the ratio shown in Table 1, dispersed for 5 minutes at a dispersion concentration of 0.2% by mass, and agitated with an agitator to make uniform paper. A fiber slurry (0.2% concentration) was prepared. Dilute and disperse the slurry with a large amount of water using a cylinder paper machine, form a web on a cylinder wire so that the dry weight is 40 g / m ² , and touch roll with a cylinder dryer with a surface temperature of 130 ° C. was dried while applying a pressure of 400 N/cm ² to obtain a wet-laid nonwoven fabric 10 .

(Preparation of filter material for liquid filter)
Melt blown nonwoven fabrics (MB) 1 and 2 and wet laid nonwoven fabrics (WL) 1 to 9 are combined as shown in Table 2, and after superimposing three layers so as to form wet nonwoven fabric / meltblown nonwoven fabric / wet nonwoven fabric, ultrasonic heat fusion is performed. They were bonded using a device to prepare filter media for liquid filters of Examples 1 to 9 and Comparative Examples 1 and 2.

The melt-blown nonwoven fabric (MB) 1 and the wet-laid nonwoven fabric (WL) 10 are combined as shown in Table 2, and after superimposing two layers so as to form a melt-blown nonwoven fabric/wet-laid nonwoven fabric, they are joined using an ultrasonic heat-sealing device, A filter medium for a liquid filter of Example 10 was produced.

<Evaluation>
The filter media for liquid filters obtained in Examples and Comparative Examples were evaluated as follows.

[Basis Weight] (Unit: g/m ² )
Basis weight was measured according to the method specified in JIS P8124:2011 (Paper and paperboard- Basis weight measurement method).

The thickness was measured according to the method specified in JIS P8118:2014 (Paper and paperboard-Thickness test method).

[Pressure loss] (unit: Pa)
It was measured under the condition of surface wind speed of 5.3 cm/sec according to JIS B9908:2011. The lower the pressure loss, the better. If the pressure loss is less than 50 Pa, it is evaluated as “⊚”;

[Collection efficiency] (Unit: %)
It was measured under the condition of surface wind speed of 5.3 cm/sec according to JIS B9908:2011. The particles to be measured are atmospheric dust, and the collection efficiency for particles with a particle size of 0.3 to 0.5 μm is measured using a particle counter (trade name “KC-11”, manufactured by Rion). , the collection efficiency was calculated from the following formula 1.

(Formula 1)
η=(1−C2/C1)×100
η: collection efficiency (%)
C1: Particle concentration on the upstream side of the filter medium C2: Particle concentration on the downstream side of the filter medium

The higher the collection efficiency, the better. If it is 50% or more, it is "O"; if it is 30% or more and less than 50%, it is "△";

The liquid filtration efficiency and the liquid filtration rate were measured by the following method, using JIS class 8 powder diluted and dispersed in pure water to a concentration of 0.05% as a test liquid.

[Liquid filtration efficiency] (Unit: %)
The liquid filtration efficiency was measured by moistening the liquid filter material with pure water, setting the liquid filter material on a filtration holder with a filtration area of 14 cm ² using a vacuum filtration device, and placing 100 ml of the test liquid on the filtration holder. After pouring, the test liquid is vacuum-filtered at a differential pressure ΔP=200 mmHg, and after the test liquid is completely filtered, 100 ml of the test liquid is poured into the same holder and vacuum-filtered under the same conditions. Vacuum filtration is repeated a total of 10 times, and the number of 3 to 10 μm particles in the test liquid before and after the 10th filtration is measured with a liquid particle counter (KL-01) manufactured by Rion Co., Ltd. From the following formula 1, Liquid filtration efficiency was calculated.

(Formula 1)
η=(1−C2/C1)×100
η: Liquid filtration efficiency (%)
C1: Particle concentration on the upstream side of the filter medium C2: Particle concentration on the downstream side of the filter medium

The higher the liquid filtration efficiency, the better. If it is 70% or more, it is "◎". It was set as "x".

[Liquid filtration rate] (unit: cc/cm ² /min)
Liquid Filtration Rate: The liquid filtration rate was obtained from the 10th filtration time of the liquid filtration efficiency test described above. The higher the liquid filtration rate, the less clogging of the filter medium, the shorter the time required for filtration, and the better the filter medium.

The higher the liquid filtration rate ^, the better. ^If it is 15 cc/cm ² /min or more, it is " ^⊚ ". If it was less than 10 cc/cm ² /min, it was rated as “Δ”, and if it was less than 5 cc/cm ² /min, it was rated as “x”.

[Pleating workability]
A filter medium for a liquid filter is cut into 30 cm in the machine direction (MD) and 20 cm in the transverse direction (CD) of the papermaking process, and the mountain fold and valley fold are repeated every 5 cm so as to cross the machine direction. , a cylindrical metal roll having a length of 30 cm and a weight of 3 kg. If the crease is clear and there is no distortion, and the crease is not deformed when pressed, it is rated as "good". ×”. In addition, "⊚" indicates that it is very hard and is superior to "○".

The liquid filter media of Examples and Comparative Examples are liquid filter media obtained by laminating a melt-blown nonwoven fabric and a wet-laid nonwoven fabric. From the comparison between Comparative Examples 1 and 2 and Examples 1 to 10, the liquid filter material of Comparative Example 1 using a wet-laid nonwoven fabric containing main fibers with a fiber diameter of 1.8 μm (fiber diameter less than 5 μm) has a fiber diameter of 5 μm. Compared to the liquid filter media of Examples 1 to 10 using the wet-laid nonwoven fabric made of the above fibers, the pressure loss is high and the rigidity is insufficient, so the pleat processability is poor and the level is unusable. The liquid filtration rate was also low. The filter medium for a liquid filter of Comparative Example 2 using a wet-laid nonwoven fabric containing main fibers having a fiber diameter of 4.0 μm (less than 5 μm) was the same as that of Examples 1 to 10 using a wet-laid nonwoven fabric made of fibers having a fiber diameter of 5 μm or more. Compared with the filter medium for liquid filters, the pleating processability was poor, and it was at an unusable level.

The liquid filter media of Examples 8 and 9, in which the raw material resin of the melt-blown nonwoven fabric is polybutylene terephthalate, compared to Examples 6 and 7, in which the raw material resin of the melt-blown nonwoven fabric is polypropylene, have better pleating processability. It was good.

The filter medium for a liquid filter of the present invention is used for processing waste contained in the working fluid of an electric discharge machine used for engraving, cutting, etc. of metal, and cutting, polishing, etching, etc. of substrate wafers in IC production. It can be suitably used as a liquid filter for efficiently removing processing waste contained in ultrapure water used in the process to obtain a clean liquid, a liquid filter for automobile engine oil, fuel, and the like.

Claims (2)

A filter medium for a liquid filter, which is obtained by laminating a melt-blown nonwoven fabric and a wet-laid nonwoven fabric made of fibers having a fiber diameter of 5 μm or more. 2. The filter medium for a liquid filter according to claim 1, wherein the raw material resin of the meltblown nonwoven fabric is polypropylene or polybutylene terephthalate.